General information about the
nervous system.
Human Anatomy, 3rd editionPrentice Hall, © 2001
Structure of the Spinal Cord• Extends from the foramen
magnum to the first or second lumbar vertebra.
• Ends in the conus medullaris
• Filum terminale– Extends from conus
medullaris to sacral vertebrae
• Cauda equina– = filum terminale + dorsal
& ventral roots from spinal nerves that extend below conus medularis
Human Anatomy, 3rd editionPrentice Hall, © 2001
Coverings of the Spinal Cord
• 3 layers called meninges
• Dura mater– Outer layer
• Arachnoid– Middle layer
• Pia mater– Adheres tightly to the surface of the spinal cord
Human Anatomy, 3rd editionPrentice Hall, © 2001
Meninges of the Spinal Cord
Human Anatomy, 3rd editionPrentice Hall, © 2001
Meninges of the Spinal Cord
Human Anatomy, 3rd editionPrentice Hall, © 2001
Sectional Anatomy of the Spinal Cord• Inner part consists of gray matter
– Unmyelinated cell bodies, neuroglia, & dendrites
– Organized into “horns”
• Outer part consists of white matter– Tracts of
myelinated fibers– Ascending tracts
are sensory– Descending tracts
are motor
Human Anatomy, 3rd editionPrentice Hall, © 2001
Example of Ascending Nerve Tracts
Human Anatomy, 3rd editionPrentice Hall, © 2001
Spinal Nerves• Connect to the spinal cord via a dorsal and a ventral root• Dorsal root is sensory
– Contains a dorsal root ganglion
• Ventral root is motor
Human Anatomy, 3rd editionPrentice Hall, © 2001
Spinal Nerves• The roots unite into
the spinal nerve• Spinal nerves exit
through intervertebral foramen
• Split into branches, or rami.– Dorsal ramus– Ventral ramus – Regions of skin
supplied by a spinal nerve = dermatomes (“skin slices”)
Human Anatomy, 3rd editionPrentice Hall, © 2001
Dermatomes
Human Anatomy, 3rd editionPrentice Hall, © 2001
Nerve Plexuses• Plexus = “braid”• Nerves supplying the
limbs form plexuses when they leave the spinal cord– Cervical plexus
– Brachial plexus– Lumbosacral plexus
• Lumbar plexus• Sacral plexus
Human Anatomy, 3rd editionPrentice Hall, © 2001
Cervical Plexus• Formed by spinal nerves C1 – C5
– Nerves innervate the neck and shoulder region
– Phrenic nerve to the diaphragm
Human Anatomy, 3rd editionPrentice Hall, © 2001
Brachial Plexus• Formed by spinal nerves C5 – C8 and T1
– Nerves innervate the arm and shoulder• Radial nerve• Ulnar nerve• Median nerve
Human Anatomy, 3rd editionPrentice Hall, © 2001
Brachial Plexus
Human Anatomy, 3rd editionPrentice Hall, © 2001
Lumbosacral Plexus
Human Anatomy, 3rd editionPrentice Hall, © 2001
Lumbar Plexus• Formed by spinal
nerves T12 and L1 – L4.
– Innervates the medial and anterior portions of the thigh and lower abdominal regions
– Lateral femoral cutaneous nerve
Human Anatomy, 3rd editionPrentice Hall, © 2001
Sacral Plexus
• Formed by spinal nerves L4 and L5, and S1 and S2– Innervates the
posterior portion of the hip, thigh, and leg, and the genital region
– Sciatic nerve
Human Anatomy, 3rd editionPrentice Hall, © 2001
Sacral Plexus
Human Anatomy, 3rd editionPrentice Hall, © 2001
Spinal Reflexes
• Reflexes are automatic responses to stimuli
• Spinal reflexes result from the stimulation of a spinal reflex arc.
Human Anatomy, 3rd editionPrentice Hall, © 2001
Basic Elements of a Reflex Arc
Human Anatomy, 3rd editionPrentice Hall, © 2001
Midbrain
• Located btwn the diencephalon and the pons.
– 2 bulging cerebral peduncles on the ventral side. These contain:
• Descending fibers that go to the cerebellum via the pons
• Descending pyramidal tracts
– Running thru the midbrain is the hollow cerebral aqueduct which connects the 3rd and 4th ventricles of the brain.
– The roof of the aqueduct ( the tectum) contains the corpora quadrigemina
• 2 superior colliculi that control reflex movements of the eyes, head and neck in response to visual stimuli
• 2 inferior colliculi that control reflex movements of the head, neck, and trunk in response to auditory stimuli
Human Anatomy, 3rd editionPrentice Hall, © 2001
•Cranial nerves 3&4 (oculomotor and trochlear) exit from the midbrain
•Midbrain also contains the headquarters of the reticular activating system
Human Anatomy, 3rd editionPrentice Hall, © 2001
Medulla Oblongata
• Nuclei in the medulla are associated w/ autonomic control, cranial nerves, and motor/sensory relay.
• Autonomic nuclei:
– Cardiovascular centers• Cardioinhibitory/
cardioacceleratory centers alter the rate and force of cardiac contractions
• Vasomotor center alters the tone of vascular smooth muscle
– Respiratory rhythmicity centers• Receive input from the pons
– Additional Centers• Emesis, deglutition, coughing,
hiccupping, and sneezing
Human Anatomy, 3rd editionPrentice Hall, © 2001
Medulla Oblongata
• Sensory & motor nuclei of 5 cranial nerves:
– Auditory/Vestibular (8), Glossopharyngeal (9), Vagus (10), Accessory (11), and Hypoglossal (12)
• Relay nuclei
– Nucleus gracilis and nucleus cuneatus pass somatic sensory information to the thalamus
– Olivary nuclei relay info from the spinal cord, cerebral cortex, and the brainstem to the cerebellar cortex.
Human Anatomy, 3rd editionPrentice Hall, © 2001
Spinal Cord
• Functions to transmit messages to and from the brain (white matter) and to serve as a reflex center (gray matter).
• Tube of neural tissue continuous w/ the medulla at the base of the brain and extends about 17” to just below the last rib. (Ends at L1)
• Majority of the SC has the diameter of your thumb• Thicker at the neck and end of the cord (cervical and
lumbar enlargements) b/c of the large group of nerves connecting these regions of the cord w/ the arms and legs.
Human Anatomy, 3rd editionPrentice Hall, © 2001
Spinal Cord
• Surrounded by a singlelayered dura mater and arachnoid and pia mater.
• Terminates in cone shaped structure called the conus medullaris.
– The filum terminale, a fibrous extension of the pia mater, extends to the posterior surface of the coccyx to anchor the spinal cord.
• The cord does not extend the entire length of the vertebral column – so a group of nerves leaves the inferior spinal cord and extends downward. It resembles a horses tail and is called the cauda equina.
Human Anatomy, 3rd editionPrentice Hall, © 2001
Cross Sectional Anatomy of the Spinal Cord
• Flattened from front to back.
• Anterior median fissure and posterior median sulcus partially divide it into left and right halves.
• Gray matter is in the core of the cord and surrounded by white matter.
Human Anatomy, 3rd editionPrentice Hall, © 2001
• Resembles a butterfly.• 2 lateral gray masses connected by the gray
commissure.• Posterior projections are the posterior or dorsal horns.• Anterior projections are the anterior or ventral horns.• In the thoracic and lumbar cord, there also exist lateral horns.
Human Anatomy, 3rd editionPrentice Hall, © 2001
Spinal Cord & Spinal Nerves
• Spinal cord
– Truly the pathway between body and mind– Conducts impulses to and from the brain– Carries out spinal reflexes
• Spinal nerves– 31 pairs– All are mixed nerves
Human Anatomy, 3rd editionPrentice Hall, © 2001
Spinal Cord Injuries
• Can affect sensory perception; motor paralysis
• Location affects severity of the injury
• Spinal compression results from squeezing the spinal cord within the vertebral canal
• Spinal transection is the severing of the spinal cord
Spinal Cord Injuries
• Quadriplegia
• Paraplegia
http://www.apparelyzed.com/paralysis.html