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Unformatted text preview: The Nervous System The Nervous System
NURS 216, Spring 2010 Sabra Smith, MS, RN Objectives Review relevant A&P of nervous system Discuss pain, transmission and different types Discuss movement and muscular disorders Understand types and effects of spinal cord injuries Divisions of the Nervous System Divisions of the Nervous System Functional tissue: neurons sensory/afferent motor/efferent Supportive tissue PNS: Schwann cells and satellite cells CNS: oligodendrocytes, astrocytes, microglial cells, ependymal cells “glial cells” Special metabolic requirements Neural Tissue Neural Tissue Neurons Neurons CNS Supporting Cells CNS Supporting Cells Nerve Cell Communication Nerve Cell Communication Signals move along a neuron through electrical conduction, depolarization Neurons transfer signals to each other through neurotransmitters amino acids, peptides, monoamines The action of a transmitter is determined by the type of receptor to which it binds Synaptic Transmission Synaptic Transmission The Brain The Brain About three pounds 20% of cardiac output, 20% of oxygen, needs 400 kcal daily Oxygen and glucose demand are CONSTANT Brainstem, cerebellum, diencephalon, limbic system, cerebrum Medulla oblongata – controls many reflexes Pons – connector between cerebellum halves, midbrain and medulla Cerebellum – muscle coordination, balance, posture Midbrain – contains substantia nigra, which helps control movement Brainstem: Hindbrain & Brainstem: Hindbrain & Midbrain Diencephalon Diencephalon At the inner core of the cerebrum Thalamus, hypothalamus, subthalamus, epithalamus Processes sensory information and coordinates body’s response, maintains internal body conditions Limbic System Limbic System Not a specific area of the brain, but a connection of several structures Cingulate, hippocampus Controls mood, emotions, sex drive, memory Cerebrum Cerebrum Largest portion of the brain Control of all sensory and motor activities, reason, memory, conscious thought Left and right hemispheres (contralateral control) Many functional areas of the cerebral cortex have been identified CNS Protection CNS Protection Three layers of meninges: pia mater – directly continuous with brain subarachnoid space arachnoid – thin, fibrous membrane dura mater – tough, stiff tissue continuous with the skull Cerebrospinal Fluid Cerebrospinal Fluid Ventricles – four connected cavities within the brain, contain CSF CSF is secreted into ventricles by the choroid plexus, provides cushion and protection CSF is clear, mostly water, electrolytes, gases and glucose Circulates around the whole CNS, reabsorbed into blood through the arachnoid layer BloodBrain Barrier BloodBrain Barrier The tight connections between endothelial cells of cerebral arteries prevent most molecules from exiting blood and entering neural tissue Water, carbon dioxide, oxygen, glucose and most lipid soluble substances (alcohol) can penetrate this barrier Most electrolytes, plasma proteins, large organic molecules cannot penetrate BloodBrain Barrier BloodBrain Barrier BloodCSF Barrier BloodCSF Barrier Choroid plexus produces CSF in the ventricles Tight junctions between cuboidal cells lining the villi keep CSF from crossing over into capillaries deep in the choroid plexus Both barriers are permeable/impermeable to similar substances, often referred to just as the BBB Autonomic Nervous System Controlled by hypothalamus and brainstem Sympathetic: control of body temperature, blood flow and pressure Parasympathetic: energy conservation and storage, maintenance of organ function during rest Most organs have dual control ANS Neurotransmission Acetylcholine (ACh) and catecholamines (epi, norepi, dopamine) ACh receptors are cholinergic (muscarinic and nicotinic) Catecholamine receptors: alpha and beta type of response elicited depends on type and location of receptor that is stimulated Somatosensory Function 3 types of sensory neurons: general somatic special somatic general visceral Pairs of sensory neurons innervate specific body regions, dermatomes Sensory Modalities Modalities are distinct types of sensation Tactile system is the baseline Thermal: cold, warmth, and pain receptors Proprioception: muscle spindle receptors and Golgi tendon organs PAIN A separate sensory modality or an extension of all types? Nocioceptors activated by “noxious” stimuli mechanical, thermal, chemical insults fast (myelinated) and slow fibers Types of Pain Cutaneous and deep somatic Visceral Referred Acute chronic Pain Disorders Neuropathies – associated with nervous system injury peripheral neuropathy trigeminal neuralgia postherpetic neuralgia Phantom limb pain Headaches Very common problem Danger signs: sudden onset, severity, accompanied by other neurologic changes, progression Classified as primary or secondary Headaches Headaches PRIMARY types: Migraines 3X more common in women, hereditary? Tensiontype most common, bandlike, dull Cluster uncommon, 8085% of sufferers are men SECONDARY causes: infection, metabolic disorders, tumors, trauma, drugs or drug withdrawal, etc. More serious: meningitis, brain tumor, cerebral aneurysm Back Pain: Back Pain: Intervertebral Disk Herniation Structure of intervertebral disk Nucleus pulposus soft, gellike center Annulus fibrosus – fibrocartilage, outer covering of nucleus pulposus Function: absorbs shock Herniated disk nucleus pulposus squeezed out of place and herniates through annulus, compressing spinal cord Herniated disk Herniated disk Lumbar Intervertebral Disk Lumbar Intervertebral Disk Herniation Signs and symptoms are localized to area of body innervated by the involved nerve roots PAIN !!! Sciatica inflammation of sciatic nerve Paresthesias “pins and needles” Motor weakness Hypoesthesia decreased sensation Decreased ankle reflex Sacral Plexus Motor Function Motor neurons and units Ultimate control by the motor cortex in frontal lobe Spinal reflexes Muscle Tone and Movement Problems Hypotonia Flaccidity Hypertonia/rigidity/spasticity Paralysis and paresis hemi para quadri GBS GBS Positive sx: pain, parasthesias Negative sx: weakness/paralysis, loss of tendon reflexes, decreased sensation Weeks 2 to 3 are the worst part, then most people begin to recover Recovery depends on extent of nerve damage GuillainBarre Syndrome GuillainBarre Syndrome Acute demyelinating disorder of the peripheral nerves Ascending paralysis, varying sensory problems Often occurs after a viral infection – autoimmune condition??? Parkinson’s Disease Parkinson’s Disease Disorder of dopamine production in the basal ganglia Lack of dopamine disrupts purposeful movement Rigidity, tremor (esp. at rest), akinesia/bradykinesia, loss of postural reflexes “leadpipe rigidity”, shuffling gait, masklike face Structures in the brain related to Parkinson's disease. Basal ganglia affect normal movement and walking; the substantia nigra produces the neurotransmitter dopamine, and the globus pallidus affects movement, balance and walking. The thalamus is a relay station for brain impulses, and the cerebellum affects muscle coordination. ALS ALS Amyotrophic Lateral Sclerosis Progressive, hits between 50 – 70 Motor neurons out of the cerebral cortex deteriorate, then their target muscles atrophy Gradual loss of fine motor control and spreading weakness ONLY affects motor function Life expectancy 2 – 5 years Multiple Sclerosis Multiple Sclerosis Average age of onset: 30 More common in women Autoimmune response after viral infection? Areas of myelin in CNS are destroyed and replaced by astrocytes Result is hard, yellow plaques around nerves in the CNS Multiple Sclerosis Multiple Sclerosis As the myelin sheath is progressively destroyed, motor and sensory function decreases Pattern is usually repeated attacks with remissions inbetween Overall, symptoms gradually worsen with more permanent loss of function after each attack Location of lesions determines specific symptoms Multiple Sclerosis Multiple Sclerosis Sensory disorders – Spasticity and weakness – Cerebellar signs – Bladder dysfunction – Mood disorders Spinal Cord Injuries Spinal Cord Injuries Often due to MVAs, falls, sports injuries Vertebral column unable to withstand much rotation, extension, or flexion Injuries often between “segments” of the spine Mechanical injury causes compression of spinal cord and disruption of blood supply Spinal Shock Spinal Shock transection= spinal cord (nerves) is severed Immediate, temporary condition after an injury “physiologic disorganization” below injury caused by loss of normal tonic stimulation Loss of reflexes and sensation, general muscle flaccidity, atony of bladder and bowel, drop in blood pressure, no perspiration, dry skin Recovery depends on severity of injury Injury Cascade Injury Cascade Primary injury is immediate – bleeding, edema, necrosis of some tissue Secondary injuries continue damage Ischemia to spinal cord causes cascade of problems lose autoregulation of blood flow inflammation/edema excessive neurotransmitter release, causing cell damage and swelling Cervical Injuries Cervical Injuries Described by location of injury: C1C7 Higher injuries are more devastating C1: often fatal, no respiratory or voluntary motor control C23: some neck control, ventilator? C4C7: better respiratory control, more use of upper extremities ThoracicLumbarSacral ThoracicLumbarSacral Often from compression fractures T212: full upper extremity use, limited trunk L15: full upper extremity and trunk use, progressive lower extremity use S15: may have foot control, bladder/bowel incontinence Autonomic Dysreflexia Autonomic Dysreflexia Can occur at any time after resolution of spinal shock Most likely in injuries T6 and above Extreme response of cardiovascular system when sympathetic nervous system is stimulated Often due to distended bladder or rectum, pressure ulcers, or shearing force on skin Extreme HTN (200300 mmHg systolic), bradycardia, headache, visual disturbance, sweating above injury site ...
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- Spring '10