anatomy ch 6

mys/myo

mys/myo

muscle

epi

above

peri

around

endo

inside

five functions of muscle tissue

producing movement, maintaining posture and body position, stabilizing joints, generating heat, and additional functions.

producing movement

is responsible for the mobility of the body as a whole. all of our movement comes from muscle contraction. these contractions enable us to respond quickly to changes in the external environment.

maintaining posture and body position

maintaining posture and body position is constantly happening through skeletal muscles. they make one tiny adjustment after another so that we are able to maintain seated posture despite the constant downward pull of gravity.

stabilizing joints

activated  by the skeletal muscles pull on the bones. muscle tendons are very important in this process, especially with joints that have poorly fitting articulating surfaces, like shoulders.

generating heat

a by-product of muscle activity. as the ATP is used to power the muscle contraction, nearly three-quarters of its energy escapes as heat, generating body heat.

additional functions

the protection of organs

muscle tissue types

skeletal, smooth, cardiac

skeletal

• Striations

• Long cylindrical

• Many nuclei

• Rapid contractions

cardiac

• Branched

• Striations

• One nucleus

• Intercalated discs

• Rapid contractions

smooth

• Tapered ends

• No striations

• One nucleus

• Slow, rhythmic contractions

gross (large) anatomy of skeletal muscles

• epimysium

• fascicle

• perimysium

• endomysium

epimysium

layer of connective tissue surrounding the entire muscle group (bicep, tricep, etc).

fascicle

bundle of many muscle fibers (cells).

perimysium

layer of connective tissue surrounding each fascicle.

endomysium

layer of connective tissue surrounding each muscle fiber(cell).

histology (micro) anatomy of skeletal muscles

• muscles made of many myofibrils

• many mitochondria

• high volume of smooth ER

myofibrils

• long cylinder made of many layers of protein filaments.

  • building muscle-adding more layers of:

• myosin (thick filaments)

• actin  (thin filaments)

  • tropomyosin

    • at rest, it blocks myosin from attaching to actin.

  • troponin 

    • controls the location of tropomyosin

    • Ca2+ binds here during contraction-> shifts tropomyosin.

• sarcomere= contractile unit of myofibril, horizontal segments of myofibril. 

many mitochondria

• Produce ATP

• Contractions use ATP

high volume of smooth ER

Stores calcium needed for contraction

muscle contraction

• neuromuscular junction

• synaptic cleft

• neurotransmitter

• acetylcholine

neuromuscular junction

place where motor neuron + muscle fiber meet.

synaptic cleft

space between motor neuron and muscle fiber.

neurotransmitter

chemical that transmits signal from neuron to another cell.

acetycholine

neurotransmitter that causes muscle fiber to contract.

• Steps:

• 1.) The brain sends signals down the motor neuron for contraction.

• 2.) acetylcholine released from the motor neuron into the synaptic cleft.

• 3.) acetylcholine binds to receptor proteins on muscle fiber

  • Receive signals from other cells

• 4.) action potential is triggered in muscle fiber

  • Rapid change in charge across cell membrane

• 5.) Action potential causes smooth ER to release calcium

• 6.) Ca2+ attaches to troponin

  • Shifts tropomyosin out of the way

• 7.) myosin attaches to actin and pulls

graded responses

• Oppositional contraction and relaxation

  • Within a muscle group→cells alternating

• Amount of power depends on:

  • The number of motor neurons sending a signal

  • Frequency of signals

• unfused tetanus

• fused tetanus

unfused tetanus

some relaxation between the signals.

fused tetanus

• no relaxation between signals

  • Max output of muscle

sources of ATP

• aerobic respiration

• anaerobic respiration

• creative phosphate

aerobic respiration

• Uses 02

• Happens in mitochondria

• Glucose + 02 → ATP

• → 36 (slow)

anaerobic respiration

• No 02 used

• Glucose → ATP 

• → 2 (fast)

• Produces lactic acid-causes muscle soreness

creative phosphate

• Limited supply

• Rapid ATP production

• 5-10 second burst

muscle fiber types

• slow oxidative fibers

• fast oxidative fibers

• fast glycolynic fibers

slow oxidative fibers

• High endurance

• Low power

fast oxidative fibers

• Moderate endurance

• Moderate power

fast glyconytic fibers

• Low endurance

• High power

exercise

• Aerobic

  • Increases blood supply (02 + glucose)

  • Increases amount of mitochondria

• VS.

• Anaerobic (resistance)

  • Increases number of layers of myosin and actin

• Muscle tone=”at rest” in unfused tetanus

What is the role of the sarcoplasmic reticulum in muscle contraction?

The role of the sarcoplasmic reticulum in muscle contraction is providing the final “go” signal for contractions. It does this by storing calcium, and then releasing it on demand when the muscle fiber is supposed to contract. 

When you look at skeletal muscle underneath the microscope, you see striations.  What is responsible for this banding pattern?

Sarcomeres are responsible for this binding pattern because they make the binds visible along the muscle fibers.

How do myosin and actin interact during a muscle contraction?

When a muscle contraction occurs, and the actin-containing filaments slide toward each other into the center of the sarcomere, these light zones disappear because the actin and myosin filaments overlap each other. Which in turn then shortens the sarcomere, then causing the muscle contraction.

how is skeletal muscle bundled/packaged?

The huge, cigar-shaped skeletal muscle fibers, containing multinucleate cells, are packaged into organs called skeletal muscles which attach to the body’s skeleton. As the skeletal muscles cover the bony “underpinnings” of our body’s, they help to form the much smoother contours of the body.