1. Muscles and Muscle Tissue9
Part A

2. The three types of muscle tissue are skeletal, cardiac, and smooth
Muscle Overview
The three types of muscle tissue are skeletal, cardiac, and smooth
These types differ in structure, location, function, and means of activation

3. Muscle terminology is similar
Muscle Similarities
Skeletal and smooth muscle cells are elongated and are called muscle fibers
Muscle contraction depends on two kinds of myofilaments – actin and myosin
Muscle terminology is similar
Prefixes – myo, mys, and sarco all refer to muscle

4. Skeletal Muscle Tissue
Has obvious stripes called striations
Is controlled voluntarily (i.e., by conscious control)
Contracts rapidly but tires easily
Is responsible for overall body motility
Is extremely adaptable and can exert forces ranging from a fraction of an ounce to over 70 pounds

5. Cardiac Muscle Tissue Occurs only in the heart
Is striated like skeletal muscle but is not voluntary
Contracts at a fairly steady rate set by the heart’s pacemaker
Neural controls allow the heart to respond to changes in bodily needs

6. Smooth Muscle Tissue
Found in the walls of hollow visceral organs, such as the stomach, urinary bladder, and respiratory passages
Forces food and other substances through internal body channels
It is not striated and is involuntary

7. Functional Characteristics of Muscle Tissue
Excitability, or irritability – the ability to receive and respond to stimuli
Contractility – the ability to shorten forcibly
Extensibility – the ability to be stretched or extended
Elasticity – the ability to recoil and resume the original resting length

8. Skeletal muscles are responsible for all locomotion
Muscle Function
Skeletal muscles are responsible for all locomotion
Cardiac muscle is responsible for coursing the blood through the body
Smooth muscle helps maintain blood pressure, and squeezes or propels substances (i.e., food, feces) through organs
Muscles also maintain posture, stabilize joints, and generate heat

9. The three connective tissue sheaths are:
Skeletal Muscle
Each muscle is a discrete organ composed of muscle tissue, blood vessels, nerve fibers, and connective tissue
The three connective tissue sheaths are:
Endomysium – fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber
Perimysium – fibrous connective tissue that surrounds groups of muscle fibers called fascicles
Epimysium – an overcoat of dense regular connective tissue that surrounds the entire muscle

10. Skeletal Muscle
Figure 9.2 (a)

11. Skeletal Muscle: Nerve and Blood Supply
Each muscle is served by one nerve, an artery, and one or more veins
Each skeletal muscle fiber is supplied with a nerve ending that controls contraction
Contracting fibers require continuous delivery of oxygen and nutrients via arteries
Wastes must be removed via veins

12. Skeletal Muscle: Attachments
Most skeletal muscles span joints and are attached to bone in at least two places
When muscles contract the movable bone, the muscle’s insertion moves toward the immovable bone, the muscle’s origin
Muscles attach:
Directly – epimysium of the muscle is fused to the periosteum of a bone
Indirectly – connective tissue wrappings extend beyond the muscle as a tendon or aponeurosis

14. Microscopic Anatomy of a Skeletal Muscle Fiber
Sarcoplasm has numerous glycosomes and a unique oxygen-binding protein called myoglobin
Fibers contain the usual organelles, myofibrils, sarcoplasmic reticulum, and T tubules
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InterActive Physiology®: Muscular System: Anatomy Review: Skeletal Muscle Tissue

15. Myofibrils are densely packed, rodlike contractile elements
They make up most of the muscle volume
The arrangement of myofibrils within a fiber is such that a perfectly aligned repeating series of dark A bands and light I bands is evident

16. Myofibrils
Figure 9.3 (b)

17. The smallest contractile unit of a muscle
Sarcomeres
The smallest contractile unit of a muscle
The region of a myofibril between two successive Z discs
Composed of myofilaments made up of contractile proteins
Myofilaments are of two types – thick and thin

18. Sarcomeres
Figure 9.3 (c)

21. Myofilaments: Banding Pattern
Thick filaments – extend the entire length of an A band
Thin filaments – extend across the I band and partway into the A band
Z-disc – (connections) that anchors the thin filaments and connects myofibrils to one another

22. Myofilaments: Banding Pattern
Thin filaments do not overlap thick filaments in the lighter H zone
M lines appear darker due to the presence of the protein desmin (filament guide)

23. Myofilaments: Banding Pattern
Figure 9.3 (c, d)

24. Contraction of Skeletal Muscle Fibers
Contraction – refers to the activation of myosin’s cross bridges (force-generating sites)
Shortening occurs when the tension generated by the cross bridge exceeds forces opposing shortening
Contraction ends when cross bridges become inactive, the tension generated declines, and relaxation is induced

25. Length-tension relationship
at 70% to 130% of resting length muscles can generate most tension because maximum number of cross bridges can be made
below 70% or more than 130% resting length results in little generation of tension because of cross bridges overlap too much or not all

26. Contraction of Skeletal Muscle (Organ Level)
Contraction of muscle fibers (cells) and muscles (organs) is similar
The two types of muscle contractions are:
Isometric contraction – increasing muscle tension (muscle does not shorten during contraction)
Isotonic contraction – decreasing muscle length (muscle shortens during contraction)

27. Motor Unit: The Nerve-Muscle Functional Unit
A motor unit is a motor neuron and all the muscle fibers it supplies
The number of muscle fibers per motor unit can vary from four to several hundred
When a motor unit fires all the fibers attached contract completely. (all or nothing response)
Muscles that control fine movements (fingers, eyes) have few fibers per motor unit

28. Motor Unit: The Nerve-Muscle Functional Unit
Figure 9.12 (a)

29. Motor Unit: The Nerve-Muscle Functional Unit
Large weight-bearing muscles (thighs, hips) have motor units with 100’s of muscle fibers
Muscle fibers from a motor unit are spread throughout the muscle; therefore, contraction of a single motor unit causes weak contraction of the entire muscle
Some motor units have larger fibers than other motor units. Muscles start with motor units with small fibers

30. The three phases of a muscle twitch are:
A muscle twitch is the response of a muscle to a single, brief threshold stimulus
The three phases of a muscle twitch are:
Figure 9.13 (a)

31. Graded Muscle Responses
Graded muscle responses are:
Variations in the degree of muscle contraction
Required for proper control of skeletal movement
Responses are graded by:
Changing the frequency of stimulation
Changing the strength of the stimulus

32. Muscle Response to Varying Stimuli
A single stimulus results in a single contractile response – a muscle twitch
Frequently delivered stimuli (muscle does not have time to completely relax) increases contractile force – wave summation
Figure 9.14

33. Muscle Response to Varying Stimuli
More rapidly delivered stimuli result in incomplete tetanus
If stimuli are given quickly enough, complete tetanus results
Figure 9.14

34. Muscle Response: Stimulation Strength
Threshold stimulus – the stimulus strength at which the first observable muscle contraction occurs
Beyond threshold, muscle contracts more vigorously as stimulus strength is increased
Force of contraction is precisely controlled by multiple motor unit summation
This phenomenon, called recruitment, brings more and more muscle fibers into play

35. Stimulus Intensity and Muscle Tension
Figure 9.15 (a, b)

36. Treppe: The Staircase Effect
Staircase – increased contraction in response to multiple stimuli of the same strength
Contractions increase because:
There is increasing availability of Ca2+ in the sarcoplasm
Muscle enzyme systems become more efficient because heat is increased as muscle contracts
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InterActive Physiology®: Muscular System: Contraction of Whole Muscle

37. Summation
Additional motor units contract before initial ones relax----form of graded response of whole muscle
Treppe--stair case effect
intial stimuli do not produce as much shortening as subsequent stimuli of same strength (They add up)

38. Treppe: The Staircase Effect
Figure 9.16

39. Types of muscle contractions
All or None principle
Applies to individual fibers
a subthreshold stimulus will generate no contraction
a threshold stimulus will generate a maximal contraction for all muscle fibers contained in a motor unit
stimuli above threshold will activate more motor units and generate more tension in muscle but will not result in greater contraction on any one fiber

40. Characteristics of muscle contraction
Can contract in graded fashion
As more motor units contract or existing motor units contract more rapidly, tension increases
strength of stimulus determines number of motor units activated

41. Strength of muscle contraction
Muscle tone--- a few alternating batteries of motor units are kept active, stabilizing posture and keeping muscles ready to respond to further stimulation
Number of motor units stimulated
size of muscle