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13A/Bi1 > NA. 5.3 Neuronal Communication > Flashcards

NA. 5.3 Neuronal Communication Flashcards

1
Q

What features are common to all sensory receptors?

A
  • Act as energy transducers which establish a generator potential.
  • Respond to specific stimuli.
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2
Q

What stimulus does a Pacinian corpuscle respond to? How?

A
  1. Pressure deforms membrane, causing
    stretch-mediated Na+ ion channels to open.
  2. If influx of Na+ raises membrane to threshold potential, a generator potential is produced.
  3. Action potential moves along sensory neuron
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3
Q

Describe the basic structure of a Pacinian corpuscle

A

Single nerve fibre surrounded by layers of connective tissue in an oval shape separated by a gel

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4
Q

Describe the features of all neurons.

A

Cell body: contains organelles & high proportion of RER.
Dendrons: branch into dendrites which carry impulses towards the cell body.
Axon: long, unbranched fibre carries nerve impulses away from cell body.

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5
Q

Describe the function of a sensory neurone

A

Transmits impulses from sensory receptors to CNS.

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6
Q

Describe the function of a motor neurone

A

Transmits impulses from relay neurons in the CNS to effectors.

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7
Q

Describe the structure and function of a relay neuron.

A

Transmits impulses between neurons

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8
Q

List some structural adaptations of neurons

A
  • many are long so can transmit over distance
  • maintain the potential difference accros their plasma membrane
  • myelin sheath
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9
Q

Describe the additional features of a Myelinated neuron.

A

Schwann cells: wrap around axon many times.
Myelin sheath: made from myelin-rich membranes of Schwann cells.
Nodes of Ranvier: very short gaps between neighbouring Schwann cells where there is no myelin sheath.

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10
Q

Name 3 processes Schwann cells are involved in.

A
  • electrical insulation
  • phagocytosis
  • nerve regeneration
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11
Q

What are the advantages of Myelination?

A

quicker transmission of an electrical impulse(5-50 times faster)

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12
Q

Differences between Myelinated and Non-myelinated neurons?

A
  • myelinated: tends to carry impulses over longer distances, faster transmission speed used for receptor to CNS and CNS to effector
  • non-myelinated : tends to be over short distances, used in coordinating body function
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13
Q

Explain why Myelinated axons conduct impulses faster than unmyelinated axons.

A

Saltatory conduction: Impulse ‘jumps’ from one node of Ranvier to another. Depolarisation cannot occur where myelin sheath acts as electrical insulator. So impulse does not travel along whole axon length.

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14
Q

What is resting potential?

A

Potential difference (voltage) across neuron membrane when not stimulated (-50 to -90 mV, usually about -70 mV in humans).

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15
Q

What is an action potential?

A

a brief reversal of the potential across the membrane of a neurone causing a positive peak (as compared to the negative resting potential)

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16
Q

How is resting potential established?

A

1.Membrane is more permeable to K+ than Na+.
2.Sodium-potassium pump actively transports 3Na+ out of cell & 2K+ into cell.
establishes electrochemical gradient: cell contents more negative than extracellular environment.

17
Q

Name the stages in generating an action potential

A
  1. Depolarisation
  2. Repolarisation
  3. Hyperpolarisation
  4. Return to resting potential
18
Q

What happens during Depolarisation?

A
  1. Stimulus → facilitated diffusion of Na+ into cell down electrochemical gradient.
  2. p.d. across membrane becomes more positive.
  3. If membrane reaches threshold potential (-50mV), voltage-gated Na+ channels open. (positive feedback mechanism).
  4. Significant influx of Na+ ions reverses p.d. to +40mV.
19
Q

What happens during Repolarisation?

A
  1. Voltage-gated Na+ channels close and voltage-gated K+ channels open.
  2. Facilitated diffusion of K+ ions out of cell
    down their electrochemical gradient.
  3. p.d. across membrane becomes more negative.
20
Q

What happens during Hyperpolarisation?

A
  1. ‘Overshoot’ when K+ ions diffuse out = p.d. becomes more negative than resting potential.
  2. Refractory period: no stimulus is large enough to
    raise membrane potential to threshold.
  3. Voltage-gated K+ channels close &
    sodium-potassium pump re-establishes resting potential.
21
Q

Explain the importance of the Refractory period.

A

No action potential can be generated in hyperpolarised sections of membrane.
•allows cell to recover after the action potential
• Ensures unidirectional impulse.
• Limits frequency of impulse transmission; larger stimuli have higher frequency.

22
Q

Why is the frequency of impulse transmission significant?

A

Enables organism to distinguish size of stimulus although all action potentials have same magnitude.
Larger stimuli result in higher frequency of transmission since they overcome hyperpolarisation more quickly.

23
Q

What is a synapses?

A

neurons generate potentials these Electrical impulse cannot cross junction between neurones so Neurotransmitters send transmit impulses between neurons/ from neurons to effectors for excitatory or inhibitory response

24
Q

What do synapses enable?

A
  • Summation of sub-threshold impulses.

* New impulses can be initiated in several different neurons for multiple simultaneous responses.

25
Q

Describe the structure of a synapse

A
  • Presynaptic neuron ends in synaptic knob: contains lots of mitochondria, endoplasmic reticulum & vesicles of neurotransmitter.
  • Synaptic cleft: 20-30 nm gap between neurons.
  • Postsynaptic neuron: has complementary receptors to neurotransmitter (ligand-gated Na+ channels).
26
Q

What happens in the presynaptic neuron when an action potential is transmitted between neurons?

A
  1. Wave of depolarisation travels down presynaptic neuron, causing voltage-gated Ca2+ channels to open.
  2. Vesicles move towards & fuse with presynaptic membrane.
  3. Exocytosis of neurotransmitter into synaptic cleft
27
Q

How do neurotransmitters cross the synaptic cleft?

A

Simple diffusion

28
Q

What happens in the postsynaptic neuron when an action potential is transmitted between neurons?

A
  1. Neurotransmitter binds to specific receptor on postsynaptic membrane.
  2. Ligand-gated Na+ channels open.
  3. If influx of Na+ ions raises membrane to threshold potential, action potential is generated.
29
Q

What happens in an inhibitory synapse?

A
  1. Neurotransmitter binds to and opens Cl- channels on postsynaptic membrane & triggers K+ channels to open.
  2. Cl- moves in & K+ moves out via facilitated diffusion.
  3. p.d. becomes more negative: hyperpolarisation so no action potential is generated
30
Q

What is a Cholinergic synapse?

A

A synapse that uses Acetylcholine as its neurotransmitter. can be excitatory or inhibitory

31
Q

What is the role of Acetylcholinesterase?

A

An enzyme found in the synaptic cleft that hydrolyses acetylcholine into acetic acid(ethanoic acid) and choline, thus preventing it from generating continually producing action potentials

32
Q

What may be found in the pre-synaptic bulb?

A
  • Many mitochondria-produce ATP as this a active process
  • lots of vesicles
  • Large amount of smooth endoplasmic reticulum to package hella vesicles
  • many voltage gated calcium ion channels
33
Q

Define summation

A

Neurotransmitter from several sub-threshold impulses accumulates to generate action potential

34
Q

What are the 2 types of summation?

A
  • temporal summation(many to 1)

* spatial summation (1 to many)

35
Q

What is the difference between Temporal and Spatial summation?

A
  • Temporal: one presynaptic neuron releases neurotransmitter several times in quick succession.
  • Spatial: multiple presynaptic neurons release neurotransmitter.
36
Q

What happens after the breakdown of Acetylcholine by Acetylcholinesterase

A

they diffuse back into the presynaptic membrane and ATP is used to reform acetylcholine, ready for storage/use

37
Q

what does it mean to get ‘habituated’ to something

A

the nervous system no longer react to a stimulus due to prolonged exposure which causes the synapse to run out of vesicles containing the neurotransmitter

13A/Bi1 (13 decks)

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