Functions of Cerebral Hemisphere Dr. Mohommed Moizuddin Khan Dr Beenish Mukhtar

Objectives of the lecture: At the end of this lecture the students should: Able to describe the general structure of the Cerebrum and Cerebral Cortex and identify the lobes of and its major regions/divisions To know the terms categorical hemisphere and representational hemisphere and should be able to summarize the difference between these hemispheres. Able to describe the primary functions of the Lobes and the Cortical Regions of the Brain. Appreciate area of body representation in motor and sensory cortex.

Cerebrum -The largest division of the brain, divided into two hemispheres, each of which is divided into four lobes. The right hemisphere functions are holistic and spatial hence it is labeled the "artistic" or "representational" hemisphere The left hemisphere is now referred to as the categorical" hemisphere. Cerebral Cortex - The outermost layer of gray matter making up the superficial aspect of the cerebrum. Cerebrum Cerebellum http://williamcalvin.com/BrainForAllSeasons/img/bonoboLH-humanLH-viaTWD.gif

CEREBRUM It is the largest part of the forebrain. It is highly developed in human. It is derived from the telencephalon. The 2 cerebral hemisphere are incompletely separated by the median or greater longitudinal fissure. They are connected by the corpus callosum. Each hemisphere has a cavity called the lateral ventricle. Longitudinal Fissure

Gyri – Elevated ridges “winding” around the brain. Cerebral Features: Gyri – Elevated ridges “winding” around the brain. Sulci – Small grooves dividing the gyri Central Sulcus – Divides the Frontal Lobe from the Parietal Lobe Fissures – Deep grooves, generally dividing large regions/lobes of the brain Longitudinal Fissure – Divides the two Cerebral Hemispheres Transverse Fissure – Separates the Cerebrum from the Cerebellum Sylvian/Lateral Fissure – Divides the Temporal Lobe from the Frontal and Parietal Lobes

Lobes of the Brain (4) Frontal Parietal Occipital Temporal http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg * Note: Occasionally, the Insula is considered the fifth lobe. It is located deep to the Temporal Lobe.

Lobes of the Brain - Frontal The Frontal Lobe of the brain is located deep to the Frontal Bone of the skull. It plays an integral role in the following functions/actions: - Emotions - Decision Making/Reasoning Personality Memory Formation

Behavior Abstract thought processes & Problem solving Attention Creative thought & Intellect Initiative & Inhibition Coordination of movements (Generalized and mass movements) Some eye movements Sense of smell Skilled movements & Some motor skills Libido (sexual urges)

Frontal Lobe - Cortical Regions Primary Motor Cortex (Precentral Gyrus) – Cortical site involved with controlling movements of the body. Broca’s Area – Controls facial neurons, speech, and language comprehension. Located on Frontal Lobe. Brodmann’s areas 44 & 45 Broca’s Aphasia – Results in the ability to comprehend speech, but the decreased motor ability (or inability) to speak and form words. Orbitofrontal Cortex – Site of Frontal Lobotomies * Possible Side Effects: - Epilepsy - Poor Emotional Responses - Perseveration (Uncontrolled, repetitive actions, gestures, or words) * Desired Effects: - Diminished Rage - Decreased Aggression - Poor Emotional Responses Olfactory Bulb - Cranial Nerve I, Responsible for sensation of Smell

The frontal lobe (anterior part of cerebrum) is concerned with MOTOR AREA The frontal lobe (anterior part of cerebrum) is concerned with the organization of movement: 1-Primary motor area. 2-Premotor area. 3-Supplementary motor area. 4- Prefrontal area (guidance of complex motor behaviour).

PRIMARY MOTOR CORTEX (PMC) In precentral gyrus & anterior part of the paracentral lobule. It corresponds to Brodmann’s area 4 . Body is represented upside down. Size of the functional area is directly proportional to the skilled movement, not to the size of the muscle. It is here that actions are conceived and initiated. The principal subcortical afferent to PMC is from Lateral ventral nucleus (LVN) of thalamus. LVN receives its input from globus pallidus & dentate nucleus.

A: Primary Motor Cortex * This graphic representation of the regions of the Primary Motor Cortex and Primary Sensory Cortex is one example of a HOMUNCULUS: Homunculus

Lesion: Upper 1/3 and paracentral lobule leads to affection of voluntary control in lower limb & perineum of the opposite side. Lower 2/3rds: affection of voluntary control of the head, neck & upper limb on the opposite side. Isolated lesion of the premotor cortex leads to apraxia. (Inability to perform skilled complex voluntary movement in spite of absence of muscle paralysis)

PREMOTOR CORTEX 6 Lies anterior to primary motor cortex. Brodmann’s area 6. It includes the posterior parts of superior, middle & inferior frontal gyri. Function: Programming & preparing for movement and control of posture. It receives its afferent from ventral anterior nucleus of thalamus. 6

SUPPLEMENTARY MOTOR CORTEX On the medial surface of the premotor cortex. The principle subcortical input to premotor and supplementary motor cortex is the ventral anterior nucleus of the thalamus. This nucleus receives its afferent from the globus pallidus & substantia nigra

It lies in posterior part of the middle fontal gyrus. It is corresponding to; Brodmann's area 8 It controls conjugate movement of the eye. Unilateral damage to area 8 causes conjugate deviation of the eyes to the side of the lesion. FRONTAL EYE FIELD

PREFRONTAL CORTEX Lies anterior to premotor area. It has rich connections with parietal, temporal and occipital cortex. Functions: Intellect. Judgment. Prediction. Motivation Planning of behaviour.

Broca’s Area Orbitofrontal Cortex Olfactory Bulb Primary Motor Cortex/ Precentral Gyrus Broca’s Area Orbitofrontal Cortex Olfactory Bulb Regions Modified from: http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg

Lobes of the Brain - Parietal Lobe The Parietal Lobe of the brain is located deep to the Parietal Bone of the skull. It plays a major role in the following functions/actions: - Senses and integrates sensation(s) Spatial awareness and perception (Proprioception - Awareness of body/ body parts in space and in relation to each other) Modified from: http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg

PRIMARY SOMATOSENSORY CORTEX In the postcentral gyrus & posterior part of paracentral lobule. It correspond to Brodmann’s areas 1, 2 and 3). Here thalamocortical neurons terminate (3rd order neuron). Input comes from ventral posterior nucleus (VPN) of the thalamus. Within the somatosensory cortex the contralateral half of body is represented upside down.

Parietal Lobe - Cortical Regions Primary Somatosensory Cortex (Postcentral Gyrus) – Site involved with processing of tactile and proprioceptive information. Somatosensory Association Cortex - Assists with the integration and interpretation of sensations relative to body position and orientation in space. May assist with visuo-motor coordination. Primary Gustatory Cortex – Primary site involved with the interpretation of the sensation of Taste.

Primary Somatosensory Cortex/ Postcentral Gyrus Somatosensory Association Cortex Primary Gustatory Cortex Modified from: http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg Regions

Lobes of the Brain – Occipital Lobe The Occipital Lobe of the Brain is located deep to the Occipital Bone of the Skull. Its primary function:- processing, integration, interpretation, of VISION and visual stimuli. Includes:- Primary Visual Cortex – for processing of image Visual association area.-for interpretation of image Modified from: http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg

PRIMARY VISUAL CORTEX Lies on medial surface of the occipital lobe. In close relation to the calcarine sulcus. It extends to the occipital pole. Brodmann’s area 17 It receives optic radiation from lateral geniculate nucleus (LGN) of the thalamus. Each lateral half of the visual field is represented in the visual cortex of the contralateral hemisphere.

VISUAL ASSOCCIATION CORTEX Brodmann’s areas 18,19 are called visual association cortex. They are interpretive to the visual image. Lesion: visual agnosia, (inability to recognize a seen object). Visual Association Area Primary Visual Cortex

Lobes of the Brain – Temporal Lobe The Temporal Lobes are located on the sides of the brain, deep to the Temporal Bones of the skull. They play an integral role in the following functions: Hearing Organization/Comprehension of language Information Retrieval (Memory and Memory Formation) Modified from: http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg

PRIMARY AUDITORY CORTEX Lies in the superior bank of the middle of the superior temporal gyrus. Hidden within the lateral fissure. Brodmann's 41, 42. Its precise location is marked by small transverse temporal gyri ( Heschl’s convolutions). Input to Primary auditory cortex is from medial geniculate nucleus (MGN) of the thalamus. Auditory radiation undergoes partial decussation in the brain stem before it reaches the (MGN).

SECONDARY AUDITORY CORTEX or AUDITORY ASSOCIATION CORTEX Lies behind the primary auditory cortex. Continuous posteriorly with the second motor speech (Wernicke’s) area. Here the heard sounds or words are interpreted. Lesion: Sensory aphasia; (inability to recognize the meaning of sounds or words with hearing unimpaired.

Temporal Lobe – Cortical Regions Primary Auditory Cortex – Responsible for hearing Primary Olfactory Cortex – Interprets the sense of smell once it reaches the cortex via the olfactory bulbs. (Not visible on the superficial cortex) Wernicke’s Area – Language comprehension. Located on the Left Temporal Lobe. - Wernicke’s Aphasia – Language comprehension is inhibited. Words and sentences are not clearly understood, and sentence formation may be inhibited or non-sensical.

Primary Auditory Cortex Wernike’s Area Primary Olfactory Cortex (Deep) Conducted from Olfactory Bulb Regions Modified from: http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg

Human physiology by Lauralee Sherwood, 9th edition References Human physiology by Lauralee Sherwood, 9th edition Text Book Of Physiology by Guyton & Hall, 11th edition Review of Medical Physiology by Ganong, 24th edition