The myelination of central and peripheral axons occurs rapidly through the first few years of life. How can this developmental process explain the improved motor abilities of infants and toddlers?
Without full myelination, information about limb movement and body position moves slowly to the CNS, and motor commands move slowly and erratically to the muscles. By the time the brain is aware of movement or position and can issue a motor command, the limb has already moved. When the motor command reaches the skeletal muscle, the response is no longer appropriate. As the neurons become fully myelinated, information processing speeds up, so we observe improved balance, coordination, and movement.
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Dual innervation means that an individual effector
A. may be excited or inhibited by a single division of the autonomic nervous system. B. receives input from both the somatic and the autonomic nervous systems. C. receives input from both the sympathetic and the parasympathetic nervous systems. D. receives two autonomic axons on each smooth muscle cell.
Which of the following is NOT a subclass of a fibrous joint?
A) gomphosis B) suture C) synchondrosis D) syndesmosis
Which of the following is true regarding the parallel elastic component (PEC) of muscular elasticity?
A. This component is provided by the muscle membranes. B. This component provides resistance when a muscle is passively stretched. C. This is the component primarily responsible for the elasticity of muscle. D. both A and B E. all of the above
A skydiver's parachute fails to deploy. After some struggle, his reserve chute deploys in time to save his life. However, his landing is harder than normal, and he feels his knee slightly hyperextend. He shakes it off and goes about his normal routine. Later that day, he begins experiencing knee pain. Two days later, he notices that his knee "pops" when he crouches and soon discovers he has dislocated his femur on the knee. What muscle was likely injured initially?
A. Soleus B. Popliteus C. Sartorius D. Quadriceps femoris E. Tensor fasciae latae