1. The Muscular System

2. The Muscular System (The machines of the body)
Muscles are responsible for all types of body movement
Three basic muscle types are found in the body (Skeletal, Cardiac, and Smooth)
Functions of Muscles
Produce movement
Maintain posture
Stabilize joints
Generate heat

3. Characteristics of Muscles
Muscle cells are elongated (muscle cell = muscle fiber)
Contraction of muscles is due to the movement of myofilaments
All muscles share some terminology
Prefix myo refers to muscle
Prefix mys refers to muscle
Prefix sarco refers to flesh
Ex. Cytoplasm in cells = Sarcoplasm in muscle cells

4. Characteristics of Smooth Muscle
Found in walls of hollow visceral organs
No striations
Involuntary, controlled by nervous and endocrine systems
Very slow, contractions, often rhythmic (propel substances through tract)
Characteristics of Cardiac Muscle
Heart only
Branching chains of striated cells
Involuntary, nervous and endocrine controlled
Slow, rhythmic contractions

5. Skeletal Muscle Characteristics
Most are attached by tendons to bones
Cells are multinucleate (largest is 1 foot long)
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by connective tissue

6. Connective Tissue Wrappings of Skeletal Muscle
Endomysium – ____________________
Perimysium – ________________________________________
Epimysium – ________________________________________
Fascia – ________________________________________
Figure 6.1

7. Skeletal Muscle Attachments
Epimysium blends into a connective tissue attachment
Tendon – cord-like structure
Aponeuroses – sheet-like structure
Sites of muscle attachment
Bones
Cartilages
Connective tissue coverings

8. Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate
Nuclei are just beneath the sarcolemma
Sarcolemma – plasma membrane of a muscle cell
Sarcoplasmic reticulum – (Endoplasmic reticulum) stores calcium that is needed for muscle contraction
Figure 6.3a

9. Microscopic Anatomy of Skeletal Muscle
Myofibril - organelle that fills muscle cells, made of bundles of myofilaments
I band = light band
A band = dark band
These give it a striped appearance.
Figure 6.3b

10. Microscopic Anatomy of Skeletal Muscle
Sarcomere – from z disc to z disc
Contractile unit of a muscle fiber, when lined up form a myofibril
Bundles of myofibrils = muscle cell
Figure 6.3b

11. Microscopic Anatomy of Skeletal Muscle
Organization of the sarcomere
Thick filaments = myosin filaments
Thin filaments = actin filaments
Figure 6.3c

12. Microscopic Anatomy of Skeletal Muscle
Myosin filaments have heads (extensions, or cross bridges)
Myosin and actin overlap somewhat
At rest, there is a bare zone that lacks actin filaments
Figure 6.3d

13. Properties of Skeletal Muscle Activity
Irritability – ability to receive and respond to a stimulus
Contractility – ability to shorten when an adequate stimulus is received
Graded Response- different degrees of skeletal muscle shortening
Frequency of stimulation and number of cells stimulated
Twitch – incomplete contraction, breaks in the impulse
Complete Tetanus is sustained and smooth contraction

14. Nerve Stimulus to Muscles
Skeletal muscles must be stimulated by a nerve to contract
(show human machine video)
Motor unit
One neuron
Muscle cells stimulated by that neuron
Figure 6.4a

15. Nerve Stimulus to Muscles
Neuromuscular junctions – where muscles and nerves interact
Synaptic cleft – gap between nerve and muscle, they DO NOT contact each other
Ach - Acetylcholine
Figure 6.5b

16. Transmission of Nerve Impulse to Muscle
Neurotransmitter – chemical released by nerve upon arrival of nerve impulse
-The neurotransmitter for skeletal muscle is acetylcholine (Ach)
Neurotransmitter attaches to receptors on the sarcolemma
Sarcolemma becomes permeable to sodium (Na+)
K+ (Potassium) leaves and inside of cell gains a + charge
Sodium rushing into the cell generates an action potential
Once started, muscle contraction cannot be stopped
Ach is broken down so a single nerve cell produces only one contraction
Cell returns to rest by diffusion of K+ in and Na+ out

18. The Sliding Filament Theory of Muscle Contraction
Activation (Ach crosses the gap) by nerve causes myosin heads to attach to binding sites on the actin.
Myosin heads then bind to the next site on the actin filament
This continued action causes the actin filaments to “slide” closer together, towards the center of the sarcomere.
This causes the muscle to shorten (contract).
The contraction ends when the Ach is broken down.
Figure 6.7

19. Muscle Response to Strong Stimuli
Muscle force depends upon the number of fibers stimulated
More fibers contracting results in greater muscle tension
Muscles can continue to contract unless they run out of energy

20. Energy for Muscle Contraction
Initially, muscles used stored ATP for energy
Bonds of ATP are broken to release energy
Only 4-6 seconds worth of ATP is stored by muscles
After this initial time, other pathways must be utilized to produce ATP

21. Energy for Muscle Contraction

22. Muscle Fatigue and Oxygen Debt
When a muscle is fatigued, it is unable to contract
The common reason for muscle fatigue is oxygen debt
Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

23. Muscles and Body Movements
Movement is attained due to a muscle moving an attached bone
Muscles are attached to at least two points
Origin – attaches to the less movable bone
Insertion- attachment to the more movable bone
Results of increased muscle use: increase in strength and smoothness
Figure 6.12

24. Head and Neck Muscles
Figure 6.15

25. Deep Trunk and Arm Muscles
Trunk Muscles
Deep Trunk and Arm Muscles

26. Muscles of the Pelvis, Hip, and Thigh
Muscles of the Lower Leg

27. Superficial Muscles: Anterior
Figure 6.21

28. Superficial Muscles: Posterior
Figure 6.22