Neurotransmission

Question 1

What is the main function of nerve cells or neurons ?

Answer 1

Is to receive o, conduct and transmit signals

Question 2

Pre -Synaptic cleft

Answer 2

Pre-synaptic terminal (at end of axon):  Storage vesicles for a particular extracellular signalling molecule (neurotransmitter)

 (How is release triggered?)  Synaptic cleft:  12-20 nm gap 

Post-synaptic membrane: transmitter-gated ion channels

Question 3

What triggers an action potential ?

Answer 3

Depolarization , of the plasma membrane

Membrane potential is less negative value inside

Question 4

Voltage -gates Na+ channel?

Answer 4

In nerve and skeletal muscle cells , a stimulus that causes sufficient depolarization promptly opens the vated gated Na+ channels allowing a small amount of Na + to enter the cell down electrical gradient

Question 5

Summary of ion gradients in resting cells

Answer 5

Na+/K+ ATPase: Actively pumps ions against electrochemical gradient

At rest, ion channels are largely closed.

The voltage generated in neurons at rest is about -70 mV to -80 mV (i.e., negative inside)

Question 6

Different stimuli might open a channel

Answer 6

The plasma membrane of all excitable cells contain

Voltage gated channel which are responsible for generating NA+ to enter the cell down

The influx of positive charge depolarizes the membrane further , thereby opening more Na+ channels which admits more Na + ions causing further depolarization

Question 7

Cytoskeleton ?

Answer 7

Dynamic and adaptable

Regulation of the dynamic behaviour and assembley of cytoskeleton filaments allow eukaryotic cells to build an enourmous range of structures from three basic filaments systems

Question 8

Different stimuli might open a channel

Answer 8

The plasma membrane of all excitable cells contain Voltage gated channel which are responsible for generating an electrical wave (action potential) that travels along the membrane.

Question 9

What happens to the transmembrane voltage as a result of: Opening sodium channels?

Answer 9

Depolarises the membrane (Na+ ions move inside down their electrochemical gradient, collapsing the negative-inside electrical gradient) 

Excitatory neurotransmitters generally open Na+ channel receptors, causing a local depolarisation at the postsynaptic membrane 

Large change, as Na+ is far from equilibrium

Question 10

What happens after Depolarisation ?

Answer 10

After depolarisation, Na+ channels inactivate, preventing further Na+ fluxes until membrane potential is restored

Depolarisation by Na+ influx increases membrane permeability to K+

Question 11

Which class of Receptors might be engaged? Why ?

Answer 11

Because the signal that needs to be propagated from one neuron to another is electrical

Involved in rapid synaptic signalling between nerve cells and other electrically excitable targets such as nerve and muscle cells

Question 12

How does our brain communicate to our muscle to contract?

Answer 12

When acetylcholine binds to its receptor on the muscle membrane it transiently opens Na+ channel inducing depolarization of the membrane

The depolarization activates voltage gated Ca2+ channels in the transverse tubules of this membrane

This induces Ca2+ channel in the sarcoplasmatic reticulum membrane

The increase in Ca2+ induces the myofibrils to contract

Question 13

What happens if there is a lack of myelin?

Answer 13

In demyelinating neurons the propagation of the nerve impulse is slow

Question 14

Do you know in which diseases this might happen?

Answer 14

In Multiple Sclerosis and many others..

Question 15

Describe the signalling at the synapse.

Answer 15

The action potential triggers the
opening of Ca2+ channels at the presynaptic neuron.

The increase in
Ca2+ triggers the release of neurotransmitter in the presynaptic cleft.

The neurotransmitter binds to its receptor on the post-synaptic neuron

Question 16

Why the neurotransmission is based on ion channels?

Answer 16

Because the
signal travelling through the axon is an action potential, an electrical
wave.

Question 17

What is myelin?

Answer 17

It is a plasma membrane that wraps up the axon of

some nerve cells, forming an electrically insulating layer.

Question 18

What is the function of myelin?

Answer 18

Myelin is essential for the proper
functioning of the nervous system as it allows faster propagation of
action potential from one node to another.

Question 19

Why micro tubules are oriented in the same direction in axons?

Answer 19

To
ensure that vescicles containing neurotransmitters travel from the
soma to the axon. Different motor proteins move vesicles in
anterograde and retrograde directions.

Question 20

Neurotransmission

Answer 20

1) When an action potential
arrives at the presynaptic site the
depolarization of the membrane

2) opens voltage gated Ca2+
channels that are clustered at the
pre-synaptic membrane.

 3)Ca2+ influx induces the release of
neurotransmitters in the synaptic
cleft.

 4)The neurotransmitter reaches the
postsynaptic neuron and binds a
transmitter-gated ion channel,
provoking an electrical change in
the postsynaptic cell.

Question 21

Why the neurotransmission is based on ion channels?

Answer 21

Because the
signal travelling through the axon is an action potential, an electrical
wave.

Question 22

What do Microtubes do ?

Answer 22

Determine the positions of membrane enclosed organelles , direct intrtracellular transport and form mitotic spindle that segregates the chromosomes during cell division

Question 23

What do Actin Filaments do ?

Answer 23

Determine the shape of the cells surface and are necessary for whole cell locomotions

Question 24

What do intermediate filaments provide ?

Answer 24

Provide mechanical strength