Brainstem Anatomy Flashcards
Ventral Surface of the Midbrain
Crus cerebri -large column of descending fibers
Interpeduncular fossa – depression
Between the crus cerebri.
Nerve emerging from Midbrain (one):
Oculomotor (3rd): from medial aspect of crus cerebri.
Dorsal Surface of the Midbrain
Marked by 4 elevations:
Two superior colliculus: concerned with visual reflexes.
Two inferior colliculus: forms part of auditory pathway.
Nerve emerging from Midbrain (one):
Trochlear (4th): just caudal to inferior colliculus
(The only cranial nerve emerging from dorsal surface of brain stem).
Cerebral aqueduct:The cerebral aqueduct, or “aqueduct of Sylvius,” connects the third and fourth ventricles providing a conduit for cerebrospinal fluid (CSF) to flow inside the brain.
Ventral Surface of the Pons-
Basilar sulcus- median groove, occupied by basilar artery.
Middle cerebellar peduncle- to enter the opposite cerebellar hemisphere.
Nerves emerging from Pons (4 nerves):
Trigeminal (CNV): from the middle of ventrolateral aspect of pons Abducens (CNVI): from sulcus between pons & pyramid. Facial (CNVII) & vestibulocochlear (CNVIII): at junction between medulla, pons & cerebellum
Dorsal Surface of the Pons
Posterior surface of the pons is hidden from view by the cerebellum. It forms upper half of the floor of the fourth ventricle.
Median sulcus- divides the pons into 2 halves.
Facial colliculus: An elevation, lies on either side of ventral median fissure. It is formed by fibers from the motor nucleus of the facial nerve as they loop over the Abducens nerve nucleus.
Ventral Surface of Medulla
Ventral median fissure: Divides the medulla into 2 halves. Its lower part is marked by decussating of most of pyramidal (corticospinal- descending motor) fibers (75%-90%).
Pyramid: An elevation, lies on either side of ventral median fissure. Produced by corticospinal tract.
Olive: An elevation, lies lateral to the pyramid. Produced by inferior olivary nucleus.
Nerves emerging from Medulla (4 nerves):
From sulcus dorsolateral to olive (from above downwards)- Glossopharyngeal (CN IX), Vagus (CN X) & cranial part of accessory (CN XI) N.
From sulcus between pyramid & olive- Hypoglossal (CN XII) N.
Dorsal Surface of Medulla
The medulla divided into caudal part (closed medulla) and the cranial part (open medulla) based on the absence or presence of the lower part of the fourth ventricle.
Closed medulla (closed part)
Dorsal median sulcus: divides the closed medulla into 2 halves.
Gracile tubercle: an elevation produced at the upper part of fasciculus gracilis, marks the site of gracile nucleus.
Cuneate tubercle: an elevation produced at the upper part of fasciculus cuneatus, marks the site of cuneate nucleus.
The decussation of sensory fibers (fasciculus gracillis, fasciculus cuneatus) happens at the level of obex ( beginning of the 4th ventricle). The medial lemniscus is formed by the crossings of the fasciculus gracillis, fasciculus cuneatus.
Open medulla ( Cranial part)
Cavity: 4th ventricle- Is widest at the level of pontomedullary junction where lateral aperture (foramen of Luschka) provides passage for CSF within the fourth ventricle to reach the subarachnoid space surrounding brain.
Obex-is the point at which the fourth ventricle narrows to become the central canal of the spinal cord. The decussation of sensory fibers happens at this point.
Area postrema- In the floor of the 4th ventricle just rostral to the obex, is the area postrema that is lack of blood brain barrier. Stimulation of this area induces vomiting (chemosensitive emetic center).
Corticospinal tract
Corticospinal (main motor) tract- -supplies the musculature of the body- (contralateral)
lesion results in CL weakness of the face, arm and leg (Hemisparesis)
Corticobulbar tracts
Corticobulbar tracts -supplies the musculature of the head and neck- (contralateral)
Lestion results in CL weakness of the face, arm and leg (Hemisparesis)
Reticulospinal tract
Reticulospinal- regulate voluntary movements reflex activity.
Vestibulospinal tract
Vestibulospinal -controlbalanceandposture. Plays a role in the control of extensors tone.
Rubrospinal tract
Rubrospinal- arises in the contralateral red nucleus of the mid brain. Plays a role in the control of flexors tone.
Medial Longitudinal Fasciculus
Medial Longitudinal Fasciculus (MLF)- contains vestibular fibers of CNVIII nerves that coordinate eye movements via CN III, IV and VI. Mediates nystagmus and lateral conjugate gaze.
Lesion results in IPSI - internuclear ophthalmoplegia (failure of adduction of the IPSI eye +nystagmus in the opposite eye as it looks laterally)
Spinothalamic tract/ Spinal lemniscus
Spinothalamic/ Spinal lemniscus- carries pain, temperature and crude touch (contralateral)
Lesion results in CL Loss of pain and temperature affecting the arm, leg and rarely the trunk
Medial lemniscus
arises from the fasciculus gracillis and fasciculus cuneatus after they decussate- carries fine touch, vibration, proprioception), (contralateral)
Lesion results in CL loss of vibration and proprioception in the arm and leg
Trigeminal lemniscus-
Trigeminal lemniscus- carries tactile, pain, and temperature impulses from the skin of the face, the mucous membranes of the nasal and oral cavities.. (Ipsilateral)
CN III (Occulomotor) n.-
Motor nucleus (general somatic efferent GSE)- to extra ocular muscles (medial, inferior and superior rectus, inferior oblique and levator palpebrae muscle).
Edinger Westfall nucleus (general visceral efferent GVE/ parasympathetic)- to ciliary body for accommodation and the sphincter muscle of iris for pupillary light reflex.
CN 4 Trochlear n. –
Motor nucleus (general somatic efferent GSE)- to superior oblique muscle
CN V Trigeminal n. -
Sensory nuclear complex
- Principal Trigeminal nucleus (General somatic afferent GSA)- sensation from face (fine touch, vibration)
- Trigeminalspinal nucleus (GSA/GVA) - face, oral cavity (pain and temperature)
- Mesencephalic nucleus(General somatic afferent GSA) - receive input from muscles of mastication,
Motor nucleus (special visceral efferent SVE/ branchial motor- muscles of mastication
CNVI- Abducens n.
Motor nucleus (general somatic efferent GSE)- innervates lateral rectus
CN VII- Facial n.
Facial n. ( special visceral efferent SVE/ Branchial motor- innervates facial muscles
Superior salivatory (GVE-general visceral efferent/parasympathetic- to lacrimal gland, submandibular and sublingual salivary glands
Gustatory ( Solitary) nucleus Special visceral afferent (GVA)
CN VIII –Vestibulocochlear n.-
Cochlear (two nuclei) ( SSA- special somatic sensory)
Vestibular ( 4 nuclei) ( SSA- special somatic sensory)
CN IX- Glossopharyngeal n.–
Ambiguus (SVE/ branchial motor nucleus) Inferior salivatory (GVE, parasympathetic)-to parotid gland Solitory nucleus (GVA)
CN X –Vagus n.-
Dorsal motor (general visceral motor nucleus GVE, parasympathetic),
Ambiguus (special visceral efferent SVE/ branchial motor)
Solitary (General visceral afferent GVA)
CNXI- Accessory n. –
Spinal accessory (General somatic efferent GSE)- Trapezius, SCM muscles
Ambiguus (special visceral efferent SVE/ branchial motor
CN XII –Hypoglossal n.-
Hypoglossal Motor nucleus-general somatic efferent GSE- muscles of the tongue
Solitary nucleus
– General visceral sensory (GVA) input from- CNIX ( middle ear, Pharynx) and CN X (larynx, abdominal viscera)
-Special visceral ( SVA)input- Taste via CN VII ( ant. 2/3 of tongue), via CN IX (post. 1/3 of tongue) and via CNX (scattered taste buds on the epiglottis)
nucleus Ambiguus
(special visceral efferent SVE/ branchial motor)- innervates muscles of palate mm. pharynx and internal laryngeal mm,. Via CNIX, CNX and CN XI
Spinal nucleus of Trigeminal nerve
Spinal nucleus of Trigeminal nerve- CN VII, CNIX and CNX have some GSA nerve fibers and these nerve fibers (from the ear, pharynx and tongue and larynx, respectively) also terminate in the spinal nucleus of the trigeminal nerve.
Cerebral peduncle
Anterior to the cerebral aqueduct, divided into two part by a pigmented band of gray matter substantia nigra.
- Anterior part crus cerebri contains descending or motor fibers- eg. corticospinal and corticobulbar fibres. - Posterior part tegmentum-contains ascending or sensory tracts, cranial nerve III and IV nucleus, reticular formation, Red nucleus and other small nucleus
The tectum or corpora quadrigemia
Posterior to the cerebral aqueduct, has two pairs of colliculi.
- Two superior colliculi: concerned with visual reflexes. - Two inferior colliculi: forms part of auditory pathway.
Substantia nigra-
extends through the whole length of the midbrain, which secretes dopamine to inhibit the excitatory neurons of the basal nuclei.
Periaqueductal gray
Gray matter surrounding the cerebral aqueduct. Contains endorphin producing cells that suppress pain. This region has been used as the target for brain –stimulating implants used in patients suffering from chronic pain.
At the level of superior colliculus
CN III oculomotor nerve nucleus
Red nucleus-pinkish-yellow color. concerned w/ muscle tone & posture-motor coordination.
Superior cerebellar peduncle
At the level of inferior colliculus
CN IV Trochlear nerve nucleus
At Caudal pontine (facial colliculus) level
Facial nucleus
Abducent nucleus
Vestibular nucleus of CNVIII
Spinal trigeminal nucleus
At Mid pontine (Trigeminal nerve) level
Trigeminal nerve nucleus (Principal motor and sensory nuclei)
At Decussation of pyramid (motor fibers) level in medulla
Central canal, Nucleus gracilis and nucleus cunatus, Spinal nucleus of CNV and CN IX .
At Decussation of medial lemnisci (sensory fibers) (obex) level of medulla
Central canal, Nucleus gracilis and nucleus cunatus, Spinal nucleus of CNV, Hypoglosal nucleus
At Olive, inferior cerebellar level of medulla
Fourth ventricle, Spinal nucleus of CNV, CN IX , X, XII nucleus, nucleus ambiguus, nucleus of tractus solitarius
Just inferior to pons in medulla
Fourth ventricle, chochlear and lateral vestibular nucleus
Midline “M” structures
Motor pathway
Medial Lemniscus
Medual longitudinal fasciculus
Motor nuclei of cranial nerves 3, 4, 6, and 12
Lateral/side “S” structures
spinocerebellar pathway
spinothalamic pathway
sensory CN nucleus
sympathetic pathway
cranial nerve nuclei locations
3&4-midbrain
5-8- pons
9-12-medulla
brainstem blood supply
midbrain:
lateral- PCA
medial- PCA
pons:
lateral- AICA
medial-basillar
medulla:
lateral- PICA
medial- ASA and vertebral arteries
Lesions of medial strucutres
Motor pathway (or cortico spinal / coreticobulbartract) : CL weakness of the face, arm and leg (Hemisparesis)
Medial Lemniscus:
CL loss of vibration and proprioception in the arm and leg
MLF:
IPSI - internuclear ophthalmoplegia (failure of adduction of the IPSI eye +nystagmus in the opposite eye as it looks laterally)
Motor nucleus and nerve:
IPSI loss of the cranial nerve that is affected (CN III, CN IV, CNVI, and CN XII)
Lesions of lateral strucutures
Spinocerebellar pathway:
IPSI Limb ataxia
Spinothalamic/spinal lemniscus pathway:
CL Loss of pain and temperature affecting the arm, leg and rarely the trunk
Sensory nucleus of the 5th cranial nerve
Nucleus Tractus solitarius:
IPSI -loss of cutaneous sensation on face
IPSI -in the loss of taste from the IPSI. one half of the tongue
Sympathetic pathway:
IPSI Homer’s syndrome- ptosis and a small pupil (miosis)
