Brain anatomy: BRAIN STEM

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Brain anatomy BRAIN STEM
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Brain Stem and cerebellum

• The brain stem includes the medulla and pons,
  located ventral to the cerebellum.
• As a result of the relatively tight packaging of
  numerous ascending and descending tracts, as well
  as nuclei, within the brain stem, even small
  lesions within it can produce very significant
  neurological deficits.

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• Next few slides show the nerve fibres or tracts
  that emerge from the brain stem

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DESCENDING AND ASCENDING TRACTS

• All descending tracts that terminate in the
  spinal cord (eg, the corticospinal tract) pass
  through the brain stem.
• In addition, several descending fiber systems
  terminate or originate in the brain stem.
• Similarly, all ascending tracts (eg, the
  spinothalamic tracts) that reach the brain stem
  or the cerebral cortex pass through part or all
  of this region other ascending tracts originate
  in the brain stem.
• The brain stem is, therefore, an important
  conduit or relay station for many longitudinal
  pathways, both descending and ascending.

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CRANIAL NERVE NUCLEI

• Almost all the cranial nerve nuclei are located
  in the brain stem. (The exceptions are the first
  two cranial nerve nuclei, which come from the
  brain itself.) Portions of the cranial nerves
  also pass through the brain stem.

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Cranial nerves

• Cranial nerve fibers with motor (efferent)
  functions arise from collections of cells (motor
  nuclei) that lie deep within the brain stem they
  are homologous to the anterior horn cells of the
  spinal cord.
• Cranial nerve fibers with sensory (afferent)
  functions have their cells of origin (first-order
  nuclei) outside the brain stem, usually in
  ganglia that are homologous to the dorsal root
  ganglia of the spinal nerves.
• The cranial nerves can be grouped
  functionally Nerves I, II, and VIII are
  devoted to special sensory input. Nerves III,
  IV, and VI control eye movements and pupillary
  constriction. Nerves XI and XII are pure motor
  (XI sternocleidomastoid and trapezius XII
  muscles of tongue). Nerves V, VII, IX, and X
  are mixed.

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Also

• CEREBELLAR PEDUNCLESThe pathways to and from the
  cerebellum pass through three pairs of cerebellar
  peduncles
• DESCENDING AUTONOMIC SYSTEM PATHWAYSThese paths
  to the spinal cord pass through the brain stem
• RETICULAR FORMATIONSeveral of these areas in the
  brain stem are vitally involved in the control of
  respiration cardiovascular system functions and
  states of consciousness, sleep, and alertness

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Arteries of the brain stem

• The next slide shows the principle arteries of
  the brain stem
• Think how compact the brain stem is?
• What would be the impact of any damage?

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