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Spinal cord, Exams of Communication

Campbell UniversityCommunication

In adult spinal cord ranges between 42 and 45 cm in length and extends inferiorly from the brain through the foramen magnum and then through the vertebral canal.

Typology: Exams

2021/2022

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Spinal cord
โ€ขThe second organ of the CNS is spinal cord which serve as communication link
between the brain and the PNS
โ€ขIn adult spinal cord ranges between 42 and 45 cm in length and extends inferiorly
from the brain through the foramen magnum and then through the vertebral canal
and ends at the level of the L1 vertebra.
โ€ขIt is considerably shorter than the vertebral column because it does not grow as
rapidly as the vertebral column during development.
โ€ขThe spinal cord gives rise to 31 pairs of spinal nerves, which exit the vertebral
column through intervertebral and sacral foramina
โ€ขThe spinal cord is divided into four regions
โ‘The cervical part- superiormost region of the spinal cord, continuous with the medulla
oblongata
โ‘The thoracic part lies inferior to the cervical part
โ‘The lumbar part is a shorter segment of the spinal cord
โ‘The sacral part
โ‘The coccygeal part is the most inferior โ€œtipโ€ of the spinal cord
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Spinal cord

  • The second organ of the CNS is spinal cord which serve as communication link between the brain and the PNS
  • In adult spinal cord ranges between 42 and 45 cm in length and extends inferiorly from the brain through the foramen magnum and then through the vertebral canal and ends at the level of the L1 vertebra.
  • It is considerably shorter than the vertebral column because it does not grow as rapidly as the vertebral column during development.
  • The spinal cord gives rise to 31 pairs of spinal nerves, which exit the vertebral column through intervertebral and sacral foramina
  • The spinal cord is divided into four regions โ‘ The cervical part- superiormost region of the spinal cord, continuous with the medulla oblongata โ‘ The thoracic part lies inferior to the cervical part โ‘ The lumbar part is a shorter segment of the spinal cord โ‘ The sacral part โ‘ The coccygeal part is the most inferior โ€œtipโ€ of the spinal cord
  • Two prominent enlargements can be seen in a external view. The cervical enlargement is located between the third cervical and the second thoracic vertebrae. Nerves emerging from this region serve the upper extremities.
  • The lumbar enlargement lies between the ninth and twelfth thoracic vertebrae. Nerves from the lumbar enlargement supply the lower extremities.
  • Immediately inferior to the lumbosacral enlargement, the spinal cord tapers to form a conelike region called the conus medullaris which makes the inferior end of spinal cord.
  • Inferior to conus medullaris there is groups of axons collectively called the cauda equina
  • Arising from the conus medullaris is the filum terminale which is an extension of the pia mater that extends inferiorly and fuses with the arachnoid mater and dura mater and anchors the spinal cord to the coccyx
  • Two grooves, an anterior median fissure and a posterior median sulcus, extend the length of the spinal cord and partially divide it into right and left portions.
  • Like the brain, the spinal cord is protected by three distinct meninges and is cushioned by cerebrospinal fluid.
  • A transverse section of the spinal cord reveals regions of white matter that surround an inner core of gray matter.
  • The gray matter of the spinal cord is shaped like the letter H or a butterfly; it consists of dendrites and cell bodies of neurons, unmyelinated axons, and neuroglia.
  • Projections of the gray matter within the spinal cord are called horns , and are named according to the direction in which they project. โ‘ The paired posterior horns extend posteriorly. Contain cell bodies and axons of interneurons as well as axons of incoming sensory neurons โ‘ The paired anterior horns project anteriorly. Contain somatic motor nuclei, which are clusters of cell bodies of somatic motor neurons that provide nerve impulses for contraction of skeletal muscles โ‘ Paired Lateral horns extend to the sides between the posterior and anterior horns. Contain autonomic motor nuclei, which are clusters of cell bodies of autonomic motor neurons that regulate the activity of cardiac muscle, smooth muscle, and glands.
  • The gray commissure forms the crossbar of the H. In the center of the gray commissure is a small space called the central canal; it extends the entire length of the spinal cord and is filled with cerebrospinal fluid. At its superior end, the central canal is continuous with the fourth ventricle
  • The spinal cord has six columns of white matter

called funiculi which are named according to their

relative position within the spinal cord.

โ‘ The two anterior funiculi are located between the two

anterior horns of gray matter, to either side of the anterior median fissure. โ‘ The two posterior funiculi are located between the two posterior horns of gray matter, to either side of the posterior median sulcus. โ‘ Two lateral funiculi are located between the anterior and

posterior horns of gray matter.

Spinal nerves

  • Spinal nerves are the paths of communication between the spinal cord and specific regions of the body.
  • There are 31 pair of spinal nerves. โ‘ 8 pairs of cervical nerves (C1โ€“C8), โ‘ 12 pairs of thoracic nerves (T1โ€“T12), โ‘ 5 pairs of lumbar nerves (L1โ€“L5), โ‘ 5 pairs of sacral nerves (S1โ€“S5), โ‘ 1 pair of coccygeal nerves (Co1).
  • A spinal nerve is a mixed nerve attached to the spinal cord by a posterior (dorsal) root, composed of sensory fibers, and an anterior (ventral) root, composed of motor fibers
  • The posterior root is formed from merger of posterior rootlets which arise from posterior root ganglion which itself is attached to spinal cord. Posterior root axons bring sensory information. The posterior root ganglion is made up of cell bodies of sensory neurons.
  • The anterior root is formed from merger of multiple anterior rootlets which arise from spinal cord. The anterior root consists of axons of motor neurons, which convey motor impulses away from the CNS.

Spinal Plexus

  • Except in thoracic nerves, T2 through T12, the anterior rami of the spinal nerves combine and then split again as networks of nerve fibers referred to as nerve plexuses
  • The principal plexuses are the cervical plexus, brachial plexus, lumbar plexus, and sacral plexus
  • Nerves emerging from the plexuses are named according to the structures they innervate
  • The anterior rami of spinal nerves T2โ€“T12 do not enter into the formation of plexuses and are known as intercostal or thoracic nerves. These nerves directly connect to the structures they supply in the intercostal spaces. They supply the intercostal muscles, rib cage, abdominal muscles and skin of these areas
  • The cervical plexus is positioned deep on the side of the neck, lateral to the first four cervical vertebrae.
  • It is formed by the anterior rami of the first four cervical nerves (C 1 โ€“ C 4 ) and a portion of C 5.
  • Branches of the cervical plexus innervate the skin and muscles of the neck and portions of the head and shoulders.
  • Some fibers of the cervical plexus also combine with the accessory and hypoglossal cranial nerves to supply dual innervation to some specific neck and pharyngeal muscles.
  • An important nerve that originate from cervical plexus with contribution from brachial plexus is phrenic nerve. It descend along each side of the neck to enter the thorax, after passing through mediastinum reaches the diaphragm

Brachial plexus

  • The brachial plexus is positioned to the side of the last four cervical vertebrae and the first thoracic vertebra.
  • It is formed by the anterior rami of C 5 through T 1 , with occasional contributions from C 4 and T 2.
  • From its emergence, the brachial plexus extends downward and laterally, passes over the first rib behind the clavicle, and enters the axilla.
  • Each brachial plexus innervates the entire upper extremity of one side, as well as a number of shoulder and neck muscles.
  • Structurally, the brachial plexus is divided into roots, trunks, divisions, and cords.
  • The roots of several spinal nerves unite to form trunks in the inferior part of the neck. These are the superior, middle, and inferior trunks. Posterior to the clavicles, the trunks divide into divisions, called the anterior and posterior divisions. In the axillae, the divisions unite to form cords called the lateral, medial, and posterior cords. The cords are named for their relationship to the axillary artery, a large artery that supplies blood to the upper limb. The principal nerves of the brachial plexus branch from the cords.
  • The important nerves that arise from the brachial plexus are axillary nerve, musculocutaneous nerve, radial nerve, ulnar and medial nerve

Lumbar plexus

  • The lumbar plexus is positioned to the side of the

first four lumbar vertebrae.

  • It is formed by the anterior rami of spinal nerves L 1

through L 4 and some fibers from T 12.

  • The nerves that arise from the lumbar plexus

innervate structures of the lower abdomen and

anterior and medial portions of the lower extremity.

Sacral Plexus

  • The sacral plexus lies immediately inferior to the lumbar plexus.
  • It is formed by the anterior rami of spinal nerves L 4 , L 5 ,and S 1 through S 4.
  • The nerves arising from the sacral plexus innervate the lower back, pelvis, perineum, posterior surface of the thigh and leg, and dorsal and plantar surfaces of the foot.
  • Because some of the nerves of the sacral plexus also contain fibers from the nerves of the lumbar plexus through the lumbosacral trunk, these two plexuses are frequently described collectively as the lumbosacral plexus.