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Muscular SystemMuscular System

Skeletal Muscle MovementsSkeletal Muscle Movements

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The Muscular SystemThe Muscular System

Welcome to the muscular system! While movement is the most commonly-remembered function of the muscular system, there are a few other important functions as well. In addition to allowing voluntary and involuntary movement, the muscular system is also responsible for maintaining body posture and for temperature regulation.

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Muscle ArrangementMuscle Arrangement

Tendons &Tendons &aponeurosesaponeurosesLigamentsLigamentsTerminologyTerminology–– OriginOrigin (head)(head)–– BellyBelly–– InsertionInsertion

Most of our focus for this the muscular system will deal skeletal muscles. We’ll look more closely at cardiac muscle and smooth muscle with other systems. Skeletal muscles are attached to bones at at least one end, but the muscle itself does not directly attach. Instead, the muscle is attached by a strong dense connective tissue called a tendon which sheaths the entire muscle and attaches it to the bone. Insome areas of the body, tendons form wide sheets of dense connective tissue. We call these attachments aponeuroses.Most skeletal muscles cross at least one joint and, when they contract, they pull the bones on either side of the joint closer together. The end of a muscle that is the most stationery (and usually more proximal) is called the muscle’s origin. The end that moves more (and is usually more distal) is the insertion. The fatter part in between is the belly. The origin does the pulling while the insertion gets pulled. When we use these terms, we might say that the biceps originates on the humerusand scapula, which it inserts on the radius and ulna.

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Notice that when then biceps muscle contracts, it pulls the insertion (the end attached to the bones of the forearm) closer to the origin (the end attached to the arm).

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These are some general rules of thumb that apply to (almost) all skeletal muscles. Rule #4 is especially important to understand: when a muscle contracts, it pulls the insertion closer to the origin. In order for a joint to move the opposite direction, a different muscle (usually on the other side of the joint) has to contract. Muscles often work in pairs this way. For example, when the biceps contracts, the elbow flexes. In order to extend the elbow, we must contract the triceps muscle (on the posterior side of the upper limb).

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MovementsMovements

Flexion and extensionFlexion and extension

We have names for the different types of movements that our joints and muscles allow. Generally speaking, the type of movements that a joint is capable of is determined by the type of joint involved.Flexion means to “bend” a joint, usually out of anatomic position. Extension means to straighten the joint or return it to anatomical position. Bending the elbow or the knee, for example, are flexions. Unbending them are extensions.

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MovementsMovements

DorsiflexionDorsiflexion and plantar flexionand plantar flexion

We have special terms that we use for ankle and wrist movement (we don’t use flexion or extension for the hands or feet). Bending the ankle so that the top of the foot rises (such as when trying to walk on your heels) is dorsiflexion. Pointing the toes downward (such as when trying to walk on tiptoes) is plantar flexion. Similar movements of the wrist are dorsiflexion and palmar flexion.

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MovementsMovements

RotationRotation

Rotation means to move a joint in a circular motion around an axis. Generally, the axis is in line with the joint, longitudinally. Turning the head left and right is an example of rotation. You can also rotate the hip, the shoulder, and the forearm.

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MovementsMovements

Abduction andAbduction andadductionadductionCircumductionCircumduction

Circumduction means to move a body part (upper limb, lower limb, finger, etc.) in a circular motion around an axis. It differs from rotation because the axis of rotation does not go through the insertion. Think of circumduction as making cone-shaped movements.Abduction means to move the insertion away, usually away from the midline of the body (or the midline of a limb). If you move your upper limb away from your body, you are abducting it. You can also abduct your fingers by spreading them out. The opposite of abduction is adduction.

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MovementsMovements

Inversion and Inversion and eversioneversionSupinationSupination and and pronationpronationOppositionOpposition& reposition& reposition

These movements are a little more specialized:Inversion and eversion refer only to the foot. Inverting the foot means to rotate it so that the plantar region is facing medially. The opposite movement is eversion.Supination and pronation refer only to the forearm and hand. When you supinateyour forearm, you turn your palm and forearm so they are facing forward or facing upward. When you pronate your forearm, you turn them so they are facing dorsally or downward.Opposition and reposition refer only to the thumb. When you roll them thumb so that it is facing the rest of the digits, you have opposed your thumb. The opposite movement is reposition.

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InteractionsInteractions

Prime movers (agonists)Prime movers (agonists)and antagonistsand antagonistsSynergistsSynergistsFixatorsFixators (stabilizers)(stabilizers)

Although we will often talk about the contraction of just one muscle at a time, please keep in mind that muscles work together to accomplish movements and maintain body posture. As we’ve already mentioned, muscles can only pull – they never push. For this reason, muscles often work in pairs: one muscle (the prime mover or agonist) accomplishes the main movement at a joint while another muscle or group (the antagonist) pulls in the opposite direction. For example, for elbow flexion, the biceps is the prime mover (it flexes the elbow) while the triceps is the antagonist (it extends the elbow). In the knee joint, the hamstrings are the prime movers while the quadriceps are the antagonists.Synergists are smaller muscles that assist a prime mover. They give added strength and stability, allowing for a smooth movement. Fixators are muscles that contract to stabilize the origin during a movement. Think about abducting the upper limb for example: the scapula and clavicle need to be held firmly in place during this movement, so fixators contract to accomplish this.