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IMS Nerves and muscles > 2 Neural signalling > Flashcards

2 Neural signalling Flashcards

1
Q

4 factors contribute to membrane resting potential

A
  1. intracellular charged proteins
  2. Na+/K+ pump
  3. sodium ions
  4. potassium ions
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2
Q

intracellular proteins

A

negative groups on surface = -ve

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3
Q

Na+/K+ pump

A

3 Na out
2 K in
= overall net negative p.d

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4
Q

sodium ions

membrane not very permeable to Na ions

A

membrane is only slightly permeable to Na+, so its effects on resting potential are small

net inward diffusion of Na+ slightly adds to the positivity of the cell = brings up to -65mV

both conc + electrical gradient pull Na+ in

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5
Q

potassium gradient

A

K+ out = conc gradient through channels

K+ in = electrical gradient pulls in due to -ve charge in cell

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6
Q

cell resting membrane potential =

A

close to but not equal to the potassium equilibrium potential as there is also a small leak for sodium ions

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7
Q

an action potential is…

away from cell body -> towards axon terminal

A

the means by which a neuron sends information down its axon, away from the cell body.
The action potential (spike/impulse) is an explosion of electrical activity that is created by a depolarising current

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8
Q

at RP

-65mV

A

all voltage gated Na+ and K+ channels closed

non-voltage dependent K+ channels are open

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9
Q

phases of AP 1

A

Na+ channels open
Na+ enters nerve cell
Membrane potential rises towards zero

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10
Q

phases of AP 2 = DEPOLARISATION

A

If threshold potential reached, voltage gated Na+ channels open
Na+ ions flow into cell
Action potential spike results

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11
Q

phases of AP 3 = REPOLARISATION

happen after reversal potential

A

Na+ channels close when Na+ equilibrium potential is reached
Voltage gated K+ channels open and K+ ions flow out of cell
Membrane potential reverses

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12
Q

phases of AP 4 = HYPERPOLARISATION

A

K+ ions continue to flow out of cell while Na+ channels closed
Hyperpolarisation results

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13
Q

AP = all or nothing principle

A

Membrane has to be depolarised beyond threshold for an AP to be generated
Further increase above threshold -> higher AP frequency not larger AP amplitude

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14
Q

absolute refractory period

= on graph the spike up to before hyperpolarisation

A

no further action potentials can be elicited = ensures AP propagation is one way

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15
Q

relative refractory period

= on graph starts at hyperpolarisation (end of repolarisation)

A

a larger stimulus can result in action potential

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16
Q

non-myelinated neuron AP conduction

A

wave along entire length of axon

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17
Q

myelinated neuron AP conduction

A

jumps along between Nodes of Ranvier = faster

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18
Q

Receptor potential caused by

A

detection of stimulus by receptor which then causes an AP is above threshold

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19
Q

stronger the RP

A

higher freq of AP generated

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20
Q

2 main sensory receptors in muscle

A
  1. muscle spindle

2. golgi tendon organ (GTO)

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21
Q

muscle spindle and GTO are both

A 
mechanoreceptors = pressure changes
proprioceptors = position and movement
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22
Q

muscle spindle stimulated when

A

muscle is passively stretched

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23
Q

GTO responds to

A

tension = stimulated when its associated muscle contracts or stretches in response to tension

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24
Q

muscle spindle found in

A

muscle = modified muscle fibre

25
Q

GTO found in

A

tendon

26
Q

muscle spindle description

A

bundle of modified skeletal muscle fibres (intra-fusal fibres) enclosed in connective tissue capsule

Intra-fusal fibres detect stretch/initiate reflex

27
Q

GTO description

A

small bundles of tendon (collagen) fibres enclosed in a layered capsule with dendrites coiling between and around the fibres

stimulated when the associated muscle contracts

sets up reflex causing muscle to relax and removing stimulation

28
Q

spindle is activated when

A

muscle is stretched passively = initates a reflex

-> when muscle contracts and shortens it’s switched off

29
Q

purpose of muscle spindle

A

prevent muscle from being overstretched

30
Q

Knee-jerk reflex pathway

= monosynaptic pathway as only 1 synapse

A
  • Muscle stretch stretches spindle - increased discharge of sensory nerves
  • Increased firing of the motoneurone and the muscle contracts
  • NO SPINAL INTERNEURONE involved in this case.
  • Effect - reduce the stretch of the muscle.
  • Specific for the muscle stretched
31
Q

GTO activated when

A

muscle is actively contracted (also at times when passively stretched)

32
Q

purpose of GTO

A

tension detector that protects muscle against excess load

33
Q

GTO

inverse stretch reflex

A

Stimulated by excessive tension during muscle contraction or passive stretch

Causes a reflex inhibition of the muscle ……relaxation

34
Q

2 types of synapse

A
  1. electrical

2. chemical

35
Q

electrical synapse

A

direct passage of current via ions flowing through gap junctions

occurs in some parts of CNS

36
Q

chemical synapse

A

release of vesicles containing chemical transmitter which has an effect on receptors on a target cell

37
Q

gap junctions in electrical synapses

pores between cells effectively mean that the cytoplasm of the two cells is in continuity

A

formed by channels called connexons

connexons are made of protein molecules (connexins)

38
Q

process of chemical transmission across synaptic cleft

A
  • AP reaches axon terminal of presynaptic cell
  • triggers Ca 2+ entry into cell
  • triggers release of neurotransmitter from vesicles which fuse with presynaptic membrane
  • transmitter diffuses across the synaptic cleft
  • acts on specific receptors in the postsynaptic membrane (cell body or dendrite)
39
Q

neurotransmitter =

A

a substance shown to be released by a neurone and have a physiological action on specific receptors on a target cell

40
Q

neuromodulator =

A

a substance that is released and modifies the action of a transmitter, but doesn’t have a direct action itself

41
Q

neuroactive substance =

A

a neutral term if a substance is known to have an effect in the CNS but its precise action is not known

42
Q

different types of neurotransmitter substances

A
  • amines
  • amino acids
  • peptides
  • purines (ATP)
43
Q

7 major neurotransmitters

A 
acetylcholine (ACh)
norepinephrine
dopamine
gamma-aminobutyric acid (GABA)
glutamate
serotonin
histamine
44
Q

amine neurotransmitters…

A 
Dopamine (DA)
  Noradrenaline (Norepinephrine)(NA)
  Adrenaline (Epinephrine)
  Histamine
  Serotonin
45
Q

amino acid neurotransmitters…

A

Gamma-aminobutyric acid (GABA)
Glutamate (Glu)
Glycine (Gly)

46
Q

peptide neurotransmitters…

A 
Dynorphin 
  Enkephalins
  Neuropeptide Y (NPY)
Calcitonin gene-related peptide (CGRP)
  Somatostatin
Galanin
  Substance P (SP)
Thyrotropin-releasing  hormone (TRH)
Vasoactive intestinal polypeptide
47
Q

Ionotropic receptor

A

= ion channels and comprise mostly 4 or 5 similar protein subunits arranged around a central pore that is normally closed to ion movements. When the transmitter (ligand) binds it causes a conformational change that briefly opens the pore and ions pass through to cause a rapid change in the resting potential of the underlying cytoplasm

effect is to hyperpolarise or depolarise the postsynaptic cell

48
Q

Metabotropic receptor

A

= single, long protein molecules, mostly crossing the cell membrane 7 times (7 trans-membrane domains)

  • no ion pore
  • ligand binds there is a conformational change in the molecule that causes the intracellular part to interact with a G-protein that then sets off a chain of intracellular events, that may include opening of ion channels
49
Q

ionotropic vs metabotropic receptor response speed

A

ionotropic = faster

50
Q

EPSP =

A

excitatory post-synaptic potential

51
Q

IPSP =

A

inhibitory post-synaptic potential

52
Q

binding of what causes EPSP

A

glutamate, ACh

53
Q

binding of what causes IPSP

A

GABA, glycine

54
Q

EPSP what ion influx

A

Na+ = depolarise cell towards threshold potential and may initiate an AP

55
Q

IPSP what ion influx

A

Cl- = hyperpolarise cell and make may initiation of an AP less likely i.e. inhibition

56
Q

purpose of EPSP

A

Decrease resting membrane potential (make more +ve)
i.e. closer to threshold for depolarization

EPSP’s add up to produce threshold potential to generate AP

57
Q

purpose of IPSP

A

Hyperpolarize post synaptic membrane
Increase membrane potential
i.e. moving it further from threshold for depolarization

58
Q

affect of same postsynaptic neurone can receive numerous excitatory and inhibitory inputs to its cell body

A

net effect of these EPSPs and IPSPs that determine whether it will fire an action potential

IMS Nerves and muscles (5 decks)

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