3/ cells of the nervous system 2

Question 1

how many different neurons?

Answer 1

85 billion

Question 2

how can neurons be classified by structure?

Answer 2

number of neurites, dendritic geometry, connections (where do they project - sensory/motor), axon length (local or long distance)

Question 3

how can neurons be classified by gene expression?

Answer 3

• underlies structural differences
• defines neurotransmitter expression

Question 4

unipolar neurons - pure and pseudo DIAGRAM

Answer 4

• only 1 neurite coming off cell body
• eg dorsal root ganglion
• peripheral process part of axon too
• small area for receiving synaptic input - highly specialised function
• reliable relay of info
• pure unipolar: one cell body, one axon
• Pseudounipolar: initially 1 axon then splits into 2 (ends dendritic)

Question 5

bipolar neurons

Answer 5

• 2 neurites off cell body
• dendrites and axon coming off cell body in different directions
• eg retinal bipolar cells
• small area for recieving synaptic input = highly specialised function
• reliable relay of info

Question 6

multipolar neurons

Answer 6

• multiple neurites coming off cell body
• one (?) axon and multiple dendrites
• majority of neurons in the brain
• large area for receiving synaptic input
• high levels of convergence - take input from multiple places and integrate into an output
• eg purkinje cell

Question 7

how many contacts does a multipolar neuron receive?

Answer 7

around 150,000

Question 8

brief stellate neurons

Answer 8

• multipolar neurons
• dendrites in all directions from cell body

Question 9

brief pyramidal neurons

Answer 9

• multipolar
• triangular
• many dendrites from cell body, one esp long dendrite w more dendrites coming off it

Question 10

where do sensory neurons project

Answer 10

• cell body in PNS, presynaptic terminals in CNS

Question 11

where do motor neurons project

Answer 11

• cell bodies in CNS, presynaptic terminals in PNS

Question 12

classes of motor neurons

Answer 12

• largest class is interneuron
• includes relay or projection neurons which connect brain regions
• and local interneurons which have short axons and process info in local circuits

Question 13

glia function as nerve glue

Answer 13

• fill space around neurons
• extracellular space of 20nm between glia and neurons
• can proliferate throughout life, unlike neurons

Question 14

astrocytes

Answer 14

• type of glia
• make up most cells in CNS
• controls environment surrounding neurons - right ions eg potassium
• spatial domains
• unique marker - glial fibrillary acidic protein GFAP, can be stained to show well defined cell body
• many subtypes
• have their own area to look after
• buffer extracellular potassium
• form part of blood brain barrier
• couple neuronal activity to blood supply

Question 15

other roles performed by glia and subtype of glia that performs each

Answer 15

• homeostatic: astrocytes (CNS), satellite cells (PNS), enteric glia (ENS)
• myelinating cells: oligodendrocytes (CNS), Schwann cells (PNS)
• phagocytic: microglia (CNS), Schwann cells and macrophages (PNS) - leakages from damaged neurons causing harm

Question 16

glia don’t have neurites they have…

Answer 16

processes

Question 17

astrocytes as fuel suppliers

Answer 17

• glycogen stores of brain
• provide 5-10 min supply w/o sufficient blood to brain
• metabolise glycogen and supply lactate
• endfeet take up glucose
• can detect when neurons are more active - convert more glycogen to lactate

Question 18

tripartite synapse

Answer 18

• terminates neurotransmitter activity
• recycles neurotransmitters to presynaptic terminals
• astrocytes have receptors too
• 3 things: astrocyte, synapse and neuron

Question 19

microglia

Answer 19

• key role in tissue surveillance and phagocytosis, aware of apoptotic cells
• harmful roles in neurodegenerative diseases - manipulate to protect cells??
• activated, sends out process, eats dead cells

Question 20

oligodendrocytes

Answer 20

• similar to Schwann cells but in CNS, except can myelinate MULTIPLE cells but Schwann only does 1
• myelinating oligodendrocytes form myelin sheaths of CNS axons
• 15-30 processes from cell body to myelin sheath

Question 21

Schwann cells

Answer 21

• forms myelin sheaths of PNS
• one Schwann cell provides one myelin segment to a single axon

Question 22

myelin sheath formation

Answer 22

• oligo cytoplasm wraps many times around the axon
• cytoplasm squeezed out of between layers by compaction
• myelin sheaths maintain contact w glial cells for nourishment

Question 23

function of myelin

Answer 23

• insulating (fat)
• creates nodes of ranvier - saltatory conduction