Module 1 PhysioEx 3- Neurophysiology of Nerve Impulses

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<b>resting membrane potential</b>

= potential difference btwn the inside of the cell (intracellular) and the outside of the cell (extracellular) across the mmb – steady-state condition that depends on the resting permeability of the mmb to ions

sodium-potassium pump

intracellular [Na+] is low intracellular [K+] is high – ion diffuses down its conc. gradient from high to low conc. – K+ ions diffuse out, leaving net neg chg

What is the approximate concentration of K+ inside a typical cell (intracellular concentration)?

150 mM

What is the approximate concentration of K+ outside a cell (extracellular concentration)?

5 mM

What is the approximate concentration of Na+ inside a cell (intracellular concentration)?

5 mM

What is the approximate concentration of Na+ outside a cell (extracellular concentration)?

150 mM

What is the polarity of the resting membrane potential (voltage)?

negative

What does it mean that the voltage just inside the membrane is negative?

There are more negative charges than positive charges just inside the membrane.

The membrane of most cells, including neurons, contains passive, open,
K+ leak channels. Given the normal K+ concentrations and the resultant concentration gradient, which direction would K+
be expected to move (diffuse) through these leak channels?

out of the cell

What effect does increasing extracellular K+ have on the net diffusion of K+ out of the cell?

It decreases the net diffusion of K+ .

Which way would Na+ move across the membrane if there were open Na+ channels?

Na+ would diffuse into the cell.

The membrane has open K+ channels, and changing extracellular K+ concentration results in a change in membrane
potential. Changing the extracellular Na+ concentration does not significantly change the membrane potential. What do
your results suggest about the number or state (open or closed) of Na+ channels in the resting membrane of a neuron?

Na+ channels are mostly closed.

A negative membrane potential was recorded when the tip of the microelectrode was

both inside the cell body and inside the axon.

Which of the following caused a change in membrane potential from -70 to -40 in the cell body?

an increase in extracellular K+

Which of the following has the most negative voltage?

between the inside of the axon and the outside of the axon with control K+ ECF

<b>sensory receptor</b>

= receiving end of a sensory neuron has receptor proteins that can generate a signal (receptor potential) when the sensory neuron is stimulated by an appropriate, adequate stimulus

<b>sensory transduction</b>

= the energy in the stimulus is changed into an electrical response that involves the opening/closing of mmb ion channels – occurs at the receptor ending of the sensory neuron – type of signal transduction where the signal is the sensory stimulus

graded potentials

= local potentials – the amplitude of the receptor potential increases w/ stimulus intensity

Assuming that the resting potential of a sensory neuron is -70 mV, which of the following represents a depolarization?

change to -60 mV

Which of the following is a sensory modality (type of sense)?

e. all of the above Touch smell sight pain

Which of the following is a sensory stimulus?

All of the above pressure chemical odorants light

Which of the following is true of the response of a sensory neuron to the appropriate sensory stimulus?

it can be called a receptor potential, and it is a graded potential it is a change in the resting membrane poetintial

<b>depolarization</b>

= response that is a change in mmb potential from negative resting potential to a less negative level – less polarized

Why didn’t the Pacinian corpuscle respond to high-intensity light?

Light-transducing proteins are not present in the Pacinian corpuscle.

Judging from these results, does light have a smell?

no

Why did the free nerve ending respond to several different modalities?

The sensory end of this nerve is less specialized.

A very intense stimulus can sometimes stimulate sensory neurons that have evolved for a different modality. Thus, with
a blow to the eye, one "sees stars." In this example the photoreceptors in the eye are responding to

intense pressure.

Olfactory receptor neurons respond to low concentrations of chemical odorants because there are membrane proteins in
the receptor ending of this sensory neuron that

can bind and respond to the specific odorant.

The sequence of events starting with a sensory stimulus and ending with a change in membrane potential is called

sensory transduction.

Starting at a resting membrane potential of -70 mV, a change to which of the following represents the largest receptor
potential?

a change to -50 mV

<b>action potential</b>

= signal conducted by axons

<b>nerve</b>

= bundle of axons

<b>axon hillock</b>

= region where the axon extends from the cell body – initial segment in a myleinated axon

<b>trigger zone</b>

= junction of axon hillock and initial segment where an action potential is usually initiated

<b>propagated</b>

= conducted = regenerated action potential down the membrane of the axon

<b>voltage-gated sodium channels</b>

open when the mmb depolarizes – each sodium channel that opens allows Na+ ions to diffuse into the cell down their electrochemical gradient – potassium leak via passive channels establishes and maintains the negative resting mmb potential – action potential is generated when the threshold is reached when enough sodium channels open to overcome the K+ leak

after-hyperpolarization

= undershoot = phase: flux thru extra voltage-gated potassium channels opposes the depolarization of the mmb to threshold, causes mmb potential to become transiently more negative than the resting potential at the end of an action potential

all-or-none event

action potential has a constant amplitude, regardless of stimulus intensity

absolute refractory period

time after an action potential when the neuron cannot fire a second action potential, no matter how intense the stimulus

relative refractory period

time after an action potential when a second action potential can be generated if the stimulus intensity is increased

axon codes the stimulus intensity as _____

frequency (the number of action potentials) per unit of time

propagation ensures that the ____ of the action potential does not diminish as it is conducted along the axon

amplitude

propagation/conduction occurs because there are ________ located along the axon and because the __________ that constitutes the action potential

voltage-gated sodium and potassium channels; large depolarization

<b>conduction velocity</b>

know both distance of the action potential travel and mount of time it takes velocity (distance per time, m/s)

experimental stimulus artifact

marker of the stimulus time

<b>myelination</b>

special wrapping of the membrane from glial cells (neuroglia) around the axon

CNS – oligodendrocytes

glia that wrap around the axon

PNS – Schwann cells

glia that wrap around the axon

axon terminal

end of each branch of axon that releases packets of chemical neurotransmitters from synaptic vesicles

<b>synaptic vesicles</b>

= small intracellular mmb-bound vesicles

<b>neurotransmitters</b>

= extracellular signal molecules that act on local targets as paracrine agents, on the neuron releasing the chemical as autocrine agents, and sometimes as hormones (endocrine agents) that reach their target(s) via circulation

these chemicals are released by ____ and diffuse across the ______ ______ to the target

exocytosis; synaptic gap or cleft (receiving end of another neuron or a muscle or gland) -> open/close mmb ion channels and cause mmb potential in target cell to change

<b>chemical synapse</b>

= region where the neurotransmitter is released from one neuron and binds to a receptor on a target cell

<b>postsynaptic potential</b>

= synaptic potential = change in mmb potential of the target

exocytosis of synaptic vesicles is normally triggered by an increase in _______ ions in the axon terminal through calcium channels that are opened by _____ of the action potential

calcium; depolarization

chemical synapses

sensory neurons communicate w/ interneurons that process the info – interneurons also communicate w/ motor neurons that stimulate muscles and glands

if the threshold is reached, an _____ is generated and propagated

action potential

if the stimulus is more intense, then action potentials are generated at a ______ frequency, causing the release of _____ neurotransmitter at the next synapse

higher; more

excitatory synapse

chemical neurotransmitter binds to receptors at the receiving end of the next cell (cell body or dendrites of interneuron), causing ion channels to open –> depolarization twd threshold

depolarizing synaptic potential is _____ in amplitude, depending on the ______ of neurotransmitter and the ______ of channels that open

= excitatory postsynaptic potential graded; amount; number

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