cells of the brain

Question 1

what are common features in neurons

Answer 1

• single cell body
• most are dendrites (receptive in function & possess synapses)
• have an axon (carries info away from cell body)
• have terminal boutons (responsible for transfer of info)

Question 2

what are nissl bodies and why are they present in cell bodies

Answer 2

consist of RER and contain RNA and are the sites of protein synthesis.
nerve cells are metabolically active & therefore nissl granules are v prominent

Question 3

how are the neurofilaments organised & what do they contain

Answer 3

assembled into larger neurofibrils
they also have a system of neurotubules that are involved in transport of materials throughout the cell

Question 4

what specialised structure do dendrites display and how does this help its function

Answer 4

have membrane protrusions called spines which have concentration of polyribosomes in dendritic spines which mediate local protein synthesis

Question 5

what is the roles of dendrites

Answer 5

dendrites emanate from the cell body and play a critical role in receiving info

Question 6

what is the axon responsible for?

Answer 6

responsible for transmitting information

Question 7

where is the action potential generated?

Answer 7

at the non myelinated initial segment of axon, just distal to the axon hillock

Question 8

what three components does the synapse consist of?

Answer 8

• ther terminals of the presynaptic axon (input)
• a target on the postsynaptic cell (integrative)
• a zone of apposition (conductive)

Question 9

what does the zone of apposition produce

Answer 9

electrical synapse - the presynaptic terminal & the postsynaptic cell are in very close apposition at regions termed gap junctions
chemical synapse - a cleft separates the 2 cells (20-40nm)

Question 10

how do electrical synapses enter the postsynaptic cell

Answer 10

enters directly through specialised bridging channels called gap junction channels which physically connect the cytoplasm of the presynaptic & postsynaptic cell

Question 11

how does a chemical synapse enter the postsynaptic cell

Answer 11

release of chemical transmitter from the nerve terminal which diffuses across a synaptic cleft which separates both cells and binds to receptor molecules on postsnyaptic membrane

Question 12

what are four key roles of astrocytes

Answer 12

• nourishing neurons: take up glucose from circulation and deliver energy substrates to neurons
• regulating extra-cellular concs. of ions, neurotransmitters & other molecules
• modulating synaptic signalling
• development of synapses

Question 13

how is a tri-partite syanpse formed and what is the purpose of it

Answer 13

astrocytes envelop between two neurons and use high affinity transport channels to rapidly uptake released neurotransmitters which are converted and end product is transferred back to neurons

Question 14

what is dangerous about high concentrations of extracellular neurotransmitters

Answer 14

can lead to excitotoxicity and the death of neurons

Question 15

what kind of astrocytic dysfunctions are observed in diseases

Answer 15

• defects in K+ channels on astrocytes have been found to contribute to stroke % migraine
• accumulation of ions & water in astrocytes can contribute to severe brain swelling after head injury
• astrocytic defects in glutamate uptake contribute to excess excitation of spinal motor neurons in motor neuron disease

Question 16

what myelin sheath does oligodendrocytes produce

Answer 16

central nervous system myelin

Question 17

what type of myelin sheath do schwann cells produce

Answer 17

produce peripheral nervous system myelin

Question 18

what is saltatory conductions

Answer 18

having node of ranviers & axons w/ myelin so the speed of action potential increases

Question 19

what do non myelinated schwann cells assist in

Answer 19

participates in the neuromuscular junction. they oerlap the axonal terminal of the motor neuron when it forms the connection w/ the muscle

Question 20

what is the most characteristic feature of microglial cells

Answer 20

their rapid activation in response to environmental change in the CNS. they can become macrophages or also presenting antigens to lympocytes and secreting cytokines & chemokines

Question 21

how do microglia function regarding to alzheimer’s disease

Answer 21

they are activated and contribute to excessibr synaptic pruning. in late stages the amyloif beta tangles cause pathological changes in microglia called microgliosis that contribute to neurodegeneration by secreting inflammatory factors

Question 22

what are the 3 things the blood brain barrier is formed by

Answer 22

• endothelial cells (EC): interconnected by very complex interendthelial tight junctions
• pericytes (PC): smooth muscle like cells
• endfeet (AE): astrocytic projections

Question 23

what role does the BBB have

Answer 23

tightly regulates movement of ions, molecules and cells between blood & brain, essential for neuronal homeostasis & protects brain tissue from toxins & pathogens

Question 24

reasons for leakiness in BBB

Answer 24

• loss of tight junctions between brain endothelial cells
• increased permeability of the adherens junctions
• increased vesicular transport to move nolecules & proteins across the barrier

Question 25

why does the ventricles of the brain lined with the ependyma

Answer 25

helps move cerebrospinal fluid through the ventricular system

Question 26

what is the choroid plexus and its role

Answer 26

covers thin blood vessels that project into the ventricles, filter plasma from the blood & secrete an ultrafiltrate in the ventricles called cerebrospinal fluid.

Question 27

what is the role of cerebrospinal fluid

Answer 27

encases the brain & provides nourishment, protein and ion homeostasis as well as protects the brain from physical trauma