Category Zoology

Skeletal muscles come in many shapes and sizes, with each muscle adapted for its position in the body and the job it does.

Quadrate muscles

These are rectangular hard-working muscles. Quadrate muscles are stabilizers along with whatever other function they perform.  The rhomboids are a quadrate muscle. While they work to retract the scapula they also stabilize the shoulder blade onto the trunk.

Fusiform muscles

These powerful muscles, such as the biceps, usually bend or straighten a limb. Sometimes, included in the parallel muscle group, these muscles are more spindle-shaped, with the muscle belly being wider than the origin and insertion. Examples are, Biceps Brachii and Psoas major.

Circular muscles

These muscles control body openings, such as the mouth or bladder. These muscles appear circular in shape and are normally sphincter muscles which surround an opening such as the mouth, surrounded by Obicularis Oris and Obicularis Oculi surrounding the eyes.

Triangular muscles

This muscle is narrow at one end and broad at the other. This allows a range of movement, such as at the shoulder.

Strap muscles

These are long muscles that are not especially strong but have good endurance. The infrahyoid muscles, or strap muscles, are a group of four pairs of muscles in the anterior (frontal) part of the neck. The four infrahyoid muscles are: the sternohyoid, sternothyroid, thyrohyoid and omohyoid muscles.

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This rear view of the deep muscles shows skeletal muscles from the head to the feet. They hold the head and back upright, keep the shoulders steady, pull the arms back, straighten the thighs, bend the knees, and point the toes down.

Occipitofrontalis

This muscle stretches from the frontal bone to the occipital bone at the back of the skull. Occipitofrontalis is a long and wide muscle of the scalp, spanning from the eyebrows to the superior nuchal lines of occipital bones. Together with temporoparietalis, it comprises the epicranial group of the muscles of facial expression.

Rhomboid muscles

These diamond-shaped muscles pull the shoulders back towards the spine. It helps connect the shoulder blades to the rib cage and spine. It also helps you maintain good posture.

Rhomboid pain is felt under the neck between the shoulder blades and spine. It’s sometimes referred to as shoulder blade pain or upper back pain.

Infraspinatus

This muscle helps to stablilize the shoulder joint and rotate the arm outwards.  It arises mostly from the infraspinous fossa of scapula, and connects it to the proximal humerus. 

Serratus anterior

This muscle helps to stabilize the shoulder blade. The serratus anterior muscle is a fan-shaped muscle at the lateral wall of the thorax. Its main part lies deep under the scapula and the pectoral muscles. It is easy to palpate between the pectoralis major and latissimus dorsi muscles. In athletic bodies the muscle may be even visible to the naked eye along the ribs underneath the axilla.

Serratus posterior inferior

This muscle has a jagged edge, which attaches to the ribs. The serratus posterior muscles extend obliquely from the vertebral column to the rib cage. The main function of these muscles is to facilitate the act of respiration; the serratus posterior superior muscle elevates the ribs, while the serratus posterior inferior muscle depresses the ribs. These actions are particularly important in forced respiration.

Medial head of triceps brachii

This deep part of the triceps brachii muscle straightens the elbow. The medial head of the Triceps brachii arises from inferior two thirds of humerus to insert, along with the other two heads of the triceps, on the olecranon of the ulna.

Erector spinae

This muscle group supports the spine. They extend on either side of the vertebral column, between the base of the cranium superiorly and pelvis inferiorly. 

Transverses abdominis

This helps to stabilize the pelvis and lower back when moving. Along with the external abdominal oblique and the internal abdominal oblique, it comprises the lateral abdominal muscles. Combined with the two anterior abdominal muscles (rectus abdominis and pyramidalis), these muscles make up the anterolateral abdominal wall.

Extensor carpi ulnaris

This muscle helps to straighten the wrist. This muscle belongs to the superficial forearm extensor group, along with anconeus, brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum and extensor digiti minimi muscles.

Gluetus medius

A pair of muscles keeps the pelvis level when you are walking. Gluteus medius is a large fan-shaped muscle located in the posterior hip, extending from the ilium to the proximal femur. Together with the gluteus maximus, gluteus minimus and tensor fasciae latae muscles, it belongs to the muscles of the gluteal region.

Adductor compartment of the thigh

The adductor magnus is the largest muscle in the medial compartment. It lies posteriorly to the other muscles.

Functionally, the muscle can be divided into two parts; the adductor part, and the hamstring part.

Semimemvranosus

This muscle is one of the hamstrings, which bend the knee. Semimembranosus is one of four posterior thigh muscles that are responsible for extending the hip. The other three muscles that belong to the hip extensor group are semitendinosus, biceps femoris and gluteus maximus. 

Popliteus

This muscle helps with bending the knee. The popliteus muscle is a small muscle that forms the floor of the popliteal fossa. It belongs to the deep posterior leg muscles, along with tibialis posterior, flexor digitorum longus and flexor hallucis longus.

Flexor hallucis longus

This muscle bends the big toe. Flexor hallucis longus muscle is a powerful muscle that comprises the deep layer of the posterior compartment of the leg. It belongs to a group called the deep flexors of the calf, which also include popliteus, flexor digitorum longus and tibialis posterior muscles.

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There are three types of muscle in the body. Bones are covered mostly in skeletal muscle, which creates movement by pulling on the bones. Smooth muscle keeps the digestive and other systems moving, while cardiac muscle causes the heart to beat non-stop.

Skeletal muscle

Found in the arms and legs, the long thread-like fibres of skeletal muscles shrink and shorten to move the bones. These are voluntary muscles, which means that we decide to move them.

Smooth muscle

Packed together in layered sheets, smooth muscle lines the walls of the digestive system, the airways, and the bladder. These muscles work automatically, to keep, vital body functions working.

Cardiac muscle

The walls of the heart are formed by cardiac muscle. This must contract continually to keep the heart beating. Cardiac muscle never gets tired, unlike other types of muscle.

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This front view of the skeleton shows the body’s deepest layer of skeletal muscles. Skeletal muscles in the back and neck work to keep the body upright, while those in the arms and legs are used for walking, running, and all kinds of other physical activities.

Sternothyroid

This strap-like muscle at the front of the neck the larynx down.  It is a part of a group of muscles called the infrahyoid muscles. There are four such muscles that are grouped into superficial and deep layers.

Pectoralis minor

This muscle helps to stabilize the shoulder blade when the arm moves. It is one of the anterior axioappendicular (thoracoappendicular) muscles, together with the pectoralis major, subclavius and serratus anterior.

Together with other muscles of the region it produces various movements of the scapula and can be used as an accessory muscle of respiration.

Brachialis

The brachialis helps to bend the elbow. It is fusiform in shape and located in the anterior (flexor) compartment of the arm, deep to the biceps brachii. The brachialis is a broad muscle, with its broadest part located in the middle rather than at either of its extremities.

Intercostal muscles

These muscles between the ribs help with breathing by raising the ribs up and out. The muscles are broken down into three layers, and are primarily used to assist with the breathing process. The three layers are: external intercostal muscles, internal intercostal muscles, and the innermost intercostal muscles.

Posterior rectus sheath

This tissue is formed by the tendons of abdominal muscle. It is an extension of the tendons of the external abdominal oblique, internal abdominal oblique, and transversus abdominis muscles. 

Transversus abdominis

This muscle helps to stabilize the pelvis and lower back when moving. Along with the external abdominal oblique and the internal abdominal oblique, it comprises the lateral abdominal muscles. Combined with the two anterior abdominal muscles (rectus abdominis and pyramidalis), these muscles make up the anterolateral abdominal wall.

Flexor digitorum profundus

This muscle helps to bend the fingers. Flexor digitorum profundus is a fusiform muscle located deep within the anterior (flexor) compartment of the forearm. Along with the flexor pollicis longus and pronator quadratus muscles, it comprises the deep flexor compartment of the forearm.

Gluteus medius

This muscle moves the thigh outwards. Together with the gluteus maximus, gluteus minimus and tensor fasciae latae muscles, it belongs to the muscles of the gluteal region.

Pectineus

This muscle helps to lift the thigh. Fascial compartments of the thigh muscles are specific in that each of them is innervated by a particular nerve. Due to having dual innervation, pectineus is one of a few muscles classified into two compartments at the same time; anterior and medial. The others being adductor longus and adductor magnus.

Adductor compartment of thigh

These muscles bring the thighs together. The adductor magnus is the largest muscle in the medial compartment. It lies posteriorly to the other muscles.

Functionally, the muscle can be divided into two parts; the adductor part, and the hamstring part.

Vastus intermedius

This is one of the four parts of the strong quadriceps muscle at the front of the thigh. Vastus Intermedius is located centrally, underneath Rectus femoris in the anterior compartment of the thigh and on each side of it: Vastus medialis and Vastus Lateralis respectively. It is one of the four muscles that form the quadriceps femoris muscle. Tensor of Vastus Intermedius is a new muscle that is part of the Quadriceps.

Patella (kneecap)

The patella is the kneecap bone. It lies within the quadriceps tendon. This large tendon from the powerful thigh muscles (quadriceps) wraps round the patella and is attached to the top of the lower leg bone (tibia). The quadriceps muscles straighten the knee.

Extensor digitorum longus

This long muscle lifts up the foot and the toes. Besides EDL muscle, this compartment also contains the tibialis anterior, extensor hallucis longus and fibularis (peroneus) tertius muscles.

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Every single movement your body makes is produced by the muscular system. Muscles are layers of hardworking tissue that shape the body, keep it upright, and move it around.

Muscle tissue is made of long cells called fibres, which use energy to contract, or shorten, pulling different parts of the body into position. Movements are controlled by nerve signals from the brain. Sometimes you move your muscles consciously, such as when you sit down, or turn to look at something. But other muscle movements, such as your heartbeat, or when you blink your eyes, hapopen without you thinking about them.

There are three distinct types of muscles: skeletal muscles, cardiac or heart muscles, and smooth (non-striated) muscles. Muscles provide strength, balance, posture, movement and heat for the body to keep warm.

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Bones have different shapes and sizes, depending on their functions. There are five kinds of bone in the human skeleton.

Long bones

These bones are longer than they are wide and are found in the arms, hands, legs, and feet. They support the body’s weight and allow it to move.

Short bones

Roughly cube-shaped bones in the wrist and ankle allow some movement and provide stability to the joints.

Flat bones

Shield-like flat bones protect organs such as the heart and brain.

Irregular bones

These bones have complex shapes, to perform specific roles. For example, the vertebrae allow the back to bend and rotate, and protect the spinal cord.

Sesamoid bones

These small, roundish bones protect tendons and joints from wear and tear. The patella protects the knee joint. It sits inside the tendon that attaches the thigh muscle to the shinbone.

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