Cells of the Nervous System

Question 1

What is the Central Nervous System?

Answer 1

• Brain ( cerebral hemispheres, brainstem. cerebellum).
• Spinal Cord

Question 2

What is the Peripheral Nervous System?

Answer 2

• Nerve fibres originating from the CNS.

Question 3

What are gyri and sulci?

Answer 3

• Gyri = ridges of cerebral hemispheres.
• Sulci = valleys of cerebral hemispheres.

Question 4

What are the four regions each cerebral hemisphere is separated into?

Answer 4

1. Frontal Lobe
2. Parietal Lobe
3. Temporal Lobe
4. Occipital Lobe

Question 5

What is the frontal lobe responsible for?

Answer 5

Responsible for executive functions such as personality.

Question 6

What is the parietal lobe responsible for?

Answer 6

Contains somatosensory cortex responsible for processing tactile information.

Question 7

What is the temporal lobe responsible for?

Answer 7

Contains:

• Hippocampus - short term memory
• Amygdala - behaviour
• Occipital - processing of visual behaviour

Question 8

What is the occipital lobe responsible for?

Answer 8

Processing of visual information.

Question 9

What does the brainstem consist of?

Answer 9

• Midbrain
• Pons
• Medulla

Question 10

Where is the cerebellum? What does it do?

Answer 10

• Attached to the brainstem.
• Important role in motor coordination, balance and posture.

Question 11

What does the spinal cord do?

Answer 11

Extends down from medulla, acts as conduit for neural transmission, but can coordinate some reflex actions.

Question 12

What is a mature neuron?

Answer 12

Non-dividing excitable cell.

Main function is to receive and transmit information in the form of electrical signals.

Heterogenous morphology

Question 13

What does the fact that neurones are polymorphous mean?

Answer 13

Can’t be classified on the basis of shape, location or function.

Question 14

What do unipolar neurons look like?

Answer 14

Cell body (with nucleus) + single axonal projection.

Question 15

What do pseudo-unipolar neurones look like?

Answer 15

Single axonal projection bifurcates (forks into two).

Question 16

What do bipolar neurones look like?

Answer 16

2 projections from cell body = 1 axon + 1 dendrite

Question 17

What do multipolar neurones look like?

Answer 17

Most common type of neuron.

Numerous projections from cell body, but only one axonal projection.

3 types:

• Pyramidal cells
• Purkynje cells
• Golgi cells

Question 18

What are the common features of a neuron?

Answer 18

Soma/ Cell Body/ Perikaryon

Axon

Dendrites

Question 19

What is the soma?

Answer 19

Cell body/perykaryon

• Contains nucleus (main nucleus & nucleolus) & ribosomes.
• Neurofilaments —> structure & transport of proteins for e.g. to end of axon/dendrites.

Question 20

What is an axon?

Answer 20

Long process (aka nerve fibre).

• Originates from soma at axon hillock.
• Can branch off into ‘collaterals’.
• Usually covered in myelin.

Question 21

What are dendrites?

Answer 21

Highly branched cell body.

NOT covered in myelin.

Receive signals from other neurons.

Question 22

What does neurones being excitable cells mean?

Answer 22

• Artificially generated resting membrane potentials.
• Therefore can generate bio-electrical signals to communicate with other cells.

Question 23

What are ion channels and pumps used for?

Answer 23

Cell membranes are impermeable to K+, Na+, Cl- and Ca2+ ions.

Ion channels/pumps regulate the transport of these ions across the membrane.

Question 24

What does the impermeability of the cell membrane to ions and the use of ion channels and pumps result in?

Answer 24

Results in an uneven ion distribution.

High extracellular: Na+ & Cl-

Low extracellular: K+

Question 25

What does the uneven ion distribution across a cell membrane result in?

Answer 25

Uneven ion distribution = difference in ion concentration ---\> creates a potential difference across membrane = RESTING MEMBRANE POTENTIAL

Question 26

What is the resting membrane potential of a neuron?

Answer 26

Negative charge inside compared to outside. RMP is around -70mV. Concentrated around the inside of the cell membrane. Outside of cell membrane is around 0mV. ---\> Resting membrane potential is usually -40mV to -90mV.

Question 27

Describe the concentrations of Ca2+ inside/outside of the cell membrane.

Answer 27

Concentration of Ca2+ outside cell is quite low, but concentration of Ca2+ inside cell is very low = high concentration gradient = Ca2+ move down concentration gradient into cell through channel or transporter protein.

Question 28

Describe the Voltage-Gated Channels at RMP.

Answer 28

Voltage-Gated Sodium and Potassium Channels are closed at RMP .(VGSCs & VGKCs). For an action potential, 3 Na in for every 2 K out.

Question 29

What is an Action Potential?

Answer 29

**Depolarisation** and subsequent **repolarisation** of a membrane.

Question 30

How does membrane depolarisation occur?

Answer 30

A change in ion channel configuration opens the VGSC = Na+ influx ---\> further depolarisation until around +40mV. Na channels have faster kinetics than K channels, so Na opens (and closes) first.

Question 31

How does membrane repolarisation occur?

Answer 31

Na channels begin to close and K channels open ---\> membrane potential becomes more negative towards -70mV again.

Question 32

What is the role of the Sodium-Potassium-ATPase pump?

Answer 32

Restores ion gradient imbalances after an action potential by pumping 3 Na out and 2 K in (against the concentration gradients).

Question 33

How does the Sodium-Potassium ATPase pump work?

Answer 33

1. Resting configuration = Na+ enters vestibule and upon phosphorylation is transported through the protein. 2. Active configuration = Na+ has been removed, so K+ enters vestibule. 3. Pump retuns to resting configuration, so K+ is transported back into the cell.

Question 34

What is saltatory conduction?

Answer 34

Action potential spreads along the axon by jumping between Nodes of Ranvier.

Question 35

Why is Saltatory Conduction important?

Answer 35

Axons are myelinated. Myelin prevents AP spreading due to its high resistance and low capacitance. Nodes of Ranvier = small gaps in the myelin intermittently along axon, with high concentrations of Na and K channels. Saltatory conduction = much faster than cable transmission.

Question 36

What are neurotransmitters used for?

Answer 36

AP can't travel from pre-synaptic terminal to post-synaptic terminal, so bioelectrical signal ---\> biochemical signal ---\> bioelectrical signal.

Question 37

What happens when an AP reaches the pre-synaptic terminal?

Answer 37

AP opens Voltage-Gated Ca2+ channels at pre-synaptic terminal = Ca2+ influx. Binds to vesicles containing neurotransmitters. Vesicles exocytose and release contents into synaptic cleft.

Question 38

What do neurotransmitters after being released into the synaptic cleft?

Answer 38

Bind to receptors/ion channels on post-synaptic terminal, causing propagation of the signal.

Question 39

After binding to receptors on the post-synaptic membrane, what happens to the neurotransmitters?

Answer 39

Neurotransmitters dissociate from the receptors and are either: * Metabolised by enzymes in synaptic cleft. * Recycled by transporter proteins In some cases, taken back to presynaptic terminal. = Neurotransmitter Reuptake.