Nerves

Question 1

Where are photoreceptors found (light intensity + wavelength)?

Answer 1

Eyes

Question 2

Where are mechanoreceptors found (sound) ?

Answer 2

Chochlea- ear

Question 3

Where are mechanoreceptors found (pressure)?

Answer 3

Pacinian corpuscle- skin

Question 4

Where are thermoreceptors found (temperature)?

Answer 4

Skin

Question 5

Where are chemoreceptors found (volatile chemicals)?

Answer 5

Olfactory cells- nasal cavity

Question 6

Where are chemoreceptors found (soluble chemicals)?

Answer 6

Taste buds

Question 7

What do sensory receptors do?

Answer 7

They convert specific types of stimuli to generator potentials by causing geated sodium ion channels to open, creating a potential difference across the cell membrane.

Question 8

What can generator potentials lead to?

Answer 8

Generator potentials can lead to an action potential being initiated- a nerve impulse.

Question 9

What is a pacinian corpuscle?

Answer 9

A mechanoreceptor that responds to pressure.

Question 10

How does a pacinian corpuscle respond to pressure?

Answer 10

1) Pressure applied to layers
2) Gated sodium channels open
3) A generator potential is created.
4) If enough channels open, an action potential is produced.

Question 11

What are the 3 types of neurone?

Answer 11

Sensory, relay and motor

Question 12

What is the direction of nerve impulse transmission in sensory neurones?

Answer 12

From receptor to central nervous system (CNS)

Question 13

What is the direction of nerve impulse transmission in relay neurones?

Answer 13

Between sensory and motor neurones, within the CNS.

Question 14

What is the direction of nerve impulse transmission in motor neurones?

Answer 14

From the CNS to an effector, e.g. muscle or gland.

Question 15

Describe a sensory neurone

Answer 15

Has 1 long myelinated dendron and a short axon with a myelinated sheath.

Question 16

Describe a motor neurone

Answer 16

Has a long axon with a myelinated sheath. Has lots of short unmyeliated dendrites.

Question 17

What is an action potential?

Answer 17

An action potential is a depolarisation of the cell membrane so the inside becomes more positive than the outside.

Question 18

What is a nerve impulse?

Answer 18

The transmission of an action potential along a neurone.

Question 19

What is the resting potential?

Answer 19

IT is maintained at about -60mV inside the cell compared to outside the cell.

Question 20

What happens when the stimulus is intense?

Answer 20

When a stimulus has a high intensity a large number of action potentials are generated and it is these that are brain interprets, for instance, as a bright light or loud sound.

Question 21

What is a refractory period?

Answer 21

When a region of the neurone is hyperpolarised, no further action potentials can be produced.

Question 22

Why does a refractory period take place?

Answer 22

This is because the Na+ and K+ need to be re-distributed so that a resting potential can be re-established.

Question 23

Explain how the myelin sheath speeds up a nerve impulse

Answer 23

The myelin sheath insulates the neurone. Na+ and K+ can only pass across the membrane in the gaps between the Schwann cells - nodes of Ranvier. This leads to the action potentials jumping from one node to the next- saltatory conduction.

Question 24

What are synapses?

Answer 24

Junctions between neurones where chemicals called neurotransmitters are used to pass on action potentials.

Question 25

Describe the action of neurotransmitters across a synapse

Answer 25

1) Action potential arrives at synaptic knob.
2) Calcium-gated channels open and calcium ions diffuse in.
3) Calcium ions cause neurotransmitter vesicles to fuse with the presynaptic membrane.
4) Acetylcholine diffuses across the synaptic cleft to bind with receptors on sodium ion channels.
5) Sodium ion channels open and a generator potential is created (EPSP- excitatory post-synaptic potential).
6) If the EPSP is of sufficient magnitude an action potential is produced.

Question 26

What are the important roles of synapses in summation and control?

Answer 26

Allow for convergence of signals from many neurones to one neurone

Allow for the divergence of signals from one neurone to many neurones.

Question 27

What are the other roles of synapses?

Answer 27

Ensure impulses travel in one direction only

Filter out low-level stimuli

Amplify low-level stimuli

Allow new (neuronal) pathways to occur- the basis for conscious thought and memory.

Question 28

What is summation?

Answer 28

Summation refers to the way several small potential changes can combine to produce one large potential difference. It can be temporal or spatial and allows low-level stimuli to be amplified.