neurotransmission

Question 1

what structures compose the central nervous system?

Answer 1

• Brain
• Spinal cord

Question 2

what structures make up the peripheral nervous system?

Answer 2

sensory neurons - afferent nerves

motor neurons - efferent nerves

Question 3

what is the difference between the somatosensory system and the autonomic system?

Answer 3

somatosensory = neurons that recieve sensory information and control movement of skeletal muscle

autonomic system = neurons that receive sensory information and regulate movement of smooth muscle and cardiac muscle as well as glandular secretion - sympathetic and parasympathetic

Question 4

what do the terms afferent and effferent mean?

Answer 4

afferent = transmit information towards the CNS

efferent = transmit information away from the CNS

Question 5

what are the two kinds of postsynaptic potentials?

Answer 5

• excitatory post-synaptic potential - small depolarizaiton
• inhibitory post-synaptic potential -hyperpolarization (holding of resting membrane potential) by opening of K+ channel and the neurotransmitter binding opening Cl- channels

Question 6

what is the “threshold voltage”?

Answer 6

-55 mV = when a certain spot on the neuron reaches this value, an action potential is generated

Question 7

describe the process of an action potential

Answer 7

• depolarization pushes membrane potential across the action potential threshold
• reduced voltage opens several voltage-gated Na+ channels in that portion of the plasma membrane - Na+ influx leads to further depolarization
• voltage gated K+ channels open (and Na+ channels close)- K+ efflux repolarises plasma membrane
• voltage- gated K+ channels close (leaving plasma membrane hyperpolarized)
• resting membrane potential restored by Na+/K+ pump

Question 8

describe the ‘action potential graph’ from the perspective of the voltage gated sodium channels/potassium channels

Answer 8

Question 9

what is the refractory period?

Answer 9

period when a further stimulus applied to a neuron or muscle fiber will not trigger another action potential - membrane is depolarized and the neuron is refractory -

Question 10

can you get smaller / larger aciton potentials?

Answer 10

no they are all or none

• strong stimuli produce action potentials of the same amplitude as weak stimuli - the strength of the stimulus is encoded in the frequency of the action potentials that it generates

Question 11

describe the steps of synaptic transmision

Answer 11

1. action potential reaches and depolarizes axon terminal
2. depolarisation actiates voltage-gated presynaptic Ca2+ channels (Ntype, Ptype)
3. localised Ca2+ entry triggers exocytosis of neurotransmitters (NTs) from synaptic vesicles into the synaptic cleft, through the activation of Ca2+ sensitive fusion proteins
4. NTs diffuse into the synaptic cleft
5. NTs bind and activate receptors on the post-synaptic membrane
6. inactivation of neurotransmitters

Question 12

how does an electrical synapse travel between two cells?

Answer 12

two cells are connected by gap junctions - formation of channels between the cytosolic compartments of the two cells - permit communication between cells by the direct propagation of ionic current from one cell to the other

Question 13

what sort of transmission is between neural cells?

Answer 13

chemical transmission - unlike the electrical transmission in muscle cells

the change in voltage cuases the calcium channels to open- this calcium causes the vesicle terminals to bind to the cleft - they release the neurotransmitters

Question 14

what types of neurotransmitters are inhibitory?

Answer 14

GABA and glycine

Question 15

what kind of neurotransmitters are excitatory?

Answer 15

acetylcholine and glutamate

Question 16

what neurotransmitters can be both excitatory and inhibitory?

Answer 16

serotonin, dopamine, noradrenaline

Question 17

what occurs at an excitatory synapse?

Answer 17

the NT at an excitatory synapse depolarises the post-synaptic membrane potential - they continue the depolarization across the post-synaptic cleft so it excites the next channel

Question 18

what occurs at the inhibitory synapse?

Answer 18

the NT an inhibitory synpase hyperpolarizes the post-synaptic membrane potential

ex) the binding of GABA A to GABA A receptors on the post-synaptic membrane activates ligand-gated chloride channels - the Cl- influx hyperpolarizes the post-synaptic membrane potential

Question 19

what are ionotropic receptors?

Answer 19

they are ligand gated ion channels - NT binding increases permeability to ions

Fast synaptic transmission

Question 20

what are metabotropic receptors?

Answer 20

• G protein couple receptors
• slower synaptic transmission
• NT binding triggers activation of G protien that either directly modifies function of ion channels or triggers the production of a chemical second messenger that modifies ion channels
• mediates short term as well as long term effects (gene expression)

Question 21

local anaesthetics like lidocaine work how?

Answer 21

by blocking the voltage gated Na+ channels

Question 22

where are neurotransmitters synthesized?

Answer 22

they are synthesized locally within the axon terminal

Question 23

how are neurotransmitters inactivated?

Answer 23

• inactivated/degraded by enzymes in the synaptic cleft or
• taken up by presynaptic neuron via transporter protein -repackaged and recycled s

Question 24

how do Selective serotonin reuptake inhibitors work?

Answer 24

they give serotonin a longer time to sit in the synaptic cleft - allowing more time to be taken up by the receptors

Question 25

myelin is what? what is it made of?

Answer 25

it is a fatty sheat around axons formed by

• schwann cells in PNS
• Oligodendrocytes in CNS

Question 26

what are the “ nodes of ranvier”?

Answer 26

they are the gaps between myelinated regions of the axon - they are dense with voltage gated Na+ channels- action potential appears to “jump’ from node to node

Question 27

what determines nerve conduction velocity?

Answer 27

diameter of the axon - larger axons are faster than smaller axons

myelination - myelinated axons conduct faster than unmyelinated axons

Question 28

what is “saltatory conduction”

Answer 28

the term for the action potential jumping from one unmyelinated node to the next node

Question 29

What factors interfere with nerve conduction?

Answer 29

• local anaesthetics
• demyelination
• cold - cold temperatures slow action potentials
• ischaemia

Question 30

What is Multiple Sclerosis?

Answer 30

autoimmune disease - attack myelin sheat by immune cells (CD4) and antibodies -

symptoms = fatigue, vision problems, tingling and numbness, muscle weakness, impaired balance

-corticosteroids or interferon beta used to reduce inflammation/immune respone

Question 31

what is the compound action potential (CAP) ?

Answer 31

CAP is the sum of individual “all or none” action potentials arising more or less simultaneously in a large number of individual axons in a stimulated large “compound nerve”

• most nerves, axons can vary in diameter, degree of myelination, excitability threshold and conduction spee