Cranial Nerves Flashcards
(16 cards)
Describe the difference between upper and lower motor neurones:
Upper:
- located in cerebral cortex
- axons project caudally to lower motor neurones in brainstem and spinal cord
- damage results in paralysis, exaggerated tendon reflexes, paresis or increased motor tone
Lower:
- located in brainstem or spinal cord
- damage results in loss of tendon reflexes, muscle atrophy, flaccid paralysis, paresis or full paralysis
Describe motor (descending) pathway:
1st order neurone arises in cerebral cortex
Its axon synapses with a 2nd order neurone, located in internuncial, grey column of spinal cord
2nd order synapses with 3rd order neurone, the lower motor neurone in the anterior grey column
Describe the corticobulbar tract:
Arises mainly in lateral aspect of primary motor cortex
Synapses with cranial nerve nuclei (most innervate CN bilaterally)
Unilateral innervation to the area of the facial nerve nuclei which supplies the muscles of the lower quadrant of the face
Describe the sensory pathways:
The cell bodies of the primary neurone are usually located outside the central nervous system in sensory ganglia
Secondary neurone cell bodies located in dorsal gray matter of brainstem
Tertiary neurones located in the thalamus and their axons project to the somatosensory cortex in the parietal lobe
Describe the position, associated nuclei and function of cranial nerve I :
Olfactory nerve
Function - sense of smell
Exit - cribriform plate of ethmoid bone to olfactory bulb
Nerve - purely sensory
Detail:
- primary sensory neurones in the olfactory epithelium act as sensory receptors, transmitting sensation via central processes
- secondary sensory neurones in the olfactory bulb relay olfactory sensation to the brain
- olfactory system is a complex communication network that sends fibres to autonomic centres for visceral responses in response to smell
Describe the position, associated nuclei and function of cranial nerve II :
Optic nerve (CN II):
Function - vision
Exit - optic canal
Nerve - purely sensory
Detail:
- transduction of light signals into electrical signal
- sends signals via LGN to primary visual cortex for processing
Not true cranial nerve because it is an extension of the diencephalon (CNS tract), myelinated by oligodendrocytes instead of Schwann cells
Describe the position, associated nuclei and function of cranial nerve III :
Oculomotor nerve
Function - movements of the eye
Exit - midbrain (superior orbital fissure)
Cranial nerve of midbrain
Nerve - purely motor nerve
- somatic motor component of
CNIII nerve innervates 4 of the 6 extraocular muscles controlling eye movement - fibres that innervate these
muscles originate in the oculomotor nucleus which is situated in the midbrain - visceral motor component (parasympathetic innervation) controls pupillary reflex and accommodation
Describe the position, associated nuclei and function of cranial nerve IV :
Trochlear nerve:
Function - Innervates the superior oblique muscle, which depresses, abducts, and intorts the eyeball
Exits on dorsal aspect of midbrain
Nerve - purely motor nerve
Cell bodies in trochlear nucleus of midbrain
Describe the position, associated nuclei and function of cranial nerve V :
Trigeminal nerve
Sensory components:
- ophthalmic division V1 transmits sensation from the upper eyelid, forehead and scalp to a point just beyond the vertex of the skull
- maxillary division V2 carries sensation from the lower eyelid, upper lip and teeth, the maxillary aspect of the face and a lateral strip in the temporal area
- mandibular division V3 transmits sensation from the
lower lip and teeth, oral cavity and skin over the mandible, continues up to ear
Sensory nuclei:
- spinal trigeminal nucleus (from the medulla into the caudal pons) for pain, temperature
- principal sensory nucleus (pons) for disc touch
- mesencephalic nucleus for proprioception
Motor components:
- motor nucleus of CNV is located in the mid pons
- innervates muscles of mastication (medial and lateral pterygoid, masseter and temporalis)
- innervates mylohyoid, anterior belly of digastric, tensor tympani and tensor veli palatini
Describe the position, associated nuclei and function of cranial nerve VI :
Abducens nerve:
Nerve - purely motor
Function - abduction of eye
Cranial cavity exit is superior orbital fissure
- emerges on ventral aspect
of brainstem at the
pontomedullary junction - innervate lateral rectus extraocular muscle: abducts eyeball
- abducens nucleus which is located in the pons
- connection with the contralateral medial rectus muscle via the oculomotor nucleus between the right lateral rectus and left medial rectus muscle to permit these muscles to work in tandem for optimal movement of the eye
Describe the position, associated nuclei and function of cranial nerve VII :
Facial nerve:
- mixed nerve
- exits skull via stylomastoid foramen
Motor component:
- facial motor nucleus is located in the pons
- innervation to muscles of facial expression, platysma, stylohyoid, stapedius
- branches = temporal, zygomatic, buccal, mandibular and cervical
- visceral motor components (parasympathetic innervation) controls lacrimal, sublingual and submandibular glands + these fibres originate in superior salivatory nucleus
Sensory component:
- visceral afferent taste fibres innervate anterior 2/3 of tongue
- they terminate in nucleus of solitary tract
- sensation from soft palate, nasal cavity and middle ear, pain, touch, temperature fibres transmit information from external ear and external acoustic meatus
- travel via spinal trigeminal tract
- innervation to lacrimal, submandibular and sublingual glands + cell bodies located in superior salivary nucleus
Describe the position, associated nuclei and function of cranial nerve VIII :
Vestibulocochlear nerve
Structure:
- vestibular nerve and cochlear nerve enclosed within the same connective tissue sheath
- both enter brainstem at pontomedullary junction
- exits skull at internal acoustic meatus located in the temporal bone
- purely sensory nerve
Vestibular nerve:
- neurones project to vestibular nuclei of pons, medulla and cerebellum
- function is balance and proprioception
- vestibular nuclei
Cochlear nerve:
- cell bodies in spiral ganglion of cochlea
- neurones project to cochlear nuclei of medulla
- function is hearing
Describe the position, associated nuclei and function of cranial nerve IX:
Glossopharyngeal nerve
Mixed nerve
Exits via jugular foramen
Motor component:
- parasympathetic innervation of parotid gland fibres originator from inferior salivatory nucleus of medulla
- motor innervation to stylopharyngeus muscle with fibres originating from nucleus ambiguus of medulla (pharynx elevated during speech and swallowing)
Sensory component:
- taste sensation to posterior 1/3 of tongue carried by CNIX where they will synapse in the nucleus solitarius before travelling to the sensory cortex via the thalamus
- chemoreceptors from the carotid body monitor oxygen tension in blood and baroreceptors in the carotid sinus monitor arterial blood pressure
- these sensations are
relayed via CNIX to the cardiorespiratory aspect of the
tractus solatarius (solitary tract) to control response - sensation from posterior 1/3 of tongue, pharynx, tympanic membrane and external ear – spinal trigeminal tract and nucleus
Describe the position, associated nuclei and function of cranial nerve X:
Vagus nerve
CNX emerges from the medulla as several rootlets, they converge as a single root that exits the skull through the jugular foramen
Motor component:
- innervates all muscles of pharynx except stylopharyngeus and tensor veli palate and these fibres originate in nucleus ambiguus
- parasympathetic fibres of CNX originate in dorsal motor vagus nucleus in brainstem and influenced by hypothalamus, reticular formation
- responsible for visceral control and acts to slow down the cardiac cycle, pulmonary branches cause bronchoconstriction and oesophageal branches act to speed up peristalsis
Sensory component:
- Afferent fibres from abdominal viscera, heart, lungs, baroreceptors & chemoreceptors project to the nucleus of the tractus solitarius (NTS)
- Reflex control of cardiovascular, respiratory, and gastrointestinal functions via connections with the reticular formation and hypothalamus
- Pain, touch, and temperature sensation from the larynx, pharynx, external ear, tympanic membrane, and posterior cranial fossa meninges synapse in the spinal trigeminal nucleus, projecting to the thalamus and sensory cortex
- Taste from the epiglottis is carried via CNX to the NTS.
dorsal motor nucleus of the vagus provides parasympathetic autonomic control,
Describe the position, associated nuclei and function of cranial nerve XI:
Accessory nerve:
Function - motor innervation to sternocleidomastoid, trapezius and intrinsic laryngeal muscles
Nerve - purely motor
Exit - jugular foramen
Detail:
- cranial root composed of vagus nerve fibres from nucleus ambiguus
- Accessory nerve arises from spinal accessory nucleus in posterolateral ventral horn of the cervical spinal cord
Describe the position, associated nuclei and function of cranial nerve XII :
Hypoglossal nerve:
Function:
- supplies motor innervation to all intrinsic tongue muscles
- supplies motor innervation to all extrinsic tongue muscles except palatoglossus
Nerve - purely motor
Motor fibres originate in the hypoglossal nucleus
Exit - hypoglossal canal
