ACTION POTENTIAL and cranial nerves Flashcards
Resting Potential:
neuron is not stimulated at
threshold level
Action Potential
neuron responds to stimulus,
send “message” along axon
* Depolarization
* Repolarization
potential = difference in charge (measured in volts)
Impulse Transmission: General Points
Ions move through protein channels in axon membrane.
* Synaptic knobs/terminal boutons release NT into
synaptic cleft.
* ONLY NT crosses synapse—not the impulse itself.
* Electrochemical transmission
* NT causes postsynaptic receptor to open or close its
ion channel.
Resting membrane potential
Positive and negative ions unequally distributed on
each side of membrane
* Usually inside around -65 to -70 mV
* More _Ka+____ inside and ___Na+___ outside
* Membrane channels “gated” by electric potential
and neurotransmitter
Depolarization
Interior of cell is usually negatively charged
* To generate impulse, must depolarize (reverse the polarity) the cell to
trigger an action potential
* Neuron’s membrane opens with an impulse large enough to reach threshold
(minimum change of +10 mV): Na+ channels open
* Threshold is all or nothing—need impulse to reach threshold to activate action potential
* Many subthreshold impulses at same time can also activate action potential
* Allows (+) sodium ions to flow INTO cell
* Causes interior of cell to become less negatively charged (depolarized)
* This must occur at each node of Ranvier to propagate the signal to the terminal
endings
* Now, interior of cell is more positively charged with respect to exterior
environment
Repolarization/Falling Phase & Hyperpolarization
Na+ channels close (no more inward flux of Na+)
* K+ channels now open (K+ flows out of cell) due to cell reaching high
electrical charge
* Repolarization (going back to negative inside and positive outside) will
result in undershoot (extensively negative state): Hyperpolarization, or
cell interior becoming extremely negative, -80 mV
* After that, K channels close (no more outward flow of K) and need to
get back to resting potential (-70 mV); to reach resting state, Na ions
are pumped out (three of them) and K ions are pumped back in (two of
them) via sodium-potassium pumps. (These pumps are working
continuously throughout the process from rest to depolarization to
repolarization.)
- Absolute refractory period
Absolute refractory period
After the AP, another
cannot activate until cell
returns to resting state.
Relative refractory period
Relative refractory period
Period during which
another AP can be initiated,
but requires a greater
stimulus than before
What are the cranial nerves
I Olfactory
II Optic
III Oculomotor
IV Trochlear
V Trigeminal
VI Abducens
VII Facial
VIII Vestibulocochlear
IX Glossopharyngeal
X Vagus
XI Accessory
XII Hypoglossal
Cranial Nerves
12 pairs
* Know name AND Roman numeral
* Know functions
* Sensory
* Motor
* Both
* CN I and II in _forebrain__________
* CN III–XII in ___brainstem________
CN I:
Special sensory: Olfactory
* Smell (information integrates with taste flavor)
CN II
Special sensory: Optic
* Vision
CN III
CN III: Motor: Oculomotor
* Eye movement: lid, pupil, lens
CN IV
Motor: Trochlear
* Eye movement (superior oblique): rotation
CN V:
BOTH SENSORY AND MOTOR: Trigeminal
* Sensory (touch, pain, temperature)
* Ophthalmic (sensory only)
* Maxillary
* Mandibular
* Motor (maxillary and mandibular branches)
* Muscles of mastication
* Tensor veli palatini
* Upward, anterior movement of larynx
CN VI
Motor: Abducens/abducent
* Eye movement: lateral rectus muscle
CN VII:
BOTH SENSORY AND MOTOR: Facial
* Sensory:
* ___taste_____ (anterior 2/3 of tongue—sweet, sour, bitter)
* Motor:
* Innervates muscles of facial expression (and stapedius)
* Corticobulbar fibers to motor neurons for lower ½ of face
(mostly crossed)
* Corticobulbar fibers to motor neurons in upper ½ of face
(distributed bilaterally)
CN VIII
Mostly sensory:
Vestibulocochlear/vestibuloacoustic/auditory
* Auditory information
* Vestibular feedback
* Enter brainstem at lower pontine region
* Some vestibular fibers terminate in cerebellum—
why?
* Testing:
* Audiologist (hearing)
* ENT: dizziness, tinnitus
* Neurologist
CN IX:
BOTH SENSORY AND MOTOR:
Glossopharyngeal
* Sensory
* General sensation from palate,
* Posterior 1/3 of tongue (bitter taste), pharynx
* Motor
* Contributes to ______swallowing_____, innervation of
stylopharyngeus and upper pharyngeal constrictors
(muscles aiding in swallow)
* Autonomic control of visceral organs (glands)
CN X:
BOTH SENSORY AND MOTOR: Vagus
* Sensory: from visceral organs, pharynx, larynx
* Motor:
* Innervates muscles of larynx, pharynx, velum
* Dorsal motor nucleus
* Autonomic motor information to visceral organs
*Coronary circulation, HR, tracheal and bronchial
contraction and relaxation
*Autonomic reflexes
* Synapses on cardiac muscles
Testing
* Palatal elevation
* Gag reflex
* If both volitional and reflexive movement of palate
diminished suspect LMN lesion
* Assessing: swallowing, voice evaluation,
laryngoscopy, videostroboscopy
CN X innervation
* Superior laryngeal branch
* Sensory to mucous membrane down to vocal folds
* Controls __cricithyroid_____________ muscle—important for phonation/
pitch
* Recurrent laryngeal branch
* Innervates intrinsic muscles of larynx and epiglottis (overall
motor control to larynx)
* Also receives afferent projection (sensory)
* Part of reticular feedback loop that enables gagging, coughing,
swallowing
CN XI
Motor: Accessory
* Contains LMN for trapezius and sternocleidomastoid
* Turning the head and moving the shoulders
* Ipsilateral shoulder shrug
* Turning head to contralateral side
CN XII
Motor: Hypoglossal
* Extrinsic and intrinsic muscles of ipsilateral ½ of
tongue
