synapses

Question 1

where do chemical synapses occur?

Answer 1

between neurons and neurone/muscle cells/gland cells

Question 2

describe the sequence of events at a chemical synapse?

Answer 2

• 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

Question 3

give examples of amino acid derived transmitters

Answer 3

acetylecholine, dopamine, GABA, noradrenaline, seratonin

Question 4

give examples of peptide transmitters

Answer 4

substance P, VIP, enkephalins, endorphins

Question 5

what determines the effect of the transmitter?

Answer 5

type of receptors and 2nd messengers in post-synaptic cell

Question 6

what happens when the transmitter causes depolarisation?

Answer 6

Excitatory post-synaptic potential (EPSP)
Brings MP nearer to firing threshold

Question 7

what happens when the transmitter causes hyperpolarisation?

Answer 7

Inhibitory post-synaptic potential (IPSP)
Takes MP further from firing threshold

Question 8

are postsynaptic potentials big or small?

Answer 8

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

Question 9

what is required for a post-synaptic cell to fire and how does this occur?

Answer 9

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

Question 10

what is required for a post-synaptic cell to fire and how does this occur?

Answer 10

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

Question 11

describe convergence in neuronal connections

Answer 11

each neuron recieves many inputs from other cells

Question 12

describe divergence in neuronal connections

Answer 12

each neuron synapses with many other cells

Question 13

what do convergence and divergence of neurons create?

Answer 13

a complex network of neurons

Question 14

what is the neuromuscular junction?

Answer 14

• 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

Question 15

what is the transmitter at the neuromuscular junction?

Answer 15

acetylecholine

Question 16

describe the sequence of events at the neuro muscular junction

Answer 16

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

Question 17

what can affect synaptic activity?

Answer 17

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

Question 18

how does botox work?

Answer 18

Botox (botulinum toxin) is used to paralyse facial muscles to remove wrinkles- it prevents the release of the transmitter from the motor nerve

Question 19

how does botox work?

Answer 19

Botox (botulinum toxin) is used to paralyse facial muscles to remove wrinkles- it prevents the release of the transmitter from the motor nerve