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.
To understand the process of stepping up a step and reaching up to a shelf, let's break it down into two parts: the nerve impulse transmission and the muscle actions involved.
Part 1: Nerve Impulse Transmission
1. The process starts in the brain, specifically in the primary motor cortex, which initiates voluntary movements. Let's assume you decide to step up a step or reach up to a shelf.
2. The motor cortex sends an electrical signal, known as a nerve impulse or action potential, to the spinal cord through a long, thread-like structure called the motor neuron or efferent neuron.
3. The nerve impulse travels down the spinal cord until it reaches the specific level related to the muscles involved in the movement. For stepping up a step, it would primarily involve the legs, and for reaching up to a shelf, it would involve the arms and shoulder muscles.
4. At the appropriate level of the spinal cord, the nerve impulse reaches the motor neuron's synapse, which is a small gap. To cross this gap and continue the transmission, the nerve impulse needs to convert into a chemical signal.
5. The nerve impulse triggers the release of neurotransmitters, such as acetylcholine, into the synapse. These neurotransmitters diffuse across the synapse and bind to receptors on the next neuron known as the motor end plate.
6. The binding of neurotransmitters to the motor end plate triggers another nerve impulse in the second neuron. This neuron is called a motor unit and consists of the motor neuron and the muscle fibers it innervates.
7. The new nerve impulse travels through the motor unit, further down to the muscle fibers it innervates.
8. The nerve impulse enters the muscle fibers through specialized structures called neuromuscular junctions, which contain receptors for the neurotransmitters. This triggers the release of calcium ions within the muscle fiber.
Part 2: Muscle Contraction - Sliding Filament Theory
1. When calcium ions are released within the muscle fiber, they bind to specific protein molecules called troponin, resulting in a change in the troponin-tropomyosin complex's shape.
2. The shape change of troponin and tropomyosin exposes the binding sites on the actin filament.
3. Another protein molecule called myosin heads, present on the thicker myosin filaments, attach to the exposed binding sites on the actin filament.
4. ATP (adenosine triphosphate), a molecule used for energy, is broken down into ADP (adenosine diphosphate) and inorganic phosphate, releasing energy. This energy is used to change the position of the myosin heads, causing them to pull the actin filaments towards the center of the sarcomere.
5. This sliding of the actin and myosin filaments results in the shortening of the sarcomere, which is the basic contractile unit of the muscle.
6. As the sarcomeres shorten throughout the muscle fibers, the whole muscle contracts, causing the desired movement, such as stepping up a step or reaching up to a shelf.
For stepping up a step, the muscles involved primarily include the quadriceps (thigh muscles) for extension of the knee joint and the hamstrings and calf muscles for stabilizing and providing support during the movement. The joint involved is the knee joint.
For reaching up to a shelf, the muscles involved primarily include the deltoid (shoulder muscle), biceps, and triceps (arm muscles). The joints involved are the shoulder joint and elbow joint.
Note: The specific arrangement of muscles and bones can vary between individuals. The above description provides a general understanding of the processes involved in stepping up and reaching up.