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Biology Hope > Neuronal Communication > Flashcards

Neuronal Communication Flashcards

1
Q

what are neurones

A

transmit electrical impulses rapidly around the body so an organism can respond to changes in its internal and external environment

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2
Q

what is the structure of a neuron

A

Cell body - nucleus surrounded by a cytoplasm
Dendrons - extensions from cell body - dendrites transmit electrical impulses
Axons - elongates nerve fibres that transmit impulses away from the cell body

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3
Q

what are the types of neurones

A

Sensory - transmit impulses from sensory receptors to CNS

Relay - transmit impulses between sensory and motor neurones

Motor - transmit impulses to a muscle / gland (effector)

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4
Q

what are myelinated neurones

A
  • myelin sheath made from Schwann cells
  • acts as an insulating layer and allows myelinated neurones to conduct the impulse at a faster speed
  • nodes of Ranvier allow the impulse to jump
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5
Q

what are sensory receptors

A

transducers - convert stimulus they detect into a nerve impulse

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6
Q

what are examples of sensory receptors

A

mechanoreceptors - pressure
chemoreceptor - chemicals
thermoreceptor - heat
photoreceptor - light

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7
Q

what are Pacinian corpuscles

A
  • detect mechanical pressure
  • deep within the skin
  • stretched mediated sodium channel that transports sodium ions
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8
Q

how do pacinian corpuscles work

A
  • in resting state the stretch mediated sodium ion channels in sensory neurone membrane are too narrow
  • applied pressure to pacinian corpuscles changes the shape
  • sodium ion channels widen and ions diffuse into the neurone
  • influx of sodium ions depolarise the membrane = generator potential
  • generator potential creates an action potential
  • action potenital is transmitted along neurones to the CNS
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9
Q

what is resting potential

A
  • outside of the membrane is more positively charged
  • membrane is polarised as there is a potential difference
  • occurs due to the movement of sodium and potassium ions
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10
Q

how is a resting potential created

A
  • Na+ actively transported out of the axon and K+ in by intrinsic protein (sodium potassium pump)
  • every 3 Na+ pumped out 2 K+ pumped in
  • more Na+ ions outside the membrane than in thee axon cytoplasm
  • Na+ diffuses back into the axon down electrochemical gradient
  • gated Na+ channels are closed and K+ channels are open
  • K+ ions can diffuse out of the axon
  • more positively charged ions outside of the axon then inside creating resting potenital
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11
Q

what is an action potential

A
  • caused by the rapid movement of Na+ and K+ ions across the axon membrane through voltage gated ion channels
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12
Q

what are the 5 stages in an action potential

A
  • stimulus
  • depolarisation
  • repolarisation
  • hyperpolarisation
  • resting potential
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13
Q

in an action potential what happens at the stimulus

A
  • sodium ion channels open
  • voltage gated sodium channels closed
  • must meet threshold of excitation
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14
Q

in an action potential what happens at depolarisation

A
  • voltage gated Na+ channels open
  • Na+ ions pass into axon down electrochemical gradient
  • reduces potential difference
  • inside of the axon is less negative
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15
Q

in an action potential what happens at repolarisation

A
  • at +30mv all Na+ voltage channels close
  • K+ voltage gated channels open
  • K+ ions diffuse out of the axon down the concentration gradient
  • returns resting potential
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16
Q

in an action potential what happens at hyperpolarisation

A
  • K+ channels are slow to close
  • too many K+ ions diffuse out of the neurone
  • potential difference is more negative than the normal resting potential
17
Q

in an action potential what happens at resting potential

A
  • once al K+ channels are closed the sodium potassium pump restores the resting potential
  • Na+ can then repolarise again
18
Q

what is the all or nothing principle

A

an impulse is only transmitted if the initial stimulus is sufficient enough to increase the membrane potential above a threshold potential

19
Q

what is the refractory period

A
  • ensures action potentials are discrete events (separate)
  • new action potential are generated ahead
  • impulse only travels in one direction
  • creates a minimum time between action potentials
20
Q

what is the speed of conduction

A
  • how quickly an impulse is transmitted along a neurone
  • myelination
  • diameter of axon
  • temperature
21
Q

how does myelination affect the speed of conduction

A
  • increases the speed that action potentials travel
  • depolarisation cannot occur at the myelin sheath
  • action potentials only occur at the nodes
  • Schwann cells allow the impulse to jump from one node to the next (saltatory conduction)
22
Q

how does the diameter of the axon affect the speed of conduction

A
  • thick axons = impulse travels at high speeds
  • axon membrane has a greater surface area
  • increases rate of diffusion of ions which increases the rate of action potentials
  • greater volume of cytoplasm reduces electrical resistance and action potential moves faster
23
Q

how does temperature affect the speed of conduction

A
  • more impactful on ectotherms
  • cold conditions slow down nerve impulses
  • cold = less kinetic energy available for facilitated diffusion of Na+ and K+ ions
24
Q

what is the synaptic cleft

A

gap that separates the axon of one neurone from the dendrite of the next

25
Q

what is the presynaptic neurone

A

neurone along which the impulse has arrived

26
Q

what is the postsynaptic neurone

A

neurone that receives the neurotransmitter

27
Q

what are synaptic vesicles

A

vesicles containing neurotransmitters that fuse with the presynaptic membrane and release contents into the synaptic cleft

28
Q

what are excitatory neurotransmitters

A
  • result in depolarisation of the postsynaptic neurone
  • if meets threshold it triggers an action potential
    -acetylcholine
29
Q

what are inhibitory neurotransmitters

A
  • result in hyperpolarisation of the postsynaptic membrane
  • prevents an action potential being triggered
30
Q

how is an impulse transmitted across a synapse

A
  • action potential reaches the end of the presynaptic neurone
  • depolarisation of presynaptic membrane causes calcium ion channels to open
  • calcium ions diffuse into the presynaptic knob
  • synaptic vesicles with neurotransmitters fuse which presynaptic membrane
  • neurotransmitters are released into the synaptic cleft by exocytosis
  • neurotransmitters diffuse across the synaptic cleft and binds with receptor molecules on the postsynaptic membrane
  • sodium ion channels open
  • sodium ions diffuse into the postsynaptic neurone
  • triggers an action potential
  • neurotransmitters are recycled or destroyed once an impulse is sent
31
Q

how does transmission occur across a cholinergic synapse

A
  • arrival of an action potential at the presynaptic neurone causes calcium ion channels to open
  • calcium ions enter synaptic knob
  • influx of calcium ions causes synaptic vesicles to fuse with presynaptic membrane and release ACh into the synaptic cleft
  • Ach fuse with receptor sites on the sodium channel in postsynaptic neurone
  • Na+ channels open and ions diffuse rapidly along concentration gradient
  • influx of Na+ generates action potential in postsynaptic neurone
  • ACHnase hydrolyses Ach into choline and acetyl to diffuse into presynaptic neurone
  • prevents from continuously generating action potentials
  • ATP in mitochondria is used to recombine choline and ethanoic acid into Ach
32
Q

what is the role of a synapse

A
  • ensures impulses only travel from the presynaptic to the postsynaptic neurone
  • allow an impulse from one neurone to be transmitted to a number of neurones
33
Q

what is summation

A

effect of multiple impulses can be added together

34
Q

what is spatial summation

A
  • number on presynaptic neurones connected to one postsynaptic neurone
  • each releases neurotransmitters which build up to a high enough level in the synapse to trigger an action potential in the single postsynaptic neurone
35
Q

what is temporal summation

A
  • a single presynaptic neurone releases neurotransmitters as a result of an action potential several times
  • builds up in the synapse until the quantity is sufficient to trigger an action potential

Biology Hope (27 decks)

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