1.5 Generation and Propagation of Action Potentials Flashcards

1
Q

What are the ways neurons are stimulated

A
  • a neurotransmitter being released from an adjacent neuron
    -an external chemical
    -physical pressure or touch
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2
Q

What does the stimulation of a neuron cause

A

It causes Na (and other) ion channels to open which helps to generate a nerve impulse

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3
Q

What are the 2 types of potentials and over what distances do they act

A

graded potentials act as short distance signals and action potentials act as long distance signals

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4
Q

Where do graded potentials and action potentials occur

A

graded potentials occur in the soma or dendrites, whereas action potentials are only in the axon

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5
Q

What is a post synaptic potential and how is it generated

A

A graded potential in the dendrites of a neuron that has just received a signal. To generate it, a ligand (e.g a neurotransmitter) binds to ligand gated Na+ channels on the post synaptic membrane. This causes the channels to open and Na+ enters the cell. The ligand is then broken down.

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6
Q

What happens if a post synaptic potential then depolarises

A

It is an excitatory PSP and the membrane potential can move towards the threshold for an action potential.

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7
Q

What happens if a post synaptic potential hyperpolarises

A

It is an inhibitory PSP and the membrane potential moves away from the threshold for an action potential

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8
Q

Describe the flow of graded potentials

A

They occur in the active area of the membrane and the magnitude of the potential corresponds with the magnitude of the stimulus. The GPs spread decrementally by local current flow, from the active area to the inactive areas. The GPs die over a short period of time

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9
Q

Describe the 2 types of summation

A

temporal summation - several impulses from one neuron over time

spatial summation - impulses from several neurons at the same time

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10
Q

Describe the threshold potential

A

If enough EPSPs add together, the threshold potential (-55mv) aka suprathreshold is reached and the depolarisation “runs away”, peaking at +35mv. This is the action potential

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11
Q

Describe the stages of how an action potential is generated across a membrane.

A

once ligand gated Na+ channels have allowed Na+ in, the membrane depolarises to the suprathreshold level, this then opens voltage gate Na+ channels so even more Na+ enters (flowing down the electrochemical gradient). This is the runaway effect and an example of positive feedback. The Na+ channels then reset to inactivate and close and the voltage K+ channels then open. So Na is leaving and K is coming in (both flowing down the electrochemical gradient) , this then repolarises the membrane, and it goes all the way down to hyperpolarising, below resting level of -90mV (”undershooting”) - movement of ions down the electrochemical gradient coming from further away quickly corrects this. Ion channels are then inactivated Before the voltage gated K+ channels are inactivated and it returns to threshold potential.

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12
Q

Describe the gates in gated channels when the channels are activated and when they are inactivated

A

When the gated channels are activated the activation gate is open and the inactivation gate is closed

When the gated channels are inactivated the activation gate is closed and the inactivation gate is open

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13
Q

Constant ion exchange would lead to an ionic imbalance overtime (eventually leading to failure) , however why is this not an issue.

A

Only 1/3000 ions are exchanged for every AP and also the Na+/K+ pump restores the balance

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14
Q

In each area of the axon, how is resting potential restored following the action potential

A

the Na+/K+ pump

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15
Q

What 2 factors is nerve impulse speed dependent on

A

Nerve impulse speed is dependent upon the axon diameter, the wider the axon, the faster the transmission speed

Nerve impulse speed is also dependent on if the axon is myelinated, myelinated axons are faster

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16
Q

Describe why myelinated axons are faster

A

In myelinated axons, the myelin sheath surrounds the axon other than little gaps called the nodes of ranvier. The nodes of ranvier are the only places where the voltage gated channels are exposed. Therefore APs can only take place at the nodes. This allows for saltatory conduction, which speeds the AP transmission up as it jumps from node to node. This propagates the AP 50 times faster

17
Q

Describe the impulse speed, length and myelination of autonomic axons for smooth and cardiac muscle

A

-unmyelinated
-0.3-1.3 micrometers
-0.7-2.2 m/s

18
Q

Describe the impulse speed, length and myelination of pain axons

A

-both myelinated and unmyelinated
-1-5 micrometers
-12-30 m/s

19
Q

Describe the impulse speed, length and myelination of sensory muscle position axons

A

-myelinated
-12-22 micrometers
-70-120 m/s