Exam 2 - Lecture 22 (Membrane Potential 3) Flashcards
You turn a dog’s hind paw’s dorsal surface down into the ground while the dog is in a standing position. The dog is able to correct the movement by returning the plantar surface of its paw back to the ground. This test examines the sense of _____.
What sensory receptors are involved?
Proprioception; Golgi-tendon organ and muscle spindle
Where are Meissner’s corpuscles located and what are their function?
Located in the skin at the tip of the dermal papillae; sense touch and vibrations < 100 Hz
What are the 3 steps in CNS recognition of sensory stimulus?
- Sensory stimulus generates receptor potential
- Receptor potential goes over threshold
- AP
What is the length of the axon that is myelinated?
> 1 micrometer
What are 2 structures that are unique to myelinated axons (besides the myelin sheath)?
- Internodes
2. Nodes of Ranvier
What do oligodendrocytes make and where?
Myelin in the CNS
What do Schwann cells form and where?
Myelin in the PNS
What two things affect the speed of a signal along an axon?
size and whether it is myelinated or not
What can be used as an example to explain the flow of electrical current down an axon?
wire cable
What is STE and what does it equal?
signal transmission efficiency; = membrane resistance divided by longitudinal resistance (Rm/Rin)
When membrane resistance increases, _____ current is lost across the cable.
Less (Rm)
How can a current travel without significant decrement?
Low longitudinal resistance (Rin); faster speed and longer distance
What is the flow of electrical current down nonmyelinated axons?
Local current spreads along axon, activating adjacent VG Na+ and K+ channels, generating AP
Where are VG Na+ and K+ channels located in a nonmyelinated axon?
All along the axon
Propagation of an AP is _____ (decremental/nondecremental).
Nondecremental
How does a myelin sheath around an axon affect STE?
Increases STE
Local current reaches a _____ (longer/shorter) distance in a myelinated axon.
longer
Where are VG Na+ and K+ channels located in a myelinated axon?
Nodes of Ranvier/between two internodes
What is myelin?
Plasma membrane of oligodendrocytes or Schwann cells
What is saltatory conduction?
AP jumps from node of Ranvier to node of Ranvier
How do larger axon diameters affect Rin (inside resistance)?
Decrease Rin
How does myelination affect Rm (membrane resistance)?
Increases
Larger myelinated axon = _____ internode and _____ conduction speed
longer; faster
What are 2 ways that diameter of axons are classified?
- Letter system
2. Numerical system (sensory fibers)
What are 2 examples of demyelination disease?
- Multiple sclerosis (human)
2. Degenerative myelopathy
What is multiple sclerosis?
Demyelination disease where Ab’s attach own myelin sheaths
What is degenerative myelopathy and what does it result in?
Myelin sheaths are attached in the spinal cord; results in progressive muscle weakness and incoordination, complete paralysis, muscle atrophy
What is degenerative myelopathy similar to in humans?
ALS
Loss of myelin _____ STE and APs cannot reach the NoR.
decrease
What happens to VG Na+ and K+ channels that reappear along demyelinated areas of axons?
Return of VG channels diminishes with repeated demyelination episodes
