Muscular System

three basic muscle types in the body

skeletal, cardiac, smooth

characteristics of skeletal muscle

most are attached by tendons to bones

cells are multinucleated

striated — have visible banding

voluntary — subject to conscious control

functions of skeletal muscles

• supports body to remain upright

• provides movement (bones)

• provides pressure (blood/lymph)

• protects internal organs/bones

• stabilizes joints

connective tissue of skeletal muscle

cells are surrounded and bundled by connective tissue

endomysium

encloses a single muscle fiber

perimysium

wraps around a fascicle (bundle) of muscle fibers

epimysium

covers the entire skeletal muscle

fascia

on the outside of the epimysium

muscle

composed of bundles of skeletal muscle fibers called fascicles

fascicles

surrounded by connective tissue as are the muscle fibers composing them

muscle fiber

each is a cell with a plasma membrane, cytoplasm, and an endoplasmic reticulum

sarcolemma

plasma membrane

sarcoplasm

cytoplasm

sarcoplasmic reticulum

• endoplasmic reticulum

• stores and releases Ca

• surrounds the myofibril

H zone

bare zone that lacks actin filaments

myofibrils

• long organelles inside muscle cell

• aligned to give distinct bands

I band

• light band

• contains only thin filaments

A band

• dark band

• contains the entire length of thick filaments

sarcomere

contractile unit of a muscle fiber

myosin filaments

thick

actin filaments

thin

sliding filament model of muscle contraction

• muscles stimulated by CNS

• impulses travel down T-tubules releasing Ca ions from the SR

• muscle contracts because the sarcomeres shorten

• the sarcomere shortens because the actin filaments slide past the myosin filaments approaching each other from the ends of the sarcomere

• the i-band shortens while the z-bands move inward as the h-zone disappears

• atp supplies the energy for the myosin filaments to do work for the muscle contraction

excitability (responsiveness or irritability)

ability to receive and respond to a stimulus

contractility

ability to shorten when adequate stimulus is received

exentsibility

ability of muscle cells to be stretched

elasticity

ability to recoil and resume resting length after stretching

motor unit

one motor neuron and all the skeletal muscle cells stimulated by that neuron

neuromuscular junction

association site of axon terminal of the motor neuron and muscle

synaptic cleft

• gap between nerve and muscle

• area between nerve and muscle is filled with interstitial fluid

neurotransmitter

chemical released by nerve upon arrival of nerve impulse

acetylcholine

neurotransmitter for skeletal muscles

all or none law

all muscle fibers in a motor unit are stimulated at once so that they all contract or don’t

muscle twitch

when motor unit is stimulated by infrequent electric impulses a single contraction takes place lasting a fraction of a second

what is achieved when maximal contraction occurs (a sustained contraction)

tetanus

muscle tone

when some motor units are always contracted but not enough to cause movement

glycogen and fat

sources of energy stored in muscle

blood glucose and plasma a fatty acids

sources of energy derived from blood

three stages of muscle twitch

• latent period

• contraction period

• relaxation period

latent period

period of time between CNS stimulation and the beginning of muscle contraction

contraction period

muscle is shortening

relaxation period

muscle is returning to its original length

creatine PO4 pathway

• fastest and simplest way for muscles to produce ATP for energy to contraction of muscles

• formed during muscle resting and storage is limited

fermentation

produces ATP by breaking down glucose producing lactate (glycogen → glucose)

lactate formation

results in muscle aches and fatigue

celllular respiration

more likely to s upply energy when exercise is sub-maximal in intensity — not an immediate source

concentric contraction of muscles

muscles shorten during contraction

eccentric contraction of muscles

muscles lengthen during contractions (negative phase of the lift)

five rules of skeletal muscles

1. with a few exceptions, all skeletal muscles cross at least one joint

2. typically, the bulk of a skeletal muscle lies proxximal to the joint crossed

3. all skeletal musclces have at least two attachments: origin and insertion

4. skeletal muscles can only pull

5. during contraction, a skeletal muscle insertion moves towards origin

origin

attachment to a moveable bone

insertion

attachment to an immovable bone

flexion

• decreases the angle of the joint

• brings two bones closer together

• hinge joints (knee and elbow)

extension

• opposite of flexion

• increases angle between two bones

rotation

• movement of bone around its longitudinal axis

• ball and socket joints

abduction

movement of limb away from midline

adduction

movement of limb toward midline

circumduction

• combo of flexion, extension, abduction, and adduction

• ball and socket

dorsiflexion

lifting the foot so that the superior surface approaches the shin

plantar flexion

depressing the foot

inversion

turn sole of foot medially

eversion

turn sole of foot laterally

supination

forearm rotates laterally so palm faces anteriorly

pronation

forearm rotates medially so palm faces posteriorly

opposition

move thumb to touch the tips of other fingers on the same hand

prime mover/agonist

muscle with the major responsibility for a certain movement

antagonist

muscle that opposes or reverses a prime mover

synergist

muscle that aids a prime mover in a movement nd helps prevent rotation

fixator

stabilizes the origin of a prime mover

cardiac muscles

• striations, one nucleus, branching cells

• joined to another muscle cell at an intercalated disc

• involuntary and found only in the heart

smooth muscle

• lack striations, spindle-shaped cells, single nucleus

• involuntary, found in the walls of hollow organs

how do skeletal muscles fibers differ?

power, speed and duration of muscle contraction generated

power

related to the diameter of a muscle fiber

fast twitch fibers

• fast rate of AP propagation along the sarcolemma

• quick on their Ca++ release and re-uptake by the SR

• stronger contraction

• initiate contraction more quickly

• produce a contraction of shorter duration

glycolytic fibers

• specialize in providing ATP more rapidly through glycolysis

• less extensive capillary network, few mitochondria, smaller amounts of myoglobin → white fibers

• fatigue easily

slow oxidative fibers (type I)

half the diameter, slow myosin ATPase, slower, less powerful contractions

fast-oxidative fibers (Type II)

intermediate size, fast myosin ATPase, fast, powerful contractions primarily though aerobic cellular respiration

fast glycolytic fibers (Type IIB)

fast anaerobic fibers, most prevalent muscle fiber type, largest in diameter, contains fast myosin ATPase, provides both power and speed, can only contract for short bursts, fibers appear white because of the lack of myoglobin and mitochondria

tendon

• ends of a muscle

• thick, cord-like structures that attach muscle to boe, muscle to skin or muscle tomuscle

aponeurosis

thin flattened sheet of tendon

sphincter

concentrically arranged muscle fascicles around an opening or recess

parallel muscles

has a central body, contracts = shortens

convergent muscle

widespread muscle fascicles over a broad area that converge on a common attachment site, pectoralis major

pennate muscles

the fascicles exhibit the same angle with respect to their tendon

unipennate muscle

all of the muscle fascicles are on the same side of the tendon, extensor digitorum

bipennate mscle

fascicles on both sides of the tendon, interosseus muscles on both the palmar and dorsal sides of the metacarpalsm

multipennate muscles

have branches of tendon within the muscle and fascicles arranged on both sides of each tendon branch, triangular deltoid

facial nerve

7th cranial nerve (CN VII)

epicranius

composed of the occipitofrontalis muscle and the epicranial aponeurosis, raises eyebrow and wrinkles skin of forehead

corrugator supercilia

draws eyebrows together

orbicularis oculi

closes eyes

levator palpebrae superioris

elevates the eye brows when eyes open

nasalis muscle

elevates the corners of the nostrils

procerus muscle

wrinkling of the nose

orbicularis oris

closes the mouth (kisser)

depressor labii inferioris

pulls lower lip inferiorly

depressor anguli oris

frown muscle

Levator labii superioris

Pulls the upper lip superiorly

Levator anguli oris

Pulls the corners of the mouth superiorly and laterally

Zygomaticus major/Zygomaticus minor

Work with the levator aguli oris muscle to smile

Risorius

Pulls the corner of the lips laterally (closed mouth smile)

Mentalis

Protrudes the lower lip