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The Nervous System Spinal Cord, Spinal Nerves


The Nervous System Spinal Cord, Spinal Nerves & Tracts Anatomy Chapters 14 & 15 The Spinal Cord Begins at foramen magnum, runs through vertebral foramen (spinal ... – PowerPoint PPT presentation

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Title: The Nervous System Spinal Cord, Spinal Nerves

The Nervous SystemSpinal Cord, Spinal Nerves
  • Anatomy Chapters 14 15

The Spinal Cord
  • Begins at foramen magnum, runs through vertebral
    foramen (spinal canal), ends at L2 vertebral
    level by forming conus medularis
  • The spinal cord (as well as the brain) is well
    protected by bones, CT membranes (meninges), and
    fluid (cerebrospinal fluid (CSF))

Meninges membranes that surround and protect
the CNS
  • Three layers
  • Dura mater
  • Arachnoid mater
  • Pia mater

Dura Mater tough, fibrous CT outer membrane
one layer thick around spinal cord with epidural
space external
Arachnoid mater spidery web-like middle
layer Pia Mater delicate, thin inner layer
Filum terminale - extension of pia mater extends
from tip of cord to coccyx to anchor cord in
place Denticulate ligaments - anchor cord
Subarachnoid space between arachnoid pia
mater contains cerebrospinal fluid (CSF) Lumbar
cistern area of subarachnoid space below the
conus medularis site for lumbar puncture
(spinal tap)
Spinal Cord Anatomy
  • Begins at foramen magnum ends at L2 vertebral
    level by forming conus medularis
  • Has 2 thickened areas-
  • cervical enlargement - supplies nerves to upper
  • lumbar enlargement - supplies nerves to lower

  • Made up of 31 spinal cord segments

Dorsal root ganglion (DRG)
Dorsal root
Ventral root
  • Each spinal cord segment has a pair of
  • dorsal roots with their associated dorsal root
    ganglia (DRG)
  • ventral roots

  • Each dorsal root contains the axons of sensory
  • Each dorsal root ganglion contains the cell
    bodies of these sensory neurons
  • Each ventral root contains the axons of motor

The dorsal ventral roots of each segment come
together at the intervertebral foramen (IVF) to
form a mixed spinal nerve
Spinal Nerves
  • Part of the PNS
  • Contain both motor sensory fibers
  • 31 pair of nerves each nerve forms from union
    of dorsal/ventral root of spinal cord segment
    exits between vertebra at IVF
  • 8 pair cervical spinal nerves 1st cervical
    nerve exits between occipital bone C1, 8th
    cervical nerve exits the IVF between C7-T1
  • 12 pair thoracic spinal nerves
  • 5 pair lumbar nerves
  • 5 pair sacral nerves
  • 1 pair coccygeal nerves

Below the conus medularis, spinal nerves must
angle downward (in the subarachnoid space) before
exiting their IVF/sacral foramina. These spinal
nerves make up the cauda equina
Cauda equina
Sectional Anatomy of the Spinal cord
Gray commissure
The spinal cord has a narrow central canal
surrounded by horns of gray matter connected by
commissures. Gray matter horns contain sensory
motor nuclei (groups of cell bodies) glial
cells. Gray matter is surrounded by white matter
columns (aka funiculi) which are made up of
groups of myelinated axons creating organized
ascending descending tracts (aka fasciculi).
Tracts (Motor Sensory Pathways)(Chap. 15)
  • Groups of axons found in the white matter
    columns of the spinal cord that carry specific
  • Ascending tracts - carry sensory information up
    the spinal cord to areas of the brain (eventually
    terminating in cerebrum or cerebellum)
  • Descending tracts carry motor information from
    the brain down to specific levels of the spinal
    cord (eventually terminating on skeletal muscles)

Ascending Tracts
  • Three major groups of pathways transmit somatic
    sensory information originating from receptors,
    up the spinal cord to the brain
  • Spinothalamic tracts
  • Posterior column pathways
  • Spinocerebellar tracts

Spinothalamic tracts
Anterior spinothalamic tract (ASTT) crude touch
pressure Lateral spinothalamic tract (LSTT)
pain temperature
Posterior Column Pathways
  • Fasciculus cuneatus fasciculus gracilis
  • conscious proprioception (joint position)
  • discriminitive (fine) touch (2-point
    discrimination, stereognosis, graphism)
  • vibration
  • pressure

Spinocerebellar Tracts
  • Anterior spinocerebellar tract (ASCT) Posterior
    spinocerebellar tract (PSCT)
  • unconscious proprioception (from golgi tendon
    organs, muscle spindles joint capsules)
  • muscle tone
  • balance

Descending Pathways
  • Carry motor signals from conscious unconscious
    areas of the brain, down the spinal cord to
    control contraction of skeletal muscles
  • Corticospinal pathways (aka Pyramidal tracts)-
    include anterior lateral corticospinal tracts,
    and corticobulbar tracts) conscious motor
  • Subconscious Motor Pathways include medial and
    lateral pathways

Corticospinal (Pyramidal) Pathways
  • Corticobulbar tracts voluntary control of
    skeletal muscles of head neck through cranial
  • Lateral corticospinal tracts (LCST) voluntary
    control of skeletal muscles in neck body
    fibers cross in pyramidal decussation of M.O.
  • Anterior corticospinal tracts (ACST) - voluntary
    control of skeletal muscles in neck body
    fibers cross at spinal cord level in anterior

Medial Lateral Pathways
Originate from subconscious areas of the brain
and are integrated with corticospinal pathways to
allow for coordination of motor activity,
maintenance of posture and muscle tone Medial
pathways unconscious control over head, eyes,
neck, trunk proximal limb muscles for gross
muscle movements include vestibulospinal,
tectospinal, reticulospinal tracts Lateral
pathways unconscious control over distal limb
muscles for precise muscle movements include
rubrospinal tracts
In order for sensory information to enter the
spinal cord and ascend in a sensory tract, and
for motor information to get from a descending
tract to reach a skeletal muscle, impulses must
travel through peripheral nerves (spinal nerves
cranial nerves)
Spinal Nerves
  • 31 pair
  • Part of PNS
  • Formed by union of ventral (motor) root and
    dorsal (sensory) root

Once formed, spinal nerves will branch into Rami
  • Dorsal ramus transmits sensations from skin of
    back neck provides motor control of deep
    muscles of back found at all spinal nerves

  • Ventral ramus provides motor control to
    muscles of extremities, anterior lateral trunk
    transmits sensations from all but skin of back
    found at all spinal nerves

  • Rami communicantes (white ramus gray ramus)
    carry autonomic motor fibers (ANS) to smooth
    muscles glands in ventral body cavity transmit
    visceral sensations only found at T1-L2 spinal

Nerve Plexuses
Adjacent ventral rami will form complex
interwoven networks of nerve fibers (axons) known
as a nerve plexus Four plexuses cervical,
brachial, lumbar, sacral Emerging from each
plexus will be specifically named peripheral
nerves, which will contain fibers from multiple
spinal cord levels
Cervical plexus (C1-C5)
Motor control for muscles of neck region, levator
scapulae, scalenes, SCM trapezius (along with
CN XI), and diaphragm Sensory from upper chest,
shoulder, neck ear regions
  • Phrenic nerve (C3-C5)

Brachial plexus (C5-T1)
Motor to sensory from pectoral girdle region
upper extremities
  • Axillary nerve (C5-C6)
  • Musculocutaneous nerve (C5-7)
  • Radial nerve (C5-T1)
  • Median nerve (C6-T1)
  • Ulnar nerve (C8-T1)

Lumbar plexus (T12-L4)
Motor to muscles of abdominal, pelvic and lower
extremity (anterior medial) regions Sensory
from skin of abdomen, pelvis lower extremity
  • Femoral nerve (L2-L4)
  • Lateral femoral cutaneous nerve (L2-L3)
  • Iliohypogastric nerve (T12-L1)
  • Obturator nerve (L2-L4)

Sacral plexus (L4-S4)
Motor to muscles of pelvis and lower extremity
(gluteal, posterior femoral, lower leg
foot) Sensory from posterior pelvis, posterior
thigh, anterior, posterior lateral leg
  • Sciatic nerve (L4-S3)
  • Tibial nerve
  • Common peroneal (fibular) nerve

Ventral rami from T2-T11 do not participate in a
plexus. Instead they form individual intercostal
nerves (aka thoracic nerves) Motor supply to
intercostal abdominal muscles sensory from
anteriolateral thorax/abdomen