Nervous System Chapter 9

9.1 Introduction Neurons – mass of nerve cells that transmits information (nerve impulses) to nerves, tissues, or cells (3 big parts): Cell body – contains nucleus and two extensions Dendrites – receive the nerve impulse (shorter and more of them) Axons – transmit information away from the cell body (single long fiber)

Neuron basic structure

A Nerve is a bundle of axons Nervous tissues also include neuroglial cells which are supporting cells 2 parts make up the nervous system: 1. Central Nervous System (CNS) Brain & spinal cord 2. Peripheral Nervous System (PNS) Peripheral nerves throughout the body

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General Functions of Nervous system Three basic functions: 1. Sensory function Gathers info by detecting changes inside and outside the body Have sensory receptors at the ends of the peripheral nerves which send impulses to central nervous system sensory neurons

2. Integrative function 3. Motor function Info is brought together and interpreted, to create sensations, create thoughts, add to memory, make decisions 3. Motor function A Responses to nerve impulses Signals are sent from the CNS to effectors (muscles or glands). The goal is usually to maintain stable homeostasis

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2 categories of the motor functions in the nervous system: 1. Somatic nervous system Consciously control skeletal muscles 2. Autonomic nervous system Controls the involuntary effectors (heart, smooth muscle in blood vessels, and various glands)

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Neuroglial cells Specialized cells in nervous tissue that fill spaces, provide structural frameworks, produce myelin, and carry on phagocytosis (5 types) 1. Microglial cells – scattered throughout central Nervous system, support neurons and phagocytize bacterial cells and cellular debris http://img.tfd.com/dorland/thumbs/microglia.jpg

2. Olgiodendrocytes – provide insulating layers of myelin (myelin sheaths) around axons within the brain and spinal cord. 3. Astrocytes – Connect blood vessels to neurons http://blustein.tripod.com/Oligodendrocytes/08-zoom.jpg http://thebrain.mcgill.ca/flash/a/a_01/a_01_cl/a_01_cl_ana/a_01_cl_ana_2a.jpg

4. Ependymal cells - forms a membrane that covers brain parts 5. Schwann cells - Form the insulating myelin sheath around the neurons http://www.northland.cc.mn.us/biology/AP2Online/Nervous/images/ependymal_cells.gif http://207.204.17.60/wp-content/uploads/2010/04/Image4252.gif

Neuron Structure

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Neuron structural differences

Neuron functional differences http://www.usmanscience.com/12bio/classnotes/nervous_system_notes_files/image002.gif

Threshold http://www.siumed.edu/~dwade/phys310/6ap_files/image002.jpg

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Action Potential animation

Nerve impulse