Chapter 7 The Nervous System

Functions of the Nervous System 1. Sensory input – gathering information  monitor changes inside and outside the body  Changes = stimuli 2. Integration  process and interpret input and decide on action 3. Motor output  response to stimuli  activates muscles or glands

Structural Classification 1. Central nervous system (CNS)  Brain  Spinal cord 2. Peripheral nervous system (PNS)  Nerves outside the brain & spinal cord

2 Divisions of the PNS Sensory (afferent) division  Nerve fibers that carry information to the central nervous system Motor (efferent) division  Nerve fibers that carry impulses away from the central nervous system

2 Parts of Motor Division 1. Somatic = voluntary 2. Autonomic = involuntary Which side is fight or flight response?

Neuroglia : Support Cells 1. Astrocytes  Abundant, star-shaped cells  Brace neurons  Form barrier between capillaries and neurons  Control chemical environment of brain

2. Microglia  Spider-like phagocytes  Dispose of debris 3. Ependymal cells  Line cavities of brain and spinal cord  Circulate cerebrospinal fluid

4. Oligodendrocytes  Produce myelin sheath around nerve fibers in CNS 5. Satellite cells  Protect neuron cell bodies 6. Schwann cells  Form myelin sheath in the peripheral nervous system

Neurons = nerve cells 1.specialized to transmit messages 2.Major regions  Cell body – nucleus and metabolic center of the cell  Processes – fibers that extend from the cell body

Neuron Anatomy  Cell body a. Nissl substance – specialized rough endoplasmic reticulum b. Neurofibrils – intermediate cytoskeleton that maintains cell shape c. Nucleus d. Large nucleolus

 Processes - Extensions outside the cell body a. Dendrites – conduct impulses toward the cell body b. Axons – conduct impulses away from the cell body

Axons and Nerve Impulses  Axons end in axonal terminals  terminals contain vesicles with neurotransmitters  Synaptic cleft – gap between adjacent neurons

Nerve Fiber Coverings  Schwann cells – produce myelin sheaths in jelly-roll like fashion  Nodes of Ranvier – gaps in myelin sheath along the axon Figure 7.5

Neuron Cell Body Location  In CNS (Most) 1. Gray matter – cell bodies and unmylenated fibers 2. Nuclei – clusters of cell bodies within the white matter of the central nervous system  Outside CNS 1. Ganglia – collections of cell bodies

1. Sensory (afferent) neurons  Carry impulses from sensory receptors to CNS a. Cutaneous sense organs b. Proprioceptors – detect stretch or tension 2. Motor (efferent) neurons  Carry impulses from CNS 3. Interneurons (association neurons)  Found in neural pathways in CNS  Connect sensory and motor neurons Functional Classification of Neurons

Structural Classification of Neurons 1.Multipolar neurons – many extensions from cell body 2. Bipolar neurons – one axon and one dendrite 3. Unipolar neurons –short single process leaving cell body

Properties of Neurons 1. Irritability –respond to stimuli 2. Conductivity –transmit impulses  plasma membrane at rest is polarized  Fewer + ions inside than outside the cell

Starting a Nerve Impulse  Depolarization – a stimulus depolarizes the neuron’s membrane  allows Na + to flow inside membrane  exchange of ions initiates an action potential in neuron

The Action Potential  If action potential (nerve impulse) starts, it is propagated over the entire axon  K+ rush out after Na+ rush in, which repolarizes the membrane  Sodium-potassium pump restores the original configuration - requires ATP  Impulse moves toward the cell body  Impulses travel faster when fibers have a myelin sheath

Impulses are able to cross the synapses  Neurotransmitter released from nerve’s axon terminal  Dendrite of the next neuron has receptors that are stimulated by neurotransmitter  Action potential is started in the dendrite Continuation between Neurons