The Nervous System (Part 5)
The Diencephalon
The diencephalon (Figure 21) is composed of the thalamus, subthalamus, hypothalamus, and the epithalamus (O’ Sullivan and Siegelman, 2006).
Figure 21
The thalamus (Figure 22) is a large ovoid mass of gray matter which serves as a cell station to all main sensory systems (except the olfactory pathway). The thalamus contains two groups of nuclei: the sensory and the motor nuclei. The sensory nuclei relay sensory information from the body, face, retina, cochlea, and taste receptors to cerebral cortex and subcortical regions. The motor nuclei relay movement information from cerebellum and globus pallidus to precentral motor cortex.
Figure 22. The thalamus
The subthalamus (Figure 23) lies inferior to the thalamus. The structure of the subthalamus is extremely complex and contains the cranial ends of the red nuclei and the substantia nigra. These nuclei have important connections with the corpus striatum as a result, it is involved in controlling muscular activities. The subthalamus also contains important tracts that pass up from the tegmentum to the thalamic nuclei.
Figure 23. The substantia nigra
The hypothalamus (Figure 24) is the part of the diencephalon that extends from the ptic chiasma to the caudal border of the mammillary bodies. It is responsible for the integration and control of the autonomic nervous system and neuroendocrine system functions. It also maintains body homeostasis by regulating body temperature, eating, water balance, emotions, sexual behavior, and anterior pituitary functions.
Figure 24. Hypothalamus
The epithalamus in turn, has the habenular nuclei that integrate olfactory, visceral, and somatic afferent pathways. It also houses the pineal gland that influences the pituitary gland and several organs, as well as our circadian rhythm (Melatonin).
The Midbrain
The midbrain (mesencephalon) belongs to a group of brain structures known as the brainstem. Other parts of the brainstem include the pons and the medulla oblongata.
Figure 25. The midbrain
Figure 26.
The midbrain connects the pons to the cerebrum. The superior peduncle in turn connects the midbrain to the cerebellum.
Parts of the crus cerebri, substantia nigra, tegmentum, and the red nuclei are inclusive of the midbrain. These parts are important for movement control and coordination, and contain cranial nerve nuclei (oculomotor and trochlear nerves).
The superior colliculus is an important relay station for vision and visual reflexes. The inferior colliculus, on the other hand, relays to the cortex stimuli for hearing and auditory reflexes.
The midbrain also contains endorphin-producing cells that are used by the body in suppressing pain (opiate system).
The Hindbrain
The hindbrain (Figure 27) is composed of the pons, the medulla oblongata, and the cerebellum.
Figure 27
The Pons
The Pons is named after the Latin word for bridge (Encyclopedia of Neurological Disorders, 2007). The pons in fact bridges the two hemispheres and connects the midbrain to the medulla oblongata. It is also connected to the cerebellum via the middle peduncle.
The pons is involved in motor control, sensory analysis, and levels of consciousness and sleep (reticular formation). Some structures within pons are linked to the cerebellum, involving them in movement and posture.
In addition the pons is also important in modulating pain. It also contains severl cranial nerve nuclei: abducens, trigeminal, facial, and vestibulocochlear.
The Medulla Oblongata
The medulla oblongata connects the spinal cord to the pons. It contains important centers for vital functions like cardiac, respiratory, and vasomotor centers. It also contains relay nuclei of the dorsal columns of the spinal cord, fibers of which cross to contralateral side to give rise to medial lemniscus. Its inferior cerebellar peduncle relays the dorsal spinocerebellar tract to the cerebellum. The corticospinal tracts also cross in this area of the brain at the cervicomedullary junction. It also holds structures that are important in head movement control and gaze stabilization.
The Cerebellum
The cerebellum is located behind dorsal pons and medulla. It is joined to brainstem by three pairs of peduncles: superior, middle, and inferior. It is also comprised of two hemispheres divided in between by the vermis.
The three major parts of the cerebellum include the archicerebellum (flocculonodular lobe), the paleocerebellum (rostral cerebellum), and the neocerebellum (posterior lobe).
The archicerebellum connects with the vestibular system and is concerned with equilibrium and regulation of muscle tone. It also aids in processing the vestibule-ocular reflex. The paleocerebellum on the other hand, controls the synergistic movement of the muscles that is important in maintaining posture and fluidity in functional movements. Lastly the neocerebellum ensures that the body’s movements are accurate in terms of timing, distance, and force, which is important in movement coordination.
The diencephalon (Figure 21) is composed of the thalamus, subthalamus, hypothalamus, and the epithalamus (O’ Sullivan and Siegelman, 2006).
Figure 21
The thalamus (Figure 22) is a large ovoid mass of gray matter which serves as a cell station to all main sensory systems (except the olfactory pathway). The thalamus contains two groups of nuclei: the sensory and the motor nuclei. The sensory nuclei relay sensory information from the body, face, retina, cochlea, and taste receptors to cerebral cortex and subcortical regions. The motor nuclei relay movement information from cerebellum and globus pallidus to precentral motor cortex.
Figure 22. The thalamus
The subthalamus (Figure 23) lies inferior to the thalamus. The structure of the subthalamus is extremely complex and contains the cranial ends of the red nuclei and the substantia nigra. These nuclei have important connections with the corpus striatum as a result, it is involved in controlling muscular activities. The subthalamus also contains important tracts that pass up from the tegmentum to the thalamic nuclei.
The hypothalamus (Figure 24) is the part of the diencephalon that extends from the ptic chiasma to the caudal border of the mammillary bodies. It is responsible for the integration and control of the autonomic nervous system and neuroendocrine system functions. It also maintains body homeostasis by regulating body temperature, eating, water balance, emotions, sexual behavior, and anterior pituitary functions.
Figure 24. Hypothalamus
The epithalamus in turn, has the habenular nuclei that integrate olfactory, visceral, and somatic afferent pathways. It also houses the pineal gland that influences the pituitary gland and several organs, as well as our circadian rhythm (Melatonin).
The Midbrain
The midbrain (mesencephalon) belongs to a group of brain structures known as the brainstem. Other parts of the brainstem include the pons and the medulla oblongata.
Figure 25. The midbrain
Figure 26.
The midbrain connects the pons to the cerebrum. The superior peduncle in turn connects the midbrain to the cerebellum.
Parts of the crus cerebri, substantia nigra, tegmentum, and the red nuclei are inclusive of the midbrain. These parts are important for movement control and coordination, and contain cranial nerve nuclei (oculomotor and trochlear nerves).
The superior colliculus is an important relay station for vision and visual reflexes. The inferior colliculus, on the other hand, relays to the cortex stimuli for hearing and auditory reflexes.
The midbrain also contains endorphin-producing cells that are used by the body in suppressing pain (opiate system).
The Hindbrain
The hindbrain (Figure 27) is composed of the pons, the medulla oblongata, and the cerebellum.
Figure 27
The Pons
The Pons is named after the Latin word for bridge (Encyclopedia of Neurological Disorders, 2007). The pons in fact bridges the two hemispheres and connects the midbrain to the medulla oblongata. It is also connected to the cerebellum via the middle peduncle.
The pons is involved in motor control, sensory analysis, and levels of consciousness and sleep (reticular formation). Some structures within pons are linked to the cerebellum, involving them in movement and posture.
In addition the pons is also important in modulating pain. It also contains severl cranial nerve nuclei: abducens, trigeminal, facial, and vestibulocochlear.
The Medulla Oblongata
The medulla oblongata connects the spinal cord to the pons. It contains important centers for vital functions like cardiac, respiratory, and vasomotor centers. It also contains relay nuclei of the dorsal columns of the spinal cord, fibers of which cross to contralateral side to give rise to medial lemniscus. Its inferior cerebellar peduncle relays the dorsal spinocerebellar tract to the cerebellum. The corticospinal tracts also cross in this area of the brain at the cervicomedullary junction. It also holds structures that are important in head movement control and gaze stabilization.
The Cerebellum
The cerebellum is located behind dorsal pons and medulla. It is joined to brainstem by three pairs of peduncles: superior, middle, and inferior. It is also comprised of two hemispheres divided in between by the vermis.
The three major parts of the cerebellum include the archicerebellum (flocculonodular lobe), the paleocerebellum (rostral cerebellum), and the neocerebellum (posterior lobe).
The archicerebellum connects with the vestibular system and is concerned with equilibrium and regulation of muscle tone. It also aids in processing the vestibule-ocular reflex. The paleocerebellum on the other hand, controls the synergistic movement of the muscles that is important in maintaining posture and fluidity in functional movements. Lastly the neocerebellum ensures that the body’s movements are accurate in terms of timing, distance, and force, which is important in movement coordination.
