Neurotransmitters

• the brain is a neural network that sends and receives messages

Structure of Neurons

Soma: cell body, holds nucleus

Dendrites: first place message is received

Axon: like the spinal cord of the neuron, messages travel through the axon

Myelin Sheath: fatty substance that protects and insulates axon

Axon terminal: message goes to leave the neuron

Terminal button: releases neurotransmitters to next neuron for communication

Neurons communicate via a process called neurotransmission which uses electrochemical energy:

1. A neural impulse (Electrical energy) runs through the presynaptic neuron

2. The terminal buttons then release a chemical substance called neurotransmitters

3. These neurotransmitters then cross the synapse to the post synaptic neuron

Neurotransmission

• A neuron has resting potential when not activated

• In resting potential, negatively charged ions are inside the axon and positive ions are outside the neuron

• An electrical impulse known as action potential is the initiated in the soma and travels along the axon towards the axon terminals

*this turns the negative ions inside the axon to positive and the positive ions outside the neuron are turned negative

• An action potential is an all or nothing process- once it begins it cannot come back

• Inside the axon terminal, neurotransmitters are stored in synaptic vesicles

• When activated, neurons will release neurotransmitters across the synapse

• A receptor on the dendrite of the post-synaptic neuron will receive this neurotransmitter

• This part of neurotransmission requires chemical energy

*as information enters the neuron, it’s resting potential becomes action potential

Synaptogenesis- creating a new neural pathway:

• Dendrites receive neurotransmitters (chemical signals)

• Dendrites send them to the soma and nucleus to make a decision whether to fire a message or not fire a message

• If it decides to fire a message it sends an electrical impulse down the axon in the form of action potential

• There is myelin sheath surrounding the myelin sheath to speed up the action potential and protect the axon, the gaps between the myelin sheath are called nodes of ranvier

• action potential then reaches the axon terminals, causing the synaptic vesicles to release neurotransmitters into the synapse

• the neurotransmitter and the receptor site on dendrites work as a lock and key model, if the neurotransmitter is not complementary to the receptor site it will be absorbed by the axon terminals on the presynaptic neuron for later use

• neurotransmitters all have different shapes as they are made of different chemicals, so they are only complementary with receptors that have a complementary shape

Neurotransmitters:

• chemical substance released by terminal button of neuron, they are necessary for neural communication and typically made of smaller molecules

• sometimes neurotransmitters can be released by the pre-synaptic neuron, but not received by the post synaptic neuron

• this is when the terminal button reuptakes the neurotransmitter and hold the message until it needs to be used again

• this is how responses can be monitored and controlled

• different neurotransmitters sent from the pre-synaptic neuron affect the activity of the post-synaptic neuron in different ways

Some neurotransmitters are excitatory and increase the likelihood that a neuron will fire an action potential, whilst others are inhibitory and decrease the likelihood that a neuron will fire action potential.

• neurotransmitters and receptors are like a lock and key- the neurotransmitter must find the specific type of receptor that it can bind with

Neurotransmitters: have very specific impacts from one neuron to the target neuron

Neuromodulators: released in the same way as neurotransmitters but have broader effects on multiple neurons at the same time

Excitatory Neurotransmitters:

• have excitatory effects on neurons, increase likelihood of action potential firing e.g glutamate

Glutamate: excitatory neurotransmitter that sends signals to other cells to create large brain networks, responsible for learning

• it helps with the formation and retrieval of memory, which in turn helps learning

• it stimulates the post-synaptic neurons to perform their functions

Glutamate:

• the main excitatory neurotransmitter, enhancing information transmission and stimulating the post synaptic neuron to fire

• release of glutatmate is associated with learning and helping to consolidate lasting memories (long term potentiation)

• high levels of glutamate can lead to the over stimulation of the NS, resulting in migraines, seizures and anxiety

Inhibitory Neurotransmitters:

• have inhibitory effects and decrease the likelihood that a neuron will fire an action potential e.g GABA

• block or prevent postsynaptic neurons from firing

GABA: type of inhibitory neurotransmitter that blocks or inhibits brain signals, it blocks messages of anxiety, stress etc.

GABA:

• major inhibitory neurotransmitter in the CNS

• GABA makes postsynaptic neuron less likely to fire (acts as a brake)

• it’s role is to maintain neurotransmission at an optimal or the ‘best possible’ level

• low levels of GABA is associated with anxiety, phobias and seizures (the NS can’t calm itself down)

• associated with long term depression as GABA will inhibit pathways that are no longer needed

Glutamate and GABA work in conjunction to balance the Nervous System

• glutamate excites and is our accelator (GO)

• GABA calms and is our brake (STOP)

• too much or too little of each can have harmful consequences = crash

NEUROMODULATORS:

• work with neurotransmitters to enhance inhibitory and excitatory effects, creating widespread impacts

• they enhance signal transmission, are effective on groups of neurons and their effects can last longer

• they are chemical messengers and are released in the same way as neurotransmitters

• a subclass of neurotransmitters that work across wider region of brain rather than across a single synapse

• the improve the effectiveness of the message transmission by increasing or decreasing the responsiveness of neurons to certain neurotransmitters

• they can control the amount of neurotransmitters released or increase the number of receptor sites on dendrites to regulate neural activity

• neurotransmitters = direct text message, work across a single synapse, direct, targeted quick

• neuromodulators= group email, wider impact, take longer to take to take effect but last longer, more diffusive effect

• they are released into multiple synapses and the bloodstream

Dopamine:

• neuromodulator involved in drive, motivation and movement

• it has been associated with addictive behaviours like gambling as humans chase that “dopamine hit”

• it is also associated with to-do lists and explains why they are such powerful motivators

• when you look at your phone, dopamine levels increase, this makes you feel happier, driving you to continue, if you go off of your phone dopamine will decrease, so you go on your phone again to increase levels

• it can be both excitatory or inhibitory and can also act as a neuromodulator, associated with pleasure and wellbeing

*TRIPLE M= mood movement and motivation

• dopamine improves the mood by reinforcing the activity of the reward pathway

• when you experience something rewarding, the brain releases dopamine into these brain areas which results in feelings of pleasure and euphoria

• leads to people wanting to repeat the behaviour that gave them the dopamine hit

• behaviours that may be perceived to be rewarding due to the release of dopamine includes eating, gambling, drugs

Serotonin:

• an inhibitory neurotransmitter and neuromodulator, so it does not stimulate brain activity

• neuromodulator that is known as a mood stabiliser that plan important role in wellbeing and happiness

• irregular serotonin levels have been linked to mental health issues like depression and anxiety

• serotonin also plays an important role in digestion, metabolism and stress

• its effects can help counterbalance excessive excitatory effects of other neurotransmitters as GABA does with glutamate

• serotonin is widely described as a mood stabiliser with low levels of it associated with mood disorders such as depression

• 90% of your serotonin is produced in the gut, so it plays a large role in the communication between the gut and brain (brain-gut axis)

• serotonin regulates the daily sleep-wake cycle including when we fall asleep, how much we sleep, when we wake and feeling awake throughout the day

• there is a relationship between serotonin and melatonin

Neurotransmitter and Neuromodulators Together

• they both work together to enhance our functioning

• however they can also exacerbate negative impacts

• for example Parkinson’s disease involves the degeneration of the nervous system, causing tremors, the disease is associated with low levels of dopamine (causing problems with movement) and with high levels of GABA (this influences dopamine and blocks important messages)

NEUROTRANSMITTERS:

• single or few synapses

• faster, localised effect

• targets an adjacent post synaptic neuron

• released into the synapse

• e.g glutamate and GABA

NEUROMODULATORS:

• multiple synapses

• slow, widespread effect

• targets a wide area/ group of neurons

• sometimes released into the synapse, sometimes released outside the synapse into neural tissue

• changes the effectiveness of neural transmission

• e.g dopamine and serotonin