The Muscular System

smooth muscle

Fiber appearance: no striations, spindle-shaped, 1 nucleus
Involuntary
Location: walls of visceral organs and blood vessels

Anatomy of a muscle

large mucscle--> small muscle--> fascicle--> myofiber (cell)--> myofibril--> myofilaments

What are skeletal muscle cells specifically called?

muscle fibers (myofibers)

Layers of fascia

-epimysium
-perimysium
-endomysium

perimysium

covers each fascicle

ATP

energy storage compound

neuromuscular junction

where motor neuron meets muscle fiber

calcium

ion stored in sacs

Structure of the sarcomere. What causes the striations?

Arrangement of protein filaments in myofibrils causes striations
Border: Z line to Z line
Myosin overlapped with part of actin: dark band
Actin not overlapped with myosin: white band

Difference between neuromuscular junction and motor unit

Motor unit: one motor neuron stimulating many muscle fibers
Neuromuscular junction: one motor neuron, one fiber

Steps that occur when a nerve impulse reaches a muscle and how muscle contraction occurs

1. impulse travels down motor neuron--> NM junction
2. neuron releases acetylcholine (ACh)
3. ACh travels across synaptic cleft--> plate of fiber--> sarcolemma T system--> SR
4. Sarcoplasmic reticulum (SR) releases Ca^+2
5. Ca^+2 stimulates myofibrils
6. Crossbridges form/ATP activated: filaments slide, causing sarcomere to shorten: contraction

How is ATP supplied to muscles (3 ways)? What is oxygen debt?

1. cellular respiration
2. creatine phosphate breakdown
3. fermentation: occurs when oxygen is in short supply (oxygen debt); lactic acid builds up

What is meant by "all or none response"?

muscle fibers contract completely or not at all

summation

second stimulus before 1st cycle is complete (no rest)

tetany

sustained contraction

What causes muscle "tone"?

small number fibers stay contracted

origin

the fixed, immovable end of muscle attachment

example of muscle named for size

gluteus maximus

example of muscle named for action

flexor digitorium

electromyography

recording of electrical events in contraction

myotonia

muscle doesn't relax after contraction

What is meant by "cardiac markers"?

protein elevations that follow a heart attack

clinical term for a heart attack

myocardial infarction

3 types of muscle tissue

-skeletal
-cardiac
-smooth

skeletal muscle

Fiber appearance: striated, cylindrical, multinucleated
Voluntary
Location: attached to skeleton or skin

cardiac muscle

Fiber appearance: striated, cylindrical, 1 nucleus, fibers interlock at intercalated disks
Involuntary
Location: heart walls

Four functions of skeletal muscle

1. Movement of body parts
2. Support
3. Heat production
4. Tendons of muscles stabilize joints

fascicle

bundle of muscle fibers

Why are muscle cells referred to as "fibers"?

They are elongated

endomysium

covers each individual myofiber

epimysium

covers the entire skeletal muscle

sarcolemma

plasma membrane of a muscle fiber

T system

tubule composing transverse system

myosin

thick myofilament

actin

thin myofilament

myofibril

cylindrical cords composed of protein filaments
-a series of sarcomeres are its units

sarcomere

the working unit of skeletal muscle fiber

Sliding filament theory

Crossbridges form between actin and myosin--> myosin "pulls" actin filaments together--> sarcomere shortens in length: contraction

Three requirements for muscle contraction

1. Innervation
2. Ca^+2
3. ATP

Innervation

nerve stimulus

What may happen after depletion of ATP?

fatigue

twitch

single stimulus-contraction-relaxation sequence in a muscle fiber

hypertrophy

increase in muscle size
Ex: benefit of exercise

atrophy

decrease in muscle size due to nerve damage, broken bones, etc
Ex: bedridden patients; muscle not used

insertion

the movable end of muscle attachment

group action

prime movers and synergists working together

prime mover

major contracting muscle in a body action

synergist

muscle that assists the major contracting muscle in a body action

antagonist

a skeletal muscle that can produce the opposite motion of the prime mover and that relaxes when the prime mover contracts
-does not contract during a specific body action

example of muscle named for shape

deltoid (triangle)

example of muscle named for direction of fibers

rectus femoris (straight)

example of muscle named for location

tibialis anterior

example of muscle named for number of attachments

triceps brachii

charleyhorse

muscle cramp, especially calf; often occurs at night

muscular dystrophy

genetic, degenerative disease of muscle

myalgia

muscle aches/pain

myasthenia gravis

decreased ACh--> impairs nerve impulses at NM junction--> weakness, muscle fatigue

myoglobin

protein in muscle tissue that carries oxygen
-elevated in blood/urine following muscle trauma

myoma

a benign tumor of muscle tissue

myositis

inflammation of muscle tissue

What 2 cardiac markers are most often used to help diagnose heart attacks?

CK-MB and troponin