Brain Stem The brain stem occupies the posterior

Brain Stem Ø The brain stem occupies the posterior cranial fossa. Ø The brain stem lying in front of the cerebellum and fourth ventricle. Ø The brain stem formed of the following parts Ø 1. Medulla oblongata. Ø 2. Pons. Ø 3. Midbrain. The internal structure : Ø Tracts▼▲(lemnisci) Ø Ø • • • cranial nerves III --- XII control of : respiration cardiovascular system consciousness

Medulla oblongata The lower part : Closed medulla containing the central canal The upper part: Open medulla containing the fourth ventricle. Studied at 3 levels: 1 - open medulla. 2 - closed medulla Ø Sensory decussation Ø Motor decussation The outline: v resembles the cervical segment of the spinal cord. v central canal. Tracts & Nuclei: • ▼▲ tracts as cervical. • • • Gracile & cuneate nuclei. Cranial N. Nuclei. Dorsal root--- Trigeminal N& T

Closed medulla = Motor decussation Spinal N & T of trigeminal

Closed medulla Spinal N & T of trigeminal

closed medulla = sensory decussation Cranial N. Nuclei • Spinal nucleus and tract of V • motor nucleus of X (vagus) • Hypoglossal N

Closed medulla

Open medulla Tracts & Nuclei: On both sides of the midline, there are 3 tracts: • medial longitudinal bundle • medial tecto-spinal tract • medial lemniscus. The fully formed olivary nuclei 3 Posterior spinocerebellar T disappear Cranial nerve Nuclei: 1 - Spinal nucleus and tract of V 2 - XII 3 - X : dorsal motor nucleus, X + IX + XI nucleus ambiguous & solitary nucleus 4 - VIII- vestibular nuclei

• Pons: 3 - levels • 1 - lower pons (facial colliculus) • 2 - middle pons (trigeminal nuclei) • 3 - upper pons (4 lemnisci) The pons consists of two parts: A- The Basis Pontis (ventrally) It consists of: 1 - Pontine nuclei: which appear as scattered gray matter masses. 2 - Transverse pontine fibers (Diagnostic). 3 - Descending longitudinal fibers (pyramidal fibers). B- The Pontine Tegmentum (dorsally). It contains: 1. tracts, lemnisci, 2. cranial nerve N 3. cerebellar peduncles The Pons

The Pons The Basis Pontis • Expanded anterior part Ø Descending longitudinal fibers Ø Pontine nuclei Ø Transverse pontine fibers The Pontine Tegmentum Is the upward continuation of the medulla. It contains: 1 -Tracts ascending & descending 2 - lemnisci 3 - cranial nerve nuclei. 4 - cerebellar peduncles.

Pons at the level of facial colliculus Tracts & Nuclei • Inferior cerebellar peduncles lateral to the 4 th ventricle. • Vestibular nuclei. • Facial colliculus. • Trapezoid body= 1 -Cochlear nuclei fibers. 2 - trapezoid nuclei, 3 -superior olive, ►►►►Lateral lemniscus

Pons at the level of trigeminal nuclei Tracts & Nuclei • Superior cerebellar peduncles lateral to the 4 th ventricle. • Anterior ( Ventral spino-cerebellar tract ) disappears. • The spinal lemniscus. 4 Nuclei of V 1 -spinal nucleus and tract. 2 -main sensory nucleus, 3 -motor nucleus, 4 -mesencephalic nucleus. 4 • middle level

Pons at the level of the four lemnisci ? 4 ? 3 1 2 upper level 4 lemnisci: Ascending 3. Spinal lemniscus (lateral & ventral spino-thalamic tracts) 4. Lateral lemniscus (cochlear fibers)

The midbrain

Divided by line passing through the aqueduct of Sylvius into: v ventral part (cerebral peduncle) v dorsal part (tectum).

The cerebral peduncle: 1. Crus cerebri : corticobulbar, cortico-pontine & cortico-spinal tracts. Tectum: 2 superior colliculi. 2 inferior colliculi. 2. Substantia Nigra: pigmented masses of gray matter that belong to the extra-pyramidal system. Tectum: 3 3. Tegmentum: contains certain nuclei, nerve tracts & decussations. 2 1

Midbrain at the level of the inferior colliculus (lower level) Inferior colliculus The tegmentum contains: • MLB, MTS. • The 4 lemnisci. • The decussating fibers of superior cerebellar peduncles. • The mesencephalic nucleus of the trigeminal (5 th) • the trochlear (4 th ) cranial nerves. • The tectum at inf. colliculus ►►►► lateral lemniscus

Midbrain at the level of the superior colliculus (upper level) The tegmentum contains: • MLB &3 lemnisci. • The mesencephalic nucleus of trigeminal (5 th ) • The dorsal tegmental decussation of tecto-spinal tract. • The ventral tegmental decussation of rubro-spinal tract. • The red nucleus. • Complex nuclei of oculomotor (3 rd ) nerves. Superior colliculus

superior colliculus inferior colliculus