Lecture 6 & 7 - Brainstem & Cranial Nerves Flashcards
Where is the brainstem positioned?
The brainstem is positioned between the forebrain and the spinal cord
Where is the brainstem connected to the cerebellum?
The brainstem is connected dorsally/posteriorly to the cerebellum
How many cranial nerves are associated with the brainstem?
10 pairs of cranial nerves
What is the midbrain comprised of?
The midbrain is comprised of the cerebral peduncles (crus cerebri), colliculi, substantia nigra, red nucleus, cranial nerves (oculomotor and trochlear), cerebral aqueduct, superior cerebellar peduncle, and mamillary bodies
What is the function of the cerebral peduncle?
The cerebral peduncle helps anchor the cerebrum to the brainstem
Where do the axons associated with the cerebral peduncles travel?
The cerebral peduncle includes axons that descend from the cerebral cortex to the brainstem and spinal cord. These axons pass longitudinally on the ventral surface of the midbrain.
What is the other name from the cerebral peduncles?
Crus cerebri
What cranial nerves innervate the cerebral peduncles and where?
The cerebral peduncle is innervated by the III cranial nerves (oculomotor) anteriorly and the IV cranial nerves (trochlear) posteriorly.
What is the general function of the colliculi (as a whole)?
To connect cerebellum to the brainstem
What are the two divisions of the colliculi?
The colliculi are divided into the superior and inferior colliculi.
What is the superior colliculi associated with?
The superior colliculi is associated with visual relay and reflex centres.
What does the superior colliculi do with sensory input?
The superior colliculi receives inputs from the retina and projects it to vision related areas in the cortex
What is the function of the superior colliculi?
The superior colliculi detects the movement of objects in the visual field and relays information to neurons innervating the muscles that control eye movement.
What is the inferior colliculi associated with?
The inferior colliculi is associated with auditory relay and reflex nuclei.
What is the function of the inferior colliculi?
Hearing:
The relay of auditory information from hearing receptors of the ear to the sensory cortex.
Generating reflex response to sound.
Where is the colliculi located?
Posterior to the cerebral aqueduct
Inferior to thalamus
Where is the substantia nigra located?
The substantia nigra is located deep to the cerebral peduncle.
What gives the substantia nigra its colour?
The substantia nigra gets it colour from melanin pigment, a precursor of dopamine.
What is the substantia nigra made of?
The substantia nigra is made of the pars compacta (SNpc) and pars reticulata (SNpr)
What does the SNpr inhibit and why?
The SNpr of the substantia nigra inhibits input to the thalamus as it has connections similar to the internal division of the globus pallidus.
Where is the red nucleus located?
The red nucleus lies deep to the substantia nigra
What gives the red nucleus its colour?
The rich blood supply and iron pigment in the red nucleus gives it its colour
What is the function of the red nucleus?
To act as a relay nucleus in some descending motor pathways
What is associated with the pons?
The pons are associated with 4 cranial nerves (V-VIII), the 4th ventricle, as well as the middle cerebellar peduncle.
What does the pons act as?
The pons acts as a conduit that contains both ascending sensory and descending motor tracts.
What is the pontine nucleus?
The pontine nucleus is a collection of nerves in the pons that makes up the pneumotaxic centre
What is the pneumotaxic centre?
The pneumotaxic (respiratory) centre works together with the medullary centre to maintain normal rhythm of breathing
Where is the pons located?
Superior to the medulla oblongata
Inferior to cerebellum
Anterior/Inferior to 4th ventricle
What is associated with the medulla?
The medulla is associated pyramids, olives, cranial nerves (IX-XII), 4th ventricle, and inferior cerebellar peduncle.
Where are the medulla pyramids and olives located relative to each other?
Pyramids medially
Olives laterally
Describe the axons of the medulla pyramids
The medulla pyramid contains motor axons that are a part of the corticospinal (pyramidal) tract. The axons of the pyramidal tracts, the pyramidal decussation, cross over to the opposite side at the level just above the medulla-spinal junction (at the level of the foramen magnum).
What does the medullary olives contain?
The olives contain the inferior olivary nuclei.
What does the inferior olivary nuclei do?
The inferior olivary nuclei relay the sensory information to the cerebellum
What is found superior to the medulla?
The floor of the 4th ventricle and the superior cerebellar peduncle
What two tracts are found at the medulla?
The fasciculus cuneatus (medial) and the fasciculus gracilis (lateral). These are also known as the dorsal columns in the spinal column.
What is the location of the fasciculus cuneatus and fasciculus gracilis relative to each other?
Fasciculus cuneatus (medial)
Fasciculus gracilis (lateral)
What centres does the medulla have control over?
The medulla has a role of maintaining homeostasis in the cardiovascular centre, respiratory centre, and other reflex centres
What is the role of the medulla in the cardiovascular system?
Cardiac centre - adjusts rate and force of heart beat to meet the body’s needs.
Vasomotor centre - change blood vessel diameter to regulate blood pressure.
What is the role of the medulla in respiratory centres?
The medulla acts on the respiratory centre to control the rate and depth of breathing (along with the pons).
What is the role of the medulla in other reflex centres?
On our other reflex centres, the medulla controls activities such as coughing, sneezing, gagging, swallowing, vomiting, and sweating.
Describe the functional association between the medulla and the hypothalamus
The medullary reticular centres receives input from the hypothalamus and then carries it to target structure(s)
How does cross-sectional anatomy in the medulla differ from that of the spinal cord?
When we reach the medulla, the segmental arrangement of the spinal cord stops. Instead, the columns of white matter become distinct tracts and the grey mater is arranged into distinct nuclei.
What are our cranial nerves?
From most anterior to posterior:
I. Olfactory
II. Optic
III. Oculomotor
IV. Trochlear
V. Trigeminal
VI. Abducens
VII. Facial
VIII. Vestibulocochlear
IX. Glossopharyngeal
X. Vagus
XI. Accessory
XII. Hypoglossal
What cranial nerves are associated with the forebrain?
I. Olfactory
II. Optic
What cranial nerves are associated with the midbrain?
III. Oculomotor
IV. Trochlear
What cranial nerves are associated with the pons?
V. Trigeminal
VI. Abducens
VII. Facial
VIII. Vestibulocochlear
What cranial nerves are associated with the medulla?
IX. Glossopharyngeal
X. Vagus
XI. Accessory
XII. Hypoglossal
What is the olfactory nerve (1)?
The olfactory nerves (I) are tiny sensory nerves (filaments) that provide our sense of smell
Where do the olfactory nerves run?
The olfactory nerves run from the nasal mucosa and pass-through cribriform plate of ethmoid bone to synapse with the olfactory bulb.
Describe the course of information in the olfactory tract
The olfactory tract receives input from the olfactory receptor cells which collate in the olfactory bulb. From here the tract goes to various parts of the brain.
What parts of the brain does the olfactory tract go to? (5)
Olfactory cortex of the temporal nerve
Hippocampus
Amygdala
Hypothalamus
Reticular formation
What does the optic nerves enable?
Vision
Describe the course of optic tract
The optic nerve axons arise from the retina of the eye. Each optic nerve passes through a hole in the back of our orbit (optic foramen). From here the optic nerves converge to form the optic chiasm and continues on as the optic tracts.
What do nasal retina see?
Temporal visual field
What do the temporal retina see?
Nasal visual field
What does the optic nerve refer to?
Axons of the retinal ganglion cells
What happens at the optic chiasm?
Fibres that originated from nasal retina can cross over to the opposite side
What does the optic tract contain?
contains crossed axons from nasal
retina & uncrossed axons from
temporal retina
What does the lateral geniculate nucleus of the thalamus do?
Processes & relays visual
information to visual cortex
What does the primary visual cortex (occipital lobe) do?
Process basic visual information
Conscious perception of visual images
What does the visual association areas (occipital lobe) do?
Processes visual information concerned
with shape, colour & movement
What does the ventral parts of the temporal lobe do during Complex Visual Processing?
identify objects in the visual field (what)
What does the Parietal cortex do during Complex Visual Processing?
assess the spatial location of objects (where)
What does the Frontal cortex do during Complex Visual Processing?
uses visual information to guide movement
What is cranial nerve III?
Oculomotor nerve
What is the oculomotor nerve?
The oculomotor nerves are made up of mixed nerves (chiefly motor) that acts as the motor of the eye
Where does the oculomotor nerves axons extend and pass through?
The oculomotor axons extend from the ventral midbrain adn pass through the superior orbital fissure to the eye
Where is the superior orbital fissure found?
At the back of the eye
What are the type of axons in the oculomotor nerves?
Somatic motor axons
Parasympathetic (autonomic) motor axons
Sensory (proprioceptor) afferents
What do the oculomotor somatic motor axons innervate?
Four of the six extrinsic eye muscles (inferior oblique muscle and superior, inferior and medial rectus muscles)
Levator palpebrae
What movements are the oculomotor somatic motor axons responsible for?
Moving eyeball - extrinsic eye muscles
Raising upper eyelid - levator palpebrae superior muscle
What do the oculomotor parasympathetic motor axons innervate?
Constrictor muscles of iris
Ciliary muscle
What movements are the oculomotor parasympathetic (autonomic) motor axons responsible for?
Pupil constriction - constrictor muscles of iris
Controlling shape of lens for visual focusing - ciliary muscle
Where do the oculomotor sensory (proprioceptor) afferents travel?
Eye muscles to midbrain
What is the function of the oculomotor nerves?
Provide most of the movement of each eye
Also:
- opening of eyelid
- constriction of pupil
- focusing
What does damage to the oculomotor nerve cause?
Damage causes drooping upper eyelid, dilated pupil, double vision, difficulty focusing & inability to move eye in certain directions
What is cranial nerve IV?
Trochlear nerve
What is the only cranial nerve to emerge from dorsal brainstem?
Trochlear nerve
What is the function of the trochlear nerve?
Provide eye movement (downward and lateral)
What type of nerve is the trochlear?
Primarily motor
What do the trochlear nerves supply?
Supply somatic motor axons to (& carry proprioceptor
axons from) the superior oblique muscle
What is the trochlea?
Tendon that hooks around the superior oblique muscle of the eye
What does damage to the trochlear nerve cause?
Damage causes double vision & inability to rotate eye inferolaterally
Where do the trigeminal axons extend?
Axons extend from face to pons (S) & pons to muscles (M)
Where are trigeminal sensory neuron cell bodies located?
Cell bodies of sensory neurons are located in large trigeminal ganglion
What are the 3 divisions of trigeminal nerves?
Ophthalmic division (V1)
Maxillary division (V2)
Mandibular division (V3)
What division is the V1 trigeminal nerves?
Ophthalmic
What division is the V2 trigeminal nerves?
Maxillary
What division is the V3 trigeminal nerves?
Mandibular
Where does the V1 trigeminal axons run from?
Axons run from face to pons via superior orbital fissure
Where does the V2 trigeminal axons run from?
Axons run from face to pons via foramen rotundum
Where does the V2 trigeminal axons run from?
Axons pass through skull via foramen ovale
What is the function of the V1 trigeminal nerves?
Convey sensory impulses from skin of anterior scalp, upper eyelid & nose, & from nasal cavity mucosa, cornea & lacrimal (tear) gland
What is the function of the V2 trigeminal nerves?
Convey sensory impulses from nasal cavity mucosa, palate, upper teeth, skin of cheek and upper lip
What is the function of the sensory V3 trigeminal nerves?
Convey sensory impulses from anterior tongue (except taste buds), lower teeth, skin of chin, & temporal region of scalp
What is the function of the motor V3 trigeminal nerves?
Supply motor axons to (carry proprioceptor axons from) muscles of mastication
What is the largest cranial nerve?
Trigeminal
What it the main function of the trigeminal nerve?
Main sensory nerve from face (transmitting afferent impulses from touch, temperature & pain receptors)
Supply motor axons to muscles of mastication
What does damage of trigeminal nerve cause?
Damage produces loss of sensation & impaired chewing
What type of nerves are the trigeminal nerves?
Mixed nerves
(mainly sensory)
What is Tic Douloureux (Trigeminal Neuralgia)
Inflammation of trigeminal nerve (pressure on nerve root)
- excruciating pain
Provoked by a sensory stimulus in area of supply
- analgesics - partially effective
- Nerve cut in severe case to relieve pain (but causing sensation loss)
What is cranial nerve V?
Trigeminal nerve
What is cranial nerve VI?
Abducens
What does the abducens nerve supply?
Axons leave inferior pons & pass through superior orbital fissure to eye (lateral rectus muscle)
What is the function of the abducens nerves?
Eye movement (abducts the eyeball)
What does damage to the abducens nerves cause?
Damage results in inability to rotate eye laterally & at rest eye rotates medially
What is cranial nerve VII?
Facial nerves
Where do the facial nerve axons emerge?
From pons
What do the facial nerves supply?
Axons emerge from pons, enter temporal bone via internal auditory meatus and run within bone (through inner ear cavity) before emerging through stylomastoid foramen; course to lateral aspect of face
What are the five branches of facial nerves?
Temporal
Zygomatic
Buccal
Mandibular
Cervical
What type of nerve are the facial nerves?
Mixed nerves
(Majorly motor)
What do the facial nerve motor axons supply?
Supply motor axons to (convey proprioceptor impulses from) skeletal muscles of face (muscles of facial expression), except for chewing muscles served by cranial nerve V
What facial muscle does the facial nerves NOT supply?
Chewing muscles which are supplied by cranial nerve V
What is the function of the facial nerves?
Transmit parasympathetic (autonomic) motor impulses to lacrimal (tear) glands, nasal & salivary glands
Convey sensory impulses from taste buds of anterior 2/3 of tongue
Facial expression
What does damage to the facial nerve cause?
Damage produces sagging facial muscles & disturbed sense of taste (missing sweet, salty & umami)
What is Bell’s palsy?
Characterised by paralysis of facial muscles (affected side) & partial loss of taste sensation
Viral infection causing inflammation of facial nerve
Symptoms: lower eyelid droops, corner of mouth sags, tears drip continuously, eye cannot be completely closed, paralysed face is ‘pulled’.
Treatment: steroids, rest
What is cranial nerve VIII?
Vestibulocochlear Nerves
Where do Vestibulocochlear Nerves axons emerge and supply?
Axons arising from hearing & equilibrium apparatus within inner ear of temporal bone, passing through internal acoustic meatus to enter brainstem at the pons medulla border
What is the function of the Vestibulocochlear Nerves?
Provide hearing (cochlea nerves) and sense of balance (vestibular nerves)
What type of nerve is the vestibulocochlear nerves?
Purely sensory
What does damage to the vestibulocochlear nerves cause?
Damage produces deafness, dizziness, nausea, loss of balance and nystagmus (rapid involuntary eye movements)
What is cranial nerve IX?
Glossopharyngeal nerves
Where do glossopharyngeal nerve axons emerge from?
Axons emerge from medulla & leave skull through jugular foramen
What do the motor glossopharyngeal nerves supply?
Supply motor axons to (carry proprioceptor fibres from) a pharyngeal muscle - stylopharyngeus
Provide parasympathetic motor axons to parotid
salivary gland
What type of nerve is the glossopharyngeal nerves?
Mixed nerves
What is the function of the glossopharyngeal nerves?
Provide control over swallowing, salivation, gagging, sensations from posterior 1/3 of tongue, control of blood pressure & respiration
What do the sensory glossopharyngeal nerves supply?
Sensory axons conduct taste & general sensory impulses from pharynx & posterior 1/3 of tongue
Conducting sensory impulses from chemoreceptors in the carotid body & pressure receptors of carotid sinus
What does damage to the glossopharyngeal nerve cause?
Damage results in loss of bitter & sour taste, and impaired swallowing
What is cranial nerve X?
Vagus nerve
Where do the vagus axons emerge from?
Axons emerge from medulla, pass through skull via jugular foramen, descend through neck region into thorax & abdomen
What do the vagus nerves supply?
Supply motor axons to (carry proprioceptor fibres from) skeletal muscles of pharynx & larynx
Parasympathetic motor fibres supply heart, lungs & abdominal viscera
Conducting sensory impulses from thoracic & abdominal viscera
Transmitting sensory impulses from chemoreceptors in the carotid & aortic bodies, & pressure receptors of carotid sinus
Conducting sensory impulses from taste buds of posterior tongue & pharynx
What is the only cranial nerve to extend beyond the head & neck to the thorax & abdomen?
Vagus nerve
What type of nerve is the vagus nerves?
Mixed
Majority of motor axons are parasympathetic
What is the function of the vagus nerves?
Provide swallowing & speech; regulate activities of major viscera
What does damage to vagus nerves cause?
Damage causes hoarseness or loss of voice, impaired swallowing & digestive system mobility
Fatal if both are cut
What is cranial nerve XI?
Accessory nerves
What are the two types of accessory nerve root?
Cranial root
Spinal root
What type of nerve is the accessory nerves?
Mixed nerves
primarily motor
What does the cranial root of the accessory nerve join with?
Vagus nerve
What does the cranial root accessory nerve supply?
Supply motor axons to larynx, pharynx & soft palate
What does damage to the cranial root of the accessory nerves cause?
Damage causes hoarseness or loss of voice & impaired swallowing
What does damage to the spinal root of the accessory nerves cause?
Damage causes impaired head, neck & shoulder movement. eg. unable to shrug on one side if unilateral injury
What do the spinal root accessory nerves supply?
Supplies motor axons to (conveys proprioceptor impulses from) trapezius & sternocleidomastoid muscles, therefore provides head, neck & shoulder movement
What type of nerve is the accessory nerves?
Mixed nerves
(primarily motor)
What is cranial nerve XII?
Hypoglossal nerve
Where do the hypoglossal axons arise and emerge from?
Axons arise by a series of roots from medulla, exit from skull via hypoglossal canal to tongue
Axons emerge between the pyramid & olive
What do the hypoglossal nerves supply?
Supply somatic motor axons to (convey proprioceptor impulses from) intrinsic & extrinsic muscles of tongue
What is the function of the hypoglossal nerves?
Provide tongue movements of speech, food manipulation & swallowing
