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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: Ö¨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)