Chapter 5

Ch 5 Muscles

Muscle Types

Terms & movements

Muscles their functions/ movements

Anatomy of Skeletal Muscles

Muscle contraction (NMJ, Sliding Filament Theory, Aerobic vs Anerobic)

Anatomical Terms

1. Origin; the attachment of a muscle to a bone or structure that does not move when the muscle contracts

   1. A muscle has an attachment to a bone or another structure at each end, one attachment must be anchored for the muscle to be able to pull at the other end, the origin is the site of the anchored end.

2. Insertion: the attachment of a muscle to a bone or structure that does move when the muscle contracts 

3. Intrinsic muscle: Refers to a muscle having its origin and insertion located in the same body region 

4. Extrinsic muscle: Refers to a muscle having its origin in a different body region than the insertion 

5. Fixator: a muscle that holds an origin stable for another muscle 

6. Synergists: Muscles that have the same action 

7. Prime mover: The main muscle that performs the action, helped by synergists 

8. Antagonist: A muscle that has an opposing action

9. Muscle Actions

10. Flexion: Action that bends a part of the body anteriorly

11. Extension: Action that bends a part of the body posteriorly

12. Abduction: movement of a part of the body away from the midline 

13. Adduction: movement of a part of the body toward the midline

14. Protraction: a movement that brings part of the body forwards

15. Retraction: Movement that brings part of the body backward

16. Lateral excursion: Movement of the jaw laterally to either side 

17. Medial excursion: Movement of the jaw back to the midline 

18. Dorsiflexion: position of standing on the heels with the toes pointing up off the floor

19. Plantar flexion: position of standing on tiptoes with the heels off the floor

20. Inversion: Position in which the soles of the feet are together, facing each other

21. Eversion: Position in which the soles of the feet point away from each other 

22. Rotation: the act of spinning on an axis

23. Circumduction: the act of making a circle with part of your body 

24. Supination: rotation that turns the palms up 

25. Pronation: rotation that turns the palms down

26. Opposition: the act of bringing the thumb to the palm 

27. Reposition: the act of taking the thumb away from the palm 

28. Elevation: the act of closing the jaw or raising the shoulders 

29. Depression: The act of opening the jaw, or lowering the shoulders 

Head and Neck Muscles 

1. Orbicularis oris: closes and protrudes lips, as in kissing 

2. Orbicularis oculi: Closes eye 

3. Frontalis: Raises eyebrow and wrinkles the skin of the forehead 

4. Occipitals: Fixes epicranial aponeurosis as an origin for the frontalis muscle 

5. Temporalis: Elevates, retracts, and causes medial and lateral excursion of the mandible 

6. Buccinator: Compresses cheeks

7. Masseter: Elevates mandible 

8. Platysma: Depresses mandible and draws the corner of the mouth and lip downward 

9. Sternocleidomastoid: Individually each muscle rotates the head, together, the bring the head forward and down

10. Zygomaticus major: Draws the mouth’s angle upward and outwards 

Thorax and Abdomen Muscles 

1. Pectoralis major: Flexes and adducts humerus

2. Pectoralis minor: Depresses and protracts shoulder 

3. Serratus anterior: Protracts shoulder 

4. Diaphram: Prime mover for breathing 

5. External Intercostals: Expand the thoracic cavity during inspiration 

6. Internal Intercostals: Compress the thoracic cavity during forced expiration

7. External abdominal oblique: Compresses abdomen, flexes spine, and allows rotation at the waist, origin at ribs 

8. Internal abdominal oblique: Compresses abdomen, flexes spine, and allows rotation at the waist, origin at Iliac Crest

9. Rectus abdominal: Flexes spine 

10. Transverse abdominal: Compresses abdomen 

Back Muscles 

1. Trapezius: Extends head 

2. Latissimus dorsi: Extends, adducts, and medially rotates the humerus

3. Erector spinae: Hold the spine erect for posture and extends spine

4. Gluteus medius: Abducts and medially rotates hip

5. Gluteus maximus: Extends and laterally rotates hip 

6. Shoulder and arm muscles 

7. Deltoid: Abducts humerus 

8. Biceps brachii: Flexes elbow, origin at scapula  

9. Triceps brachii: extends elbow 

10. Brachialis/ Brachioradialis: flexes elbow, origin at humerous 

Muscles of the Forearm

1. Extensor Carpi Radialis: Extends and abducts wrist

2. Extensor Carpi Ulnaris: Extends and adducts wrist

3. Palmaris Longus: Flexes wrist

4. Flexor Carpi Radialis: Flexes and abducts wrist

5. Flexor Carpi Ulnaris: Flexes and adducts wrist

6. Extensor Digitorum: Extends fingers

7. Flexor Digitorum: Flexes fingers

Muscles of the Thigh

1. Tensor Fasciae Latae: Abducts and medially rotates hip

2. Gracilis: Flexes knee and adducts hip

3. Adductor Longus: Adducts hip

4. Pectineus: Adducts and flexes hip

5. Iliacus: Flexes hip

6. Iliopsoas: Flexes hip

7. Psoas major: Flexes hip 

8. Sartorius: Flexes knee and hip

9. Rectus Femoris: Extends knee and flexes hip

10. Vastus Lateralis: Extends knee

11. Vastus Medialis: Extends knee

12. Vastus Intermedius: Extends knee

13. Biceps Femoris: Flexes knee and extends hip

14. Semitendinosus: Flexes knee

15. Semimembranosus: Flexes knee

Muscles of the Leg

1. Gastrocnemius: Plantar-flexes foot

2. Soleus: Plantar-flexes foot

3. Peroneus (Fibularis): Everts foot

4. Tibialis Anterior: Dorsiflexes and inverts foot

Anatomy of a Skeletal Muscle

1. Muscle Structure Overview

   • Tendon: Connects muscle to bone. Composed of tough connective tissue that transmits the force from muscle contraction to bones.

   • Epimysium: The outermost layer of connective tissue surrounding the entire muscle.

   • Perimysium: Connective tissue that surrounds groups of muscle fibers (fascicles).

   • Endomysium: A thin layer of connective tissue that encases individual muscle fibers (cells).

2. Fascicle

   • Bundles of muscle fibers wrapped together by the perimysium.

   • Allows for strength and flexibility in muscle movement.

3. Function of Connective Tissues

   • The epimysium, perimysium, and endomysium collectively support, protect, and transmit forces generated by the muscle.

Anatomy of a Skeletal Muscle Cell

1. Sarcolemma

   • The plasma membrane of a muscle cell.

   • Encloses the muscle fiber and helps transmit electrical impulses.

2. Sarcoplasmic Reticulum

   • A specialized form of smooth endoplasmic reticulum in muscle cells.

   • Stores and releases calcium ions necessary for muscle contraction.

3. Myofibrils

   • Cylindrical structures within muscle fibers.

   • Contain repeating units of sarcomeres, which are the functional units of muscle contraction.

4. Sarcomeres

   • Composed of overlapping thick filaments (myosin) and thin filaments (actin).

   • Responsible for the striated appearance of skeletal muscles and their ability to contract.

Microscopic View of Muscle Fiber

1. Z-Line: Forms the boundary of a sarcomere. Thin filaments (actin) attach here.

2. M-Line: Located in the middle of the sarcomere, anchoring the thick filaments (myosin).

3. Overlap of Myofilaments

   • Areas of overlap between myosin and actin are essential for contraction.

   • The sliding filament mechanism enables these filaments to slide past each other during muscle contraction.

Muscle Types 

1. Skeletal Muscle: Controls voluntary movements, appears striped, and is attached to bones for body motion.

2. Cardiac Muscle: Found only in the heart, it works involuntarily to pump blood and has specialized connections for coordination.

3. Smooth Muscle: Found in hollow organs, it works involuntarily to move substances like food or blood without conscious control.

Neuromuscular junction: 

• The neuromuscular junction is the site where stimulation of a muscle cell by a nerve 

• A small gap called the synaptic cleft separates the nerve ending (synaptic knob) from the muscle fiber.

• The nerve releases a chemical messenger, acetylcholine (ACh), into the synaptic cleft, which binds to receptors on the muscle cell membrane (sarcolemma).

• This triggers an electrical signal in the muscle fiber, initiating contraction.

• A minimum amount of ACh, called the threshold, is required to activate the muscle, and the response follows an all-or-nothing principle—either the muscle contracts fully or not at all.

Sliding Filament Theory 

The Sliding Filament Theory involves thick myofilaments grabbing thin myofilaments and pulling them toward the center of the sarcomere

1. Nerve Impulse: A nerve impulse arrives at the muscle, signaling contraction.

2. Calcium Release: Calcium ions (Ca²⁺) are released from the sarcoplasmic reticulum, bind to troponin, and cause tropomyosin to shift, exposing binding sites on actin.

3. Cross-Bridge Formation: Myosin heads (thick filaments) attach to the exposed binding sites on actin (thin filaments).

4. Power Stroke: Myosin heads pull the actin filaments toward the center of the sarcomere, shortening the muscle.

5. ATP Binding: ATP binds to the myosin heads, causing them to detach from the actin.

6. ATP Hydrolysis: ATP splits into ADP and phosphate, re-cocking the myosin heads for the next cycle.

7. Calcium Reuptake: ATP is used to pump calcium back into the sarcoplasmic reticulum, ending the contraction and relaxing the muscle.

This process repeats as long as calcium is present and ATP is available, enabling sustained muscle contraction.

Aerobic vs Anaerobic

aerobic respiration:  which uses oxygen to produce 36 ATP molecules per glucose, supports long-duration activities and is efficient but slower

anaerobic respiration: which does not use oxygen, produces 2 ATP molecules per glucose, is faster, but results in lactic acid buildup and supports short bursts of intense activity.

Functions of the Muscle System 

1. Movement: a gradual recruitment of additional motor units makes a smooth contraction 

2. Stability

3. Control of body openings and passages

4. Communication: Facial muscles, and throat

5. Heat Production: Muscles provide body heat