7.Excitability and excitation: general characteristics. Propagation of action potentials along the nerve fibers. Nerve fiber types. Flashcards
What are the main biological properties of neurons
Excitability and conductivity
What is the significance of excitability and conductivity
transmission of information
afferent fibers transmit from peripheral organs to CNS
Efferent fibers transmit from CNS to periheral organs
How does propagation of action potentials occur
spread of local currents from active regions to inactive regions
ELECTROTONIC CONDUCTION
What is conduction velocity
The speed at which action potentials travel along nerve fiber
What are the cable properties that are major concepts in conduction velocity
Time constant and length constant
the higher the permeability, the lower the resistance, and vice versa.
Longitudinal resistance (Rl ): is the resistance that counteracts electric
current in the cytosol and ECF.
What are 2 factors that affect time constant
membrane resistance + membrane capacitance
Time constant is highest when both of these are high
How can you increase the conduction velocity of a nerve
Increasing nerve diamter- the larger the fiber, the lower the internal resistance
Myelination- myelin increases membrane resistance but decreases membrane capacitance. High resistance means it forces the action potential to take path of least resistance
At nodes of Ranvier, the resistance is low-saltatory conduction
What is rheobase
The lowest intensity of stimulus that can cause A.P after prolonged stimulation
What is chronaxie
Time requires for a stimulus that is 2x rheobase to induce a A.P
Rehobase is the minimum intensity of stimulus to induce AP
What is the Erlanger and Gasser classification of nerve fibres
A- alpha, beta, delta, gamma
B
C
Which is the fastest nerve fiber
A
largest diameter
skeletal muscle, receptors of muscle spindle etc
If the action potential is stimulated in the middle of the nerve fiber, how will the impulse travel
Action potential travels in both directions, centrally and peripherally
What is the threshold potential
-55mv
What determines the excitability of given excitable tissue
Difference between resting membrane potential (-70mV) and threshold potential (-55mV)
What is the law for all or nothing stating
Upon threshold or above threshold all APs have the same amplitude