In details

The mechanism of muscle contraction


In the contraction of skeletal muscle fibers, sarcomere shortening occurs: actin filaments “glide” over those of myosin, thanks to certain binding points that form between these two filaments, leading to the formation of actomyosin.

For this slip to happen, there is a large amount of two important elements: Ca ions ++ and ATP. In this case it is up to the myosin molecule to “break down” (hydrolyze) the ATP, releasing the energy needed for contraction to occur.

Briefly, muscle contraction activity can be represented by:

The stimulus to muscle contraction

THE smooth musculature It is controlled by the nerves of the autonomic nervous system. The sympathetic and parasympathetic divisions act on the smooth muscle activity of the digestive and excretory organs.

However, smooth muscle tissue can also be stimulated to function by distending the organ wall. This is what happens, for example, when the bolus is passing through the digestive tract. The distension caused by enlargement of the intestinal wall causes a contraction response in the smooth muscle of this wall. As a result, a wave of peristalsis is generated, which drives the food forward.
On the other hand, striated musculatureMost of the time, it is under voluntary control. Nervous branches move into muscle tissue and branch out, reaching individual muscle cells or groups of them.
Each junction point between a nerve end and the muscle cell plasma membrane corresponds to a synapse. This junction is known by the name of motor plate. The nerve impulse travels through the neuron and reaches the motor plate. The muscle cell membrane receives the stimulus. It generates an electric current that propagates through this membrane, reaches the cytoplasm and triggers the mechanism of muscle contraction.

Muscle-Brain Circuit

The nerves are connected and communicate their signals through synapses. The movement of a muscle involves two complex nerve pathways: the sensory nerve pathway to the brain and the motor nerve pathway to the muscle. This circuit consists of twelve basic steps, which are indicated below:

  1. Sensitive receptors on the skin detect sensations and transmit a signal to the brain.
  2. The signal is transmitted along a sensory nerve to the spinal cord.
  3. A spinal cord synapse connects the sensory nerve to a spinal cord nerve.
  4. The nerve crosses to the opposite side of the spinal cord.
  5. The signal is transmitted and ascends through the spinal cord.
  6. A synapse in the thalamus connects the spinal cord to the nerve fibers that transmit the signal to the sensory cortex.
  7. The sensory cortex detects the signal and causes the motor cortex to generate a motion signal.
  8. The nerve that transmits the signal crosses to the other side at the base of the brain.
  9. The signal is transmitted downward by the spinal cord.
  10. A synapse connects the spinal cord to a motor nerve.
  11. The signal proceeds along the motor nerve.
  12. The signal reaches the motor plate, where it stimulates muscle movement.