Muscles

1. Muscles No Striations 3 Types of Muscle Skeletal Muscle  Reacts to nervous system stimulation Cardiac Muscle  Can respond to nervous system stimulation or independent Smooth Muscle  Responds to a variety of mechanisms Striations  Intercalated Disk 

2. Skeletal Muscles & Bones More than 600 skeletal muscles in the body Usually arranged in pairs Some work together to promote the same movement (synergistically) Others work in opposition (anatagonistically) or reverse the movement of each other

3. Example of Antagonism Biceps and Triceps When biceps contract, triceps relax When biceps relax, triceps contract

4. Muscle Contraction & Bones Origin  Bone of attachment that stays motionless during movement Insertion  Bone of attachment that moves during contraction Example Biceps Brachii (contracted) Insertion is the radius Origin is the scapula

5. Muscle Fiber Structure & Function Sarcomere  functional unit of a muscle fiber Each end of the sarcomere is defined by a Z-line Thick Filaments are called myosin Thin filaments are called Actin

6. Muscle Contraction Skeletal muscles always pull on bones, never push Nerve impulse stimulates the muscle fiber to contract Thick myosin filaments grab and pull the thin actin filaments closer together, shortening the muscle The point where myosin “grabs” actin filament is called a cross bridge ATP is split by an enzyme to form ADP This reaction creates a “high energy” myosin that binds (and pulls) actin A single contraction consists of multiple pulls of myosin After death, no ATP, myosin stays “stuck” to actin, rigor mortis sets in

7. Muscle Contraction

8. Muscle Contraction Animation

9. Skeletal Muscle Types & Exercise 2 Types of Skeletal Muscle Slow Muscle Fibers (Red)  Cells in this muscle are packed with iron-rich proteins that bind to oxygen. Lots of blood vessels attach to slow muscle fibers. These fibers contract slowly, but can hold the contraction for long periods of time Examples: Muscles of the legs and back Fast Muscle Fibers (White)  Fewer blood vessels; relatively small amount of mitochondria. These muscles contract very quickly; but cannot contract for long periods of time Example  Muscles of the hands

10. Exercise Benefits of Exercise for Muscles Increases the size and number of mitochondria Increases the diameter and number of blood vessels supplying the muscle Increases the amount of myoglobin (which binds to hemoglobin)

11. Muscle Contraction & Activation Muscle contraction can be studied by removing the calf leg from a frog and attaching it to an electrical physiograph which initiates electrical currents through the muscle Single muscle fibers have an all or none approach to electrical stimulation A weak electrical stimulus will likely have no effect on the fiber When the stimulus reaches a threshold, the single fiber contracts completely The intensity of a muscle contraction is a result of the number of muscle fibers shortening

12. Muscle Twitch A muscle fiber can be given an instant burst of electrical stimulation This causes the muscle fiber to contract and immediately relax This action is called a muscle twitch

13. Muscle Twitch Components of a Muscle Twitch Contraction Period  period when the muscle fiber is actively shortening Relaxation Period  Period when the muscle fiber is lengthening Latent Period  Period when the muscle fiber is recovering (refractory period) If a muscle fiber is exposed to 2 threshold stimuli within a very short period of time, it will respond to the first but not the second stimulus

14. Summation & Tetanus If a muscle fiber is given a rapid series of threshold stimuli before the muscle relaxes, muscle maintains constant tension, called summation, or tetanus Most muscles rarely undergo tetanus because some fibers are contracting while others are relaxing

15. Muscle Activation Muscles are highly innervated by nerve fibers Brain initiates electrical impulse Electrical impulses are transmitted through axons Axon carries the impulse away from the CNS to the muscle fiber At the end of each axon is a bulb, which contains little packages called synaptic vesicles Inside the vesicles is a neurotransmitter called acetylcholine Acetylcholine empties into the muscle fiber, and stimulates the release of calcium from storage sacs in the muscle itself The calcium attaches to actin filaments and allows for the binding of myosin Myosin then pulls on the actin filaments, causing contraction

16. Muscle Activation

17. Muscle

18. Muscle Activation Neuron Animation

19. Muscle Movements Flexion: moving a part so that the angle at the joint is decreasing Example: Bending elbow up Extension: moving a part so that the angle at the joint is increasing Example: straightening the arm from a bent elbow Abduction: moving a bone away from the midline of the body Example: moving the arms out from the body (from the supine position) Adduction: moving a bone toward the midline of the body Example: moving the arm back down Rotation: Movement of a bone along the axis Examples: Lateral, Medial, Axial

20. Muscle Movements Circumduction: A combination movement that involves flexion/ extension and adduction/abduction when a bone moves in a circle around an axis Example: moving the whole arm in a circle; moving the whole leg in a circle Elevation: Movement of bone upward Example: Movement of the shoulder up Depression: Movement of bone downward Example: movement of shoulder down

21. Muscle Movements Protraction: Pushing out from the torso (shoulder and jaw) Retraction: pulling back towards the torso (shoulder jaw) Dorsiflexion: bending the foot upward Example: walking on the heels Plantarflexion: bending the foor down toward the surface Example: pointing toes Eversion: Movement of the soles of the feet outward so they are facing away from each other Inversion: movement of the soles of the feet so they are facing toward each other Opposition: movement of the thumb toward the pinkie Pronation: movement of the palm so that the palm is facing down Supination: movement of the palm so that the palm is facing up