Lecture 3: Structure and Function of cells of the NS

Question 1

Dendrites

Answer 1

-Branch out from cell body, increase the surface area

Question 2

Axon terminals

Answer 2

• communicate with dendrites of other neurons

- when nerve impulses reach terminal boutons they release neurotransmitters

Question 3

Soma

Answer 3

-Nucleus (DNA), mitochondria (energy) and endoplasmic reticulum (protein synthesis)

Question 4

Axon (inside myelin sheath)

Answer 4

• carries info (action potential) from the cell body to the terminal boutons:
• afferent carry info into a region
• efferent carry info away from a region

Question 5

What percentage of cells in the brain are glial?

Answer 5

80%

Question 6

Glial cells: Astrocytes

Answer 6

provide physical support, nutrients and involved in phagocytosis (helps prevent infection and fight against disease in the brain)

Question 7

Glial cells: Microglia

Answer 7

Phagocytosis and prevention against infection

Question 8

Glial cells: Oligodendrocytes

Answer 8

support axons and produces myelin sheath in CNS

Question 9

Glial cells: Schwann cells

Answer 9

supports axons and produces myelin sheath in PNS

Question 10

Myelin sheath

Answer 10

• 80 % lipid; 20% protein
• Consists in segments with small portions of uncoated axon between segments (Nodes of Ranvier)
• The function of the myelin sheath is to increase the speed at which the axon propagates an electrical signal

Question 11

What is electrical transmission?

Answer 11

=within the neutron, along the axon

Question 12

What is chemical transmission

Answer 12

=between the neuron

• involves the release of neurotransmitters from the terminal to the post synaptic cell
• Impulse at terminal causes release of neurotransmitter into synapse which interact with specialized receptors on adjacent neurons

Question 13

The cell membrane

Answer 13

• Known as bilayer
• Protein channels: allow certain ions to move in and out of the cell
• Membrane is selectively permeable: allows certain ions to cross it at certain times
• Sodium, potassium, chlorine, and calcium cross through channels that are sometimes closed

Question 14

Neuron at rest overview

know in more detail

Answer 14

At rest, you have the sodium potassium pump that maintains your resting potential of -70 by pumping out sodium ions and replacing them with potassium ions

Question 15

Chloride ions

Answer 15

• Concentration and electrical gradient balance
• want to go from high concentration to a low concentration, want to stay on outside of the cell as its more positive and they are negatively charged. So concentration and electrical gradients balance each other out

Question 16

The resting potential, why bother?

Answer 16

• Allows brain cells to respond very quickly to external stimuli
• When brain cell is stimulated sodium is going to rush into the cell so maintaining this resting state in which the cell is more negative, mean that once you get this stimulation, the sodium ions are going to rush into the cell and create an action potential
• So by maintaining this negative resting potential it enables neurons to respond quickly to external stimuli

Question 17

What happens when brain cell is activated?

Answer 17

**

Question 18

Rues regarding action potentials

Answer 18

• Action potential only travels in one direction: from cell body to axon terminals because of hyperpolarization
• Myelination speeds up propagation of action potential: *saltatory conduction. Because action potential jump between the gaps in myelin sheath
• Refractory period**go over
• All or nothing law: neuron will only fire if threshold of excitation reached
• Rate law intensity represented by rate

Question 19

First 4 stages of Communication between neurons: synapse

Answer 19

1. Action potential reaches the terminal bouton in the pre-synaptic neuron
2. Depolarisation of the terminal bouton
3. Synaptic vesicles migrate and fuse with the presynaptic membrane
4. Vesicles release chemical neurotransmitter into the synaptic cleft

Question 20

Last 4 sarges of Communication between neurons: synapse

Answer 20

5. Neurotransmitter attaches to binding sites of receptors on the postsynaptic membrane.
6. Degeneration: neurotransmitters are broken down and deactivated by enzymes
7. Re-uptake: neurotransmitters taken back up by the pre-synaptic terminal
8. Auto-receptors on the presynaptic membrane become activated by the neurotransmitter in the synapse and this causes a decrease in synthesis or release of neurotransmitter

Question 21

Excitatory postsynaptic potentials

Answer 21

*depolarising

• Na+ channel (sodium) opens: excitatory post-synaptic potential (EPSP)
• Partial depolarisation (decrease in the negative state i.e. more positive)
• Increases the likelihood that the postsynaptic neuron will fire

Question 22

Inhibitory postsynaptic potentials

Answer 22

*hyperpolarising

• K+ channel opens (potassium): inhibitory post-synaptic potential (IPSP)
• Hyperpolarisation (increase in the negative i.e. it becomes more negative)
• Decreases the likelihood that the postsynaptic neuron will fire

Question 23

Integration of post-synaptic potentials

Answer 23

• Each postsynaptic neuron will have synapses with many presynaptic neurons
• Neural integration: interaction of excitatory and inhibitory synapses on a particular neuron
• The rate at which a neuron fires is dependent upon the relative activity of the excitatory and inhibitory synapses on the postsynaptic dendrites and soma