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A characteristic fixed facial expression produced by contraction of facial muscles.

The rotator cuff is the group of shoulder muscles and tendons that surround and help stabilize the humeral head. Their coordinated activity supports movement as well as joint centering. Stability is therefore an active control problem in addition to a property of passive joint shape.

Samuel J. Sober is a researcher in motor learning and the control of skilled movement. His laboratory combines recordings from neurons and muscles, behavioral experiments and computational analysis to investigate how the nervous system produces and adjusts movement. These approaches connect an animal's observable performance with candidate mechanisms for controlling it.^[ref]

With Michael S. Brainard, Samuel J. Sober tested whether adult birds continually correct vocal errors. A microphone captured Bengalese finch song and processing equipment altered its pitch before playing it through headphones. Compensatory changes in the birds' pitch showed adjustment to a measurable error in auditory feedback. Unlike deafening alone, this manipulation supplied an error that a change in behavior could reduce.^[ref]

The scapula is the flat shoulder bone carrying the glenoid cavity, which articulates with the humeral head. Its broad surfaces and processes provide muscle attachments. Movement of the scapula against the thoracic wall contributes to the range of shoulder movement beyond motion at the glenohumeral joint alone.

The scapular spine is the prominent ridge on the posterior scapula. It separates the supraspinous and infraspinous regions and extends laterally toward the acromion. Its shape provides attachment and leverage for shoulder muscles.

The semimembranosus is a medial hamstring muscle contributing to hip extension, knee flexion and medial rotation of the flexed leg. Its tendon also gives an expansion associated with the oblique popliteal ligament. One muscle can therefore contribute to both active motion and passive support.

A sensory neuron carries information about a stimulus toward the central nervous system. Its input can concern the external world or the body's own state. For example, stretching a muscle spindle changes the activity of a sensory neuron; the resulting action potentials help the spinal cord regulate muscle activity through a reflex.^[ref]

Many sensory neurons supplying the body have their soma in a dorsal root ganglion and a branching axon with peripheral and central processes. Thus the soma is not simply an obligatory relay between an input dendrite and an output axon. Other sensory pathways use different arrangements; a sensory function does not specify one universal neuron shape.^[ref]

Shivering is involuntary muscle activity that increases metabolic heat production. Its thermal role differs from purposeful movement even though both use muscle metabolism. The resulting temperature change depends on heat loss as well as the extra heat generated.

heat generation through muscle activity associated with shivering.

Skeletal muscle is striated muscle tissue organized into long multinucleate fibers and supporting connective tissues. Neural activation recruits force that is transmitted to attachments. Its output depends on fiber properties, recruitment and mechanical loading, not only the amount of muscle present.

A contractile muscle class whose cells lack the conspicuous sarcomeric striations of skeletal and cardiac muscle. Differentiated smooth-muscle layers can also mechanically constrain neighbouring growing tissues.

A smooth muscle cell is a contractile cell without the regular visible striations of skeletal and cardiac muscle. It contributes to structures such as vessel walls and the digestive tract. Its activity can change both local force and the geometry of a hollow organ.

Soft tissue broadly denotes the body's non-bony supporting and connecting tissues, such as muscle, fat, fascia, vessels and nerves, with usage varying by context. It is a practical anatomical category rather than one histological tissue type.

Steven E. Schraffordt led a dissection study of the pudendal nerve and its terminal branches. Examination of 28 cadavers documented variations relevant to the motor supply of the external anal sphincter. In five specimens, interconnecting inferior rectal and perineal branches formed a local nerve plexus near the sphincters.^[ref]

This is a practical contribution of anatomical observation: an intact muscle can lose function if its nerve supply is injured. A schematic branching pattern therefore needs to be interpreted alongside documented variation when considering pelvic anatomy.

The stylopharyngeus is a muscle running from the styloid region into the pharyngeal wall. It elevates the pharynx during swallowing and is supplied by the glossopharyngeal nerve. Its innervation distinguishes it from several neighboring pharyngeal muscles.

The stylopharyngeus muscle is the stylopharyngeus, a pharyngeal elevator supplied by the glossopharyngeal nerve. It links the styloid region to the pharyngeal wall. The expanded name identifies the same anatomical muscle rather than an additional neighboring structure.

A late neurological manifestation of syphilis involving posterior sensory pathways of the spinal cord. Loss of position sense can impair coordination despite preserved muscle strength, connecting the affected pathway with the clinical pattern.

A tendon is dense connective tissue transmitting force from muscle to an attachment, commonly a bone. Parallel organization of its matrix supports tensile loading. Elasticity and geometry affect force transmission, so a tendon is not an absolutely rigid connector.

A tendon reflex is a muscle response elicited by a brief stretch, commonly produced by tapping its tendon. Stretch activates sensory input to a spinal circuit that can excite the corresponding motor neurons.

Its size depends on both the local reflex pathway and descending influences. An altered response can therefore inform localization, but an isolated brisk or weak response does not uniquely identify the underlying disease.

The tensor tympani muscle is a middle-ear muscle attaching to the malleus. Its contraction alters the mechanics of the tympanic membrane and ossicular chain. Its innervation is associated with the mandibular division of the trigeminal nerve, rather than the facial supply to stapedius.