External Morphology of the cerebrum

By Dr. Noura Osman

28-12-2009

drnosman@yahoo.com

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