Brainstem

Lecture.3

By

Dr.Faris Al-Haddad

M.B.Ch.B, PhD AnatomyCollege of Medicine,

Hawler Medical UniversityArbil, Iraq

e-mail: [email protected]

BrainstemBrainstem

BrainstemBrainstem A stalklike shaped

structure occupies the posterior cranial fossa of the skull and connects the narrow spinal cord with the expanded forebrain.

It consists of: 1. Medulla oblongata, 2. Pons,3. Midbrain

Functions of Brainstem: (1)A coduit for ascending tracts and

descending tracts connecting the spinal cord to the different parts of the higher centers in the forebrain;

(2) it contains important reflex centers associated with the control of respiration and the cardiovascular system and with the control of consciousness;

(3) it contains the important nuclei of cranial nerves III through XII.

Medulla Oblangata

Gross Gross Appearance : Appearance :

• Connects the pons Connects the pons superiorly with the superiorly with the spinal cord spinal cord inferiorly.inferiorly.

• Its conical in shape Its conical in shape inferiorly, & is inferiorly, & is broad superiorlybroad superiorly..

• The junction of medulla The junction of medulla and spinal cord is at :and spinal cord is at :

1.1. corresponds corresponds approximately to the approximately to the level of :level of :

Foramen MagnumForamen Magnum

2. the origin of the 2. the origin of the anterior and posterior anterior and posterior roots of the roots of the 1st cervical 1st cervical spinal nervespinal nerve..

• The central canalThe central canal of the spinal cord of the spinal cord contin-ues upward contin-ues upward into the lower half of into the lower half of the medulla; the medulla;

• in the upper half of in the upper half of the medulla, it the medulla, it expands as expands as the the cavity of the 4th cavity of the 4th ventricleventricle

Anterior surface of medulla

1. Anterior median fissure : continues with that

of spinal cord.2. Pyramid : Contains

corticospinal fibers3. Decussation of

pyramids: site of cross-over of

cortico-spinal fibers to the opposite side.

4. Olive : underlies Inferior olivary nuclei.• rootlets of the

hypoglossal nerve emerges from

groove between pyramid & olive.

5. Inferior cerebellar peduncle : which connect the

medulla to the cerebellum

• In the groove between the olive and the inferior cerebellar peduncle emerge the roots of :

1. Glossopharyngeal

2. Vagus nerves

3. Cranial roots of Accessory nerve

Posterior surface of Medulla

• the superior half of the medulla oblongata forms the lower part of the floor of the 4th ventricle .

• The posterior surface of the inferior half of the medulla is continuous with posterior aspect of the spinal cord.

UP

1/2

Low

1/2

Features posteriorly are:• Posterior median sulcus.

on each side of the median sulcus, there is an, the

• Gracile tubercle, elongated swelling produced by the underlying gracile nucleus.

• Cuneate tubercle, lateral to the gracile tubercle is a similar swelling, produced by the underlying cuneate nucleus.

Blood Supply of Blood Supply of MedullaMedulla

is supplied by the :1. Vertebral artery, 2. Anterior spinal

artery3. Posterior spinal

artery 4. Posterior inferior cerebellar artery, 5. Basilar arteries.

Internal features of Medulla Oblangata

Level Decussation of PyramidsCavity Central canal

Nuclei

Nucleus gracilis & Nucleus cuneatus, Spinal nucleus of cranial nerve V, Accessory nucleus

Motor TractsDecussation of Corticospinal tracts, Pyramids

Sensory Tracts

Spinal tract of cranial nerve V, Posterior spinocerebellar tract, Lateral spinothalamic tract, Anterior spinocerebellar tract

A

A.Transverse sections of the medulla oblongata: Level of decussation of the

pyramidsCentral canal

Nuclei :

1. N. Gracilis2. N. Cunatus

3. Spinal N. of trigeminal nerve

4. Accessory N.

Tracts :1. Spinal tract of cranial nerve V,

2. Posterior spinocerebellar tract,

3. Lateral spinothalamic tract,

4. Anterior spinocerebellar tract

Fasciculi Cunatus & gracilis

Level Decussation of medial lemnisciCavity Central canal

NucleiNucleus gracilis, Nucleus

cuneatus, Spinal nucleus of cranial nerve V, Accessory

nucleus, Hypoglossal nucleusMotor Tracts Pyramids

Sensory Tracts

Decussation of medial lemnisci, Posterior spinocerebellar tract, Lateral spinothalamic tract, Anterior spinocerebellar tract,Spinal tract of cranial nerve V,

B

Medial Lemnisci : Axons of relay neurons in the posterior

column nuclei ( Gracile & Cunate )course anteromedially (internal arcuate fibers) and cross to the opposite side (sensory decussation) above the pyramids to form the medial lemniscus. The medial lemniscus thus carries the same modalities of sensation carried by the dorsal column.

B. Transverse sections of the medulla oblongata: Level of decussation of

medial lemnesci

Pyramids

Nuclei : 1. N. Gracilis2. N. Cunatus

3. Spinal N. of trigeminal nerve

4. Accessory N.

5. Hypoglosal N


2. Posterior spinocerebellar tract,



Fasciculi Cunatus & gracilis

Level Olives, Inferior cerebellar peduncleCavity Fourth ventricle

Nuclei

Inferior olivary nucleus, Spinal nucleus of cranial nerve

V, Vestibular nucleus, Glossopharyngeal nucleus, Vagal

nucleus, Hypoglossal nucleus, nucleus ambiguus, nucleus of tractus solitarius

Motor TractsPyramids, Medial longitudinal fasciculus, Tectospinal

tract,

Sensory Tracts

Medial lemniscus, Lateral spinothalamic

tract, Anterior spinocerebellar tract, Spinal tract of cranial nerve V

C

Inferior olivary nucleusInferior olivary nucleus OliveOlive of the medulla is the appearance of the

inferior olivary nuclei, which are laminae of laminae of gray mattergray matter posterolateral to the pyramids. consists of three nuclear groups :

1. Principal olive (the largest of the complex)2. Dorsal accessory olive3. Medial accessory olive• Its a relay station between the cortex,

subcortical structures, medulla, spinal cord, & cerebellum

• The major output of the inferior olivary complex is to the cerebellum (olivocerebellar tract).

Nucleus AmbiguusNucleus Ambiguus• Is also known as Ventral motor nucleus of

vagus. • It is a column of cells situated about

halfway between the inferior olive and the nucleus of the spinal tract of the trigeminal nerve.

• Axons of neurons in this nucleus course dorso-medially and then turn ventrolaterally to emerge from the lateral surface of the medulla between the inferior olive and the inferior cerebellar peduncle.

• These axons convey special visceral efferent impulses to muscles of the pharynx and larynxpharynx and larynx : (pharyngeal constrictors, cricothyroid, intrinsic muscles of the larynx, levator veli palatini, palatoglossus, palatopharyngeus, and uvula).

• In addition to the vagus nerve, the nucleus ambiguus contributes efferent fibers to the

1. glossopharyngeal (cranial nerve IX) 2. accessory (cranial nerve XI) nerves.

Nucleus of Tractus SolitariusNucleus of Tractus SolitariusDivided into two zones : 1. Infero-medial zone is concerned with general

visceral sensation and primarily cardio-respiratory function. The zone receives input via

• Glossopharyngeal (cranial nerve IX) • Vagus (cranial nerve X). 2. Supero-lateral zone is concerned with special

visceral (taste) function. This zone receives taste sensations via three cranial nerves:

• Facial nerve (cranial nerve VII) conveys taste sensations from the anterior 2/3 of the tongue,

• Glossopharyngeal nerve (cranial nerve IX) conveys taste sensations from the posterior 1/3 of the tongue,

• Vagus nerve (cranial nerve X) conveys taste sensations from the epiglottis

Medial longitudinal fasciculus• Is situated beneath the floor of the fourth

ventricle on either side of the midline. • Its the main pathway that connects the

vestibular and cochlear nuclei with the nuclei controlling the extraocular muscles (oculomotor, trochlear, and abducent nuclei).

C. Transverse sections of the medulla oblongata: Level of decussation of

Olivary nuclieI.

C. P

I.C.P : Inferior cerebellar peduncle

Nuclei :

Spinal nucleus of cranial nerve V,

Dorsal accessory olivary nucleusInferior olivary nucleus,Medial accessory olivary nucleus

Nuclei : Vagal nuclei : 1. dorsal nucleus 2. nucleus of tractus solitarius 3. nucleus ambigious

Nuclei :Hypoglossal nucleus,

Glossopharyngeal nuclei : 1. inferior salivatory n. 2. main motor n.

Vestibular nuclei : 1. medial n. 2. inferior n.

Cochear nuclei : 1. posterior n 2. anterior n.




Medial longitudinal fasciculus,

Tectospinal tract,

Medial lemniscus,

Clinical Notes1. Raised Pressure in the Posterior Cranial Fossa

and Its Effect on the Medulla Oblongata :• In patients with tumors of the posterior cranial

fossa, the intracranial pressure is raised, there is a downward herniation of the medulla & cerebellar tonsils through the foramen magnum.

• This will produce the symptoms of : A. headache, neck stiffness, B. paralysis of the glossopharyngeal, vagus, accessory, and hypoglossal nerves owing

to traction.

• In these circumstances, it is extremely dangerous to perform a lumbar puncturedangerous to perform a lumbar puncture because the sudden withdrawal of cerebrospinal fluid may precipitate further herniation of the brain through the foramen magnum and a sudden sudden failure of vital functionsfailure of vital functions, resulting from pressure and ischemia of the cranial nerve nuclei present in the medulla oblongata.

2. Vascular Disorders of the Medulla OblongataA Lateral Medullary Syndrome:

• The lateral part of the medulla oblongata is supplied by the posterior inferior cerebellar artery, which is usually a branch of the vertebral artery.

• Thrombosis of either of these arteries produces the following signs and symptoms:

1.dysphagia and dysarthria due to paralysis of the ipsilateral palatal and laryngeal muscles (innervated by the nucleus ambiguus);

2.analgesia and thermoanesthesia on the ipsilateral side of the face (nucleus and spinal tract of the trigeminal nerve);

4. Vertigo, nausea, vomiting, and nystagmus (vestibular nuclei);

5. Ipsilateral Horner syndrome (descending sympathetic fibers);

6. Ipsilateral cerebellar signs—gait and limb ataxia (cerebellum or inferior cerebellar peduncle);

7. Contralateral loss of sensations of pain and temperature (spinothalamic tract).

B. Medial Medullary Syndrome

• The medial part of the medulla oblongata is supplied by the vertebral artery.

• Thrombosis of the medullary branch produces the following signs and symptoms:

1.Contralateral hemiparesis (pyramidal tract),

2.Contralateral impaired sensations of position and movement and tactile discrimination (medial lemniscus),

3.Ipsilateral paralysis of tongue muscles with deviation to the paralyzed side when the tongue is protruded (hypoglossal nerve).

Pons

Anterior

surface :

• The pons is anterior to the cerebellum

• connects the medulla oblongata to the midbrain.

• The anterior surface is convex from side to side

PONS

• Transverse fibers that converge on each side to form the middle cerebellar peduncle.

• Basilar groove a shallow groove in the midline, lodges the basilar artery.

• Trigeminal nerve emerges on each side from the anterolateral surface of the pons. Each nerve consists of a smaller, medial part, known as the motor root, and a larger, lateral part, known as the sensory root.

• In the groove between the pons and the medulla, emerge, from medial to lateral:

1. Abducent nerve,

2. Facial nerve,

3. Vestibulocochlear nerves.

Posterior surface• Its triangular is hidden by

cerebellum • It forms floor of upper1/2

of 4th ventricle • The posterior surface is

limited laterally by the superior cerebellar peduncles

• divided into symmetrical halves by a median sulcus.

• Lateral to median sulcus is an elongated elevation : Medial eminence,

• Medial eminence is bounded laterally by :

Sulcus limitans. • Inferior end of the medial

eminence is expanded as : Facial colliculus,

(which is produced by the root of the facial nerve winding around the

abducent nucleus)

• Lateral to the sulcus limitans is the :

Area vestibuli (produced by the underlying vestibular nuclei).

Blood Supply of Pons :By the 1. basilar artery2. Anterior cerebellar 3. Inferior cerebellar, 4. superior cerebellar

arteries.

Internal features of Pons

Level Facial colliculusCavity Fourth ventricle

Nuclei

Spinal nucleus of cranial nerve V, Abducent nucleus, Facial nucleus, Medial vestibular nucleus, Pontine nuclei,

Trapezoid nuclei

Motor Tracts

Corticospinal and Corticonuclear tracts,

Transverse pontine fibers, Medial longitudinal

fasciculusSensory Tracts

Spinal tract of cranial nerve V; Medial lemnisci

A

Pontine nucleiPontine nuclei

The very large mass of gray matter filling the pons and serving as a major way station in impulse conduction from the cerebral cortex of one hemisphere to the posterior lobe of the opposite cerebellar hemisphere through transverse pontine ransverse pontine fibers fibers by way of the middle cerebellar peduncle .

Trapezoid BodyTrapezoid Body

It is formed by ascending auditory fibers that cross to the opposite side of the brainstem.

The corticobulbar (or corticonuclear) tract

• A white mater pathway connecting the cerebral cortex to the brainstem.

• originates in motor cortex of the frontal lobe, rostral to the central sulcus internal capsule, the posterior limb of the internal capsule, midbrain ( mid1/3 cerebral peduncles).

• The muscles of the face, head and neck are controlled by the corticobulbar system, which terminates on lower motor neurons within brainstem.

• This is in contrast to the corticospinal tract in which the cerebral cortex connects to spinal motor neurons, and thereby controls movement of the upper and lower limbs.

Transverse section through the pons : at the level of the facial

colliculus.

M.C

.PI.C

.P

MCP & ICP : Middle & Inferior cerebllar peduncles respectively

4th ventricle

Medial vestibular nucleus,

Abducent nucleus,

Facial nucleus

Spinal tract & nucleus of cranial nerve V,

Trapezoid nucleus Pontine nuclei,

Transverse pontine fibers

Corticospinal and Corticonuclear tracts, ,

Medial longitudinal fasciculus

Medial lemniscus

Level Trigeminal nucleiCavity Fourth ventricle

NucleiMain sensory and motor

nucleus of cranial nerve V, Pontine nuclei, Trapezoid nuclei

Motor TractsCorticospinal and

corticonuclear tracts, Transverse pontine fibers,

Medial longitudinal fasciculusSensory Tracts Medial lemnisci

B

Transverse section through the pons : at the at the level of the trigeminal

nuclei..S.C.P

SCP : Superior cerebellar peduncle

4th ventricle

Nuclei of cranial nerve V: 1. Main sensory n.2. Motor n.

Trapezoid nuclei

Pontine nuclei,

Medial longitudinal fasciculus

Medial lemnisci

Transverse pontine fibers

Corticospinal and Corticonuclear tracts,

Clinical NotesPontine Hemorrhage

If the hemorrhage occurs from one of the arteries and is unilateral, there will be:

1. facial paralysis on the side of the lesion (involvement of the facial nerve nucleus and, therefore, results in lower motor neuron palsy)

2. paralysis of the limbs on the opposite side (involvement of the corticospinal fibers as they pass through the pons).

3. There is often paralysis of conjugate ocular deviation (involvement of the abducent nerve nucleus and the medial longitudinal fasciculus).

• When the pontine hemorrhage is extensive and bilateral, the pupils may be “pinpoint” (involvement of the ocular sympathetic fibers); there is commonly bilateral paralysis of the face and the limbs. The patient may become poikilothermic because severe damage to the pons has cut off the body from the heat-regulating centers in the hypothalamus.

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Brainstem