Chapter 8


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CHAPTER 8 THE NERVOUS SYSTEM PDBio 362 I. ORGANIZATION OF THE NERVOUS SYSTEM (Fig. 8-1) A. Information flow in nervous system 1. Receptor afferent path integrating center efferent path effector B. Brain and spinal cord = Central nervous system (CNS) [see Ch. 9] 1. Afferent and efferent neurons = Peripheral nervous system (PNS) a) Afferent neurons link sensory receptors to CNS [see Ch. 10] b) Efferent neurons carry information from CNS to effectors [see Ch. 11] (1) Somatic motor neurons: Control skeletal muscles [see Ch. 12 and 13] (2) Autonomic neurons (visceral nervous system): Control smooth and cardiac muscle; endocrine and exocrine tissues; some adipose tissue [see Ch. 11] II. CELLS OF THE NERVOUS SYSTEM A. Two cell types: 1. Nerve cells =Neurons 2. Support cells = Glial cells (glia, neuroglia) III. Neurons A. Functional unit of nervous system B. Neurons classified structurally or functionally. Physiology focuses on function. Based on function C. Classes: 1. Sensory neurons (afferent): Carry environmental information from sensory receptors - CNS a) Structurally vary from model neuron (Fig. 8-3a, b) 2. Interneurons: Lie entirely in the CNS the inbetween in the spinal chord (1) Complex branching processes synapse with many neurons (Fig. 8-3c, d) 3. Efferent neurons (Fig. 8-3e): integrating center effector a) Autonomic efferent neurons have varicosities that store and release neurotransmitter Dendrites A. Thin, branched processes that receive incoming signals B. Branching increases surface area, allows multiple contact with other neurons C. Incoming signals transferred to integrating region in neuron V. Axons Carry Outgoing Signals to the Target A. Most neurons have single axon = Projection of cell body originating from axon hillock 1. Axons vary in length B. Nerve = Collection of axons C. Axon function: 1. Transmits electrical signals from neuron integrating center to axon terminal 2. At axon terminal, electrical signal usually translated into chemical signal at the synapse D. Axons may branch, forming collaterals E. Axon terminals contain mitochondria and membrane-bound vesicles filled with neurocrine molecules that are secreted near target cells exocytosis and endo require ATP F. Axon terminal meets target cell at synapse 1. Presynaptic cell = Cell delivering message to synapse 2. Postsynaptic cell = Cell receiving signal across synapse G. Axons have fibers and filaments, but lack ribosomes and ER a. No protein synthesis H. Protein synthesis occurs in cell body 1. Proteins packaged into vesicles 2. Vesicles are transported to axon I. Axonal transport = Process of transporting vesicles down axon to axon terminal 1. Two types: a) Slow axonal transport (0.2-2.5 mm/day) (1) Utilizes axoplasmic flow 1
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(2) Carries components such as enzymes that are not quickly consumed b) Fast axonal transport (up to 400 mm or 15.75 inches per day) (1) Utilizes kinesins and microtubules to actively walk vesicles up or down axon (2) Forward (anterograde): synaptic/secretory vesicles and mitochondria from cell
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