Nervous Tissue I Flashcards
What is the basic structural and functional unit of the nervous system?
neuron
Other names for the cell body?
soma, perikaryon
What is the trophic, metabolic center of the cell?
cell body
What are the three shapes cell bodies of neurons may take?
spherical
ovoid
angular
What is the membrane of the cell body specialized for?
impulse generation
What organelles would you find in the cell body of a neuron?
GA, mitochondria, nissl bodies, free ribosomes
What are nissl bodies?
stacks of rER
Describe the nucleus of a neuron.
Large, clear, and euchromatic with a dense nucleolus
Why don’t neurons form tumors?
In adults there is no mitosis
Can neurons divide?
In general, NO
But, in the adult brain some neural stem cells retain the ability to regenerate and may migrate to the site of injury
What filaments are found in the cell bodies of neurons?
neurofilaments (intermediate), microfilaments (actin) and microtubules
What is lipofuscin? what color does it stain?
lysosomal enzymatic residue
Accumulation of degraded cell organelles and debris present in long-lived cells such as organelles
yellowish-brown pigment
What is the axon hillock? how does it stain?
The funnel-shaped origin of the axon
pale staining due to a lack of rER
What is chomatolysis?
dissolution of nissl substance following injury
What increases the receptive area of neurons?
dendrites
Are dendrites myelinated?
Never
What is the function of dendrites?
They receive information from receptor cells and transmit this information to the cell body
membrane specialized for impulse generation
What is the function of axons?
Relay action potentials away from the cell ody to the axon terminals and then transmit them to other neurons, smooth, skeletal, or cardiac muscle cells, or gland cells
membrane specialized for impulse conduction
What organelles might be found in the axon?
NO rER
may contain mitochondria, microtubules, neurofilaments, vesicles, and sER
What is the axolemma?
the axon cell membrane
What is the axoplasm?
the axon cytoplasm
What is the initial segment of the axon? why is it important?
Segment of axon distal to the axon hillock and proximal to where myelination begins
Action potential is initiated here
Describe the cell membrane of the initial segment of the axon.
Dense undercoating with numerous ion channels
Where are collateral branches located?
near the hillock
branches off of the main axon
What are the terminal arborizations?
terminal axonal branches
What are terminal buttons? what are other names for terminal buttons?
aka axon terminals or end bulbs
The dilated ends of arborizations which form synapses
*some prtn synthesis may occur here
Which direction is anterograde transport? retrograde?
anterograde is away from the cell body
retrograde is toward the cell body
What is the microtubule-associated motor protein involved in anterograde transport?
kinesin
What is the microtubule-associated motor protein involved in retrograde transport?
dynein
What molecules are transported via the slow anterograde transport system?
tubulin molecules, actin molecules, and neurofilament proteins
moves .2-.4 mm/day
Which transport system do viruses and toxins use?
Retrograde transport
enter the nerve endings and travel to the CNS
What molecules are carried via the fast transport system? which direction?
bidirectional!
membranous organelles such as sER, synaptic vesicles and mitochondira; sugars; aa; nucelotides; NT; and calcium
requires ATP
What are bipolar neurons associated with?
special senses
Can be found in the retina, inner ear, and nose
What anatomical classification would motor neurons and interneurons fall under?
multipolar neurons
*multipolar is the most common type of neuron
Where would you find unipolar neurons?
enclosed in CN sensory ganglia and dorsal root ganglia
Do impulses enter the cell body of unipolar cells?
No
Impulses are transmitted down the axon, bypassing the cell body
Where do skeletal motor (somatic efferent) neurons go?
to skeletal muscle fibers
Where do visceral motor (visceral efferent) neurons go?
to smooth muscle, cardiac muscle, or glands
*Autonomic
What do somatic afferent neurons receive?
Sensory stimuli from the environment
What do visceral afferent neurons receive?
Sensory stimuli from the viscera
Where are the interneurons located?
confined to the CNS
99.9% of neurons!- multipolar
What is the function of neuroglia cells?
both physical and physiological support protecting nerve cells
Which is more numerous- neuroglia or neurons?
neuroglia (3-4 neuroglial cells per neuron)
Can neuroglial cells form tumors?
YES because unlike neurons they divide
Does the CNS contain connective tissue?
NO
the only connective tissue found in the brain is associated with blood vessels
What are the defining physical features of astrocytes?
largest of glial cells with “vascular feet”, “pedicles”
What are the functions of astorglial cells? (5)
1) Ensheathe all blood vessels covered by basal lamina
2) Assist in the formation of the Blood-Brain-Barrier
3) Surround periphery of brain and spinal cord forming a layer deep to pia mater
4) Form scar tissue following nerve tissue injury (tissue repair)
5) Monitor the ionic and chemical composition in extracellular space around nerve cells
Where are protoplasmic astrocytes found?
Primarily in gray matter, granular cytoplasm, processes cover synapses, neurons and blood vessels
Where are fibrous astrocytes found?
Primarily in white matter, associated with blood vessels and pia mater, cover the nodes of ranvier and synapses
Long thin processes are light staining
How prevalent are fibrous astrocytomas?
Fibrous astrocytomas make up about 80% of primary brain tumors in the adult
Where are oligodendrocytes found?
In white matter they form rows and each oligo myelinates one or more than one axon
Which cells are known as the CNS housekeepers?
Microglia because they are phagocytic
Describe microglia.
Small cell bodies, elongated nuclei (other glia have round), condensed chromatin
Present in both gray and white matter
Which cells line the brain and spinal cord cavities?
cuboidal-columnar ependymal cells
They have motile cilia which move the CSF
They also cover the choroid plexus which forms CSF
What are other important features of Ependymal cells?
abundant mitochondria, apical GA, sparse rER, gap junctions and zonula adherens
Where is an ependymoma located?
A tumor growing in the fourth ventricle
Compresses surrounding structures as it expands
5% of primary brain tumors
Describe an unmyelinated axon in the CNS.
not covered by glia (wear their birthday suit)
Describe an unmyelinated axon in the PNS.
occupy a groove of a Schwann cell
One Schwann cell may envelop many axons
Are there nodes of Ranvier along unmyelinated axons?
Nope
If an axon is myelinated within the CNS, it is myelinated by ….
oligodendrocytes
If an axon is myelinated within the PNS, it is myelinated by ….
Schwann cells
Is myelin a substance that is ‘secreted’ on the axon by a cell?
NO
Myelin is formed by concentric layers of cell membranes (myelin sheath) which have a high lipid content
What is the function of myelin?
Myelin increases impulse conduction and insulates axons
What is a node of Ranvier?
The unmyelinated segment of an axon between two Schwann cells or oligodendrocytes
If an immature Schwann cell is in close proximity to a large-diameter axon, what will it develop into?
A myelinating cell
small-diameter–> nonmyelinating cells
Define mesaxon.
Fused cell membranes
What is an internodal segment?
Insulated (myelin-covered) segments of axon
Where are schwann cells derived from?
neural crest
Where would you expect to find nerve coverings?
ONLY associated with NERVES in the PNS
Which nerve covering encloses individual axons?
Endonerium
What synthesizes the endonerium?
schwann cells
Describe the endoneurium.
Delicate layer of loose connective tissue with collagen fibrils
What is the order of coverings of a myelinated peripheral nerve? (hint: 5)
myelin sheath basal lamina endoneurium perineurium epineurium
Which covering layer surrounds a nerve bundle?
perineurium
Which covering surrounds a ‘gross nerve’?
epineurium
A dense irregular connective tissue (fibrous coat) with elastic fibers which covers several nerve bundles, which together form the gross nerve
What is the name for cytoplasm trapped in concentric layers of cell membranes of Schwann cells myelinating an axon?
Schmidt-Lanterman cleft
What is the function of Satellite cells?
support cells that surround the cell bodies of neurons housed in ganglia
analogous function to schwann cells
Do Satellite cells form myelin?
NO
What is optic neuritis?
Inflammation of the optic nerve
symptoms: visual loss affecting one eye, pain when moving eye, papilledema
What is the most common cause of optic neuritis?
multiple sclerosis or other demyelinating disease
What is MS?
autoimmune disease causing progressive demyelination of white matter in the CNS resulting in decreased velocity of impulse propagation in affected axons
Possible root cause is immune system responding to an oligodendropathy
