50 Fun Facts About Muscular System

How many distinct types of muscle tissue does the human body have?

Skeletal, cardiac and smooth, and only the first is under voluntary control.

Roughly how many muscles does an adult human body contain?

The exact count varies with the method used to count them.

Which organ system joins with the muscular system to form the musculoskeletal system?

Tendons connect the two, letting muscles pull on bones to create movement.

Which muscle type can work completely on its own, without the nervous system?

Its rhythm is set by the sinus node, which the autonomic nervous system only influences.

Which muscle type is non-striated?

It lines organs and vessels and contracts slowly but strongly.

What are the basic building blocks of striated muscle tissue called?

Myofibrils are made of sarcomeres, and a contraction shortens every sarcomere at once.

Which theory best explains how muscle fibers contract?

Actin and myosin filaments overlap and slide toward each other within the sarcomere.

Which two proteins slide past each other to shorten a muscle?

Myosin forms the thick filaments and actin the thin ones.

Which molecule powers the swivelling of the myosin heads during contraction?

Used ATP becomes ADP, which muscles must constantly recharge.

Which ion is released from the sarcoplasmic reticulum to trigger contraction?

It uncovers the binding sites on actin, then gets pumped back into storage when the muscle relaxes.

What fast-acting stored chemical helps regenerate ADP back into ATP in muscle?

Its stores last only about ten seconds of all-out effort but refill within five minutes.

What neurotransmitter is released at the neuromuscular junction to fire a skeletal muscle?

It binds to receptors on the muscle cell and sets off the electrical changes that release calcium.

A fault at the neuromuscular junction causes the prolonged contractions of which disease?

A loss of function at the same junction produces paralysis instead.

A nerve cell plus all the muscle fibers it controls is called what?

Fine movements use few motor units; powerful ones recruit many.

Which part of the brain mostly coordinates motor units for fluid, unconscious movement?

It is why you can drive a car without thinking about each muscle.

What connects a muscle to a bone?

Ligaments, by contrast, connect bone to bone.

Roughly what share of a healthy young adult's body weight is skeletal muscle?

Men average about 61% more skeletal muscle than women in Western populations.

The word muscle comes from the Latin musculus, meaning what?

A flexed biceps was thought to look like a mouse's back; Greek mys also means both.

What is the striped middle layer of the heart wall called?

The epicardium sits outside it and the endocardium inside.

Heart muscle cells connect at branching junctions known as what?

Skeletal muscle is arranged in regular parallel bundles instead.

Which tiny skin muscles make body hair stand up?

They are the reason for goosebumps.

Which fiber class is slow-twitch, red and rich in myoglobin and mitochondria?

It sustains aerobic activity, which is why endurance athletes have more of it.

Which is the fastest-contracting muscle fiber class found in humans?

Some older books confusingly called it type IIB, a fiber humans do not actually express.

Why do rodents have such pale flesh?

Type IIb is anaerobic, glycolytic and poor in myoglobin.

Muscle tissue is roughly how much denser than fat?

Muscle is about 1.06 kg per liter against roughly 0.92 for fat.

About what share of the soleus muscle is slow-twitch type I fiber?

The eye's orbicularis oculi is only about 15% type I, and the quadriceps about 52%.

Chimpanzee muscle is about 67% fast-twitch; how much more power does it produce than human muscle?

Humans win instead at aerobic tasks like walking long distances.

About how many muscle fibers does a young adult male's biceps contain?

A single 10 cm fiber in it can hold as many as 3,000 nuclei.

What is the cell membrane of a muscle fiber called?

The cytoplasm inside is the sarcoplasm, and the nuclei are pressed flat against the membrane.

Which dormant muscle stem population under the basement membrane supplies new nuclei for repair?

Exercise or injury activates them to supply new nuclei for growth and repair.

Why does an adult have fewer muscle cells than a newborn?

Exercised fibers grow by adding myofibrils rather than by making new cells.

What does the word deltoid mean in a muscle name?

Quadratus means four-sided, teres round and serratus saw-toothed.

A muscle with three heads is called what?

Biceps means two heads and quadriceps four.

What does an adductor muscle do?

Abductors move away; flexors decrease a joint angle and extensors increase it.

In muscle naming, what does the word latissimus mean?

Longissimus is longest, maximus largest and vastus huge.

Which stretch receptors sit in the fleshy belly, not at the junction with bone?

Golgi tendon organs sit at the muscle-tendon junction and sense tension instead.

What name is given to the connective tissue wrapping each individual muscle fiber?

Perimysium wraps each fascicle and epimysium the whole muscle; together they are the mysia.

Roughly what share of the body's heat comes from muscle contraction?

Shivering is the body deliberately contracting muscles to make heat in extreme cold.

Signalling molecules secreted by muscle after contraction are called what?

Interleukin 6 is the most studied; they are thought to carry many of exercise's health benefits.

Which regulatory protein changes shape when it binds the trigger ion, letting contraction start?

That shift moves tropomyosin off the myosin-binding sites on actin.

What is the smallest skeletal muscle in the human body?

Just over a millimeter long, it steadies the stapes, the body's smallest bone, in the middle ear.

What is the single largest muscle in the human body?

It is the main extensor of the hip and shapes the buttocks.

Which thigh muscle, once called the tailor's muscle, is the longest in the body?

It runs as a thin strap down the front of the thigh.

Which chewing muscle is the most superficial and one of the strongest?

In toothed whales it has been repurposed into the fatty melon used for echolocation.

Which sheet of skeletal muscle is the most important muscle of breathing?

It has more mitochondria and capillaries than any other skeletal muscle.

Why is the right half of the breathing muscle slightly higher than the left?

The diaphragm is an upward-curved, C-shaped dome of muscle and fibrous tissue.

Besides bending the elbow, what does the biceps do to the forearm?

Both of its heads arise on the scapula and insert on the radial tuberosity.

Which heel cord is the thickest of its kind in the human body?

It ties the calf muscles to the heel bone to point the foot.

Muscular dystrophy, a group of more than 30 progressive muscle-wasting disorders, is caused by what?

Duchenne and Becker are among the most common types.

Myositis and myasthenia gravis are the two main muscle conditions of what kind?

Polymyositis and dermatomyositis are forms of myositis.