The Spinal Cord
November 11th 2007 14:28
The Spinal Cord
The spinal cord is a cylindrical mass of nerve tissues extending from the foramen magnum in the skull to the area between the first and second lumbar vertebrae at the conus medullaris. It is divided into three major sections (Figure 31) namely the cervical (C1-C8 spinal segments), thoracic (T1- T12 segments), lumbar (L1- L5), and sacral (S1- S5 segments).
Enlargements can be seen at the cervical and lumbosacral junctions of the spinal cord. These enlargements are sites where the brachial plexus and the lumbosacral plexus originate. These groups of peripheral nerves (brachial and lumboscral) control the upper and lower extremity functions.
The groups of spinal nerve roots from the conus medullaris to the most inferior aspect of the spine is collectively known as the cauda equina.
Figure 30. The end portion of the spinal cord
Looking at the transverse section of the spinal cord we shall see two major layers: an inner and an outer layer (Figure 31).
Figure 31. The layers of the spinal cord
The inner is composed of gray matter, seen as an H-shaped pillar with anterior and posterior gray columns or horns, joined by a thin gray commissure containing the central canal.
The anterior horn of the spinal cord is where impulses for muscular contraction from the brain exit in order to reach the muscles. The posterior gray column on the other hand, receives sensory stimuli from the sensory nerves in order for the stimuli to be passed on to the brain.
However lateral horns can also be found in the thoracolumbar junction that give rise to the preganglionic fibers of the autonomic nervous system.
The outer layer of the spinal cord is composed of white matter. It is also where the ascending and descending fiber systems for signal transmission are found.
The tables below show the ascending and descending tracts of the spinal cord. These also show their contributions to overall nervous system function.
Table 4. Ascending Tracts (sensory functions)
Table 5. Descending Tracts (Motor functions)
Myotomes (www.apparelyzed.com)
Each muscle in the body is innervated by a particular level or segment of the spinal cord and by its corresponding spinal nerve.
C3,4 and 5 supply the diaphragm (the large muscle between the chest and the belly that we use to breath).
C5 also supplies the shoulder muscles and the muscle that we use to bend our elbow .
C6 is for bending the wrist back.
C7 is for straightening the elbow.
C8 bends the fingers.
T1 spreads the fingers.
T1 –T12 supplies the chest wall & abdominal muscles.
L2 bends the hip.
L3 straightens the knee.
L4 pulls the foot up.
L5 wiggles the toes.
S1 pulls the foot down.
S3,4 and 5 supply the bladder. bowel and sex organs and the anal and other pelvic muscles
Dermatomes
In the same manner any part of the body may be cutaneously innervated by a spinal segment and its corresponding spinal nerve (Figure 32).
Figure 32. Dermatome
The spinal cord is a cylindrical mass of nerve tissues extending from the foramen magnum in the skull to the area between the first and second lumbar vertebrae at the conus medullaris. It is divided into three major sections (Figure 31) namely the cervical (C1-C8 spinal segments), thoracic (T1- T12 segments), lumbar (L1- L5), and sacral (S1- S5 segments).
Enlargements can be seen at the cervical and lumbosacral junctions of the spinal cord. These enlargements are sites where the brachial plexus and the lumbosacral plexus originate. These groups of peripheral nerves (brachial and lumboscral) control the upper and lower extremity functions.
The groups of spinal nerve roots from the conus medullaris to the most inferior aspect of the spine is collectively known as the cauda equina.
Figure 30. The end portion of the spinal cord
Looking at the transverse section of the spinal cord we shall see two major layers: an inner and an outer layer (Figure 31).
The inner is composed of gray matter, seen as an H-shaped pillar with anterior and posterior gray columns or horns, joined by a thin gray commissure containing the central canal.
The anterior horn of the spinal cord is where impulses for muscular contraction from the brain exit in order to reach the muscles. The posterior gray column on the other hand, receives sensory stimuli from the sensory nerves in order for the stimuli to be passed on to the brain.
However lateral horns can also be found in the thoracolumbar junction that give rise to the preganglionic fibers of the autonomic nervous system.
The outer layer of the spinal cord is composed of white matter. It is also where the ascending and descending fiber systems for signal transmission are found.
The tables below show the ascending and descending tracts of the spinal cord. These also show their contributions to overall nervous system function.
Table 4. Ascending Tracts (sensory functions)
Table 5. Descending Tracts (Motor functions)
Myotomes (www.apparelyzed.com)
Each muscle in the body is innervated by a particular level or segment of the spinal cord and by its corresponding spinal nerve.
C3,4 and 5 supply the diaphragm (the large muscle between the chest and the belly that we use to breath).
C5 also supplies the shoulder muscles and the muscle that we use to bend our elbow .
C6 is for bending the wrist back.
C7 is for straightening the elbow.
C8 bends the fingers.
T1 spreads the fingers.
T1 –T12 supplies the chest wall & abdominal muscles.
L2 bends the hip.
L3 straightens the knee.
L4 pulls the foot up.
L5 wiggles the toes.
S1 pulls the foot down.
S3,4 and 5 supply the bladder. bowel and sex organs and the anal and other pelvic muscles
Dermatomes
In the same manner any part of the body may be cutaneously innervated by a spinal segment and its corresponding spinal nerve (Figure 32).
Figure 32. Dermatome
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