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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 Functional Classification of Neurons 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 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 Continuation between Neurons 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