Neurons structure and function

Question 1

What is a neuron?

Answer 1

A specialised cell that is electrically and chemically excitable
A basic cellular unit of nerves and brains
Responsible for transmitting information to other nerve cells, gland cells and muscles

Question 2

Describe the structure of a presynaptic cell

Answer 2

Has a cell body that contains the nucleus and other organelles
Has dendrites to receive information from other neurons

Question 3

Describe the structure of a postsynaptic cell

Answer 3

Has a cell body that contains the nucleus and other organelles
Receives information from the axon terminals

Question 4

How are ion channels opened and closed?

Answer 4

By specific triggers;
Ligands
Voltage conditions
Association with structural elements

Question 5

What is a graded potential?

Answer 5

A potential at the cell body
A change from the resting potential that is proportional to the magnitude of the stimulus
A means of integrating stimuli because the membrane can respond with proportional amounts of depolarisation or hyperpolarisation

Question 6

What is conduction with decrement?

Answer 6

A graded potential ‘s signal will decrease with distance

Question 7

Describe how conduction with decrement occurs?

Answer 7

Neurotransmitter binds to a ligand gated Na+ channel
The Na+ enters through the open channel
The current will spread through the cell
The signal strength will then decrease with distance

Question 8

What is spatial summation?

Answer 8

Where signals arriving from dendrites will be summed over a certain space at the axon hillock

Question 9

What is temporal summation?

Answer 9

Signals arriving at the axon hillock from dendrites will be summed over time

Question 10

What are the activation and inactivation gates in Na+ channels?

Answer 10

The activation gate opens and allows ions to pass through

The inactivation gate plugs the pore preventing ion passage

Question 11

What is the resting potential?

Answer 11

-70mV

Question 12

What is the threshold potential?

Answer 12

-55mV

Question 13

What is the potential at which the membrane will begin to repolarise?

Answer 13

+30mV

Question 14

Explain how Na+ channels are activated

Answer 14

At resting potential the inactivation gate plugs the pore preventing Na+ entry
A suprathreshold depolarising graded potential causes the activation gate to open allowing Na+ to enter the cell
Positive feedback loop causes more Na+ channels to open and more Na+ enters the cell
The inactivation gate closes as membrane approaches +30mV preventing Na+ entry and the K+ channels open
K+ leaves the cell which repolarises the membrane
ATPase is Na+/K+ pump
Overshoots-hyperpolartisation then equilibrium

Question 15

What is the all-or-nothing principle?

Answer 15

When it comes to an action potential, the threshold value of around -55mV is needed to produce an action potential, anything less than this will not result in the production of an action potential

Question 16

Describe the features of a graded potential

Answer 16

Vary in magnitude
Vary in duration
Decay with distance 
Occur in dendrites and the cell body
Caused by the opening/closing of many kinds of ion channels

Question 17

Describe the features of an action potential

Answer 17

Always the same size and shape 
Always the same duration
Don't decay with distance 
Occur in axons 
Caused by the opening/closing of voltage gated ion channels

Question 18

Describe how action potentials move across synapses?

Answer 18

Action potential arrives at axon terminal
Voltage gated Ca2+ channels open and Ca2+ enters the cell and signal to the vesicles
The vesicles move to the plasma membrane
Docked vesicles release neurotransmitter by exocytosis
The neurotransmitter diffuses across the synaptic cleft to the postsynaptic cleft
The neurotransmitter binds to receptors on the post synaptic cell

Question 19

Explain how acetylcholine moves from the presynaptic cell to the postsynaptic cell

Answer 19

Acetyl CoA is made in the mitochondria
Choline acetyl transferase catalyses the conversion of acetyl CoA and choline into acetylcholine
Acetylcholine is packaged into synaptic vesicles
Acetylcholine is released into synapses
Acetylcholine binds to receptors on the postsynaptic cell
Acetylcholinesterase breaks down the acetylcholine into acetate and choline thus terminating the signal in the postsynaptic cell
The presynaptic cell takes up and recycles the choline and the acetate diffuses out of the cell

Question 20

What are Glial cells?

Answer 20

A group of different cells surrounding neurons to provide support and insulation

Question 21

What do astrocytes do?

Answer 21

Maintain homeostasis

Question 22

What do microglial cells do?

Answer 22

Remove damaged neurons and tackle infections

Question 23

What do oligodendrocytes do?

Answer 23

Wrap around neurons for insulation

Question 24

What are Schwann cells?

Answer 24

Oligodendrocytes of the periphery

Question 25

What do Schwann cells do?

Answer 25

Produce the myelin sheath

Question 26

What is the myelin sheath?

Answer 26

An extended and modified plasma membrane that is wrapped around the axon in a spiral

Question 27

How fast are action potentials in myelinated axons?

Answer 27

Up to 100m/s

Question 28

Are axons myelinated in invertebrates?

Answer 28

No