Neuronal Communication Flashcards

1
Q

What are sensory receptors?

A

Specialized cells that detect specific stimuli

Act as energy transducers which establish a generator potential

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2
Q

Describe the basic structure of a Pacinian Corpuscle

A

Sensory neuron wrapped in connective tissue called lamellae

Membrane contains stretched mediated channel proteins

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3
Q

How is the Pacinian Corpuscle stimulated?

A

Pressure deforms membrane, causing stretch mediated Na+ channels to open

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

Action potential moves along sensory neuron

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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

Carry electrical impulses from sensory receptor to CNS

Long dendron

Long axon

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5
Q

Describe the structure and function of a relay neuron

A

Carry electrical impulses within CNS to other neurons

Lots of short axons and dendrons

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6
Q

Describe the structure and function of a motor neuron

A

Carries electrical impulses from CNS to effectors

One long axon and multiple dendrites

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7
Q

Describe the additional structure 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 neighboring Schwann cells where there is no myelin

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8
Q

Explain why myelinated axons conduct impulses faster than unmyelinated axons

A

Saltatory conduction - impulses jump between nodes of Ranvier.

Faster than continuous depolarisation

impulse does not travel along whole axon length

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9
Q

How does axon diameter affect transmission speed?

A

Larger diameter means less resistance to ion flow so wave of depolarization travels faster

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10
Q

What is resting potential?

A

Potential difference across neuron membrane when not stimulated

-70mV

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11
Q

How is resting potential established?

A

Na/K pumps - 3:2
3 Na+ out and 2 K+ in

Some voltage gated K+ channels open, so some K+ leaks out

Voltage gated Na+ channels closed

Organic anions inside axon

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12
Q

Name the stages in generating an action potential

A

Depolarisation

Repolarisation

Hyperpolarisation

Refractory period

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13
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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14
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

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15
Q

What happens during hyperpolarisation?

A

Voltage becomes more negative than resting potential

Excess of K+ ions leaves the axon

16
Q

Explain the importance of the refractory period?

A

Ensures discrete impulses - no action potential can be generated immediately after

Ensures action potentials travel in one direction

Limits number of impulse transmissions

17
Q

What is summation in synapses?

A

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

Temporal summation - single neuron fires action potentials in quickly

18
Q

Describe the structure of a synapse

A

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

Synaptic cleft - gap between neurons

Postsynaptic neuron - has complementary receptors to neurotransmitters

19
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

Influx of Ca2+ into presynaptic knob

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

exocytosis of neurotransmitters into the synaptic cleft

20
Q

How do neurotransmitters cross the synaptic cleft?

A

simple diffusion

21
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

22
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

23
Q

What are cholinergic synapses?

A

Use acetylcholine as primary neurotransmitter. Exitatory or inhibitory.

24
What is the difference between temporal and spatial summation?
Temporal - one presynaptic neuron releases neurotransmitters several times in quick succession to generate action potential in postsynaptic neuron Spatial - multiple presynaptic neurons release neurotransmitters which converge to one postsynaptic neuron to generate action potential
25
What happens to acetylcholine from the synaptic cleft
Hydrolysis into acetate and choline by acetylcholinesterase AChE Ethanoic acid and choline diffuse back into presynaptic membrane ATP used to reform acetylcholine for storage in vesicles
26
How does temperature affect transmission speed?
Higher temp increases diffusion of ions so faster depolarization and transmission