THE NERVOUS SYSTEM NEURONS Chapter 10, 11

· Organization of the nervous system 264-270

· Cell types

Neuroglia 284

Neurons 282

· Anatomy of a neuron: 282

1. Dendrites

2. Soma- cell body

Nissl bodies

Voltage-regulated Na+ and K+ channels

are absent in the dendrites and cell bodies

3. Axon-- Axon hillock

· Myelin sheath- formed by Schwann cells

Node of Ranvier

· Synapse- junction between a presynaptic and a postsyn. cell

Electrochemical 314-318

1. Spatial summation (317) - neurotransmitter released

simultaneously from several presyn. Knobs

converging on one postsyn. neuron

2. Temporal summation- successive waves of transmitter release due to successive activation

of presynaptic neuron

· Electrical synapses- found in cardiac and smooth muscles

Gap junction- contact area- low electrical

Resistance 314

· Chemical synapse316

Offers more opportunity for modification of

messages to satisfy changes

· Types neurons- afferent, efferent, sensory, motor

· Types according to number of processes-

Multipolar, bipolar, unipolar

· Action potential(AP)- nerve impulse- voltage regulated 292-305

· Permeability of the axon membrane to sodium and

potassium is regulated by gates

· The opening of voltage regulated gates produces action potential

· Action potentials are all-or-none events

· Refractory period- 306

Absolute refractory period- Na gates open

Relative refractory period - K gates open

· Stronger stimuli- AP produced at greater frequency

Recruitment- stronger stimuli activate more neurons