1. Chapter 6 The Muscular System

2. Functions of Muscular System
Produce movement and manipulate the environment
Maintain posture
Stabilize joints
Generate heat
Slide 6.8

3. The Muscular System
Muscles are responsible for all types of body movement
Three basic muscle types are found in the body
Skeletal muscle
Cardiac muscle
Smooth muscle

4. Similarities of all Types of Muscles
Muscle cells are elongated (muscle cell = muscle fiber)
Contraction of muscles is due to the movement of microfilaments
All muscles share some terminology
Prefix myo refers to muscle
Prefix mys refers to muscle
Prefix sarco refers to flesh
Slide 6.2

5. Differences in the types of muscles
Slide 6.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

6. Differences in the types of muscles
Slide 6.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

7. Skeletal Muscle Characteristics
Most are attached by tendons to bones
Cells are multinucleate
Striated – have visible banding
Voluntary – subject to conscious control
Cells are surrounded and bundled by connective tissue
Skeletal, striated, voluntary

8. Skeletal Muscle Attachments
Tendon – cord-like structure
Aponeuroses – sheet-like structure
Sites of muscle attachment
Bones
Cartilages
Connective tissue coverings
Tendon
Aponeuroses

9. Cardiac Muscle Characteristics
Has striations
Usually has a single nucleus
Joined to another muscle cell at an intercalated disc
Involuntary; the heart has a pacemaker
Found only in the heart
Figure 6.2b
Cardiac, striated, involuntary

10. Smooth Muscle Characteristics
Has no striations
Spindle-shaped cells
Single nucleus
Involuntary – no conscious control
Found mainly in the walls of hollow organs
Arranged in layers
2 layers
Figure 6.2a
Smooth, no striations, involuntary

11. Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate
Nuclei are just beneath the sarcolemma
Sarcolemma (organelle) – specialized plasma membrane
Figure 6.3a

12. Microscopic Anatomy of Skeletal Muscle
Sarcoplasmic reticulum (organelle)
Specialized smooth ER that surrounds all myofibrils
Stores Ca ions to be able to release them on demand
Figure 6.3a

13. Microscopic Anatomy of Skeletal Muscle
Myofibril (organelle)
Bundles of myofilaments
Myofibrils are aligned to give distrinct bands
I band = light band
A band = dark band
Figure 6.3b

14. Microscopic Anatomy of Skeletal Muscle
Sarcomere
Chains of contractile units in myofibrils
Two types of myofilaments
Thick = myosin
Thin = actin
Figure 6.3b

15. Microscopic Anatomy of Skeletal Muscle
Thick filaments = myosin filaments
Composed of the protein myosin
Figure 6.3c

16. Microscopic Anatomy of Skeletal Muscle
Thin filaments = actin filaments
Anchored to the Z disc
Composed of the protein actin
Figure 6.3c

17. Microscopic Anatomy of Skeletal Muscle
Myosin filaments have heads (extensions, or cross bridges)
Myosin heads link the thick and thin during contraction
Myosin and actin overlap somewhat
Figure 6.3d

18. Microscopic Anatomy of Skeletal Muscle
Thick (myosin) and thin (actin) filaments produce the striations in skeletal muscle
Figure 6.3d

19. Organizational levels of Skeletal Muscle
Organ – the muscle (biceps)
Fiber – a muscle cell
Myofibril – organelle composed of sarcomeres and myofilaments
Sarcomeres – unit of myofibril
Myofilament – actin and myosin

20. Skeletal Muscle Cell Nucleus – control center
Sarcolemma – plasma membrane
Sarcoplasm – cytoplasm

21. Skeletal Muscle Cell
Sarcoplasmic reticulum – storage of calcium ions to be released when stimulated by an impulse
T-tubules – surround the myofibrils and assist in delivering ions

22. Skeletal Muscle Cell Mitochondria (lots) – provide energy and ATP
Myofibril – composed of thick and thin filaments and many sarcomeres

23. From nerve stimulus to sarcomere contraction
Muscle Contraction
From nerve stimulus to sarcomere contraction

24. Nerve Stimulus to Muscles
1. Skeletal muscles must be stimulated by a nerve to contract
Motor unit is composed of:
One neuron
All muscle cells stimulated by that neuron
One nerve cell branches into axonal terminals
Figure 6.4a

25. Nerve Stimulus to Muscles
Axonal terminals form junctions with sarcoplasm called neuromuscular junctions
Nerve and muscle do not make contact there is a gap
Synaptic cleft – gap between nerve and muscle
Gap is filled with interstitial fluid
Figure 6.5b

26. Nerve Stimulus to Muscles
2. Action potentials are sent down the neuron in response to a stimuli
Because the two cells do not touch, the action potential cannot ‘jump the gap’
Figure 6.5b

27. Nerve Stimulus to Muscles
3. The neuron communicates indirectly with the muscle cell by releasing a neurotransmitter
The neurotransmitter for skeletal muscle is acetylcholine (ACh) and it is stored in the axonal terminal
4. Sarcolemma has receptors for Ach and causes an action potential in muscle cell

28. Transmission of Nerve Impulse Wrap-up
How does the neurotransmitter produced by the motor neuron cause the skeletal muscle to contract?
What is the neurotransmitter in muscle cells?
What is the synaptic cleft?
What makes up a motor unit?
List the steps of transmission of a nerve impulse.

29. The Sliding Filament Theory of Muscle Contraction
Put your right palm on the back of your left hand.
Now slide your right palm toward your left elbow
What happened to the distance between your elbows?
This is how muscle contraction works!
Figure 6.7
Slide 6.17a

30. The Sliding Filament Theory of Muscle Contraction
Activation by nerve causes calcium to be released by the sarcoplasm reticulum
Calcium binds to actin and exposes myosin binding sites where the myosin heads attach and form a crossbridge
ATP is used as the energy source
Figure 6.7
Slide 6.17a

31. The Sliding Filament Theory of Muscle Contraction
The thin filament slides past the thick filament towards the center as each myosin head attaches and detaches
Distance between Z discs shortens as actin moves toward the center
The result is that the entire muscle is shortened (contracted)
Figure 6.7
Slide 6.17b

32. The Sliding Filament Theory of Muscle Contraction
Length of the A band (myosin and actin) stays the same
Length of the H zone (only thick filaments) shortens
Length of the I band (thin filaments) shortens
Figure 6.7
Slide 6.17b

33. The Sliding Filament Theory
Go to figure 6.8 in your book and summarize the steps for the sliding filament theory and explain how a muscle contracts

34. Transmission of Nerve Impulse to Muscle Contraction
1. Nerve impulse sent and received by axonal terminal
2. Neurotransmitter (acetylcholine) is released upon arrival of nerve impulse
3. Diffuses across synaptic cleft and attaches to receptors on the sarcolemma
4. Triggers an action potential of the muscle cell
5. The action potential causes the SR to release calcium ions
6. The calcium ions bind with the actin filaments to open the binding site for myosin
7. Myosin heads bind to them with the help of ATP
8. The cell contracts