Muscles

Z-Line

Z-Line The structure indicated is the Z-disc/Z-line formed between adjacent sarcomeres. A sarcomere is the name given to the basic unit of muscle, composed of sliding protein filaments of actin and myosin. Myosin filaments are thick, actin filaments are thin. These two filaments overlap each other, and their ability to slide past each other forms the basis of the theory of muscle contraction and relaxation. Under electron microscopy, the overlapping pattern of these thick and thin protein filaments gives rise to darker and lighter areas (bands), as well as distinct lines. The thinner actin filaments are all bound to the …

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Z-Line

Abductor Pollicis Brevis

Abductor Pollicis Brevis The structure indicated is the abductor pollicis brevis muscle of the hand. The abductor pollicis brevis muscle is one of the intrinsic muscles of the hand that belongs to the thenar group. The thenar group of intrinsic hand muscles consist of three muscles: Abductor pollicis brevis Flexor pollicis brevis Opponens pollicis All the intrinsic muscles of the hand, except the thenar muscles and the lateral two lumbrical muscles are innervated by the deep branch of the ulnar nerve. The thenar muscles and the lateral two lumbrical muscles are innervated by the median nerve.  A useful mnemonic for …

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Abductor Pollicis Brevis

Omohyoid

Omohyoid The structure indicated is the omohyoid muscle. The omohyoid muscle is one of four infrahyoid muscles which lie in the anterior triangle of the neck. The infrahyoid muscles, as the name suggests, attach to the hyoid bone and lie below it. Contraction of the infrahyoid muscles then causes depression of the hyoid bone. The infrahyoid muscles are often referred to as the strap muscles due to their strap-like appearance. The four infrahyoid muscles are: Omohyoid Sternohyoid Thyrohyoid Sternothyroid The omohyoid muscle sits lateral to the sternohyoid muscle and is comprised of two muscle bellies (superior and inferior) connected by …

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Omohyoid Muscle

Genioglossus

Genioglossus The structure indicated is the genioglossus muscle of the tongue. The genioglossus muscle is one of the extrinsic muscles of the tongue. The muscles involved with the tongue consist of intrinsic muscles which lie within the tongue itself, and the extrinsic muscles which attach to the tongue and are responsible for depression, elevation, protraction and retraction of the tongue. There are four sets of extrinsic tongue muscles: Genioglossus Hyoglossus Palatoglossus Styloglossus The genioglossus is a large muscle which extends anteriorly from the chin, to the tongue. The genioglossus is involved in depression and protrusion of the tongue. Origin: Superior …

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Genioglossus

Lateral Head of Gastrocnemius Muscle

Lateral Head of Gastrocnemius Muscle The structure indicated is the lateral head of the gastrocnemius muscle. The gastrocnemius muscle is the most superficial muscle of the posterior compartment of the leg. The muscles in the posterior compartment of the leg are separated into a superficial group and a deep group. The superficial group consists of the following leg muscles: Gastrocnemius Plantaris Soleus The deep group consists of the following leg muscles: Popliteus Flexor hallucis longus Flexor digitorum longus Tibialis posterior The gastrocnemius is one of the largest muscles in the leg and has two heads which form its origin, the …

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Lateral Head of Gastrocnemius Muscle

Eccentric Muscle Contraction

Eccentric Muscle Contraction This diagram is illustrating eccentric muscle contraction. When muscles generate tension, they can either lengthen, shorten, or stay the same length. Muscle contraction is therefore classified into three main types: Concentric muscle contraction – muscle shortens Eccentric muscle contraction – muscle lengthens Isometric muscle contraction – muscle remains the same length

Eccentric Muscle Contraction

Epimysium

Epimysium The structure indicated in this diagram is the epimysium. Skeletal muscle fibres are organised into bundles, called fascicles. Each fibre within the fascicle is surrounded by connective tissue called endomysium. Surrounding each fascicle (bundle), is the perimysium. Extensions of the perimysium project into the fascicles to blend with the endomysium. Surrounding the groups of fascicles is the epimysium, which covers the outer surface of the muscle. The epimysium is composed of dense irregular connective tissue. The epimysium can extend beyond the fleshy muscle fibres to form tendons or aponeuroses, which then form attachments to the periosteum of bones.

Epimysium

Iliocostalis Lumborum

Iliocostalis Lumborum The muscle indicated is the iliocostalis lumborum muscle, one of the erector spinae group of back muscles. The back muscles can be divided into three groups of muscles: Superficial Intermediate Deep group The erector spinae muscles belong to the deep (intrinsic) group of back muscles and are the largest group of intrinsic back muscles. There are three main erector spinae muscles, from lateral to medial: Iliocostalis Longissimus Spinalis Each of these three muscles is further subdivided into separate parts: Lumborum Thoracis Cervicis Capitis Origin: sacrum, iliac crest, spinous processes of lumbar vertebrae and thoracic vertebrae T11 and T12 …

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Iliocostalis Lumborum

Iliacus Muscle

Iliacus Muscle The muscle indicated is the iliacus muscle. The iliacus originates in the iliac fossa on the inside of the pelvic bone. The iliacus combines with the psoas major to enter the anterior compartment of the thigh and insert via a common tendon on the lesser trochanter of the femur. The iliacus and psoas are thus collectively referred to as the iliopsoas muscle – they act synergistically to flex the thigh at the hip joint, as well as acting to cause lateral rotation of the thigh. The iliopsoas muscles are the strongest hip flexors. Origin: Iliac fossa Insertion: Base …

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Iliacus

Orbicularis Oris Muscle

Orbicularis Oris The muscle indicated is the orbicularis oris muscle. The orbicularis oris muscle is one of the muscles of facial expression belonging to the oral group. The muscles of facial expression can be organised into functional groups to provide a more structured approach to understanding the muscles. The functional groups include the following: Orbital group Nasal group Oral group Other The oral group of muscles includes muscles that are responsible for moving the lips and the cheek. There are 11 muscles included in this functional group: orbicularis oris, depressor anguli oris, depressor labi inferioris, mentalis, risorius, buccinator, zygomaticus major, …

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Orbicularis Oris