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

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

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

No. 23No. 23

1. The Brain Stem(2)1. The Brain Stem(2)

ⅡⅡ) Internal Structure) Internal Structure

The internal structure of brain stem The internal structure of brain stem comprisescomprises

nuclei of cranial nervesnuclei of cranial nerves,, nuclei of non-cranial nervesnuclei of non-cranial nerves,, ascendingascending and and descending tracts,descending tracts, reticular formationreticular formation..

1. The nuclei of cranial nerves1. The nuclei of cranial nerves (1) The quality and sorts(1) The quality and sorts The nuclei of cranial nerves represent seven kiThe nuclei of cranial nerves represent seven ki

nds of qualities and arranged medialolaterally nds of qualities and arranged medialolaterally six horizontal functional columns. Three motosix horizontal functional columns. Three motor columns and four sensory columns are situatr columns and four sensory columns are situated medial and lateral to the sulcus limitans resed medial and lateral to the sulcus limitans respectively.pectively.

① ① The The generalgeneral somatic motor nucleussomatic motor nucleus It supplies the skeletal muscles evolved from tIt supplies the skeletal muscles evolved from t

he myotome, e.g. the extrinsic muscles of the he myotome, e.g. the extrinsic muscles of the eye and the muscles of tongue.eye and the muscles of tongue.

Four pairs of nuclei.Four pairs of nuclei. Nucleus of oculomotor nerve,Nucleus of oculomotor nerve, Nucleus of trochlear nerve,Nucleus of trochlear nerve, Nucleus of abducent nerve,Nucleus of abducent nerve, Nucleus of hypoglossal nerve.Nucleus of hypoglossal nerve.

② ② The The special visceral motor nucleusspecial visceral motor nucleus It supplies the skeletal muscles evolved from tIt supplies the skeletal muscles evolved from t

he branchimere, e.g. the muscles of expressiohe branchimere, e.g. the muscles of expression, mastication, pharynx, larynx, sternocleidomn, mastication, pharynx, larynx, sternocleidomastoid and trapezius.astoid and trapezius.

Four pairs of nuclei:Four pairs of nuclei: Motor nucleus of trigeminal nerve,Motor nucleus of trigeminal nerve, Nucleus of facial nerve,Nucleus of facial nerve, Nucleus ambiguous,Nucleus ambiguous, Nucleus of accesory nerve.Nucleus of accesory nerve.

③ ③ The The general visceral motor nucleusgeneral visceral motor nucleus It is also called the parasympathetic nervous cIt is also called the parasympathetic nervous c

olumn.olumn. It controls the activities of smooth muscle, carIt controls the activities of smooth muscle, car

diac muscle and glands in the head, neck, thordiac muscle and glands in the head, neck, thorax and abdomen.ax and abdomen.

Four pairs of nuclei.Four pairs of nuclei. Accessory nucleus of oculomotor nerve,Accessory nucleus of oculomotor nerve, Superior salivatory nucleus,Superior salivatory nucleus, Inferior salivatory nucleus,Inferior salivatory nucleus, Dorsal nucleus of vagus nerve.Dorsal nucleus of vagus nerve.

④ ④ The The special visceral sensory nucleusspecial visceral sensory nucleus It receives the first order afferent fibers which originatIt receives the first order afferent fibers which originat

e from the taste buds.e from the taste buds. One pair of nuclei.One pair of nuclei. Nucleus of solitary tarct.Nucleus of solitary tarct. ⑤ ⑤ The The general visceral sensory nucleusgeneral visceral sensory nucleus It receives the first order afferent fibers which originatIt receives the first order afferent fibers which originat

e from the viscera and heart and vessels in the head, ne from the viscera and heart and vessels in the head, neck, thorax and abdomen.eck, thorax and abdomen.

One pair of nuclei.One pair of nuclei. Nucleus of solitary tarct.Nucleus of solitary tarct.

⑥ ⑥ The The general somatic sensory nucleusgeneral somatic sensory nucleus It receives the first order afferent fibers which It receives the first order afferent fibers which

originate from the skin, muscle, muscular tendoriginate from the skin, muscle, muscular tendon, and most part of oral and nasal mucous mon, and most part of oral and nasal mucous membrane.embrane.

Three pairs:Three pairs: Mesencephalic nucleus of trigeminal nerve,Mesencephalic nucleus of trigeminal nerve, Pontine nucleus of trigeminal nerve,Pontine nucleus of trigeminal nerve, Spinal nucleus of trigeminal.Spinal nucleus of trigeminal.

⑦ ⑦ The The special somatic sensory nucleusspecial somatic sensory nucleus It receives the first order fibers originate from tIt receives the first order fibers originate from t

he vestibulocochlear organs (equilibrant and she vestibulocochlear organs (equilibrant and spiral organs) in the internal ear. Including:piral organs) in the internal ear. Including:

vestibular nuclei,vestibular nuclei, cochlear nuclei.cochlear nuclei.

(2) Functional columns of nuclei of cranial nerves and t(2) Functional columns of nuclei of cranial nerves and the their nuclei’ locations and functionshe their nuclei’ locations and functions

1) The 1) The general somtic motor columngeneral somtic motor column ① ① Oculomotor nucleusOculomotor nucleus (Ⅲ) (Ⅲ) It is located ventromedially to the central gray matter It is located ventromedially to the central gray matter

at the level of the superior colliculus.at the level of the superior colliculus. The fibers from the nucleus course ventrally, leave the The fibers from the nucleus course ventrally, leave the

brain medial to the cerebral peduncle, join the oculobrain medial to the cerebral peduncle, join the oculomotor nerve, supply most of the extraocular muscles motor nerve, supply most of the extraocular muscles except the lateral rectus and the superior obliquus, i.e.except the lateral rectus and the superior obliquus, i.e. the superior rectus, inferior rectus, medial rectus, infe the superior rectus, inferior rectus, medial rectus, inferior obliquus, levator palpebraerior obliquus, levator palpebrae superiorissuperioris..

② ② Trochlear nucleusTrochlear nucleus (Ⅳ) (Ⅳ) It lies in the ventral region of the central gray matter clIt lies in the ventral region of the central gray matter cl

ose to the midline at the level of the superior colliculuose to the midline at the level of the superior colliculus.s.

Its outgoing fibers pass laterally and dorsally round thIts outgoing fibers pass laterally and dorsally round the central gray matter. They reach the cranial end of the central gray matter. They reach the cranial end of the superior medullary velum, decussating with those of e superior medullary velum, decussating with those of the opposite side and become the unique cranial nervthe opposite side and become the unique cranial nerve which emerges from the dorsal surface of the brain se which emerges from the dorsal surface of the brain stem, form the trochlear nerve, innervating the superiotem, form the trochlear nerve, innervating the superior obliquus.r obliquus.

③ ③ Abducent nucleusAbducent nucleus (Ⅵ) (Ⅵ) It lies deeply in the facial colliculus.It lies deeply in the facial colliculus. The fibers from the nucleus of abducent nerve The fibers from the nucleus of abducent nerve

course ventrally and inferiorly, emerge througcourse ventrally and inferiorly, emerge through the bulbopontine sulcus, forming the abduch the bulbopontine sulcus, forming the abducent nerve, control the lateral rectus.ent nerve, control the lateral rectus.

④ ④ Hypoglossal nucleusHypoglossal nucleus (Ⅻ) (Ⅻ) It lies under the hypoglossal triangle and extenIt lies under the hypoglossal triangle and exten

ds down to the closed part of medulla oblongads down to the closed part of medulla oblongata, on each side of the median plane.ta, on each side of the median plane.

The fibers originating from hypoglossal nucleuThe fibers originating from hypoglossal nucleus run ventrolaterally, finally emerging from the s run ventrolaterally, finally emerging from the anterolateral sulcus to become the (anterolateral sulcus to become the (rootletsrootlets oof)f) hypoglossal nervehypoglossal nerve, control the movements , control the movements of lingual muscles.of lingual muscles.

2) The 2) The special visceral motor columnspecial visceral motor column ① ① The The motor nucleus of trigeminal nervemotor nucleus of trigeminal nerve (Ⅴ) (Ⅴ) It lies lateral to abducent nucleus.It lies lateral to abducent nucleus. The fibers originating from this nucleus leave tThe fibers originating from this nucleus leave t

he brain between the basilar part and the midhe brain between the basilar part and the middle peduncle of cerebellum, form the motor rodle peduncle of cerebellum, form the motor root of trigeminal nerve, innervating the massetot of trigeminal nerve, innervating the masseter.er.

② ② The The facial nucleusfacial nucleus (Ⅶ) (Ⅶ) It is situated at the ventrolateral part of the retIt is situated at the ventrolateral part of the ret

icular formation, ventromedial to the spinal tricular formation, ventromedial to the spinal tract and nucleus of trigeminal nerve.act and nucleus of trigeminal nerve.

The fibers from the nucleus course dorsomediThe fibers from the nucleus course dorsomedially, round the dorsal side of nucleus of abducally, round the dorsal side of nucleus of abducent nerve, turn ventrolaterally, forming genu oent nerve, turn ventrolaterally, forming genu of facial nerve, emerge through the bulbopotine f facial nerve, emerge through the bulbopotine sulcus, constitute the facial nerve, innervate tsulcus, constitute the facial nerve, innervate the activities of facial muscles.he activities of facial muscles.

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

③ ③ The The nucleus ambiguusnucleus ambiguus (Ⅸ,Ⅹ,Ⅺ) (Ⅸ,Ⅹ,Ⅺ) It is placed deeply in the reticular formation.It is placed deeply in the reticular formation. The fibers arising from the nucleus ambiguous The fibers arising from the nucleus ambiguous

leaving the brain stem behind the olive, providleaving the brain stem behind the olive, provides the special visceral efferent fibers for the gles the special visceral efferent fibers for the glossopharyngeal nerve, vagus nerve and craniaossopharyngeal nerve, vagus nerve and cranial root of accessory nerve, innervate pharyngeal root of accessory nerve, innervate pharyngeal, laryngeal, and soft palatine muscles.l, laryngeal, and soft palatine muscles.

④ ④ The The spinal accessory nucleusspinal accessory nucleus (Ⅺ) (Ⅺ) It is located in the gray matter of the lower parIt is located in the gray matter of the lower par

t of the medulla oblongata, and gives rise to eft of the medulla oblongata, and gives rise to efferent fibers to supply the sternocleidomastoiferent fibers to supply the sternocleidomastoid and trapezius. In corresponding to the spinal d and trapezius. In corresponding to the spinal roots of the accessory nerve, the spinal nucleuroots of the accessory nerve, the spinal nucleus of accessory nerve may extend downwards as of accessory nerve may extend downwards as low as the level of the fifth cervical segment s low as the level of the fifth cervical segment of the spinal cord.of the spinal cord.

3) The 3) The general visceral motor columngeneral visceral motor column ① ① The The accessory oculomotor nucleusaccessory oculomotor nucleus (Ⅲ)(Ⅲ) This nucleus is situated dorsally to the nucleus of oculoThis nucleus is situated dorsally to the nucleus of oculo

motor nerve.motor nerve. The preganglionic parasymjpathetic fibers travel in the The preganglionic parasymjpathetic fibers travel in the

oculomotor nerve to relay in the oculomotor nerve to relay in the ciliary ganglionciliary ganglion, subse, subsequently in the short ciliary nerves to innervate the ciliary quently in the short ciliary nerves to innervate the ciliary muscle and the sphincter pupillae.muscle and the sphincter pupillae.

The oculomotor nucleus and the accessory oculomotor The oculomotor nucleus and the accessory oculomotor nucleus constitute the nucleus constitute the oculomotor nuclear complexoculomotor nuclear complex..

② ② The The superior salivatory nucleussuperior salivatory nucleus (Ⅶ) (Ⅶ) It is situated in the reticular formation.It is situated in the reticular formation. The parasympathetic preganglionic fibers from this nThe parasympathetic preganglionic fibers from this n

ucleus join in the facial nerve, control the secretion of ucleus join in the facial nerve, control the secretion of submandibular gland, sublingual gland and lacrimal gsubmandibular gland, sublingual gland and lacrimal gland.land.

③ ③ The The inferior salivatory nucleusinferior salivatory nucleus (Ⅸ) (Ⅸ) It is near to the rostral end of the dorsal nucleus of vagIt is near to the rostral end of the dorsal nucleus of vag

us.us. It sends preganglionic parasympathetic fibers into the It sends preganglionic parasympathetic fibers into the

glossopharyngeal nerve, controls the secretion of parglossopharyngeal nerve, controls the secretion of parotid gland.otid gland.

④ ④ The The dorsal nucleus of vagus nervedorsal nucleus of vagus nerve (Ⅹ) (Ⅹ) It lies under the vagus triangle lateral to the hypoglossIt lies under the vagus triangle lateral to the hypogloss

al nucleus.al nucleus. The preganglionic parasympathetic fibers originating The preganglionic parasympathetic fibers originating

from the dorsal nucleus of vagus nerve emerge posterifrom the dorsal nucleus of vagus nerve emerge posterior to the olive, join the vagus nerve, and control the acor to the olive, join the vagus nerve, and control the activities of smooth muscle, cardiac muscle and glands tivities of smooth muscle, cardiac muscle and glands or the organs in the neck, thoracic cavity and a large nor the organs in the neck, thoracic cavity and a large number of abdominal visceral organs. umber of abdominal visceral organs.

4) 4) The visceral sensory columnThe visceral sensory column The The nucleus of solitary tractnucleus of solitary tract (Ⅶ,Ⅸ,Ⅹ) (Ⅶ,Ⅸ,Ⅹ) It is situated around the solitary tract, ventrolateral to It is situated around the solitary tract, ventrolateral to

the dorsalnucleus of vagus nerve.the dorsalnucleus of vagus nerve. The upper part (end) of this nucleus receives the speciThe upper part (end) of this nucleus receives the speci

al visceral sensory (taste) fibers, while the lower part ral visceral sensory (taste) fibers, while the lower part receives the general visceral sensory fibers.eceives the general visceral sensory fibers.

The solitary tract constitutes a composite descending The solitary tract constitutes a composite descending bundle of visceral afferent fibers consisting of the pribundle of visceral afferent fibers consisting of the primary afferent fibers from the facial, glossopharyngeal mary afferent fibers from the facial, glossopharyngeal and vagus nerves which enter the brain stem by passiand vagus nerves which enter the brain stem by passing through the posterolateral sulcus. This tract conveng through the posterolateral sulcus. This tract conveys the gustatory stimulus and general visceral stimuluys the gustatory stimulus and general visceral stimulus to the adjacent nucleus of solitary tract.s to the adjacent nucleus of solitary tract.

In fact, the nucleus of solitary tract is shared by these tIn fact, the nucleus of solitary tract is shared by these three cranial nerves. hree cranial nerves.

5) The 5) The general somatic sensory columngeneral somatic sensory column ① ① The The mesencephalic nucleus of trigeminal nervemesencephalic nucleus of trigeminal nerve

(Ⅴ)(Ⅴ) It located in the lateral margin of the central gray mattIt located in the lateral margin of the central gray matt

er around the mesencephalic aueduct.er around the mesencephalic aueduct. It is concerned with the conduction of the proprioceptIt is concerned with the conduction of the propriocept

ive impulses of masseter, facial muscles, and extraocuive impulses of masseter, facial muscles, and extraocular muscles, from the trigeminal nerve.lar muscles, from the trigeminal nerve.

② ② The The pontine nucleus of trigeminal nervepontine nucleus of trigeminal nerve (Ⅴ) (Ⅴ) It lies on the lateral side of the motor nucleus, it extenIt lies on the lateral side of the motor nucleus, it exten

ds inferiorly and continues with the spinal nucleus of tds inferiorly and continues with the spinal nucleus of trigeminal nerve. The pontine nucleus receives the pririgeminal nerve. The pontine nucleus receives the primary afferent fibers of the trigeminal nerve, correlatinmary afferent fibers of the trigeminal nerve, correlating to the transmission of tactile sensibility of head and g to the transmission of tactile sensibility of head and face. The descending fibers are the spinal tract of trigeface. The descending fibers are the spinal tract of trigeminal nerve.minal nerve.

The second order fibers from this nuculeus decussate The second order fibers from this nuculeus decussate to the opposite side to join the trigeminal lemniscus.to the opposite side to join the trigeminal lemniscus.

③ ③ The The spinal nucleus of trigeminal nervespinal nucleus of trigeminal nerve (Ⅴ, (Ⅴ,Ⅶ,Ⅸ,Ⅹ)Ⅶ,Ⅸ,Ⅹ)

It is directly continuous with the substantia gelIt is directly continuous with the substantia gelatinosa of the dorsal gray column of the spinal atinosa of the dorsal gray column of the spinal cord.cord.

It lies on the medial side of the It lies on the medial side of the spinalspinal tract of tract of trigeminal nervetrigeminal nerve and is concerned with the m and is concerned with the mediation of pain and thermal sensibilities of thediation of pain and thermal sensibilities of the trigeminal area.e trigeminal area.

The general somatic sensory fibers of trigeminThe general somatic sensory fibers of trigeminal nerve transmit pain and thermal sensibilitieal nerve transmit pain and thermal sensibilities, enter the pons, and then descend into the ms, enter the pons, and then descend into the mudulla oblongata, constitute the spinal tract of udulla oblongata, constitute the spinal tract of trigeminal nerve, and terminate the spinal nuctrigeminal nerve, and terminate the spinal nucleus of trigeminal nerve. This nucleus receives leus of trigeminal nerve. This nucleus receives primary afferent fibers from the trigeminal, facprimary afferent fibers from the trigeminal, facial, glossopharyngeal and vagus nerves.ial, glossopharyngeal and vagus nerves.

The second order fibers originating from this nThe second order fibers originating from this nucleus cross to the opposite to from the trigeucleus cross to the opposite to from the trigeminal lemniscus.minal lemniscus.

6) The 6) The special somatic sensory columnspecial somatic sensory column ① ① The vestibular nuclei (Ⅷ)The vestibular nuclei (Ⅷ) They are situated deep in the vestibular area.They are situated deep in the vestibular area. They are divided into the They are divided into the medial, inferior, latmedial, inferior, lat

eraleral and and superior vestibular nucleisuperior vestibular nuclei. The nuc. The nuclei receive the major afferent fibers from the vlei receive the major afferent fibers from the vestibular nerve. The efferent fibers of the comestibular nerve. The efferent fibers of the complex constitute vestibulospinal tract, correlatiplex constitute vestibulospinal tract, correlating muscular tension, vestibulocerebellar tract, ng muscular tension, vestibulocerebellar tract, and medial longitudinal fasciculus.and medial longitudinal fasciculus.

② ② The cochlear nuclei (Ⅷ)The cochlear nuclei (Ⅷ) They are situated ventrolateral and dorsal to tThey are situated ventrolateral and dorsal to t

he inferior cerebellar peduncle.he inferior cerebellar peduncle. They are divided into the They are divided into the dorsal cochlear nucldorsal cochlear nucl

euseus and the and the ventral cochlear nucleusventral cochlear nucleus. These t. These two nuclei receive afferent fibers from the cochwo nuclei receive afferent fibers from the cochlear nerve. lear nerve.

2. The nuclei of non-cranial nerves2. The nuclei of non-cranial nerves (1) The nuclei of non-cranial nerves in medulla oblonga(1) The nuclei of non-cranial nerves in medulla oblonga

tata ① ① Gracile nucleusGracile nucleus and and cuneatecuneate nucleusnucleus They are situated in the deep of the gracile tubercle aThey are situated in the deep of the gracile tubercle a

nd cuneate tubercle respectively.nd cuneate tubercle respectively. The fibers of the fasciculi gracilis and cuneatus have aThe fibers of the fasciculi gracilis and cuneatus have a

scended ipsilaterally through the spinal cord, and the scended ipsilaterally through the spinal cord, and the majority terminate in their respective nuclei.majority terminate in their respective nuclei.

The gracile and cuneate nuclei are the important relay The gracile and cuneate nuclei are the important relay stations for conducting deep and fine touch sensatory stations for conducting deep and fine touch sensatory impulses.impulses.

② ② The The inferior olivary nucleusinferior olivary nucleus It is deep in the olive of medulla oblongata.It is deep in the olive of medulla oblongata. This nucleus may be the relay station between This nucleus may be the relay station between

the cerebrum, red nucleus and the cerebellum.the cerebrum, red nucleus and the cerebellum. ③ ③ The The accessory cuneate nucleusaccessory cuneate nucleus ( (lateral culateral cu

neate nucleusneate nucleus))

(2) The nuclei of non-cranial nerves in pons(2) The nuclei of non-cranial nerves in pons ① ① The The pontine nucleipontine nuclei They are scattered throughout the basilar part of the They are scattered throughout the basilar part of the

pons, constitute relay stations on the pathway from thpons, constitute relay stations on the pathway from the cerebral cortex to the cerebellum.e cerebral cortex to the cerebellum.

The axons of the cells of pontine nuclei form the transThe axons of the cells of pontine nuclei form the transverse fibers of the pons (verse fibers of the pons (pontocerebellar fiberspontocerebellar fibers). The). These fibers run transversely, crossing the median plane, fse fibers run transversely, crossing the median plane, form the middle cerebellar peduncle, enter the cerebelorm the middle cerebellar peduncle, enter the cerebellar hemisphere of the opposite side.lar hemisphere of the opposite side.

② ② The The superior olivary complexsuperior olivary complex ③ ③ The The nucleus of lateral lemniscusnucleus of lateral lemniscus

(3) The nuclei of non-cranial nerves in midbrain(3) The nuclei of non-cranial nerves in midbrain ① ① TheThe red nucleusred nucleus The red nucleus is situated in the center of the The red nucleus is situated in the center of the

tegmentum. It appears pinkish color in fresh stegmentum. It appears pinkish color in fresh specimen.pecimen.

It receives the fibers from the contralateral sidIt receives the fibers from the contralateral side of cerebellum via the superior cerebellar pede of cerebellum via the superior cerebellar peduncle.uncle.

The efferent fibers decussate in the ventral tegThe efferent fibers decussate in the ventral tegmental decussation to constitute the mental decussation to constitute the rubrospirubrospinal tractnal tract. .

② ② The The substantia nigrasubstantia nigra It lies between the tegmentum of the midbrain, extenIt lies between the tegmentum of the midbrain, exten

ding throughout the whole length of the midbrain. Thding throughout the whole length of the midbrain. The cells of subatantia nigra rich in melanotic pigment ae cells of subatantia nigra rich in melanotic pigment and dopaminend dopamine

③ ③ The The superior colliculussuperior colliculus It serves as reflex center correlating movement of the It serves as reflex center correlating movement of the

head and eyes used to localize and follow visual stimuhead and eyes used to localize and follow visual stimuli. It may also respond to auditory stimuli by the affereli. It may also respond to auditory stimuli by the afferent fibers from inferior colliculi and to somatic stimuli bnt fibers from inferior colliculi and to somatic stimuli by the spinotectal tract.y the spinotectal tract.

④ ④ The The inferior colliculusinferior colliculus They are reflex centers for auditory responses They are reflex centers for auditory responses

and concerned in the ability to localize the souand concerned in the ability to localize the source of sounds. rce of sounds.

⑤ ⑤ The The pretectal regionpretectal region (pretectal nuclei) (pretectal nuclei) It is the center of pupillary reflex situating at thIt is the center of pupillary reflex situating at th

e junction of the midbrain and the diencephale junction of the midbrain and the diencephalons.ons.

3. The long ascending and descending tracts.3. The long ascending and descending tracts. (1) The ascending tracts(1) The ascending tracts ① ①The The medial lemniscusmedial lemniscus The second order fibers arise from the gracile and cunThe second order fibers arise from the gracile and cun

eate nuclei go anteromedially, wind around the ventreate nuclei go anteromedially, wind around the ventral side of central canal, forming the al side of central canal, forming the internal arcuate finternal arcuate fibersibers, and then bend medially to reach the median pl, and then bend medially to reach the median plane, where they decussate with the corresponding fibane, where they decussate with the corresponding fibers of the opposite side, forming the ers of the opposite side, forming the decussationdecussation of of medial lemniscusmedial lemniscus. After decussation, the fibers ascen. After decussation, the fibers ascend along the two side of median line, constituting the d along the two side of median line, constituting the medial lemniscus.medial lemniscus.

In the medulla oblongataIn the medulla oblongata: posterior to the pyramid.: posterior to the pyramid. In the ponsIn the pons: penetrating the trapezoid body.: penetrating the trapezoid body. In the midbrainIn the midbrain: dorsolateral to the red nucleus.: dorsolateral to the red nucleus. The medial lemniscus terminates in the ventral posterThe medial lemniscus terminates in the ventral poster

olateral nucleus of thalamus.olateral nucleus of thalamus. This tract connect deep and fine touch sensation.This tract connect deep and fine touch sensation.

② ②The The spinal lemniscus (spinothalamic tract)spinal lemniscus (spinothalamic tract) After the anterior and posterior spinothalamic tracts aAfter the anterior and posterior spinothalamic tracts a

scend to the medulla oblongata, we definite the two trscend to the medulla oblongata, we definite the two tracts as spinal lemniscus.acts as spinal lemniscus.

It lies dorsolaterally to the inferior olivary nucleus and,It lies dorsolaterally to the inferior olivary nucleus and, As it ascends to the pons and midbrain it lies dorsolat As it ascends to the pons and midbrain it lies dorsolaterally to the medial lemniscus, terminating in the venterally to the medial lemniscus, terminating in the ventral posterolateral nucleus.ral posterolateral nucleus.

The spinothelamic lemniscus connects superficial senThe spinothelamic lemniscus connects superficial sensation of somatic trunk and limbs. sation of somatic trunk and limbs.

③③The The trigeminal lemniscustrigeminal lemniscus The axons of the cells of the pontine and spinal nuclei The axons of the cells of the pontine and spinal nuclei

of trigeminal nerve, cross the median plane to form thof trigeminal nerve, cross the median plane to form the e trigeminal lemniscustrigeminal lemniscus ascending with the medial leascending with the medial lemniscus to the thalamus.mniscus to the thalamus.

It lies dorsolaterally to the medial lemniscus, terminatIt lies dorsolaterally to the medial lemniscus, terminates in the ventral postomedial nucleus of thalamus.es in the ventral postomedial nucleus of thalamus.

The trigeminal lemniscus relates to the conduction of The trigeminal lemniscus relates to the conduction of the tactile and pressure impulses; and the pain and ththe tactile and pressure impulses; and the pain and thermal impulses from the skin, mucous membrane, corermal impulses from the skin, mucous membrane, cornea, conjunctiva and the meninges through the brancnea, conjunctiva and the meninges through the branches of the trigeminal nerve.hes of the trigeminal nerve.

④ ④The The lateral lemniscuslateral lemniscus The efferent fibers from the cochlear nuclei run mediaThe efferent fibers from the cochlear nuclei run media

lly in the ventral part of the tegmentum, intersecting lly in the ventral part of the tegmentum, intersecting with the vertical fibers of medial lemniscus to form trawith the vertical fibers of medial lemniscus to form trapezoid body. Then the fibers cross the median raphe apezoid body. Then the fibers cross the median raphe and decussate with the corresponding fibers of the oppnd decussate with the corresponding fibers of the opposite side to form the principal ascending auditory patosite side to form the principal ascending auditory pathway, the hway, the lateral lemniscuslateral lemniscus. .

It lies dosolaterally to the medial leminicus and termiIt lies dosolaterally to the medial leminicus and terminates in nates in medial geniculate bodymedial geniculate body. .

It connects auditory impulses.It connects auditory impulses. ⑤ ⑤ The medial longitudinal fasciculusThe medial longitudinal fasciculus ⑥ ⑥ The ventral spinocerebellar tract and dorsal spinoceThe ventral spinocerebellar tract and dorsal spinoce

rebellarrebellar

(2) The descending tracts(2) The descending tracts The The pyramidal tractpyramidal tract:: The axons originating from the giant pyramidal cells The axons originating from the giant pyramidal cells

(Betz cells) and other pyramidal cells of various sized (Betz cells) and other pyramidal cells of various sized which are located in the precentral gyrus and anterior which are located in the precentral gyrus and anterior part or paracentral lobule constitute the strong pyrampart or paracentral lobule constitute the strong pyramidal tract. idal tract.

In the course of descending this tract pass through the In the course of descending this tract pass through the posterior limb and genu of internal capsule, the middlposterior limb and genu of internal capsule, the middle 3/5 of bottom of cerebral peduncle, the basilar part e 3/5 of bottom of cerebral peduncle, the basilar part of pons, and the pyramid of medulla oblongata. of pons, and the pyramid of medulla oblongata.

The pyramidal tract includes the The pyramidal tract includes the corticonuclear tractcorticonuclear tract and and corticospinal tractcorticospinal tract..

The The corticonuclear tractcorticonuclear tract ( (corticobulbar tractcorticobulbar tract)) termi terminate in the cranial nuelei of brain stem and the corticonate in the cranial nuelei of brain stem and the corticospinal tract in the anterior horn of the spinal cord.spinal tract in the anterior horn of the spinal cord.

In the lower part of the pyramid, about 85% of fibers oIn the lower part of the pyramid, about 85% of fibers of corticospinal tract cross the median plane and contif corticospinal tract cross the median plane and continue down the spinal cord in the lateral funiculus as thnue down the spinal cord in the lateral funiculus as the e lateral corticospinal tractlateral corticospinal tract. The uncrossed fibers ret. The uncrossed fibers retain their ventromedial position and descend in the antain their ventromedial position and descend in the anterior funiculus of the spinal cord as the erior funiculus of the spinal cord as the anterior cortianterior corticospinal tractcospinal tract..

The pyramidal tract concerned with controlling the voThe pyramidal tract concerned with controlling the voluntary movements of skeletal muscles.luntary movements of skeletal muscles.

4. The 4. The reticular formation of brain reticular formation of brain stemstem

In the brain stem, there is an extensive In the brain stem, there is an extensive field of intermingled gray and white matter field of intermingled gray and white matter collectively termed the reticular formation.collectively termed the reticular formation.

According to the traditional view, the According to the traditional view, the reticular formation forms the central core reticular formation forms the central core throughout the brain stem; lying laterally throughout the brain stem; lying laterally between posterior and anterior horns;between posterior and anterior horns;

(1) The main nuclei of the reticular formation of brain st(1) The main nuclei of the reticular formation of brain stemem

1) Cerebellar reticular formation nuclei1) Cerebellar reticular formation nuclei 2) Raphe nuclei2) Raphe nuclei 3) Medial (central) gigantocellular nuclei3) Medial (central) gigantocellular nuclei 4) Lateral parvicellular (small—celled) nuclei4) Lateral parvicellular (small—celled) nuclei (2) The functions of the reticular formation(2) The functions of the reticular formation The reticular formation is an important integration ceThe reticular formation is an important integration ce

nter for the vital activity; its major functions may sum nter for the vital activity; its major functions may sum up as follows:up as follows:

Somatomotor control,Somatomotor control, The activation of the behavioral arousal,The activation of the behavioral arousal, Visceromotor control.Visceromotor control.

ⅢⅢ. Transverse sections of brain stem. Transverse sections of brain stem

1) The transverse section through the medulla 1) The transverse section through the medulla ablongata at the level of the pyramidal decussablongata at the level of the pyramidal decussationation

2) The transverse section through the pons at t2) The transverse section through the pons at the level of facial colliculushe level of facial colliculus

3) The transverse section of the midbrain t3) The transverse section of the midbrain through the superior colliculushrough the superior colliculus