Module 3 - Nervous System

Question 1

An Astrocyte is a glial cell in the CNS. Describe its function

Answer 1

• regulates ion concentrations and neurotransmitters
• forms the blood-brain barrier (stops toxins from getting into the brain, by only letting lipid soluble molecules through)

Question 2

Schwann and oligodendrocytes make up myelin. What is myelin and what would happen if these cells were defective?

Answer 2

Myelin insulates the axon, allowing for quicker and more efficient conduction of action potentials
If defective, neuron could become non-functional or there could be a leakage of electrical activity

Question 3

Na/K ATPase pumps 3 Na ions out of the cell, and 2 K into the cell. What is the concentration of Na+ and K+ on either side of the cell membrane?

Answer 3

Both sides add up to 155mM

Inside the cell= 140mM K+, 15mM Na+
Outside the cell= 5mM K+, 150mM Na+

Question 4

What is the difference between hyperpolarisation and depolarisation? How does each one occur?

Answer 4

Hyper- inside the cell becomes more negative,p as K channels open and it moves with its concentration gradient out of the cell

De- inside becomes more positive - Na channels open and Na comes inside the cell

Question 5

Describe the difference between the absolute refractory period (ARP) and the relative refractory period (RRP)?

Answer 5

ARP- no AP is possible no matter how large the stimulus is.
RRP - a second AP is possible once the sodium channels move from inactive to closed. Once closed, they can be opened again by a second stimulus

Question 6

How do local anaesthetics work?

Answer 6

They lock the sodium channels in the inactive state, meaning further action potentials cannot be generated.

Question 7

Describe the 3 factors that influence conduction speed down an axon.

Answer 7

1. Axon diameter. Larger diameter = less resistance = faster
2. Temperature. Warmer = faster
3. Myelination. Myelin insulated the axon, meaning the AP only needs to occur at the nodes of ranvier (this jumping is known as saltatory conduction)

Question 8

What is multiple sclerosis?

Answer 8

A condition where the immune system eats away at the myelin layer of the axons. This disrupts the communication between the brain and the body.

Question 9

What do neurotransmitters do?

Answer 9

They help electrical impulses cross the synaptic cleft.

Question 10

What happens with an action potential reaches the synaptic cleft?

Answer 10

The AP opens up Ca- channels. The calcium then fuses with vesicles containing neurotransmitters, which are then released into the synaptic cleft through exocytosis

Question 11

What is the difference between EPSPs and IPSPs?

Answer 11

E- excitatory potential at post synaptic neuron if depolarisation occurs. Negative out, positive in. AP likely to occur if temporal / spatial arrangement reaches threshold

I- inhibitory potential if hyperpolarisation occurs. Negative in and positive out. No AP will occur

Question 12

There are 2 types of chemical synaptic transmission. Direct and indirect. What is the difference and what are some examples of neurotransmitters for each one?

Answer 12

• direct = neurotransmitters open channels on the postsynaptic neurone which leads to a graded potential.
  - example neurotransmitter: amino acids
• indirect = binds to a receptor on postsynaptic neurone which releases a second messenger (takes longer than direct).
  - example: GCPR

Question 13

How are neurotransmitters removed from the synaptic cleft? Why is it important that this happens ASAP?

Answer 13

Enzymes are present to break down the transmitter acetylcholine. All other transmitters have a transporter that takes them back into vesicles in the presynaptic neurone to be recycled.
This process needs to happen quickly to prevent constant stimulation and the excessive firing of action potentials

Question 14

Describe the different divisions of the peripheral nervous system.

Answer 14

Somatic and autonomic.
Somatic = voluntary
Autonomic = involuntary - parasympathetic and sympathetic

Para- ‘rest and digest’ calming responses
For example, decreasing the heart rate promotes emptying the bladder

Sympathetic - ‘fight or flight’ opposite^ responses. Need more oxygen
For example, increasing the heart rate inhibits emptying the bladder

Question 15

What is cerebrospinal fluid?

Answer 15

A fluid that protects the CNS

It supplies nutrients and hormones as well as removing waste

Question 16

What is the difference between grey matter and white matter, and where are they located within the CNS

Answer 16

Grey = unmyelinated axons, dendrites and cell bodies 
White = myelinated axons 
Brain= grey on outside, white inside 
Spine = white on outside, grey inside