Nerve Tissue

*The answer is C.* Schwann cells produce myelin in the peripheral nervous system, whereas oligodendrocytes produce myelin in the central nervous system. Astrocytes, neural crest cells, and basket cells do not produce myelin.

Myelination of peripheral nerves is accomplished by (A) astrocytes. (B) oligodendrocytes. (C) Schwann cells. (D) neural crest cells. (E) basket cells.

*The answer is C.* The axon hillock is devoid of large organelles, such as Nissl bodies and Golgi cisternae, but it does contain microtubules arranged in bundles and permits passage of neurofilaments, mitochondria, and vesicles into the axon.

The axon hillock contains (A) rough endoplasmic reticulum. (B) ribosomes. (C) microtubules. (D) Golgi complex. (E) synaptic vesicles.

*The answer is E.* The neural crest differentiates to neurons and satellite cells fo the spinal ganglion.

A 2-year-old boy presents with hearing impairment, poliosis (a white shock of hair), complete heterochromia and sectoral heterochromia, hypertelorism, a low hairline with eyebrows that touch in the middle, white pigmentation of the skin, and suspected neurologic deficits. He is diagnosed with Waardenburg syndrome with a mutation in the PAX-3 gene that affects neural crest differentiation. Which of the following structures would most likely also be affected in this patient? a. Purkinje cells b. Pyramidal neurons c. Ventral horns of the spinal cord d. Astrocytes e. Neurons and satellite cells of the spinal ganglion

*The answer is D.* Large neurons with eccentric nuclei are visible in this image. The satellite cells do not form a continuous circle surrounding the neurons. These are the characteristic features of autonomic ganglia. Other than connective tissue, the image does not show any particular target tissue that would suggest a parasympathetic ganglion (choice C). Dorsal root ganglion (choice A) neurons have centrally located nuclei and are surrounded by a continuous layer of satellite cells. Enteric ganglia (choice B) are situated between smooth muscle layers in the gastrointestinal wall (not visible in this preparation). Ventral horn of the spinal cord (choice E) is characterized by large multipolar motor neurons.

A 68-year-old man with a history of hyperlipidemia suffers a ruptured abdominal aneurysm and expires. During the autopsy, ganglia are collected from different locations and examined by light microscopy (shown in the image). Which of the following best characterizes this particular ganglion? (A) Dorsal root ganglion (B) Enteric ganglion (C) Parasympathetic ganglion (D) Sympathetic ganglion (E) Ventral horn of the spinal cord

*The answer is E.* Large neurons (arrows) are the most prominent structures observed in this section of spinal cord. These neurons are characteristic features of the ventral horn of the spinal cord. As described previously, the dorsal horn of the spinal cord (choice C) contains smaller sensory interneurons. Anterior funiculus (choice A) and posterior funiculus (choice D) are located in the white matter. The central canal (choice B) is lined by low columnar cells.

A area of the spinal cord segment is examined at high magnification (shown in the image). This region of spinal cord is appropriately described as which of the following? (A) Anterior funiculus (B) Central canal (C) Dorsal horn (D) Posterior funiculus (E) Ventral horn

*The answer is A.* In a transverse section of the spinal cord, the peripheral white matter can be subdivided into the posterior, lateral, and anterior funiculus. These regions contain ascending and descending tracts of axons of varying lengths. The longest axons extend all the way from the brain (brainstem and cerebrum) to the most caudal portion of the spinal cord. The other components listed as choices are supporting structures found in white matter, but they do not represent major functional components in this location.

For the spinal cord segment, which of the following is the predominant component of the lateral funiculus in the white matter indicated by Line 3? (A) Axons (B) Blood vessels (C) Cell bodies of neurons (D) Dendrites (E) Glial cells

*The answer is A.* Synaptic vesicles are found in terminal boutons.

Which statement best describes synaptic vesicles A. Found in terminal boutons B. Found in synaptic clefts C. Contain lysosomal enzymes D. Bud directly from RER E. Found in dendrites neat the postsynaptic membrane

*The answer is B.* Under normal conditions, a space does not exist between the dura and the arachnoid. However, the dural border cell layer (the innermost part of the dura) is composed of flattened fibroblasts and constitutes a plane of structural weakness. A subdural space may develop following blunt force trauma to the head, with the tearing of bridging veins. In contrast to the epidural space, the subdural space can expand. Because hematomas represent venous hemorrhage, they usually stop bleeding after 25 to 50 mL have accumulated, owing to local compression of affected veins. However, this tamponade may lead to venous thrombosis (intravascular coagulation of blood), which may prove fatal. Blunt force applied in the mid-sagittal plane will typically affect both cerebral hemispheres. Therefore, it is not surprising that subdural hematomas are frequently bilateral.

A 25-year-old man is rushed to the emergency room in a coma following an accident at work. MRI shows an expanding subdural hematoma over the left hemisphere. From your knowledge of basic histology you understand that this patient's subdural hematoma formed between which of the following pairs of tissues/ structures? (A) Arachnoid mater and pia mater (B) Dura mater and arachnoid mater (C) Periosteum and dura mater (D) Pia mater and brain proper (E) Skull and its periosteum

*The answer is D.* Neuronal cell bodies that cluster together in the peripheral nervous system are referred to as ganglia. Homologous structures in the CNS are referred to as nuclei. Neuroglial cells that surround neurons in a ganglion are termed satellite cells. Satellite cells are small, cuboidal cells. Satellite cells in dorsal root ganglia form a complete monolayer surrounding the central neurons. Astrocytes and oligodendrocytes (choices A and C) are neuroglial cells found in the CNS. Schwann cells (choice E) nourish and support peripheral nerve fibers.

A 27-year-old man suffers a gunshot wound to the thorax and expires. A dorsal root ganglion near the bullet track is examined at autopsy (shown in the image). The arrows identify the nuclei of which of the following types of cells? (A) Astrocytes (B) Neurons (C) Oligodendrocytes (D) Satellite cells (E) Schwann cells

*The answer is D.* The patient has myasthenia gravis, an autoimmune disease in which the body produces antibodies to receptors for the neurotransmitter acetylcholine (ACh), which are expressed on the postsynaptic membrane of muscles. In normal individuals, motor nerve terminals release ACh, which binds to ACh receptors on muscle cells, resulting in depolarization and muscle contraction. Because of the autoantibodies, the number of receptors is reduced in myasthenia gravis, which results in reduced synaptic transmission and consequently in reduced muscle activation.

A 33-year-old woman is referred to the neurology clinic because she has experienced weakness of the eye muscles for the past 2 months. Subsequently, she has experienced diplopia (double vision) and difficulty swallowing, and her speech is slurred. Physical examination shows bilateral ptosis (drooping eyelid), unstable gait, and shortness of breath. Laboratory studies show autoantibodies to the acetylcholine receptor, the receptor for the transmitter that mediates synaptic transmission between motor neurons and skeletal muscle. In which of the following structures do these antibodies bind? A. Axon hillock of motor neurons B. Dendrites of motor neuron C. Presynaptic motor neuron membrane D. Postsynaptic muscle membrane E. Synaptic vesicles in motor neurons

*The answer is B.* Glial fibrillar acidic protein (GFAP) is found predominantly in astrocytes.

A 35 year old male was diagnosed with a brain tumor. Immunohistochemistry done on biopsied brain tissue revealed it was positive for GFAP proteins . What is the likely cell origin of the tumor? A. Microglia B. Astrocyte C. Purkinje cell D. Oligodendroglia E. Pyramidal cell

*The answer is D.* Multiple sclerosis (MS) is a chronic demyelinating disease. It is the most common chronic CNS disease of young adults in the United States. The disorder affects sensory and motor functions and is characterized by exacerbations and remissions over years. Forty percent of cases are marked by eye problems, such as loss of visual fields, blindness in one eye, or diplopia. The demyelinated plaque is the hallmark of MS. Evolving plaques are marked by selective loss of myelin, influx of chronic inflammatory cells, and accumulation of edema fluid. Intracellular deposits of alpha-synuclein (choice B) are observed in patients with Parkinson disease. Beta-amyloid protein (choice C) accumulates in the cerebral cortex as extracellular plaques in patients with Alzheimer disease.

A 35-year-old woman complains of blurred vision. Two months later, the patient develops double vision and numbness in the fingers of her left hand. MRI shows scattered plaques in the patient's brain and spinal cord. The patient is diagnosed with multiple sclerosis. The plaques observed in this patient represent selective loss of which of the following proteins of the central nervous system? (A) Acetylcholine receptors (B) Alpha-synuclein (C) Beta-amyloid protein (D) Myelin (E) Tubulin

*The answer is D.* Each neuron has one axon that conveys electrical and chemical information away from the cell body to other neurons or to target cells (e.g., muscle fiber). Axons can be very long, such as those originating from first-order motor neurons located in the ventral horn of the spinal cord. They may travel a long distance to reach the skeletal muscle that they innervate (greater than 1 m). Axons that originate from interneurons are typically short. Protein synthesis(choice C) is the major function of the neuronal cell body. Dendrites and cell bodies receive impulses from other neurons (choices A and B). Uptake and degradation of neurotransmitters (choice E) takes place at synaptic junctions.

A 35-year-old woman injures her common fibular nerve in a motorcycle accident. Which of the following best describes the primary function of neuronal axons within this major division of the sciatic nerve? (A) Convey signals to dendrites (B) Receive signals from other neurons (C) Synthesize structural proteins (D) Transmit signals to other cells (E) Uptake of neurotransmitters

*The answer is B.* The oligodendrocytes are targeted.

A 35-year-old woman presents with weakness and spasticity in the lower left extremity, visual impairment and throbbing in the left eye, difficulties with balance, fatigue, and malaise. There is an increase in cerebrospinal fluid (CSF) protein, elevated gamma globulin, and moderate pleocytosis. MRI confirms areas of demyelination in the anterior corpus callosum. Imaging identifies plaques which are hyperintense on T2-weighted and fluid attenuated inversion recovery (FLAIR) images, and hypointense on T1-weighted scans. Which of the following cells are specifically targeted in her condition? a. Microglia b. Oligodendrocytes c. Astrocytes d. Schwann cells e. Multipolar neurons

*The answer is B.* Microglia are representatives of the distributed monocyte-macrophage system. They are derived from monocytesthat migrate into the brain as it becomes vascularized during embryonic and fetal development. Microglia are the only type of neuroglial cell that is not derived from glioblasts of neuroectodermal origin. Glioblasts (choice A) and neuroblasts (choice D) are precursors for macroglial cells and neurons, respectively. These stem cell populations are derived themselves from neuroepithelial cells (choice E) that are present in the wall of the neural tube during early development.

A 36-year-old woman suffers a concussion while skiing. CT scan of the brain reveals a massive cerebral contusion of the left frontal lobe. The woman lies comatose for 20 days but then expires. A section of brain from the patient is stained with H&E and examined by light microscopy (shown in the image). The cells identified are derived from which of the following stem cell populations during development of the nervous system? (A) Glioblasts (B) Granulocyte/monocyte progenitor cells (C) Neural crest cells (D) Neuroblasts (E) Neuroepithelial cells

*The answer is C.* Microglia are the smallest neuroglial cells in the CNS, and they are inconspicuous healthy tissue. Microglia respond quickly to CNS injury (e.g., ischemia, trauma, or infection) and proliferate to become reactive microglial cells. In regions of injury or infectious disease, microglia accumulate in large numbers and demonstrate an infiltrative phenotype with characteristic thin elongated nuclei. This distinctive nuclear morphology makes them readily visible in routine H&E preparations (shown in the image). None of the other choices show this nuclear morphology.

A 36-year-old woman suffers a concussion while skiing. CT scan of the brain reveals a massive cerebral contusion of the left frontal lobe. The woman lies comatose for 20 days but then expires. A section of brain from the patient is stained with H&E and examined by light microscopy (shown in the image). The cells with elongated nuclei indicated by the arrows are best described as which of the following? (A) Astrocytes (B) Endothelial cells (C) Microglial cells (D) Oligodendrocytes (E) Sensory neurons

*The answer is A.* Astrocytes contain bundles of intermediate filaments that are composed primarily of glial fibrillary acidic protein (GFAP). The image shows the results of immunostaining using antibodies directed against GFAP. Astrocytes are identified as large cells with "stellate" processes projecting in all directions. Astrocytes have been called the "fibroblast" of the CNS because of their critical role in supporting neurons in the brain and spinal cord. Proliferation of astrocytes and microglia in response to injury is referred to as gliosis. Gliosis in the central nervous system is the equivalent of scar formation elsewhere in the body. In spinal cord injuries, axonalregeneration can be seen up to 2 weeks. However, after 2 weeks, gliosis has taken place and attempts at axonal regeneration come to an end. Axonal regeneration in the central nervous system occurs only in the hypothalamohypophysial region, where glial and capillary barriers do not inhibit directed cell migration (axonal path finding). Axonal regeneration appears to require intimate contact with extracellular fluids containing plasma proteins. The other cells listed as choices do not proliferate in response to injury, and they do not stain with antibodies against GFAP.

A 36-year-old woman suffers a concussion while skiing. CT scan of the brain reveals a massive cerebral contusion of the left frontal lobe. The woman lies comatose for 20 days but then expires. A section of the patient's brain is stained at autopsy using an antibody directed against an intermediate filament protein (shown in the image). This immunohistochemical labeling technique identifies which of the following cells? (A) Astrocytes (B) Endothelial cells (C) Microglial cells (D) Neurons (E) Oligodendrocytes

*The answer is E.* Astrocytes are the most numerous glial cells in the CNS. Two kinds of astrocytes have been identified: fibrous and protoplasmic. Fibrous astrocytes are primarily located in the white matter and have relatively few but long processes. Some of the processes can be very long and even span the entire thickness of the brain. Protoplasmic astrocytes possessing a large number of short and branched processes are found in the gray matter of the CNS. Astrocytes with their radiating processes form a network within the CNS that supports and modulates neuronal activities. The expanded "perivascular feet" of some of the processes of protoplasmic astrocytes terminate on capillaries and contribute to the formation of the "blood-brain barrier." The "perineural feet" of protoplasmic astrocytes cover bare areas of myelinated axons at synapses and at the nodes of Ranvier. Defense against pathogens and phagocytosis (choices A and D) are important functions of microglial cells. Myelination of axons (choice C) and production of cerebrospinal fluid (choice B) are the principal functions of oligodendrocytes and ependymal cells, respectively.

A 36-year-old woman suffers a concussion while skiing. CT scan of the brain reveals a massive cerebral contusion of the left frontal lobe. The woman lies comatose for 20 days but then expires. A section of the patient's brain is stained at autopsy using an antibody directed against an intermediate filament protein (shown in the image). Which of the following best describes the primary function of the cells that are identified in the brain of the patient? (A) Defense against pathogens and neoplastic cells (B) Generation of cerebrospinal fluid (C) Myelination of neuronal axons (D) Phagocytosis of senescent neurons (E) Support and nourishment of neurons

*The answer is C.* The ciliated, cuboidalcolumnar cells that line the brain ventricles and spinal canal are termed ependymal cells. The epithelial-like ependymal cell layer forms a barrier between the cerebrospinal fluid and brain parenchyma and regulates fluid transport between these two compartments. At specific locations within the ventricular system, ependymal cells are modified to form a choroid plexus with associated capillaries that secrete cerebrospinal fluid. None of the other cells listed as choices displays a low columnar epithelial morphology.

A 46-year-old man with malignant glioblastoma develops cardiorespiratory failure and expires. A section of the patient's brain near the lateral ventricle is examined by light microscopy (shown in the image). The arrows identify which of the following cells? (A) Astrocytes (B) Endothelial cells (C) Ependymal cells (D) Microglial cells (E) Oligodendrocytes

*The answer is B.* The functional components of neurons include axon, dendrite, cell body (soma), and synaptic junction. Axons and dendrites provide the core "circuitry" for the nervous system. Axons carry nerve signals away from neuronal cell bodies, whereas dendrites convey signals inward toward neuronal cell bodies. Based on the number of processes extending from the cell body, neurons can be classified as pseudounipolar (unipolar), bipolar, or multipolar. Motor neurons and communicating interneurons are common examples of multipolar neurons. The multipolar neuron identified in this patient's spinal cord shows multiple cellular processes. Bipolar neurons (choice A) have one axon and one dendrite. They are usually associated with special sensory organs, such as those for sight, taste, smell, and hearing. Pseudounipolar neurons (choice C) are commonly sensory neurons, whose cell bodies are located in dorsal root ganglia. Purkinje and pyramidal cells (choices D and E) are multipolar neurons located in the cerebellum and cerebral cortex, respectively.

A 48-year-old man died in a motor vehicle accident and a spinal cord specimen is harvested at autopsy. A smear preparation of the patient's gray matter is stained with H&E and examined by light microscopy (shown in the image). For the spinal cord preparation, the cell indicated by the arrow is classified as which of the following? (A) Bipolar (B) Multipolar (C) Pseudounipolar (D) Purkinje (E) Pyramidal

*The answer is C.* The human nervous system contains over 10 billion neurons that serve as the major functional units of the nervous system. From an anatomic and functional point of view, the nervous system is the most complex organ system in the body. In this smear preparation of spinal cord gray matter, the large cell bodies are neurons with multiple cellular extensions (processes). The nuclei of various neuroglial cells (choices A, B, and D) are visible as small dark-stained dots in the background and are indistinguishable from one another in this preparation. Satellite cells (choice E) surround and support neurons located in ganglia of the peripheral nervous system.

A 48-year-old man died in a motor vehicle accident anda spinal cord specimen is harvested at autopsy. A smear preparation of the patient's gray matter is stained with H&E and examined by light microscopy (shown in the image). The arrow identifies which of the following cells of the central nervous system? (A) Astrocyte (B) Microglial cell (C) Neuron (D) Oligodendrocyte (E) Satellite cell

*The answer is E.* Synaptic vesicles are characterized features of the presynaptic bouton terminals. They are membrane-bound structures containing neurotransmitters. At a nerve impulse, the membrane of synaptic vesicles fuse with the plasma membrane of the presynaptic axon end bulb, thereby release the neurotransmitter into the synaptic cleft. Herring bodies (choice B) are dilated nerve endings of unmyelinated nerves in the posterior pituitary. These nerves store oxytocin and antidiuretic hormone. None of the other structures listed release neurotransmitters.

A 53-year-old woman presents to the emergency room complaining of blurred vision and difficulty speaking (dysarthria). She reports eating a large quantity of home-canned vegetables. The patient subsequently progresses to respiratory arrest and expires. For the patient described, the neurotransmitter that stimulates contraction of the thoracic diaphragm is normally released from which of the following terminal end-bulb structures? (A) Golgi membranes (B) Herring bodies (C) Nissl bodies (D) Nuclear pores (E) Synaptic vesicles

*The answer is A.* Botulinum toxin is associated with improperly canned foods that are stored without refrigeration. Ingested toxin from the bacterium Clostridium botulinum is rapidly absorbed into the blood from the small intestine. Circulating toxin binds presynaptic nerve terminals and inhibits the release of acetylcholine (ACh), resulting in the paralysis of all skeletal muscles including the respiratory muscles. ACh is the neurotransmitter at the neuromuscular junction. The ACh receptors on the skeletal muscle cells are transmitter-gated Na+ channels. The released ACh at the nerve impulse at the neuromuscular junction interact with the ACh receptors and initiate the contraction of the muscle. Neurons using ACh as their neurotransmitter are referred as cholinergic neurons, including presynaptic sympathetic and parasympathetic neurons. None of the other neurotransmitters listed as choices activates skeletal muscle of the thoracic diaphragm.

A 53-year-old woman presents to the emergency room complaining of blurred vision and difficulty speaking (dysarthria). She reports eating a large quantity of home-canned vegetables. The patient subsequently progresses to respiratory arrest and expires. Inhibition of the release of which of the following neurotransmitters most likely caused paralysis of respiratory muscles in this patient? (A) Acetylcholine (B) Dopamine (C) Epinephrine (D) Norepinephrine (E) Serotonin

*The answer is C.* The image shown is a section of normal lip. The structure indicated by the arrow demonstrates high cellularity and a wavy appearance. It is weakly basophilic compared to the surrounding structures and reveals wavy darker-stained nerve axons. Transverse and oblique sections of skeletal muscle fibers (choice D) occupy most of the field. These fibers have eosinophilic cytoplasm and peripheral nuclei. Dense regular connective tissue (choice A) and smooth muscle (choice E) are not present. Loose connective tissue (choice B) with small blood vessels fills out space between skeletal muscle fibers and the peripheral nerve.

A 62-year-old woman presents with a small mass on the upper surface of her lip. Physical examination reveals a pearly nodule with rolled borders and central ulceration. The nodule is subsequently removed and examined by light microscopy. Which of the following tissues is located within the circle? (A) Dense regular connective tissue (B) Loose connective tissue (C) Peripheral nerve (D) Skeletal muscle (E) Smooth muscle

*The answer is D.* Neurons in paravertebral and prevertebral ganglia are postsynaptic, sympathetic neuronal cell bodies. Their axons conduct visceral motor information to various target tissues, including visceral organs, blood vessels, and sweat glands. Visceral afferent nerve fibers (choice E) from thoracic and abdominal viscera travel with sympathetic efferent fibers, but their cell bodies are located in dorsal root ganglia. Interneurons (choice A) and somatic efferent neurons (choice B) are located in the CNS. Somatic sensory neurons (choice C) are located in the dorsal root ganglia.

A 68-year-old man with a history of hyperlipidemia suffers a ruptured abdominal aneurysm and expires. During the autopsy, ganglia are collected from different locations and examined by light microscopy (shown in the image). Which of the following best characterizes neurons present in the ganglion? (A) Interneurons (B) Somatic efferent neurons (C) Somatic sensory neurons (D) Visceral efferent neurons (E) Visceral sensory neurons

*The answer is D.* Oligodendrocytes are the myelin-forming cells in the CNS. Concentric layers of oligodendrocyte plasma membrane form the myelin sheath surrounding axons. In contrast to the peripheral nervous system, where a single Schwann cell envelopes an axon to form an internodal segment, each of the many tongue-like processes of a single oligodendrocyte in the CNS wraps a portion of an axon to form an internodal segment. Thus, a single oligodendrocyte can form multiple internodal segments surrounding one or more neuronal axons. On routine H&E-stained slides, oligodendrocytes exhibit a memorable "fried egg" appearance with central, small, dark round nuclei surrounded by a halo of vacuolated cytoplasm. None of the other choices show this distinctive cellular morphology.

A 68-year-old man with dementia suffers a massive stroke and expires. At autopsy, a section of the patient's brain is stained with H&E and examined by light microscopy (shown in the image). The large cells with pale cytoplasm and central nuclei represent which of the following types of cells? (A) Astrocytes (B) Ependymal cells (C) Microglial cells (D) Oligodendrocytes (E) Sensory neurons

*The answer is A.* Three connective tissue layers (meninges) cover the brain and spinal cord. The outmost layer is the tough dura mater, composed of dense connective tissue. Arachnoid mater adheres to the inner surface of the dura and extends web-like trabeculae to the pia mater on the surface of the CNS. The arachnoid and pia are collectively termed leptomeninges. The space between arachnoid and pia mater contains CSF and is referred to as the subarachnoid space. Meningitis is a dangerous infection caused by a variety of microorganisms. Leptomeningitis denotes an inflammatory process that is localized to the pia/arachnoid. This compartment holds the cerebrospinal fluid—an excellent culture medium for most pathogens. In untreated cases of bacterial meningitis, delirium gives way to coma and death.

A 7-year-old girl is brought to the emergency room with fever, vomiting, and convulsions. The patient is febrile to 39.5°C (104°F). Physical examination reveals cervical pain and rigidity. A lumbar spinal puncture is performed to obtain cerebrospinal fluid to help make a diagnosis. The enlarged subarachnoid space that your needle enters (lumbar cistern) is formed (lined) by which of the following tissues/structures? (A) Arachnoid mater and pia mater (B) Dura mater and arachnoid mater (C) Periosteum of vertebral body and dura mater (D) Pia mater and spinal cord proper (E) Vertebral body and its periosteum

*The answer is B.* Neurotransmitters are small endogenous chemicals that are released at synaptic junctions and bind to receptors on postsynaptic membranes. They serve to transmit signals from one neuron to another neuron or target cell. Parkinson disease (PD) is a common movement disorder characterized pathologically by the loss of dopamine-producing neurons in the midbrain (substantia nigra). Clinically, PD features tremors at rest, muscular (cogwheel) rigidity, expressionless countenance, emotional lability, and dementia late in the course of the disease.

A 72-year-old man complains of balance problems. Physical examination reveals reduced facial expression, resting tremor, and slowness of voluntary movements (bradykinesia). The patient is subsequently diagnosed with Parkinson disease. The patient's symptoms are caused by a deficiency of which of the following neurotransmitters? (A) Acetylcholine (B) Dopamine (C) Nitric oxide (D) Norepinephrine (E) Serotonin

*The answer is A.* Astrocytes are the ubiquitous supporting glial cells of the CNS, and they react to pathologic insults. When damage occurs in the CNS, astrocytes become activated and proliferate to eventually form cellular scar tissue. The process is referred as reactive gliosis, and the resulting permanent scar is termed a plaque. Many CNS diseases and injuries cause reactive gliosis. Current research is aimed at discovering methods for limiting gliosis in stroke patients. Microglial cells (choice D) are involved in removing necrotic debris from sites of injury, but they do not form glial scars. None of the other cells listed are involved in reactive gliosis.

A 76-year-old man suffers a stroke and can no longer move his upper and lower limbs on the right side. MRI of the brain reveals a large plaque composed of cellular scar tissue. Which of the following cells is the principal mediator of scar formation in the brain of this patient? (A) Astrocyte (B) Ependymal cell (C) Injured neuron (D) Microglia (E) Oligodendrocyte

*The answer is A.* Synapses are specialized structures that permit rapid neuron-neuron or neuron-target communication. Synapses occur between axons and many other structures, including dendrites, cell bodies, axons of other neurons, and the plasma membranes of target cells. Since each neuron has only one axon that conducts the action potential (impulse) away from the neuronal cell body, the presynaptic element in a synapse is typically an axon terminal. The axon terminal at the synapse usually appears as an enlarged tip (referred to as bouton or end-bulb). Neurotransmitters are released from end-bulbs into the synaptic cleft. Golgi apparatus (choice D) is an intracellular organelle that regulates protein and lipid glycosylation. None of the other choices represents a presynaptic element.

A chemical synapse is typically composed of a presynaptic element, as well as a synaptic cleft and postsynaptic membrane. Which of the following represents a presynaptic element of a chemical synapse? (A) Axon (B) Cell body (C) Dendrite (D) Golgi apparatus (E) Plasma membrane of target cell

*The answer is E.* The dorsal horn of the spinal cord gray matter processes sensory information. The cell bodies of the sensory neurons are located in dorsal root ganglia (also refer as primary sensory neurons). Sensory interneurons and projection neurons are the major neurons found in the dorsal horn of the spinal cord. Sensory interneurons receive and process impulse conveyed by collateral fibers from the central processes of some primary sensory neurons. The central processes of some other primary sensory neurons synapse with projection neurons. Long axonal processes arise from the projection neurons and form ascending sensory pathways. Motor neurons (choice A) are located in the ventral horn of the spinal cord. Postsynaptic sympathetic neurons (choice B) are found in paravertebral and prevertebral sympathetic ganglia. Presynaptic parasympathetic neurons (choice C) are located in the brainstem and the intermediolateral gray of sacral spinal cord segments S2-S4 (craniosacral flow). Presynaptic sympathetic neurons (choice D) are situated in the intermediolateral horn of the thoracic and upper lumbar spinal cord segments (T1-L2).

A high magnification view of the dorsal horn of the spinal cord segment is shown in the image. Which of the following neurons are located in this region of the spinal cord? (A) Motor neurons (B) Postsynaptic sympathetic neurons (C) Presynaptic parasympathetic neurons (D) Presynaptic sympathetic neurons (E) Sensory interneurons

*The answer is B.* Connective tissue is an important component of peripheral nerves. Nerve axons, along with their myelin sheaths and associated Schwann cells, are enveloped within several layers of connective tissue. The outermost irregular connective tissue layer wrapping a peripheral nerve is termed epineurium. It is continuous with dura mater in the CNS. It binds nerve fascicles together and contains nutrient arteries. Epineurium is lost near the termination of nerve fibers with free nerve endings but contributes to the capsules of encapsulated nerve endings. The collagen bundles in the epineurium are largely responsible for the remarkable tensile strength of peripheral nerves. Endoneurium and perineurium (choices A and E) are not readily identifiable at this magnification.

A longitudinal section of the median nerve obtained at autopsy is stained with H&E and examined by light microscopy (shown in the image). The asterisk identify which of the following nerve-associated structures? (A) Endoneurium (B) Epineurium (C) Nerve fascicles (D) Nerve fibers (E) Perineurium

*The answer is A.* In this high-magnification photomicrograph, axons appear as dark-stained lines. The myelin sheath (choice E) that surrounds axons has been extracted during tissue processing and is represented here as a clear halo. The numerous nuclei visible in this image belong to either Schwann cells or fibroblasts. It is not always possible to distinguish these cells based on nuclear morphology. The pink-stained area surrounding individual nerve fibers represents endoneurium (choice D). Endoneurium is composed of a thin layer of connective tissue containing collagen fibers (choice B). The cytoplasm of Schwann cells (choice C) is poorly visible.

A longitudinal section of the nerve fascicle described in is stained with H&E and examined by light microscopy (shown in the image). The arrows identify which of the following nerve-associated structures? (A) Axon (B) Collagen fiber (C) Cytoplasm of Schwann cell (D) Endoneurium (E) Myelin sheath

*The answer is A.* In this teased preparation of a peripheral nerve, the axon is visible as the dark red line within the myelinated nerve fiber. Axons (also referred to as nerve fibers) are cell processes that conduct action potentials away from neuronal cell bodies. In this slide preparation, the myelin sheath was removed by solvent extraction and appears as empty (or foamy) space surrounding the axons. Numerous Schwann cell nuclei (choice E) are observed in this image residing along the myelin sheath.

A peripheral nerve collected at autopsy is teased apart, fixed to a slide, and stained with H&E (shown in the image). The arrows identify (A) Axon (B) Collagen fiber (C) Myelin sheath (D) Node of Ranvier (E) Nucleus of Schwann cell

*The answer is D.* Axons in the peripheral nervous system may be myelinated, poorly myelinated, or unmyelinated. Thickness of the myelin sheath is determined largely by the axon's diameter. The diameters of peripheral nerve fibers may differ widely. Larger fibers, with thicker myelin sheaths, typically conduct action potentials faster than the smaller nerve fibers. Most of the small fibers in the peripheral nervous system are poorly myelinated or unmyelinated. These axons are, however, still in direct contact with Schwann cells. The lack of myelination combined with the small axon diameter results in a relatively slow conduction of nerve action potentials. Osmium tetroxide (OsO4) is a heavy metal salt that is commonly used to fix lipids and identify lipid-rich myelin membranes. In this transverse section of a peripheral nerve, most fibers exhibit a dark-stained myelin sheath. Other nerve fibers (e.g., those indicated by arrows in this image) are poorly myelinated. None of the other choices show this morphology.

A peripheral nerve is collected at autopsy of a 70-yearold woman with a history of diabetes and hypertension. A transverse section of a nerve fascicle is fixed and stained with osmium tetroxide (OsO4) in order to identify membrane lipids (shown in the image). The arrows identify which of the following nerve-associated structures? (A) Endoneurium (B) Myelinated nerve fiber (C) Perineurium (D) Poorly myelinated nerve fiber (E) Schwann cell nucleus

*The answer is D.* The most likely source of this specimen is the region of gray matter.

A report from a hospital pathology laboratory indicates that a microscope slide with a small specimen of neural tissue contains "numerous GFAP-positive" cells. What is the most likely source of this specimen? a. A region of white matter b. A sensory ganglion c. An autonomic ganglion d. A region of gray matter e. Pia mater

*The answer is C.* The cell body (soma) of a neuron contains a large nucleus and prominent nucleolus, as well as perinuclear cytoplasm. The small perinuclear structures that stain intensely blue in this preparation are termed Nissl bodies. Electron microscopy has demonstrated that Nissl bodies are composed of rough endoplasmic reticulum and aggregates of free ribosomes. Thus, Nissl bodies are sites of active protein synthesis and posttranslational modification. Lysosomes and peroxisomes (choices B and D) are intracellular organelles that may be present in the perinuclear region of some neurons; however, these organelles cannot be identified at this magnification. Heterochromatin (choice A) and segmented nuclei (choice E) are not cytoplasmic organelles.

A section of a spinal cord specimen at autopsy is stained with Luxol fast blue and cresyl violet (shown in the image). Cell bodies of large neurons are observed in this section. Which of the following best describes the dark-stained structures indicated by lines within the neuronal cell bodies? (A) Heterochromatin (B) Lysosomes (C) Nissl bodies (D) Peroxisomes (E) Segmented nuclei

*The answer is B.* In this spinal cord preparation, myelin is stained dark blue. Therefore, the peripheral white matter appears darker than the central gray matter. The butterfly-shaped gray matter is clearly apparent in this section. Line 5 denotes the ventral horn of gray matter. Line 1 denotes a subdivision within the white matter that is termed the posterior funiculus. The area indicated by Line 4 is the central canal. Line 3 points to the lateral funiculus, another subdivision within the white matter.

A segment of spinal cord (C5-C6) is collected at autopsy and stained for myelin with Luxol fast blue and cresyl violet (shown in the image). Which of the numbered lines points to the dorsal horn of gray matter? (A) Line 1 (B) Line 2 (C) Line 3 (D) Line 4 (E) Line 5

*The answer is B.* Nissl bodies are regions with concentrated RER and other polysomes.

A study reported the observations done on a naturally mummified human brain found in the Bushveld of South Africa. After a histological examination, it was found that there was near complete degradation of micro anatomical structures with only a few "Nissl Bodies" in neural microstructure. A confirmatory EM study revealed Nissl bodies showing features seen in the image below which identifies them as which one of the following? A. Synaptic vesicles and acetylcholine B. Polyribosomes and rough endoplasmic reticulum C. Lipoprotein and melanin D. Neurofilaments and microtubules E. Smooth endoplasmic reticulum and mitochondria

*The answer is B.* Groups of nerve fibers bundled together are referred to as nerve fascicles. Nerve fascicles are surrounded by perineurium—a thin sheath composed of concentric layers of specialized epithelial-like connective tissue cells. Collagen fibers may be present between layers of the perineurial cells surrounding large nerve fascicles. Perineurium is continuous with the arachnoid layer of the meninges in the CNS. Distally, perineurium contributes to the capsule of many terminal nerve endings and receptors, including Pacinian and Meissner corpuscles, as well as muscle spindles and Golgi tendon organs. Perineurium may be open-ended in certain locations (e.g., near neuromuscular junctions), where the endoneurial space communicates freely with the interstitial fluid compartment of the body. On this trichrome-stained section, collagen fibers appear blue, whereas cells and axons appear red. Perineurium (Line 2) is seen as a thin red layer with interspersed collagen fibers. This layer surrounds the nerve fascicle that occupies the lower right-hand corner of the image. Collagen bundles within the epineurium (Line 1) also appear blue. The very thin, blue-stained layer indicated by Line 5 represents endoneurium—a fine layer of loose connective tissue surrounding individual nerve fibers.

A transverse section of a nerve is stained with Mallory trichrome and examined by light microscopy (shown in the image). Which of the numbered lines indicates perineurium? (A) Line 1 (B) Line 2 (C) Line 3 (D) Line 4 (E) Line 5

*The answer is C.* Acetylcholine is the neurotransmitter for myoneural junctions as well as for preganglionic sympathetic and preganglionic and postganglionic parasympathetic synapses

Acetylcholine is the only neurotransmitter in which of the following regions of the nervous system? (A) Central nervous system (B) Presynaptic sensory cortex (C) Myoneural junctions (D) Postganglionic sympathetic synapses (E) Motor cortex

*The answer is B.* After transecting an axon, complete axonal degeneration occurs distal to the injury.

After transecting an axon, which change occurs distal to the injury? A. Chromatolysis B. Complete axonal degeneration C. Degeneration of the myelin sheath back to the initial segment D. Movement of the nucleus to an eccentric position in the soma E. Neurite outgrowth from the distal stump.

*The answer is D.* The electron micrograph shows myelinated nerve fibers interspersed with groups of unmyelinated nerve fibers. Myelin sheaths are concentric layers of lipid-rich Schwann cell membrane that wrap around axons in the peripheral nervous system. Myelination serves to isolate axons from their surrounding extracellular environment, thereby enabling rapid, salutatory conduction of nerve impulses. Endoneurium (choice A) and perineurium (choice E) are connective tissues that surround nerve fibers and nerve fascicles, respectively. Epineurium (choice B) is connective tissue that binds nerve fascicles together and contains nutrient arteries.

An 80-year-old woman with a history of diabetic neuropathy suffers a stroke and expires. At autopsy, a peripheral nerve is stained with osmium tetroxide (OsO4), sectioned, and examined by electron microscopy (shown in the image). Which of the following best describes the structures that are indicated by the arrowheads? (A) Endoneurium (B) Epineurium (C) Glycocalyx (D) Myelin sheath (E) Perineurium

*The answer is C.* Long axons within a peripheral nerve are myelinated by multiple Schwann cells, resulting in a segmented myelin sheath. The junction where two successive Schwann cells meet is referred to as a node of Ranvier, and the myelin sheath between two sequential nodes of Ranvier is referred as an internodal segment (choice B). These segments are approximately 1 mm in length. Thus, a 1-m nerve leaving the spinal cord is associated with over 1,000 Schwann cells. The axon at the node of Ranvier is not myelinated but is covered by interdigitating processes arising from adjacent Schwann cell membranes. Nodes of Ranvier appear as small gaps in the myelin sheath (shown in the image). Schmidt-Lanterman clefts (choice E), also termed myelin clefts, are spaces containing Schwann cell cytoplasm that lies between adjacent myelin membrane lamellae. Schmidt-Lanterman clefts, endoneurium, and perineurium (choices E, A, and D) are also not visible in this preparation.

Another peripheral nerve specimen is fixed and stained with OsO4 and examined by light microscopy (shown in the image). The arrow identifies which of the following nerve-associated structures? (A) Endoneurium (B) Internodal segment (C) Node of Ranvier (D) Perineurium (E) Schmidt-Lanterman clefts

*The answer is D.* Nodes of Ranvier represent gaps or interruptions in the myelin sheath of axons. At these gaps, axons are separated from the extracellular (interstitial) space by finger-like projections of Schwann cell membranes and cytoplasm. Two adjacent nodes mark an internodal segment of the sheath. This makes nerve fibers appear as a "string of sausages." None of the other choices shows this distinctive morphology.

Arrowheads on the image shown identify which of the following nerve-associated structures? (A) Axon terminal (B) Capillary (C) Internodal segment (D) Node of Ranvier (E) Synapse

*The answer is E.* Axons of motor neurons in the anterior horn exit the spinal cord through the anterior root. The posterior root serves as the entry point for sensory fibers coming into the posterior horn region of the spinal cord. The posterior column and ventral white commissure are fiber tracts located solely within the spinal cord.

As they leave the spinal cord and course peripherally to skeletal muscle, the axons of motor neurons must pass through which of the following structures? A) Posterior column B) Posterior root C) Ventral white commissure D) Posterior horn E) Anterior root

*The answer is E.* Multiple sclerosis is an immune-mediated disease exhibiting chronic and progressive dysfunction of the nervous system due to demyelination of the CNS and optic nerves, striking the 20- to 40-year age group affecting 1.5 times more women than men. There are random episodes of inflammation, edema, and demyelination of axons followed by periods of remission. Each episode may reduce the vitality of the patient and be sufficient to cause death within months (see Chapter 9 V B Clinical Considerations).

Episodes of demyelination are associated with (A) meningitis. (B) Huntington chorea. (C) spina bifida. (D) Parkinson disease. (E) multiple sclerosis.

*The answer is E.* Schwann cells are neuroglial cells that support peripheral nerves. Schwann cell membranes form myelin sheaths that envelope many nerves. Unmyelinated nerve fibers are also enveloped and supported by Schwann cells (though they lack myelin sheaths). Astrocytes (choice A) and oligodendrocytes (choice C) are neuroglial cells of the central nervous system. Fibroblasts (choice B) form endo-, peri-, and epineurium. Satellite cells (choice D) nourish and support ganglion cells (neurons) of the peripheral nervous system.

For the nerve specimen shown, the arrow identifies the nucleus of which of the following glial/stromal cells? (A) Astrocyte (B) Fibroblast (C) Oligodendrocyte (D) Satellite cell (E) Schwann cell

*The answer is B.* Dendrites are shorter processes than axons. A neuron typically has many dendritesthat receive impulses from other neurons. Because they are often highly branched, it is common to refer to neurons as having a dendritic "tree." Signals from the dendritic tree are summed in the cell body and axon hillock resulting in various outcomes, including initiation of a new action potential. Neurons only have one axon. The image shown here does not provide enough detail to unambiguously identify an axon. None of the other choices show the distinctive features of neuronal dendrites.

For the spinal cord preparation, the arrowheads identify which of the following cellular/ subcellular structures? (A) Axons (B) Dendrites (C) Nissl bodies (D) Nucleoli (E) Synaptic junctions

*The answer is D.* Myelin surrounding nerve fibers in the white matter of the brain and spinal cord is composed of concentric layers of oligodendrocyte cell membrane. Multiple, tongue-like processes of individual oligodendrocytes are able to myelinate multiple nearby axons. Schwann cells (choice E) produce myelin for axons in the peripheral nervous system.

In the central nervous system, myelin is produced and maintained by which of the following types of cells? (A) Astrocytes (B) Microglial cells (C) Neurons (D) Oligodendrocytes (E) Schwann cells

*The answer is D.* Functionally related nerve cell bodies are usually clustered together in the CNS and are referred as a nucleus. Examples include facial nucleus, pontine nucleus, and nucleus ambiguous. Functionally related axons are bundled together (choice B) and form subdivisions within the white matter. There are a variety of names for bundled axons, including fasciculus, funiculus, lemniscus, peduncle, and tract. None of the other choices describes nuclei within the CNS.

In the central nervous system, the term "nucleus" refers to which of the following? (A) Aggregate of pyramidal cells in the cerebral cortex (B) Bundle of functionally related axons (C) Bundle of functionally related dendrites (D) Cluster of functionally related neuronal cell bodies (E) Collection of Purkinje cells in the cerebellum

*The answer is A.* In the choroid plexus water from capillaries is transported directly into the cerebrospinal fluid by the ependyma.

In the choroid plexus water from capillaries is transported directly into the cerebrospinal fluid by what structure(s)? a. Ependyma b. Astrocytes c. Cells of the arachnoid mater d. Lining of the central canal e. Microglial cells

*The answer is C.* Neural crest cells migrate throughout the body and give rise to ganglia and other structures, including portions of the adrenal medulla, but they do not contribute to the development of preganglionic autonomic nerves, adrenal cortex, or the dorsal horns of the spinal cord.

Neural crest cells give rise to which of the following? (A) Dorsal horns of the spinal cord (B) Adrenal cortex (C) Sympathetic ganglia (D) Preganglionic autonomic nerves (E) Somatic motor neurons

*The answer is B.* Nissl bodies are large, granular basophilic bodies composed of polysomes and rough endoplasmic reticulum. They are found only in neurons (in the soma cytoplasm).

Nissl bodies are composed of (A) synaptic vesicles and acetylcholine. (B) polyribosomes and rough endoplasmic reticulum. (C) lipoprotein and melanin. (D) neurofilaments and microtubules. (E) smooth endoplasmic reticulum and mitochondria.

*The answer is C.* Preganglionic sympathetic axons pass through the white communicating rami to enter the sympathetic trunk. Postganglionic sympathetic axons course through gray rami and might be found in dorsal and ventral primary rami.

Preganglionic sympathetic axons pass through which of the following structures? A) Dorsal root B) Dorsal primary rami C) White rami D) Gray rami E) Ventral primary rami

*The answer is B.* The large neurons present in the ventral horn of the spinal cord are lower motor neurons that provide somatic innervation to skeletal muscle. Adipose tissue, smooth muscle, and sweat glands (choices A, D, and E) are innervated by autonomic nerves, whose cell bodies are located in the peripheral nervous system. Skin (choice C) is innervated by sensory nerve fibers, whose cell bodies are located in dorsal root ganglia.

Regarding the spinal cord section observed in the image, which of the following tissues/structures is innervated directly by the neurons that are indicated by the arrows? (A) Adipose tissue (B) Skeletal muscle (C) Skin (D) Smooth muscle (E) Sweat gland

*The answer is C.* Neural crest cells originate from neuroectoderm along the margins of neural folds during early development. Neural crest cells undergo an epithelial-mesenchymal transition and migrate extensively throughout the embryo giving riseto many structures including Schwann cells, autonomic nervous system, and head mesenchyme. Glioblasts (choice A) and neuroblasts (choice D) are precursor cells for macroglial cells (e.g., astrocytes and oligodendrocytes)and neurons, respectively. Monocytes (choice B) are derived from hematopoietic stem cells; they enter the CNS as it becomes vascularized and differentiate as microglial cells. Neuroepithelial cells (choice E) are stem cells for all neurons and macroglial cells of the CNS.

The cell indicated by the arrow in the image was derived from which of the following stem cell populations during embryonic and fetal development? (A) Glioblasts (B) Monocytes (C) Neural crest cells (D) Neuroblasts (E) Neuroepithelial cells

*The answer is C.* Synaptic vesicles release neurotransmitter into the synaptic cleft by exocytosis. In this process, the vesicle membrane is incorporated into the presynaptic membrane. Although these vesicles contain neurotransmitter, they do not manufacture it.

Synaptic vesicles possess which of the following characteristics? (A) Manufacture neurotransmitter (B) Enter the synaptic cleft (C) Become incorporated into the presynaptic membrane (D) Become incorporated into the postsynaptic membrane (E) Release neurotransmitter via endocytosis

*The answer is C.* Arachnoid mater and pia mater are both composed of thin layers of loose connective tissue. The pia invests immediately on and follows the contour of the surface of the brain and spinal cord. The arachnoid bridges the dura and pia and exhibits delicate extensions (trabeculae) within the subarachnoid space.

The arachnoid mater of the central nervous system is primarily composed of which of the following types of tissue? (A) Dense irregular collagenous connective tissue (B) Elastic connective tissue (C) Loose collagenous connective tissue (D) Reticular connective tissue (E) Simple columnar epithelial tissue

*The answer is D.* The barrier function of the blood-brain barrier is formed by tight (occluding) junctions (zonulae occludens) between the endothelial cells that comprise the lining of brain capillaries. Adding to the impermeability are the nonfenestrated nature of the capillary endothelium and the paucity or absence of pinocytotic vesicles that represent the physiologic pores seen in other endothelia. Astrocytes form end-foot processes around the brain capillaries that induce and maintain the blood-brain barrier, but do not form the barrier itself.

The blood-brain barrier protects the brain from exposure to large toxic molecules, but presents a serious hurdle for delivering therapeutic drugs to the central nervous system. What is the cellular basis of the blood-brain barrier? A. End feet of astrocytes covering brain capillaries B. Fenestrations between brain capillary endothelial cells C. Gap junctions between brain capillary endothelial cells D. Tight (occluding) junctions between brain capillary endothelial cells E. Tight (occluding) junctions between ependymal cells F. Tight (occluding) junctions between microglia

*The answer is A.* In this transverse section of a peripheral nerve, axons appear as red-stained dots surrounded by a clear halo. This "empty space" indicated by Line 3 represents the myelin sheath in living tissue that is removed during tissue embedding and processing. An individual axon and its associated myelin sheath are enclosed by endoneurium (Line 5).

The red-stained central dot indicated by Line 4 in the image shown represents which of the following structures? (A) Axon (B) Endoneurium (C) Fibroblast nucleus (D) Myelin sheath (E) Schwann cell nucleus

*The answer is E.* The nuclei applies to collections of neuronal cell bodies (somata) in the central nervous system.

What term applies to collections of neuronal cell bodies (somata) in the central nervous system? a. Ganglia b. Neuroglia c. Nodes d. White matter e. Nuclei

*The answer is C.* Microglia are the bone marrow-derived mononuclear phagocytes of the CNS. They respond quickly to pathogens and insults to mediate repair and healing. Microglia play critical role in defense against infectious microorganisms and neoplastic cells. As macrophage-like phagocytic cells, they function to remove injured cells and necrotic debris. However, they are not as efficient as tissue macrophages present in other locations throughout the body. None of the other choices describes the function of microglia.

Which of the following best describes the function of microglia in the central nervous system? (A) Establishment of blood-brain barrier (B) Myelination of neuronal axons (C) Phagocytosis and defense against injury (D) Production of cerebrospinal fluid (E) Support and nourishment of neurons

*The answer is B.* Nodes of Ranvier represent gaps in the myelin sheath. Here, the axon is covered by thin cell membranes with a high concentration of voltage-gated Na+ and K+ channels. Action potentials spread rapidly along the internodal segments of the myelinated axon. They jump (are regenerated) from one node of Ranvier to the next. This discontinuous impulse conduction along the axons is referred to as saltatory conduction. In unmyelinated axons, Na+ and K+ channels are uniformly distributed, and impulses are conveyed continuously and more slowly. None of the other choices describe the function of nodes of Ranvier.

Which of the following best describes the function of nodes of Ranvier in the peripheral nervous system? (A) Release and degradation of neurotransmitters (B) Saltatory conduction of nerve impulse (C) Uptake of oxygen and nutrients (D) Formation of neuromuscular junctions (E) Location of satellite cells for repair of nerve injury

*The answer is E.* Sensory neurons located in dorsal root ganglia are pseudounipolar neurons. They possess a single axon that leaves the neuronal cell body and forms two axonal branches: peripheral and central. These neurons are described as being pseudounipolar because their two axonal processes arise from a single process. The peripheral axon travels to receptors in target organs such as skin or muscle. The central axon reaches the CNS where the impulse is further processed. Bipolar neurons (choice A) have two processes: one axon andone dendrite. They are typically found in special sensory organs. Interneurons (choice B) are located in the CNS, where they form a complex communicating and integrating neuronal network. Interneurons and motor neurons (choice C) are both multipolar neurons that contain one axon and a various number of dendrites (dendritic tree).

Which of the following best describes the neurons that are present in the ganglion described in the image? (A) Bipolar (B) Interneuron (C) Motor (D) Multipolar (E) Pseudounipolar

*The answer is A.* Neuronal axons arise from a pyramidal-shaped area of the cell body that is referred to as the axon hillock (small hill). The axon hillock lacks Nissl bodies and a Golgi complex but does contain microtubules, neurofilaments, mitochondria, and various intracellular vesicles. Centromeres, centrosomes, and kinetochores (choices B, C, and D) help organize microtubules in the mitotic spindle apparatus. Centrosomes (choice C) are also organizing centers in cilia and flagella.

Which of the following cellular structures gives rise (origin) to the cell projection that conducts impulses away from the cell body? (A) Axon hillock (B) Centromere (C) Centrosome (D) Kinetochore (E) Nissl body

*The answer is E.* Cell bodies of both somatic and visceral sensory neurons are located within dorsal root ganglia (DRG). Thus, pseudounipolar neurons in DRG may process somatic sensation from the body wall or visceral sensory information arising from internal organs. Visceral motor and autonomic motor neurons (choices A and D) typically provide motor innervation to the viscera and glands; their postsynaptic neurons are located in the sympathetic or parasympathetic ganglia. Multipolar neurons located in the ventral horn of the spinal cord provide somatic motor innervation to skeletal muscle (choice C). Interneurons (choice B) are in the CNS.

Which of the following describes the function of neurons that are located in dorsal root ganglia of the nervous system? (A) Autonomic motor (B) Interneuron communicating (C) Somatic motor (D) Visceral motor (E) Visceral sensory

*The answer is B.* After an action potential reaches a synapse at an axon terminal, there is calcium ion influx at the presynaptic terminal.

Which of the following events occurs immediately after an action potential reaches a synapse at an axon terminal? a. Vesicle fusion with the presynaptic terminal membrane b. Calcium ion influx at the presynaptic terminal c. Neurotransmitter binding to receptors on the postsynaptic membrane d. Neurotransmitter release into the synaptic cleft e. Binding of the neurotransmitter at the presynaptic terminal

*The answer is A.* The perivascular feet of astrocytes also contribute to the formation of the blood-brain barrier. Neuroglial astrocytes send out foot processes that terminate on capillaries and help maintain tight junctions between the endothelial cells. Recent research has shown that the integrity of endothelial tight junctions in the CNS depends on the normal function of astrocytes. None of the other cells listed contribute to the development or function of the blood-brain barrier.

Which of the following glial cells contributes to the formation of the blood-brain barrier in the central nervous system? (A) Astrocytes (B) Ependymal cells (C) Microglial cells (D) Oligodendrocytes (E) Schwann cells

*The answer is E.* The blood-brain barrier effectively separates the nervous system from the rest of the body. It controls the passage of substances from the blood into the CNS and protects the brain and spinal cord from fluctuating levels of electrolytes and hormones, as well as potential toxins of microorganisms. The blood-brain barrier is also instrumental in providing a stable balance of electrolytes in the interstitial environment surrounding CNS tissue. The blood-brain barrier forms and is maintained by continuous-type capillaries that are sealed together by zonula occludens. These tight junctions efficiently prevent the diffusion of solutes and fluid components from blood into neural tissue. A complete and continuous basal lamina surrounding the endothelial cells further ensures the elimination of gaps. None of the other choices form tight junctions between cells.

Which of the following intercellular junctions is essential for maintaining the integrity of the blood-brain barrier? (A) Gap junctions (B) Hemidesmosomes (C) Macula adherens (D) Zonula adherens (E) Zonula occludens

*The answer is C.* The connective tissue layer that surrounds individual fascicles in large peripheral nerves is important as part of the blood-nerve barrier in the nerve.

Which of the following is a characteristic of the connective tissue layer that surrounds individual fascicles in large peripheral nerves? a. A delicate region of connective tissue in contact with Schwann cells b. Called the dura mater c. Important as part of the blood-nerve barrier in the nerve d. Rich in myelin e. The thickest sheath of connective tissue in the nerve

*The answer is D.* Nissl substance are large masses of free polyribosomes and RER. This becomes more abundant with age.

Which of the following is characteristic of the chromatophilic material called Nissl substance in neural tissue? a. Found throughout neurons b. Site of mRNA translation for proteins of the axolemma c. Most abundant in unipolar neurons d. Becomes more abundant as an individual gets older e. An example of intermediate filament proteins

*The answer is E.* Each bundle of nerve fibers is surrounded by the perineurium, which consists primarily of several layers of epithelioid cells. Tight junctions between these cells exclude most macromolecules. The external coat of nerves, the epineurium, surrounds many fascicles but does not exclude macromolecules. The layer of reticular fibers that covers individual nerve fibers is the endoneurium; it also does not exclude macromolecules.

Which of the following statements is characteristic of the perineurium? (A) It is a fascia surrounding many bundles of nerve fibers. (B) It is the fascia surrounding a single nerve fiber. (C) It is a thin layer of reticular fibers covering individual nerve fibers. (D) It is a fascia that excludes macromolecules and forms the external coat of nerves. (E) It consists in part of epithelioid cells that surround a bundle (fascicle) of nerve fibers.

*The answer is E.* Perineurium envelops nerve fiber bundles (fascicles) and is composed of concentric layers of perineurial cells and sparse collagen fibers. Perineurial cells connect to one another via tight junctions (zonula occludens), creating an effective blood-nerve barrier that ensures isolation of peripheral nerve fibers from the interstitial fluid compartment of the body. The role of perineurium as a blood-nerve barrier in the peripheral nervous system is analogous to the role of arachnoid mater in establishing a blood-brain barrier in the CNS. Endoneurium (choice A), a layer of loose connective tissue, wraps individual nerve fibers. Epineurium (choice B) is composed of irregular connective tissue and provides considerable tensile strength to the peripheral nerve. Myelin (choice C) is composed of concentric layers of Schwann cell membranes and ensures rapid conduction of action potentials. Node of Ranvier (choice D) provides saltatory conduction of nerve impulses.

Which of the following structures contributes to the formation of a blood-nerve barrier in the peripheral nervous system? (A) Endoneurium (B) Epineurium (C) Myelin sheath (D) Node of Ranvier (E) Perineurium

*The answer is A.* The nervous system is divided anatomically into central nervous system (CNS) and periphery nervous system (PNS). The CNS is composed of the brain and spinal cord. It is situated within the cranial cavity and spinal canal of the vertebral column. The brain itself consists of the cerebrum, cerebellum, and brainstem. The PNS distributes cranial and spinal nerves to every part of the body, conducting impulses to-and-from the CNS. The other structures listed as choices are components of the PNS.

Which of the following structures is a component of the central nervous system? (A) Brainstem (B) Dorsal root ganglion (C) Enteric nervous system (D) Paravertebral sympathetic chain (E) Postsynaptic parasympathetic ganglion

*The answer is B.* Between the apex of the axon hillock and the beginning of the myelinated nerve axon, there is a short, unmyelinated segment that is referred as the initial segment. Recent research has demonstrated that the action potential of a nerve axon is summed in the axon hillock and then generated within the initial axon segment. The other choices do not generate new action potentials.

Which of the following structures of a neuron is responsible for the generation of an action potential that is conducted from one neuron to another neuron? (A) Dendritic tree (B) Initial segment (C) Myelin sheath (D) Nissl body (E) Synapse

*The answer is B.* The combination of a motor neuron and all the muscle fibers innervated by that motor neuron is called a motor unit.

Which of the following terms applies to the combination of a motor neuron and all the skeletal muscle fibers contacted by that motor neuron? A) Golgi tendon organ B) Motor unit C) Propriospinal neurons D) Skeletal muscle fibers

*The answer is B.* Multipolar motor neurons in the spinal cord are situated in the ventral horn. Their axons constitute the periphery nerves that innervate and activate contraction of voluntary skeletal muscle. Cardiac muscle (choice A), smooth muscle (choice D), and sweat glands (choice E) are innervated by autonomic nerve fibers. Skin (choice C) is innervated by sensory nerve fibers.

Which of the following tissues/structures is most likely innervated by the cell identified in this image? (A) Cardiac muscle (B) Skeletal muscle (C) Skin (D) Smooth muscle (E) Sweat glands

*The answer is E.* The white matter consists mainly of axons and neuroglial cells.

Which structure consists mainly of axons and neuroglial cells A. Arachnoid mater B. Dura mater C. Gray matter D. Pia mater E. White matter

*The answer is A.* Arachnoidmater contains contains trabeculae around which cerebrospinal fluid (CSF) flows.

Which structure contains trabeculae around which cerebrospinal fluid (CSF) flows? a. Arachnoid mater b. Ependyma c. Dura mater d. Pia mater e. Gray matter