Nervous system

Question 1

Describe a sensory neurone?

Answer 1

• Short axon
• Found in dorsal root ganglion
• Transmits impulses from sense organs towards CNS

Question 2

Describe a motor neurone?

Answer 2

• Long axon
• Found in grey matter
• Transmits impulses from CNS to an effector

Question 3

Describe a relay neurone?

Answer 3

• Short axon
• Found in grey matter
• Connects sensory and motor neurone

Question 4

Describe nerve nets?

Answer 4

• Non myelinated axons
• Slow conduction speed
• Hydra and jellyfish have nerve nets
• Allows them to sense light and chemicals and detect physical contact

Question 5

What are the 2 parts of the nervous system?

Answer 5

• Central nervous system - brain and spinal cord
• Both surrounded and protected by membrane called meninges
• Peripheral nervous system - comprised of somatic nervous system (nerves that originate in brain/spinal cord)
• Includes sensory and motor neurones

Question 6

What are the parts of the motor neurone?

Answer 6

• Dendrite
• Axon
• Schwan cell
• Myelin sheath
• Nodes of Ranvier
• Cell body

Question 7

What are the transport proteins in the axon membrane?

Answer 7

• Voltage gated potassium channels
• Voltage gated sodium channels
• Permanently open potassium channels
• Potassium/sodium pump

Question 8

Define resting potential?

Answer 8

• Potential difference between inside and outside of a membrane when a nerve impulse is not being conducted

Question 9

Define action potential?

Answer 9

• Rapid change in potential difference across membrane

Question 10

Describe the all or nothing law?

Answer 10

• For an action potential to be generated, depolarisation of an axon membrane must exceed threshold value (10-15 mv above resting potential)
• Stimulus weaker than threshold value will not generate an action potential
• The greater the stimulus above the threshold value the greater frequency of action potentials along the axon and the stimulus may generate action potentials in more than one neurone

Question 11

What is propagation of nerve impulses?

Answer 11

• When axon is stimulated voltage gated sodium channels open and sodium rushes in, depolarising membrane
• Causes local circuits to be set up which makes sodium channels in next part of membrane open and depolarises next part of membrane

Question 12

What is the refractory period?

Answer 12

• After an action potential, voltage gated sodium channels are inactivated for a short time and cannot open to allow influx of sodium into the membrane

Question 13

Why does the refractory period occur?

Answer 13

• Prevents action potential being generated in opposite direction as prevents membrane behind firing again
• Prevents a second action potential being generated to close to the first

Question 14

What affects the speed of nerve impulses?

Answer 14

• Myelination
• Diameter of axons
• Temperature

Question 15

How does myelination affect speed of nerve impulses?

Answer 15

• Myelinated neurones transmit action potential faster
• Insulates axons so stops ions moving in/out membrane
• Action potential only occurs at nodes of Ranvier so impulse jumps from one node to the next speeding up transmission - This is called saltatory conduction
• If axon is unmyelinated, propagation is instead by local circuits

Question 16

How does diameter of axon affect speed of transmission?

Answer 16

• The greater the diameter, the lower the resistance to ion flow so the greater speed of transmission

Question 17

How does temperature affect the speed of transmission?

Answer 17

• As temp increases, so does speed as it speeds up rate of respiration which produces ATP

Question 18

What is acetylcholinesterase?

Answer 18

• Enzyme which hydrolyses acetylcholine in synaptic cleft into choline and ethanoic acid
• These molecules diffuse back across synaptic cleft and ATP is used to reform neurotransmitter molecules and store them in vesicles

Question 19

Functions of synapses?

Answer 19

• Transmits impulses between neurones
• Makes sure impulses only travel in one direction - this is because vesicles containing the transmitter are only in the presynaptic neurone and the receptor molecules are only on the post synaptic membrane
• Allow acclimatisation - after repeated stimulation a synapse may run out of neurotransmitter, this allows them to filter out low level stimuli
• Allow summation

Question 20

What is summation?

Answer 20

• Temporal summation - a post synaptic neurone may only be stimulated if there are frequent action potentials in the pre synaptic membrane
• Spatial summation - a post synaptic neurone may only be stimulated if several pre synaptic neurones receive stimulation

Question 21

What are excitatory drugs?

Answer 21

• Stimulate nervous system by creating more action potentials

Question 22

What are inhibitory drugs?

Answer 22

• Inhibit nervous system by reducing number of action potentials produced

Question 23

What is agonist?

Answer 23

• Substance that binds to receptor and activates it, just like the normal neurotransmitter

Question 24

What is antagonist?

Answer 24

• Substance that binds to receptor but doesn’t activate it, just blocks neurotransmitter (like a competitive inhibitor of an enzyme)

Question 25

Describe organophosphorus insecticides?

Answer 25

- Block/inhibit acetylcholinesterase - This prolongs effects of acetylcholine which remains in synaptic cleft and causes repeated depolarisation of post synaptic neurone - Results in repeated firing of action potentials along post synaptic neurones - If this happens between motor neurones and muscle then repeated contractions of muscle will occur

Question 26

Steps in a reflex arc?

Answer 26

1. Stimulus 2. Receptor 3. Sensory neurone 4. Relay neurone 5. Motor neurone 6. Effector 7. Response

Question 27

What is a dendrite?

Answer 27

- Dendrite - thin extensions that carry impulses towards cell body

Question 28

What is an axon?

Answer 28

- Axon - long extension that transmits impulses away from body

Question 29

What is a schwan cell?

Answer 29

- Schwan cell - cells that surround neurones and insulate them

Question 30

What is the myelin sheath?

Answer 30

- Myelin sheath - Schwan cells grow around axons to form multi layered fatty sheath, acts as an electrical insulator that speeds up transmission along axon

Question 31

What are the nodes of ranvier?

Answer 31

- Nodes of Ranvier - area along axon where myelin sheath is missing

Question 32

What is the cell body?

Answer 32

- Cell body - part of neurone that contains nucleus, RER, mitochondria ect