What is a muscle?
A muscle is an element of our bodies that allows us to move with our bodies. All the muscles in the human body are made up of fleshy tissue attached to our skeleton. For example, if you move your arm, you can feel the muscles moving underneath your skin.
The human muscles are the pink parts shown below:
While we can control some of our muscles (voluntarily), others, like our heart, do their jobs without us needing to think about them at all (involuntary).
What do the major muscles of the human body do?
All muscles allow us to access parts of our bodies – this includes the limbs like the arms and legs, as well as the face, which makes different expressions using smaller muscles.
Keep reading to learn how many muscles are in the human body!
Even when we are sleeping or resting and all the muscles in our bodies are relaxed, some muscle fibers will contract so that we can breathe or move our eyes.
Every muscle comprises a pair; one side will contract to help part of your body move one way and release to let your body part move the other way. So, for example, when you lift your forearm, you use your biceps, but when you move it back down, it is your triceps at work.
Look at the illustration below to see how the two muscles work together to move the forearm.
Muscles can also contract or relax as part of a reflex or an essential part of their process – like the heart.
Types of muscles
All the muscles in the human body belong to one of the following three groups:
- Skeletal muscles: muscles that are attached to the bone via tendons. These muscles are vital for movement.
- Smooth muscles: these muscles, also known as visceral muscles, are found in different organ systems, such as the digestive and respiratory systems.
- Cardiac muscle: a muscle found only in the heart. This muscle allows the heart to beat.
The Muscle Types – a closer look
Skeletal muscles
There are over 650 skeletal muscles in the human body, accounting for 40% of overall body weight. Generally, lean muscles are grouped into opposing pairs, such as the biceps and triceps found on the front and back of the upper arm, respectively. Skeletal muscles are voluntary muscles, meaning we have conscious control over them.
Skeletal muscles enable us to move and perform daily activities. They play an essential role in the mechanics of the respiratory system, posture and balance, and they protect the vital organs in our body.
A simple way to look at all of the skeletal muscles in the human body is to divide them up based on what part of the body they serve.
Muscles of the head and neck
Have you ever noticed that you can contort your face into different shapes? This is because our head and neck contain a bunch of skeletal muscles, and skeletal muscles can be controlled.
The skeletal muscles located in the face, head, and neck include:
- Zygomaticus: This human muscle allows us to pull different facial expressions and lift the corners of our mouths. Without this muscle, we wouldn’t be able to smile!
- Masseter: The masseter muscle is one you may have heard of before. This important muscle is located in the jaw and is used to close the mouth and chew food.
- Eye (extraocular) muscles: The eye muscles are a group of muscles that control the movements of the eyes. They also allow us to open and close our eyelids.
- Muscles of the tongue: This is another group of muscles that help us to life and lower our tongues. This group of muscles also assists us in moving our tongues in and out of our mouths.
- Sternocleidomastoid: This skeletal muscle may be difficult to pronounce, but it plays a major role in allowing us to rotate and tilt our heads to the side. This muscle is also involved in listing the head forward.
Muscles of the trunk
Some examples of the skeletal muscles located in the torso and abdomen are:
- Erector spinae: This is a group of muscles that support the spine and allow our spines to bend, arch, and twist.
- Oblique muscles: This group of muscles includes both the external and internal obliques. These human muscles aid us in bending to the side and twisting at the waist.
- Intercostal muscles: The intercostal muscles can be found all around the ribs. Their job is to assist us with inhaling and exhaling.
- Diaphragm: The diaphragm is the large skeletal muscle that separates the torso from the abdomen. This muscle helps us breathe by contracting and relaxing when we exhale.
- Levator ani: This group of skeletal muscles supports all of the organs and tissues around the pelvis. These muscles play a key role in helping us carry out different bowel movements.
Muscles of the upper extremities
The skeletal muscles located in the upper extremities are responsible for moving our shoulders, arms, wrists, and hands. Some examples of these muscles are as follows:
- Trapezius: The trapezius muscle is multi-purpose. It allows us to tilt our heads back, raise our shoulders, and move our shoulder blades together.
- Pectoralis major: This skeletal muscle is located in the upper chest area and is used to help our arms perform rotational, vertical, and lateral movements.
- Deltoid: The function of the deltoid muscle is to lift or rotate the arm at the shoulder.
- Biceps brachii: This skeletal muscle allows us to flex our forearms and bend our elbows.
- Triceps brachii: The triceps brachii skeletal muscles extend the forearm and straighten the elbow.
Muscles of the lower extremities
The lower extremities’ skeletal muscles involve all the muscles that move our legs and feet. Some examples of these muscles include:
- Gluteus maximus: The gluteus maximus is a skeletal muscle you have likely heard of before. This muscle is involved in the movement of our hips and thighs. It plays a key role in helping us maintain good posture, stand up from a sitting position, and go up a set of stairs.
- Quadriceps: A quadriceps is a group of muscles found at the front of the thigh. These muscles all work together to straighten the leg at the knee.
- Hamstrings: The hamstrings are a group of skeletal muscles in the back of our legs. The function of the hamstring muscles is to help us extend our thighs and to bend our legs at the knee.
- Tibialis anterior: This is the skeletal muscle we use to lift our feet off the ground.
- Soleus: The soleus muscle, on the other hand, is the skeletal muscle we use to lower our feet back to the ground. This human muscle is also super useful for helping us maintain good posture while walking.
Shapes of skeletal muscles
So, we’ve discussed what skeletal muscles are and how they work, but what exactly do they look like? Well, there are four main shapes that skeletal muscles can take:
- Spindle – Skeletal muscles shaped like a spindle are the widest in the middle section and taper off at both ends. An example of a spindle-shaped skeletal muscle is the biceps.
- Flat – Flat-shaped skeletal muscles are, as the name suggests, very balanced in their appearance. The diaphragm is an example of a flat-shaped skeletal muscle.
- Triangular – Skeletal muscles with a triangular shape are wider at the bottom and taper at the top. For example, the deltoid muscles are triangular-shaped skeletal muscles.
- Circular – Circular-shaped skeletal muscles have a ring-like appearance. Strengths of this shape include the muscles surrounding the mouth and pupils.
The neuromuscular system
The neuromuscular system comprises the brain, nerve, and skeletal muscles, all working together to spark a movement within the body. It takes between 50 and 200 branches of specialized nerve cells, called motor neurons, to serve just one muscle. These motor neurons connect directly to the skeletal muscle. The tip of each motor neuron, called a presynaptic terminal, combines with the power known as the neuromuscular junction.
Smooth muscles
Smooth muscles are involuntary muscles since smooth muscle motion happens without conscious awareness.
One way of organizing the different smooth, or visceral muscles in the body, is based on the system that they’re found in. For example, smooth muscles are located in the following methods in the body:
- Digestive system: The smooth muscles in the digestive system contract to help food move through your digestive tract.
- Respiratory system: The smooth muscle tissue in this system allows our airways to widen and narrow.
- Cardiovascular system: Smooth muscle is found in the walls of our blood vessels and helps with blood flow. It also plays a role in regulating our blood pressure.
- Renal system: The smooth muscle in the renal system helps regulate the bladder’s urine flow.
- Reproductive system: Smooth muscle plays different roles in the male and female reproductive systems.
Cardiac Muscle
We have just one cardiac muscle located in the heart. The cardiac muscle pumps blood around the body and stimulates its contractions, known as our heartbeat. Signals from the nervous system control the rate of contraction.
The cardiac muscle is involuntary.
What are muscles made of?
Muscles in the human body are made of thousands of tiny fibers, which all lie in the same orientation. They are grouped, and each group is filled with even more groups of smaller muscle fibers called fibrils. The smallest of these are almost microscopic, but they give muscles their pulling power.
How many muscles are in the human body?
If you’ve ever wondered how many muscles are in the human body, it’s surprisingly hard to tell! Okay, so it’s not the answer you were looking for, but it can be not easy to know what to count and not, and some anatomists don’t always agree on what’s countable.
Some muscle tissue can’t be separated into countable muscles. Many muscles, like the four-part quadriceps, are normally split into different parts that, depending on your viewpoint, may or may not count as different muscles. Some people’s strengths are more divided than others!
Okay, but really, how many muscles are in the human body? While it’s impossible to give you an exact number, there are around 700 named skeletal muscles.
If we include smooth muscles, however, the job is impossible. This is because smooth muscle blends with other smooth muscles and even exists at a microscopic level. So it’s impossible to say where one smooth muscle stops and the next begins.
The cardiac muscle is nice and simple, though, with just one to count!
Fun facts about muscles
The muscular system is what lets your body move. Muscles control all your little and big movements, from smiling. Some of these muscles you can control, and some work without having to think about it.
Here are a few great fun facts about muscles in your body:
- Forces are split into three groups: smooth (involuntary muscles in your organs), cardiac (the muscles that help your heart), and skeletal (attached to the bones and help with everyday tasks)
- Your body contains more than 600 muscles: the muscles in your arms and legs and those that keep your heart beating or help you digest food.
- The smallest muscles are: In your ear! It is called the stapedius and connects your eardrum to your ear.
- The strongest muscle is your jaw! The Masseter muscle in your jaw can close with a force as great as 100 kg.
- Your heart works the hardest: it is busy pumping 2500 gallons of blood around your body daily. The heart beats approximately 100,000 times a day!
- Your eyes are the busiest: they constantly move and adjust as you read, watch TV or look around.
- Muscles account for 40% of our total body weight.
- It takes 17 muscles in the face for us to smile and 43 muscles to frown!
- Muscle memory is created by practicing an action over and over again. When we repeat an action, our muscles fine-tune themselves to make themselves more precise at that action.
Muscular system vocabulary
- Muscle – a band or bundle of fibrous tissue that contracts or tenses, allowing for movement or maintaining a position.
- Joints – where two bones join together (attach) to allow movement.
- Involuntary muscles – muscles that contract or move without conscious control (smooth and cardiac).
- Cardiac muscle – a specialized type of muscle tissue that forms the heart.
- Skeletal muscles – muscles that are attached to the bone via tendons. These muscles are vital for movement.
- Ligament – the tissue that connects two bones to form a joint.
- Tendon – tissue that attaches a muscle to other body parts, usually bones.
- Smooth muscles – muscles found in different organ systems, such as the digestive and respiratory systems.
- Voluntary muscle – a muscle we have conscious control over moving (skeletal muscles).
- Contract – when the muscle bunches up, shortening it and pulling on the bone it is attached to.
- Protein – the basic material of tissue structure. They are the most important component of skeletal muscles.
