Chapter 10 (2)

• Intrinsic muscles are entirely contained within a region, such as the hand. Extrinsic muscles act on a designated region but have attachment elsewhere. E.g. finger movements are extrinsic muscles in the forearm.
• Action is the effect produced by a muscle to produce or prevent movement. Four categories of muscle action are Prime mover, Synergist, Antagonist, and Fixator.
• (1)Prime mover (agonist) is the muscle producing most of the force during a particular action. (2)Synergist is the muscle that aids the prime mover and may contribute additional force, modify the direction of movement, or stabilize a nearby joint. (3)Antagonist is the muscle that opposes the action of the prime mover. It contracts to prevent excessive movement or relaxes to give prime mover control over an action. Antagonistic pairs are muscles that act on opposite sides of a joint. (4)Fixator is the muscle that prevents the movement of bone.
• Innervation of a muscle refers to the identity of the nerve that stimulates it. Knowing innervation enables the diagnosis of nerve, spinal cord, and brainstem injuries from muscle tests.
• Spinal nerves arise from the spinal cord. They emerge through the intervertebral foramina and immediately branch into posterior and anterior rami. They innervate muscles below the neck.
• Plexus is a web-like network of spinal nerves adjacent to the vertebral column.
• Cranial nerves arise from the base of the brain. They emerge through the skull foramina. They innervate the muscles of the head and neck and are numbered CN I to CN XII.
• When it comes to blood supply the muscular system receives about 1.24 L of blood per minute at rest (one-quarter of the blood pumped by the heart). During heavy exercise, total cardiac output rises, and the muscular system’s share is more than three-quarters (11.6 L/min). Capillaries branch extensively through the endomysium to reach every muscle fiber.
• Muscles are named in Latin that describe distinctive aspects of the structure, location, or action of a muscle. Examples: Depressor labii inferioris and Flexor digiti minimi brevis.
• Muscles of facial expression attach to the dermis and subcutaneous tissues of the face. They tense the skin and produce facial expressions, innervated by the facial nerve (CN VII). Paralysis causes the face to sag. These muscles are found in the scalp, forehead, around the eyes, nose, mouth, and in the neck.
• Four pairs of muscles produce biting and chewing movements of the mandible; The temporalis, masseter, medial pterygoid, and lateral pterygoid.
• Depression means to open your mouth. Elevation means biting and grinding. Protraction means jut the jaw out and incisors can cut. Retraction means making rear teeth meet and jutting the jaw back into the mouth. Lateral and medial excursion are used to grind food.
• Inferior attachments belong on the vertebral column, thoracic cage, and pectoral girdle. In contrast, superior attachments belong to the cranial bones. The actions of these attachments include; flexion (tipping the head forward), extension (holding the head erect), lateral flexion (tipping the head to one side), AND rotation (turning the head to the left and right).
• Muscles acting on the head include; Neck flexors (sternocleidomastoid), and neck extensors (trapezius and splenius capitis).
• Contralateral movement means movement of the head toward the opposite side, AND ipsilateral movement means movement of the head toward the same side.
• Muscles of the trunk include four functional groups; Muscles of respiration, muscles that support the abdominal wall, movement of the vertebral column, and muscles that support the pelvic floor.
• Since breathing requires the use of muscles enclosing the thoracic cavity the muscles of respiration are the diaphragm, the external intercostals, and the internal intercostals.
• Inspiration means air intake and Expiration means the expelling air.