Dr.Sultan
12-02-2007, 08:05 PM
Muscles are made up of functional units called motor units. Each motor unit consists of a motor neuron and all the muscle fibers it branches to and communicates with via neuromuscular junctions. When any motor neuron is stimulated (sends a nerve impulse) all the muscle fibers it communicates with (i.e. all the muscle fibers in the motor unit) will contract with all the force they can generate or they will not contract at all (all or none principle). In a given muscle there are many motor units. The motor units vary in their excitability. Some motor units can be excited by a weak stimulus while others require a strong stimulus.
At the lowest stimulus strength that results in some contraction (i.e. threshold), only a few motor units are stimulated. By increasing the strength of stimulus, an increased number of motor units can be "recruited" to increase contraction force, and a greater displacement (muscle contraction) is recorded on the graph. The strength of the contraction (displacement) is the sum of the force exerted by all the motor units that are excited. So this experiment demonstrates the phenomenon called multiple motor unit summation (or recruitment).
• When a single nerve enters a muscle it splits and makes neuromuscular junctions (NMJs) with several muscle cells
• A nerve and the muscle cells it makes NMJs with is called a motor unit
• When the nerve fires the whole motor unit is stimulated and the muscle cells contract together
• Muscles with large motor units have coarse movements
• Muscles with small motor units give fine, graded movements
the contractile response to electrical stimulation of 1 motor point as opposed to simultaneous stimulation of multiple motor points in the muscle belly.
for optimal control of muscle contraction in functional electrical stimulation, electrodes may need to be inserted into multiple motor points for a given muscle.
وللتعرف على هذه النقاط على الجسم البشري افتح المرفق
At the lowest stimulus strength that results in some contraction (i.e. threshold), only a few motor units are stimulated. By increasing the strength of stimulus, an increased number of motor units can be "recruited" to increase contraction force, and a greater displacement (muscle contraction) is recorded on the graph. The strength of the contraction (displacement) is the sum of the force exerted by all the motor units that are excited. So this experiment demonstrates the phenomenon called multiple motor unit summation (or recruitment).
• When a single nerve enters a muscle it splits and makes neuromuscular junctions (NMJs) with several muscle cells
• A nerve and the muscle cells it makes NMJs with is called a motor unit
• When the nerve fires the whole motor unit is stimulated and the muscle cells contract together
• Muscles with large motor units have coarse movements
• Muscles with small motor units give fine, graded movements
the contractile response to electrical stimulation of 1 motor point as opposed to simultaneous stimulation of multiple motor points in the muscle belly.
for optimal control of muscle contraction in functional electrical stimulation, electrodes may need to be inserted into multiple motor points for a given muscle.
وللتعرف على هذه النقاط على الجسم البشري افتح المرفق