Cerebrum (Sensory and Motor Cortex) 2024 PDF

CEREBRUM (SENSORY AND MOTOR CORTEX) OUTLINE INTRODUCTION LOBES OF THE CEREBRAL CORTEX FRONTAL LOBE PARIETAL LOBE TEMPORAL LOBE OCCIPITAL LOBE INSULAR LOBE INTRODUCTION CEREBRUM= CEREBRAL CORTEX + BASAL GANGLIA Cerebral cortex is the outer covering of the Cereb...

CEREBRUM (SENSORY AND MOTOR CORTEX) OUTLINE INTRODUCTION LOBES OF THE CEREBRAL CORTEX FRONTAL LOBE PARIETAL LOBE TEMPORAL LOBE OCCIPITAL LOBE INSULAR LOBE INTRODUCTION CEREBRUM= CEREBRAL CORTEX + BASAL GANGLIA Cerebral cortex is the outer covering of the Cerebrum while the Basal ganglia is the inner part of the cerebrum. The cerebrum of the central nervous system is the uppermost part of the brain. It is composed of the basal ganglia, cerebral cortex, and olfactory cortex. INTRODUCTION Cerebral cortex consists of two hemispheres which are separated by a deep vertical fissure. This separation is complete anteriorly and posteriorly. It is the largest part of the Central Nervous System. It is an area of 2.2m2 in humans The cerebral cortex consists of gray matter that surrounds the deeper white matter. LOBES OF CEREBRAL CORTEX In each hemisphere, there are there surfaces: Lateral, Medial and Inferior surfaces. The cerebral cortex consists of four (4) lobes which are Frontal lobe, Parietal lobe, Occipital lobe and Temporal lobe. The frontal lobe is mainly involved in motor functions while the other three lobes are involved more in sensory functions. CEREBRAL DOMINANCE Cerebral dominance is related to handedness i.e. preference of the individual to use right or left hand. This was investigated by ROGER SPERY in 1945. He noted that one cerebral hemisphere is more specialized for specific functions than the other hemisphere More than 90% of individuals are right-handed and in these people the left hemisphere is dominant and it controls the analytical process and the language related functions such as speech, reading and writing. BRODMANN AREAS It refers to the regions of the Cerebral cortex defined on the basis of how the cells are organized in the brain or it’s cytoarchitecture. These areas were originally defined and numbered in 1909 by KORBINIAN BRODMANN depending on the Laminar organization of neurons in the cortex. FRONTAL LOBE OF THE CEREBRAL CORTEX The frontal lobe is the largest lobe in the cerebral cortex and is located in the front of the brain as the name suggests. The frontal lobe forms a third of the cortical surface of the Cerebrum It extends from frontal pole to the central sulcus and is limited below by the Lateral sulcus. It is divided into two (2) parts viz: a.) PRECENTRAL CORTEX which is located posteriorly b.) PREFRONTAL CORTEX which is located anteriorly FRONTAL LOBE OF THE CEREBRAL CORTEX  PRECENTRAL CORTEX This is the posterior part of the frontal lobe of the cerebrum. It is also known as EXCITOMOTOR CORTEX OR AREA because the stimulation of different points in the area causes activity of discrete skeletal muscles. The Precentral cortex is further divided into 3 parts which are: i.) PRIMARY MOTOR AREA Ii.) PREMOTOR AREA Iii.) SUPPLEMENTARY MOTOR AREA FRONTAL LOBE OF THE CEREBRAL CORTEX  PRECENTRAL CORTEX  PRIMARY MOTOR AREA It extends throughout the Precentral gyrus and the adjoining lip of the central sulcus Brodmann areas 4 and 4S are present here. The role of the primary motor cortex is to initiate and execute voluntary muscle movements. The primary motor cortex sends motor information down through the spinal cord and out to skeletal muscles to tell them to move. FRONTAL LOBE OF THE CEREBRAL CORTEX  PRIMARY MOTOR AREA  AREA 4 This is a tapering strip of area situated in Precentral gyrus of the frontal lobe. Its broad end lies superiorly at the upper border of the hemisphere and most of the efferent fibers of Primary motor area arise from this area. AREA 4 is the center for movement, as it sends all efferent (corticospinal) fibers of Primary motor area. It activates the lower motor neurons in the spinal cord through the fibers of corticospinal tracts. Electrical stimulation of AREA 4 causes discrete isolated movements in the opposite side of the body. The groups of muscles or single isolated muscle may be activated depending upon the area stimulated. FRONTAL LOBE OF THE CEREBRAL CORTEX  PRIMARY MOTOR AREA  AREA 4S AREA 4S is called SUPPRESSOR AREA It forms a narrow strip anterior to AREA 4. It scrutinizes and suppresses the extra impulses produced by AREA 4 and prevents exaggeration of movements. FRONTAL LOBE OF THE CEREBRAL CORTEX  PRECENTRAL CORTEX  PREMOTOR AREA This is the second part of the Precentral cortex of the frontal lobe. It has AREAS 6,8,44 and 45. It is anterior to the Primary motor area in the Precentral cortex. It is concerned with control of postural movements by sending motor signals to Axial muscles (muscles near the midline of the body). It is similar to the Primary motor area in structure except for the absence of giant pyramidal cells in the ganglionic layer. FRONTAL LOBE OF THE CEREBRAL CORTEX  PREMOTOR AREA  AREA 6 It is in the posterior portions of the Superior, middle and Inferior frontal gyri. It is subdivided into 6a and 6b It is concerned with the co-ordination of movements initiated by Area 4. It helps to make the skilled movements more accurate and smooth. Electrical stimulation of Area 6a in humans causes discrete isolated movements in the opposite side of the body. FRONTAL LOBE OF THE CEREBRAL CORTEX  PREMOTOR AREA  AREA 8 Called FRONTAL EYE FIELD It lies anterior to Area 6 in the Precentral cortex. It is concerned with movements of eyeball. It is involved in the planning, control and execution of eye movements. It receives afferent fibers from dorsomedial nucleus of Thalamus and Occipital lobe. It sends efferent fibers to Oculomotor nuclei in Tegmentum of midbrain. It is concerned with conjugate movements of the eyeball. Stimulation of this area causes conjugate movements of eyeballs to the opposite side, opening and closing of eyelids, pupillary dilatation and lacrimation. FRONTAL LOBE OF THE CEREBRAL CORTEX  PREMOTOR AREA  AREA 44 and 45 (BROCA’s AREA) The Broca’s area is the motor area for speech It is present in the Left hemisphere (dominant hemisphere) of Right handed people and in the Right hemisphere of Left handed people. It is a special region of Premotor cortex situated in the Inferior frontal gyrus. AREA 44 is located in PARS TRIANGULARIS and AREA 45 in PARS OPERCULARIS of this gyrus. FRONTAL LOBE OF THE CEREBRAL CORTEX  PREMOTOR AREA  AREA 44 and 45 (BROCA’s AREA) It is responsible for movements of tongue, lips and larynx, which are involved in speech. Lesion of Broca’s Area leads to APHASIA; which refers to impaired or absent comprehension or production of, or communication by speech, writing or signs due to an acquired lesion of the Dominant cerebral hemisphere. FRONTAL LOBE OF THE CEREBRAL CORTEX  PRECENTRAL CORTEX  SUPPLEMENTARY MOTOR AREA This is the third part of the Precentral cortex of the frontal lobe. Located in the medial surface of the frontal lobe close to the primary motor area. It is suggested that it is concerned with co-ordinated skilled movements, Voluntary movements Lesion in this area causes the head and eyeballs to turn towards the affected side. FRONTAL LOBE OF THE CEREBRAL CORTEX  PRECENTRAL CORTEX The motor association cortex is made up of the premotor cortex and the supplementary motor cortex. The function of the motor association cortex is to plan and coordinate movements, whereas the primary motor cortex is more involved in actually executing the movement itself. FRONTAL LOBE OF THE CEREBRAL CORTEX  PREFRONTAL CORTEX OR ORBITOFRONTAL CORTEX It is the anterior part of the frontal lobe of the cerebral cortex, in front of Areas 8 and 44. It occupies the medial, lateral and inferior surfaces and it includes orbital gyri, medial frontal gyrus and the anterior portions of the Superior, middle and inferior frontal gyri. The following areas are present in the Prefrontal cortex: 9,10,11,12,13,14,23,24,29 and 32. Areas12,13,14,23,24,29 and 32 are in the medial surface while Areas 9,10 and 11 are in the lateral surface. FRONTAL LOBE OF THE CEREBRAL CORTEX  PREFRONTAL CORTEX OR ORBITOFRONTAL CORTEX Area 13, along with HIPPOCAMPUS, UNCUS and AMYGDALA sends fibers to mamillary body of hypothalamus via Fornix. This area is concerned with Emotional activity. It’s Functions includes: It forms the center for the higher functions like emotions, learning, memory and social behaviour. Short term memories are registered here. It is the center for planned actions It is the seat of Intelligence. So, it is also called the ORGAN OF THE MIND. It is responsible for the personality of the individuals. It is responsible for the various autonomic changes during emotional conditions because of it’s connections with hypothalamus and brainstem. FRONTAL LOBE OF THE CEREBRAL CORTEX  PREFRONTAL CORTEX OR ORBITOFRONTAL CORTEX Initially, this area was considered as inexcitable to electrical stimulation. Hence, it was called the SILENT AREA or ASSOCIATION AREA. But now, it is known that the stimulation of this area with low voltage electrical stimulus causes changes in the activity of digestive, cardiovascular, respiratory and excretory systems and other autonomic functions. Removal of the Prefrontal cortex in humans causes lack of initiation and loss of mental alertness. Very little or no change occurs in memory, judgment and intelligence. FRONTAL LOBE OF THE CEREBRAL CORTEX  BROCA’S AREA (AREA 44) Broca’s area is usually located in the dominant hemisphere, so for most people this will be the left hemisphere since they are right-handed. Broca’s area stimulates the muscles that help us produce speech and form words. FRONTAL LOBE OF THE CEREBRAL CORTEX  SUMMARY FRONTAL LOBE CONTAINS: PRIMARY MOTOR CORTEX MOTOR ASSOCIATION AREA (PREMOTOR AREA + SUPPLEMENTARY MOTOR AREA) FRONTAL EYE FIELD PREFRONTAL CORTEX (PREFRONTAL ASSOCIATION AREA) BROCA’S AREA FRONTAL LOBE OF THE CEREBRAL CORTEX  APPLIED PHYSIOLOGY FRONTAL LOBE SYNDROME is a condition of injury or ablation of the prefrontal cortex. Symptoms include Emotional instability, lack of concentration, difficulty in planning, loss of moral and social sense, failure to realize the seriousness of the condition. Other features include Hyperphagia, loss of control over sphincter of urinary bladder or rectum, disturbance in orientation and slight tremor PARIETAL LOBE OF THE CEREBRAL CORTEX It extends from central sulcus and merges with occipital lobe behind and temporal lobe below. The central sulcus divides the parietal lobe from the frontal lobe while the lateral sulcus (aka Sylvian fissure) separates the parietal from the temporal lobe. Separated from Occipital lobe by Parieto-occipital sulcus and from Temporal lobe by SYLVIAN SULCUS. Divided into 3 functional areas as follows: PRIMARY SOMATOSENSORY CORTEX SOMATOSENSORY ASSOCIATION CORTEX POSTERIOR ASSOCIATION AREA In addition to these 3 areas, a part of sensory motor area is also situated in the parietal lobe. PARIETAL LOBE OF THE CEREBRAL CORTEX The overall function of the Parietal lobe is SOMATOSENSORY. The parietal lobe is involved in making us consciously aware of somatic sensations such as touch, pain, pressure, temperature, vibration, etc. The parietal lobe also plays a key role in processing and analyzing somatosensory information to provide meaning and understanding to the stimulus. Lastly, the parietal lobe is involved in proprioception as it processes sensory stimuli and provides us with spacial and body position awareness. PARIETAL LOBE OF THE CEREBRAL CORTEX  PRIMARY SOMATOSENSORY CORTEX  Aka SOMATOSENSORY AREA I or PRIMARY SENSORY AREA Has 3 areas which are Areas 3,1 and 2. The anterior part of this forms Area 3 and the posterior aspect forms Areas 1 and 2. It receives sensory fibers from Thalamus via Parietal part of Thalamic radiation. It is responsible for perception and integration of cutaneous and kinesthetic sensations. Area 1 is concerned with sensory perception while Areas 2 and 3 are involved in the integration of these sensations PARIETAL LOBE OF THE CEREBRAL CORTEX  PRIMARY SOMATOSENSORY CORTEX  Aka SOMATOSENSORY AREA I or PRIMARY SENSORY AREA It sends sensory feedback to the Premotor area and is also concerned with the movements of head and eyeballs. It is responsible for recognition of the discriminative features of sensations such as spatial recognition, recognition of intensity of different stimuli, recognition of similarities and differences between the stimuli PARIETAL LOBE OF THE CEREBRAL CORTEX  SOMATOSENSORY ASSOCIATION CORTEX  Aka SOMATOSENSORY AREA II Located in the Posterior area to the primary somatosensory cortex It receives sensory impulses from Somesthetic area I and from the Thalamus directly. The function of the somatosensory association cortex is to analyze and process somatic stimuli. By analyzing, processing, and comparing the stimulus to old memories, we are able to recognize and understand what the somatosensory stimulus is. PARIETAL LOBE OF THE CEREBRAL CORTEX  SOMATOSENSORY ASSOCIATION CORTEX  Aka SOMATOSENSORY AREA II It allows us to identify stimuli even with our eyes closed especially if we have held something similar before. The somatosensory association cortex is also involved in proprioception and spacial awareness as we process somatic stimuli. It has 2 areas which are Areas 5 and 7 PARIETAL LOBE OF THE CEREBRAL CORTEX  POSTERIOR ASSOCIATION AREA Located in the posterior parietal lobe, and it also extends into the occipital and temporal lobe. The somatosensory stimuli from the parietal lobe, the visual stimuli from the occipital lobe, and the auditory stimuli from the temporal lobe all meet in the posterior association area. Concerned with synthesis of various sensations perceived by somesthetic area I. PARIETAL LOBE OF THE CEREBRAL CORTEX  POSTERIOR ASSOCIATION AREA The union of somatosensory, visual, and auditory stimuli in the posterior association area is important for proprioception and allows us to develop spatial awareness of our body position and surroundings. PARIETAL LOBE OF THE CEREBRAL CORTEX  APPLIED PHYSIOLOGY Lesion or ablation of Parietal lobe (sensory cortex) results in the following disturbances: 1.) Contralateral disturbance of cutaneous sensations 2.) Disturbances in kinesthetic sensations 3.) Loss of tactile localization and discrimination TEMPORAL LOBE OF THE CEREBRAL CORTEX it is located on the side of the brain. It includes FOUR (4) functional areas which include: a.) PRIMARY AUDITORY AREA b.) AUDITORY ASSOCIATION CORTEX c.) WERNICKE’S AREA d.) PRIMARY OLFACTORY CORTEX/OLFACTORY ASSOCIATION CORTEX TEMPORAL LOBE OF THE CEREBRAL CORTEX The temporal lobe functions to make us consciously aware of auditory stimuli such as various pitches, frequencies, and sounds. The temporal lobe also processes and analyzes auditory stimuli so we can recognize them. Also involved in the sense of smell as well. TEMPORAL LOBE OF THE CEREBRAL CORTEX  PRIMARY AUDITORY AREA It includes Areas 41 and 42 Areas 41 and 42 are located in Anterior Transverse Gyrus and Lateral surface of Superior temporal gyrus. Wernicke’s area is in the upper part of Superior temporal gyrus posterior to areas 41 and 42. The primary auditory cortex functions to make us consciously aware of auditory stimuli. TEMPORAL LOBE OF THE CEREBRAL CORTEX  PRIMARY AUDITORY AREA It is concerned with perception of auditory impulses, analysis of pitch and determination of intensity and source of sound. Areas 41 and 42 are concerned only with the perception of auditory impulses. Wernicke’s area is responsible for interpretation of sound and it does this with the help of Auditopsychic area. TEMPORAL LOBE OF THE CEREBRAL CORTEX  AUDITORY ASSOCIATION CORTEX The auditory association cortex will analyze sounds, compare them to old auditory memories, and form new memories. This analysis will help us recognize the sound and provide meaning and understanding to what it is we are hearing. TEMPORAL LOBE OF THE CEREBRAL CORTEX  WERNICKE’S AREA Wernicke’s area is similar to Broca’s area in that it is usually in the dominant hemisphere. Wernicke’s area is involved in comprehension and understanding of written and spoken language. The same way Broca’s area was involved in the production of speech and actual formation of words; Wernicke’s area is important for the understanding and comprehension of the language. TEMPORAL LOBE OF THE CEREBRAL CORTEX  PRIMARY OLFACTORY CORTEX/OLFACTORY ASSOCIATION CORTEX Located deep in the temporal lobe on the medial aspect is the primary olfactory cortex and the olfactory association cortex. The primary olfactory cortex makes us consciously aware of smells, and the olfactory association cortex helps us process and analyze those smells. TEMPORAL LOBE OF THE CEREBRAL CORTEX  APPLIED PHYSIOLOGY  TEMPORAL LOBE SYNDROME Aka KLUVER BUCY SYNDROME It occurs after the bilateral ablation of temporal lobe along with Amygdaloid and Uncus. It can manifest in different ways such as Aphasia (disturbance of speech), Auditory disturbances such as Tinnitus (noise in the ear) and auditory hallucinations; disturbances in smell and taste sensations and visual hallucinations OCCIPITAL LOBE OF THE CEREBRAL CORTEX This is also called VISUAL CORTEX It consists of 3 functional areas a.) PRIMARY VISUAL AREA: AREA 17 b.) VISUAL ASSOCIATION AREA: AREA 18 c.) OCCIPITAL EYE FIELD: AREA 19 It receives afferent fibers from Lateral geniculate body It sends efferent fibers to Superior Colliculus and Lateral geniculate body. OCCIPITAL LOBE OF THE CEREBRAL CORTEX  PRIMARY VISUAL CORTEX The primary visual cortex is located in the posterior occipital lobe, and it functions to make us consciously aware of visual stimuli. The eyes send visual information to the primary visual cortex, and we become consciously aware of the stimuli. It causes conscious awareness of vision. OCCIPITAL LOBE OF THE CEREBRAL CORTEX  VISUAL ASSOCIATION CORTEX The visual association cortex is located anterior to the primary visual cortex. Similar to how the somatosensory association cortex helped analyze and recognize somatosensory stimuli, the visual association cortex helps us analyze and process visual stimuli. Much of the information delivered from the eyes to the primary visual cortex will then be sent to the visual association cortex to be processed and analyzed. The visual association cortex will compare visual stimuli to previous visual memories and/or form new memories. The processing and analyzing of visual information will then provide meaning and understanding to the visual stimulus, and help us recognize what it is we are seeing. OCCIPITAL LOBE OF THE CEREBRAL CORTEX  FUNCTIONS Primary visual area is concerned with perception of visual impulses. Visual Association area is concerned with interpretation of visual impulses Occipital eye field is concerned with movements of the eyes.  APPLIED PHYSIOLOGY Lesion in the upper and lower part of visual cortex results in HEMIANOPIA Bilateral lesion leads to total blindness. INSULAR CORTEX (INSULAR LOBE) This is the area responsible for the sense of taste in the human body. It functions to process taste, visceral sensations, autonomic control, and possibly vestibular control/equilibrium. In order to locate this functional cortical area that processes taste, we have to look deep into the lateral sulcus and pry apart the frontal and temporal lobes. LIMBIC LOBE The limbic lobe is one structure of many that make up the limbic system. Some textbooks and materials include the limbic lobe with the other cerebral lobes and that is why I included it here. The limbic lobe is one structure that makes up the limbic system, with some of the other main structures being the amygdala, hippocampal formation, thalamus, and hypothalamus. The overall function of the limbic system includes learning, memory, emotions, behavior, and smell. READ UP MOTOR HOMUNCULUS BROCA’S AREA, WERNICKE’S AREA CEREBRAL DOMINANCE AND HANDEDNESS SUMMARY  THANK YOU FOR LISTENING