Module 11 Flashcards
What does the motor unit consist of?
Alpha motor neurons and all fibers it innervates
What two ways is the skeletal muscle innervated?
Motor unit
Neuromuscular junction
What is the muscle to nerve ratio of the motor unit?
Small 1:5 in tongue muscles; small ratio if if needs to be more precise
Large 1:900 in leg; for gross movements
What is the neuromuscular junction?
Termination of a peripheral nerve fiber on skeletal muscles
Where is the motor end-plate?
Where the axon terminal synapses with the muscle fiber
Is the motor end plate part of the post synaptic membrane?
Yes!
What is the ratio of motor end plates per muscle fiber?
1:1; one end plate to EVERY fiber
What is the mV of the membrane potential in a neuro at rest?
-70 mV
What is membrane potential?
Measure of voltage between two points: the voltage across the membrane
How is MP (membrane potential) created?
Metabolic activity that:
Continuously diffuses potassium (K+)
and
SELECTIVE transport of substances through cell membrane using gating mechanisms
Inside of the cell there is a HIGH concentration of…
Anions (An-) Potassium ions (K+)
Outside of the cell there is a HIGH concentration of…
Sodium ions (Na+) Chloride ions (Cl-)
The resting cell is permeable and impermeable to what ions?
Impermeable to Na+
Permeable to K+ (so they leak out leaving An- which cause the cell to remain negative)
What is neuron excitability?
Allows neuron to respond to stimulus
Sends signals in electrical forms
What is it called when the signal is transmitted over a nerve fiber and the MP goes through a series of changes?
Action potential
What is an action potential?
Nerve impulse
How are AP elicited?
By anything that suddenly increases the permeability of the cell membrane to Na+
What two types of stimulus can elicit an action potential?
Physical
Chemical
How much membrane potential increase is needed to evoke an AP?
+10 mV or more
How do transmission of neural signals occur?
Release of chemical stimulus (neurotransmitter)
Physical stimulus (pressure/pain/temperature)
What is the difference between polarization, depolarization and repolarization?
Polarization- resting state
Depolarization- positive change
Repolarization- return to resting state
How is AP conducted in myelinated axons?
Via saltatory conduction
Axon jumps from node to node (fasted conduction)
How is AP conducted in unmyelinated axons?
General spread of AP
Gradual depolarization (slower conduction)
How does AP Code information?
By response frequency
What is a refractory period?
Period IMMEDIATELY after the AP is triggered
Name the 2 components of a refractory period
Absolute refractory period
Relative refractory period
Is a refractory period shorter in smaller diameter neurons?
No!! It’s shorter in longer diameter neurons
What is the absolute refractory period?
Neuron said to be hyperpolarized
AP can not be generated
Last for 2 msec
What is the relative refractory period?
Membrane is NOT fully repolarized
AP can be produced with a STRONG stimulus
what is the ALL or nothing principle?
Adequate stimulus fires to AP; it can not be partially fired
What two things can neurotransmitters influence the post-synaptic membrane to do?
Excite
Or
Inhibit
What’s a generator potential?
Grades depolarization response
Is the GP an ALL OR NOTHING event?
NO! Relies on summation, collective effect of multiple arriving stimuli
What is the difference between the AP release and neurotransmitter release?
AP reaches terminal bouton
neurotransmitter released from vesicles (acts on post synaptic membrane)
How do generator potential create an action potential?
Stimulus must reach the axon hillock and receive neural summation
What are the two types of neural summation for generator potential?
Temporal summation
Spatial summation
What is a temporal summation?
Sub-threshold stimuli must occur within a critical period of time
What is a spatial summation?
Multiple stimuli converge on post synaptic membrane at the same time
How to generator potential code responses?
According to the intensity of the stimulus
Weak stimulus; small potential (voltage change)
Strong stimulus; large potential (voltage change)
What is an EPSP (excitatory post-synaptic potential)?
Excitation of receptor (soma/dendrite)
Neurotransmitter partially depolarizes post synaptic membrane
Generates GP
CREATES likelihood of new AP
What is an IPSP (Inhibitory post-synaptic potential)?
Neurotransmitter hyperpolarizes the receptor (makes negative)
Prevents neuron from firing
Prevents development of GP
DECREASE likelihood of new AP
