Download - External Morphology Of The Cerebrum
External Morphology of the cerebrum
By Dr. Noura Osman
28-12-2009
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 Frontal Lobe
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
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 Temporal Lobe
this cerebral area mediates the processing of primary visual information.
The Occipital Lobe
Language Areas
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
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.
Medial View of the Right Hemisphere
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.
External Attachment of the cranial nerves