How Nerves Work

Question 1

What is the function of dendrites?

Answer 1

Receive information from its surrounding environment

Question 2

What are afferent neurones?

Answer 2

Sensory neurones of the peripheral nervous system that detect information.

Question 3

What are interneurones?

Answer 3

Neurones of the central nervous system that receive information from afferent neurones and decide what to do.

Question 4

What are efferent neurones?

Answer 4

Motor neurones that receive instruction from interneurones and send a signal to an effector to carry out a response.

Question 5

What are Astrocytes?

Answer 5

Glia cells that maintain the environment for neurones.

They also surround blood vessels and forth blood brain barrier.

Question 6

What are Oligodendrocytes?

Answer 6

Glial cells that form myelin sheaths around neurones of the central nervous system.

Question 7

What are Microglia?

Answer 7

Glia cells that are phagocytic hoovers and mop up infection surrounding neurones.

Question 8

What are the 4 different lobes of the Cerebrum?

Answer 8

Frontal lobe
Temporal lobe
Parietal lobe
Occipital lobe

Question 9

What 3 structures make up the Brainstem?

Answer 9

Midbrain
Pons
Medulla Oblongata

Question 10

What 2 structures make up the Diencephalon?

Answer 10

Thalamus

Hypothalamus

Question 11

What is the resting membrane potential?

Answer 11

The voltage difference across a cell membrane when it is in its resting state.

Question 12

What creates the Resting membrane potential within a cell?

Answer 12

Leaky potassium channels.
K+ moves down conc. gradient which creates an electrical gradient which is exactly equal and opposite to the conc. gradient.

Question 13

What are some different types of graded potential?

Answer 13

Generator potential - at sensory receptors
Postsynaptic potential - at synapses
Endplate potential - at neuromuscular junctions
Pacemaker potential - in pacemaker tissues

Question 14

What is the role of a graded potential?

Answer 14

Determines when an action potential is fired.

Question 15

What are some properties of Graded potentials?

Answer 15

Decremental - membrane potential gets smaller as you travel along axon as leaky channels open.
Local- can only be used over short distances due to being decremental.
Graded - the stronger the stimulus, the more channels get opened, the bigger the current flow and therefore the bigger the potential fired.

Question 16

How can graded potentials be both excitatory or inhibitory?

Answer 16

Firing an action potential requires the graded potential to reach to a threshold (-55mV). The graded potential can either hyper-polarise or depolarise depending on which ion channels are open/closed.

Question 17

How are postsynaptic potentials hyper-polarised?

Answer 17

Cl- or More K+ are opened so either Cl- flows in creating a fast IPSP, or K+ leaks out creating a slow IPSP.
This takes them away from threshold so it is inhibitory.
GABA and glycine do this.

Question 18

How are postsynaptic potentials depolarised?

Answer 18

Transmitters open channels permeable to Na+ and K+ but more Na+ gets out than K+ so causes a depolarisation. This causes a fast EPSP.
Blocking K+ channels can also cause a depolarisation but it is only a slow EPSP.

Question 19

How are postsynaptic potentials produced?

Answer 19

A neurotransmitter opening or closing ion channels - ligand gated ion channels.

Question 20

How are action potentials produced?

Answer 20

Depolarisation of the membrane potential opening ion channels - voltage gated ion channels.

Question 21

What is meant by graded potentials can summate?

Answer 21

They can add to each other so threshold is produced quicker. The effects of more than one stimulus are added together.

Question 22

What is integration?

Answer 22

Looking at all the inputs whether they are synapses or stimuli and deciding whether to fire an action potential or not.

Question 23

Describe the main stages of an action potential?

Answer 23

RMP sits at -70mV
Graded potential fired, reaches threshold of -55mV
Sudden massive depolarisation as Na+ channels open and action potential is fired, overshoots to +30mV.
Rapid depolarisation to a little below RMP.

Question 24

Name some toxins that block the voltage gated Na+ channels to prevent action potentials form being fired?

Answer 24

Local anaesthetics
Tetrodotoxin - pufferfish
Saxitoxin - shellfish.

Question 25

What are some properties of action potentials?

Answer 25

They have a threshold
They are all or none
Mediated by voltage gated channels.
Stimulus depends on firing frequency.
Self-propagating 
Have a refractory period
Travel slowly.

Question 26

What is the function of the refractory period?

Answer 26

The local current flow also spreads back when the signal fires along the axon but refractory prevents another AP being fired, keeps it going in right direction.

Question 27

Why do large axons increase conduction velocity?

Answer 27

Large axons decrease axial resistance - the depolarisation can reach further, need less Na+ channels which take time to open.

Question 28

What cells in the peripheral nervous system form myelin?

Answer 28

Schwann cells.

Question 29

How does myelin increase the conduction velocity?

Answer 29

Increased resistance of the membrane allows AP to spread like a local current without much decrement. Insulates the axon.

Question 30

What are the stages of AP at a NMJ causing muscle contraction?

Answer 30

1- Motor neurone reaches end of axon.
2- Ca2+ enters via voltage gated channels
3- Acetylcholine is released and diffuses across synapse.
4- Na+ channel are opened by Acetylcholine binding. Na+ enters.
5-Na+ channels evoke an endplate potential.
6-Adjacent membrane depolarised to threshold
7-Voltage gated Na+ channels open firing a new AP, ACh is removed by Acetylcholinesterase.