Nervous system + action potential

Question 1

What is dorsal root known as…

What is the ventral root known as…

Answer 1

Dorsal - Sensory

Ventral - motor

Question 2

Answer 2

Multipolar neurons have extensive dendritic network attached to their cell bodies. These are the most common types of neuron found within the nervous system

Bipolar neurons have an extended dendritic arm, which is often associated with sensory organs such as the retina and olfactory system

Pseudounipolar neurons are similar to bipolar neurons but the dendritic extension and the axon has been fused during development. These neurons are sensory and tend to be found associated with visceral sensations (such as the sensation of stomach fullness)

Question 3

The arrival of an action potential triggers what on pre synaptic neurone

Answer 3

It causes voltage gated Ca2+ channels to open to enable an influx of Ca2+ which causes neurotransmitter vesicles to fuse to the presynaptic membrane

Question 4

On the post synaptic receptor I what happens when neurotransmitters bind to it

Answer 4

It opens the channels allowing an influx of ions into the post synaptic neurone

Question 5

What happens in excitatory neurotransmission

Answer 5

The neurotransmitter binds to a receptor on the post synaptic membrane which allows positive ions through i.e Na+ which has a depolarises the membrane. If the membrane then reaches the threshold potential then an action potential is triggered

Question 6

What happens in inhibitory neurotransmission

Answer 6

The neurotransmitter binds to a receptor on the post synaptic membrane which allows negative ions through i.e Cl- which hyperpolarises the membrane. Which moves it away farther from the threshold potential so more excitatory input is required to trigger an action potential.

Question 7

What is the autonomic nervous system responsible for

Answer 7

Involuntary processes

Question 8

Autonomic system is comprised of 1.sympathetic and 2.parasympathetic

Answer 8

1. Fight or flight
2. Rest and digest

Question 9

How do sympathetic neurones transmit information

Answer 9

Pre-ganglionic sympathetic neurons release acetylcholine onto nicotinic receptors. Post-ganglionic neurons release noradrenaline onto adrenergic receptors (salivary glands are the exception, where post-ganglionic neurons release acetylcholine)

Question 10

How to parasympathetic neurones transmit information

Answer 10

Parasympathetic neurons also have their cell bodies in the spinal cord. These pre-ganglionic neurons project to the target organ where they synapse on post-ganglionic neurons either within or very close to the target organ. Pre-ganglionic neurons release acetylcholine onto nicotinic receptors and post-ganglionic neurons release acetylcholine onto muscarinic receptors

Question 11

How do somatic neurones transmit information

Answer 11

the somatic nervous system, which also has cell bodies in the spinal cord, which project directly to the target organ. In the case of somatic motor neurons innervating muscle, these neurons release acetylcholine onto nicotinic receptors

Question 12

What is the somatic system responsible for

Answer 12

Voluntary processes

Question 13

Photoreceptive ganglion cells in the retina detect Light, transmit the information to an area of the brain called the…

Answer 13

Edinger-westphal nucleus which activates parasympathetic nervous system to constrict the pupil - does not require conscious control.

Question 14

The medulla function in autonomic system

Answer 14

Has many regions which directly connect with parasympathetic and sympathetic nerves, receives information from hypothalamus as well as sensory information from the viscera

Question 15

What does an action potential diagram look like

Answer 15

Question 16

How is an action potential triggered

Answer 16

There will sensitive ion channels that will open in response to a change e.g mechanoreceptors are pressure sensitive and when opened will allow an influx of positive ions

This makes the membrane depolarised if the amount of depolarisation reaches the threshold potential an action potential will be generated

Question 17

When the threshold potential is reached…

Answer 17

The voltage gated sodium channels open at -55mv allowing a great influx of Na+ so the membrane becomes positive relative to the outside

The level of depolarisation is so high it activates neighbouring voltage gated sodium channels allowing for Na+ so the action potential can propagate down the axon

Question 18

How does lidocaine work as an anaesthetic

Answer 18

Blocks voltage gated sodium channels preventing propagation of action potentials in pain sensing fibres

Question 19

At peak potential…

Answer 19

The voltage gated sodium channels close into a voltage insensitive state so it is in the absolute refractory period (during depolarisation and repolarisation) - no more action potentials can be fired

At the same time voltage gated k+ channels open so k+ leaves down its conc gradient

Question 20

What happens during repolarisation

Answer 20

The reflux of k+ ions leaves which makes the membrane potential more negative

There is an undershoot that occurs - hyperpolarisation - as the voltage gated k+ channels stay open longer than required

Once it reaches -70 to -75mv the voltage gated channels become sensitive again

During hyperpolaristaion it is called the relative refractory period as theoretically an action potential can be triggered but the amount of depolarisation required is much greater

Question 21

What happens if there was not a refractory period

Answer 21

The second sodium channel would trigger the first channel again which means the action potential will be moving backwards

So with the refractory period we can ensure it is only moving in one direction - towards the sodium channels that are still voltage sensitive

Question 22

After an action potential has fired how do we reset back to normal

Answer 22

Na-K-ATPase re-establishes correct concentration balance by moving 2k+ inside and 3Na+ out

Question 23

What happens to the resting potential in a person with hyperkalaemia

Answer 23

We can see from the Goldman-Hodgkin-Katz equation when k+ conc increases from 4 to 10mmol/l the resting membrane potential decreases coming closer to the threshold potential so action potentials can start firing spontaneously

Question 24

In myelinated neurones voltage gated Na+ channels only exist at the…

Answer 24

Nodes of ranvier as the myelin acts as an insulator so Na+ cannot be discharged through Na-k-ATPase nor can k+ leak from leak channels

Therefore the action potential jumps from node to node known as saltatory conduction

Question 25

The larger diameter neurone will

Answer 25

will express a higher number of voltage gated sodium channels compared with a small diameter neuron, meaning the sodium conductance is greater, thus increasing the speed of depolarisation

There will also be less resistance

Question 26

What is temporal and spatial summation

Answer 26

Spatial summation – where multiple synapses fire simultaneously, leading to a large influx of sodium across the whole body of a neuronal soma

Temporal summation – where a single synapse fires multiple times within a very short time space