ACTION POTENTIAL and cranial nerves

Question 1

Resting Potential:

Answer 1

neuron is not stimulated at
threshold level

Question 2

Action Potential

Answer 2

neuron responds to stimulus,
send “message” along axon
* Depolarization
* Repolarization
potential = difference in charge (measured in volts)

Question 3

Impulse Transmission: General Points

Answer 3

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.

Question 4

Resting membrane potential

Answer 4

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

Question 5

Depolarization

Answer 5

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

Question 6

Repolarization/Falling Phase & Hyperpolarization

Answer 6

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.)

Question 7

• Absolute refractory period

Answer 7

Absolute refractory period
After the AP, another
cannot activate until cell
returns to resting state.

Question 8

Relative refractory period

Answer 8

Relative refractory period
Period during which
another AP can be initiated,
but requires a greater
stimulus than before

Question 9

What are the cranial nerves

Answer 9

I Olfactory
II Optic
III Oculomotor
IV Trochlear
V Trigeminal
VI Abducens
VII Facial
VIII Vestibulocochlear
IX Glossopharyngeal
X Vagus
XI Accessory
XII Hypoglossal

Question 10

Cranial Nerves

Answer 10

12 pairs
* Know name AND Roman numeral
* Know functions
* Sensory
* Motor
* Both
* CN I and II in _forebrain__________
* CN III–XII in ___brainstem________

Question 11

CN I:

Answer 11

Special sensory: Olfactory
* Smell (information integrates with taste  flavor)

Question 12

CN II

Answer 12

Special sensory: Optic
* Vision

Question 13

CN III

Answer 13

CN III: Motor: Oculomotor
* Eye movement: lid, pupil, lens

Question 14

CN IV

Answer 14

Motor: Trochlear
* Eye movement (superior oblique): rotation

Question 15

CN V:

Answer 15

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

Question 16

CN VI

Answer 16

Motor: Abducens/abducent
* Eye movement: lateral rectus muscle

Question 17

CN VII:

Answer 17

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)

Question 18

CN VIII

Answer 18

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

Question 19

CN IX:

Answer 19

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)

Question 20

CN X:

Answer 20

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

Question 21

CN XI

Answer 21

Motor: Accessory
* Contains LMN for trapezius and sternocleidomastoid
* Turning the head and moving the shoulders
* Ipsilateral shoulder shrug
* Turning head to contralateral side

Question 22

CN XII

Answer 22

Motor: Hypoglossal
* Extrinsic and intrinsic muscles of ipsilateral ½ of
tongue