Brain & Cranial Nerves

Brain & Cranial Nerves - Brain & Cranial Nerves...

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Unformatted text preview: Brain & Cranial Nerves Rostral Caudal Landmarks of the Brain • The brain is divided into three major portions – cerebrum – cerebellum – brainstem Embryonic Development •The nervous system develops from ectoderm, the outermost germ layer of an embryo •By the third week of development, a dorsal streak called the neuroectoderm appears along the length of the embryo •The neuroectoderm eventually thickens to form the neural plate •gives rise to all neurons and glial cells except the microglia (comes from mesoderm) •The neural plate sinks and forms a neural groove with a raised neural fold along each side •The neural fold fuses along the midline creating a hollow channel called the neural tube. •forms the motor nerves, the central of the cord, and the ventricles of the brain As the neural tube develops, ectodermal cells along the margin, called the neural crest, separate to other locations and becomes •neural sensory cells, •sympathetic neurons, •Schwann cells, •and other types of cells By the end of the fourth week, the neural tube exhibits the three dilations called the forebrain, midbrain, and hindbrain Gross Anatomy of the Brain • Forebrain(Prosencephalon) – telencephalon • Cerebral Hemispheres – Cerebral Cortex Basal ganglia Basal forebrain nuclei Amygdaloid Nucleus – diencephalon • Thalamus and Hypothalamus • Midbrainmesencephalon • Hindbrain(Rhombencephalon) – metencephalon • Pons and Cerebellum – mylencephalon • Medulla Oblongata Forebrain (Prosencephalon) – telencephalon • Cerebral Hemispheres – Cerebral Cortex Basal ganglia Basal forebrain nuclei Amygdaloid Nucleus – diencephalon • Thalamus and Hypothalamus Midbrain (mesencephalon) Hindbrain (rhombencephalon) – metencephalon • Pons and Cerebellum – mylencephalon • Medulla Oblongata Midbrain (mesencephalon) • • • • tegmentum-rostral part of the brainstem superior colliculus- important for visual system reflexes inferior colliculusimportant for auditory system function. cerebral peduncle- huge bundle of axons traveling from the cerebral cortex into/ through the brainstem; fibers are important for voluntary motor function. • red nucleus (not shown) - normal motor function • substantia nigra (not shown)- normal motor function Cerebrum • 83% of brain • two hemispheres • Gyri- thick folds • Sulci- shallow grooves on the brain surface • longitudinal fissure- deep grooves that separates hemispheres Cerebrum Corpus Callosum •prominent landmark for anatomical description •located at the bottom of the longitudinal fissure •is a bundle of nerve fibers that connect the hemispheres Cerebrum • prominent sulci divide each hemisphere into five anatomically and functionally distinct lobes – frontal • – parietal • – – parieto-occipital sulcus- caudal boundary occipital temporal • – central sulcus- posterior boundary lateral sulcus- separate from parietal lobe insula- deep to the lateral sulcus Cerebral Histology • Cerebral cortex is a 2-3mm thick layer of tissue covering the cerebrum which contains about 40% of the mass of the brain with about 14-16 billion neurons. • Composed of two principal types of neurons – Stellate cells- have spherical somas with dendrites projecting for short distances in all directions • are concerned with receiving sensory input – Pyramidal cells- tall and triangular with an apex that points toward the brain surface and has thick dendrite with many branches and small knobby dendritic spines • are the output neurons that transport signals to other parts of the CNS Cerebral Histology • About 90% of the cerebral cortex is a six layered tissue called the neocortex because of it recent evolutionary development. • The layers are numbered I (outer layer) to VI (most inner layer) and vary from one part of the cerebrum to another in thickness, cellular composition, synaptic connections, size of neurons, and destination of their axons. – layer IV is thickest in sensory regions and layer V in motor regions – all axons that leave the cortex and enter the white matter arise from layers III, V, and VI. Cerebral Cortex Histology • • • • • • (1) Plexiform layer (molecular layer)- mostly fibers running parallel to surface, neuroglial cells, and a few horizontal cells of Cajal (2) Outer granular cell layer; small pyramidal cells (stellate cells) (3) a layer of medium pyramidal cells (4) Inner granular layer; many small granule cells (stellate cells) (5) Large pyramidal cells (Betz cells) (6) a layer of polymorphic cells- cells with diverse shapes (fusiform cells) Pyramidal cells• recognized by their relatively large somata and by their prominent apical dendrites (i.e., the upward "apex" on the "pyramid"). – • "owl-eye" or "fried-egg" nuclei. The giant Betz cells are extremely large pyramidal cells of the motor (precentral) cortex. Meninges (three fibrous membranes that enclose the brain and spinal cord) • Same as those of the spinal cord – dura mater (pachymeninx) • composed of relatively avascular connective tissue. • there are two major dural folds in the cranium: – FALX CEREBRI - a fold lying in the longitudinal fissure between the cerebral hemispheres. – TENTORIUM CEREBELLI - a horizontal fold separating the cerebral hemispheres from the cerebellum. – arachnoid mater – pia mater Dura Mater • Composed of relatively avascular connective tissue. • There are two major dural folds in the cranium: – FALX CEREBRI - a fold lying in the longitudinal fissure between the cerebral hemispheres. – TENTORIUM CEREBELLI - a horizontal fold separating the cerebral hemispheres from the cerebellum. • has a protective function – it prevents shuddering movements of the brain within the cranial cavity and the folds prevent damage to nervous tissue during sudden rotational movements. • In the cranial cavity the dura adheres to the periosteum lining the cranium, so there is no EPIDURAL SPACE, except at the venous sinuses. • In the vertebral canal, the spinal dura is separated from the periosteum of the vertebrae by a space containing epidural fat and the veins which drain the spinal cord. Injection of local anaesthetic Epidural Epidural Arachnoid Mater • Internal to the dura mater • Is an avascular membrane • Lies between the pia mater internally and the dura mater externally • It is separated from the pia mater by the subarachnoid cavity or space, which is filled with cerebrospinal fluid. • Called arachnoid because the cobweblike trabeculae crossing the subarachnoid spave to become continuous with the pia mater. Pia Mater • A delicate translucent membrane that closely contours the spinal cord and brain • Acts as a floor and anchor for the blood vessels that travel over the surface of the brain periosteal layer meningeal layer • the dura in the cranial cavity consist of two layer – periosteal layer- equivalent to the periosteum of the cranial bone, lies close to the bone with no epidural space – meningial layer- continues into the vertebral column • the two layers are separated in places by the dural sinuses (spaces that collect blood that has circulated through the brain) • In certain places, the meningeal layer of the dura mater folds inward to separate major parts of the brain – falx cerebre- extends into the longitudinal fissure between the right and left cerebral hemispheres – tentorium cerebelli- stretches like a roof over the posterior cranial fossa and separates the cerebellum from the overlying cerebrum Cranial Cavities • Anterior cranial fossa • Middle cranial fossa • Posterior cranial fossa Flax Cerebri A A. Superior sagittal sinus B B. Inferior sagittal sinus E C. Falx cerebri (dual fold) C D. Confluence of sinuses E. Dura mater (meningeal layer) D A. Tentorium cerebelli B. Midbrain tegmentum C. Temporal bone(Petrous part) D. Inferior sagittal sinus E. Confluence of sinuses F. Transverse sinus G. Sigmoid sinus . superior saggital sinus inferior saggital sinus straight sinus transverse sinus • The separations of the two layers of the dura mater create the dural venous sinuses. The venous sinuses receive the blood from the veins draining the brain, and this blood flows from the venous sinuses to the internal jugular veins. The walls of the sinuses are line by endothelium. J. Cavernous K. Superior Sagittal • The brain has four internal chambers called ventricles – lateral ventricles- two lateral ventricles, one in each cerebral hemisphere – third ventricles- beneath the corpus callosum and surrounded by the thalamus. – fourth ventricle- between the hemispheres of the cerebellum. Ventricles • • • • • interventricular foramen (Foramen of Monro)- tiny passage that connects lateral ventricles to the third ventricle cerebral aqueduct (aqueduct of Sylvius )- small canal that passes down the core of the midbrain and leads to the fourth ventricle (a small chamber between the pons and cerebellum central canal- extension of the fourth ventricle through the medulla oblongata into the spinal cord. Foramina of Luschka- One of the two lateral openings draining the fourth ventricle into the subarachnoid space at the cerebellopontine angle. Foramen of Magendie-, medially connects the ventricle with the subarachnoidal space. Ependymal Cells • Ciliated cells that line the brain's ventricles and the spinal cord's central canal and which circulates the spinal fluid inside the brain ventricles and the connecting central canal of the spinal cord. Choroid Plexus • • • • • • Found on the walls or roof of each of the four ventricles. Formed by an invagintion of the vascular pia mater ( the tela choroidea ) The epithelium that lines the choroid plexus is classified as simple cuboidal. The cells will exhibit cilia and microvilli at their free surface. This epithelial lining continues into the spinal cord and forms the ependyma. Using materials brought in the circulation, the cells of the choroid plexus synthesize the components of the cerebrospinal fluid and secrete it into the lumen of the ventricles. •Arachnoid Villi- cauliflower like extensions of the arachnoid that protrudes through the dura mater into the superior sagittal sinus •CSF penitrates through the walls of the arachnoid villi and mixes with the blood in the sinus •CSF produced in the lateral ventricles pass througth the interventricular foramina ( of Monro ) to the third ventricle •and then through the cerebral aqueduct (of Sylvius ) into the fourth ventricle. •The CSF reaches the subarachnoid space through the median aperture ( of Magendie ) and through the lateral apertures ( of Luschka ) of the fourth ventricle. •flows upward over the medial and lateral surfaces of the cerebral hemispheres toward the superior sagittal sinus, •is taken up by the arachnoid granulations Arachnoid Granulations (Villi) • This is where the cerebrospinal fluid produced in the choroid plexuses of the ventricles and which has circulated out of the foramina of Magendie and Luschka and into the subarachnoid space is reabsorbed. • The nodular white excresences seen here over the cerebral hemispheres at the vertex on both sides of the central fissure with falx cerebri of the brain are the arachnoid granulations. Cerebrospinal fluid • produced by the choroid plexuses of the lateral, third and fourth ventricles. • Aids in maintaining the chemical environment of the central nervous system and the removal harmful chemical waste. • provides a protective buoyancy for the brain which effectively makes the weight of the brain 1/30th of its actual weight, • Similar in chemical composition to plasma but with a lot less proteins • The entire CSF is replaced four times a day so that the total amount of CSF produced is approximately 600ml in 24 hours. Frontal Lobe Frontal Lobe • Frontal Lobe– voluntary and planned motor behaviors - such things as voluntary movement of eyes, trunk, limbs and the many muscles used for speech • The motor speech area (Broca's area) is usually in the frontal lobe of the left hemisphere regardless of which hemisphere is dominant for handedness (i.e. the left hemisphere for right handers). – It is one of the main language areas in the cerebral cortex because it controls the motor aspects of speech. – senory reception, and integration of somesthetic, taste, and some visual information Broca's aphasia • • • Aphasia is an impairment of language, affecting the production or comprehension of speech and the ability to read or write. Persons with a Broca aphasia can usually understand what words mean, but have trouble performing the motor or output aspects of speech. ("Expressive," "Nonfluent," or "Motor" Aphasia) Aphasia is always due to injury to the brainmost commonly from a stroke, particularly in older individuals. normal Yes ... ah ... Monday ... er Dad and Peter H ... (his own name), and Dad ... er hospital ... and ah ... Wednesday ... Wednesday nine o'clock ... and oh ... Thursday ... ten o'clock, ah doctors ... two ... an' doctors ... and er ... teeth ... yah. Motor Homunculus primary motor cortex • is one of the principal areas involved in motor function. • The role is to generate neural impulses that control the execution of movement. • the left hemisphere of the brain controls the right side of the body, and the right hemisphere controls the left side of the body. Other Cortical Regions Involved in Motor Function (Secondary Motor Cortices) • posterior parietal cortexinvolved in transforming visual information into motor commands. – Ex: determining how to steer the arm to a glass of water based on where the glass is located in space. • premotor cortex-involved in the sensory guidance of movement, and controls the more proximal muscles and trunk muscles of the body. – Ex: the premotor cortex would help to orient the body before reaching for the glass of water. • supplementary motor area (SMA)- It is involved in the planning of complex movements and in coordinating two-handed movements. • • • • • • • Neurons in M1, SMA and premotor cortex give rise to the fibers of the corticospinal tract. the only direct pathway from the cortex to the spine is the main pathway for control of voluntary movement in humans. fibers descend through the brainstem where the majority of them cross over (disscusates) to the opposite side of the body. there are other motor pathways which originate from subcortical groups of motor neurons (nuclei). These pathways control posture and balance, coarse movements of the proximal muscles, and coordinate head, neck and eye movements in response to visual targets. Subcortical pathways can modify voluntary movement through interneuronal circuits in the spine and through projections to cortical motor regions. Parietal Lobe Concerned with sensory reception and integration of somesthetic (touch, pressure, stretch, movement, heat, cold, and pain), taste, and some visual informatioan Sensory Homunculus Parietal Lobe • Right Parietal Lobe - Damage to this area can cause visuo-spatial deficits (e.g., the patient may have difficulty finding their way around new, or even familiar, places). • Left Parietal Lobe - Damage to this area may disrupt a patient's ability to understand spoken and/or written language) Various parts of it are important for the sense of hearing, for certain aspects of memory, and for emotional/affective behavior. Temporal Lobe Temporal Lobe • Various parts of it are important for the sense of hearing, for certain aspects of memory, and for emotional/affective behavior. • Right Lobe - Mainly involved in visual memory (i.e., memory for pictures and faces). • Left Lobe - Mainly involved in verbal memory (i.e., memory for words and names). Wernicke's aphasia • associated with the ability to understand and produce meaningful speech • Individuals with Wernicke's aphasia speak extremely fluently but with no informative purpose ("fluent aphasia“, receptive aphasia) normal Well this is .... mother is away here working her work out o'here to get her better, but when she's looking, the two boys looking in other part. One their small tile into her time here. She's working another time because she's getting, too. Occipital Lobe It is crucial for the sense of sight. Basal Ganglia: Subcortical Nuclei Involved in Movement • A group of nuclei lying deep in the subcortical white matter of the frontal lobes that organizes muscle driven motor movements of the body behavior. • The caudate, putamen, and the globus pallidus are the major components. • Functionally associatied with the subthalamic nucleus (located in the lateral floor of the diencephalon) and the substantia nigra (in midbrain) are often included. Caudate Nucleus • • An elongated, arched gray mass closely related to the lateral ventricle throughout its entire extent and consisting of a head, body, and tail. The caudate nucleus and putamen form a functional unit (the neostriatum) of the corpus striatum that control voluntary movement. The caudate organizes and filters information that is sent to the frontal lobe, particularly information from the limbic system. • striatum (caudate + putamen + nucleus accumbens), •the corpus striatum (striatum + globus pallidus), or • the lenticular nucleus (putamen + globus pallidus) Basal Ganglia • • • The basal ganglia and cerebellum are large collections of nuclei that modify movement on a minute-to-minute basis. Motor cortex sends information to both, and both structures send information right back to cortex via the thalamus. (Remember, to get to cortex you must go through thalamus.) The output of the cerebellum is excitatory, while the basal ganglia are inhibitory. The balance between these two systems allows for smooth, coordinated movement, and a disturbance in either system will show up as movement disorders. Basal Ganglia Responsible for: • Selecting and maintaining purposeful motor activity while suppressing unwanted or useless movement. • Helping monitor and coordinate slow, sustained contractions related to posture and support. • Inhibiting muscle tone throughout the body (proper muscle tone is normally maintained through a balance of excitatory and inihibtory inputs to the neurons that inervate skeletal muscle). • Although there are many different neurotransmitters used within the basal ganglia (principally ACh, GABA, and dopamine) Basal Ganglia • The function of the basal ganglia is often described in terms of a "brake hypothesis". • To sit still, you must put the brakes on all movements except those reflexes that maintain an upright posture. • To move, you must apply a brake to some postural reflexes, and release the brake on voluntary movement. • In such a complicated system, it is apparent that small disturbances can throw the whole system out of whack, often in unpredictable ways. • The deficits tend to fall into one of two categories: – the presence of extraneous unwanted movements – or an absence or difficulty with intended movements. Lesions of the Basal Ganglia Parkinson's disease, • results from the slow and steady loss of dopaminergic neurons in Substantia nigra pars compacta (SNpc). • The three symptoms usually associated with Parkinson's are tremor, rigidity, and bradykinesia. – The tremor is most apparent at rest. – Rigidity is a result of simultaneous contraction of flexors and extensors, which tends to lock up the limbs. – Bradykinesia, or "slow movement", is a difficulty initiating voluntary movement, as though the brake cannot be released. • A normally pigmented substantia nigra is seen grossly in the midbrain on the right, but the midbrain on the left from the patient with Parkinson's disease shows a pale substantia nigra. A normally pigmented substantia nigra is seen on the left, but the patient with Parkinson's disease has decreased neurons and pigment as seen microscopically at the right. Lesions of the Basal Ganglia Huntington's disease, or chorea • is a hereditary disease of unwanted movements. • It results from degeneration of the caudate and putamen, and produces continuous dance-like movements of the face and limbs. • A related disorder is hemiballismus, – flailing movements of one arm and leg, which is caused by damage (i.e., stroke) of the subthalamic nucleus. Choreiform Gait Demonstration • This is a hyperkinetic gait seen with certain types of basal ganglia disorders. There is intrusion of irregular, jerky, involuntary movements in both the upper and lower extremities. Cerebellum • the largest part of the hind brain • consist of – cerebellar hemisphers connected by a narrow bridge-like vermis – three pairs of stalks, cerebellar peduncles connect the crebellum to the brainstem • inferior peduncle to the medulla oblongata • middle peduncle to the pons • superior peduncle to the midbrain – the peduncles are nerve fibers that carry all signals between the cerebellum and the rest of the brain • Receives most of its input from the pons • Spinocerebellar tracts enter through the inferior peduncle • Motor output leaves the cerebellum through the superior peduncle • • • • • • • The cerebellum is known to be the place in the brain where learned movements are stored, therefore, it has a large amount of control over the coordination of movements the cerebellum receives input from various other parts of the brain (and spinal cord). One such brain part is called the inferior olive, which itself receives sensory information from many parts of the brain and spinal cord. It then relays this info to the cerebellum. In the cerebellum, the data are analyzed and a course of action is quickly decided. Each and every piece of information that leaves the cerebellum does so through the Purkinje cells. symptom of damage is ataxia (including the loss of coordination and difficulty with speech) begin to show. tandem gait finger-nose • Each hemisphere exhibits slender, parallel folds called folia (gyri) separated by shallow sulci • Has a cortex of gray matter and a deeper layer of white matter called arbor vitae which exhibits branching and a fernlike pattern Midbrain Midbrain • Contains the rostral end of the reticular formation (which results in the loss of consciousness or coma if impaired). Tectum- rooflike region dorsal to the aqueduct consisting of the Corpora Quadrigemina Corpora Quadrigemina (four twins) • The dorsal or posterior part has the superior colliculus, which is important for visual system reflexes • The inferior colliculus, which is important for auditory system function. Midbrain • The ventral or anterior part has the cerebral peduncle, which is a huge bundle of axons traveling from the cerebral cortex into/ through the brainstem; fibers are important for voluntary motor function. • Red nucleus- so named because they have a pinkish color in fresh Brain specimens, because of an abundant Blood supply. The red nuclei aid in the unconscious regulation and coordination of motor activities. Midbrain Substantia nigra• A nuclear mass between the Tegmentum and Cerebral Peduncles, is a pigmented region of the midbrain with cytoplasmic Melanin Granules that give it a dark grayto-black color. – has interconnections with other Basal Ganglia Nuclei of the Cerebrum and is involved in Coordinating Movement and Muscle Tone. • Sends inhibitory signals to the thalamus and basal ganglia • Degeneration of the neurons leads to muscle tremors of Parkinson’s disease Midbrain • Medial lemniscus- a continuation of the gracile and cuneate tracts of the spinal cord and brainstem • Contains two cranial nerve nuclei that control eye movement: Cranial Nerves III (Oculomotor) and IV (Trochlear). The Cerebellum ("little brain") • The cerebellum is involved in the coordination of movement • it compares what you thought you were going to do (according to motor cortex) with what is actually happening down in the limbs (according to proprioceptive feedback), and corrects the movement if there is a problem. • is also partly responsible for motor learning, such as riding a bicycle. • Unlike the cerebrum, which works entirely on a contralateral basis, the cerebellum works ipsilaterally. • The cerebellum operates in 3's: – there are 3 highways leading in and out of the cerebellum, – there are 3 main inputs, and – there are 3 main outputs from 3 deep nuclei. They are: CEREBELLAR PEDUNCLES – bundles of fibers connecting the cerebellum with the underlying brain stem • There are 3 pairs: – inferior- transmit info about ongoing movement from spinal cord – middle- sensory info from pons – superior-main output path • info to thalamus and brain stem • info to red nucleus of midbrain (red nucleus relays info from cerebellum to spinal cord) The 3 deep nuclei are the • fastigial- is primarily concerned with balance, and sends information mainly to vestibular and reticular nuclei. • interposed, and dentate nuclei- The dentate and interposed nuclei are concerned more with voluntary movement, and send axons mainly to thalamus and the red nucleus. Clinical deficits associated with cerebellar lesions • Dysmetria (inability to correctly judge distance) or past pointing • dysdioadochokinesia- inability to carry out fast alternating movements • intention or movement tremor • nystagmus- eye condition characterised by rapid, jerky eye movements • dysarthria- speech disorder charactorized by slow, weak imprecise, and uncoordinated • hypotonia The diencephalon is part of the forebrain and is located above the midbrain. •It contains two major organs: • thalamus • hypothalamus. The thalamus is a major relay center to the cortex for all sensations except for smell. consists of many nuclei, including the - lateral geniculate nucleus- transmits visual information, - medial geniculate nucleus- transmits auditory information. Hypothalamus • • • • • lies just inferior to the thalamus. governs reproductive, homeostatic and circadian functions. integrates autonomic and endocrine functions with behavior. controls the pituitary gland. coordinates the peripheral (see peripheral nervous system) expression of emotional states. Dm - dura mater; SS - subaracnoid space; A - aracnoid; PM - pia mater Spinothalmic Tract ...
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This note was uploaded on 12/08/2011 for the course AMY 2A taught by Professor Jamesivey during the Spring '06 term at Riverside Community College.

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