Histology lecture Flashcards
What are the three functions of the nervous system?
Sensory inputIntegrationMotor output
Describe the two types of cells found in nervous tissue.
Nerve cells/neurons: main functional cells of the nervous system that generate and transmit action potentialsNeuroglia, glia, or supporting cells:these are much smaller than nerve cell and they have a supportive role
The three special characteristics of neurons are?
Extreme longevity- can function for 100 yearsMost are amiotic- lose their ability to divide as they become communication links in the nervous systemHigh metabolic rate: they will die within a few minutes without oxygen
What goes on in the neuron cell body?
It is the biosynthetic center of the neuron. It makes necessary molecules and sends them down the line
True or false, action potentials are associated with the cell body?
False. They are not
What are Nissl bodies?
clumps of ribosomes
What do the dendrites do?
They are the main receptive/main input regions of the neuron
Are dendrites myelinated? Why or why not?
No- no action potentials here.
What is the purpose of the axon/nerve fiber?
Generation and conduction of action potentials
How many axons can a neuron have?
Just one
A collection of cell bodies in the CNS is called….
a nucleus
A collection of cell bodies in the PNS is called…
a ganglion
What is the axon hillock?
It is kind of the base of the cell body where the axon begins to start- no organelles found here and it’s not myelinated
Where are interneurons found?
Between motor and sensory neurons
How are neurons classified?
By the number of dendritic processes
Which types of neurons are the most abundant?
multipolar
Where are unipolar neurons mainly found?
In the PNS
True or false, multipolar neurons are usually for special sensory?
False- most are for motor function or are interneurons
Which neurons are responsible for special sense?
bipolar neurons
Which neurons are responsible for general sensory?
Unipolar neurons
There are 5 types of synapses, which are the two most common?
Axodendritic synapseAxosomatic synapse
What are pre and postsynaptic neurons?
Presynaptic neurons carry the signal towards the synapse Postsynaptic neurons carry the signal away from the synapse
What are the two types of synapses? Explain them.
Electrical synapses: found in the heartChemical synapses: the electrical signal is turned into a chemical signal and the neurotransmitter that is released by the axon terminals diffuses across the synaptic cleft where it is received, processed and then turned back into an electrical signal
How does chemical transmission occur at the neuronal synapse?
-Voltage is propagated to the end of the axon-Ca2+ channels open which facilitate the fusion of vesicles carrying NT’s to cross the synaptic cleft-NT’s bind to receptors on the post synaptic membrane, each receptor being a ligand-gated channel-the channel opens, ions flow in creating the new charge that is then propagated
What are the three ways neurotransmitters are removed from the postsynaptic receptor?
Degradation by enzymesRe-uptake by astrocytes or the presynaptic terminalDiffusion away from the synapse
True or false, neuroglia are supportive cells?
True
What is the job of the oligodendrocytes?
They produce the myelin sheath in the CNS
What is the role of an astrocyte?
It can get rid of excess neurotransmitterit is associated with capillaries and contributes to the blood-brain barrier
Where are astrocytes found?
They are found in both the white and gray matter of the brain and spinal cord, BUT MOSTLY IN THE GRAY MATTER
True or false, ependymal cells are epithelial cells?
False. They are not
Where are ependymal cells found?
They are low columnar or cuboidal cells that line spaces in the CNS
Ependymal cells have extensions that help to move CSF around, true or false?
Truth
What is the key defining factor for microglial cells?
The nuclei are elongated. On astrocytes and oligodendrocytes the nuclei are rounded
Where do microglia originate from?
Monocytes
How many internodal sheaths can a single schwann cell form?
One
What are satellite cells?
They surround the neuronal cell bodies in a supportive capacity
What makes white matter white?
All the myelin (the oligodendrocytes are plentiful because they are the ones that make myelin)
What is gray matter composed of?
neuronal cell bodies and dendrites, unmyelinated axons and their terminals, as well as astrocytes are found here. Gray matter is gray due to Nissl bodies and lack of myelin
What are clusters of neuronal cell bodies called in the CNS and the PNS?
CNS- nucleus (think the center)PNS- ganglion (think out in your gangly arms and stuff)
What is a bundle of neuronal axons called in the CNS and the PNS?
CNS: tractPNS: nerve
Connective tissue coverings associated with nerves
- endoneurium (cover axon)2. perineurium (cover fascicle or bundle)3. epineurium (cover entire nerve)
Nerves can be classified by what direction they’re transmitting as well as where they originate from. What are these?
Sensory (afferent)Motor (efferent)Mixed (both motor and sensory)Cranial nerves- originate at the brainSpinal nerves- originate at the spinal cord
What are the functions of a myelin sheath?
Protect and electrically insulate axons from other axonsIncrease the speed of tranmission
How are nerve fibers myelinated in the PNS?
A schwann cell associates with an axon and wraps it, forming an internodal segment. Each successive layer fuses together
Do schwann cells that wrap the axon have a nucleus?
Yep. and it’s often fairly big and noticeable
The rate of impulse propagation depends on what?
Axon diameter: the large the diameter the faster it goesMyelination- continuous versus saltatory conduction
