Muscle Tissue:

There are three different types of muscle tissue. These include the skeletal muscles which are under voluntary control and are made of striated muscle tissue, the visceral muscles which are under involuntary control and are made of smooth muscle tissue, and cardiac muscle tissue which is found only in the heart. Cardiac muscle tissue has properties in common with each of the other two types. An interesting exception to the visceral muscles being under involuntary control is the diaphragm, which controls breathing. This muscle is normally under involuntary control (we don’t usually have to think about breathing), but a person can exert a limited amount of voluntary control also (for example, purposely holding one’s breath or breathing quickly or deeply).

Muscle cells contain filaments of two kinds of proteins, actin and myosin, which slide past each other as the muscle contracts. After a muscle contracts, ATP (produced in the muscle cells’ mitochondria) is needed to relax the muscle and return the actin and myosin filaments to their normal positions. When a person (or other animal) dies and the mitochondria are no longer producing ATP, the muscles cannot relax. This stiffening of the muscles is called rigor mortis. Muscle contraction is initiated when an electrical impulse from a nerve cell reaches its associated muscle cell(s), causing positively- and negatively-charged ions to switch places all along the muscle cell (fiber). Movement of Ca++ ions in/out of the muscle cell (fiber) is important in both contraction and relaxation of the muscle, so if a person doesn’t ingest enough calcium, some could be taken out of the bones to supply the muscles with what they need to contract and relax. Any given muscle fiber reacts in an “all or none” response — it is either relaxed or contracted, and the variability in contraction of the overall muscle is based on the number of fibers which contract.

It is important to remember that muscles can only pull or contract, not push. Thus, many muscles come in sets of antagonists that do opposite jobs. For example, the muscle on the “top” of your arm bends the arm at the elbow while the muscle “under” your arm straightens the arm.

Turkey and Friend
Skeletal muscles can be further subdivided into two sub-types depending on their use or function, and the chemical composition of each is slightly different. Think of a Thanksgiving turkey: the first question asked is invariably, “Do you want white or dark meat?” These correspond to white and red muscle tissue, respectively. Think of where the white and dark meat are found: dark meat is found in the legs and other constantly-used posture muscles, while white meat is found in the “breast,” or flight muscles. Turkeys and chickens aren’t known for flight, so these flight muscles get infrequent, quick bursts of use. Because the posture muscles are constantly used, they need a more constant, steady supply of oxygen. Thus red muscle tissue contains an extra chemical called myoglobin which is a special protein-type molecule for oxygen storage. The presence of myoglobin in posture muscles enables the sustained contractions necessary to maintain proper posture and walk, so in a turkey, red muscle tissue is found in the legs and other support muscles. The presence of myoglobin gives the muscle tissue its red or dark color. White muscles that are only used occasionally don’t have myoglobin in their tissue. Since turkey flight muscles are only used for short, quick flights, they don’t need as much oxygen, thus don’t need myoglobin to store it, and appear “white” in color. The locations of myoglobin-containing muscles in an organism’s body is a genetically-controlled, species-specific trait. For example, some birds that spend more time flying than turkeys and chickens also have myoglobin in their breast muscles.

Skeletal muscles can be classified as one of several different types including:

Flexing a Joing
Flexor Muscle (click to show animation)
A muscle which bends a joint
Extending a Joint
Extensor Muscle (click to show animation)
A muscle which straightens a joint
A muscle which moves a body part away from the midline of the body
A muscle which moves a body part toward the midline of the body

Human Muscles:


pectoralis major deltoid deltoid deltoid deltoid triceps brachii triceps brachii biceps brachii biceps brachii rectus abdominis trapezius trapezius trapezius latissimus dorsi gluteus maximus sartorius sartorius quadriceps femoris quadriceps femoris gracilis gracilis gracilis biceps femoris semitendinosus gastrocnemius gastrocnemius gastrocnemius achilles tendon

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Unfortunately, your text has no good illustration of the locations of the main muscles in the human body. The main muscles include:

pectoralis major
the muscles in the upper chest
abductor muscle over the shoulder
triceps brachii
extensor muscle on the back of the arm: the term “brachii” distinguishes from biceps femoris
biceps brachii
flexor muscle on the front of arm
rectus abdominis
the segmented muscles up the center front of the abdomen
internal muscle that divides the thorax and abdomen
muscle that forms the back of the neck
latissimus dorsi
mid-back muscle over the kidneys
gluteus maximus
the seat or rump muscle
leg-rotator muscle attached at the outer top of the thigh and inside by the knee
quadriceps femoris
the main extensor muscle on the front of the femur
slender muscle along the inside of the thigh, holds the legs together
flexor muscles on the back of the thigh which include:
biceps femoris
the lateral or outer one: the term “femoris” distinguishes from biceps brachii
the medial or inner one
the calf muscle, consists of two halves and ends in. . .
Achilles tendon
an extension of the gastrocnemius down around the back of the heel
Together, these two extend the foot.

Muscle Identification Practice:

Identify these muscles

New Muscle

Copyright © 1996 by J. Stein Carter. All rights reserved.
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(Clipart modified from Corel Presentations 8)