1. No. 23
1. The Brain Stem(2)

2. Ⅱ) Internal Structure The internal structure of brain stem comprises
nuclei of cranial nerves,
nuclei of non-cranial nerves,
ascending and descending tracts,
reticular formation.

3. 1. The nuclei of cranial nerves
(1) The quality and sorts
The nuclei of cranial nerves represent seven kinds of qualities and arranged medialolaterally six horizontal functional columns. Three motor columns and four sensory columns are situated medial and lateral to the sulcus limitans respectively.

4. ① The general somatic motor nucleus
It supplies the skeletal muscles evolved from the myotome, e.g. the extrinsic muscles of the eye and the muscles of tongue.
Four pairs of nuclei.
Nucleus of oculomotor nerve,
Nucleus of trochlear nerve,
Nucleus of abducent nerve,
Nucleus of hypoglossal nerve.

5. ② The special visceral motor nucleus
It supplies the skeletal muscles evolved from the branchimere, e.g. the muscles of expression, mastication, pharynx, larynx, sternocleidomastoid and trapezius.
Four pairs of nuclei:
Motor nucleus of trigeminal nerve,
Nucleus of facial nerve,
Nucleus ambiguous,
Nucleus of accesory nerve.

6. ③ The general visceral motor nucleus
It is also called the parasympathetic nervous column.
It controls the activities of smooth muscle, cardiac muscle and glands in the head, neck, thorax and abdomen.
Four pairs of nuclei.
Accessory nucleus of oculomotor nerve,
Superior salivatory nucleus,
Inferior salivatory nucleus,
Dorsal nucleus of vagus nerve.

7. ④ The special visceral sensory nucleus
It receives the first order afferent fibers which originate from the taste buds.
One pair of nuclei.
Nucleus of solitary tarct.
⑤ The general visceral sensory nucleus
It receives the first order afferent fibers which originate from the viscera and heart and vessels in the head, neck, thorax and abdomen.

8. ⑥ The general somatic sensory nucleus
It receives the first order afferent fibers which originate from the skin, muscle, muscular tendon, and most part of oral and nasal mucous membrane.
Three pairs:
Mesencephalic nucleus of trigeminal nerve,
Pontine nucleus of trigeminal nerve,
Spinal nucleus of trigeminal.

9. ⑦ The special somatic sensory nucleus
It receives the first order fibers originate from the vestibulocochlear organs (equilibrant and spiral organs) in the internal ear. Including:
vestibular nuclei,
cochlear nuclei.

10. (2) Functional columns of nuclei of cranial nerves and the their nuclei’ locations and functions
1) The general somtic motor column
① Oculomotor nucleus (Ⅲ)
It is located ventromedially to the central gray matter at the level of the superior colliculus.
The fibers from the nucleus course ventrally, leave the brain medial to the cerebral peduncle, join the oculomotor nerve, supply most of the extraocular muscles except the lateral rectus and the superior obliquus, i.e. the superior rectus, inferior rectus, medial rectus, inferior obliquus, levator palpebrae superioris.

11. ② Trochlear nucleus (Ⅳ)
It lies in the ventral region of the central gray matter close to the midline at the level of the superior colliculus.
Its outgoing fibers pass laterally and dorsally round the central gray matter. They reach the cranial end of the superior medullary velum, decussating with those of the opposite side and become the unique cranial nerve which emerges from the dorsal surface of the brain stem, form the trochlear nerve, innervating the superior obliquus.

12. ③ Abducent nucleus (Ⅵ) It lies deeply in the facial colliculus.
The fibers from the nucleus of abducent nerve course ventrally and inferiorly, emerge through the bulbopontine sulcus, forming the abducent nerve, control the lateral rectus.

13. ④ Hypoglossal nucleus (Ⅻ)
It lies under the hypoglossal triangle and extends down to the closed part of medulla oblongata, on each side of the median plane.
The fibers originating from hypoglossal nucleus run ventrolaterally, finally emerging from the anterolateral sulcus to become the (rootlets of) hypoglossal nerve, control the movements of lingual muscles.

14. 2) The special visceral motor column
① The motor nucleus of trigeminal nerve (Ⅴ)
It lies lateral to abducent nucleus.
The fibers originating from this nucleus leave the brain between the basilar part and the middle peduncle of cerebellum, form the motor root of trigeminal nerve, innervating the masseter.

15. ② The facial nucleus (Ⅶ)
It is situated at the ventrolateral part of the reticular formation, ventromedial to the spinal tract and nucleus of trigeminal nerve.
The fibers from the nucleus course dorsomedially, round the dorsal side of nucleus of abducent nerve, turn ventrolaterally, forming genu of facial nerve, emerge through the bulbopotine sulcus, constitute the facial nerve, innervate the activities of facial muscles.

16. The upper portion of the nucleus which innervates the muscles of expression above the eye fissure (the frontal belly of occipitofrontalis and the orbicularis oculi), receives fibers from the corticonuclear tract of both sides, while the lower portion, which innervates the muscles of the lower part of the face, receives the fibers from those of the opposite side only.

17. ③ The nucleus ambiguus (Ⅸ,Ⅹ,Ⅺ)
It is placed deeply in the reticular formation.
The fibers arising from the nucleus ambiguous leaving the brain stem behind the olive, provides the special visceral efferent fibers for the glossopharyngeal nerve, vagus nerve and cranial root of accessory nerve, innervate pharyngeal, laryngeal, and soft palatine muscles.

18. ④ The spinal accessory nucleus (Ⅺ)
It is located in the gray matter of the lower part of the medulla oblongata, and gives rise to efferent fibers to supply the sternocleidomastoid and trapezius. In corresponding to the spinal roots of the accessory nerve, the spinal nucleus of accessory nerve may extend downwards as low as the level of the fifth cervical segment of the spinal cord.

19. 3) The general visceral motor column
① The accessory oculomotor nucleus (Ⅲ)
This nucleus is situated dorsally to the nucleus of oculomotor nerve.
The preganglionic parasymjpathetic fibers travel in the oculomotor nerve to relay in the ciliary ganglion, subsequently in the short ciliary nerves to innervate the ciliary muscle and the sphincter pupillae.
The oculomotor nucleus and the accessory oculomotor nucleus constitute the oculomotor nuclear complex.

20. ② The superior salivatory nucleus (Ⅶ)
It is situated in the reticular formation.
The parasympathetic preganglionic fibers from this nucleus join in the facial nerve, control the secretion of submandibular gland, sublingual gland and lacrimal gland.
③ The inferior salivatory nucleus (Ⅸ)
It is near to the rostral end of the dorsal nucleus of vagus.
It sends preganglionic parasympathetic fibers into the glossopharyngeal nerve, controls the secretion of parotid gland.

21. ④ The dorsal nucleus of vagus nerve (Ⅹ)
It lies under the vagus triangle lateral to the hypoglossal nucleus.
The preganglionic parasympathetic fibers originating from the dorsal nucleus of vagus nerve emerge posterior to the olive, join the vagus nerve, and control the activities of smooth muscle, cardiac muscle and glands or the organs in the neck, thoracic cavity and a large number of abdominal visceral organs.

22. 4) The visceral sensory column
The nucleus of solitary tract (Ⅶ,Ⅸ,Ⅹ)
It is situated around the solitary tract, ventrolateral to the dorsalnucleus of vagus nerve.
The upper part (end) of this nucleus receives the special visceral sensory (taste) fibers, while the lower part receives the general visceral sensory fibers.

23. The solitary tract constitutes a composite descending bundle of visceral afferent fibers consisting of the primary afferent fibers from the facial, glossopharyngeal and vagus nerves which enter the brain stem by passing through the posterolateral sulcus. This tract conveys the gustatory stimulus and general visceral stimulus to the adjacent nucleus of solitary tract.
In fact, the nucleus of solitary tract is shared by these three cranial nerves.

24. 5) The general somatic sensory column
① The mesencephalic nucleus of trigeminal nerve (Ⅴ)
It located in the lateral margin of the central gray matter around the mesencephalic aueduct.
It is concerned with the conduction of the proprioceptive impulses of masseter, facial muscles, and extraocular muscles, from the trigeminal nerve.

25. ② The pontine nucleus of trigeminal nerve (Ⅴ)
It lies on the lateral side of the motor nucleus, it extends inferiorly and continues with the spinal nucleus of trigeminal nerve. The pontine nucleus receives the primary afferent fibers of the trigeminal nerve, correlating to the transmission of tactile sensibility of head and face. The descending fibers are the spinal tract of trigeminal nerve.
The second order fibers from this nuculeus decussate to the opposite side to join the trigeminal lemniscus.

26. ③ The spinal nucleus of trigeminal nerve (Ⅴ,Ⅶ,Ⅸ,Ⅹ)
It is directly continuous with the substantia gelatinosa of the dorsal gray column of the spinal cord.
It lies on the medial side of the spinal tract of trigeminal nerve and is concerned with the mediation of pain and thermal sensibilities of the trigeminal area.

27. The general somatic sensory fibers of trigeminal nerve transmit pain and thermal sensibilities, enter the pons, and then descend into the mudulla oblongata, constitute the spinal tract of trigeminal nerve, and terminate the spinal nucleus of trigeminal nerve. This nucleus receives primary afferent fibers from the trigeminal, facial, glossopharyngeal and vagus nerves.
The second order fibers originating from this nucleus cross to the opposite to from the trigeminal lemniscus.

28. 6) The special somatic sensory column
① The vestibular nuclei (Ⅷ)
They are situated deep in the vestibular area.
They are divided into the medial, inferior, lateral and superior vestibular nuclei. The nuclei receive the major afferent fibers from the vestibular nerve. The efferent fibers of the complex constitute vestibulospinal tract, correlating muscular tension, vestibulocerebellar tract, and medial longitudinal fasciculus.

29. ② The cochlear nuclei (Ⅷ)
They are situated ventrolateral and dorsal to the inferior cerebellar peduncle.
They are divided into the dorsal cochlear nucleus and the ventral cochlear nucleus. These two nuclei receive afferent fibers from the cochlear nerve.

30. 2. The nuclei of non-cranial nerves
(1) The nuclei of non-cranial nerves in medulla oblongata
① Gracile nucleus and cuneate nucleus
They are situated in the deep of the gracile tubercle and cuneate tubercle respectively.
The fibers of the fasciculi gracilis and cuneatus have ascended ipsilaterally through the spinal cord, and the majority terminate in their respective nuclei.
The gracile and cuneate nuclei are the important relay stations for conducting deep and fine touch sensatory impulses.

32. ② The inferior olivary nucleus
It is deep in the olive of medulla oblongata.
This nucleus may be the relay station between the cerebrum, red nucleus and the cerebellum.
③ The accessory cuneate nucleus (lateral cuneate nucleus)

34. ② The superior olivary complex ③ The nucleus of lateral lemniscus
(2) The nuclei of non-cranial nerves in pons
① The pontine nuclei
They are scattered throughout the basilar part of the pons, constitute relay stations on the pathway from the cerebral cortex to the cerebellum.
The axons of the cells of pontine nuclei form the transverse fibers of the pons (pontocerebellar fibers). These fibers run transversely, crossing the median plane, form the middle cerebellar peduncle, enter the cerebellar hemisphere of the opposite side.
② The superior olivary complex
③ The nucleus of lateral lemniscus

36. (3) The nuclei of non-cranial nerves in midbrain
① The red nucleus
The red nucleus is situated in the center of the tegmentum. It appears pinkish color in fresh specimen.
It receives the fibers from the contralateral side of cerebellum via the superior cerebellar peduncle.
The efferent fibers decussate in the ventral tegmental decussation to constitute the rubrospinal tract.

37. ② The substantia nigra
It lies between the tegmentum of the midbrain, extending throughout the whole length of the midbrain. The cells of subatantia nigra rich in melanotic pigment and dopamine
③ The superior colliculus
It serves as reflex center correlating movement of the head and eyes used to localize and follow visual stimuli. It may also respond to auditory stimuli by the afferent fibers from inferior colliculi and to somatic stimuli by the spinotectal tract.

39. ④ The inferior colliculus
They are reflex centers for auditory responses and concerned in the ability to localize the source of sounds.
⑤ The pretectal region (pretectal nuclei)
It is the center of pupillary reflex situating at the junction of the midbrain and the diencephalons.

41. 3. The long ascending and descending tracts.
(1) The ascending tracts
①The medial lemniscus
The second order fibers arise from the gracile and cuneate nuclei go anteromedially, wind around the ventral side of central canal, forming the internal arcuate fibers, and then bend medially to reach the median plane, where they decussate with the corresponding fibers of the opposite side, forming the decussation of medial lemniscus. After decussation, the fibers ascend along the two side of median line, constituting the medial lemniscus.

43. In the medulla oblongata: posterior to the pyramid.
In the pons: penetrating the trapezoid body.
In the midbrain: dorsolateral to the red nucleus.
The medial lemniscus terminates in the ventral posterolateral nucleus of thalamus.
This tract connect deep and fine touch sensation.

44. ②The spinal lemniscus (spinothalamic tract)
After the anterior and posterior spinothalamic tracts ascend to the medulla oblongata, we definite the two tracts as spinal lemniscus.
It lies dorsolaterally to the inferior olivary nucleus and, As it ascends to the pons and midbrain it lies dorsolaterally to the medial lemniscus, terminating in the ventral posterolateral nucleus.
The spinothelamic lemniscus connects superficial sensation of somatic trunk and limbs.

46. ③The trigeminal lemniscus
The axons of the cells of the pontine and spinal nuclei of trigeminal nerve, cross the median plane to form the trigeminal lemniscus ascending with the medial lemniscus to the thalamus.
It lies dorsolaterally to the medial lemniscus, terminates in the ventral postomedial nucleus of thalamus.
The trigeminal lemniscus relates to the conduction of the tactile and pressure impulses; and the pain and thermal impulses from the skin, mucous membrane, cornea, conjunctiva and the meninges through the branches of the trigeminal nerve.

48. ④The lateral lemniscus
The efferent fibers from the cochlear nuclei run medially in the ventral part of the tegmentum, intersecting with the vertical fibers of medial lemniscus to form trapezoid body. Then the fibers cross the median raphe and decussate with the corresponding fibers of the opposite side to form the principal ascending auditory pathway, the lateral lemniscus.
It lies dosolaterally to the medial leminicus and terminates in medial geniculate body.
It connects auditory impulses.
⑤ The medial longitudinal fasciculus
⑥ The ventral spinocerebellar tract and dorsal spinocerebellar

50. (2) The descending tracts
The pyramidal tract:
The axons originating from the giant pyramidal cells (Betz cells) and other pyramidal cells of various sized which are located in the precentral gyrus and anterior part or paracentral lobule constitute the strong pyramidal tract.
In the course of descending this tract pass through the posterior limb and genu of internal capsule, the middle 3/5 of bottom of cerebral peduncle, the basilar part of pons, and the pyramid of medulla oblongata.

51. The pyramidal tract includes the corticonuclear tract and corticospinal tract.
The corticonuclear tract (corticobulbar tract) terminate in the cranial nuelei of brain stem and the corticospinal tract in the anterior horn of the spinal cord.
In the lower part of the pyramid, about 85% of fibers of corticospinal tract cross the median plane and continue down the spinal cord in the lateral funiculus as the lateral corticospinal tract. The uncrossed fibers retain their ventromedial position and descend in the anterior funiculus of the spinal cord as the anterior corticospinal tract.
The pyramidal tract concerned with controlling the voluntary movements of skeletal muscles.

53. 4. The reticular formation of brain stem
In the brain stem, there is an extensive field of intermingled gray and white matter collectively termed the reticular formation.
According to the traditional view, the reticular formation forms the central core throughout the brain stem; lying laterally between posterior and anterior horns;

55. 1) Cerebellar reticular formation nuclei 2) Raphe nuclei
(1) The main nuclei of the reticular formation of brain stem
1) Cerebellar reticular formation nuclei
2) Raphe nuclei
3) Medial (central) gigantocellular nuclei
4) Lateral parvicellular (small—celled) nuclei
(2) The functions of the reticular formation
The reticular formation is an important integration center for the vital activity; its major functions may sum up as follows:
Somatomotor control,
The activation of the behavioral arousal,
Visceromotor control.

56. Ⅲ. Transverse sections of brain stem
1) The transverse section through the medulla ablongata at the level of the pyramidal decussation

58. 2) The transverse section through the pons at the level of facial colliculus

60. 3) The transverse section of the midbrain through the superior colliculus