Brain Stem(1).ppt

Section two the brain The brain consists of four parts: brain stem, cerebellum, diencephalon and telencephalon.

I. The brain stem includes medulla oblongata, pons , midbrain

(I) External features 1. The ventral surface of brain stem ① medulla oblongata • pyramid, decussation of pyramid, • olive, • four pairs of cranial nerves emerge from the medulla oblongata ( IX-XII, glossopharyngeal N, vagus N, accessory N and hypoglossal N)

② pons • basilar sulcus, • middle cerebellar peduncles , • four pairs of cranial nerves emerge from the pons ( V- VIII, the trigeminal N, abducent N, facial N and vestibulocochlear N)

③ midbrain • cerebral peduncles, • two pairs of cranial nerves emerge from the midbrain ( III – IV, the oculomotor N and trochlear N)

2. The dorsal surface of brain stem ① the medulla oblongata • striae medullares • gracile tubercle, • cuneate tubercle, • hypoglossal trigone • vagal trigone

② pons • median sulcus • sulcus limitans • medial eminence:facial colliculus • vestibular area • locus ceruleus

③ midbrain • superior and inferior colliculi ( quadrigeminal body ). the superior colliculi are involved in visual reflexes and the inferior involved the auditory reflexes. • brachium of superior colliculus (pass to the lateral geniculate body) • brachium of inferior colliculus (pass to the medial geniculate body) • trochlear nerve • superior cerebellar peduncles and superior medullary velum

3 The rhomboid fossa ①Boundaries • upper: superior cerebellar peduncles • lower: inferior cerebellar peduncles, cuneate and gracile tuberlces

4. The fourth ventricle ①Location: among cerebellum, the dorsal surface of the medulla oblongata and pons ② Communication: continuous below with the central canal and above with the mesencephalic (cerebral ) aqueduct

Fourth ventricle

(II) Internal structure of brain stem 1. Features ①The fourth ventricle appears ②Relation between the motor nucleus and sensory nucleus is medial and lateral ③Gray and white matters are not continuous ④Cranial nerve nuclei have seven functional components ⑤The region of reticular formation is widely

2. Cranial nerve nuclei(seven types)

①General somatic efferent(motor) nuclei: innervate striated muscles that are derived from somites and involved in eye and tongue movements. Such as: hypoglossal nucleus of XII, oculomotor nucleus of III, trochlear nucleus of IV, and abducens nucleus of VI .

②General visceral efferent(motor) nuclei: innervate smooth muscles and the glands in the head, neck and torso(trunk). Such as: accessory oculomotor nucleus (Edinger-Westphal) of III, superior salivatory nucleus of VII, inferior salivatory nucleus of IX and dorsal motor nucleus of X.

③Special visceral efferent(motor) nuclei: innervate muscles that are derived from the brachial arches and are involved in chewing, making facial expressions, swallowing, producing vocal sounds, and turning the head. Such as: • trigeminal motor nucleus of V, • facial nucleus of VII, • ambiguous nucleus of IX, X, and XI, • spinal accessory nucleus of XI.

④General visceral afferent(sensory) nuclei: receive the visceral sense from the head, neck and torso. Such as : nucleus of solitary tract of VII,IX, and X. ⑤Special visceral afferent(sensory) nuclei: receive taste sense. Nuclei are the same as the ④.

⑥General somatic afferent(sensory) nuclei: receive sense from the skin and mucosa of the head. Such as : mesencephalic nucleus of V, pontine nucleus of V, nucleus of spinal trigeminal tract .

⑦Special somatic afferent(sensory) nuclei: receive the senses of hearing and equilibrium. Such as : four vestibular nuclei and two cochlear nuclei.

3 Other nerve nuclei ①Medulla: gracile nucleus and cuneate nucleus ②Pons: pontine nucleus ③Midbrain: superior and inferior colliculi; red nucleus; substantia nigra

gracile nucleus and cuneate nucleus

pontine nuclei

inferior colliculus

Superior colliculus; red nucleus; substantia nigra

4 Ascending tracts ①Medial lemniscus: gracile and cuneate nuclei give rise to a crossed fiber bundle to form medial lemniscus.

Medial lemniscus

②Spinal lemniscus: It is continuous with the spinothalamic tract in the spinal cord.

③Lateral lemniscus: The fibers arising from the contralateral anterior and posterior cochlear nuclei, and superior olivary nucleus, and the ipsilateral olivary nucleus make up the lateral lemniscus.

④Trigeminal lemniscus: The pontine nucleus of V, nucleus of spinal trigeminal tract give rise to a crossed fiber bundle to form the trigeminal lemniscus.

5 Descending tracts ①Pyramidal system: consists of the corticospinal tract(pyramidal tract) and corticonuclear tract

Pyramidal tract

Corticonuclear tract

6 Reticular formation ① Definition(term): is localized in the tegmentum of the brain stem (with exception of the conspicuous fiber bundles and nuclei of the brain stem), the lateral hypothalamic area, and the medial, intralaminar, and reticular nuclei of the thalamus.

Reticular formation

This area is characterized by a diffuse, seemingly unorganized structure with interlacing cells and fibers.Scattered through the reticular formation lie some cell accumulations with ill defined boundaries(reticular nuclei: unpaired raphe nuclei,paired medial nuclei , paired lateral nuclei). Most reticular neurons are fairly large, and it is notable that the larger neurons are found more medially while the smaller ones are located more laterally.

②Function • control respiration and cardiovascular system functions; • states of consciousness,sleep, and alertness.