5) Neural Tissue Physiology

define membrane potential

separation of electrical charge across the plasma membrane

the inner surface of most plasma membranes are…

negative

the direction and magnitude of net ion flux depends on…

concentration and electrical gradients

explain why potassium experiences opposing electrical and concentration gradients

inside cell negative → K+ wants to go/stay in cell

lots of K+ inside cell → K+ wants to move out of cell

define current

movement of electrical charge

define resistance

hinders movement of electrical charge

resting membrane potential, range

-70mV, -40 to -90mV

why does resting membrane potential exist?

unequal ion distribution across membrane

how is the resting membrane potential maintained?

Na-K pump creates gradients for ions to passively move through leak channels

ions concentrated outside the cell

Na+, Cl-

ions concentrated inside the cell

K+, organic anions

sodium-potassium pump exchanges…

3 Na+ out, 2 K+ in

what gives electrically excitable tissues, the ability to propagate action potentials down its axons?

voltage-gated ion channels

types of ion channels

leak, mechanically gated, ligand gated, voltage gated

mechanically gated channels are associated with…

sensory axons

ligand gated channels are important for…

graded potentials

permeability of leak channels

always open or open/close spontaneously

how do voltage gated ion channels work?

reversibly change shape in response to change in membrane charge

neuron resting membrane potential range

-70 to -80mV

at resting state, all Na-K pumps are…

closed

what is an action potential?

rapid depolarization and subsequent polarization

A

partial depolarization to excitation threshold

B

large depolarization, Na channels open and flood into cell

C

Na channels close and K channels open, leaving cell

D

rapid repolarization

E

hyperpolarization

F

absolute refractory period

in the absolute refractory period, ion channels are doing what?

sodium channels are open/inactivated

define absolute refractory period

no AP possible, regardless of magnitude of stimulus

period E

relative refractory period

define relative refractory period

very large stimulus can initiate AP

define graded potential

local change in membrane potential

excitatory postsynaptic potentials make likelihood of reaching threshold…

more likely = depolarizing

inhibitory postsynaptic potentials make likelihood of reaching threshold…

less likely = hyperpolarizing

graded potentials are associated with ________ distances

short

APs are associated with ________ distances

long

define summation

when graded potential overlap before they disappear

amplitude of graded potentials

variable the stimulus

amplitude of action potentials

all or none

spatial summation combines…

multiple inputs at the same time

temporal summation combines…

repeated inputs in rapid succession

how are APs propagated along axons?

local region depolarizes adjacent region to threshold, regenerating AP in successive regions of the axon

why does AP travel in one direction?

refractory period

continuous propagation occurs along…

unmyelinated axons

saltatory propagation occurs along…

myelinated axons

pace of continuous propagation

slow

pace of saltatory propagation

fast, energy efficient

________ fiber diameter = faster conduction because there’s ________ resistance

larger, less

number of voltage gated Na channels is ________ in areas of myelin

lower

what does multiple sclerosis affect?

myelination

define synapse

communication zone between neuron and another cell

in electrical synapses, cells communicate through…

gap junctions (connexons)

electrical synapses allow what to pass directly between cells?

ions

electrical synapses are found…

brain and eye

chemical synapses communicate across ________ via ________

synaptic cleft, neurotransmitters

what does the postsynaptic effect of chemical synapses depend on?

amount of neurotransmitter, sensitivity of postsynaptic cell

neurotransmitters are released via ________

exocytosis

in the release of neurotransmitters, what causes the fusion of vesicles with presynaptic membrane

voltage gated Ca channels open and flood synaptic end bulb

synaptic integration

neuron combines all incoming EPSPs and IPSPs to decide whether to fire AP

the initial segment has a ________ threshold

lower

a synapse located close to the trigger zone will produce a ________ voltage change than if it was farther away

larger

synaptic strength depends on…

neurotransmitter release, calcium entry, presynaptic receptor activity

axoaxonic neuron function

influence (facilitate or inhibit) amount of Ca that enters terminal end bulb or amount of neurotransmitter synthesized

where are axoaxonic neurons common?

sensory pathways

what are autoreceptors?

receptors on the presynaptic membrane that detect neurotransmitters released by that cell

autoreceptor function

negative feedback to decrease amount of neurotransmitter in terminal end bulb

define convergent synapses

many inputs from different neurons into 1

define divergent synapses

1 neuron distributes info to many

define synaptic fatigue

neuron cannot transmit signal bc neurotransmitter cannot get recycled fast enough

cholinergic synapses location

NMJs with skeletal muscle fibers, neuron-neuron synapses in PNS, NMJs and NGJs in ANS, many synapses in CNS

cholinergic synapses release…

ACh

________ can block or impede the normal process of neurotransmitter release from the nerve terminal

drugs

the effect of neurotransmitters depends on…

the receptor

ACh usually promotes ________, but inhibits ________

APs, cardiac NMJs

how does botulism toxin affect nerve terminal?

prevents release of ACh at NMJ, causing flaccid paralysis