Download Dr. Mustafa Neuroanatomy lecture (7) Mid brain The regions of the

Dr. Mustafa
Neuroanatomy lecture (7)
Mid brain
The regions of the mid brain:
1- The tectum which is dorsal to the cerebral aqueduct.
2- The tegmentum which is ventral to the cerebral aqueduct.
3- The crus cerebri or the cerebral peduncle which are ventral
to tegmentum.
At the tectal region of the mid brain, there are two pairs of
rounded structures which are called the colliculi. Two
superior and two inferior colliculi.
The cross section of the mid brain at level of the
inferior colliculus:
1- There are two rounded swellings which are called the
inferior colliculi. They are considering as the reflex center for
the auditory stimuli. They receive input from the lateral
lemniscus and give output to the medial geniculate body of
the thalamus. This inferior colliculus will direct the attention
to the unexpected sound.
Dr. Mustafa
Neuroanatomy lecture (7)
2- At the level of the inferior colliculus, in the tegmentum,
there is the nucleus of the trochlear nerve (4th cranial nerve)
that supplies the superior oblique muscle of the eyeball, the
fibers of this nerve will decussate before leaving the mid
brain and leave through the posterior aspect of the mid brain
(all the cranial nerves leave through the lateral or ventral
parts of the brain stem except the 4th cranial nerve).
3- At this level, in the tegmentum, there is large decussation
of the superior cerebellar peduncle (between the mid brain
and cerebellum).
4- The substantia nigra is very clear structure in the section
of the mid brain and has a characteristic black color due to
melanin pigmentation. The substantia nigra is an important
motor center.
The connections of the substantia nigra:
The input to the substantia nigra is from the cerebral cortex
and gives output (project) to the thalamus, and there is
reciprocal connection to the corpus striatum. The pathway
between the substantia nigra and the corpus striatum is an
important pathway contains the neurotransmitter called the
dopamine. The low amount of dopamine will affect this
pathway that lead to Parkinson's disease.
Dr. Mustafa
Neuroanatomy lecture (7)
Dr. Mustafa
Neuroanatomy lecture (7)
The second cross section of the mid brain is at the
level of the superior colliculus:
1- At the tectal region, there is the superior colliculus which
is considered as an important reflex center of the visual
stimuli.
The connection of the superior colliculus:
The input is from the lateral geniculate body of the thalamus,
and the output to cranial nerve nuclei of the 3rd, 4th and 6th
cranial nerves.
The reciprocal connection is with the spinal cord. The cerebral
cortex is controlling strongly the reflex activity of the superior
colliculus.
The functions of the superior colliculus of the mid brain:
a-
Direct the attention or direction of the gaze
toward the target by rapid shifting of the direction of
the gaze reflexly that strongly controlled or affected
by the cerebral cortex input to the superior colliculus.
Dr. Mustafa
Neuroanatomy lecture (7)
b-
Responsible for follow up of the object in the
visual field.
c-
It directs the attention or the direction of the
head toward the source of the cutaneous stimuli.
2- At this level, the tegmentum contain cranial nerve nucleus
of the oculomotor (3rd) nerve. This nucleus has two
important groups:
a- General somatic nucleus for innervation of the extra
ocular muscles except lateral rectus and superior oblique.
b- Parasympathetic nucleus for supplying two muscles
inside the eyeball; these are the sphincter pupillae and
ciliary muscle (that responsible for accommodation). This
nucleus also is called Edinger- Westphal nucleus or
called accessory oculomotor nucleus.
3- Red nucleus which has red color in fresh section. It has
the following functions:
a- Alternative pathway for corticospinal tract.
b- Coordination of the movement through its connection
with the cerebellum.
4- Ventral tegmental area of Tasi which is situated between
the red nucleus and the substantia nigra. This Tasi area
contains dopamine. Some studies were showed an
increase
in
the
dopamine
level
in
schizophrenic patients.
5- Substantia nigra also presents at this level.
this
area
in
Dr. Mustafa
Neuroanatomy lecture (7)
The crus cerebri or the cerebral peduncle:
It is situated ventral to tegmental region and it is composed
of large bundles of white matter. These fibers have the
following arrangements:
1- The lateral 1/5th of fibers is occupied by the
temporopontine fibers.
2- The
middle
3/5th
of
fibers
is
made
up
of
corticospinal and corticonuclear fibers (pyramidal
fibers).
3- The
medial
1/5th
frontopontine fibers.
of
fibers
is
made
up
of
Dr. Mustafa
Neuroanatomy lecture (7)
Cerebellum
(tree of life?)
Dr. Mustafa
Neuroanatomy lecture (7)
Dr. Mustafa
Neuroanatomy lecture (7)
Its shape has attracted interest. It has two hemispheres join by
the vermis in midline. The cerebellar surface has folds which are
called folia (folium) and in between them there are the sulci.
Dr. Mustafa
Neuroanatomy lecture (7)
The lobes and fissures of the cerebellum:
1- The anterior lobe is that part of the cerebellum that
is anterior to the primary fissure.
2- The posterior (or middle) lobe of the cerebellum that
is posterior to the primary fissure and it is the
largest lobe.
3- The floculonodular lobe is that part of cerebellum
that
is
surrounded
by
the
dorsolateral
or
posterolateral fissure.
4- The deep horizontal fissure separates the superior
surface from the inferior surface of the cerebellum.
Dr. Mustafa
Neuroanatomy lecture (7)
The gray matter of the cerebellum:
1- The cortex of the cerebellum is made up of the following
layers:
a- The outer layer is the molecular layer.
b- The middle layer is the Purkinje cell layer.
c- The inner layer is the granular layer.
Dr. Mustafa
Neuroanatomy lecture (7)
These layers of the cerebellar cortex are uniform all over the
cerebellar cortex (not like the Broadman areas of the cerebral
cortex).
2- Intracerebellar nuclei:
Dr. Mustafa
Neuroanatomy lecture (7)
Four masses of gray matter are embedded in the white
matter of the cerebellum on each side of the mid line. From
lateral to medial, these nuclei are:
Dentate, emboliform, globose and fastigial (or roof) nuclei.
The emboliform and globose nuclei are called together
nucleus interpositum. The dentate nucleus is the largest
nucleus of the cerebellum.
Dr. Mustafa
Neuroanatomy lecture (7)
The white matter of the cerebellum:
There is a small amount of white matter in the midline
vermis, while there is a large amount of white matter in each
cerebellar hemisphere. The white matter is made up of three
groups of fibers:
1- Intrinsic fibers: connect different regions of the
cerebellum.
2- Afferent fibers: form the greater part of the white
matter and end in the cerebellar cortex. These
afferent fibers are of two groups:
A- Climbing
fibers:
these
are
afferent
fibers
to
cerebellum. They are from the contralateral inferior
Dr. Mustafa
Neuroanatomy lecture (7)
olivary nucleus and go up to the cerebellar cortex
winding around the dendrites of Purkinje cells
(middle cell layer of the cerebellar cortex).
B- Mossy fibers: these afferent fibers end in the granular
layer forming the cerebellar glomerulus.
3- Efferent fibers of the cerebellum.
The peduncles:
They are the connections of the cerebellum with the
brain stem.
- The
inferior
cerebellar
peduncle
connects
the
connects
the
cerebellum to medulla oblongata.
- The
middle
cerebellar
peduncle
cerebellum to pons.
- The superior cerebellar peduncle connects the
cerebellum to mid brain.
The functional divisions of the cerebellum:
1- Archicerebellum: it is represented by the floculonodular
lobe. It receives input from vestibular nuclei and so can
also be called the vestibulocerebellar system. The size of
the archicerebellum is small in human, but relatively large
in fish.
2- Paleocerebellum: it is represented by the anterior lobe and
it receives the spinocerebellar tracts. The anterior lobe is
an
intermediate
in
size.
The
function
of
the
Dr. Mustafa
Neuroanatomy lecture (7)
paleocerebellum
is
unconscious
proprioception
and
muscle tone.
3- Neocerebellum: it is represented by the posterior lobe
which has about 80% of the cerebellar size. It receives
input from the pons and so can also be called the
pontocerebellar system. The function of Neocerebellum is
the coordination.
The neuronal circuit or connections of the Neocerebellum:
Fibers from motor area of the cerebral cortex to the pons
(corticopontine fibers), then from pons, the fibers will pass to
the contralateral side of the posterior lobe of the cerebellum
(pontocerebellar fibers). These pontocerebellar fibers will
pass to the deep nuclei of the cerebellum (especially the
dentate nucleus), then the fibers will leave the cerebellum
through the superior cerebellar peduncle (decussation fibers).
Then fibers will cross to other side. Some of the fibers will
end into the red nucleus and other fibers will end into the
thalamus. The fibers from the thalamus will back to the motor
area of the cerebral cortex.
This above circuit is responsible for coordinate of the motor
activity with each motor order of movement from the cerebral
cortex, so the cerebellum can modify the pattern of movement
to ensure maximum efficiency and minimum effort. Thus, the
posterior lobe of the cerebellum can be considered as a
motor center for coordination of the movement.
Dr. Mustafa
Neuroanatomy lecture (7)
The functional aspects of the cerebellum:
1- Ipsilateral control (coordinate the same side of
the body movements).
Dr. Mustafa
Neuroanatomy lecture (7)
2- The somatotopic presentation:
The midline vermis coordinate the movement of
trunk and head.
The cerebellar hemispheres are responsible for
limbs.
3- The cerebellar preserve and compensation: the
uniform structure of the cerebellar cortex can
compensate the damage to other cerebellar
cortex, and so 80% damage to cerebellar cortex
will lead to appearance of the cerebellar
dysfunction (unlike cerebral cortex).
Note: ֍Tonsils: Protrusions on the inferior surface of
cerebellum.
The features of cerebellar dysfunction:
1- Hypotonia: because of the damage to the spinocerebellar
pathways that are responsible for muscle tone.
2- Ataxia.
3- Intension tremor (no tremor at rest).
4- Vertigo and nystagmus.
But no paralysis, and no sensory loss.
Dr. Mustafa
Neuroanatomy lecture (7)
Dr. Mustafa
Neuroanatomy lecture (7)
Dr. Mustafa
Neuroanatomy lecture (7)