Week 8 neurotransmission

Question 1

Neurones

Answer 1

Neurone: Responsible for
communication
-Action potential / neurotransmission
-Information transmits from dendrite to axon terminal -> many have a lipid sheath called
myelin
-Action potential generated in axonal hillock and travels down axon ->excitable membrane

Question 2

Bioelectricity

Answer 2

Membrane potential (difference) is fundamental to all cells
Membrane potential is a result of ion gradients

Question 3

Excitable cells (bioelectricity)

Answer 3

Membrane potential changes in response to stimuli

Question 4

Nerve impulses (bioelectricity)

Answer 4

Changes in membrane potential that travel down nerves

Question 5

Ion gradients

Answer 5

-Cell membrane is highly impermeable to ions -> allows formation of ion gradients (membrane potential difference)
-Allows electrical signalling and excitability

Question 6

Membrane potential is the basis of;

Answer 6

–Neurotransmission
–Muscle contraction
–Secretion -> hormones, neurotransmitters, digestive enzymes, mucus,
surfactant
–Immune responses

Question 7

Inside the cell

Answer 7

Low Ca2+, Low Na+, High K+

Question 8

Outside the cell

Answer 8

High Ca2+, High Na+, Low K+

Question 9

Charge across membrane

Answer 9

-70mV

Question 10

An excitable membrane needs;

Answer 10

-A negative membrane potential
-Ion concentration gradients
-Ion channels
->Voltage gated
->Ligand gated
Sodium Na+
Potassium K+
Calcium Ca2+

Question 11

Negative membrane potential (ion gradient)

Answer 11

Neurons have a negative membrane potential
More negative on the INSIDE of the cell than the outside -> when at rest
Membrane potential is due to unequal ion distribution
->A gradient of ions across the membrane which provides a DIFFUSION gradient and a MEMBRANE POTENTIAL

Question 12

Neurones (nerve cells)

Answer 12

-Neurones are highly specialised cells
-Transmit information as electrical signals (nerve impulses or action potentials)
-Action potentials only travel one way
-Propagated by axon (begins at axonal hillock)

Question 13

Neurone at Rest

Answer 13

-Resting membrane potential
of a neuron is -70 mV
Maintained by:
-An energy dependent
pump which moves the
ions across the membrane

Question 14

Neurone: Action potential

Answer 14

An action potential changes the membrane potential to +30mV

Question 15

Action Potential

Answer 15

Electrical impulses formed by ions moving into the neurone
The axonal action potential (depolarization and repolarization) is made up
of movement in sodium (+ charged ion) and potassium (+ charged ion)
Signal received at dendrites causes dendritic depolarisation

Question 16

Dendritic depolarisation

Answer 16

-Ligand gated ion channels
-Metabotropic channels (involves a chain of other molecules to open channel)
This depolarisation opens voltage gated sodium channels

Question 17

Action potential propagation

Answer 17

-Dendrite: ligand gated ion
channels open
-Axon: voltage gated ion
channels open

Question 18

Action potential detail

Answer 18

Stimulus = electrical,
mechanical or chemical
Axon AP = electrical
Stimulus has to be strong
enough to reach threshold
potential
->Enough depolarisation to open
first NaV
->Sodium channels in the
membrane are sensitive to
voltage and open when the
THRESHOLD membrane potential is reached
The AP is all or Nothing

Question 19

Action potential direction

Answer 19

The action potential is propagated
down the axon by voltage sensitive channels
-When as action potential occurs, Na+ voltage sensitive channels open due to the local change in membrane potential
->This causes more Na+ channels to open
-Na+ channels behind the action potential become inactive
-Therefore the action potential can only move in ONE direction

Question 20

Action potential phases

Answer 20

-Depolarisation ->Na+ channels
open
-Repolarisation ->K+ channels
open
-Refractory period->Re-establishment of resting potential - Na+/K+ exchange
-Return to resting state

Question 21

Myelination CNS

Answer 21

Central nervous system ->
Oligodendrocytes

Question 22

Myelination PNS

Answer 22

Peripheral nervous system ->
Schwann Cells

Question 23

Saltatory conduction

Answer 23

Axons in most vertebrate
neurones are myelinated
Mostly covered in fatty substance –> myelin
Only nodes of Ranvier are
exposed
Action potential ‘jumps’ from
one node to the next
-Much faster neurotransmission
-Much more energy efficient

Question 24

Action potential at end of neurone

Answer 24

At the end of the axon is the synapse
-Presynaptic neuron, synaptic cleft, post synaptic neurone
->Presynaptic terminal contains synaptic vesicles
->Post synaptic terminal has receptors that neurotransmitter binds to

Question 25

Synpase

Answer 25

-Impulse dependent release
-Membrane depolarisation opens voltage gated calcium channels
-Calcium influx triggers vesicles to move to the presynaptic
membrane
-Vesicles fuse with the membrane and release their content into the synapse

Question 26

Neurotransmission at the synapse

Answer 26

-AP depolarises terminal (opens
voltage gated calcium channels)
-Calcium enters cell
-Triggers vesicles to move to the
presynaptic membrane. Vesicles fuse with the membrane and leading to exocytosis of synaptic vesicles
-Neurotransmitter diffuses across cleft
-Binds with receptors on the
postsynaptic cell
-Initiates a response in the
postsynaptic cell

Question 27

Neurotransmitter Receptors

Answer 27

Post-synaptic effects depend upon the transmitter and the receptor it binds to;
-Ionotropic/ligand gated
-Metabotropic (G-protein coupled /GPCR
Some neurotransmitters will bind to both kinds of receptors;
-Ionotropic responses are faster
-Metabotropic responses can have more diverse effects

Question 28

Receptors: Ligand gated (ionotropic) and GPCRs

Answer 28

Ligand gated ionotropic receptors fast
-Metabotropic (G-protein coupled/ GPCRs)
-Metabotropic responses can have more diverse effects