1. Muscle Mechanics

2. Muscles are named by………….
Location
Shape
Action
Number of heads or divisions
Attachments
Fiber direction
Size of the muscle
Eg Tibialis anterior Eg Rhomboids major/minor Rectus abdominis Eg Ex. Carpi ulnaris –extension of the wrist Eg Biceps brachii, Triceps brachii Eg Sternocleidomastoid muscle Eg Internal oblique Eg Pectoralis major – large Pectoralis minor - small

3. Arrangement of skeletal muscle fibers

4. Muscle Fiber Arrangement
Parallel – longer, ROM
Strap Eg Sartorius, Rectus abdominis, Sternocleidomastoid
Fusiform Eg Biceps, Brachialis
Rhomboidal Eg Rhomboids, Gluteus maximus
Triangular Eg Pectoralis major

5. Oblique – shorter, greater strength
Unipennate Semi membrinosus
Bipennate Rectus femoris
Multipennate Deltoid

6. Muscle Contraction Nerve impulse reaches myoneural junction
Acetylcholine is released from motor neuron
Ach binds with receptors in the muscle membrane to allow sodium to enter
Sodium influx will generate an action potential in the sarcolemma

9. Muscle Contraction Continued
Action potential travels down T tubule
Sarcoplamic reticulum releases calcium
Calcium binds with troponin to move the troponin, tropomyosin complex
Binding sites in the actin filament are exposed

10. Muscle Contraction Continued
Myosin head attach to binding sites and create a power stroke
ATP detaches myosin heads and energizes them for another contaction
When action potentials cease the muscle stop contracting

11. Muscular Attachments Origin Insertion On more stable bone
Closer to the trunk
Insertion
On more mobile bone
Closer to distal end of bone
Normal muscle action: Insertion towards origin
Eg During elbow flexion

12. Reversal of muscle action
Origin moves toward insertion
More movable segment is stabilized
Eg; Elbow flexion in a person hanging on a bar, humerus moves towards the elbow

13. Voluntary muscle contraction
Main 5 types,
Concentric contraction force generated is sufficient to overcome the resistance
muscle shortens as it contracts.
Eccentric contraction force generated is insufficient to overcome the external load on the muscle
muscle fibers lengthen as they contract.
Use in the means of decelerating a body part or object, or lowering a load gently rather than letting it drop.

14. Isometric contraction muscle remains the same length.
force precisely matches the load, and no movement results.

15. Isotonic contractions the tension in the muscle remains constant despite a change in muscle length.
This can occur only when a muscle's maximal force of contraction exceeds the total load on the muscle.

16. In isovelocity contraction (sometimes called "isokinetic"), the muscle contraction velocity remains constant, while force is allowed to vary.
True isovelocity contractions are rare in the body

17. Motor Unit All the muscle cells controlled by one nerve cell
A motor unit is all the muscle cells controlled by one nerve cell. This diagram represents two motor units. Motor unit one illustrates two muscle cells controlled by one nerve cell. When the nerve sends a message it will cause both muscle cells to contract. Motor unit two has three muscle cells innervated by one nerve cell.

18. Motor Unit Ratios Back muscles Finger muscles Eye muscles 1:100 1:10
Motor units come indifferent sizes. *The ratio is about one nerve cell to 100 muscle cells in the back. *Finger muscles have a much smaller ratio of 1:10. *Eye muscles have a 1:1 ratio because of the precise control needed in vision.

19. Muscle spindle One type of proprioceptors
Sensory receptors within the belly of a muscle
Primarily detect changes in the length of this muscle
They convey length information to the central nervous system via sensory neurons
Responses of muscle spindles to changes in length also play an important role in regulating the contraction of muscles

20. Anatomy
Found within the belly of muscles embedded in extrafusal muscle fibers
Muscle spindles are composed of 3-12intrafusal fibers
Encapsulated by connective tissue, and are aligned parallel to extrafusal muscle fibers

22. Muscle spindle has both sensory and motor components.
Primary and secondary sensory nerve fibers spiral around and terminate on the central portions of the intrafusal muscle fibers
Gamma and beta motoneurons are called fusimotor neurons, because they activate the intrafusal muscle fibers. Gamma motoneurons only innervate intrafusal muscle fibers
Alpha motoneurons innervate both extrafusal and intrafusal muscle fibers and so are referred to as skeletofusimotor neurons

23. Stretch reflex
When a muscle is stretched, primary sensory fibers of the muscle spindle respond
transmit this activity to the spinal cord in the form of changes in the rate of action potentials
many alpha motor neurons of the receptor-bearing muscle
The reflexly-evoked activity in the alpha motoneurons is then transmitted via their efferent axons to the extrafusal fibers of the muscle, which generate force and thereby resist the stretch.

24. Golgi tendon organ
Another type of proprioceptors which is located at the insertion of tendon into the skeletal muscle.
It provides the sensory component of the Golgi tendon reflex
Provide information about the changes in muscle tension
made up of strands of collagen that are connected at one end to the muscle fibers and at the other merge into the tendon proper.

25. innervated by a single afferent type 1b sensory fiber that branches and terminates as spiral endings around the collagen strands

26. Function
When the muscle generates force, the sensory terminals are compressed.
This deforms the terminals of the Ib afferent axon
Opening stretch-sensitive cation channels depolarizing and fires nerve impulses that are propagated to the spinal cord
The Ib sensory feed back generates spinal reflex and supraspinal responses which control muscle contraction.
Main spinal reflexes associated with Ib afferent activity is the autogenic inhibition reflex which helps regulate the force of muscle contractions

28. Skeletal muscle fiber types
Type I
Type II A
Type II B
Type I slow oxidative or red fibers, generate most of their ATP from glucose
have a high oxidative capacity

29. Type II B fast glycolytic or white fibers
Have the ability to take up glucose and lack myoglobin
Low oxidative capacity, and a high glycolytic capacity
Type II A
Very high oxidative capacity and a high glycolytic capacity
Not very much found in humans

30. Energy sources for muscle contractions
Aerobic
Anaerobic
Oxygen is used
Break down of fat, protein & carbohydrates
Can provide energy for a long period
Oxygen is not used
Break down of phosphocreatine
Can provide energy for muscle contraction for a period of sec

31. Muscle Fatique Lack of oxygen causes ATP deficit
Lactic acid builds up from anaerobic respiration
Muscle fatigue is often due to a lack of oxygen that causes ATP deficit. Lactic acid builds up from anaerobic respiration in the absence of oxygen. Lactic acid fatigues the muscle.

32. Muscle Atrophy Weakening and shrinking of a muscle May be caused
Immobilization
Loss of neural stimulation
Muscle atrophy is a weakening and shrinking of a muscle. It can be caused by immobilization or loss of neural stimulation.

33. Muscle Hypertrophy Enlargement of a muscle More capillaries
More mitochondria
Caused by
Strenuous exercise
Steroid hormones
Hypertrophy is the enlargement of a muscle. Hypertrophied muscles have more capillaries and more mitochondria to help them generate more energy. Strenuous exercise and steroid hormones can induce muscle hypertrophy. Since men produce more steroid hormones than women, they usually have more hypertrophied muscles.

34. Properties of muscle Excitability/Irritability Contractility
Muscles has following properties
Excitability/Irritability
Contractility
Extensibility
Elasticity

35. Excitability/Irritability:
ability to receive and respond to stimuli inside or outside the body
Contractility:
ability to shorten to ½ its resting length when receive adequate stimulus

36. Extensibility: Elasticity:
Ability to be stretched 2 times as far as it is able to be shortened
Elasticity:
Ability to resume resting length after stretch or shortening

37. Length tension diagram of a muscle

38. Strength of muscles
Depends upon the number of fibers in the physiological cross-section
Physiological cross-section - which passes through practically all of the fibers
Anatomical cross section –
unipinnate and bipinnate muscles the physiological cross-section may be nearly at right angles to the anatomical cross-section