Anatomy Text (Final) copy PDF

### Lymphoid Tissue - **Lymphoid tissue:** collections of lymph tissue other than lymph nodes. - Palatine tonsils, adenoids, Payer's patches of intestine and nodules of the spleen. - **The Spleen:** largest lymphoid organ in the body. - Lies below the diaphragm. - Functions: 1...

### Lymphoid Tissue - **Lymphoid tissue:** collections of lymph tissue other than lymph nodes. - Palatine tonsils, adenoids, Payer's patches of intestine and nodules of the spleen. - **The Spleen:** largest lymphoid organ in the body. - Lies below the diaphragm. - Functions: 1. Destroys worn-out RBCs. 2. Acts as reservoir for blood cells of all kinds. 3. Produces lymphocytes in the lymph nodules. - **Lymph Ducts:** 1. **Right lymph duct:** drains lymph from the right side of the head and neck, right side of the thorax, and the right upper limb. 2. **Thoracic duct:** begins as cisterna chyli in the abdomen and receives lymph from the whole body except the right side of the head and neck, the right side of the thorax, and the right upper limb. ### Serous Membranes - **Definition:** membranes that cover moving organs to reduce friction with the surroundings. - **Varieties** 1. **Pericardium:** serous sac surrounding the heart. 2. **Pleura:** serous sac surrounding each lung. 3. **Peritoneum:** serous sac surrounding many abdominal organs. 4. **Synovial sheaths:** surrounding tendons. 5. **Synovial membranes:** line capsules of synovial joints. 6. **Bursae:** synovial sheath between the tendon of the muscle and the joint. ### Neuroscience #### Introduction to the Nervous System - **Structure of Nervous System:** formed of neurons, neuroglia, and synapses. ### Nerve Cells (neurons) - **Structure of Nerve Cells:** a nerve cell is formed of a cell body and processes. - **Cell Body (soma):** - Has a nucleus and cytoplasm. The nucleus is usually central and contains nucleolus. - The cytoplasm contains cell organelles and cell inclusions. - **Cell Organelles:** - **Nissl bodies:** formed of rough endoplasmic reticulum and free ribosomes; concerned with protein synthesis. - **Mitochondria:** for the production of energy; considered power houses of the cell. They are the main source of energy compound ATP through cellular respiration. They contain DNA in a single chromosome containing 37 genes. Mitochondrial DNA is inherited from mothers only. Mitochondrial defects are present in many diseases such as Autism, Diabetes Militus, Myopathies, Dementia and Alzheimer. - **Lysosomes:** considered as the stomach of the cell; for intracellular digestion. They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. They are considered as Suicide Bags of the cell and are involved in the programmed cell death (Apoptosis). - **Golgi apparatus:** for formation of synaptic vesicles and modification of proteins; considered as the Post Office of the cell. It packages and labels items which it then sends to different parts of the cell. For example, the Golgi apparatus adds a mannose-6-phosphate label to proteins destined for lysosomes. - **Neurofilaments and neurotubules:** for cell shape and intracellular transport. - **Cell Inclusion:** - **Lipofuscin pigment:** yellow pigment that accumulates with aging, may be old lysosomes. It accumulates early in some diseases such as Alzheimer's and Parkinson's Disease. - **Melanin pigment:** for the production of catecholamines. It's present in variable amounts in the different parts of the brain. Patients with Parkinson's Diseases had 50% the amount of neuromelanin in the substantia nigra as compared to similar patients of their same age without Parkinson's. - **Processes:** - **Single axon:** the largest process of a nerve cell; extends from 1mm up to 1m (as in the sciatic nerve). - May be myelinated (for faster conduction) or unmyelinated. Myelin is destroyed in multiple sclerosis (MS). - Terminate by telodendria which end by the synaptic bulbs. - Communicates a nerve cell with other nerve cells or with an effector organ (glands and muscles). - **Dendrites:** short and highly branched processes; receive impulses from other neurons and transmit them toward the cell body . - **Functions of Nerve Cells:** - Receive stimuli - Transmit information - Process and interpret information - Store information (memory) - React according to situation - **Classification of Nerve Cells:** - **According to shape:** - **Unipolar neurons:** they have one process. - **True unipolar:** have one process that functions as a dendrite (as in amacrine cells of the retina). - **Pseudounipolar:** one process that divides into a peripheral branch that acts as a dendrite and a central branch that acts as an axon (sensory ganglion neurons). - **Bipolar neurons:** with one axon and one dendrite; present in the retina, olfactory nerve cells, and vestibular and cochlear ganglia of the inner ear. - **Multipolar neurons:** they have one axon and several dendrites; form most of nerve cells in the nervous system (as anterior horn cells of the spinal cord). They may have long axons such as Golgi Type I cells or short axons as in Golgi Type II cells. - **According to diameter of the Process (thickness of myelin):** - **Type A:** (thickest) B (medium), and C (thinnest). The thickest are the fastest (10-120 meters per second) and the thinnest are the slowest (5-25 meters per second) in transmission of impulses. - **According to function:** - **Sensory neurons:** transmit impulses from receptors to the central nervous system (pain touch, vision .. etc.). - **Motor neurons:** transmit impulses from the CNS to muscles and glands (effector organs). - **Interneurons:** transmit information from one neuron to another as basket cells in the cerebral cortex. - **Others:** these are more specialized types in the CNS - **According to neurotransmitter they produce:** - **Cholinergic neurons:** acetylcholine is released. - **GABAergic neurons:** GABA is released. It is the A. Ch homologue in the brain (Inhibitory). - **Glutamatergic neurons:** glutamate is released in the brain (Excitatory). - **Dopaminergic neurons:** released in the CNS. Dopamine is connected to mood and behavior. - **Serotonergic neurons:** released in the CNS and can act as excitatory or inhibitory. It is linked to depression and some psychological disorders. ### Supporting cells (neuroglial cells) - Non-neuronal cells supporting the neurons. They supply neurons with metabolites, repair damage, play a defense role, and build up myelin. - **Central neuroglia (in the central nervous system):** - **Astrocytes:** transport metabolites to neurons and repair damaged neural tissues. - **Oligodendrocytes:** synthesize myelin sheath in the CNS. - **Microglia:** play roles in phagocytosis and defense against infection. - **Ependymal cells:** line the walls of the brain and spinal cord cavities. - **Peripheral neuroglia (in the peripheral nervous system):** - **Schwann cells:** synthesize the myelin sheath in the peripheral nerves. - **Satellite cells:** surround the nerve cells inside the peripheral ganglia. ### Synapses - **Definition:** sites of functional contacts between nerve cells or between a nerve cello and effector organs such as muscle or gland. - **Structure:** 1. **Pre-synaptic element:** an axon terminal containing synaptic vesicles. 2. **Synaptic cleft:** a space of 20 nm between the pre and postsynaptic elements. 3. **Post-synaptic element:** usually a dendrite. - **Types of Synapses:** 1. Axodendritic synapse: between axon and dendrite. 2. Axonaxonic synapse: between axon and axon. 3. Axosomatic synapse: between axon and cell body. 4. Neuromuscular junction (motor end plate): between axon and muscle fiber. ### Divisions of Nervous System - Divided into central and peripheral systems. #### Central Nervous System - **The Brain:** - **Location:** enclosed in the calvaria of the skull covered by 3 layers of meninges. - **Divisions:** - **Cerebrum:** - **Two cerebral hemispheres:** contain higher motor and sensory centers - **Diencephalon:** includes the thalamus and the hypothalamus. - **Thalamus:** sensory relay station except for olfaction. - **Hypothalamus:** principle autonomic and endocrine center. - **Cerebellum:** for muscle co-ordination and maintenance of equilibrium. - **Brain stem:** formed of midbrain, pons, and medulla oblongata. It contains vasomotor, respiratory, vomiting, sleep centers, and cranial nerve nuclei. - **Structure of the brain:** - **Cerebral hemisphere:** has outer gray matter and a core of white matter. - **Outer layer (cortex):** consists of the bodies of nerve cells. Cells aggregate to form Centers. These centers are specialized to perform special functions such as motor, sensory or thinking functions. - **Inner core:** consists of axons that form tracts or pathways. In addition, collections of nerve cells are present inside the brain called basal ganglia (wrong name). They perform special functions. - **The brain contains cavities that are called ventricles.** - Each cerebral hemisphere contains a lateral ventricle. - Between the two thalami there is the third ventricle. - Between the brain stem and the cerebellum is the fourth ventricle. - The ventricles are filled with cerebrospinal fluid (CSF). - **The Spinal Cord:** - **Length:** 42 cm in females and 45 cm in males. - **Location:** occupies the upper two-thirds of the vertebral canal. - **Beginning:** below foramen magnum as continuation of medulla oblongata. - **End (differs with age):** lower end is conical and called conus medullaris. - **During early embryonic life:** The spinal cord fills the vertebral canal. - **In newborns:** at the level of L3 (third lumbar vertebra). - **In adults:** at the level of the lower border of L1 or the disc between L1 and L2. This is because the vertebral column grows faster than the spinal cord. - **Segments:** 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. - **Enlargements:** - **Cervical enlargement:** from C5 to T1 (origin of brachial plexus). - **Lumbo-sacral enlargement:** from L2 to S2 (origin of lumbo-sacral plexus). - **Fissures and Sulci:** - **Anterior median fissure:** a deep fissure on the anterior surface. - **Posterior median sulcus:** a shallow midline groove on the posterior surface. - **Anterior lateral sulcus:** one on each side. It marks the attachment of the ventral root. - **Posterior lateral sulcus:** one on each side . It marks the attachment of the dorsal root. - **Posterior intermediate sulcus:** separates the gracile tract from the cuneate tract. - **Structure of the spinal cord:** unlike cerebral hemispheres, it has an inner gray matter and an outer white matter. - **Gray matter:** H-shaped in cross section; consists mainly of nerve cell bodies. - It has 2 anterior horns (contains cell bodies of motor cells), 2 posterior horns (contains bundles of axons of nerve cells called tracts), and 2 lateral horns (contain autonomic nerve cell bodies - sympathetic from T1 to L2 and parasympathetic from S2 to S4). - **White matter:** consists of axons of nerve cells - **Central canal:** has a central cavity that corresponds to the brain ventricles. - **Relation of Spinal Cord Segments to Vertebrae:** - Spinal cord segments are present higher than the corresponding vertebrae due to faster growth of the vertebral column than the spinal cord. - **Cervical region:** segment is one spine higher than corresponding spine. (C6 segment is opposite C5 spine). - **Upper thoracic region:** segment is 2 spines higher than corresponding spine (T5 segment is opposite T3 spine). - **Lower thoracic region:** segment is 3 spines higher than corresponding spine (T 10 segment is opposite T7 spine). - **All sacral segments:** lie opposite T12 and L1 spines. - **Coverings of the Central Nervous System (CNS)** - **Skeletal Coverings:** - **Brain:** covered by bones of the cranium (calvaria). - **Spinal cord:** covered by a cylindrical case of bone (vertebral canal). - **Meningeal Coverings:** - **Pia mater:** delicate membrane adherent to the brain and contains arteries and veins. Extends downward from the conus medullaris as filum terminale. - **Arachnoid mater:** delicate membrane that has neither arteries nor veins between pia and dura. It is connected to pia by arachnoid trabeculae. It extends downward around the spinal cord and ends at the level of S2 vertebra. - **Dura mater:** outer dense, strong fibrous layer. It is formed of 2 layers: - **Outer endosteal layer:** endosteum of the skull. - **Inner meningeal (fibrous) layer:** the 2 layers separate in some areas to form venous spaces called venous sinuses. Spinal dura (around the spinal cord) is formed of the meningeal layer only. Spinal dura ends at the level of S2. - **Meningeal Spaces:** - **Epidural space:** potential space between dura and skull bones and the vertebral canal. The cranial epidural space contains meningeal vessels. The spinal epidural space contains the internal vertebral venous plexus. - **Subdural space:** potential space between dura and arachnoid maters. Contains superficial cerebral veins on their way to dural venous sinuses. - **Subarachnoid space:** space located between arachnoid and pia maters. It contains CSF. It is dilated below the conus medullaris forming the Lumbar cistern. - **Blood Supply of CNS:** - **Blood Supply of Brain:** - **Internal carotid and vertebral arteries:** supply blood to the brain. - **Brain veins and venous sinuses:** drain to internal jugular veins then to the heart. - **End arteries:** common in the brain. If end arteries fail to supply blood to a specific area, that area will die (cerebral stroke). - **Blood Supply of Spinal Cord:** - **Spinal cord:** supplied by spinal and radicular arteries. - **The venous blood:** drained by the vertebral plexuses of veins. - **Cerebro-Spinal Fluid (CSF):** - Clear fluid found in cavities of the CNS which are the ventricles of the brain, sub-arachnoid space, and central canal of the spinal cord. #### Peripheral Nervous System - **Cranial Nerves:** - 12 pairs (I to XII), which are connected to the brain. All arise from the brain stem except olfactory (from the nose) and optic (from the retina): - **Olfactory Nerve (I):** pure sensory nerve; carries the information of the sense of smell. It may regenerate after injury. Injury causes loss of smell. - **Optic Nerve (II):** pure sensory nerve; carries the information of the sense of vision from the retina to the brain. It never regenerates after injury. It is considered part of the brain as it is covered by meninges and surrounded by CSF. It is the mirror of the brain. Injury causes loss of vision (blindness). - **Oculomotor Nerve (III):** motor nerve; supplies all muscles of the eye except the superior oblique and lateral rectus muscles. Injury causes ophthalmoplegia. Contains autonomic fibers. - **Trochlear Nerve (IV):** motor nerve; supplies one muscle of the eye (the superior oblique) which moves the eye downwards and lateral. Injury causes vertical squint and may be double vision. - **Trigeminal Nerve (V):** mixed nerve; its sensory part receives general sensation from the face and the anterior 2/3 of the tongue. Supplies all muscles of mastication (chewing). Contains autonomic fibers to the salivary glands in the mouth and lacrimal gland. It has 3 large branches - Ophthalmic, Maxillary and Mandibular. Irritation of the trigeminal nerve causes Trigeminal Neuralgia which is severe pain in the area of distribution of the nerve. - **Abducent Nerve (VI):** motor nerve; supplies one muscle of the eye (the lateral rectus) which moves the eye laterally. Injury causes lateral squint and may be double vision. - **Facial Nerve (VII):** mixed nerve; its sensory part receives taste sensation from the anterior 2/3 of the tongue. Its motor part supplies all muscles of expression (face). Contains autonomic fibers to the parasympathetic ganglia of the head and neck. Injury of the facial nerve causes Facial Palsy. - **Vestibulo-cochlear Nerve (VIII):** transmits sound and equilibrium (balance) information from the inner ear to the brain. Injury may cause hearing loss, vertigo, loss of equilibrium, motion sickness, nystagmus and tinnitus. - **Glossopharyngeal Nerve (IX):** mixed nerve; contains general sensory fibers from the posterior one third of the tongue, external ear and upper pharynx. Contains special sensory fibers that receive taste from the posterior one third fo the tongue (bitter and sour taste). Contains motor fibers to the stylopharyngeus muscle of the pharynx which helps swallowing. Contains autonomic parasympathetic fibers to the parotid salivary gland. Contains afferent visceral fibers from carotid sins and aortic bodies (baroceptors and chemceptors) which adjust blood pressure and blood pH respectively. Damage to the nerve causes loss of bitter and sour tastes and impaired swallowing. Irritation of the nerve causes Glossopharyngeal Neuralgia which is severe pain in the ear, back of the tongue, upper pharynx and throat. The pain is precipitated by chewing, coughing, laughing and swallowing. - **Vagus Nerve (X):** mixed nerve; considered a very important parasympathetic source to control heart rate, gastrointestinal movement, respiratory passages, and sweating. Contains general sensory fibers from the most posterior part of the tongue and skin behind the auricle. receives taste from the most posterior part of the tongue. Contains motor fibers to the larynx to produce sounds and speech. Contains afferent visceral fibers from carotid sins and aortic bodies (baroceptors and chemceptors) to adjust blood pressure and blood pH respectively. Irritation of the vagus may cause bradycardia and even cardiac arrest. Vagal triggering areas are the carotid bulb in the neck, epigastrium and testicles. A blow to the vagal trigger zone may cause cardiac arrest. - **Accessory Nerve (XI):** pure motor nerve; has spinal and cranial parts and supplies 2 important muscles - trapezius and sternomastoid. Injury affects sternomastoid and upper trapezius. - **Hypoglossal Nerve (XII):** motor nerve of the tongue. When injured the tongue points to the affected nerve. - **Spinal Nerves:** - 31 pairs, distributed as follows: - **Cervical region:** 8 - **Thoracic region:** 12 - **Lumbar region:** 5 - **Sacral region:** 5 - **Coccygeal region:** 1 - **Formation:** Each spinal nerve, except C1 and coccygeal nerves arise by 2 roots: - **Ventral Root:** motor (efferent) - Motor axons of the anterior horn cells to supply the skeletal muscles. - Autonomic axons of lateral horn cells (T1 to L2 and S2 to S4) to viscera. - **Dorsal Root:** sensory (afferent) - Dorsal root ganglion which contains pseudounipolar cells. - The 2 roots join at the intervertebral foramen to form the spinal nerve trunk. - **Branches (Divisions):** nerve trunk divides immediately into 2 primary rami: - **Anterior (Ventral) Primary Ramus (larger in size):** - Runs anteriorly and may join each other to form plexuses. - Attached to the sympathetic ganglion by 2 rami communicants - white ramus (myelinated) and gray ramus (unmyelinated). - **Posterior (Dorsal) Primary Ramus (smaller in size):** - Doesn't share in the formation of plexuses. - Runs backward to supply muscles and skin of the back. - Not attached to the sympathetic ganglia. #### Autonomic Nervous System - **Formation:** consists of the ***sympathetic system*** (Thoraco-Lumbar outflow) and the ***parasympathetic system*** (Cranio-sacral outflow). For - **Preganglionic fibers:** arise from a nucleus in the brain stem or spinal cord and relay in the autonomic ganglia. - **Autonomic ganglia:** sympathetic or parasympathetic. - **Postganglionic fibers:** arise from the autonomic ganglia to supply organs. - **Origin:** - **Sympathetic system:** originate form lateral horn cells of the spinal cord segments from T1-L2 or L3. Sympathetic fibers accompany corresponding spinal nerves to reach sympathetic ganglia through white rami communicans. - **Para-sympathetic system:** - **Cranial outflow:** originates from the brainstem via III, VII, IX and X nerves. - **Sacral outflow:** from spinal cord segments S2, 3, 4 via S2, 3, 4 nerves. - **Function:** - **Sympathetic system:** inhibitory to everything except the heart. It causes vasoconstriction, decreased peristalsis of the gut, contraction of the sphincters and acceleration of the heart. - **Para-sympathetic system:** opposes the sympathetic system. It is excitatory (secretomotor) to everything except the heart. It increases glandular secretion and peristalsis of the gut. It causes relaxation of the sphincters and inhibition of the heart. - **Ganglia:** - **Sympathetic Ganglia:** - **Paravertebral Ganglia:** 2 sympathetic chains around the vertebral column. - **Prevertebral Ganglia:** in the abdomen in front of the vertebral column. - **Para-sympathetic (Terminal) Ganglia:** are present in or near visceral walls. ### Terminology of Nervous System - **Neuron:** functional and structural unit fo the nervous system. - **Neuroglial cells:** supporting cells - **Nucleus:** collection of nerve cells inside the central nervous system. - **Ganglion:** collection of nerve cells outside the central nervous system. - **Synapse:** site of functional contact between nerve cells or between a nerve cell and an effector organ such as muscle or gland. - **Nerve:** collection of bundles of axons (nerve fibers). - **Bundle:** collection of axons with different origin, termination and function. - **Tract:** collection of axons, with the same origin, termination and function. - **Commissure:** band of nerve fibers connecting the right and left halves of the brain or spinal cord. ### Techniques Used for Visualization of Nervous System 1. **Computerized Tomography (CT Scan):** CT Scan produces cross sections of any part of the body including the brain. 2. **Magnetic Resonance Imaging (MRI):** MRI produces cross sections of any part of the body like the CT Scan. It is safer (does not use radiation) and provides better resolution sections than the CT Scan. Inventors of MRI have been awarded a Nobel prize for medicine in 2003. 3. **Positron Emission Tomography (PET Sccan):** - New and safe technique that studies brain anatomy and functions. - A radiotracer is injected into a blood vessel. It is concentrated in tissues of interest. - Decay of the radiotracer results in positron emission which can be traced and imaged. - Especially used in differentiating different types of tumors and metastasis. 4. **Cerebral Angiography:** Radiographic visualization of cerebral blood vessels after injecting a contrast medium. It's important in detecting cerebrovascular diseases such as vascular stenosis or aneurysms. ### Higher Brain Function: Cortical Areas of The Brain - **Personality center:** - **Site:** frontal pole (anterior to the premotor area). - **Function:** 1. Makeup of personality 2. Regulation of depth of feeling and reactions (behavior) to situations (comedy or drama). 3. Higher intellectual functions, such as production of ideas and judgment. - **Lesion:** Loss of personality and appreciation for any social behavior. - **Motor areas:** - **Primary motor area (area 4):** - **Site:** precentral gyrus, anterior wall of the central sulcus and paracentral lobule (anteriorly). - **Body Representation:** opposite 1/2 of the body is represented upside down. - **Lower 1/3:** head region. - **Upper 2/3:** neck, upper limb, trunk, hip, thigh, knee and then the leg, foot, and perineum in the paracentral lobule. - **Functions:** initiation of highly skilled movements such as playing piano and typing. - **Arterial supply:** - Anterior cerebral artery (upper 1/4 and paracentral lobule). - Middle cerebral artery (lower 3/4). - **Lesion:** Contralateral hemiplegia with all signs of upper motor neuron lesion. - **Premotor area (area 6):** - **Site:** anterior to motor area. - **Function:** - **Stereotyped movements of groups of muscles via connections with basal ganglia.** - **Execution of learned motor activity.** - **Lesion:** apraxia; difficulty in performing a learned movement without paralysis. - **Motor speech area (Broca's area, areas 44 and 45):** - **Site:** posterior part of the inferior frontal gyrus of the dominant hemisphere. - **Function:** coordinates actions of speech muscles (lips, tongue, and larynx). - **Arterial supply:** middle cerebral artery. - **Lesion:** - **Motor aphasia (expressive aphasia):** paralysis of speech. - **Lesion in non-dominant hemisphere (usually right):** no effect. - **Frontal eye field area (area 8):** - **Site:** posterior part of the middle frontal gyrus. - **Function:** horizontal movement of both eyes opposite side. - **Arterial supply:** middle cerebral artery. - **Lesion:** ipsilateral deviation of both eyes due to unopposed action of intact area 8. - **Sensory areas:** - **General (somatic) sensory area (areas 3, 1, 2):** - **Site:** postcentral gyrus, posterior wall of the central sulcus and posterior part of the paracentral lobule. - **Input:** main sensory thalamic radiation from the ventral posterior thalamic nucleus for perception of all sensations from the opposite side except olfaction. - **Representation of the body:** similar to the motor area (area 4). - **Arterial supply:** similar to the motor area (area 4). - **Lesion:** - **Acute stage :** loss of all sensations on the opposite side of the body and face. - **After recovery:** crude pain, temperature and touch return (represented at the thalamus). - **Somatic sensory association area (areas 5, 7 and 40):** - **Site:** superior parietal lobule (area 5, 7) and the supramarginal gyrus (area 40). - **Function:**stereognosis and interpretation of senses perceived in the general sensory area. - **Arterial supply:** middle cerebral artery. - **Lesion:** - **Astereognosis:** inability to recognize objects by touch when the eyes are closed. - **Unilateral neglect (lesion in area 40):** inability to recognize left from right. - **Primary Gustatory area (taste area, area 43):** - **Site:** lower end of the general sensory area. - **Function:** discrimination of different taste sensations. - **Primary auditory area (Heschl's area, areas 41 and 42):** - **Site:** in the middle of the upper surface of the superior temporal gyrus. - **Input:** auditory radiation from the medial geniculate body for the perception of sounds from the two ears, mainly from the opposite ear. - **Arterial supply:** middle cerebral artery. - **Lesion:** bilateral diminution of hearing, mainly on the opposite side. - **Auditory association area (Wernicke's area, area 22):** - **Site:** in the dominant hemisphere in the posterior part of the superior temporal gyrus. - **Function:** recognition of sounds. A sensory speech area (we learn by hearing). - **Arterial supply:** middle cerebral artery. - **Lesion:** auditory agnosia and sensory aphasia (unable to understand spoken language). - **Primary visual area (area 17):** - **Site:** lips of the calcarine sulcus (above and below the calcarine sulcus). - **Input:** optic radiation from the lateral geniculate body for the perception of light. - **Retina representation:** temporal fibers (same eye) and nasal fibers (opposite eye): - **Macula:** posterior 1/3 of the calcarine sulcus. - **Upper part of the retina:** above the calcarine sulcus (cuneus). - **Lower part of the retina:** below the calcarine sulcus (lingual gyrus). - **Arterial supply:** posterior cerebral artery. - **Lesion:** contralateral homonymous hemianopia with macular sparing. - **Visual association area (areas 18, 19, and 39):** - **Site:** - **Areas 18 and 19:** are present above and below the primary visual area 17. - **Area 39:** in the angular gyrus. - **Function:** - **Recognition of what we see (association area).** - **Color vision:** is localized in the inferior association area. - **Angular gyrus:** comprehension of written language. - **Arterial supply:** posterior and middle cerebral arteries. - **Lesion:** - **Visual agnosia:** inability to recognize what we see. - **Loss of color vision** in lesions of the inferior association area. - **Alexia (inability to read) and agraphia (inability to write):** lesions of the angular gyrus. - **Primary Vestibular area:** - **Site:** face area of general sensory area and the anterior part of the superior temporal gyrus. - **Function:** conscious awareness of the position of the body in space. - **Arterial supply:** middle cerebral artery. - **Lesion:** disorientation in space. - **Primary olfactory area:** - **Site:** Uncus - **Function:** receive sense of olfaction. - **Lesion:** irritation of the uncus causes olfactory hallucinations. - **Olfactory association area (area 28):** - **Site:** anterior part of the parahippocampal gyrus (area 28) and amygdaloid nucleus. - **Function:** discrimination of different odors. - **Sensory speech areas (areas 22, 39, and 40):** - **Site:** in the following areas of the dominant hemisphere: - **Wernicke's area (area 22):** for spoken language. - **Angular gyrus (area 39):** for written language. - **Supramarginal gyrus (area 40):** - **Formulation of speech related to size, shape, and texture of objects via connections with the general sensory area.** - **Recognition of an individual's body image (left from right side).** - **Connection:** sensory speech areas are connected with the motor speech area (Broca's area) by the superior longitudinal fasciculus to answer a spoken or a written question. - **Arterial supply:** middle cerebral artery. - **Lesion in the dominant hemisphere:** - **Lesion in Wernicke's area:** - **Sensory aphasia:** total inability to understand spoken or written language. - **Auditory agnosia:** inability to recognize sounds and to repeat sentences. - **Lesion limited to the angular gyrus:** - **Alexia:** inability to read (the visual information is not processed in area 39). - **Agraphia:** inability to write. - **Lesion limited to the supramarginal gyrus:** - **Tactile agnosia (astereognosis):** inability to recognize objects by touch (eyes closed). - **Unilateral neglect:** inability to recognize his left from right side. - **Lesion in non-dominant hemisphere:** Disturbances in drawing and in construction. ### Higher Brain Functions: Disorders 1. **Aphasia:** language disorder due to a lesion in the dominant hemisphere. - **Global aphasia:** the patient is unable to speak, read or write. It is due to an extensive lesion involving Broca's area, the inferior parietal lobule, the angular gyrus, Wernicke's area and the point of confluence between parietal, occipital, and temporal lobes. - **Motor aphasia:** lesion is in Broca's area; words are difficult to say. The patient unable to speak but the language is understood and the ability to write is normal. - **Sensory aphasia:** lesion is in Wernicke's area. Speech is fluent, but words are meaningless (word salad). No understanding of spoken or written language. - **Conduction aphasia:** lesion is in the arcuate bundle that connects Wernicke's area with Broca's area. The same as sensory aphasia but the patient is able to understand written and spoken language without the ability to produce them. 2. **Agnosia:** inability to recognize a stimulus by any given sense even though the sensory pathway, primary sensory cortex and mental status are intact. - **Tactile agnosia (astereognosis):** inability to recognize objects by touch due to the supramarginal gyrus legion or a defect in the somatic sensory association areas. - **Astatognosia:** inability to recognize the position of body parts in the space caused by the localized lesion in the sensory association area of the parietal lobe. - **Visual agnosia:** inability to recognize objects by vision. It's due to the lesion in the visual association areas (areas 18 and 19). It may be general or limited as in: - **Prospagnosia:** inability to recognize faces (face blindness) due to the localized lesion in the visual association area (at the medial temporo-occipital junction). - **Dyslexia:** inability to recognize written words or the meaning of written words (word blindness) due to the lesion in the association area of the dominant occipital lobe. - **Auditory agnosia:** inability to recognize familiar sounds. It's due to the lesion in Wernicke's area (area 22) of the dominant hemisphere. 3. **Apraxia:** inability to perform a certain motor activity without paralysis: - **Motor apraxia (callosal apraxia):** inability to perform motor activity upon oral command although it is normally done spontaneously. It's due to the lesion in the corpus callosum or premotor area 6. For example, when asked the patient to open the door with his key, he's not able to but instead shakes his waist. - **Speech apraxia:** the patient is unable to produce words although the bulbar muscles are intact and able to produce other motor actions such as mastication. The lesion is in Broca's area and the lower part of primary motor area 4. - **Writing ap