Introduction to CNS part 2

Question 1

What is the nature of the neuronal signal and how is it caused

Answer 1

Electrical
Caused by negative electrons: lights or motors
Carried by charged ions

Question 2

Give examples of the bodies natural anion and cations

Answer 2

1. Postive cations: Na+, Ca2+, K+

2. Negative anions: Cl-, protein anions

Question 3

How do ions cross the membrane

Answer 3

1. Separated by extracellular and intracellular environments
2. Passage of ions through channels is a passive process, ion species will flow in direction determined by concentration gradient

Question 4

What is the resting membrane potential?

Answer 4

-70mV

Question 5

What is the post synoptic potential

Answer 5

1. Dendrites receiving signals from other neurons that open ion channels in the dendrites to produce graded responses
2. Grading depends on volume of neurotransmitter and receptor present
3. Leads to inhibitory or excitatory response

Question 6

What is an inhibitory response

Answer 6

IPSPs: more positive

Due to influx of negative ions (Cl-)

Makes inside of cells even more negative: hyper polarisation

Dependent on this whether cell will fire action potential or not

Question 7

What is an excitatory response

Answer 7

EPSPs: more negative

due to influx of Na+ and Ca2+ ions

Makes inside of cells less negative: depolarises

Dependent on this whether cell will fire action potential or not

Question 8

What is spatial summation

Answer 8

Dependent on IPSPs and EPSPs where they recieve thousands of inputs from other neurons

This determines whether AP fires or not

Occurs at axon initial segment

Question 9

How does an action potential then occur

Answer 9

1. After temporal and spatial summation, there is a large enough depolarisation at Axon Hillock: AP fires
2. This propagates from dendrite to axon terminals where presynapes are located
3. Results in neurotransmitter release from presynaptic into the synaptic cleft

Question 10

Describe the neurotransmitter release (7)

Answer 10

1. Neurotransmitter molecules are synthesised from precursors under enzyme influence
2. Neurotransmitter molecules are stored in vesicles
3. Neurotransmitter molecules that are leaked are destroyed by enzymes
4. AP: vesicles fuse with presynaptic membrane and release their neurotransmitter molecules into synapse
5. Release neurotransmitter molecules bind with auto receptors and inhibit subsequent neurotransmitter release
6. Released neurotransmitter molecules bind to post synaptic receptors
7. Release neurotransmitter molecules are deactivated either by reuptake or enzymatic degradation

Question 11

Describe where small neurotransmitters are synthesised and transported

Answer 11

Synthesised in cytoplasm of bouton

Transported across vesicle membrane

Stored next to membrane

Question 12

Describe where large neurotransmitters are synthesised and transported

Answer 12

Synthesised in cytoplasm of cell body

Packaged by cell body’s golgi complex

Transported by microtubules to buttons

Question 13

Give an example of an Ionotropic and metabotropic receptors and describe them

Answer 13

Ionotropic: GABA
Fast
IPSP and EPSPs
Ligand gated ion channel

Metabotropic: Slower
Receptor activates intracellular signals
May active or close ion channels
May stimulate or decrease gene expression

Question 14

Give examples of small neurotransmitters

Answer 14

Amino acids: glutamate
Monoamines: glycerine
Soluble gases: Nitric oxide
Acetylcholine

Question 15

Give examples of large neurotransmitters

Answer 15

Neuropeptides: endorphins, oxytocin, substance P and neuropeptide Y

Question 16

Give examples of amino acid neurotransmitters and describe what it is

Answer 16

1. Fast acting
2. Example: glutamate, aspartate, glucose and GABA
3. Glutamate: most common excitatory transmitter
4. GABA: most common inhibitory transmitter

Question 17

Give examples of neurotransmitter mono amines and describe what it is

Answer 17

1. Synthesised from single AA
2. Neurons mostly present in brain stem
3. Diffuse effects
4. Dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline), Serotonin (5-HT)

Question 18

What are the common agonists for a glutamate receptor

Answer 18

AMPA
NMDA
Kainite

Question 19

Describe the GABAa receptor, what is it, how does it work, examples of drugs used on it

Answer 19

Ligand gated ion channel

GABA is released from pre synapse and binds to the orthosteric binding site on GABAa receptor

Other drugs acting at allosteric sites or within pores can modulate GABA actions

GABA binding causes opening of conducting pore: allows Cl- to pass

Inhibitory as Cl- flows into cell causing hyper polarisation

Examples drugs on it:
Ethanol, Diazepam, can be used to modulate site to the point it will open (increases opening and switched on longer)

Question 20

Explain each step in relation to the ions channels opening for an action potential

Answer 20

1. K+ channels opening
2. Na+ channels opening: depolarising cell
3. Additional Na+
4. Na+ channel inactivated
5. Gated channels close

Question 21

What is the role of myelination

Answer 21

Insulates axons

Force depolarisation down the axon to prevent K+ leaving

Depolarisation of AP: hops down axon: rapid salatory conduction

Question 22

what are autoreceptors

Answer 22

Self regulation of neurotransmitter release, often located presynaptically, activation tend to decrease further release of neurotransmitter from presynaptic cell