General myology

What is the basic rule of muscle action?

Muscles only pull, never push — they contract (active shortening) and relax (passive lengthening).

What is the muscle "origin"?

The attachment closer to the center of the body — the proximal attachment.

What is the muscle "insertion"?

The attachment farther from the center of the body — the distal attachment.

What is a tendon?

Connective tissue that attaches muscle to bone. The origin tendon is usually short; the insertion tendon can be long.

What is an aponeurosis?

A broad, flat tendon, typical of flat muscles.

What is a raphe?

A median (midline) tendon where a muscle pair both originate from a single shared tendon.

How does a ligament differ from a tendon?

A ligament connects bone to bone; a tendon connects muscle to bone.

For a muscle to act on a joint, what must it do?

Cross the joint — muscles attach to bones but act on joints, and may cross one, several, or a whole region of joints.

What is the "flexor surface" of a joint?

The side of the joint where the act of flexion decreases the resting angle.

What is the "extensor surface" of a joint?

The side of the joint where the act of extension increases the resting angle (generally opposite the flexor surface).

In the manus/pes, what position do the proximal and distal digital joints rest in?

Hyperextension.

What does "adduct" mean?

To draw a limb/structure toward the midline — "add to the body."

What does "abduct" mean?

To draw a limb/structure away from the midline — "take away from the body."

What is medial rotation also called?

Pronation — rotating toward the midline.

What is lateral rotation also called?

Supination — rotating away from the midline.

What is circumduction?

Moving a limb "in a circle," combining several joint motions.

What are intrinsic muscles?

Muscles confined entirely to a structure.

What are extrinsic muscles?

Muscles that connect a structure to the rest of the body.

Give examples of extrinsic muscle groups.

Thoracic limb muscles, laryngeal muscles, hyoid muscles, tongue muscles, eyeball muscles, and ear muscles.

Which tongue muscles produce complicated local movement of the tongue?

Intrinsic tongue muscles (extrinsic tongue muscles — genioglossus, hyoglossus, styloglossus — move the tongue as a unit).

What characterizes cutaneous muscles?

They lie just deep to the skin, move the skin, have minimal or no skeletal attachment, and are often the "twitch" muscles (e.g., cutaneus trunci).

Name the four muscles of mastication.

Masseter, temporalis, digastricus, and pterygoids.

What is the difference between epaxial and hypaxial muscles?

Epaxial muscles lie dorsal to the transverse processes of the vertebrae; hypaxial muscles lie ventral to the transverse processes.

Name the three epaxial muscle systems running from pelvis to skull base.

Transversospinalis system, longissimus system, and iliocostalis system.

What is the main function of the muscles of the body wall?

Layered muscles that contain/support the viscera, help support the vertebral column and body as a whole, and include the muscles of respiration.

What is synsarcosis?

A union between parts of the skeleton by muscle alone, with no bony articulation (e.g., how the thoracic limb attaches to the trunk).

When the forelimb is weight-bearing ("immobile"), what does contraction of an extrinsic thoracic limb muscle (e.g., brachiocephalicus) do?

Moves the body relative to the limb — e.g., left brachiocephalicus contraction moves the head and neck to the left.

When the forelimb is non-weight-bearing ("mobile"), what does contraction of the brachiocephalicus do?

Moves the limb relative to the body — advances the forelimb and extends the shoulder joint.

Which forearm region contains extensors of the carpus and digits?

The cranio-lateral forearm (the caudo-medial forearm contains the flexors).

Which leg (crus) region contains flexors of the hock and extensors of the digits?

The cranio-lateral leg (the caudal leg contains extensors of the hock and flexors of the digits).

What is the general action of the cranial thigh muscles (e.g., quadriceps)?

Flexors of the hip and extensors of the stifle.

What is the general action of the caudal thigh muscles (e.g., hamstrings)?

Extensors of the hip, and extensors/flexors of the stifle.

What is the general action of lateral pelvis muscles (e.g., gluteals)?

Flexors and extensor of the hip joint.

What is the general action of medial pelvis muscles?

Rotators of the hip joint.

What are the sources used to name a muscle?

Action, shape, attachments, location, and number of heads.

Give an example of a muscle named for its shape.

Deltoideus — Greek letter delta-shaped.

How many heads does the triceps brachii have in dogs vs. humans?

4 heads in dogs; 3 heads in humans.

How many heads does the biceps brachii have in dogs vs. humans?

1 head in dogs; 2 heads in humans.

What are the different types of muscle?

Smooth muscle and striated muscle (striated muscle includes skeletal and cardiac muscle).

How can a muscle attach to bone?

Via tendons — short at the origin, sometimes long at the insertion, flat (aponeurosis) on flat muscles, or shared as a midline raphe between paired muscles.

What movements can muscles produce at joints?

Flexion/extension, adduction/abduction, medial (pronation)/lateral (supination) rotation, circumduction, and stabilization; in the head/neck/tail also raising/lowering and moving left/right.

What is the difference between intrinsic and extrinsic muscles (summary)?

Intrinsic muscles are confined to one structure; extrinsic muscles connect that structure to the rest of the body (e.g., tongue, eyeball, ear, thoracic limb).

What are the major groups of muscles in the body?

Cutaneous muscles, head muscles (facial expression, mastication, tongue), muscles of breathing/swallowing, neck muscles, vertebral column muscles (epaxial/hypaxial), body wall muscles, and thoracic and pelvic limb muscles.

Give an example of a muscle of facial expression.

Orbicularis oculi (closes the eyelids).

Give an example of a masticatory muscle.

Masseter (or temporalis, digastricus, pterygoids).

Give an example of a neck muscle.

Sternocephalicus (or brachiocephalicus, omohyoid).

Give an example of an epaxial muscle.

Longissimus (part of the longissimus system).

Give an example of a body wall muscle.

External intercostal (or rectus abdominis, external abdominal oblique).

Give an example of a thoracic limb muscle.

Triceps brachii (or brachiocephalicus, deltoideus, extensor carpi radialis).

Give an example of a pelvic limb muscle.

Biceps femoris (or sartorius, gastrocnemius).