General information about the nervous system.. Human Anatomy, 3rd edition Prentice Hall, © 2001 Structure of the Spinal Cord Extends from the foramen

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


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


Meninges of the Spinal Cord


Meninges of the Spinal Cord


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


Example of Ascending Nerve Tracts


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


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”)


Dermatomes


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


Cervical Plexus• Formed by spinal nerves C1 – C5

– Nerves innervate the neck and shoulder region

– Phrenic nerve to the diaphragm


Brachial Plexus• Formed by spinal nerves C5 – C8 and T1

– Nerves innervate the arm and shoulder• Radial nerve• Ulnar nerve• Median nerve


Brachial Plexus


Lumbosacral Plexus


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


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


Sacral Plexus


Spinal Reflexes

• Reflexes are automatic responses to stimuli

• Spinal reflexes result from the stimulation of a spinal reflex arc.


Basic Elements of a Reflex Arc


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


•Cranial nerves 3&4 (oculomotor and trochlear) exit from the midbrain

•Midbrain also contains the headquarters of the reticular activating system


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


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.


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.


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.


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.


• 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.


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


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

Documents

General information about the nervous system.. Human Anatomy, 3rd edition Prentice Hall, © 2001 Structure of the Spinal Cord Extends from the foramen