THE MUSCULAR

SYSTEM

Overview: Guiding Questions

What types of cells are found in muscle tissue?

How are these cells specialized to carry out their function?

What does BMI measure?

What types of cells are found in the muscle tissue? How are they

specialized to carry out their function?

FUNCTIONS CONTRACTILE CELLS

Pumping blood throughout the body

Moving the skeletal system

Passing food through the digestive system

Specialized cell membrane and cytoskeleton that permit them to change their shape

Cytoskeleton allows shortening in one or more planes (contraction)

Laid out as sheets of muscle tissue that produce coordinated contractions

What do contractile cells need to carry out their function?

Blood Supply

High energy needs

Oxygen

Remove metabolic wastes

Glucose

Electrolytes

calcium

From bones

What does BMI measure?

Compares the amount of muscle mass with the body fat composition.

A certain degree of leanness is known to reduce heart disease and metabolic disorders.

Muscle: What are contractile proteins? How can we classify

muscle tissue?

Contractile proteins: Proteins of the cytoskeleton involved in contraction (shortening) of muscle cellsAppearan

ce

Voluntary or Involuntary

Location

Appearance

Non-StriatedStriatedUniform

arrangement of contractile proteins

Can see microscopically

Stronger Contractions

Randomized pattern of contractile

proteins

Cannot see microscopically

Weaker contractions

Voluntary or Involuntary

Large degree of control

Some unconsciously (breathing)

Some contractions are intentional

Contract without conscious control

Jobs that are automatic or in conjunction with other organ systems

Voluntary Involuntary

Location

Cardiac Skeletal Smooth

Spindle or teardrop cells

Fibers not visible

Weak contractions

that last a long time

Linings of BVsTubular organs

Most involuntary

Large cells with distinct

striations

Strong directional

contractions

Attach to bones and joints that

produces body movement

Most are voluntary

Make up the heart

Striated

Connected by intercalated

disks

Involuntary

Types of Muscle Tissue: Guiding Questions

Briefly describe myogenesis. Briefly characterize the three types of

muscle cells How do contractile proteins contribute to

skeletal function? Why is the “intrinsic beat” of cardiac

muscle cells significant? Why is “peristalsis” significant? Describe the relationship between muscle

cells and muscle fibers

Briefly describe myogenesis:

Muscle develops in mesoderm cells: myogenesis

Stem cells form myoblasts Myoblasts move to other developing tissues to

form the 3 muscle types Growth factors (chemicals that act as signals

to initiate cell division & differentiation) by tissues give direction as to what type of muscle needs to form.

Briefly Characterize the 3 Types of Muscle Cells

Cardiac Skeletal Smooth• Lining of BV, digestive organs, urinary system, respiratory system•Nonstriated•Weak involuntary contractions can last for a long time•Dilation and constriction of BV and tubular structures in respiratory system•Peristalsis: laid in sheets in digestive system. Moves food & wastes through

•Provides movement•Large cells with distinct striations•Powerful contractile capabilities•One cell is composed of several myoblasts that fuse into a muscle fiber—why so many nuclei?•Each fiber stimulated by a motor nerve cell that controls several muscle fibers at once

•Form around large BV and form heart•Strong contractions •Not conscious control•Have 2 nuclei per cell•Cells are branched•Communicate thru intercalated disks•Intrinsic beat: all cardiac cells act in unison, coordinated thru intercalated disks

Cardiac Muscle: Branching, striated cells fused at plasma membranes.

Skeletal Muscle: Long, striated cells with multiple nuclei

Smooth Muscle: Long, spindle-shaped cells each with a single nucleus

What type of muscle cells?

Now, you should be able to answer these questions!

How do contractile proteins contribute to skeletal function?

Why is the “intrinsic beat” of cardiac muscle cells significant?

Why is “peristalsis” significant? Describe the relationship between muscle

cells and muscle fibers

Muscle Cell Structure Guiding Questions

Describe the basic structure of skeletal muscle cells

Briefly summarize the various types of fibers found in a muscle cell

Describe the relationship between myofibrils, muscle fibers, and fasciculi

Why is a sarcomere called the “contractile unit” of the muscle?

Organization of (skeletal) muscle

Skeletal muscle fibers located in muscles Entire muscle

surrounded by epimysium, a CT layer

Subdivided into fiber bundles called fascicles (fasciculi)

Fascilcles surrounded by perimysium, also CT

Membranes

Portions of perimysium extend into the endomysium Thin layer of CT that

covers each muscle fiber

Muscle fiber (bundle)= multinucleate cell

SARCOMERE

Sarcomere= basic (functional) contractile unit Separated by each other by

dark Z lines/discs Actin & myosin slide past

each other as the muscle contracts

Contraction requires Ca2+ and ATP

Actin Myosin

Sarcomere

Other Key Points

About Sarcomeres

Z-line/disc – vertical protein bands that hold sarcomere to sarcolemma.

I Bands Lighter areas of non-overlap between actin and

myosin Contain the Z-lines.

Dark Bands = A Bands Areas where some overlap occurs = “Striations” on the slide Coincide with the length of myosin myofilaments. H-zone – light area within A-band

Sarcoplasmic Reticulum Each myofibril is surrounded by network

of tubes and storage sacs (Transverse tubules and sarcoplasmic reticulum)

Releases Ca2+ ions when stimulated by motor neuron

Triggers contraction (more on this later…)

MICROSCOPIC STRUCTURE

Muscle FIBERS: grouped into bundles (fasciculi)

= 1 cell! Fibers contain myofibrils

with: ACTIN: thin myofilaments

Also contain: Tropomyosin Troponin

MYOSIN: thick myofilaments, with “swiveling” arm and head

TITIN: elastic fibers that hold myosin in place, controlling stretch of sarcomere

Another look…

Muscle Cell Function Guiding Questions

How would a muscle appear to change microscopically during a contraction?

What are the three stages of muscle contraction? What is the role of neurotransmitters during muscle

contraction? Describe the ion concentrations found inside and

outside a resting muscle cell Briefly describe the events that occur during the

muscle contraction phase. What is the role of ATP during this phase? What must occur for a muscle cell to “fully” recover

after a contraction? What occurs during “rigor mortis”?

Muscle Contraction

Sarcomeres shorten, distance between z-lines reduced

Thick and thin myofilaments overlap more during contraction

3 stages: Neural stimulation Muscle cell contraction Muscle cell relaxation

Motor Unit Stimulation of a muscle by a nerve

impulse (motor nerve) is required before a muscle can shorten

Neuromuscular junction: point of contact b/w nerve ending and the muscle fiber it innervates.

Motor unit: motor neuron + muscle cell

Neuromuscular Junction

Neural Stimulation

Motor neuron releases neurotransmitters to stimulate a contraction Acetylcholine (Ach) binds to receptors

located on sarcolemma Changes transport proteins found in

sarcolemma Alters transport of ions

Normally, more Sodium (Na+) ions outside muscle cell, while Potassium (K+) higher inside

Sodium/Potassium pumps maintain this unequal concentration

Excitable condition

When stimulated, ion channels open, depolarizing the cell Na+ flows in, K+ out sarcoplasmic reticulum releases stored

calcium Ca2+ travels to sarcomere, initiating muscle

contraction phase

Muscle Contraction Animation

Click here to view animation

Sliding filament theory In the absence of

Calcium ions…Troponin “hat” sits

on Tropomyosin filament These blocks access to the myosin head’s binding site on actin.

TroponinTropomyosinCa2+

When Calcium is released by the Sarcoplasmic reticulum it diffuses into the muscles binds to the troponin “hat” shifting both the troponin and tropomyosin

filament

Myosin splits ATP and undergoes a conformational change into a high-energy state.

The head of myosin binds to actin Forms a cross-bridge between the thick

and thin filaments.

The energy stored by myosin is released ADP and phosphate released from

myosin. The myosin molecule relaxes

Causes rotation of the globular head This leads to the sliding of the

filaments. This cycle continues until Ca2+ ions gone

(and stimulus stops)

ATP binds to cross bridge, causing cross bridge to disconnect from actin.

Splitting of ATP leads to re-energizing/ repositioning of the cross bridge.

Relaxation Phase

Complete contraction of muscle cell requires several cycles of neural stimulation and contraction phases

Ca2+ ions transported back to sarcoplasmic reticulum (req. ATP)

When the calcium level decreases troponin locks tropomyosin back into the

blocking position thin filament (actin) slides back to the resting

state (when ATP binds to myosin head)

Relaxation phase occurs when no more neural stimulations are exciting the sarcolemma Na+/K+ pump returns ions to resting

state Muscle cell remains in contracted, but

pliable state Must be “stretched” back into position

Review of the Role of ATP

1. ATP transfers its energy to the myosin cross bridge, which in turn energizes the power stroke.

2. ATP disconnects the myosin cross bridge from the binding site on actin.

3. ATP fuels the pump that actively transports calcium ions back into the sarcoplasmic reticulum.

Rigor Mortis

In death… Calcium leaks out of sarcoplasmic

reticulum into sarcomere Causes muscle tension = rigor mortis Muscle cell structures start breaking down,

causing muscle to loosen (unless body becomes dehydrated)

Creatine phosphate

Stores energy in muscle cells Collects energy from ATP, stores for long

periods of time Transfers back to ATP when needed

Glycogen

Stored form of glucose Energy reserve for muscle action Continuous supply needed to produce

ATP

Myoglobin

Red pigment that stores oxygen for muscle cells “Grabs” oxygen from hemoglobin in blood High affinity for oxygen

Allows cells to produce large amounts of ATP

Musculature Guiding Questions

What determines a muscle’s morphology?

Distinguish between a muscle’s origin and insertion

Gross Skeletal Muscle Types Guiding Questions

Review the location of the various gross skeletal muscle types listed on page. 231

List, and briefly describe, the various terms that describe the muscle structures, patterns, and shapes

Parallel or Pinnate

Parallel general-purpose muscles Sheets of muscle cells that run in the same

direction Contractions for moving light loads over a

long distance Pinnate

Feather-pattern Great strength for moving heavy loads over a

short distance Strong movements for the arms and legs

Gross Muscle Cell Types/TermsMuscle group Shape Function

Deltoid Triangular Pulling power

Trapezius Trapezoid Pulling power

Rhomboideus Diamond Holding power for scapulae

Serratus Saw-toothed

Short movements of the arms, rib cage, and shoulders

Biceps 2 heads Upper arms

Triceps 3 heads Upper arms

Quadriceps 4 heads Upper legs

Size Description

Maximus Largest muscle in the group

Minimus Smallest muscle in the group

Longus Longest muscle in the group (arms and legs)

Brevis Shortest muscle in the group (arms and legs)

Skeletal Muscle Structure Guiding Questions

In words, briefly review the basic structure of a skeletal muscle

What occurs to a muscle during atrophy? Hypertrophy?

Review: Muscle Cell Structure

C

B

A

E(fluid in cells)

D(membrane)

H

G

F

A (blue line)

B (Red line)

FE

C CD

E

A (blue line)

B (Red line)

C C

G

G

EF

What occurs to a muscle during atrophy? Hypertrophy?

Atrophy Lose sarcomere proteins

Causes muscle shrinkage Loss of contraction strength & size Can happen with a lack of neural stimulation

Hypertrophy Regular use causes increased blood flow Increase in muscle diameter and thus muscle

strength Genetic differences / variation in blood flow

may cause an increase in sarcomere density without increase in muscle size

Skeletal Muscle Action Guiding Questions

How are “graded effects” accomplished during a muscle contraction?

Differentiate between strength and endurance.

What is an antagonistic effect? Why are these essential to normal muscle function?

List and briefly describe the various categories of muscle action.

Origin vs. Insertion

Origin – point of attachment of a muscle that remains fixed during contraction

Insertion – point of attachment of a muscle connected to movable component on other end

Shortening/contraction = moves insertion closer to origin

Threshold

All muscle fibers contract with a particular strength when threshold neural stimulation reached

How are muscles able to perform at different “powers”? Graded effects can be accomplished by:

Contracting more fascicles = more strength Muscles working together

Endurance = producing contracting and relaxing fascicle groups

Differentiate between strength and endurance

Strength = ability to do more work Endurance = longer period of work

What is an antagonistic effect? Why are these essential to normal muscle function?

One muscle opposes or resists the action of another

Weakens muscle strength Gravity can have antagonistic effect Essential!

Pulls relaxed muscles back to original strength Cartilage can do this (in ribcage during

breathing) Synergism = muscles work together

Categories of Muscle Action

Muscle Action

Movement Antagonistic Toward….

Abductor Away from midline Adductors

Adductor Toward the midline Abductors

Depressor Downward movement Levator

Extensor Increase angle of joint Flexor

Flexor Decrease angle of joint

Extensor

Levator Upward movement Depressor

Pronator Turn palm down Supinator

Rotator Turn along longitudinal axis

None

Sphincter Decrease size of opening

None-attached to skin or connective tissue

Supinator Turn palm up Pronator

Tensor Posture, make body part more rigid, tense

Many

Isotonic or Isometric?

Another way to define muscle action

Isotonic: muscle is actively shortening or lengthening. Lifting/lowering weights

Isometric: muscle remains steady in length, undergoing indistinguishable pulses of shortening and lengthening Pushing against something too

heavy to move

Pathology of Musculature Guiding Questions

Differentiate between muscle strains and sprains

Differentiate between spasms and cramps of muscles

How are rigid and flaccid paralysis different?

What causes tetanus? Review the various myopathies listed on p.

242. Make a chart/concept map to summarize the major characteristics of each.

Strain vs. Sprain

Strain Overworking

muscle Pain, swelling in:

Fascia Joints Ligaments Tendons

Due to tearing of muscle/tendon fibers Nerves

stretched/swollen

Sprain More severe Sudden/violent

stress on joint/muscle

Causes tearing: Ligament Muscle Tendon

Damage to blood vessels

Strain vs. Sprain

Spasms vs. Cramps

Spasm = involuntary, abnormal contractions of a muscle/group Many causes Often associated with pain

Cramps = painful contraction of muscle Extreme exertion can cause May develop while working in cold Poisons, bacterial infections

Rigid vs. Flaccid Paralysis

Paralysis = complete failure of muscle function Caused by muscle stiffness? Rigid Lack of muscle contraction? Flaccid

Many causes (infection, injury, degeneration)

Causes of Tetanus (aka lockjaw)

Soil bacteria (Clostridium tetani)infect nervous system

Produce poisons that block nerve signals at neuromuscular junction, cause rigid paralysis (severe muscle spasms). Can cause muscle tears/spinal fractures if severe

Do you have your tetanus “shot”?

For tomorrow…

Reading “Aging of the Musculature” Bring textbook…

Make concept map of pathology and aging sections (like the one I made for you last time)

Try to think about “groupings” you could use to make a web “Overwork” “Trauma” “Abnormal muscle control” Etc…

Aging of the Musculature Guiding Questions

What can cause cachexia? Why do muscles require a high protein

turnover? What is the role of IGF-1 in muscle

health?