Ga - Spine, Spinal Cord, And Spinal Nerves

Front 1

In a newborn child, the spine consists of...

Back 1

-7 cervical vertebrae in the neck,
-12 thoracic vertebrae in the thorax (chest),
-5 lumbar vertebrae in the abdomen, and
-5 sacral vertebrae and 4 coccygeal vertebrae in the pelvis.

Front 2

Sacrum and Coccyx

Back 2

By adulthood, the 5 sacral vertebrae have fused with each other to form a wedge-shaped bone called the sacrum, and the 4 coccygeal vertebrae have fused with each other to form an arrowhead-shaped bone called the coccyx.

Front 3

Cervical Curvature

Back 3

-The spine in a midgestational fetus is concave anteriorly.
-At sometime between late intrauterine life and 3 to 4 months after birth, a secondary curvatuve that is concave posteriorly appears in the neck region. This Cervical Curvature is an adaptation by the cervical region of the spine to support the head.

Front 4

Lumbar Curvature

Back 4

o At some time between 12 and 18 months after birth, another secondary curvature that is concave posteriorly appears in the lumbar region. This Lumbar Curvature is an adaptation by the lumbar region of the spine to support the upper body in the upright position.

Front 5

Why do these curvatures form and what about the other 2 vertebrae?

Back 5

-The formations of the cervical and lumbar curvatures arise primarily from changes in the shapes of intervertebral discs.
-The spinal curvatures in the thoracic and sacral regions retain their anterior concavity after development of the cervical and lumbar curvatures. The curvatures in the thoracic and sacral regions are called, respectively, the Thoracic and Sacral Curvatures.

Front 6

Kyphosis, Lordosis, and Scoliosis

Back 6

-An exaggerated thoracic curvature is called a Kyphosis (hunch)
-An exaggerated lumbar curvature is called a Lordosis.
-An abnormal lateral curvature of the spine is called a Scoliosis.

Front 7

Typical Vertebrae - which ones are typical vertebrae and what are they composed of?

Back 7

-In an adult, all the vertebrae from the 3rd cervical vertebra down to the 5th lumbar vertebra share a common structure, and thus are called typical vertebrae.
-A typical vertebra is composed of a Body anteriorly and a Vertebral Arch posteriorly. The space encircled by the body and vertebral arch is called the Vertebral Foramen; the spinal cord descends through this foramen.

Front 8

Pedicles and Laminae

Back 8

-The vertebral arch is composed of paired Pedicles and paired Laminae.
-The pedicles, which are the most anterior parts of the vertebral arch, project posterolaterally from the body;
-The laminae, which are the most posterior parts of the vertebral arch, fuse with each other in the midline

Front 9

Seven processes project outward from the vertebral arch.

Back 9

-A Spinous Process projects posteriorly from the region of union of the laminae.
-A Transverse Process projects laterally on each side from the region of union between the pedicle and lamina.
-Superior and Inferior Articular Processes on each side respectively project superiorly and inferiorly from the pedicle.

Front 10

How does an adjacent pair of typical vertebrae connect to each other?

Back 10

-Each typical vertebra forms two synovial joints and one secondary cartilaginous joint with (a) the vertebra above and (b) the vertebra below.
-Between each adjacent pair of typical vertebrae, the inferior articular processes of the vertebra above form a pair of synovial joints with the superior articular processes of the vertebra below, and the body of the vertebra above forms a secondary cartilaginous joint with the body of the vertebra below.

Front 11

Secondary Cartilaginous Joint

Back 11

-Also called a Symphysis
-Is a joint in which the articular surfaces of the bones are covered with plates of hyaline cartilage, and the hyaline cartilage plates are united by a plate of fibrous cartilage.

Front 12

Intervertebral Discs - what are they, how are they named, and what are the two regions in these discs??

Back 12

-The intervertebral discs are the discs of fibrous cartilage that unites the bodies of adjacent vertebra in their secondary cartilaginous joints.
-Each intervertebral disc is named for the vertebra immediately above it. For example, the intervertebral disc between the 3rd and 4th cervical vertebrae is called the intervertebral disc of the 3rd cervical vertebra.
-Each intervertebral disc consists of a central region called the Nucleus Pulposus surrounded by a circumferential region called the Anulus Fibrosis

Front 13

Nucleus Pulposus - what is it and what's its function (1)

Back 13

The nucleus pulposus is a gelatinous mass with a very high water content (70 to 80%);
-it functions as a noncompressible but deformable pad of tissue between the bodies of two vertebrae.

Front 14

Anulus Fibrosis - what is it and what's its function (1)

Back 14

The anulus fibrosis is a fibrocartilaginous band of tissue that retains in place the more fluid nucleus pulposus.

Front 15

How many pairs of spinal nerves emerge from the spinal cord as it descends through the vertebral canal and what do they consist of?

Back 15

-31 pairs of spinal nerves emerge from the spinal cord as it descends through the vertebral canal. They consist of
-8 pairs of Cervical Spinal Nerves (C1-C8),
-12 pairs of Thoracic Spinal Nerves (T1-T12),
-5 pairs of Lumbar Spinal Nerves (L1-L5),
-5 pairs of Sacral Spinal Nerves (S1-S5), and
-1 pair of Coccygeal Spinal Nerves (Co1).
-The spinal nerves in each group are numbered, with the first pair in each group being the most superior pair.

Front 16

Intervertebral Foramen - what are they?

Back 16

-Each spinal nerve (except for C1) exits the spine by passing through an Intervertebral Foramen.
The intervertebral foramina of the spine are the spaces on each side between the pedicles of adjacent vertebrae. C1 exits the spine by passing between the base of the skull and the 1st cervical vertebra.

Front 17

Where does each spinal nerve exit the spine?

Back 17

-The thoracic, lumbar, sacral, and coccygeal spinal nerves each exit the spine immediately BELOW the vertebra of the same name. For example, T5 exits the spine via the intervertebral foramen immediately below the 5th thoracic vertebra.
-The cervical spinal nerves (except for C8) each exit the spine immediately ABOVE the vertebra of the same name. For example, C4 exits the spine via the intervertebral foramen immediately above the 4th cervical vertebra.
-C8 exits the spine via the intervertebral foramen between the 7th cervical and the 1st thoracic vertebrae.

Front 18

How does each spinal nerve begin and where does it go?

Back 18

-Each spinal nerve begins as an Anterior Root and a Posterior Root that respectively emerge from the anterolateral and posterolateral aspects of the spinal cord.
-As the roots exit the spine via an intervertebral foramen, they unite with each other to form a Spinal Nerve Trunk. -The spinal nerve trunk extends for only a few millimeters before branching into two nerve bundles called the Anterior and Posterior Rami.

Front 19

Spinal Cord Segment

Back 19

-The transverse segment of the spinal cord that gives rise to the anterior and posterior roots for each pair of spinal nerves is called the Spinal Cord Segment for the spinal nerve pair.

Front 20

Lower Motor Neurons and Anterior Gray Horns

Back 20

-Each spinal cord segment bears the cell bodies of the motor fibers that the segment’s spinal nerve pair transmits to the periphery. The motor neurons are called Lower Motor Neurons, and their cell bodies reside within the Anterior Gray Horns of the segment

Front 21

Posterior Root Ganglion

Back 21

-Also called dorsal root ganglion or vertebral ganglion
-The cell bodies of the sensory fibers that each segment’s spinal nerve pair transmits from the periphery reside, on each side, within the enlargement, called the Posterior Root Ganglion (dorsal root ganglion, vertebral ganglion), that occurs along the length of the posterior root.

Front 22

Path of motor fibers versus that of sensory fibers

Back 22

-All the motor fibers that exit each spinal nerve segment exit via the anterior roots only of that segment’s spinal nerve pair.
-All the sensory fibers that enter each spinal cord segment enter via the posterior roots only of that segment’s spinal nerve pair.
-The roots and rami of spinal nerves thus differ in that whereas rami transmit both motor and sensory fibers, anterior roots transmit motor fibers only and posterior roots transmit sensory fibers only.

Front 23

Deep Tendon Reflexes (Myotatic Reflexes, Phasic Stretch Reflexes) - neuromuscular spindles and homonymous lower motor neurons - where they are and what they do

Back 23

-Every skeletal muscle harbors in its interior stretch receptor organs called Neuromuscular Spindles. -Sensory nerve fibers extend from the neuromuscular spindles into the spinal cord, where they form synapses with Homonymous Lower Motor Neurons
-Homonymous lower motor neurons are lower motor neurons that innervate the same skeletal muscle innervated by the sensory fibers.
-The homonymous lower motor neurons reside in the same spinal cord segments into which the sensory fibers extend.

Front 24

Myotatic Reflexes - When a skeletal muscle is stretched...

Back 24

-When a skeletal muscle is stretched, the increased tension excites the muscle’s neuromuscular spindles and the sensory fibers innervating the spindles.
-The sensory fibers transmit action potentials to the homonymous lower motor neurons, and the excited lower motor neurons elicit a brief contraction of the skeletal muscle.
-The reflexive contraction of a skeletal muscle in response to a stretching stimulus is called a Myotatic Reflex (phasic stretch reflex).

Front 25

DTR during a physical examination - how it's done and its implications

Back 25

-During the physical examination of a patient, it is common practice for the examiner to try to elicit myotatic reflexes from certain muscles in the upper and lower limbs; this is because abnormal myotatic reflexes indicate neuromuscular disease or injury.
-These myotatic reflexes are frequently called deep tendon reflexes because the examiner elicits the myotatic reflexes by using a reflex hammer to suddenly stretch the tendon of insertion of an upper or lower limb muscle.

Front 26

Dermatomes - what are they, where are they found, and what provides them with what they use

Back 26

-The segmental derivation of the spinal nerves is manifested on the surface of the body by the segmental innervation of the skin. In other words, the cutaneous sensory neurons of the spinal nerves innervate the body’s skin in a segmental, strip-like fashion. The strip-like area of skin innervated by the cutaneous sensory neurons of a spinal nerve is called the Dermatome of that spinal nerve.
-The dermatomes collectively cover all the body surface except for most for the face. Every spinal nerve pair except for the C1 pair has a dermatome.
-A spinal nerve provides most (BUT NOT ALL) of the cutaneous sensory fibers in its dermatome. A significant number of cutaneous sensory fibers are provided by the spinal nerves that innervate bordering dermatomes.

Front 27

Conus Medullaris - what is it, and where is it during birth and adulthood

Back 27

-The lower end of the spinal cord is called the Conus Medullaris
-At birth, the conus medullaris generally lies at the level of the 2nd or 3rd lumbar vertebra.
-During childhood and adolescence, the spine grows longitudinally faster than the spinal cord.
-The consequence of this growth differential is that In An Adult The Conus Medullaris Generally Lies At The Level Of The Lower Border Of The Body Of The 1st Lumbar Vertebra.

Front 28

Cauda Equina

Back 28

-Because the spinal cord is not as long as the spine, the anterior and posterior roots of the lowest spinal nerves must descend to or below the level of the conus medullaris before exiting the spine.
-The collection of spinal nerve roots that descends below the conus medullaris resembles the collection of hairs at the end of a horse’s tail, and thus the collection is called the Cauda Equina (which is the Latin expression for horse’s tail).

Front 29

Meninges

Back 29

-The brain and the spinal cord are enveloped by three membranes called the Meninges. -The spinal meninges (the meninges that envelop the spinal cord) are direct continuations of the cranial meninges (the meninges that envelop the brain).
-For both the brain and spinal cord, the innermost meningeal layer is called the Pia Mater, the middle layer the Arachnoid Mater, and the outermost layer the Dura Mater.

Front 30

Subarachnoid Space (location) and Cerebrospinal Fluid (CSF)(composition/concentration)

Back 30

-The space between the arachnoid mater and pia mater is called the subarachnoid space. The subarachnoid space is filled with a fluid called cerebrospinal fluid (CSF). -CSF is a clear, colorless, watery fluid derived from blood plasma; it normally contains only a few lymphocytes. Although its electrolyte concentration closely resembles that of blood plasma, its protein concentration is markedly lower.

Front 31

CSF Path and Function (1)

Back 31

-CSF is secreted into a series of four chambers within the brain and ultimately flows into the subarachnoid space surrounding the brain and spinal cord.
-CSF serves to support the brain and spinal cord in a fluid environment of uniform pressure.

Front 32

Meningitis - what is it, how is it caused, where does it infect, and symptoms

Back 32

-Meningitis is inflammation of the meninges. In most cases, inflammation is the result of infection by bacterial, viral, or parasitic agents.
-The infectious process almost invariably extends throughout the subarachnoid space to involve both the cranial and spinal meninges.
-Cases of viral meningitis are generally benign and self-limiting in duration. Cases of bacterial meningitis have serious sequelae (serious conditions resulting as a consequence of disease) or a fatal outcome if not promptly treated with appropriate antibiotics.
-Symptoms of meningitis include fever, headache, alterations in mental status (such as lethargy or confusion), photophobia (enhanced sensitivity to light), stiff neck, and nausea and vomiting. It is believed that most of these symptoms are a consequence of increased intracranial pressure and inflammation of sensory nerves.

Front 33

Lumbar Puncture

Back 33

-Also called a spinal tap
-In cases of suspected meningitis, a sample of CSF is collected for cell count, bacterial culture, and chemical analysis.
-The collection procedure is called a Lumbar Puncture (spinal tap) because the CSF is drawn through a needle that punctures the spinal dura mater and arachnoid mater in the lower lumbar region of the spine.

Front 34

The lower lumbar region is selected for a spinal tap because of the following anatomical relationships:

Back 34

-The spinal subarachnoid space extends inferiorly farther than the spinal cord. Whereas the conus medullaris ends in an adult at the lower border of the body of the 1st lumbar vertebra, the subarachnoid space ends at the lower border of the body of the 2nd sacral vertebra.
-This difference between the lower limits of the spinal cord and spinal subarachnoid space makes it possible to collect samples of CSF from the lower lumbar region without risking direct damage to the spinal cord.

Front 35

To perform a lumbar puncture...

Back 35

-The patient is either seated or lain in a lateral decubitus position (a sidelying position), with the lumbar portion of the spine maximally flexed (the flexion increases the heights of the spaces between the spinous processes of the lumbar vertebrae).
*The highest point of the iliac crest is used to mark the level of the spinous process of the 4th lumbar vertebra. In most instances, the needle is inserted into the interspinous space between the spinous processes of the 4th and 5th lumbar vertebrae. *

Front 36

The spinal needle gains entrance into the subarachnoid space by passing through the following series of tissues:

Back 36

-skin
-superficial fascia, -supraspinous ligament, -interspinous ligament
-one of the flaval ligaments
-the connective tissue of the epidural space
-the dura mater
-the arachnoid mater