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Central Nervous System Chapter 13 CNS Coverings • Bone • Meninges – Dura Mater: white fibrous tissue – Arachnoid membrane: cobweb-like layer – Pia Mater: adheres to outer surface of brain & cord; contains blood vessels • Spaces surrounding meninges – Epidural space: (“on the dura”) btwn dura mater and bone coverings – Subdural space: (“under the dura”) btwn dura mater and arachnoid space – Subarachnoid space: under arachnoid; outside pia mater http://faculty.irsc.edu/FACULTY/TFischer/AP1/meninges.jpg Cerebral Spinal Fluid (CSF) • Protective cushion of fluid • Brain monitors CSF to help maintain homeostasis – Ex: CO2 levels • Fluid spaces – Subarachnoid space – Spinal cord – Ventricles (4) Formation of CSF • Fluid separated from blood in choroid plexuses – Choroid plexus: network of capillaries that project into ventricles – Lined with ependymal cells • Circulation: – Separation in choroid plexuses ventricles central canal of spinal cord & subarachnoid spaces blood Diagnostic Study – Lumbar Puncture • Removal of CSF from subarachnoid space in lumbar region of spinal cord • Above/below L4, locate iliac crest • Side-lying, knees to chest • Sterile technique • CSF tested for abnormalities – Blood counts, bacteria, pressure • Administer diagnostic agents or medications http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19078.jpg Hydrocephalus • Internal hydrocephalus – Obstruction blocks drainage of CSF from ventricles (1-3) • Ex: tumor • External hydrocephalus – Obstruction in subarachnoid space causes build up of CSF in subarachoid space • Hemorrhage blood clots • Treatment – Infants • Unfused sutures cranium swells • Shunt placement btwn lateral and 4th ventricles – Adults • Pressure compresses brain coma, death http://bryanking.net/wp-content/uploads/2009/02/national_hydrocephalus_foundation.jpg http://www.choa.org/images/graphics/hydrocephalus.jpg http://www.articleslounge.com/wp-content/uploads/2009/06/Hydrocephalus.jpg Spinal Cord - Structure • Extends from foramen magnum to L1 • Fissures – Anterior median fissure (larger) – posterior median sulcus • Nerve Roots – Project from each side of spinal cord – Dorsal nerve root: carry sensory information to spinal cord • Unipolar neurons • Cell bodies make up dorsal root ganglion – Ventral nerve root: carry motor information that exits spinal cord – Dorsal + ventral nerve roots = spinal nerve • Gray matter (“H” in the center of the spinal cord) – Anterior, posterior, lateral horns (or columns) – Contains interneurons and cell bodies of motor neurons • White matter (surrounds gray matter) – Anterior, posterior, lateral columns – Contains bundles of axons (tracts) Spinal Cord - Functions Two main functions: 1. Conduction routes to/from brain 2. Integration or reflex center for all spinal reflexes Spinal Cord – Conduction Routes • Ascending tracts – conduct sensory impulses up to the brain – Lateral spinothalamic: pain, temperature, crude touch opposite side – Anterior spinothalamic: crude touch and pressure – Fasciculi gracilis and cuneatus: discriminating touch & pressure sensations (vibrations, stereognosis, twopoint discrimination), conscious kinesthesia – Anterior & posterior spinocerebellar: unconscious kinesthesia – Spinotectal: touch that triggers visual reflexes Spinal Cord – Conduction Routes • Descending tracts – conduct motor impulses down from the brain – Lateral corticospinal: voluntary movement, contraction of small muscle groups (hands, fingers, feet, toes of opposite side) – Anterior corticospinal: same as above but affect muscles on same side – Reticulospinal: maintain posture during movement – Rubrospinal: coordination of body movement & posture – Tectospinal: head and neck movement during visual reflexes – Vestibulospinal: coordination of posture & balance Spinal Cord – Reflex Centers • Center of reflex arc • Switching from afferent to efferent – 3 neuron arc interneuron – 2 neuron arc synapse btwn afferent & efferent • Located in gray matter (“H”) Brain • Consists of: – 100 billion neurons – 900 billion glial cells • Weighs approx 3 lbs in an adult • Mature neurons are incapable of cell division – Only during prenatal and beginning months of life – Malnutrition hinders neuron growth/development Brain - Divisions • Brainstem – Medulla oblongata – Pons – Midbrain • Cerebellum • Diencephalon – Thalamus – Pineal body – hypothalamus • Cerebrum – Cortex – Corpus callosum Brainstem • Medulla Oblongata – Enlarged extension of the spinal cord – Located just above the foramen magnum • Reflex centers: cardiac, vasomotor, respiratory • Pons – White matter & reticular formation – Reflex centers for CN 5-8 • Midbrain – White matter & reticular formation – Reflex centers for CN 3-4 Cerebellum • Structure – – – – Lower posterior portion of brain Outer region cortex gray matter Internal areas white matter Grooves sulci; raised areas gyri • Function – Produce skilled movements by coordinating muscle groups – Posture (unconscious) – Maintains balance Cerebellar Disease • Diseases of the cerebellum (tumor, abscess, trauma, hemorrhage) produce abnormalities in muscle coordination • Most common – ataxia (muscle incoordination) • Signs/symptoms: – Hypotonia – Tremors – Disturbances in gait & balance Diencephalon • Thalamus – Dumbbell-shaped mass of gray matter – Forms walls of third ventricle – Functions: • Processes auditory & visual input • Conscious recognition of pain, temperature & touch • Emotional responses (associates sensory impulses with pleasantness vs unpleasantness) Diencephalon • Hypothalamus – Lie beneath thalamus and forms the floor of the 3rd ventricle – Functions: • Controls responses made by autonomic effectors • Maintains water balance • Endocrine function – release hormones that regulate actions of the anterior pituitary gland • Waking state (alert and arousal) • Regulating appetite • Maintaining normal body temperature Diencephalon • Pineal Body – Located just above the midbrain – Functions: • Regulates biological clock • Produces melatonin Cerebrum • Largest, upper division of the brain • Two halves – right & left hemispheres – Communicate via corpus callosum • Cerebral cortex – surface of the cerebrum; gray matter – Gyri & sulci (shallow) or fissures (deep) – Frontal lobe, parietal lobe, temporal lobe, occipital lobe Functional Areas of the Cerebral Cortex (fig 13-16) Functions of the Cerebral Cortex • Postcentral gyrus – termination area for sensory pathways – Touch, pressure, temperature, body position • Precentral gyrus – primary motor area – Neurons in this area control individual muscles Functions of the Cerebral Cortex Language • Speech centers are located in frontal, parietal & temporal lobes • In 90% of the population these areas are found in the left hemisphere • Aphasia = language defects • Broca’s area – unable to articulate words; able to make vocal sounds • Wernicke’s area – deficit in language comprehension Functions of the Cerebral Cortex - Emotions • Experiencing and expressing emotions involves the function of the limbic system – Area of the brain that surrounds the corpus callosum – For proper expression the limbic system functions with the cerebral cortex Functions of the Cerebral Cortex Memory • Temporal, parietal and occipital lobes • Limbic system also plays a role – Removal of hippocampus inhibits a person from recalling new information Disorders of the Central Nervous System Cerebrovascular Accident (CVA) • Aka Stroke • Hemorrhage or cessation of blood flow through cerebral blood vessels • Lack of oxygen to neurons causes cell damage or death • If motor areas are affected, patient loses function on opposite side of the body – (motor neurons cross over from side to side in the brainstem) • Hemiplegia – paralysis (loss of voluntary muscle control) on one whole side of the body http://www.strokegenomics.org/img/stroke_hem_web.jpg Cerebral Palsy • Permanent, non-progressive damage to motor control areas of the brain • Damage present at birth or shortly after birth; remains throughout life • Possible causes: – Prenatal infection, trauma to head before/during/after birth, reduced oxygen supply to brain • Results in impairment to voluntary muscles • Most common spastic paralysis: involuntary contractions of affected muslcles Dementia • Dementia: degeneration of neurons that affect memory, attention span, intellectual capacity, personality & motor control Alzheimer’s Disease (AD) • Lesions develop in the cortex of the brain • Result is dementia • No known cause; no effective treatment • Genetic basis http://www.crystalinks.com/alzheimersbrain.jpg Seizures • Sudden bursts of abnormal neuron activity that cause temporary changes in brain function • Mild seizures – Small changes in level of consciousness, motor control & sensory preception • Severe seizures – Convulsions (jerky, involuntary movements) & sometimes unconsciousness • Treatment – Drugs (phenobarbital, valproic acid) block neurotransmitter activity in affect areas inhibits bursts of explosive neuron activity http://theness.com/neurologicablog/?p=27