Neuronal Communication

Question 1

What is the function of the cell body?

Answer 1

Contains the nucleus, cytoplasm and other organelles. Vesicles contain neurotransmitters

Question 2

What are dendrons?

Answer 2

Dendrons split into dendrites

Dendrons carry an action potential towards the cell body

Question 3

What is an axon?

Answer 3

Axons are elongated nerve fibres which carry nerve impulses away from the cell body.

They can be short or long depending on the type or neurone.

Question 4

Features of sensory neurons

Answer 4

Short dendrites
One long dendron
One short axon

Question 5

Features of motor neurons

Answer 5

Many short dendrites
One long axon
Myelinated or non-myelinated

Question 6

Features of relay neurones?

Answer 6

Short dendrites
One axon

Question 7

What is the nervous communication pathway

Answer 7

Stimulus -> Receptor -> CNS -> Effector -> response

Question 8

What is the role of sensory receptors?

Answer 8

Sensory receptors convert the energy of a stimulus into electrical energy (they are transducers).

The are specialised cells and each sensory receptor will respond to only one type of stimulus

Question 9

Explain the processes of detecting a stimulus.

Answer 9

Once a stimulus is detected, the receptor cell changes the permeability of its cell membrane.

Ions move into and out of the cell via ion pumps and ion channels.

The charge on the ions create a potential difference. This is called the generator potential.

A generator potential is required in a sensory receptor for an action potential to be generated

Question 10

How does a bigger stimulus affect the generator potential?

Answer 10

A bigger stimulus produces a bigger movement of ions across the membrane

This causes a bigger change in potential difference and thus a greater generator potential

Question 11

What is an example of a sensory receptor?

Answer 11

The pacinian corpuscle.

It is found in the skin and detects pressure and vibration

The end of a sensory neurone is found within the centre of the corpuscle which is surrounded by many layers of connective tissue. Each layer is separated by a layer of viscous gel.

Question 12

How do corpuscles only respond to changes in pressure and not when it’s constant?

Answer 12

They don’t respond when pressure is constant as the sodium ion channels remain open and thus a resting potential is not established

Question 13

Why is it important that we don’t feel anything when pressure is constant?

Answer 13

So we don’t constantly receive unnecessary information - preventing cognitive overload

Question 14

what is the synaptic cleft?

Answer 14

A gap between the dendrite of one neurone and axon terminal of another

Question 15

what is the presynaptic neurone?

Answer 15

the neurone along which the impulse has arrived

Question 16

what is the postsynaptic neurone?

Answer 16

the neurone that recieves the neurotransmitter

Question 17

What is the refractory period?

Answer 17

After an action potential the neurone cell membrane cannot be excited again straight away. This is due to the ion channels recovering and can’t be made to open.

Question 18

Why is the refractory period important?

Answer 18

Ensures action potentials don’t overlap (discrete)

Ensures action potentials are unidirectional (can’t travel backwards)

Question 19

What are the 2 stages of the refractory period?

Answer 19

• The absolute refractory period (1ms), nothing happens
• The relative refractory period (5ms long), an action potential may occur only if the stimulus is more intense than the normal threshold.

Question 20

what are myelin sheaths made up of?

Answer 20

they are made up of many layers of plasma membranes produced by Schwann cells

Question 21

How does saltatory conduction occur in myelinated neurones?

Answer 21

K+ and Na+ ions cannot diffuse through the insulating myelin sheath. The myelinated neurone is only permeable to ions at the nodes of Ranvier.

between the nodes of Ranvier, sodium ions diffuse rapidly. This allows the wave of depolarisation to ‘jump’ from node to node, making the conduction faster.

Question 22

How do non-myelinated neurones conduct action potentials?

Answer 22

In non-myelinated neurones, the impulse does not jump, but instead transmits along the nerve fibre.

Depolarisation occurs along the entire length of the neurone.

It takes more time for each region to be depolarised.

Question 23

What is the speed of transmission in non-myelinated neurones?

Answer 23

up to 1m/s

Question 24

What is the speed of transmission in myelinated neurones?

Answer 24

up to 100 m/s

Question 25

How does axon diameter affect the speed of the impulse?

Answer 25

The bigger the axon diameter, the faster the impulse is transmitted. This is due to less resistance to the diffusion of ions through the cytoplasm.

Question 26

How does temperature affect the speed of the impulse?

Answer 26

The higher the temperature, the faster the speed of the impulse. This is because ions diffuse faster at higher temps. until approx. 40 degrees as the protein channels will start to denature.

Question 27

What does the size of the stimulus determine?

Answer 27

The stronger/bigger the stimulus is, the frequency of action potentials increase.

Question 28

How does the brain determine how intense a stimulus is?

Answer 28

from the frequency of the action potentials arriving in the sensory region of the brain.

Question 29

What is the change in potential difference when the neurone goes from resting potential to action potential?

Answer 29

approx. -75mV to +35mV

Question 30

Name 3 ways in which the resting potential is established.

Answer 30

--> Voltage-gated K+ ion channels closing --> Sodium-potassium pump --> K+ ion leak channels

Question 31

A generator potential is caused by the movement of what ions?

Answer 31

Sodium ions (Na+)

Question 32

What causes the voltage-gated sodium ion channels to open?

Answer 32

A stimulus with a potential difference that exceeds the threshold

Question 33

How is the neurone repolarised?

Answer 33

--> Na+ V.G close --> K+ V.G open --> K+ ions leave membrane

Question 34

explain the process of synaptic transmission

Answer 34

When an action potential arrives at the end of the presynaptic neurone, it causes calcium ion channels to open. Calcium ions flood into the the axon terminal and stimulates the synaptic vesicles to move toward the membrane of the presynaptic neurone. The vesicles fuse with the membrane, releasing acetyl choline (neurotransmitters) into the synaptic cleft via exocytosis. Acetylcholine diffuses across the synaptic cleft and binds to receptors on sodium ion channels, openeing them. sodium ions flood into the postsynaptic neurone as a result. The postsynaptic neurone depolarises, and if the threshold is reached an action potential is generated. Acetycholinesterase in the synaptic cleft breaks down acetylcholine into ethanoic acid and choline. Choline and ethanoic acid thendiffuse back into the presynaptic neurone where ATP from the mitochondria recombines them into acetylcholine and moves it back into the vesicles.

Question 35

What is saltatory conduction?

Answer 35

When the action potential in a myelinated neurone jumps from node to node allowing it to travel faster as an action potential doesn’t need to be generated along the entire length (only at nodes of ranvier)

Question 36

What is the all-or-nothing principle?

Answer 36

If depolarisation (caused by a stimulus) does not exceed -55mV, an action potential and impulse will not be produced (nothing).

Question 37

After an action potential has been generated, the membrane enters a refractory period where it can’t be stimulated because Na+ channels are recovering and can’t be opened. Give 3 reasons why this is important.

Answer 37

1) ensures discrete impulses (makes sure each impulse is separate) 2) ensures the action potentials travel in one direction, as if they travelled in two directions it would prevent a response 3) it limits the number of impulse transmission. This is important ti prevent over reaction to a stimulus

Question 38

What is summation?

Answer 38

The rapid build-up of neurotransmitters in the synapse to help generate an action potential by two methods: spatial or temporal summation

Question 39

What is spatial summation?

Answer 39

Many different neurones collectively trigger a new action potential by combining the neurotransmitter they release in order to exceed the threshold value

Question 40

What is temporal summation?

Answer 40

One neurone releases neurotransmitter repeatedly over a short period of time to add up to enough to exceed the threshold value