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Biology OCR (y13 content) > 5.1.3 (Neuronal communication) > Flashcards

5.1.3 (Neuronal communication) Flashcards

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1
Q

What features are common to all sensory receptors

A

1) act as transducers (senses -> electrical signals)

2) respond to specific stimuli’s

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2
Q

structure of Pacinian corpuscle

A
  • single nerve fibre surrounded by layers of connective tissues
  • tissues separated by viscous gel and in a capsule
  • stretch mediated Na+ channels on plasma membrane
  • capillary runs along base layer of the tissues
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3
Q

How does Pacinian corpuscle respond to stimulus and how

A
  • responds to PRESSURE and deforms the membrane
  • causes stretch-mediated Na+ ion channels to open
  • Na+ enters the membrane to pass the threshold potential -> generator potential is produced
  • action potential -> through the sensory neurone
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4
Q

Describe the features of neurons

A

Cell body
Dendrons
Axons

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5
Q

what are the features of the cell body in neurons

A
  • contains organelles
  • high proportion of RER
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6
Q

what are the features of the Dendron in neurons

A
  • branch into dendrites
  • carry impulse TOWARDS cell body
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7
Q

what are the features of the Axon in neurons

A
  • Long
  • unbranched fibre
  • carries nerve impulses AWAY from cell body
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8
Q

Describe the structure & function of SENSORY neurons

A
  • usually unipolar
  • transmits impulses from receptors to CNS
    -located in peripheral nervous system
  • Long axon
  • axon terminals
  • myelinated
  • dendrites
    -c ell body in the middle of the axon
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9
Q

describe structure & function of RELAY neurons

A

-usually bipolar
-transmits impulses between neurons

-high-branched dendrites
- cell body
- short axon + dendron
- some myelinated
- highly branched axon terminals

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10
Q

describe the structure & function of the MOTOR neuron

A
  • usually multipolar
  • transmits impulses from RELAY neuron in the CNS to EFFECTORS
  • dendrites
  • no dendron
  • long axon
  • cell body (in CNS)
  • axon terminals
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11
Q

Describe the features of a MYELINATED neuron

A
  • Schwann cells
  • Myelin sheath
  • Nodes Of Ranvier
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12
Q

what is the Schwann cell?

A

cells wrapped around the axon to make the myelin sheath

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13
Q

what is the Myelin sheath?

A

made from the myelin-rich schwaan cells membranes

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14
Q

what is the Nodes Of Ranvier?

A

short gaps between Schwann cells where there is no myelin sheath

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15
Q

What 3 processes are Schwann cells involved in?

A
  • electrical insulation
  • phagocytosis
  • nerve regeneration
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16
Q

explain why a myelinated axon conducts impulses faster than an unmyelinated axon

A

SALTATORY CONDUCTION:

  • impulse “JUMPS” from one NOD to another
  • Depolarisation cannot occur where myelin sheath acts as an insulator
  • so impulse does not travel along the whole axon length
17
Q

where are myelinated neurons found in the body?

A

most neurons in CNS and PNS (involved in spinal reflex)

18
Q

where are NON-MYELINATED neurons found in the body?

A

group C nerve fires involved in transmitting secondary pain

19
Q

what is resting potential

A

Voltage across neuron membrane when there is no stimulus

(-60mV)

20
Q

How is resting potential established

A
  • membrane is more permeable to K+ than Na+

-Na-K pump transports 3 Na+ OUT and 2 K+ IN the cell

  • establishing an electrochemical gradient.
  • cell is negative internally than externally
21
Q

what are the 4 stages in generating an action potential

A

1) Depolarisation
2) Repolarisation
3) Hyperpolarisation
4) returning to resting potential

22
Q

what happens during depolarisation

A

1) Stimulus -> facilitated diffusion of Na+ into cell down electrochemical gradient

2) Potential Diff across membrane = more POSITIVE

3) if the membrane reaches threshold potential (-50mV) voltage gates Na+ channel open.

4) significant influx of Na+ ions reverses potential difference to +40mV

23
Q

What happens during REPOLARISATION

A

1) voltage-gated Na+ channels close & voltage-gated K+ channels open

2) Facilitated diff of K+ out of cells down electrochemical gradient

3) Potential diff across membrane becomes more negative

24
Q

What happens during HYPERPOLARISATION

A

1) Overshoot when K+ diffuse OUT
2) Potential diff becomes more NEGATIVE than resting potential
3) REFRACTORY period: no stimulus large enough to raise membrane potential to threshold
4) voltage-gates K+ channels close
5) sodium-potassium pump re-establishes resting potential

25
Q

Explain the importance of the REFRACTORY period

A

1) ensures unidirectional impulse
2) ensures discrete impulse
3) limits impulse frequency

26
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).

27
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 Ca?+ channels to open.
  2. Vesicles move towards & fuse with presynaptic membrane.
  3. Exocytosis of neurotransmitter into synaptic cleft.
28
Q

How do neurotransmitters cross the synaptic cleft?

A

simple diffusion

29
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 Nat channels open.
  3. If influx of Na* ions raises membrane to threshold potential, action potential is generated.
30
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.
31
Q

Define summation and name the 2 types.

A

Neurotransmitter from several sub-threshold impulses accumulates to generate action potential.
• temporal summation
• spatial summation
NB no summation at neuromuscular junctions.

32
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.

33
Q

What are cholinergic synapses?

A

Use acetylcholine as primary neurotransmitter.
Excitatory or inhibitory. Located at:
• motor end plate (muscle contraction)
• preganglionic neurons (excitation)
• parasympathetic postganglionic neurons (inhibition e.g. of heart or breathing rate)

34
Q

What happens to acetylcholine from the synaptic cleft?

A
  1. Hydrolysis into acetyl and choline by acetylcholinesterase (AChE).
  2. Acetyl & choline diffuse back into presynaptic membrane.
  3. ATP is used to reform acetylcholine for storage in vesicles.

Biology OCR (y13 content) (3 decks)

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