1. Chapter 7: The Muscular System

2. Types of Muscle

3. The Muscular System Skeletal Muscle Has Three Primary Functions:
Skeletal movement
Posture maintenance
Heat generation

4. The Muscular System Muscle Structure Fascicles
Bundles of muscle cells (fibers) that make up a whole muscle
Connective tissue
Hold fascicles and whole muscle together
Three layers
Endomysium
Perimysium
Epimysium
Tendons

5. The Muscular System Muscle Cells in Action
Motor unit: A single neuron and all the muscle fibers it stimulates
Small motor units used for fine movements
Large motor units used for broad movements

6. The Muscular System Muscle Cells in Action
Neuromuscular junction (NMJ): The point at which a nerve fiber contacts a muscle fiber
A type of synapse
NMJ anatomy
Motor neuron
Neurotransmitter (acetylcholine; ACh)
Motor end plate (on muscle fiber)
Contains acetylcholine receptors

7. The Muscular System Muscle Cells in Action
NMJ allows motor neuron to stimulate muscle fiber to become electrically excited (action potential)
Action potential stimulates muscle contraction
Events at the NMJ
Ach is released from motor neuron into synaptic cleft
Ach diffuses across synaptic cleft towards motor end plate
Ach binds to receptors on motor end plate and stimulates action potential

8. The Muscular System Muscle Cells in Action
The sarcomere is the functional unit of contraction in the skeletal muscle fiber
Sarcomere anatomy:
Thick filaments (myosin)
Thin filaments (actin)
Regulatory proteins
Troponin
Tropomyosin

9. The Muscular System Muscle Cells in Action
Sarcomeres contract via the sliding filament mechanism:
Myosin heads bind to actin, forming cross-bridges
Using stored energy, myosin heads pull actin filaments together within the sarcomeres and the cell shortens
New ATP is used to detach myosin heads and move them back into position for another “power stroke”

10. Figure 7-4 Sliding filament mechanism of skeletal muscle contraction.10

11. The Muscular System Muscle Cells in Action
Calcium regulates sarcomeric contraction within the muscle cell:
Action potential from NMJ travels to sarcoplasmic reticulum (SR)
SR releases calcium into cytoplasm
Calcium shifts troponin and tropomyosin off of thin filament soit blocks the sites on actin filaments where cross-bridges form
Muscle relaxes when stimulation ends and calcium is pumped back into SR

12. The Muscular System Summary of Events in a Muscle Contraction
ACh is released from neuron ending into synaptic cleft at NMJ
ACh binds to motor end plate and produces action potential
Action potential travels to sarcoplasmic reticulum (SR)
SR releases calcium into cytoplasm
Calcium shifts troponin and tropomyosin so that binding sites on actin are exposed

13. The Muscular System
Summary of Events in a Muscle Contraction (continued)
Myosin heads bind to actin, forming cross-bridges
Using stored energy, myosin heads pull actin filaments together within sarcomeres and cell shortens
New ATP is used to detach myosin heads and move them back to position for another “power stroke”
Muscle relaxes when stimulation ends and calcium is pumped back into SR

14. The Muscular System Energy Sources Muscle contraction requires ATP
Skeletal muscle prefers to produces ATP via aerobic metabolism, which requires
Oxygen
Glucose
Storage compounds ensure an adequate supply of oxygen and glucose for aerobic ATP metabolism
Myoglobin
Stores additional oxygen, located in muscle cells
Glycogen

15. The Muscular System Energy Sources
During strenuous activity, muscle cells use anaerobic ATP metabolism which causes an oxygen debt and does not require ATP
Breakdown of creatine phosphate
Anaerobic glycolysis
Lactic acid accumulation and oxygen debt
Excess postexercise oxygen consumption
After strenuous exercise, person takes in extra oxygen (via rapid breathing) to remove lactic acid and replenish energy stores

16. The Muscular System Effects of Exercise
Improved balance, joint flexibility
Increased muscle size (hypertrophy)
Improved muscle tissue
Vasodilation
Strengthened heart muscle
Improved breathing and respiratory efficiency
Weight control
Stronger bones

17. The Muscular System Types of Muscle Contractions
Partial (muscle tone or tonus)
Partially contracted state that is normal
Isotonic
No change in tension
Muscle length shortens
Movement
Isometric
Great increase in tension
Muscle length unchanged
No movement

18. The Mechanics of Muscle Movement
Tendons attach muscles to bones.
Origin: Attached to more fixed part of skeleton
Insertion: Attached to more movable part of skeleton

19. Figure 7-6 Muscle attachments to bones.19

20. The Mechanics of Muscle Movement
Muscles Work Together
Many muscles function in pairs
Prime movers
Movement by a muscle
Antagonists
Produces opposite movment
Synergists
helpers

21. The Mechanics of Muscle Movement
Levers and Body Mechanics
Musculoskeletal system as a lever system
Lever—bone
Fulcrum—joint
Force—applied by muscle
Three classes of levers
First class
Second class
Third class—most body systems

22. 22

23. Skeletal Muscle Groups
Characteristics for Naming Muscles
Characteristic
Example
Location
Temporalis; near the skull’s temple
Size
Gluteus maximus; the largest
Shape
Serratus anterior; serrated edge
Direction
External oblique; runs obliquely
Number of heads
Biceps brachii; two heads
Action
Flexor digitorum; flexes toes

25. 25

26. Skeletal Muscle Groups
Muscles of the Head and Neck
Name
Location
Function
Orbicularis oculi
Encircles eyelid
Closes eye
Levator palpebrae superioris
Posterior orbit to upper eyelid
Opens eye
Orbicularis oris
Encircles mouth
Closes lips*
Buccinator
Fleshy part of cheek
Flattens cheek; helps in eating, whistling, and blowing wind instruments
Temporalis
Above and near ear
Closes jaw
Masseter
At angle of jaw
Closes jaw-used for chewing*
Sternocleidomastoid
Along lateral neck, to mastoid process
Flexes head; rotates head toward opposite side from muscle, moves head*

27. Figure 7-10 Muscles of the head and neck.27

28. Skeletal Muscle Groups
Muscles That Move the Shoulder and Arm
Name
Location
Function
Trapezius
Posterior neck and upper back to clavicle and scapula
Raises shoulder and pulls it back; superior portion extends and turns head
Latissimus dorsi
Middle and lower back, to humerus
Extends and adducts arm
Pectoralis major
Superior, anterior chest, to humerus
Flexes and adducts arm
Serratus anterior
Inferior to axilla on lateral chest
Moves shoulder forward; aids in raising arms, punching, or reaching forward
Deltoid
Covers shoulder joint, to lateral humerus
Abducts arm; flexes and extends arm

29. Skeletal Muscle Groups
Muscles That Move the Forearm and Hand
Name
Location
Function
Biceps brachii
Anterior arm along humerus, to radius
Flexes forearm; supinates forearm and hand
Brachialis
Deep to biceps brachii; inserts at anterior elbow joint
Forceful flexor of forearm
Brachioradialis
Lateral forearm from distal end of humerus
Flexes forearm
Triceps brachii
Posterior arm, to ulna
Extends forearm

30. Skeletal Muscle Groups
Muscles That Move the Forearm and Hand (continued)
Name
Location
Function
Flexor carpi group
Anterior forearm, to hand
Flexes hand
Extensor carpi group
Posterior forearm, to hand
Extends hand
Flexor digitorum group
Anterior forearm to fingers
Flexes fingers
Extensor digitorum group
Posterior forearm to fingers
Extends fingers

31. Figure 7-11 Muscles that move the forearm and hand.31

32. Skeletal Muscle Groups
Muscles of the Trunk
Name
Location
Function
Diaphragm
Dome-shaped partition between thoracic and abdominal cavities
Dome descends to enlarge thoracic cavity from top to bottom
Intercostals
Between ribs
Elevate ribs and enlarge thoracic cavity
Muscles of abdominal wall:
External oblique
Internal oblique
Transversus abdominus
Rectus abdominis
Anterolateral abdominal wall
Compress abdominal cavity and expel substances from the body; flex spinal column
Levator ani
Pelvic floor
Aids defecation
Erector spinae
Group of deep vertical muscles between sacrum and skull
Extends vertebral column to produce erect posture

33. Figure 7-12 Muscles of respiration.33

34. Figure 7-13 Muscles of the abdominal wall.34

35. Skeletal Muscle Groups
Muscles That Move the Leg and Thigh
Name
Location
Function
Gluteus maximus
Superficial buttock, to femur
Extends thigh
Gluteus medius
Deep buttock, to femur
Abducts thigh
Iliopsoas
Crosses anterior hip joint, to femur
Flexes thigh
Adductor group
Medial thigh, to femur
Adducts thigh
Sartorius
Crosses anterior thigh from ilium to medial tibia
Flexes thigh and leg (to sit cross-legged)
Gracilis
Pubic bone to medial surface of tibia
Adducts thigh at hip; flexes

36. Skeletal Muscle Groups
Muscles That Move the Leg and Thigh (continued)
Name
Location
Function
Quadriceps femoris
Rectus femoris
Vastus medialis
Vastus lateralis
Vastus intermedius
Anterior thigh, to tibia
Extends leg
Hamstring group
Biceps femori
Semimembranosus
Semitendinosus
Posterior thigh; ischium and femur to tibia and fibula
Flexes leg at knee; extends and rotates thigh at hip

37. Figure 7-15 Muscles of the thigh.
How many muscles make up the quadriceps femoris? 37

38. Skeletal Muscle Groups
Muscles That Move the Foot
Name
Location
Function
Gastrocnemius
Posterior leg, to calcaneus, inserting by the Achilles tendon
Plantar flexes foot
Soleus
Posterior leg deep to gastrocnemius
Tibialis anterior
Anterior and lateral leg, to foot
Dorsiflexes and inverts foot
Fibularis longus
Lateral leg, to foot
Everts foot
Flexor digitorum group
Posterior leg and foot to inferior surface of phalanges
Flexes toes
Extensor digitorum group
Anterior surface of leg bones to superior surface of phalanges
Extends toes

39. Figure 7-16 Muscles that move the foot.39

40. Effects of Aging on Muscles
Beginning at about age 40
Gradual loss of muscle cells
Loss of power
Tendency to flex hips and knees
Decrease in height