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OAP B > NERVOUS SYSTEM > Flashcards

NERVOUS SYSTEM Flashcards

1
Q

DORSAL ROOT GANGLION CONTAINS CELL BODIES OF WHAT?

A

SENSORY NEURONS

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2
Q

A BUNDLE OF FIBRES LOCATED WITHIN THE CNS IS A WHAT?

A

TRACT

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3
Q

ACTION POTENTIAL VS GRADED POTENTIAL DISTANCES

A

AP - short + long distances

GP - short distances only

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4
Q

WHAT DO LIGAND-GATED CHANNELS RESPOND TO?

A

chemical stimuli (ligand binds to receptor)

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5
Q

WHAT DO MECHANICALLY-GATED CHANNELS RESPOND TO?

A

mechanical vibration or pressure stimuli

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6
Q

WHAT DO VOLTAGE-GATED CHANNELS RESPOND TO?

A

direct changes in membrane potential

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7
Q

WHAT DO LEAK CHANNELS RESPOND TO?

A

they randomly open + close

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8
Q

RESTING MEMBRANE POTENTIAL

A

-> membrane of non-conducting neurons are positive OUTSIDE and negative INSIDE:

  1. unequal distribution of ions across plasma membrane + selective permeability to Na+ and K+
  2. most anions (-ve) cannot leave cell
  3. Na+/ K+ pumps
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9
Q

POTENTIAL ENERGY DIFFERENCE AT REST

A

-70mV

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10
Q

WHAT HAPPENS DURING AN AP?

A

neuron undergoes a rapid depolarisation of a large fixed size and then repolarises again

AP arises at trigger zone + propagates down the axon + each spike is followed by a refractory period

AP is an all or none phenomenon

magnitude of response given by spike rate (not spike size)

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11
Q

WHAT HAPPENS DURING A GRADED POTENTIAL?

A

neuron undergoes depolarisation (excitatory) or hyperpolarisation (inhibitory) of variable size

amplitude (size) of potential indicates response magnitude

GPs arise usually in dendrites, don’t propagate or have refractory periods

if enough GPs occur within an area of membrane, an AP may be generated

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12
Q

THRESHOLD OF MEMBRANE POTENTIAL

A

-55mV (initiates an AP)

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13
Q

ACTION POTENTIAL GENERATION

A

once membrane potential hits threshold:

voltage-gated Na+ activation gates open; Na+ rushes in + depolarises neuron until membrane potential reaches +30mV

voltage-gated K+ channels open; outflow of K+; Na+ channels inactivating + RMP reached

outflow of K+ continues; Na+ channels in resting state; K+ gates closing + RMP reached

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14
Q

REFRACTORY PERIOD

A

occurs after AP generation, neuron needs to rest ~0.4-4ms before next spike can occur

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15
Q

WHERE DOES AP ARISE?

A

at trigger zone (axon hillock) - propagates down the axon

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16
Q

ABSOLUTE REFRACTORY PERIOD

A

impossible to evoke another AP - Na+ channels are inactivated

17
Q

RELATIVE REFRACTORY PERIOD

A

later, a stronger than usual stimulus is required to evoke an AP (part of Na+ channels recovered)

18
Q

WHAT CHANNELS ARE ONLY PRESENT AT THE NODES?

A

Na+ channels

19
Q

SALTATORY VS CONTINUOUS CONDUCTION

A

saltatory conduction occurs in myelinated axons only

continuous conduction occurs in unmyelinated axons only

20
Q

THE LARGER THE AXON, WHAT HAPPENS TO IMPULSE PROPAGATION?

A

larger the axon, the faster the impulse propagation

21
Q

TEMPORAL SUMMATION

A

many stimuli in a close span of time

repeated stimuli can have a cumulative effect + can produce a nerve impulse when a single stimuli is too weak

22
Q

SPATIAL SUMMATION

A

many neurons firing simultaneously in the same location

synaptic input from several locations can have a cumulative effect + trigger a nerve impulse

combining of EPSPs + IPSPs across dendrite from simultaneous arrival of APs at various synapses

23
Q

SYNAPTIC INTEGRATION

A

combining of excitatory + inhibitory signals acting on adjacent membrane regions of a neuron

for an AP to occur, sum of both excitatory + inhibitory postsynaptic potentials must be greater than a threshold value

24
Q

ELECTRICAL SYNAPSE

A

electric current from one neurone is passed directly through a GAP JUNCTION (bidirectional)

sends simple depolarising signals

cell membranes aligned parallel

between large presynaptic neuron + small postsynaptic neuron (a lot of current to depolarise a cell)

25
Q

CHEMICAL SYNAPSE

A

neurotransmitter released from presynaptic neuron

diffuses across the synaptic cleft

binds with a receptor on the postsynaptic membrane

fast - transmitter gated ion channels (uses amino acids)

slow - G protein coupled ion channels

26
Q

NEUROTRANSMITTERS

A
  • must be present in the presynaptic neuron
  • must be released in response to presynaptic depolarisation + release must be calcium dependent
  • specific receptors for it must be present on postsynaptic cell
27
Q

SYNAPTIC TRANSMISSON

A

** transfer of info from end of axon of one neuron to the next

AP depolarises presynaptic membrane of synaptic terminal - Ca++ influx through voltage-gated channels

calcium activates proteins (sterine + neurine) attached to vesicles (containing a neurotransmitter) - pulling vesicles to membrane - opening vesicles + dumping their neurotransmitter contents into synaptic cleft (exocytosis - active transport)

neurotransmitter molecules diffuse across synaptic cleft + bind to receptors on subsynaptic membrane initiating response

28
Q

WHAT ARE THE TYPES OF SYNAPTIC CONNECTIONS BETWEEN NEURONS?

A

AXODENDRITIC - axon terminal ends on a dendrite

AXOSOMATIC - axon terminal ends on a cell body

AXOAXONIC - axon terminal ends on another axon

DENDRODENDRITIC SYNAPSE - dendrite makes synapse with another dendrite

29
Q

IONOTROPIC RECEPTORS

A

channel opens in response to ion binding

contains 4-5 subunits

fast speed of action

ligand-gated ion channels

30
Q

METABOTROPIC RECEPTORS

A

channel opens in response to second messengers

contains 1 subunit

slow speed of action

G-protein coupled receptors

31
Q

RHEOBASE

A

measure of membrane excitability

32
Q

CHRONAXIE

A

minimum time required for an electric current double the strength of the rheobase to stimulate a muscle or a neuron

33
Q

GRADED POTENTIAL

A

change in membrane potential that varies in size

34
Q

EXCITATORY POSTSYNAPTIC POTENTIAL (EPSP)

A

promotes excitation of postsynaptic membrane

GP that decays over time + space

cumulative effect of EPSPs are the basis for temporal + spatial summation

if Na+ ions are the carrier, MP of postsynaptic cell is depolarised

35
Q

INHIBITORY POSTSYNAPTIC POTENTIAL (IPSP)

A

temporary hyperpolarisation of a membrane - prevents APs

if Cl- or K+ ions are carrier, MP of postsynaptic cell is hyperpolarised

36
Q

SYNAPSE COMPOSITION

A
  • presynaptic terminal
  • postsynaptic cell
  • zone of apposition
37
Q

GAP JUNCTION CHANNELS

A

connect communicating cells at an electrical synapse

consist of a pit of cylinders (connexons)

always open

serve to synchronise the activity of a set of neurons

38
Q

LENGTH CONSTANT

A

measure of how effective a given synapse is in contributing to spatial summation

gives distance that it takes an EPSP or IPSP to decrease 37% of its original value at synapse

directly proportional to membrane resistance
+ inversely proportional to longitudinal resistance of cytoplasm:
- leakier the membrane, shorter the length constant
- narrower the dendrite, shorter the length constant

39
Q

WHY CHEMICAL TRANSMISSION?

A

more flexible; produces more complex behaviours

plasticity

can amplify neuronal signals

directly gated are comparatively fast
- mediate behaviour

indirectly are slower
- memory, learning

OAP B (14 decks)

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