HUF 2-41 Functions of neurons and glia

Question 1

Major cell types in brain

Answer 1

Neurons

Glia

Question 2

Interneurons

Answer 2

Neurons that are confined to a nucleus

Question 3

Projection neurons

Answer 3

Neurons that project to other brain areas

Question 4

Interconnections of neurons

Answer 4

synaptic connections
=> neural circuits
=> specific functions

e.g. Primary visual cortex (V1): detect contrast and ‘see’ lines

Question 5

How do neurons do computation?

Answer 5

single cell level:

• receive multiple input signals
• integrate them
• transform to output signal according to computation rule

Neurons connect to each other in specific patterns to form neural circuits

Question 6

How does brain do massive parallel computation?

Answer 6

• Extensive short-range interconnections
  => complicated local circuitries within brain area
  e.g. hypothalamus
• Complicated long-range connections among subsystems
  => massive parallel computation device

Question 7

Specific brain regions perform specialised functions

Answer 7

• Brain lesion => clues
  e. g. Broca’s area: human left frontal lobe; speech
• Brain stimulation; brain imaging (fMRI, PET scan)

Question 8

How does brain organise information?

Answer 8

• Use ‘maps’ to represent information
  e. g. motor homuculus, sensory homuculus
• Place cells: visual world (hippocampus)
• Grid cells: spatial environment (entorhinal cortex)

Question 9

Information flow in neurons and neural circuits

Answer 9

Dendrites
=> soma (integrative)
=> axon (conductive)
=> nerve terminal
=> dendrite of another neuron

Action potentials

• rapid reversal of RMP from negative to positive in ms.
• depolarisation: Na+ influx through VGNC
• repolarisation and hyperpolarisation: K+ efflux through K+ channels

Question 10

Properties and functions of action potential

Answer 10

1. Triggered by membrane depolarisation (RMP less -ve.)
2. Threshold needs to be reached
3. All-or-nothing
4. Refractory period (unexcitable)
5. AP propagates without changing the size (no attenuation)

Question 11

Synaptic transmission

Answer 11

1. Membrane depolarisation opens VGCC in presynaptic terminals
2. ↑ [Ca2+]
3. Exocytosis of NT
4. NT released to synaptic cleft and binds to NTR on dendrite or soma
5. Binding of NT to NTR opens or closes post-synaptic membrane ion channel for specific ion
   => EPSP / IPSP

Question 12

Properties of neurotransmitters

Answer 12

• Excitatory: NT depolarised post-synaptic neuron
• Inhibitory: NT hyperpolarises post-synaptic neuron
• Whether NT is E or I depends on NTR
• Multiple NT subtypes with different action / function
• NTR: drug targets

Question 13

Glia (Neuroglia)

Answer 13

• Supporting cells of nervous system (CNS, PNS)
• Central cell body and branching processes
• Outnumber neurons in 10:1
• Half of mass of brain
• Smaller than neurons; can divide throughout life
• CNS: astrocyte, microglia, oligodendrocyte, ependyman call
• PNS: Schwann cell, satellite cell

Question 14

Major functions of glial cells

Answer 14

CNS
- Oligodendrocyte: myelin sheaths
- Astrocytes:
> support for CNS
> BBB
> secrete neurotrophic factors
> take up K+, NT
- Microglia: act as scavengers (modified immune cells)
- Ependymal cells: barriers between compartments

PNS

• Satellite cells: support cell bodies
• Schwann cells: myelin sheaths

Question 15

Role of astrocytes in synaoses

Answer 15

• Bidirectional communication between neurons and astrocytes
• Astrocytic projections envelops synapse
  => Tripartite synapse
• Possess many of the same NTR as neurons
  => Calcium-based signalling cascades in astrocytes
• Release active substances regulating synaptic activity
  => Gliotransmitter (ATP, glutamate, D-serine…)