Chapter 21 The Nervous System Nervous System Central

Chapter 21 The Nervous System

Nervous System • Central nervous system (CNS) consists of the: – Surrounded by protective membranes called: • Dura: • Arachnoid: – Subarachnoid space: » Contains: • Pia: – Adheres to the surface of the:

Nervous System • Brain and spinal cord are encased in protective bony structures – Cranium: – Vertebral column: • CSF acts as a cushion to protect the brain

Brain • Divided into: – Cerebrum, cerebellum, brain stem • Has four cavities called ventricles – Contain CSF

Blood Supply of the Brain • Arterial blood supply – Large vessels enter base of skull – Vessels join to form arterial circle at base of brain • Branches of the circle supply all parts of the brain • Venous blood – From brain into large venous sinuses in dura – Sinuses eventually drain into jugular veins

Blood Supply of the Brain Arterial Blood Supply Venous Blood Return

Nervous System • Tissues of brain and spinal cord are composed of: – Supporting cells called: – Nerve cells called: • Neurons contain long processes called nerve fibers which conduct nerve impulses • Some nerve fibers are surrounded myelin which helps insulate and increase speed of nerve impulses – Myelinated nerve fibers make up white matter of brain & spinal cord – Gray matter is made up of neurons, neuroglia, & unmyeliated nerve fibers

Nervous System • Sensory or afferent nerves transmit impulses: • Motor or efferent nerves transmit impulses: • Cerebral cortex receives sensory input & initiates voluntary motor activity – Spinal cord relays information between parts of the body and the brain – Left side of brain controls right side of body and vice-versa

Muscle Paralysis • A muscle that is: • Two types: – Flaccid paralysis – Spastic paralysis

Cerebral Injury • A severe blow to the head may cause brain injury • Injury to the brain may cause loss of consciousness & various neurological disturbances • Injured region of brain may swell but cranial cavity is rigid and doesn’t give – Swelling is restricted & compresses the swollen brain, leading to: • Adversely affects:

Skull x-ray illustrating large skull fracture (arrows) associated with extensive injury to underlying brain. Fig. 21 -2

Mechanism of injury to frontal and temporal poles of brain caused by blow to back of head.

Cerebral Injury • Large blood vessels over surface of brain may be torn by force of injury – Blood may accumulate in different locations depending on which vessels are damaged • Epidural hemorrhage: – Between the: • Subdural hemorrhage – Between the: • Subarachnoid hemorrhage: – Between the: – Epidural & subdural hematoma may compress the brain & impair function

Neural Tube Defects • Failure of the neural tube to close properly • Follow a multifactoral pattern of inheritance – Means many causes – Factors are usually both genetic & environmental • Deficiency of folic acid in the first trimester is an important cause

Neural Tube Defects • Spina bifida – Malformation of the caudal neural tube and related vertebral arches • Name means split spine in reference to: – Diagnosis: maternal blood test and amniocentesis looking for elevated levels of: • Diffuses from fetal blood into amnionic fluid & mothers blood through open neural tube defect

Neural Tube Defects • Spina bifida – Types: • Spina bifida occulta – Failure of the vertebral arches in the lower lumbar region to fuse – Symptoms produced: • Spina bifida cystica with meningocele – Saclike protrusion consisting only of: • Spina bifida cystica with meningomyelocele – Saclike protrusion consisting of: – There is often a severe neurological deficit below the level of the sac

Various types of spina bifida.

Large thoracic meningomyelocele covered by thin membrane Fig. 21 -6

Stroke • Also called cerebrovascular accident or CVA • Is the name for any injury to brain tissue from: • 3 types of stroke – Cerebral thrombosis: most common • thrombosis of cerebral artery or a major artery supplying the brain which is narrowed by: – Cerebral embolus: occurs less frequently • blockage of cerebral artery by fragment of blood clot from: – Cerebral hemorrhage: most serious type of stroke • usually from rupture of a cerebral artery in person with:

Infarct, right cerebral hemisphere from thrombosis of middle cerebral artery Fig. 21 -10

Coronal section of brain illustrating large cerebral hemorrhage that has compressed and displaced the cerebral ventricles. Fig. 21 -14

Stroke • Diagnosis – Cerebral angiogram • Radiopaque die is injected into the carotid & vertebral arteries • The dye is followed using x-rays in order to visualize blood flow through vessels – Carotid endarterectomy • Surgical removal of arteriosclerotic plaque that may occlude the carotid arteries & impede cerebral blood flow • Performed by making an incision in the carotid artery and removing the plaque

Stroke • Manifestations – Clinical effects of stroke depend on the location & severity of the brain damage – Extensive damage may cause partial paralysis by disrupting nerve fibers – Hemiplegia: a stroke involving one cerebral hemisphere often leads to weakness on the opposite side

Transient Ischemic Attack • Often referred to as a TIA • Brief episodes of neurologic dysfunction such as: • Episodes tend to last for: – After the episode the symptoms: • Usually caused by an embolization of material from plaque in carotid artery – Obstructs: • One-third of patients eventually suffer major stroke • Treatment: endarterectomy or medical therapy

Transient Ischemic Attack

Cerebral Aneurysm • Congenital aneurysm – – – Congenital weakness in arterial wall allows lining to protrude Weakness is congenital but aneurysm develops in adult life Rupture causes subarachnoid hemorrhage People with hypertension are more prone Treatment: aneurysm occluded surgically

Dissection of vessels from the brain of a person with large congenital cerebral aneurysm. Fig 21 -16

A cerebral aneurysm (arrow) demonstrated by an angiogram. Fig 21 -18 b

Undersurface of brain, illustrating subarachnoid hemorrhage secondary to ruptured cerebral aneurysm. Fig 21 -17

Infections of the Nervous System • Nervous system can be infected by bacteria, fungi, & viruses • Meningitis is an infection affecting the: • Encephalitis is an infection of: • Meningoencephalitis is an infection of both the: • Symptoms of CNS infection include fever, headache, stiff neck, & alteration of consciousness & neurologic symptoms if brain involved • Spinal tap is performed to diagnose

Meningitis from Bacteria • Most cases of bacterial meningitis are caused by two organisms 1. 2. • A third organism was a common cause in children but is routinely immunized against 3.

Meningitis from Bacteria • Meningococcus (Neisseria meningiditis) – Occurs primarily in: – Often becomes epidemic where people live in close quarters such as: – If a person is infected, all people with close contact to this person have to be treated with antibiotics • Pneumococcus (Streptococcus pneumoniae) – Occurs sporadically in: – Not transmitted from person to person so close contacts don’t have to be treated

Bacterial meningitis, illustrating purulent exudate in the meninges Fig. 21 -19

Viral Infections • Many viruses may affect the nervous system including: measles, mumps, herpes simplex virus, intestinal and respiratory viruses, cytomegalovirus, poliomyelitis virus, & arborviruses • Can cause meningitis & encephalitis • Encephalitis can be very serious and unfortunately there is no treatment for viral infection

Alzheimer Disease • Is a chronic progressive disease – Characterized by progressive failure of recent memory & difficulties in thinking, reasoning, & judgement – Often associated with emotional disturbances such as: • Brain shows loss of neurons with atrophy of the cerebral cortex – Neurofibrillary tangles: – Neurotic plaques: • No specific treatment; but some drugs may temporarily improve cerebral function

Multiple Sclerosis • Chronic disease characterized by randomly distributed degeneration of the myelin sheaths of nerves found in the brain & spinal cord • Probably an autoimmune disease in generally predisposed individual – Most likely initiated by a viral infection in a genetically predisposed person • Neurologic symptoms depend on location of plaques – Demyelination disrupts nerve impulses – Remission of symptoms occur after an attack • MRI demonstrates plaques in CNS – No cure

Coronal section of brain illustrating areas of gilial scarring (arrows) adjacent to ventricle in multiple sclerosis. Fig. 21 -22

Multiple sclerosis demonstrated by MRI. Fig. 21 -23

Parkinson Disease • Most cases unknown etiology • Some develop subsequent to viral infection of nervous system or toxic drugs • Manifestations – – Progressive loss of neurons in substantia nigra of midbrain Rigidity of voluntary muscles Tremors of fingers and extremities Decreased dopamine in CNS • Treatment: relieved by L-dopa – Embryonic stem cells may be key to successful treatment; possible to induce stem cells to differentiate into dopamineproducing neurons to treat disease

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