Brain Stem PDF

Brain stem Brain stem Stalk like in shape Connects spinal cord to higher centers of forebrain Parts: 1. Medulla oblongata 2. Pons 3. Midbrain Internal structure of medulla 1. Level of decussation of pyramids(motor / close medulla) 2. Level of decussation of leminisci (sensory/ close medulla) 3. Leve...

Brain stem Brain stem Stalk like in shape Connects spinal cord to higher centers of forebrain Parts: 1. Medulla oblongata 2. Pons 3. Midbrain Internal structure of medulla 1. Level of decussation of pyramids(motor / close medulla) 2. Level of decussation of leminisci (sensory/ close medulla) 3. Level of olives (open medulla) 4. Level Just Inferior to the Pons Level of decussation of pyramids Decussation of pyramids Fasciculus gracilis and the fasciculus cuneatus nucleus gracilis and the nucleus cuneatus (posterior to the central gray matter) Spinal nucleus of the trigeminal nerve Central canal The lateral and anterior white columns of the spinal cord is unchanged Level of decussation of leminsci Sensory decussation Leminisci are formed by internal arcuate fibers internal arcuate fibers emerge from anterior aspect of nucleus gracilis and nucleus cuneatus Decussation takes place posterior to pyramids Spinal nucleus of the trigeminal nerve (lateral to the internal arcuate fibers) spinal lemniscus lateral to the decussation of the lemnisci The spinocerebellar vestibulospinal, and the rubrospinal tracts (anterolateral) Central canal Level of sensory decussation 1----ant. Median fissure 2-----post. Median sulcus 6-----nucleus gracile 7-----nucleus cuneatus 8-----int. arcute fibers 9---- decussation of medial leminiscus 10----pyramids Level of olives (open medulla) inferior part of 4th ventricle Pyramids ICP (posterolateral corner) Medial leminiscus RF Spinal nucleus of trigeminal and its tract (anteriomedial to ICP) Nuclei of 12th 11th 10th & 9th Inf Olivary nucleus Medial longitudinal fasciculus Olivary nuclear complex Mainly Inf. Olivary nucleus Gray matter is shaped like a crumpled bag with its mouth directed medially Responsible of the elevation olive Has communications with spinal cord, cerebellum & cortex Function is associated with voluntary muscle movement Nucleus ambiguus Large motor neurons Situated deep in RF Emerging fibers join 9th, 10th and 11th (cranial root of accessory) An elongated nucleus in the medulla oblongata that gives rise to the motor fibers of the glossopharyngeal, vagus, and accessory (cranial) nerves supplying striated muscle of the larynx and pharynx and soft palat Medial longitudinal fasciculus Small tract of nerve fibers situated on each side of the midline Posterior to med. Leminiscus Anterior to 12th nucleus It is composed largely of ascending fibers from the vestibular nuclei and cochlear nuclei ascending to the motor nuclei (third, fourth and sixth) Central gray matter 1. 2. 3. 4. Lies beneath the floor of 4th ventricle Passing from M to L: Hypoglossal nucleus Dorsal nucleus of vagus Solitary nucleus Vestibular nuclei (medial and inferior) Medulla oblongata at the level of olives Level Just Inferior to the Pons No major changes Lateral vestibular nucleus replaced the inferior vestibular nucleus Cochlear nuclei visible on the anterior and posterior surfaces of the inferior cerebellar peduncle. Pons Located anterior to cerebellum 1 inch long Anterior surface is convex & shows transverse fibers that converge on each side to form middle cerebellar peduncle Located between the midbrain and medulla oblongata Contains the nuclei of cranial nerves V, VI, VII and VIII Gross appearance (anterior surface) Basilar groove (midline)..lodges basilar artery 5th nerve emerges from anterolateral surface (small motor (medial) and large sensory (lateral) 6th 7th & 8th emerges at pontomedullary junction M→L Pons – anterior view Pons (posterior view) Its hidden by from view by cerebellum Forms the upper half of floor of 4th ventricle Triangular in shape Median sulcus Medial eminence Sulcus limitans Facial colliculus (inf end of medial eminence) Area vestibuli (Lateral to sulcus limitans) Internal structure of pons Its divided by transversely running fibers of trapezoid body into: 1. Tegmentum (post part) 2. Basal part (ant part) levels Level through caudal part (facial colliculus) Level through cranial part (trigeminal nuclei) The trapezoid body is part of the acoustic pathway Made up of fibers derived from cochlear nuclei lateral lemniscus: tract of axons in the brainstem that carries information about sound from the cochlear nucleus to the contralateral inferior colliculus of the midbrain Cochlear nuclei---trapezoid body---lateral lemniscus----inf colliculus-----medial geniculate body----auditory cortex Level through caudal part (facial colliculus) Medial lemniscus most anterior part of the tegmentum, long axis running transversely Facial nucleus posterior to the lateral part of the medial lemniscus MLF: beneath the floor of the fourth ventricle on either side of the midline Abducent nucleus: beneath the floor of the upper part of the fourth Spinal nucleus of trigeminal and its tract: anteromedial aspect of ICP Medial vestibular nucleus: lateral to the abducent nucleus Level through caudal part (facial colliculus) Basilar part of pons contain small masses of nerve cells called pontine nuclei Corticopontine fibers terminate in pontine nuclei Axons of these cells give origin to transverse fibers of the pons which cross the midline and intersect the corticospinal & corticonuclear tracts, breaking them into small bundles Transverse fibers enter MCP to cerebellum This connection is the main pathway linking cerebellum to cerebral cortex Facial Nerve Nuclei Parasympathetic Nuclei: Location: Posterolateral to the main motor nucleus - superior salivatory: receives from the hypothalamus - Lacrimal nucleus: receives from – hypothalamus (Emotional) – sensory nuclei of the trigeminal (reflex ) Level through caudal part (facial colliculus) Level through cranial part (trigeminal nuclei) Motor nucleus of trigeminal n: beneath the lateral part of thefourth ventricle within the reticular formation Main Sensory nucleus of trigeminal n (lateral) SCP: posterolateral to the motor nucleus of V Trapezoid body Medial leminiscus Lateral leminiscus, Spinal leminiscus: lateral extremity of the medial lemniscus Level through cranial part (trigeminal nuclei) The Brain Stem – The Midbrain Lies between the diencephalon and the pons Central cavity – the cerebral aqueduct Cerebral peduncles located on the ventral surface of the brain divided by the substantia nigra into: Crus cerebri: Anterior Tegmentum: Posterior  Contain pyramidal (corticospinal) tracts Superior cerebellar peduncles  Connect midbrain to the cerebellum Midbrain ant. View Interpeduncular fossa Crus cerebri 3rd nerve emerges from medial side of crus cerebri in the interpeduncular fossa The Midbrain-posterior view Corpora quadrigemina – the largest nuclei  Divided into the superior and inferior colliculi ▪ Superior colliculi – nuclei that act in visual reflexes ▪ Inferior colliculi – nuclei that act in auditory reflexes Trochlear nerve emerges below the level of inf. Colliculus (from posterior surface) Occulomotor nerve emerges at the level of sup. colliculus Sup.brachium (to lateral geniculate body) Inf. Brachium (to medial geniculate body) 4th emerges The Brain Stem – The Midbrain Imbedded in the white matter of the midbrain  Two pigmented nuclei  Substantia nigra – neuronal cell bodies contain melanin ▪ Functionally linked to the basal nuclei  Red nucleus – lies deep to the substantia nigra ▪ Largest nucleus of the reticular formation Cerebral peduncle is divided into crus cerebri (ant) & tegmentum (post) Tectum is post to cerebral aqueduct Substantia nigra is situated between the tegmentum and crus cerebri Trochlear nucleus lies close to midline in the central gray matter (posterior to MLF) Trochlear nerves decussate in the superior medullary velum Decussation of sup. cerebellar peduncles (central part of the tegmentum anterior to the cerebral aqueduct) RF is lateral to decussation Medial, spinal ,trigeminal & lateral leminisci (Posterior to Substantia nigra) Level of inf. colliculus Substantia nigra Crus cerebri Mesencephalic nucleus of trigeminal (lateral to cerebral aqueduct) MLF Level of inferior colliculus Level of superior colliculus EdingerWestphal nucleus pretectal nucleus: close to the lateral part of the superior colliculus. Red nucleus Rounded mass of gray matter Situated bt cerebral aqueduct and substantia nigra Reddish blue(vascularity & iron containing pigment) Afferents from: cerebral cortex,cerebellum,substa ntia nigra, thalamic nuclei, spinal cord Efferent to: spinal cord, reticular formation. thalamus and substantia nigra involved in motor coordination. Crus cerebri Corticospinal & corticonuclear fibers (middle) Frontopontine fibers (medial) Temporopontine fibers (lateral) these descending tracts connect the cerebral cortex with spinal cord, cranial nerves nuclei, pons & cerebellum Level at superior colliculus Superior colliculus Occulomotor nucleus (posterior to MLF) Occulomotor n emerges through red nucleus Edinger-Westphal nucleus pretectal nucleus: close to the lateral part of the superior colliculus. MLF Medial , trigeminal, spinal leminiscus (no lateral leminiscus) Red nucleus Substantia nigra Crus cerebri RF Substantia nigra Large motor nucleus is a brain structure located in the midbrain plays an important role in reward, addiction, and movement. Substantia nigra is Latin for "black substance" due to high levels of melanin has connections with basal ganglia ,cerebral cortex Concerned with muscle tone Parkinson's disease is caused by the death of neurons in the substantia nigra Reticular Formation Deeply placed continuous network of nerve cells and fibers that extend from the spinal cord through the medulla, the pons, the midbrain, the subthalamus, the hypothalamus, and the thalamus Divided into three longitudinal columns:  Median column: intermediate-size neurons  Medial column: large neurons  Lateral column: small neurons General function:  Control of skeletal muscle  Control of somatic and visceral sensations  Control of the autonomic nervous system  The reticular activating system. Reticular Formation In Medulla Raphe nuclei  Pallidus  Obscurus  Magnus Medial medullary reticular area  Central nucleus of the medulla  Gigantocellular reticular nucleus Lateral medullary reticular area  Ventrolateral reticular area  Lateral reticular nucleus  Parvocellular nucleus Reticular Formation In Pons Raphe nuclei  Magnus  Pontis  Superior central  Dorsal Medial reticular area  Gigantocellular reticular nucleus  Caudal  Oral Lateral reticular area  Parvocellular nucleus  Medial parabrachial nucleus  Lateral parabrachial nucleus Reticular Formation In Midbrain Raphe nuclei  Posterior (dorsal) raphe nucleus: anterior PAG Medial reticular area  Cuneiform nucleus  Subcuneiform nucleus Participates in the ascending systems that: Regulate states of consciousness. Project to the thalamus (thalamic reticular nucleus) Ascending fiber system is largely responsible for maintaining an alert, wakeful state and thus forms part of the ascending reticular activating system Reticular Formation Deeply placed posterior to the olivary nucleus Widespread connections Arousal of the brain as a whole Reticular activating system (RAS) Maintains consciousness and alertness Basilar artery Branches of basilar artery  anterior inferior cerebellar artery (AICA) supplies inferior surface of the cerebellum  Pontine arteries supply pons  superior cerebellar artery supplies superior surface of cerebellum and pons Blood supply of spinal cord 58 Medial medullary syndrome (Dejerine syndrome) Symptoms  Contralateral hemiparesis(pyramidal and corticospinal damage)  Contralateral loss of proprioception and vibratory sense (medial lemniscus)  Deviation of the tongue to the ipsilateral side when it is protruded (hypoglossal root or nucleus injury) 59 Lateral medullary syndrome (Wallenberg syndrome) Symtoms  contralateral loss of pain and temperature sensation from the body (anterolateral system)  ipsilateral loss of pain and temperature sensation from the face (spinal trigeminal tract and nucleus),  vertigo and nystagmus (vestibular nuclei),  loss of taste from the ipsilateral half of the tongue (solitary tract and nucleus),  hoarseness and dysphagia (nucleus ambiguus or roots of cranial nerves IX and X)  Ipsilateral Horner syndrome: hypothalamospinal fibers 60 61 Vascular lesions of the posterior spinal artery Symptoms  ipsilateral loss of proprioception and vibratory sense  ipsilateral loss of pain and temperature sensation from the face 62 64 65 Foville syndrome Due to: Occlusion of the paramedial branches ipsilateral abducens nerve paralysis contralateral hemiparesis variable contralateral sensory loss reflecting various degrees of damage to the medial lemniscus Millard-Gubler syndrome If the area of damage is shifted somewhat laterally to include the root of the facial nerve along with corticospinal fibers, the patient has a contralateral hemiparesis and an ipsilateral paralysis of the facial muscles 66