Brain stem

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Brain stem reticular formation

• Dr. Najam Siddiqi
• MBBS, PhD (Japan) Postdoc (USA)

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What is brain stem ?

• Medulla oblongata
• Pons
• Midbrain

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What are contents of brain stem?

• Ascending descending tracts
• Cranial nerve nuclei
• Reticular formation nuclei and fibres forming a
  network
• Other nuclei

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Brain stem--Ventral view
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Brain stem--Dorsal view
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Midbrain at Superior Colliculus level
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Oculomotor nerve (Pretectal Edinger-Westphal
nucleus)
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Mid brain at Inferior colliculus level
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Trochlear nerve (IV)
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Pons
Ventral view
Dorsal view
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Pons
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Trigeminal nerve (V) (sensory/motor)
Muscles of mastication, tensor tympani, tensor
veli palatini, mylohyoid, digastric
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Trigeminal nerve (sensory)
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Abducent nerve (VI)
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Facial nerve (VII) Sensory/parasympathetic
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Medulla oblongata
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Facial nerve (motor)
Muscles of facial expression, Post. belly of
digastric, STAPEDIUS
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Medulla oblongata
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Glossopharyngeal nerve (IX)
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Vagus nerve (X)

• Parasympathetic nerve to the viscera Gut,
  respiratory system, heart
• Motor muscles of palate, pharynx, larynx
• Sensory larynx, trachea, gut, aortic arch
  receptors, taste buds in post. oral cavity

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Spinal accessory nerve (XI)
Striated muscles of larynx, Sternocleido-mastoid,
Trapezius
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Hypoglossal nerve (XII) motor
Intrinsic muscles of the tongue, hyoglossus,
genioglossus, styloglossus
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Olfactory nerve (I)
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Optic nerve (II)
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Vestibulocochlear nerve (VIII)
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Reticular Formation (RF)

• Resembles a net of neurons and nerve fibers from
  the spinal cord to the cerebrum
• Separated by huge dendritic tree
• Connected by immense number of afferent and
  efferent axons
• Lie in brainstem tegmentum of midbrain, pons and
  medulla
• Extent to thalamus, hypothalamus, cerebrum
• Cranial nerve nuclei are not part of it
• It influence skeletal muscle activity, somatic
  and visceral sensations, autonomic and endocrine
  functions and level of consciousness

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• Arousal of the brain as a whole
• Certain reticular neurons send continuous stream
  of impulses to cortexkeeps the cortex alert and
  conscious this part is called Reticular
  Activating System (RAS)
• RAS acts as a FILTER for the flood of sensory
  inputs. Disregard almost 99 of all sensory
  impulses as unimportant

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Reticular Activating System (RAS)

• RAS is inhibited by sleep centers located in
  hypothalamus
• Depressed by alcohol, sleep inducing drugs,
  tranquilizers
• Severe injury to RAS result in irreversible coma

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Motor activity

• Via reticulospinal tract, motor nuclei projects
  to motor neurons in the spinal cord to help
  control skeletal muscles
• Other nuclei such as vasomotor, cardiac and
  respiratory centers of medulla are automatic
  centers regulate visceral motor functions

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Nuclei of RF

• Midline column (Midline Raphe nuclei) extent the
  entire length of the median/paramedian plane of
  brainstem
• Medial column (Medial gigantocellular--large
  cell nuclei) pontomedullary tegmentum
• Lateral column (Lateral parvicellular small cell
  nuclei) from medullocervical region to midbrain
• Cerebellar reticular formation nuclei connected
  to cerebellum

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Afferents

• Ascending and descending pathways
• Auditory and optic pathways
• Spinal afferents includes spinoreticular tracts
• Spinothalamic tract from thalamus, subthalamus,
  epithalamus, corpus striatum, limbic system
• Brainstem afferents includes sensory tracts from
  Trigeminal, Cochlear, vestibular nuclei.
• Tectoreticulat tract
• Reticuloreticular tract
• Cerebellar afferents

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Afferents

• Limbic afferents includes Habenular nuclei,
  mamillary bodies
• Hypothalamus afferents
• Basal ganglia afferents
• Cerebral cortex afferents

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Efferent projections

• Reticulobulbar tract-cranial nerve nuclei
• Reticulospinal tractanterior horn cells of
  spinal cord
• Reticulothalamic tract-- to thalamus,
  hypothalamus
• Limbic system, cerebral cortex, red nucleus,
  corpus striatum, cerebellum, tectum,
• To sympathetic and parasympathetic outflow

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Functions

• 1. Control of muscle tone and reflexes mediates
  postural reflexes through alpha and gamma motor
  neurons
• 2. Muscles of facial expression
• 3. Influence all ascending pathways Central
  transmission of sensory impulses
• 4. Control of Autonomic nervous system
• Respiration, Cardiovascular functions

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Functions

• 5. Arousal and level of consciousness Ascending
  reticular formation system stimulation will
  arouse the sleeping person, mediates alerting
  responses and consciousness and maintain the
  cerebrum in a waking state
• 6. Influence on the biological clock--Sleep
  serotonin-secreting neurons in raphe nuclei
  mediate non-REM sleep
• 7. Control of endocrine nervous system

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Sleep disorders

• Somnambuslim (sleep walking)
• Enuresis
• Narcolepsy
• Cataplexy an attack of paralysis of somatic
  muscles precipitated by bouts of laughter or
  crying/strong emotional stimuli

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Hang on
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