CH. 7: MUSCLE SYSTEM

What are the functions of skeletal muscle?

• Produces voluntary movement

• Stabilizes joints

• Maintains posture

• Generates body heat

Muscle tissue contracts in responce to

stimulation

What are the 3 types of muscle tissue?

• Skeletal

• Cardiac

• Smooth

What are the characteristics of skeletal muscle?

• Cylindrical cells

• Striated

• Multiple, peripheral nuclei

• Voluntary

• Attached to skeleton

What are other facts regarding the muscle tissue?

• Makes up “flesh” of body (~40% by weight)

• Most “meat” is skeletal muscle

Muscles are organs; give examples and what they do

• Fibers (muscle cells)

• Motor neurons (stimulate to contract)

• Blood vessels (supply nutrients, oxygen)

• Connective tissue (re-inforce)

Connective tissue coverings provide

strength, support, & insulation

What are the connective tissue coverings?

• Endomysium

• Perimysium

• Epimysium

• Fascia

Endomysium

Around each muscle fiber; insulates

Perimysium

Around fascicles (bundles of cells)

Epimysium

Around entire muscle (bundles of fascicles)

Fascia

collective term for C.T. around & between muscles

Connective tissue attachments join muscles to:

bones, cartilages, or to CT coverings of other muscles

Tendons

cordlike bundles of collagen fibers

Aponeuroses (sing. -sis)

sheetlike arrangements of collagen fibers

Muscle Fibers (skeletal muscle cells):

Long, cylindrical, multinucleate

Sarcolemma

cell membrane

T-tubules

Cell membrane extensions deep into the muscle cell

Sarcoplasm

cytoplasm

Muscle Fibers (cells) have numerous

mitochondria

Sarcoplasmic Reticulum

Smooth E.R., stores Ca2+

What are myofibrils?

• Contractile organelles

• Lie parallel to one another

• Run entire length of cell

• Composed of Myofilaments (Protein)

What are the 2 myofilaments in myofibrils?

• Actin

• myosin

Actin

Thin myofilament

Myosin

Thick myofilament

Describe thick myofilament

• Myosin heads free, project out from ends

• Myosin tails attached, central

• Myosin heads can attach to actin, forming crossbridges

Describe Thin myofilament

• Actin & regulatory proteins

  • Tropomyosin

  • Troponin

Tropomyosin

Covers sections of actin

Troponin

• Attaches to actin & tropomyosin

• Binding site for Ca2+

Describe Sarcomeres

• Contractile units of myofibrils

• Source of fiber’s striations

• Banding caused by overlapping arrangement of myofilaments (Actin & Myosin)

What are the parts of a sarcomere?

• A (dark) bands

• I (light) bands

• Z line

• H zone

• M line

A (Dark) bands

correspond to length of myosin filaments

I (Light) bands

actin (no myosin)

Z line

anchor for myofilaments; separates sarcomeres

H zone

center of A band; no actin

M line

Narrow region at center of H zone; anchor for myosin

Fibers must be _________ to contract

stimulated

Motor neurons deliver the

stimulus

Neuromuscular Junction (NMJ)

point of communication between a motor neuron and a fiber

Fibers & Motors Neurons do not

touch

Neurotransmitter molecules bind to and stimulate

muscle fibers

Neuromuscular Junction (NMJ) Anatomy

• Axon Terminal

• Synaptic Cleft

• Motor End Plate

Axon Terminal

end of motor neuron

Synaptic Cleft (gap)

space between axon terminal & motor end plate

Motor End Plate

• Sarcolemma at NMJ

• Invaginated (infolded)

• High SA (surface area)

• ACh (acetylcholine) receptors

“All-or-None” Law

At threshold, a fiber will contract to its maximum extent

Describe the “All-or-None” Law

• No “partial” contractions of individual fibers

• Increasing stimulus strength has no additional effect

In the “All-or-None”, a single nerve impulses

one contraction

A muscle is composed of

motor units

Motor Unit

a motor neuron and all the fibers it controls

Number of fibers varies

2-2000

Each motor unit responds

independently

All muscle cells in a motor unit respond

maximally, or they don’t respond at all

Strength of contraction is determined by

number of motor units stimulated

Recruitment

Process of increasing the number of motor units responding

Strength increases as number of

motor units recruited increases

Skeletal muscles are capable of

Graded Responses

Different degrees of shortening occur by

• Changing the number of motor units activated

• [Changing frequency of stimulation]

Red Slow is

Slow Oxidative

White Fast is

fast glycolytic

Intermediate

Fast Oxidative-Glycolytic

Whole muscles contain all 3 types of fibers, which are

• Red Slow (Slow Oxidative)

• White Fast (Fast Glycolytic)

• Intermediate (Fast Oxidative-Glycolytic)

All fibers within same motor unit are of the

same type

Recruitment begins with

red-slow, followed by intermediate, then white-fast

Describe Red Slow:

• Fewer myofibrils, weaker

• Requires oxygen to make ATP

• Lots of myoglobin, mitochondria, capillaries

• Contracts slowly; fatigues slowly

• Recruited first

• Endurance, postural 

Describe White Fast

• Most myofibrils, strongest & widest in diam.

• Makes ATP without oxygen

• Low myoglobin, fewer mitochondria & capillaries

• High glycogen stores

• Contracts rapidly, fatigues rapidly

• Short-term, powerful movements

• Recruited last

• May hypertrophy in response to training

Describe Intermediate

• Intermediate diameter/number of myofibrils

• Lots of myoglobin, mitochondria, capillaries

• Can make some ATP without oxygen

• Contracts rapidly, moderately resistant to fatigue

• The second fiber type recruited

• Postural & occasional rapid, powerful contractions (e.g. gastrocnemius) 

Skeletal muscle cells do not undergo

mitosis

Exercise does not increase the number of

skeletal muscle cells

Hypertrophy

Enlargement of muscle cells due to exercise

Describe what happens during hypertrophy?

• The number of actin and myosin myofilaments increases

• Mitochondria increase

• Blood supply increases

Atrophy

Decrease in the size of muscle cells due to lack of use

Describe what happens during Atrophy

• The number of actin and myosin myofilaments decreases

• Mitochondria decrease

• Blood supply decreases

Body movements are produced by contraction of

skeletal muscle

Shortening of a skeletal muscle results in

movement of attachments

Movement depends on

joint, attachments

Skeletal muscles have at least two attachments

• One attachment is relatively immobile

• The other attachment is more mobile

Origin

Less movable attachment

Insertion

More movable attachment

Action

What the muscle “does”

Describe Action

• Moves insertion toward origin

• The “movement” produced

Flexion

decreases angle between bones

Extension

increases angle between bones

Rotation

movement around an axis

Abduction

moves appendage away from midline

Adduction

moves appendage toward midline

Circumduction

moves appendage in a circle around joint

BODY MOVEMENTS

• DO THEM

• WRITE THEM

• ANYTHING TO KNOW THEM

Prime Mover (Agonist)

Muscle primarily responsible for an action

Antagonist

Muscle(s) that resist prime mover, or move opposite to it

Synergist

Muscle(s) that assist(s) prime mover

Fixator

Stabilize origin of prime mover or hold the bone still so all tension is used to move insertion

Muscle attachments

Origin and/or insertion (e.g. sternocleidomastoid)

Muscle action example

Adductor magnus

Direction of muscle fibers example

Rectus abdominis

Location of muscle example

Temporalis

Size of muscle example

Gluteus maximus

Number of origins/heads example

Biceps brachii

Shape of muscle example

Deltoid

MUSCLES

• MEMORIZE THEM

• ANATOMY

• LOOK AT THEM