Neuronal - 5

Question 1

What is the cell body

Answer 1

Contains the nucleus and large amounts of RER associated with production of proteins and neurotransmitters

Question 2

What do dendrites do

Answer 2

Carry nerve impulses towards the cell body

Question 3

What is the axon

Answer 3

A single long fibre that carries nerve impulses away from the cell body

Question 4

What are schwann cells

Answer 4

surround axon many times, protecting and providing electrical insulation

Question 5

What is the myelin sheath

Answer 5

Forms covering of axon and made of membranes

Question 6

What are nodes of ranvier

Answer 6

Gaps between adjacent schwann cells where there is no myelin sheath

Question 7

What are the three types of neurones

Answer 7

Motor
Sensory
Relay

Question 8

What are sensory receptors

Answer 8

Specialised cells or sensory neurone ending that can detect changes in the environment
Are transducers

Question 9

What is the Pacinian corpuscle

Answer 9

Rings of connective tissue wrapped around the end of a sensory neurone

Question 10

How does pressure effect the Pacinian corpuscle

Answer 10

Pressure deforms the connective tissue and pushes against the nerve ending
This causes stretched mediated Na+ channels to open

Question 11

What are the 3 types of proteins found in the cell membrane of neurones

Answer 11

Na+/K+ pumps
Voltage gated Na+ channels
Voltage gated K+ channels

Question 12

What are voltage gated sodium channels

Answer 12

Allow Na+ through
Open at a particular voltage
Use facilitated diffusion
Usually kept closed

Question 13

What are voltage gated potassium channels

Answer 13

Allow K+ through
Open at a particular voltage
Use facilitated diffusion
Usually closed

Question 14

What are Na+/K+ pumps

Answer 14

Specialised carrier proteins
Use active transport
One ATP molecule
3:2 ratio
Polarised membrane

Question 15

Why does resting potential occur

Answer 15

Na/K pumps working

Some voltage gated K+ channels open so k+ leaks out

Voltage gated Na+ channels closed

Organic anions inside axon

Question 16

What is generator potential

Answer 16

A small depolarisation caused by a sodium ions entering the cell

Question 17

What is an action potential

Answer 17

The mode through which a neuron transports electrical signals
Is a brief change in the voltage across the membrane

Question 18

What causes action potential

Answer 18

Voltage gated K+ and Na+ channels

Question 19

What happens at the threshold potential

Answer 19

All Na+ channels open

Question 20

Explain what happens during a action potential

Answer 20

A stimulus is detected which causes stretched mediated sodium channels to open, meaning sodium diffuses in

This causes a threshold potential

This causes voltage gated sodium channels to open

So more Na+ moves into the cell causing depolarisation, until the voltage reaches +40mv

This causes the voltage gated sodium channels to close and the voltage gated potassium channels to open

k+ moves out of the cell causing repolarisation

The k+ channels close at -70mv, leaving everything in the wrong place, known as hyperpolarisation

Na+/k+ pumps re-establish resting potential

Question 21

What is the all or nothing response

Answer 21

If the depolarisation is not great enough to reach threshold, then an action potential and impulse are not produced

Question 22

How is an action potential transmitted in an unmyelinated neurone

Answer 22

Na+ diffuses into the neurone through a channel

There is a localised high concentration of Na+ inside the neurone

Na+ diffuses along the inside of the neurone

Na+ gates are now opened due to depolarisation

Question 23

How is an action potential transmitted in a myelinated neurone

Answer 23

Ionic exchanges can only occur at nodes of Ranvier

Na+ and k+ ions cant diffuse through myelin

Action potentials jump from one node to the next

Called saltatory conduction

Question 24

Advantages of myelin sheath

Answer 24

Insulates
Speeds up transmission
Fewer channels needed

Question 25

What affects the speed of an impulse

Answer 25

Axon diameter
Temperature

Question 26

What is a synapse

Answer 26

Where two neurons meet but don’t touch

Has presynaptic and postsynaptic neurons

Has a gap called a synaptic cleft

Involves the diffusion of neurotransmitters

Question 27

What is a cholinergic synapse

Answer 27

Where the neurotransmitter is acetylcholine

Question 28

How is an action potential transmitted across a synpase

Answer 28

Action potential arrives at the synaptic bulb

Voltage gated Ca2+ channels open

Ca2+ diffuse into the synaptic bulb

Synaptic vesicles containing acetylcholine move and fuse with presynaptic membrane

Ach is released by exocytosis and diffuses across synaptic cleft

Ach molecules bind to receptors on the Na+ channels on the postsynaptic membrane

Na+ channels open

Na+ diffuses into postsynaptic membrane

Producing a generator potential

Question 29

How is acetylcholine recycled

Answer 29

Ach is broken down by a hydrolytic enzyme called acetylcholinesterase

Hydrolyses the Ach into ethanoic acid and choline

Sodium channels close

Ethanoic acid and choline diffuse back across the synaptic cleft into the presynaptic bulb and remade into Ach

Question 30

What are the features of synapses

Answer 30

Several presynaptic neurones might converge to one postsynaptic neurone

One presynaptic neurone diverges to several postsynaptic neurones

Unidirectionality

Filter out low level stimuli

Acclimatisation

Summation

Inhibition

Question 31

What are the 2 types of summation

Answer 31

Spatial
Temporal

Question 32

What is spatial summation

Answer 32

A number of different presynaptic neurones share the same synaptic cleft
involves multiple neurones

Question 33

What is acclimatisation

Answer 33

Repeated stimulation leads to exhaustion of vesicles of Ach

Question 34

What is temporal summation

Answer 34

A single presynaptic neurone releases neurotransmitters many times over a short period

Involves one neurone