Neuronal Communication

Question 1

What is sensory adaptation?

Answer 1

When neural or sensory receptors in the brain changes/reduces their sensitivity to continuous unchanging stimuli.

Question 2

What is Habituation?

Answer 2

An organism may show a decrease in response to a stimulus after repeated presentations.
start it ignore stimulus after repeat exposure of it.

Question 3

What is sensitisation?

Answer 3

Opposite of habituation

Question 4

What is a nerve?

Answer 4

A nerve is an enclosed cable like bundle of nerve fibres/nerves/cells.

Question 5

Explain the whole branch of the Human Nervous System.

Answer 5

• CNS - PNS
• Somatic NS - Autonomic NS
• Sympathetic NS - Parasympathetic NS

Question 6

What does the Peripheral NS have?

Answer 6

Cranial, spinal nerves containing sensory and motor neurones.

Question 7

What is the Somatic nervous system?

Answer 7

Voluntary movements, and involuntary reflexes. It has output to skeletal muscles via motor neurones.

Question 8

What is the Autonomic NS?

Answer 8

Involuntary output to smooth muscles or glands or cardiac muscle/ internal glands.

Question 9

What is the Sympathetic NS?

Answer 9

It is an internal alarm, fight or flights using noradrenaline neurotransmitters and accelerator nerves.

Question 10

What is the Parasympathetic NS?

Answer 10

It is a relaxing response and neurotransmitter is acetylcholine and many axons in the vagus nerves.

Question 11

Describe the Spinal Cord?

Answer 11

It is a column of nervous tissue running down the back. Neurones feed into and come out of it.
There were 31 nerves connecting the Spinal cord with various body regions.

Question 12

What is ganglion?

Answer 12

Swelling that contains lots of synapses/cell body.

Question 13

What is grey matter?

Answer 13

• lots of synapses
• unmyelinated relay neurones
• numerous cell bodies.

Question 14

What is white matter?

Answer 14

• myelinated axons of neurones
• few cell bodies

Question 15

What is the Pacinian Corpuscles?

Answer 15

They respond to pressure and are found in the skin. They contain a single sensory neurone at the centre of each corpuscle and at its ending are stretch mediated Na+ channels.

Question 16

Explain the Mechanism of the Pacinian Corpuscle.

Answer 16

At resting state the potential difference is -65mv.
A stimuli occurs.
the lamellae is then compressed and PC is then stretched causing the connective tissue to deform, this causes the Na+ channels to open and the Na+ diffuse into the membrane.
This depolarises the membrane changes the potential difference. (mv)
Increased positive charge inside the axon is called the receptor potential/generator potential.
Harder the pressure the more channels open and so the greater receptor potential.
If the potential is greater than the threshold potential (-55mv). Than an action potential will occur.
Action potential greater than +44 mv.

Question 17

What is the all or nothing response?

Answer 17

It is when a certain level of stimulus, the threshold value, always triggers a response. If it was not reached no action potential.
The threshold value is the minimum.
An action potential is always the same size.

Question 18

What does the sensory neurone contain?

Answer 18

Cell body on axon.
Schwann cell.
Dendron.
Dendrites.
Axon.
Nodes of Ranvier
carries towards CNS

Question 19

What does the motor neurone contain?

Answer 19

Cell body in CNS.
Axon.
Nodes of Ranvier.
Synaptic bulbs and endings.
carries towards effectors.
https://images.app.goo.gl/YhnpUzbM3KhhRjjN9

Question 20

What does relay neurone contain?

Answer 20

Lots of short dendrites.
Axon
Synaptic Bulbs
Dendron

Question 21

What is myelin sheath?

Answer 21

They are insulated by an individual fatty myelin sheath.
It is about 1/3 of peripheral neurones are myelinated.
The myelin sheath is made up of Schwann cells and it wrapped around multiple times and tightly around the neurone. It is about 1mm long and there is gap between them called the nodes of ranvier.
Each time the Schwann cells grow around the axon a double layer of phospholipid bilayer is laid down.

Question 22

What is myelination?

Answer 22

It prevents ion movement across the neuron membranes so movement can only occur at the nodes of ranvier.
The impulse jumps from node to node [saltatory conduction] making conduction more rapid.

Question 23

Explain non-myelinated neurones.

Answer 23

They are enveloped by the Schwann cell, the un-myelinated neurones are enclosed loosely by the Schwann cell and there are no extra layers. Ion movement is not prevented so the action potential travels across the neurone in a wave of conduction rather than jumping from node to node.
Transmission is slower.

Question 24

What is the speed of conduction determined by?

Answer 24

• diameter of axon [greater dia = faster transmission]
• myelination [myelin = 120m/s, non-mye = 0.5m/s]
• temperature [increase in temp = increase in propagated factor]

Question 25

What is occurring at the resting potential?

Answer 25

It is found that the inside always has a slightly negative electrical potential compared with outside. [-65mv].
At rest Na+ is higher on the outside relative to the inside and K+ is higher on the inside compared to the outside.
Anions are too large and cannot leave the axon.

Question 26

What is the sodium/potassium pump?

Answer 26

While the neurone is at rest it is still actively pumping ions using the pump.
Pumps 2K+ in and 3Na+ out.

Question 27

What happens when a stimuli occurs at a neurone?

Answer 27

Depolarisation occurs, Na+ channels open and Na+ diffuses in , axon becomes less negative [generator potential], if threshold met [-55mv] or exceeded positive feedback will occur, causing more voltage gated channels to be open possible causing an action potential. [+44mv]

Repolarisation occurs, Na+ channels close and K+ channels open, K+ diffuse out down electrical gradient. And the potential difference goes back to normal [-65mv].

Hyperpolarisation, occurs where PD undershoots slightly making the cell hyperpolarised. [more negative to less than -90mv]

Then the Na+/K+ pump restores the normal distribution of ions, returning it to rest.

Question 28

What is the refractory period?

Answer 28

resting Na+/K+ distribution to be restored and membrane has to be repolarised.

Question 29

What is absolute refractory period?

Answer 29

• no additional stimulus can produce action potential.

Question 30

What is relative refractory period?

Answer 30

Only a more intense stimulus can produce another action potential.

Question 31

Explain the transmission of the action potential in a non-myelinated neurone.

Answer 31

• voltage gated Na+ channels open and Na+ diffuses in [depolarisation]
• Localised depolarisation occurs = 40+ action potential
• Na+ diffuses along to next region via local current [very short], from high to low conc.
• This causes a slight depolarisation further along which meet the threshold causing more VG channels open so +40mv potential difference occurs.

Question 32

Explain Saltatory conduction.

Answer 32

• Na+ diffuse in [generator potential].
• Threshold potential so positive feedback occurs and more VG channels open.
• Action potential occurs.
• Na+ diffuses to the next node via longer local current.
• Node reaches threshold, and VG channels open and action potential occurs.
• Region behind the action potential will repolarise.
  The myelin prevent ion movement and ion leakage to prevent dissipation. therefore the transmission jumps from node to node.

Question 33

What are the advantages of saltatory conduction?

Answer 33

• Uses minimum channels, as AP jumps from node to node, Myelinated neurones have longer section with no VG Na+ channels present. This saves time.
• Myelin sheath prevents the dissipation of the signal as it prevents Na+ leaking out through the membrane over the longer local currents.
• Saltatory conduction uses less energy as less Na+/K+ channels are needed as these are only found at the nodes- repolarisation only required at the nodes.

Question 34

Explain the mechanism of synapses. using acetylcholine as the e.g. of neurotransmitters.

Answer 34

The local current arrives at synaptic bulb.

Action potential causes voltage gated calcium channels to open. Ca2+ floods into cytoplasm of the pre-synaptic neurone.

Calcium ions cause vesicles containing acetylcholine to fuse with the presynaptic membrane emptying acetylcholine into the synaptic cleft by exocytosis.

Acetyl choline is released and diffuses across the synaptic cleft.

Acetylcholine molecules bind with complementary ligand gated receptors in the post synaptic membrane causing them to open Na+ channels.

Na+ diffuse in through the open channels in the postsynaptic membrane depolarising the membrane. If sufficient generator potentials combine then the threshold potential is reached and a new AP is generated.

If the ACh remained bound to the post synaptic membrane action potentials would fire continuously.
And so to prevent this from happening an enzyme, called acetylcholine esterase, hydrolyses acetyl choline to ethanoic acid and choline.

Entire sequence of events form arrival of initial AP to reformation of ACh takes about 5-10ms. The ethanoic acid and choline are recycled entering the synaptic bulb and combined using ATP and stored in vesicles again.

Question 35

Explain excitatory post synaptic potential.

Answer 35

The membrane potential of the post synaptic neurone moves closer to the threshold due to a small depolarisation as neurotransmitter causes opening of channels which allow positive charges to enter the post synaptic neurone.

Question 36

Explain inhibitory post synaptic potential.

Answer 36

Membrane potential of post synaptic neurone moves away from the threshold due to a small hyperpolarisation, as a neurotransmitter causes opening of channels which allow negative charges to enter the post synaptic neurone and or positive charges to leave the post synaptic neurone.

Question 37

Roles of synapses.

Answer 37

• allow neurones to communicate = neuronal communication is a type of cell signalling.

-ensures one-way transmission between neurones, post and pre synapses ensures one way transmission.

• divergence = one presynaptic neurone might diverge to many post synaptic neurones so action potential can be transmitted to several pasts of the body and/or brain.

-summation = type of neural integration whereby all input from several post synaptic are added together.

• memory and learning = synaptic membranes are adaptable so new synapses can form between neurones involved if the brain frequently receives information about two things at the same time.
• synaptic fatigue prevent over stimulation = constant stimulation leads to reduction in neurotransmitter release.
• allow weak background stimuli to be filtered out as only stimulation strong enough is passed on.

Question 38

What are the 2 different types of summation?

Answer 38

Spatial summation [convergence] = A post synaptic neurone can receive excitatory and inhibitory potential. It then summates all the stimuli and if the sum of the EPSPs overcomes the IPSPs to reach the threshold potential then an action potential is generated.

Temporal summation= repeated stimulation of the same synaptic ending in rapid succession may occur until sufficient neurotransmitters is released to allow ESPSs to combine to reach the threshold potential and produce an action potential.

Question 39

What as EPSPS?

Answer 39

Excitatory post synaptic potentials.