The Nervous System Flashcards

1
Q

What is the CNS

A

Brain and spinal cord

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2
Q

How is a reflex response activated

A

Receptor cells detect the stimulus and the nerve impulse is carried along the sensory neurone and enters the spinal cord via the dorsal root. This then passes along the relay neurone and out of the spinal cord through the ventral root on the motor neurone which causes the effect in the effector.

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3
Q

What is the sensory neurone

A

Carries the impulse from the sensory organ to the CNS

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4
Q

What is the relay neurone

A

Found in the CNS and connects the sensory and motor neurones

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5
Q

What is the motor neurone

A

Carries the response impulse from the CNS to the effector

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6
Q

What is the grey matter of the spinal cord

A

It contains cell bodies and synapses.

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7
Q

What is the white matter of the spinal cord

A

It contains axons coated in fatty myelin

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8
Q

List three characteristics of a reflex

A

Automatic
Protective
Fast

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9
Q

Describe the nervous system of hydra (nerve net)

A

no recognisable CNS and fewer types of receptor cells and therefore responds to a limited number of stimuli. Hydra cannot detect the direction of a stimulus. The greater the intensity of the stimulus the more nerve cells are triggered initiating a greater response. Impulses travel more slowly and in all directions

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10
Q

Describe resting potential

A

No impulse is being transported and the resting potential difference is -70mv. This is achieved by sodium-potassium pumps pumping 3Na+ out and only 2K+ in making the outside of the cell membrane is more positive than inside, making the membrane polarised.

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11
Q

Describe action potential

A

The presence of a stimulus opens Na+ channels allowing them to flood the axon, depolarising the membrane and creating a potential difference of +40mv. The Na+ channels then shut

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12
Q

Describe hyper-repolarisation

A

When the Na+ channels close, the K+ channels open. K+ exit the axon. A potential difference of -80mv is achieved because the membrane is very permeable to K+ and too many leave. The sodium-potassium pump restores the resting potential and the membrane
becomes polarised again.

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13
Q

Describe the refractory period

A

No further action potentials can be propagated along the axon until polarisation has been restored. No action potential can occur during depolarisation and repolarisation as they cause an absolute refractory period, but during hyper-repolarisation an action potential can be generated if the stimulus is strong enough

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14
Q

Describe the all or nothing law

A

If the intensity of a stimulus does not reach a certain threshold, no action potential will be generated. This prevents the brain from being overloaded by small unnecessary stimuli

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15
Q

What factors affect the speed of nerve transmission

A

Temperature – Increases in temperature increase kinetic energy and therefore speeds up the transport of ions; this speeds up nerve transmission.
Diameter of the axon – The greater the diameter of the axon the lower the resistance to the movement of ions. Giant squids have axons up to 1mm in diameter allowing them to react quickly in low temperatures.
Myelination - Schwann cells wrap around the axon and secrete myelin which is an electrical insulator. Therefore the impulse jumps between nodes of Ranvier (gaps in the myelin) which speeds up transmission

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16
Q

Describe synaptic transmission

A

When an action potential reaches the presynaptic membrane Ca2+ channel open allowing Ca2+ to enter the synaptic knob. Synaptic vessels, containing neurotransmitter, migrate towards the presynaptic membrane and fuse with it, then releasing the neurotransmitter by exocytosis.The neurotransmitter diffuses across the synaptic cleft and binds to receptor
proteins on the post synaptic membrane. This opens Na+ channel allowing Na+ to flood into the post synaptic neurone. If sufficient Na+ enters the post synaptic neuron an action potential will be generated in that nerve cell.

17
Q

Why does the synaptic knob have many mitochondria

A

If the neurotransmitter stays in the synaptic cleft it would keep initiating impulses. They are hydrolysed down to their component parts and diffuse back to the synaptic knob where they are repackaged into synaptic vessels. ATP is required which is why there are lots of mitochondria.

18
Q

List the functions of a synapse

A
Transmit information form neurone to neurone
Pass impulses in one direction
Act as junctions
Prevents overstimulation
Filter out low level stimuli
19
Q

Layers of the meninges from top down

A

Dura mater
Arachnoid Mater
Pia Mater