Nerves

Question 1

What is a reflex?

Answer 1

An automatic and involuntary action which prevents injury

Question 2

What are the steps in a reflex arc?

Answer 2

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

Question 3

What are the two parts of the central nervous system?

Answer 3

Brain and spinal cord

Question 4

Describe the nervous system of Hydra

Answer 4

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

Question 5

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

Answer 5

Dendrite

Question 6

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

Answer 6

Axon

Question 7

How is resting potential maintained in a neurone?

Answer 7

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

Question 8

What happens during depolarisation?

Answer 8

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

Question 9

What happens during repolarisation?

Answer 9

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

Question 10

Why can’t an action potential travel backwards?

Answer 10

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

Question 11

What is the all or nothing law?

Answer 11

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

Question 12

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

Answer 12

Myelination, temperature, axon diameter

Question 13

Why does axon diameter affect speed of nerve impulse propagation?

Answer 13

Larger diameter decreases electrical resistance to flow of ions

Question 14

Why does temperature affect speed of nerve impulse propagation?

Answer 14

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

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

How do organophosphorus insecticides affect a synapse?

Answer 18

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