Spinal cord
 Traditional starting point for detailed
consideration of CNS
 Uniform and simple organization of other
parts of CNS
 Very important in day-to-day activities that
we don’t even think about
 Contains all neurons supplying the muscles
used in bodily movements, as well as a major
population of autonomic nerves
 Receives all sensory input from body and
some from head- performs initial processing
on most of this input
 The spinal cord provides a crucial information
conduit, connecting the brain with most of
the body.
 It is the target of a number of disease
processes, some of which (eg, spinal cord
compression) are treatable but rapidly
progressive if not treated.
 Failure to diagnose some disorders of the
spinal cord, such as spinal cord compression,
can be catastrophic and may relegate the
patient to a lifetime of paralysis.
 A knowledge of the architecture of the spinal
cord and its coverings, and of the fiber tracts
and cell groups that comprise it, is essential.
Basic facts
 Length 42-45 cm
 Maximum dia. 1 cm
 Weight 35 g
 Anatomically segmented in terms of
attached nerve roots
 Spinal segment= portion of spinal cord giving
rise to a spinal nerve
 31 segments- 8 cervical, 12 thoracic, 5 lumbar,
1 coccygeal
 No external signs of segmentation
 2 enlargements- cervical and lumbar
 Ends caudally in a pointed conus medullaris
 Enlargements contain large number of motor
neurons
 Cervical enlargement is in C5-T1 segmentssupplies upper limb
 Lumbar enlargement- L2 –S3 segments;
supplies lower limbs
 Spinal cord segments are related
systematically to areas of skin and muscles
 The sensory component of each spinal nerve
is distributed to a dermatome, a well-defined
segmental portion of the skin
 in many patients there is no C1 dorsal root,
there is no C1 dermatome
 when a C1 dermatome does exist as an
anatomic variant, it covers a small area in the
central part of the neck, close to the occiput
 dermatomes for C5, C6, C7, C8, and T1 are
confined to the arm
 C4 and T2 dermatomes are contiguous over
the anterior trunk.
 thumb, middle finger, and fifth digit are
within the C6, C7, and C8 dermatomes,
respectively
 Nipple-T4
 Umbilicus – T 10
 The territories of dermatomes tend to
overlap, making it difficult to determine the
absence of a single segmental innervation on
the basis of sensory testing
 Knowledge of segmental skin and muscle
innervation helps in diagnosis of injuries in or
around spinal cord
Myotomes
 myotome refers to the skeletal musculature
innervated by motor axons in a given spinal
root
 Most muscles are innervated by motor axons
that arise from several adjacent spinal roots.
 Nevertheless, lesions of a single spinal root,
in many cases, can cause weakness and
atrophy of a muscle
Segment-Pointer Muscles.
Root
Muscle
 C5






 C5
 C6
 C7
 L3, L4
 L5
 S1
Deltoid
Biceps
Brachioradialis
Triceps
Quadriceps femoris
Extensor hallucis
longus
 Gastrocnemius
Correlation between length of
spinal cord and vertebral column
 Spinal cord approaches adult length before
vertebral canal
 Until 3rd month of fetal life- same growth
rates
 Later- body and vertebral column grow faster
than spinal cord
 At birth spinal cord ends at L3 vertebra
 At few months of age- ends about the level of
L1 vertebra
 Nerves exit through same intervertebral
foramina as they did in fetal life
 Each dorsal root ganglion is at the level of
appropriate foramen
 The lower nerve roots have to travel longer
distances to reach their foramina of
 Below L1 -L2 level of vertebral column the
collection of dorsal and ventral roots is called
cauda equina
Spinal Gray Matter Is Regionally
Specialized
 The anterior horn contains the cell bodies of
the large motor neurons that supply skeletal
muscle
 These alpha motor neurons, also referred to
as lower motor neurons, are the only means
by which the nervous system can exercise
control over body movements, whether
voluntary or involuntary;
 a number of different parts and pathways of
the nervous system can influence these lower
motor neurons, but they alone can elicit
muscle contraction.
 Destruction of the lower motor neurons
supplying a muscle or interruption of their
axons therefore causes complete paralysis of
that muscle.
 Lower motor neuron lesions cause paralysis
of a type called flaccid paralysis, indicating
that the muscle is limp and uncontracted.
 Two columns of motor neurons in the anterior
horn of the cervical cord are recognized as
separate entities.
 The spinal accessory nucleus extends from
the caudal medulla to about C5.
 The phrenic nucleus, containing the motor
neurons that innervate the diaphragm, is
located in the medial portion of the anterior
horn in segments C3 to C5..
 This makes injuries to the upper cervical
spinal cord a matter of grave concern
 destruction of the descending pathways that
control the phrenic nucleus and other
respiratory motor neurons renders a patient
unable to breathe
 The gray matter that is intermediate to the
anterior and posterior horns has some
characteristics of both and also contains the
spinal preganglionic autonomic neurons.
 In addition, at some levels it includes a
distinctive region called Clarke's nucleus.
 The preganglionic sympathetic neurons for
the entire body lie in segments T1 through L3
 most of them located in a column of cells
called the intermediolateral cell column,
which forms a pointy lateral horn on the
spinal gray matter
 Their axons leave through the ventral roots.
 Cells in a corresponding location in segments
S2 to S4 constitute the sacral
parasympathetic nucleus but do not form a
distinct lateral horn.
 Their axons leave through the ventral roots
and synapse on the postganglionic
parasympathetic neurons for the pelvic
viscera
Clarke's nucleus (or the
nucleus dorsalis)
 rounded collection of large cells located on
the medial surface of the base of the
posterior horn from about T1 to L2.
 particularly prominent at lower thoracic levels
 important relay nucleus for the transmission
of information to the cerebellum
 may also play a role in forwarding
proprioceptive information from the leg to
the thalamus.
 Because of its prominent role in sensory
processing, it is treated by many as part of
the posterior horn.
 The remainder of the intermediate gray
matter is a collection of various projection
neurons, sensory interneurons, and
interneurons that synapse on motor neurons.
 The posterior horn consists mainly of
interneurons whose processes remain within
the spinal cord and of projection neurons
whose axons collect into long, ascending
sensory pathways.
 This area of gray matter contains two
prominent parts, the substantia gelatinosa
and the body of the posterior horn
 Both are present at all spinal levels.
 Between the substantia gelatinosa and the
surface of the cord is a relatively pale-staining
area of white matter called Lissauer's tract.*
 This tract stains more lightly than the rest of
the white matter ;contains the finely
myelinated and unmyelinated fibers with
which the substantia gelatinosa deals.
 The body of the posterior horn consists
mainly of interneurons and projection
neurons that transmit various types of
somatic and visceral sensory information
 In this respect it functionally overlaps parts of
the intermediate gray matter.
substantia gelatinosa
 distinctive region of gray matter that caps
the posterior horn
 In myelin-stained preparations this region
looks pale compared with the rest of the gray
matter because it deals mostly with finely
myelinated and unmyelinated sensory fibers
that carry pain and temperature information.
Rexed’s laminae
Rexed's laminae
 Lamina I
 This thin marginal layer contains neurons that
respond to noxious stimuli [pain,
temperature] and send axons to the
contralateral spinothalamic tract.
 Lamina II- substantia gelatinosa
 made up of small neurons, some of which
respond to noxious stimuli.
 Substance P, a neuropeptide involved in
pathways mediating sensibility to pain, is
found in high concentrations in laminas I and
II.
 Laminas III and IV
[nucleus proprius]
Their main input is from fibers that convey
position and light touch sense.
 Lamina V
contains cells that respond to both noxious and
visceral afferent stimuli.
 Lamina VI
 deepest layer ,contains neurons that respond
to mechanical signals from joints and skin.
Lamina VII
 contains the cells of the dorsal nucleus
(Clarke's column) medially as well as a large
portion of the ventral gray column.
 Clarke's column contains cells that give rise to
the posterior spinocerebellar tract.
 also contains the intermediolateral nucleus
(or intermediolateral cell column) in thoracic
and upper lumbar regions.
 Preganglionic sympathetic fibers project
from cells in this nucleus, via the ventral roots
and white rami communicantes, to
sympathetic ganglia.
Laminas VIII and IX
 represent motor neuron groups in the medial
and lateral portions of the ventral gray
column
 The medial portion (also termed the medial
motor neuron column) contains the LMNs
that innervate axial musculature
 The lateral motor neuron column contains
LMNs for the distal muscles of the arm and
leg
 flexor muscles are innervated by motor
neurons located close to the central canal
 extensor muscles are innervated by motor
neurons located more peripherally
Lamina X
 represents the small neurons around the
central canal or its remnants.
White Matter
 composed of myelinated and unmyelinated
nerve fibers.
 The fast-conducting myelinated fibers form
bundles (fasciculi) that ascend or descend for
varying distances
 Fiber bundles with a common function are
called tracts
 The lateral and ventral white columns contain
tracts that are not well delimited and may
overlap in their cross sectional areas
 the dorsal column tracts are sharply defined
by glial septa
Location of tracts
Descending tracts in the Spinal
Cord.
 Lateral corticospinal
(pyramidal) tract
 Fine motor function
(controls distal
musculature)
Modulation of
sensory functions
 Anterior
corticospinal tract
 Vestibulospinal tract
 Gross and postural
motor function
(proximal and axial
musculature
 Postural reflexes
 Rubrospinal
 Reticulospinal
 Motor function
 Modulation of
sensory
transmission
(especially pain)
Modulation of spinal
reflexes
 Descending
autonomic
 Tectospinal
 Medial longitudinal
fasciculus
 Modulation of
autonomic
functions
 Reflex head turning
 Coordination of
head and eye
movements
Ascending tracts
 Dorsal column
system
 Spinothalamic
tracts
 Fine touch,
proprioception,
two-point
discrimination
 Sharp pain,
temperature, crude
touch
 Dorsal spinocerebellar
tract
 Movement and
position mechanisms
 Ventral spinocerebellar
 Movement and
position mechanisms
Somatotopic organization (segmental
arrangement) in the spinal cord.
Spinal Cord Circulation
Arteries-Anterior Spinal
Artery
 formed by the midline union of paired
branches of the vertebral arteries
 descends along the ventral surface of the
cervical spinal cord, narrowing somewhat
near T4.
Posterolateral Spinal Arteries
 arise from the vertebral arteries and course
downward to the lower cervical and upper
thoracic segments.
Radicular Arteries
 Some (but not all) of the intercostal arteries
from the aorta supply segmental (radicular)
branches to the spinal cord from T1 to L1.
 The largest of these branches, the great
ventral radicular artery, also known as the
arteria radicularis magna, or artery of
Adamkiewicz, enters the spinal cord
between segments T8 and L4
 usually arises on the left and, in most
individuals, supplies most of the arterial
blood supply for the lower half of the spinal
cord.
 occlusion in this artery is rare, it results in
major neurologic deficits (eg, paraplegia, loss
of sensation in the legs, urinary
incontinence).
Posterior Spinal Arteries
 paired arteries
 much smaller than the single large anterior
spinal artery
 branch at various levels to form the
posterolateral arterial plexus.
 supply the dorsal white columns and the
posterior portion of the dorsal gray columns.