Neuronal Communication Flashcards

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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

Describe the basic structure of a Pacinian Corpuscle

A

Single nerve fibre surrounded by layers of connective tissue contained by a capsule

Stretch-mediated Na+ channels on membrane

Capillary runs along the base layer of tissues

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3
Q

What stimulus does a Pacinian corpuscle respond to? How?

A

Pressure deforms membrane, causing Na+ channels to open

If influx of Na+ raises membrane to threshold potential, a generator potential is produced

Action potential moves along sensory neurone

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4
Q

Describe the features of all neurons

A

Cell body - contains organelles and 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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4
Q

Describe the structure and function of a sensory neuron

A

Usually unipolar

Transmits impulses from receptors to CNS

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5
Q

Describe the structure and function of a relay neuron

A

Usually bipolar

Transmits impulses between neurons

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6
Q

Describe the structure and function of a motor neuron

A

Usually multipolar

Transmits impulses from relay neurons in the CNS to effectors

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7
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

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8
Q

Name the 3 processes Schwann cells are involved in

A

Electrical insulation

Phagocytosis

Nerve regeneration

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9
Q

Explain why myelinated axons conduct impulses faster than unmyelinated axons

A

Saltatory conduction - impulses jump from nodes of Ranvier. Depolarisation cannot occur where myelin sheaths act as electrical insulator

so impulse does not travel along whole axon length

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10
Q

Where are myelinated and non-myelinated neurons found in the body?

A

Myelinated - most neurons in CNS

Non-myelinated - Group C nerve fibres involved in transmitting secondary pain

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11
Q

What is resting potential?

A

Potential difference across neuron membrane when not stimulated

-70mV

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12
Q

How is resting potential established?

A

Na/K pumps - 3:2
Na+:K+
Some voltage gated K+ channels open, so some K+ leaks out

Voltage gated Na+ channels closed

Organic anions inside axon

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13
Q

Name the stages in generating an action potential

A

Depolarisation

Repolarisation

Hyperpolarisation

Refractory period

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14
Q

What happens during depolarisation?

A

Facilitated diffusion of Na+ into cell

Potential difference across membrane becomes more positive

If membrane reaches threshold potential, voltage-gated Na+ channels open

Potential difference reaches +30mV

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15
Q

What happens during repolarisation?

A

Voltage-gated Na+ channels close and voltage-gated K+ channels open

Facilitated diffusion of K+ ions out of cell

Potential difference across membrane becomes more negative

16
Q

What happens during hyperpolarisation?

A

‘Overshoot’ when K+ ions diffuse out and potential difference becomes more negative than resting potential

Refractory period - no stimulus is large enough to raise membrane potential to threshold

Voltage gated K+ channels close and sodium-potassium pump creates resting potential

17
Q

Explain the importance of the refractory period?

A

No action potential can be generated in hyperpolarised sections of membrane

Ensures unidirectional impulse

Ensures discrete impulses

Limits frequency of impulses transmission; larger stimuli have higher frequency

18
Q

Why is the frequency of impulse significant?

A

Enables organism to distinguish size of stimulus although all action potentials have same magnitude

Larger stimuli results in higher frequency of transmission because they overcome hyperpolarisation faster

19
Q

What is summation in synapses?

A

Spatial summation - lots of presynaptic neurone converge on a single postsynaptic neurone

Temporal summation - single neuron fires action potentials in quick succession, releasing lots of neurotransmitters into the synaptic cleft

20
Q

Describe the structure of a synapse

A

Presynaptic neuron ends in synaptic bulb - contains lots of mitochondria, ER and vesicles of neurotransmitter

Synaptic cleft - gap between neurons

Postsynaptic neuron - has complementary receptors to neurotransmitters

21
Q

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

A

Wave of depolarisation travels down presynaptic neuron causes voltage-gated Ca2+ channels to open

Vesicles move towards and fuse with the membrane of the presynaptic bulb

exocytosis of neurotransmitters into the synaptic cleft

22
Q

How do neurotransmitters cross the synaptic cleft?

A

simple diffusion

23
Q

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

A

Neurotransmitters bind to specific complementary receptors of postsynaptic membrane

Ligand-gated Na+ channels open

If influx of Na+ ions raises membrane to threshold potential, an action potential is generated

24
Q

What happens in inhibitory synapse?

A

Neurotransmitter binds to and opens Cl- channels on postsynaptic membrane and triggers K+ channels to open

Cl- moves in and K+ moves out via facilitated diffusion

potential difference becomes more negative - hyperpolarisation so no actionpotential

25
Q

Define summation and name the 2 types

A

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

Temporal summation

Spatial summation

26
Q

What are cholinergic synapses?

A

Use acetylcholine as primary neurotransmitter. Exitatory or inhibitory.

27
Q

What is the difference between temporal and spatial summation?

A

Temporal - one presynaptic neuron releases neurotransmitters serveral times in quick succession

Spatial - multiple presynaptic neurons release neurotransmitters

28
Q

What happens to acetylcholine from the synaptic cleft

A

Hydrolysis into acetyl and choline by acetylcholinesterase AChE

Acetate and choline diffuse back into presynaptic membrane

ATP used to reform acetylcholine for storage in vesicles