Lecture 7,8: Brain &Cranial Nerves

Transcription

1 Lecture 7,8: Brain &Cranial Nerves Dr. Amjad El-Shanti MD,MPH, PhD Assistant professor of Public Health- Epidemiology Principal Parts of Brain The brain of an average is one the largest organs of the body (about 1300 g weight). The brain is mushroom shaped. The brain is divided into four principal parts: 1. Brain stem 2. Diencephalon 3. Cerebrum 4. Cerebellum 1

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3 Protection & Coverings of Brain Three components are responsible for covering and protection of brain: 1. Cranial bones of skull. 2. Cranial meninges. 3. Cerebrospinal fluid. 3

4 The ventricles Cerebrospinal Fluid Most of the CerebroSpinal Fluid is formed within the Lateral Ventricles of the Cerebrum by the Choroid Plexus. Cerebrospinal Fluid is a clear, colorless liquid of low specific gravity that in health has between two and three Lymphocytes per cubic millimeter. Its volume is between 100 and 140 ml in adults, and the normal pressure varies from between 70 and 200 mm of water with the patient on his side. Total protein in adults varies from 20 to 45 %mg with glucose varying from 50 to 75 %mg. Chlorides are between 120 and 230m eq/lit. 4

5 From the Lateral Ventricles, fluid traverses the InterVentricular Foramina into the Third Ventricle. Here, presumably, the Choroid Plexus of the Third Ventricle contributes fluid, which then passes through the Aqueduct Of Sylvius into the Fourth Ventricle, where further additions are made by the Choroid Plexus in the roof of the Fourth Ventricle. The fluid then enters into the SubArachnoid Space through a median aperture called the Foramen Of Magendie and lateral apertures called Foramina Of Luschka. Some fluid passes downward into the Spinal SubArachnoid Space, but the major portion rises through the Tentorial Notch and finds its way slowly over the surface of the Hemispheres to be absorbed mainly through the Arachnoid Villi and Granulations into the Venous System. The mechanisms of CSF absorption, mainly through the PeriNeural Lymphatics, and in addition, in abnormal pressure states it appears possible for CSF to be absorbed through the Ependyma. Each blood vessel, as it enters the Brain tissue, incorporates a Prolongation of the SubArachnoid Space by which CerebroSpinal Fluid can come in contact with the Neurons themselves. Any obstruction to the Ventricular System, either by blockage of the foramen of Monro, the aqueduct of Sylvius, or of the Foramen of Magendie and Luschka, will create a Non-Communicating type of HydroCephalus, in which the Ventricular System will dilate. Pressure within the Ventricular System in Hydrocephalus can increase in an acute and fatal manner. If absorption is interfered with there develops a HydroCephalus classified as Communicating. 5

6 Formation, circulation and absorption of Cerebro- spinal fluid Lateral Ventricle Arterial blood Interventricular foramina CSF Heart Third Ventricle Venous blood Choroid Plexus CSF Cerebral aqueduct Arachnoid villi of dural venous sinuses CSF Fourth Ventricle Subarachnoid space Lateral & median apertures Blood Supply of Brain The brain is well supplied with oxygen and nutrients by blood vessels that form the cerebral arterial circle (circle of willis). Blood vessels that enter brain tissues pass along the surface of the brain, and as they penetrate inward, they are surrounded by loose fitting layer of pia matter. The space between the penetrating blood vessels and pia mater is called peri -vascular space. 6

7 Although the brain composes only about 2% of total body weight, it utilizes about 20% of the oxygen used by entire body. The brain is one of the most metabolically active organs of the body and the amount of oxygen it uses varies with the degree of mental activity. If blood flow to brain is interrupted even briefly leading to unconsciousness. 1-2 minute interruption may weaken thee brain cells by starving them of oxygen. If the cell are totally deprived of oxygen for 4 minutes, many are permanently injured. Lysosomes of brain cells are sensitive to decreased oxygen concentration. If a condition of depriving persists long enough, lysosomes break open and release enzymes that bring about self destruction of brain cells. The principal source of energy for brain cells is the glucose which is found in the blood supply the brain. The supply of glucose to the brain must be continuous, because carbohydrate storage in the brain is limited. 7

8 If blood entering the brain has a low glucose level, the followings may occur: 1. Mental confusion 2. Dizziness 3. Convulsions 4. Loss of consciousness. Both o 2 and Co 2 have potent effects on cerebral blood flow: 1. Co 2 increases cerebral blood flow by combining with water to form (H 2 Co 3 ) then breaks down into HCo 3 - and H + which cause vasodilatation. 2. Decreased o 2 cause vasodilatation and increased cerebral blood flow. Glucose, oxygen and certain ions pass rapidly from the circulating blood into brain cells. Other substances such as creatinine, ure, chloride, insulin, and sucrose enter quite slowly. Still other substances : proteins and most antibiotics do not pass at all from the blood into brain cells. The differential rates of passage of certain materials from the blood into most parts of the brain are based upon a concept called Blood- Brain- Barrier. 8

9 Blood brain barrier functions as as a selective barrier to protect cells from harmful substances. This barrier is absent or less selective in the hypothalamus and roof of the fourth ventricle. Capillaries of the brain differ structurally from other capillaries (Brain capillaries are constructed by of more densely packed cells and are surrounded by large numbers of neuroglial cells and a continuous basement membrane). The substances that cross the barrier are either very small molecules or require the assistance of a carrier molecule to cross by active transport. Brain stem 9

10 10 Brain Stem The lower extension of the brain where it connects to the spinal cord. Neurological functions located in the brainstem include those necessary for survival (breathing, digestion, heart rate, blood pressure) and for arousal (being awake and alert). Most of the cranial nerves come from the brainstem. The brainstem is the pathway for all fiber tracts passing up and down from peripheral nerves and spinal cord to the highest parts of the brain. The brain stem includes: Medulla oblongata, Pons of Verillii and Midbrain

11 11 Medulla Oblongata Is a continuation of upper portion of spinal cord and forms the inferior part of the brain stem. Position: superior to the level of the foramen magnum and extendds upward to the inferior portion of the pons. Size: 3cm in length. Contents: all ascending and descending tracts that communicate between the spinal cord and various parts of the brain. These tracts constitute the white matter of the medulla.

12 Two roughly triangular structures are located on the ventral side of medulla called pyramids. Pyramids are composed of the largest motor tracts that pass from the outer region of cerebrum (cerebral cortex) to the spinal cord. Just above the junction of the medulla with spinal cord, most of the fibers in the pyramids cross to the right side, and most of the fibers in right pyramids cross to the left. This crossing called Decussation of pyramids. The principal motor fibers that undergo decussation belong to the lateral corticospinal tracts. These tracts originate in the cerebral cortex and pass inferiorly to the medulla. The fibers cross in the pyramids and descend in lateral columns of the spinal cord. Terminating in the anterior gray horns. They synapse in in the anterior gray horns with motor neurons that terminate in skeletal muscles. Fibers originate in left cerebral cortex activate muscle on the right side. Decussation explains why motor areas of one side of cerebral cortex control muscular movements on the opposite side of the body. 12

13 Details of medulla with pyramids decussattion The dorsal side of the medulla contains two pairs of prominent nuclei: 1. Left and right nucleus gracilis (slender). 2. Left and right nucleus cuneatus (wedge). These nuclei receive sensory fibers from ascending tracts (right and left Fasciculus gracilis and Fasciculus cuneatus) of the spinal cord and relay the sensory information to the opposite side of the medulla. Then the information is conveyed to the thalamus and then to the sensory areas of the cerebral cortex. Nearly all sensory impulses received on one side of the body cross in the medulla or spinal cord and are perceived in the opposite side of the cerebral cortex. 13

14 In addition to the conduction pathway for motor and sensory impulses between brain and spinal cord, the medulla contains an area of dispersed gray matter containing some white fibers. This region called the reticular formation. Portions of reticular formation are also located in the spinal cord, Pons, midbrain and Diencephalon. The reticular formation functions in consciousness and arousal. Reticular Formation 14

15 Within the medulla are three vital reflex centers of reticular system: 1. Cardiac center: regulates heartbeat and force of contraction. 2. Medullary rhythmicity area: adjusts the basic rhythm of breathing. 3. Vasomotor (vasoconstrictor) center: regulates the diameter of blood vessels. Other centers in the medulla are considered non vital and coordinates swallowing, vomiting, coughing, sneezing, and hiccupping. The medulla also contains the nuclei of origin for several pairs of cranial nerve: 1. VIII (Vestibulo -cochlear nerves). Concerned with hearing and equilibrium. 2. IX (Glosso -pharyngeal nerves) related 3. X (Vagus nerves) relay impulses from and to thoracic and abdominal viscera. 4. XI (The cranial portions of the accessory nerve) convey impulses related to head and shoulder movements. 5. XII (Hypoglossal nerves) convey impulses that involve tongue movements. 15

16 On each lateral surfaces of medulla is an oval projection called olive. Olive contains an inferior olivary nucleus and two accessory olivary nuclei. Those nuclei are connected to the cerebellum by fibers. Group of vestibular nuclear complex is associated with medulla (lateral, medial, inferior). But the superior associated with pons. This nuclear group is responsible for sense of equilibrium. Hard blow to the base of the skull can be fatal? Non fatal medullary injury may be indicated by: 1. cranial nerve malfunctions on the same side of body as the area of medullary injury. 2. Paralysis and loss sensation on the opposite side of the body. 3. Irregularities of respiratory control. 16

17 Pons of Verillii Pons means bridge lies directly above medulla and anterior to the cerebellum. Size: 2.5 cm in length. Contents: it consists of white fibers scattered through with nuclei. It is abridge connecting the spinal cord with the brain, and parts of the brain with each other. The transverse fibers connect with the cerebellum through middle cerebellar peduncles. The longitudinal fibers belong to the motor and sensory tracts that connect the spinal cord or medulla with the upper parts of the brain stem. 17

18 The nuclei for certain paired cranial nerves are contained in the pons, these include: 1. V (Trigeminal nerves) relay impulses for chewing and for sensations of the head and face. 2. VI (Abducens nerves) regulate certain eye ball movements. 3. VII (Facial nerves) conduct impulses related to taste, salivation, and facial expression. 4. Vestibular branch of VIII nerves connected with equilibrium. There are other important nuclei in the reticular formation of the pons: 1. Pneumotaxic area 2. Apneusic area Those area together with the medullary rhythmicity are in the medulla help control respiration. 18

19 Midbrain (Mesencephalon) Extends from the pons to the lower portion of diencephalon. Size: 2.5 cm in length. The cerebral aqueduct passes through the midbrain and connects the third ventricle above with the fourth ventricle below. The ventral portion of midbrain contains a pair of fiber bundles referred to as cerebral peduncles. Cerebral peduncles contain: 1. many motor fibers that convey impulses from the cerebral cortex to the pons and spinal cord. 2. Sensory fibers that pass from the spinal cord to the thalamus. Cerebral Peduncles constitute the main connection for tracts between upper parts of the brain and lower parts of the brain and spinal cord. 19

20 The dorsal portion of the midbrain is called Tectum (Roof). Tectum contains four rounded eminences (Corpora quadrigemina): 1. Two superior colliculi serve as centers for movements of the eye balls and head in response to visual and other stimuli. 2. Two inferior colliculi serve as centers for movements of the head and trunk in response to auditory stimuli. The midbrain contains the Substantia nigra: a large heavily pigmented nucleus near the cerebral peduncles. A major nucleus in the reticular formation of the midbrain is the red nucleus. Fibers from cerebellum and cerebral cortex terminate in the red nucleus. The red nucleus is also origin of cell bodies of the descending rubrospinal tract. Other nuclei in the midbrain are associated with cranial nerves: 1. III (Oculomotor nerves) mediate some movements of the eyeballs and changes in pupil size and lens shape. 2. IV (Trochlear nerves) conduct impulses that move the eye balls. Medial lemniscus is a common band of white fibers containing axons that convey impulses for fine touch, proprioception, and vibrations. This lemniscus is common to the medulla, pons and midbrain. 20

21 Diencephalon dia = through, encephalon = brain Consists principally of the 1. Thalamus 2. Hypothalamus. Thalamus Thalmus = inner chamber. It is an oval structure above the midbrain. Size: 3 cm in length and constitutes four-fifths of the diencephalon. It consists of two oval masses of mostly gray matter organized into nuclei that form the lateral walls of the third ventricle. The masses are joined by a bridge of gray matter called intermediate mass. Each mass is deeply embedded in a cerebral hemisphere and is bounded laterally by internal capsule. 21

22 Thalamus There are some portions of white matter inside the gray matter of thalamus masses: 1. Stratum Zonale : covers the dorsal surface 2. External medullary lamina: covers the lateral surface 3. Internal medullary lamina: divide the gray matter masses into: A. Anterior nuclear group B. Medial nuclear group C. Lateral nuclear group. 22

23 Within each group are nuclei that assume various roles: Some nuclei in the thalamus serve as relay stations for all sensory impulses except smell: 1. Medial geniculate nuclei (Hearing) 2. Lateral geniculate nuclei (Vision) 3. Ventral posterior nuclei (general sensations and taste). Other nuclei are centers for synapses in the somatic motor system: 1. Ventral anterior nuclei (Voluntary motor actions + Arousal). 2. Ventral Lateral Nuclei (Voluntary motor actions). Thalamus is the principal relay station for sensory impulses that reach the cerebral cortex from the spinal cord, brain stem, cerebellum, and parts of the cerebrum. Thalamus also functions as an interpretation center for some sensory impulses such as pain, temperature, light touch, and pressure. Thalamus also contains 1. reticular nucleus in the reticular formation which in some ways seems to modify neuronal activity in thalamus. 2. Anterior nucleus in the floor of the lateral ventricle which is concerned certain emotions and memory. 23

24 Hypothalamus A small portion of the diencephalon. It forms the floor and part of lateral walls of the third ventricle. It is protected partially by the sella turcica of the sphenoid bone. Information from the external environment comes to the hypothalamus via afferent pathways originating in the peripheral sense organs (Sound, taste, smell and somatic sensations). Afferent impulses monitoring the internal environment arise fro internal viscera and reach the hypothalamus. Other parts of hypothalamus continually monitor: 1. Water level 2. Hormone concentrations 3. temperature of blood. Hypothalamus have several very important connections with the pituitary gland. Despite its small size, the nuclei in hypothalamus control many body activities, some of them related to homeostasis. Differentiation of hypothalamic nuclei is far from precise, but it is possible to identify certain nuclei. Within a given nucleus there may be several kinds of cells that can be differentiated histologically. The localization of function is not specific to the individual nuclei with a few exceptions. Certain functions tend to overlap nuclear boundaries. for this reason functions are attributed to regions rather than specific nuclei. 24

25 The chief functions are attributed to regions rather than specific nuclei: 1. It controls and integrates the autonomic nervous system. (The main regulator of visceral activities). 2. It involved in the reception and integration of sensory impulses from the viscera. 3. It is the principal intermediary between the nervous system and the endocrine system: Regulates secretion of hormones of anterior pitutary gland by regulating factors. Produces two hormones (ADH), (OT) which stored in posterior pituitary gland then released when needed by the body. 4. It is the center for the (Mind -over- body) phenomenon in case of strong emotions which may lead to psychosomatic disorders with continued psychological stress. 5. It is associated with feelings of rage and aggression. 6. It controls normal body temperature. (Thermostat cells). 7. It regulates food intake through two centers: A. Feeding (Hunger) center stimulated by hunger sensations from the empty stomach. B. Satiety center when stimulated sends out impulses that inhibit the feeding center. 25

26 8. It contains thirst center which its cells stimulated when extra-cellular fluid volume is reduced which producing sensation of thirst. 9. It is one of the centers that maintains the waking state and sleep patterns. 10.It exhibits properties of a self-sustained oscillator and, as such, acts as peacemaker to drive many biological rhythms. Cerebrum It is supported by the brain stem and forming the bulk of the brain. The surface of cerebrum is composed of gray matter (2-4 mm) thick and is referred to as cerebral cortex. The cortex containing billions of cells (consists of 6 layers of nerve cell bodies in most area). Beneath the cortex lies the cerebral white matter. 26

27 During embryonic development, when there is a rapid increases in brain size, the gray matter of the cortex enlarges out of proportion of underlying white matter. As a result of the previous development, the cortical region rolls and folds upon itself. The folds of cerebral cortex called Gyri (Convolutions). The deep grooves between folds are referred to as Fissures. Shallow grooves between folds are Sulci. The most prominent fissure is the longitudinal fissure: The fissure which separates the cerebrum into right and left halves (Hemispheres). The two hemispheres of cerebrum are connected internally by Corpus callosum. Corpus Callosum: Large bundle of transverse fibers composed of white matter connect the two hemisphere of cerebrum with each other. Flax cerebri (Cerebral fold): An extension of dural matter between the two hemispheres of cerebrum that encloses the superior and inferior sagittal sinuses. 27

28 Cerebral Lobes Cerebral Lobes Each cerebral hemisphere is subdivided into Four Lobes: 1. Frontal Lobe 2. Parietal Lobe 3. Temporal Lobe 4. Occipital Lope The central sulcus separates the frontal lobe from the parietal lobe. Precentral gyrus: anterior to the central sulcus and it is a land mark for the primary motor area of the cerebral cortex. Postcentral gyrus: posterior to the central sulcus and it is a land mark for the general sensory area of the cerebral cortex. 28

29 Lateral cerebral sulcus: Separates the frontal lobe from the temporal lobe. Parietooccipital sulcus: separates the parietal lobe from the occipital lobe. Transverse Fissure: separates the cerebrum from the cerebellum. The frontal, parietal, temporal, and occipital lobes are named after the bones that cover them. A fifth part of the cerebrum lies deep within the lateral cerebral fissure, and under the parietal, frontal, and temporal lobes: (Insula). Olfactory (I) and optic (II) nerves of cranial nerves are associated with specific lobes of cerebrum. White Matter of cerebrum The white matter underlying the cortex consists of myelinated axons running in three directions: 1. Association Fibers: connect and transmit impulses between gyri in the same hemisphere. 2. Commissural Fibers: transmit impulses from the gyri in one cerebral hemisphere to the corresponding gyri in the opposite cerebral hemisphere. (e.g. Corpus callosum, anterior commissure, posterior commissure). 3. Projection fibers: from ascending and descending tracts that transmit impulses from the cerebrum to other parts of the brain and spinal cord (e.g. internal capsule). 29

30 Basal Ganglia (Cerebral Nuclei) They are paired masses of gray matter in each cerebral hemisphere: 1. Corpus striatum (Stripped body) : *The largest of a basal ganglia of each hemisphere. *It consists of Caudate and Lentiform Nuclei. *The lentiform is subdivided into : lateral portion (Putamen) and medial portion (Globus Pallidus) 2. Claustrum nucleus: thin sheet of gray matter lateral to putamen. 3. Amygdaloid (Alamond) nucleus: located at tail end of caudate nucleus. 4. Substantia nigra: large nucleus in midbrain whose axons terminate in caudate and putamen nuclei 5. Subthalamic nucleus: lies against the internal capsule connected mainly with globus pallidus 6. Red nucleus: They are interconnected by many fibers. They are also connected to: cerebral cortex, thalamus, hypothalamus Parts of Basal Ganglia 30

31 Functions of Basal ganglia: Caudate nucleus and putamen nucleus control large subconscious movements of skeletal muscles (Swinging the arms while walking). Globus pallidus is concerned with regulation of muscle tone required for specific body movements. Lentiform (Shaped like lens) Corpus Striatum Caudate (Tail) Globus Pallidus (Pale Ball) Putamen (shell) 31

32 Damage of basal ganglia Damage to basal ganglia results in abnormal body movements (e.g. Uncontrollable shaking: tremor, and involuntary movements of skeletal muscles). Destruction of Substantial portion of caudate nucleus leads to the paralysis of the opposite side of the body (often affected by stroke). Lesion in subthalamic nucleus results in a motor disturbance on the opposite side of body called (hemiballismus) : 1. involuntary movements occurring suddenly with great force rapidity. 2. Purposeless, 3. withdrawal, 4. Jerky 5. Spontaneous 6. affect the proximal portions of extremities (severely) 7. Especially arms. Limbic System Limbic (Border) system: is a wishbone shaped group of structures that encircles the brainstem and functions in the emotional aspects of behavior related to survival. Certain components of cerebral hemispheres and diencephalon: 1. Limbic lobe: formed by two gyri of cerebral hemisphere (Cingulate and hippocampal gyri) 2. Hippocampus: Extension of hippocampal gyrus till the floor of lateral ventricle. 3. Amygdaloid nucleus: Located at tail of caudate nucleus. 4. Mammillary bodies of hypothalamus: Two round masses close to the midline near the cerebral peduncles. 5. Anterior nucleus of thalamus: Located in the floor of the ventricle. 32

33 Limbic system Functions of limbic system 1. Hippocampus with portions of cerebrum functions in memory. ( Damage results in memory in impairment: forget recent events). 2. Amygdaloid nucleus assumes as a major role in controlling the overall pattern of behavior. 3. Certain areas of Limbic system (related to hypothalamus and thalamus) is associated with pain and pleasure. So it assumes a primary function of emotions (pain, pleasure, anger, rage, fear, sorrow, sexual feelings, docility and affection), so it is called (Emotional or visceral brain). 33

34 Functional areas of cerebral cortex Functional areas of cerebral cortex Functions of the cerebrum are numerous and complex. The cerebral cortex is divided into three main functional areas: 1. Sensory areas: interpret sensory impulses. 2. Motor areas: control muscular movement. 3. Association areas: concerned with emotional and intellectual processes. Each area is numbered according to k. Brodman s cytoarchitectural map of the cerebral cortex (1909) : attempt to correlate structure and function. 34

35 Functional Areas of the cerebrum by Brodman s Classification Functional Areas of the cerebrum 35

36 Sensory Areas Primary somesthetic (Primary sensory area)1,2,3: Located directly posterior to the central sulcus of the cerebrum in the postcentral gyrus. Extends from longitudinal fissure to lateral sulcus. Receives sensations from cutaneous, muscular, and visceral receptors in various parts of the body. The size of the portion of sensory area receiving stimuli from body is not dependent on the size of the part but on the number of receptors the part contains (Large portion is the area receives impulses from lips). Major function: Localization exactly the points of the body where the sensations originate. Thalamus is capable of localizing a sensations in a general way but can not distinguish between specific areas of stimulation. Somatosensory cortex of left cerebral hemisphere 36

37 Secondary somesthetic (Secondary sensory area): Small region in the posterior wall of lateral sulcus in line with the postcentral sulcus. Involved mainly in less discriminative aspects of sensation. Somesthetic association (Sensory association area) 5,7: Receives input from the thalamus, other lower portions of the brain, and primary somesthetic area. Role: integrates and interprets sensations determining the exact shape and texture of an object without looking to it. Determining the orientation of one object to another as they are felt. Sensing the relationship of one body part to another. Storage of memories of past sensory experiences. Other sensory areas of cerebral cortex: 1. Primary visual area (17): Located at medial surface of occipital lobe. Receives sensory impulses from the eyes. interprets shape, color, and movement. 2. Visual association area (18,19): Located in occipital lobe. Receives sensory signals from primary visual area and thalamus. Relates present to past visual experiences with recognition and evaluation of what is seen. 3. Primary auditory area (41,42): Located in superior part of temporal lobe near lateral sulcus. Interprets the basic characteristics of sound such as pitch, and rhythm. (anterolateral portion of the area responds to low pitches, while posterolateral portion responds to high pitches). 4. Auditory association area (22): Located inferior to primary auditory area. Determines if sound is speech, music or noise. Interprets the meaning of speech by translating words into thoughts. 37

38 5. Primary gustatory area (43): Located at the base of postcentral gyrus above the lateral cerebral sulcus in parietal cortex. Interprets the sensations related to taste. 6. Primary olfactory area: Located in the temporal lobe on the medial aspect. Interprets sensations related to smell. 7. Gnostic area (5, 7, 39,40): It is common integrative area located among somesthetic, visual, and auditory association areas. Receives impulses from theses areas as well as from taste, smell areas, thalamus, lower portions of brain stem. Integrates sensory interpretations from association areas and impulses fro other areas leading to formation of common thought. Transmits signals to other parts of brain to cause appropriate response. 38

39 Motor Areas Primary motor area (4): Located in the precentral gyrus of the frontal lobe. Consists of regions that control specific muscles or groups of muscles. Stimulation of a specific point of the primary motor area results in muscular contraction on the opposite side of the body (usually). Premotor area (6): Anterior to primary motor area. Concerned with learned motor activities of a complex and sequential nature. Generates impulses that cause a specific group of muscles to contract in specific consequences (e.g. Writing). Controls skilled movements. Frontal eye field area (8): Located frontal cortex and included in Premotor area (sometimes). Controls voluntary scanning movements of eyes (e.g. Searching for a word in a dictionary). Language areas: Translation of speech or written words into thoughts. This involves sensory areas (primary auditory, auditory association, primary visual, visual association, and gnostic). Broca s area (motor speech area),44: Located in frontal lobe just superior to lateral sulcus. Translation of thoughts into speech. From this area a sequence of signals is sent to the Premotor regions that control the muscles of larynx, pharynx, and mouth. 39

40 Association Areas Made of association tracts that connect motor and sensory areas. Occupies the greater portion of lateral surfaces of occipital, parietal, and temporal lobes, and the frontal lobes anterior to the motor areas. Concerned with memory, emotions, reasoning, will, judgment, personality traits, and intelligence. 40

41 Brain Lateralization Gross examination of the brain would suggest that it is bilaterally symmetric. By C.T. scans for detailed examinations. It is found that there are anatomical differences between the two hemispheres. In left-handed people: The parietal and occipital lobes of right hemisphere are usually narrower than the corresponding lobes of the left hemisphere. The frontal lobe of left hemisphere is narrower than that of the right hemisphere. there are also several functional differences between both sides of brain: In most people, Left hemisphere is more important for: Right hand- control Spoken Written language Numerical and scientific skills Reasoning Right hemisphere is more important for: Left-hand control Musical and artistic awareness Space and pattern perception Insight Imagination Generating mental images of sight, sound, touch, taste, and smell in order to compare relationshipsl. 41

42 Cerebellum Cerebrum: Cerebellum 42

43 Cerebellum The second largest portion of brain (1/8 of brain mass). Occupies the inferior and posterior aspects of the cranial cavity. (posterior to medulla and pons and blow occipital lobes). Separated from cerebrum by transverse fissure by an extension of the cranial dura mater called Tentorium Cerebelli. (Tentorium encloses the transverse sinuses) Shape: like a butterfly: The central constricted area is the vermis (worm-shaped). Lateral wings or lobes are referred to as hemispheres. Between the two hemispheres Falx Cerebelli :another extension of dura mater contains occipital sinuses Each hemisphere consists of lobes that are separated by deep and distinct fissures. Structure of Cerebellum 43

44 Cerebellum & surrounding regions A= Midbrain B= Pons C= Medulla Oblongata D= Spinal Cord E= Fourth Ventricle F= Arbor Vitae G=Tonsil H= Anterior Lobe I= Posterior lobe Anterior and posterior lobes are concerned with subconscious movements of skeletal muscles. Flocculonodular lobe is concerned with the sense of equilibrium. The surface of cerebellum called cortex: consists of gray matter in a series of slender parallel ridges called Folia. Folia are less prominent than gyri of cerebral cortex. Beneath the gray matter are white matter tracts called (Arbor Vitae) resemble branches of a tree. Deep within the white matter are masses of gray matter: (Cerebellar nuclei). 44

45 The cerebellum is attached to the brain stem by three paired bundles of fibers called cerebellar peduncles: 1. Inferior cerebellar peduncles: connect the cerebellum with the medulla at the base of brain stem and with spinal cord. 2. Middle cerebellar peduncles: Connect the cerebellum with the pons. 3. Superior cerebellar peduncles: Connect the cerebellum with the midbrain. Projection fibers of cerebellum (Peduncles) 45

46 Functions of Cerebellum 1. The cerebellum is a motor area of brain concerned with certain subconscious movements in the skeletal muscles (movements are required for coordination, maintenance of posture and balance): essential for delicate movements such as playing the piano. Transmits impulses that control postural muscles that is, it maintains normal muscle tone. Maintains body equilibrium. 2. Plays role in person s emotional development, modulating sensations of anger and pleasure. Cranial Nerves Of 12 pairs of cranial nerves, 10 originate from the brain stem, but all leave the skull through foramina of the skull. The cranial nerves are designated with roman numerals and with names: The roman numerals indicate the order in which the nerves arise from the brain (front to back). The names indicate the distribution or function. Some cranial nerve contain only sensory fibers and thus called (Sensory nerves). The remainder contain both sensory and motor fibers and are referred to as (Mixed nerves). The cell bodies of sensory fibers are found outside the brain, whereas the cell bodies of motor fibers lie in nuclei within the brain. 46

47 Types of cranial nerves Sensory nerves: I, II, VIII Mixed nerves: III, IV, V, VI, VII, IX, X, XI,XII. In past, there was thought that III, IV, XI, XII are entirely motor, but now it is known that these cranial nerves also contain some sensory fibers from propioceptors in muscles they innervate. CNN # Name Foramen Function I Olfactory Cribiform Plate Special Sensory: Smell II Optic Optic Canal Special Sensory: Sight III Oculomotor Superior Orbital Fissure Somatic Motor: Superior, Medial, Inferior Rectus, Inferior Oblique Visceral Motor: Sphincter Pupillae IV Trochlear Superior Orbital Fissure Somatic Motor: Superior Oblique 47

48 CNN # Name Foramen Function V Trigeminal V1: Sup Orb Fissure V2: Foramen Rotundum V3: Foramen Ovale Somatic Sensory: Face Somatic Motor: Mastication, Tensor Tympani, Tensor Palati VI Abducens Superior Orbital Fissure Somatic Motor: Lateral Rectus VII Facial Internal Auditory Canal Somatic sensory: Posterior External Ear Canal Special Sensory: Taste (Anterior 2/3 Tongue) Somatic Motor: Muscles Of Facial Expression Visceral Motor: Salivary Glands, Lacrimal Glands VIII VestibuloCochlear Internal Auditory Canal Special Sensory: Auditory/Balance CNN # Name Foramen Function IX Glossopharyngeal Jugular Foramen Somatic Sensory: Posterior 1/3 Tongue, Middle Ear Visceral Sensory: Carotid Body/Sinus Special Sensory: Taste (Posterior 1/3 Tongue) Somatic Motor: Stylopharyngeus Visceral Motor: Parotid Gland X Vagus Jugular Foramen Somatic Sensory: External Ear Visceral Sensory: Aortic Arch/Body Special sensory: Taste Over Epiglottis Somatic Motor: Soft Palate, Pharynx, Larynx (Vocalization and Swallowing) Visceral Motor: Bronchoconstriction, Peristalsis, Bradycardia, Vomitting XI Spinal Accessory Jugular Foramen Somatic Motor: Trapezius, Sternocleidomastoid XII Hypoglossal Hypoglossal Canal Somatic Motor: Tongue 48