Patho Test 2: Structure/Fx of Neurons
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Unipolar Neurons are________
An example of one would be_________
Unipolar neurons branch right after leaving the cell body
Pseudounipolar Neurons have _____ process with dendrite that travels_______ the CNS, but axons travel _______ the CNS (cranial and spinal nerves).
- away from the CNS
- to the CNS
- Sensory neurons
BiPolar neurons have _______ distinct processes. The cell body sits in the ________
- Rods and Cones of retina
Multi-polar neurons are the ___________common.
- Most common
- Muscular, association neurons
Sensory neurons transmit impulses from
____________ to the CNS.
- sensory receptors
- "you drop something on your toe and you feel it"
Motor neurons transmit impulses from___________ to _________
- from the CNS
- an effector organ via neuromuscular junction
"message comes from the brain that something has fallen on your toe, and you move your foot in response"
Neuroglia include 4 cell types
- 1. Astrocytes
- 2. Oligodendrocytes "Schwann Cells"
- 3. Microglia
- 4. Ependymal Cells
What is the function of Astrocytes?
- Fill the spaces between neurons and blood vessels in the CNS
- Form the Blood-Brain Barrier
What is the function of Oligodendroglia?
- Deposit Myelin in the CNS
- "Schwann Cells"
What is the function of the Microglia?
Remove debris from CNS by phagocytosis
What is the function of Ependymal cells?
Line CSF filled cavities in ventricles and epidural space
What is Wallerian degeneration?
What 4 things happen distal to the cut?
- Distal to the axon cut
- 1. Swelling appears
- 2. Neurofilaments (structured support) hypertrophy
- 3. Myelin sheath shrinks and degenerates
- 4. axon portion distal to the cut, degenerates and disintegrates
What happens Proximal to the cut (only as far back as the next Node of Ranvier?)
- 1. swelling
- 2. dispersal of Nissl substances
- 3. increase in cell metabolic activity, protein synthesis and mitochondrial activity
- 4. New terminal sprouts project from proximal segment and continue the work of the axon
How is Nerve regeneration limited? What 5 factors limit a nerve's ability to regenerate?
- 1. Must be Myelinated axon
- 2. Location: Must occur in the PNS (not in CNS)
- 3. Type of injury
- 4. Inflammatory response
- 5. scar tissue formation
What does the Presynaptic neuron do?
Brings the impulse to the synapse
What does the postsynaptic neuron do?
Takes the message downstream
What is a synaptic bouton?
a synaptic vessice
3 Types of Summation
- 1. temporal
- 2. spatial
- 3. facilitation
Describe temporal summation
repeated impulses of one neuron on the same synapse, combines the impulses
Describe spatial summation
Combined impulses from several neurons to have effect on 1 neuronal synapse
Describe facilitation summation?
The nerve is used to receiving information and so it takes less time to conduct
Neurons generate and conduct _______ and ________ impulses by selectively changing the _______ portion of their plasma membrane and by influencing other nearby neurons by the release of_________
What are the 4 Connections btw pre and post synaptic neurons?
What is Saltatory Conduction?
flow of ions between segments of myelin, not the entire length of the axon; makes conduction faster
How is conduction velocity increased?
- 1. myelin coating
- 2. larger axons
What is the axon hillock?
cone-shaped, nissl-free area where the axon leaves the cell body
WHat is the Nissl body/substance?
The ER and ribosomes of the neuron; used for protein synthesis
Which neurons can continue to divide?
What portion of the CNS is composed of Neuroglia?
- 5-10 x more than neurons
What does the Somatic Nervous System do?
Contains motor and sensory pathways which regulate voluntary movement of skeletal muscles via afferent and efferent pathways
What is an afferent pathway?
Pathway from the body to the CNS
What is an efferent pathway?
From the CNS to the effector organ
What does the Autonomic N.S. control? It is composed of the ________ and the _________
- Involuntary control of organ systems
- Sympathetic N.S.
- Parasympathetic N.S.
Name the 3 ascending (sensory) spinal cord pathways
- 1. Spinothalamic
- 2. Dorsal Column
- 3. Spinocerebellar
Name the 2 Efferent (Motor) pathways
- 1. Pyramidal or Corticospinal
- 2. Extrapyramidal
Where do the afferent spinal pathways cross over?
Where do the descending/efferent spinal pathways cross over?
Anterior white commissure of the brain stem
How many neurons are involved in each pathway?
What information is carried in the Spinothalamic Tract?
- Light touch
What information is carried in the Dorsal Column tract?
- Deep pressure
What information is carried in the Spinocerebellar Pathway?
What information is carried in the Pyramidal/Corticospinal Tract?
Skeletal muscle tone; voluntary muscle movement
Extrapyramidal Tract carried ________ information
Skeletal muscle activity regarding balance and posture
Where are the upper motor neurons located and where do their axons extend?
Prefrontal gyrus of the CNS with axons that project to the lower motor neurons
Where are the lower motor neurons and where do they project?
- In the ventral horn of the spinal cord gray matter and the motor nuclei of the cranial nerves.
- They project to the skeletal muscle fibers
What is the blood supply to the brain in volume (ml/min)?
What primarily regulates blood supply to the brain?
What happens when the blood supply to the brain is cut off?
1. Co2 will cause vasodilation that brings in more blood to increase O2 levels
What is normal intracranial pressure?
5-15 mmHg or 60-180 mm H2O
What happens in stage 1 of increased ICP?
What are the first and second things the body does to compensate?
- 1. Displacement of CSF from cranium to lumbar cistern.
- 2. Vasoconstriction and external compression of the venous system.
- Initially there is no obvious change in ICP or patient.
What happens in stage 2 of increased ICP?
- Increased CSF reabsorption
- Continued expansion of intracranial contents. ICP is now increased which leads to further cranial vasoconstriction and increased systolic BP. Patient is now restless, confused, drowsy and has breathing changes
What happens in Stage 3 increased ICP?
ICP begins to approach arterial pressure, brain tissue experiences hypoxia, hypercapnia. Patient has marked decrease in arousal, hyperventilation, widened pulse pressure, bradycardia, small, slugglish pupils
What is the Monroe-Kellie hypothesis?
the volume of one of the intracranial cavity constiuents increases, a reciprocal decrease in volume of one or both of the others will occur
________ fibers are myelinated, large. fast
________ fibers are unmyelinated, small, not as fast
Delta fibers are in which spinal tract? they are stimulated by ____________ types of stimulus.
- severe mechanical deformation or extreme temperature which cause you to reflexively withdraw from the stimulus
C-Fibers are in which spinal tract?
What type of pain do they carry?
- Dull, burning, aching, pooly localized, longer lasting
Under what circumstances can PNS nerves regenerate?
- 1. If the neurilemma is intact
- 2. If the injury is farther away from the cell body
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