Nervous - week 3

Question 1

what is a synapse

Answer 1

how neurons communicate

a site where neurons can exchange information

2 types: electrical and chemical synapse

Question 2

electrical synapse

Answer 2

site of cell-to-cell communication where neurons directly exchange ions through channels that span the 2 communicating cells (like a bridge)
- exchange of ions can lead to an AP developing in the next cell

Question 3

chemical synapse

Answer 3

cell-to cell communication where excitable cells release chemicals called neurotransmitters to communicate

3 main components:

1. pre-synaptic neuron: transmits the info towards the synaptic cleft via its axon terminals, to the dendrites of the next neuron
2. synaptic cleft: small space between the axon terminals of one neuron and dendrites of another
3. post-synaptic neuron: transmits info away form the synaptic cleft, from its dendrites towards its own soma

Question 4

neurotransmitters

Answer 4

chemicals that neurons release to communicate with one another
- chemicals bind to ion channels or receptors on the next cell, leading to ion influx into the cell

Question 5

what is excitation-contraction coupling

Question 6

graded potentials

Answer 6

changes in membrane potential that vary according to the size of the stimulus

Question 7

EPSPs

Answer 7

sub threshold depolarizations

properties:
- don not produce AP
- localized - depolarization is confined to one area of the plasma membrane
- magnitude of depolarization = magnitude of stimulus (meaning they are graded
- can be summed to produce larger depolarizations
- therefore multiple EPSPs required to create an AP
- produced by neurotransmitters that open Na+ and K+ channels

Question 8

IPSPs - inhibitory post-synaptic potentials

Answer 8

hyperpolarizing potentials

properties:
- localized - hyperpolarization is confined to one area of the plasma membrane
- magnitude of hyperpolarization = magnitude of stimulus meaning they are graded
- can be summed up like EPSPs
- bring neuron further away for AP
- produced by neurotransmitters that open K+ (moving it out of the cell) or Cl- channels (moving it into the cell)

Question 9

axon hillock

Answer 9

the “trigger zone”
- both IPSPs and EPSPs decay as they move towards the axon hillock
- IPSPs and EPSPs sum up at the axon hillock

AP will only be elicited only if the depolarization at the axon hillock is large enough to reach threshold

Question 10

2 ways to strengthen EPSPs

Answer 10

1. temporal summation: additive effect produced by many EPSPs that have been generated at the same synapse by series of high frequency AP on the presynaptic neuron

one neuron fires repeatedly

2. summation - additive effect
   - produced by many EPSPs that have been generated at many different synapses on the same post-synaptic neuron at the same time

many neurons fire at the same time to produce EPSPs in post synaptic neuron

Question 11

excitatory neurotransmitter

Answer 11

leads to depolarization of the membrane in form of EPSPs
- if depolarization strong enough, may fire and AP

Question 12

inhibitory neurotransmitter

Answer 12

leads to hyperpolarization of the post synaptic membrane in the form of IPSPs

• makes it harder to generate AP

Question 13

nicotinic receptors

Answer 13

type of ACh receptor

respond to acetylcholine at certain synapse
when ACh binds to them, they open ion channels –>Na+ flows in –> causes depolarization

found at NMJ

it is a ligand-gated ion channel
- ACh (ligand) binds → channel opens → ions flow (mainly Na⁺ in, K⁺ out)

easy way to remember: Nicotinic = fast + muscle and autonomic

they span the plasma membrane of the post synaptic cell

Question 14

muscarinic receptors

Answer 14

not ion channels themselves but when they bind to ACh activate a series of biochem rxns on the cytoplasmic side cell
will further activate and open ion channels in the post synaptic cell membrane

known as slow transmission
Muscarinic = Slow + Smooth muscle & organs (parasympathetic)
(Think: “M for Muscles that Move slowly and Manage organ stuff”)\

found in organs

Question 15

end plate current

Answer 15

generates end plate potentials could lead to AP causing contraction of muscles

Question 16

myasthenia Gravis

Answer 16

chronic autoimmune neuromuscular disease that is characterized by weakness in the skeletal muscle

• weakness develops because body elicits antibodies against the nicotinic receptors and blocks the binding of ACh and degrading of nicotinic receptors

administering acetylcholinesterase blockers to delay symptoms and progression pf disease

Question 17

what do acetylcholinesterase blockers for myasthenia Gravis

Answer 17

degradation of ACh is slowed down therefore ACh is present in the synaptic cleft for longer
this increases chances that it will bind to nicotinic receptors in muscle cells reducing weakness