Ch 9: Nerve Tissue & the Nervous System & Q Bank Flashcards
Development of Nerve Tissue
Nervous tissue develops in the early embryo when the dorsal ectoderm neural plate folds lengthwise to form
the neural tube, the precursor of the CNS, and releases neural crest cells, precursors for much of the PNS.
Neurons
There are many kinds of neurons, but all consist of a
cell body (perikaryon) containing the nucleus, a long cytoplasmic extension called the axon, and one or more shorter processes called dendrites.
The Neurons
eurons use the common cell property of excitability to produce and move an
action potential (nerve impulse) along the axon to excite another neuron or other effector cell.
Neurons
Such nerve communication is transmitted to another neuron or effector cell via a synapse, where neurotransmitter is released at
the presynaptic membrane and binds receptors on the postsynaptic cell, initiating a new action potential there.
Glial Cells
required to support neurons in many ways, consist of six major types:
- Oligodendrocytes
- Astrocytes
Oligodendrocytes wrap processes around portions of axons in the CNS, forming myelin sheaths that insulate the axons and facilitate nerve impulses.
Astrocytes, the most numerous cell of the CNS, all produce hundreds of processes to cover and provide regulated microenvironments for neuronal perikarya, synapses, and capillaries.
Glial Cells
- Ependymal cells
- Microglia
Ependymal cells are epithelial-like cells, lacking basement membranes, which line the fluid-filled cerebral ventricles and central canal of the spinal cord.
Microglia differs from all other glial cells in originating from blood monocytes, not from neural tissue precursors; they mediate immune defense activity within the CNS.
Glial Cells
- Schwann cells (neurolemmocytes)
- Satellite cells
Schwann cells (neurolemmocytes) enclose all axons in nerves of the PNS, producing myelin sheaths around large-diameter axons, whose impulse conductivity is augmented at the nodes of Ranvier between successive Schwann cells.
Satellite cells are located within PNS ganglia, aggregated sensory or autonomic neuronal cell bodies, where they enclose each perikaryon and regulate its microenvironment.
Central Nervous System
Within the brain and spinal cord, regions rich in neuronal perikarya and astrocytes comprise the gray matter and
regions containing tracts of myelinated axons comprise white matter.
Central Nervous System
Hundreds of different neurons make up the CNS; large, unique Purkinje neurons characterize the cortex of the cerebellum, and
layers of small pyramidal neurons form the cerebral cortex.
Central Nervous System
The CNS is completely enclosed by three connective tissue layers called Meninges
(1) the tough external dura mater; (2) the middle arachnoid layer; and (3) the delicate pia mater that directly contacts neural tissue.
Central Nervous System
The arachnoid layer contains much CSF, which helps
cushion the CNS within its bony enclosure.
Central Nervous System
The choroid plexus consists of elaborate folds of vascularized pia mater covered by ependyma that project from walls of the cerebral ventricles;
there water is removed from capillaries and transferred into the ventricles as cerebrospinal fluid (CSF).
Central Nervous System
In most CNS regions, neurons are also protected by the blood-brain barrier, consisting of
the perivascular feet of astrocytic processes and the nonfenestrated capillary endothelial cells’ tight junctions.
Peripheral Nervous System
Peripheral nerves consist of axons from motor neurons (in the spinal cord), sensory neurons, and autonomic neurons (in ganglia); all the axons are enclosed within
a series of Schwann cells, but only large (myelinated) axons have myelin sheaths and nodes of Ranvier.
Peripheral Nervous System
Endoneurium is a thin connective tissue layer immediately surrounding Schwann cells in peripheral nerves. It..
is containing a few nonfenestrated capillaries and much reticulin.
Peripheral Nervous System
Groups of axons (with Schwann cells and endoneurium) are surrounded by
perineurium, consisting of layered, squamous fibroblastic cells joined by tight junctions to make a blood-nerve barrier.
Peripheral Nervous System
In large peripheral nerves, groups of axons are subdivided as fascicles, each of which is surrounded by perineurium.
Surrounding the perineurium is a thick, outermost layer of dense irregular connective tissue, the epineurium.
Peripheral Nervous System
Ganglia, which can be either sensory or autonomic, contain neuronal cell bodies and their satellite cells
and are surrounded by connective tissue continuous with that of nerves.
Neural Plasticity & Regeneration
Certain regions of the CNS, such as near the ependyma, retain rare neural stem and progenitor cells that allow some replacement of neurons throughout life
neural plasticity involving formation and remodeling of synaptic connections is also prevalent throughout life.
Neural Plasticity & Regeneration
The complexity and distances of the neuronal and glial interconnections with the CNS make
regeneration and restoration of function within this tissue after major injury very difficult.
Neural Plasticity & Regeneration
The more simply organized peripheral nerves
have better capacity for axonal regeneration,
a process involving reactivation of the perikaryon,
Schwann cells, and macrophages.
- Which of the following is characteristic of the chromatophilic material called Nissl substance in neural tissue?
- Which of the following events occurs immediately after an action potential reaches a synapse at an axon terminal?
- 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?
- b. Site of mRNA translation for proteins of the axolemma
- b. Calcium ion influx at the presynaptic terminal
- d. A region of gray matter
- In the choroid plexus water from capillaries is transported directly into the cerebrospinal fluid by what structure(s)?
- What term applies to collections of neuronal cell bodies (somata) in the central nervous system?
- Which structure contains trabeculae around which cerebrospinal fluid (CSF) flows?
- Ependyma
- Nuclei
- Arachnoid mater
- Which of the following is a characteristic of the connective tissue layer that surrounds individual fascicles in large peripheral nerves?
- Important as part of the blood-nerve barrier in the nerve
- 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
- A 22-year-old man receives a severe, traumatic compression injury to his radial nerve during a motorcycle crash. He shows an advancing Tinel sign. Which one of the following characterizes regeneration of axons after this nerve injury?
a. It occurs in the absence of motor nerve action potentials.
b. It occurs at a rate of about 100 mm/d.
c. It occurs in the segment distal to the site of axon damage.
d. It occurs by a process that involves Schwann cell proliferation.
e. It occurs in conjunction with degeneration and phagocytosis of the endoneurium.
- 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
