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Diencephalon, Brain Stem, Cerebellum, Basal Ganglia. Sensory and Motor Pathways

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Diencephalon, Brain Stem, Cerebellum, Basal Ganglia. Sensory and Motor Pathways Diencephalon, brain stem, cerebellum, basal ganglia. Sensory and motor pathways. Sándor Katz M.D.,Ph.D. Diencephalon - overview • Located below the corpus callosum and above the midbrain • Part of the telencephalon • Forms the lateral wall of the third ventricle Diencephalon Diencephalon - parts • Epithalamus • Thalamus • Subthalamus • Hypothalamus Pineal body Thalamus • Almost all of the sensory pathways are relayed via the thalamus and project to the cerebral cortex. • Major descending motor tracts from the cerebral cortex generally bypass the thalamus. Thalamus Consequently, a lesion of the thalamus or its cortical projection fibers caused by a stroke or other disease leads to sensory disturbances. Thalamic Nuclei Specific nuclei: • Anterior nuclei (Recive afferent fibers from the mammillary body.) • Medial nuclei (Recive afferent fibers from ventral and intralaminar nuclei, hypothalamus, mesencephalon and globus pallidus.) • Ventral nuclei: VA, VL, VPL, VPM (Recive afferent fibers- position sense, vibration, pressure, touch, pain and temperature- from the trunk and limbs.) • Dorsal nuclei: LD, LP, Pulvinar (Recive afferent fibers from other thalamic nuclei.) They have direct connections with specific areas of the cerebral cortex. Nonspecific nuclei: have no direct connections with the cerebral cortex. Part of the general arousal system, they are connected directly to the brainstem. Thalamic Nuclei - Metathalamus • Lateral geniculate body (component of the visual pathway) • Medial geniculate body (component of the auditory pathway) They belong to the category of specific thalamic nuclei. Subthalamus • Subthalamic nuclei • Zona incerta • Globus pallidus Hypothalamus - overview • It is the lowest level of the diencephalon, situated below the thalamus. • The hypothalamus is the command center for all autonomic functions in the body. • Over 30 hypothalamic nuclei located in the lateral wall and floor of the third ventricle. Hypothalamus Hypothalamic Nuclei Anterior (rostral) group: Hormone synthesis. • Preoptic nucleus • Paraventricular nucleus • Supraoptic nucleus Middle (tuberal) group: Controls hormone release from the anterior lobe of the pituitary gland. • Dorsomedial nucleus • Ventromedal nucleus • Tuberal nuclei Posterior (mammillary) group: Activates the sympathetic nervous system when stimulated. • Posterior nucleus • Mammillary nuclei of mammillary body Functions of the hypothalamus Region or nucleus Function • Anterior preoptic region • Maintain constant body temperature. Lesion: central hypothermia. • Midanterior and posterior • Activate sympathetic nervous system regions • Activate parasympathetic nervous system • Paraventricular and anterior regions • Oxitocin production - uterine • Supraoptic and paraventricular contractions. Vasopressin - regulation of water balance, lesion: diabetes insipidus. nuclei • Regulate appetite and food intake. • Anterior nuclei Lesion: obesity or anorexia. Brain stem – overview It is divided macroscopically into three parts: • Mesencephalon • Pons • Medulla oblongata Brain stem Midbrain - mesencephalon Tectum (quadrigeminal plate): • Superior colliculi (part of the visual pathway) • Inferior colliculi (part of the auditory pathway) Cerebral aqueduct Tegmentum (nuclei, ascending-, descending pathways) Cerebral peduncles Midbrain Pons and medulla oblongata Dorsal wall is formed by the rhomboid fossa. Pons Reticular Formation • Respiratory and circulatory regulation • Swallowing center • Vomiting center • Reticular activating center (wake up function) • Effect on the motor system Cerebellum - overview Cerebellum - overview Cerebellum - peduncles Cerebellum - functions Cerebellum - histology Cerebellum - histology Cerebellum - histology Basal Ganglia • Modulate and regulate specific cortical functions • Preparation, planning, execution of motor activity • Related nuclei: • subthalamic nucleus of diencephalon • substantia nigra of mesencephalon • VA, VL thalamic nuclei Sensory pathways - receptors Sensory pathways - receptors Meissner’s corpuscle Pacinian corpuscle Sensory pathways (ascending tracts)- Fasciculus gracilis and cuneatus • Both tracts convey fibers for position sense (conscious proprioception) and fine cutaneous sensation (touch, vibration, fine pressure sense, two-point discrimination) =EPICRITIC SENSATION. • The fasciculus gracilis carries fibers only from the lower limbs, while the fasciculus cuneatus carries fibers only from the upper limbs, therefore it is not presented in the spinal cord below the T3 level. Sensory pathways(ascending tracts)- Fasciculus gracilis and cuneatus • Muscle-, tendon receptors and Vater-Pacini corpuscles for conscious proprioception. Receptors about the hair follicles and additional receptors mediate the fine touch sensation of the skin. • 1st neuron: pseudounipolar neurons in the dorsal root ganglion. • The axons ascend ipsilaterally in the posterior funiculi to the gracile and cuneate nuclei (2nd neuron) in the medulla oblongata. • The axons cross in the medial lemniscus to the VPL of thalamus (3rd neuron). • The axons of the third neurons terminate in the primary somatosensory cortex, located in the postcentral gyrus. Sensory pathways(ascending tracts)- Spinothalamic tracts • The anterior spinothalamic tract is the pathway for crude touch and pressure sensation, while the lateral spinothalamic tract conveys pain, temperature, tickle, itch and sexual sensation =PROTOPATHIC SENSATION. Sensory pathways(ascending tracts)- Lateral spinothalamic tract • Free nerve endings in the skin function as receptors for pain and temperature sensation. • The cell bodies of these nerve endings are located in the dorsal root ganglion (1st neuron). • The central processes of first neurons pass through the dorsal root into the white matter of the spinal cord (dorsolateral tract of Lissauer), then they terminate on funiculate neurons in the gray matter (2nd neuron). • The axons of second neurons cross in the anterior commissure in the corresponding spinal segment and ascend in the anterolateral funiculus on the opposite (contralateral)side. • They terminate in the VPL of thalamus (3rd neuron). • The axons of third neurons radiate to the primary somatosensory cortex in the postcentral gyrus. Sensory pathways(ascending tracts)- Anterior spinothalamic tract • Impulses from tactile corpuscules and from receptors about the hair follicles. • The cell bodies of these axons are located in the dorsal root ganglion (1st neuron). • The axons pass through the dorsal root and enter the gray matter where terminate on funiculate neurons (2nd neuron). • The axons of second neurons cross in the anterior commissure and ascend in the opposite anterior funiculus. • The axons terminate in the VPL of thalamus (3rd neuron). • The axons of third neurons radiate to the primary somatosensory cortex in the postcentral gyrus. Sensory pathways(ascending tracts)- Spinocerebellar tracts Sensory pathways(ascending tracts)- Posterior spinocerebellar tract • Muscle spindles and tendon receptors convey proprioceptive information from lower body part to pseudounipolar neurons in the dorsal root ganglion (1st neuron). • The axons terminate at the dorsal nucleus (Clark’s) of gray matter (2nd neuron), which spans spinal cord segments C8 to L3. • The axons of the second neurons ascend ipsilaterally to the cerebellum, entering through the inferior cerebellar peduncle. • The axons terminate with mossy fibers in the stratum granulosum of cerebellar cortex. Sensory pathways(ascending tracts)- Anterior spinocerebellar tract • Muscle spindles and tendon receptors convey proprioceptive information from lower body part to pseudounipolar neurons in the dorsal root ganglion (1st neuron). • The axons terminate at the dorsal gray horn (2nd neuron), which spans spinal cord segments L4 to S3. • The axons of the second neurons cross in the anterior commissure and ascend contralaterally to the cerebellum, entering through the superior cerebellar peduncle. • The axons terminate with mossy fibers in the stratum granulosum of cerebellar cortex. Motor pathways(descending tracts)- Pyramidal tracts • The most important pathway for voluntary motor function. • Some of its axons, the corticonuclear fibers terminate at the cranial nerve nuclei. • Others, the corticospinal fibers terminate on the motor neurons in anterior horn of gray matter. • A third group, the corticoreticular fibers are distributed to nuclei of reticular formation. Motor pathways(descending tracts)- Pyramidal (corticospinal) tracts • The tracts originate in the motor cortex at the pyramidal cells (1st neuron). • The corticospinal fibers pass through the internal capsule, continuing into the brainstem and spinal cord. • The fibers descend to the pyramidal decussation in the medulla oblongata, where approximately 80% of them cross to the opposite side. The fibers continue into the spinal cord where they form the lateral corticospinal tract, which has somatotopic organization: the fibers for the sacral cord are the most lateral, while the fibers for the cervical cord are the most medial. Motor pathways(descending tracts)- Pyramidal (corticospinal) tracts • The remaining 20% of corticospinal fibers continue to descend without crossing, forming the anterior corticospinal tract, which borders the ventral median fissure. • The anterior corticospinal tract is particularly well developed in the cervical cord, but is not present in the lower thoracic, lumbar or sacral cords. • The axons of the pyramidal cells terminate via intercalated cells on alpha and gamma
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