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Physl 210A > Nerve and Muscle > Flashcards

Nerve and Muscle Flashcards

1
Q

Neurons:

A

Make up 10% of the nervous system. They are larger than glia

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2
Q

glial cells function

A
  • Glia cells make myelin: Oligodendrocytes in the CNS and Shwann cells in the PNS. They are also involved in forming the blood brain barrier
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3
Q

myelin

A

Fatty substance that wraps around the axon of the neuron to speed up transmission of nerve impulses along the axon

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4
Q

afferent neurons

A
  • Afferent neurons take information from the periphery to the CNS (spinal cord). They are excitatory. They can be attatched to sensory receptors like touch receptors.
    ◦ Enter the dorsal part of the spinal cord
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5
Q

efferent neurons

A
  • Efferent nuerons take information from the CNS (spinal cord) to the periphery. They are excitatory
    ◦ Enter the ventral part of the spinal cord. They leave through the ventral root
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6
Q

Interneurons

A

Interneurons: They are entirely within the CNS. They carry information inebtween efferent and afferent neurons. It can be excitatory or inhibitory (however never both)

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7
Q

mixed peripheral nerve

A
  • Mixed peripheral nerve: contains both efferent and afferent nerves. Information is coming towards the spinal cord (afferent) or away from the spinal cord (efferent). This is how information reaches the spinal cord
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8
Q

white matter

A
  • White matter contains myelin. This is fatty white matter that wraps around the axon. (White=fat)
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9
Q

grey matter

A
  • Grey matter contains cell bodies and parts of the neuron that don’t have myelin.
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10
Q

Dedrites

A
  • Dendrites: extend from the cell body and receive input from cells
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11
Q

Cell body

A

Cell body: Where the nucleus is situated. (proteins and genes)

The impulse only goes away from the cell body towards the axon terminal or the synaptic terminal

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12
Q

axon hillock

A

initial segment of the axon where action potentials are initiated

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13
Q

axon length

A

very short in the spinal cord and very long going to the muscle

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14
Q

bipolar cell

A
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15
Q

pseudo unipolar cell

A
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16
Q

multipolar cells

A
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17
Q

phospholipid layer

A

Bilayer

Impermeable to ions

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18
Q

Protein pumps

A

they’re specific to a given ion, and they allow ions to move either down their electrochemical gradient, or In the case of the sodium potassium pump, they use energy in the form of hydrolysis of ATP to move ions in a given direction, regardless of the electrochemical gradient.

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19
Q

Sodium potassium pump

A
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20
Q

ion channels

A

Open/closed at rest to allow the free flow of ions in or out of the cell. They depend on the electrochemical gradient

No energy is used

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21
Q

leak channels

A

Ion channels that are always open are called passive or leak channels. They are selective to specific ions to go down the concentration gradient into or out of the cell to achieve equilibrium

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22
Q

ligand channel

A

ligand-gated ion channels are closed at rest and they need a ligand to bind to a receptor in order to open the channel.

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22
Q

Resting membrane potential

A

-70

measure of the electrical potential difference between the inside of the cell and the outside of the cell.

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23
Q

Sodium potassiun pump

A

When ATP is hydrolyzed there is a conformational change in the pump.

3 sodium move out of the cell, 2 potassium enter the cell

When phosphate is removed from its binding site, there will be another conformational change and the pump will return to its normal conformation

Electrogenic: moves charge across the membrane

creates gradients

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24
Q

potassium leak channels

A

There is more potassium inside of the cell. Therefore the chemical gradient will force potassium out of the cell

The inside of the cell is negative and potassium is positive, so the electrical gradient will force potassium into the cell

The equilibrium potential for potassium is -90, meaning it will leave the cell to make the cell at this potential

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25
Q

equilibrium potential

A

The electrical and chemical force will be equal and opposite to each other at an equilibrium potential

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26
Q

sodium leak channels

A

more sodium outside of the cell. Therefore chemically it will be driven in the cell (chemical gradient)

The equilibrium potential for sodium is +60. This means that more sodium will want to enter the cell (electrical gradient)

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27
Q

relation of leak channels to equilibrium

A

the more leak channels you have for a given ion, the closer resting membrane potential is to the equilibrium potential for that ion (the more permanent the ion, the greater its ability to force the membrane potential to its own equilibrium potential)

Therefore there is more potassium channels

28
Q

chloride

A

more outside of the cell then in

equilibrium potential for chloride is at the resting membrane potential

29
Q

Action Potentials

A
  1. physical or chemical stimuli disrupts the steady state by causing voltage gated ion selective channels (sodium to open). The activation gate for the sodium channels is going to move. This allows sodium moves down its electochemical gradient and enter through the voltage gated channel. These gates are closed until threshold is reached. Sodium will make the cell positive
  2. Membrane potential is going to reach that of sodium (+60)
  3. After a fixed amount of time, the activation gate for sodium is going to move, and the inactivation gate will block off the channel. This will prevent sodium from entering
  4. The voltage gated potassium channel is going to have its activation gate move, allowing potassium to leave the cell and make it negative.

The voltage gated sodium and potassium have the same thresholds for avtivation. Sodium channels are much faster, which causes them to open before potassium channels

30
Q

stretch receptor sodium channels

A

At rest, the pores in the stretch receptor at the efferent neuron are too small for sodium to enter

When the muscle is tapped, the muscle is stretched, also stretching the receptor. This allows sodium to enter ion channels that it coulnd’t fit through before. Sodium can enter the afferent fibre and depolarize the afferent fibre

31
Q

What is happening for the channel to reach threshold

A

By tapping the patellar tendon, the receptor is stretched, allowing sodium to enter the cell and make it more positive. When the cell reaches -55, this is when the voltage gated sodium channels open

32
Q

repolarizaton

A

The voltage-cated potassium channels open and you get a relatively fast repolarization of the membrane potential.

33
Q

hyperpolarization

A

During the after-hyperpolarization phase, we have sodium leak channels, we have potassium leak channels, we have the sodium-potassium pump active.

We also have some of those voltage-gated potassium channels which remain open. They haven’t closed yet. So because we have that extra permeability to potassium, we’re a little bit closer to the potassium equilibrium potential.

As they start to close, the cell gets close to its resting membrane potential

34
Q

refractory period

A

an action potential cannot be generated

35
Q

absolute refractory period

A

impossible to generate an action potential

the voltage-gating sodium channels are open, so they are unable to open again. Therefore you cannot generate another action potential in this neuron. The inactivation gate is blocking the channel

36
Q

relative refractory period

A

harder to generate another action potential: stronger stimulus is needed. The inactivation gate has moved.

The potassium channels are open. Potassium is leaving making the cell more negative. This makes it harder to make the cell positive enough

37
Q

electronic conduction

A

deplorization of neighbouring tissue along an axon

As the action potential is generated in one region of the axon, it triggers the opening of voltage-gated sodium channels in the adjacent region, allowing them to reach threshold
This sequential opening of sodium channels and depolarization allows the action potential to propagate along the axon in one direction, from the initial site of stimulation toward the spinal cord

slow process

38
Q

how does an action potential travel in one direction only across the axon

A

This is due to the refractory period. The sodum channels are already open (the inactivation gate is blockign them). this prevents the potential from going backwards

39
Q

saltatory conduction

A

When an action potential is initiated at the initial segment of the axon hillock it depolarizes the membrane.

In myelinated axons, the action potential, can travel through the myelin without losing current

At the nodes, where the membrane is exposed, the action potential is regenerated. The myelin-covered segments of the axon do not require continuous regeneration of the action potential.

40
Q

myelin

A

Insulator: prevents the current from leaking out of the membrane

41
Q

nodes of ranvier

A

Nodes of ranvier are in between the myelinated segments (myelin is discontinous)

The voltage-gated sodium channels are at the nodes of ronge and that is where the action potential is going to need to be regenerated.

42
Q

schwann cells myelinated

A

A single schwann cell is required to generate a single myelinated segment (PNS)

43
Q

oligodendrocytes myelination

A

A single oligodendrocyte ensheaths multiple segments. More efficient (CNS)

44
Q

what is happening in a myelinated axon

A

in a myelinated axon both sultatory conduction and electronic conduction are occurring.

45
Q

what determines speed

A

Speed is determined by how thick the nerve fibre (not myelin) is and how much myelin there is

46
Q

where would the fastest nerve fibres be

A

-skeletal muscle for a stretch reflex

  • proprioceptors for body position
47
Q

second fastest fibres

A

mechanoreceptors: touch and pressure

48
Q

slowest fibres

A

Sharp pain that happens immediately is from groups 3, but the dull throbbing pain after is from the slower group 4 receptors

49
Q

what is the function of electrical synapses

A

It’s thought to play a fairly large role in synchronizing large groups of neurons to fire simultaneously.

50
Q

Electrical synapses

A

Allow for molecules to pass between synaptic terminals in either direction (bidirectional)

Electrical: coordinates large amounts of neurons at the same time; difficult to change

51
Q

connexons

A

electrical synapses: The connexons on one cell’s membrane interact with those on the neighboring cell, creating a continuous channel that connects the cytoplasm of the two cells.
This allows direct communication and passage of ions, metabolites, and signaling molecules between the cells. (physical coupling)

open state: allow the free flow of molecules

closed state

can occur anywhere, axons, cell bodies, dendrites

52
Q

chemical synapses

A

Between presynatpic and postsynaptic terminal of the dendrite

larger gap than electrical synapse

The release of a neurotransmitter (ligand) moves across the gap between the presynaptic cell and the postsynaptic cell, and it will bind to a receptor for that ligand on the postsynaptic cell.

inhibition is only possible with chemical synapses

53
Q

Directly gated chemical synapses

A

stretch reflex

synaptic vesicles contain neurotransmittes. They fuse with the presynaptic membrane and release their contents into the synaptic gap.

The neurotransmitter will bind to the iontropic receptor on the postsynaptic cell. Attatched to the receptor is an ion channel. When the neurotransmitter binds, this opens the ion channel

Effects are fast and short lasting. Once the neurotransmitter is released from the receptor, the ion channel closes and depolarization stops

54
Q

excitatory neurotransmitter

A

glutamate. this causes sodium channels to open and sodium to enter the cell.

55
Q

inhibitory neurotransmitter

A

glutamate and glycine

open channel permebale to potassium or chloride. Equilibrium potential for potassium is -70, so potassium will leave the cell

chloride will hyperpolarize the cell

56
Q

indirectly gated chemical channel

A

No iontropic receptor. Metatropic receptor

slow events, but long lasting like protein synthesis or memories

Activates second messenger system. G proteins are activated which activates adenyl cyclase.

This convertws ATP to cAMP (second messenger). This activates protein kinases which phosphorylate a channel and cause it to open or close. Depolarization or hyperpolarization can occur

57
Q

synaptic transmission

A
  1. action potential arrives in presynaptic terminal
  2. presynaptic terminal depolarizes
  3. voltage gated calcium channels open
  4. calcium causes the presynaptic vessels to fuse with the presynaptic membrane
  5. Transmitter released by exocytosis and diffuse across the synaptic clef. They bidn ot and open ligand gated ion channels
  6. Ions flow acrossed the membrane to depolarize or hyperpolarize the cell
  7. transmitter removed and recyled or degraded. Ion channel closes. PSP ends
58
Q

temporal summation

A

Multiple post synaptic potentials overlap in time

If a presynaptic neuron repeatedly releases neurotransmitters over a short period, the effects of the EPSPs or IPSPs can accumulate, potentially reaching the threshold for an action potential.

59
Q

spatial summation

A

Spatial summation involves the addition of PSPs from different synapses on different regions of the postsynaptic neuron. These occur at the same time. The effects of the EPSPs or IPSPs can accumulate, potentially reaching the threshold for an action potential.

60
Q

EPSP and IPSP amplitude

A

small amplitude that as they travel decreases in amplitude. The location where the IPSP or EPSP is generated effects the postsynaptic potential. EPSP and IPSP can have an action potential generated at the axon hillock. Because the signal does not have to travel, the amplitude will be higher

61
Q

amplitude in PSP and AP

A

PSP: much smaller. Amplitude is graded. It can be depolarizing or hyperpolarizing

AP: Much larger. They are all or nothing which means that its the exact same amplitude.

61
Q

PSP and AP duration

A

AP: msec; faster

PSP: msec-sec; slower

61
Q

Synaptic Integration

A

The process of summing together all the inputs into a pattern of action potential outputs in the postsynaptic cell

61
Q

Synaptic integration increases the complexity of behaviour

A

given the exact same stimulus in different situations, the response of the central nervous system is going to vary.

Whether or not your expecting something. This can cause inhibitory or excitaotry input from the cortex to the spinal cord

62
Q

PSP and AP location

A

AP: generated at action hillock and travel down to the synaptic terminals

PSP: Dendrites and soma of postynaptic cell

62
Q

PSP and AP conduction

A

AP: active/long: Regenerated at every point along the axon as they travel

PSP: Passive (Short distances)

62
Q

Function of a PSP and AP

A

Neurotransmitters will cause the PSP to either be inhibited or excitatory in relation to threshold. If the summation of impulses is enough to depolarize the membrane to threshold an AP will be released.

If the summation of impulses is enough to depolarize the membrane, an action potential will be conducted ot hte therminal where it can cause another PSP in the postsynaptic neuron

63
Q

Stretch reflex

A

Physl 210A (8 decks)

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