Synapses

Question 1

What are the two types of signals that can cross a synapse?

Answer 1

• electrical

- chemical

Question 2

How do electrical signals travel across synapses?

Answer 2

• Involves two neurons with channels between them formed by connexons
• Change in membrane potential transmitted to post-synaptic cells as a post-synaptic potential (PSP)
• Rate defined by the number of channels
• Bidirectional

Question 3

When are electrical signals commonly used?

Answer 3

Found where high speed is needed e.g escpae routes or when a group of cells must produce synchronous activity

Question 4

Describe the structure of chemical synapses

Answer 4

• Presynaptic terminal contains swellings known as boutons
• High mitochondrial density
• Vesicles containing neurotransmitter found in the presynaptic terminal
• Post synaptic density which is associated with post-synaptic memory

Question 5

Describe the process by which neurotransmitter is released

Answer 5

• Depolarisation opens voltage dependent Ca2+ channels
• Ca2+ inflow opens the fusion pore linking the inside and the outside of the cell
  Note: Ca2+ inflow has little effect on the membrane potential

Question 6

Describe two types of non-spiking synapses

Answer 6

1. Sub-threshold depolarisation can cause Ca2+ release

2. Neurotransmitter released at normal resting state

Question 7

What does the effect of a neurotransmitter depend on?

Answer 7

Its receptor

Question 8

What are the two types of post-synaptic potential?

Answer 8

EPSP - exitatory

IPSP - inhibitory

Question 9

How prolonged is the effect of neurotransmitter binding?

Answer 9

Short-lived. Binding is reversible, or is quickly broken down by enzymes and reuptaken

Question 10

Name two typical neurotransmitters involved in an EPSP

Answer 10

Ach, glutamate

Question 11

What does the number of ion channels open on the post synaptic membrane depend on?

Answer 11

Number of receptors filled with neurotransmitter/ammount released

Question 12

How can PSPs summate?

Answer 12

• As they have no refractory period
• However will decrement with distance, if does not cause spike then response dies away with distance
• Can integrate IPSPs with EPSPs for decision making

Question 13

Name two inhibitory neurotransmitters and describe their effect on the PSP

Answer 13

• GABA and glycine

- Cause hyperpolarisation

Question 14

What are the characteristics of ionotropic receptors?

Answer 14

• Ligand gated
• Fast acting
• Transmitter binds to receptor causing a main electrical effect

Question 15

Describe the process by which metabotropic receptors enact a change in the post-synaptic membrane

Answer 15

• Neurotransmitter binds to receptor which interacts with G protein converting GTP to GDP
• This interacts with an enzyme to form a complex and further activate 2nd messenger molecules
• 2nd messengers open ion channels and also go on to influence functions such as metabolism and transcription
• Neuromodulation can control neurotransmitter release

Question 16

Give the 6 major clases of neurotransmitter and examples

Answer 16

amino acids - glutamate, GABA, glycine
Gasotransmitters - nitric oxide (NO), carbon monoxide (CO)
Monoamines - Dopamine, serotonin
Trace amines - phenethylamine
Peptides - substance P, opioid peptides
Purines - ATP
note: Ach belongs in none of these groups

Question 17

What type of receptors do amino acids, Ach, monoamines and peptides typically use?

Answer 17

amino acids - ionotropic
ach - both
mono-amines and peptides - are larger and so usually are metabotropic

Question 18

How does Nitric Oxide work as a neurotransmitter?

Answer 18

• Diffuses through membranes (non-vesicular) to all cells in the nearby area activating a variety of second messengers
• Has some non-neural functions such as vasodilation
• Synthesized in neurons containing Ca-dependent nitric oxide synthase