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U3- anatomy of the nervous system.docx

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PSYC 271
Monica Valsangkar- Smyth

L3 Anatomy of the Nervous System Jan/ 26/12 1. General Layout of the Nervous - The Nervous System is divided between the Central Nervous System System and the Peripheral Nervous System - CNS is composed of the brain and spinal cord and consists of 12 Central nervous System pairs of cranial nerves with sensory or motor functions Peripheral Nervous System o Ex. If one of the optic nerves are damaged, you can lose sight in that eye. o If there is a lesion in the visual cortex, you can only see in the central region of the visual field. - PNS is comprised of somatic and autonomic nervous systems and have nerves that project from the spinal cord - The Somatic Nervous system (SNS) is the part of the PNS that Afferent nerves interacts with the external environment and is composed of afferent nerves, which carry sensory signals from the skin, skeletal muscles…etc to the CNS Efferent Nerves - Efferent nerves carry motor signals from CNS  skeletal ** think efferent = exit muscles. - Autonomic Nervous System (ANS) is the part of the peripheral Autonomic Nervous system nervous system that regulates the body’s internal environment. Sympathetic nerves - Consists of sympathetic nerves, which are autonomic motor Parasympathetic nerves nerves that project in the lumbar(back) and thoracic(chest) regions - Parasympathetic nerves which project from brain and sacral (lower back) of the spinal cord. - Sympathetic neurons synapse onto second-stage neurons away The Meninges from target but parasympathetic synapse on close distance. - Type of deficit can tell us a lot about where in the brain the damage occurred - The brain and spinal cord are protected by the skull and vertebrae Dura mater and 3 membranes/ meninges Arachnoid mater 1. Dura mater ( tough mother) outer layer Pia mater 2. Arachnoid mater (spidery mother) - Beneath is the subarachnoid space, which has many large blood vessels and cerebrospinal fluid. The Ventricles and CSF 3. Pia mater ( gentle mother) - Adheres to the surface of the CNS. Choroid Plexuses - Choroid plexuses, capillary networks that protrude into ventricles manufactures the cerebrinospial fluid CSF - CSF circulates through: 1. Ventricular system – cerebral ventricles are 4 large internal chambers of the brain. 2. Central canal of spinal cord 3. Subarachnoid space 4. Absorbed through large channels/blood-filled spaces called sinuses in the dura mater 5. Enters the jugular veins of the neck. - The purpose of the CSF is to support and cushion the brain. - If the flow of the CSF is blocked, maybe through a tumor, Hydrocephalus hydrocephalus / too much fluid can increase intercerebral pressure and brain damage can occur - An operation in which a hole is drilled through the skull and a shunt tube is inserted onto the ventricle beneath the skin, with a pressure relief valve in the abdominal cavity, allows the CSF to pass into the abdomen to be reabsorbed into the blood supply. 2. Neuroanatomical techniques 1. Golgi stain permitted individual neurons to be studied for the first time if interested in seeing shape of neurons. 2. Nissl stain highlights cell bodies of all neurons, allowed estimation of cell density in tissue and viewing structure 3. Electron microscopy allows visualization of neuronal ultrastructure – extremely detailed 4. Myelin Stain: highlights myelinated pathways; less useful for studying individual axons 5. Tract tracing techniques: highlight individual axons; may be retrograde (trace back from terminal fields) or anterograde (trace from soma  terminal fields) by injecting chemicals and tracing their paths. 3. Orientation and Direction in the - Directions in the nervous system are normally described relative Vertebrate Nervous System to the neuraxis, an imaginary line drawn though the spinal cord Neuraxis up to the front of the forebrain. **This can be a little confusing because some of the terms differ depending on whether you’re an animal with a linear neuraxis (alligator) or upright (human) First Axis Anterior - Anterior means toward the nose or front Posterior - Posterior: toward the tail or back Second Axis Dorsal - Dorsal is toward the surface of the back or top of the head (ex. Ventral Dorsal fin) - Ventral is the surface of the chest or bottom of the head - Superior and Inferior are also used to refer to the top and bottom of the primate head. - Third Axis Medial - Medial is toward the midline of the body Lateral - Lateral is outside or away from the midline. Slicing Planes 1. Horizontal: a Horizontal slice parallel to the ground Transverse/cross-section/frontal 2. Transverse / cross-section/frontal : A slice you would get if slicing a loaf of bread Sagittal or salami / vertical. ** Because of our upright posture, cross sections of the spinal cord are parallel to the ground and right halves. 3. Sagittal: A midsagittal section that separates the left and right halves of the brain. Describing Brain Damage - Ipsilateral (same side of body) or contralateral (on opposite side) o Ex. Stroke to one side of the brain can cause motor problems on the opposite side of the body or The Crossed Brain contralateral side. - Each of its symmetrical halves responds to sensory stimulation from the opposite or contralateral side of the body as well as controlling the muscles on the opposite side. - Since nearly all fibers of motor and somatosensory systems cross, numerous crossings or decussations of sensory and motor fibres are found along the center of the nervous system. 4. Blood Supply to the Brain - The brain receives ~20% of blood flow from the heart because it can’t store fuel or temporarily extract energy without oxygen - Therefore a consistent blood supply is essential Major Arteries to the Brain - Two systems of arteries supply blood to the brain: Carotid 1. Carotid arteries - Arise in the neck and co externally (face/scalp) and internally to the anterior 3/5 of the cerebrum Vertebral 2. Vertebral arteries - Go from the posterior 2/5 of the cerebrum, cerebellum and brainstem Circle of Willis - The carotid and vertebasilar arteries form a circle of communicating arteries called the Circle of Willis - The anterior, middle and posterial cerebral all come from this Circle  gives rise to branches that supply the cortex and deeper structures (basal ganglia, thalamus, and internal capsule) with blood. - Having 2 major sources of blood supply improves the chances of any region of the brain to receive blood if a major artery is blocked. Blood Brain Barrier - Exists between the blood and the fluid that surrounds the cells of the brain. - It is selectively permeable. Capillaries in the brain don’t have caps in them and therefore many substances can’t leave the blood. - Since messages are transmitted within the brain and if composition of the intracellular and extracellular fluids of neurons is changed even slightly, the transmission of information would be affected - This barrier isn’t uniform o Ex. Medulla oblongata – area postrema region that controls vomiting has a thin blood-brain barrier so it can detect the presence of toxic substances in the blood. - The blood-brain barrier doesn’t impede the passage of all large molecules, some large molecules that are critical for normal brain function (e.g. glucose) are actively transported through cerebral blood vessel walls. T: pg 51-74 1. Neurons - Neurons are cells that are specialized for the reception, conduction and transmission of electrochemical signals. External Anatomy of Neurons 1. Cell membrane: the semipermeable membrane that encloses the neuron 2. Dendrites: the short processes emanating from the cell body, which receive most of the synaptic contacts from other neurons 3. Axon hillock: the cone shaped region at the junction between the axon and the cell body. 4. Cell body: the metabolic center of the neuron, also called the soma. 5. Axon: the long narrow process that projects from the cell body 6. Myelin: the fatty insulation around many axons 7. Nodes of Ranvier: Gaps between sections of myelin 8. Buttons: the buttonlike endings of the axon branches, which release chemicals into synapses
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