1. Chapter 9
Muscular System

2. Types of Muscle
Cardiac
Involuntary
Smooth
Skeletal
Voluntary

3. Types of Muscle
Cardiac muscle: Found only in the heart, consists of short, branching fibers that fit together at intercalated disks. It appears striped, or striated. Involuntary muscle because it contracts automatically.
Smooth muscle: Found in the digestive tract, blood vessels, bladder, airways, and uterus, smooth muscle is nonstriated. Involuntary muscle because it contracts automatically (such as when the digestive tract processes food).
Skeletal muscle: Is attached to bone and causes movement of the body. It appears markedly striated. Voluntary muscle because it can be contracted at will.

4. Skeletal Muscle Structure
A skeletal muscle cell is called a muscle fiber. Skeletal muscle consists of bundles of tiny fibers that run the length of the muscle.
Muscle fiber
Endomysium
Fascicle
Perimysium
Epimysium
Fascia

5. Skeletal Muscle Structure
Endomysium covers each muscle fiber.
Muscle fibers are grouped in bundles called fascicles. Perimysium encases the fascicles. Epimysium, surrounds the muscle as a whole and binds all the muscle fibers together.
Fascia surrounds the muscle outside the epimysium. (Deep fascia lies between muscles, whereas superficial fascia resides just under the skin.)

6. Structure of Muscle Fibers
Myofibril
Sarcolemma
Myofilaments
Sarcoplasmic reticulum
Transverse (T) tubule

7. Structure of Muscle Fibers
The membrane surrounding each muscle fiber (or cell) is called a sarcolemma.
The cytoplasm of the cell is called sarcoplasm.
Long protein bundles called myofibrils fill the sarcoplasm. (Myofibrils store glycogen and oxygen.)
Sarcoplasmic reticulum (SR) surrounds each myofibril.
Transverse (T) tubules extend across the sarcoplasm.
Myofibrils consist of even finer fibers, called myofilaments. Two types of myofilaments: thin and thick.
Thick = myosin.
Thin = actin.
Arrangement gives skeletal muscle its striated appearance.

8. Question A single muscle cell is called a: myofilament. muscle fiber.
myofibril.
fascicle.

9. Sliding-Filament Model of Contraction
View animation on “Sliding-filament model of contraction”

10. Sliding Filament Model
The thin and thick myofilaments stack to form the myofibrils; they are arranged in a type of lattice-work to form sarcomeres. A Z disc, or Z line, serves as an anchor point for the thin myofilaments. The section between the Z disks is the sarcomere.

11. Sliding Filament Model
When a muscle begins to contract, the myosin latches on to the actin, forming a cross bridge.
The sliding-filament model of contraction – the sarcomere shortens because the filaments slide over the top of one another.
Muscle contraction requires ATP.

12. View animation on “How muscle fibers contract and relax”
Muscle Contraction
View animation on “How muscle fibers contract and relax”

13. Muscle Contraction
The connection between a motor neuron and a muscle fiber is a neuromuscular junction.
The synaptic cleft is a narrow space between the end of the motor nerve and the muscle fiber.

14. Muscle Contraction
Muscle contraction involves the following sequence of events:
Impulse reaches the end of a motor neuron, causing vesicles to fuse with cell membrane and release a neurotransmitter called acetylcholine (ACh).
Ach diffuses across synaptic cleft, stimulating receptors in the sarcolemma.
This sends electrical impulse over sarcolemma and inward along the T tubules, which then causes sacs in sarcoplasmic reticulum to release calcium.
Calcium binds with troponin on actin filament to expose attachment points. In response, myosin heads grab on to the thin filaments and muscle contraction occurs.

15. Muscle Tone
Length-tension relationship – strength of contraction depends on length of fibers before contraction begins.

16. Question
During muscle contraction, the sarcoplasmic reticulum releases which substance?
Calcium
Acetylcholine
ATP
Acetylcholinesterase

17. Contraction of a Muscle
Motor unit: A neuron and all the fibers it stimulates
Threshold: The minimum voltage needed to cause muscle fiber contraction
Twitch: Single, brief contraction

18. Other Factors Affecting Muscle Contraction
Frequency of stimuli
Strength of stimulus
Type of contraction

19. Question
A condition of rapid contraction with only partial relaxation is called:
incomplete tetanus.
complete tetanus.
twitch.
treppe.

20. Energy Source for Contraction
Fatty acids
Creatine phosphate
Glucose

21. Energy Source for Contraction
All muscle contraction – requires energy in the form of adenosine triphosphate (ATP)
At rest – plenty of oxygen so aerobic respiration breaks down fatty acids
Beginning exercise – supply of oxygen drops so muscles break down high-energy creatine phosphate (CP) making fuel for about 20 seconds of high-energy activity or about 1 minute of moderate activity

22. Energy Source for Contraction
Continued exercise – muscles switch to anaerobic respiration of glucose; generates energy quickly and is useful for intense bursts of activity but produces lactic acid, which leads to muscle fatigue.
After about 10 minutes of moderate activity – supply of oxygen increases and muscles shift back to aerobic respiration making more ATP than anaerobic.

23. Muscle Function
Origin
Belly
Insertion

24. Muscle Function
Skeletal muscles work in groups to create movement: The main muscle triggering the movement is the prime mover; the muscles that assist are synergists; the muscles balancing these movements are antagonists.
When the prime mover contracts, the antagonist must relax and give the prime mover control. Antagonists oppose the action of the prime mover. The prime mover for one movement is the antagonist for the opposite movement.

25. Question At rest, muscles obtain most of their energy by metabolizing:
glucose.
lactic acid.
creatine phosphate.
fatty acids.

26. Major Muscles of the Body
Muscles are named according to
Size
Shape
Location
Number of origins
Direction of muscle fibers
Actions
The body has more than 600 muscles.
Note: A table in the textbook details how muscles are named.

27. Muscles of the Head and Neck
Frontalis
Temporalis
Orbicularis oculi
Zygomaticus
Masseter
Orbicularis oris
Sternocleidomastoid
Trapezius

28. Muscles of the Head and Neck
The following are muscles of facial expression:
Frontalis
Orbicularis oculi
Zygomaticus
Orbicularis oris
Buccinator
The following are muscles of chewing:
Temporalis
Masseter
The following are muscles that move the head:
Sternocleidomastoid
Trapezius

29. Muscles of the Trunk External intercostals Internal intercostals
Diaphragm

30. Muscles of the Trunk
Some muscles of the trunk participate in respiration and form the abdominal wall. Additional muscles support and allow movement in the vertebral column; other muscles lie on top of each other to form the pelvic floor.
The following muscles are involved in breathing:
External intercostals
Internal intercostals
Diaphragm

31. Muscles That Form the Abdominal Wall
Rectus abdominis
External oblique
Linea alba
Transversus abdominis
Internal oblique

32. Muscles That Form the Abdominal Wall
The muscles of the abdominal wall are as follows:
Rectus abdominis
Transversus abdominis
Internal oblique
External oblique
The aponeuroses of the muscles that form the abdominal wall meet in the midline of the abdomen to form a tough band of connective tissue called the linea alba (white line).

33. Which muscle or muscle group elevates the ribs during inspiration?
Question
Which muscle or muscle group elevates the ribs during inspiration?
Temporalis
Internal intercostals
External intercostals
External oblique

34. Muscles of the Shoulder and Upper Arm
Deltoid
Pectoralis major
Serratus anterior

35. Muscles of the Shoulder and Upper Arm
Key muscles are:
Deltoid
Pectoralis major
Serratus anterior

36. Muscles of the Neck, Shoulder, and Back
Trapezius
Supraspinatus
Infraspinatus
Rotator cuff
Teres minor
Latissimus dorsi

37. Muscles of the Neck, Shoulder, and Back
Trapezius
Latissimus dorsi
Rotator cuff
Nicknamed the “SITS” muscles: supraspinatus, infraspinatus, teres minor, and subscapularis

38. Muscles That Move the Forearm
Brachialis
Biceps brachii
Triceps brachii
Brachioradialis
Pronator muscle

39. Muscles That Move the Forearm
Key muscles are:
Brachialis
Biceps brachii
Triceps brachii
Brachioradialis
Pronator muscle
Supinator muscle
Flexors
Extensors
Muscles in the hands work with the flexors and extensors to help the fingers make delicate movements.

40. Muscles of the Thigh (Anterior View)
Adductor magnus
Iliacus
Iliopsoas
Psoas major
Adductor brevis
Adductor longus
Gracilis
Sartorius
Rectus femoris
Vastus lateralis
Vastus medialis

41. Muscles of the Thigh (Anterior View)
Iliopsoas (acting in opposition to the gluteus maximus) consists of the iliacus and psoas major.
Sartorius
Adductor muscles (adductor magnus, adductor brevis, adductor longus, and gracilis).
Quadriceps femoris consists of four muscles: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.

42. Muscles of the Hip and Thigh (Posterior View)
Gluteus medius
Gluteus maximus
Biceps femoris
Semitendinosus
Semimembranosus

43. Muscles of the Hip and Thigh (Posterior View)
The gluteal muscles consist of the following:
Gluteus medius
Gluteus maximus
Gluteus minimus
Hamstrings consist of the biceps femoris, semitendinosus, and semimembranosus.

44. Muscles That Act on the Foot
Gastrocnemius
Soleus
Calcaneal (Achilles) tendon

45. Muscles That Act on the Foot
Bulging calf muscle consists of the gastrocnemius and the soleus
Common tendon of the gastrocnemius and soleus is the calcaneal (Achilles) tendon.

46. Muscles That Act on the Foot
Tibialis anterior
Soleus
Extensor digitorum longus

47. Muscles That Act on the Foot
Digitorum longus
Tibialis anterior
Extensor digitorum longus

48. Question Which muscle is the prime mover when flexing the forearm?
Biceps brachii
Triceps brachii
Brachialis
Brachioradialis