brainstemthe posterior part of the medulla between the posterior median sulcus and the...
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www.khaleelalyahya.net
BRAINSTEM
Khaleel Alyahya, PhD, MEd
Resources
Essential of Human
Anatomy & Physiology
By Elaine Marieb and Suzanne Keller
Human Brain
By John Nolte
Clinical
Anatomy
By Richard Snell
Atlas of Human Anatomy
By Frank Netter
Gray’s Anatomy
By Richard Drake, Wayne
Vogl & Adam Mitchell
KENHUB
www.kenhub.com
Brainstem
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“The brain stem is a vital
structure for our basic survival.
It contains key centers that
enable us to breath and our
hearts to beat.” (KENHUB)
Brain
• Cerebrum
• Diencephalon
• Cerebellum
• Brain Stem
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By Khaleel Alyahya, PhD, MEd
Introduction
▪ It consists of three parts:
• Midbrain
• Pons
• Medulla Oblongata
▪ It plays an important role in the regulation of cardiac andrespiratory functions.
▪ It regulates the central nervous system and is important inmaintaining consciousness.
▪ Regulating the sleep cycle.
▪ It provides the pathway for fibers tracts running betweenhigher and lower neuronal centers.
▪ Each part of brain stem is connected to cerebellum bycerebellar peduncles (superior, middle & inferior).
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By Khaleel Alyahya, PhD, MEd
Functions
▪ Conduction
• Provides the pathway for fibers tracts runningbetween higher and lower neuronal centers.
▪ Cranial nerves iii-xii emerge from the brainstem.
• These cranial nerves supply the face, head, andviscera.
▪ Integration
• Involved in cardiovascular system control, respiratorycontrol, pain sensitivity control, alertness, awareness,and consciousness.
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By Khaleel Alyahya, PhD, MEd
Overview
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By Khaleel Alyahya, PhD, MEd
MIDBRAIN
Introduction
▪ The most superior of the three regions of thebrainstem, and the smallest of the three regions.
▪ Located between Diencephalon superiorly and Ponsinferiorly
▪ Two bulging cerebral peduncles (little feet ofcerebrum)
• Hold up the cerebrum
▪ Cerebral Aqueduct
• Connects the 3rd ventricle with the 4th ventricle
▪ Portion of the CNS associated with:
• Vision
• Hearing
• Motor Control
• Sleep/Wake
• Temperature Regulation 9
By Khaleel Alyahya, PhD, MEd
Division
▪ It can be divided into two main parts:
• Tectum: located posterior to the cerebral aqueduct
• Paired cerebral peduncles: located anteriorly andlaterally.
o Internally, the cerebral peduncles are furtherseparated by the substania nigra into the cruscerebri (anterior) and the tegmentum(posterior).
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By Khaleel Alyahya, PhD, MEd
Tectum
▪ It houses four rounded prominencesnamed colliculi (the corpora quadrigemina) which sitdirectly inferior to the pineal gland.
▪ There are two superior and two inferior colliculiseparated by the cruciform sulcus.
▪ Extending laterally from each colliculi are thequadrigeminal brachium:
• Superior quadrigeminal brachium forms a pathwaybetween the superior colliculus and the retina of theeye.
• Inferior quadrigeminal brachium conveys fibersfrom the lateral lemniscus and inferior colliculus tothe medial geniculate body.
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By Khaleel Alyahya, PhD, MEd
Cerebral Peduncles
▪ The paired cerebral peduncles extend from thecerebral hemispheres to converge as they meet thepons.
▪ They are separated anteriorly in the midline bythe interpeduncular fossa.
▪ The oculomotor nerve (CN 3rd) is seen exiting frombetween the peduncles while the optic tract runsaround the superior border of the midbrain.
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By Khaleel Alyahya, PhD, MEd
Internal Structure
▪ The anteriolateral surface of the midbrain houses thepaired crus cerebri.
▪ Four fiber tracts run within the crus:
• Frontopontine fibers – located most medially.
• Corticospinal fibers – motor fibers from the primary motorcortex.
• Corticobulbar tracts – motor fibers from the primary motorcortex.
• Temporopontine fibers – located posterolaterally.
▪ Posteriorly is the substantia nigra – a pigmented nucleusthat separates the two regions of the cerebral peduncles.
▪ The cerebral aqueduct is a midline structure surroundedby central gray matter.
▪ The decussation of the superior cerebellar peduncles canbe seen centrally at this level.
▪ At the very posterior pole, we find the tectum which, atthis level, contains the inferior colliculus.
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By Khaleel Alyahya, PhD, MEd
Overview
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By Khaleel Alyahya, PhD, MEd
Weber’s Syndrome
▪ Described in 1863 by German-born physician.
▪ A form of stroke characterized by the presence of anipsilateral oculomotor nerve palsy andcontralateral hemiparesis or hemiplegia.
▪ Affect several structures in midbrain including;
• Substantia nigra
o Contralateral parkinsonism causing movement disorderof the contralateral body.
• Oculomotor nerve fibers
o Ipsilateral oculomotor nerve palsy with a drooping eyelidand fixed wide pupil pointed down and out. This leadsto diplopia.
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By Khaleel Alyahya, PhD, MEd
Benedikt’s Syndrome
▪ Caused by a lesion like infarction, hemorrhage ortumor in the tegmentum of the midbrain andcerebellum.
▪ It can also result from occlusion of the posteriorcerebral artery or paramedian penetrating branchesof the basilar artery.
▪ Characterized by the presence of an oculomotornerve palsy and cerebellar ataxia including tremor.
▪ Similar to Weber’s Syndrome.
• Weber’s associated with hemiplegia (paralysis)
• Benedikt's associated with hemiataxia (disturbedcoordination of movements).
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By Khaleel Alyahya, PhD, MEd
PONS
Introduction
▪ Latin word means bridge.
▪ The largest part of the brainstem.
▪ Located:
• Superior to the medulla oblongata
• Inferior the midbrain
• Anterior to the cerebellum.
▪ It includes:
• Tracts that conduct signals from the cerebrum downto the cerebellum and medulla.
• Tracts that carry the sensory signals up into thethalamus
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By Khaleel Alyahya, PhD, MEd
Anterior Surface
▪ The anterior surface is marked by a bulging formedby the transverse pontocerebellar fibers.
• It results from corticopontocerebellarfibers running horizontally, bringing informationfrom the cerebral cortices and the pontine nuclei tothe dentate nucleus of the cerebellum
▪ The basilar groove demarcates the midline of theventral surface and is where the basilar artery islocated.
▪ There are four cranial nerves emerging from Pons:
• Trigeminal (5th)
• Abducent (6th)
• Facial (7th)
• Vestibulocochlear (8th)
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By Khaleel Alyahya, PhD, MEd
Posterior Surface
▪ It consists mainly of two pairs of thick stalks called cerebellarpeduncles.
▪ It connected to the cerebellum by the middle cerebellarpeduncles.
▪ Removal of the cerebellum will reveal the underlying fourthventricle.
▪ The Pons contains nuclei that relay signals from the forebrainto the cerebellum.
▪ The medial eminence marks the midline of the floor.
▪ The facial colliculus is a bulging formed by the fibers of thefacial nerve looping around the abducens nucleus.
▪ The stria medullaris of the fourth ventricle is a bundle ofnerve fibers crossing transversely from the lateral aspect intothe midline.
▪ The angle formed at the junction of the pons, medulla, andcerebellum is another anatomical landmark and isnamed cerebellopontine angle.
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By Khaleel Alyahya, PhD, MEd
Internal Anatomy
▪ The pons is comprised of two major components,the ventral pons and the tegmentum.
▪ The ventral pons contains the pontine nuclei, which areresponsible for coordinating movement.
▪ Fibers from the pontine nuclei cross the midline andform the middle cerebellar peduncles on their way to thecerebellum.
▪ The tegmentum is a set of nuclei found throughout thebrainstem that are responsible for arousaland attentiveness.
▪ The tracts passing through the pons including:
• Descending corticospinal tracts responsible for voluntarymotor control of the body.
• Descending corticobulbar tracts responsible for voluntarymotor control of face, head and neck.
• Ascending medial lemniscus tracts responsible for finetouch, vibration and proprioception.
• Ascending spinothalamic tracts responsible for pain andtemperature sensation
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By Khaleel Alyahya, PhD, MEd
Overview
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By Khaleel Alyahya, PhD, MEd
MEDULLA OBLONGATA
Introduction
▪ The lower half of the brainstem.
▪ It contains the cardiac, respiratory, vomiting andvasomotor centers.
▪ Control autonomic functions (involuntary);
• Breathing
• Heart rate
• Blood Pressure
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By Khaleel Alyahya, PhD, MEd
Anterior Surface
▪ The superior margin of the medulla is located at the junctionbetween the medulla and pons, while the inferior margin ismarked by the origin of the first pair of cervical spinalnerves.
▪ In the midline of the medulla is the anterior medianfissure, which is continuous along the length of the spinalcord. (it is interrupted temporarily by the decussation of thepyramids).
▪ There are two sulci are visible; the anterolateral sulcus andthe posterolateral sulcus.
▪ The pyramids are paired swellings found between theanterior median fissure and the anterolateral sulcus.
▪ This elevation is caused by the corticospinal tract.
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By Khaleel Alyahya, PhD, MEd
Anterior Surface
▪ The olives are another pair of swellings located laterally tothe pyramids between the anterolateral and posterolateralsulci.
▪ It caused by a large mass of gray matter known as theinferior Olivary nucleus.
▪ Arising from the junction between the pons and medulla isthe abducens nerve (CN VI).
▪ Extending out of the vanterolateral sulcus is the hypoglossalnerve (CN XII).
▪ In the posteriolateral sulcus, three more cranial nerves jointhe medulla (CN IX, CN X, and CN XI).
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By Khaleel Alyahya, PhD, MEd
Posterior Surface
▪ The posterior part of the medulla between the posteriormedian sulcus and the posterolateral sulcus contains tractsthat enter it from the Posterior Funiculus of the spinal cord.
• Fasciculus gracilis, lying medially.
• Fasciculus cuneatus, lying laterally.
▪ The posterior aspect of the medulla is occupied by atriangular fossa, which forms the lower part of the floor ofthe fourth ventricle.
• The fossa is bounded on either side by the inferiorcerebellar peduncle, which connects the medulla tothe cerebellum.
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By Khaleel Alyahya, PhD, MEd
Overview
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By Khaleel Alyahya, PhD, MEd
Cranial Nerves
▪ There are four cranial nerves emerging from MedullaOblongata:
• Hypoglossal (12th): from sulcus between pyramid &olive
• Cranial part of accessory (11th): from sulcusdorsolateral to olive (from above downwards)
• Vagus (10th)
• Glossopharyngeal (9th)
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By Khaleel Alyahya, PhD, MEd
Internal Structure
▪ The internal structures of the medulla must be viewed incross section to understand the layout.
▪ Three levels of the medulla are typically discussed (inferior tosuperior):
• Level of decussation of the pyramids.
• Level of decussation of the medial lemnisci.
• Level of the olives.
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By Khaleel Alyahya, PhD, MEd
Level of Pyramid Decussation
▪ This is the major decussation point of the descending motorfibers.
▪ Most of motor fibers located within the pyramids crossdiagonally and posteriorly and continue down the spinalcolumn as the lateral corticospinal tracts.
▪ At this level, the central portion of the medulla contains graymatter, while the outer portions consist of white matter.
▪ The posterior white matter contains the fasciculusgracilis and the more lateral fasciculus cuneatus.
▪ Corresponding portions of gray matter extend to theseregions and are the nucleus gracilis and nucleus cuneatus,respectively.
▪ Unchanged from the spinal cord, the spinocerebellartracts (posterior and anterior) are located laterally, with thelateral spinothalamic tract situated between them.
▪ The large trigeminal nucleus and tracts can be foundposterior to these tracts.
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By Khaleel Alyahya, PhD, MEd
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BLOOD SUPPLY
Medulla Oblongata
▪ Anterior and Lateral portions are supplied by:
• Anterior spinal artery
• Small branches of the vertebral artery
▪ Posterior portions are supplied by:
• Posterior spinal artery
• Small branches of the posterior inferior cerebellarartery (PICA)
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By Khaleel Alyahya, PhD, MEd
Pons
▪ Branches of the basilar artery
▪ Contribution of:
• Anterior inferior cerebellar artery (AICA)
• Superior cerebellar artery
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By Khaleel Alyahya, PhD, MEd
Midbrain
▪ Mainly by:
• Posterior cerebral artery
• Some contribution from the superior cerebellarartery
▪ In addition, the anterior choroidal artery and theposterior communicating artery may contribute toblood supply.
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By Khaleel Alyahya, PhD, MEd
Overview
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By Khaleel Alyahya, PhD, MEd
Cranial Nerves of Brainstem
▪ Midbrain
• Oculomotor nerve (3rd)
• Trochlear (4th)
▪ Pons
• Trigeminal (5th)
• Abducent (6th)
• Facial (7th)
• Vestibulocochlear (8th)
▪ Medulla Oblongata
• Glossopharyngeal (9th)
• Vagus (10th)
• Cranial Part of Accessory (11th)
• Hypoglossal (12th)
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By Khaleel Alyahya, PhD, MEd
Brainstem Stroke Syndrome
▪ Involving a stroke of the brainstem causingimpairment both cranial nuclei and of the longtracts.
▪ Someone may have vertigo, dizziness and severeimbalance.
▪ The symptoms of vertigo, dizziness or imbalanceusually occur together.
• dizziness alone is not a sign of stroke though.
▪ Brainstem stroke can also cause diplopia, slurredspeech and decreased level of consciousness.
▪ Further, stroke may lead to locked-in syndrome.
• Condition in which a patient is aware but cannotmove or communicate verbally due to completeparalysis of nearly all voluntary muscles in the bodyexcept for vertical eye movements and blinking
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