With what structures are fibrous astrocytes associated?
Associated with blood vessels and pia mater Cover nodes of Ranvier and synapses
What type of cancer makes up 80% of primary brain tumors in adult?
What kind of neuroglia form rows in white matter?
Oligodendrocytes (oligodendroglia) smaller than astrocytes
What organelles are found in oligodendrocyte?
Many mitochondria Golgi apparatus rER Microtubules
What kind of neuroglia have small cell bodies and elongated nuclei? (other gila have round nuclei)
Microglia Condensed chromatin
Where are microglia found?
In both grey and white matter
What kind of neuroglia are phagocytic (CNS housekeepers)?
Microglia (derived from monocytes)
What are cuboidal-columnar cells lining brain and spinal cord cavities, containing CSF?
What structures are found in ependymal cells?
Motile cilia which move CSF Abundant mitochondria apical Golgi apparatuses sparse rER Gap junctions and zonula adherens
Describe unmyelinated axons in CNS
not covered by glia
Describe unmyelinated axons in PNS
Occupy a groove of Schwann cell; forms longitudinal uninterrupted sheath along length of axon
One Schwann cell envelops many axons
T/F There are no nodes of Ranvier along unmyelinated axons
What is function of myelin?
Increase impulse conduction and insulate neurons
What is mesaxon?
Fused cell membranes
From what structure are Schwann cells derived?
Neural crest cells
What is myelin?
Lipoprotein formed by concentric layers of cell membrane which have a high lipid content (~80%)
T/F Myelin is a substance that is secreted on the axon by a cell
Describe myelination of nerve cell axons in PNS
Schwann cell wraps its membrane repeatedly around one internode of a single axon, forming myelin sheath Each myelinated axon is covered by a series of Schwann cells
What is name of uninsulated segment of axon?
Nodes of Ranvier
What is name of insulated segment of axon?
Internodal segment (internode)
What is delicate layer of loose connective tissue with collagen fibrils that covers individual axons?
What cells synthesize endoneurium?
Describe layers of myelinated axon in PNS
Myelin sheath, basal lamina, endoneurium
What is specialized connective tissue, lined by layers of perineural cells, that surrounds a nerve bundle?
What inhibits passage of macromolecules between nerve cells?
What is enclosed by perineurium?
Schwann cell-ensheathed axons and endoneurium
What is dense irregular connective tissue with elastic fibers that covers several nerve bundles to form gross nerve?
What are satellite cells?
Support cells that surround cell bodies of neurons housed in ganglia Function analogous to Schwann cell but do NOT form myelin
What is optic neuritis?
Inflammation of optic nerve
What is most common cause of optic neuritis?
Multiple sclerosis (or other demyelinating disease)
What is affected by MS?
White matter (myelinated axons) of CNS Any myelinated tract (bundle of axons) may be affected
What causes MS?
Autoimmune attack of myelin sheath formed by oligodendrocytes--demyelination of CNS nerve cell axons
What cranial nerves are susceptible to demyelination during MS?
Only optic nerve (CN II)--is tract of CNS
The other 11 CNs are components of PNS
What are typical symptoms of optic neuritis?
Visual loss affecting one eye (sometimes both) Pain when moving eye Papilledema (depending on segment of optic nerve affected) Pupil of affected eye will not respond to light normally (if visual acuity severely impaired)
What is papilledema?
Swelling of optic disk
What is treatment of optic neuritis?
IV coritcosteroids over 3-5 days Most cases completely within weeks or months
What is ependymoma?
Tumor that grows into (4th) ventricle, compresses surrounding structures as it expands 5% of primary brain tumors
What are clefts of Schmidt-Lanterman?
Schwann cell cytoplasm trapped in concentric layers of cell membrane myelinating an axon
What is a bundle of nerve cell axons in PNS?
How many cranial nerves are present?
How many spinal nerves are present?
What are collections of nerve cell bodies in PNS?
What is example of sensory ganglia in PNS?
Cranial nerve sensory ganglia Dorsal root ganglia
What is example of autonomic ganglia in PNS?
Sympathetic trunk, visceral ganglia Parasympathetic--ganglia associated with CNs and intramural ganglia within visceral walls
What is voluntary nervous system?
Somatic motor system Influences skeletal muscle to produce movement
What is involuntary nervous system?
Autonomic nervous system/visceral motor system Influences smooth muscle, cardiac muscle and glands
What nervous system is involved in "fight, firght, or flight" response?
What nervous system is referred to as "thoracolumbar outflow"?
SANS (Connects with thoracic and lumbar regions of spinal cord-- T1-L2(3))
What nervous system maintains homeostasis?
What nervous system is referred to as "cranosacral outflow"?
What is cranial outflow portion of PANS?
PANS connects with brain through CNs (oculomotor, facial, glossopharyngeal, vagus)
What is sacral outflow portion of PANS?
PANS connects with spinal cord through sacral spinal nerves S2-S4
What is a junction between a neuron and another cell where action potential (nerve impulse) is transmitted from cell to cell?
What kind of cell can postsynaptic cell be?
Another neuron Muscle cell (smooth, cardiac, skeletal) Gland cell
Where are electrical synapses found in human?
NOT common in mammals Present in brainstem, retina, and cerebral cortex
Describe electrical synapse
Gap junctions allow ions (electrical current) to pass from cell to cell
Which type of synapse results in faster impulse transmission: electrical or chemical?
What is most common type of synapse?
What structures are contained within terminal bouton (presynaptic component)?
Presynaptic membrane Mitochondria sER Synaptic vesicles
What are contained within synaptic vesicles?
What is presynaptic density?
Cone-shaped structures that represent active site of synapse
What is a narrow extracellular space between presynaptic and postsynaptic membranes?
What structures are contained with postsynaptic component?
With what modality are bipolar neurons associated?
Describe sense of smell
When inspire air, odorous substances dissolve in mucus blanket that covers olfactory epithelium Then travel to receptors at dendritic terminals of bipolar neurons Causes neurons to fire and send info to CNS (olfactory bulb)
What are receptors of vision?
Bipolar neurons synapse with rods and cones in neural retina
What are receptors in cochlea and vestibular apparatus?
Bipolar neurons in cochlear and vestibular ganglia synapse with hair cells
Where is cell body of pseudounipolar neuron located?
CN sensory ganglia DRG
Where are dendrites of pseudounipolar neurons located?
Monitor skeletal muscle length Proprioception--respond to stretch
When are golgi tendon organs stimulated?
When load is placed on muscle, creating tension on tendon, GTOs are stimulated
What are extrafusal muscle fibers?
Typical skeletal muscle cells (fibers)
What occurs when extrafusal fibers are stimulated?
Muscle cells contract to produce movement
What kind of neurons innervate extrafusal fibers?
Motor-- alpha motor neurons Sensory-- pseudounipolar neurons
What are muscle spindles?
Specialized mechanoreceptor (proprioceptor) that monitors skeletal muscle length
How are muscle spindles oriented?
Parallel to longitudinal axis of extrafusal muscle fibers
Describe structure of muscle spindle
2-12 intrafusal fibers (each covered by a thin capsule) enclosed by a fibrous capsule
What are the 2 distinct types of intrafusal fibers?
Nuclear bag fibers Nuclear chain fibers
Describe intrafusal fibers
Noncontractile region with nuclei in center Skeletal muscle contractile portion with myofibrils at 2 polar ends
What are 2 types of nuclear bag fibers?
What stimulates static nuclear bag fibers?
Changes in muscle length
What stimulates dynamic nuclear bag fibers?
Rate of change in muscle length
What stimulates nuclear chain fibers?
Changes in muscle length
What provides sensory innervation to intrafusal fibers?
Sensory--pseudounipolar neurons with Type Ia (annulospiral primary endings) and Type II (flower spray secondary endings) fibers
What provides motor innervation to intrafusal fibers?
Gamma motor neurons
What fibers become activated at onset of muscle stretch/tension to innervate intrafusal fibers?
Annulospiral (primary) endings--Type Ia
What fibers become activated when stretch is in progress?
Flower spray (secondary) endings--Type II
Where are golgi tendon organs located?
Where muscle inserts into tendon
How are golgi tendon organs arranged?
What innervates golgi tendon organs?
Receives sensory innervation NO motor innervation (do not have contractile portion)
What do golgi tendon organs monitor?
Amount of tensioin placed on skeletal muscle
What happens if injury occurs to axons in CNS?
Minimal or no regeneration of tract axons
If minimal regeneration occurs--does NOT lead to recovery of function
Why do axons in CNS not regenerate following injury?
Basal lamina and Schwann cell tunnels formed in PNS following injury are non-existent in CNS
Oligodendrocytes/myelin may release inhibitory factor, impeding regrowth of axons
Astrocytes may not release enough GF to support sprouting axons
T/F Neurologic deficits following nerve cell injury in CNS are permanent
What happens following nerve cell injury in CNS?
Neuron forms sprouts Astrocytes proliferate--hypertrophy, forming scar tissue to replace damaged tissue Guiding tunnels not formed Scar tissue gets in way/prevents axon sprouts from reaching target (axon sprouts pull back)
What cells are activated in CNS to clean up debris following nerve cell injury?