In human anatomy, the infraspinatus muscle is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa. As one of the four muscles of the rotator cuff, the main function of the infraspinatus is to externally rotate the humerus and stabilize the shoulder joint, it attaches medially to the infraspinous fossa of the scapula and laterally to the middle facet of the greater tubercle of the humerus. The muscle arises by fleshy fibers from the medial two-thirds of the infraspinatous fossa, by tendinous fibers from the ridges on its surface; the fibers converge to a tendon, which glides over the lateral border of the spine of the scapula and passing across the posterior part of the capsule of the shoulder-joint, is inserted into the middle impression on the greater tubercle of the humerus. The trapezoidal insertion of the infraspinatus onto the humerus is much larger than the equivalent insertion of the supraspinatus, the reason why the infraspinatus is involved in rotator cuff tears about as as the supraspinatus.
The tendon of this muscle is sometimes separated from the capsule of the shoulder-joint by a bursa, which may communicate with the joint cavity. The suprascapular nerve innervates the infraspinatus muscles; these muscles function to abduct and laterally rotate the arm, respectively. The infraspinatus is fused with the teres minor; the infraspinatus is the main external rotator of the shoulder. When the arm is fixed, it abducts the inferior angle of the scapula, its synergists are teres minor and the deltoid. The infraspinatus and teres minor rotate the head of the humerus outward. Additionally, the infraspinatus reinforces the capsule of the shoulder joint. From an evolutionary prospective, the pectoral muscles – the pectoralis major and pectoralis minor – are thought to have evolved from a primitive muscle sheet that connected the coracoid to the humerus. In late reptilians and early mammals, this muscle structure was displaced dorsally; this article incorporates text in the public domain from page 441 of the 20th edition of Gray's Anatomy Saladin, Kenneth.
Anatomy and Physiology: the Unity of Form and Function. 7th ed. McGraw Hill Education, 2014. Pp. 343, 346, 491, 543. Funk, Lennard. Rotator Cuff Biomechanics. Shoulderdoc.co.uk. TheFresh Healthcare Marketing, 11 Feb 2016. Web. Anatomy figure: 03:03-04 at Human Anatomy Online, SUNY Downstate Medical Center ExRx
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A nerve is an enclosed, cable-like bundle of nerve fibres called axons, in the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system; each axon within the nerve is an extension of an individual neuron, along with other supportive cells such as Schwann cells that coat the axons in myelin. Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium; the axons are bundled together into groups called fascicles, each fascicle is wrapped in a layer of connective tissue called the perineurium. The entire nerve is wrapped in a layer of connective tissue called the epineurium. In the central nervous system, the analogous structures are known as tracts; each nerve is covered on the outside by a dense sheath of the epineurium. Beneath this is a layer of flat cells, the perineurium, which forms a complete sleeve around a bundle of axons.
Perineurial septae subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium; this forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, meshwork of collagen fibres. Nerves are bundled and travel along with blood vessels, since the neurons of a nerve have high energy requirements. Within the endoneurium, the individual nerve fibres are surrounded by a low-protein liquid called endoneurial fluid; this acts in a similar way to the cerebrospinal fluid in the central nervous system and constitutes a blood-nerve barrier similar to the blood-brain barrier. Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation, the amount of endoneurial fluid may increase at the site of irritation; this increase in fluid can be visualized using magnetic resonance neurography, thus MR neurography can identify nerve irritation and/or injury.
Nerves are categorized into three groups based on the direction that signals are conducted: Afferent nerves conduct signals from sensory neurons to the central nervous system, for example from the mechanoreceptors in skin. Efferent nerves conduct signals from the central nervous system along motor neurons to their target muscles and glands. Mixed nerves contain both afferent and efferent axons, thus conduct both incoming sensory information and outgoing muscle commands in the same bundle. Nerves can be categorized into two groups based on where they connect to the central nervous system: Spinal nerves innervate much of the body, connect through the vertebral column to the spinal cord and thus to the central nervous system, they are given letter-number designations according to the vertebra through which they connect to the spinal column. Cranial nerves innervate parts of the head, connect directly to the brain, they are assigned Roman numerals from 1 to 12, although cranial nerve zero is sometimes included.
In addition, cranial nerves have descriptive names. Specific terms are used to describe their actions. A nerve that supplies information to the brain from an area of the body, or controls an action of the body is said to "innervate" that section of the body or organ. Other terms relate to whether the nerve affects the same side or opposite side of the body, to the part of the brain that supplies it. Nerve growth ends in adolescence, but can be re-stimulated with a molecular mechanism known as "Notch signaling". If the axons of a neuron are damaged, as long as the cell body of the neuron is not damaged, the axons would regenerate and remake the synaptic connections with neurons with the help of guidepost cells; this is referred to as neuroregeneration. The nerve begins the process by destroying the nerve distal to the site of injury allowing Schwann cells, basal lamina, the neurilemma near the injury to begin producing a regeneration tube. Nerve growth factors are produced causing many nerve sprouts to bud.
When one of the growth processes finds the regeneration tube, it begins to grow towards its original destination guided the entire time by the regeneration tube. Nerve regeneration is slow and can take up to several months to complete. While this process does repair some nerves, there will still be some functional deficit as the repairs are not perfect. A nerve conveys information in the form of electrochemical impulses carried by the individual neurons that make up the nerve; these impulses are fast, with some myelinated neurons conducting at speeds up to 120 m/s. The impulses travel from one neuron to another by crossing a synapse, the message is converted from electrical to chemical and back to electrical. Nerves can be categorized into two groups based on function: An afferent nerve fiber conducts sensory information from a sensory neuron to the central nervous system, where the information is processed. Bundles of fibres or axons, in the peripheral nervous system are called nerves, bundles of afferent fibers are known as sensory nerves.
An efferent nerve fiber conducts signals from a motor neuron in the central nervous system to muscles. Bundles of these fibres are known as efferent nerves; the nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body. In vertebrates it consists of two main par
Opponens pollicis muscle
The opponens pollicis is a small, triangular muscle in the hand, which functions to oppose the thumb. It is one of the three thenar muscles, lying deep to the abductor pollicis brevis and lateral to the flexor pollicis brevis; the opponens pollicis originates from the flexor retinaculum of the hand and the tubercle of the trapezium. It passes downward and laterally, is inserted into the whole length of the metacarpal bone of the thumb on its radial side. Like the other thenar muscles, the opponens pollicis is innervated by the recurrent branch of the median nerve. In 20% of the population, opponens pollicis is innervated by the ulnar nerve. Https://nervesurgery.wustl.edu/ev/upperextremity/median/thenarbranch/Pages/OpponensPollicis.aspx The opponens pollicis receives its blood supply from the Superficial palmar arch. Apposition of the thumb is a combination of actions that allows the tip of the thumb to touch the tips of other fingers; the part of apposition that this muscle is responsible for is the flexion of the thumb's metacarpal at the first carpometacarpal joint.
This specific action cups the palm. Many texts, for simplicity, use the term opposition to represent this component of true apposition. In order to appose the thumb, the actions of a number of other muscles are needed at the thumb's metacarpophalangeal joint. Note that the two opponens muscles are named so because they oppose each other, but their actions appose the bones; this article incorporates text in the public domain from page 461 of the 20th edition of Gray's Anatomy
Fascial compartments of arm
The fascial compartments of arm refers to the specific anatomical term of the compartments within the upper segment of the upper limb of the body. The upper limb is divided into the arm and the forearm; each of these segments is further divided into two compartments which are formed by deep fascia – tough connective tissue septa. Each compartment encloses specific nerves; the compartments of the arm are the anterior compartment of the arm and the posterior compartment of the arm, divided by the lateral and the medial intermuscular septa. The compartments of the forearm are the anterior compartment of the forearm and posterior compartment of the forearm The lateral intermuscular septum extends from the lower part of the crest of the greater tubercle of the humerus, along the lateral supracondylar ridge, to the lateral epicondyle, it is perforated by the radial profunda branch of the brachial artery. The medial intermuscular septum, is thicker than the lateral intermuscular septum, it extends from the lower part of the crest of the lesser tubercle of the humerus below the teres major, passes along the medial supracondylar ridge to the medial epicondyle.
It is perforated by the ulnar nerve, the superior ulnar collateral artery, the posterior branch of the inferior ulnar collateral artery. The anterior compartment of the arm is known as the flexor compartment of the arm as its main action is that of flexion; the anterior compartment is one of the two anatomic compartments of the upper arm, the other being the posterior compartment. The anterior compartment contains three muscles; these muscles are all innervated by the musculocutaneous nerve which arises from the fifth and seventh cervical spinal nerves. The blood supply is from the brachial artery; the posterior compartment of the arm is known as the "extensor compartment", as its main action is extension. The muscles of this compartment are the triceps brachii and anconeus muscle and these are innervated by the radial nerve, their blood supply is from the profunda brachii. The triceps brachii is a large muscle containing three heads a lateral and middle; the anconeus is a small muscle. Some embryologists consider it as the fourth head of the triceps brachia as the upper and lower limbs have similar embryological origins, the lower limb contains the quadriceps femoris muscle which has four heads, is the lower limb equivalent of the triceps.
Anterior compartment of the forearm Posterior compartment of the forearm Compartment syndrome Fascia Fascial compartments of leg lesson4nervesofant&postarm at The Anatomy Lesson by Wesley Norman elbow/muscles/muscles2 at the Dartmouth Medical School's Department of Anatomy Dissection at tufts.edu https://web.archive.org/web/20080103065905/http://anatomy.med.umich.edu/musculoskeletal_system/axilla_ans.html
The triceps triceps brachii, is a large muscle on the back of the upper limb of many vertebrates. It is the muscle principally responsible for extension of the elbow joint; the long head arises from the infraglenoid tubercle of the scapula. It extends distally anterior to the teres posterior to the teres major; the medial head arises proximally from the groove of the radial nerve. The medial head is covered by the lateral and long heads, is only visible distally on the humerus; the lateral head arises from the dorsal surface of the humerus and proximal to the groove of the radial nerve, from the greater tubercle down to the region of the lateral intermuscular septum. Each of the three fascicles has its own motorneuron subnucleus in the motor column in the spinal cord; the medial head is formed predominantly by small type I fibers and motor units, the lateral head of large type IIb fibers and motor units and the long head of a mixture of fiber types and motor units. It has been suggested that each fascicle "may be considered an independent muscle with specific functional roles."The fibers converge to a single tendon to insert onto the olecranon process of the ulna and to the posterior wall of the capsule of the elbow joint where bursae are found.
Parts of the common tendon radiates into the fascia of the forearm and can cover the anconeus muscle. All three heads of the triceps brachii are classically believed to be innervated by the radial nerve. However, a study conducted in 2004 determined that, in 20 cadaveric specimens and 15 surgical dissections on participants, the long head was innervated by a branch of the axillary nerve in all cases. A tendinous arch is the origin of the long head and the tendon of latissimus dorsi. In rare cases, the long head can originate from the lateral margin of the scapula and from the capsule of the shoulder joint; the triceps is an extensor muscle of the elbow joint and an antagonist of the biceps and brachialis muscles. It can fixate the elbow joint when the forearm and hand are used for fine movements, e.g. when writing. It has been suggested that the long head fascicle is employed when sustained force generation is demanded, or when there is a need for a synergistic control of the shoulder and elbow or both.
The lateral head is used for movements requiring occasional high-intensity force, while the medial fascicle enables more precise, low-force movements. With its origin on the scapula, the long head acts on the shoulder joint and is involved in retroversion and adduction of the arm, it helps stabilise the shoulder joint at the top of the humerus. The triceps can be worked through either isolation or compound elbow extension movements and can contract statically to keep the arm straightened against resistance. Isolation movements include cable push-downs, lying triceps extensions and arm extensions behind the back. Examples of compound elbow extension include pressing movements like the push up, bench press, close grip bench press, military press and dips. A closer grip targets the triceps more than wider grip movements. Static contraction movements include pullovers, straight-arm pulldowns and bent-over lateral raises, which are used to build the deltoids and latissimus dorsi. Ruptures of the triceps muscle are rare, only occur in anabolic steroid users.
The triceps reflex, elicited by hitting the triceps, is used to test the function of the nerves of the arm. This tests spinal nerves C6 and C7, predominately C7, it is sometimes called a three-headed muscle, because there are three bundles of muscles, each of different origins, joining together at the elbow. Though a named muscle, the triceps surae, is found on the lower leg, the triceps brachii is called the triceps; the plural form of triceps was tricipites, a form not in general use today. In the horse, 84%, 15%, 3% of the total triceps muscle weight correspond to the long and medial heads, respectively. Many mammals, such as dogs and pigs, have a fourth head, the accessory head, it lies between the medial heads. In humans, the anconeus is sometimes loosely called "the fourth head of the triceps brachii". Illustration: upper-body/triceps-brachii from The Department of Radiology at the University of Washington Anatomy photo:06:11-0100 at the SUNY Downstate Medical Center Photo at Ithaca College Muscles/TricepsBrachii at exrx.net
The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint. It arises from its medial two-thirds and from the lower two-thirds of the groove on the axillary border of the scapula; some fibers arise from tendinous laminae, which intersect the muscle and are attached to ridges on the bone. The fibers pass laterally and coalesce into a tendon, inserted into the lesser tubercle of the humerus and the anterior part of the shoulder-joint capsule. Tendinous fibers extend to the greater tubercle with insertions into the bicipital groove; the tendon of the muscle is separated from the neck of the scapula by a large bursa, which communicates with the cavity of the shoulder-joint through an aperture in the capsule. The subscapularis is separated from the serratus anterior by the subscapularis bursa; the subscapularis is supplied by the upper and lower subscapular nerves, branches of the posterior cord of the brachial plexus.
The subscapularis adducts it. It is a powerful defense to the front of the shoulder-joint, preventing displacement of the head of the humerus; the Gerber Lift-off test is the established clinical test for examination of the subscapularis. The bear hug test for subscapularis muscle tears has high sensitivity. Positive bear-hug and belly press tests indicate significant tearing of subscapularis. There is no singularly imaging device or technique for a satisfying and complete subscapularis examination, but rather the combination of the sagittal oblique MRI / short-axis US and axial MRI / long-axis US planes seems to generate useful results. Additionally, lesser tuberosity bony changes have been associated with subscapularis tendon tears. Findings with cysts seem to be more specific and combined findings with cortical irregularities more sensitive. Another fact for the subscapularis muscle is the fatty infiltration of the superior portions, while sparing the inferior portions. Since the long biceps tendon absents itself from the shoulder joint through the rotator cuff interval, it is possible to distinguish between the supraspinatus and the subscapularis tendon.
Those two tendons build the interval sling. Mack et al. developed an ultrasonographic procedure with which it is possible to explore the complete rotator cuff within six steps. It unveils the whole area from the subedge of the subscapularis tendon until the intersection between the infraspinatus tendon and musculus teres minor. One of six steps does focus on the subscapularis tendon. In the first instance the examinator guides the applicator to the proximal humerus as perpendicularly as possible to the sulcus intertubercularis. Gliding now medially shows the insertion of the subscapularis tendon; the subscapularis tendon lies 3 to 5 cm under the surface. Quite deep for ultrasonography, therefore displaying through a penetrative 5 MHz linear applicator is worth a try, and it turned out to ease a detailed examination of the muscle which just abuts to the scapula. However, the tendon of primary interest does not get mapped as as desired; as anatomical analysis showed, it is only by external rotation possible to see the ventral part of the joint socket and its labrum.
While at the neutral position the tuberculum minus occludes the view. Summing up it is through an external arm rotation and a medially applied 5 MHz sector sonic head possible to display the ventral part of the joint socket and its labrum with notedly lower echogenicity; the following sectional planes are defined for the sonographic examination of the different shoulder joint structures: Primarily in abdominal imaging, tissue harmonic imaging gets more and more valued and used additionally to conventional ultrasonography. THI involves the use of harmonic frequencies that originate within the tissue as a result of nonlinear wave front propagation and are not present in the incident beam; these harmonic signals may arise differently at anatomic sites with similar impedances and thus lead to higher contrast resolution.” Along with higher contrast resolution it has an elevated signal-to-noise ratio and reduced inter- and intraobserver variability compared with conventional US. Additionally it is possible to nearly eliminate ordinary US artifacts, i.e. side-lobe, near-field artifacts, reverberation artifacts.
As aforementioned THI has led to enhanced abdominal, breast and cardiac sonography. For musculo-skeletal aspects THI has not been used that much, although this method features some useful potential. For example, for the still tricky discrimination between the presence of a hypoechoic defect and/or loss of the outer tendon convexity/non-visualization of the tendon, between partial- and full-thickness rotator cuff tears. In comparison to a checking MR Arthrography Strobel K. et al. has arrived at the conclusion that through THI it is possible to achieve a improved visibility of joint and tendon surfaces superior for subscapularis tendon abnormalities. This article incorporates text in the public domain from page 440 of the 20th edition of Gray's Anatomy