1. The Muscular System

2. Functions of Muscle Tissue
Movement Facilitation
Thermogenesis
Postural Support
Regulation of Organ Volume
Protects Internal Organs
Pumps Blood (HEART)

3. Characteristics of Muscle Tissue
Contractility – able to shorten.
Extensibility (Flexibility) – able to lengthen.
Elasticity – able to return to original shape.
Excitability (Irritability) – able to respond to a stimulus.

4. Skeletal Muscle Attached to bones
Striated appearance under a microscope
Voluntary control (conscious control)
Multinucleated
Myofilaments - contractile elements of each muscle fiber

5. Cardiac Muscle Forms the bulk of heart wall (Myocardium) Striated
Involuntary (typically)
Fibers are quadrangular and branching
Cardiac fibers typically have a centrally located nucleus
Sarcolemmas connected by intercalated discs
Strengthens cardiac muscle tissue
Propagates an action potential from cell to cell through specialized structures on the intercalated discs called gap junctions

6. Smooth (Visceral) Muscle
Located in walls of hollow internal surfaces such as:
blood vessels - stomach
urinary bladder - intestines
Non-striated in appearance
Involuntary (typically)
Can be stretched to great lengths
Allows for tremendous size variability

7. Smooth (Visceral) Muscle

8. Smooth (Visceral) Muscle

9. Skeletal Muscle Tissue Structures

10. Skeletal Muscle Structures
Epimysium – Tissue covering the outer layer of the whole muscle
Perimysium – Tissue that surrounds the outside of bundles (fascicle) of muscle fibers
Fascicles – bundles of muscle fibers
Endomysium – Tissue that surrounds the muscle fibers
Sarcolemma – muscle cell membrane
Sarco = flesh

11. Muscle Tissue Structures
T-tubule – transverse tubes which run throught the muscle fiber. Electrical impulses are transmitted through these.
Sarcoplasm – cytoplasm of the muscle
Myofibrils – contractile portion of the muscle cell composed of myofilaments (actin and myosin)
Sarcoplasmic reticulum – Stores and releases calcium ions

12. Muscle Tissue Structures

13. Sarcomere

14. Muscle Tissue Histology
Myofilaments - structural components of myofibrils
Myosin - thick myofilaments
Actin - thin myofilaments

15. Regions of a Sarcomere

16. Myosin Thick myofilaments Occupy the A Band of the sarcomere
Overlap free ends of the actin myofilament
Shaped like a golf club
Long, thick protein molecule (tail)
Globular head at the ends

17. Actin Thin myofilaments Anchored to the Z Line
Two stranded protein molecule intertwined around each other
Associated with two regulatory proteins
Tropomyosin - long stranded protein molecule that follows the contour of actin
Troponin - protein located at regular interval along the tropomyosin that covers the active sites on actin. Has three subunits

18. Myofilaments

19. Muscle Action Potential
An electrical impulse that originates at the motor end plate, travels along the length of the sarcolemma, down a transverse tubule, and causes the muscle to contract.

20. Sliding Filament Theory of Muscular Contraction
Due to an action potential, the actin and myosin myofilaments slide past one another shortening the sarcomere
No change in length of myofilaments
H Zone narrows or disappears
I Band narrows or may disappear
A Band remains the same length

21. Muscle Nerve Interaction
Neuron - nerve cell
Axon - long, threadlike process that transmits impulse away from cell body (may be up to 1 meter in length)
Motor Unit - motor neuron and all the muscle fibers it innervates
Neuromuscular Junction - junction between axon terminal and muscle fiber

22. Neuromuscular Junction

23. Neuromuscular Junction

24. Neuromuscular Junction

25. Muscle Nerve Interaction
Motor End Plate - location on the muscle fiber at the end of an axon terminal
Synaptic End Bulb - distal end of axon terminal
Synaptic Vesicles - membrane enclosed sacs within the synaptic end bulbs that store neurotransmitters

26. Muscle Nerve Interaction
Synaptic Cleft - space between axon terminal and motor end plate
Subneural Clefts - folds in sarcolemma along the synaptic gutter
Acetylcholine (Ach) - neurotransmitter released from synaptic vesicles that initiates an action potential in a muscle

27. Muscle Response to Nervous Stimuli
All or None Principle
Once a threshold stimulus is applied to a motor unit the muscle fibers innervated by that motor unit will contract to their fullest potential
Threshold Stimulus - the weakest stimulus from a neuron that will initiate a muscular contraction

28. Events Leading to Muscular Contraction
An action potential travels down the motor neuron. When it arrives at the synaptic knob, the membrane of the nerve at the synaptic cleft is depolarized, thereby increasing the Ca++ permeability of the membrane.
Ca++ diffuses from outside of the synaptic knob to inside the synaptic knob.

29. The influx of Ca++ into the nerve causes the release of Ach.
Ach is ejected into the synaptic cleft, diffuses across the cleft, and depolarizes the muscle membrane.
This increases the permeability of the muscle membrane to Na+.
Na+ rushes into the muscle cell, depolarizing the membrane as it travels away from the motor end plate thus initiating an action potential.

30. Ach is quickly broken down in the cleft by Ach-ase so that each action potential arriving from the nerve initiates only one action potential within the muscle.
The action potential spreads across the muscle membrane and down the T-tubules deep into the muscle cell.
The action potential of the T-tubules depolarizes the membrane of the nearby sarcoplasmic reticulum which results in the release of Ca++ into the sarcoplasm.

31. Ca++ is very quickly removed out of the sarcoplasm by the sarcoplasmic reticulum so the effects of one action potential are very short lived and produce a very small contraction.
Many action potentials are necessary to produce enough force to produce a strong or prolonged muscle contraction.
The Ca++ released from the sarcoplasmic reticulum binds with troponin and cause troponin to change shape.

32. Muscle Contraction Events

33. When troponin changes shape, it physically moves the other regulatory protein, tropomyosin, out of the way exposing the active sites on the actin myofilament.
Since the heads or cross-bridges of myosin have a very strong affinity for the active sites on actin, they make contact immediately after the active sites have been exposed.
The acto-myosin complex has ATPase activity and ATP is split into ADP + P and energy is released.

34. The energy released by the splitting of ATP is used to produce movement of the cross-bridges, sliding the actin and myosin filaments past one another which causes the sarcomere to shorten and the muscle to contract and produce force.
The myosin cross-bridge has a low affinity for ADP but a very high affinity for ATP.
It discards the ADP and becomes recharged with a new ATP.

35. Muscle Contraction Events

36. The myosin then releases its hold on the active sites on actin, swivels back to its original position, and is ready to respond to another action potential.
When another action potential comes along the entire process is repeated.
It takes many action potentials to produce enough shortening of the sarcomeres to generate enough force to produce movement of a body segment.

37. Muscle Contraction Events

38. Muscle Origin and Insertion
Body segment with most mass
Usually more proximally located
Usually larger surface area of attachment
Insertion
Body segment with least mass
Usually more distally located
Usually smaller surface area of attachment
Gaster (Belly)
Fleshy portion of the muscle between the tendons of the origin and insertion

39. Roles of Skeletal Muscles
Agonist (Prime Mover)
Muscle responsible for the majority of force
Antagonist
Performs the opposite movement
Synergist
Muscle that assists the agonist
provides additional force
redirects the force of the agonist
Fixator (Stabilizer)
Stabilizes a body segment so the prime mover can act more effectively

40. Selected Skeletal Muscles (Head/Neck)
Masseter
Sternocleidomastiod
Trapezius

41. Selected Skeletal Muscles (Upper Extremity)
Deltoid
Rotator Cuff
Supraspinatus
Infraspinatus
Teres minor
Subscapularis
Biceps brachii
Triceps brachii
Brachialis
Wrist Flexors
Wrist Extensors
Pronators
Supinator

42. Selected Skeletal Muscles (Thorax)
Pectoralis Major
Latissumus Dorsi
Rectus Abdominus
External Oblique
Diaphragm

43. Selected Skeletal Muscles (Lower Extremity)
Gluteus maximus
Gluteus medius
Quadriceps
Rectus femoris
Vastus lateralis
Vastus medialis
Vastus intermedius
Hamstrings
Semimembranosus
Semitendinosus
Biceps Femoris
Gracilis
Sartorius
Gastrocnemius
Soleus
Tibialis Anterior

44. Selected Skeletal Muscles (Lower Extremity)

45. Anterior Skeletal Muscles

46. Posterior Skeletal Muscles

47. Muscle Actions Biceps brachii – Flexes forearm
Triceps brachii – Extends forearm
Brachialis – Flexes forearm
Flexors – Flexes wrist and fingers
Extensors – Extends wrist and fingers
Pronator – Pronates forearm
Supinator – Supinates forearm

48. Muscle Actions Deltoid – Abducts arm Diaphragm – Aids in breathing
Rectus abdominis – Flexes vertebral column.
Sternocleidomastoid – Flexes and rotates head
Trapezius – Elevates and retracts shoulders
Pectoralis major – pulls arm across chest
Latissimus dorsi – pulls arm across back
External oblique – rotates trunk

49. Muscle Actions Gastrocnemius – Extends foot (tiptoe)
Tibialis anterior – dorsiflexes and inverts foot
Soleus – plantar flexes foot
Quadriceps (Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius) – Extends lower leg
Rotator cuff (Supraspinatus, Infraspinatus, Teres minor, Subscapularis) – stabilizes shoulder

50. Muscle Actions
Hamstrings (Semimembranosus, semitendinosus, biceps femoris) – Flexes lower leg
Gluteus maximus – extends thigh
Gluteus medius – abducts thigh
Sartorius – rotates thigh (sit cross legged)
Gracilis – adducts thigh
Masseter – elevates the jaw (chewing)

51. Muscle Diseases and Disorders

52. Myalgia (Fibromyalgia)
Painful disorders of muscles, tendons, and surrounding soft tissue

53. Muscular Dystrophies
Muscle destroying diseases characterized by the degeneration of individual muscle fibers
Leads to progressive atrophy of skeletal muscles
Due to a genetic defect

54. Medial Tibial Stress Syndrome (Shin Splints)
Pain in the front of the lower leg
Tendonitis of the tibialis posterior muscle
Inflammation of the periosteum
Exaggerated enlargement of muscles within the epimysium
Treatment:
RICE
strengthen tibialis anterior muscle
stretch calf muscles
support the arch if needed

55. Sprains
the forcible wrenching or twisting of a joint with partial or complete rupture or injury to joint attachments without dislocation
1st Degree Sprain = stretching of ligaments
2nd Degree Sprain = partial tearing of ligaments
3rd Degree Sprain = complete tear of ligaments

56. Strains pulling or overstretching a muscle soft tissue (Muscle) injury
same classification of injury as previously discussed for sprains (1st, 2nd, 3rd degree)