Neurones / ST / Summation

Question 1

What is divergence in terms on neuronal pathways

Answer 1

When 1 presynaptic neurone branches into large number of postsynaptic neurones

(Collaterals)

Question 2

What is convergence

Answer 2

When large numbers of presynaptic neurones converge to affect 1 or less postsynaptic neurones (summation)

Question 3

What is spatial summation (convergence)

Answer 3

When EPSPs originate at different locations on a neurone due to 2+ excitatory neurones

Question 4

Why do more neurones come together in summation to allow epsps

Answer 4

Because separately , the excitatory post synaptic potential would be sub threshold

Together they can be suprathreshold

Can fire an ap in post synaptic neurone axon hillock

Question 5

Why can summation sometimes be postsynaptic inhibition?

Answer 5

If one of the neurones converging graded potentials are hyperpolarising (iPsp)

Eg through Cl- entering cell or k+ out = ipsp

This would mean the summed potential is sub threshold

No AP fired

Question 6

What is temporal summation

Answer 6

Graded potential (epsp) from the same presynaptic neurone happen close together

The EPSP then join into a an EPSP which is suprathreshold

Question 7

What is post synaptic modulation?

Answer 7

When the neurone in summation receives modulation signals that decide the strength of the signal

If modulation signal in neurone is above threshold

Neurone decides an AP

Question 8

Why can synaptic modulation have big effect eg if the signal is below threshold

Answer 8

Due to divergence meaning 1 neurone decides whether many target cells (collaterals) respond/are stimulated

Question 9

What is pre synaptic modulation

Answer 9

Modulation pre synapse of a cell which is either inhibitory or excitatory. You can purposefully use pre synaptic modulation to stop or stimulate a cell

Question 10

How could presynaptic modulation be used to inhibit 1 cell

Answer 10

An inhibitory neurone firing an ipsp to a cell is added pre synapse (damping the action potential) This causes no NTS to be released and the cell therefore doesn’t respond

Question 11

Name the 2 different receptors and the channels they are on on the synapse

Answer 11

Ionotropic receptors - on ligand gated ion channels

Metabotropic receptors - on G protein coupled receptors

Question 12

What happens in an EPSP graded potential and an IPSP graded potential via the ionotropic receptors on ligand channels

Answer 12

If EPSP- Na will move in when a conformational change has occurred depolarisation occurs

If IPSP - Cl can move in through the ligand channel or K+ can move out. Hyperpolarising the cell

Question 13

When a molecule binds to the metabotropic receptor what happens

Answer 13

This activates a secondary messenger pathway

Question 14

When a secondary messenger pathway on the G protein coupled receptor is activated, what 3 things does this do

Answer 14

Modifies proteins/ regulates synthesis of new proteins
Eg new ligand channels

Or causes ion ligand channels to close (with the K+ channel in EPSP) or Na channel in IPSP

Or causes ion ligand channels to open
(If Na channel causes EPSP)
If Cl or K channel = IPSP

Question 15

Name the 6 types of NTs that are in the normal synapse

Answer 15

AcH

Amines - eg dopamine , adrenaline

Purines - ATP , AMP

Some polypeptides

Amino acids - GABA , glycine , glutamate

Gases - NO

Question 16

What is the main excitatory neurotransmitter in the brain (because it uses ionotropic receptors on ca,k and Na Ligand channels)

Answer 16

Glutamate

Question 17

What are the 2 main inhibitory NTs due to them binding to ionotropic receptors on Cl- channels?

Answer 17

GABA and glycine

Question 18

Name some NTs that bind to mono tropic receptors

Answer 18

Adrenaline
AcH
ATP
Histamine

Question 19

What is the ionotropic and metabotropic receptors called that bind to AcH

Answer 19

Ionotropic = nicotinic

Metabotropic = muscarinic receptor

Question 20

What is synaptic plasticity

Answer 20

Once synapses form they aren’t fixed

Synaptic transmission can change depending on sensory input eg Past events

Responsible for things like memory

Question 21

What is an example of synaptic plasticity and where was it found

Answer 21

Long term potentiation

Found in hippocampus (how memory works)

Question 22

Explain the process of long term potentiation with glutamate involvement

Answer 22

When glutamate is released into the synapse, it binds to the ionotropic receptors on a NA ligand gated channel.

This triggers an EPSP

Repeated stimulation of this with glutamate causes depolarisation

Depolarisation causes mg2+ on the nmda receptor to eject causing calcium to move into the cell

The cell then becomes more sensitive to glutamate and can even release more

Question 23

How does long term potentiation work?

Answer 23

Repetitive stimulation through binding of glutamate - synaptic efficacy

Question 24

What is AcH effect on the metabotropic receptor on heart muscle

Answer 24

G protein activates secondary messenger
Camp produced

Causes k+ channels to open and k+ leaves the cell = hyperpolarisation