Neuronal communication

Question 1

What are the 3 types of neurons called?

Answer 1

Sensory, motor and relay neurons

Question 2

What is the nervous system made up of?

Answer 2

A complex network of cells called neurones

Question 3

What is the role of sensory neurons?

Answer 3

To transmit nerve impulses from receptors to the centeral nervous system (CNS)- the brain and spinal cord

Question 4

What is the role of motor neurons?

Answer 4

Transmit nerve impulses from the CNS to effectors.

Question 5

What is the role of relay neurons?

Answer 5

Transmit nerve impulses between sensory neurones and motor neurones.

Question 6

What is a stimulus detected by and then what happens?

Answer 6

Detected by receptor cells and a nerve impulse is sent along a sensory neurone.

Question 7

What happens when a nerve impulse (action potential) reaches the end of a neurone?

Answer 7

Chemicals called neurotransmitters take the information across to the next neurone, which then sends a nerve impulse.

Question 8

What does the CNS do?

Answer 8

Processes information, decides what to do about it and sends impulses along motor neurones to an effector.

Question 9

What is the process of the nervous system, starting from the stimulus of seeing a friend waving?

Answer 9

Receptors- light receptors (photoreceptors) in your eyes detect the wave.
(Action potential sent along sensory neurone)
CNS- CNS processes information and decides what to do about it.
(Action potential sent along motor neurone)
Effectors- Muscle cells are stimulated by motor neurones
Response- Muscles contract to make your arm wave.

Question 10

What is the role of sensory receptors?

Answer 10

They are transducers- they convert a stimulus energy into a nerve impulse

Question 11

What is a mechanoreceptor?

Answer 11

A type of sensory receptor for pressure and movement stimuli.

Question 12

What is an example of a mechanoreceptor?

Answer 12

A Pacinian corpuscle

Question 13

Where are pressure receptors located?

Answer 13

Deep in skin, mainly in fingers and feet

Question 14

What does the sensory neurone in the Pacinian corpuscle have?

Answer 14

Has special channel proteins in its plasma membrane

Question 15

What do the membrane of the Pacinian corpuscle have? And what does this allow?

Answer 15

Have stretch-mediated channels.
These open and allow NA+ (sodium ion) to enter the sensory neurone only when they are stretched and deformed.

Question 16

What happens when pressure is applied to the Pacinian corpuscle?

Answer 16

It deforms the neurone plasma membrane, stretches and widens the NA+ (sodium ion) channels and so NA+ diffuses in which leads to the establishment of a generator potential.

Question 17

What happens when a neuron is not conducting an impulse?

Answer 17

There is a differnece between the electrical charge inside and outside the cell, this is known as the resting potential.

Question 18

What is the resting potential voltage and why?

Answer 18

-70mV
Because there are more positive ions, Na+ and K+, outside compared to inside, therefore the inside of the neurone is comparatively more negative.

Question 19

What is the resting potential maintained by?

Answer 19

• Maintained by a sodium-potassium pump, involving active transport and ATP.
• The pump moves 2 K+ ions in and 3 NA+ ions out of the axon.
• This creates an electrochemical gradient causing K+ to diffuse out and NA+ to diffuse into the axon.
• The membrane is more permable to K+ ions and so more are moved out of the axon, resulting in the -70mV.

Question 20

Why is the axon membrane more permable to potassium ions than sodium ions?

Answer 20

• Because many of the potassium ion channels are permanently open, whereas the sodium ions channels aren’t always open.
• And because there are more potassium ion channels embedded in the membrane.

Question 21

What is an action potential?

Answer 21

When a neurone’s voltage increases beyond a set threshold.

Question 22

What is an increase in voltage known as and why?

Answer 22

Depolarisation becasue the membrane becomes more permable to NA+ (sodium ions).

Question 23

What does a stimulus trigger (in the graph)?

Answer 23

Sodium ion channels to open in the membrane allowing sodium ions to diffuse into the neurone down an electrochemical gradient.

Question 24

What happens if a large enough stimulus is detected by the neurone?

Answer 24

The resting potential can be converted into an action potential
- The potential difference must reach a threshold of around -55mV to trigger depolarisation.

Question 25

What happens when depolarisation occurs?

Answer 25

Voltage-gated sodium ion channels in the axon membrane open - More sodium ions diffuse into the axon down the electrochemical gradient This is an example of positive feedback.

Question 26

What potential difference across the membrane will an action potential reach (i.e. depolarisation)?

Answer 26

+30 mV

Question 27

What happens very shortly after the potential difference has reached +30mV and what is this called?

Answer 27

Repolarisation - The sodium ion voltage-gated channel proteins close. - Potassium ion voltage-gated channel proteins open, allowing the diffusion of potassium ions out of the axon, down their concentration gradient. - This returns the potential difference to normal -70mV. Example of negtaive feedback.

Question 28

What is hyperpolarisation?

Answer 28

Because potassium ion channels are slow to close, which results in too many potassium ions diffusing out causing a short period of hyperpolarisation. - This means that the potential difference becomes more negtaive than the normal resting potential.

Question 29

What happens after an action potential?

Answer 29

After an action potential, the neurone cell membrane can't be excited again straight away. This is because the ion channels are recovering.

Question 30

What is the all-or-nothing principle?

Answer 30

The idea that if the threshold is not reached (-55mV), an action potential won't fire.

Question 31

What is myelin sheath formed from?

Answer 31

Schwann cells

Question 32

What can't happen in myelinated neurones?

Answer 32

In sections of the axon that are surrounded by myelin sheath, depolarisation cannot occur, as the myelin sheath stops the diffusion of sodium ions.

Question 33

Where can depolarisation happen in myelinated neurones?

Answer 33

Depolarisation (action potentials) can only occur at the nodes of Ranvier.

Question 34

What is saltatory conduction?

Answer 34

When the presence of Schwann cells means the action potentials 'jump' from one node to the next.

Question 35

What does saltatory conduction allow?

Answer 35

Allows the impulse to travel much faster (up to 50 times faster) than in an unmyelinated axon in the same diameter.

Question 36

What factors affect the speed of conduction along a neurone?

Answer 36

Myelinated The diameter of the axon Temperature

Question 37

How does the diameter of the axon affect the speed of conduction?

Answer 37

An impulse will be conducted at a higher speed along neurones with thicker axons comapred to those with thinner axons.

Question 38

Why do thicker axons conduct impulses at a higher speed?

Answer 38

- Thicker axons have an axon membrane with greater SA over which diffusion of ions can occur -> This increases rate of diffusion of sodium and potassium ions through protein channels, which in turn increases the rate at which depolarisation and action potentials can occur.

Question 39

What is a synapse?

Answer 39

The junction where two neurones meet is known as a synapse.

Question 40

What are cholinergic synapses?

Answer 40

Synapses that use acetylcholine (ACh) as a neurotransmitter.

Question 41

What happens when an electrical impulse arrives at the end of axon on the presynaptic neurone?

Answer 41

- Vesicles move towards, and fuse with, the presynaptic membrane. - Chemical messengers called neurotransmitters are released from vesicles at the presynaptic membrane. - The neurotransmitters diffuse across the synaptic cleft and temporarily bind with receptor molecules on the post-synaptic membrane. - This triggers an impulse which travels along the postsynaptic neurone.

Question 42

What happens to the neurotransmitters after they have temporarily binded with the receptors on the post-synaptic neurone?

Answer 42

The neurotransmitters are either destroyed or recycled to prevent continued stimulation of the second neurone, which could cause repeated impulses to be sent.

Question 43

What stimulated the ACh-containing vesicles to fuse with the presynaptic membrane?

Answer 43

- The arrival of the action potential which causes depolarisation of the membrane. - Which stimulates the voltage-gated calcium ion channel proteins to open. - Calcium ions diffuse down an electrochemical gradient from the tissue fluid surrounding the synapse into the synaptic knob. Which stimulates the vesicles to fuse with the presynaptic membrane.

Question 44

What type of receptors does ACh temporarily bind with?

Answer 44

Cholinergic receptors

Question 45

What is the process by which ACh diffuses across the synaptic membrane?

Answer 45

Exocytosis

Question 46

What happens when the ACh binds to the cholinergic receptors?

Answer 46

- Sodium channels open in the postsynaptic membrane - Sodium ions diffuse down the electrochemical gradient into the cytoplasm causing depolarisation of the postsynaptic membrane, restarting the electrical impulse once the threshold is reached.

Question 47

How do synapses ensure the one-way transmission of impulses?

Answer 47

Because the neurotransmitters is released on one side and its receptors are on the other side-chemical transmission cannot occur in the opposite direction.

Question 48

What can excitatory neurotransmitters do?

Answer 48

Stimulate the generation of an action potential in a postsynaptic neurone. - This is done by opening the sodium ion channels in the post-synaptic membrane which causes depolarisation if a threshold is reached.

Question 49

What can inhibitory neurotransmitters do?

Answer 49

Can prevent the generation of an action potential in the post-synaptic neurone - They do this by opening the potassium ion channels in the post-synaptic membrane which causes hyperpolarisation of the membrane.

Question 50

What is the threshold

Answer 50

-55 mV