Lecture 17: Action Potential

neuron

basic functional unit of the nervous system (conducts messages & integrates info)

dendrites

tree like extensions of a neuron that receive info & send signals to cell body

cell body (soma)

contains organelles & integrates info received by neuron

axon hillock

where signals are generated

axon

long structure that transmits signals away from cell body & towards another neuron / effector (ex: muscle)

synaptic terminals

end of axon & communicates with other neurons/effectors

SEQ neuron structures

1. dentriites (stimulus first)

2. cell body (soma)

3. axon hillock

4. axon

5. synaptic terminals

afferent neuron (sensory)

carries information from sensory receptors TO the processing center

interneurons

neurons found only in the CNS (responsible for integration)

integration

the NS’s process of receiving, organizing, and evaluating sensory info before sending instructions

efferent neuron (motor)

carries information FROM the processing center TO an effector

SEQ neuron types

1. sensory receptor

2. afferent neurons

3. interneurons (processing center)

4. efferent neurons (motor)

5. effector (gland / muscle)

what is membrane potential (MP)?

the electrical charge difference between the inside and outside of a cell

what causes MP?

an uneven distribution of ions which creates electrical energy

True or Flase: ALL cells have membrane potential

True

how is MP measured?

millivolts (mV)

what is the Na+ / K+ pump?

a pumps that uses active transport to move ions AGAINST their concentration gradient (needs ATP)

One complete Na+ / K+ cycle…

pumps 3 Na+ OUT of cell and pumps 2 K+ INTO cell

how to remember Na+ / K+ pump?

salty banana (sodium OUT, potassium IN)

what are ungated ion channels?

always open channels that use facilitated diffusion to move ions from HIGH to LOW concentration

what are voltage-gated ion channels?

channels that use facilitated diffusion and open and close based off changes in voltage

what is resting potential?

when the axon is at rest and the membrane potential is = -70 mV (voltage gated Na+ / K+ channels are closed?

what is depolarization?

when the membrane potential becomes less negative (MORE positive / moves closer to zero)

what is hyperpolarization?

when the MP moves BELOW resting potential / becomes MORE negative (-70 mV to -90 mV)

If the MP changes from -70 to -50 mV, the neuron is…

depolarizing

If the MP changes from -70 to -90 mV, the neuron is…

hyperpolarizing

If the MP reaches -55 mV…

the threshold is reached and an action potential is triggered

if the MP does not reach threshold then…

an action potentional does NOT occur

what is an action potential (AP)?

rapid change in membrane potential that occurs when depolarization reaches threshold

SEQ action potential

1. resting state (-70 mV)

2. stimulus (some Na+ channels open)

3. rising phase (most Na+ chanells open, Na+ rushes in, spike of +35mV)

4. falling phase (Na+ channels close & K+ channels open, K+ exits)

5. undershoot (some K+ channels remain open / returns to -70mV)

if more Na+ channels open THEN…

depolarization occurs (less negative)

if K+ channels stay open longer THEN…

more K+ exits & greater hyperpolarization (more negative)

if the channels do not reset & repolarize THEN…

another AP cannot be generated normally

continuous conduction

where an AP occurs step by step by step along an unmyelinated axon (slow & inefficient / uses more E)

saltatory conduction

where an AP “jumps” from node to node