Stretching Anatomy 2nd Edition PDF
Anatomy and Physiology of Stretching
Muscles such as the biceps brachii are complex organs composed of nerves,
blood vessels, tendons, fascia, and muscle cells. Nerve cells (neurons) and muscle
cells are electrically charged. The resting electrical charge, or resting membrane
potential, is negative and is generally around –70 millivolts. Neurons and
muscle cells are activated by changing their electrical charges. Electrical signals
cannot jump between cells, so neurons communicate with other neurons and
with muscle cells by releasing specialized chemicals called neurotransmitters.
Neurotransmitters work by enabling positive sodium ions to enter the cells and
make the resting membrane potential more positive. Once the resting membrane
potential reaches a threshold potential (generally –62 millivolts), the cell becomes
excited, or active. Activated neurons release other neurotransmitters to activate
other nerves, causing activated muscle cells to contract.
Besides being altered to cause excitation, the membrane potential can be
altered to cause either facilitation or inhibition. Facilitation occurs when the resting
membrane potential is raised slightly above normal but below the threshold
potential. Facilitation increases the likelihood that any succeeding neurotransmitter
releases will cause the potential to exceed the threshold. This enhances the
chances of the neuron’s firing and activating the target. Inhibition occurs when
the resting membrane potential is lowered below the normal potential, thereby
decreasing the likelihood of reaching the threshold. Usually this prevents the
neuron from activating its target.