Nervous System Chapter 9

What are the major functions of the nervous system? (9.1) Sensory input – monitoring stimuli occurring inside and outside the body Integration (processing) – interpretation of sensory input Motor output – response to stimuli by activating effector organs

Central Nervous System (CNS): includes the brain and spinal cord – this is where information processing occurs. Emotions, intelligence, memory Peripheral Nervous System (PNS): includes the neural tissue of the rest of the body that contains receptors to detect sensory information. (9.2)

Afferent (sensory) neurons – carry to the brain (CNS) for analysis that are activated by external stimuli Efferent (motor) neurons – carry away from CNS to muscles, glands, and tissue. (9.3)

Neural Tissue Organization Three Functional Classes of Neurons 1. Sensory neurons Deliver information to CNS 2. Motor neurons Stimulate or inhibit peripheral tissues 3. Interneurons (association neurons) Located between sensory and motor neurons Analyze inputs, coordinate outputs Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Somatic nervous system (SNS) – controls muscle contractions Autonomic nervous system (ANS) – provides involuntary regulation of smooth muscle, cardiac muscle, and tissues. Examples: breathing, heart beat, digestion, and saliva production (9.4)

Autonomic NS (9.5) Can be divided into: Sympathetic Nervous System “Fight or Flight” Parasympathetic Nervous System “Rest and Digest” These 2 systems are antagonistic. Typically, we balance these 2 to keep ourselves in a state of dynamic balance.

Sympathetic (9.5) “ Fight or flight” response CENTRAL NERVOUS SYSTEM Brain Spinal cord SYMPATHETIC Dilates pupil Stimulates salivation Relaxes bronchi Accelerates heartbeat Inhibits activity Stimulates glucose Secretion of adrenaline, nonadrenaline Relaxes bladder Stimulates ejaculation in male Sympathetic ganglia Salivary glands Lungs Heart Stomach Pancreas Liver Adrenal gland Kidney “ Fight or flight” response Release adrenaline and noradrenaline Increases heart rate and blood pressure Increases blood flow to skeletal muscles Inhibits digestive functions

Parasympathetic (9.5) “ Rest and digest ” system CENTRAL NERVOUS SYSTEM Brain PARASYMPATHETIC Spinal cord Stimulates salivation Constricts bronchi Slows heartbeat Stimulates activity Contracts bladder Stimulates erection of sex organs Stimulates gallbladder Gallbladder Contracts pupil “ Rest and digest ” system Calms body to conserve and maintain energy Lowers heartbeat, breathing rate, blood pressure

Summary of differences (9.5) Autonomic nervous system controls physiological arousal Sympathetic division (Exciting) Parasympathetic division (calming) Pupils dilate EYES Pupils contract Increases SALIVATION decreases Perspires SKIN Dries Increases RESPIRATION Decreases Accelerates HEART Slows Inhibits DIGESTION Activates Secrete stress hormones ADRENAL GLANDS Decrease secretion of stress hormones

Figure 8-1 1 of 7 CENTRAL NERVOUS SYSTEM PERIPHERAL 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 Somatic sensory receptors (monitor the outside world and our position in it) Visceral sensory receptors (monitor internal conditions and the status of other organ systems) Skeletal muscle Cardiac muscle Glands Adipose tissue Figure 8-1 1 of 7 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Types of Neuroglial cells (9.6) Astrocytes-star shaped cells that connect neurons together and to their blood supply. Microglia- function as phagocytes by engulfing foreign invaders. Ependymal- (epithelial-like) provide a barrier between brain and spinal fluid. Oligodendrocytes- connect thick neuronal fibers and produce an important insulating material called the myelin sheath.

Neurons Basic unit of the nervous system allowing for functional electric system. All neural functions involve the communication of neurons with one another and other cells.

Neuron Structure (9.7) Dendrites (branches) – receive incoming signals Axon (trunk) – carries outward signal toward synaptic terminals. Synaptic terminal – space between two different neurons (dendrite and axon)

Nerve Fiber Coverings (9.7/9.8) Schwann cells – produce myelin sheaths in jelly-roll like fashion Nodes of Ranvier – gaps in myelin sheath along the axon Figure 7.5 Slide 7.12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Reflex Arc (9.9) Reflex – rapid, predictable, and involuntary responses to stimuli Reflex arc – direct route from a affector neuron, to an interneuron, to an effector Figure 7.11a Slide 7.23 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Simple Reflex Arc (9.9) Video Figure 7.11b, c Slide 7.24 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Nerve Impulse Transmission (9.10) Resting potential: A nerve cell at rest, or inactive has more positive charges outside the cell giving the neuron a slightly negative charge (-70mv) Threshold potential: a change (stimulus) in the charge of the resting neuron changes to at least - 55mv allowing for an action potential to occur. Action potential: the electrical change allows sodium to flow into the cell causing the cell to be depolarized (the neuron changes it’s electrical charge to become positive) Nerve Impulse Transmission (9.10)

Nerve Impulse Transmission (9.10) Within the neuron’s membrane, there are sodium-potassium pumps allowing for chemical exchange. When a threshold potential is applied to the neuron, an action potential (nerve impulse) travels down the neuron. The nerve impulse will jump from the axon to the dendrite of another neuron across a synapse by the use of neurotransmitters Nerve Impulse Transmission (9.10)

(9.11)

What is saltatory conduction? (9.12) Myelin sheath found on the axon insulates and doesn’t allow the depolarization of the membrane. The action potential must jump from one node of Ranvier to the next. This makes the action potential move faster down the axon. Some can reach speeds of 100 m/s. Unmyelinated neurons propagate slow action potentials that must move from one site to the next. This is called continuous conduction. What is saltatory conduction? (9.12)

Saltatory conduction

Rates of AP Conduction Which do you think has a faster rate of AP conduction – myelinated or unmyelinated axons? Which do you think would conduct an AP faster – an axon with a large diameter or an axon with a small diameter? The answer to #1 is a myelinated axon. If you can’t see why, then answer this question: could you move 100ft faster if you walked heel to toe or if you bounded in a way that there were 3ft in between your feet with each step? The answer to #2 is an axon with a large diameter. If you can’t see why, then answer this question: could you move faster if you walked through a hallway that was 6ft wide or if you walked through a hallway that was 1ft wide?

Synapse Review Synapses are gaps between neurons Exists between the axon of one neuron and the dendrite of another. Neurons can connect to a large number of other neurons to transmit signals (This accounts for the complexity of the nervous system) When an action potential reaches the end of an axon, neurotransmitters are stimulated to flood the gap and bond to ion channels on the post synaptic neuron. This causes an action potential to be produced.