Nervous system Physiology (I) Flashcards by Neil Rochon

What are large negatively charged organic ions (org-) ?

they are non-diffusable proteins

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what are the important Ions in the cell

Na+, K+,Cl-,Ca++ and org-

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Explain a nerve impulse.

when a neuron is excited it gets stimulated (usually on the cell body or dendrites) an electrical impulse gets generated and propagated along the axon

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which Ion does not exit the cell?

org-

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What do Ions diffuse through?

Ion channels

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What are the ion channel types?

gated and non-gated

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what is a non-gated channel?

it is always open. Cell membrane is more permiable to K+ at rest.

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what differences are their between different gated channels?

voltage gates, chemical gates, thermal gates and mechanical gates

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what kind of chemicals help open voltage gates?

neurotransmitters and hormones.

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what is Resting Membrane Potential?

a charge difference when the cell is at rest which exists just across the cell membrane.

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what is the charge inside the cell at RMP?

-70 mV

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How does the Na+/K+ pump work?

1 ATP gets broken down and it pumps 3 Na+ Ions out of the cell and pumps 2 K+ back into the cell. (both of which are being pumped against their concentration gradients)

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what is the effect of the Na+/K+ pump on the cell?

It MAINTAINS concentration gradients of Na+ and K+ and also contributes in a small amount to the RMP

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Can org- cross the membrane at any time?

no it can’t dude

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Out of K+ and Na+ which Ion has more non-gated channels?

K+ (membrane is more permeable to K+ then Na+)

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What kind of cells are electrically excitable?

ONLY muscle and nerve cells.

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Electrically excitable are capable of producing departures from ______ in response to _____ which means their is a change in _______ ___ ____ _______

Resting membrane Potential, stimuli, external and internal environment

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what happens when a neuron is stimulated?

Gated channels open, MP changes… producing a graded potential and if the threshold potential is reached…. BOOM action potential

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what is a Graded Potential?

When a stimulus causes a small change in MP

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where does a GP usually happen? and what happens to the gated channels?

usually on cell body of dendrites. Gated channels open (changes membrane permeability

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what are the possible results to a cells being stimulated?

depolarization (closer to zero e.g. -70mV to -65 mV) and hyperpolarization (further away from zero e.g. -70 mV to -75 mV)

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are GP short lived or long lived?

short lived… GPS are short distance signals.

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the magnitude and distance traveled by potential varies directly with what?

It varies directly with the strength of the stimulus.

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what happens after a GP?

the cell goes back to RMP after a depolarization or hyperpolarization

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what is essential to initiating a nerve impulse?(action PotentialP

Graded Potential (G)

how does an action potential (AP) happen?

if a GP is strong enough, or if multiple GP's summate to be strong enough, a critical stimulus happens and that leads to an action potential.

what are the steps to an action potential?

Critical stimulus, GP reaches threshold, Action potential

what is the threshold for an action potential to occur?

-55mV

Explain the depolarization phase.

Voltage gated channels respond to MP change... Na+ permeability increases... gates open, Na+ diffuses in which increases MP opening even more Na+ gates (positive feedback mechanism) ...Na+ diffuses in, causing depolarization to 30+mV (inside membrane become positive)

Explain the repolarization phase.

Na+ channels close and become inactive and Na+ levels return to resting levels... Voltage gated K+ channels are open... K+ diffuses out

Explain the after-hyperpolarization phase.

K+ are slow to close | Na+ channels are reactivated(but closed) and can respond to stimuli

when does the Na+/K+ ATPase work?

It is always working to maintain gradients

how many action Potentials does it take to cause a measurable change in the [ions] in the cell?

10,000s

How big does a stimulus have to be while in the Absolute Refractory Period?

trick question... The absolute refractory period prevents AP summation and NO action potential can be generated regardless of the stimulus size

The absolute Refractory Period can result from either:

All voltage-gated Na+ channels are open There are no more that can open ) or; Na+ channe;s are inactive (cannot open until MP reches RMP)

Can an AP occur durring the relative refractory period?

yes but the stimulus has to be greater than normal stimulus

which channels are reactivated when MP passes RMP?

Na+

Are Na+ channels open or closed durring the relative refreactory period?

closed but they can be open if the stimulus is great enough.

Whats going on is the K+ channels during the relative refractory period?

they are open and membrane is hyperpolarized.

what is the all or none principle?

ALL: If the threshold for an action potential is reached... AP will happen and its the same every time (same max depolarization ) and NONE: if the threshold is not met there will not be an action potential

What the point of the Acion Potential Propagation?

it is to act as a communication mechanism, an AP must be propagated along the axon's entire length.

explain the depolarization durring an action potential.

positive ions moves towards more negative charge on adjacent membrane which make the adjacent membrane depolarize to reach the threshold.

which way does the movement of charge occur?

it occurs in both direction but the AP moves in one direction because the preceding membrane is in the refractory period

How does the AP change when moving along the membrane?

it does not change... same AP every time

Where does the AP propagate to?

Along the axons entire length to the axon terminal

how does the charge move in both directions but the AP only moves in one direction?

AP only moves in one direction because the preceding membrane is still in the refractory period which means it can not be stimulated

AP propagates to where?

Goes from the entire length of the axon to the axon terminal

what does the rate of propagation depend on?

fiber diameter and myelination (unmyelinated vs myelinated)

what does a larg diameter for an axon do?

it allows for fater propagation

what what can we say about the rate of propagation in unmyelinated fibres?

Na+ channels are adjacent to each other= continuous conduction= slower propagation.

why do myelinated fibres have fast propagation?

because the current jumps from node of ranvier to another which makes it faster.

what is saltadory conduction?

it is the conduction in which the current is leaping from one node of ranvier to another.

What is the diameter size of a type A and type C fibre?

Type A has a large diameter and type C haas a small diameter.

out of type a and type C fibres, which one is myelinated and which is unmyelinated?

Type a is myelinated and type C is unmyelinated.

what are the speeds of both Types of Fibres?

type A = about 130m/sec and type C propagate at about 0.5m/s

where are type A fibres found?

mostly in sensory neurons and motor neurons to skeletal muscles

where are type C fibres found?

they are found in the autonomic nervous system and some pain fibres

What is a Excitatory PSPs (EPSPs) ?

it is a graded potential (depolarisation)

what is the nt in Excitatory postsynaptic Potentials?

acethylcholine(ACh) or glutamate

WHat is the nt in Inhibitory postsynaptic potentials?

nt is often glycine or GABA

what causes Excitatory PSPs ?

due to the opening of Na+(or Ca++) channels, or closing of K+ channels

What causes Inhibitory PSPs (IPSPs) ?

due to opening of Cl- or K+ channels

where does PSPs occur?

on cell body or dendrites

where is the Synaptic Transmission at the neuromuscular Junction located?

between axon terminal & an individual muscle fibre