Skeletal, Muscular and Integumentary Systems
Vocabulary: neuromuscular junction, acetylcholine
Your skeletal system isn't just your bones; it's your bone marrow, cartilage, and ligaments all make up this important body system.
As an embryo, you are made up almost completely of cartilage. Cartilage is tough, yet elastic connective tissue. As the embryo develops, the cartilage is replaced with bone. The body of an adult still contains some cartilage on the nose, the rib cage, the spine and in the pelvic area. Cartilage is particularly useful because it allows for some movement in the area, yet still provides protection and structure.
Humans have an endoskeleton, which means our bones are inside our bodies. Our bones are made up up two parts: compact bone (found on the outside of the bone) and spongy bone (the inner part of the bone). Bones give support to our bodies and protect our internal organs. Bones also help us move, store minerals like calcium, and are where blood cells form. Joints are areas where two bones meet, and bones are held together with a connective tissue called ligaments.
The muscular system is made up of three types of muscle tissue: skeletal, smooth and cardiac. Skeletal muscles are attached to bones and help us move. Smooth muscle is found in the walls of structures like the intestines and stomach, and are not generally able to be controlled voluntarily. Cardiac muscle makes up the heart, and is also not generally under voluntary control.
In order for skeletal muscles to contract and move, the nervous system is involved. Motor neurons from the central nervous system make connections with the skeletal muscles. The neuron and muscle cells have a small gap called a neuromuscular junction or synaptic cleft in between them. A neurotransmitter (chemical messenger) called acetylcholine diffuses across the synapse, delivering the impulse to the muscle cells.
Tendons connect muscles to bones. The way the tendons connect to the bone helps the bone act like a lever for the muscles to be pulled. Skeletal muscles can pull in only one direction, so usually they work with another muscle that is pulling in the opposite direction.
Oxygen is delivered to the muscles via the circulatory system. Oxygen is needed in the muscles in order for cellular respiration to occur. Cellular respiration produces the ATP (energy) needed to power the muscles and help us move. During heavy exercise, the muscles may not receive enough oxygen to keep with the energy demands. In this case, lactic acid fermentation would occur, which produces energy in the absence of oxygen. This can lead to a burning sensation in the muscles due to the build up of lactic acid.
The integumentary system includes the skin, glands (sweat and oil), hair and nails. Your skin is your largest organ, as it covers your entire body. The skin plays many roles in helping your body maintain homeostasis. It aids in blocking out UV radiation from the sun and keeps out potential microorganisms that could cause disease. Also, the skin helps to regulate your body temperature through sweating, which also excretes wastes. There is a layer of fat under your skin that helps protect your body from injury. Your skin can even sense things, like temperature and pain, because of the nerves found in the dermal layer.
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