Skeletal Muscles

2 Skeletal Muscle Actions Skeletal muscles generate a great variety of body movements. The action of each muscle depends upon the type of joint it is associated with and where the muscle is attached on either side of that joint.

3 Body Movement Four Basic Components of Levers: 1. Rigid bar – bones 2. Fulcrum – point on which bar moves; joint 3. Object - moved against resistance; weight 4. Force – supplies energy for movement; muscles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Force (a) First-class lever ResistanceForce ResistanceForce Fulcrum Resistance Fulcrum Force Fulcrum Resistance (b) Second-class lever ResistanceForce Resistance Fulcrum (c) Third-class leverForce

4 Levers and Movement Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Radius Resistance Fulcrum Ulna (a) (b) Fulcrum Force Forearm movement Biceps brachii contracting muscle Relaxed muscle Triceps brachii contracting muscle Relaxed muscle

5 Origin and Insertion Origin – immovable end Insertion – movable end Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Radius Coracoid process Origins of biceps brachii Tendon of long head Tendon of short head Biceps brachii Insertion of biceps brachii

6 Interaction of Skeletal Muscles Prime mover (agonist) – primarily responsible for movement Synergists – assist prime mover Antagonist – contraction causes movement in the opposite direction of the prime mover

Muscles of Facial Expression & Mastication

8 A.Muscles of Facial Expression Muscles of facial expression attach to underlying bones and overlying connective tissue of skin, and are responsible for the variety of facial expressions possible in the human face. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Epicranius (Frontalis, Occipitalis; also note the Epicranial aponeurosis) Raises eyebrow “surprised” look; horizontally wrinkles skin of the forehead Orbicularis oculi Closes or blinks eye, compresses lacrimal gland to aid in flow of tears on surface of eye Orbicularis oris “Kissing muscle” closes and puckers lips

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Buccinator “Trumpeter muscle” compresses cheek inward, aids in blowing air out of the mouth keeps food in contact with teeth Zygomatic major, Zygomatic minor Lifts corners of the mouth when smiling Platysma Pulls angle of mouth downward as when pouting; helps lower the mandible (open the mouth)

18 B.Muscles of Mastication Chewing movements include up and down as well as side-to-side grinding motions of muscles attached to the skull and lower jaw. Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Masseter Raises the jaw (closes mouth) Temporalis Raises the jaw (tensing this muscle is associated with TMJ (Temporomandibular joint syndrome – p. 308)

Medial pterygoid Raises the mandible and moves it side to side Lateral pterygoid Lowers the mandible, protracts mandible to make it protrude, moves mandible side to side

Clinical Application TMJ Syndrome – pg. 308 (new text)

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24 Muscles of Facial Expression and Mastication Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Epicranial aponeurosis Frontalis Occipitalis Epicranius Masseter Sternocleidomastoid Temporalis Orbicularis oculi Zygomaticus major Zygomaticus minor Buccinator Orbicularis oris Platysma Buccinator Medial pterygoid Lateral pterygoid Temporalis (a) (c)(b)

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Sternocleidomastoid One – Rotates head to the opposite side Both – Flex head; raise sternum during forceful inspiration Splenius capitis One – Rotates head to the same side Both – Extend head; Hyperextend head Semispinalis capitis One – Rotates head to the same side Both – Extend head; Hyperextend head *Write the origin/insertion for these 3 muscles in your notes (no table on your handout) – pg. 308

Sternocleidomastoid