One Flashcards
What does the neuron doctrine state?
The neuron doctrine asserts that each neuron is a self-contained entity and separated from other cells, including other neurons, by extracellular space.
What embryological layer are neurons derived from? When does neurogenesis end? What does this mean concerning injury or damage to neurons?
Ectoderm.
Neurogenesis largely completed after weeks to months after birth.
For the most part, neurons that degenerate or are destroyed after this will not be replaced.
What implications does the nature of destruction of CNS neural tissue (stroke, trauma) have? Can return of function ever happen? How? Describe an example of this.
The clinical significance of these facts is that destruction of CNS neural tissue from, e.g., trauma or stroke produces permanent functional deficits. Return of function following such events is due to the functional reorganization of undamaged brain tissue rather than the regeneration of neural structures.
For a striking example of what this entails, consider Rasmussen’s Encephalopathy, which produces intractable seizures of diffuse origin on one side of the brain exclusively in children. The treatment of last resort in this condition is hemispherectomy, i.e., removal of the entire cerebral cortex on the affected side of the brain. Recovery from these surgeries is remarkable, particularly when the procedure is done before two years of age. However, the procedure is done in children up to about age 14. Children that recover from such surgeries without post surgical complications (the majority) often return to school as soon as about two weeks. Lateralized functions, such as speech, migrate to the remaining hemisphere. Memory and general intelligence, which frequently are impaired by the seizures, often improve by comparison to the presurgical status. The contralateral limbs are minimally paralyzed. Essentially, these children live near normal lives when all goes well following these
surgeries.
What are 3 general parts of a neuron? In which part is the nucleus located in? What is the nucleus like? In which part is Nissl substance located? What is it? In which part is the golgi apparatus located? What do lysosomes result in in neurons?
Dendrites, Axons, Soma (perikaryon)
Nucleus-large, spherical, one nucleolus-in soma
Nissl substance-In soma and larger dendritic bodies-Rough ER
Golgi-In soma and larger dendritic bodies
Lysosome results in lots of lipofuscin in neurons with aging
What are two things that happen in the perikaryon? Which organelles are located there?
Regulatory functions and protein synthesis.
What do dendrites do? How? What are they like morphologically? What are spines? Where are synapses on dendrites?
They receive info and transmit it to the soma in the form of altered membrane potential.
They are tapered. The diameter decreases as you go away from the soma. They have varied amounts and types of branching.
Spines are minute surface projections from the dendrite.
Synapses are frequently on spines, but can also be on the shaft of a dendrite.
What are multipolar neurons? Bipolar? Unipolar? Which types of neurons are CNS neurons? Which type are PNS? Which nerves are unipolar?
Multipolar neurons have several dendrites.
Nearly all CNS neurons are multipolar
Bipolar neurons have one dendrite and one axon.
PNS neurons may be multipolar, as in autonomic ganglia, bipolar, as in the olfactory mucosa and the ganglia of the auditory and vestibular parts of the VIII nerve.
Unipolar neurons have only one connection to the soma from which both the axon and dendrite come off.
Unipolar neurons are very rare, but the sensory (dorsal root) ganglia of spinal nerves and cranial nerves V, VII, IX, and X exhibit a modification of bipolar morphology that looks a lot like unipolar and is referred to as pseudounipolar.
How many axons does each neuron have? What are bundles of axons in the PNS called? In the CNS? What are they like morphologically? What is collateral branching? Preterminal?
One axon per neuron
In the PNS, they’re called nerves
In the NCS, they’re called tracts or fasciculi
Collateral branching diverges at right angles anywhere along the shaft of the axon and may extend to distant distinct sites
Preterminal branchings are terminal branchings that end in axon terminals.
What are 3 main types of neuronal cytoskeleton? What is each like? What is their function? What are they made out of? What is axoplasmic transport? What happens if an axon is damaged?
Neurofilaments-Stable, polymerized structural proteins-bones of the neuron
Microfilaments-Actin and various types of myosin—>motility of neurons and their processes
Microtubules-alpha and beta tubulin-maintenance of neuronal shape and stability as well as axoplasmic transport
Axoplasmic transport-transport of organelles and molecules along microtubules from soma to axon and the reverse. If an axon is damaged, this can’t occur and the axon degenerates and the cell sickens.
How does the morphology of dendrites and axons affect the spread of current
Dendritic and axonic diameter are inversely related to electrical resistance.
Dendrites grow larger as they get closer to the cell which means resistance is decreasing meaning the impulse is likely to go towards the cell.
Axons with a greater diameter transmit impulses faster.
What are 3 types of supporting cells and two subtypes found in the CNS? What are 2 types in the PNS? What is another name for a neuron supporting cell?
CNS: Macroglia (astrocytes, oligodendrocytes), Microglia, Ependymal
PNS: Schwann cells, Capsular Cells
They are called neuroglia (nerve glue)
What is the embryonic origin of microglia? What do they do?
Microglia are non-neuronal cells of mesenchymal origin that are activated under conditions of injury or inflammation of the brain. They are inconspicuous in the healthy brain but once activated, they phagocytose debris in the same way that cells belonging to the Reticuloendothelial system do.
What are ependymal cells? Where are they found? What is their embryonic origin and what kinds of cells are they? What are their function? What do they combine with astrocytic process to form?
Ependymal cells line the ventricles of the brain and the central canal of the spinal cord. They comprise a single layer of closely packed cuboidal or columnar cells that is the remnant of the embryonic proliferative epithelium. Ependymal cells are metabolically very active and are thought to have both secretory and absorptive functions. Tight junctions between adjacent ependymal cells contribute to the integrity of a brain-CSF barrier. Processes of the ependymal cells intertwine with astrocytic processes to form the subependymal or internal limiting membrane.
What is the choroid plexus? What is its function? Where is it located? What two types of cells does it consist of and what does each do?
Within the roof of each of the four ventricles of the brain, ependymal cells come into physical contact with pia mater, a delicate connective tissue covering of the surface of the brain. The contact between these two tissues gives rise to the differentiation of a highly vascularized tissue called choroid plexus, which synthesizes cerebrospinal fluid and secretes it into the ventricular system. Ependymal cells comprise the secretory part and the pia mater
the vascular and supporting part of the choroid plexuses.
What are two types of astrocytes? What is each like? Where is each located? How are their functions different?
Protoplasmic-Short, thick, dendrite like processes w/ numerous tuft like branches. In gray matter (dendrites, axon terminals, soma)
Fibrous-Fewer, thinner processes. In white matter (axons)
Their function is basically the same. They look different do to location.
