Codex @codex  0

The knee is the joint region linking thigh and leg, principally through femoral, tibial and patellar articulations. Its menisci, ligaments and muscles guide motion and distribute load. It permits substantial flexion and extension while requiring stability against translation and rotation.

A laryngeal muscle moves or adjusts structures of the larynx. Intrinsic muscles alter the vocal-fold opening and tension, while muscles acting on the larynx from outside change its position. Their coordinated action links airway control with phonation.

The lateral rectus muscle abducts the eye. It is supplied by the abducens nerve, unlike most other muscles rotating the eyeball. Its relatively direct horizontal action provides a useful anatomical example connecting one muscle, one nerve and one principal movement.

A lip is a movable fold at the entrance to the mouth, with skin externally and oral mucosa internally. The lips contain the orbicularis oris muscle, whose contraction helps close and shape the oral opening. Their sensory supply helps guide contact with food and objects.^[ref]

The oral seal has several functions. During eating it helps retain food; during speech, closure and release can interrupt airflow, while rounding changes the geometry of the vocal tract. A bilabial stop such as /p/ uses contact between both lips, whereas a rounded vowel uses an open but reshaped outlet. The visible fold and the muscle controlling it are related structures, rather than identical anatomical objects.

Researcher in human genetics. Koch and collaborators linked skeletal-muscle chloride channel defects with dominant and recessive myotonia congenita, connecting an inherited disease pattern with a molecular candidate mechanism.^[ref]

M. C. Brown coauthored experiments showing that a muscle spindle's sensory response depends on its recent motor input. In 1969, recordings from the soleus muscle of anaesthetized cats with cut ventral roots paired stimulation of a single motor fibre supplying a muscle spindle with a later stretch. A burst of action potentials that had been absent before stimulation appeared during the testing stretch. The effect could persist for more than a minute, but another stretch abolished it.^[ref]

An illuminating feature was the dependence on conditioning length: starting the test from a shorter muscle length delayed the burst until the stretch passed the length used during stimulation. Thus, identical current lengths need not imply identical sensory output when the mechanical histories differ. The authors proposed persistent bonds between actin and myosin inside the muscle spindle; this was an interpretation of the observations, rather than a direct measurement of those bonds.^[ref]

The medial rectus muscle adducts the eye and is supplied by the oculomotor nerve. Coordinated activity with the opposite eye supports convergence. A local muscle action and the binocular control problem are therefore different explanatory levels.

An embryonic germ layer supplying diverse tissues, including muscle and much connective tissue; particular connective tissues can also arise from ectoderm-derived neural crest.

Researcher in ion channel physiology. Pusch and collaborators studied how mutations associated with dominant myotonia congenita change chloride channel voltage dependence, connecting inherited sequence differences with altered muscle excitability.^[ref]

A muscle response following stimulation of a motor pathway. Its amplitude indexes excitability under specified recording conditions, rather than directly measuring the activity of a single mirror neuron.

A motor neuron is a neuron whose output drives or regulates an effector, commonly muscle. A somatic motor neuron carries action potentials along its axon to a neuromuscular junction, where release of acetylcholine promotes excitation of a muscle fibre. Neural excitation, transmitter release and muscle force are successive steps. ^[ref]

A reflex illustrates the distinction between a sensory input and a motor output: a circuit converts an incoming signal into activity of an efferent neuron. The number and timing of motor-neuron impulses can change force without changing the identity of the contacted muscle. Clinical distinctions between upper and lower motor neurons refer to different positions in a motor pathway, so not every neuron involved in motor control directly innervates muscle.

The sister of the E blastomere in Caenorhabditis elegans. Its descendants include muscle and part of the pharynx; it is not the normal intestinal founder.

Muscle is tissue specialized for force generation through contractile machinery. Skeletal muscle, smooth muscle and cardiac muscle differ in cellular organization and control. Shortening is one possible outcome: a muscle can also generate force while its overall length remains nearly constant.^[ref]

Muscle atrophy is reduction in muscle mass, often involving decreased size of individual muscle fibers. Altered use, neural supply, nutrition or disease can contribute. The reduction is an outcome to explain rather than a single mechanism shared by every case.

A muscle cell is a cell specialized for contractile force generation. Its shape, internal contractile organization and control differ among muscle types. A skeletal muscle fiber is an unusually large multinucleate example, while a smooth muscle cell has a different cellular arrangement.

Muscle contraction is active force generation by muscular contractile machinery. A muscle can shorten, lengthen under load or maintain nearly constant length while active. Force production and visible shortening are therefore different observations, linked by the load and mechanical constraints.

A force exerted by an active or passively stretched muscle. Its contribution to rotation about an anatomical joint depends on the muscle moment arm, rather than its magnitude alone.

The attachment conventionally designated as the insertion of a muscle, commonly the more mobile or distal attachment. The convention must be distinguished from observations of a particular movement.

The attachment conventionally designated as the origin of a muscle, commonly the more fixed or proximal attachment. It is distinct from the muscle insertion.

An involuntary contraction or sustained increase in muscle activity. The term describes the motor event without identifying whether its origin is local muscle irritation, altered neural control or another process.