CH 4

depolarization

decrease in potential; membrane

(rising phase- Na+ goes in)

repolarization

return to resting potential after depolarization

(falling phase, K+ goes out)

hyperpolarization

increase in potential; membrane more negative

graded potentials

act as short-distance signals

action potentials

act as long-distance signals

graded potentials

* The degree of depolarization is related to the magnitude of the stimulus


* bigger stimulus, bigger subthreshold potential until it reaches threshold

action potentials

• Excitable cell membrane is depolarized to **threshold potential**.

• **At threshold**, changes in Na+ and K+ permeability are initiated.

sodium

the _ channel opens first to reach threshold

concentration

the sodium channel uses the _ gradient to depolarize

potassium

the _ channel opens at the peak of the action potential

chemical and electrical

the potassium channel uses the *_* gradient and the *_* gradient to repolarize

hyperppolarization

this occurs when the potential gets a little more negative than resting state and Na/K pump re-establishes resting state gradients

at the same time

(all or none law)

action potentials occur _ or not at all

frequency

variable strengths of stimuli are coded by varying _ not size

absolute refractory period

period when a patch of membrane cannot be re-stimulated

( occurs during the rise and fall of the action potential )

relative refractory period

period during which a patch of membrane can only be re-stimulated by a stronger than normal stimulus

( occurs during hyperpolarization)

sodium

leaks into resting cell

potassium

pumped into resting cell

potassium

contributes most to resting membrane potential

A- (protein)

found only in ICF

sodium

rising phase of action potential

sodium

at threshold channel is activated and opened

potassium

its channel opens at peak of action potential

sodium

contributes to depolarizing membrane potential

myelin

some axons are wrapped in _ to improve AP conduction velocity

axon

have action potentials that start at axon terminals

dendrites

have graded potentials

contiguous conduction

• Occurs in **unmyelinated nerve fibers**

• **Slow** conduction velocity.

• The spread of the action potential along each patch of membrane down the axon.

• Local current flow between adjacent membrane patches.

myelin

• Thick layer of lipids that cover axon at regular intervals.

• Acts as an insulator to prevent leakage of current.

nodes of ranvier

• A bare patch of membrane

• Between the myelinated regions

• Current can flow across the nodes

saltatory conduction

• Occurs in **myelinated** nerve fibers.

• **Fast** conduction velocity

• Action potential 50 times faster

• The impulse **“jumps”** from node to node, skipping over the myelinated sections of the axon.

synapse

the junction between neurons

electrical synapses

neurons connected directly by gap junctions

chemical synapses

chemical messenger is transmitted across the junction separating neurons

( **most common** )

chemical synapse

_ involves a junction between an **axon terminal** of one neuron and the **dendrites or cell body** of a second neuron

presynaptic neuron

• **releases** neurotransmitter (NT)

• in many systems it exhibits **NT reuptake**

postsynaptic neuron

where the NT binds to **receptors**

calciuminflux

_ at axon terminal necessary for NT release

excitatory post-synaptic potential (EPSP)

binding of NT opens Na+ channels that result in a small depolarization called _

excitatory post-synaptic potential (EPSP)

brings the cell closer to threshold

inhibitory post-synaptic potential (IPSP)

binding of NT opens either K+ or Cl- channels resulting in a small hyperpolerization called _

inhibitory post-synaptic potential (IPSP)

cell moves away from threshold

blocking receptor by an antagonist drug

modifying neurotransmitter interaction with the postsynaptic receptor

stimulating the receptor with an agonist drug

replacing a deficient neurotransmitter with a substitute transmitter