Brain stem

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Brain stem Cerebellum
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The brain

• Telencephalon
• Diencephalon
• Cerebellum
• Brain stem

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The brain stem

• Consists of
• Midbrain
• Pons
• Medulla oblongata

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Medulla oblongata

• Ventral surface
• Pyramid contain pyramidal tract (corticospinal
  tract)
• Decussation of pyramid formed by crossing fibers
  of corticospinal tract
• Olive produced by underlying inferior olivary
  nucleus
• Anterolateral sulcus rootlets of hypoglossal
  nerve emerge from it
• Retroolivary sulcus rootlets of
  glossopharyngeal, vagus and accessory nerves
  emerge from it

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Medulla oblongata

• Dorsal surface
• Lower portion
• Gracile tubercle produced by underlying gracile
  nucleus
• Cuneate tubercle marks the site of cuneate
  nucleus
• Inferior cerebellar peduncle
• Obex
• Upper portion forms the lower half of rhomboid
  fossa

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Pons

• Ventral surface
• Basilar part
• Basilar sulcus
• Bulbopontine sulcus from medial to lateral, the
  abducent, facial and vestibulocochlear nerves
  appear
• Middle cerebellar peduncle
• Trigeminal nerve
• Pontocerebellar trigone the junction of medulla,
  pons and cerebellum

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Pons

• Dorsal surface
• Superior cerebellar peduncle
• Superior medullary velum
• Trochlear nerve

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Midbrain

• Ventral surface
• Crus cerebri
• Interpeduncular fossa oculomotor nerves emerge
  from medial of crus cerebri
• Posterior perforated substance

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Midbrain

• Dorsal surface
• Superior colliculus constitute centers for visual
  reflexes
• Inferior colliculus associated with auditory
  pathway
• Brachium of superior colliculi
• Brachium of inferior colliculi

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Fourth ventricle
Central canal ?fourth ventricle ?mesencephalic
aqueduct?third ventricle

• Position
• Situated ventral to cerebellum, and dorsal to
  pons and cranial half of medulla

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• Boundaries
• Inferolateral gracile and cuneate tubercles,
  inferior cerebellar peduncle
• Superolateral superior cerebellar peduncle
• Lateral recess

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• Features
• Median sulcus
• Sulcus limitans
• Vestibular area overlies vestibular nuclei
• Acoustic tubercle overlying dorsal cochlear
  nucleus
• Medial eminence
• Striae medullares

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• Facial colliculus overlies nucleus of abducent
  n. and genu of facial nerve
• Hypoglossal triangle verlying hypoglossal
  nucleus
• Vagal triangle overlies dorsal nucleus of vagus
  nerve
• Inferior Fovea
• Area postrema

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• Roof
• Anterior part formed by superior cerebellar
  peduncle and superior medullary velum
• Posterior part formed by inferior medullary
  velum and choroid plexus of fourth ventricle
• Three apertures
• Median aperture of fourth ventricle
• Two lateral apertures of fourth ventricle

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Internal structures

• Gray matter
• Cranial nerve nuclei
• Relay nuclei

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Names of cranial nerves

• ? Olfactory nerve
• ? Optic nerve
• ? Oculomotor nerve
• ? Trochlear nerve
• ? Trigeminal nerve
• ? Abducent nerve
• ? Facial nerve
• ? Vestibulocochlear nerve
• ? Glossopharyngeal nerve
• ? Vagus nerve
• ? Accessory nerve
• ? Hypoglossal nerve

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Functional components

• General somatic afferent fibers (GSA) transmit
  exteroceptive and proprioceptive impulses from
  head and face to somatic sensory nuclei
• Special somatic afferent fibers (SSA) transmit
  sensory impulses from special sense organs of
  vision, equilibrium and hearing to the brain
• General visceral afferent fibers (GVA) transmit
  interoceptive impulses from the viscera to the
  visceral sensory nuclei
• Special visceral afferent fibers (SVA) transmit
  sensory impulses from special sense organs of
  smell and taste to the brain
• General somatic efferent fibers (GSE) innervate
  skeletal muscles of eye and tongue
• Special visceral efferent fibers (SVE) transmit
  motor impulses from the brain to skeletal muscles
  derived from brachial (gill) arches of embryo.
  These include the muscles of mastication, facial
  expression and swallowing
• General visceral efferent fibers (GVE) transmit
  motor impulses from the general visceral motor
  nuclei and relayed in parasympathetic ganglions.
  The postganglionic fibers supply cardiac
  muscles,smooth muscles and glands

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Classification of cranial nerves

• Sensory cranial nerves contain only afferent
  (sensory) fibers
• ?Olfactory nerve
• ?Optic nerve
• ? Vestibulocochlear nerve
• Motor cranial nerves contain only efferent
  (motor) fibers
• ? Oculomotor nerve
• ? Trochlear nerve
• ?Abducent nerve
• ? Accessory nerv
• ? Hypoglossal nerve
• Mixed nerves contain both sensory and motor
  fibers---
• ?Trigeminal nerve,
• ? Facial nerve,
• ?Glossopharyngeal nerve
• ?Vagus nerve

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Sensory cranial nerves
N. Location of cell body and axon categories Cranial exit Terminal nuclei Main action
? Olfactory cells (SVA) Cribrifom foramina Olfactory bulb Smell
? Ganglion cells (SSA) Optic canal Lateral geniculate body Vision
? Vestibular ganglion(SSA) Internal acoustic meatus Vestibular nuclei Equilibrium
? Cochlear ganglion (SSA) Internal acoustic meatus Cochlear nuclei Hearing
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Motor cranial nerves
N. Nucleus of origin and axon categories Cranial exit Main action
? Nucleus of oculomotor (GSE) Superior orbital fissure Motor to superior, inferior and medial recti inferior oblique levator palpebrae superioris
? Accessory nucleus of oculomotor (GVE) Superior orbital fissure Parasympathetic to sphincter pupillea and ciliary muscles
? Nucleus of trochlear nerve (GSE) Superior orbital fissure Motor to superior oblique
? Nucleus of abducent nerve (GSE) Superior orbital fissure Motor to lateral rectus
? Nucleus of accessory nerve (SVE) Jugular foramen Motor to sternocleidomastoid and trapezius
? Nucleus of hypoglossal nerve( GSE) Hypoglossal canal Motor to muscles of tongue except palatoglossus
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General somatic efferent nuclei

• Nucleus of oculomotor n.
• Nucleus of trochlear n.
• Nucleus of abducent n.
• Nucleus of hypoglossal n.

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Special visceral motor nuclei

• Motor nucleus of trigeminal n.
• Nucleus of facial n.
• Nucleus ambiguous
• Accessory nucleus

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Special visceral efferent nuclei
Nucleus Site Cranial n. Function
Motor nucleus of trigeminal n. Pons ? Masticatory muscles, tensor palati t. tympani
Nucleus of facial n. Pons ? Facial m., platysma, posterior belly of digastric, stylohyoid, stapedius
Nucleus ambiguus Medulla ?,?.? Skeletal m. of pharynx, larynx and upper part of esophagus
Accessory nucleus Medulla-cervical cord ? Sternocleidomastoid, trapezius
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General visceral motor nuclei

• Accessory oculomotor nucleus
• Superior salivatory nucleus
• Inferior salivertory nucleus
• Dorsal nucleus of vagus n.

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General visceral efferent nuclei
Nucleus Site Cranial nerve Function
Accessory oculomotor nucleus Midbrain ? Sphincter pupillae and ciliary m.
Superior salivatory nucleus Pons ? Submandibular, sublingual and lacrimal glands
Inferior salivertory nucleus Medulla ? Parotid gland
Dorsal nucleus of vagus n. medulla ? Many cervical, thoracic and abdominal viscera
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Visceral sensory nuclei ( general and special )

• Nucleus of solitary tract

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Visceral sensory nuclei ( general and special )
Nucleus Site Cranial n. Function
Nucleus of solitary tract Medulla ?,?,? Taste and visceral sensation
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General somatic afferent nuclei

• Mesencephalic nucleus of trigeminal n.
• Main sensory nucleus of trigeminal n.
• Spinal nucleus of trigeminal n.

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General somatic sensory nuclei
Nucleus Site Cranial n. Function
Mesencephalic nucleus of trigeminal n. Midbrain ? Proprioception of head
Main sensory nucleus of trigeminal n. Pons ? Tactile sensation of face
Spinal nucleus of trigeminal n. Medulla upto 2nd cx. seg. ? Pain and temperature sense of face
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Special somatic afferent nuclei

• Cochlear nuclei 2
• - Dorsal
• - Ventral
• Vestibular nuclei 4
• - Superior
• - Inferior
• - Medial
• - Lateral

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Special somatic afferent nuclei
Nucleus Site Cranial n. Function
Cochlear nuclei Pons and medulla ? Sense of hearing
Vestibular nuclei Pons and medulla ? Sense of equilibrium
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Non-cranial nerve nuclei
Nucleus Site
Gracile nucleus Medulla (underneath gracile tubercle)
Cuneate nucleus Medulla (underneath cuneate tubercle)
Superior olivery nucleus Pons
Pontine nucleus pons
Nucleus of inferior colliculus Midbrain
Gray matter layers of superior colliculus Midbrain
Red nucleus Midbrain
Substantia nigra Midbrain
Pretectal area Midbrain
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Cerebellum

• Site Posterior cranial fossa, behind pons
  medulla oblongata.
• 2 Surfaces Superior Inferior.
• 3 Parts
• Vermis
• - Superior indistinct from sup. surface.
• - Inferior lodged in the vallecula.
• 2 Lobes

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Cerebellum

• 3 Fissures
• Primary
• Horizontal
• Posterolateral
• Functional Divisions
• Archi-cerebellum vestibulo-cerebellum.
• Paleo-cerebellum spino-cerebellum.
• Neo-cerebellum ponto-cerebellum.

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Cerebellum