Situation: You need to step up on a step to reach an object on a high shelf.
Instructions: (Part one) Trace the nerve impulse, listing the steps in as much detail as possible, from which your brain sends the message to the appropriate muscles to step up one step. Include the steps involved in transmitting the impulse from one neuron to another and then to the muscle fiber. Include in this the steps involved in the actual muscle fiber contraction – Sliding filament theory. (Part two) Specify which muscles are pulling on which bones and what types of joints are involved in stepping up on the step. Next, specify which muscles are pulling on which bones and what types of joints are involved to reach up above your head to the shelf.
Part One:
1. The process begins with the activation of sensory receptors in your feet, which detect the presence of the step.
2. These sensory receptors send electrical signals, known as nerve impulses, through sensory neurons to the spinal cord.
3. In the spinal cord, the sensory neurons synapse with interneurons, which transmit the nerve impulses to motor neurons.
4. The motor neurons extend from the spinal cord to the appropriate muscles involved in stepping up on the step.
5. When the nerve impulse reaches the muscle fibers, it triggers the release of calcium ions from the sarcoplasmic reticulum, a network of tubules within the muscle fiber.
6. The calcium ions bind to a protein called troponin, causing it to change shape and exposing binding sites on the actin filaments within the muscle fiber.
7. Myosin heads, which are part of the myosin filaments, bind to the actin filaments, forming cross-bridges.
8. ATP (adenosine triphosphate), a molecule which stores and releases energy, is then broken down into ADP (adenosine diphosphate) and Pi (inorganic phosphate), releasing energy.
9. The energy released from ATP hydrolysis causes the myosin heads to pivot, pulling the actin filaments towards the center of the sarcomere - a basic unit of muscle contraction.
10. This sliding of actin and myosin filaments continues, resulting in the shortening of sarcomeres, and ultimately muscle fiber contraction.
Part Two:
Stepping up on the step involves several muscles and joints:
1. Quadriceps femoris muscles: These muscles, located in the front of the thigh, contract to extend the knee joint, allowing you to straighten your leg and lift your foot onto the step.
2. Hamstring muscles: Located in the back of the thigh, the hamstrings help to flex the knee joint during the step-up process.
3. Gluteus maximus muscle: This large muscle in the buttocks helps to extend the hip joint, providing the force needed to propel your body upward onto the step.
4. Ankle joint: The muscles of the calf, including the gastrocnemius and soleus muscles, contract to plantarflex the ankle, allowing your toes to push off the ground and lift your body onto the step.
To reach up above your head to the shelf, additional muscles and joints are involved:
1. Deltoid muscle: The deltoid muscle forms the rounded contour of the shoulder and is responsible for lifting your arm away from your body and raising it up towards the shelf.
2. Biceps brachii muscle: The biceps muscle, located in the upper arm, contracts to flex the elbow joint, helping to bring your hand closer to your shoulder.
3. Elbow joint: The hinge joint at the elbow allows for flexion, enabling you to bring your hand closer to the shelf.
4. Wrist joint: The muscles of the forearm, including the flexor muscles, contract to flex the wrist joint, allowing you to bring your hand closer to the shelf.
It is important to note that there are many additional muscles and joints involved in these movements, and the examples provided above are just a few of the key players.