Life Cycle - Human Biology (5B)

  • Exploring reflexes.
  • Calculating reflex time.
  • involuntary muscle
  • voluntary muscle
  • meterstick (or yardstick)

Students determine their own reflex time.


Muscle cells are part of a complex system involving muscles, tendons, nerves, hormones, blood vessels, and sense organs.  Muscle contraction resembles a change in the elastic constraints of a spring.  In order for a muscle to pick up and lift some weight, the "spring" contracts to accomplish the work.  The energy from muscle contraction comes from sugars and fats stored within the muscle.  

The term involuntary muscle is used to indicate that this type of muscle is not subject to our conscious control.  Smooth and cardiac muscles are involuntary.  Imagine if we had to control our heart pumping or food passage in order to live!  
Voluntary muscles indicate that the muscle is under the conscious control of that particular animal. Skeletal muscles are voluntary, in that we control their actions and whether to make them more responsive.  Voluntary muscles in the body are usually attached to the skeleton in such a way that they are stretched near their optimal length.  Muscles can pick up weight not directly but through a lever system.

  1. In this activity,  students will see if they can improve their voluntary muscle reflexes by repeating a skill.  The skill involves preventing a meterstick from falling between two fingers.    
  2. Go over directions on the lab sheet with students.  Tell them to make sure they remember where they started on the meterstick.  In order to avoid confusion it may be best to have the whole class begin at one place on the meterstick.  
  3. Have the students record their reflex times and then graph them on the lab sheet. In most cases, there will be improvement from the first trial to the last trial.  You may want to discuss what happens when a person does not have control of his muscles.  There are several diseases that are due to muscle disorders.  Muscular dystrophy is the wasting of the trunk and limb muscles.  Poliomyelitis (Polio) is a disease which involves the connective tissue and leads to the destruction of the muscle fibers.  

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