Lecture 3 - fMRI Flashcards
fMRI relies on the fact that…
deoxygenated haemoglobin disrupts the homogeneity of the magnetic field
EPSPs cause a neuron to become…
depolarized
The influx of the following ion is critical for neurotransmitter release…
calcium
The resting membrane potential of a neuron is approximately…
-60/65 mV
Which voltage-gated ion channel opens at the onset of an action potential?
Sodium channels open first
Resulting in a flood of Na+ ions
= rising phase
What two forces drive the movement of ions?
Diffusion and electrical
What does the sodium potassium pump do?
Takes 3 sodium ions from inside cell to outside
Takes 2 potassium ions from outside to inside
This pump is responsible for resting state potential (-60mv)
What energy molecule does the sodium potassium pump require?
ATP
Adenosine Triphosphate
What is hyperpolarization?
More negative
What is depolarization?
More positive
What is the threshold for triggering action potential?
-50mv
Do actions potentials vary in size?
Obvs not
“All or nothing principle”
Which forces pull Na+ into the cell once sodium channels open?
Electrical and diffusion
What happens at maximum positivity?
Sodium channels close
Potassium channels open and potassium leaves cell
What happens when potassium channels open?
Neuron becomes negative
= hyperpolarization
What is an EPSP?
Graded potential which causes depolarization
What is an IPSP?
Graded potential which causes hyperpolarization
Action potential time course
- EPSP add up
- Voltage gated sodium channels open (trigger each other)
- Sodium comes into cell
- Depolarization (reaches threshold)
- Continued depolarization (peaks at +40mv) - Sodium channels close (inactivated state)
- Potassium leaves cell through leak channels because of diffusion and electrical force
- Potassium also leaves through voltage gated potassium channels
- Falling phase/undershoot - Voltage gated potassium channels close (slowly)
- Absolute Refractory period
- cannot trigger another action potential - Relative Refractory period
- difficult to trigger another action potential
EPSP at the synapse
AP travels down axon
AP depolarizes pre-synaptic membrane causing voltage-dependent Ca2+ ion channels to open
Ca2+ influx = vesicles to fuse with pre-synaptic membrane
Neurotransmitter e.g. glutamate released into synapse
Neurotransmitter binds with receptors on post-synaptic ion channels which opens them
Ions (e.g. Na+) flow into post-synaptic cell
= EPSP/ depolarization
IPSP at the synapse
AP travels down axon
AP depolarizes pre-synaptic membrane causing voltage-dependent Ca2+ ion channels to open
Ca2+ influx = vesicles to fuse with pre-synaptic membrane
Neurotransmitter e.g. GABA released into synapse
Neurotransmitter binds with receptors on post-synaptic ion channels which opens them
Ion movement causes resting state potential of post-synaptic membrane to become more negative (i.e. further away from threshold)
- This may occur due to e.g. influx of Cl- or efflux of K+
= IPSP
What are axons insulated by?
Why is this good?
Myelin sheath
Without Myelin, conduction of APs 100 times slower
What do APs jump between?
Nodes of ranvier
What happens to the neurotransmitter released into synaptic cleft?
It is either broken down by an enzyme or ‘re-uptake’ occurs
what is an agonist?
Enhances (some prevent re-uptake)
