Neuronal Responses

Question 1

where are synapses located (6)

Answer 1

1. axosecretory: axon -> blood stream
2. axoaxonic: axon -> axon (esp. axon hillock)
3. axodendritic: pre - post synaptic cleft (majority)
4. axoextracellular: axon -> no connection, into extracellular fluid (e.g. to adrenal gland)
5. axosomatic and axosynaptic: axon -> soma OR another exon terminal

Question 2

describe syanpse of neuromuscular junction

Answer 2

Neuromuscular junction (between motor neuron and muscle)

(- perirphery NS)

• NT: acetylcholine.

- Ach binds to receptor: nicotinic acetylcholine receptor (nAChR), Na+ enters muscle cell = depolarisation

- purely excitatory inputs: one NT, one receptor: always causes an AP.

= muscle contraction

Question 3

why are synapses more complicated than neuromuscular junctions?

Answer 3

• most synpases have both excitatory and inhibitory inputs

- most synpases have different / lots of NTs

(generation of AP depends on sum of all inputs to depolarise neurone above threshold)

Question 4

what is the receptor used for Ach synapse at neuromuscular junction?

Answer 4

Nictotinic ACh receptor

Question 5

how do inhibitory post synpatic potentials work?

Answer 5

- K+ permeability increased

OR
- increased Cl- perm.

Question 6

give an example of direct and indirect inhibitory post synaptic pontetial

Answer 6

indirect: Muscarinic ACh receptor:

• G-protein activated
• acts via 2nd messenger

- indirectly opens K+ channel

direct: GABA_A receptor:

• opens Cl- channel

BOTH: = hyperpolarisation

Question 7

describe the relationship (in terms of frequency) between NT and receptor types

Answer 7

have few NT (energy saving), but many use multiple receptor types: NT have different roles depending on which receptor use

e.g. ACh uses nicotonic and muscarinic receptors

Question 8

what and describe are the two classes of cell surface receptor types for synapses?

Answer 8

ligand gate ion channels:

• opens pore for ions
• very fast
• aka ionotropic

G-protein coupled receptors (GPCR)

• activated receptor activates G proteins that affects enzymes
• metabotropic
• slow
• can have bigger effect

Question 9

which ACh receptor is ionotropic and which is metabotropic?

Answer 9

iontropic ACh receptor: nicotonic receptors. (PNS, bit in CNS)

metabotropic ACh receptor: muscarinic receptor

Question 10

which is the main excitatory NT in CNS?

use one or both type of receptors?

how can the ionotropic receptors be classified?

Answer 10

- glutamate

• both ionotropic and metabatropic receptores
• 3 ionotropic receptors classified as:
  a) NMDA
  b) Non-NMDA
  i) AMPA
  ii) Kainate

Question 11

what is main inhibitory CNS NT?

how work (basic)?

Answer 11

GABA: calming effect

• allows Cl- into cell: hyperpolarisation

Question 12

what class of drugs binds to GABA_a receptor?

Answer 12

cause a conformational change: channel stays open for longer, more Cl- enter cause more hyperpolirastion: induces sleep

• *- Benzodiazepines** bind to GABAA receptor, causing structural change
• Allows more Clto move through the channel into neuron & hyperpolarises the neuron
• Sedative, sleep-inducing, anxiolytic

Question 13

g-protein receptor:

why do they give more diverse response c.f. ionotropic receptors?

(what is structure like?)

Answer 13

• gives a more diverse response depending on what G-protein is linked to

- (structure:

a) 7 transmembrane segments
b) lots of different ligands
c) over 700 GPCR)

Question 14

describe basic overview of glutamate G-protein coupled receptor response?

Answer 14

G-protein coupled receptor –> G protein comple (intracellular) –> enzyme (+/-) –> 2nd messenger

its the second messenger which causes varied responses:

- e.g. cAMP released: inhibitory

• IP₃ or DAG released: excitatory

Question 15

describe the sequence of events that could happen with G-protein coupled receptor

Answer 15

1. NT is released - binds to G-protein coupled receptor
2. Activates G-protein complex
3. Enzyme from G-protein complex could cause ATP -> cAMP
4. cAMP could cause the opening of another channel (e.g. a Na+ / Ca2+ channel)
5. Na+ / Ca2+ can trigger opening of Cl - (turns off the system)

Question 16

what could happen in GPCR if there is too much ligand?

Answer 16

might use Ca2+ to open Cl- channel to rebalance and regain resting membrane potential -> switches excitatory signal off

Question 17

why do you need less GPCRs to make a respnse (c.f. ionotropic receptors)?

which out of ionotropic or metabotropic, needs more to make a response on post-synaptic cleft?

Answer 17

need more ionotropic

GPRC: secondary messengers amplify signals to downstream target molecules - can need just one ligand binding to one GPCR

Question 18

what are the three main type of 2nd messengers of GPCR?

Answer 18

- hydrophilic water soluble (IP3₃, cAMP, Ca2+)

- hydrophobic water insoluble (DAG and PIP₃)

- gases (NO, CO and ROS)

Question 19

how do you strengthen new synapses?

Answer 19

strengthen synpases:

- sleep!

a) shrink spines that are not being used to allow for more new spines to form
b) strengthens synapses after learning

Question 20

how does receptor modulation by NTs occour?

Answer 20

receptor modulation by other NTs:

- NTs influence accumulation of opposite NTs on post-synaptic membrane

_e.g. ionotropic glutamate receptor fires excitatory response BUT also feedback to GABA receptor and causes to disperse (_and vice versa)

causes a balance of inhib and excitatory systems.

Question 21

how does modulation of signals occur (adaptation)?

Answer 21

• if important sensory information: no adaptation. stimulus maintained all the time
• less important sensory information: decay magnitude of the generator potential
  a) slow adaptation (e.g. olfactory system)
  b) rapid adaptation - declines over a more narrow window (c.f. slow)

Question 22

give skin sensory receptors example that do

rapidly adapting

slowly adapting

Answer 22

rapidly adapting: Meissner corpuscles (light touch), Pacinian corpsucles (vibration)

slowly adapting: Merkel cells (pressure, texture), Ruffini endings (stretching of skin)

Question 23

fun info

Answer 23

bc of refractory period, only have a set speed of generation AP

but CAN change the frequency of AP - increase transmission rate.

neurones have specific function -> go to one area of brain: encode one type of information (pressing eyeball)

Question 24

how do reflexes work?

Answer 24

goes to the spinal cord, dont go to brain for reflex to occur: prevents overloading occuring of brain

Question 25

what is tonic adaptation?

Answer 25

Tonic receptors adapt slowly and inform about the presence and strength of a stimulus.

Question 27

what is the name for rapid adaptation to stimulus?

Answer 27

phasic