lecture 9

Question 1

a synapse is

Answer 1

the region where a neuron meets its target cell

Question 2

electrical synapse

Answer 2

• involve the flow of charged ions from one neuron or cell to its neighbour (through gap junctions)

or

• a gap junction where current flows directly from one cell to another

Question 3

chemical synapse

Answer 3

electrical signals (AP) in the presynaptic cell are converted momentarily to chemical signals (neurotransmitter) and then once we get to the postsynaptic cell it’s converted back to an electrical signal (graded potential —-> AP)

Question 4

steps involved in chemical neurotransmission at the synapse

Answer 4

1. AP arrives at axon terminal and causes a wave of depolarization (Na rushing in)
2. the depolarization causes voltage gated Ca2+ channels to open and calcium rushes in
3. entry of calcium triggers exocytosis of neurotransmitters and then they are released into the synaptic cleft and diffuse across and bind to neurotransmitter gated channel in the postsynaptic cell
4. cell response: if sodium channel= depolarization and EPSP, if Cl channel=IPSP

Question 5

termination of stimulus

Answer 5

• neurotransmitters are returned back to the axon terminal for reuse or transported into glial cells
• enzymes can inactivate neurotransmitters (acetylcholinesterase)
• neurotransmitters can diffuse out of synaptic cleft

Question 6

what criteria does a neurotransmitter need to meet

Answer 6

• chemical must be found in the presynaptic neuron
• chemical must be released in response to depolarization at the axon terminal
• chemical must ac on specific receptors on the postsynaptic neuron to an cause an effect
• after release, the chemical signal must be terminated
• application of chemical directly to the postsynaptic neuron should have the same affect as it did when it was released by a neuron

Question 7

ionotropic

Answer 7

fast, mediated by receptor channels

Question 8

metabotropic

Answer 8

slow, mediated by GPCRs

Question 9

integration of information

Answer 9

Divergent pathway: one presynaptic neuron branches to pass in for to many downstream neurons
Convergent pathway: many presynaptic neurons send input to smaller number of postsynaptic neurons

Question 10

Name and describe a synaptic disease

Answer 10

myasthenia gravis:
- attacks neuromuscular junction between somatic motor neurons and skeletal muscle
- symptoms include weakness and fatigue
- caused by autoimmune-mediated decrease in acetylcholine receptors
- treated with anti-cholinesterase to increase the lifetime of acetylcholine in the synapse