CMB1004- L13: building a functional neural pathway from singal neurones

What is divergence in a neuronal pathway?

a presynaptic neurone branches to affect a large number of postsynaptic neurones

wha are co-lateral axons

branches of axons that affect a large number of axons

what is convergence in a neuronal pathway

a large number of presynaptic neurones converge to affect a smaller number of postsynaptic neurones

how does convergence influence a postsynaptic cell

multiple inputs can influence the output signal of the postsynaptic cell

what is spatial summation

the process where graded potentials (EPSPs) from multiple neurons combine to reach a suprathreshold signla and generate an AP

what happens during spatial summation if the EPSPs are subthreshold individually

the subthreshold EPSPs sum at the trigger zone to create a suprathreshold signal, resulting in an AP

why is it called spatial summation

because the EPSPs originate simultaneously at different locations on the neurone

what is postsynaptic inhibition

a form of spatial summation where two EPSPs are diminished by an IPSP, resulting in a subthreshold summed potential and no AP

what is required for summation of graded potentials from a single presynaptic neurone (temporal)

the graded potentials must arrive at the trigger zone close enough together in time

what is temporal summation

summation of multiple graded potentials from one presynaptic neurone,

how are temporal and spatial summation often related

many graded potentials incorporate both temporal and spatial summation- postsynaptic integration

what does postsynaptic integration allow for

the neurone to evaluate the strength and duration of the signals, if the signal is above threshold, the neurone fires an AP

what is an example of postsynaptic modulation

postsynaptic inhibition, which involves summing an IPSP to inhibit a cell AP

why might inhibition occur at specific sites rather than all at once

to selectively inhibit specific regions, such as the axon terminal, where inhibition is needed

where do neurones terminate in postsynaptic modulation

neurones terminate on or close to presynaptic axon terminals

similarities of mechanisms in the NS and NMJ

1. Action potentials

2. voltage gated Ca 2+ channels open

3. Ca2+ concentration rises and causes exocytosis

4. NT diffuses across synaptic cleft

What are the differences in postsynaptic mechanisms between the nervous system and NMJ?

• NT identity and receptor identity differ.

• They work differently depending on the system.

What are the two main methods by which neurotransmitters work?

1. Ligand-gated ion channels (ionotropic receptors).

2. G protein-coupled receptors (metabotropic receptors) that activate second messenger systems.

What happens in ionotropic receptors?

The ion channel opens when the neurotransmitter binds to the receptor.

Name neurotransmitters and ions associated with ionotropic receptors.

• ACh: Na⁺, K⁺.

• Glutamate: Na⁺, K⁺, Ca²⁺ (main EPSP-forming NT in the brain).

• GABA, Glycine: Cl⁻ (GABA is the main IPSP-producing NT in the brain)

What are metabotropic receptors?

G coupled protein receptors

Give examples of neurotransmitters associated with metabotropic receptors.

Adrenaline, histamine, cholecystokinin, ATP, and ACh.

What adds diversity to neurotransmitter systems like ACh?

ACh has both ionotropic (nicotinic) and metabotropic (muscarinic) receptors.

What is synaptic plasticity?

• The ability of synapses to change based on variations in electrical activity.

• Synaptic circuits can rearrange over time.

• Allows learning and memory through changes in synaptic transmission.

What is long-term potentiation (LTP)?

A process where repetitive stimulation at a synapse increases the efficacy of synaptic transmission.

Describe the steps of long-term potentiation (LTP). 7 steps

1. Glutamate is released.

2. Glutamate binds to AMPA and NMDA receptors.

3. AMPA (a Na⁺ channel) triggers an EPSP.

4. NMDA is initially blocked by Mg²⁺ and has no effect.

5. Repetitive stimulation causes greater depolarisation, ejecting Mg²⁺ from NMDA.

6. Ca²⁺ flows through NMDA.

7. Postsynaptic cell becomes more sensitive to glutamate and enhances glutamate release from the presynaptic cell.

What are the effects of LTP?

• Increases quality and quantity of synaptic transmission.

• Prevented by removing Ca²⁺ from the extracellular medium.