Subdivisions of Vertical Columns Motor nuclei Somatic motor closest to midline eyes, tongue CN III, IV, VI, XII Branchial motor Lateral position Branchial arches: chewing, expression, middle ear, pharynx, larynx, sternomastoic, trapezius CN V, VII, XI N. ambiguus (IX, X) Visceral motor ventral / ventrolateral Parasympathetic: glands, smooth muscle, heart, lungs, GI above splenic flexure Edinger-Westfall (III) Sup. & Inf. salivatory Sensory nuclei General sensory lateral to branchial motor Face, sinuses, meninges All modalities CN V mainly Also CN VII, IX, X Visceral sensory lateral to visceral motor Taste; cardiorespiratory, GI info N. of the solitary tract (CN VII, IX, X) Special sensory furthest lateral Balance; hearing CN VIII (vestibular) CN VIII (cochlear)
Midbrain Connects pons and cerebrum with forebrain Cruscerebri
Shortest brain stem,not more than
2cm in length,lies in the posterior cranial Fossa.
For descriptive purpose,divided into
Dorsal tectum and right and left cerebral Peduncles.
Each cerebral peduncles divide further
into ventral cruscerebri and a dorsal Tegmentum by a pigmented lamina “ Substantianigra”
Cerebral peduncles contains:
-Descending fibers that go to the cerebellum via the pons -Descending pyramidal tracts
Running through the midbrain is the hollow cerebral aqueduct which connects the 3rd and 4th ventricles of the brain.
Superior colliculi The roof of the aqueduct ( the tectum) contains the corpora quadrigemina 2 superior colliculithat control reflex movements of the eyes, head and neck in response to visual stimuli 2 inferior colliculithat control reflex movements of the head, neck, and trunk in response to auditory stimuli Inferior colliculi Corpora quadregemina Superior and inferior colliculiseperated by cruciform sulcus Superior colliculi larger and darker than inferior colliculi,the difference In colour due to superficial neurons in Superior colliculi
Internal Structure of Midbrain Cross section at two levels
Level of inferior colliculus
Level of superior colliculus
Internal structure Transverse section of midbrain Common to both at inferior and superior colliculus:
Cruscerebri (or basis pedunculi):
- Consists of fibres descending from cerebral cortex. - Its medial one-sixth is occupied by coticopontine fibres from frontal lobe,lateral one-sixth fibres from temporal,occipital and parietal lobes,the intermediate two third by corticospinal and cortico- nuclear fibres.
- Present immediately behind and medial to basis pedunculi. - It appears dark as neuron within it contain pigment. ( neuromelanin )
Internal Structure of Midbrain Cross section at inferior colliculus
Section at the level of inferior colliculus Inferior colliculus
- large mass of grey matter lying in the tectum - Forms cell station in auditory pathway.
- Lies in the ventral part of central grey matter
Mesencephalic nucleus of trigeminal nerve:
- Lies in lateral part of the central grey matter
- Fibres of ventral spinothalamic tract
- Fibres of lateral spinothalamic and spinotectal tract.
Inferior colliculus Trochlear nerve(N) Mesencephalic nucleus of V cranial nerve Medial longitudinal fasciculus
Cross section at
Level of superior colliculus
Section at the level of superior colliculus Two large masses of grey matter seen at this level
Superior colliculus in the tectum
– Receives visual input from retina and frontal and occipital eye fields – Receives auditor input from inferior colliculus – Mediates audiovisual refflexes
Commissure of superior colliculus
– Connects two superior colliculus
Brachium of superior colliculus
– Pathway for fibres from superior colliculus to Cortex
Section at the level of superior colliculus……contd.
Cerebral aqueduct and periaqueductal
Red nucleus in the tegmentum
- Lies in the anterior part of the tegmentum, dorsomedial to the substantianigra - It is called because of reddish colour which is due to the presence of iron pigment in its neurons.
- Related to the ventral part of central grey matter
Medial longitundinal fasciculus
– Vestibular fibres that coordinate eye movements – Interconnects ocular motor CN 3, 4, 6
Central tegmental tract
Section at the level of superior colliculus……contd.
– Spinal afferent tract
– Spinal afferent tract
– Receives GAGAergic input from caudate putamen – Projects dopaminergicfibres to caudate putamen – Projects nondopminergicfibres to thalamus
Superior colliculus Edingerwestfal nucleus Occulomotor nucleus Red nucleus – relay from cortex and cerebellum to spinal cord, inferior olive, reticular formation, cerebellum Controls arm movement
– Arise from precentral and postcentral Gyri – May synapse directly on motor neurons or indirectly via interneurons (corticoreticular fibers) – Innervate sensory relay nuclei – Innervate cranial nerve motor nuclei bilaterally, with the exception of upper face division of the facial nucleus – Innervates the ipsilateral spinal nucleus of CN 11, which supplies the sternocleidomastoid muscle and the contralateral spinal nucleus of CN 11, which innervates the trapezius muscle
The pons shows a convex anterior surface
with prominent transversely running fibres. These fibres collect to form bundles,the middle cerebellar peduncles.
Trigeminal nerve emerges from the anterior
surface,at the junction between pons and middle cerebellar peduncle.
The anterior surface of pons is marked in the
midline by a shallow groove,thesulcusbasilariswhich lodges the basilar artery. Pons s Sulcusbasilaris
Subdivided into ventral and dorsal part Ventral part of the pons contains
Recievescorticopontinefibres from frontal,
temporal,parietal and occipital lobes of cerebrum
The efferent fibres form the transverse fibres
It has been estimated that there are about twenty
million neurons in pontinenuclei.Most of them are glutaminergic.
Vertically running corticospinal and corticopontine
Transversely running fibres arising in pontine nuclei
Dorsal part of pons Midpons
The dorsal part of the pons may be regarded as continuation
of the part of the medulla behind the pyramids.
Superiorly continous with the tegmentum of the midbrain.
Occupied predominately by reticular formation
Posterior surface help to form floor of fourth ventricle
The dorsal part is bounded laterally by inferior cerebellar
peduncle in the lower part of the pons and superior cerebellar peduncle in upper part. DORSAL PART Upper pons
Dorsal surface of pons Six ascending tract 1 Dorsal and ventral cochlear nuclei – Receives auditory input from the cochlea through CN 8 2 Trapezoid body – Formed by decussating fibres of the ventral cochlear nuclei 3 Superior olivary nucleus – Auditory relay nucleus that receives input from the cochlear nuclei and contributes to lateral lemniscus 4 Lateral lemniscus » Auditory pathway that conducts most contralateral cochlear input 5 Medial lemniscus » Spinal afferent pathway 6 Spinal lemniscus » Spinal afferent pathway
4th Ventricle Connection of pons to cerebellum Restiform body (inf. cerebellar peduncle) Middle cerebellar peduncle Medial lemniscusAscending 2nd order sensory neurons Descending upper motor neurons
Section through lower part of the pons
Abducent nucleus of CN 6
• Lateral gaze
Dorsal and ventral cochlear nuclei of CN8
Medial, lateral and superior vestibular
nuclei of CN 8 • Receive proprioceptive input from vestibular systems and cerebellum • Projects to cerebellum and medial longitudinal fasciculus
Spinal trigeminal tract of CN 5
Facial nucleus of CN 7 • Gives rise to fibres that innervate the muscles of
Superior olivary nucleus
– Auditory relay nucleus that receives input from the cochlear nuclei and contributes to lateral lemniscus
Cranial Nerves of Lower Pons Vestibular Nuclei Pure sensory lateral location Balance
Cranial Nerves of Lower Pons At a slightly higher level Abducens N. nucleus Abduction of eye Longest, most vulnerable CN Facial N. nucleus Muscles of face
Mid Pons Lateral lemniscus Trapezoid body fibers from dorsal column (position and vibration) Medial leminiscus fibers from dorsal column (position and vibration) Pontine nuclei Trapezoid body : transverse fibers in pontinetegmentum
Mid Pons Medial lemniscusfibers from dorsal column (position and vibration) Motor trigeminal nucleus Trigeminal tractpain, temperature, touch from contralateral face Principal trigeminal sensory nucleus Cranial nerve nuclei and Lemniscal sensory system – in tegmentum of the pons
Section through upper part of pons
Superior cerebellar peduncle
Principal sensory nucleus of CN 5
– Receives discriminative tactile and pressure sensation from face, terminates in thalamus
» Auditory pathway that conducts most contralateral cochlear input
– Formed by decussating fibres of the ventral cochlear nuclei
Upper Pons Pediculopontine Nucleus Locus ceruleus Parabrachial Nucleus Some neurons release acetylcholine Other neurons release glutamate They assist in learning and voluntary motor control, e.g. locomotion, saccadic e
External structure of medulla
Most inferior region of the brain stem.
Becomes the spinal cord at the level of the foramen magnum.
Medulla is broad above ,joins with pons
narrow below, continous with spinal cord
Length is about 3cm, width is about 2cm
at its upper end
Surfaces shows series of fissures
Anterior median fissure
Posterior median fissure
Medulla oblongata Spinal cord
External surface of medulla Ventral surface of medulla oblongata contains
elevation between anterior median
Formed due to decussation of corticospinal
Oval swelling between anterolateral
posterolateralsulcus,half an inch long
Produced by large mass of gray
matter called inferior olivary nucleus Olive Pyramid
Pyramid Olive Anterolateral fissure Anterior median fissure
Posterior part of medulla oblongata The posterior part of medulla contains
Fasciculus gracilis medially ending in rounded
elevation ,called nucleus gracilis
Fasciculus cuneatus laterally ending in rounded
Posterior part of the medulla forms
the floor of the fourth ventricle
elevation in the lower part of medulla lateral to fasciculus cuneatus.
DORSAL SURFACE OF MEDULLA OBLONGATA Floor of fourth ventricle Obex Gracile tubercle Posterior median sulcus Posterior median fissure Cuneate tubercle
Internal Structure of Medulla Cross section at three levels Level of pyramidal decussation
Level of Pyramidal Decussation Lateral corticospinal tract 75 – 90% Gracile nucleus spinal nucleus of V From pons to C4 Pyramidal tract Anterior corticospinal tract -- fibers to innervate muscles of trunk
Internal Structure of Medulla Cross section at level of lemniscaldecussation
Level of LemniscalDecussation Gracile nucleus Medial longitudinal fasciculus Cuneate nucleus Medial lemniscus Carries 2nd order sensory neurons to VPL thalamus Internal arcuate fibers
Cross section at level of Level ofinferior olivary nuclei
Level of Inferior Olives Vestibular nuclei Medial Inferior Hypoglossal nucleus CN XII Inferior cerebellar peduncle= Restiform body Inferior olivary nuclei Relay between cortex, vestibular nuclei, cerebellum, basal ganglia, and dorsal column nuclei
Cranial Nerves of the Medulla N. solitarious Sensory nucleus for CN VII, IX, X Vestibular nuclei Posterior 1/3 of the tongue Dorsal motor nucleus of X N. ambiguus Motor nucleus for CN IX, X & XI Spinal trigeminal tract CN V, VII, IX, X Stylopharyngeus (lifts pharynx) Sensation behind ear
CN IX: Glossopharyngeal Nerve N. solitarious Sensory nucleus for CN VII, IX, X Posterior 1/3 of the tongue Inf. salivatory nucleus Parotid gland, parasympathetic N. ambiguus Motor nucleus for CN IX, X & XI Stylopharyngeus (lifts pharynx) Spinal trigeminal tract CN V, VII, IX, X Sensation behind ear
CN X: Vagus Nerve Dorsal motor nucleus of X Parasympathetic, preganglionic N. solitarious Sensory nucleus for CN VII, IX, X Taste, epiglottis Cardiorespiratory N. ambiguus Motor nucleus for CN IX, X & XI Pharynx Larynx Spinal trigeminal tract CN V, VII, IX, X Ear
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