Nervous System II Flashcards
What are the parts of a neuron?
Dendrite, cell body, axon, axon hillock, axoplasm, axolemma, end bulb
What does a dendrite do?
Receives information
What does the cell body of a neuron do?
Receives information
Has the nucleus, organelles, and the metabolic center
What does an axon do?
Sends information
What does the axon hillock do?
Initiates the signal out
What is the axoplasm?
Cytoplasm in the axon
What is the axolemma?
The cel membrane of an axon
What is the end bulb?
Where chemical transmission happens
What are the three polarities of a neuron?
Unipolar, bipolar, multipolar
A bipolar neuron is….
Rare in the body
Found in the eye, olfactory, inner ear
Most sensory neurons are…..
polarity
Unipolar
Multipolar neurons are…..
Most common in the body
Most neurons in the brain and spinal cord
What are the three protective coatings of neurons?
Endoneurium
Perineurium
Epineurium
What is endoneurium?
A protective sheath around a single axon
What is perineurium?
Protective coating surrounding a fascicle of axons running in the same direction
What is epineurium?
A protective coating surrounding the whole spinal nerve
What do neurons produce and transmit?
Electrochemical signals
What is the lifespan of a neuron?
A lifetime- extreme longevity
Can neurons divide?
No, they’re amitotic
exceptions apply
What is a neuron’s metabolic rate?
High…need lots of O2 and glucose
How many neurons in a human?
1 trillion
What is neuroglia?
Cells that support, protect and nourish neurons
What is the ratio of neuroglia: neurons?
50:1
Name the 5 neuralgia cells
Schwann cell Oligodendrocyte Microglia Astrocytes Ependymal cells
What does a Schwann cell do?
Forms a myelin sheath in the PNS
These cells “wrap” their membrane around an axon, leaving most of their cytoplasm and organelles pushed to the side
What is the composition of myelin?
80% lipid
20% protein
The gap between Schwann cells is the ________ of _______ and exposes the ____________.
Nodes of Ranvier
axolemma
What is the neurilemma?
The cytoplasm towards the outside of the myelin in a Schwann cell; or the sheath of Schwann
What does an oligodendrocyte do?
Forms a myelin sheath in the CNS
Whats does an oligodendrocyte look like?
An octopus
How many processes can an oligodendrocyte have and what is their function?
Up to 15. One cell makes many sheaths nearby
Each process reaches out to a nearby nerve fiber (axon) and spirals around it like a Schwann
Myelin sheaths in the PNS are formed by ___________ ______ while in the CNS they are formed by ______________.
Schwann cells
Oligodendrocyte
What is a microglia?
A phagocytic cell in the CNS
Microglia are a type of _______
cell
Macrophage
What do microglia develop from?
Develop from a white blood cell called monocyte
Who do microglia do?
Wander through the CNS, phagocytizing dead material and foreign matter
Are thought to do a full check-up of the brain a few times a day
What does a concentration of microgleal cells indicate?
Become concentrated in areas damaged by infection, trauma, or stroke. So their presence is a clue to the location of an injury site.
What is the most abundant neuroglial cell?
Astrocyte
What shape are astrocytes?
Star shaped
The extensions of astrocytes are called _________ ______and form __________ __________ with the epithelial cells of blood capillaries.
Perivascular feet
Tight junctions
Perivascular feet and tight junctions help form the _______ _______ _______.
Blood brain barrier.
What does the blood brain barrier do?
The BBB strictly controls which substances are able to get from the bloodstream into nervous tissue.
How to astrocytes promote neuron growth and synaptic formation?
By nourishing neurons and secreting growth factors
What can astrocytes absorb? And why?
They can absorb K+ and neurotransmitters- to prevent them from reaching excessive levels
What is an ependymal cell?
Line brain ventricles (small spaces in the brain) and the central canal in spinal cord
What does an ependymal cell look like?
Resemble a simple cuboidal epithelium, but no basement membrane and instead contain root-like processes that penetrate the underlying nervous tissue
What do ependymal cells do?
Non-ciliated Ependymal cells, or specialized ependymal secrete CSF,
Ciliated cells move CSF around
What is the resting potential of a neuron?
-70mV
Stimulation of a neuron changes the ________ of it’s _______.
Permeability
Cell membrane
What are the stages of electrical neurotransmission?
Depolarization
Repolarization
Hyperpolarization
What is depolarization?
1st: Na+ flows in. Then the Na+ gates close.
What is repolarization?
K+ flows out
What resets the Na+ and K+ balance of the cell? Why is this important?
The Na+K+ pump
The cell can retransmit once the balance is realigned
Why does hyperpolaziation occur?
Because the K+ channel closes more slowly
What is the electrical threshold of a neuron? Why is it important?
-55mV. If the threshold is not met, no signal is sent
When an atom is myelinated the impulse goes faster, this is called __________ __________.
Saltatory Conduction
In a myelinated cell, where do Na+ and K+ change positions?
Only at the nodes of Ranvier
What are some neurotransmitters in the CNS?
ACh or acetylcholine
NE or norepherine
DA or dopamine
GABA
What are some neurotransmitters in the PNS?
ACh or acetulcholine
NE or norepherine
How many known neurotransmitters are there?
100+
Why is Ca++ important to nerve transmission?
It cant occur without it.
What is AChE?
Acetylcholinesterase
What does AChE do?
Acetylcholinesterase is an enzyme found on the membrane and in the synaptic gap.
It “eats” extra ACh
What does AChE break ACh into?
Acetate and choline.
What is the synaptic gap?
Space between two synapses.
