Chapter 9

Muscular System

Function of Skeletal Muscles

• The functions include movement, heat production, and posture.– Movement - contraction of muscles.– Heat production - maintains

homeostasis of temperature.– Posture - maintenance of partial

muscle contraction. •Allows sitting, standing

Muscle and Muscle Fiber Structure

• A muscle is composed of many muscle fibers (muscle fiber = muscle cell). The individual muscles are separated from each other and held in place by a covering called the FASCIA. This fascia also forms TENDONS and APONEUROSES (layers of tendons) connecting muscles to bones and muscles to muscles.

Microscopic Structure of Skeletal Muscles

• Composed of bundles of fibers, not cells.

• Fibers:– Sarcolemma - plasma

membrane of the muscle.– Sarcoplasma - cytoplasm of

a fiber.– Sarcoplasmic reticulum –

like the endoplasmic reticulum, tunnels throughout fiber.

– Contains many mitochondria and several nuclei - more ATP production.

Microscopic Structure of Skeletal Muscles Continued• Fibers:

– Myofibrils - bundles of very fine fibers that extend through the sarcoplasm.

– Each myofibril is made of many protein filaments called myofilaments.

2 Types of Myofilaments

• Myosin -Thick filaments

• Actin - Thin filaments

Movement• Actin and Myosin

filaments are arranged in an overlapping pattern of light (“I” bands) and dark (“A” bands). In the middle of each “I” band is a line called a “Z” line. The section of a myofibril from one Z-line to the next Z-line is called a SARCOMERE. The arrangement of these sarcomeres next to each other produces the STRIATIONS of the skeletal muscle fibers.

Movement Continued• Myosin and actin

interact• Myofibrils pull toward

sarcomere• Sarcomeres shorten,

myofibrils shorten, muscle shortens = contraction.

• All-or-None Law– contract with all

force possible under conditions or do not contract at all.

Energy Sources• ATP - Adenosine

Triphosphate• Breakdown bonds

between the phosphate groups provides energy for contraction.

• Creatine Phosphate provides energy for the regeneration of ATP.

• For more intense contractions, generation of ATP comes from food intake - Cellular respiration.

• ATP is made in the mitochondria.

Energy Sources Continued

• Only 25% of energy produced during cellular respiration is used in metabolic processes – the rest is in the form of HEAT. This is what produces our body heat and maintains body temperature. More muscle activity = more heat.

Connective Tissue Components

• Epimysium - sheath that envelopes each muscle

• Perimysium - extension of sheath between fiber bundles - like a partition.

• Endomysium - extension of sheath between individual fibers.

Connective Tissue Components Continued

• Tendon - extention of three above structures from the muscle to its other end which is continuous with the periosteum (fiberous tissue that covers bone)– Shin splints - tendon not

torn because of strength, but can be pulled away from bone.

• Tendon sheath - tube shaped structure, encloses certain tendons - ex. wrist, ankle– Lined with synovial fluid– Allows easy movement

Connective Tissue Components Continued

• Deep fascia - extension from epi, peri, and endomysium of muscles and their attachment to bone.

Contraction Clip

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html

• http://www.dnatube.com/video/5034/Contraction-of-muscle-function-of-neuromuscular-junction

• http://www.dnatube.com/video/1952/Sliding-filament-causes-contraction-of-muscle

• http://www.dnatube.com/video/1951/Molecular-basis-of-muscle-contration

Muscle Names

Reason for muscle names

• Action - Flexor, extensor

• Direction of fibers• Location - Femoris• Number of

divisions• Shape• Points of

attachment

Muscle Groupings

• Muscles are grouped according to location.

• Muscles are grouped according to function.

Principles of Skeletal Muscle Function

Contract only if stimulated (nerves)

Principles of Skeletal Muscle Function Continued

• Types of Contractions– Tonic - continual, partial contraction - tautness (occurs

only when awake).– Isotonic - contraction remains the same, but length of

muscle changes = shortens (walking, running, lifting an object).

– Isometric - muscle length remains the same, muscle tension increases (push against wall).

– Convulsions - abnormal, uncoordinated contractions.

Principles of Skeletal Muscle Function

Continued

•Produce movement by pulling on bones

•Bones serve as levers, and joints serve as fulcrums of the levers.

•Muscles move parts other than where they lie.

Principles of Skeletal Muscle Function

Continued

•Act in groups•Prime movers - contraction produces movement (primarily responsible for producing an action).

•Antagonists - relaxation of muscle while prime movers are contracting.

* antagonist of a flexor is an extensor*

•Synergists - contract at same time as prime, assist in movement.

Skeletal Muscle Contraction

•Neurotransmitter must stimulate muscle - acetylcholine for muscle contraction.

•ATP must be present at the same time

•Decrease acetylcholine = muscle relaxation

Energy Sources for Contraction

           Creatine phosphate

1. contains high energy phosphate bonds

2. stores excess energy released from mitochondria

3. decrease ATP---- energy from creatine turns to ADP—ADP is coverted to ATP

4. creatine is depleted rapidly in active muscles

5. can ingest extra creatine to increase body supply.

Muscle Fatigue

•Inability of muscle to contract

•Due to accumulation of lactic acid

•Could coincide with cramping due to a lack of ATP

• Partial muscle contraction after death

•Can continue for 72 hours

Rigor Mortis

                        

Posture

                        

  Maintenance

1. Muscles exert continual pull on bone in opposite direction (extensors).

2. Tonicity (elastic tension of living muscles) allows pull against gravity

a. Absent during sleep

b. Will not counteract gravity

c. Cannot sleep standing up

Importance of good posture

1. Decreases work on muscles2. Bad posture puts strain on ligaments3. Bad posture interferes with respiration, digestion, etc…

Posture Continued

                        

                        

Trapezius

                        

Anterior

Muscles

                        

Posterior

Muscles