neuronal communication

Question 1

What are neurones?

Answer 1

Specialised nerve cells which make up the nervous system and transmit electrical impulses rapidly around the body to respond to stimuli.

Question 2

What is the function of the soma/cell body?

Answer 2

The soma contains the nuceli of the nerve cell which is surrounded by cytoplasm and contains lots of ER and mitocondria for neurotransmitter production.

Question 3

What are dendrons?

Answer 3

Dendrons are extensions which derive from the cell body and branch into smaller branches called dendrites for transmitting impulses towards cell body.

Question 4

What are axons?

Answer 4

Axons are cables which transmit impulses away from the cell body to be received by other neurones.

Question 5

What is the myelin sheath?

Answer 5

Acts as an insulating layer which covers the axon.

Question 6

What are the nodes of ranvier?

Answer 6

Gaps between Schwann cells that result in the faster transmission of electrical impulses. They have no myelin sheath.

Question 7

What is the purpose of a sensory neuron? What is its structure?

Answer 7

A neurone which transmits impulses from the sensory receptors to a relay , motor neurone or to the CNS.
They have a nuclei in the middle of the axon and have one dendron + one axon.

Question 8

What is the purpose of a relay neurone? What is its structure?

Answer 8

Transmits impulses between neurones.

Has its cell body in the centre of the cell and has a short axon but many dendrons and dendrites.

Question 9

What is the purpose of a motor neurone? What is its structure?

Answer 9

A motor neurone will transmit impulses from a relay to an effector such as a muscle or gland to elicit a response.
Has the structure of a typical neurone with one long axon and many short dendrites.

Question 10

What is a myelinated neurone?

Answer 10

Neurones with axons covered with mylein sheaths made up of many layers of plasma membrane provided by the wrapping of Schwann cells. It acts as an insulating layer to conduct electrical impulses at a faster speed.

Question 11

What is the function of the noes of Ranvier?

Answer 11

Allow electrical impulses to jump from one node to the next to allow faster transmission.

Question 12

What is a sensory receptor?

Answer 12

Found in sensory organs, they detect changes in the environment and convert the stimuli into a nerve impulse to be passed to the CNS.

Question 13

What is a transducer and why is a sensory receptor a transducer?

Answer 13

A transducer will convert a stimuli into a nerve impulse. The sensory receptor converts the environmental stimuli into a nerve impulse.

Question 14

What is the pacinan corpuscle and how does it moderate?

Answer 14

A type of sensory receptor found in the skin and soles of your feet which detect mechanical pressure.
Moderates via stretched mediated sodium channels which can change shape to change its permeability to NA+ ions.

Question 15

How does the pacinan corpuscle convert the pressure stimuli into a nerve impulse?

Answer 15

1] At resting potential, neurone membrane is too narrow to allow NA+ to pass.
2] When pressure is applied, pacinan corpuscle stretches causing it to be more permeable to NA+.
3] NA+ influx changes potential causing it to become polarised and trigger an action potential to the CNS.

Question 16

How does nervous transmission occur?

Answer 16

An impulse sent across a neurone will temporarily alter the potential difference across the axon membrane switching it between resting potential and action potential.

Question 17

What is resting potential?

Answer 17

Resting potential is when the neurone is not transmitting an impulse .
The outside of the membrane is more + charged than the inside and is polarised. Potential difference is -70 mV.
Established by movement of NA+ and K+ ions.

Question 18

How is resting potential maintained?

Answer 18

+Sodium-potassium pump will actively transport NA+ out and pump K+ in but more NA+ will be pumped out than K+ in, 3:2 ratio.
+NA+ cannot diffuse back in as most gated NA+ ion channels are closed.
K+ channels remain open so they can diffuse back out into axon.

Question 19

What is an action potential?

Answer 19

An action potential is triggered when a stimuli is detected causing the energy to temporarily reverse charges.
Membrane is depolarised and potential difference inside the membrane will become +40 mV.
Action potential causes the membrane to be more permeable to ions.

Question 20

Describe the process which an action potential is triggered and returns back to resting state.

Answer 20

1] The membrane is at resting potential at -70mV, some K+ ion channels are closed but Na+ voltage gated ion channels are closed.
2] Stimuli energy causes Na+ voltage gated ion channels to open so the membrane is more permeable. Na+ ions will diffuse in.
3] The influx of Na+ ions will cause more Na+ ion channels to open via positive feedback.
4] Potential difference reaches 40mV , action potential is triggered.
5] Na+ ion gated channels will close whereas K+ ion voltage gates will open, Na+ ions can no longer enter the membrane by diffusion.
6] Re-polarisation occurs where K+ ions diffuse out the membrane down the electrochemical gradient to make the outside more negative.
7] Leads to hyper polarisation as it will be more negative than resting potential. K+ voltage ion gates will close and it will reestablish to -70mV via the sodium-potassium pump.

Question 21

What is the propagation of action potentials ?

Answer 21

When an initial stimuli triggers , it causes the first region of the membrane to be depolarised which acts as a stimuli for the next region to be depolarised. This will occur across the membrane like a mexican wave.

Question 22

What is the refractory period and what do they ensure?

Answer 22

A short period of time where the axon cannot be excited again where Na+ ion voltage-gated channels remain closed to prevent the propagation of the action potential backwards and forwards.
Ensures that action potentials are unidirectional and do not overlap.

Question 23

What is saltatory conduction? Why is it faster than a continuous wave of depolarisation?

Answer 23

The way an electrical impulse will jump from one node of Ranvier to the next allowing faster conduction.
Depolarisation can only occur at the nodes of Ranvier as they have no mylein sheath.
This is faster than a wave of depolarisation because each time channels open and close it takes time, therefore reducing the places it occurs will increase action potential transmission.

Question 24

Why is saltatory conduction more energy efficient?

Answer 24

Re-polarisation requires ATP using the sodium-potassium pump, so reducing the amount of re-polarisation required then less ATP will be used.

Question 25

Apart from mylenation, what factors affect speed of action potential?

Answer 25

Axon diameter- The larger the axon diameter the faster the impulse as there is less resistance to the flow of ions
Temperature: Higher temperature = faster the impulse as the ions will diffuse at a faster temperature however too high will cause the proteins to denature such as the sodium-potassium pump

Question 26

What is the all or nothing principle?

Answer 26

A certain level of threshold is required to be reached for an action potential to be triggered. If this is reached then no matter how large the impulse is , the same sized threshold will trigger the action potential.

Question 27

How can you tell if a stimulus is strong?

Answer 27

You can tell if a stimuli is strong if it exceeds the threshold and action potentials have a higher frequency of appearing.
The larger the stimulus the more frequently action potentials will appear.

Question 28

What is a synapse?

Answer 28

A junction between two neurones where impulses are transmitted via the chemicals called neurotransmitters.

Question 29

What is the synaptic cleft?

Answer 29

A gap which separates the axon of a neurone form the dendrite of another neurone.

Question 30

What is the synaptic knob?

Answer 30

The swollen end of a presynaptic neurone which contains many mitocondria and ER to manufacture neurotransmitters.

Question 31

What are synapatic vesicles?

Answer 31

Vesicles which containing neurotransmitters that will fuse with the presynaptic neurone to release contents into synaptic cleft.

Question 32

What is an excitatory neurotransmitter? Give an example.

Answer 32

NT which result in the depolarisation of the post synaptic neurone to trigger an action potential if a threshold is reached.
E.G Acetylcholine

Question 33

What is an inhibitory neurotransmitter?

Answer 33

Result in the hyperpolarisation of the post synaptic neurone to prevent an action potential being triggered.

Question 34

How does transmission occur across a synpase?

Answer 34

1] The action potential reaches the end of the pre-synaptic neurone
2] Depolarisation of the presynaptic neurone causes it to open calcium ion channels
3] Calcium ions diffuse into the pre-synaptic knob.
4] Triggers synaptic vesicles with neurotransmitters to fuse with presynaptic membrane and to be released into synaptic cleft
5] Diffuses across and binds to a specific receptor molecule on post synaptic neurone
6] Causes sodium channels to open and diffuse into post synaptic neurone which triggers an action potential

Question 35

After an action potential is triggered, why must neurotransmitters be removed?

Answer 35

To prevent the stimuli from being maintained and so another stimuli can arrive. Any neurotransmitters left in the synaptic cleft is removed and reabsorbed into the pre-synaptic neurone after being broken down.

Question 36

What occurs in a cholinergic synapse?

Answer 36

These synapses use acetylcholin common between a motor neurone and effector cell such as a muscle.