Propagation Of The Nerve Impulse Flashcards
All - or - nothing principle
Stating that once an action potential is elicited on a nerve fiber it travels the entire length of the fiber
Antidromic conduction
Construction of a nerve impulse in a direction opposite to its normal direction
Nerve/ muscle impulse
Transmission of an action potential(depolarization process) along the entire length of a nerve or muscle
Orthodromic conduction
Conduction of nerve impulse in the normal direction
Saltatory conduction
The jumping of the nerve impulse from one node of rancher to another in the myelinated nerve fiber
When does spread of depolarization along a nerve membrane stop
Occasionally when the action potential reaches a points on the membrane at which it does not generate sufficient voltage to stimulate the next area of the membrane the depolarization stops
How does continued Propagation of an impulse through out the nerve fiber occur
The ratio of action potential to threshold Excitation must be at all times greater than 1 this greater than 1 requirement is calls the safety factor for Propagation
Safety factor for Propagation
The requirement that the ratio of action potential to threshold Excitation must be at all times greater than 1.
Characteristics of nerve trunk
Nerve consist of many large net fibers which are myelinated and more small nerve fibers that are unmyelinated. Nerve trunk contain twice as many unmyelinated fingers as myelinated fibers
Structure of myelinated fiber
Central core is the axon. Axon is filed with axoplasm viscid intracellular fluid. Surrounding the Axon is a myelin steath deposited by schwann cells. And every 1-3mm among the length of myelin sheath is node of ranvier
Part of the nerve that conducts AP
Membrane of the Axon conducts the action potential.
how is myelin sheath deposited by schwann cells
Schwann cells envelops the Axon forming multiple layers of schwann cell membrane containing the lipid substance shingomyelin Between 2 successive schwann cells a small uninsulated area where ions could flow into the Axon the area called node of ranvier
Sphingomyelin
Lipid sub present in myelin sheath. Excellent electrical insulator that decreases ion flow through the membrane.
How do ions flow into the Axon
Between 2 successive schwann cells a small uninsulated area 2-3 micrometers in length where ions could flow into the Axon the area called node of ranvier
Saltatory conduction is valued for 2 reasons
- Increases the velocity of nerve transmission in myelinated fibers as much as 5to 50 folds
- Conserves energy for the Axon because only nodes depolarization leading to less loss of ions therefore requiring little energy expenditure to reestablish Na and K concentration across the membrane after series of nerve impulse
Repolarization occurs with little transfer of ions why
- Excellent insulation by the myelin sheath
2. Decrease in membrane capacitance
Erlanger and Gasser classified nerves based on
- Diameter
- Myelination
- Conduction velocity
Fiber types
A alpha, A beta, A gamma, A delta, B and C
Golgi tendon organ(GTO)
proprioceptive sensory receptororgan that senses changes in muscle tension. It lies at the origins and insertion of skeletal muscle fibers into thetendonsof skeletal muscle
A alpha fiber diameter, Myelination, conduction velocity and type of fiber /receptor supplied
16micrometers
Myelinated
100m/sec
Golgi tendon Organs, muscle spindles, extrafusal muscle fibers
A beta fiber diameter, Myelination, conduction velocity and type of fiber /receptor supplied
8 micrometers
Myelinated
50 m/sec
Muscle spindles, skin mechanoreceptors
A gamma fiber diameter, Myelination, conduction velocity and type of fiber /receptor supplied
5micro meters
Myelinated
25 m/sec
Intrafusal muscle fibers
A delta fiber diameter, Myelination, conduction velocity and type of fiber /receptor supplied
4 micrometers
Myelinated but thin
15 m/sec
Skin receptors
B fibers fiber diameter, Myelination, conduction velocity and type of fiber /receptor supplied
3 micrometers
Myelinated
8 m/sec
Preganglionic autonomic fibers
C fibers fiber diameter, Myelination, conduction velocity and type of fiber /receptor supplied
1 micrometers
Unmyelinated
1m/sec
Preganglionic autonomic, skin receptors
