IC2 Flashcards
phases of action potential generation
1) resting membrane potential at -60mV, determined by distribution of K+, Cl-, Na+
2) depolarisation stimulus: voltage gated calcium channels open in response to AP arriving at the axon terminal > excitatory neurotransmitter released at the neuromuscular junction (NMJ) and synapses within the CNS open ligand-gated channels
3) threshold membrane potential: as the cell depolarises, voltage-gated Na+ channels open.
4) rising phase: Na+ rapidly enters the cell through the voltage-gated Na+ channel.
5) overshoot phase: top of rising phase, inside of the cell becomes more positive, reversing the membrane potential polarity
6) falling phase: voltage-gated Na+ channels are inactivated and voltage-gated K+ channels open, increasing permeability to K+ and movement into the cell = membrane potential rapidly repolarises.
7) recovery phase: voltage-gated K+ channels close and membrane potential returns to normal
electrical events at the neuromuscular junction
nerve impulse travel from brain > spinal cord > arrival of AP at pre synaptic cell > depolarisation > voltage gated ca2+ channels open > ca2+ influx > fusion of synaptic vesicle w pre-synaptic membrane > transmission of Act to synaptic cleft (NMJ) > ACh bind to post synaptic ligand-gated channels (NICOTINIC RECEPTORS) > ….
what is sensory transduction?
transformation of external stimulus to action potential is called sensory transduction.
greater the stimulus strength, greater the frequency of action potentials (intensity = frequency)
process of sensory transduction
application of stimulus > depolarisation of receptor membrane at the sensory nerve ending > AP travels to the trigger zone of associated primary afferent > AP moves through myelinated axon (not all are myelinated) > reaches axon terminal causing the release of transmitter
nociceptors and their axons?
FOR PAIN
nociceptors are free nerve endings for which sensory transduction occurs.
nociceptor axons include C- and A-delta fibres
sensory receptors and signal transduction
sensory receptors are sensory nerve endings that on stimulus > sensory transduction > AP in same cell/adjacent cell > primary afferent nerve fibres > CNS
what are the different types of sensory receptors and their stimuli
mechanoreceptor
- mechanical energy (touch, pressure eg vibration, sound)
nociceptor
- tissue damage
chemoreceptor
- chemicals
photoreceptor
- light
thermoreceptor
- heat cold
proprioception
- sense position of body in space
example of axon of mechanoreceptor and signal transduction process
A-beta myelinated receptor
has an ENCLOSED NERVE ENDING (not free nerve ending like nociceptors)
what is the area of skin that will excite a receptor called
receptive field
properties of C- and A-delta axons
C- axons are NOT myelinated
A-delta axons are only THINLY myelinated
nerve endings are FREE (NOT enclosed)
TrpV1
protein molecule found on the membrane of nerve endings of NOCICEPTORS;
responds to high temps and certain chemicals eg capsaicin
gated channel that allows the permeation of calcium ions on stimulation.
how does myelination affect sensory transduction?
thick myelination = faster conduction of signal.
no myelin eg in C = slowest conduction
what happens in individuals with CIPA?
congenital insensitivity to pain with anhidrosis (CIPA)
- insensitivity to superficial and deep pain stimuli = decreased or loss of sensation WHILE RETAINING touch, vibration, position senses.
could be due to absence of nerve growth factor (NGF) dependent C/A-delta fibres due to loss of function mutation in NTRK1 gene on chromosome 1q21-22.
what are the post-synaptic targets in a neuronal cell?
target for excitatory synapse is DENDRITE
for inhibitory synapse is SOMA
movement of K+ in the neuronal cell?
movement OUT
- diffusion down gradient via leakage channels = negative charge on the inner plasma membrane face
movement INTO
- negative charged established attracts K+ back into the cell
electrochemical gradient
how does hypokalemia affect signal transduction?
eg overuse of diuretics resulting in hypokalemia
concentration of k+ outside is decreased causing the gradient to favor movement out of cell = hyperpolarised = cells become less excitable = muscle paralysis?
Broca’s area
damage
found in left hemisphere
damage = difficulty expressing language
how do signals move in an axon during signal transduction?
the AP jumps from node to node (saltatory conduction)
between nodes of Ranvier, found between myelinated axons.
Wernicke’s area
damge
found in left hemisphere
damage = difficulty comprehending language
depression is marked by effect of which part of the brain
subgenual anterior cingulate cortex (ACC)
found anterior to the hypothalamus, at the frontal cortex region
increased activity of subgenual ACC associated with depression
brain stimulation of subgenual ACC may decrease activity = decrease depression symptoms.
limbic structure
HIPPOCAMPUS
lesions of the medial temporal, more specifically hippocampus =
loss of memory for events (part of declarative memory) = eg Alzheimer’s
AMYGDALA
- also found in the limbic structure, involved in emotion and emotional memory = involved in mood changes
Urbach wiethe disease
= amygdala
emotion and emotional memory
for mood changes
= cannot recognise facial expressions or emotions.
what is equilibrium potential and how to calculate?
E = 58log(ECF/ICF)
equilibrium potential represents the potential at which the inward and outward gradients acting on the ion balance out and there is no net movement of ion across the membrane
ie electrochemical gradient of potassium in the neuron due to the leakage channels vs pull from negative charge
E vs MP
membrane potential represents the concentration and permeability of the ions distributed across the membrane
effect of E on MP
membrane potential will try to push towards the E value.
equilibrium between the movements = membrane potential remains at -80/60mV
if negative E = move out
if positive E = move in
size of E affects rate of movement
absolute refractory period
VS
relative refractory period
absolute:
- during the rise and peak
- second AP cannot be initiated
relative:
- hyperpolarisation after the fall
different types of synpases
electrical synapse:
- small synaptic cleft, current generated in the presynaptic neuron flows directly into the postsynaptic cell via gap-junction channels (specialised bridging channels)
chemical synapse:
- separated by synaptic cleft
consider NMJ
what does frontal lobe play a part in?
involved in personality traits
