BIOL 111 Lecture Notes - Lecture 58: Electrochemical Gradient, Action Potential, Quadriceps Femoris Muscle
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BIOL 111 – Organismal Biology
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Nerves at Work
•!spinal reflex arc – brain isn’t involved in sensory-motor impulse
o!e.g. knee-jerk reflex
o!involves the spinal cord (CNS) and 2 neurons (PNS – one afferent and one
efferent)
o!banging the patellar tendon causes the tendon to pull on quadriceps and dendrites
stretch. This creates impulses, impulses travels to spinal cords via sensory
neurons and the impulse is transferred to motor neurons and travels from spinal
cord. The impulse triggers response in effector and quadriceps contracts, which
cause the lower leg to extend
•!physiologically, neurons work electrochemically
o!electro – difference in charge across the cell membrane
o!chemical – charge due to specific ions (Na+, K+, Cl-) and negatively-charged
proteins
•!when neurons are at rest:
o!Na+ is mostly on the outside of the cell membrane
o!K+ is inside and outside (mainly inside) and Cl- and negatively-charged proteins
are inside
!!an electrochemical gradient forms across membrane
!!voltage difference between outside and inside is the cell’s membrane
potential
!!the voltage difference when a neuron is at rest, ready to conduct impulse
is its resting potential
!!inside of cell is more negative when at rest
•!measuring membrane potential
o!electrodes are inserted into axon (both inside and outside)
!!this can chart electrical potential across membrane over course of an
impulse
o!the resting potential is-60mV
•!the nerve impulse is called an action potential
o!this involves a rapid voltage change that occurs in 1-2 milliseconds
o!nerve impulses involves three major processes: