1. Muscular System- contains over 700 muscles

2. Some functions of Skeletal Muscle
Movement of body parts
Maintains posture
Muscle contraction generate heat which helps regulate body temperature
Allow us to change our facial expressions

3. Characteristics of Muscles
All muscles are excitable, contractile, extensible, and elastic
Excitable: respond to stimuli
Contractile: shorten
Extensible: stretch
Elastic: return to their original length after being shortened or stretched

4. Skeletal Muscles Work in Opposing Pairs
Each muscle is attached to a bone by a tendon
The origin of the muscle is attached to the bone that remains stationary during movement
The insertion is attached to the bone that moves
Bones act as levers in working with skeletal muscles to produce movement

5. Skeletal Muscles Work in Pairs
Muscles work in opposing pairs called antagonistic pairs
Agonist- prime mover; It contracts during a movement
Antagonist-muscle that relaxes during a movement
Synergist- muscle that assist in a movement

6. Ways Skeletal Muscles are Named
Direction of muscle fibers
Size of muscle
Shape of the muscle
Location of the muscle
Number of heads of origins
Origin & Insertion
Action of the muscle

7. Naming Some Superficial Skeletal Muscles
Triceps brachii
• Straightens arm
at elbow
Pectoralis major
• Flexes and rotates arm
Serratus anterior
• Boxer’s muscle; important in
Reaching and pushing
External oblique
• lateral rotation of trunk
(twisting from side to side)
compresses abdomen
Rectus abdominis
• Compresses abdomen
and Flex the trunk
Adductor longus
• adducts and flexes thigh
At the hip joint
Sartorius
• Bends lower leg at
knee, bends and
rotates thigh at hip
Quadriceps femoris
• extends leg at knee
Tibialis anterior
• Flexes foot toward knee
(a) Front view
Figure 6.2a

8. Naming Some Superficial Skeletal Muscles
Biceps brachii
• Bends forearm at
elbow,
Deltoid
• Raises arm
Trapezius
• Raises, turns, and
lowers the shoulder;
turns head
Latissimus dorsi
• “Swimmer’s muscle”
Rotates and draws arm
backwards (toward the body)
Gluteus maximus
• Extends and rotates
thigh when walking
Hamstring group
• bend the leg at the knee
Gastrocnemius
• Raises the foof off the floor
(b) Back view
Figure 6.2b

9. Parts of a skeletal muscle

10. Parts of a skeletal muscle
A muscle is made up of bundles of muscle cells (fibers)
Each bundle is called a fascicle
Epimysium- connective tissue covering of a muscle
Perimysium- connective tissue covering of fascicle
Endomysium- connective tissue covering of each muscle cell (fiber)

11. Myofibrils
Myofibril- is a rod-like structure within a muscle cell (fiber)
Figure 6.3

12. Myofibrils
Myofibril- contain striations produced by alternating thick (myosin) and thin (actin) filaments
Figure 6.3

13. Sacromeres (c) A diagram and
Z line
One sarcomere
(c) A diagram and
electron micrograph
of a myofibril
Z line
Z line
One sarcomere
Actin
Myosin
(d) A sarcomere, the contractile unit of a skeletal muscle, contains actin and
myosin myofilaments.
Figure 6.3c–d

14. Sacromeres
A Sarcomere is a unit on a myofibril
The ends of each sarcomere are marked by dark protein bands called Z lines
actin and myosin proteins alternate within the sarcomere

15. Sacromeres Actin is attached to the z-line.
Myosin filaments lie in the middle of the sarcomere, they are not attached directly to the z-line.
Video
Myosin attaches to actin and pulls it toward the center of the sarcomere to produce muscle contraction

16. Neuromuscular Junction
Neuromuscular Junction is a junction between a motor neuron and a muscle membrane
Figure 6.7 (1 of 2)

17. Skeletal Muscle Contraction
Contraction is triggered when a nerve impulse travels down a motor neuron until it reaches the neuromuscular junction
The motor neuron releases acetylcholine into the synaptic cleft.
Acetylcholine binds to receptors on the muscle membrane

18. Skeletal Muscle Contraction
The binding of acetylcholine to the muscle membrane causes Ions to flow across the membrane generating an impulse
Figure 6.7 (2 of 2)

19. Skeletal Muscle Contraction
Structures called T- tubules carry the impulse inside the muscle cell to the sarcoplasmic reticulum which release Ca++
When Ca ++ is free inside a muscle cell, myosin attaches to actin and pulls it producing muscle contraction
Figure 6.7 (2 of 2)

20. Muscle Contraction Spinal cord Motor neuron Neuromuscular junction
Skeletal
muscle cells
Motor unit
Figure 6.8

21. Skeletal Muscle Contraction
Contraction is triggered when a nerve impulse travels down a motor neuron until it reaches the neuromuscular junction
The motor neuron releases acetylcholine into the synaptic cleft.
Acetylcholine binds to receptors on the muscle membrane
The binding of acetylcholine to the muscle membrane causes Ions to flow across the membrane generating an impulse
Structures called T- tubules carry the impulse inside the muscle cell to the sarcoplasmic reticulum which release Ca++
When Ca ++ is free inside a muscle cell, myosin attaches to actin and pulls it producing muscle contraction

22. Myogram- a recording of a muscle contraction
Figure 6.9

23. Myograms Muscle twitch- single contraction
Wave summation- three to four contractions
Taken to the extreme, a sustained powerful contraction is called tetanus

24. ATP Comes from Many Sources
Figure 6.10

25. ATP for Muscle Contraction Comes from Many Sources
Sources of ATP:
The initial source is the ATP stored in the muscle cells
then the ATP formed from the creatine phosphate reserves
When those sources are depleted, the muscles depend upon stored glycogen
Glycogen is converted to glucose and then to ATP through aerobic respiration or lactic acid fermentation

26. Skeletal muscles contain both Slow and Fast twitch cells
Slow-twitch cells
Loaded with mitochondria, and therefore deliver prolonged, strong contractions
Fast-twitch cells
Contract rapidly and powerfully but with much less endurance
They rely on lactic acid fermentation as their source of energy, and therefore tire quickly

27. Slow twitch Fibers
Figure 6.11 (1 of 2)

28. Fast-Twitch Fibers
Figure 6.11 (2 of 2)

29. Aerobic Exercise; Resistance Exercise
Increases endurance and coordination
Resistance exercise
Builds strength