Brainstem

Question 1

Function of the reticular system

Answer 1

Control over level of conscousness

Perception of pain

Regulation of cardiorespiratory system

Question 2

What is found on the dorsal suface of the medulla?

Answer 2

The midline is marked by a dorsal median sulcus which is continuous with that of the spinal cord.

In the caudal part, the dorsal columns (fasciculi gracilis and cuneatus) continue rostrally from the spinal cord to their termination in the nuclei gracilis and cuneatus, the locations of which are marked by two small elevations, the gracile and cuneate tubercles

Question 3

Answer 3

Question 4

Answer 4

Question 5

What is the “closed” portion of the medulla

Answer 5

The caudal two thirds contain the rostral continuation of the central canal of the spinal cord.

In passing rostrally, the central canal moves progressively more dorsally until in the rostral medulla it opens out into the fourth ventricle (open medulla)

Question 6

What proprtion of the fourth ventricle is accounted for by the medulla?

Answer 6

The caudal 1/3rd of the ventricular floor is accounted for by the medulla while the rostral two thirds is made up of the dorsal aspect of the pons.

Question 7

Where is the fourth ventricle widest?

Answer 7

At the level of the pontomedullary junction at which a lateral recess extends to the lateral margin of the brainstem (this is where the foramen of Luschka is found).

Question 8

What structures constitute the lateral walls of the rostral portion of the fourth ventricle?

Answer 8

The superior and inferior cerebellar peduncles

Question 9

What is found at the most superior aspect of the fourth ventricle?

Answer 9

The cerebral aqueduct which passes throughout the length of the midbrain.

Question 10

What are the four paired elevations on the dorsal aspect of the midbrain?

Answer 10

The superior and inferior colliculi

Question 11

Where does the trochlear nerve emerge?

Answer 11

Immediately caudal to the inferior colliculus

Question 12

What are visible on the ventral surface of the medulla?

Answer 12

Prominent longitudinal columsn, the pyramid which run either side of the ventral median fissure.

Lateral to the pyramid lies an elongated elevation, the olive, within which lies the inferior olivary nucleus

Question 13

Inferior olivary nucleus

Answer 13

This has connections primarily with the cerebellum and is involved in the control of movement.

Question 14

Answer 14

Question 15

Answer 15

Question 16

What delineates the transition from medulla to pons on the ventral surface of the brainstem?

Answer 16

The transverse system of fibres (the transverse pontine fibres) that originate from cells in the ventral pons and pass through the contralateral middle cerebellar peduncle to enter the cerebellar hemisphere. This massive system obscures the underlying pyramidal tracts

Question 17

Features of the ventral surface of the midbrain?

Answer 17

Consists of a large column of descending fibres on either side, the crus cerebri or basis penduculi.

The two crura are separated by the interpeduncular fossa (basal cistern).

The crus cerebri is continuous with the internal capsule of the cerebral hemispherse and consists of corticobulbar and corticospinal fibres.

Question 18

What portion of the brainstem is this?

Answer 18

Caudal part of the medulla

Question 19

What happens to the pattern of grey and white matter as there is the transition from spinal cord to medulla?

Answer 19

The ventral horn becomes much more attenuated, the dorsal horn is replaced by the caudal part of the trigeminal sensory nucleus.

Question 20

Trigeminal sensory nucleus

Answer 20

Regarded as the brainstem homologue of the dorsal horn as it receives afferent fibres conveying general sensation from the head, which enter the brainstem in the trigeminal nerve.
It is a large nucleus that extneds the whole length of the brainstem and into the upper segments of the spinal cord.

The caudal part is particularly associated with pain and temperature.

Question 21

Where does the trigeminal nerve attach and what is the significance?

Answer 21

It attaches to the pons and therefore fibres that terminate in the parts of the trigeminal nucleus caudal to this level descend in the spinal tract of the trigeminal which lies immediately superficial to the nucleus

Question 22

What portion of the medulla is this?

Answer 22

Question 23

What are the features of the mid-medulla

Answer 23

Pyramids are prominent above their decussation ventrally.

Dorsally the ascending fibres of the dorsal columsn reach their termination in their respsective nuclei.

The dorsal columns consist of first-order sensory neurones with their cell bodies lying in the DRG of spinal nerves. They terminate in their nuclei upon the cell bodies of the second order neurones which course ventrally and medially, decussating as the internal arcuate fibres.

Question 24

What happens to nerve fibres after the internal arcuate fibres

Answer 24

They turn rostraly, forming a distinct tract, the medial lemniscus, which runs through the rostral medulla, the pons and the midbrain to terminate on third-order neurones in the VPN of the thalamus

Question 25

What portion of the brainstem is this?

Answer 25

Rostral medulla

Question 26

What are the features of the rostral medulla

Answer 26

Pyramids remain conspicuous ventrally. Immediately dorsal to the medial aspect of the pyramid lie the ascending fibres of the medial lemniscus. In the midline is the medullary part of the brainstem raphe nuclear complex (nucleus raphe magnus) Dorsolateral to the medial lemniscus is the inferior olivary nucleus. Dorsal to the nucleus and lateral to the medial lemniscus lie second-order sensory fibres, ascending tot he VPN from the trigemnial nucleus (trigeminothlamic tract or tigeminal lemnsicus) and from the SC (spinal lemniscus) Posteriorly is the fourth ventricle and a number of cranial nerve nuclei includin the hypoglossal, motor nuclues of thhe vagus. Most caudal aspect of the ventricular floor is known as the area postrema. In the latral part of the floor of the fourth ventricle are the vestibular nuclei. Ventromedial to the hypoglossal nucleus is the MLF.

Question 27

Inferior olivary nucleus

Answer 27

Found within the prominence of the olive. It has the form of a crenated bag, with an opening (hilum) facing medially through which afferent and efferent fibres pass. It is concerned with the control of movement and receives afferents from the motor and sensory cortices of the cerebral hemisphere and from the red nucleus of the midbrain. Its main efferent connection is to the cerebellum via the inferior cerebellar peduncle. Within the cerebellum, axons originating from the inferior olivary nucleus (climbing fivres), end in excitatory synpases in the dentate nucleus and upon Purkinje cells of the cerebellar cortex

Question 28

Nucleus raphe magnus

Answer 28

Located in the midline of the rostral medulla. Major origin of serotonergic neurones

Question 29

Cranial nerve relations to the fourth ventricle (medullary portion)

Answer 29

Immediately beneath the ventricle floor, just lateral to the midline is the hypoglossal nucleus. Lateral to the hypoglossal nucleus lies the dorsal motor nucleus of the vagus. In the lateral part of the floor of the fourth ventricle is the vestibular nuclei which receives primary afferent fibres from the vestibular nuclei. The MLF is ventromedial to the hypoglossal nuclei

Question 30

Restiform body

Answer 30

Dorsolateral part of the rostral medulla- inferior cerebellar peduncle. Consists of fibres passing between the medulla and cerebellum. Prominent amongst these are the olivocerebellar fibres.

Question 31

Location of the cochlear nuclei

Answer 31

On the dorsal and lateral aspects of the cerebellar peduncle which receive afferent fibres from the cochlear nerve

Question 32

Nucleus solitarius

Answer 32

Medial to the inferior cerebellar peduncle and ventral to the vestibular nuclei. Surrounds a small dense fascicle of fibres (solitary tract). The nucleus solitarius receives visceral afferent fibres entering the brainstem in the facial, GPA and vagus nerves.

Question 33

Nucleus ambiguus

Answer 33

Deep beneath the ventricular floor, ventral to the nucleus solitarius and dorsal to the inferior olivary nucleus is the nucleus ambiguus which sends motor fibres into the GPA, vagus nerve and cranial roots of the accessory nerve and from there to the muscles of the pharynx and larynx

Question 34

Divisions of the pons

Answer 34

Ventral or basal portion and a dorsal portion (tegmentum)

Question 35

Structure of the ventral portion of the pons

Answer 35

Marked by numerous transversely orientated fascicles of pontocerebellar fibres that originate from scattered cell groups, the pontine nuclei, and pass into the contralateral side of the cerebellum through the middle cerebellar peduncle (brachium pontis) Corticospinal fibres appear as small separate bundles running longitudinally between the fascicles of transverse pontine fibres.

Question 36

What portion of the brainstem is this?

Answer 36

Caudal pons

Question 37

What portion of the brainstem is this?

Answer 37

Mid-pons

Question 38

What portion of the brainstem is this?

Answer 38

Rostral pons

Question 39

What happens to ascending fibres of the medial lemniscus in the pons?

Answer 39

Become separated from the pyramid and displaced dorsally, together with the spinal lemniscus and trigeminothalamic tract by the intervening transverse pontocerebellar fibres. The medial lemniscus also rotates through 90 degrees so that it lies almost horizonatlly, marking the boundary between ventral and tegmental portions of the pons.

Question 40

Trapezoid body.

Answer 40

In the caudal to mid-pons, there is an additional group of transversely running fibres, located close to the ascending lemnniscal fibres but dorsal to the pontocerebellar fibres. This consists of acoustic fibres, crossing the brainstem from the cochlea nuclei. They ascend into the midbrain as the lateral lemniscus and terminate in the inferior colliculus

Question 41

Cranial nerve arrangement in the pontine tegementum

Answer 41

Beneath the floor of the fourth venticle in the pontine tegmentum lie the abducens, the facial motor nucleus and the trigeminal motor nucleus. The trigeminal sensory nucleus reaches its maximum extent in the pons, adjacent to the origin of the trigeminal nerve.

Question 42

Arrangement of structures in the rostral pons

Answer 42

Superior cerebellar peduncles form the lateral walls of the fourth ventricle with the thin superior medullary velum spanning between them to form its roof. The superior cerebellar peduncles converge towards the midline as they pass into the midbrain, in the most rostral part of the pons, the fourth ventricle becomes greatly attenuated as it merges into the cerebral aqueduct. Central grey matter beings to encompass the lumen. At this level lies a group of pigmented neurones- the locus coeruleus

Question 43

Superior cerebellar peduncle

Answer 43

Found in the rostral portion of the pons and constitute the roof of the fourthe ventricle. Consists mainly of cerebellar efferents concerned with the coordination of movements that are destined for the red nucleus of the midbrain and the VLN of the thalamus.

Question 44

Locus coerulus

Answer 44

Midline group of pigmented neurones found in the rostral pons which are the major site of noradrenergic neurones

Question 45

Arrangement of the midbrain

Answer 45

Formally divided intom the dorsal and ventral portions at the level of the cerebral aqueduct. Dorsal= tectum, which consists mainly of the inferior and superior colliculi. Ventral portion is the tegmentum which is bounded ventrallly by the massive fibre system of the crus cerebri. The cerebral peduncle refers to the whole of the ventral midbrain on either side, excluding the tectum

Question 46

What portion of the brainastem is this?

Answer 46

Pontomesencephalic junction

Question 47

What portion of the brainstem is this?

Answer 47

Caudal midbrain

Question 48

What portion of the brainstem is this

Answer 48

Rostral midbrain

Question 49

Inferior colliculus

Answer 49

Found in the caudal part of the tectum. Constitutes part of the asceding acoustic projection. Ascending auditory fibres run in the lateral lemniscus, which terminates in the inferior colliculus Efferent fibres from the colliculus terminate inthe MGN of the thalamus which in turn projects to the auditory cortex of the temporal lobe.

Question 50

Superior colliculus

Answer 50

Rostral tectum of the midbrain. Part of the visual system. Main afferents are corticotectal fibres originating from the visual cortex of the occipital lobe and from the frontal eye field of the frontal lobe. These inputs are concerned with controlling movements of the eyes such as smooth pursuit or saccadic eye movemnts. They are also involved in the accommodation reflex.

Question 51

Pretectal nucleus

Answer 51

Small number of fibres running in the optic tract terminate just rostral to the superior colliculus in the pretectal nucleus which has connections with the nearby midbrain preganglionic PNS (Edinger Westphal nucleus) controlling the smooth muscle of the eye and the puipillary light reflex

Question 52

Where are the trochlear and oculomotor nuclei

Answer 52

Found in the ventral part of the periaqueductal grey matter at the level of the inferior and superior colliculi respectively. The Edinger Westphal nucleus lies close to the oculomotor nucleus.

Question 53

Medial longitudinal fasciculus

Answer 53

Lies close to the EW, trochlear and oculomotor nuclei which links them to the abducens in the pons and the vetibular nerve in the medulla.

Question 54

Arrangement of structures at the level of the inferior colliculus

Answer 54

Central portion of the tegmentum is dominated by the superior peduncles (branchium conjunctivum), these fibres originate in the cerebellum coursing ventromedially as they run into the midbrain. The superior cerebellar peduncles decussate in the midline beneath the inferior colliculus. The central portion is occupied by the red nucleus.

Question 55

How does the red nucleus project to the inferior olivary nucleus?

Answer 55

Via the central tegmental tract

Question 56

What is found at the most ventral part of the midbrain tegmentum and how is this arranged?

Answer 56

The substantia nigra, which consists of two subnuceli, the pars compacta and the pars reticulata

Question 57

Pars compacta

Answer 57

Consists of pigmented melanin-containing neurones that synthesise dopamine as thier transmitter. These neurons project to the caudate nucleus and putamen of the basal ganglia and constitute the nigrostriatal pathway which is important for voluntary movement, posture and muscle tone.

Question 58

What happens to dopamine containing neuroesn of the pars compacta?

Answer 58

Extend dorsomedially from the ventromedial part of the pars compacta into a region known as the ventral tegmental area. These cells of the VTA are the origin of he ascending mesolimbicc dopaminergic pathway and innervate a number of forebrain sturcutes including the nucleus accumbens, amygdala, septum, cingulate, orbital and prefrontal cortices.

Question 59

Pars reticulatat

Answer 59

The non-pigmented subdivision of the substantiat nigra which is considered to be a functional homologue of the internal segment of the globus pallidus.

Question 60

Crus cerebri

Answer 60

Ventral to the substantia nigra. Consists entirely of the descending cortical efferent fibres that have left the cerebral hemisphere by traversing the internal capsule. Approximately the middle 50% of the crus consits of corticobulbar and corticospinal fibres.

Question 61

What is found either side of the corticobulbar and corticospinal fibres in the crus cerebri?

Answer 61

Corticopontine fibres that originate from widespread regions of the cortex and termiante in the pontine nuclei of the ventral pons.

Question 62

Descending reticulospinal tracts

Answer 62

Originated from the medullary and pontine reticular formation. Predominantly influence muscle tone and posture. Within the reticular formation of the medulla lies a group of particulalrly large cell bodies, the reticularis gigantocellularis that controibutes descendign fibres to the lateral reticulospinal tract.

Question 63

Reticular activating system

Answer 63

Some of the ascending fibres of the reticular formation. These neurones, many of which are cholinergic, receive input either directly or indirectly from multiple sensory sources. Through mainly the intralaminar nuclei of the thalamus, they cause activaiton of the cerebral cortex and heightened arousal.