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Basal Ganglia نور عريقاتد. الرا عبدر ّبه جرايدة 11 Anatomy 1|P ag e Basal Nuclei Definition:1 Clusters of gray matter that are located within the cerebral hemisphere, they consist of Corpus striatum, Claustrum and Amygdaloid nucleus. As you can see here, the corpus striatum and the amygdaloid nucleus. - Corpus striatum is divided in two ways: Anatomically: 1. Lentiform nucleus A wedge-shapednucleus located lateral to the thalamus, consists of lateral Putamen and medial Globus pallidus. ____________________________________________________________________________________1: some books may consider substantia nigra and subthalamic nucleus as one of the basal nuclei. However, we will follow the aforementioned definition for basal nuclei. 2|P ag e 2. Caudate nucleus Large nucleus which is closely related to lateral ventricle, consists of head, long body and long tail. The head forms the lateral wall of the anterior horn of the lateral ventricle. The body forms part of the floor of the body of the lateral ventricle. The tail continues into the roof of the inferior horn of the lateral ventricle and terminates anteriorly into the amygdaloid nucleus. Functionally: 1. The striatum Consists of caudate and putamen nuclei and the strands of gray matter connecting them. Forms the major site for input or afferent fibers to basal nuclei. 2. Pallidum It’s the globus pallidus itself but this is a functional name. Forms the major site for output from basal nuclei. - The amygdaloid nucleus: As you can see in the previous picture, the lateral side has been removed. It’s situated in the temporal lobe and it is part of the limbic system. 3|P ag e Notes about this figure: o Note the head of caudate nucleus and the anterior horn of the lateral ventricle. o The paleness of the globus pallidus is due to the presence of a high concentration of myelinated nerve fibers. o The lentiform nucleus is separated from thalamus by the posterior limb of internal capsule which is a band of nerve fibers (white matter). o The lentiform is separated from the caudate by the anterior limb of internal capsule. o The lentiform is separated from the claustrum (strand of gray matter) by the external capsule. o Lateral to the claustrum is the subcortical white matter of the insula. 4|P ag e **Connections between Cerebral Cortex, Basal Nuclei, Thalamic Nuclei, and Spinal Cord This illustrated figure shows different pathways o From the cerebral cortex we have the corticostriate fibers which are somatotopically organized, they are arising from all parts of the cerebral cortex. Somatotopical arrangement: a term in neuroscience means each part of the cerebral cortex projects axons to a specific part of the caudate-putamen complex (striatum), so it’s not a random connection but point to point correspondence. 5|P ag e o Fibers projecting from substantia nigra1 to striatum, striatonigral fibers. o Fibers arising from the intra laminar nuclei of the thalamus, thalamocortical fibers. o Fibers ascending from the brainstem to the striatum. o Note those fibersbetween striatum and substantia nigra. The pathway is mutual in both ways. There are fibers arising from striatum and terminating in substantia nigra called striatonigral fibers and the vice versa are called Nigrostriate fibers. So there is input coming into the striatum being processed and then there is outputfrom the striatum to the output areaof basal nuclei again referred to as globus pallidus or pallidum. There are fibers from globus pallidus that are collectively called pallidofugal fibers which are divided into four groups: Two groups terminating eventually in the thalamus and join in the subthalamus to form what is called thalamic fasciculus:ansa lenticularis and fasciculus lenticularis. pallidotegmental fibers, which terminate in the caudal tegmentum of the midbrain. pallidosubthalamic fibers, which pass to the subthalamic nuclei. From the thalamus axons are projected to the cerebral cortex, there is no direct connection between the basal nuclei and the spinal cord. The influence exerted by the basal nuclei to the spinal cord is being through the cerebral cortex. As you know there is pre-central gyrus which is the site for the primary motor cortex those neurons projecting their fibers as a corticospinal tract to command the lower motor neurons located in the spinal cord. : substantia nigra that divides the cerebral peduncles of the midbrain into posterior tegmentum and anterior crus cerbri. 1 6|P ag e Regarding brainstem lecture there will be only two questions. Focus on what mentioned here. It’s very important to know the level at which the key landmarks are located i.e. you can look at the section you can find structures or landmarks. By recognizing them you can say this is from this level so you need to know.For example: o Thedecussation of the pyramid occurs in the caudal part of medulla oblongata. o At the level of the facial colliculus which passes through the caudal part of pons you need to know that you can see the roots and the nuclei of the facial nerve and the abducent nerve, 7th and 6th respectively. The question is: the structure that is present at the level of facial colliculus is? You need to know that the winding of the root of the facial nerve round the nucleus of the abducent nerve is what produces the facial colliculus. The facial colliculus is the inferior end of the median eminence which is present at the posterior aspect of pons. 7|P ag e Through the cranial part of pons you need to know there are the motor and the principle main or chief sensory nuclei of trigeminal nerve. At the level of inferior colliculiof midbrain you can see the decussation of the superior cerebellar pedunclesand you can identify the trochlear nerve and nucleus. Through the superior colliculiof midbrain there is the red nucleus you can also identify the nuclei of the oculomotor nerve. 8|P ag e