Muscle Contraction Research Paper

1. The number of muscle fibers that are innervated by a motor neuron is dependent on what muscle it is. Fine motor movements, such as typing, would need only a few muscle fibers. This means that the thumb has only a few fibers, but the thigh, back, and biceps have many. These need a lot more force to be exerted, which is why they need more muscle fibers. Using your thumb and bladder does not require many muscle fibers.
2. Alpha motor neurons innervate extrafusal muscles but gamma motor neurons innervate only intrafusal muscle fibers (within the muscle spindle). When both alpha neurons and gamma neurons are present, muscle fibers with the muscle spindles are pulled parallel to the extrafusal contraction causing the muscle movement. Therefore, if they are activated within the extrafusal muscle fibers, the force developed in those areas would increase. The firing of gamma motor neurons in sync with alpha motor neurons pulls muscle spindles, innervating the muscle. The spindle is innervated by type Ia sensory fiber that goes on to synapse with alpha motor units. Therefore, there are more motor units being put to work and the type 1a afferents maintain their sensitivity. …show more content…
The stretch reflex, also known as knee jerk reflex, needs a stimulus to start. A perfect example would be when the doctor taps your tendon to stretch the muscle. The receptors are the muscle spindles, which fire action potentials. The action potential travels down through a sensory neuron, which is the afferent path. The sensory neuron synapses in the spinal cord. The effector is the extrafusal muscle fiber. From there, it goes down the two effector pathways: 1) The interneurons inhibit the somatic motor neuron, which allow the hamstring to relax. 2) The somatic motor neuron will cause the quadriceps muscle to swing