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Biological Sciences
BIOL 1412
Paul Messing

BIOL1412 01 20 2014 Neuronal Physiology H. Action Potential Propagation: (continued) Fiber Types: 1) Type A - large diameter - myelinated - propagated AP @ ~130 m/sec - most sensory neurons & motor neurons to skel. muscles 2) Type C - small diameter - unmyelinated - propagated AP @ ~0.5 m/sec - found in autonomic NS (ANS) and some pain fibers Neural Physiology * Comparison of GP and AP: (see Table 11.2) Characteristic Graded Potential (GP) Action Potential (AP 1. Location dendrites/cell body axon hillock/axon 2. Strength of MP variable all-or-none (+30mV 3. Summation YES NO 4. Repolarization current dies away Na+ gates close; K+ gates open 5. Types of Gates chemical, mechanical, thermal only voltage (i.e. NOT voltage) 6. Distance Travelled short (1-2 mm) & dies away produced anew on axon & propagates over long distances 7. Refractory Period Absent Present I. Synaptic Transmission (ST) at Neuronal Junction: (Fig. 11.16) - NS depends on chains of neurons connected by junctions called synapses - presynaptic neuron to postsynaptic neuron transmission * Steps: (Fig. 11.17) 1) AP arrives at axon terminal (synaptic end bulb) 2) Ca++ voltage gates open (due toAP) and Ca++ enters (higher [Ca++] outside!) 3) rise in Ca++ triggers exocytosis of neurotransmitter (nt) containing vesicles 4) nt crosses synaptic cleft, binds to specific receptors on postsynaptic membrane - receptors = chemically-gated ion channels ⇒ open in response to nt 5) gated ion channels open - allowing movement of
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