Neurophysiology Facts Flashcards
Location of hair cells in vestibular apparatus
On cupulla (ridge in ampulla - widening at end of loops), with base anchored to bone beneath; in cochlea (hearing), utricle, saccule
parasympathetic system pre- and post-ganglionic nerve length
preganglionic: long postganglionic: short (synapse at terminal ganglion, which may be in target organ)
2 requirements for an excitable cell
selectively permeable membrane, differential charged ion distribution
E_Na+
+60mV, goes down concentration gradient (towards inside), down electric gradient from K+ (towards inside)
soma location: PNS sensory neurons
dorsal root ganglion (just outside spinal cord)
Mechanism: mechanoreceptors
open stretch-sensitive ion channels
[Na+] inside cell at rest
15mM
Factor(s) contributing to membrane resistivity to electrotonic propagation
Number of leak channels in membrane, amount of myelin
Which spinal nerve does NOT carry both sensory & motor neurons?
C1 (uppermost; cervical 1) - only motor
Why is RMP closer to E_K than E_Na?
More potassium leak channels -> higher permeability of K+ (permeability 1:50 Na+:K+ at rest)
Use & meaning of I, II, III, IV classification system
SENSORY neuron type - based on fiber diameter I > II > III > IV
Semi-circular canal function
detect head rotation/angular acceleration of head
Where do hair cells in the vestibular apparatus project into?
Endolymph (fluid inside membrane)
parasympathetic neuron origin in spinal cord
cranial nerves and sacral region (top & bottom)
neuromuscular junction neurotransmitter
Acetylcholine
What is special about the fluid in the utricle & saccule vs. vestibular apparatus?
Topped by otolith - layer with density (and inertia) increased by CaCO3 crystals
State of membrane ion channel gates in stage 1 (resting) of AP propagation
Na+ activation: closed Na+ inactivation: open K+ activation: closed
reason for absolute refractory period
most Na+ channels have inactivation gate closed, so they are unavailable -> can’t get to threshold no matter how big the stimulus
What sends signals to the Medial vestibular nucleus, and where do they go from there?
utricle & saccule; passed on to trunk & neck for posture correction
type of signal propagation at nodes of Ranvier
active, via voltage-gated ion channels; SLOW (high membrane capacitance)
[K+] inside cell at rest
150mM
Threshold to open voltage-gated ion channels
-40mV
CNS excitatory neurotransmitter & receptors
Glutamate AMPA receptor: g_Na=g_K -> V=0mV NMDA receptor: uses Na+, K+, Ca++ (long-term changes)
Use & meaning of ABC classification system
neuron type - based on conduction velocity A(alpha>beta>gamma>delta)>B>C considers myelination, neuron diameter e.g. alpha motor neuron
[Na+] outside cell at rest
150mM
State of membrane ion channel gates in stage 5 (recovery from inactivation) of AP propagation
Na+ activation: closed Na+ inactivation: open(ing) K+ activation: closed
Benefits of post-synaptic membrane organization in NMJ
- ACh receptors very close to ion channels -> EPP doesn’t have to travel far - lots of Na+ channels ensures V_m reaches threshold - reliable & safe
Are hair cells aligned in the utricle & saccule?
no; go all directions
Mechanism: nociceptors, chemoreceptors, photoreceptors
G-protein coupled, indirectly open channels
[K+] outside cell at rest
5mM
sympathetic neuron origin in spinal cord
thoracolumbar region (middle)
Generator Potential: refractory period? graded/all-or-nothing? passive/active propagation?
no, graded, passive
Describe +ve feedback in depolarization
Initial depolarization increases V_m -> opens some Na+ channels -> further depol -> open more Na+ channels -> … -> all Na+ channels open
Are hair cells aligned on the cupulla?
yes
directions sensed by saccule
position/movement relative to gravity: front/back, up/down
How is RMP established?
RMP: resting membrane potential -Na+/K+ ATPase constitutively moves ions to maintain supply -leak channels change permeability to establish RMP
State of membrane ion channel gates in stage 4 (AHP - After HyperPolarization) of AP propagation
Na+ activation: closed Na+ inactivation: closed K+ activation: open (closing slowly)
Formula for (electrotonic) length constant
lambda = sqrt(R_m/R_a), R_m = membrane resistivity, R_a = axial resistivity
Why is active propagation effective/efficient?
-Don’t have to depolarize entire membrane -Depolarization of one segment causes electrotonic propagation, depolarizing segment further down enough to reach threshold -Individual ions don’t have to travel the length of the axon
Where do signals from the vestibular apparatus go?
Vestibular nuclei, in brain stem
What sends signals to the Inferior vestibular nucleus, and where do they go from there?
all parts of vestibular apparatus; passed on to cerebellum for movement coordination
Structure of pre-synaptic membrane in NMJ
- vesicles of neurotransmitter (ACh) in rows (active zone); transported from soma - vesicle movement controlled by Ca++ & snare proteins
Structure on hair cells used to generate signal, and mechanism
kinocilium -pushed by linked stereocilia (smaller so sway easier, together move stiffer kinocilium) -opens/closes Na+/K+ gated ion channels -ion diffusion to bottom of cell opens/closes V-gated Ca++ channels -incr/decr glutamate release on Cranial Nerve VIII
What sends signals to the Superior vestibular nucleus, and where do they go from there?
canals of the vestibular apparatus; passed on to MLF (medial longitudinal fasciculus for eye movement coordination)
accessory myelin cells
Peripheral Nervous System: Schmann cells Central Nervous System: oligodendrocytes
How do graded (generator & other) potentials create an action potential?
Temporal or spatial summation
nerves used for special senses
cranial nerves
sympathetic system pre- and post-ganglionic nerve length
preganglionic: short postganglionic: long (synapse in ganglion just outside spinal cord)
State of membrane ion channel gates in stage 3 (falling) of AP propagation
Na+ activation: open Na+ inactivation: closed -> Na+ UNAVAILABLE K+ activation: open
steps of synaptic transmission
- Na+ AP reaches terminal button 2. depolarization opens V-gated Ca++ channels -> Ca++ influx stimulates vesicle mov’t to membrane 3. exocytosis of neurotransmitter 4. NT diffuses across synaptic cleft & binds receptors 5. Opens ligand-gated ion channels on post-synaptic membrane, changing V_m (PSP); PSP attenuates via electrotonus to soma (ONLY place AP can start)
Structure of post-synaptic membrane in NMJ
- folded to increase surface area - ACh receptors on top of folds (close to where ACh is released) - Na+ channels (V-gated) in bottoms of folds (perijunctional zones) - ACh esterase held near here for ACh breakdown (accurate control)
Gate(s) on Na+, K+ channels
Na+: activation, inactivation K+: activation only
autonomic system neurotransmitter (between neurons)
Acetylcholine
Factor(s) contributing to axial resistivity to electrotonic propagation
Diameter of axon
systems that exert control over autonomic nervous system
spinal cord, medulla, hypothalamus, prefrontal cortex
Relation between signal strength from vestibular apparatuses on opposite sides of head
one increases while the other decreases, since the fluid goes the same way but the hairs are oppositely oriented (“forward” hair movement gives same change in signal, but one side moves forward & other back)
afferents of autonomic nervous system detect…
pressure, osmolarity, temperature, sexual stimuli, pain & stretch in viscera
State of membrane ion channel gates in stage 2 (rising) of AP propagation
Na+ activation: open Na+ inactivation: open K+ activation: closed (opening v. slowly)
Type of receptors & neurons used to sense pain & temperature
free nerve endings in skin, unmyelinated neurons (slow)
CNS inhibitory neurotransmitter & receptors & effect
GABA GABA_A receptors: increase Cl- permeability; E_Cl = -70mV (voltage clamp) GABA_B receptors: increase K+ permeability; E_K = -90mV (hyperpolarization) -prevents unwanted motion
reason for relative refractory period
some Na+ channels still inactivated (unavailable), but enough available that a large stimulus (depolarization) can open enough of them to get to threshold
Shape & location of vestibular apparatus
labyrinth of (3) membrane-lined loops in temporal bone, connected to cranial nerve VIII
location of AP (after sensor) in myelinated sensory neurons
1st node of Ranvier, NOT the soma
Mechanism of phasic mechanoreceptors
Pacinian corpuscule (accessory; layered & fluid-filled) wrapped around sensory nerve ending; on first pressure, puts pressure on sensory nerve (signal) b/c fluid incompressible, but fluid quickly moves away, releasing pressure (stops firing)
Requirement for sensory neuron to generate AP
generator potential reaches threshold
Into which structure do the loops of the vestibular apparatus open?
Utricle, then saccule (chambers)
role of sensors
signal transduction (stimulus to AP)
E_K+
-90mV, concentration gradient (towards outside) balances with charge gradient (towards inside)
steps of signal transmission through NMJ
- Na+ AP reaches terminal button 2. depolarization opens V-gated Ca++ channels -> Ca++ influx stimulates vesicle mov’t to membrane 3. exocytosis of ACh into synaptic cleft 4. ACh diffuses across cleft to ACh receptors 5. opens ligand-gated ion channels on motor end plate, depolarizing muscle (EPP); ACh esterase degrades ACh in synaptic cleft
State of membrane ion channels at rest
available
Acetylcholine esterase function
removes Acetylcholine from NMJ to stop signal
soma location: PNS motor neurons
CNS (spinal cord)
type of signal propagation beneath myelin layer
electrotonus (passive, FAST (low membrane capacitance))
Info from hair cells in utricle
head position with respect to gravity, linear side-to-side and front-to-back head movement
What sends signals to the Lateral vestibular nucleus, and where do they go from there?
utricle & saccule; passed on to limbs for posture correction
nerves used for general senses
SOMATIC: cranial V, spinal nerves except C1
Direction of graded potential movement
bi-directional (both ways along membrane)
of axon terminals per muscle fiber & result
1; must be reliable
What coordinates eye movement with head movement?
Vestibulo-ocular reflex (CVIII - audiovestibular, CIII - oculomotor (medial), CVI - abducens (lateral))
directions sensed by utricle
position/movement relative to gravity: front/back, left/right
