External Morphology Of The CerebrumPresentation Transcript
External Morphology of the cerebrum By Dr. Noura Osman 28-12-2009 [email_address]
The Frontal Lobe
The Frontal Lobe The Frontal Lobe The frontal lobes play a major role in the planning and execution of complex actions, language expression, abstract reasoning and the emotions. The pre-central gyrus contains a primary motor center, which mediates very fine motor control. It interacts with the cerebellum, basal ganglia and brainstem nuclei in order to perform this mediation. Dorsal-Lateral damage causes problems with generating hypotheses and maintaining or shifting "set". There is also reduced verbal fluency, paucity of ideas, poor organizational strategy for learning tasks, and problems with motor programming and sequential motor tasks. Orbital-frontal damage is marked by personality changes, lack of insight, disinhibition, flat affect, irritability, antisocial behaviors, and cumpulsive utilization of objects.
The Parietal Lobe
The Parietal Lobe The postcentral gyrus of the parietal lobe is involved with the primary reception and processing of somatic sensory information, or that derived from the sense receptors in the skin, muscles and joints. This sensory information includes tactile or touch sensitivity in the skin, sensations of hot and cold, pressure exerted on the skin surface and the sense we have of the position of our joints and muscles. The parietal lobe is also involved in the integration of auditory, visual and somatic information by its interconnections with primary sensory areas in the temporal (auditory) and occipital (vision) lobes. Damage to the Angular Gyrus (left posterior-superior temporal and inferior parietal junction) of the left parietal lobe is associated with impaired ability to perform mental calculations, as well as impaired reading and writing (alexia with agraphia). Damage to the right Patietal lobe is associated with impaired spatial orientation. Combined damage to the left parietal and occipital areas causes unilateral spatial neglect in left-hemisphere-language-dominant patients. Contalateral damage causes impaired perception of visual detail. Prosopagnosia (impaired perception of faces) is a condition in which the "gestalt" processing of the Right Hemisphere is damaged, leaving only the detail-oriented Left hemisphere to break down the face piece-by-piece
The Temporal Lobe
The Temporal Lobe Structures in the temporal lobe mediate a wide variety of functions, such as auditory processing (superior temporal gyrus), language comprehension (left hemisphere superior temporal gyrus), memory (hippocampus), smell (uncus), and the emotions (limbic system). One-half of the visual projections pass through the temporal lobe as they course from the lateral geniculate of the the thalamus to the primary visual cortex in the occipital lobe. Damage to the Superior Temporal Gyrus of the right temporal lobe has been associated with impaired auditory perception and memory; patients often report hearing music or songs. Damage to the left Superior Temporal Gyrus of the left temporal lobe (Wernike's Area) is associated with impaired language comprehension.
The Occipital Lobe this cerebral area mediates the processing of primary visual information.
Language Ability and Aphasia Language is mediated by the left hemisphere in most adults and is broadly divided into receptive, associational and expressive components. Most clinical syndromes of language disorder (aphasia) represent impairment of these components, singly, or in some combination. The sensory aspects of language are represented in the superior temporal lobe (auditory language; Wernicke's area) and occipital lobe (visual language-reading). Expressive or motor control areas reside in the left frontal lobe (Broca's area). Structures such as the arcuate fasciculus (A) form interconnections between these functional areas. An example of predominantly motor aphasia is Broca's famous patient Lebourgne, who could understand spoken and written language but could not form language expressions in speech or writing. He could only utter the phrase "Tan". Lebourgne's lesion involved Broca's area in the frontal lobe. Aphasic patients with predominantly receptive or sensory aphasia cannot understand spoken or written language. They speak in an expressively fluent manner but the speech content is jumbled and confused, often to the point of complete jumbled nonsense. More subtle language disorders involving association areas result in specific aphasia syndromes, such as alexia (reading disorder) without agraphia (writing disorder), in which the patient can express language in writing but cannot comprehend what is written. This is most often due to specific injury of the left occipital/parietal area and the posterior section of the corpus callosum.
Sensory & Motor Areas Areas
Primary Motor and Somatosensory Areas The primary motor and somatosensory control areas lie on either side of the central sulcus. This is the groove separating the blue and yellow areas above. Motor control resides on the precentral gyrus and somatosensory areas are on the postcentral gyrus. The motor contraol area interacts with structures such as the crebellum, basal ganglia and red nucleus to control motor function. The sensory area depicted here only mediates the somatic senses, or those whose receptors are in the skin, muscles and connective tissue. Other senses, such as vision and hearing are mediated by other parts of the brain.
Medial View of the Right Hemisphere This medial view presents the brain as if it was split down the middle from front to back. Here, the medial surfaces of the lobes are presented. The corpus callosum, brainstem and cerebellum have been dissected through the midline. The complexity of the brain increases from the brainstem up to the cortex, roughly following the phylogenetic course of development. Lower brainstem areas have well-defined functions that involve the simple control of autonomic activity, such as respiration, sleep cycles, arousal and rote motor actions. Higher brainstem and subcortical areas mediate basic life processes (e.g. hunger & thirst), the initial processing of sensory information, and more sophisticated control of motor actions. The cerebral cortex controls many of the lower systems, allows for very fine motor control, and mediates the more sophisticated functions, such as language and reasoning, which we label intellectual or cognitive. In general, the greater the cortical complexity and size, the greater the intelligence of the organism.
Enlarged Medial View
Medial View of the Right Hemisphere Enlarged Med. Veiw (red) Corpus Callosum: This structure consists of a large number of nerve cell axons that form the major pathways interconnecting the two cerebral hemispheres. Superior Colliculus: This structure is a center that mediates the control of eye movements an visual attention. Inferior Colliculus: The inferior colliculus is a relay center for auditory information Mammillary Body: This structure is a component of the limbic system. Check that section for more information. Cerebellum: The cerebellum is a component of the motor system. Check the section on the cerebellum and brainstem for more information.
Enlarged Medial View
Medial View of the Right Hemisphere Enlarged Medial View (Blue) Anterior Commissure: The anterior commissure connects parts of the limbic system and olfactory (smell) sensory system across the hemispheres. This is a view of it in cross-section. Parolfactory Gyrus: The Parolfactory Gyrus and the Gyrus Rectus are prominent gyri of the inferior medial frontal lobe. Frontal Lobe: This is the inferior and medial surface of the frontal lobe. Nuclei in this area have important connections with the limbic system. Mammillary Body: This structure is a component of the limbic system. Check that section for more information. Optic Chiasm: This structure is composed of crossing fibers in the vision system. This is a view of the optic chiasm in cross-section. Check the section on Visual Pathways for more information. Gyrus Rectus: The Gyrus Rectus and the Parolfactory Gyrus are prominent gyri of the inferior medial frontal lobe. Temporal Lobe: This is the medial surface of the temporal lobe. Pons: This is a prominent structure of the brainstem.
The Superior Surface (Top)
The Superior Surface (Top): A view from the top of the brain highlights the many gyri and sulci. The two hemispheres are divided by the midline longitudinal fissure. The hemispheres are connected by a thick band of fibers called the corpus callosum. It lies beneath the cortex and is not depicted here. Cortex of the precentral gyrus plays a role in the control of movements or motor actions. The postcentral gyrus mediates the somatic senses, or those arising from the skin, muscles and connective tissues (touch, position sense and motion sense).
The Inferior Surface
The Inferior Surface (Bottom) The bottom view of the brain reveals the frontal and temporal lobes, the brainstem and the cerebellum. The olfactory (smell) bulbs and pathways can be seen as they lie on the surface of the frontal lobe. The optic nerves and optic chiasm are immediately posterior to these. Visual information passes from the eyes, through the chiasm and temporal- parietal areas to the visual cortex of the occipital lobe. The brainstem contains many structures involved in basic life processes, such as respiration, sleep, hunger, and arousal. The cerebellum is involved in the control of movement.
Enlarged Inferior Surface
The Inferior Surface (Detailed): Pons (blue): The pons is a major structure of the brainstem. It consists largely of pathways that traverse the cerebellar hemispheres and cranial nerve nuclei and pathways. Optic Chiasm (red): The optic chiasm is the crossing point for the visual pathways. A lesion here produces a characteristic visual perception syndrome. Check the section on the visual pathways for more information. Infundibulum (yellow): The infundibulum is the structure that connects the hypothalamic nuclei to the pituitary. Check the Hypothalamus for more information. Parahippocampus (green): The parahippocampal gyrus lies over the hippocampus in this image. It contains pathways that connect the hippocampus with other areas of the cerebral cortex. Uncus (purple): This structure represents an extension of the parahippocampal gyrus. Fusiform (orange): The Occipitotemporal gyrus (or Fusiform gyrus) represents the inferior boundary of the occipital and temporal lobes.
The Inferior Surface (Detailed): Pons (blue): The pons is a major structure of the brainstem. It consists largely of pathways that traverse the cerebellar hemispheres and cranial nerve nuclei and pathways. Mammillary Body (red): This view depicts both mammillary bodies from below. They are part of the limbic system. Olive (yellow): The inferior olivary nucleus consists of three subsections that have prominent connections with the cerebellum.
Insula The Insula: If the inferior part of the frontal lobe and superior part of the temporal lobe were drawn apart, or removed as you see here, the process would reveal a section of the cortex called, the Insula.