Excitable Cells

Question 1

What are the different types of ion channels in regards to what opens them?

Answer 1

Ligand gated
Force gated - mechanosensative
Temperature gated - thermosensative
Voltage gated
Leakage channels - permeability is relatively constant

Question 2

What is an example of a ligand gated channel?

Answer 2

ACh receptor - 5 subunits one for the binding of ACh.
Binding causes a conformational change which is transferred to the transmembrane domain opening the channel

Question 3

Give a basic general description of how voltage gated channels work.

Answer 3

Have a different conformation based on it the membrane is hyperpolarised (pore often closed) or depolarised (pore often open)
They have lateral voltage sensor regions and a central pore region
Changes in the potential difference initiate changes in cationic amino acids.

Question 4

Why are leak channels important in synapses and axons?

Answer 4

Active over the full physiological range of voltage, are responsible for the resting potential
In particular the electrochemical gradient of K+ through K2p channels.

Question 5

What is a focal stimuli?

Answer 5

A stimuli that challenges the human system of homeostasis, requires most of the persons attention.

Question 6

What are graded potenials?

Answer 6

A localised potential change, that is graded by the intensity of the stimuli.
Can be different sizes do not follow the all or nothing rule of action potentials
Related to passive conduction, in which the signal decreases in size further away from the stimuli

Question 7

How does a graded potential become an action potential?

Answer 7

Depolarises past the threshold

Question 8

What two different channels open to result in an action potential?

Answer 8

Fast Na+ channels - cause the potential (inward current)
Followed by slow K+ channels - help stop the potential (outward current)
Note thousands of channels contribute to the overall electrical behaviour of the cell

Question 9

Give a basic overview of the processes involved in an action potential.

Answer 9

Depolarisation reaches the threshold level
Na+ channels open
Na+ moves in
Na+ channels close and K+ channels open
K+ moves out
K+ channels close
The sodium potassium pump resets the membrane potential.

Question 10

How is the action potential propagated in the CNS and PNS?

Answer 10

By saltatory conduction
CNS axons are insulated by oligodendrocytes
PNS axons are insulated by Schwann cells
Voltage gated channels are concentrated at Nodes of Ranvier allows the action potential to jump between nodes.
This increases the speed of conduction

Question 11

What is important to remeber about axon conduction velocities?

Answer 11

Vary based on the function and location of the axon
This is due to variation in the level of insulation.
Larger diameter axons tends to have a higher level of insulation so a greater speed of conduction.

Question 12

What are the two different types of synapses?

Answer 12

Chemical
Electrical

Question 13

Give an overview of electrical synapses?

Answer 13

Are the minority and are conceptually simpler and encode simpler information
Facillitated by transmembrane proteins proteins called connexons, allows charge to pass directly between axons.
Normally synchronise the activity of groups of axons.

Question 14

Give an overview of chemical synapses.

Answer 14

More common
Action potential at the presynaptic triggers the opening of voltage-gated Ca2+ channels and the influx of calcium ions cause neurotransmitters to be released across the synapse.

Question 15

What types of molecules can be neurotransmitters? Tom Butts not pharmacy

Answer 15

Small molecules (including amino acids) - more common
Peptides - more variation as encoded by genes

Question 16

What is the difference between ionotropic and metabotropic NT receptors?

Answer 16

Ionotropic receptors are typically ligand gated ion channels, NT directly results in ion transport

Metabotropc NT receptors indirectly lead to the transport of ions, are often GPCRs so lead to the activation of another channel by second messenger models.

Question 17

What type of NT receptor is ACh receptor and where is it found?

Answer 17

A ionotropic NT receptor
Found in the brain, spinal cord, skeletal muscle and smooth muscle.

Question 18

What type of NT receptor is GABA A?

Answer 18

Ionotropic

Question 19

Give an example of a metabotropic receptor.

Answer 19

mGluRs
Metabotropic glutamate receptors
Binding of glutamate induces a conformational change which activates G-proteins which directly and indirectly open ion channels.

Question 20

What is meant by summation of an action potential?

Answer 20

Can be spatial or temporal.
Determins whether an action potential will be generated at the post synaptic membrane based on combined signals which may be inhibitory or excitatory and from the same or different sources

Question 21

What are the different types of summation?

Answer 21

Temporal - multiple repeated signals in close proximity from one source
Spatial - signals from multiple sources

Question 22

What are the different circuit architecture of neuron network?

Answer 22

Diverging - one input (neuron) gives rise to many output (neurons)
Converging - multiple inputs (neurons) give rise to one output (neuron)
Reverberating - each neuron on the pathway links back to the previous one (may be indirectly)
Parallel after-discharge - one input neuron diverges into many parallel branches of different length, which then converge back onto the same one output neuron to give many fast repeating signals.

Question 23

Explain the process of long term potentiation.

Answer 23

Lots of strong repeated stimuli
Glutamate is released from the presynaptic membrane, binds to AMPA and NMDA receptors on the post synaptoc membrane
AMPA receptor opens - soidum ions enter and depolarise the post synaptic membrane
NMDA is blocked by a magnesium ion so does not open
A sufficient depolarisation and conc of Na+ causes a postive charge to collect around the NMDA, forces the Mg+ ion out of the NMDA receptor.
Na+ and Ca+ now enter through the NMDA receptor.
Ca+ leads to a cascade of events by kinases, AMPA channels are phosphorylated so are more efficient, also increases the number of AMPA receptors in the post synaptic membrane.

Question 24

What is the mechanism of long term depression?

Answer 24

Many small stimuli
Glutamate receptors
Small influx of calcium throught the NMDA receptors, after magnesium ion removed from NMDA receptor due to sodium ion influx from AMPA receptor.
Calcium activates phosphatase enzyme.
Removes AMPA receptors from the post synaptic membrane by removing the phosphate group