chapter 11 muscular system ii anatomy and physiology

Endomysium

Thin sleeve of loose connective tissue surrounding each muscle fiber

Perimysium

Thicker connective tissue sheath wrapping muscle fibers into bundles (of ~20 to 60 fibers) called fascicles

Fascicles

Bundles of muscle fibers that are visible to the naked eye

Epimysium

Fibrous sheath surrounding the entire muscle

Fascia

Sheet of fibrous connective tissue separating muscles or muscle groups

Superficial fascia

Separates skin and hypodermis from underlying muscle

Intermuscular septa

Deeper, thicker fascia that divides muscles into muscle compartments

Muscle compartments

Groups of muscles with similar function and common blood, nerve supply

Fusiform muscles

Thick in the middle with fascicles converging on each tapered end

Parallel muscles

Uniform in width; fascicles are parallel

Triangular (convergent) muscles

Fan shaped muscles, broad at one end with fascicles converging at the other, narrower end

Pennate muscles

Feather shaped muscles; oblique fascicles lead to a tendon that runs the length of the muscle

Unipennate muscles

A type of pennate muscle where fascicles are arranged on one side of the tendon

Bipennate muscles

A type of pennate muscle where fascicles are arranged on both sides of the tendon.

Multipennate muscles

A type of pennate muscle with multiple tendons and fascicles arranged around them

Circular muscles (sphincters)

Fascicles are in rings around certain body openings and passages; control passage of material

Direct (fleshy) attachment

Very little separation between muscle and bone; narrow gap between muscle and bone spanned by collagen fibers

Indirect attachment

A fibrous cord or sheetlike tendon attaches muscle to bone

Muscle belly

The thick midregion between its tendons

Aponeurosis

A broad sheet of tendon

Brachialis

An example of a muscle with direct attachment

Biceps brachii

An example of a muscle with indirect attachment.

Attachments

Can be moving (attached to the moving bone) or stationary (attached to the immobile bone)

Origin

Stationary end of a muscle

Insertion

Moving end of a muscle

Intrinsic muscle

Entirely contained within a region, having both attachments there

Extrinsic muscle

Acts upon a region but originates elsewhere

Muscle Innervation

Identity of the nerve that stimulates a muscle

Spinal nerves

31 pairs that arise from the spinal cord and innervate muscles below the neck

Plexus

Weblike networks of spinal nerves adjacent to the vertebral column

Cranial nerves

Nerves that arise from the base of the brain and innervate muscles of the head and neck

Prime mover (agonist)

Muscle that produces most of the force during a joint action

Synergist

Muscle that aids the prime mover

Antagonist

Muscle that opposes the prime mover

Fixator

Muscle that prevents a bone from moving

Example of muscle action

In elbow flexion, brachialis is the prime mover, biceps brachii is a synergist, triceps brachii is an antagonist, and the rhomboids are fixators

Lever

Any elongated, rigid object that rotates around a fixed point called the fulcrum

Effort arm

Part of lever from fulcrum to point of effort

Resistance arm

Part of lever from fulcrum to point of resistance

Bone as a lever

In the body, a bone acts as a lever, a joint is the fulcrum, effort is generated by a muscle

First-class lever

Fulcrum is in the middle (EFR), like a seesaw.

Example of first-class lever

Rocking of the skull on atlanto-occipital joint of neck.

Second-class lever

Resistance is in the middle (FRE), like carrying a load in a wheelbarrow.

Example of second-class lever

Flexion of femur by the quadriceps femoris (rectus femoris)

Third-class lever

Effort is applied between the fulcrum and resistance (FER)

Example of third-class lever

Flexion of elbow.

Mechanical advantage (MA)

Ratio of output force to input force.

MA formula

MA = (Length of effort arm (LE) / Length of resistance arm (LR)).

MA greater than 1.0

Lever produces more force, less speed and distance

MA less than 1.0

Lever produces more speed and distance, less force

Muscle names

Typically describe the structure, location, or action of a muscle

Blood and nerve supply to skeletal muscles

Muscles have blood supply and nervous innervation to them

Cranial and spinal nerves

Belong to the peripheral nervous system.

Facial muscles

Allow for expressions; contribute to speech, chewing, and other functions

Innervation of facial muscles

All but one are innervated by CN VII (facial nerve)

Occipitofrontalis

Overlies dome of cranium

Orbicularis oculi

Sphincter of eyelid, closes eye

Orbicularis oris

Muscles encircling mouth

Buccinator

Muscle of the cheeks; functions in chewing, sucking, blowing

Platysma

Thin, superficial muscle of upper chest and lower face; helps open mouth and tenses skin of chin and neck

Galea aponeurotica

Facial nerve

Occipitofrontalis, Frontal Belly

Elevates eyebrows in glancing upward and expressions of surprise or fright; draws scalp forward and wrinkles skin of forehead

Occipitofrontalis, Occipital Belly

Retracts scalp; fixes galea aponeurotica so frontalis can act on eyebrows

Levator Palpebrae Superioris

Elevates upper eyelid, opens eye

Corrugator Supercilii

Draws eyebrows medially and downward in frowning and concentration; reduces glare of bright sunlight

Nasalis

Widens nostrils; narrows internal air passage between vestibule and nasal cavity

Levator Labii Superioris

Elevates angle of mouth as in smiling

Levator Anguli Oris

Elevates angle of mouth as in smiling

Zygomaticus Major

Draws angle of mouth upward and laterally as in laughing

Zygomaticus Minor

Elevates upper lip, exposes upper teeth in smiling or sneering

Risorius

Draws angle of mouth laterally in expressions of laughing, horror, or disdain

Depressor Anguli Oris

Draws angle of mouth laterally and downward in opening mouth or sad expressions

Depressor Labii Inferioris

Draws lower lip downward and laterally in chewing and expressions of melancholy or doubt

Mentalis

Elevates and protrudes lower lip in drinking, pouting, and expressions of doubt or disdain; elevates and wrinkles skin of chin

Genioglossus

Unilateral action draws tongue to one side; bilateral action depresses midline of tongue or protrudes tongue.

Hyoglossus

Depresses tongue.

Styloglossus

Draws tongue upward and posteriorly; aids in swallowing.

Palatoglossus

Elevates root of tongue and closes oral cavity off from pharynx; forms palatoglossal arch at rear of oral cavity.

Temporalis

Elevation, retraction, and lateral and medial excursion of the mandible.

Masseter

Elevation of the mandible, with smaller roles in protraction, retraction, and lateral and medial excursion.

Medial Pterygoid

Elevation, protraction, and lateral and medial excursion of the mandible, as in grinding food between the rear teeth.

Lateral Pterygoid

Depression (in wide opening of the mouth), protraction, and lateral and medial excursion of the mandible, as in grinding food between the rear teeth.

Digastric

Depresses mandible when hyoid is fixed; opens mouth as when ingesting food or yawning; elevates hyoid when mandible is fixed.

Geniohyoid

Elevates and protracts hyoid when mandible is fixed; geniohyoid and digastric are the main muscles for opening the mouth.

Mylohyoid

Spans mandible from side to side and forms floor of mouth; elevates floor of mouth in initial stage of swallowing.

Stylohyoid

Elevates and retracts hyoid, elongating floor of mouth; roles in speech, chewing, and swallowing are not yet clearly understood.

Infrahyoid Muscles

Enable the suprahyoid muscles to open the mouth.

Ansa cervicalis

Depresses hyoid after it has been elevated.

Omohyoid

Depresses hyoid after it has been elevated.

Sternohyoid

Depresses hyoid after it has been elevated.

Thyrohyoid

Depresses hyoid; with hyoid fixed, elevates larynx as in singing high notes.

Sternothyroid

Depresses larynx after it has been elevated in swallowing and vocalization; aids in singing low notes.

Pharyngeal Muscles

Encircle pharynx on its posterior & lateral sides, forming a muscular funnel that aids in swallowing. Push food from pharynx into esophagus.

Pharyngeal Constrictors

During swallowing, contract in order from superior to middle to inferior constrictor to drive food into esophagus.

Pterygoid Muscles

Move mandible during chewing.

Suprahyoid Group

Four muscle pairs superior to the hyoid bone; elevate hyoid bone and assist in mouth movements.

Infrahyoid Group

Four muscle pairs inferior to the hyoid bone; depress hyoid bone and provide other functions.

Sternocleidomastoid

Unilateral action tilts head slightly upward and toward the opposite side; bilateral action draws the head straight forward and down.

Trapezius

Largest and most superficial neck extensor.

Splenius Capitis

One of the neck extensors.