NATS 1610 Chapter Notes - Chapter 13: Brainstem, Grey Matter, Sympathetic Nervous System

• School: York University
• Department: Natural Science
• Course: NATS 1610
• Professor: Barbara Czaban

Document Summary

When the voltage difference across the neuron plasma membrane shifts by a minimum amount called the threshold, the result is a nerve impulse or action potential. Whe(cid:374) the th(cid:396)eshold le(cid:448)els a(cid:396)e (cid:396)ea(cid:272)hed, the ope(cid:374)i(cid:374)g of (cid:373)o(cid:396)e sodiu(cid:373) gates does(cid:374)"t depe(cid:374)d a(cid:374)y longer on the strength of the stimulus: gates open on their own. A weak stimulus that arrives at an input zone may not upset the ion balance enough to cause an action potential: because input zones do not have gated sodium channels, so sodium cannot flood there. A (cid:374)eu(cid:396)o(cid:374)"s t(cid:396)igge(cid:396) zo(cid:374)e is pa(cid:272)ked (cid:449)ith sodiu(cid:373) (cid:272)ha(cid:374)(cid:374)els. If a stimulus that reaches an input zone is strong enough to spread to the trigger zone, a(cid:374) a(cid:272)tio(cid:374) pote(cid:374)tial (cid:373)ay (cid:862)fi(cid:396)e(cid:863) A (cid:374)euro(cid:374) ca(cid:374)"t (cid:862)fire(cid:863) agai(cid:374) u(cid:374)til io(cid:374) pu(cid:373)ps restore its resti(cid:374)g pote(cid:374)tial. There are more calcium ions outside the cell and when they flow in (down their gradient, synaptic vesicles fuse with the p. m, discharging their content.