Cerebral Edema
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10. At an autopsy, a third-year medical student w as handed a slice of the cerebrum and w as asked w hat proportion of central nervous tissue is made up by neuroglia. How w ould you have answ ered that question? Which cells are present in the largest numbers—neurons or neuroglial cells?
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11. A 23-year-old man, w hile in the army in Vietnam, received a penetrating gunshot w ound to the left side of his head. At the operation, the neurosurgeon w as able to remove the bullet from the left frontal lobe of his brain. Apart from a slight w eakness of his right leg, the patient made an uneventful recovery. Eighteen months later, the patient started to have severe generalized attacks of convulsions, during w hich he lost consciousness. Since this time, the attacks have occurred irregularly at about monthly intervals. Each attack is preceded by a feeling of mental irritability, and tw itching of the right leg occurs. A diagnosis of epilepsy w as made by the examining neurologist. Is it possible that this patient's attacks of epilepsy are related to his gunshot w ound in Vietnam? Is traumatic epilepsy a common
condition? What treatment w ould you recommend?
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12. A 42-year-old w oman visited her physician because she w as suffering from very severe headaches. Until 6 months ago, she experienced only an occasional mild headache. Since that time, her headaches gradually have become more severe, and their duration has increased. They now last 3 to 4 hours and are so intense that she has to lie dow n. She has felt sick on tw o occasions, but she has vomited on only one occasion. The headaches are generalized in nature and are made w orse by coughing or straining. A physical examination revealed sw elling of both optic discs w ith congestion of the retinal veins and the presence of multiple retinal hemorrhages. Weakness of the lateral rectus muscle of the right eye also w as detected. Anteroposterior radiographs of the skull show ed displacement of the calcified pineal gland to the left side. Anteroposterior and lateral radiographs of the skull show ed some degree of calcification in a localized area in the right cerebral hemisphere. These findings, together w ith those obtained from CT scans of the brain and magnetic resonance imaging (MRI), made the diagnosis of a right-sided cerebral tumor certain.
Surgical exploration confirmed the presence of a large infiltrating tumor of the right parietal lobe. What is the most common type of tumor found in such a site in a middle-aged patient? How w ould you treat such a patient?
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Review Questions
Directions: Each of the numbered items in this section is followed by answers. Select the ONE lettered answer that is CORRECT.
1. The follow ing statements concern the cytology of a neuron:
(a) A unipolar neuron is one that gives rise to a single neurite that divides a short distance from the cell body into tw o branches, one proceeding to some peripheral structure and the other entering the central nervous system.
(b) A bipolar neuron is one that has tw o neurites that emerge together from the cell body.
(c) Nissl substance is found in the axon of a neuron.
(d) The Golgi complex does not synthesize cell membranes.
(e) Melanin granules are not found in the neurons of the substantia nigra.
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2. The follow ing statements concern the cytology of a neuron:
(a) The protein molecules projecting from the surface of the microtubules take no part in rapid transport in axoplasm.
(b) The protein molecules that extend through the full thickness of the plasma membrane of a neuron serve as sodium and potassium channels.
(c) There is strong experimental evidence to suggest that the gates of the sodium and potassium channels are formed by actin molecules.
(d) The size of the nucleolus in a neuron is unrelated to the volume of cytoplasm possessed by neurons.
(e) A synapse is the site w here tw o neurons come together and their membranes are in contact; interneuronal communication occurs.
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3. The follow ing statements concern the axon:
(a) The initial segment of the axon is the first 500 µm after it leaves the axon hillock.
(b) The nerve impulse generated by a neuron does not originate at the initial segment of an axon but on the dendrite.
(c) The action potential is produced by the sudden influx of Na+ ions into the cytoplasm.
(d) Follow ing the influx of Na+ ions in the production of the action potential, the permeability for Na+ ions increases further, and the permeability for K+ ions ceases.
(e) The spread of the action potential along the microtubules of the axon constitutes the nerve impulse.
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4. The follow ing statements concern a nerve impulse:
(a) The refractory period is the duration of the nonexcitable state of the plasma membrane follow ing the passage of a w ave of repolarization.
(b) Subthreshold stimuli, w hen applied to the surface of a neuron, cannot be summated.
(c) Inhibitory stimuli are believed to produce their effect by causing an influx of K+ ions through the plasma membrane of the neuron.
(d) Hyperpolarization can be produced by causing an influx of K+ ions through the plasma membrane.
(e) The axolemma is the site of nerve conduction.
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5. The follow ing statements concern the structure of a synapse:
(a) Synapses may be axodendritic, axosomatic, or axoaxonic.
(b) The synaptic cleft is the space betw een the presynaptic and postsynaptic membranes and measures about 200 nm.
(c) The subsynaptic w eb lies beneath the presynaptic membrane.
(d) Presynaptic vesicles do not contain the neurotransmitter substance.
(e) All neurons produce and release several types of transmitter substances at all their nerve endings.
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6. The follow ing statements concern a neuron:
(a) Nerve fibers are the dendrites and axons of a neuron.
(b) The volume of cytoplasm w ithin the nerve cell body alw ays far exceeds that found in the neurites.
(c) Golgi type I neurons have very short axons.
(d) Golgi type II neurons have very long axons.
(e) Golgi type II neurons form the Purkinje cells of the cerebellar cortex.
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7. The follow ing statements concern the neuron organelles and inclusions:
(a) Centrioles are not found in mature nerve cells.
(b) Lipofuscin granules tend to disappear w ith age.
(c) The Nissl substance fills the axon hillock but is absent from other areas of the cytoplasm.
(d) Microfilaments contain actin and do not assist in cell transport.
(e) Mitochondria are found in the dendrites and axons.
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8. The follow ing statements concern dendrites:
(a) A dendrite conveys a nerve impulse aw ay from the nerve cell body.
(b) Dendritic spines are small projections of the plasma membrane that increase the receptor surface area of the dendrite.
(c) The cytoplasm of dendrites does not contain ribosomes and agranular endoplasmic reticulum.
(d) Most dendrites expand in w idth as they extend from the nerve cell body.
(e) Dendrites rarely branch.
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9. The follow ing statements concern neuromodulators:
(a) Neuromodulators may coexist w ith the principal (classic) transmitter at a single synapse.
(b) They often diminish and shorten the effect of the principal transmitter.
(c) They never act through a second messenger.
(d) They have a brief effect on the postsynaptic membrane.
(e) Acetylcholine (muscarinic) is not a good example of a neuromodulator.
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10. The follow ing statements concern the neurobiology of neuron structures:
(a) A lysosome is a membrane-bound vesicle covered w ith ribosomes.
(b) A terminal bouton is the postsynaptic part of an axon.
(c) A receptor is a protein molecule on the postsynaptic membrane.
(d) Nissl substance is formed of the smooth surfaced endoplasmic reticulum.
(e) Microtubules provide a mobile track that allow s specific organelles to move by molecular motors.
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11. The follow ing statements concern neuroglia:
(a) Fibrous astrocytes are located mainly in the gray matter of the central nervous system.
P.69 (b) Replacement gliosis follow s the death of neurons in the central nervous system and is due to the proliferation of astrocytes.
(c) Astrocytes are not involved in the absorption of gamma-aminobutyric acid (GABA)GABA secreted by the nerve terminals.
(d) Oligodendrocytes are responsible for the formation of the myelin of nerve fibers in the peripheral nervous system.
(e) A single oligodendrocyte can form, by means of its processes, only one internodal segment of myelin on the same axon.
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12. The follow ing statements concern the microglial cells:
(a) Microglial cells resemble connective tissue mast cells.
(b) Microglial cells are larger than astrocytes or oligodendrocytes.
(c) Microglial cells migrate into the central nervous system during adult life.
(d) In the presence of damaged neurons, microglial cells become branched.
(e) In degenerative lesions of the central nervous system, the circulating blood contributes cells to the population of microglial cells.
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13. The follow ing statements concern the ependymal cells:
(a) Choroidal epithelial cells do not secrete cerebrospinal fluid.
(b) The ependymocytes line the ventricular system but do not permit the cerebrospinal fluid to enter the extracellular spaces of the nervous tissue.
(c) Tanycytes have short, unbranched basal processes, many of w hich have end feet placed on the capillaries of the median eminence.
(d) The ependymal cells form a single layer, and many possess microvilli and cilia.
(e) Ependymal cells are incapable of absorbing substances from the cerebrospinal fluid.
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14. The follow ing statements concern the extracellular space:
(a) The space is formed by the gaps betw een the neurons and not the gaps betw een the neuroglial cells.
(b) The space surrounds the lymphatic capillaries present in the brain and spinal cord.
(c) The space is not in continuity w ith the subarachnoid space.
(d) The space is filled w ith tissue fluid.
(e) The space is not continuous w ith the synaptic cleft betw een tw o neurons.
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15. The follow ing statements concern tumors of neuroglia:
(a) They form about 5% of all intracranial tumors.
(b) Apart from the ependymomas, tumors of neuroglia grow slow ly and are not highly invasive.
(c) They commonly infiltrate betw een neurons, causing the minimum disturbance of function.
(d) They are nonmalignant and easily removed surgically.
(e) As they expand, they raise the intracranial pressure.
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16. The follow ing statements concern neuroglial cells:
(a) They tend to be larger than nerve cell bodies.
(b) Heat increases the action potential in an axon and reduces the signs and symptoms in multiple sclerosis.
(c) Oligodendrocytes are found some distance aw ay from nerve cell bodies and their neurites.
(d) Multiple sclerosis is a disease involving the oligodendrocyte.
(e) Like Schw ann cells, oligodendrocytes are surrounded by a basement membrane.
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17. The follow ing general statements concern the neuroglial cells:
(a) The microglial cells have straight processes w ith spinelike projections.
(b) The astrocytes form a scaffold for developing neurons.
(c) Oligodendrocyte processes are not continuous w ith the myelin sheaths.
(d) The ependymal cells have no cilia on their free borders.
(e) Macroglia is the term used to distinguish the larger oligodendrocytes from the smaller astrocyte.
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Additional Reading
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Authors: Snell, Richard S.
Title: Clinical Neuroanatomy, 7th Edition Copyright ©2010 Lippincott Williams & Wilkins
> Table of Contents > Chapter 3 - Ner ve Fiber s, Per ipher al Ner ves, Receptor and Effector Endings, Der matomes, and Muscle Activity