Nervous System 3.8

Question 1

What is myelin sheath made of?

Answer 1

Schwann cell

Question 2

What are nodes of Ranvier?

Answer 2

The impulse has to jump at every node of Ranvier speeding up the impulse.

Question 3

How to tell it is a sensory neuron?

Answer 3

The cell body is in the middle.

Question 4

How is the relay neuron different to the sensory neuron?

Answer 4

The relay neuron cell body is much bigger.

Question 5

Why can the impulses only move in one way in the relay neuron?

Answer 5

The synaptic ends are only at the bottom.

Question 6

Why doesn’t relay neurons need myelin?

Answer 6

As it is not very long.

Question 7

How is the motor neuron different?

Answer 7

The cell body is at the end.

Question 8

What are dendrites?

Answer 8

Thin fibers carrying impulses towards a cell body.

Question 9

What are axons?

Answer 9

Thin fibers carrying impulses away from a cell body.

Question 10

What are the two main divisions of the nervous system?

Answer 10

The central nervous system and the peripheral nervous system.

Question 11

What is the dorsal root?

Answer 11

Emerges from the spinal cord, travels to the dorsal root ganglion and allows sensory neurons to enter the spinal cord.

Question 12

What is the ventral root?

Answer 12

Emerges from the spinal cord and allows motor neurons to leave the spinal cord.

Question 13

What is a reflex?

Answer 13

A rapid, automatic response to a sensory stimulus by the body which serves as a protective mechanism.

Question 14

What is a nerve net?

Answer 14

Consists of interconnected nerve cells with short extensions allowing a response to a limited number of stimuli.

Question 15

What are the 3 neurons?

Answer 15

Sensory, relay and motor.

Question 16

What is the function of a sensory neurone?

Answer 16

Carries nerve impulse from the receptors to the cns by the dorsal root.

Question 17

What is the function of a motor neurone?

Answer 17

Carries nerve impulses from the cns to the effectors by the ventral root.

Question 18

What is the function of a relay neurone?

Answer 18

Links the sensory neurone to the motor neurone in the spinal cord.

Question 19

What is the function of dendrites?

Answer 19

Receive nerve impulses from other neurones.

Question 20

What is the function of the axon?

Answer 20

A long fibre that conducts nerve impulses away from the cell body.

Question 21

What are axon terminals?

Answer 21

Branched endings of an axon that approach the muscle fibre.

Question 22

What is a synaptic end bulb?

Answer 22

The end of an axon that is bulbous shaped and contains synaptic vesicles filled with neurotransmitters.

Question 23

What is action potential?

Answer 23

The temporary change in electrical potential across the membrane of an axon in response to the transmission of a nerve impulse.

Question 24

What is resting potential?

Answer 24

Potential difference across a neurone membrane when not stimulated.

Question 25

What are the stages of an action potential?

Answer 25

Depolarisation, repolarisation, hyperpolarisation and retun to resting potential.

Question 26

What happens during depolarisation?

Answer 26

Stimulus causes a change in the voltage across an axon membrane, opening voltage gated sodium channels which diffuse into the axon. Potential difference across membrane becomes more positive and membrane depolarises.

Question 27

What happens during repolarisation?

Answer 27

Voltage gated sodium channels close and voltage gated potassium channels open and facilitated diffusion of potassium ions out of cells down their electrochemical gradient. Membrane repolarises as potential difference across membrane becomes more negative.

Question 28

What happens during hyperpolarisation?

Answer 28

Potassium ions diffuse out and potential difference becomes very negative so membrane hyperpolarises and prevents another impulse form happening.

Question 29

What is the refractory period?

Answer 29

Time period after an action potential during which further action potentials are prevented.

Question 30

Why can myelinated axons conduct impulses faster than unmyelinated axons?

Answer 30

Saltatory propagation: Impulse jumps from one node of ranvier to another instead of travelling the whole axon length.

Question 31

How does temperature affect the speed of conduction of nervous impulses?

Answer 31

The higher the temperature, the faster the speed of conduction.

Question 32

What is a synapse?

Answer 32

The junction between two nerve cells or a nerve cell and an effector.

Question 33

What is the function of synapses?

Answer 33

Electrical impulse cannot cross junction so neurotransmitters send impulses between neurons or from neurons to effectrions.

Question 34

What is the synaptic cleft?

Answer 34

A small gap between neurons across which a nerve impulse is transmitted by neurotransmitters.

Question 35

Describe synaptic transmission in the presynaptic neurone.

Answer 35

Wave of depolarisation travels down the presynaptic neuron causing voltage gated calcium channels to open which cause vesicles of acetylcholine to move towards and fuse with the presynaptic membrane. Exocytosis of neurotransmitter into synaptic cleft.

Question 36

How do neurotransmitters cross the synaptic cleft?

Answer 36

Simple diffusion.

Question 37

Describe synaptic transmission in the postsynaptic neuron.

Answer 37

Acetylcholine diffuses across synaptic cleft and binds to specific receptors on postsynaptic membrane. Ligand gated sodium channels open and if influx of sodium ions raises membrane to threshold potential, action potential is generated.