Trace the impulse, listing the steps in as much detail as possible, from which your brain sends the message to the appropriate muscles to lift a glass of water to drink. As in the previous Application Assignment (parts one and two), detail the steps involved in the transmission of the neural impulse to the muscle fiber and then the steps involved in the sliding filament mechanism. Then, specify which muscles are pulling on which bones and what type of joints are involved. (Part two) Finally, trace the path of the water from the mouth to the urethra, listing the path in as much detail as possible.
To trace the impulse from your brain to the muscles involved in lifting a glass of water, and to explain the steps in detail, follow these steps:
1. Initiation of the impulse in the brain: The decision to lift a glass of water originates in the brain. It begins with the activation of the motor cortex, which sends an electrical signal called an action potential.
2. Transmission of the impulse: The action potential moves down the motor neurons, which are long, thread-like cells that transmit signals from the brain to the muscles. The impulse travels through the axons of these neurons.
3. Arrival at the neuromuscular junction: The motor neurons terminate at the neuromuscular junction, which is the point where the neurons meet the muscle fiber. At this junction, the action potential triggers the release of a chemical called acetylcholine into the synaptic cleft.
4. Binding of acetylcholine: Acetylcholine binds to specific receptors on the muscle fiber's membrane, leading to the depolarization of the muscle cell.
5. Initiation of the sliding filament mechanism: The depolarization of the muscle cell activates the release of stored calcium ions from the sarcoplasmic reticulum, a network of tubes within the muscle. Calcium ions bind to troponin molecules, exposing myosin-binding sites on the thin actin filaments in the muscle.
6. Cross-bridge formation: Myosin heads on the thick myosin filaments form cross-bridges by binding to actin, resulting in the contraction of the muscle fiber. This repetitive process of myosin heads binding, pulling, detaching, and rebinding is known as the sliding filament mechanism.
7. Contraction of muscles: As the muscle fibers contract, connecting tendons, which are fibrous connective tissues, pull on bones, causing movement. The muscles involved in lifting a glass of water are primarily the muscles of the arm and hand.
8. Muscles involved: The muscles typically engaged in lifting a glass of water include the biceps brachii and brachialis in the upper arm, which contract to flex the elbow joint. The muscles in the forearm, such as the flexor digitorum superficialis and flexor carpi radialis, help control wrist and finger movements.
9. Joint involvement: The joints used in lifting a glass of water are primarily the elbow joint, which allows for flexion and extension, and the wrist joint, which enables movements such as flexion, extension, and supination/pronation.
Now, to trace the path of water from the mouth to the urethra:
1. Mouth: Water enters the body through the mouth.
2. Pharynx: The water passes through the throat and enters the pharynx, a region behind the mouth and nasal cavity.
3. Esophagus: From the pharynx, the water travels down the esophagus, a muscular tube connecting the pharynx to the stomach.
4. Stomach: The water enters the stomach, where it gets mixed with digestive enzymes and gastric juices.
5. Small intestine: The partially digested water moves from the stomach into the small intestine. Here, nutrients and water are absorbed into the bloodstream.
6. Large intestine: The remaining water, along with waste products, enters the large intestine, also known as the colon.
7. Absorption and formation of feces: In the large intestine, water is further absorbed, and the remaining waste material is compacted to form feces.
8. Rectum: The feces are stored in the rectum until evacuation is appropriate.
9. Anus: When ready, the feces pass through the anus, the opening at the end of the digestive system, and are expelled from the body.
10. Urethra: The water that was absorbed into the bloodstream and processed by the kidneys as urine travels from the bladder through the urethra, a tube that carries urine out of the body.
These steps provide a detailed explanation of both the neural impulse pathway involved in lifting a glass of water and the path taken by water within the human body.