accessory muscles

Examples of accessory muscles in the following topics:

• Inspiration

  • These muscles are referred to as accessory muscles of inhalation.
  • Sternocleidomastoid muscle: muscles that connect the sternum to the neck and allow for rotation and turning of the head.
  • Trapezius muscle: muscles in the shoulders, which retracts the scapula and expands the upper part of the thoracic cavity.
  • The accessory muscles assist breathing by expanding the thoracic cavity in a similar way to the diaphragm.
  • A common problem in novice singers is breathing with the accessory muscles of the neck, shoulder, and ribs instead of the diaphragm, which gives them a much smaller air supply than what is needed to sing properly.

• Accessory (XI) Nerve

  • The accessory nerve (cranial nerve XI) controls the muscles of the shoulder and neck.
  • The accessory nerve (cranial nerve XI) controls the sternocleidomastoid and trapezius muscles of the shoulder and neck.
  • The accessory nerve provides motor innervation from the CNS to the sternocleidomastoid and trapezius muscles of the neck.
  • Limited range of motion or diminished muscle strength often indicates injury of the accessory nerve.
  • Upon exiting the skull via the jugular foramen, the spinal accessory nerve pierces the sternocleidomastoid muscle before terminating on the trapezius muscle.

• Functional Anatomy of the Respiratory System

  • The respiratory system include lungs, airways and respiratory muscles.
  • During vigorous inhalation (at rates exceeding 35 breaths per minute), or in approaching respiratory failure, accessory muscles—such as the sternocleidomastoid, platysma, and the scalene muscles of the neck—are recruited to help sustain the increased respiratory rate.
  • Pectoral muscles and latissimus dorsi are also accessory muscles for the activity of the lungs.
  • Active or forced exhalation is achieved by the abdominal and the internal intercostal muscles.
  • During forced exhalation, as when blowing out a candle, the expiratory muscles, including the abdominal muscles and internal intercostal muscles, generate abdominal and thoracic pressure that force air out of the lungs.

• Neural Mechanisms (Cortex)

  • The processes that drive its functions aren't fully understood, but it works by sending signals to the spinal cord, which sends signals to the muscles it controls, such as the diaphragm and the accessory muscles for respiration.
  • Initiation of the voluntary contraction and relaxation of the internal and external intercostal muscles takes place in the superior portion of the primary motor cortex.
  • This is most likely due to the focus and mental preparation of the voluntary muscular movement that occurs when one decides to initiate that muscle movement.
  • The posterior thoracic nerves: These nerves stimulate the intercostal muscles located around the pleura.
  • These three types of nerves continue the signal of the ascending respiratory pathway from the spinal cord to stimulate the muscles that perform the movements needed for respiration.

• Muscles that Cause Movement at the Foot

  • Movement of the foot and toes requires the action of many muscles.
  • Although many extrinsic muscles attach within the dorsal compartment, there are only three intrinsic muscles which act on the foot and two extrinsic muscles which act on the foot rather than the ankle.
  • Extensor Digitorum Brevis - The extensor digitorum brevis muscle is a deep-lying intrinsic muscle lying beneath the tendon of the extensor digitorum longus.
  • Extensor Hallucis Brevis - The extensor hallucis brevis muscle is an intrinsic muscle of the foot lying between the extensor digitorum longus and lateral to extensor hallucis longus.
  • Lumbricals - The lumbricals are four small skeletal muscles, accessory to the tendons of the flexor digitorum longus and numbered from the medial side of the foot.

• 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.

• Brachial Plexus

  • The brachial plexus is responsible for cutaneous and muscular innervation of the entire upper limb, with two exceptions: the trapezius muscle is innervated by the spinal accessory nerve (CN XI) and an area of skin near the axilla is innervated by the intercostobrachial nerve.
  • Five roots: The five anterior rami of the spinal nerves, after they have given off their segmental supply to the muscles of the neck.

• Cervical Plexus

  • They are located laterally to the transverse processes between prevertebral muscles from the medial side and anteriolateral to the m. scalenus and m. levator scapulae.
  • There is anastomosis with the accessory nerve, hypoglossal nerve, and sympathetic trunk.
  • It is located deep in the neck, near the sternocleidomastoid muscle.
  • Nerves formed from the cervical plexus innervate the back of the head, as well as some neck muscles.
  • The transverse cervical nerve (superficial cervical or cutaneous cervical) arises from the second and third cervical nerves, turns around the posterior border of the sternocleidomastoideus about its middle, then passes obliquely forward beneath the external jugular vein to the anterior border of the muscle, where it perforates the deep cervical fascia and divides beneath the platysma into ascending and descending branches that are distributed to the antero-lateral parts of the neck.

• Accessory Sex Glands

  • The primary purposes of the accessory sex glands are to produce seminal fluid and to clean and lubricate the urethra.
  • Seminal vesicle fluid is expelled under sympathetic contraction of the muscularis muscle coat.
  • The prostate is sheathed in the muscles of the pelvic floor, which contract during the ejaculatory process.
  • The prostate also contains some smooth muscles that help expel semen during ejaculation.
  • They are enclosed by transverse fibers of the sphincter urethrae membranaceae muscle.

• Anatomy of the Male Reproductive System

  • The male reproductive system includes external (penis, scrotum, epididymus, and testes) and internal (accessory) organs.
  • Special muscles in the wall of the scrotum contract and relax in order to move the testes near the body.
  • The internal organs of the male reproductive system are called accessory organs.