synapses Flashcards
where do chemical synapses occur?
between neurons and neurone/muscle cells/gland cells
describe the sequence of events at a chemical synapse?
- AP depolarises presynaptic ending
- Influx of Ca 2+ into presynaptic ending
- Vesicles migrate towards plasma membrane
- Release of transmitter into cleft (exocytosis)
- Transmitter (Tx) diffuses in cleft
- Tx binds to receptors on post-synaptic cell
- changes in post-synaptic cell
- Inactivation of transmitter
- Reuptake into presynaptic cell
- Enzymic destruction
give examples of amino acid derived transmitters
acetylecholine, dopamine, GABA, noradrenaline, seratonin
give examples of peptide transmitters
substance P, VIP, enkephalins, endorphins
what determines the effect of the transmitter?
type of receptors and 2nd messengers in post-synaptic cell
what happens when the transmitter causes depolarisation?
Excitatory post-synaptic potential (EPSP)
Brings MP nearer to firing threshold
what happens when the transmitter causes hyperpolarisation?
Inhibitory post-synaptic potential (IPSP)
Takes MP further from firing threshold
are postsynaptic potentials big or small?
Postsynaptic potentials are very small
Single ones have little effect on the MP of the post-synaptic cell
Necessary for EPSPs to add together (summate)
This can happen in several ways
EPSPs and IPSPs can also summate, but they will tend to cancel each other
what is required for a post-synaptic cell to fire and how does this occur?
A post-synaptic cell will ‘fire’ only if it receives sufficient excitation to drive the MP beyond threshold
This occurs when it receives many excitatory inputs (and few inhibitory inputs) within a short time period
what is required for a post-synaptic cell to fire and how does this occur?
A post-synaptic cell will ‘fire’ only if it receives sufficient excitation to drive the MP beyond threshold
This occurs when it receives many excitatory inputs (and few inhibitory inputs) within a short time period
describe convergence in neuronal connections
each neuron recieves many inputs from other cells
describe divergence in neuronal connections
each neuron synapses with many other cells
what do convergence and divergence of neurons create?
a complex network of neurons
what is the neuromuscular junction?
- Synapse between a motor nerve and a muscle fibre
- Also referred to as ‘motor end plate’
- Area of ‘contact’ is greater than in a nerve-nerve synapse
- 1 AP in the nerve leads to muscle contraction
- The transmitter is acetylcholine
- It is broken down by an enzyme: acetyl cholinesterase
what is the transmitter at the neuromuscular junction?
acetylecholine
describe the sequence of events at the neuro muscular junction
AP depolarises motor nerve ending
Influx of Ca 2+ into nerve ending
Vesicles migrate towards plasma membrane
Release of ACh into cleft (exocytosis)
ACh diffuses in cleft
ACh binds to receptors on post-synaptic cell
Action potential in muscle cell contraction
Transmitter (ACh) broken down by acetyl cholinesterase
Choline & acetate taken up by neuron
what can affect synaptic activity?
drugs- they can enhance/suppress the synapse by affecting:
- Synthesis, storage of Tx
- Release of Tx
- Action of Tx on receptor
- Second messenger system
- Inactivation of Tx
how does botox work?
Botox (botulinum toxin) is used to paralyse facial muscles to remove wrinkles- it prevents the release of the transmitter from the motor nerve
how does botox work?
Botox (botulinum toxin) is used to paralyse facial muscles to remove wrinkles- it prevents the release of the transmitter from the motor nerve
