THE MUSCULAR SYSTEM

CHAPTER 9

FUNCTIONS OF THE MUSCULAR SYSTEM

• pull on bones to accomplish body movements

• provide muscle tone, maintain posture

• propel body fluids and food

• generate a heartbeat

FUNCTIONS OF THE MUSCULAR SYSTEM

• generate heat

• stabilize joints

• makes up about 40% of the body’s mass, over 600 skeletal muscles

• means little mouse

A COMPARISON OF THE 3 MUSCLE TYPES:

location:

SKELETAL CARDIAC SMOOTH attached to heart walls of

bones or skin visceral organs, BV’s

function:

SKELETAL CARDIAC SMOOTH

movement, pumping blood peristalsis,

posture vasoconstriction

vasodilation

cell shape & appearance:SKELETAL CARDIAC SMOOTH

multinucleate uninucleateuninucleate

striated striated not striated

cylindrical branched spindle-shaped

contraction characteristics :

SKELETAL CARDIAC SMOOTH

voluntary involuntary involuntary

slow to fast slow very slow

not rhythmic rhythmic some rhythmic

• skeletal muscle can contract rapidly & with great force, but it tires easily & must rest after short periods of activity

• smooth muscle contractions are slow and sustained

• cardiac muscle contractions are steady (set by a pacemaker), but they can be shifted into “high gear”; the cells are connected by intercalated discs & they react as a unit in an all-or-none manner

Functional characteristics of muscle

• Excitability or irritability = the ability to receive or respond to a stimulus, usually a chemical

• Contractility = the ability to shorten

• Extensibility = the ability to be stretched

• Elasticity = the ability to recoil and resume the resting length after being stretched

Gross anatomy of a skeletal muscle

• Connective tissue wrappings:– epimysium = outermost layer– perimysium = surrounds each fascicle– endomysium = surrounds each muscle fiber

Gross anatomy of a skeletal muscle

• Nerve and blood supply:– each muscle is supplied a nerve, an artery,

and a vein to supply energy & remove wastes

• Attachments:– origin = attached to the bone that does not

move– insertion = attached to the movable bone

STRUCTURE OF A SKELETAL MUSCLE

• Tendons connect muscles to bone:

STRUCTURE OF A SKELETAL MUSCLE

• composed of skeletal muscle tissue, nervous tissue, blood, CT

STRUCTURE OF A SKELETAL MUSCLE

• fascia = layers of CT that cover individual muscles & hold them in place; may form tendons, hooking up with a bone’s periosteum

STRUCTURE OF A SKELETAL MUSCLE

• aponeuroses = broad fibrous sheets of CT which attach to the coverings of adjacent muscles

• muscles are composed of bundles of fibers (muscle cells) = fascicles

• muscle fibers are made of myofibrils

– myofibrils are made of thick & thin filaments

• myosin = thick filaments

• actin = thin filaments

– arranged in an overlapping pattern the gives striated look

– Myofibrils slide over each other when muscles contract• “sliding

filament theory” of muscle contraction

– myofibrils consist of repeating units called sarcomeres = the segment of myofibril that extends from one Z line to the next (Z lines are what the actin filaments attach to)

– striated muscles are created by I bands (the light part) and A bands (the dark part)

neuromuscular junction is where a muscle fiber joins a motor neuron

• the tips of the motor neuron contain neurotransmitters to communicate with the muscle fiber & cause it to contract

• synaptic cleft = the gap between the nerve endings & the muscle cells

• motor unit = a motor neuron + all of the muscle fibers it controls

SKELETAL MUSCLE CONTRACTION

• myosin has “cross bridges” which fit into binding sites on the actin filaments, pulling on them & causing them to slide over the myosin

• sliding filament

• detailed crossbridges

4 steps of muscle contraction:

1- myosin cross bridge attaches to the actin myofilament

2- working stroke: the myosin head pivots & bends as it pulls on the actin filament, sliding it toward the M line

3- as new ATP attaches to the myosin head, the cross bridge detaches

4- as ATP is split into ADP + P, cocking of the myosin occurs

SKELETAL MUSCLE CONTRACTION

• muscle contraction is initiated by a nerve impulse (action potential)

• requires acetylcholine, calcium ions, & ATP

– acetylcholine is a neurotransmitter

3 energy sources of ATP

• creatine phosphate = allows immediate regeneration of ATP

• cellular respiration to break down glucose

• glycogen breaks down into glucose for cellular respiration

• aerobic cell respiration takes place in the presence of oxygen – makes 36 ATP per molecule of glucose

• hemoglobin carries oxygen to the cells from the blood stream

• myoglobin temporarily stores oxygen in the muscles

• during strenuous exercise, muscle cells must switch to anaerobic respiration which causes lactic acid to accumulate & cause the “burn”

• creates an oxygen debt = the amount of oxygen it takes to revert the lactic acid into glucose + restoring ATP & creatine phosphate to their original levels

• anaerobic respiration makes only 2 ATP per molecule of glucose, but it does it quickly

Energy systems used during sports:

• Requiring a surge of energy but lasts only a few seconds:– Ex = weight lifting, diving, sprinting– uses ATP and CP stores

• On-and-off burstlike activities:– Ex = tennis, soccer, 100m swim– uses anaerobic lactic acid fermentation

• Prolonged activities:– Ex = jogging, running marathons– uses aerobic respiration

• muscle fatigue = when muscles lose their ability to contract even when stimulated, usually due to lactic acid accumulation

• muscle cramps = sustained involuntary muscle contraction

• heat production via muscle contraction is significant for maintaining body temperature / homeostasis

Effect of exercise on muscles:

• Muscle inactivity leads to weakness & muscle wasting = atrophy

Effect of exercise on muscles:

• Aerobic / endurance exercise (swimming, jogging, fast walking, biking) causes:– more efficient muscle metabolism – greater endurance, strength, resistance to fatigue– boosts overall body metabolism– more efficient neuromuscular coordination– Improves gastrointestinal mobility– enhances skeletal strength– Improves the delivery of oxygen & nutrients to all

body tissues via the CV & respiratory system

• Resistance exercise (weight lifting) causes:– Increased muscle bulk due to larger muscle fibers– more mitochondria, more myofilaments, more

glycogen storage capacity– more connective tissue between cells– significantly stronger muscles

• Cross training (alternating aerobic and anaerobic activities) promotes optimal health

MUSCULAR RESPONSES• threshold stimulus = the minimal stimulus

required to cause a muscle contraction

MUSCULAR RESPONSES• all-or-none response = skeletal muscle

fibers contract completely if they contract at all, not true for the whole muscle

MUSCULAR RESPONSES

• twitch = a single, brief, jerky contraction

• summation = a rapid series of stimuli “sums up” the contractions

• tetanus = sustained contraction with no relaxation

MUSCULAR RESPONSES• more muscle cells stimulated = a stronger

muscle contraction• recruitment = when more motor units are

recruited to respond to increasing intensity of stimulation

• summation and recruitment together can produce a sustained contraction of increasing strength

MUSCULAR RESPONSES• isotonic muscle contractions = muscles

shorten, movement occurs

• isometric muscle contractions = muscles stay the same length, no movement occurs; ex. pushing against a wall

MUSCULAR RESPONSES• rigor mortis = partial muscle contraction

that happens after death

SKELETAL MUSCLE ACTIONS

• movements depend on the type of joint the muscles are associated with & the way the muscles are attached on either side of the joint

• remember: muscles pull on bones which act as levers

SKELETAL MUSCLE ACTIONS

• origin = the end of a muscle attached to the bone that doesn’t move

• insertion = the end of the muscle attached to the bone that moves

• when muscles contract, the insertion is pulled toward the origin

SKELETAL MUSCLE ACTIONS

• prime mover = one muscle in a group that causes most of the movement

• synergist = muscles that assist the prime mover

• antagonist = causes movement opposite of the prime mover

• example: the bicep is the prime mover of elbow flexion, its antagonist is the tricep – the prime mover of elbow extension

MAJOR SKELETAL MUSCLES

• naming skeletal muscles: based on many sets of criteria– direction of the fibers

• rectus = straight, oblique = slanted

– relative size of the muscle• maximus = largest, minimus =

smallest, longus = long

MAJOR SKELETAL MUSCLES

– location of the muscle

• named for the bone such as temporalis or frontalis

– number of origins or heads

• biceps = 2, triceps = 3,

quadriceps = 4

– location of the muscle’s origin & insertion• sternocleidomastoid – sternum, clavicle,

mastoid process

– shape of the muscle• deltoid = triangle • trapezius = trapezoid

– action of the muscle• flexor, extensor, adductor

SUPERFICIAL MUSCLES OF THE HUMAN BODY

• muscles of facial expression:

– lie beneath the skin of the face & scalp, used to communicate feelings through facial expression

– includes the frontalis, orbicularis oculi, orbicularis oris, zygomaticus, platysma

SUPERFICIAL MUSCLES OF THE HUMAN BODY

• muscles of mastication:

– attach to the mandible, used for chewing

– includes the masseter & temporalis

SUPERFICIAL MUSCLES OF THE HUMAN BODY

• muscles that move the head:

– found in the neck and upper back

– includes the sternocleidomastoid, sternohyoid

SUPERFICIAL MUSCLES OF THE HUMAN BODY

• muscles that move the pectoral girdle:

– most connect the scapula to nearby bones

– includes the trapezius, serratus anterior, pectoralis minor

muscles that move the arm:

– these connect the humerus to various regions of the pectoral girdle, ribs, & vertebral column

– includes the pectoralis major, teres major, latissimus dorsi, deltoid, infraspinatus

muscles that move the forearm:

– these connect the radius & ulna to the pectoral girdle or humerus

– includes the biceps brachii, brachialis, brachioradialis, triceps brachii, supinator

SUPERFICIAL MUSCLES OF THE HUMAN BODY

• muscles that move the wrist, hand, & fingers:

– these muscles arise from the distal end of the humerus and from the radius & ulna

– includes the flexor carpi radialis, flexor carpi ulnaris, palmaris longus, extensor carpi radialis longus, extensor carpi ulnaris, and extensor digitorum

muscles of the abdominal wall:

– these muscles connect the rib cage and vertebral column to the pelvic girdle

– includes the external oblique, internal oblique, transverses abdominis, and rectus abdominis

SUPERFICIAL MUSCLES OF THE HUMAN BODY

• muscles of the pelvic outlet:

– these muscles form the floor of the pelvic cavity and fill the space within the pubic arch

– includes the bulbospongiosus and ischiocavernosus

muscles that move the thigh:

– these muscles attach to the femur and to some part of the pelvic girdle

– includes the iliopsoas, gluteus maximus, gluteus medius, gluteus minimus, tensor fasciae latae, adductor longus, adductor magnus, and gracilis

SUPERFICIAL MUSCLES OF THE HUMAN BODY

• muscles that move the leg:

– these muscles connect the tibia or fibula to the femur or pelvic girdle

– includes the biceps femoris, semitendinosis, semimembranosus, sartorius, and the quadriceps femoris group = rectus femoris, vastus lateralis, vastus medialis, vastus intermedius

SUPERFICIAL MUSCLES OF THE HUMAN BODY

• muscles that move the foot, ankle, & toes:

– these muscles attach the femur, tibia, and fibula to the bones of the foot

– includes the tibialis anterior, extensor digitorum longus, gastrocnemius, soleus, and peroneus longus