Potentials

Question 1

What are the 2 ways in which hyper-polarisation can occur?

Answer 1

Fast/slow EPSP : Ionotropic - opening Cl- channels so it flows in. Metabotropic - opening K+ channels so more flows out

Question 2

What is hyperpolarisation?

Answer 2

Cell charge becomes negative - lower than -70mV

Question 3

What is depolarisation?

Answer 3

Cell charge becomes more positive - higher than -70mV. -55mV is threshold.

Question 4

What are the 2 ways in which depolarisation can occur?

Answer 4

Fast/slow IPSP : Ionotropic - allow Na+ in rapidly. Metabotropic - close leaky K+ channel so slowly depolarises

Question 5

What does IPSP and EPSP refer to?

Answer 5

Inhibitory/Excitatory post synaptic potential

Question 6

What is a generator potential?

Answer 6

Graded potential that is generated by any sense - touch, heat

Question 7

What is the ionic basis of graded potentials?

Answer 7

Ions must flow in/out the cell for a graded potential to occur. This includes Na+, K+ and Cl-. These can cause depolarisation or hyperpolarisation

Question 8

What does summate mean in regards to graded potentials?

Answer 8

2 or more graded potentials can ‘add together’ to form a larger graded potential, which could reach threshold, or to inhibit an action potential by decreasing the depolarisation.

Question 9

What are 3 examples of graded potentials?

Answer 9

Sensory receptors (generator potential), postsynaptic potential and end-plate potential

Question 10

Describe synaptic integration

Answer 10

Multiple synapses of different forms - excitatory and inhibitory - interacting with one another to depolarise or hyper polarise an axon hillock. Can be axo-dendritic synapse, axo-somatic synapse or axo-axonic synapse

Question 11

Explain the difference between axo-dendritic, axo-somatic and axo-axonic synapses

Answer 11

Axo-dendritic - directly on dendrite, excitatory.
Axo-somatic - directly on soma - inhibitory.
Axo-axonix - synapses onto pre-synaptic terminal of axo-dendritic synapse - inhibits it

Question 12

Explain the ionic basis of an action potential (to increase)

Answer 12

Threshold (55mV) reached, voltage-gated Na+ channels open and it rushes into cell, taking cell to +40mV.

Question 13

Explain how a cell returns after an action potential

Answer 13

From 40mV, voltage gates Na+ channels close and voltage gated K+ channels open, exiting. This takes cell towards -90mV (K+ equilibrium potential) and channel stays open for long time. Cell is hyper polarised but slowly returns to rest

Question 14

How can an action potential be sped up?

Answer 14

Myelination or Larger axon diameter

Question 15

What are some consequences of demyelination?

Answer 15

Multiple sclerosis in CNS - slower impulses

Question 16

What does the term ‘self propagating’ refer to in regards to an action potential?

Answer 16

Each section passes the impulse forward, depolarising along the axon with the same strength

Question 17

What does the term ‘refractory period’ refer to?

Answer 17

The period after an action potential when another action potential cannot be triggered, as the cell is in a state of hyperpolarisation

Question 18

What does ‘decremental’ mean in regards to graded potentials?

Answer 18

The potential decreases as it moves along the membrane - if threshold isn’t met

Question 19

What does ‘graded’ mean in regards to graded potentials?

Answer 19

A larger stimulus will lead to a larger graded potential and more depolarising. Very large stimulus can reach threshold

Question 20

Which type of neuron will have the highest velocity vs lowest?

Answer 20

Myelinated with large diameter = fastest velocity, e.g. motor neurone.
Un-myelinated with small diameter = slowest velocity

Question 21

What is the neuromuscular junction?

Answer 21

Where a pre-synaptic motor neutron, synaptic cleft and post-synaptic plate/end plate meet

Question 22

Explain the whole formation of an action potential at a neuromuscular junction

Answer 22

Motor neuron has action potential. Na+ flows to pre-syn terminal, causing voltage-gates Ca2+ channels to open. Ca2+ releases proteins causing vesicle exocytosis of ACh. Diffuses across syn-cleft and some binds to ACh inotropic receptor. Now open so anything with 1+ can flow in. Na+ rushes in, so post synaptic plate reached threshold, opening voltage gated Na+ channels, causing action potential at end plate. Remaining ACh broken down by ACh-esterase

Question 23

What are the 2 types of synaptic connectivity and what are the benefits?

Answer 23

Divergence allows one neutron to synapse multiple muscle fibres. Convergence means one cell can be influenced by many others, e.g. several rods converging to one axon in the retina

Question 24

Monosynaptic vs Polysynaptic pathways?

Answer 24

Monosynaptic has one synapse - e.g. sensory - motor. Polysnaptic has +1, e.g. sensory - interneuron - interneuron - motor (3 synapses)

Question 25

How many neurotransmitters are present in the neuromuscular junction?

Answer 25

Only 1 - Acetylcholine

Question 26

What is the process of synaptic transmission in the CNS?

Answer 26

Same as neuromuscular junction, but more complex as there are different pathways, no. of synapses and many different neurotransmitters.

Question 27

Which 5 types of molecules are CNS neurotransmitters?

Answer 27

Amines, amino acids, peptides, purines, gasses

Question 28

Spatial vs Temporal summation?

Answer 28

Temporal is one neuron summating into another. Spatial is multiple neurons summating into another