Notes

Skeletal Muscles (vs. Smooth Muscles)

Striated vs Smooth because the smooth muscles are the ones that control our interal organs.

• Striated (striped) appearance because they are comprised of muscle fibers.
• Move through a pull action (contraction)
• Work in pairs with a reciprocal muscles (bicep contracts & triceps relaxes)
• Stimulated by a Motor Neuron (neurons that bring the electrical pulses to muscles).

Anatomy of the Muscle Striated muscles are made of muscle fibers that have two parts, Outer and Inner: The following image represents only one muscle fiber - a muscle has many fibers

Wrapped around the intrafusal fiber, there is a sensory nerve that picks up the sensation of stretch. Good part of the innervation in the muscles senses the stretch of the muscles rather than controlling the muscle movements.

Each muscle fiber has a Gamma Motor Neuron that synapses on the intrafusal fiber. The Alpha Motor Neuron synapses on the extrafusal fibers. One alpha motor neuron can stimulate numerous fibers. This is called Motor Unit. The neural link between the alpha motor neuron and the muscle fiber is called the Neuromuscular Junction.

The Muscle -- Spindle Feedback Circuit This loop is the basis of reflexes.

The ratio between the alpha motor neuron and the number of muscle fibers it innervates is associated with the degree of dexterity needed in the movement:

• High Ratio (1:150) = contraction of large muscles
• Low Ratio (1:10) = contraction of small muscles needed for fine movements (Finger, Lips)

Motor Homunculus is related to the number of alpha motor neurons needed to innervate muscles of various regions of our body.

Comparing the Anatomy of the CNS with the Anatomy of the Neuromuscular Junction