Muscle Contraction and Respiratory System Anatomy
Muscle Contraction Process
5. Calcium ions released from the sarcoplasmic reticulum are available next to the actin and myosin.
6. The calcium ions bind to troponin molecules, modifying their structure. This change allows the myosin filaments to join them, forming cross-bridges linking the actin and myosin.
7. Segments of myosin adopt a rounded head shape extending from the body of the myosin filament. This head can degrade ATP in the presence of calcium and use its energy in the process of contraction. When the muscle fiber is activated, calcium ions activate the degradation of ATP to ADP, releasing energy. With this energy release, the heads of myosin bind to actin, and a flexing, bending movement pulls the actin filament toward the center of the sarcomere. This cycle repeats throughout the contraction, using new energy and calcium ions in each step, resulting in a shortening of the muscle. Keep in mind that during contraction, the actin filaments move toward the middle of the myofibril. As this occurs, the muscle shortens.
8. The neurotransmitter acetylcholine present in the synaptic space is deactivated by the enzyme acetylcholinesterase.
9. Calcium ions are pumped into the sarcoplasmic reticulum.
10. Without the presence of calcium, actin filaments slide back to their original position, and muscle relaxation occurs. This whole series of events takes place in milliseconds. Even when not moving, our muscles are in a state of partial contraction called muscle tone. At any given time, some muscle fibers are contracted, stimulated by messages from nerve cells. Muscle tone is an unconscious process that helps keep the muscles ready for action. When cutting the motor nerve of a muscle, that muscle is completely relaxed.
Nervous Regulation of Muscle Contraction
Contraction of different types of muscles is given by efferent pathways of the peripheral nervous system (nerves and ganglia located outside the central nervous system) either:
- Somatic: Consisting of neurons that carry information in the form of nerve impulses from the central nervous system to muscles.
- Self-Formed: By neurons that carry information from receptors to the central nervous system and neurons that carry information from the central nervous system to smooth muscles. This is divided into two:
Sympathetic Division: Participates in the organism’s reactions to stressful situations.
Parasympathetic Division: Restores balance to the body’s own sleep.
In the contraction and/or relaxation of skeletal muscle, efferent nerve fibers that make up the somatic nervous system conduct nerve impulses from specific areas of the cortex area that controls the initiation of voluntary muscles. The activity of smooth muscle or involuntary (cardiac muscles, glands in the body) is regulated by the efferent nerve fibers of the autonomic nervous system. These fibers are grouped in the various spinal nerves, which make that connection with the spinal cord. In coordination with the central nervous system (brain and spinal cord), the nervous system controls vital body functions.
Anatomy of the Respiratory System
Nostrils: There are two cavities located in the nose, allowing the passage of oxygen to our body and carbon dioxide output gripped to the media.
Nasal Cavity: The inside of the nose is coated by a mucous membrane, which helps the nose stay wet. It also has some hairs that help filter the air you breathe, blocking dirt and dust from reaching the lungs.
Oral Cavity: Also called the oral cavity, it is the space prior to the pharynx through which food is ingested.
Pharynx: A muscular tube that helps breathing, located in the neck, where both air and food pass. It is part of both the digestive system and the respiratory apparatus.
Larynx: The organ that produces the voice contains the vocal cords and is also a necessary step for respiratory gases. It also allows the passage of air into the trachea and lungs and is closed to disallow the passage of food during swallowing.
Trachea: Located in the neck, it extends from the larynx to the bronchi. It is the main airway of the lungs and is divided into two main branches called bronchi, which channel air to the lungs.
Bronchi: The air-conducting part extending from the trachea to the alveoli (part of the airways where gas exchange is performed) branches into two bronchi, one right and one left.
Lungs: The lungs are the organs of respiration where hematosis occurs, a process during which red blood cells absorb oxygen and release carbon dioxide. Protected by the ribs, they are in the rib cage on both sides of the heart, separated by the mediastinum, the name given to the space between each.
Thorax: This is comprised primarily of the ribs and sternum, which function to protect the lungs and heart, preventing them from working properly.
Diaphragm: A thin, flat muscle that separates the chest from the abdomen. This muscle actively works with respiration, phonation, and digestion.
Respiratory Center
The respiratory center is composed of several groups of neurons located bilaterally in the medulla and pons. These control the basic rhythm of breathing, which can change in response to the demands of the body. It consists of three main groups of neurons:
- A dorsal respiratory group
- A ventral respiratory group
- A pneumotaxic center