communication within and between neurons - week 4 Flashcards
resting membrane potential
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
resting membrane potential
- forces at work
diffusion
electrostatic pressure
- attraction and repulsion
- ions w/same charge repel
- ions w/different charges attract
transporter
- moves specific ions
- uses energy
action potential
- membrane depolarisation
sodium voltage gated channels opens at -55mv - sodium cations flood into the neuron
- diffusion
- electrostatic pressure
membrane becomes less -ve - membrane potential +ve
- potassium cations now leave the cell
- sodium channel closes at +40mv - potassium channels stay open
- k+ continues to leave
diffusion
electrostatic pressure
- membrane repolarisation - K+ carry on leaving
- hyperpolarisation - K+ channels close
- resting membrane potential restored
threshold potential
-55mv
if this is reached an action potential will occur
all or nothing
- always same size and shape
- higher frequency = stronger stimulus
why does the membrane depolarise?
sensory receptors
- respond to sensory information
chemical transition between neurons
signal transduction
conversion of stimuli into electrical signals
synapses
- structure
the junction between two neurons where neurons communicate by chemical means
About 20nm gap (the synaptic cleft)
presynaptic cell
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
postsynaptic neuron
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
postsynaptic potentials
- hypopolarisation
same as depolarisation
exicatory
opening of cation channels
EPSPs
postsynaptic potentials
- hyperpolarisation
inhibitory
opening of anion channels (more -ve)
IPSPs
ionotropic receptors
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
metabolic receptors
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
ligands
amino acid derivatives
glutamate
GABA
Glycine
ligands
amino acid derivatives
glutamate
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
ligands
amino acid derivatives
GABA
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
ligands
amino acid derivatives
Glycine
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)
can receptors be presynaptic
yes
negative feedback
- release of neurotransmitters can stop its own further release
retrograde signalling
- post—>pre may be important for synaptic plasticity
binding of ligands to receptors
selectivity of binding
- specific ligands at specific binding sites
- 3D shape of receptor
- some drugs bind to more than one receptor type
binding of ligands to receptors
- affinity
how well a ligands binds to a receptor
high affinity =
receptors saturated (completely bound) by a dilute solution of ligands
if binds better dont need as much ligand for same effect
ligands
monoamines
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
ligands
monoamines
dopamine
control of motor activity
role in determining activity of basal ganglia
process associated with reward
relationship to addiction
ligands
monoamines
serotonin
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
ligands
monoamines
neuropeptides
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
ligands
lipids
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
