Review of spinal cord,

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Lecture 7 Review of spinal cord, cranial nerves
and brainstem
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The spinal cord extends from the medulla to the
vertebral (or 'spinal') canal to reach the level
of the L1/L2 intervertebral space cf. the conus
medularis - it gives rise to 31 pairs of spinal
nerves 8 cervical, 12 thoracic, 5 lumbar, 5
sacral 1 coccygeal Nerves at L2 and below
have an ever- increasing distance to travel
before exiting the vertebral canal cf. the
cauda equina The spinal cord is enlarged
(widened) at the cervical and lumbar levels
these enlargements are the origins of the
brachial and lumbosacral plexuses (to innervate
the limbs)
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Different categories of nerve types

• two basic types sensory (afferent) vs. motor
  (efferent)
• for sensory nerves general vs. special senses
• for motor nerves somatic, branchiomotor or
  autonomic (parasympathetic in cranial nerves)

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Cranial nerve I OLFACTORY
Special Afferent - olfaction (sense of smell) -
sensory fibres in olfactory tract enter the basal
forebrain
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Cranial nerve II OPTIC
Special Afferent - vision -fibres project from
the retina, some cross at optic chiasma most
terminate in the thalamus in the
diencephalon Associated with the superior
colliculus of the tectum of the midbrain (dorsal
to the cerebral aqueduct)
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Cranial nerve III OCULOMOTOR
Somatic Efferent - most of the extraocular eye
muscles (eye movement) - the oculomotor nucleus
is ventral to the cerebral aqueduct in the
tegmentum of the midbrain Parasympathetic -
control of pupil diameter - Edinger-Westphal
nucleus is also in the rostral midbrain, next to
the oculomotor nucleus
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Cranial nerve IV TROCHLEAR

• Somatic Efferent
• - one extraocular eye muscle superior oblique
• movement of eyeball (down and medially)
• trochlear nucleus is ventral to the central
  canal of the midbrain in the region of the
  inferior colliculus

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Cranial nerve V TRIGEMINAL

• Motor nucleus is in the pons, medial to the
  Chief (Principal) sensory nuc.
• sensory nucleus is one continuous structure
  merges with substantia gelatinosa (spinal cord),
  extends through the medulla, pons (here its
  called the Chief nuc.) and then midbrain
• proprioceptive fibres have cell bodies in the
  trigem. mesencephalic nuc.
• - other sensory fibres have cell bodies in the
  trigeminal ganglion (outside the CNS).

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Cranial nerve VI ABDUCENS

• Somatic Efferent
• one extraocular eye muscle lateral rectus
  (moves eyes to side)
• - abducens nuc. in caudal pons, next to MLF

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Cranial nerve VII FACIAL

• Motor
• Branchiomotor Efferent - cell bodies in facial
  nucleus in caudal pons
• - muscles of facial expression
• - inner ear muscle (stapedius)
• Parasympathetic - cell bodies in superior
  salivatory nuc. in the pons
• - salivary lacrimal glands
• Sensory
• Special Afferent
• - taste (anterior 2/3 tongue) - cell bodies in
  geniculate ganglion
• Somatic Afferent
• external ear skin - cell bodies in geniculate
  ganglion
• taste fibres terminate in nucleus tractus
  solitarius
• - somatic afferent fibres terminate in trigeminal
  nuc.

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Cranial nerve VIII VESTIBULOCOCHLEAR

• Special Afferent
• balance hearing
• - sensory fibres have cell bodies in vestibular
  nuclei of rostral medulla and and cochlear nuclei
  in medulla-pons junction

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Cranial nerve IX GLOSSOPHARYNGEAL

• Motor
• Branchiomotor Efferent - cell bodies in the
  nucleus ambiguus
• - stylopharyngeus muscle (swallowing)
• Parasympathetic - cell bodies in the inferior
  salivatory nucleus
• - parotid gland (salivation)
• Sensory - cell bodies in the glossopharyngeal
  ganglia
• Special Afferent
• - taste (posterior 1/3 of tongue) - fibres
  terminate in solitary tract nuc.
• - carotid body (chemoreception) - carotid sinus
  (baroreception)
• General Afferent - fibres terminate in spinal
  trigeminal nucleus
• - pharynx
• posterior 1/3 of tongue)

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Cranial nerve X VAGUS

• Motor
• Branchiomotor Efferent - cell bodies in the
  nucleus ambiguus
• - muscles in pharynx, larynx and upper
  esophagus
• Parasympathetic - thoracic and upper abdominal
  viscera
• - cell bodies in dorsal motor nuc. of the
  vagus
• Sensory - cell bodies in vagal ganglia
• Visceral Afferent
• lungs, heart, gut, - all fibres go to
  solitary tract nuc.
• - aortic bodies (chemoreception)
• - aortic arch (baroreception)
• General Afferent
• external ear, pharynx, larynx, esophagus
• - fibres go to spinal trigeminal nuc.

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Cranial nerve XI ACCESSORY
Somatic efferent - sternocleidomastoid
trapezius muscle - movement of head and
shoulders - cell bodies in accessory nuc. in the
spinal cord
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Cranial nerve XII HYPOGLOSSAL

• Somatic efferent
• - muscles of the tongue
• movement of the tongue
• - cell bodies in the hypoglossal nucleus in the
  medulla

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General afferent fibres of the spinal cord The
dorsal column-medial lemniscus pathway (
others) discriminative touch conscious
proprioception (upper limb) conscious
proprioception for lower limb synapses in Clarkes
column ascends in spinocerebellar tract to
nucleus Z) two spinocerebellar tracts (dorsal
ventral) carry proprioceptive info to the brain
CN Fig. 8.14
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Spinothalamic tract system pain temperature
non-discriminative touch
CN Fig. 8.15
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Corticospinal tracts voluntary motor control
CN Fig. 8.16
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Caudal medulla (closed)
VH
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Rostral medulla (open medulla)

• prominent structure inferior olivary nucleus
• - receives input from motor and sensory cortices
• output to cerebellum via inferior cerebellar
  peduncles
• Also MLF (links vestibular info to oculomotor
  function)
• See CN Fig. 9.7

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• Nuclei tracts of the open medulla
• nucleus ambiguus (CN IX, X)
• dorsal motor nuc. of X
• hypoglossal nuc.
• nuc.of solitary tract
• vestibular cochlear nuc.
• spinal trigeminal tract nucleus
• inferior olive
• MLF (vestibular info)
• tectospinal tract from superior
• colliculus to the spinal cord
• spinal lemniscus (spinothalamic fibres)
• pyramids medial lemniscus
• ICP (cerebellar peduncle)
• - reticular formation

see Haines 5-12 and CN 9-6
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• Pons
• - dorsal portion above medial lemniscus called
  the tegmentum
• - pontocerebellar fibres cross over to enter the
  contralateral cerebellum via the MCP - middle
  cerebellar peduncle
• - corticospinal fibres run between bundles of
  pontocerebellar fibres
• the trapezoid body contains acoustic fibres from
  the cochlear nuclei (these ascend in the lateral
  lemniscus and terminate in the inferior
  colliculus)
• - abducens and facial nuclei

see Haines 5-17
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• The pontine tegmentum contains
• - the medial longitudinal fasciculus
• - trigeminal motor sensory nuclei tract
• The mid-pons is dominated by trigeminal nerve
  rootlets
• - contains ascending/descending fibres similar to
  lower pons
• - the superior cerebellar peduncle (SCP) connects
  the midbrain cerebellum

see Haines 5-17, 18 19
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Caudal midbrain

• inf. colliculus
• trochlear nuc.
• substantia nigra dopamine
• cell bodies)
• corticospinal tracts ("basis pedunculi" or "crus
  cerebri")
• See CN Fig. 9.12

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The rostral midbrain contains the - superior
colliculus (not at the level shown here) -
oculomotor nucleus (somatic efferent nucleus of
CN III) - red nucleus - projections to
cerebellum - nucleus of Edinger-Westphal
(parasympathetic nucleus of CN III)