Anatomy Chapter 10 Dr. Aaron BIO 3004 Mississippi State University

Myology

study of muscle tissue

Accounts for 40-50% of the total body weight

muscle

________ are capable of converting chemical energy (ATP) into mechanical energy which is used to generate force and produce movement

muscles

Skeletal muscle

attaches to and moves bone, striated and voluntary, multinucleated

Cardiac muscle

located in the walls of heart, striated and involuntary, uninucleate

Smooth muscle

in internal organs and blood vessels, nonstriated and involuntary, uninucleate

Types of muscle

skeletal, cardiac, and smooth

Functions of muscle tissue

movement, moving compounds within the human body, maintaining posture, regulating organ volume, thermogenesis, stabilizing joints

How do muscles produce movement?

skeletal muscles contract (shorten) to pull on bones

What muscles move and position the eyeball and allow for facial expressions?

Skeletal

How do muscles move compounds within the human body?

smooth muscle in blood vessels and internal organs regulate movements of material within these structures

How do muscles maintain posture?

skeletal muscles provide us with posture

How do muscles regulate organ volume?

Sphincter muscles play a role in this function

Thermogenesis

heat production

How do muscles contribute to thermogenesis?

as muscles work and contract, they generate a great deal of heat

Muscles generate ____ of our body heat

85%

Shivering

involuntary contractions of skeletal muscles

What greatly increases body temperature with involuntary contractions of skeletal muscles?

Shivering

How do muscles stabilize joints?

muscles provide strength and support to joints

What are characteristics of muscle tissue

excitability, conductivity, contractility, extensibility, elasticity

Excitability

ability to respond to a stimulus by producing electrical signals (impulses) within the body, triggered by and regulated by neurotransmitters and hormones, also major property of nerve tissue

Conductivity

ability of a muscle or nerve cell to conduct an impulse along its cell membrane

Contractility

ability of a muscle to shorten and thicken (contract) which generates force to do work, this is unique to muscle tissue

Extensibility

ability of a muscle to stretch without damage to the tissue

Elasticity

ability of a muscle to return to its original shape after stretching or contracting

Each skeletal muscles is composed of numerous muscles fibers. These fibers are essentially....

muscle cells

Connective tissue components of skeletal muscle tissue

fascia, connective tissue beneath deep fascia (epimysium, perimysium, endomysium), tendons

Fascia

sheet of fibrous connective tissue deep to the skin, cover muscles

2 layers of fascia

superficial (subcutaneous layer) and deep fascia

Superficial Fascia (subcutaneous layer)

immediately deep to the skin, composed of areolar and adipose tissue

Functions of superficial fascia

storage of water/fat, reducing heat loss from the body, providing protection, helping nerves and blood vessels enter muscle tissue

Deep fascia

composed of irregular connective tissue, separates muscles into functional groups or units

3 layers of connective tissue beneath the deep fascia

epimysium, perimysium, endomysium

Epimysium

outer layer, nearest to the deep fascia; surrounds the entire muscle

Perimysium

surrounds bundles of muscle fibers called fascicles

Fascicles

bundles of muscle fibers

Endomysium

inner layer, surrounds and separates individual muscle fibers

Tendons

connective tissue cords that attach muscle to bone (specifically to periosteum of bone)

Blood vessels

abundant in muscle tissue; rich blood supply carries nutrients and minerals required by muscles as they contract; blood also supplies muscle with an extensive supply of oxygen

Capillaries

microscopic blood vessels; abundant in the endomysium of muscle tissue; each muscle fiber is near a capillary; blood capillaries are long enough so that they can stretch with the muscle

Muscles have an extensive supply of...

nerves

Motor neurons

nerve cells that stimulate muscles to contract; these deliver the impulse that causes a muscle to contract

Motor unit

a motor neuron and all of the skeletal muscle fibers it stimulates

Neuromuscular Junction

site where nerve cells and muscle fibers meet

Synapses

actual site where a neuron meets a muscle fiber

Synaptic cleft

small gap between the neuron and the muscle fiber; separates the neuron and muscle tissue

Neurotransmitters

chemicals released by the neuron that carry impulses across the synaptic cleft to the muscle fiber

Axon

every motor neuron has one that extends from the cell body. Each extends to a group of skeletal muscle fibers.

Axons function by...

carrying impulses away from neurons (towards the muscle fibers in this case)

Axon terminals

as axons approach muscle fibers they branch into smaller axon terminals which extend onto the surface of the muscle

Synaptic End Bulbs

bulb shaped structures at the end of axon terminals; separated from muscle fibers by the synaptic cleft

Synaptic Vesicles

membrane enclosed sacs located in synaptic end bulbs; contain and store neurotransmitter acetylcholine (ACh)

When impulses reach the axon terminals...

calcium channels and calcium rushes into the axon terminal

Synaptic vesicles move to...

the edge of the synaptic end bulb at the synaptic cleft; the influx of calcium forces the vesicles to release ACh into the synaptic cleft

ACh carries

impulses across the synaptic cleft

Motor end plates

portion of a muscle fibers that is directly across the synaptic cleft from the synaptic end bulbs

Motor end plates contain

acetylcholine receptors which recognize and receive acetylcholine (along with its impulses)

At the motor end plates, ACh opens sodium (Na+) channels which allows

sodium to move into the muscle fiber; this influx of sodium initiates an impulse along the cell membrane of the muscle fiber

First step of events that occur during impulse transmission from a motor neuron to muscle fibers

nerve impulse reaches synaptic end bulbs. Calcium begins to enter the synaptic end bulb

Second step of events that occur during impulse transmission from a motor neuron to muscle fibers

Synaptic vesicles move to the edge of the synaptic end bulb that faces the synaptic cleft. The influx of calcium forces the release of ACh into the synaptic cleft

Third step of events that occur during impulse transmission from a motor neuron to muscle fibers

The ACh stimulates sodium channels on the motor end plates to open. As sodium moves into the muscle tissue, an impulse is created along the membrane of the muscle fiber

Forth step of events that occur during impulse transmission from a motor neuron to muscle fibers

the impulse is then passed further into the muscle fiber. All of the muscle fibers in a motor unit respond by contracting

Muscle tissue is composed of

thousands of long, thin cells known as muscle fibers (myofibers)

Muscle fibers run

parallel to each other

Parts of a skeletal muscle fiber

sarcolemma, sarcoplasm, myofibrils, numerous mitochondria

Sarcolemma

plasma membrane around a skeletal muscle fiber

Sarcoplasm

liquid in a skeletal muscle fiber, this is the cytoplasm of the fiber

Myofibrils

small thread-like structures in the sarcoplasm of muscle fibers; the contractile elements of the muscle fibers

Number mitochondria

involved in aerobic cellular respiration

Myofibrils have a role in

muscle contraction

3 Types of filaments in myofibrils

thick, thin, elastic

Which myofibril filaments overlap each other

thick and thin

Overlap of thick and thin myofibril filaments is responsible for

producing striation that are visible in skeletal and cardiac muscle

Sarcomeres

compartments that hold the filaments that make up myofibrils

Sarcomeres are the basic function units of

striated muscle fibers

Organization and structure of a sarcomere

z-discs (lines), the A band, the I band, the H zone, and the M line

Z Discs (Lines) of a sarcomere

plates that separate one sarcomere from another

The A Band of a sarcomere

within each sarcomere; dark area that contains thick filaments and the portion of the thin filaments that overlap the thick filaments

The I Band of a sarcomere

light region that contains on thin filaments

Which band does not contain thick filaments?

The I Band

The Z Disc passes through

the center of I band

The alternating striations of muscle tissue is produced by the

alternating dark A band and light I bands

H Zone of the sarcomere

located in the center of each A band; contains thick filaments by not thin filaments

Which zone does not contain thin filaments?

H zone

M Line of sarcomere

divides the H zone in half

2 contractile proteins in myofibrils

myosin and actin

Myosin

forms the thick filaments; shaped like 2 golf clubs that are twisted together

Myosin tails

"golf club handles" these point towards the M line in the center of the sarcomere

Myosin cross bridges (myosin heads)

extend towards the thin filaments

Actin

forms the bulk of the thin filaments

myosin cross bridges can attach to these...

Myosin binding sites on each actin molecule

2 Regulatory Proteins in the thin filaments

tropomyosin and troponin

Tropomyosin

covers the myosin binding sites on actin molecules when muscles are relaxed. This protein blocks the attachment of myosin heads to actin

Troponin

holds the tropomyosin in place in relaxed muscle tissue; it holds tropomyosin in place over the myosin binding sites of actin molecules

Elastic filaments

recently discovered, these help to hold the thick filaments in place

Sarcoplasmic Reticulum (SR)

fluid filled bags that encircle each myofibril

Terminal cisterns within SR

stores calcium; impulses can force calcium release from these into the muscle fiber

How do impulses reach the terminal cisternae?

by traveling down T-Tubules

T-Tubules

extensions of the sarcolemma that protrudes deep into the muscle fiber. These allow impulses and nutrient to travel deep into muscle fibers, encircle sarcomeres

The sliding filament mechanism of muscle contraction

states that skeletal muscle shortens as the thick and thin filaments slide past one another.