lateral rectus muscle

Examples of lateral rectus muscle in the following topics:

• Abducens (VI) Nerve

  • The abducens nerve (cranial nerve VI) controls the lateral movement of the eye through innervation of the lateral rectus muscle.
  • The abducens nerve (cranial nerve VI) is a somatic efferent nerve that, in humans, controls the movement of a single muscle: the lateral rectus muscle of the eye that moves the eye horizontally.
  • It then enters the orbit through the superior orbital fissure and innervates the lateral rectus muscle of the eye.

• Oculomotor (III) Nerve

  • The muscles it controls are the striated muscle in the levator palpebrae superioris and all extraocular muscles, except for the superior oblique muscle and the lateral rectus muscle.
  • The Edinger-Westphal nucleus supplies parasympathetic fibers to the eye via the ciliary ganglion, and controls the pupillae muscle (affecting pupil constriction) and the ciliary muscle (affecting accommodation).
  • It passes between the superior cerebellar and posterior cerebral arteries, and then pierces the dura mater anterior and lateral to the posterior clinoid process (to give attachment to the tectorium cerebella), passing between the free and attached borders of the tentorium cerebelli.
  • It then runs along the lateral wall of the cavernous sinus, above the other orbital nerves, receiving in its course one or two filaments from the cavernous plexus of the sympathetic nervous system, and a communicating branch from the ophthalmic division of the trigeminal nerve.
  • It then divides into two branches that enter the orbit through the superior orbital fissure, between the two heads of the lateral rectus (a muscle on the lateral side of the eyeball in the orbit).

• Brief Overview of Cranial Nerves

  • The trochlear nerve (IV): A motor nerve that innervates the superior oblique muscle of the eye, which controls rotational movement.
  • The abducens nerve (VI): A motor nerve that innervates the lateral rectus muscle of the eye, which controls lateral movement.
  • The facial nerve (VII): This controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity.
  • The vagus nerve (X): This is responsible for many tasks, including heart rate, gastrointestinal peristalsis, sweating, and muscle movements in the mouth, including speech and keeping the larynx open for breathing.
  • The spinal accessory (XI): This nerve controls specific muscles of the shoulder and neck.

• The Human Eye

  • Each eye has six muscles; lateral rectus, medial rectus, inferior rectus, superior rectus, inferior oblique, and superior oblique.
  • All of these muscles provide differnt tensions and torques to control the movement of the eye.

• Muscles that Cause Movement at the Knee Joint

  • Quadriceps Femoris – The quadriceps femoris is actually composed of four muscles that comprise the front of the thigh: three deep-lying vastus muscles (lateralis, intermedius, and medialis) and the rectus femoris which covers them.
  • The rectus femoris originates from the pelvis and attaches to the patella.
  • The rectus femoris additionally facilitates rotation at the hip.
  • Actions: Extends and laterally rotates at the hip, main action is flexing of the lower leg at the knee.
  • Actions: Laterally rotates the femur on the tibia “unlocking” the knee joint so that flexion can occur.

• Anterior Muscles

  • The anterior muscles of the trunk (torso) are associated with the front of the body, include chest and abdominal muscles.
  • Serratus Anterior – The serratus anterior is located in the lateral wall of the chest.
  • The flat muscles act to flex, laterally flex, and rotate the trunk.
  • Rectus Abdominis – A long vertical muscle that covers the abdomen, lying below the flat muscles.
  • Pyramidalis – Lying superficial to the rectus abdomini,s the pyramidalis is a small, triangular vertical muscle.

• Overview of Motor Integration

  • Thigh muscles, for example, can have a thousand fibers in each unit, eye muscles might have ten.
  • Muscles requiring more refined motion are innervated by motor units that synapse with fewer muscle fibers.
  • The activation of more motor neurons will result in more muscle fibers being activated, and therefore a stronger muscle contraction.
  • It is therefore a measure of how many muscle fibers of that muscle are activated.
  • The rectus femoris muscle is one of the four quadriceps muscles of the human body.

• How Skeletal Muscles Are Named

  • Parallel muscles are characterized by fascicles that run parallel to one another, and contraction of these muscle groups acts as an extension of the contraction of a single muscle fiber.
  • In Pennate muscles, the tendon runs through the length of the muscle.
  • However, these muscles tend to have relatively more muscle fibers than similarly sized parallel muscles, and thus carry more tension.
  • If the central tendon branches within a pennate muscle, the muscle is called multipennate.
  • The rectus femoris found in the thigh, and responsible for its flexion, is an example of a bipennate muscle.

• Hypotonia and Hypertonia

  • Hypertonia is the reduced ability of muscles to stretch due to increased muscle tension; hypotonia, due to chronic reduced muscle tension.
  • Hypertonia is a reduction in the ability of a muscle to stretch due to increased muscle tension; it is caused by lesions to upper motor neurons.
  • Hypotonia is the state of reduced muscle tone and tension, resulting in lessened ability to generate force from muscle contractions.
  • The long-term effects of hypotonia on a child's development and later life depend primarily on the severity of muscle weakness and the nature of the cause.
  • A muscle spindle, with γ motor neurons, sensory fibers and proprioceptor that detect the amount and rate of change of length in a muscle.

• Chewing Muscles

  • Lateral Pterygoid - The lateral pterygoid muscle has a triangular shape with two head, superior and inferior.
  • Actions - Together, the lateral pterygoids protract the jaw, working independently to produce lateral movement.
  • It is located inferior to the lateral pterygoid.
  • Produced by the lateral pterygoid, assisted by the digastric, mylohyoid and geniohyoid muscles found in the neck.
  • Highlighted in orange, the temporalis muscle is a broad muscle extending from zygomatic bone.