Nervous Tissue - Giffin Lecture Flashcards
Concept map for principles?
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What does nervous tissue consist of?
1) neurons - transmit electrical impulses from one site in the body to another, and receive and process information
2) neuroglia: non-conducting cells that are in intimate physical contact with neurons; support cells
What are neurons?
Basic unit of nervous system
Possess electrical excitability, the ability to respond to a stimulus and convert it into an action potential
Provide most of the unique functions of the nervous system, such as sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions
What do neurons consist of?
Cell body = soma
Dendrites (1 to many)
Axon (single - nerve fiber)
Cell body is also called….
What do nuclei look like for nerve cells?
Perikaryon or soma
Basically a cell nucleus surrounded by cytoplasm
Nuclei of nerve cells are: large, round, euchromatic and have a single prominent nucleolus
Cell body is what you see when you do a histology slide of a neuron… Hard to see dendrites..
Neurons are usually very active cells!
They have chunky purple stuff in the body..
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Cell Body of a neuron is abundantly supplied with…..
1) masses of rough endoplasmic reticulum (Nissl substances)
2) numerous golgi bodies
3) lots of SER
4) many mitochondria
5) extensive cytoskeleton elements
6) Nissl substance
The axon has NO nissl substance
Material synthesized in the cell body must be transported to the periphery
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What is the Nissl substance?
Rough endoplasmic reticulum
The axon hillock is close to body followed by the initial segment
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What is enriched in the initial segment of the axon?
Na+ channels
What is the axon?
Specialized for conducting signals from one nerve cell to another or to muscle fiber or gland cell
Long, thin, cylindrical projection that often join the cell body at a cone-shaped elevation called the axon hillock
NO RER!
Axons with myelin are called….
Myelinated axons
Myelin is formed by what?
Support cells
Schwann cells in the PNS
Oligodendroglia in the CNS
Cytoplasm for axon?
Plasma membrane for axon?
Axoplasm
Axolemma
Virtually all protein synthesis occurs in the cell body (some in the dendrites)
Need to be transported to distal parts - do this with microtubules and antegrade and retrograde transport
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Anterograde transport can be what?
Fast - synaptic vesicles, mitochondria - KINESISNS!
Slow B - actin, spectrin
Slow A - tubular, intermediate filaments
Retrograde transport is what?
Fast! - synaptic vesicles, mitochondria
By dyneins
What are dendrites?
Short, tapering and highly branched
Receptor processes that receive stimuli from other neurons or from the external environment
Information is transmitted to the cell body
Dendrites are…
Unmyelinated!
Dendrites have extensive arborizations to do what?
Increase SA!
Contents of cell body cytoplasm (with exception of golgi) and the cytoplasm of what are similar?
Dendrites!
Axon terminals- presynatpic endings
Usually there is only one unbranched axon per neuron
What are axon ends called?
Axon collaterals
Telodendria
Axonal terminal
Synaptic knobs
Axon terminals generate and transmit action potentials….
They secrete neurotransmitters from the axonal terminals
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There are lots of mitochondria and synaptic vesicles at axonal terminals!
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A nerve is made up of many nerve cell fibers that are bound together by connective tissue… it has three parts…
1) epineurium
2) perineurium
3) endoneurium
Epineurium
A sheath of dense collagenous CT with elastic fibers that surrounds the nerve.. Blood vessels of various sizes can be seen.
Allows nerves to be stretched
Perineurium
Composed of CT with a lamellar arrangement consisting of several concentric layers. Surrounds bundles of nerve fibers and forms the BLOOD-NERVE BARRIER which isolates the neural environment from humoral facts and cells from the circulation
Fascicles/bundles are organized by this
Endoneurium
Consists of thin layer of loose CT which surrounds the individual nerve fibers
Tight junctions between what cells form the isolating barrier in nerves?
Perineurium cells!
Conduction velocity in the axon is enhanced by …?
Myelination
Axons in the CNS are myelinated by….
Oligodendrocytes
Axons in the PNS are myelinated by….
Schwann cells!
Neural crest cells form what PNS support cells?
Schwann cells
Satellite cells
Myelination is a dynamic process, which involves the ensheathment of the axon by the glial cell and subsequently the extrusion of cytoplasm from parts of the glial cell. Adhesive proteins on the cytoplasm and extracellular side of the PM contribute to a tight opposition of the lipid bilayers… CONCENTRIC CIRCLES!
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The increased lipid content of the myelin sheath provides electrical insulation for the underlying axon
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What are nodes of ranvier?
Areas of the myelinated axon that are not covered by myelin sheath
Each schwann cell myelinated what?
A SINGLE internode!
The internode can be up to 1.5 mm in largest nerve fibers
What is concentrated at the nodes of ranvier?
Na+ voltage-gated channels
Where are potassium channels located in nerves?
Internodes
Nerve conduction is propagated/generated at nodes of ranvier
….
What is the conduction called in myelinated nerves?
Saltatory conduction
Schwann cells proliferate and remyelinate areas where it has been demyelinated… each lost myelin internode is replaced by….
Consequences?
Several shorter internodes with smaller diameter….
Consequently there are more internodes and the thickness is decreased - slower conduction
Have to make more jumps!
One schwann cell can ensheath….? Axons
But can myelinated…. ? ….axons
One schwann cell can ensheath multiple axons, but myelinated only ONE axon….
Sheathing is NOT myelination! It is just holding it into position!
Small diameter nerve fibers are ….
Non-myelinated! - just ensheathed?
Multipolar neurons
Most abundant in CNS - big for motor neurons
Many processes extend from the cell body; all are dendrites except for a single axon!
Bipolar neuron
Two processes extend from the cell body: one is a fused dendrite, the other is an axon
Rare
Found in some special sensory organs (olfactory mucosa, eye, ear).
Unipolar (pseudounipolar)
One process extends from the cell body and forms central and peripheral processes; which together comprise an axon
Found mainly in PNS - Common only in dorsal root ganglia of the spinal cord and sensory ganglia of cranial nerves
Unipolar neurons have a little neck
Cell body live together in sensory ganglia
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Two types of sensory ganglia?
Spinal (dorsal root) and cranial ganglia
Associated with spinal and cranial nerves respectively
What do the sensory ganglia contain?
Contain large sensory neurons and abundant small glial cells, called satellite cells
Sensory neurons are what type of neuron?
Pseudounipolar
One process extends from the cell body and forms central and peripheral processes, which together comprise an axon
Has a little neck for the cell body
Satellite cells
- where they derived from?
- control over what?
- supply what to what?
- act as….?
Neural crest cell derived
Control over the microenvironment of ganglia
Supply nutrients to the surrounding neurons
Act as protective, cushioning cells
Look at slides of satellite cells!
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Neuroglia or “glia”
Do not generate or propagate AP
Forms half of the CNS
Acts as “glue” that hold nervous system together
Smaller than neurons and more numerous
What can glial do that neurons cant?
Can divide and multiply in mature CNS
Can form cancers!
What are the four main functions of glial cells?
1) to surround neurons and hold them into place
2) to supply nutrients and o2 to neurons
3) to insulate one neuron from another
4) to destroy and remove the carcasses of dead neurons
What does the oligodendrocyte to/responsible for?
Responsible for forming and maintaining myelin sheath in CNS
Forms concentric circles
How many oligodendrocytes per axon?
One oligodendrocyte may myelinated one axon or several!
What do oligodendrocytes look like under a microscope?
Fried egg!
What are astrocytes?
Largest of the neuroglia
Play a role in inducing the blood-brain barrier phenotype in the brain capillaries
Provides physical and metabolic support for nerve cells
Help maintain the appropriate chemical environment for the generation of action potentials
Undergo the process of glosis - scar formation
See slides of astrocytes
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What can astrocytes be stained for?
Glial fibrillation acidic protein (GFAP)
Astrocytes foot processes surround brain capillaries and during development induce what?
Endothelial cells to form tight junctions!!
This is the basis for blood-brain barrier - a system of controlled transcapillary transport which maintains homeostasis in the CNS
When neurons are lost and brain tissue is damaged, what happens?
What is this process called?
Astrocytes proliferate, fill the gaps, and restore CSF-brain and blood-brain barriers
This process is called astrogliosis
Is for the CNS what scarring is for extraneural tissues
What are microglia?
Where do they originate?
Smallest of the glial cells
Originate in the yolk sac and populate the brain mesenchyme
Are the primary immune cells of the CNS and are similar to peripheral macrophages
Microglial nodule
Cluster of microglial cells and lymphocytes surrounding a virus-infected neuron
What are ependymal cells?
Cuboidal to columnar cells arranged in a single layer that possess microvilli and cilia
They line the ventricles of the brain and central canal of the spinal cord
Look at slide of ependymal cells that have cilia that project into the ventricle
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What is the growth cone of an axon (or dendrite) composed of?
Flat, fanlike membranes called the lamellipodia
What protrudes from the lamellipodia?
Fine tubes called fillapodia
The filipodia extend and retract constantly and explore their surroundings. When a Filipino, instead of retracting, attaches itself to a substrate, it makes…?
A growth cone that advances in that direction!
What projects into the filipodia of the growth cone?
Actin filaments!! (Growing axons)
Near the periphery of the growing axon, the actin filaments elongate by polymerization of the actin proteins… what happens in the middle by contrast?
In the central part of the lamellipodia, actin filaments are broken down.
At the center of the axon, the neurite that elongates behind the advancing growth cone, a cytoskeleton made of TUBULIN forms!
Vesicles travel along these microtubules and fuse with the growth cone’s membrane to let it expand
What happens to a neuron if it is cut in the PNS?
Regeneration!
Schwann cells degenerate and then reproliferate
