Basic explanation of how muscles, bones, and nerves work and the functions of their different parts.
The basic physiology of the human body is a very complex system to understand, but in general, the functions of the muscles, bones, and nerves can be broken down into explanations that are easy to understand.
Muscular Movement (definitions to know):
-Muscular movement- movement caused by the contraction of the myofibrils of the muscle cells.
-Troponin- A protein that regulates muscle contraction.
-Myosin- Forms the thick filaments in the muscles.
3 Types of Muscles:
-Cardiac Muscle- Makes up most of the heart wall, striated, and involuntary (moves without effort).
-Smooth Muscle- Found in the walls of internal hollow structures of the body (blood vessels and other organs). It is striated and involuntary.
-Skeletal Muscle- Found attached to bones, striated, and voluntary.
2 Types of Contractions
-Isotonic Contractions- The tension within the muscle stays the same, but the muscle as a whole shortens, producing movement. Examples: lifting weights, walking, or any other activity that causes the muscles to bulge.
-Isometric contractions- There is no change in muscle length, but there is an increase in muscle tension. Example: pushing against an immovable force (a wall, floor, etc.)
The Process of Muscular Movement
1. Nerve signals release acetylcholine (a neurotransmitter that binds to channels on the sarcolemma.)
2. Channels begin to open and allow sodium and potassium ions to diffuse, creating a polarity change.
3. An action potential begins by stimulating the release of calcium.
4. The calcium binds to troponin, leaving a space for myosin to bind to actin.
5. A cross-bridge forms and the myosin releases ADP and flexes.
6. The filaments then slide, causing the muscle to contract.
The Function of Bones
1.) Serve as framework for the body
2.) Protect internal structures of the body
3.) Produce movement by working as levers
4.) Store calcium salts
5.) Produce blood cells
Types of Bones
-Spongy/Cancellous Bone- These bones are less-densely packed with widely spaced plates of bone called trabeculae. (Trabeculae- plates of bone that follow stress lines and provide support and strength for the bone.)
-Compact Bones- These bones are densely packed and porous with millions of canals and spaces for blood vessels and bone cells.
Types of Bone Cells
-Osteoblasts- bone-forming cells.
-Osteoclasts- cells that break down bone tissue.
-Osteocytes- mature bone cells.
The Process of Bone Growth
1. Ossification (conversion of cartilage into bone) begins at the center of the shaft during fetal development.
2. Around the time of birth, the epiphyseal plate develops across the ends of the long bones.
3. The anterior lobe of the pituitary gland produces Growth Hormone (GH), also known as somatotropin, which promotes the making of protein that causes growth in the epiphyseal plate.
4. The bones continue to grow at the epiphyseal plate by calcification of new cartilage into the late teens.
5. By about early 20’s, the bones stop growing. This is when the epiphyseal plate hardens and then is called the epiphyseal line.
Two Divisions of the Nervous System
1.) Central Nervous System (CNS) - includes the brain and the spinal cord.
2.) Peripheral Nervous System (PNS) – includes all of the nerves outside of the CNS.
Three Main Plexuses
1.) Cervical Plexus- sends motor impulses to muscles in the neck and receives sensory impulses from the neck and the back of the head.
2.) Brachial Plexus- sends branches of spinal nerves to the forearm, arm, shoulder, wrist, and hand.
3.) Lumbosacral Plexus- supplies nerves to the legs and pelvis.
Process of Nerve Transmission
1. A stimulus is detected by a receptor.
2. A sensory/afferent neuron carries the impulse toward the CNS.
3. The impulse enters the gray matter of the spinal cord, where the response of the impulse is organized.
4. A motor/efferent neuron carries the impulse out through the ventral horn of the spinal cord’s gray matter and away from the CNS.
5. Then the muscle or gland outside of the CNS carries out a response. The muscle or gland would be called the effector.
*The whole process of nerve transmission from start to finish is called a reflex arc.
How are muscular movement, bone growth, and nerve transmission interrelated?
• They all interrelate because without them, we would not be able to function at all. With no muscular movement, our heart wouldn’t even beat, so we would die. Without bone growth, our bones would remain as cartilage, just like they are when we are born. There is no way cartilage would be able to protect our organs, along with the fact that our skull and ribs would crush our brain and internal organs because there would not be enough room for our internal tissues to grow; so again, we would die. Without nerve transmission, there would be nothing signaling our heart to beat, our body to move, or even our brain to think. So finally, if it wasn’t for muscular movement, bone growth, and nerve transmission, we would die. All three are necessary for life.