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Hole’s Essentials of Human Anatomy & Physiology David Shier Jackie Butler Ricki Lewis
Created by Dr. Melissa Eisenhauer
Head Athletic Trainer/Assistant Professor
Trevecca Nazarene University
Chapter 9
Lecture Outlines*
*See PowerPoint image slides for all figures and tables
pre-inserted into PowerPoint without notes.

2. Chapter 9
Nervous System

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 Introduction:
The nervous system is composed of two types of cells: neurons and neuroglia.
Neurons transmit nerve impulses along nerve fibers to other neurons. Neurons typically have a cell body, axons and dendrites.
Neuroglia carry out a variety of functions to aid and protect components of the nervous system.

5. Organs of the nervous system can be divided into the:
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Organs of the nervous system can be divided into the:
Central nervous system (CNS), made up of the brain and spinal cord
Peripheral nervous system (PNS), made up of peripheral nerves that connect the CNS to the rest of the body.

7.  General Functions of the Nervous System
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 General Functions of the Nervous System
SENSORY: Sensory receptors at the ends of peripheral nerves gather information and convert it into nerve impulses.
INTEGRATION: When sensory impulses are integrated in the brain as perceptions, this is the integrative function of the nervous system.
MOTOR: Conscious or subconscious decisions follow, leading to motor functions via effectors.

8.  Supporting cells of the Nervous System – Neuroglial Cells
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 Supporting cells of the Nervous System – Neuroglial Cells
Neuroglial cells fill spaces, support neurons, provide structural frameworks, produce myelin, and carry on phagocytosis.

9. Four neuroglial cells are found in the CNS and the last in the PNS.
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Four neuroglial cells are found in the CNS and the last in the PNS.
Microglial cells are small cells that phagocytize bacterial cells and cellular debris.
Oligodendrocytes form myelin in the brain and spinal cord.
Astrocytes are near blood vessels and support structures, aid in metabolism, and respond to brain injury by filling in spaces.
Ependyma cover the inside of ventricles and form choroid plexuses within the ventricles
Schwann cells are the myelin-producing neuroglia of the peripheral nervous system.

11. Neuroglia differs from Neurons
Resemble neurons structurally, but are not able to transmit nerve impulses
Never lose the ability to divide like neurons. Most brain tumors are formed by neuroglial cells.

12.  Neuron Structure A neuron contains the following main structures:
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 Neuron Structure
A neuron contains the following main structures:
Cell body with a nucleus as well as other cell organelles.
Branching dendrites carry impulses from other neurons (or from receptors) toward the cell body. They receive messages and each neuron can have as many as 100 dendrites.
The axon transmits the impulse away from the cell body and may give off side branches.

14. The smallest axons lack a myelin sheath and are unmyelinated fibers.
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Larger axons in the PNS are enclosed by sheaths of myelin provided by Schwann cells and are called myelinated fibers.
The outer layer of myelin is surrounded by a neurilemma (myelin sheath) made up of the cytoplasm and nuclei of the Schwann cell.
Narrow gaps in the myelin sheath between Schwann cells are called nodes of Ranvier.
The smallest axons lack a myelin sheath and are unmyelinated fibers.

16. White matter in the CNS is due to myelin sheaths in this area.
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White matter in the CNS is due to myelin sheaths in this area.
Unmyelinated nerve tissue in the CNS comprise the gray matter.

17. Multiple Sclerosis
Myelin sheaths are damaged and hardened which causes the person to lose the ability to control muscle movement.

18. Regeneration of Neurons
Peripheral neurons are able to regenerate because of the neurilemma but the CNS axons are myelinated by oligodendrocytes thus lacking neurilemma and usually do not regenerate

19. Classification of Neurons
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Classification of Neurons
Neurons can be grouped in two ways:
structural differences
bipolar, unipolar, and multipolar
functional differences
sensory neurons, interneurons, and motor neurons

20. Classification of Neurons – Structural
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Classification of Neurons – Structural
Bipolar neurons are found in the eyes, nose, and ears, and have a single axon and a single dendrite extending from opposite sides of the cell body.
Unipolar neurons are found in ganglia outside the CNS and have an axon and a dendrite arising from a single short fiber extending from the cell body.
Multipolar neurons have many nerve fibers arising from their cell bodies and are commonly found in the brain and spinal cord.

21. Classification of Neurons – Functional
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Classification of Neurons – Functional
Sensory neurons (afferent neurons) conduct impulses from peripheral receptors to the CNS and are usually unipolar, although some are bipolar neurons
Interneurons are multipolar neurons lying within the CNS that form links between sensory and motor neurons.
Motor neurons (efferent neurons) are multipolar neurons that conduct impulses from the CNS to effectors.

22. HOW DO NEURONS COMMUNICATE?
Conductivity and Impulse

23. Cell Membrane Potential
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Cell Membrane Potential
A cell membrane is usually polarized, with an excess of negative charges on the inside of the membrane; polarization is important to the conduction of nerve impulses.
Conduction: Ability to transmit impulse to other neurons, muscles, or glands.

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Resting Potential
Due to active transport, the cell maintains a greater concentration of sodium ions outside and a greater concentration of potassium ions inside the membrane.
The inside of the membrane has excess negative charges, while the outside has more positive charges.
This separation of charge, or potential difference, is called the resting potential.
Resting potential is -70 mV

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Potential Changes
Stimulation of a membrane can locally affect its resting potential.
When the membrane potential becomes less negative, the membrane is depolarized.
If sufficiently strong depolarization occurs, a threshold potential is achieved as ion channels open.
At threshold, an action potential is reached.

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Action Potential
At threshold potential, membrane permeability to sodium suddenly changes in the region of stimulation
As sodium channels open, sodium ions rush in, and the membrane potential changes and becomes depolarized.
At the same time, potassium channels open to allow potassium ions to leave the cell, the membrane becomes repolarized, and resting potential is reestablished.
This rapid sequence of events is the action potential.
The active transport mechanism then works to maintain the original concentrations of sodium and potassium ions.

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Nerve Impulse
A nerve impulse is conducted as an action potential that is reached at the trigger zone. This spreads by a local current flowing down the fiber, and adjacent areas of the membrane reach action potential.

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Impulse Conduction
Unmyelinated fibers conduct impulses over their entire membrane surface.
Myelinated fibers conduct impulses from one Node of Ranvier to the next, a phenomenon called saltatory conduction.
Saltatory conduction is many times faster than conduction on unmyelinated neurons.

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All-or-None Response
If a nerve fiber responds at all to a stimulus, it responds completely by conducting an impulse (all-or-none response)
Greater intensity of stimulation triggers more impulses per second, not stronger impulses.

32. The junction between two communicating neurons is called a synapse
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The Synapse
The junction between two communicating neurons is called a synapse
A synaptic cleft is between them across which the impulse must be transmitted by a neurotransmitter.

33. Synaptic Transmission
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Synaptic Transmission
When an impulse reaches the synaptic knobs of an axon, synaptic vesicles release a neurotransmitter into the synaptic cleft.
The neurotransmitter reacts with specific receptors on the postsynaptic membrane.

34. Excitatory and Inhibitory Actions
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Excitatory and Inhibitory Actions
Neurotransmitters that increase postsynaptic membrane permeability to sodium ions may trigger impulses and are thus excitatory.
Other neurotransmitters may decrease membrane permeability to sodium ions, reducing the chance that it will reach threshold, and are thus inhibitory.
The effect on the postsynaptic neuron depends on which presynaptic knobs are activated.

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Neurotransmitters
At least 50 kinds of neurotransmitters are produced by the nervous system, most of which are synthesized in the synaptic knobs and stored in synaptic vesicles.
When an action potential reaches the synaptic knob, calcium ions rush inward and, in response some synaptic vesicles fuse with the membrane and release their contents to the synaptic cleft.
Enzymes in synaptic clefts and on postsynaptic membranes rapidly decompose the neurotransmitters after their release.
Destruction or removal of the neurotransmitter prevents continuous stimulation of the postsynaptic neuron.

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Types of Nerves A nerve is a bundle of nerve fibers held together by layers of connective tissue. Nerves can be sensory, motor, or mixed, carrying both sensory and motor fibers.

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Nerve Pathways
The routes nerve impulses travel are called pathways, the simplest of which is a reflex arc.
A reflex arc includes:
sensory receptor
sensory neuron
interneuron in the spinal cord
motor neuron
effector

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Reflex Behavior
Reflexes are automatic, subconscious responses to stimuli that help maintain homeostasis (heart rate, blood pressure, etc.) and carry out automatic responses (vomiting, sneezing, swallowing, etc.).

41. Central Nervous System
Consists of the brain and spinal cord
The brain weighs a little over 3 pounds and is about the size of two fists.
It looks to be pinkish gray tissue, wrinkled like a walnut, with a cold oatmeal texture
Protection includes both the bones (skull and vertebrae) as well as membranes called meninges.

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Meninges
The brain and spinal cord are surrounded by membranes called meninges that lie between the bone and the soft tissues.

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Meninges (Meninx)
The outermost meninx is made up of tough, white dense connective tissue, contains many blood vessels, and is called the dura mater.
The middle meninx, the arachnoid mater, is thin and lacks blood vessels.
It does not follow the convolutions of the brain.
Between the arachnoid and pia mater is a subarachnoid space containing cerebrospinal fluid.
The innermost pia mater is thin and contains many blood vessels and nerves.
It is attached to the surface of the brain and spinal cord and follows their contours.

45. Cerebrospinal Fluid (CSF)
Protection: the CSF protects the brain from damage by "buffering" the brain. In other words, the CSF acts to cushion a blow to the head and lessen the impact.
Buoyancy: because the brain is immersed in fluid, the net weight of the brain is reduced from about 1,400 gm to about 50 gm. Therefore, pressure at the base of the brain is reduced.
Excretion of waste products: the one-way flow from the CSF to the blood takes potentially harmful metabolites, drugs and other substances away from the brain.
Endocrine medium for the brain: the CSF serves to transport hormones to other areas of the brain. Hormones released into the CSF can be carried to remote sites of the brain where they may act.

47. Blood – Brain Barrier
Neurons are kept separate from blood borne substances
Metabolic wastes like urea, toxins, and proteins are prevented from entering brain tissue.
Nutrients (like glucose), anesthetics, water, alcohol, and nicotine all easily pass through the barrier.

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Spinal Cord
The spinal cord begins at the base of the brain and extends as a slender cord to the level of the intrevertebral disk between the first and second lumbar vertebrae.

49. Structure - Spinal Cord
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Structure - Spinal Cord
The spinal cord consists of 31 segments, each of which gives rise to a pair of spinal nerves.

50. Functions – Spinal Cord
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Functions – Spinal Cord
The spinal cord has two major functions: to transmit impulses to and from the brain, and to house spinal reflexes.
Tracts carrying sensory information to the brain are called ascending tracts; descending tracts carry motor information from the brain.

51. The brain can be divided into:
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Brain
The brain is the largest, most complex portion of the nervous system, containing 100 billion multipolar neurons.
The brain can be divided into:
Cerebrum (largest portion and associated with higher mental functions)
Diencephalon (processes sensory input)
Cerebellum (coordinates muscular activity)
Brain stem (coordinates and regulates visceral activities).

53. Structure of the Cerebrum
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Structure of the Cerebrum
Largest portion of the mature brain, consisting of two cerebral hemispheres.
A deep ridge of nerve fibers, the corpus callosum, connect the hemispheres.

54. Functions of the Cerebrum
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Functions of the Cerebrum
The cerebrum provides higher brain functions, such as interpretation of sensory input, initiating voluntary muscular movements, memory, an integrating information for reasoning.

56. 4 Lobes of the Cerebrum Frontal Parietal Temporal Occipital
The names of the lobes come from the skull bones that overlie them.

58. Cerebral Cortex – Gray Matter
Folded outer layer of the cerebral hemispheres
Gray color because it contains cell bodies

59. Cerebral Cortex – Gray Matter
Covered by elevated ridges of tissue called gyri (gyrus – singular) and is the gray matter.
Shallow grooves that separate the ridges are called sulci (sulcus – singular)
Deep grooves are called fissures

60. Cerebrum - White Matter
Beneath the cortex lies a mass of white matter made up of myelinated nerve fibers connecting the cell bodies of the cortex with the rest of the nervous system

61. Parietal Lobe Interprets impulses sent from sensory receptors
Speech and ability to use words

62. Frontal Lobe
Voluntary muscle control
Problem solving and planning

63. Occipital Lobe
Area responsible for vision

64. Temporal Lobe Hearing Auditory and visual memory
Hippocampus – short term memory

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Hemisphere Dominance
Both cerebral hemispheres function in receiving and analyzing sensory input and sending motor impulses to the opposite side of the body.
Most people exhibit hemisphere dominance for the language-related activities of speech, writing, and reading.
The left hemisphere is dominant in 90% of the population, although some individuals have the right hemisphere as dominant, and others show equal dominance in both hemispheres.
The non-dominant hemisphere specializes in nonverbal functions and controls emotions and intuitive thinking.

66. Ventricles and Cerebrospinal Fluid
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Ventricles and Cerebrospinal Fluid
The ventricles are a series of connected cavities within the cerebral hemispheres and brain stem.
The ventricles are continuous with the central canal of the spinal cord, and are filled with cerebrospinal fluid.
Choroid plexuses, specialized capillaries from the pia mater, secrete cerebrospinal fluid

68. Other portions of the diencephalon include:
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Diencephalon
The diencephalon lies above the brain stem and contains the thalamus and hypothalamus.
Other portions of the diencephalon include:
optic tracts & optic chiasma
posterior pituitary
pineal gland.

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Diencephalon
The thalamus functions in sorting and directing sensory information arriving from other parts of the nervous system, performing the services of both messenger and editor
The hypothalamus maintains homeostasis by regulating a wide variety of visceral activities and by linking the endocrine system with the nervous system.
The hypothalamus regulates heart rate and arterial blood pressure, body temperature, water and electrolyte balance, hunger and body weight, movements and secretions of the digestive tract, growth and reproduction, and sleep and wakefulness.

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Diencephalon
The limbic system, in the area of the diencephalon, controls emotional experience and expression.
By generating pleasant or unpleasant feelings about experiences, the limbic system guides behavior that may enhance the chance of survival.

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Brain Stem
The brain stem, consisting of the midbrain, pons, and medulla oblongata, lies at the base of the cerebrum, and connects the brain to the spinal cord.

72. The midbrain contains centers for auditory and visual reflexes.
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Brainstem – Midbrain
The midbrain contains centers for auditory and visual reflexes.

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Brainstem - Pons
The pons, lying between the midbrain and medulla oblongata, transmits impulses between the brain and spinal cord, and contains centers that regulate the rate and depth of breathing.

74. the cardiac center that controls heart rate,
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Brainstem - Medulla Oblongata
The medulla oblongata transmits all ascending and descending impulses between the brain and spinal cord.
The medulla oblongata also houses nuclei that control visceral functions, including
the cardiac center that controls heart rate,
the vasomotor center for blood pressure control,
and the respiratory center that works, along with the pons, to control the rate and depth of breathing.
Other nuclei in the medulla oblongata are associated with coughing, sneezing, swallowing, and vomiting

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Cerebellum
The cerebellum functions to integrate sensory information about the position of body parts and coordinates skeletal muscle activity and maintains posture.

78. Peripheral Nervous System
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Peripheral Nervous System
The peripheral nervous system (PNS) consists of the cranial and spinal nerves that arise from the central nervous system and travel to the remainder of the body.
Two Divisions:
Afferent (sensory) division: nerve fibers that convey impulses to the central nervous system from sensory receptors located in various parts of the body
Efferent (motor) division: carry impulses from the CNS to effector organs, the muscles and glands

79. The 12 pairs are designated by number and name.
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Cranial Nerves
Twelve pairs of cranial nerves arise from the underside of the brain, most of which are mixed nerves.
The 12 pairs are designated by number and name.
They serve the head and neck region except the vagus nerve which extends to the thorax and abdomen

80. Thirty-one pairs of mixed nerves make up the spinal nerves.
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Spinal Nerves
Thirty-one pairs of mixed nerves make up the spinal nerves.
Spinal nerves are grouped according to the level from which they arise and are numbered in sequence, beginning with those in the cervical region.
Each spinal nerve arises from two roots: a dorsal, or sensory, root, and a ventral, or motor, root.
The main branches of some spinal nerves form plexuses
Cervical Plexuses: lie on either side of the neck and supply muscles and skin of the neck.
Brachial Plexuses: lead to the upper limbs.
Lumbrosacral: lead to the lower abdomen, external genitalia, buttocks, and legs.

82. PNS Overview Afferent (sensory) Division Efferent (motor) Division
Somatic Nervous system: allows conscious or voluntary control of skeletal muscles
Autonomic Nervous system: regulates events that are autonomic or involuntary, such as the activity of smooth and cardiac muscles and glands
Sympathetic: Emergency or Stress Reaction
Parasympathetic: Normal Conditions

83. Autonomic Nervous System
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Autonomic Nervous System
The autonomic nervous system has the task of maintaining homeostasis of visceral activities without conscious effort.
General Characteristics
The autonomic nervous system includes two divisions: the sympathetic and parasympathetic divisions, which exert opposing effects on target organs.
The parasympathetic division operates under normal conditions. Rest and digest.
The sympathetic division operates under conditions of stress or emergency. Fight or Flight.

85. Control of Autonomic Activity
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Control of Autonomic Activity
The autonomic nervous system is largely controlled by reflex centers in the brain and spinal cord.
The limbic system and cerebral cortex alter the reactions of the autonomic nervous system through emotional influence.