8 The Nervous System.

8 The Nervous System

Chapter 8 Learning Outcomes
8-1 Describe the anatomical and functional divisions of the nervous system. 8-2 Distinguish between neurons and neuroglia on the basis of structure and function. 8-3 Describe the events involved in the generation and propagation of an action potential. 8-4 Describe the structure of a synapse, and explain the mechanism of nerve impulse transmission at a synapse. 8-5 Describe the three meningeal layers that surround the central nervous system. © 2013 Pearson Education, Inc.

8-6 Discuss the roles of gray matter and white matter in the spinal cord. 8-7 Name the major regions of the brain, and describe the locations and functions of each. 8-8 Name the cranial nerves, relate each pair of cranial nerves to its principal functions, and relate the distribution pattern of spinal nerves to the regions they innervate. 8-9 Describe the steps in a reflex arc. 8-10 Identify the principal sensory and motor pathways, and explain how it is possible to distinguish among sensations that originate in different areas of the body. © 2013 Pearson Education, Inc.

8-11 Describe the structures and functions of the sympathetic and parasympathetic divisions of the autonomic nervous system. 8-12 Summarize the effects of aging on the nervous system. 8-13 Give examples of interactions between the nervous system and other organ systems. © 2013 Pearson Education, Inc.

The Nervous System and the Endocrine System (Introduction)
The nervous system and endocrine system coordinate other organ systems to maintain homeostasis The nervous system is fast, short acting The endocrine system is slower, but longer lasting The nervous system is the most complex system in the body © 2013 Pearson Education, Inc.

Functions of the Nervous System (8-1)
Monitors the body's internal and external environments Integrates sensory information Coordinates voluntary and involuntary responses © 2013 Pearson Education, Inc.

Divisions of the Nervous System (8-1)
Anatomical divisions are: The central nervous system (CNS) Made up of the brain and spinal cord Integrates and coordinates input and output The peripheral nervous system (PNS) All the neural tissues outside of the CNS The connection between the CNS and the organs © 2013 Pearson Education, Inc.

Divisions of the Nervous System (8-1)
Functional divisions are: The afferent division Includes sensory receptors and neurons that send information to the CNS The efferent division Includes neurons that send information to the effectors, which are the muscles and glands © 2013 Pearson Education, Inc.

Efferent Division of the Nervous System (8-1)
Further divided into: The somatic nervous system (SNS) Controls skeletal muscle The autonomic nervous system (ANS) Controls smooth and cardiac muscle, and glands Has two parts Sympathetic division Parasympathetic division © 2013 Pearson Education, Inc.

Figure 8-1 A Functional Overview of the Nervous System.
CENTRAL NERVOUS SYSTEM Information processing PERIPHERAL NERVOUS SYSTEM Sensory information within afferent division Motor commands within efferent division includes Somatic nervous system Autonomic nervous system Parasympathetic division Sympathetic division Receptors Effectors Smooth muscle Visceral sensory receptors (monitor internal conditions and the status of other organ systems) Somatic sensory receptors (monitor the outside world and our position in it) Skeletal muscle Cardiac muscle Glands © 2013 Pearson Education, Inc.

Checkpoint (8-1) Identify the two anatomical divisions of the nervous system. Identify the two functional divisions of the peripheral nervous system, and describe their primary functions. What would be the effect of damage to the afferent division of the PNS? © 2013 Pearson Education, Inc.

Neurons (8-2) Cells that communicate with one another and other cells
Basic structure of a neuron includes: Cell body Dendrites Which receive signals Axons Which carry signals to the next cell Axon terminals Bulb-shaped endings that form a synapse with the next cell © 2013 Pearson Education, Inc.

Neurons (8-2) Have a very limited ability to regenerate when damaged or destroyed Cell bodies contain: Mitochondria, free and fixed ribosomes, and rough endoplasmic reticulum Free ribosomes and RER form Nissl bodies and give the tissue a gray color (gray matter) The axon hillock Where electrical signal begins © 2013 Pearson Education, Inc.

Figure 8-2 The Anatomy of a Representative Neuron.
Cell body Mitochondrion Golgi apparatus Axon terminals Axon hillock Dendrite Collateral Nucleus Axon (may be myelinated) Nucleolus Nerve cell body Nucleolus Nucleus Axon hillock Nissl bodies Nissl bodies Nerve cell body LM x 1500 © 2013 Pearson Education, Inc.

Structural Classification of Neurons (8-2)
Based on the relationship of the dendrites to the cell body Multipolar neurons Are the most common in the CNS and have two or more dendrites and one axon Unipolar neurons Have the cell body off to one side, most abundant in the afferent division Bipolar neurons Have one dendrite and one axon with the cell body in the middle, and are rare © 2013 Pearson Education, Inc.

Figure 8-3 A Structural Classification of Neurons.
Multipolar neuron Unipolar neuron Bipolar neuron © 2013 Pearson Education, Inc.

Sensory Neurons (8-2) Also called afferent neurons
Total 10 million or more Receive information from sensory receptors Somatic sensory receptors Detect stimuli concerning the outside world, in the form of external receptors And our position in it, in the form of proprioceptors Visceral or internal receptors Monitor the internal organs © 2013 Pearson Education, Inc.

Motor Neurons (8-2) Also called efferent neurons
Total about half a million in number Carry information to peripheral targets called effectors Somatic motor neurons Innervate skeletal muscle Visceral motor neurons Innervate cardiac muscle, smooth muscle, and glands © 2013 Pearson Education, Inc.

Interneurons (8-2) Also called association neurons
By far the most numerous type at about 20 billion Are located in the CNS Function as links between sensory and motor processes Have higher functions Such as memory, planning, and learning © 2013 Pearson Education, Inc.

Neuroglial Cells (8-2) Are supportive cells and make up about half of all neural tissue Four types are found in the CNS Astrocytes Oligodendrocytes Microglia Ependymal cells Two types in the PNS Satellite cells Schwann cells © 2013 Pearson Education, Inc.

Astrocytes (8-2) Large and numerous neuroglia in the CNS
Maintain the blood–brain barrier © 2013 Pearson Education, Inc.

Oligodendrocytes (8-2) Found in the CNS
Produce an insulating membranous wrapping around axons called myelin Small gaps between the wrappings called nodes of Ranvier Myelinated axons constitute the white matter of the CNS Where cell bodies are gray matter Some axons are unmyelinated © 2013 Pearson Education, Inc.

Microglia (8-2) The smallest and least numerous
Phagocytic cells derived from white blood cells Perform essential protective functions such as engulfing pathogens and cellular waste © 2013 Pearson Education, Inc.

Ependymal Cells (8-2) Line the fluid-filled central canal of the spinal cord and the ventricles of the brain The endothelial lining is called the ependyma It is involved in producing and circulating cerebrospinal fluid around the CNS © 2013 Pearson Education, Inc.

Figure 8-4 Neuroglia in the CNS.
Gray matter White matter CENTRAL CANAL Ependymal cells Gray matter Neurons Myelinated axons Microglial cell Inter- node Myelin (cut) Astrocyte Axon White matter Oligoden- drocyte Node Basement membrane Capillary © 2013 Pearson Education, Inc.

Neuroglial Cells in PNS (8-2)
Satellite cells Surround and support neuron cell bodies Similar in function to the astrocytes in the CNS Schwann cells Cover every axon in PNS The surface is the neurilemma Produce myelin © 2013 Pearson Education, Inc.

Figure 8-5 Schwann Cells and Peripheral Axons.
Nodes Schwann cell nucleus Myelin covering internode Neurilemma Axons Schwann cell nucleus Myelinated axon TEM x 14,048 A myelinated axon in the PNS is covered by several Schwann cells, each of which forms a myelin sheath around a portion of the axon. This arrangement differs from the way myelin forms in the CNS; compare with Figure 8-4. Unmyelinated axon TEM x 14,048 A single Schwann cell can encircle several unmyelinated axons. Every axon in the PNS is completely enclosed by Schwann cells. © 2013 Pearson Education, Inc.

Organization of the Nervous System (8-2)
In the PNS: Collections of nerve cell bodies are ganglia Bundled axons are nerves Including spinal nerves and cranial nerves Can have both sensory and motor components © 2013 Pearson Education, Inc.

Organization of the Nervous System (8-2)
In the CNS: Collections of neuron cell bodies are found in centers, or nuclei Neural cortex is a thick layer of gray matter White matter in the CNS is formed by bundles of axons called tracts, and in the spinal cord, form columns Pathways are either sensory or ascending tracts, or motor or descending tracts © 2013 Pearson Education, Inc.

Figure 8-6 The Anatomical Organization of the Nervous System.
CENTRAL NERVOUS SYSTEM GRAY MATTER ORGANIZATION Neural Cortex Centers PERIPHERAL NERVOUS SYSTEM Gray matter on the surface of the brain Collections of neuron cell bodies in the CNS; each center has specific processing functions GRAY MATTER Ganglia Collections of neuron cell bodies in the PNS Nuclei Collections of neuron cell bodies in the interior of the CNS Higher Centers The most complex centers in the brain WHITE MATTER Nerves WHITE MATTER ORGANIZATION Bundles of axons in the PNS Tracts Columns Bundles of CNS axons that share a common origin, destination, and function Several tracts that form an anatomically distinct mass RECEPTORS PATHWAYS Centers and tracts that connect the brain with other organs and systems in the body EFFECTORS Ascending (sensory) pathway Descending (motor) pathway © 2013 Pearson Education, Inc.

Checkpoint (8-2) Name the structural components of a typical neuron.
Examination of a tissue sample reveals unipolar neurons. Are these more likely to be sensory neurons or motor neurons? Identify the neuroglia of the central nervous system. Which type of glial cell would increase in number in the brain tissue of a person with a CNS infection? In the PNS, neuron cell bodies are located in ________ and surrounded by neuroglial cells called ________ cells. © 2013 Pearson Education, Inc.

The Membrane Potential (8-3)
A membrane potential exists because of: Excessive positive ionic charges on the outside of the cell Excessive negative charges on the inside, creating a polarized membrane An undisturbed cell has a resting membrane potential measured in the inside of the cell in millivolts The resting membrane potential of neurons is –70 mV © 2013 Pearson Education, Inc.

Factors Determining Membrane Potential (8-3)
Extracellular fluid (ECF) is high in Na+ and CI– Intracellular fluid (ICF) is high in K+ and negatively charged proteins (Pr –) Proteins are non-permeating, staying in the ICF Some ion channels are always open Called leak channels Some are open or closed Called gated channels © 2013 Pearson Education, Inc.

Factors Determining Membrane Potential (8-3)
Na+ can leak in But the membrane is more permeable to K+ Allowing K+ to leak out faster Na+/K+ exchange pump exchanges 3 Na+ for every 2 K+ Moving Na+ out as fast as it leaks in Cell experiences a net loss of positive ions Resulting in a resting membrane charge of –70 mV © 2013 Pearson Education, Inc.

Figure 8-7 The Resting Potential Is the Membrane Potential of an Undisturbed Cell.
EXTRACELLULAR FLUID –30 –70 +30 mV Na+ leak channel K+ leak channel Sodium– potassium exchange pump Plasma membrane CYTOSOL Protein KEY Sodium ion (Na+) Protein Protein Potassium ion (K+) Chloride ion (Cl–) © 2013 Pearson Education, Inc.

Changes in Membrane Potential (8-3)
Stimuli alter membrane permeability to Na+ or K+ Or alter activity of the exchange pump Types include: Cellular exposure to chemicals Mechanical pressure Temperature changes Changes in the ECF ion concentration Result is opening of a gated channel Increasing the movement of ions across the membrane © 2013 Pearson Education, Inc.

Changes in Membrane Potential (8-3)
Opening of Na+ channels results in an influx of Na+ Moving the membrane toward 0 mV, a shift called depolarization Opening of K+ channels results in an efflux of K+ Moving the membrane further away from 0 mV, a shift called hyperpolarization Return to resting from depolarization: repolarizing © 2013 Pearson Education, Inc.

Graded Potentials (8-3) Local changes in the membrane that fade over distance All cells experience graded potentials when stimulated And can result in the activation of smaller cells Graded potentials by themselves cannot trigger activation of large neurons and muscle fibers Referred to as having excitable membranes © 2013 Pearson Education, Inc.

Action Potentials (8-3) A change in the membrane that travels the entire length of neurons A nerve impulse If a combination of graded potentials causes the membrane to reach a critical point of depolarization, it is called the threshold Then an action potential will occur © 2013 Pearson Education, Inc.

Action Potentials (8-3) Are all-or-none and will propagate down the length of the neuron From the time the voltage-gated channels open until repolarization is finished: The membrane cannot respond to further stimulation This period of time is the refractory period And limits the rate of response by neurons © 2013 Pearson Education, Inc.

Figure 8-8 The Generation of an Action Potential
SPOTLIGHT FIGURE 8-8 The Generation of an Action Potential Sodium channels close, voltage-gated potassium channels open, and potassium ions move out of the cell. Repolarization begins. +30 3 D E P O L A R I Z A T I O N R E P O L A R I Z A T I O N Potassium channels close, and both sodium and potassium channels return to their normal states. Resting potential 2 –40 Voltage-gated sodium channels open and sodium ions move into the cell. The membrane potential rises to +30 mV. Membrane potential (mV) –60 Threshold –70 1 Axon hillock 4 A graded depolarization brings an area of excitable membrane to threshold (–60 mV). First part of axon to reach threshold REFRACTORY PERIOD During the refractory period, the membrane cannot respond to further stimulation. Time (msec) 1 2 1 2 3 4 Depolarization to Threshold Activation of Sodium Channels and Rapid Depolarization Inactivation of Sodium Channels and Activation of Potassium Channels Closing of Potassium Channels Resting Potential Resting Potential –70 mV –60 mV +10 mV –90 mV –70 mV +30 mV Local current The axon membrane contains both voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential. The stimulus that begins an action potential is a graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at a membrane potential known as the threshold. When the voltage-gated sodium channels open, sodium ions rush into the cytoplasm, and rapid depolarization occurs. The inner membrane surface now contains more positive ions than negative ones, and the membrane potential has changed from –60 mV to a positive value. As the membrane potential approaches +30 mV, voltage-gated sodium channels close. This step coincides with the opening of voltage- gated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward resting levels. Repolariza- tion now begins. The voltage-gated sodium channels remain inactivated until the membrane has repolar- ized to near threshold levels. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting potential (about –70 mV). Until all have closed, potassium ions continue to leave the cell. This produces a brief hyperpolarization. As the voltage-gated potassium channels close, the membrane potential returns to normal resting levels. The action potential is now over, and the membrane is once again at the resting potential. = Sodium ion = Potassium ion © 2013 Pearson Education, Inc.

Sodium channels close, voltage- gated potassium channels open, and potassium ions move out of the cell. Repolarization begins. +30 3 D E P O L A R I Z AT I O N R E P O L A R I Z AT I O N Resting potential 2 Potassium channels close, and both sodium and potassium channels return to their normal states. Voltage-gated sodium channels open and sodium ions move into the cell. The membrane potential rises to +30 mV. –40 Membrane potential (mV) Threshold –60 –70 1 4 A graded depolarization brings an area of excitable membrane to threshold (–60 mV). REFRACTORY PERIOD During the refractory period, the membrane cannot respond to further stimulation. Time (msec) 1 2 © 2013 Pearson Education, Inc.

Resting Potential Depolarization to Threshold Activation of Sodium Channels and Rapid Depolarization –70 mV –60 mV +10 mV Local current The axon membrane contains both voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential. The stimulus that begins an action potential is a graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at a membrane potential known as the threshold. When the voltage-gated sodium channels open, sodium ions rush into the cytoplasm, and rapid depolarization occurs. The inner membrane surface now contains more positive ions than negative ones, and the membrane potential has changed from –60 mV to a positive value. = Sodium ion = Potassium ion © 2013 Pearson Education, Inc.

Resting Potential Inactivation of Sodium Channels and Activation of Potassium Channels Closing of Potas- sium Channels –70 mV –90 mV +30 mV The voltage-gated sodium channels remain inactivated until the membrane has repolar- ized to near threshold levels. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting potential (about –70 mV). Until all have closed, potassium ions continue to leave the cell. This produces a brief hyperpolarization. As the membrane potential approaches +30 mV, voltage-gated sodium channels close. This step coincides with the opening of voltage- gated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward resting levels. Repolariza- tion now begins. As the voltage-gated potassium channels close, the membrane potential returns to normal resting levels. The action potential is now over, and the membrane is once again at the resting potential. © 2013 Pearson Education, Inc.

Propagation of an Action Potential (8-3)
Occurs when local changes in the membrane in one site: Result in the activation of voltage-gated channels in the next adjacent site of the membrane This causes a wave of membrane potential changes Continuous propagation Occurs in unmyelinated fibers and is relatively slow Saltatory propagation Is in myelinated axons and is faster © 2013 Pearson Education, Inc.

Figure 8-9 The Propagation of Action Potentials over Unmyelinated and Myelinated Axons.
Action potential propagation along an unmyelinated axon Action potential propagation along a myelinated axon Stimulus depolarizes membrane to threshold Stimulus depolarizes membrane to threshold EXTRACELLULAR FLUID EXTRACELLULAR FLUID Myelinated Myelinated Myelinated Internode Internode Internode Plasma membrane CYTOSOL Plasma membrane CYTOSOL Myelinated Myelinated Myelinated Internode Internode Internode Local current Local current Myelinated Myelinated Myelinated Internode Internode Internode Local current Local current Repolarization (refractory period) Repolarization (refractory period) © 2013 Pearson Education, Inc.

Checkpoint (8-3) What effect would a chemical that blocks the voltage-gated sodium channels in a neuron's plasma membrane have on the neuron's ability to depolarize? What effect would decreasing the concentration of extracellular potassium have on the membrane potential of a neuron? List the steps involved in the generation and propagation of an action potential. Two axons are tested for propagation velocities. One carries action potentials at 50 meters per second, the other at 1 meter per second. Which axon is myelinated? © 2013 Pearson Education, Inc.

The Synapse (8-4) A junction between a neuron and another cell
Occurs because of chemical messengers called neurotransmitters Communication happens in one direction only Between a neuron and another cell type is a neuroeffector junction Such as the neuromuscular junction or neuroglandular junction © 2013 Pearson Education, Inc.

A Synapse between Two Neurons (8-4)
Occurs: Between the axon terminals of the presynaptic neuron Across the synaptic cleft To the dendrite or cell body of the postsynaptic neuron Neurotransmitters Stored in vesicles of the axon terminals Released into the cleft and bind to receptors on the postsynaptic membrane PLAY ANIMATION Neurophysiology: Synapse © 2013 Pearson Education, Inc.

Figure 8-10 The Structure of a Typical Synapse.
Axon of presynaptic cell Axon terminal Mitochondrion Synaptic vesicles Presynaptic membrane Postsynaptic membrane Synaptic cleft © 2013 Pearson Education, Inc.

The Neurotransmitter ACh (8-4)
Activates cholinergic synapses in four steps Action potential arrives at the axon terminal ACh is released and diffuses across synaptic cleft ACh binds to receptors and triggers depolarization of the postsynaptic membrane ACh is removed by AChE (acetylcholinesterase) © 2013 Pearson Education, Inc.

Figure 8-11 The Events at a Cholinergic Synapse.
An action potential arrives and depolarizes the axon terminal Presynaptic neuron Action potential Synaptic vesicles EXTRACELLULAR FLUID Axon terminal AChE POSTSYNAPTIC NEURON Extracellular Ca2+ enters the axon terminal, triggering the exocytosis of ACh ACh Ca2+ Ca2+ Synaptic cleft Chemically regulated sodium ion channels © 2013 Pearson Education, Inc.

Figure 8-11 The Events at a Cholinergic Synapse.
ACh binds to receptors and depolarizes the postsynaptic membrane Initiation of action potential if threshold is reached ACh is removed by AChE Propagation of action potential (if generated) © 2013 Pearson Education, Inc.

Table 8-1 The Sequence of Events at a Typical Cholinergic Synapse
© 2013 Pearson Education, Inc.

Other Important Neurotransmitters (8-4)
Norepinephrine (NE) In the brain and part of the ANS, is found in adrenergic synapses Dopamine, GABA, and serotonin Are CNS neurotransmitters At least 50 less-understood neurotransmitters NO and CO Are gases that act as neurotransmitters © 2013 Pearson Education, Inc.

Excitatory vs. Inhibitory Synapses (8-4)
Usually, ACh and NE trigger depolarization An excitatory response With the potential of reaching threshold Usually, dopamine, GABA, and serotonin trigger hyperpolarization An inhibitory response Making it farther from threshold © 2013 Pearson Education, Inc.

Neuronal Pools (8-4) Multiple presynaptic neurons can synapse with one postsynaptic neuron If they all release excitatory neurotransmitters: Then an action potential can be triggered If they all release an inhibitory neurotransmitter: Then no action potential can occur If half release excitatory and half inhibitory neurotransmitters: They cancel, resulting in no action © 2013 Pearson Education, Inc.

Neuronal Pools (8-4) A term that describes the complex grouping of neural pathways or circuits Divergence Is a pathway that spreads information from one neuron to multiple neurons Convergence Is when several neurons synapse with a single postsynaptic neuron © 2013 Pearson Education, Inc.

Figure 8-12 Two Common Types of Neuronal Pools.
Divergence Convergence A mechanism for spreading stimulation to multiple neurons or neuronal pools in the CNS A mechanism for providing input to a single neuron from multiple sources © 2013 Pearson Education, Inc.

Checkpoint (8-4) Describe the general structure of a synapse.
What effect would blocking calcium channels at a cholinergic synapse have on synapse function? What type of neural circuit permits both conscious and subconscious control of the same motor neurons? © 2013 Pearson Education, Inc.

The Dura Mater (8-5) Is the outer, very tough covering
The dura mater has two layers, with the outer layer fused to the periosteum of the skull Dural folds contain large veins, the dural sinuses In the spinal cord the dura mater is separated from the bone by the epidural space © 2013 Pearson Education, Inc.

The Arachnoid Is separated from the dura mater by the subdural space
That contains a little lymphatic fluid Below the epithelial layer is arachnoid space Created by a web of collagen fibers Contains cerebrospinal fluid © 2013 Pearson Education, Inc.

The Pia Mater Is the innermost layer
Firmly bound to the neural tissue underneath Highly vascularized Providing needed oxygen and nutrients © 2013 Pearson Education, Inc.

Checkpoint (8-5) Identify the three meninges surrounding the CNS.

Spinal Cord Structure (8-6)
The major neural pathway between the brain and the PNS Can also act as an integrator in the spinal reflexes Involving the 31 pairs of spinal nerves Consistent in diameter except for the cervical enlargement and lumbar enlargement Where numerous nerves supply upper and lower limbs © 2013 Pearson Education, Inc.

Spinal Cord Structure (8-6)
Central canal A narrow passage containing cerebrospinal fluid Surface of the spinal cord is indented by the: Posterior median sulcus Deeper anterior median fissure © 2013 Pearson Education, Inc.

31 Spinal Segments (8-6) Identified by a letter and number relating to the nearby vertebrae Each has a pair of dorsal root ganglia Containing the cell bodies of sensory neurons with axons in dorsal root Ventral roots contain motor neuron axons Roots are contained in one spinal nerve © 2013 Pearson Education, Inc.

Figure 8-14a Gross Anatomy of the Spinal Cord.
Cervical spinal nerves C3 C4 C5 C6 Cervical enlargement C7 C8 T1 T2 T3 T4 T5 T6 T7 Thoracic spinal nerves T8 Posterior median sulcus T9 T10 T11 Lumbar enlargement T12 L1 Inferior tip of spinal cord L2 Lumbar spinal nerves L3 Cauda equina L4 L5 S1 Sacral spinal nerves S2 S3 S4 S5 Coccygeal nerve (Co1) In this superficial view of the adult spinal cord, the designations to the left identify the spiral nerves. © 2013 Pearson Education, Inc.

Figure 8-14b Gross Anatomy of the Spinal Cord.
Posterior median sulcus Dorsal root Dorsal root ganglion Central canal Gray matter White matter Spinal nerve Ventral root Anterior median fissure C3 This cross section through the cervical region of the spinal cord shows some prominent features and the arrangement of gray matter and white matter. © 2013 Pearson Education, Inc.

Sectional Anatomy of the Spinal Cord (8-6)
The central gray matter is made up of glial cells and nerve cell bodies Projections of gray matter are called horns Which extend out into the white matter White matter is myelinated and unmyelinated axons The location of cell bodies in specific nuclei of the gray matter relate to their function © 2013 Pearson Education, Inc.

Sectional Anatomy of the Spinal Cord (8-6)
Posterior gray horns are somatic and visceral sensory nuclei Lateral gray horns are visceral (ANS) motor nuclei The anterior gray horns are somatic motor nuclei White matter can be organized into three columns Which contain either ascending tracts to the brain, or descending tracts from the brain to the PNS © 2013 Pearson Education, Inc.

Figure 8-15 Sectional Anatomy of the Spinal Cord.
Posterior white column Posterior median sulcus Functional Organization of Gray Matter Posterior gray commissure The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Posterior gray horn Somatic Lateral white column Lateral gray horn Visceral Sensory nuclei Dorsal root ganglion Visceral Anterior gray horn Motor nuclei Somatic Ventral root Anterior gray commissure Anterior white column Anterior white commissure Anterior median fissure The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns. POSTERIOR Structural Organization of Gray Matter Posterior median sulcus The projections of gray matter toward the outer surface of the spinal cord are called horns. Posterior gray commissure Dura mater Posterior gray horn Arachnoid mater (broken) Lateral gray horn Dorsal root Central canal Anterior gray commissure Anterior gray horn Anterior median fissure Dorsal root ganglion ANTERIOR Pia mater Ventral root A micrograph of a section through the spinal cord, showing major landmarks in and surrounding the cord. © 2013 Pearson Education, Inc.

Figure 8-15a Sectional Anatomy of the Spinal Cord.
Posterior white column Posterior median sulcus Functional Organization of Gray Matter Posterior gray commissure The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Posterior gray horn Somatic Sensory nuclei Lateral white column Lateral gray horn Visceral Dorsal root ganglion Visceral Motor nuclei Anterior gray horn Somatic Ventral root Anterior gray commissure Anterior white column Anterior white commissure Anterior median fissure The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns. © 2013 Pearson Education, Inc.

Figure 8-15b Sectional Anatomy of the Spinal Cord.
POSTERIOR Structural Organization of Gray Matter Posterior median sulcus The projections of gray matter toward the outer surface of the spinal cord are called horns. Posterior gray commissure Dura mater Posterior gray horn Arachnoid mater (broken) Lateral gray horn Dorsal root Central canal Anterior gray horn Anterior gray commissure Anterior median fissure Dorsal root ganglion ANTERIOR Pia mater Ventral root A micrograph of a section through the spinal cord, showing major landmarks in and surrounding the cord. © 2013 Pearson Education, Inc.

Checkpoint (8-6) Damage to which root of a spinal nerve would interfere with motor function? A person with polio has lost the use of his leg muscles. In which areas of his spinal cord could you locate virus-infected neurons? Why are spinal nerves also called mixed nerves? © 2013 Pearson Education, Inc.

Six Major Regions of the Brain (8-7)
The cerebrum The diencephalon The midbrain The pons The medulla oblongata The cerebellum © 2013 Pearson Education, Inc.

Major Structures of the Brain (8-7)
The cerebrum Is divided into paired cerebral hemispheres Deep to the cerebrum is the diencephalon Which is divided into the thalamus, the hypothalamus, and the epithalamus The brain stem Contains the midbrain, pons, and medulla oblongata The cerebellum Is the most inferior/posterior part © 2013 Pearson Education, Inc.

Right cerebral hemisphere Longitudinal fissure CEREBRUM
Figure 8-16a The Brain. Right cerebral hemisphere Longitudinal fissure CEREBRUM Left cerebral hemisphere A N T E R I O P O S T E R I CEREBELLUM Cerebral veins and arteries below arachnoid mater Superior view © 2013 Pearson Education, Inc.

Central sulcus Precentral gyrus Postcentral gyrus Parietal
Figure 8-16b The Brain. Central sulcus Precentral gyrus Postcentral gyrus Parietal lobe Frontal lobe of left cerebral hemisphere Lateral sulcus Occipital lobe Temporal lobe CEREBELLUM PONS Lateral view MEDULLA OBLONGATA © 2013 Pearson Education, Inc.

Corpus callosum Precentral gyrus Postcentral gyrus
Figure 8-16c The Brain. Corpus callosum Precentral gyrus Central sulcus Postcentral gyrus Fornix Thalamus Hypothalamus Frontal lobe DIENCEPHALON Pineal gland (part of epithalamus) Parieto-occipital sulcus Optic chiasm CEREBELLUM Mamillary body Temporal lobe MIDBRAIN Brain stem PONS MEDULLA OBLONGATA Sagittal section © 2013 Pearson Education, Inc.

The Ventricles of the Brain (8-7)
Filled with cerebrospinal fluid and lined with ependymal cells The two lateral ventricles within each cerebral hemisphere drain through the: Interventricular foramen into the: Third ventricle in the diencephalon, which drains through the cerebral aqueduct into the: Fourth ventricle, which drains into the central canal © 2013 Pearson Education, Inc.

Figure 8-17 The Ventricles of the Brain.
Cerebral hemispheres Cerebral hemispheres Ventricles of the Brain Lateral ventricles Interventricular foramen Third ventricle Cerebral aqueduct Fourth ventricle Pons Medulla oblongata Central canal Spinal cord Cerebellum Central canal A lateral view of the ventricles An anterior view of the ventricles © 2013 Pearson Education, Inc.

Cerebrospinal Fluid (8-7)
CSF Surrounds and bathes the exposed surfaces of the CNS Floats the brain Transports nutrients, chemicals, and wastes Is produced by the choroid plexus Continually secreted and replaced three times per day Circulation from the fourth ventricle into the subarachnoid space into the dural sinuses © 2013 Pearson Education, Inc.

Figure 8-18a The Formation and Circulation of Cerebrospinal Fluid.
Arachnoid granulations Extension of choroid plexus into lateral ventricle Choroid plexus of third ventricle Cerebral aqueduct Superior sagittal sinus Lateral aperture Choroid plexus of fourth ventricle Median aperture Arachnoid mater Central canal Subarachnoid space Spinal cord Dura mater A sagittal section of the CNS. Cerebrospinal fluid, formed in the choroid plexus, circulates along the routes indicated by the red arrows. © 2013 Pearson Education, Inc.

Figure 8-18b The Formation and Circulation of Cerebrospinal Fluid.
Superior sagittal sinus Cranium Dura mater (outer layer) Arachnoid granulation Fluid movement Dura mater (inner layer) Cerebral cortex The relation-ship of the arachnoid granulations and dura mater. Subdural space Arachnoid mater Subarachnoid space Pia mater © 2013 Pearson Education, Inc.

The Cerebrum (8-7) Contains an outer gray matter called the cerebral cortex Deep gray matter in the cerebral nuclei and white matter of myelinated axons beneath the cortex and around the nuclei The surface of the cerebrum Folds into gyri Separated by depressions called sulci or deeper grooves called fissures © 2013 Pearson Education, Inc.

The Cerebral Hemispheres (8-7)
Are separated by the longitudinal fissure The central sulcus Extends laterally from the longitudinal fissure The frontal lobe Is anterior to the central sulcus Is bordered inferiorly by the lateral sulcus © 2013 Pearson Education, Inc.

The occipital lobe Located most posteriorly The lobes are named for the cranial bone above it Each lobe has sensory regions and motor regions Each hemisphere sends and receives information from the opposite side of the body © 2013 Pearson Education, Inc.

Motor and Sensory Areas of the Cortex (8-7)
Are divided by the central sulcus The precentral gyrus of the frontal lobe Contains the primary motor cortex The postcentral gyrus of the parietal lobe Contains the primary sensory cortex © 2013 Pearson Education, Inc.

Motor and Sensory Areas of Cortex (8-7)
The visual cortex is in the occipital lobe The gustatory, auditory, and olfactory cortexes are in the temporal lobe © 2013 Pearson Education, Inc.

Association Areas (8-7) Interpret incoming information
Coordinate a motor response, integrating the sensory and motor cortexes The somatic sensory association area Helps to recognize touch The somatic motor association area Is responsible for coordinating movement © 2013 Pearson Education, Inc.

Figure 8-19 The Surface of the Cerebral Hemispheres.
Primary motor cortex (precentral gyrus) Central sulcus Primary sensory cortex (postcentral gyrus) Somatic motor association area (premotor cortex) PARIETAL LOBE Somatic sensory association area FRONTAL LOBE Visual association area Prefrontal cortex OCCIPITAL LOBE Gustatory cortex Visual cortex Insula Lateral sulcus Auditory association area Auditory cortex Olfactory cortex TEMPORAL LOBE © 2013 Pearson Education, Inc.

Cortical Connections (8-7)
Regions of the cortex are linked by the deeper white matter The left and right hemispheres are linked across the corpus callosum Other axons link the cortex with: The diencephalon, brain stem, cerebellum, and spinal cord © 2013 Pearson Education, Inc.

Higher-Order Centers (8-7)
Integrative areas, usually only in the left hemisphere The general interpretive area or Wernicke's area Integrates sensory information to form visual and auditory memory The speech center or Broca's area Regulates breathing and vocalization, the motor skills needed for speaking © 2013 Pearson Education, Inc.

The Prefrontal Cortex (8-7)
In the frontal lobe Coordinates information from the entire cortex Skills such as: Predicting time lines Making judgments Feelings such as: Frustration, tension, and anxiety © 2013 Pearson Education, Inc.

Hemispheric Lateralization (8-7)
The concept that different brain functions can and do occur on one side of the brain The left hemisphere tends to be involved in language skills, analytical tasks, and logic The right hemisphere tends to be involved in analyzing sensory input and relating it to the body, as well as analyzing emotional content © 2013 Pearson Education, Inc.

Figure 8-20 Hemispheric Lateralization.
LEFT HAND RIGHT HAND Prefrontal cortex Prefrontal cortex Speech center Anterior commissure C O R P Writing U S Analysis by touch C A Auditory cortex (right ear) L Auditory cortex (left ear) L O S U General interpretive center (language and mathematical calculation) M Spatial visualization and analysis Visual cortex (right visual field) Visual cortex (left visual field) LEFT HEMISPHERE RIGHT HEMISPHERE © 2013 Pearson Education, Inc.

The Electroencephalogram (8-7)
EEG A printed record of brain wave activity Can be interpreted to diagnose brain disorders More modern techniques Brain imaging, using the PET scan and MRIs, has allowed extensive "mapping" of the brain's functional areas © 2013 Pearson Education, Inc.

Alpha waves are characteristic of normal resting adults
Figure Brain Waves. Patient being wired for EEG monitoring Alpha waves are characteristic of normal resting adults Beta waves typically accompany intense concentration Theta waves are seen in children and in frustrated adults Delta waves occur in deep sleep and in certain pathological conditions Seconds 1 2 3 4 © 2013 Pearson Education, Inc.

Memory (8-7) Fact memory The recall of bits of information
Skill memory Learned motor skill that can become incorporated into unconscious memory Short-term memory Doesn't last long unless rehearsed Converting into long-term memory through memory consolidation Long-term memory Remains for long periods, sometimes an entire lifetime Amnesia Memory loss as a result of disease or trauma © 2013 Pearson Education, Inc.

The Basal Nuclei (8-7) Masses of gray matter Caudate nucleus
Lies anterior to the lentiform nucleus Which contains the medial globus pallidus and the lateral putamen Inferior to the caudate and lentiform nuclei is the amygdaloid body or amygdala Basal nuclei Subconscious control of skeletal muscle tone © 2013 Pearson Education, Inc.

Figure 8-22 The Basal Nuclei.
Head of caudate nucleus Lentiform nucleus Thalamus Tail of caudate nucleus Amygdaloid body Lateral view of a transparent brain, showing the relative positions of the basal nuclei Head of caudate nucleus Corpus callosum Lateral ventricle Insula Tip of lateral ventricle Putamen Amygdaloid body Lentiform nucleus Globus pallidus Frontal section © 2013 Pearson Education, Inc.

The Limbic System (8-7) Includes the olfactory cortex, basal nuclei, gyri, and tracts between the cerebrum and diencephalon A functional grouping, rather than an anatomical one Establishes the emotional states Links the conscious with the unconscious Aids in long-term memory with help of the hippocampus © 2013 Pearson Education, Inc.

Figure 8-23 The Limbic System.
Cingulate gyrus Corpus callosum Thalamic nuclei Fornix Hypothalamic nuclei Mamillary body Olfactory tract Amygdaloid body Hippocampus © 2013 Pearson Education, Inc.

The Diencephalon (8-7) Contains switching and relay centers
Centers integrate conscious and unconscious sensory information and motor commands Surround third ventricle Three components Epithalamus Thalamus Hypothalamus © 2013 Pearson Education, Inc.

The Epithalamus (8-7) Lies superior to the third ventricle and forms the roof of the diencephalon The anterior part contains choroid plexus The posterior part contains the pineal gland that is endocrine and secretes melatonin © 2013 Pearson Education, Inc.

The Thalamus (8-7) The left and right thalamus are separated by the third ventricle The final relay point for sensory information Only a small part of this input is sent on to the primary sensory cortex © 2013 Pearson Education, Inc.

The Hypothalamus (8-7) Lies inferior to the third ventricle
The subconscious control of skeletal muscle contractions is associated with strong emotion Adjusts the pons and medulla functions Coordinates the nervous and endocrine systems © 2013 Pearson Education, Inc.

The Hypothalamus (8-7) Secretes hormones
Produces sensations of thirst and hunger Coordinates voluntary and ANS function Regulates body temperature Coordinates daily cycles © 2013 Pearson Education, Inc.

The Midbrain (8-7) Contains various nuclei
Two pairs involved in visual and auditory processing, the colliculi Contains motor nuclei for cranial nerves III and IV Cerebral peduncles contain descending fibers Reticular formation is a network of nuclei related to the state of wakefulness The substantia nigra influence muscle tone © 2013 Pearson Education, Inc.

The Pons (8-7) Links the cerebellum with the midbrain, diencephalon, cerebrum, and spinal cord Contains sensory and motor nuclei for cranial nerves V, VI, VII, and VIII Other nuclei influence rate and depth of respiration © 2013 Pearson Education, Inc.

The Cerebellum (8-7) An automatic processing center
Which adjusts postural muscles to maintain balance Programs and fine-tunes movements The cerebellar peduncles Are tracts that link the cerebral cortex, basal nuclei, and brain stem Ataxia Is disturbance of coordination Can be caused by damage to the cerebellum © 2013 Pearson Education, Inc.

The Medulla Oblongata (8-7)
Connects the brain with the spinal cord Contains sensory and motor nuclei for cranial nerves VIII, IX, X, XI, and XII Contains reflex centers Cardiovascular centers Adjust heart rate and arteriolar diameter Respiratory rhythmicity centers Regulate respiratory rate © 2013 Pearson Education, Inc.

Figure 8-24a The Diencephalon and Brain Stem.
Cerebral peduncle Diencephalon Optic tract Thalamus Thalamic nuclei Cranial nerves Midbrain N II Superior colliculus N III Inferior colliculus N IV N V N VI Pons Cerebellar peduncles N VII N VIII N IX N X Medulla oblongata N XI N XII Spinal nerve C1 Spinal cord Spinal nerve C2 Lateral view © 2013 Pearson Education, Inc.

Figure 8-24b The Diencephalon and Brain Stem.
Choroid plexus Thalamus Third ventricle Pineal gland Corpora quadrigemina Superior colliculi Inferior colliculi N IV Cerebral peduncle Cerebellar peduncles Choroid plexus in roof of fourth ventricle Dorsal roots of spinal nerves C1 and C2 Posterior view © 2013 Pearson Education, Inc.

Checkpoint (8-7) Describe one major function of each of the six regions of the brain. The pituitary gland links the nervous and endocrine systems. To which portion of the diencephalon is it attached? How would decreased diffusion across the arachnoid granulations affect the volume of cerebrospinal fluid in the ventricles? Mary suffers a head injury that damages her primary motor cortex. Where is this area located? © 2013 Pearson Education, Inc.

Checkpoint (8-7) What senses would be affected by damage to the temporal lobes of the cerebrum? The thalamus acts as a relay point for all but what type of sensory information? Changes in body temperature stimulate which area of the diencephalon? The medulla oblongata is one of the smallest sections of the brain. Why can damage to it cause death, whereas similar damage in the cerebrum might go unnoticed? © 2013 Pearson Education, Inc.

Peripheral Nervous System (8-8)
Links the CNS to the rest of the body through peripheral nerves They include the cranial nerves and the spinal nerves The cell bodies of sensory and motor neurons are contained in the ganglia © 2013 Pearson Education, Inc.

The Cranial Nerves (8-8) 12 pairs, noted as Roman numerals I through XII Some are: Only motor pathways Only sensory pathways Mixed having both sensory and motor neurons Often remembered with a mnemonic "Oh, Once One Takes The Anatomy Final, Very Good Vacations Are Heavenly" © 2013 Pearson Education, Inc.

The Cranial Nerves (8-8) The olfactory nerves (N I)
Are connected to the cerebrum Carry information concerning the sense of smell The optic nerves (N II) Carry visual information from the eyes, through the optic foramina of the orbits to the optic chiasm Continue as the optic tracts to the nuclei of the thalamus © 2013 Pearson Education, Inc.

The Cranial Nerves (8-8) The oculomotor nerves (N III)
Motor only, arising in the midbrain Innervate four of six extrinsic eye muscles and the intrinsic eye muscles that control the size of the pupil The trochlear nerves (N IV) Smallest, also arise in the midbrain Innervate the superior oblique extrinsic muscles of the eyes © 2013 Pearson Education, Inc.

The Cranial Nerves (8-8) The trigeminal nerves (N V)
Have nuclei in the pons, are the largest cranial nerves Have three branches The ophthalmic From the orbit, sinuses, nasal cavity, skin of forehead, nose, and eyes The maxillary From the lower eyelid, upper lip, cheek, nose, upper gums, and teeth The mandibular From salivary glands and tongue © 2013 Pearson Education, Inc.

The Cranial Nerves (8-8) The abducens nerves (N VI)
Innervate only the lateral rectus extrinsic eye muscle, with the nucleus in the pons The facial nerves (N VII) Mixed, and emerge from the pons Sensory fibers monitor proprioception in the face Motor fibers provide facial expressions; control tear and salivary glands © 2013 Pearson Education, Inc.

The Cranial Nerves (8-8) The vestibulocochlear nerves (N VIII)
Respond to sensory receptors in the inner ear There are two components The vestibular nerve Conveys information about balance and position The cochlear nerve Responds to sound waves for the sense of hearing Their nuclei are in the pons and medulla oblongata © 2013 Pearson Education, Inc.

The Cranial Nerves (8-8) The glossopharyngeal nerves (N IX)
Mixed nerves innervating the tongue and pharynx Their nuclei are in the medulla oblongata The sensory portion monitors taste on the posterior third of the tongue and monitors BP and blood gases The motor portion controls pharyngeal muscles used in swallowing, and fibers to salivary glands © 2013 Pearson Education, Inc.

The Cranial Nerves (8-8) The vagus nerves (N X)
Have sensory input vital to autonomic control of the viscera Motor control includes the soft palate, pharynx, and esophagus Are a major pathway for ANS output to cardiac muscle, smooth muscle, and digestive glands © 2013 Pearson Education, Inc.

The Cranial Nerves (8-8) The accessory nerves (N XI)
Have fibers that originate in the medulla oblongata Also in the lateral gray horns of the first five cervical segments of the spinal cord The hypoglossal nerves (N XII) Provide voluntary motor control over the tongue © 2013 Pearson Education, Inc.

Figure 8-25 The Cranial Nerves.
Mamillary body Basilar artery Olfactory bulb, termination of olfactory nerve (I) Olfactory tract Optic chiasm Optic nerve (II) Infundibulum Oculomotor nerve (III) Trochlear nerve (IV) Trigeminal nerve (V) Abducens nerve (VI) Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Hypoglossal nerve (XII) Accessory nerve (XI) Diagrammatic view showing the attachment of the 12 pairs of cranial nerves Spinal cord Medulla oblongata Cerebellum Inferior view of the brain Vertebral Pons © 2013 Pearson Education, Inc.

Table 8-2 The Cranial Nerves

The Spinal Nerves (8-8) Found in 31 pairs grouped according to the region of the vertebral column 8 pairs of cervical nerves, C1–C8 12 pairs of thoracic nerves, T1–T12 5 pairs of lumbar nerves, L1–L5 5 pairs of sacral nerves, S1–S5 1 pair of coccygeal nerves, Co1 © 2013 Pearson Education, Inc.

Nerve Plexuses (8-8) The origin of major nerve trunks of the PNS
The cervical plexus Innervates the muscles of the head and neck and the diaphragm The brachial plexus Innervates the shoulder girdle and upper limb The lumbar plexus and the sacral plexus Innervate the pelvic girdle and lower limb © 2013 Pearson Education, Inc.

Figure 8-26 Peripheral Nerves and Nerve Plexuses.
C Cervical plexus 1 C 2 C 3 C 4 C 5 C Phrenic nerve (extends to the diaphragm) Brachial plexus C 6 7 C T 8 T 1 2 Axillary nerve T 3 T 4 T 5 T 6 T Musculocutaneous nerve 7 T 8 T 9 T 10 T 11 T 12 Radial nerve L 1 Lumbar plexus L 2 Ulnar nerve L 3 Median nerve L 4 L 5 S Sacral plexus 1 S 2 S 3 S 4 S 5 Co 1 Femoral nerve Obturator nerve Gluteal nerves Saphenous nerve Sciatic nerve © 2013 Pearson Education, Inc.

Figure 8-27 Dermatomes. C2–C3 N V C2–C3 C2 C3 C3 C4 T2 C4 C5 T3 T1 T2
L1 C6 T10 L2 T11 L4 L3 T1 C6 C7 T12 L5 L1 S S L2 4 S2 3 C8 C8 T1 L3 L1 C7 S5 S1 L5 L4 L2 S2 L5 L3 S1 L4 ANTERIOR POSTERIOR © 2013 Pearson Education, Inc.

Table 8-3 Nerve Plexuses and Major Nerves

Checkpoint (8-8) What signs would you associate with damage to the abducens nerve (N VI)? John is having trouble moving his tongue. His physician tells him it is due to pressure on a cranial nerve. Which cranial nerve is involved? Injury to which nerve plexus would interfere with the ability to breathe? © 2013 Pearson Education, Inc.

Reflexes (8-9) Rapid, automatic, unlearned motor response to a stimulus Usually removes or opposes the original stimulus Monosynaptic reflexes For example, the stretch reflex Which responds to muscle spindles, is the simplest with only one synapse The best known stretch reflex is probably the knee jerk reflex © 2013 Pearson Education, Inc.

Simple Reflexes (8-9) Are wired in a reflex arc
A stimulus activates a sensory receptor An action potential travels down an afferent neuron Information processing occurs with the interneuron An action potential travels down an efferent neuron The effector organ responds © 2013 Pearson Education, Inc.

Figure 8-28 The Components of a Reflex Arc.
Sensation relayed to the brain by axon collaterals Dorsal root Arrival of stimulus and activation of receptor Activation of a sensory neuron Information processing in the CNS REFLEX ARC Receptor Stimulus Effector Response by effector KEY Ventral root Sensory neuron (stimulated) Activation of a motor neuron Excitatory interneuron Motor neuron (stimulated) © 2013 Pearson Education, Inc.

Figure 8-29 A Stretch Reflex.
Stretching of muscle tendon stimulates muscle spindles Muscle spindle (stretch receptor) Stretch Spinal Cord REFLEX ARC Contraction Activation of motor neuron produces reflex muscle contraction © 2013 Pearson Education, Inc.

Complex Reflexes (8-9) Polysynaptic reflexes Withdrawal reflexes
With at least one interneuron Are slower than monosynaptic reflexes, but can activate more than one effector Withdrawal reflexes Like the flexor reflex, move a body part away from the stimulation Like touching a hot stove Reciprocal inhibition Blocks the flexor's antagonist To ensure that flexion is in no way interfered with © 2013 Pearson Education, Inc.

Figure 8-30 The Flexor Reflex, a Type of Withdrawal Reflex.
Distribution within gray horns to other segments of the spinal cord Painful stimulus Flexors stimulated Extensors inhibited KEY Sensory neuron (stimulated) Motor neuron (inhibited) Excitatory interneuron Inhibitory interneuron Motor neuron (stimulated) © 2013 Pearson Education, Inc.

Input to Modify Reflexes (8-9)
Reflexes are automatic, but higher brain centers can influence or modify them The Babinski sign Triggered by stroking an infant's sole, resulting in a fanning of the toes As descending inhibitory synapses develop, an adult will respond by curling the toes instead, called the plantar reflex © 2013 Pearson Education, Inc.

Checkpoint (8-9) Define reflex.
Which common reflex do physicians use to test the general condition of the spinal cord, peripheral nerves, and muscles? Why can polysynaptic reflexes produce more involved responses than can monosynaptic reflexes? After injuring his back lifting a sofa, Tom exhibits a positive Babinski reflex. What does this imply about Tom's injury? © 2013 Pearson Education, Inc.

Sensory Pathways (8-10) Are ascending pathways A sensory homunculus
Posterior column pathway Spinothalamic pathway Spinocerebellar pathway A sensory homunculus A mapping of the area of the cortex dedicated to the number of sensory receptors, not the size of the body area © 2013 Pearson Education, Inc.

Figure 8-31 The Posterior Column Pathway.
Sensory homunculus of left cerebral hemisphere KEY Axon of first- order neuron Second-order neuron Nuclei in thalamus Third-order neuron MIDBRAIN Nucleus in medulla oblongata MEDULLA OBLONGATA SPINAL CORD Dorsal root ganglion Fine-touch, pressure, vibration, and proprioception sensations from right side of body © 2013 Pearson Education, Inc.

Motor Pathways (8-10) Are descending pathways A motor homunculus
Corticospinal pathway Also called pyramidal system Medial and lateral pathways Also called extrapyramidal system A motor homunculus Represents the distribution of somatic and ANS motor innervation © 2013 Pearson Education, Inc.

Figure 8-32 The Corticospinal Pathway.
Motor homunculus on primary motor cortex of left cerebral hemisphere KEY Axon of upper motor neuron Lower motor neuron To skeletal muscles Motor nuclei of cranial nerves MIDBRAIN To skeletal muscles Motor nuclei of cranial nerves MEDULLA OBLONGATA Lateral corticospinal tract Anterior corticospinal tract To skeletal muscles SPINAL CORD Motor neuron in anterior gray horn © 2013 Pearson Education, Inc.

Table 8-4 Sensory and Motor Pathways

Checkpoint (8-10) As a result of pressure on her spinal cord, Jill cannot feel touch or pressure on her legs. What sensory pathway is being compressed? The primary motor cortex of the right cerebral hemisphere controls motor function on which side of the body? An injury to the superior portion of the motor cortex would affect the ability to control muscles of which parts of the body? © 2013 Pearson Education, Inc.

The Autonomic Nervous System (8-11)
Unconscious adjustment of homeostatically essential visceral responses Sympathetic division Parasympathetic division The somatic NS and ANS are anatomically different SNS: one neuron to skeletal muscle ANS: two neurons to cardiac and smooth muscle, glands, and fat cells © 2013 Pearson Education, Inc.

Two Neuron Pathways of the ANS (8-11)
Preganglionic neuron Has cell body in spinal cord, synapses at the ganglion with the postganglionic neuron In sympathetic division Preganglionic fibers are short Postganglionic fibers are long In parasympathetic division Preganglionic fibers are long Postganglionic fibers are "short" © 2013 Pearson Education, Inc.

Somatic nervous system Autonomic nervous system
Figure The Organization of the Somatic and Autonomic Nervous Systems. Upper motor neurons in Primary motor cortex Visceral motor nuclei in hypothalamus BRAIN BRAIN Somatic motor nuclei of brain stem Preganglionic neuron Visceral Effectors Smooth muscle Autonomic nuclei in brain stem Glands Autonomic ganglia Skeletal muscle Lower motor neurons SPINAL CORD Cardiac muscle Ganglionic neurons SPINAL CORD Somatic motor nuclei of spinal cord Autonomic nuclei in spinal cord Preganglionic neuron Adipocytes Skeletal muscle Somatic nervous system Autonomic nervous system © 2013 Pearson Education, Inc.

Neurotransmitters at Specific Synapses (8-11)
All synapses between pre- and postganglionic fibers: Are cholinergic (ACh) and excitatory Postganglionic parasympathetic synapses Are cholinergic Some are excitatory, some inhibitory, depending on the receptor Most postganglionic sympathetic synapses: Are adrenergic (NE) and usually excitatory © 2013 Pearson Education, Inc.

The Sympathetic Division (8-11)
Sympathetic chain Arises from spinal segments T1–L2 The preganglionic fibers enter the sympathetic chain ganglia just outside the spinal column Collateral ganglia are unpaired ganglia that receive splanchnic nerves from the lower thoracic and upper lumbar segments Postganglionic neurons innervate abdominopelvic cavity © 2013 Pearson Education, Inc.

The adrenal medullae Are innervated by preganglionic fibers Are modified neural tissue that secrete E and NE into capillaries, functioning like an endocrine gland The effect is nearly identical to that of the sympathetic postganglionic stimulation of adrenergic synapses © 2013 Pearson Education, Inc.

Figure 8-34 The Sympathetic Division.
Eye PONS Salivary glands Sympathetic nerves Cervical sympathetic ganglia Heart T1 T1 Cardiac and pulmonary plexuses Spinal nerves Splanchnic nerve Lung Collateral ganglion Coll- ateral ganglion Liver and gallbladder Stomach Splan- chnic nerves Spleen Pancreas Large intestine Postganglionic fibers to spinal nerves (innervating skin, blood vessels, sweat glands, arrector pili muscles, adipose tissue) Collateral ganglion Small intestine L2 L2 Adrenal medulla Kidney Sympathetic chain ganglia KEY Spinal cord Preganglionic neurons Ganglionic neurons Ovary Penis Scrotum Urinary bladder Uterus © 2013 Pearson Education, Inc.

Also called the "fight-or-flight" division Effects Increase in alertness, metabolic rate, sweating, heart rate, blood flow to skeletal muscle Dilates the respiratory bronchioles and the pupils Blood flow to the digestive organs is decreased E and NE from the adrenal medullae support and prolong the effect © 2013 Pearson Education, Inc.

The Parasympathetic Division (8-11)
Preganglionic neurons arise from the brain stem and sacral spinal cord Include cranial nerves III, VII, IX, and X, the vagus, a major parasympathetic nerve Ganglia very close to or within the target organ Preganglionic fibers of the sacral areas form the pelvic nerves © 2013 Pearson Education, Inc.

The Parasympathetic Division (8-11)
Less divergence than in the sympathetic division, so effects are more localized Also called "rest-and digest" division Effects Constriction of the pupils, increase in digestive secretions, increase in digestive tract smooth muscle activity Stimulates urination and defecation Constricts bronchioles, decreases heart rate © 2013 Pearson Education, Inc.

Figure 8-35 The Parasympathetic Division.
Terminal ganglion N III Lacrimal gland Eye PONS Terminal ganglion N VII Terminal ganglion Salivary glands N IX Terminal ganglion N X (Vagus) Heart Cardiac and pulmonary plexuses Lungs Liver and gallbladder Stomach Spleen Pancreas Large intestine Pelvic nerves Small intestine Rectum Spinal cord S2 Kidney S3 S4 KEY Urinary bladder Preganglionic neurons Ganglionic neurons Uterus Ovary Penis Scrotum © 2013 Pearson Education, Inc.

Checkpoint (8-11) While out for a brisk walk, Megan is suddenly confronted by an angry dog. Which division of the ANS is responsible for the physiological changes that occur as she turns and runs from the animal? Why is the parasympathetic division of the ANS sometimes referred to as the anabolic system? What effect would loss of sympathetic stimulation have on the flow of air into the lungs? What physiological changes would you expect in a patient who is about to undergo a root canal procedure and is quite anxious about it? © 2013 Pearson Education, Inc.

Aging and the Nervous System (8-12)
Common changes Reduction in brain size and weight and reduction in number of neurons Reduction in blood flow to the brain Change in synaptic organization of the brain Increase in intracellular deposits and extracellular plaques Senility can be a result of all these changes © 2013 Pearson Education, Inc.

Figure 8-36 SYSTEM INTEGRATOR The NERVOUS System
Body System Nervous System Nervous System Body System Provides sensations of touch, pressure, pain, vibration, and temperature; hair provides some protection and insulation for skull and brain; protects peripheral nerves Controls contraction of arrector pili muscles and secretion of sweat glands Integumentary Integumentary (Page 138) Provides calcium for neural function; protects brain and spinal cord Controls skeletal muscle contractions that results in bone thickening and maintenance and determine bone position Skeletal Skeletal (Page 188) Facial muscles express emotional state; intrinsic laryngeal muscles permit communication; muscle spindles provide proprioceptive sensations Controls skeletal muscle contractions; coordinates respiratory and cardiovascular activities Muscular Muscular (Page 241) The NERVOUS System The nervous system is closely integrated with other body systems. Every moment of your life, billions of neurons in your nervous system are exchanging information across trillions of synapses and performing the most complex integrative functions in the body. As part of this process, the nervous system monitors all other systems and issues commands that adjust their activities. However, the impact of these commands varies greatly from one system to another. The normal functions of the muscular system, for example, simply cannot be performed without instructions from the nervous system. By contrast, the cardiovascular system is relatively independent—the nervous system merely coordinates and adjusts cardiovascular activities to meet the circulatory demands of other systems. In the final analysis, the nervous system is like the conductor of an orchestra, directing the rhythm and balancing the performances of each section to produce a symphony, instead of simply a very loud noise. Endocrine (Page 376) Cardiovascular (Page 467) Lymphatic (Page 500) Respiratory (Page 532) Digestive (Page 572) Urinary (Page 637) Reproductive (Page 671) © 2013 Pearson Education, Inc.

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