AP Unit 2 - Bio185 A&P1 Unit 2 Neurons Synapses Action...

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The Nervous System: Two Anatomical Divisions A. Central nervous system (CNS) Brain Spinal cord B. Peripheral nervous system (PNS) All the neural tissue outside CNS Neural Tissue Organization: A. Two Classes of Neural Cells 1. Neurons — For information transfer, processing, and storage 2. Neuroglia — Support neurons a.k.a. Glial cells far outnumber neurons retain ability to divide B. Neuron Anatomy 1. Cell body Nissl bodies = clusters of ribosomes & RER give gray color to “gray matter” 2. Dendrites 3. Axon Collateral axons Axon hillock 4. Synaptic terminals (one or more) Synapse C. Structural Classes of Neurons 1. Multipolar Many dendrites (2 or more), one axon Most common neuron in CNS All motor neurons are multipolar 2. Unipolar Dendrite & axon continuous; cell body lies to one side Most afferent (sensory) neurons 3. Bipolar 2 processes: One dendrite, one axon – cell body between Very rare Special sense organs; relay info from receptor to other neurons ( e.g. retina, nose)
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D. Types of Neuroglia (glia) 1. Neuroglia of CNS a. Astrocytes “Star” shaped cells Part of blood-brain barrier - secrete chemicals Most numerous glial cells structural framework, repairs b. Oligodendrocytes Responsible for myelination in CNS Many oligodendrocytes required to line entire axon One oligodendrocyte may send processes to myelinate several different axons Provide glossy white color of “white matter” c. Microglia Phagocytic defense cells derived from WBCs d. Ependymal cells Lining of brain, spinal cord cavities (ventricles) Source of cerebrospinal fluid Some with cilia circulate fluid 2. Neuroglia in the PNS Schwann cells Surround all peripheral axons Responsible for myelination in PNS Each cell wraps only one axon. Many needed to cover entire axon. The Synapse: = neural communication point between two cells. Where do synapses occur? 1. Neuron-to-Neuron: 2. Neuron-to-other cell type = neuroeffector junction e.g. neuromuscular junction Structure of a Synapse: 1. Presynaptic membrane/neuron Synaptic terminal Synaptic vesicles 2. Synaptic cleft 3. Postsynaptic membrane/neuron
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Neurotransmitter receptors Neuronal Signaling: Neuronal signaling: alternating electrical signal (action potential) within a neuron and chemical signal (neurotransmitters) between neurons. A. Resting Membrane Potential: Unstimulated cell is maintained at -70 mV (refer to previous material) B. Stimulus: for example ~ Mechanical Chemical ( e.g. neurotransmitter) Temperature C. Stimulus opens ion channels : (Graded Potenial) (Note: the very first stimulus that stimulates a receptor-like neuron may be something other than a neurotransmitter; however, between two neurons the stimulus is a
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This note was uploaded on 04/03/2008 for the course BIOL 185 taught by Professor Harms during the Fall '07 term at Messiah.

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AP Unit 2 - Bio185 A&P1 Unit 2 Neurons Synapses Action...

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