1. Chapter 7 Lecture Slides
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2. Introduction Muscle tissue is specialized for contraction
Contraction moves the body and body parts
Body has three types of muscle, differing in structure and function
Skeletal muscle
Smooth muscle
Cardiac muscle

3. 7.1 Structure of Skeletal Muscle
Skeletal muscles is composed of mainly muscle fibers
Muscle fibers extend length of muscle
Muscle fibers are arranged in bundles called fascicles

4. Dense connective tissue surrounds each fiber, fascicle, and muscle
Establishes tendons to attach muscle to bone
Establishes aponeuroses to attach muscle to other muscles and connective tissues

5. Skeletal Muscle Fibers
Are multinucleated, long, thin cylinders with rounded ends that extend the length of the muscle
Sarcolemma is the plasma membrane
Sarcoplasm is the cytoplasm
Contain myofibrils, the contractile elements
Contain thin actin filaments and thick myosin filaments
Each myofibril consists of repeating contractile units called sarcomeres

8. The sacroplasmic reticulum is the name given to the smooth endoplasmic reticulum in a muscle cell.
Stores calcium (Ca2+) ions.
The transverse (T) tubule system
Invaginations of the sarcolemma that penetrate into the fiber so that they lie alongside and contact the sarcoplasmic reticulum.

9. The sacroplasmic reticulum is the name given to the smooth endoplasmic reticulum in a muscle cell.
Stores calcium (Ca2+) ions.
The transverse (T) tubule system
Extensions of the sarcolemma that penetrate into the fiber.
Carries impulses that causes the sarcoplasmic reticulum to release Ca2+.

11. Neuromuscular Interaction
A motor neuron sends impulses to a muscle fiber, which produces an action
Each muscle fiber is innervated and controlled by a motor neuron
Without nervous stimulation, a muscle fiber cannot contract

12. Motor Units A motor neuron and all the muscle fibers it contacts
Precise control: motor unit with very few muscle fibers
No precise control: motor units contain 100s of muscle fibers
Motor neuron activation causes contraction of all associated muscle fibers

14. Neuromuscular Junction
Connection between axon of motor neuron and sarcolemma of muscle fiber
Space between axon and sarcolemma is synaptic cleft
Axon terminal has vesicles with neurotransmitter acetylcholine (ACh)
Nerve impulse reaches the axon terminal and ACh is released into the synaptic cleft
ACh attaches to receptors on the sarcolemma at the motor end plate
Begins series of reactions leading to contraction

16. 7.2 Physiology of Muscle Contraction
Contraction involves a number of rapid structural and chemical changes within a muscle fiber
Explained by the Sliding Filament Model

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18. Mechanism of Contraction
ACh binds to receptors on the sarcolemma
Stimulates the release of Ca2+ from sarcoplasmic reticulum
Ca2+ binds to actin filaments, exposing active sites on actin filaments (2)
Myosin cross-bridges attach to actin active sites (3)

20. Cross-bridges detach and reattach to active sites (5-6)
Using ATP energy, cross-bridges bend and pull actin filaments towards center of sarcomere (4)
Cross-bridges detach and reattach to active sites (5-6)
Cycle repeats as long as Ca2+ and ATP are present
Acetylcholinesterase from sarcolemma decomposes Ach in the synaptic cleft
Prevent continual stimulation of muscle fiber
Prepares fiber for next stimulus

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25. Energy for Contraction
Energy comes from ATP
Due to small amount of ATP in cells, more ATP must be formed to support contractions
Two possible pathways for making energy
Creatine phosphate
Cellular respiration

26. Creatine phosphate Storage form of readily available energy
Stores energy from excess ATP
Energy is transferred back to ADP when ATP levels decrease
Depleted quickly in rapidly contracting muscle

27. Oxygen and Cellular Respiration
Cellular respiration is a 2 step process
Anaerobic phase
Aerobic phase
Requires oxygen to operate and produce ATP
Most ATP is produced during this phase
Oxygen for aerobic phase comes from
Hemoglobin in red blood cells
Myoglobin in muscle cells

28. Glucose is the main energy source
Sufficient oxygen levels allow for aerobic respiration to occur
Pyruvic acid from anaerobic phase to CO2 and H2O
Insufficient oxygen with strenuous exercise prevents aerobic respiration
Pyruvic acid from anaerobic phase converts to lactic acid
Causes discomfort and rapid, deep breathing

30. To remove lactic acid, it must be
Broken down by aerobic respiration
Converted back into glucose
Both require oxygen to occur
Oxygen debt: amount of oxygen required to metabolize lactic acid
Also restore normal ATP and creatine phosphate levels
Deep breathing occurs until debt is paid

31. Endurance training increases efficiency of aerobic cellular respiration by increasing
Number of mitochondria
Efficiency of obtaining oxygen from blood
Concentration of myoglobin

32. Fatigue: the reduced ability to do work
Occurs with continued nervous stimulation
Gradual decrease in contraction ending with an inability to contract with stimulation
Causes
Accumulated lactic acid and carbon dioxide
Depletion of ATP

33. Heat Production
Heat from muscle contraction is used to maintain normal body temperature
Decrease in body temperature results in shivering
Heat production in muscle is caused by
Cellular respiration
Other chemical reactions within the cell

34. Types of Skeletal Muscle Fibers
Muscle fibers contract at different speeds, and vary in how quickly they fatigue
Muscle fibers are classified into three main types
Slow oxidative fibers (Type I)
Fast oxidative-glycolytic fibers (Type IIA)
Fast glycolytic fibers (Type IIB)

35. Slow Oxidative Fibers (SO fibers)
Least powerful type of muscle fibers
Appear dark red (more myoglobin)
Generate ATP mainly by aerobic cellular respiration
Rich blood supply and many mitochondria
Have a slow speed of contraction
Very resistant to fatigue
Capable of prolonged, sustained contractions for many hours
Adapted for maintaining posture and for aerobic, endurance-type activities such as running a marathon

36. Fast Oxidative–Glycolytic Fibers (FOG fibers)
Intermediate fibers
Generate considerable ATP by aerobic cellular respiration (still has decent blood supply, large amount of myglobin, and many mitochondria)
Resistance to fatigue is intermediate
Generate some ATP by anaerobic glycolysis
Speed of contraction faster
Contribute to activities such as walking

37. Fast Glycolytic Fibers (FG fibers)
Generate the most powerful contractions
Have low myoglobin content
Relatively few blood capillaries
Few mitochondria
Appear white in color
Generate ATP mainly by glycolysis
Fibers contract strongly and quickly
Fatigue quickly
Adapted for intense anaerobic movements of short duration like weight lifting or sprinting

38. Types of Skeletal Muscle Fibers
Distribution and Recruitment of Different Types of Fibers
Most muscles are a mixture of all three types of muscle fibers
Proportions vary, depending on the action of the muscle, the person’s training regimen, and genetic factors
Postural muscles of the neck, back, and legs have a high proportion of SO fibers
Muscles of the shoulders and arms have a high proportion of FG fibers
Leg muscles have large numbers of both SO and FOG fibers

39. Contraction Characteristics
Contraction of a Single Muscle Fiber
Threshold stimulus is the minimal stimulus that will cause a muscle fiber to contract
At threshold, contraction of a muscle fiber always follows the all-or-none response
Always contracts completely or not at all
Contraction is not proportional to stimulus strength

40. Contraction of Whole Muscles
Muscle contractions are recorded in myograms
A single contraction due to a threshold stimulus has three intervals
Latent period
Period of contraction
Period of relaxation

41. Graded Responses Varying degrees of contraction in whole muscles
Due to presence of different motor units responding to different thresholds of stimulation
Recruitment
increasing the number of motor units to work
Maximal stimulus activates all motor units and produces maximal contraction
Further increases in stimulus strength does not produce stronger contractions

42. Muscle Tone State of partial contraction in relaxed muscle
Keeps a muscle ready to respond
Due to alternating activation of different motor units
Loss of nervous innervation results in loss of muscle tone and atrophy (decrease in muscle size)

43. 7.3 Actions of Skeletal Muscles
Origin and insertion
Insertion is the movable muscle attachment
Origin is the immovable muscle attachment
Isotonic contractions cause movement of a joint
Isometric contractions increase tension but do not cause movement

45. Effects of exercise on skeletal muscles
Strength training causes hypertrophy
Increase in myofibril number in muscle fibers
Endurance training improves the efficiency of muscle action but not hypertrophy
Increases number of mitochondria and blood vessels
Increases oxygen, nutrient, and ATP supply

46. Muscle Interactions Muscles function in groups
Groups arranged to provide opposing movements
Agonists produce an action
Antagonists produce the opposite action
Agonists and antagonists contract alternately

47. Muscle Disorders Cramps
Involuntary, painful, sustained tetanic contractions
Possible causes
Chemical changes in the muscle
Physical blow to the muscle 88

48. Strains or “pulled muscles”
Due to excessive muscle stretching
Mild strains damage only a few muscle fibers
Severe strains tear both connective and muscle tissues
Severe impairment of muscle function 91

49. Spasms
Sudden, involuntary contractions of a muscle or group of muscles
Causes
Irritation of motor neurons
Emotional stress
Neurological disorders