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Histology-Nervous Tissue (PNS)

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What are the two categories the nervous system is broken into?
Central Nervous System
Peripheral Nervous System
What makes up the central nervous system?
Brain & Spinal cord
What makes up the peripheral nervous system?
Nerves & Ganglia
The somatic and visceral nervous systems make up what part of the nervous system?
Peripheral Nervous System
For the most part is the somatic nervous system voluntary or involuntary?
Voluntary
Is the visceral nervous system voluntary or involuntary?
Involuntary
What type of nerve fibers are in the somatic nervous system?
Afferent & Efferent
In the somatic nervous system what does afferent mean?
Afferent means there is a signal from sensory neurons going to the CNS.
What does efferent mean in the somatic nervous system?
Efferent means the motor nerve signal is exiting the CNS going to a target cell (skeletal muscle).
What does the efferent nerve do in the visceral nervous system?
The efferent nerve or autonomic nerve innervate the heart, smooth muscle, and glands to provide constant motion.
Visceral efferent nerves are divided into what two divisions?
Parasympathetic & Sympathetic
What are the PNS cell types?
Neurons (nerve cells) and Glial cells (neuroglia)
How do neurons function?
Neurons function to conduct an action potential (AP).
What is the function of glial cells?
Glial cells are associated with neurons and aid in neuron function and nutrition. They do not conduct AP.
What is a neuron?
A fundamental structural and functional unit of the nervous system.
What is the purpose of the plasma membrane on a neuron?
Conducting AP.
Are neurons usually mitotic (meaning divided) in adults?
No, neurons do not divide or are not mitotic.
What is an AP passed along in neurons?
Synapse
What is a synapse?
A specialized site in a neuron where contacts with many other cells occur.
What are the three connections of neurons?
1. Connect with other neurons
2. Connect with effector organ like glands and skeletal m. (Efferent)
3. Connect with sensory structures (Afferent)
What is the structure of a neuron?
A neuron is composed of a large, pale nucleus plus a prominent nucleolus, hillock, and cell body.
What is a hillock?
A hillock is a place on a cell where an axon originates.
What are some other names for cell body?
Perikaryon or Soma
What are the two types of projections or outgrowths on a neuron?
Axons and Dendrites
How many axons and dendrites can be on a single neuron?
Axon - 1
Dendrite - many
Axons can branch what is that branch called?
Collaterals
Which AP does the axon and dendrite aid with?
Axon-outgoing AP
Dendrites-incoming AP
What is the function of dendrites?
Dendrites function to increase surface area for cell to cell signaling.
Where does the axon originate?
At the Hillock
What organelles do axons have?
Vesicles, mitochondria, intermediate filaments (neurofilaments), and microtubules.
What is the function of microtubules in an axon?
Microtubules transport molecules from the cells body to the end of the axon.
What are the types of neurons and how are they determined?
Multipolar Neurons (Most Common) = 1 axon + many dendrites
Bipolar = 1 axon + 1 dendrite
Pseudo-unipolar = 1 axon + 1 dendrite + short cytoplasmic stalk
Where are bipolar neurons found?
Retina, vestibulochochlear nerve, olfactory
Are pseudo-unipolar neurons efferent or afferent?
Afferent
What type of cells make up neuroglia?
Satellite cells and Schwann cells
What are satellite cells associated with?
Cell Bodies
What are schwann cells associated with?
Nerve Fibers
What is the function of schwann cells?
Schwann cells surround axons except in specialized areas of contact with other neurons, provide insulation, and protection.
What is the difference between myelinated and unmyelinated?
Myelinated (have multiple layers) forms myelin sheaths that are tightly wrapped around axons with schwann cell plasma membrane. This membrane is lipid-rich, has low permeability, and insulates. Unmyelinated axons lie in simple invagination in Schwann cell membrane (is not layered).
What is a node of Ranvier?
A junction between Schwann cells.
What occurs at a Node of Ranvier?
Depolarization and formation of AP and and AP jumps from one node to another.
What does a Node of Ranvier do to conduction?
Makes conduction velocity faster.
What is the faster conduction velocity known as?
Saltatory conductance
What is a general organization of the PNS?
Collection of nerve axons
Contains Schwann cells
Usually has both myelinated and unmyelinated axons
Has both afferent and efferent axons
List the nerve layers.
Epineurium
Perineurium
Endoneurium
What makes up the epineurium?
Loose and Dense Connective tissue
Where is epineurium found and what does it help with?
Vascular - oxygen transportation to the nerves
What is the perineurium?
A cellular layer around each fascicle
What kind of barrier can be created with the perineurium?
Blood-nerve barrier
What is the endoneurium made up of?
Sparse reticular and collagen fibers and fibroblasts
Where is endoneurium found?
Schwann cells, Myelin sheath, axon
Nuclei belong to which cells in the endoneurium?
Schwann cells and fibroblasts mostly
Where are nerve cell bodies located?
Nerve cell bodies are grouped in areas outside or inside the CNS.
What are groups of cell bodies called in the PNS? CNS?
PNS - ganglia (pl) or ganglion (s)
CNS - nuclei/nucleus