Neurotransmitters

  1. Cause muscles to contract or relax

  2. Cause glands to secrete products ( hormones)

  3. Activate neurons rto send nerve impulses

  4. Inhibit neurons from sending impulses

Synapses

  • Neurotransmitters are released from the axon terminal into the space between the axon terminal and the dendrite of the next cell

  • Neurotransmitters affects the activity of the next neuron- communication is called sypnatic transmition

  • Message is initiated  electrically but conveyed chemically

  • The other part of the synapse is the dendrite of the “next cell”

  • Between axon and dendrite is the synaptic cleft

    • fluid-filled space between the terminal button and the membrane of the dendrite

    • axon and dendrite do not touch each other

  • Dendrites receive the signal via receptors on its membrane – neurotransmitter receptors

  • The reactions here either excite or inhibit the post-synaptic neuron

There are two kinds of synapses

  • Excitatory synapses – excite the post-synaptic neuron to increase the rate of firing

  • Inhibitory synapses – do the opposite – when they are activated, they lower the rate at which the connecting neurons fire

  • Important to note that neurons join with many other neurons and connect with other neurons at synapses

  • This is how we can have such a wide range of sensations, perceptions and behaviours

  • Neurotransmitters are produced in the terminal button and contained within synaptic vesicles

  • axon terminal neurotransmitters synaptic vesicles synaptic gap (synaptic cleft) dendrite of next neuron

  • When the action potential fires, several synaptic vesicles fuse with the inside of the terminal button’s membrane

  • Then these burst open

  • Contents released into the synaptic cleft

  • Presynaptic vesicle Neurotransmitter reuptake Presynaptic cell Y Neurotransmitter Receptor site Postsynaptic cell

  • The released neurotransmitters then bind with the receptors, and activate them

  • Recall ligand-gated channels
    open in response to specific
    Neurotransmitters

  • Nerve impulse O o Synaptic cleft o Target cell plasma membrane Ligand- gated channel (closed) o 80 o o o O o // Ligand- gated channel (open) Neurotransmitter Synaptic vesicle

    • Once the receptors are activated, they produce either excitatory or inhibitory effects

      • do this by opening ion channels

      • excitatory synapses cause sodium ions to enter

      • inhibitory synapses cause potassium ions to leave

 

Neurotransmitters covered today

  • Glutamate

  • GABA

  • Acetylcholine

  • Monoamines

 

Over 100 types

  • Glutamate (over 90% of synapses)

  • GABA- next most comon Gamma-Amino Butryic Acid

  • Others are less common but have large roles in behaviour

  • Perform very specific functions (or else they wouldn’t be needed) – more like moderating effects rather than information transmitting

    • e.g. serotonin, dopamine, epinephrine (adrenaline) etc

 

  • Glutamate is the brain’s principle excitatory neurotransmitter

  • GABA is the brain’s principal inhibitory neurotransmitter

 

  • Work together to control many processes

 

Almost every nueron in the brain has receptors for both of these

GLlJTAMATE

 

  • All sensory organs (including skin) transmit info to the brain using glutamate

 

  • Important in the developing brain, facilitating learning / memory

 

 

GABA

 

  • drugs causing relaxation and sedation increase receptors’ sensitivity to GABA (barbiturates)

 

  • alcohol does this too - both are addictive

 

  • how anti-anxiety meds work

 

Other neurotansmitters

  • Activate or inhibit entire circuits

  • Again, they modulate rather than transmit info

  • What kind of circuits?

    • Learning/memory

    • wakefulness/vigilance

    • suppressing impulsive behaviours

    • suppressing (or enhancing) anxiety

  • Because certain drugs selectively affect the secretion of certain neurotransmitters, they have specific effects on behaviour

 

ACETYLCHOLINE

 

  • Secreted by motor neurons – responsible for muscle contraction/movement

 

  • Also works on systems – pathways or circuits of neurons

 

  • REM sleep (eye movement – dreaming)

 

  • facilitating learning (especially perceptual learning)

Controlling the hippocampus (associated with memory

 

Monoamies

 

  • Classification that includes:

 

  • Dopamine

 

  • Norepinephrine (adrenaline)

 

  • Serotonin

 

  • Produced by only a few systems/circuits – but with an enormous number of branching axons

 

  • Thus distributed throughout many brain regions

 

DOPAMINE

 

  • Associated with:

    • Movement

    • Attention

    • Learning

    • Reward

 

  • Dopamine production is increased by nicotine (increased activity of terminal buttons)

  • Dopamine reuptake inhibited by amphetamines and cocaine

 

SEROTONIN

 

  • Associated with:

    • Mood regulation

    • Regulation of Eating, Sleeping, Wakefulness

    • Regulation of Pain

 

  • Deficiencies associated with alcoholism, antisocial behaviour

 

  • LSD stimulates serotonin receptors

 

  • Affected (naturally) by exercise and light exposure

 

Monoamines & Drugs

 

  • Many drugs work on monoamines

 

  • Including common types of anti-depressants

 

  • MAOIs – Mono Amine Oxidase Inhibitors

 

  • Drugs inhibit the breakdown of monoamines, and thus makes them more available

 

  • SSRIs – Selective Serotonin Reuptake Inhibitors

 

  • And others similar to SSRI (SNRI, NRI – norepinephrine)

  • 9 Serotonin is released post-synaptic nerve ending Pre-synaptic nerve ending 5-HT SSRI blocking reabsorption of Serotonin Synapse • • Receptor sites