Download excitatory neurotransmitter

Unit 3 Psychology
Area of Study 1: How does the nervous system enable
psychological functioning?
Key knowledge: Dot point 4
“The role of neurotransmitters in the transmission of neural information between neurons (lockand-key process) to produce excitatory (as with glutamate) or inhibitory effects (as with GABA).”
Neurotransmitters
When a neural message has been received by the dendrites, it travels along the soma and down the
axon to the axon terminals. At the axon terminals, the message is converted to its chemical form to
cross the synapse. The chemical form of a neural message is known as a neurotransmitter.
When the neurotransmitters are released from the axon terminals, they cross the synapse to the
next neuron in the neural pathway. The post-synaptic dendrites have receptor sites that are
designed for a specific neurotransmitter. When that neurotransmitter reaches the receptor site it is
absorbed and the message can be converted back to an electrical impulse to continue along the
neuron.
Any neurotransmitters that are not absorbed at receptor sites in the post-synaptic dendrites are reabsorbed (a process known as “re-uptake”) by the pre-synaptic axon terminals.
There are many different types of neurotransmitters, each with a specific role to play in the body.
Some neurotransmitters are excitatory (such as glutamate) and some are inhibitory (such as
GABA).
Excitatory neurotransmitters: chemical messages that stimulate the next neuron to fire.
Inhibitory neurotransmitters: chemical messages that make the next neuron less likely to fire.
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Glutamate – excitatory neurotransmitter
Glutamate is a neurotransmitter in the CNS. It is involved in a range of activities in the brain
including: learning, memory, perception, thinking and movement. When glutamate is released into
the synapse it is absorbed by NMDA receptor sites on the post-synaptic dendrites.
Glutamate is excitatory, so it stimulates the neurons in a neural pathway to fire. This is very
important in memory and learning. High levels of glutamate are found within the hippocampus in
the brain. The hippocampus is where the majority of long term memories are consolidated in
preparation for storage in the brain. Glutamate stimulates the neurons to fire and create the
‘memory trace’. When the memories are retrieved, glutamate stimulates the neurons in the
memory trace (neural pathway) enabling the information to be brought back to conscious
awareness.
As memory and learning are interconnected, the same applies to learning. When we learn new
information, skills, etc., glutamate stimulates the neurons in the pathway to fire together. This
creates Long Term Potentiation (LTP). LTP is the strengthening of neural connections through use,
i.e.: Practice makes perfect. The more we use neural pathways the faster they respond and stronger
they get.
Caffeine has the ability to stimulate the activity of glutamate within the CNS. Excessive amounts of
glutamate can lead to inappropriate neuronal connections and neurodegenerative diseases such as
Motor Neuron Disease and Huntington’s disease.
Gamma-amino butyric acid (GABA) – inhibitory neurotransmitter
GABA is a neurotransmitter in the CNS. It is involved in slowing neural transmissions within the CNS
and calming the body’s responses. When GABA is released into the synapse it inhibits the firing of
the next neuron in the neural pathway.
GABA has an opposing effect on the body to Glutamate.
One of the main roles of GABA is to assist in the ‘switching off’ of the Sympathetic Nervous System.
The Sympathetic Nervous System activates a person’s fight-or-flight response when a threat or
stressor is present. This prepares the body for action. When the stress or threat has passed, GABA
is released into the synapse and inhibits the firing of the neurons to assist in returning the body to
homeostasis.
Low levels of GABA in the CNS, can lead to excess activity of the neurons which may result in
seizures or anxiety disorders, such as phobia.
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Neurotransmitter
Acetylcholine
Location of Neurons
Motor neurons of PNS;
brainstem; base of forebrain
(hippocampus)
Effects
Excitatory effect at synapse with
voluntary muscle, causing contraction;
role in hippocampus of brain in memory
consolidation
Dopamine
CNS
Mainly inhibitory – involved in voluntary
movements, learning, memory,
emotional arousal and feelings of
pleasure. Deficiencies are linked to
Parkinson’s disease. Inhibits glutamate
release. Excess linked to schizophrenia.
Serotonin
CNS
Mainly inhibitory – involved in sleep,
arousal levels and emotional
experience. Deficiencies linked to
anxiety, mood disorders and insomnia.
Gamma-amino butyric
Interneurons in many CNS
Mainly inhibitory – involved in the
acid (GABA)
sites
experience of a range of emotions; acts
as a hormone to stimulate the
sympathetic NS.
Glutamate
Interneurons in many CNS
Excitatory – communication between
sites; cerebral cortex; spinal
adjacent brain cells. Too little results in
cord
lack of signalling. Excess results in selfdestruction of neurons, death of
adjacent cells.
Inhibitory – blocks the transmission of information from one neuron to another.
Excitatory – assists transmission of information from one neuron to another.
Lock-and-key process
There are many neurotransmitters within the body and each type has its own
distinct shape. The receptor sites that absorb the neurotransmitters are designed
to only receive a specified neurotransmitter. Therefore the receptor sites have a
matching shape to the neurotransmitter.
The neurotransmitter is called a ‘key’ and it fits in the specific receptor site ‘lock’. Only the right shaped
neurotransmitter can unlock the receptor site to be absorbed by the post-synaptic dendrite.
A synapse can have more than one type of neurotransmitter in it at any time and the dendrites also have
receptor sites for more than one type of neurotransmitter. The lock-and-key process ensures that neurons
fire correctly, maintaining the body’s functioning.
*Psych Book – Activity 4
**Student Activity Manual – 1.8
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