Brain stem & reticular Brain stem & reticular formation formation

Dr. Najam SiddiqiDr. Najam Siddiqi

MBBS, PhD (Japan) Postdoc (USA)MBBS, PhD (Japan) Postdoc (USA)

What is brain stem ?What is brain stem ?

Medulla oblongataMedulla oblongata PonsPons MidbrainMidbrain

What are contents of brain stem?What are contents of brain stem?

Ascending & descending tractsAscending & descending tracts Cranial nerve nuclei Cranial nerve nuclei Reticular formation nuclei and fibres Reticular formation nuclei and fibres

forming a networkforming a network Other nucleiOther nuclei

Brain stem--Ventral viewBrain stem--Ventral view

Brain stem--Dorsal viewBrain stem--Dorsal view

Midbrain at Superior Colliculus Midbrain at Superior Colliculus levellevel

Oculomotor nerve Oculomotor nerve (Pretectal & Edinger-Westphal nucleus)(Pretectal & Edinger-Westphal nucleus)

Mid brain at Inferior colliculus levelMid brain at Inferior colliculus level

Trochlear nerve (IV)Trochlear nerve (IV)

Trigeminal nerve (V) (sensory/motor)Trigeminal nerve (V) (sensory/motor)

Muscles of mastication, tensor tympani, tensor veli palatini, mylohyoid, digastric

Trigeminal nerve (sensory)Trigeminal nerve (sensory)

Abducent nerve (VI)Abducent nerve (VI)

Facial nerve (VII) –Facial nerve (VII) –Sensory/parasympatheticSensory/parasympathetic

Medulla oblongataMedulla oblongata

Facial nerve (motor)Facial nerve (motor)

Muscles of facial expression, Post. belly of digastric, STAPEDIUS

Medulla oblongataMedulla oblongata

Glossopharyngeal nerve (IX)Glossopharyngeal nerve (IX)

Vagus nerve (X)Vagus nerve (X)

Parasympathetic Parasympathetic nerve to the viscera: nerve to the viscera: Gut, respiratory Gut, respiratory system, heartsystem, heart

Motor:Motor: muscles of muscles of palate, pharynx, palate, pharynx, larynxlarynx

SensorySensory: larynx, : larynx, trachea, gut, aortic trachea, gut, aortic arch receptors, taste arch receptors, taste buds in post. oral buds in post. oral cavitycavity

Spinal accessory nerve (XI)Spinal accessory nerve (XI)

Striated muscles of larynx,Sternocleido-mastoid,Trapezius

Hypoglossal nerve (XII) motorHypoglossal nerve (XII) motorIntrinsic muscles of the tongue, hyoglossus, genioglossus, styloglossus

Olfactory nerve (I)Olfactory nerve (I)

Optic nerve (II)Optic nerve (II)

Vestibulocochlear nerve (VIII)Vestibulocochlear nerve (VIII)

Reticular Formation (RF)Reticular Formation (RF) Resembles a net of neurons and nerve fibers Resembles a net of neurons and nerve fibers

from the spinal cord to the cerebrumfrom the spinal cord to the cerebrum Separated by huge dendritic treeSeparated by huge dendritic tree Connected by immense number of afferent and Connected by immense number of afferent and

efferent axonsefferent axons Lie in brainstem tegmentum of midbrain, pons Lie in brainstem tegmentum of midbrain, pons

and medullaand medulla Extent to thalamus, hypothalamus, cerebrumExtent to thalamus, hypothalamus, cerebrum Cranial nerve nuclei are not part of itCranial nerve nuclei are not part of it It influence skeletal muscle activity, somatic and It influence skeletal muscle activity, somatic and

visceral sensations, autonomic and endocrine visceral sensations, autonomic and endocrine functions and level of consciousnessfunctions and level of consciousness

Arousal of the brain as a wholeArousal of the brain as a whole Certain reticular neurons send continuous Certain reticular neurons send continuous

stream of impulses to cortex—keeps the stream of impulses to cortex—keeps the cortex alert and conscious; this part is cortex alert and conscious; this part is called called Reticular Activating System (RAS)Reticular Activating System (RAS)

RAS acts as a RAS acts as a FILTERFILTER for the flood of for the flood of sensory inputs. Disregard almost 99% of sensory inputs. Disregard almost 99% of all sensory impulses as unimportantall sensory impulses as unimportant

Reticular Activating System (RAS) Reticular Activating System (RAS)

RAS is inhibited by sleep centers located RAS is inhibited by sleep centers located in hypothalamusin hypothalamus

Depressed by alcohol, sleep inducing Depressed by alcohol, sleep inducing drugs, tranquilizersdrugs, tranquilizers

Severe injury to RAS result in irreversible Severe injury to RAS result in irreversible comacoma

Motor activityMotor activity

Via reticulospinal tract, motor nuclei Via reticulospinal tract, motor nuclei projects to motor neurons in the spinal projects to motor neurons in the spinal cord to help control skeletal musclescord to help control skeletal muscles

Other nuclei such as Other nuclei such as vasomotor, cardiac vasomotor, cardiac and respiratory centersand respiratory centers of medulla are of medulla are automatic centers regulate visceral motor automatic centers regulate visceral motor functionsfunctions

Nuclei of RFNuclei of RF

Midline columnMidline column: (Midline Raphe nuclei): (Midline Raphe nuclei) extent the extent the entire length of the median/paramedian plane of entire length of the median/paramedian plane of brainstembrainstem

Medial columnMedial column: (Medial gigantocellular--large cell : (Medial gigantocellular--large cell nuclei)nuclei) pontomedullary tegmentum pontomedullary tegmentum

Lateral columnLateral column: (Lateral parvicellular small cell : (Lateral parvicellular small cell nuclei)nuclei): from medullocervical region to midbrain: from medullocervical region to midbrain

Cerebellar reticular formation nucleiCerebellar reticular formation nuclei: connected : connected to cerebellumto cerebellum

AfferentsAfferents

Ascending and descending pathwaysAscending and descending pathways Auditory and optic pathwaysAuditory and optic pathways Spinal afferents includes spinoreticular tracts Spinal afferents includes spinoreticular tracts Spinothalamic tract from thalamus, subthalamus, Spinothalamic tract from thalamus, subthalamus,

epithalamus, corpus striatum, limbic systemepithalamus, corpus striatum, limbic system Brainstem afferents includes sensory tracts from Brainstem afferents includes sensory tracts from

Trigeminal, Cochlear, vestibular nuclei.Trigeminal, Cochlear, vestibular nuclei. Tectoreticulat tractTectoreticulat tract Reticuloreticular tractReticuloreticular tract Cerebellar afferentsCerebellar afferents

AfferentsAfferents

Limbic afferents includes Habenular Limbic afferents includes Habenular nuclei, mamillary bodiesnuclei, mamillary bodies

Hypothalamus afferentsHypothalamus afferents Basal ganglia afferentsBasal ganglia afferents Cerebral cortex afferentsCerebral cortex afferents

Efferent projectionsEfferent projections

Reticulobulbar tract-cranial nerve nucleiReticulobulbar tract-cranial nerve nuclei Reticulospinal tract—anterior horn cells of Reticulospinal tract—anterior horn cells of

spinal cordspinal cord Reticulothalamic tract-- to thalamus, Reticulothalamic tract-- to thalamus,

hypothalamushypothalamus Limbic system, cerebral cortex, red nucleus, Limbic system, cerebral cortex, red nucleus,

corpus striatum, cerebellum, tectum, corpus striatum, cerebellum, tectum, To sympathetic and parasympathetic outflowTo sympathetic and parasympathetic outflow

FunctionsFunctions

1. 1. Control of muscle tone and reflexesControl of muscle tone and reflexes: : mediates postural reflexes through mediates postural reflexes through alpha alpha and gamma motor neuronsand gamma motor neurons

2. 2. Muscles of facial expressionMuscles of facial expression

3. 3. Influence all ascending pathwaysInfluence all ascending pathways: Central : Central transmission of sensory impulsestransmission of sensory impulses

4. 4. Control of Autonomic nervous system:Control of Autonomic nervous system:

Respiration, Cardiovascular functionsRespiration, Cardiovascular functions

FunctionsFunctions5. Arousal and level of consciousness:5. Arousal and level of consciousness:

Ascending reticular formation system: Ascending reticular formation system: stimulation will arouse the sleeping person, stimulation will arouse the sleeping person, mediates alerting responses and mediates alerting responses and consciousness and maintain the cerebrum consciousness and maintain the cerebrum in a waking state in a waking state

6. Influence on the biological clock-6. Influence on the biological clock--Sleep: -Sleep: serotonin-secreting neurons in raphe nuclei serotonin-secreting neurons in raphe nuclei mediate non-REM sleepmediate non-REM sleep

7. Control of endocrine nervous system7. Control of endocrine nervous system

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