Chapter 7 The Nervous System

1. Chapter 7The Nervous System

2. 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

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

4. 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

5. 2 Parts of Motor Division 1. Somatic = voluntary 2. Autonomic = involuntary Which side is fight or flight response?

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

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

8. 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

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

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

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

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

13. 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

14. 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

15. 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

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

17. 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

18. 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

19. 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

20. 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