How Nerves Work

Question 1

Give the three subdivisions of the nervous system

Answer 1

• the brain
• the spinal cord
• peripheral nerves

Question 2

What are the two subdivisions of the peripheral nervous system?

Answer 2

• sympathetic nervous system

- autonomic nervous system

Question 3

Give the five components of the neurone

Answer 3

• cell body/soma
• dendrites
• initial segment
• axon
• axon terminals

Question 4

What part of the neurone contains the nucleus?

Answer 4

Soma

Question 5

At what part of the neurone is the information for making action potentials arranged?

Answer 5

Initial segment

Question 6

What part of the neurone is an important route for the information from other neurones?

Answer 6

Dendrites

Question 7

What part of the neurone takes the action potential elsewhere?

Answer 7

Axon

Question 8

What part of the neurone connects with other nerves/muscles and releases neurotransmitter?

Answer 8

Axon terminals

Question 9

What is the typical RMP of neurones?

Answer 9

around -70mV

Question 10

What pumps are present in the cell membrane?

Answer 10

Sodium/potassium pumps

Question 11

What do potassium specific ions channels in the membranes allow?

Answer 11

Potassium to flow out down the conc gradient through facilitated diffusion

Question 12

The electrical gradient pulling the potassium back into the cell eventually becomes equal to the conc gradient pushing the ions out of the cell. This alone would create a resting potential of -90mV, so why is RMP closer to -70mV?

Answer 12

Due to the permeability of the membrane to other ions and leaky channels

Question 13

How do neurones communicate?

Answer 13

Using action potentials

Question 14

What are action potentials?

Answer 14

Large all or nothing signals that can self propagate

Question 15

What needs to happen before an AP can be fired?

Answer 15

A graded potential must reach a significant level

Question 16

Give features of graded potentials

Answer 16

• vary in intensity with intensity of stimulus
• decremental
• can only transmit over very short distances
• can be inhibitory or excitatory depending on which ion channels are open
• can summate through temporal or spatial summation

Question 17

What happens once a graded potential reaches the correct threshold?

Answer 17

Action potential will be fired

• voltage gated sodium channels in the membrane open
• sodium rushes in
• this causes huge depolarisation of the neurone
• this in turn causes K+ channels to open
• cell repolarises then hyper polarises

Question 18

What effect do these graded potentials have?

Answer 18

Change the potential of the neurone to around +40mV

Question 19

Are action potentials graded or all or nothing?

Answer 19

All or nothing

Question 20

Intensity of an AP is not shown in amplitude but instead by

Answer 20

frequency

Question 21

Action potentials are

Answer 21

self-propagating, since the charge created by influx of Na+ ions spreads a bit up the axon, opening the channels there too, allowing further influx and propagation of the signal

Question 22

What three types of nerve fibre are there and what are their functions?

Answer 22

Afferent (sensory) - detect changes or sensory stimuli

Interneurones - contained within the spinal cord, decide what to do about the stimulus

Efferent (motor) - if an excitatory response is warranted, these neurones carry the signal to the effector tissues or cells

Question 23

Neurones can be ___ or ___,

and ___ or ___

Answer 23

large or small

myelinated or unmyelinated

Question 24

Large axons allow for

Answer 24

a much faster transmission speed, since resistance is decreased

Question 25

Faster transmission speed allows for

Answer 25

the charge to travel further up the axon when Na+ channels are opened, which in turn allows them to be placed further apart and less are needed

Question 26

Since the most time consuming part is the opening of these channels, reducing the number needed

Answer 26

increases transmission time

Question 27

Myelination also speeds up transmission by

Answer 27

surrounding the axon in a lipid sheath formed from Schwann cells (replaced by oligodendrocytes in the CNS)

Question 28

Sodium channels are only found

Answer 28

in the nodes of Ranvier between these sheaths which allows the transmission to travel further due to the insulation provided

Question 29

Give an example of a demyelinating disease

Answer 29

Multiple sclerosis

Question 30

Describe the consequences of demyelinating disease

Answer 30

- eat holes in the Schwann cells - results in rapid decay of APs - preventing APs from reaching the next node and from propagating - conduction falls

Question 31

At the NMJ, the motor end plate from the neuronal axon comes to the muscle and

Answer 31

forms a synapse

Question 32

On the muscle side of the synapse lies the

Answer 32

sarcolemma

Question 33

The membrane of the sarcolemma has junctional folds with

Answer 33

ACh receptors, leading deeper into the muscle allowing for deeper contraction

Question 34

Describe the process of neuromuscular transmission

Answer 34

- AP in axon opens Ca2+ channels in presynaptic terminal - triggers fusion of vesicles and ACh is released into the cleft - diffuses across and binds to receptors in the junctional folds - ligand gated Na+/K+ channels are opened - local end plate potential is produced which always reaches threshold so AP is fired, opening up voltage gated Na+ channels - ACh is removed by acetylcholinesterase

Question 35

Neuronal synapses are similar to the neuromuscular junctions, but the few differences make a huge amount of differences. List these differences

Answer 35

- wide range of neurotransmitters - range of postsynaptic potentials - anatomical arrangements of synapses - synaptic connectivitty

Question 36

Give the four types of postsynaptic potentials

Answer 36

- fast EPSPs - slow EPSPs - fast IPSPs - slow IPSPs

Question 37

Give the three anatomical arrangements of synapses

Answer 37

- axo-somatic - axo-dendritic - axo-axonal

Question 38

Give the two types of synaptic connectivity

Answer 38

- convergence | - divergence