1. MUSCLES
and
MOVEMENT

2. General Function Movement or locomotion
of Muscle Tissue
Movement or locomotion
Heat production – maintain the body’s homeostasis of temperature
Posture – using partial contraction of the “anati-gravity” muscles

3. Contractility Specific Function of Skeletal Muscle Tissue
Excitability or irritability
The ability to be stimulated or simply stated “responds to stimulus” from nerve signals
Contractility
The ability to contract or shorten
including contraction without movement
isometric contraction is muscle tissue contracting, tension increasing but the there is not enough strength to “move the fixed object”

4. Extensibility
The ability to extend or stretch allowing muscles to return to their resting length after a contraction
They may also extend while still exerting force as when lowering a heavy object

5. Muscle cells are different than other body cells
Muscle cells have a long, thin, thread-like shape
During tissue development cells fuse together to form a multi-nuclei cell that becomes a muscle cell
Adult muscle cells can even have some of the stem cells hanging out to produce more muscle cells after an injury.

6. Muscle cells have similar parts but different names
Sacrolemma – plasma membrane
Sarcoplasm – cytoplasm contains many mitochondria and more than one nuclei
Sarcoplasmic reticulum (SR) – a type of endoplasmic reticulum however the SR stores and pumps calcium ions

7. T tubules – transverse tubules that allow electrical impulses traveling along the sarcolemma to move deep into the cell
The SR butts up against both sides of the T tubule in a muscle fiber (called a triad)
Impulses travel along the T tubule to stimulate the membranes of the SR to pump Ca++ into the channels of the SR causing the contraction to happen

8. Myofribrils – not found in other cells
cytoskeletal filaments that extend lengthwise along the muscle fiber and fill the sarcoplasm.
Myofribrils are made up of finer fibers called Myofilaments of which there are two types
Thick filaments
Thin filaments

9. Sarcomere – is a contractile unit located between the Z lines.
Many sarcomeres line up end to end to form a myofibril
Look at page 399 box use overhead for picture
The microscopic bands give the muscle the “striated” name

10. Myofilaments Myofilaments are made of 4 types of proteins
myosin make up the thick filaments
actin, tropomyosin and troponin make up the thin filaments
The myosin heads of the thick filaments are chemically attracted to the actin molecules on the thin filaments. They are called “cross bridges” because they bridge the gap between the think and thin filaments

11. Muscles are at rest unless they are stimulated by a motor neuron
The motor neuron endplate forms a junction called a neuromuscular junction.
The narrow gap between the nerve and the fiber is called a synapse or synaptic cleft
The nerve releases a neurotransmitter acetylcholine into the gap to begin the electrical impulses in the sarcolemma
-excitation-

12. The impulse is conducted over the muscles fiber’s sarcolemma
When it reaches the t-tubule it spread deeper into the fiber where it release Ca++ into the SR
The calcium ions combine with troponin molecules in the thin filament causing it to shift to expose the actin molecule

13. This is called the sliding-filament model
4. The myosin heads are chemically attracted to the actin so they “grab” it and pull, then grab the next actin and pull past it and so on until an 80% contraction is reached
This is called the sliding-filament model

14. Muscle fibers contract to about 80% or their starting length
If a muscle is pulling against an immovable object it is still in a state of active contraction and uses energy to maintain the contraction.

15. Types of Muscle Fibers

16. Contains type I myosin in the thick filaments
Slow twitch
Contains “red fibers”
Red fibers have a high concentration of myoglobin, a redish pigment used by muscle cells to store oxygen in the muscle cell itself – gives the muscle its red color
Contains type I myosin in the thick filaments
that reacts or contracts at a slow rate and is able to produce ATP at a rate that keeps pace with the muscle’s energy needs, this type of muscle is found in anti-gravity muscles--because they can contract for a long time and not fatigue—and in the muscles used for endurance activies

17. Fast Twitch White fibers They contain very little myoglobin
Contain type II myosin that contracts more rapidly than slow fibers and has t-tubules that are more efficient at delivering Ca++ to the SR
Rapid contraction depletes ATP rapidly even though they tend to contain a higher concentration of glycogen
they have fewer mitochondria and rely on anaerobic respiration to regenerate more ATP
Fast twitch muscles have great force but cannot sustain activity for very long because of lactic acid production from anaerobic activity
Fingers, eyes, muscles used by sprinters

18. muscles of the leg would be a good example
Intermediate fibers
Have characteristics in between both fast and slow twitch muscle fibers
They are more fatigue resistant than fast fibers yet can generate more force more quickly than slow fibers
Example would be:
Muscles that are anti-gravity yet are needed for other activities such as jumping
muscles of the leg would be a good example

19. Page 406 in the text

20. Motor Unit
Consists of the nerve that stimulates the muscles fibers and the muscle fibers it is stimulating
Some motor units are only a few muscle fibers
Some motor units have thousands of muscle fibers
Fine motor movements have smaller motor units that only stimulate a few fibers at time , gross motor movements have large motor units that stimulate many fibers at once

21. Myography Twitch contraction Threshold stimulus Terms you need to know
Graphing muscle contraction
Terms you need to know
Threshold stimulus
The amount of stimulus applied to make a muscle contract
Twitch contraction
A quick jerk of the muscle

22. Use the information that you learned about the physiology to explain what is happening on the myograph

23. Twitch contractions rarely happen the body
We can’t make our muscles twitch individually
Our nervous system “smooths out” our muscle movements
Smooth movements are more useful – sustained movements
Prevents injury to muscle groups

24. The staircase effect is why we warm up before exercise.
Calcium diffused through the sarcoplasm of muscles has not had time to relax and pump all of it back into their SR so the muscle can contract with more force.
The relaxation phase become shorter and finally disappears – the muscle stays in partial contraction called a contracture
After a while the muscle becomes fatigued and won’t respond to even the strongest stimuli

25. Ever had your muscles shake after over working them?
That is what you are feeeling!
It is rarely the entire muscle but certain motor units that are fatigued causing the shaking

26. Tetanus
This graphic represents what a sustained contraction looks like.
In a normal body tetanus results from two factors working together at the same time
Rapid –fire of nerve fibers that permit this wave summation to happen in each fiber
Coordinated contractions of different motor units in a muscle organ in an overlapping sequence or “relay team” effect
This is called muscle Tone

27. Tonic contraction or “tone”
Muscles organs with less than normal “muscle tone” are called flacid
Muscles organs with more than normal muscle tone are called spastic
Stretch sensors in muscles and tendons detect the degree of stretch and adjust the strength of the tonic contraction. This mechanism is a negative feedback mechanism located in the spinal cord.

28. Graded Strength Principle
Muscle organs can produce varying degrees of strength
Influenced by the individual “type” of fibers
Fast twitch, slow twitch or intermediate
Number of motor units contracting
more units are recruited when more strength is needed

29. The maximum strength of a muscle is directly related to the initial length of it fibers
If a muscle contractions begins from a shortened length its sarcomers are already compressed
If the muscle begins a contraction from an overstretched length it cannot develop much tension because the thick and thin myofilaments are too far apart to effectively pull and shorten the sarcomeres.

30. Now feel the stretch reflex, page 412
Try flexing you biceps: extended, 90 degrees and completely flexed Page 411 bottom of the 2nd column
Now feel the stretch reflex, page 412

32. Concentric Contraction Movement result in shortening of muscle
Effects of Exercise on Skeletal Muscles
Page 412
Concentric Contraction
Movement result in shortening of muscle
Eccentric Contraction
Movement results in lengthening of muscle

33. Isometric contraction
Muscle stays the same length as tension increases
“Tightening to resist a force”