Nervous System III PDF

Cerebrum, Brainstem, Cerebellum Cerebrum Constitutes largest part of the brain. Contains two hemispheres separated by median cleft = longitudinal fissure Two hemispheres are connected to each other by large commissure = Corpus callosum Each hemisphere contains an irregular c...

Cerebrum, Brainstem, Cerebellum Cerebrum Constitutes largest part of the brain. Contains two hemispheres separated by median cleft = longitudinal fissure Two hemispheres are connected to each other by large commissure = Corpus callosum Each hemisphere contains an irregular cavity containing CSF = lateral ventricle Composed of: Grey matter (cortex- externally) White matter (internally) Cortex is thickest in motor area & thinnest at occipital pole. Has numerous convolutions (gyri) and these are separated by fissures (sulci) of varying depth (increase surface area) White matter consists of nerve fibres which transmit impulses to and from the cortical nerve cells and from one cortical area to another. It encloses some larger and smaller masses of grey matter such as corpus striatum, claustrum, amygdaloid body. Consists of 4 lobes viz: Frontal Parietal Occipital Temporal - Correspond in surface extent to the cranial bones from which they take their names. Surfaces of cerebrum Consists of 3 surfaces viz : Supero-lateral Medial Inferior Inferior surface Inferior surface Medial surface Supero-lateral surface of cerebrum - Divided into frontal, parietal, occipital and temporal parts by central, parieto-occipital and lateral sulci. FRONTAL LOBE Anteriorly superior and inferior frontal sulcus dividing it to superior, middle and inferior frontal gyri Posteriorly Pre – central sulcus & pre-central gyrus - (The motor area) TEMPORAL LOBE Has superior & inferior temporal sulci which divides it into superior, middle & inferior temporal gyri. PARIETAL LOBE - Divided into superior & inferior parietal lobule by intra-parietal sulcus OCCIPITAL LOBE - Divided by transverse occipital sulcus & consists of superior & inferior Occipital gyri. Medial surface of cerebrum. FRONTAL LOBE Corpus Callosum- connects the two hemispheres Cingulate Sulcus and Cingulate gyrus below it Medial Frontal gyrus – extends above cingulate gyrus to the superior border The Central Sulcus - on the medial surface & is a continuation from the supero-lateral surface and its surrounded by the Paracentral Lobule  PARIETAL LOBE Paracentral Lobule – part of it behind the central sulcus Pre-cuneus – the area before the parieto-occipital sulcus OCCIPITAL LOBE The Cuneus – bounded superiorly by the parieto-occipital sulcus and inferior by the calcarine sulcus. The Lingual gyrus – lies between the calcarine and the collateral sulcus. Inferior surface of cerebrum. Divided into 2 parts Small Ant. (orbital part): – olfactory sulcus, gyrus rectus; – H-shaped sulcus with anterior, posterior, lateral & medial orbital gyri Large post. part:  – Collateral sulcus, – occipito-temporal sulcus, medial and lateral occipito- temporal gyri, – parahippocampal gyrus Uncus: hook-like projection at anterior end of parahippocampal gyrus The poles Consists of 3 poles viz: Frontal Occipital Temporal Functional Localization. Cerebral cortex is necessary for conscious awareness and thought, memory and intellect. It is the region to which all sensory modalities ascend and are consciously perceived and interpreted based on previous experience. Cerebral cortex is the highest level at which motor systems is represented. –Actions are conceived and initiated. Homunculi Refers to a distorted-looking image of a person in which the hands, face, lips, and tongue are enlarged to reflect the relative size of the areas of the brain's motor cortex and sensory cortex that were thought to be devoted to each of those body parts. ✓ Motor -corresponds to the precentral gyrus -contains a detailed topographically organized map (motor homunculus) of the opposite body half -large areas represent the muscles of the hand and face ✓ Sensory -postcentral gyrus corresponds to the primary somatosensory cortex (sensory homunculus)  Functional areas ✓ Speech Broca's area, or the motor speech area, lies just above the lateral sulcus in the frontal lobe ✓ Auditory temporal operculum houses the primary auditory cortex ✓ Vision - situated on the posterior pole and medial aspect of the cerebra hemisphere in the occipital lobe -it is in the region of the calcarine sulcus -It is the receiving area for visual impressions Motor – Frontal Lobe. Primary motor cortex - Precentral gyrus + wall of central sulcus. Voluntary skilled movement Premotor (2nd motor) area Anterior to precentral gyrus: for internal urge to carry out a movement. Programmes skill motor activity Frontal eye field Anterior to premotor area (MFG): controls voluntary conjugate movement of eyes Prefrontal cortex  Remainder of frontal lobe: highest brain functions – abstract thinking, decision making, anticipated effects of specific line of action taken, social behaviour Broca’s expressive speech (44,45) inferior frontal gyrus (Lt side in Rt handed individuals) Sensory – Parietal lobe. Primary somatosensory area ▪ Tactile sense, tingling sensation, fine touch, position, movements of parts of the body; post-central gyrus – area 3,1,2 2nd somatosensory area ▪ Less discriminative sensation is medial surface of postcentral gyrus. Somatosensory association area ▪ Identification of 3-dimensional object held in the hand without looking – superior parietal lobule. ▪ Inferior lobule – interface with visual and auditory areas Gustatory (Taste)  ▪ Inferior end of postcentral gyrus Vision – Occipital lobe Primary visual cortex (Area 17) – Calcarine sulcus on medial surface of occipital lobe. – Receives optic radiations for vision. Association visual cortex (Areas 18 & 19) – Rest of occipital lobe surrounding primary visual cortex. – Interprets visual information (shape & accommodation reflex Hearing – Temporal lobe Primary auditory cortex superior surface of STGyrus (transverse temporal gyri (Heschl convolutions). Receives input from MGB of thalamus. Higher frequencies activate lateral stripes Lower frequencies act on medial stripes Auditory association cortex (sensory) “Wernicke’s area”; adjacent to primary auditory cortex Interpretation of auditory information (understanding spoken word and reading The Brainstem ❖ Located between the cerebrum and the spinal cord - Provides a pathway for tracts running between higher and lower neural centers Consists of the midbrain, pons, and medulla oblongata. ❖ Each region is about an inch in length. Microscopically, it consists of deep gray matter surrounded by white matter fiber tracts ❖ Produce automatic behaviours necessary for survival. Midbrain Pons Medulla obongata Ventral surface of brain stem Ventral – Lateral View of brainstem The midbrain Connects pons and cerebrum with forebrain Shortest brain stem,not more than 2cm in length,lies in the posterior cranial Fossa. For descriptive purpose,divided into Dorsal tectum and right and left cerebral Peduncles. Each cerebral peduncles divide further into ventral crus cerebri and a dorsal Tegmentum by a pigmented lamina “ Substantia nigra” Cerebral peduncles contains: -Descending fibers that go to the cerebellum via the pons -Descending pyramidal tracts Running through the midbrain is the hollow cerebral aqueduct which connects the 3rd and 4th ventricles of the brain The pons. The pons shows a convex anterior surface with prominent transversely running fibres. These fibres collect to form bundles, the middle cerebellar peduncles. Trigeminal nerve emerges from the anterior surface at the junction between pons and middle cerebellar peduncle. The anterior surface of pons is marked in the midline by a shallow groove, the sulcus basilaris which lodges the basilar artery. The medulla oblongata External structure of medulla ❑ Most inferior region of the brain stem. ❑ Becomes the spinal cord at the level of the foramen magnum. ❑ Medulla is broad above, joins with pons narrow below, continuous with spinal cord ❑ Length is about 3cm, width is about 2cm at its upper end.  Surfaces shows series of fissures. ❑ Anterior median fissure Spinal cord ❑ Posterior median fissure Ventral surface of medulla oblongata contains Pyramid elevation between anterior median and anterolateral sulcus Formed due to decussation of corticospinal fibres. Olive Oval swelling between anterolateral posterolateral sulcus,half an inch long Produced by large mass of gray matter called inferior olivary nucleus Olives Pyramids THE CEREBELLUM LOCATION. Largest part of hind-brain & occupies most of posterior cranial fossa Separated from occipital lobes of cerebral hemispheres by tentorium cerebelli Lies dorsal to pons & medulla, from which it is separated by fourth ventricle Joined to brain stem by three bilaterally paired cerebellar peduncles, & these contain all the afferent and efferent fibres associated with cerebellum. EXTERNAL FEATURES. Consists of two cerebellar hemispheres united to each other through median vermis Has two surfaces – superior & inferior Superior surface is convex. Inferior surface shows a deep median notch – vallecula – separates right & left hemispheres Anterior aspect of cerebellum marked by deep notch- occupied by pons & medulla Posteriorly- narrow deep notch occupied by falx cerebelli Each hemisphere divided into three lobes. Anterior Lobe Lies on anterior part of superior surface Separated from middle lobe by primary fissure Posterior (Middle) Lobe Largest lobe Limited in front by primary fissure (on superior surface) & posterolateral fissure (on inferior surface) Flocculonodular Lobe Smallest lobe Lies on inferior surface in front of posterolateral fissure SUB-DIVISIONS Divided into numerous small parts by fissures Each fissure cuts the vermis & both hemispheres Horizontal fissure Separates superior from inferior surface. PRIMARY FISSURE Separates anterior from middle lobe on superior surface POSTEROLATERAL FISSURE Separates middle from flocculonodular lobe on inferior surface. PARTS OF THE VERMIS PARTS OF THE VERMIS- INFERIORLY - Tuber - Pyramid - Uvula and Nodule SUBDIVISION OF CEREBELLAR HEMISPHERES. SUPERIORLY Simple Lobule Superior semilunar Lobule Inferior semilunar Lobule INFERIORLY - Quadrangular Lobule - Ala - Biventral Lobule - Tonsil - Flocculus - MORPHOLOGICAL & FUNCTIONAL DIVISIONS ARCHICEREBELLUM Made up of flocculonodular lobe & lingula Chiefly vestibular in its connections Controls axial musculature & bilateral movements used for locomotion & maintenance of equilibrium. PALEOCEREBELLUM Made up of anterior lobe, pyramid, uvula Connections chiefly are spinocerebellar Controls tone, posture & crude movements of limbs NEOCEREBELLUM Made up of middle lobe (largest part of cerebellum) minus pyramid & uvula of inferior vermis Chiefly cortico-cerebellar in its connections Concerned with regulation of fine movements of body CONNECTIONS OF CEREBELLUM Fibres entering or leaving cerebellum are grouped to form three peduncles which connect cerebellum to midbrain, pons & medulla. GREY MATTER OF CEREBELLUM Consists of cerebellar cortex & cerebellar nuclei 4 pairs of nuclei 1. Dentate nucleus 2. Globose nucleus 3. Emboliform nucleus 4. Nucleus Fastigii FUNCTIONS OF CEREBELLUM Cerebellum controls same side of body i.e. influence is ipsilateral. Co-ordinates voluntary movements so that they are smooth, balanced & accurate. Chiefly done by neocerebellum. Dysfunction gives rise to inco-ordination of movements. Controls tone, posture & equilibrium Chiefly done by archicerebellum & paleocerebellum Cerebellar lesions give rise to hypotonia & disturbances of equilibrium.