Exam 2: Nerves Flashcards
Cell body
spherical, ovoid, or angular
trophic, metabolic center
Most protein synthesis occurs here (Golgi apparatus, mitochondria, basophilic clumps, free ribosomes)
Nissl bodies
stacks of rER
nucleus
large, clear, euchromatic, dense nucleolus
neurons do not form tumors because
typically neurons in adults do not divide (mitosis), however some neural stem cells and glial cells can divide and differentiate into nerve cells
lipofuscin
yellowish-brown pigment, lysosomal enzymatic reisdue
melanin granules
pigment present in certain neurons (substantia nigra)
Axon hillock
origin of axon, funnel-shaped, pale - no rER
chromatolysis
dissolution of Nissl substance following injury
dendrites
radiate from soma, branch and taper, increase receptive area of neuron, usually no GA
never myelinated - receive stimuli and transmit information to cell body
Axon
cylindrical, varies in length
no rER, contains microtubules, neurofilaments, and vesicles
Relays action potentials away from cell body to axon terminals
axolemma
axon cell membrane - specialized for impulse conduction
axoplasm
axon cytoplasm
initial segment
segment of axon between axon hillock and where myelination begins
action potential initiated here
Axoplasmic transport
transport of macromolecules, organelles, and vesicles along axon
anterograde transport
away from cell body
uses Kinesin
slow or fast transport systems
Kinesin
microtubule-associated motor protein used in anterograde transport
slow transport system
carries tubulin molecules, actin molecules, and neurofilament proteins from cell body to terminal boutons
retrograde transport
towards cell body
uses Dynein
Dynein
microtubule-associated motor protein used in retrograde transport
fast transport system
bidirectional
carries membranous organelles, sugars, aa, nucleotides, neurotransmitters, and calcium
requires ATP
bipolar neurons
2 processes - one dendrite and axon
In retina, inner ear, nose - senses of smell, vision, hearing, and balance
multipolar neurons
most common type
numerous dendrites and single axon
unipolar (pseudounipolar) neurons
single process (axon) arising from cell body which separates into 2 processes impulses bypass the cell body Enclosed in sensory ganglia and DRG
Motor (efferent) neuron
multipolar
skeletal (somatic) - to skeletal muscle fibers
visceral - to smooth muscle, cardiac muscle, or glands - autonomic
Sensory (afferent) neurons
somatic - receive sensory stimuli from environment
visceral - receive sensory stimuli from viscera
interneurons
multipolar, confined to CNS
99.9% of neurons
Neuroglia
provide physical and physiological support protecting nerve cells
Astrocytes (astroglia)
largest, processes have feet, ensheathe all blood vessels covered by basal lamina
Assists in formation of blood-brain barrier
protoplasmic astrocytes
primarily in gray matter
have granular cytoplasm
processes cover synapses, neurons, and blood vessels
fibrous astrocytes
primarily in white matter
have long, thin processes and light staining
associated with blood vessels and pia mater
cover nodes of Ranvier and synapses
Oligodendrocytes
smaller than astrocytes, found in white matter
myelinates one or more axons
Microglia
small cell bodies with elongated nuclei, condensced chromatin
in both gray and white matter
derived from monocytes
phagocytic
Edendymal cells
cuboidal-columnar cells lining brain and spinal cord cavities, cover choroid plexus
contain cerebralspinal fluid
Unmyelinated Axons in CNS
not covered by glia
unmyelinated axons in PNS
occupy a groove in a Schwann cell - no nodes of Ranvier; one Schwann cell envelops many axons
Myelinated axons in CNS
myelinated by oligodendrocytes
Myelinated axons in PNS
myelinated by Schwann cells - wrap membrane repeatedly around one internode of single axon
myelin
high lipid content, increases impulse conduction
Schwann cell in unmyelinated neurons
Many axons in one Schwann cell;
Axon pushed through groove in Schwann cell;
Uninterrupted sheath along length of axon;
No nodes of Ranvier
Schwann cell in myelinated neurons
One axon per Schwann cell;
Schwann cell wraps around internode of axon;
Many Schwann cells along length of axon;
node of Ranvier - unmyelinated segments of axon between 2 Schwann cells
Peripheral nerve coverings (connective tissue)
associated only with nerves in PNS (not CNS)
endoneurium
delicate layer of loose connective tissue with collagen fibrils, covers individual axons
Goes over myelin sheath if cell is myelinated
Perineurium
surrounds nerve bundle
lined by layers of perineurial cells
epineurium
dense, irregular connective tissue (fibrous coat) with elastic fibers
Covers several nerve bundles - form gross nerve
Satellite cells
support cells that surround cell bodies of neurons housed in ganglia
do not form myelin
Most common cause of optic neuritis is
multiple sclerosis
Multiple sclerosis
progressive demyelination of white matter in CNS
Decreased velocity of impulse propagation
Which cranial nerve is myelinated by oligodendrocytes and thus susceptible to demyelination from MS?
optic nerves (CN II)
gray matter
nerve cell bodies and neuroglia - cerebral cortex, cerebellar cortex, nuclei
white matter
mostly myelinated nerve cell axons
Ganglia
collections of nerve cell bodies in PNS
Sympathetic division of ANS
fight or flight response
thoracolumbar outflow
Parasympathetic division of ANS
maintains homeostasis
Craniosacral outflow
Enteric division
controls peristalsis, gland secretion, and blood flow through GI tract
functions independent of CNS
collection of neurons in wall of GI tract
Electrical impulses
not common - present in brain stem, retina, and cerebral cortex
Have gap junctions - current pass from cell to cell
Chemical impulses
most common type of synapses
uses ions and neurotransmitters
Choroid Plexus
in ventricles of brain
consists of holds of pia mater covered by simple cuboidal epithelium - ependymal cells
Produces CSF
anterograde changes in nerve injury repair
distal to site of injury - axonal degeneration and elimination of debris
retrograde reaction and neural regeneration
proximal to site of injury; cell body swells, Nissl bodies move to periphery, nucleus moves away from center of cell body, formation of free ribosomes and protein synthesis, axon grows sprouts and grows into endoneurium toward target cell
