Nerves Flashcards

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1
Q

What is a reflex?

A

An automatic and involuntary action which prevents injury

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2
Q

What are the steps in a reflex arc?

A

stimulus >receptor> sensory neurone >relay neurone (in CNS) > motor neurone >effector> response.

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3
Q

What are the two parts of the central nervous system?

A

Brain and spinal cord

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4
Q

Describe the nervous system of Hydra

A

A radially symmetrical nerve net, consisting of one type of unmyelinated neurone

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5
Q

Which part of a motor neurone carries impulses towards the cell body?

A

Dendrite

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6
Q

Which part of a motor neurone carries impulses away from the cell body?

A

Axon

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7
Q

How is resting potential maintained in a neurone?

A

sodium-potassium pumps actively transport 3 sodium ions out of the neurone and 2 potassium ions into the neurone per ATP hydrolysed, some K+ channels allow K+ to ?leak? out, there are large protein anions in the cytoplasm

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8
Q

What happens during depolarisation?

A

Voltage gated sodium channels open and sodium rapidly diffuses into the axon, down an electrochemical gradient. Potential difference increases to +40mV

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9
Q

What happens during repolarisation?

A

Voltage gated potassium channels open and potassium rapidly diffuses out of the axon, down an electrochemical gradient. Potential difference decreases to -90mV

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10
Q

Why can’t an action potential travel backwards?

A

The refractory period means that Na+ channels behind the action potential are inactivated

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11
Q

What is the all or nothing law?

A

All action potentials are the same size and strength. They will only happen if the threshold is exceeded

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12
Q

Which three factors affect the speed at which a nerve impulse can propagate?

A

Myelination, temperature, axon diameter

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13
Q

Why does axon diameter affect speed of nerve impulse propagation?

A

Larger diameter decreases electrical resistance to flow of ions

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14
Q

Why does temperature affect speed of nerve impulse propagation?

A

Higher temperature increases the kinetic energy, increasing the speed at which ions diffuse

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15
Q

How does propagation of a nerve impulse happen when there is no myelin?

A

Local circuits causing voltage gated sodium channels to open along the entire axon membrane

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16
Q

How does propagation of a nerve impulse happen whenthe axon is myelinated?

A

Saltatory conduction means the impulse will jump between Nodes of Ranvier due to electrical insulation

17
Q

How does neurotransmitter cause an action potential in a post synaptic membrane?

A

Released by exocytosis, diffuses across cleft, binds to receptors, opens ligand gated Na+ channels, causes depolarisation

18
Q

How do organophosphorus insecticides affect a synapse?

A

They inhibit acetylcholinesterase, meaning acetylcholine is not broken down and remains in the cleft, continuing to bind to receptors and open Na+ channels- excitatory