Lab 7Muscles and Muscle Tissue

Gilbert R. Pitts, Ph.D., Joseph R. Schiller, Ph.D., and Amy L. Thompson, Ph.D.

Lab 7 Activities1. Review histology of skeletal, cardiac, and smooth muscle

(macerated and intact)2. Identify structures of sarcomeres on electron micrographs

[ultrastructure]3. Describe how the arrangement of fascicles in a muscle relates

to power and range of motion4. Describe the classification of muscles into functional groups5. Describe the conventions used in the naming of muscles6. Identify the muscles and their actions on models and diagrams7. Use PhysioEx Exercise 2--Skeletal Muscle Physiology to learn

basic concepts of muscle physiology: latent period, treppe, multiple motor unit summation/recruitment, and temporal summation (including tetany)

Some Muscle TerminologyMyology: the scientific study of muscle

muscle fibers = muscle cells

myo, mys & sarco: word roots referring to muscle

microscopic anatomy -- location --

regulation by the endocrine system and the nervous system

Three Types of Muscle:skeletal, cardiac, and smooth

They differ in:

Characteristics of Skeletal Muscle• Attached to bones

• Voluntary (conscious) control (usually)

• Contracts quickly, tires easily (fatigable)

• Undergoes graded contraction

Skeletal Muscle Cells • Long, cylindrical cells

• Striated (banded)

• Multinucleate

Striations /Sarcomeres • Z discs (lines): the boundary

between sarcomeressarcomeres; proteins anchor the thin filaments

• A (anisotropic) band: overlap of thick (myosin) filaments & thin filaments

• I (isotropic) band: thin (actin) filaments only

• Z line: bisects each I band

• H zone: thick filaments only

• M line: proteins anchor the adjacent thick filaments

Sarcomeres • Components of the muscle

fiber with myofilaments arranged into contractile units

• The functional unit of striated muscle contraction

• Produce the visible banding pattern (striations)

• The myofilaments between two successive z discs

• Sliding filament mechanism for contraction

Characteristics of Cardiac Muscle• Forms most of heart wall

(myocardium)

• Involuntary (unconscious)

• Autorhythmicity (contracts w/out external stimuli)

• Fast contraction, non-fatigable

• Intrinsic rhythm modified by neural and hormonal signals

Cardiac Muscle Cells

• Striated

• Uninucleate

• Branched

• Intercalated discs – gap junctions

– desmosomes

Characteristics of Smooth Muscle• found in the walls of hollow

internal structures (digestive, respiratory, reproductive tracts, blood vessels)

• Arrector pili, pupil of the eye, etc.

• Involuntary (unconscious) & may be autorhythmic

• Long, slow contractions, non-fatigable

Smooth Muscle Cells • Nonstriated = smooth

(no sarcomeres)

• Uninucleate

• May gap junctions

Smooth Muscle Cells

• Actin and Myosin contractile proteins are not organized into sarcomeres; instead the fibers attach to the dense bodies under the cell membrane

Connective Tissue Coverings of

Skeletal Muscle • Superficial Fascia:

"hypodermis"

• Deep Fascia: lines body walls & extremities; binds muscle together, separating them into functional groups

• Epimysium: wraps an entire muscle

• Perimysium: subdivides each muscle into fascicles, bundles of 10-100 muscle fibers

• Endomysium: wraps individual muscle fibers

Arrangement of Fascicles

• Range of motion: depends on length of muscle fibers (fascicles); long fibers = large range of motion – parallel and fusiform

muscles

• Power: depends on total number of muscle fibers; many fibers = great power – convergent, pennate,

bipennate, multipennate

Attachments (to bone)• Derived from connective tissue elements:

– insertion: the part of a muscle attached to the bone that moves (relative to a particular motion)

– origin: the part of a muscle attached to the stationary bone

– direct attachment: connective tissue coverings fused directly to periosteum

– indirect attachment: connective tissue coverings gathered into a tendon or aponeurosis that attaches to periosteum

• tendon: cord (of dense regular connective tissue)

• aponeurosis: sheet (of dense regular connective tissue)

The Neuromuscular

Junction • Structure where motor neuron

communicates with skeletal muscle fiber

• Two parts:– Axon terminal

– Motor end plate

• Separated by synaptic cleft

Summary of Muscle Structure

Muscle Functional Groups• Muscles are classified into functional groups

according to their role in producing a particular movement:

– prime mover(s) (= agonists): the muscle(s) primarily responsible for the movement

– antagonist(s):  the muscle(s) that oppose (or reverse) the movement caused by the prime mover.

– synergist(s):  the muscle(s) that assist the prime mover

– fixator(s): the muscle(s) that immobilize the origin of the prime mover

Naming Skeletal Muscles• Location of the muscle• Shape of the muscle• Relative Size of the muscle• Direction/Orientation of the muscle fibers/cells• Number of Origins• Location of the Attachments• Action of the muscle

• Know the muscle names as described in Lab Manual Lab 7 (pp. Lab 7-1 to Lab 7-24)

Muscles Named by Location

• Epicranius (around cranium)

• Tibialis anterior (front of tibia)

tibialis anterior

Naming Skeletal Muscles by Shape

• Deltoid (triangle)

• Trapezius (trapezoid, 2 parallel sides)

• Serratus (saw-toothed)

• Rhomboideus (rhomboid, 4 parallel sides)

• Orbicularis and sphincters (circular)

Rhomboideusmajor

Trapezius

Deltoid

Serratus anterior

Muscles Named by Size

• Maximus (largest)• Minimis (smallest)

• Longus (longest)• Brevis (short)

• Major (large)• Minor (small)

Psoas major

Psoas minor

Muscles Named by Direction of Fibers

• Rectus (straight) - parallel to the body’s long axis

• Oblique

rectusabdominis

external oblique

Transverse – at right angles to the body’s long axis

transversus abdominis

• Biceps (2)

• Triceps (3)

• Quadriceps (4)

Muscles Named for Number of Origins

biceps brachii

Muscles Named for Origin and Insertion

Sternocleidomastoid originates from sternum and clavicle and inserts on mastoid process of temporal bone

origins

insertion

Muscles Named for Action

• Flexor carpi radialis (extensor carpi radialis) –flexes wrist

• Abductor pollicis brevis (adductor pollicis) –flexes thumb

• Abductor magnus – abducts thigh

• Extensor digitorum – extends fingers

adductormagnus

Skeletal Muscles

Know the muscles, their origins and insertions as described in your Lab Manual 7.

Contraction of a Skeletal Muscle• The Motor Unit = Motor Neuron + Muscle Fibers to

which it connects (Synapses)  

Myogram: The Recording of Electrical Activity During Muscle Contraction

• Stimulus: nerve impulse or electrical charge

• All or none rule: all the muscle fibers of a motor unit contract all the way  

• Twitch: a single contraction of all the muscle fibers in a motor unit (one nerve signal)  

Components of the Myogram

• 1. latent period: delay between stimulus and response  

• 2. contraction phase: tension or shortening occurs  

• 3. relaxation phase: relaxation or lengthening  

• refractory period: time interval after excitation when muscle will not respond to a new stimulus

Contraction of a Skeletal Muscle

• Graded muscle responses - moving a load• Force of muscle contraction varies depending

on needs - how much tension is needed?

• Twitch does not provide much force

• Contraction force can be altered in 3 ways:

1. changing the frequency of stimulation

2. changing the force of stimulation

3. changing the muscle’s length

Graded Muscle Responses • Twitch: a single contraction• Wave (temporal) summation: contractions repeated

before complete relaxation, leads to progressively stronger contractions

Graded Muscle Responses• Unfused (incomplete) tetanus: frequency of

stimulation allows only incomplete relaxation  

• Fused (complete) tetanus: frequency of stimulation allows no relaxation  

Graded Muscle ResponsesTreppe: the staircase effect• “warming up” of muscle

Multiple Motor Unit Summation ( Recruitment)

The stimulation of more motor units leads to more forceful muscle contraction  

Contraction of a Skeletal Muscle• Isometric Contraction = Muscle does not shorten• Tension increases

Contraction of a Skeletal Muscle• Isotonic Contraction = tension does not change• Length shortens

Force of Contraction

1. Number of muscle fibers contracting (recruitment)

2. Size of muscle

3. Series elastic elements

4. Degree of muscle stretch

PhysioEx MAP First Screen

Select: Exercise 2: Skeletal Muscle Physiology

PhysioEx MAP Next Screen

Complete Activities 1-4 and 6;

5

Exercise 2: Skeletal Muscle Physiology: Activity 1-3: [The Muscle Twitch and Latent Period]

We suggest you read the Overview and Introduction and take the Pre-lab Quiz before conducting the Experiment and take the Post-lab Quiz after conducting the Experiment for each of the 5 Activities. You do not need to print out or turn in any of the 5 Pre- and Post-lab quizzes.

Exercise 2: Skeletal Muscle Physiology: Activity 1-3: [The Muscle Twitch and Latent Period]

Follow the detailed PhysioEx instructions on pages 7-25 to 7-32 in your manual and record data in the charts in those pages and answer the questions on the pages as you go.

Exercise 2: Skeletal Muscle Physiology: Activity 4: [The Effect of Stimulus Frequency …]

• Notice the frequency of the stimuli (stimuli/sec) can be adjusted as indicated by the multiple stimuli button

Exercise 2: Skeletal Muscle Physiology: Activity 6: [The Skeletal Muscle Length-Tension Relationship]

PhysioEx Homework to Turn In

You will have four tables of data to print from PhysioEx: Activities 2, 3, 4, & 6 to turn in.

You will have 9 questions to answer about the PhysioEx Activities on pp. 7-33 & 7-34 in the

Lab Manual to turn in.

End Lab 6 Presentation

Antagonists of the Forearm

Antagonists of the Thigh

Antagonists of the Foot