Term of the Day

Duchenne Muscular Dystrophy (DMD): Inherited, sex-linked, recessive, muscle-destroying disease. Females are carriers of the abnormal gene, but the disease almost exclusively strikes males. The gene results in the lack of an important protein called dystrophin, which is crucial for maintaining the structural integrity of the sarcolemma. DMD is typically diagnosed between ages 2 and 6 as previously normal children become clumsy and begin to fall more frequently. The degenerative process progresses from the extremities to the head and trunk. Death comes when the diaphragm and other inspiratory muscles are damaged. Patients rarely live beyond their 20s and die of respiratory failure.

Concept of the Week : The Motor Unit

The cell bodies of motor neurons that innervate skeletal muscles are located in the ventral horn of the grey matter of the spinal cord. Axons of these nerves leave via the ventral root and travel to the appropriate skeletal muscle.

A single motor neuron can form synapses with many muscle fibers, due to a multiplicity of axon collaterals. An individual motor neuron and all the muscle fibers it innervates is called a motor unit, the functional unit of the neuromuscular system.

Motor units can vary in size. The smallest consist of a single motor neuron that innervates just a few muscle cells. Such an arrangement is typical in situations where very precise control of fine movements is necessary (e.g. finger or eye movements). A large motor unit may innervate hundreds of muscle cells. Such units are responsible for gross movements such as leg or trunk movements. The smaller the motor unit, the greater precision of fine motor skills.

Term of the Day

Hilton's Law: Joints (articulations) have an extensive nerve supply. These articular nerves are actually branches of the nerves that supply the overlying skin and the muscles that move the joint. Hilton's Law essentially says that the nerves that supply a joint also supply the muscles that move the joint and the skin covering their attachments.