Midbrain pdf - D. Rafid

Done by

Dr.Rafid Remthan Al-Temimi

Clinical Radiology

CAMB,DMRD,M.B.Ch.B.,.

المرحلة

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التشريح

امعة ذي قار

كلية الطب

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رافد

رمثان التميمي

Brain stem, 1

part

Midbrain

• The midbrain or mesencephalon is a portion of the central nervous system associated with vision,

hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation.

Forebrain

midbrain

hindbrain

2 Cerebral

hemisphere+ 2

lateral cavity

Deep

portion

(thalamus

hypothalamus

) with their cavity

( the 3

ventricle )

Connect the

forebrain with

the hindbrain

Adequate

cerebellum

pons

Medulla

oblongata

Cerebellum

vemtricle

University Of Thi-Qar

College Of medicine

Anatomy lecture . 2

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

University Of Thi-Qar

College Of medicine

Anatomy lecture . 2

stage

Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Midbrain

• connects

cerebellum

the pons

and

with

the

diencephalon ( structures lateral to the 3

ventricle ).

• Specifically, the midbrain consists of :

 Tectum“Corpora quadrigemina”

inferior colliculi

superior colliculi

 cerebral peduncle

midbrain tegmentum

crus cerebri

substantia nigra

 Cerebral aqueduct :

connect the 3

and

ventricles

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Cerebral peduncle

Two cylindrical masses situated at the base of
the brain largely hidden by the temporal
lobes

They  emerge  from  the  upper    surface  of  the
pons  &  diverge    as  they  pass  upward  to
disappear  into  the  substance    of  the  cerebral
hemispheres

The interpeduncular fossa between them is
occupied by the posterior perforated
substance

They are surrounded by the parahippocampal
gyrus & optic tracts

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Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Cerebral peduncles

• The cerebral peduncles are structures at the

front of the midbrain which  arise from the front
of  the  pons  and    contain  the  large  ascending
(sensory)    and  descending  (motor)  nerve  tracts
that  run  to  and  from  the  cerebrum    from  the
pons.

• Mainly,

the three common areas that give rise to

the cerebral peduncles are

the cerebral cortex,

the spinal cord and the cerebellum.

• The cerebral peduncle, by most classifications, is

everything in the midbrain except the tectum.

 Cerebral peduncles include the

Crus cerebri

Substantia nigra

Tegentum

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Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Crus cerebri

• The cerebral crus (crus cerebri) is the anterior

portion of the cerebral peduncle which contains
the motor tracts

• In some older texts this is called the cerebral

peduncle but presently it is usually limited to
just the anterior white matter portion of it.

• So, cerebral crus composed of nerve fibers ( It is

a white mater ) !

Cortico-ponto-cerebellar fibers

Corticonuclear fibers

Corticospinal fibers

• PART OF THE MOTOR PATHWAY !!!

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Substantia nigra

• Main afferent :

corpus striatum ( basal ganglia )

• Main efferent :

thalamus

• Functionally to the extrapyramidal system ..

• WILL BE STUDIED WITH THE EXTRAPYRAMIDAL SYSTEM !!

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Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Tegmentum

1. Red nuclei

2. White mater

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Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Red nucleus

• structure in the rostral midbrain

involved in

motor coordination

•

It is pale pink in color;

the color is believed to

be due to iron

, which is present in the red

nucleus in at least two different forms:
hemoglobin and ferritin

• It comprises a caudal

magnocellular

and a

rostral

parvocellular

part.

• It is located in the tegmentum of the midbrain

next to the substantia nigra.

•The red nucleus and substantia nigra are

subcortical centers of the extrapyramidal motor
system

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Red nucleus connections

• The red nucleus

receives

many inputs from the

cerebellum of the opposite side and an input from
the motor cortex of the same side.

• The red nucleus has two sets of efferents:-

1. In humans, the majority of the output goes to the

bundle of fibers continues  through the medial
tegmental field  toward the inferior olive of the
same  side, to form part of a pathway  that
ultimately influence the cerebellum.

2. The other

projection)

output (the rubrospinal

goes

the

rhombencephalic reticular formation and spinal
cord of the opposite side, making up the
rubrospinal tract

• because of the well-developed cerebral cortex, the

corticospinal tract has taken over the role of the
rubrospinal.

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Red nucleus functions

• where the corticospinal tract is dominant (as in primates), the

rubrospinal tract may be considered to be vestigial

. Therefore,

here the red nucleus is less important in motor functions than
in many other mammals. However, the

crawling of babies

controlled by the red nucleus, as is arm swinging in typical
walking. The red nucleus may play an additional role in

controlling muscles of the shoulder and upper arm via
projections of its magnocellular part

. In humans, the red

nucleus also has sparse control over hands, as the rubrospinal
tract is more involved in large muscle movement such as that
for arms (but not the legs, as the tract terminates in the
superior thoracic region of the spinal cord).

Fine control of the

fingers is not modified by the functioning of the red nucleus

(rather it relies on the corticospinal tract)

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Tegmentum white mater

1. The superior cerebellar peduncle:

• Enter the midbrain tegmentum
• decussate at the level of the inferior colliculi on their

way to the red nuclei

2. The medial longitudinal

fasciculus:

• In the mid-brain it is situated on the ventral aspect

of the cerebral aqueduct

• It consists largely of fibers which connect the

nuclei of the hind- brain and mid-brain to each

other

• MLF is the main central connection for the

oculomotor nerve, trochlear nerve, and abducens

nerve.

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Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Tegmentum white mater

3. The medial lemniscus:

• -Arise in the gracile & cuneate nuclei of the

medulla ( of opposite site ) & decussate there as
internal arcuate fibres.

• -In the midbrain it attains dorsolateral position

4. The lateral lemniscus:

• From trapezoid body

• terminates, on cells of the inferior colliculus and

medial geniculate body for auditory reflexes

• Both the trapezoid body and lateral lemniscus

contain  cell  stations  which    make  connexions
with  the  extraocular    nuclei  via  the  medial
longitudinal  bundle.

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Tegmentum white mater

The vestibulospinal tract:

-Arise in the vestibular nuclei
-Some of them descend in the spinal cord & some
ascend in the tegmentum of the midbrain

The tectospinal tract:

-Arise in the superior colliculi
-Decussate

& descend

near

the midline

The rubrospinal tract:

-Arise in the red nucleus
-Cross the midline & descends into the
lateral funiculus of the spinal cord

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Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Corpora quadrigemina ( tectum )

• Tecum is region of the brain, specifically the

dorsal

part of the midbrain

• Corpora quadrigemina are the

four colliculi—

two

inferior, two superior—located on the tectum of
the dorsal aspect of the midbrain.

• The corpora quadrigemina are

reflex centers

involving vision and hearing

Pulvinir

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Superior colliculi

• The brachium of superior

colliculus

(or

superior

brachium)

extends

from

colliculus,

the

and,

laterally

superior

passing

between

the

pulvinar ( not shown )

and

medial geniculate

body

continued

into

eminence

called

(1)

, is partly

an the

lateral geniculate body

(2)

, and partly into the

optic

tract (3) .

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Inferior colliculi

• principal midbrain nucleus of the auditory

pathway

and receives input from several

peripheral brainstem nuclei in the auditory
pathway, as well as inputs from the auditory
cortex.

• Its bimodal neurons are implied in

auditory-

somatosensory interaction

, receiving projections

from somatosensory nuclei. This

underlie a filtering of
effected

sounds

vocalization,

chewing,

multisensory integration may

self- from

respiration activities

• Inferior brachium

pass to the

medial geniculate body

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Note

• Lateral geniculate and medial geniculate

bodies are part of the diencephalon (
Forebrain ) !!

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Cerebral aqueduct

• 1.8 cm long

• Traverses the midbrain

• Surrounded by a layer of gray

matter called the

(periaqueductal)

choroid

central

gray

• Contains

plexus

• Transmits

CSF from the

third

the

fourth

ventricle

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Nuclei in periaqueductal grey mater

• 1) The nuclei of oculomotor nerve

(level with the superior colliculi)

• 2) The nucleus of the trochlear nerve

(level

with the inferior colliculi

the

• ( 1 & 2 lie in the ventral part of the gray )

• 3- The mesencephalic nucleus of the

trigeminal

nerve

extends along

the entire

length of the

aqueduct in the lateral part of gray

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Oculomotor nerve

Nerve

Modality

Nuclei

Location

Distribution

Parasympathetic
innervation to

Edinger-

sphincter pupillae and

SVE

wesphal

Midbrain

ciliary

nucleus

muscles that constrict

Oculomotor

pupil and

nerve

accommodate lens of
eye

To eye muscles except

Nucleus of

lateral rectus (

GSE

oculomotor

Midbrain

abducens ) and

nerve

superior oblique (
trochlear

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Oculomotor nerve

nuclei

1 E-W nuclei

2 motor nucleus

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Trochlear nerve

Nerve

Modality

Nucleus

Lcation

Distribution

Trochlear

nerve

GSE

Nucleus of
trochlear
nerve

Midbrain

To superior
oblique
muscle

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Reticular formation

• Gray and white mater

• More in the tegmentum ( midbrain )

• Upward connection  thalamus and

cortex.

• Downward connection  to spinal cord.

• RF is filter for stimuli !!

Prevent repetitive stimuli

Enhance infrequent stimuli

Allow important repetitive stimuli for example
the pain stimuli

• Sleep  RF

• RF diseases  Grades of coma !?

• GA ( general anesthesia ) drugs act on RF !

• Analgesic drugs have one of its

mechanism action through the RF

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

Reticular formation connections

• Afferent from :-

Various

sensory pathways

and systems

Other parts of CNS

Factors infleucing the activity of RF (

e.g. drugs and hormones )

• Efferent to :-

1. Autonomic and locomotor control centres of

brainstem and spinal cord.

2. Cranial nerve nuclei, e.g. dorsal

nucleus of vagus.

3. Cerebral cortex—indirectly through

diencephalic nuclei.

4. Red nucleus, substantia nigra and

tectum of midbrain

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

1 Superior colliculus

2 Inferior colliculus

3 Cerebral peduncle

4 Interpeduncular cistern

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Dr.Rafid Al-Temimi

Dr.Rafid Remthan AL-Temimi,Clinical Radiology,CAMB, 2020

University Of Thi-Qar

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Dr.Rafid Al-Temimi

Thank you with best wishes