Lec 10 - Brainstem and Cranial nerves

• The brainstem is the most caudal and primitive part of the brain
• The brainstem consists of the midbrain, pons, and medulla oblongata
• Brainstem functions

  • a passageway for nerve connections (fiber tracts) between the cerebrum and spinal cord
  • involved in face and neck innervation (cranial nerves)
  • involved in highly programmed automatic behaviours that ensure survival (consciousness, respirations, blood pressure)
• The medulla is continuous with the spinal cord
• The anterior midbrain consists of

  • cerebral peduncles
  • interpeduncular fossa
• The anterior pons consists of

  • cerebellar peduncles
• The anterior medulla consists of

  • pyramids
  • olives
  • anterior median fissure
• The pyramids of the medulla are paired white matter structures; motor fibers of descending tracts
• The olives of the medullar are efferent connections with cerebellum; movement control
• Label the areas of the anterior brainstem

  A) cerebral peduncles

  B) interpeduncular fossa

  C) ventral groove

  D) pons

  E) cerebellar peduncles

  F) pyramids

  G) olives

  H) anterior median fissure

  
• The ventral groove on the anterior pons is where the basilar artery sits
• The posterior midbrain consists of

  • superior colliculus (visual reflex)
  • inferior colliculus (auditory reflex)
• The posterior pons consists of

  • superior cerebellar peduncles
  • middle cerebellar peduncles
  • inferior cerebellar peduncles
• The posterior medulla consists of

  • fasciculus cuneate
  • fasciculus gracile
  • obex
• The fasciculus cuneate and fasciculus gracile are paired white matter structures of sensory ascending tracts - proprioception, temperature, pain
• The lateral recess at the ponto-medullary junction is how the 4th ventricle communicates with the subarachnoid space
• The area postrema on the posterior medulla does not contain a blood-brain barrier. It senses blood chemicals and if the blood chemicals are off, it will induce vomiting. Known as the vomiting center
• Label the posterior brainstem

  A) superior colliculus

  B) inferior colliculus

  C) superior cerebellar peduncle

  D) middle cerebellar peduncle

  E) inferior cerebellar peduncle

  F) lateral recess

  G) 4th ventricle

  H) area postrema

  I) obex

  J) fasciculus cuneate

  K) fasciculus gracile

  
• The midbrain can be divided into

  • tectum
  • tegmentum
  • basis pedunculi
• The tectum is the posterior midbrain, the tegmentum is the core of the midbrain, and the basis pedunculi is the anterior that consists of the cerebral peduncles
• All four colliculus (superior and inferior) of the midbrain together are called the corpora quadrigemina
• The red nucleus is a part of the tegmentum (midbrain) that has a role in motor function. It receives contralateral cerebellar projections and sends projections to the ipsilateral thalamus
• The basis pedunculi is made up of the cerebral peduncles (crus cerebri) and the substantia nigra
• The cerebral peduncles transmits descending corticospinal and corticobulbar fibers (motor)
• The cerebral aqueduct runs through the midbrain (passage between 3rd and 4th ventricle)
• The periaqueductal gray (next to the cerebral aqueduct in the midbrain) is the site of crude pain localization and perception
• Label the sections of the midbrain

  A) tectum

  B) tegmentum

  C) basis pedunculi

  D) cerebral aqueduct

  E) periaqueductal gray

  F) red nucleus

  G) cerebral peduncles

  H) substantia nigra

  
• The pons is traversed by bundles of ascending and descending fibers. The white matter bundles are interrupted by gray matter nuclei called pontine nuclei

  
• The caudal medulla is known as the closed part of the medulla and the rostral medulla is the open part of the medulla
• Pyramidal decussation is where 85% of the fibers will cross to the contralateral side. If you have a lesion above this point, the effect will be on the contralateral side.
• the pyramidal decussation is found in the medulla
• The olives (medulla) are formed by inferior olivary nucleus. Olives have gray matter in them from being a remnant of the cerebellum but they are part of the medulla
• 11 cranial nerves emerge from the ventral brainstem and one (CN IV) is dorsal
• The midbrain has the nuclei of CN III & IV
• The pons has the nuclei of CN V, VI, VII
• CN VII and VIII emerge at the cerebello-pontine angle
• The medulla oblongata is continuous with the spinal cord and contain the nuclei of CN VIII, IX, X, and XII - CN XI nuclei is located in the rostral portion of the spinal cord
• CN IX, X, and XI emerge/enter medulla lateral to olive, whereas CN XII emerge medial to olive (between olive and pyramid)
• Cranial nerves

  • CN I - olfactory
  • CN II - optic
  • CN III - oculomotor
  • CN IV - trochlear
  • CN V - trigeminal (ophthalmic, maxillary, mandibular)
  • CN VI - abducens
  • CN VII - facial
  • VIII - vestibulocochlear
  • IX - glossopharyngeal
  • X - vagus
  • XI - accessory
  • XII - hypoglossal
• CN I carries sensory information (smell) from olfactory receptors distributed in olfactory mucosa at the roof of the nasal cavity to the olfactory bulb situated in the anterior cranial fossa