Lecture 3 - Action Potentials/Synapses/Neurotransmitters

Question 1

Definition of Potential Difference

Answer 1

An uneven distribution of +ve and -ve charges.

Question 2

Definition of Membrane Difference

Answer 2

Potential difference across a membrane.

Question 3

Membrane Potential of undisturbed cell

Answer 3

+ve charge on the outside, -ve charge on the inside

Question 4

Cell membrane resting potential of a neuron

Answer 4

-70mV

Question 5

Ion content of Extracellular Fluid

Answer 5

High Concentration of Na+ and Cl-

Question 6

Ion content of Intracellular Fluid

Answer 6

High Concentration of K+ and Pr- (Proteins)

Question 7

Function of Selective Permeability of Membrane

Answer 7

Maintains differences in Extra/Intracellular Fluid

Question 8

2 types of Channels in Membrane

Answer 8

Leak - always open
Gated - open/closed

Question 9

Chemical Concentration gradient across membrane in Passive Movement

Answer 9

K+ moves out faster than Na+ moves in

Question 10

Electrical Gradient across membrane in Passive Movement

Answer 10

+ve outer membrane repels K+ ions
-ve inner membrane attracts Na+ ions

Question 11

Stronger Gradient in Passive Movement

Answer 11

Chemical Conc Gradient Stronger
Therefore K+ still moves out
Therefore net loss of +ve ions

Question 12

Sodium/Potassium ion exchange pump

Answer 12

3 intracellular Na+ for 2 Extracellular K+

Question 13

2 conditions for disturbing resting potential

Answer 13

Altering of Membrane permeability to Na+/K+
Altering of Na+/K+ exchange pump

Question 14

Chemically gated channel mechanism (Na+)

Answer 14

At resting state, channel remains closed
In the presence of Acetylcholine at a binding site, conformational change occurs
Channel opens, allowing Na+ into the cell

Question 15

Depolarisation Definition

Answer 15

Shift of membrane potential towards 0mV

Question 16

Repolarisation Definition

Answer 16

Restoring of resting membrane potential

Question 17

Hyperpolarisation Definition

Answer 17

Shift of Membrane potential away from 0mV

Question 18

3 types of gated channels

Answer 18

Chemically Gated
Voltage Gated
Mechanically Gated

Question 19

Voltage Gated Channel mechanism (Na+)

Answer 19

Gate closed at -70mV
During Depolarisation, activation (outer) gate opens
Na+ enters cell
At +30mV, inactivation (inner) gate closes

Question 20

Mechanically Gated Channel mechanism (Na+)

Answer 20

Gate closed at resting state
When membrane is distorted, channel opens
Na+ enters cell
Once distortion ends, gate closes

Question 21

Graded potential definition (2 points)

Answer 21

Potential produced when gated channel opens
Local to limited portion of cell membrane

Question 22

6 Steps of Graded Potential Mechanism

Answer 22

Stimuli exposed to membrane
Sodium channel opens
Depolarisation occurs
Movement of Na+ produces local current
Depolarises local membrane
Once stimuli is removed, repolarisation occurs

Question 23

Action Potential Definition

Answer 23

Electrical Signal that affects entire membrane surface
Change in permeability of cell membrane

Question 24

Excitable Membranes Definition

Answer 24

Membranes in Skeletal Muscle fibres/axons that can conduct action potentials

Question 25

Start point of Action Potential in neuron

Answer 25

Axon Hillock

Question 26

Direction of Action Potentials

Answer 26

Along axon length towards synaptic terminals

Question 27

All or None Principle

Answer 27

Every stimulus, no matter the size, generates identical action potential

Question 28

Action Potential Threshold

Answer 28

-60mV

Question 29

6 Steps in Action Potential Generation

Answer 29

Graded depolarisation brings excitable membrane to threshold (-60mV) Voltage Gated Na+ channels open Na+ enters cell At +30mV, Na+ channels close, Voltage Gated K+ channels open Repolarisation occurs Once at resting potential, Voltage Gated K+ channels close

Question 30

Propagation of Action Potential Definition

Answer 30

Movement of Action Potential across Axon

Question 31

2 types of Propagation

Answer 31

Continuous Saltatory

Question 32

4 Steps of Continuous Propagation

Answer 32

Action Potential develops in initial segment, depolarised to +30mV Na+ ions spread away from open voltage gated channel in initial segment, causes graded depolarisation in next segment Action Potential develops in new segment whilst initial segment repolarises Cycle repeats

Question 33

Continuous Propagation Speed

Answer 33

1m/sec

Question 34

Schwann Cell Definition

Answer 34

Cell wrapped around neuron to provide protection and insulation

Question 35

Condition of Continuous Propagation

Answer 35

Occurs in unmyelinated axons

Question 36

Condition of Saltatory Propagation

Answer 36

When Continuous Propagation can't occur Occurs in Myelinated Axons

Question 37

Saltatory Propagation Speed

Answer 37

18-140m/sec

Question 38

4 Steps of Saltatory Propagation

Answer 38

Action Potential developed at initial segment, depolarised to +30mV Local current produces graded depolarisation that brings neighboring axolemma to threshold (-60mV) Action Potential develops at next node Cycle repeats

Question 39

Synapse Definition

Answer 39

Site of communication between nerve cell and some other cell

Question 40

Most common type of Synapse

Answer 40

Chemical Synapse

Question 41

3 Locations of Synapses

Answer 41

Dendrite On a cell body Along length of Axon

Question 42

Direction of communication across Synapses

Answer 42

1 direction Presynaptic Neuron to Postsynaptic Neuron/other cell

Question 43

6 Parts of a Synapse

Answer 43

Axon Terminal Mitochondrion Synaptic Vesicles Presynaptic Membrane Postsynaptic Membrane Synaptic Cleft

Question 44

Function of Synaptic Vesicles

Answer 44

Contain Neurotransmitters

Question 45

Synaptic Cleft Definition

Answer 45

Narrow space between Pre/Postsynaptic Membranes

Question 46

2 types of Neurotransmitters

Answer 46

Excitatory Inhibitory

Question 47

Excitatory Neurotransmitters Features

Answer 47

Causes depolarisation of postsynaptic membranes Promotes action potentials

Question 48

Inhibitory Neurotransmitters Features

Answer 48

Causes hyperpolarisation of postsynaptic membranes Suppresses action potentials

Question 49

2 Acetylcholine (ACh) Features

Answer 49

Most common neurotransmitter Released at Cholinergic Synapses

Question 50

Locations of Cholinergic Synapses

Answer 50

Common in CNS All Neuron-Neuron synapses in PNS All Neuromuscular/Neuroglandular junctions in Parasympathetic division of ANS

Question 51

8 Events at Cholinergic Synapse

Answer 51

Action potential depolarises axon terminal of presynaptic neuron Calcium ions enter axon terminal ACh release via exocytosis ACh diffuses across synaptic cleft ACh binds to postsynaptic membrane Chemically gated Na+ channels Depolarisation ends ACh broken down by AChE and reabsorbed into axon terminal as choline ACh resynthesized

Question 52

5 Important Neurotransmitters

Answer 52

Acetylcholine Norepinephrine (or noradrenaline) Dopamine Serotonin Gamma aminobutyric acid (GABA)

Question 53

Enzyme that breaks down Acetylcholine

Answer 53

Acetylcholinesterase (AChE)

Question 54

4 Features of Norepinephrine

Answer 54

Excitatory Neurotransmitter Used in brain/ANS Released at adrenergic synapses Broken down by Monoanime oxidase

Question 55

4 Features of Dopamine

Answer 55

CNS Neurotransmitter Both excitatory/inhibitory Released by Dopaminergic Synapses Dopamine deficiency linked to muscle stiffness

Question 56

4 Features of Serotonin

Answer 56

CNS Neurotransmitter Involved in Sleep/Wake cycles Serotonin deficiency important in context for depression Released by Serotonergic Synapses

Question 57

2 Features of GABA

Answer 57

Inhibitory Neurotransmitter Involved in anxiety reduction in CNS