Neurotransmission

Question 1

properties of synaptic transmission

Answer 1

• rapid transmission
• integration of info
• summation of info
• adaptable, dynamic
• plasticity, changes neural pathways
• important for memory and learning

Question 2

describe basic structure of a neurone

Answer 2

dendrites with spines lead to a soma (cell body) leaving the soma is an axon which ends in nerve terminals.

spines are membranous protrusions of the dendrites which contain synaptic proteins. These are where synapses occur and each dendrite has many spines.

Question 3

what are dendrites

Answer 3

where information is received on a neurone

Question 4

between neurones what kind of transmission occurs?

Answer 4

chemical, it only takes around 2ms, VERY FAST

Question 5

where does neurotransmission occur?

Answer 5

at the synapse. Presynaptic terminal releases neurotransmitter, which diffuses across 20-100nm gap, then binds to postsynaptic membrane receptors, triggering a response.

Question 6

what would you see under microscope when looking at an asymmetric synapse?

Answer 6

vesicles primed for exocytosis in presynaptic terminal. post synaptic density, full of proteins like receptors and proteins that help binding of neurotransmitter.

Question 7

what are the 3 stages of synaptic transmission?

Answer 7

1) biosynthesis, packaging, release of neurotransmitter
2) receptor action
3) inactivation of response

Question 8

types of neurotransmitter

Answer 8

Amines
Amino acids
Neuropeptides

Question 9

examples of amino acid neurotransmitter

Answer 9

glutamate (major STIMULATOR in CNS)
glycine
GABA

Question 10

examples of amine neurotransmitter

Answer 10

Noradrenaline

Dopamine

Question 11

example of a neuropeptide

Answer 11

opioid peptides

Question 12

what diversity is there in neurotransmitter action

Answer 12

• differ in speed of effects (micro seconds to milliseconds)
• vary in abundance

multiple transmitter effects are integrated to provide a wide variety of functional responses

Question 13

how is neurotransmitter release triggered?

Answer 13

Action potential depolarises presynaptic membrane which triggers VGCCs to open. influx of calcium causes exocytosis.

Question 14

how is the transmitter recycled?

Answer 14

actively pumped back into the presynaptic bouton or glial cell after usually being broken down by enzymes.

Question 15

how are vesicles primed and released at the synaptic terminal?

Answer 15

vesicles containing neurotransmitter are primed on the cytoplasmic leaflet of the presynaptic membrane.
vesicle proteins interact with the membrane proteins in the active zone holding it in place so that when an AP arrives there is rapid release.
this vesicle complex contains synaptotagmin, a calcium sensitive protein, which changes conformation when calcium binds. hence fusion and exocytosis of neurotransmitter.
vesicles then refill.

Question 16

vesicular protein complexes are targeted by neurotoxins give examples

Answer 16

TETANUS causes paralysis
BOTULINUM causes flaccid paralysis
(These causes transmitter not to be released)
LATROTOXIN (spider) stimulates transmitter release to depletion so cannot reform.

Question 17

how do receptor kinetics affect how fast transmission is?

Answer 17

ionotropic receptors have fast stimulatory or inhibitory transmission (eg nicotinic receptors)

GPCR needs triggering of enzyme which is slow (eg muscarinic in PNS and dopamine receptor in CNS)

Question 18

action of the glutamate receptor

Answer 18

opens sodium channel allowing influx of Na+. leading to an EPSP, excitatory post synaptic potential

Question 19

action of Pentameric GABA Receptor

Answer 19

allows inlfux of chloride which hyperpolarises membrane hence is inhibitory as threshold is raised for response. (IPSP)

Question 20

action of glycine receptor

Answer 20

influx of Cl-

Question 21

types of glutamate receptor

Answer 21

AMPA Receptor, which open in response to glutamate allowing allows influx of Na+. these are rapidly onset.

NMDA receptors have slower onset, only work if cell has already been depolarised and allow Ca2+ and Na+ influx, these serve as coincidence detectors (in learning/memory processes).

Question 22

what does the NMDA receptor do?

Answer 22

influx of calcium and sodium, slow onset, only opens after cell already depolarised. this causes phosphorylation of AMPA receptors allowing more Na+ conductance and transcription to make new synapses occurs. this means next time a stimulus triggers neurotransmitter release, the response will be greater. this contributes to memory and learning.

Question 23

how is glutamate synthesised and reuptaken?

Answer 23

synthesised from the TCA cycle,
reuptake occurs using an EAAT, excitatory amino acid transporter back into the presynaptic terminal itself or a CNS Glial cell which forms glutamine using glutamine synthase.

Question 24

what causes epilepsy?

Answer 24

abnormal firing of post synaptic membrane due to excess of glutamate in synapse or decreased levels of GABA. this leads to seizures.

Question 25

what is a seizure?

Answer 25

transient alteration in behaviour due to disordered synchronous rhythmic firing of brain neurones

Question 26

types of seizure

Answer 26

partial, originating from one side of the brain
generalised, involving both parts of the brain
manifestation arises from which part of the brain is associated:
absence
tonic - clonic
myoclonic
atonic

Question 27

How is GABA synthesised?

Answer 27

from glutamate from TCA cycle, Glutamic acid decarboxylase converts glutamate to GABA.

Question 28

How is GABA re-uptaken into glial cells and the presynaptic terminal?

Answer 28

using the GABA Transporter (GAT). in glial cells, GABA is then converted into succinyl semialdehyde using GABA transaminase.

Question 29

how to anticonvulsants/antiepileptics generally work?

Answer 29

increase amount of GABA (inhibitory) in the synapse

Question 30

how does phenobarbital and diazepam work?

Answer 30

enhances conductance of Cl- by promoting GABAR action

Question 31

how does vigabatrin work?

Answer 31

inhibits GABA transaminase

Question 32

how does Tiagabine work?

Answer 32

blocks the GABA Transporter