The Muscular System
Last week we took a look at the skeletal system (The Amazingly Designed Human Body – Part 3). We saw how the bones in our body not only provide a support structure to help give us shape and the ability to stand upright, but it also had several other functions. Today, we will take a look at the muscular system with its various parts and functions.
The muscular system is made up of over 600 muscles and tendons. It also accounts for 40% of our bodyweight. The percentage of bodyweight is greater in men than in women.
Muscles are what allow us to move, run, look up, reach out, and hold a Bible in our hands to read. In a way, they are similar to both hydraulic cylinders and rubber bands. Hydraulic cylinders do work by extension or contraction of the piston or rod. Oppositely, most muscles operate by contraction and then relaxation. Rubber bands have an elastic characteristic that allows them to be stretched and then return to normal shape. Likewise, many of our muscles are also stretched and pulled and then return to normal shape.
Muscles are divided two ways. The first division has to do with whether or not you can consciously, control the muscles.
- Voluntary Muscles – These are muscles that you can consciously move and control, such as your fingers, hands, arms and legs.
- Involuntary Muscles – These are muscles that function automatically without your conscious control, such as your heart, muscles surrounding the arteries, digestive tract and diaphragm. Some may argue that you can control the diaphragm when you hold you breathe or take a deep breath, but as a rule, it functions on a regular basis without you thinking about it.
The second division of the muscular system involves their type and function. Some sources divide this group into 3 divisions and others into 5 divisions. I choose to use the 5 division separation as it helps demonstrate more diversity among the muscles.
- Skeletal Muscles – Skeletal muscles also known as striated muscles, are those that attach to one bone, cross over a joint and attach to another bone. Skeletal muscles always work in pairs. One muscle will contact while the opposite relaxes. Skeletal muscles are voluntary muscles.
- Smooth Muscles – Smooth muscles are generally thin and flat. They are involuntary muscles that operate without you thinking about them. When examined under a microscope they do not have the striated look that skeletal muscles have. Examples of smooth muscles are muscles that line the arteries, stomach, intestines and control eye movement. Most smooth muscles are involuntary muscles.
- Cardiac Muscles – These are the muscles of the heart. They are involuntary muscles that are controlled by the sinus node. Cardiac muscles are also striated muscles, but do differ from skeletal muscles.
- Facial Muscles – Facial muscles are a group of over 40 muscles that control your face, allowing you to smile, frown, grin, sneer and laugh. Some are attached to bones and some aren’t. An interesting fact is that it takes only 17 facial muscles to smile and 42 to frown.
- Tongue Muscles – The tongue is a group of muscles sheathed in a course outer lining. They are unique in that it only attaches at one end. The tongue muscles allow you to talk and swallow.
As mentioned above skeletal muscles are also referred to as striated muscles. These muscles are made up of numerous muscle fibers or sarcomeres. The sarcomeres are made up actin and myosin filaments. Myosin filaments are thicker than the actin filaments, which is what gives the striated appearance. These two fibers move back and forth across each other as the muscle contracts and relax. The process of contraction is a complex one involving nerve stimulation of the actin and myosin filaments. The key elements involved are sodium and calcium ions. An imbalance or shortage of these ions can result in muscle fatigue and/or cramping.
There are 3 main functions of our muscles:
- Movement – The primary function of muscles is movement. Without muscles, we would be as stationary as a tree.
- Body Temperature – Humans are warm blooded which means that we maintain a fairly constant body temperature. Heat is generated by work. The working parts of the body are the muscles. The more the muscles contract and relax, the more heat we generate. If our body temperature gets too high, heat exhaustion then heat stroke and death can be the result. If the body temperature gets too low, the muscles will begin to involuntarily contract and relax, causing us to shiver.
- Digestion – Muscles are involved with eating, swallowing, digestion and the elimination of waste. Muscles help us chew the food. Smooth muscles line the esophagus to help move food down into the stomach. The stomach and intestines are also lined with layers of smooth muscles that continue to move the food through them. Eventually all that is left is waste material which is moved through the colon and pushed out of the body.
For you trivia buffs, here are some interesting facts about muscles:
- The largest muscle in the human body is the gluteus maximus, which comprises the largest portion of your buttocks.
- The smallest muscle is the stapedius, located in the middle ear.
- The longest muscle in the human body is the sartorius that starts as tendons attached to the anterior superior iliac spine (upper part of pelvic bone), runs diagonally across the front of the thigh down to the outside edge of the knee and attaches to the upper part of the tibia.
- The strongest muscles are the jaw or chewing muscles.
- The most active muscles are the eye muscles. It is estimated that they contract over 100,000 times a day.
- Some individual muscles cells can reach up to a foot in length.
- Muscles have the ability to mend themselves when they are torn and damaged. Some years ago, the plantar muscles in my one foot kept tearing because they were stretched too tight. The surgeon detached one end of the muscles where they attached to the heel bone and allowed them to reattach themselves, which made them longer and less likely to tear.
After 6000 years of the Curse and a build up of mutations and pathogens, there are many diseases and conditions that can affect our muscles. Among those are muscular dystrophy, cerebral palsy, compartment syndrome, myasthenia gravis, amyotrophic lateral sclerosis (Lou Gehrig’s Disease), dermatomyositis, fibrodysplasia ossifican progressive and the list goes on and on. They all serve as a reminder of Adam’s sin, our own mortality and the need of a Savior.
There is so much more that could be said about the muscular system, but when you look at how they are so intricately woven together around the human body to allow for all of our different movements and functions, the picture really says it all.
I praise you, for I am fearfully and wonderfully made.
Wonderful are your works; my soul knows it very well.
My frame was not hidden from you,
when I was being made in secret,
intricately woven in the depths of the earth. Psalm 139:14-15.
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Take a journey from conception to birth with Dr. David Menton, former professor of anatomy at the prestigious Washington University School of Medicine in St. Louis. Dr. Menton provides both a biblical and scientific answer to the question of when life begins.
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