Brainstem

Question 1

What is the organisation of the brainstem?

Answer 1

Midbrain
Pons
Medulla

Question 2

What is contained within the midbrain?

Answer 2

Midbrain – associated with hearing, vision, motor control, sleep and wakefulness, alertness, temp regulation.
Blood supply: PCA, Superior Cerebellar & Basilar
CN’s III & IV

Question 3

What is contained within the Pons?

Answer 3

Pons – Contains nuclei that deal with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, expressions, facial sensation, and posture.
CN’s V-VIII
Blood supply – Pontine arteries

Question 4

What is contained within the Medulla?

Answer 4

Medulla – Contains cardiac, respiratory, vomiting, and vasomotor centres.
CN’s IX - XII
(Bulbar – nerves/tracts associated with medulla)
Blood supply – Anterior & posterior spinal artery, PICA, Vertebral.

Connects pons superiorly with spinal cord inferiorly

Junction of Medulla and Spinal Cord
 level of foramen magnum and pyramidal decussation

Junction of Medulla and Pons
Anteriorly: Inferior edge of basilar pons
Posteriorly: Inferior edge of middle and inferior cerebellar peduncles

Conical shape with its broad extremity directed superiorly

Central canal of spinal cord continues upward into lower half of medulla
In upper half of medulla central canal expands as the cavity of 4th ventricle

Dorsal horn of spinal cord is replaced by caudal part of trigeminal sensory nucleus, which is homologous to dorsal horn of spinal cord

Question 5

What are the cerebral peduncles of midbrain?

Answer 5

Comprised of many motor tracts to the body and face

Question 6

What are the superior and inferior colliculus of midbrain involved with?

Answer 6

Involved in visual and auditory processing and associated reflexes

Question 7

What is the midbrain (Mesencepahlon) comprised of?

Answer 7

Composed of tectum and tegmentum.
Serves important functions in motor activity, particularly eye movements (MLF), and in auditory and visual processing.
CN’s III and IV Nuclei located within midbrain.

Midbrain tegmentum – Red nucleus/periaqueductal grey/substantia nigra

Tectum - Inferior and superior colliculi

Crus Cerebrii /cerebral peduncle – Corticospinal, corticobulbar, conticopontine
Substangia nigra – interactions with basal ganglia>thalamus>cortex motor coordination
Portion of reticular formation – concerned with arousal and alertness

Question 8

In the midbrain, what is the tectum?

Answer 8

Roof of midbrain posterior to cerebral aqueduct
Consists largely of inferior and superior colliculi

Question 9

In the midbrain, what is the Tegmentum?

Answer 9

Mid part of midbrain anterior to cerebral aqueduct (aqueduct of silvus) and posterior to crus cerebri (Cerebral peduncles)

Question 10

in the midbrain, where is the Crus Cerebri?

Answer 10

Separated from tegmentum by substantia nigra

Question 11

What is the superior colliculi’s functions?

Answer 11

Main efferents are corticotectal fibres originating from visual cortex of occipital lobe and from frontal eye field of frontal lobe
Concerned with controlling movements of eyes, such as following a moving object (smooth pursuit) or altered direction of gaze (saccadic eye movements)
Just anterior to superior colliculus is pretectal nucleus, part of pathway mediating the pupillary light reflex
Corticotectal fibers from visual cortex are involved in accommodation reflex.

Question 12

What is the inferior colliculi’s functions?

Answer 12

Involved in auditory reflexes and in determining the side on which a sound originates
Receive input from both ears and project to medial geniculate nucleus of thalamus

Question 13

What is the pretectal nuclei’s role?

Answer 13

the pretectal nuclei receive afferents from the retina and the optic tectum, and they are involved in modulating motor responses to visual input

Question 14

What are the Descending & Ascending Tracts of the brainstem?

Answer 14

All descending tracts terminating in spinal cord pass through brainstem

All ascending tracts that reach brainstem or cerebral cortex pass through part or all of this region

Other ascending tracts originate in brainstem

Important conduit or relay station for many longitudinal pathways

Question 15

What are the Descending Autonomic System Pathways?

Answer 15

Pass to spinal cord via brain stem

Question 16

What are the cranial nerve nuclei?

Answer 16

Almost all the cranial nerve nuclei are located in the brain stem.

Exceptions are CN1 and 2, which are invaginations of the brain itself

Question 17

What is the Reticular Formation?

Answer 17

Complex matrix of neurones extending throughout tegmentum of brain stem

Controls respiration, cardiovascular system functions and states of consciousness, sleep and alertness

Descending reticulospinal tracts influence muscle tone and posture

Interconnected nuclei located throughout the brainstem.

Includes descending pathways to the spinal cord via the reticulospinal tracts of the descending reticular formation and ascending pathways to the cortex in the ascending reticular activating system (ARAS) (wakefulness and wake-sleep transition).

Reticulospinal tracts of the spinal cord = function in maintaining tone, balance, and posture—especially during body movements. Reticulospinal - Act on Alpha and gamma motor neurons – proximal limbs

Pontine reticular formation – involved in horizontal eye movements – saccades.
Raphe nuclei –within – serotonin – mood production.

Cardiovascular control – The reticular formation includes the cardiac and vasomotor centers of the medulla oblongata.

Pain modulation - origin of the descending analgesic pathways.
Sleep and consciousness

Question 18

What is the relationship with Tegmentum and Nuclei?

Answer 18

The tegmentum is the location of several cranial nerve (CN) nuclei. The nuclei of CN III and IV are located in the tegmentum portion of the midbrain. The nuclei of CN V to VIII are located in the tegmentum at the level of the pons. The nuclei of CN IX, X, and XII are located in that of the medulla

Question 19

Where is the pons located?

Answer 19

Between midbrain and medulla
Ventral portion is basis pontis
Dorsal portion is tegmentum

Question 20

Where is the junction of pons and midbrain?

Answer 20

Imaginary line drawn from exit of trochlear nerve posteriorly to superior edge of basis pontis anteriorly commissure posteriorly to caudal edge of mammillary bodies

Question 21

in the pons, What is the basis pontis?

Answer 21

Contains corticospinal tracts

Pontine nuclei receive input from cerebral cortex via corticopontine pathway

Pontine nuclei project pontocerebellar fibres to cerebellum via middle cerebellar peduncle

Question 22

In the pons, what does the tegmentum house?

Answer 22

Contains cranial nerve nuclei for abducens (CN VI), facial (CN VII) and trigeminal (CN V)

Question 23

What is the anterior median fissure of the medulla?

Answer 23

Continuous inferiorly with anterior median fissure of spinal cord (Anterior spinal artery)

Question 24

What is the posterior median sulcus of the medulla?

Answer 24

Continuous inferiorly with posterior median sulcus of spinal cord

Question 25

How is the 4th ventricle of the medulla formed?

Answer 25

Formed by posterior surface of superior half of medulla

Question 26

What are the pyramids of medulla?

Answer 26

Bundles of corticospinal nerve fibres
Taper inferiorly and majority (75-90%) of fibres cross over to opposite side  decussation of pyramids

Question 27

Where does the anterior corticospinal tract decussate?

Answer 27

Anterior corticospinal tract – decussate at spinal level. Extend to Tx region. Motor to trunk muscles.

Question 28

Where does the lateral corticospinal tract decussate?

Answer 28

Lateral corticospinal tract – decussate in pyramids of medulla – limbs

Question 29

in the medulla, where does the corticospinal tract decussate?

Answer 29

Begins to decussate at transition between medulla and spinal cord

Question 30

in the medulla, What is the Descending Spinal Tract of CN V?

Answer 30

Cell bodies located in trigeminal ganglion  convey pain, temperature and crude touch from face  spinal nucleus of CNV in pons, which extends inferiorly through medulla & upper part of cervical spinal cord as far as 2nd cervical segment

Question 31

What is the medial longitudinal fasciculus in the medulla?

Answer 31

Arises in vestibular nuclei  descends into cervical cord to carry out its functions
More anteriorly it carries projections from vestibular nuclei to abducens, trochlea & oculomotor nuclei
Important pathway involved with control of gaze & head movements

Question 32

in the medulla, what is the tectospinal tract?

Answer 32

Descending axons from superior colliculus in midbrain  cervical spinal cord
Involved with controlling neck and trunk movements in response to visual stimuli

Question 33

What is the MLF?

Answer 33

The medial longitudinal fasciculus carries information about the direction that the eyes should move.
Connects the CN III (Oculomotor nerve), IV (Trochlear nerve) and VI (Abducens nerve), and integrates movements directed by the gaze centers (frontal eye field) and information about head movement (from cranial nerve VIII, Vestibulocochlear nerve).
Integral in saccadic eye movements as well as vestibulo-ocular and optokinetic reflexes.

Question 34

In the ascending tracts of the medulla, what are the gracile nucleus and the cuneate nucleus?

Answer 34

Relay nuclei of dorsal column pathway
Give rise to medial lemniscus (crossed fibre bundle)

Spinothalamic, spinoreticular & ventral spinocerebellar tracts continue upward through medulla

Spinocerebellar & cuneocerebellar tracts continue into inferior cerebellar peduncle

Question 35

What is the anatomy of the lateral medulla?

Answer 35

Structures that make up the lateral medulla include the inferior cerebellar peduncle, vestibular nuclei, trigeminal nucleus and tract, spinothalamic tract, descending sympathetic fibres, nucleus ambiguous and nucleus solitarius. The region of the lateral medulla is bordered by the anterior lateral sulcus ventrally, the posterior lateral sulcus dorsally, the pons rostrally and the spinal cord caudally.

Question 36

What is contained within the Tegmentum of the medulla?

Answer 36

Contains cranial nerve nuclei for abducens (CN VI), facial (CN VII) and trigeminal (CN V)

Contains all the ascending tracts from spinal cord/lower brain stem and many of the descending systems

Trochlear (CN IV) and oculomotor nuclei (CN III) are found in upper tegmentum

Question 37

What is the red nucleus of the medulla?

Answer 37

Occupies central portion
Receives crossed efferent fibres from cerebellum
Sends fibers to thalamus and contralateral spinal cord via rubrospinal tract

Important component of motor co-ordination

Question 38

What is the crus cerebri of the medulla?

Answer 38

Massive fiber bundle including corticospinal, corticonuclear (corticobulbar) and corticopontine pathways

Corticonuclear fibers from motor cortex to efferent nuclei of cranial nerves are homologous to corticospinal fibres

Question 39

What is the Substantia Nigra?

Answer 39

Receives afferent fibres from cerebral cortex and striatum
Sends dopaminergic efferents to striatum
Plays a key role in motor control
Degeneration of it is seen in Parkinson’s disease

Question 40

What is the periaqueductal gray matter of the medulla?

Answer 40

Surrounds cerebral aqueduct
Contains descending autonomic tracts as well as endorphin producing tracts that suppress pain