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Neuroscience > 2.1 Cellular Physiology Of The Brain > Flashcards

2.1 Cellular Physiology Of The Brain Flashcards

1
Q

what are the different components of the central nervous system?

A

neurones

supporting glia cells (ependymal cells astrocytes, microglial cells and oligodendrocytes)

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2
Q

what is the purpose of glia cells?

A

to support, nourish and insulate neurones

remove waste

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3
Q

describe the structure of astrocytes

A

star like structure that has perineuonal feet thar sit on blood vessels that contain gap junctions

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4
Q

what is the function of astrocytes?

A 
structural support 
Help to provide nutrition for neurones
– glucose-lactate shuttle 
Remove neurotransmitters (uptake)
– control concentration of neurotransmitters (especially important for glutamate (toxic)
Maintain ionic environment
– K+ buffering 
Help to form blood brain barrier (perineural feet)
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5
Q

what is the function of an oligodendrocyte?

A

myelinates the axons of neurones in the CNS (similar to schwann cells in the PNS)
unlike the schwann cells a single oligodendrocyte can wrap around multiple different axons simultaneously

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6
Q

what does a microglial cell look like?

A

long flat nucleus

few processes

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7
Q

what is the function of microglial cells?

A

resident macrophage of the CNS:
immune function
remove damaged nerve cells
sense increased K+ ions
thought to digest neurofibrillary tangles (Alzheimers)
recognise foreign material and become activated
phagocytosis to remov derbis and foreign material

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8
Q

what is the function of ependymal cells?

A

ependymal cells line the choroid plexus and secrete CSF into the ventricles
have cilia to move the CSF

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9
Q

describe the energy source of neurones

A

nutrients transported across the BBB

  1. glucose transported through the endothelium via GLUT1 and into the neurone from the interstitial space via GLUT3
  2. astrocytes produce lactate which can be transferred to neurones to supplement the supple of glucose (glucose lactate shuttle)
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10
Q

how do astrocytes help in the regulation of neurotransmitters?

A

have transmitters for glutamate, helps keep the extracellular concentrations low. as glutamate is toxic in high concentrations

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11
Q

why are astrocytes located near synapses?

A

to facilitate the termination of synaptic response by mopping up the glutamate and removing it from the synaptic cleft

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12
Q

describe the role of astrocytes in maintaining neurone membrane polarity

A

high levels of neuronal activity leads to a rise in K+ in the brain ECF
astrocytes take up the K+ to prevent the rising levels depolarising the neurones and causing unwanted activity

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13
Q

what is the function of the BBB?

A

limits diffusion of substances from the blood to the brain ECF
maintains correct environment for neurones

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14
Q

what forms the blood brain barrier?

A

tight junctions between the endothelial cells
basement membrane surrounding the capillaries
end feet of the astrocyte processes

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15
Q

describe the diffusion of substances across the BBB

A

diffusion: water, CO2, O2
Transporter: Glucose (GLUT1), Na+, Cl-, K+, amino acids

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16
Q

why is the CNS described as immune privileged?

A

CNS inhibits the initiation of the pro inflammatory response of T-cells as too much inflammation in the rigid skull would be harmful
can be seen as the CNS does not undergo rapid rejection of allografts

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17
Q

what are the 4 main sections of a neurone?

A

axon
cell soma / cell body
dendrites
terminals

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18
Q

describe the process of neurotransmitter movement at the terminal

A

depolarisation at the terminal opens voltage gates calcium channels, allowing calcium to enter the terminal
vesicles fuse and release the neurotransmitter into the synapse
neurotransmitter diffuses freely across the synaptic cleft and binds to the receptors on the post synaptic membrane

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19
Q

what are the 3 chemical classes of neurotransmitters in the CNS ?

A

amino acids e.g. GABA, glutamate, glycine
biogenic amines e.g. acetyl choline, noradrenaline, dopamine, serotonin, histamine
peptides e.g. somatostatin, cholecystokinin

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20
Q

what is the major excitatory neurotransmitter of the CNS?

A

glutamate

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21
Q

what are the main inhibitory neurotransmitters of the CNS?

A

GABA is the main inhibitory transmitter in the brain

Glycine acts as an inhibitory neurotransmitter mostly in the brainstem and spinal cord

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22
Q

what are the recepetors of glutamate in the CNS?

A
  1. ionotropic (ligand gated ion channels). permeable to Na+ and K+ causing depolarisation and increased excitability
    - AMPA receptors (Na+ and K+)
    - Kainate receptors (Na+ and K+)
    - NMDA receptors ( Na+, K+ and Ca2+)
  2. Metabotropic ( g protein coupled receptor )
    - either alpha q or alpha i
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23
Q

how do neurotransmitters cause fast excitatory responses in the post synaptic cell?

A

glutamate binds to ionotropic receptors (NMDA/Kainate/AMPA) on the postsynaptic membrane. Causes depolarisation of the membrane and allows more AP to fire
Increased firing of AP called excitatory postsynaptic potential (EPSP)

24
Q

what glutamate receptors are present in glutaminergic synapses?

A

NMDA

AMPA

25
Q

Describe how AMPA and NMDA receptors work together in the glutaminergic synapses

A
  1. AMPA receptors mediate the initial fast depolarisation
  2. NMDA receptors are activated after AMPA as they need glutamate to bind and the cell to be depolarised to allow ion flow through the channel (ion channel is initially blocked by magnesium)
26
Q

what is meant by synaptic plasticity?

A

the change in synaptic strength depending on activity of the synapse. The greater the activity at the synapse the greater the strength of the synapse

27
Q

what is meant by long term potentiation?

A

Repeated presynaptic stimulation of a nerve, either naturally or in vitro, that results in the long-lasting increased strength of a synapse and is thought to be necessary for learning and memory formation.

28
Q

describe how glutamatergic receptors have a role long term potentiation

A

activation of NMDA receptors allows calcium to enter the neurone. This can upregulate AMPA receptors in the post synaptic membrane
Hence strong high frequency stimuation causes long term potentiation

29
Q

describe the role of glutamate in excitotoxicity

A

too much glutamate can cause over stimulation of the NMDA receptors and too much calcium entry into neurones.
too much calcium causes excitotoxicity

30
Q

in what common pathology is glutamate excitotoxicity seen?

A

stroke. damaged cells release glutamate, causing over stimulation of NMDA receptors

31
Q

what triggers an inhibitory post synaptic potential

A

entry of Cl- into neurones via integral Cl- channels in GABAa and glycine receptors.

32
Q

how do inhibitory neurotransmitters act?

A

GABAa and glycine receptors have integral Cl- channels. When the ligands bind, Cl- enters the cell, causing hyperpolarisation and decreased AP firing (inhibitory post-synaptic potential)

33
Q

what medications bind to GABAa receptors?

A

benzosdiazepines

barbiturates

34
Q

How do barbiturates affect the action of GABAa

A

enhance the response of GABAa receptors to GABA

  • previously used as an anxiolytic and sedative
  • sometimes now used as an antiepileptic
  • rarely used as risk of fatal overdose and dependence and tolerance
35
Q

how do benzodiazepines affect the action of GABA

A

Bind to GABAa receptors, increasing the response to GABA

  • have a sedative and anxiolytic effects
  • used to treat anxiety, insomina, epilepsy
36
Q

where is glycine released?

A

by inhibitory interneuornes within the spinal cord and brainstem

37
Q

describe the mechanism of action of the patellar reflex response

A 
hit patellar tendon
stretch quadriceps muscle
sensed by muscle spindle
afferent neurone sent to spinal cord
excitatory neurone releases glutamate
motor neurone activated, Ach released from muscle neurone, causes contraction of quadriceps. 
Reciprocal muscles (Hamstrings) relax.
Inhibitory interneurone, glutamate released from muscle spindle onto inhibitory glycenergic neurone. Inhibits the motor neuron to the hamstrings.
38
Q

name some biogenic amines that act as neurotransmitters in the CNS?

A
  • acetylcholine
  • dopamine
  • noradrenaline
  • serotonin (5-HT)
  • mostly act as neuromodulators
  • confined to specific pathways
39
Q

What is the role of ACh in the PNS?

A 
Nicotinic ACh receptors:
- neuromuscular junction
– ganglion synapse in ANS
Muscarinic ACh receptors:
– postganglionic parasympathetic
40
Q

Describe the role of ACh in the CNS

A

– acts at both nicotinic and muscarinic receptors in the brain
– mainly excitatory
– receptors often present on presynaptic terminals to enhance the release of other
transmitters

41
Q

describe the cholinergic pathways in the brain

A

neurones originate in the basal forebrain (nucleus basalis) and the brainstem.
Give perfuse projections to many parts of the cortex and hippocampus
also local cholinergic interneurones in the corpus striatum

42
Q

what is the role of cholinergic pathways in the CNS?

A

involved in arousal, learning, memory and motor control

43
Q

why are cholinesterase inhibitors used to alleviate symptoms of Alzheimers disease?

A

As degeneration of the cholinergic neurones in the nucleus basalis is associated with alzheimers disease. Cholinesterase inhibitors are used to alleviate symptoms of Alzheimers disease

44
Q

what are the 3 main dopaminergic pathways of the CNS?

A

nigrostriatal (motor control)
mesocortical (mood arousal and reward)
mesolimbic (mood, arousal and reward)

45
Q

what is the underlying neuropathology of parkinsons disease?

A

loss of dopaminergic neurones from the substantia nigra. Therefore less stimulation of the nigrostriatal pathway and less input into the corpus striatum

46
Q

what is the 1st line treatment for parkinsons disease?

A

Can be treated with levodopa - converted to dopamine by DOPA decarboxylase
(AADC)

47
Q

what is the underlying neuropathology in schizophrenia?

A

May be due to release of too much dopamine
– amphetamine releases dopamine & noradrenaline
– produces schizophrenic like behaviour
– antipsychotic drugs are antagonists at dopamine D2 receptors

48
Q

why is carbidopa given alongside levodopa?

A

to stop levodopa breakdown in the peripheral vascular system, before it reaches the CNS.
Inhibits AADC

49
Q

where is noradrenaline used in the nervous system

A

peripherally acts as a transmitter at the postganglionic synapse of the sympathetic autonomic nervous system
- in the CNS acts as a neurotransmitter in the cortex, hypothalamus, amygdala, cerebellum
Operates through G protein-coupled α- and β-adrenoceptors in the CNS and PNS

50
Q

where are noradrenic neurones located in the CNS?

A

locus coeruleus in the pons and medulla

51
Q

what is the function of noradrenaline in the CNS?

A

increased wakefulness
locus coeruleus is inactive during sleep, activity increases during behavioural arousal.
depression may be associated with deficiency of NA

52
Q

how do amphetamines increase wakefulness?

A

increases release of noradrenaline and dopamine

53
Q

what is the function of 5-hydroxytryptamine?

A

also known as serotonin, functions are to increase wakefulness and effect mood.

54
Q

what is the function of the raphe nuclei?

A

Found in the brain stem, they have 5-HT1 receptors which are coupled with Gi/Go-protein-inhibiting adenyl cyclase. Function as autoreceptors in the brain and decrease the release of serotonin.

55
Q

what are SSRIs?

A

SSRIs (serotonin selective reuptake

inhibitors). Used in the treatment of depression and anxiety disorders

Neuroscience (20 decks)

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