Category Zoology

The brain and the spinal cord – the mass of nerves running down the backbone – make up the central nervous system (CNS). This coordinates most of the body’s activities, from blinking and breathing to seeing and standing. Nerves branch out to the rest of the body via the peripheral nervous system (PNS).

Brain

The brain is made of four parts; cerebrum, diencephalon, cerebellum and brainstem. Together these parts process the incoming information from peripheral tissues and generate commands; telling the tissues how to respond and function. These commands tackle the most complex voluntary and involuntary human body functions, from breathing to thinking. The control centre of the nervous system, this is home to more than 100 billion neurons.

Cranial nerves

Cranial nerves are peripheral nerves that emerge from the cranial nerve nuclei of the brainstem and spinal cord. They innervate the head and neck. Twelve pairs of cranial nerves relay signal between the brain and the head, face, and neck.

Spinal cord

The body’s primary communications highway, this carries all nerve signals between the body and brain. It also has the ability to generate commands but for involuntary processes only, i.e. reflexes. However, its main function is to pass information between the CNS and periphery. 

Brachial plexus

The brachial plexus can be very challenging while studying anatomy. Even though it is essentially just a network or ‘bunch’ of nerves, it seems like it has very complex origin and branches, and students often get lost while reading the textbooks. This collection of nerves supplies the muscles and skin of the arm and hand.

Musculocutaneous nerve

The musculocutaneous nerve is responsible for very important function we use every day, bending/flexing our elbows. Tasks such as lifting a cup and brushing our teeth can become very difficult if the nerve is not functioning well. This nerve supplies muscles in the upper arm and gives feeling in the forearm.

Intercostal nerve

The intercostal nerves are the somatic nerves that arise from the anterior divisions of the thoracic spinal nerves from T1 to T11. These nerves in addition to supplying the thoracic wall also supply the pleura and peritoneum. The intercostals nerve supplies the muscles and skin of the thorax (chest).

Axillary nerve

One of the terminal branches of the brachial plexus is the axillary nerve, which is derived from the posterior cord (C5-6). It travels through the quadrangular space together with the posterior circumflex artery and vein. The axillary nerve supplies muscles and sensation in the shoulder.

Median nerve

The median nerve is the branch of the brachial plexus that supplies most of the superficial and deep flexors in the forearm, thenar and lumbrical muscles. It also gives sensation to certain areas of the skin of the hand. Most of the muscles in the forearm and hand, and some skin of the hand, is supplied by this nerve.

Phrenic nerve

The phrenic nerve is a bilateral, mixed nerve that originates from the cervical nerves in the neck and descends through the thorax to innervate the diaphragm. It is the only source of motor innervation to the diaphragm and therefore plays a crucial role in breathing. Messages to and from the diaphragm are carried by this nerve.

Radial nerve

The radial nerve is an essential component of the upper limb innervation network. It innervates essentially all the muscles on the posterior aspect of our arms, and is therefore a large nerve. This nerve supplies muscles in the back of the arm and the skin of the lower arm.

Lumbar plexus

A “plexus” is a branching network. The lumbar plexus supplies the skin and muscle of the lower back. The lower limbs have the tremendous responsibility of mobilizing and stabilizing the human body. Muscles of the pelvic region, posterior abdominal wall, and the fifty-nine muscles of the lower limb, as well as their corresponding joints, are innervated by branches of the lumbosacral plexus. 

Ulnar nerve

The ulnar nerve can broadly be described as the nerve of the hand, as the nerve innervates the vast majority of the intrinsic hand muscles. It is one of the most clinically applicable nerves, due to its superficial course, and clinically apparent role in hand function. This article shall discuss the anatomy of the ulnar nerve, its precise course, as well as the clinical relevance it has. Supplying muscles in the forearm and hand, this nerve gives the ‘funny bone’ tingle if you knock your elbow.

Femoral nerve

The femoral nerve is a mixed nerve of the lower limb that innervates the muscles and skin of the hip and thigh. The femoral nerve originates from the lumbar plexus, from the ventral rami of L2-L4 spinal nerves. In fact, it is the longest branch of the lumbar plexus. The skin and muscle of the pelvis and leg are supplies by this web of nerves.

Sciatic nerve

The thickest and longest nerve in the body, this links the spinal cord to muscles in the legs and feet. The sciatic nerve starts as a collection of nerve fibers in the lower spine. These nerve fibers, or roots, exit the spinal canal through a number of openings in the bones at each level of the lower spine called foramina.

Saphenous nerve

The saphenous nerve is a sensory branch of the femoral nerve (lumbar plexus L3, L4), and supplies sensation to the anteromedial, medial and posteromedial surface of the leg. The saphenous nerve is the largest terminal cutaneous branch of the femoral nerve (dorsal divisions of the ventral rami of L2-L4).The saphenous nerve supplies the skin on the inner leg.

Common peroneal (fibular) nerve

The common fibular nerve, also known as the common peroneal nerve, is one of two main muscular branches of the sciatic nerve. A branch of the sciatic nerve, this supplies the front and side of the lower leg.

Superficial peroneal nerve

The superficial fibular nerve is a nerve of the lower limb. In older texts, it is known as the superficial peroneal nerve. Supplying the skin and muscles of the leg and foot, this is one of the fibular nerves.

Deep peroneal (fibular) nerve

The deep peroneal nerve, more commonly known as the deep fibular nerve innervates a number of muscles in the leg and foot, which are essential for normal gait and movement of the ankle. This nerve supplies the muscles of the leg and foot.

Tibial nerve

The tibial nerve is one of two main muscular branches of the sciatic nerve that innervates the triceps surae, plantaris, popliteus, tibialis posterior, flexor digitorum longus and flexor hallucis longus muscles. This is the biggest branch of the sciatic nerve. It produces a “pins” and “needles” feeling in the legs if it is squashed.

Plantar nerve

The plantar nerves are a pair of nerves innervating the sole of the foot. They arise from the posterior branch of the tibial nerve. The plantar nerve is responsible for the tickling sensation when the soles of the feet re touched.

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This is the body’s communication and control network. The brain sends and receives messages along the spinal cord and billions of interconnecting nerve cells wired up to every part of the body.

The nervous system works like a high-speed internet, sending electrical signals at great speed through nerve cells called neurons. Sensory nerves send signals to the brain from sense receptors all over your body. At the same time, going in the opposite direction, motor nerves send signals from the brain, telling the muscles to move.

Functionally, the nervous system has two main subdivisions: the somatic, or voluntary, component; and the autonomic, or involuntary, component. The autonomic nervous system regulates certain body processes, such as blood pressure and the rate of breathing, that work without conscious effort, according to Merck Manuals. The somatic system consists of nerves that connect the brain and spinal cord with muscles and sensory receptors in the skin.

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Although you may not be aware of them, some muscles stand out from the rest. Meet the muscles breaking records in your body.

Strongest muscle

There are different contenders for this title, depending on how you define “strong”. But the muscle that exerts the greatest force is probably the soleus (calf muscle).

Longest muscle

The sartorious is the longest muscle in the human body. This superficial skeletal muscle runs the length of the thigh.

Largest muscle

The gluteus maximus is the biggest muscle. It covers most of the buttocks and helps the body stand up.

Smallest muscle

The stapedius is the smallest muscle. Only about 1 mm (0.04 in) long, it is found inside the ear.

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At first glance, muscle names may appear difficult to read, but they have all been given a unique Latin name to describe them. This name can be understood around the world. The chosen name relates to specific characteristics of the muscle, such as its size, shape, location, and what it does.

Occipitofrontalis

This muscle extends over the skull to the eyebrows. Together with temporoparietalis, it comprises the epicranial group of the muscles of facial expression.

Sternocleidomastoid

The sternocleidomastoid muscle is a two-headed neck muscle, which true to its name bears attachments to the manubrium of sternum (sterno-), the clavicle (-cleido-), and the mastoid process of the temporal bone (-mastoid). This turns the head.

Right trapezius

The trapezius muscle is a large, triangular, paired muscle located on the posterior aspect of the neck and thorax. When viewed together, this pair forms a diamond or trapezoid shape, hence its name. The trapezius lies on top of the other back muscles.

Left trapezius

Although each of the two trapezius muscles is triangular, together they make a four-sided shape called a trapezium.

Deltoid

The deltoid is a thick, triangular shoulder muscle. It gets its name because of its similar shape to the Greek letter ‘delta’ (?). The muscle has a wide origin spanning the clavicle, acromion and spine of scapula. This muscle lifts the shoulder and upper arm.

Teres major

The teres major is a thick muscle of the shoulder joint. It spans from the inferior aspect of the scapula to the proximal part of the humeral shaft. This muscle pulls the arm towards the body and turns it inwards.

Triceps brachii

Triceps brachii is a three-headed (tri – three, cep – head) muscle of the arm. It represents the only constituent of the posterior muscle group of the arm, spanning almost the entire length of the humerus. The triceps brachii muscle consists of a long, medial and lateral head, that originate from their respective attachments on the humerus and scapula, and insert via a common tendon on the ulna. 

Triceps brachii tendon

This is where the fleshy parts of the three-headed triceps brachii muscle meet.

Latissimus dorsi

The latissimus dorsi muscle is the widest muscle in the human body. It is relatively thin and covers almost all back muscles at the posterior trunk, except the trapezius. This is a large, flat muscle, which helps to pull the arm into the body and turn it inwards.

Transversus abdominis

The transversus abdominis is a broad paired muscular sheet found on the lateral sides of the abdominal wall. Along with the external abdominal oblique and the internal abdominal oblique, it comprises the lateral abdominal muscles.  This muscle provides stability for the pelvis.

Gluteus maximus

The gluteus maximus is the most superficial gluteal muscle that forms the prominence of the gluteal region. Along with the gluteus medius, gluteus minimus and tensor fasciae latae, it belongs to the gluteal group of the hip muscles. This large muscle helps to move the hip and thigh.

Adductor magnus

The adductor magnus muscle is a large triangular muscle of the lower limb, with its apex situated on the hip bone, and its base on the linea aspera of the femur. It is situated both in the posterior and medial fascial compartments of the thigh. The distribution of this muscle in two compartments is reflected in the fact that it receives dual nerve supply. Regardless of its position, the adductor magnus muscle is classified as a muscle of the medial compartment of the thigh. 

Gracilis

Gracilis muscle is a long and slender muscle located in the medial (adductor) compartment of the thigh. It forms part of the adductor muscle group together with adductor longus, adductor brevis, adductor magnus and pectineus muscles. 

Biceps femoris

Biceps femoris is a long muscle of the posterior aspect of the thigh. Together with the semitendinosus and semimembranosus muscles, it makes the group of muscles commonly known as the hamstrings.

Semitendinosus

Semitendinosus is a fusiform muscle of the posterior compartment of thigh. Along with semimembranosus and long head of biceps femoris it comprises a group called the hamstring muscles.

Gastrocnemius

Gastrocnemius is a large muscle located in the posterior leg. Posteriorly, is the most superficial of the muscles of the leg, and forms the bulk of the calf.

Soleus

The soleus muscle is a wide flat leg muscle found on the posterior leg. It runs from just below the knee to the heel and lays immediately deep to the gastrocnemius. These two muscles, along with the plantaris muscle, belong to the group of superficial posterior compartment calf muscles. Together with the gastrocnemius, this strong muscle forms what is known as the calf muscle.

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These fan-shaped or feather-shaped muscles have densely packed fibres, making them strong. There are different kinds of pinnate muscle, each adapted for specific work.

Unipennate muscle

The fibres of these muscles fan out from the narrow point at which they insert into the tendon. This makes the muscle strong. Some hand muscles are unipennate.

Bipennate muscle

This has fibres running diagonally from each side of a tendon, like a feather. This makes the muscle even stronger, but less mobile. The rectus femoris muscle at the front of the thigh is bipennate.

Multipennate muscle

This powerful muscle has many rows of fibres running from a central tendon. The deltoid (shoulder) muscle is multipennate.

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Superficial muscles are just beneath the skin. Those at the front of the body create different facial expressions, move the head forwards and sideways, bend the arms and move them forwards, bend the body forwards and sideways, bend the legs, straighten the knees, and lift the feet.

Frontails

The frontalis muscle is a thin, wide, four-sided muscle located at the top front of the skull (in the area of the forehead). Specifically, this muscle originates from the galea aponeurotica and extends down the forehead and inserts or attaches to the skin around the eyebrows and top of the nose. 

Orbicularis oculi

Orbicularis oculi is a paired facial muscle that surrounds each orbit and the adjacent periorbital region. Together with corrugator supercilii and levator palpebrae superioris, it belongs to the circumorbital and palpebral group of muscles that surround the eye. This closes the eye.

 Temporalis

The temporalis muscle is a thin, fan-shaped muscle situated within the temporal fossa of the skull. Along with the medial pterygoid, lateral pterygoid and masseter muscles, it belongs to the group masticatory muscles. The temporalis muscle runs superficially, from the temporal bone to the coronoid process of mandible. This muscle pulls the lower jaw up.

Orbicularis oris

Orbicularis oris is a complex circular muscle that surrounds the orifice of the mouth and forms the majority of the lips. It belongs to a large group of muscles of facial expression called the buccolabial group. This muscle purses the lips.

Platysma

This broad sheet of thin muscle lies just under the skin of the neck. It arises in the upper thoracic and shoulder regions from a fascia that covers the pectoralis major and deltoid muscles. 

Pectoralis major

The pectoralis major is a paired, superficial muscle located on the anterior surface of the thoracic cage. If you’re a gym lover, you’ll hear these muscles also being referred to as the pecs muscles.

Deltoid

The deltoid is a thick, triangular shoulder muscle. It gets its name because of its similar shape to the Greek letter ‘delta’ (?). The muscle has a wide origin spanning the clavicle, acromion and spine of scapula. It passes inferiorly surrounding the glenohumeral joint on all sides and inserts onto the humerus. 

Biceps brachii

The biceps brachii muscle is one of the chief muscles of the arm. The origin at the scapula and the insertion into the radius of the biceps brachii means it can act on both the shoulder joint and the elbow joint, which is why this muscle participates in a few movements of the arm. This bends the elbow.

Rectus abdominis

Rectus abdominis, informally known as the abs muscle, is a long muscle of the anterior abdominal wall. In those with low body fat, it is clearly visible beneath the skin forming the ‘six pack’. It extends from the rib cage all the way to the pubic bone. This paired muscle is often shortened to the “abs”.

Linea alba

This connective tissue connects abdominal muscles on the left and right. It extends between the inferior limit of the sternum and the pubis, separating the rectus abdominis muscles. In leaner, more muscular individuals, it is visible externally as a longitudinal, shallow groove. 

Brachioradialis

Brachioradialis is a fusiform muscle located in the lateral part of the posterior forearm. Along with extensor carpi radialis brevis and extensor carpi radialis longus, it comprises the radial group of forearm muscles, which belong to the superficial layer of posterior forearm muscles.  This muscle helps to bend the elbow.

External oblique

External abdominal oblique is a paired muscle located on the lateral sides of the abdominal wall. Along with internal abdominal oblique and transversus abdominis, it comprises the lateral abdominal muscles. In a broader picture, these muscles make up the anterolateral abdominal wall together with two anterior abdominal muscles; the rectus abdominis and pyramidalis. This muscle helps to twist the torso.

Tensor fasciae latae

Tensor fasciae latae is a fusiform muscle located in the lateral aspect of the thigh. It belongs to the muscles of the gluteal region, along with the gluteus maximus, gluteus medius and gluteus minimus muscles. This muscle lifts the thigh away from the body.

Pectineus

Pectineus is a flat muscle found in the superomedial part of the anterior thigh. Fascial compartments of the thigh muscles are specific in that each of them is innervated by a particular nerve. 

Adductor longus

The adductor longus is a large, fan-shaped muscle located in the medial aspect of the thigh. It belongs to the adductors of the thigh, together with adductor brevis, adductor magnus, adductor brevis, pectineus and gracilis muscles.

Rectus femoris

The quadriceps femoris muscle, commonly known as the quad muscle, is the strongest muscle of the human body. It is located in the anterior compartment of the thigh, together with the sartorius. This is one of the four quadriceps muscles.

Sartorius

This is the longest muscle in the body. Together with the quadriceps femoris, it belongs to the anterior (extensor) muscles of the thigh. It enables you to sit cross-legged.

Vastus medialis

This is one of the four quadriceps muscles. It is the most medial, or inner, of the quadriceps muscles. It extends the entire length of the thigh. The portion of the muscle that is just above the knee is sometimes referred to as the vastus medialis obliquus, or VMO. This muscle is used to extend the leg at the knee and to stabilize the patella, which is also known as the kneecap.

Vastus lateralis

This is one of the four quadriceps muscles, which straighten the knee. Together, the quadriceps acts on the knee and hip to promote movement as well as strength and stability. They provide power for and absorb the impact of daily activities such as walking, running, and jumping.

Gastrocnemius

Gastrocnemius is a large muscle located in the posterior leg. Posteriorly, is the most superficial of the muscles of the leg, and forms the bulk of the calf. This is the largest calf muscle.

Tibialis anterior

Tibialis anterior is a fusiform muscle found in the anterior part of the leg. Lying superficially in the leg, this muscle is easily palpable lateral to the anterior border of tibia. This raises the foot upwards.

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