Download Brain stem & reticular formation (RAS)

Brain stem & reticular
formation
Dr. Najam Siddiqi
MBBS, PhD (Japan) Postdoc (USA)
What is brain stem ?
 Medulla
oblongata
 Pons
 Midbrain
What are contents of brain stem?
 Ascending
& descending tracts
 Cranial nerve nuclei
 Reticular formation nuclei and fibres
forming a network
 Other nuclei
Brain stem--Ventral view
Brain stem--Dorsal view
Midbrain at Superior Colliculus
level
Oculomotor nerve
(Pretectal & Edinger-Westphal nucleus)
Mid brain at Inferior colliculus level
Trochlear nerve (IV)
Trigeminal nerve (V) (sensory/motor)
Muscles of mastication,
tensor tympani, tensor
veli palatini, mylohyoid,
digastric
Trigeminal nerve (sensory)
Abducent nerve (VI)
Facial nerve (VII) –
Sensory/parasympathetic
Medulla oblongata
Facial nerve (motor)
Muscles of facial
expression,
Post. belly of
digastric,
STAPEDIUS
Medulla oblongata
Glossopharyngeal nerve (IX)
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
Spinal accessory nerve (XI)
Striated muscles
of larynx,
Sternocleidomastoid,
Trapezius
Hypoglossal nerve (XII) motor
Intrinsic muscles of the tongue, hyoglossus, genioglossus,
styloglossus
Olfactory nerve (I)
Optic nerve (II)
Vestibulocochlear nerve (VIII)
Reticular Formation (RF)
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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
 Arousal
of the brain as a whole
 Certain reticular neurons send continuous
stream of impulses to cortex—keeps 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
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
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
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
Afferents
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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
Afferents
 Limbic
afferents includes Habenular nuclei,
mamillary bodies
 Hypothalamus afferents
 Basal ganglia afferents
 Cerebral cortex afferents
Efferent projections

Reticulobulbar tract-cranial nerve nuclei
 Reticulospinal tract—anterior 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
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
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
Hang on