Situation: You need to step up on a step to reach an object on a high shelf over your head. Your starting point should be anatomical position and your finishing point should be the position you are in once your hand has reached the object overhead.
(Part 1) Trace the nerve impulse, listing the “macroscopic” structures and steps in as much detail as possible, from which your brain sends the message to the appropriate muscles to step up one step.
(Part 2) Include the steps involved in transmitting the impulse “microscopically” through an individual neuron, from one neuron to another, and then from the neuron to the muscle fiber.
(Part 3) Include in this the steps involved in the actual muscle fiber contraction – a.k.a. the Sliding filament theory.
(Part 4) Specify the movements, muscles, bones, and joints involved in stepping up on the step. Explain any and all movements individually across each joint involved specifying the actions involved (i.e. flexion, extension, etc.), the muscles causing such actions, the bones being pulled on by said muscles, the types of joints involved, and how these movements collectively relate to the overall scenario/movements in this application.
(Part 5) Next, specify the movements, muscles, bones, and joints involved in reaching up above your head to the object on the shelf. Again, explain any and all movements individually across each joint involved specifying the actions involved (i.e. flexion, extension, etc.), the muscles causing such actions, the bones being pulled on by said muscles, the types of joints involved, and how these movements collectively relate to the overall scenario/movements in this application..
Part 1: The nerve impulse involved in stepping up one step begins in the brain. The motor cortex, located in the frontal lobe of the brain, initiates the signal. The impulse then passes through the internal capsule, which is a collection of nerve fibers connecting the brain with the spinal cord.
Next, the impulse travels downward through the brainstem, specifically the medulla oblongata and the spinal cord. In the spinal cord, the impulse synapses with motor neurons in the ventral horn. These motor neurons then carry the signal to the muscles responsible for stepping up.
Part 2: At a microscopic level, the nerve impulse travels through individual neurons. Within a neuron, the impulse is conducted along the axon, which is surrounded by a myelin sheath. The myelin sheath insulates the axon and speeds up the conduction of the impulse.
When the impulse reaches the end of one neuron, called the presynaptic terminal, it triggers the release of neurotransmitters into the synaptic cleft. These neurotransmitters diffuse across the synaptic cleft and bind to receptors on the dendrites of the next neuron, known as the postsynaptic neuron. This transmission between neurons occurs through a process called synaptic transmission.
Part 3: Muscle fiber contraction occurs through a process known as the sliding filament theory. When the nerve impulse reaches the muscle fibers, it stimulates the release of calcium ions from the sarcoplasmic reticulum within the muscle cell.
Calcium ions bind to troponin molecules on the thin filaments of the muscle fiber. This binding causes a conformational change in troponin, which moves tropomyosin away from the active sites on the actin filaments.
Myosin heads on the thick filaments then bind to the exposed active sites on actin, forming cross-bridges. ATP is then hydrolyzed by the myosin heads, providing energy for the myosin heads to change conformation and pull the actin filaments inward. This shortens the sarcomere, the basic contractile unit of a muscle fiber, resulting in muscle fiber contraction.
Part 4: Stepping up on a step involves several movements, muscles, bones, and joints. The main joints involved are the hip joint, knee joint, and ankle joint.
1. Hip joint: Flexion of the hip joint is required to lift the leg and step up on the step. The muscles involved include the hip flexors, such as the iliopsoas and rectus femoris. These muscles pull on the femur (thigh bone), causing it to move towards the torso.
2. Knee joint: Extension of the knee joint is necessary to straighten the leg and bear weight on the step. The quadriceps muscles, located on the front of the thigh, contract to extend the knee. These muscles pull on the patellar tendon, which in turn pulls on the tibia (shinbone) and straightens the leg.
3. Ankle joint: Dorsiflexion of the ankle joint helps lift the foot and clear the step. The muscles involved in ankle dorsiflexion include the tibialis anterior and extensor hallucis longus. These muscles pull on the foot bones, specifically the tibia and metatarsals.
Overall, the movements at the hip, knee, and ankle joints collectively allow the body to step up on the step by lifting the leg, straightening the knee, and clearing the foot.
Part 5: Reaching up above your head to the object on the shelf involves movements, muscles, bones, and joints primarily in the upper extremities.
1. Shoulder joint: Flexion and abduction of the shoulder joint are required to reach above the head. The muscles responsible for these movements include the deltoid, pectoralis major, and anterior fibers of the serratus anterior. These muscles pull on the humerus (upper arm bone) to lift and move the arm.
2. Elbow joint: Extension of the elbow joint is necessary to straighten the arm fully. The triceps brachii muscle is primarily responsible for elbow extension. It pulls on the ulna and humerus, straightening the arm.
3. Wrist joint: Extension of the wrist joint allows the hand to tilt back, which assists in reaching. The extensor muscles of the forearm, such as the extensor carpi radialis longus and extensor carpi ulnaris, pull on the hand bones, specifically the metacarpals.
4. Finger joints: Extension of the finger joints is required to grip and grasp the object on the shelf. The extensor muscles of the forearm continue into the fingers, allowing for finger extension.
Collectively, the movements at the shoulder, elbow, wrist, and finger joints facilitate reaching up above the head to reach the object on the shelf.