ANATOMY___PHYSIOLOGY_I_BRAIN_AND_CRANIAL_NERVES[1] -...

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Unformatted text preview: ANATOMY & PHYSIOLOGY I BIOL 2401 JARED GILMORE M.S., B.S. BIOLOGY PROFESSOR SAN JACINTO COLLEGE BRAIN REGIONS The adult brain is composed of 100 billion neurons and 1000 billion neuroglia. It can be divided into 4 major parts: BRAIN STEM, DIENCEPHALON,CEREBRUM and the CEREBELLUM PROTECTION: 1. cranium 2. meninges: 3 membranes that surround the brain and the spinal cord. a. DURA MATER: tough fibrous membrane b. ARACHNOID: middle membrane ( web-like) c. PIA MATER: inner delicate membrane Between the arachnoid and the pia mater is a space called the SUBARACHNOID SPACE. This contains CSF, cerebrospinal fluid. 3. cerebrospinal fluid: This clear, colorless fluid is produced in the brain by a set of specialized capillaries ( microscopic blood vessels) called the CHOROID PLEXES. It contains substances that include glucose, proteins, some ions, some white blood cells. The CSFs duties include: a. delivery of nutrients to the brain cells and removes some wastes b. allows brain to float in cranium c. shock absorber The brain is not solid, but has spaces within it called VENTRICLES. It is within these ventricles that the CSF is produced by the c.p. from BLOOD, circulated through the ventricles within the brain and through the central canal of the spinal cord, as well as passing outward to the subarachnoid space and circulating the surrounding area of the CNS. EPENDYMAL CELLS line portions of the CSF circulatory pathway and help with the movement of this material. The CSF will gradually be reabsorbed back into the blood at the superior portion of the brain through the ARACHNOID VILLI, finger-like extensions of the arachnoid that pass the CSF back into the blood through the SUPERIOR SAGITTAL SINUS. HYDROCEPHALUS: a condition in which the pathway of the CSF is blocked, usually due to a tumor or an inflammation. In children, this may result in an expansion of the cranium and brain damage. In adults, brain damage can occur. The treatment includes placement of a SHUNT from a ventricle into the abdominal cavities. Flow of Cerebrospinal Fluid MENINGES VENTRICLES BRAIN REGIONS MENINGES BRAIN SUPPLY BLOOD SUPPLY OF THE BRAIN: The brain is well supplied with blood vessels that bring the needed O2 and nutrients to the active cells and removes waste. At the base of the brain is a circle of vessels called the CIRCLE OF WILLIS. The adult brain accounts for only 2% of the total weight of the body, yet is 20% of O2 available in the body. A brief interruption of blood flow causes unconsciousness. If cells are deprived for 4 minutes,they may be permanently injured, due to the rupturing of the lysosomes. Glucose, O2, CO2, water and most lipid soluble substances like alcohol, caffeine and heroin pass rapidly from blood into brain cells. Other substances, like proteins and many antibiotics, will not pass at all. This is due to an unusual anatomical feature of the brain called the BLOOD BRAIN BARRIER. BBB is formed by brain capillaries that are less permeable than other capillaries in the body. The endothelial cells are very tight, and with the astrocytes in the area, are thought to selectively pass some substances and inhibit the passage of others. There are several areas of the brain that lacks the BBB ( 3rd and 4th ventricles). It is thought that some substances can breach the BBB here such as the HIV (AIDS virus) = AIDS-related dementia. BRAIN SUPPLY BRAIN STEM 1. Brain Stem ( medulla oblongata, pons, midbrain = cerebral peduncles, corpora quadrigemina, nuclei) a. medulla oblongata: a continuation of the spinal cord, forming the inferior portion of the brain stem. All ascending tracts (sensory) and descending tracts (motor) connect the s.c. and the brain. ( tract: bundle of neuron fibers within the CNS). The M.O. is an area where DECUSSATION of tracts occurs = crossing over from right to left and left to right. This allows for CONTRALATERAL CONTROL of body. M.O. is involved with many INVOLUNTARY FUNCTIONS. There are clusters of gray matter within the white matter. These gray area concentrations are called NUCLEI and each are composed mostly of cell bodies. Examples: a. Cardiovascular center - regulates rate and force of heartbeat and diameter of vessels. b. Medullary rhythmicity center - adjusts rhythm of breathing. In 1950s = During the polio epidemic, before the development of the vaccine, many ended up on respirators because the polio virus targets the respiratory center of the medulla. c. vomiting center, coughing center. sneezing center, hiccuping center b. pons: ( bridge) This is an area that connects medulla to other portions of the brain.It is composed of tracts. c. midbrain = cerebral peduncles + corpora quadragemina +nuclei 1.cerebral peduncles: fiber tracts that takes information to the brain. 2.corpora quadragemina: 4 bodies on the posterior side of brain. The 2 superior bumps are the SUPERIOR COLICULI, involved with reflex movements of the eyes, head and neck in response to visual stimuli. The 2 INFERIOR COLICULI are involved with reflex movement of the head in response to auditory stimuli. 3. nuclei example: SUBSTANTIA NIGRA – involved with maintaining muscle tone and coordinating movements. The major pathology of this area is PARKINSON ’S DISEASE. Parkinson’s is characterized by tremor of extremities and head as well as rigidity of muscles. DOPAMINE is a inhibitory neurotransmitter, which is produced by the substantia nigra. The level decreases with Parkinson ’s disease because the cells of the nuclei degenerate. It can be treated by administering a precursor of dopamine – L-dopa. Stem cell transplantation from fetal and adult brains is also being investigated. Administering dopamine is not helpful because it cannot cross the blood-brain barrier. The L-Dopa that is administered will be able to cross the BBB and be converted into dopamine by CNS neurons. BRAIN STEM BRAIN STEM CRANIAL NERVES DIENCEPHALON 2. DIENCEPHALON: areas surrounding the 3rd ventricle. Includes thalamus and hypothalamus, as well as the pineal gland. a. thalamus: principal relay area for sensory input going to the cerebral cortex for interpretation. Also important in learning, awareness, strong emotions like fear and rage. It is composed of many nuclei b. hypothalamus: located inferior to the thalamus. Has many nuclei and very important to maintaining homeostasis. There are centers that deal with rage, aggression, thirst, hunger, body temperature, pleasure, feeling of fullness after a meal etc. This area is extremely important in regulation of hormones. c. pineal gland: gland found inside of the brain, the size of a pea. Secretes the hormone MELATONIN, and therefore is an endocrine gland. Seems to be involved with the wake – sleep cycle and perhaps the onset of puberty. DIENCEPHALON CEREBELLUM 3. CEREBELLUM: Occupies the lower posterior aspect of the brain. Each cerebellular lobe is connected by the VERMIS, an area in the center that resembles a worm. The unusual arrangement of white and gray matter resemble a tree and is referred to as the ARBOR VITAE, the tree of life. The main function of this area is control of the muscles of the body that are involved with balancing and constantly receives input from receptors in the muscles, tendons, joints and eyes. Injury to cerebellum results in clumsy, disorganized movements. CEREBELLUM CEREBELLUM CEREBRUM CEREBRUM The cerebrum is supported on the brain stem and composes most of the brain. It consists of 2 HEMISPHERES, which are connected by fiber tracts. The largest fiber tract is the CORPUS COLLOSUM. The surface of the cerebrum is not smooth in higher animals, but has convolution, called gyri (gyrus) and sulci (sulcus).This increases the surface area of the brain and allows space for more neurons. In humans, there is a thin layer of gray matter on the surface of the cerebrum. This cerebral cortex contains billions of unmyelinated neurons that are associated with higher thinking and performance ( reading, speaking, etc.). Under this area, there is white matter which is referred to as the CEREBRAL MEDULLA (not to be confused with the medulla oblongata). There are nerve tracts that fall into 3 main catagories: ASSOCIATION FIBERS – connect areas within the same hemispheres. COMMISSURAL FIBERS – connects one hemisphere to the other. PROJECTION FIBERS – tracts between the brain and parts of spinal cord. Within the medulla are collections of gray matter, mostly NUCLEI ( collections of cell bodies) The cerebrum can also be anatomically divided into 5 different lobes. Frontal, parietal, temporal, occipital and insula ( internal). Within the cerebrum, there will be a group of structures that are collectively referred to as the LIMBIC SYSTEM. This includes areas like the AMYGDALA and the HIPPOCAMPUS which are involved with basic responses such as memory, emotions, reproduction, eating – all concerned with survival. Lesions of this area result in uncontrolled eating, increased sexual activity and loose of fear. One of the major sources of sensory stimulation into the limbic system is olfaction. The sense of smell is vital to many organisms. Some animals can smell water as well as detect PHEROMONES, which are molecules released by one member of a species and causes a reaction in another member of the same species. An example is the pheromones released by a dog when she is in heat . This will attract male dogs to her from as far away as 2 miles. Pheromones appear to also occur in humans and it has been suggested that those released by women during the menstrual cycle will have an effect on the cycle of other women living near them. CEREBRUM CEREBRUM CRANIAL NERVES CRANIAL NERVES NUMBER CN I NAME Olfactory nerve CN II Optic nerve CN III Oculomotor CN IV CN V Trochlear Trigeminal fissure EXAMPLE OF FUNCTION olfaction vision superior orbital fissure eyeball movement a. Ophthalmic branch superior orbital fissure sensory info. from skin around eye “ “ CN VII Facial CN VIII CN IX Vestibulocochlear Glossopharyngeal hearing and balance taste CN X CN XI CN XII Vagus Accessory Hypoglossal controls internal organs swallowing tongue movement superior orbital “ upper jaw rotundum c. mandibular branch CN VI Abducens optic foramen eyeball movement b. maxillary branch Foramen/Fissure cribriform plate of ethmoid f. “ “ “ lower jaw and chewing f. ovale eyeball movement superior orbital fissure secretion of saliva and tears stylomastoid foramen internal auditory meatus Jugular foramen Jugular foramen Jugular f. and f. magnum Hypoglossal canal CRANIAL NERVES BRAIN STRUCTURES OLFACTORY NERVE OPTIC NERVE OCULOMOTOR NERVE TROCHLEAR NERVE TRIGEMINAL NERVE ABDUCENS NERVE FACIAL NERVE VESTIBULOCOCHLEAR GLOSSOPHARYNGEAL VAGUS NERVE SPINAL ACCESORY HYPOGLOSSAL NERVE 12 CRANIAL NERVES ...
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