communication within and between neurons - week 4

Question 1

resting membrane potential

Answer 1

phospholipid bilayer is a barrier
- transporter proteins and channel proteins
- Na+K+ATPase most important transporter
-higher conc. Na+ outside
-higher conc. K+ inside

the conc. difference means ions continuously move down their conc. gradients through ions channels
- outside +ve inside is -ve

sodium tends to move in but transporter pushes them out
- KIN, NOUT

difference in -70mv

Question 2

resting membrane potential

• forces at work

Answer 2

diffusion

electrostatic pressure
- attraction and repulsion
- ions w/same charge repel
- ions w/different charges attract

transporter
- moves specific ions
- uses energy

Question 3

action potential

Answer 3

1. membrane depolarisation
   sodium voltage gated channels opens at -55mv
2. sodium cations flood into the neuron
   - diffusion
   - electrostatic pressure
   membrane becomes less -ve
3. membrane potential +ve
   - potassium cations now leave the cell
   - sodium channel closes at +40mv
4. potassium channels stay open
   - k+ continues to leave
   diffusion
   electrostatic pressure
   - membrane repolarisation
5. K+ carry on leaving
   - hyperpolarisation
6. K+ channels close
   - resting membrane potential restored

Question 4

threshold potential

Answer 4

-55mv

if this is reached an action potential will occur

all or nothing
- always same size and shape
- higher frequency = stronger stimulus

Question 5

why does the membrane depolarise?

Answer 5

sensory receptors
- respond to sensory information

chemical transition between neurons

Question 6

signal transduction

Answer 6

conversion of stimuli into electrical signals

Question 7

synapses

• structure

Answer 7

the junction between two neurons where neurons communicate by chemical means

About 20nm gap (the synaptic cleft)

Question 8

presynaptic cell

Answer 8

input neuron
- brings info to synapse

terminals
- inside, vesicles contain neurotransmitters

neurotransmitter release
- into synaptic cleft
- via fusion of vesicles into the cell membrane of the terminal

Question 9

postsynaptic neuron

Answer 9

output neuron
- recieves information at synapse

dendrites
- the usual position of the synapse on the postsynaptic neuron

receptors
- released neurotransmitters bind to receptors
- many receptors are also ion channels
- binding opens the channel
- conductance of the postsynaptic changes

Question 10

postsynaptic potentials
- hypopolarisation

Answer 10

same as depolarisation

exicatory

opening of cation channels

EPSPs

Question 11

postsynaptic potentials
- hyperpolarisation

Answer 11

inhibitory

opening of anion channels (more -ve)

IPSPs

Question 12

ionotropic receptors

Answer 12

group of transmembrane ion channels that open or close in response to the binding of a chemical messenger (ligand)

lignd gated ion channels through which ions pass in response to neurotransmitters
eg. nictinic acetycholine receptor

ligand binds –> changes 3D shape –> channel opens

Question 13

metabolic receptors

Answer 13

subtype of membrane receptors that do not form an ion channel pore but use signal transduction mechanisms (often G proteins) to activate a series of events using second messenger chemicals
eg. glutamate receptors
eg. dopamine receptors

ligand binds –> changes 3D shape —> activates G proteins —> activates an intracellular signalling cascade

Question 14

ligands

amino acid derivatives

Answer 14

glutamate

GABA

Glycine

Question 15

ligands

amino acid derivatives

glutamate

Answer 15

most abundant excitatory neurotransmitter

derived from glutamic acid

doesnt bind to all receptors, at least 8, both ionotropic and metabolic

learning and memory
- ionotropic AMDA and NMDA

dysfunction proposed to play role in schizophrenia

potentially influenced by glial activity

Question 16

ligands

amino acid derivatives

GABA

Answer 16

most abundant inhibitory neurotransmitter

produced by glutamate by a specific enzyme family

binds to both ionotropic (GABAA) and metabolic (GABAB) receptors

useful function
- reduced random firing action)

diverse function
- treatment of anxiety disorders
- therapeutic drugs target GABAergic neurotransmission

Question 17

ligands

amino acid derivatives

Glycine

Answer 17

appears to have to distinct roles in CNS

inhibitory
- act as a neurotransmitter in its own right
- mirroring in spinal cord (GABA in brain)
–> receptor are ionotropic and are functional equivilants of GABA receptors

excitatory
- critical role as part in glutamatergic neurotransmission
- considered a co-agonist for NMDA receptors meaning both glycine and glutamate are required to bind and activate the NMDA receptor

so can be considered excitatory or inhibitory depending on context (of receptor)

Question 18

can receptors be presynaptic

Answer 18

yes

negative feedback
- release of neurotransmitters can stop its own further release

retrograde signalling
- post—>pre may be important for synaptic plasticity

Question 19

binding of ligands to receptors

Answer 19

selectivity of binding
- specific ligands at specific binding sites
- 3D shape of receptor
- some drugs bind to more than one receptor type

Question 20

binding of ligands to receptors
- affinity

Answer 20

how well a ligands binds to a receptor

Question 21

high affinity =

Answer 21

receptors saturated (completely bound) by a dilute solution of ligands

if binds better dont need as much ligand for same effect

Question 22

ligands

monoamines

Answer 22

shared chemical composition

not easily described as exciatory or inhibitory

most receptors G- protiens coupled (metabolic)

functionally have interest in the context of behaviour
- somehow enhance or suppress the drive (for glutamate or GABA)
–> neuromodulator

Question 23

ligands
monoamines

dopamine

Answer 23

control of motor activity

role in determining activity of basal ganglia

process associated with reward

relationship to addiction

Question 24

ligands
monoamines

serotonin

Answer 24

found in neuronal terminals throughout the CNS

location of receptors in brain inconsistant
- some types wide spread others not
- paricular pre/post synpatic locations

fundamental action as found in the photobrains of primitive organisms and in anatomically equivilent places to humans

behavioural perspective
- long association w/ psychological disorders such as depression and its treatment

Question 25

ligands
monoamines

neuropeptides

Answer 25

appear to have specific receptors (sometimes multiple) which mediate their actions
- some in highly restricted areas of the brain
- hypothalamus (feeding+regulation)

opioids
- psychotropic effects - substance abuse
physiologically believed to have diverse roles and therapeutically are key targets for pain management

similar to monoamines
- receptors found on neurons that also contain receptors for classical transmitters
- also most terminal that release neuropeptides also release one of the classical transmitters

Question 26

ligands

lipids

Answer 26

cannaboid receptor

lipophilic nature of endocannabinoids challenges out concept of a neurotransmitter
—> cannot be stored in a vesicle

at least 2 receptors for endocannaboids
- CB1 and CB2

CB1 - CNS

CB2 - peripheral associated w/ cells of immune system