Action potentials, synapses and neurotransmitters

Question 1

Define potential difference

Answer 1

An uneven distribution of charges

Question 2

Why is a membranes resting potential negative?

Answer 2

Greater positive charge on the outside of the cell more negative inside

Question 3

What is the resting potential of a neuron?

Answer 3

-70mV

Question 4

What is the difference between extracellular and intracellular fluid?

Answer 4

Extracellular contains a high concn of Na+ and Cl- ions
Intracellular contains a high concn of K+ and Pr- (proteins)

Question 5

What is a leak channel?

Answer 5

Always open

Question 6

What is a gated channel?

Answer 6

Open/closed depending on circumstances

Question 7

How is resting potential maintained?

Answer 7

The sodium/potassium pump moves 3 Na+ ions out and 2K+ ions in
A chemical concn gradient moves K+ out and an electrical gradient attracts Na+ ions

Question 8

What does a stimulus do? (Resting potential)

Answer 8

Opens gated ion channels which accelerates movement of ions.

Question 9

What happens when a stimulus opens chemically gated channels?

Answer 9

Increases Na+ entry to cell causing depolarisation when the stimulus is removed we get hyperpolarisation

Question 10

Define depolarisation

Answer 10

When the membrane potential shifts towards 0mV- more +ve ions on inner surface off the cell

Question 11

Define hyperpolarisation

Answer 11

Opens K+ channels and membrane potential shifts past -70mV to -80mV

Question 12

Define repolarisation

Answer 12

Stimulus is removed and restored to resting potential

Question 13

What is a graded potential?

Answer 13

Any stimuli that opens a gated channel affects a limited portion of the cell membrane
Cant affect enormous cells and isn’t limited to the nervous system

Question 14

What steps of graded potentials

Answer 14

1. Resting membrane exposed to chemical which opens Na+ ion channels causing depolarisation
2. Local current - depolarises nearby cell membranes
3. Stimulus is removed and repolarisation occurs

Question 15

What is an action potential?

Answer 15

Change in the permeability of entire excitable membrane
Begins at the axon hillock then along the axon if it reaches the threshold

Question 16

Outline the steps of the generation of an action potential

Answer 16

1. Depolarisation of membrane to threshold
2. Na+ channels open and rapid depolarisation
3. At 30mV Na+ channels are closed and K= channels are opened
4. K+ channels close and we get a brief hyperpolarisation and then a return to normal permeability

Question 17

Continuous propagation of an action potential

Answer 17

1. AP in segment 1 depolarises membrane to +30mV
2. Local current formed as Na+ ions spread and depolarises the second segment
3. Second segment develops an action potential as first enters the refractory period
   4 Cycle repeats travels in 1 direction at 1m/s

Question 18

Define refractory period

Answer 18

Period of time of recovery where an action potential cant be generated. Allows APs to be discrete and unidirectional

Question 19

Define saltatory propagation

Answer 19

Action potentials of a myelinated neuron jump from node to node at 18-140 m/s

Question 20

Compare graded potentials and action potentials

Answer 20

GP - depolarising and hyperpolarising dependent on stimulus intensity
AP- always depolarising - all or none law
GP- No threshold
AP- threshold
GP- No refractory period
AP- refractory period

Question 21

What is the all or none law?

Answer 21

For every stimulus that brings the membrane over the threshold then an identical action potential is generated

Question 22

Define synapse

Answer 22

Site of communication between a nerve cell and another cell

Question 23

What does the synaptic terminal contain?

Answer 23

Mitochondria, vesicles with a specific neurotransmitter, endoplasmic reticulum

Question 24

Define neurotransmitter

Answer 24

Chemical compounds released by 1 neuron to affect the membrane potential of another

Question 25

Define excitatory neurotransmitters

Answer 25

Cause depolarisation of the postsynaptic membrane and promote AP

Question 26

Define inhibitory neurotransmitters

Answer 26

Cause hyperpolarisation of post synaptic membranes and suppress AP

Question 27

What is the most common synapse?

Answer 27

Cholinergic - all neuron to neuron synapses in the PNS and all NMJs and NGJs in parasympathetic ANS

Question 28

Outline the events at a cholinergic synapse

Answer 28

1. AP arrives depolarises the presynaptic neuron
2. Ca2+ ions enter the cystol of the axon terminal. ACh is released from vesicles via exocytosis
3. Diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane opening Na+ channels leading to graded depolarisation
4. AChE breaks down ACh into acetate and choline which is reabsorbed and resynthesized to form ACh in the vesicles

Question 29

Outline Norepinephrine

Answer 29

Excitatory
Brain and ANS
Adrenergic synapses
Broken down by monoamine oxidase

Question 30

Outline dopamine

Answer 30

Both excitatory and inhibitory (Precise control)
CNS - brain
Dopaminergic synapses
Lack = muscle stiffness

Question 31

Outline serotonin

Answer 31

CNS
Interacts with other neurotransmitters e.g. NE for regulation of sleep wake cycles
Serotonergic synapses

Question 32

Outline Gamma Aminobutyric Acid (GABA)

Answer 32

Inhibitory
Incompletely understood
CNS - reduces anxiety