Neurotransmission in the Brain

1. State the main neurotransmitters and understand how the associated receptors mediate their action 2. Define the term neuromodulator and give examples 3. Describe how EPSPs and IPSPs are generated at excitatory and inhibitory synapses within the CNS

What two ways can neurotransmitter chemicals act?

**Ionotropic - open ion channels in post-synaptic membrane (fast only)**

**GPCR - triggers metabolic changes (fast or slow)**

**Acetylcholine**

Used by spinal cord neurons to control muscles and by brain to regulate memory.  Mainly excitatory.

Dopamine

Linked to feelings of pleasure, when released by the brain reward system. 

GABA

The major inhibitory neurotransmitter in the brain.

Glutamate

The major excitatory neurotransmitter in the brain. FAST (IONOTROPIC)

Glycine

Mainly by neurons in the spinal cord.  It has inhibitory and excitatory effects.

Noradrenaline

PNS - it is part of the flight-or-flight response.  CNS - it regulates various processes, such as mood.

Serotonin

Involved in mood, appetite, and sensory perception.  In spinal cord, it is involved in pain pathways.

In the brain, the _____ __form terminal endings on the__ ______of other neurones. These endings contain__ __ ________ like at the nmj.

1. axons
2. dendrites
3. synaptic vesicles

Motor neuron cell bodies are found in the _______ of the spinal cord.

ventral horn

Sensory fibres from _____________ synapse on these motor neurons. 

muscle spindle receptors

**A single muscle spindle  sensory nerve fibre (axon)** can be stimulated with wire hook electrodes on the__________.

dorsal roots

What happens when a single action potential reaches the sensory nerve synapse it does NOT generate an action potential in the motorneuron?

a **small depolarisation** of 5-10 millivolts in the motor neurone aka an  **excitatory post synaptic potential or ‘EPSP’**

What is temporal summation?

If a SINGLE sensory nerve fibre is stimulated but instead of a single shock a **high frequency burst** of shocks is given fibre  then the EPSPs **add together in time** and generate an action potential in the post-synaptic cell.

What normally accounts for over 80% of the surface area of a CNS neurone?

dendrites (most excitatory synapses)

Where are there **no sodium channels?**

**in the dendrites or cell body**

Where is the site of action potential generation?

axon hillock

Does a single EPSP generate enough current to depolarise the axon hillock to the action potential threshold?

No

What is hyperpolatisation aka **inhibitory post synaptic potential or IPSP?**

**final stage** of an action **potential after depolarization** and **repolarization** in action potential

How is the IPSP produced?

by the activity of an **inhibitory interneurone** between the sensory nerve axon and the motor neuron.

An example of IPSP activtion?

**is benzodiazepine which increases permeability to chloride.**

How is IPSP caused by inhibitory transmitters **GLYCINE or GABA?**

They bind to receptors which open Cl- specific channels in the cell membrane.

**How is glutamate neurotransmission initiated?**

**calcium has to enter the presynaptic  terminal to initiate fusion of glutamate vesicles and allow glutamate release.**

**By how many mechanisms is glutamate neurotransmission TERMINATED?**

2

How does the glutamate neurotransmission of **Reuptake** occur?

**Glutamate transporters** exist in the membranes of the presynaptic terminals and adjacent glial cells

Removing glutamate asap after each synaptic release.

How does the glutamate neurotransmission of **GABA Inhibition** occur?

‘fast’ glutamate synapses in the brain> there are also GABA synapses from local inter-neurones.

This is called pre-synaptic inhibition.