neurotransmitters

what is the nervous system?

it’s a system composed of neurons (nervous cells)

what are the 3 parts of a neuron?

the body (soma), dendrites, and the axon

• dendrites & axons are filaments that extrude from soma - generally multiple dendrites but always a single axon

whats the function of the dendrite, soma & axon?

dendrite & soma - receive signals from other neurons

axon - transmit signals further

what forms a synapse?

a synapse is formed when the axon of one neuron approaches the dendrite or soma of another neuron

SO - a synapse/synaptic gap is a structure that connects 2 neurons

• can also be thought of as the gap between neurons

is the nature of information transmission in the nervous system, entirely chemical?

no, it’s partly chemical & partly electrical

what happens if a neuron exceeds its threshold of excitation?

if a neuron exceeds its threshold of excitation that’s received from other neurons, the neuron “fires” - it’ll create a brief pulse called action potential, which’ll travel along the axon to other neurons, passing that excitation further

is action potential all or nothing?

yes, there’s no such thing as “firing strongly” or “firing weakly”

when the pulse reaches the end of the axon, it is at the synaptic gap where the mechanism of transmission becomes chemical

whats a neurotransmitter

a chemical messenger that’s stored in axon & released into synaptic gap & transmits info from one neuron to the other

• they’re constantly synthesized in the neuron & moved to axon terminal to be stored there

what happens when the action potential reaches the end of the axon?

when the action potential reaches the end of the axon, a neurotransmitter is released from the axon terminal into synaptic gap, and goes to next neuron

what can happen to the neurotransmitter when it’s available in the synaptic gap?

its available for a short time period

during this time, it can be destroyed (metabolized), pulled back into the pre-synaptic axon terminal through reuptake, or reach the post-synaptic membrane & bind to a receptor on its surface

what happens if there’s lots of neurotransmitters in the synaptic gap?

their effects will be amplified

what happens if the neurotransmitter binds to a receptor in the post-synaptic membrane?

if it does this, the process will alter membrane potential & will contribute to activating an electric pulse in post-synaptic neuron

• chemical mechanism becomes electrical again

what is the presynaptic neuron

the neuron where signal is initiated

whats the postsynaptic neuron

the neuron that receives the signal

what are excitatory neurotransmitters (1/2 groups of neurotransmitters)

allows the impulse to cross the synapse

excite or stimulate the postsynaptic neuron & increase the likelihood of it firing an action potential

what are inhibitory neurotransmitters (2/2 groups of neurotransmitters)

stop impulse & prevent it from crossing synapse

they also reduce or prevent the likelihood that the post-synaptic neuron will reach action potential & fire a neuron

are always in a state of balance

what happens if excitatory or inhibitory neurotransmitters exceed their optimal ranges in the brain, and are there neurotransmitters that’re both excitatory & inhibitory?

this can cause a behavioural malfunction (like a mental disorder)

and yes, neurotransmitters, like serotonin, are both excitatory & inhibitory, depending on the neural network which they’re interacting with

what are agonists (1/2 of ‘things’ that affect neurotransmitters)

chemicals that enhance the action or effect of neurotransmitters

they do this by binding to receptor site of post-synaptic neuron

what are antagonists (2/2 of ‘things’ that affect neurotransmitters)

counteract a neurotransmission & prevent a signal from being passed further

they do this by blocking receptor sites on post-synaptic neuron