musclular system

3 types of muscular tissues

skeletal, cardiac, and smooth

THE MAJOR FUNCTIONS OF ALL THREE TYPES OF MUSCLE:

movement of the body

maintenance of posture

respiration

production of body heat

production of body heat

constrictions of organs and vessels

contraction of the heart

Skeletal Muscle Tissue

-named because of its attachment to bones

-voluntary

-striated

-Associated connective tissue,

-constitutes about 40% of the body's weight

-responsible for many body movements.

-Most skeletal muscles are also controlled subconsciously to some extent

fiver diameter is very large (10-100)

fiber length is 100meanm-30cm

movement of the body

Most skeletal muscles are attached to bones and are responsible for the majority of body movements, including walking, running, chewing, and manipulating objects with the hands.

maintainance of posture

Skeletal muscles constantly maintain tone, which keeps us sitting or standing erect

respiration

Skeletal muscles of the thorax carry out breathing movements

production of body heat

When skeletal muscles contract, heat is given off as a by-product. This released heat is critical for maintaining body temperature.

communication

Skeletal muscles are involved in all aspects of communication, including speaking, writing, typing, gesturing, and smiling or frowning.

constriction of organs and blood vessels

The contraction of smooth muscle within the walls of internal organs and vessels causes those structures to constrict. This constriction can help propel and mix food and water in the digestive tract; remove materials from organs, such as the urinary bladder or sweat glands; and regulate blood flow through vessels.

contraction of the heart

The contraction of cardiac muscle causes the heart to beat, propelling blood to all parts of the body.

Striation

Alternating light and dark bands

voluntary

activity that can be consciously controlled

diaphragm

example of skeletal muscles that also is controlled subconsciously to some extent

Cardiac Muscle Tissue

-found only in the walls of the heart

-striated like skeletal muscles

-involuntary

-fiber diameter is large (10-20)

-fiber length is 50-100mean m

pacemaker

The contraction of the heart is initiated by a node of tissue called

Smooth Muscle Tissue

-located in the walls of hollow internal structures

-lacks striation

-usually involuntary

-most widely distributed type of muscle in the body

-fiber diameter is small (3-8)

-fiber length is 30-200

contraction of the heart

it provides the major force for moving blood through the circulatory system

Functions of Muscular Tissue

producing body movements

stabilizing body positions

moving substances within the body

generating heat

contracting

______ of muscles produces heat

shivering

increases heat production

Excitabilitiy

ability to respond to stimuli

contractility

ability to contract forcefully when stimulated

extensibility

ability to stretch without being damaged

elasticity

ability to return to an original length

Fascia/Fasicle

Dense sheet or broad band of irregular connective tissue that surrounds bundles of muscles fibers

skeletal muscle tissue

fascia/fascicle

epimysium

perimysium

endomysium/muscular fascia

Epimysium

The outermost layer

Separates 10-100 muscle fibers into bundles called fascicles

Perimysium

Surrounds numerous bundles of fascicles

Endomysium

Separates individual muscle fibers from one another

Tendon

Cord that attach a muscle to a bone

connective tissue components

tendons

aponeurosis

Aponeurosis

Broad, flattened tendon

SOMATIC MOTOR NEURONS

Neurons that stimulate skeletal muscle to contract are

skeletal muscle tissue

nerve and blood supply

-Neurons that stimulate skeletal muscle to contract are SOMATIC MOTOR NEURONS

-The axon of a somatic motor neuron typically branches many times

-Each muscle fiber is in close contact with one or more capillaries

hypertrophy

Muscle growth occurs by ________

microscopic anatomy

-The number of skeletal muscle fibers is set before you are born

-Most of these cells last a lifetime

- Muscle growth occurs by hypertrophy-An enlargement of existing muscle fibers

Testosterone and human growth hormone stimulate hypertrophy

Satellite cells retain the capacity to regenerate damaged muscle fibers

hypertrophy

An enlargement of existing muscle fibers

Testosterone and human growth

hypertrophy is stimulated by what?

Satellite cells

they retain the capacity to regenerate damaged muscle fibers

atrophy

Sarcolemma

-The plasma membrane of a muscle cell

-Two delicate connective tissue layers are located just outside the sarcolemma

-The deeper and thinner of the two is the EXTERNAL LAMINA-It consists mostly of reticular (collagen) fibers and is so thin that to see it, a powerful electron microscope is needed.

-The second layer also consists mostly of reticular fibers, but it is a much thicker layer, called the ENDOMYSIUM

muscle fibers

cells that are found in skeletal muscle

skeletal muscle fiber anatomy

The cells found in skeletal muscle are highly specialized with a unique structure. As previously noted, each cell is called a muscle fiber. Skeletal muscle fibers are long, cylindrical cells, each with several nuclei located near the plasma membrane. A single fiber can extend the entire length of a muscle. In most muscles, the fibers range from approximately 1 millimeter (mm) to about 4 centimeters (cm) in length and from 10 micrometers to Muscle contraction is much easier to understand when we consider the structure of a muscle fiber.

SKELETAL MUSCLE FIBER ANATOMY

-sarcolemma

-tranverse (t tubules)

-sarcolplasm

-myofibrils

-filaments (myofilaments)

sarcoplasmic reticulum

sarcomeres

Transverse (T tubules)

-Tunnel in from the plasma membrane

-Muscle action potentials travel through the T tubules

-They occur at regular intervals along the muscle fiber and extend inward, connecting the extracellular environment with the interior of the muscle fiber

- T tubules lie ADJACENT to the highly organized smooth endoplasmic reticulum, called the SARCOPLASMIC RETICULUM in skeletal muscle fibers

Sarcoplasm

-the cytoplasm of a muscle fiber

-Sarcoplasm includes glycogen used for synthesis of ATP and a red-colored protein called myoglobin which binds oxygen molecules

-Myoglobin releases oxygen when it is needed for ATP production

Myofibrils

-Thread like structures which have a contractile function

-approximately 1–3 μm in diameter that extends the length of the muscle fiber.

A myofibril contains two kinds of LONG, THIN protein filaments, called MYOFILAMENTS

Sarcoplasmic reticulum (SR)

-Membranous sacs, which encircles each myofibril,

-Stores calcium ions (Ca++)

-release of Ca++ triggers muscle contraction

Filaments

-Function in the contractile process

-Two types of filaments (Thick and Thin)

-There are two thin filaments for every thick filament

sarcomeres

-Compartments of arranged filaments

-Basic functional unit of a myofibril

Z discs

- Separate one sarcomere from the next

- Thick and thin filaments overlap one another

components of sarcomeres

z discs

A band

I band

H zone

M line

A band

- Darker middle part of the sarcomere

- Thick and thin filaments overlap

I band

- Lighter, contains thin filaments but no thick filaments

-Z discs passes through the center of each I band

H zone

center of each A band which contains thick but no thin filaments

M line

Supporting proteins that hold the thick filaments together in the H zone

contractile proteins

Generate force during contraction

1. 1) myosin

1.2) actin

3 muscle proteins

Myofibrils are built from three kinds of proteins

1) contractile proteins

2) regulatory proteins

3) structural proteins

1.1) myosin

- Thick filaments

- Functions as a motor protein which can achieve motion

- Convert ATP to energy of motion

- Projections of each myosin molecule protrude outward (myosin head)

1.2) actin

- Thin filaments

- Actin molecules provide a site where a myosin head can attach

structural protein

-Align the thick and thin filaments properly

-provide elasticity and extensibility

-Link the myofibrils to the sarcolemma

2.1) titin

2.2) nebulin

2.3) dystrophin

regulatory poteins

-Switch the contraction process on and off

-Tropomyosin and troponin are also part of the thin filament

-In relaxed muscle, myosin is blocked from binding to actin

-Strands of tropomyosin cover the myosinbinding sites

-Calcium ion binding to troponin moves tropomyosin away from myosin-binding sites

-Allows muscle contraction to begin as myosin binds to actin

2.2) Nebulin

Helps align thin filaments

2.1) titin

- Stabilize the position of myosin

- accounts for much of the elasticity and extensibility of myofibrils

Neuromuscular junction (NMJ)

Action potentials arise at the interface of the motor neuron and muscle fiber

2.3) Dystrophin

links thin filaments to the sarcolemma

CONTRACTION AND RELAXATION OF SKELETAL MUSCLE (THE SLIDING FILAMENT MECHANISM)

-MYOSIN heads attach to and "walk" along the thin filaments at both ends of a sarcomere

-MYOSIN MOLECULES shaped like golf club Each MYOSIN MOLECULE consists of TWO MYOSIN HEAVY CHAINS wound together to form a ROD PORTION lying parallel to the myosin myofilament and TWO MYOSIN HEADS that extend laterally

-FOUR LIGHT MYOSIN CHAINS are attached to the heads of each myosin molecule

-Each MYOSIN MYOFILAMENT consists of about 300 myosin molecules arranged so that about 150 of them have their heads projecting toward each end.

-Progressively pulling the thin filaments toward the center of the sarcomere

-Z discs come closer together and the sarcomere shortens Leading to shortening of the entire muscle

contraction cycle

-The onset of contraction begins with the sarcoplasmic reticulum releasing calcium ions into the muscle cell

-Where they bind to actin opening the myosin binding sites

1) ATP hydrolysis

2) formation of cross-bridge

3) power stroke

4) detachment of myosin from actin

ATP hydrolysis

Hydrolysis of ATP reorients and energizes the myosin head

Formation of crossbridge

Myosin head attaches to the myosin-binding site on actin

Power stroke

During the power stroke the crossbridge rotates, sliding the filaments

Detachment of myosin from actin

-As the next ATP binds to the myosin head, the myosin head detaches from actin

-The contraction cycle repeats as long as ATP is available and the Ca++ level is sufficiently high

-Continuing cycles applies the force that shortens the sarcomere

EXCITATION-CONTRACTION COUPLING (ECC)

-An increase in Ca++ concentration in the muscle starts contraction

-A decrease in Ca++ stops it

- Action potentials causes Ca++ to be released from the SR into the muscle cell

- Ca++ moves tropomyosin away from the myosinbinding sites on actin allowing crossbridges to form -

-The muscle cell membrane contains Ca++ pumps to return Ca++ back to the SR quickly ✓ Decreasing calcium ion levels

-As the Ca++ level in the cell drops, myosinbinding sites are covered and the muscle relaxes

Length-Tension Relationship

-The forcefulness of muscle contraction depends on the length of the sarcomeres •

-When a muscle fiber is stretched there is less overlap between the thick and thin filaments and tension (forcefulness) is diminished •

-When a muscle fiber is shortened the filaments are compressed and fewer myosin heads make contact with thin filaments and tension is diminished

THE NEUROMUSCULAR JUNCTION

Motor neurons have a threadlike axon that extends from the brain or spinal cord to a group of muscle fibers

Neuromuscular junction (NMJ)

Neuromuscular junction (NMJ) Action potentials arise at the interface of the motor neuron and muscle fiber

Synapse

where communication occurs between a somatic motor neuron and a muscle fiber

Synaptic cleft

Gap that separates the two cells

Neurotransmitter (acetylcholine)

Chemical released by the initial cell communicating with the second cell

Synaptic vesicles

Synaptic vesicles Sacs suspended within the synaptic end bulb containing molecules of the neurotransmitter acetylcholine (Ach)

Motor end plate

-The region of the muscle cell membrane opposite the synaptic end bulbs

-Contain acetylcholine receptors

NERVE IMPULSES ELICIT A MUSCLE ACTION POTENTIAL IN THE FOLLOWING WAY

1)RELEASE OF ACETYLCHOLINE Nerve impulse arriving at the synaptic end bulbs causes many synaptic vesicles to release ACh into the synaptic cleft

2) ACTIVATION OF ACH RECEPTORS Binding of ACh to the receptor on the motor end plate opens an ion channel Allows flow of Na+ to the inside of the muscle cell

3) PRODUCTION OF MUSCLE ACTION POTENTIAL The inflow of Na+ makes the inside of the muscle fiber more positively charged triggering a muscle action potential The muscle action potential then propagates to the SR to release its stored Ca++

4) TERMINATION OF ACH ACTIVITY Ach effects last only briefly because it is rapidly broken down by acetylcholinesterase (AChE)

Botulinum toxin

-Blocks release of ACh from synaptic vesicles

- May be found in improperly canned foods

- A tiny amount can cause death by paralyzing respiratory muscles

USED AS A MEDICINE (BOTOX®)

Strabismus (crossed eyes)

Blepharospasm (uncontrollable blinking)

Spasms of the vocal cords that interfere with speech

Cosmetic treatment to relax muscles that cause facial wrinkles

Alleviate chronic back pain due to muscle spasms in the lumbar region

curare

-A plant poison used by South American Indians on arrows and blowgun darts

-Causes muscle paralysis by blocking ACh receptors inhibiting Na+ ion channels

-Derivatives of curare are used during surgery to relax skeletal muscles

Anticholinesterase

--Slow actions of acetylcholinesterase and removal of ACh

--Can strengthen weak muscle contractions

-Ex: Neostigmine

-Treatment for myasthenia gravis

-Antidote for curare poisoning

-Terminate the effects of curare after surgery

three ways to produce ATP

creatine phosphate, anaerobic cellular respiration, ◼ 3) By aerobic cellular respiration

Muscle Metabolism (Production of ATP in Muscle Fibers)

-A huge amount of ATP is needed to: o Power the contraction cycle o Pump Ca++ into the SR •

-The ATP inside muscle fibers will power contraction for only a few seconds •

- ATP must be produced by the muscle fiber after reserves are used up •

-Muscle fibers have three ways to produce ATP o

1)From creatine phosphate o

2) By anaerobic cellular respiration o

3) By aerobic cellular respiration

creatine phosphate

-Excess ATP is used to synthesize creatine phosphate o Energy-rich molecule

-Creatine phosphate transfers its high energy phosphate group to ADP regenerating new ATP

-Creatine phosphate and ATP provide enough energy for contraction for about 15 seconds

anaerobic respiration

-Series of ATP producing reactions that do not require oxygen

-Glucose is used to generate ATP when the supply of creatine phosphate is depleted

-Glucose is derived from the blood and from glycogen stored in muscle fibers

-Glycolysis breaks down glucose into molecules of pyruvic acid and produces two molecules of ATP

-If sufficient oxygen is present, pyruvic acid formed by glycolysis enters aerobic respiration pathways producing a large amount of ATP

-If oxygen levels are low, anaerobic reactions convert pyruvic acid to lactic acid which is carried away by the blood -Anaerobic respiration can provide enough energy for about 30 to 40 seconds of muscle activity

aerobic respiration

-Activity that lasts longer than half a minute depends on aerobic respiration

-Pyruvic acid entering the mitochondria is completely oxidized generating ✓ ATP ✓ carbon dioxide ✓ Water ✓ Heat

-Each molecule of glucose yields about 36 molecules of ATP

-Muscle tissue has two sources of OXYGEN ✓ 1)Oxygen from hemoglobin in the blood ✓ 2) Oxygen released by myoglobin in the muscle cell

-MYOGLOBIN AND HEMOGLOBIN are oxygen-binding proteins

-Aerobic respiration supplies ATP for prolonged activity Aerobic respiration provides more than 90% of the needed ATP in activities lasting more than 10 minutes

muscle fatigue

-Inability of muscle to maintain force of contraction after prolonged activity

-Factors that contribute to muscle fatigue:

✓ Inadequate release of calcium ions from the SR Depletion of creatine phosphate

✓ Insufficient oxygen

✓ Depletion of glycogen and other nutrients

✓ Buildup of lactic acid and ADP Failure of the motor neuron to release enough acetylcholine

OXYGEN CONSUMPTION AFTER EXERCISE

-After exercise, heavy breathing continues and oxygen consumption remains above the resting level

-Oxygen debt -The added oxygen that is taken into the body after exercise

-This added oxygen is used to restore muscle cells to the resting level in three ways

✓ 1)to convert lactic acid into glycogen

✓ 2) to synthesize creatine phosphate and ATP

✓ 3) to replace the oxygen removed from myoglobin

-The tension or force of muscle cell contraction varies

-Maximum Tension (force) is dependent on

✓ The rate at which nerve impulses arrive

✓ The amount of stretch before contraction

✓ The nutrient and oxygen availability

✓ The size of the motor unit

oxygen debt

The added oxygen that is taken into the body after exercise

motor units

-Consists of a motor neuron and the muscle fibers it stimulates

-The axon of a motor neuron branches out forming neuromuscular junctions with different muscle fibers

-A motor neuron makes contact with about 150 muscle fibers

-Control of precise movements consist of many small motor units

✓ Muscles that control voice production have 2 - 3 muscle fibers per motor unit

✓ Muscles controlling eye movements have 10 - 20 muscle fibers per motor unit

✓ Muscles in the arm and the leg have 2000 - 3000 muscle fibers per motor unit

-The total strength of a contraction depends on the size of the motor units and the number that are activated

Synaptic vesicles

Sacs suspended within the synaptic end bulb containing molecules of the neurotransmitter acetylcholine (Ach)

TWITCH CONTRACTION

-The brief contraction of the muscle fibers in a motor unit in response to an action potential

-Twitches last from 20 to 200 msec L

LATENT PERIOD (2 MSEC)

-A brief delay between the stimulus and muscular contraction

-The action potential sweeps over the sarcolemma and Ca++ is released from the SR

CONTRACTION PERIOD (10–100 MSEC)

-Ca++ binds to troponin

-Myosin-binding sites on actin are exposed

-Cross-bridges form

RELAXATION PERIOD (10–100 MSEC)

-Ca++ is transported into the SR

-Myosin-binding sites are covered by tropomyosin

-Myosin heads detach from actin

✓ Muscle fibers that move the eyes have contraction periods lasting 10 msec

✓ Muscle fibers that move the legs have contraction periods lasting 100 msec.

RELAXATION PERIOD

-When a muscle fiber contracts, it temporarily cannot respond to another action potential

✓ Skeletal muscle has a refractory period of 5 milliseconds

✓ Cardiac muscle has a refractory period of 300 milliseconds

MUSCLE TONE

-A small amount of tension in the muscle due to weak contractions of motor units

-Small groups of motor units are alternatively active and inactive in a constantly shifting pattern to sustain muscle tone

-Muscle tone keeps skeletal muscles firm

- Keep the head from slumping forward on the chest

TYPES OF CONTRACTIONS

1. isotonic contraction

2. isometric contraction

isotonic contraction

The tension developed remains constant while the muscle changes its length Used for body movements and for moving objects Picking a book up off a table

✓ Concentric - muscle shortens

✓ Eccentric - muscle lengthens