Anatomy and Physiology of Spinal Cord

1. SPINAL CORD
Dr. Tanuja Sawant
Associate Professor
Tilak Ayurved Mahavidyalaya, Pune

2. INTRODUCTION
 Information highway between brain and body
 Extends through vertebral canal from foramen
magnum to L1
 Each pair of spinal nerves receives sensory
information and issues motor signals to muscles and
glands
 Spinal cord is a component of the Central Nervous
System while the spinal nerves are part of the
Peripheral Nervous System
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3. ANATOMY OF THE SPINAL CORD
 Cylinder of nerve tissue within the vertebral canal
(thick as a finger)
 The length is about 45 cm in men and 43 cm in
women
 Anatomic course originates in the brainstem before
coursing through the foramen magnum. The spinal
cord continues distally through the cervical and
thoracic regions of the spinal column before
terminating as a tapered structure known as the
conus medullaris.
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4.  31 pairs of spinal nerves arise from cervical,
thoracic, lumbar and sacral regions of the cord
 Each cord segment gives rise to a pair of spinal
nerves
 Cord width ranges from 0.64-0.83 cm in the
thoracic region to 1.27-1.33 cm in the cervical and
lumbar regions
 Cervical and lumbar enlargements
 Medullary cone (conus medullaris) = tapered tip
of cord
 Cauda equinae is L2 to S5 nerve roots resemble
horse’s tail
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6. MENINGES AND SPACES
 Epidural space - fatty space between the bony framework of the
spinal vertebral column and the thick dura mater surrounding the
spinal cord. It contains adipose tissue and blood vessels.
 Dura mater - Thick outermost covering (meninges) of the spinal
cord, extending down to the level of the S2 vertebra
 Arachnoid mater - The middle covering of the spinal cord
 Subarachnoid space - Space between the arachnoid mater and
the innermost covering of the spinal cord. It contains Cerebrospinal
fluid.
 Pia mater - The innermost covering of the spinal cord, intimately
adhering to its surface, it stabilizes the spinal cord through lateral
extensions of the pia called the denticulate ligaments, extending
between the ventral and dorsal roots unto the dura mater.
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8. CROSS-SECTIONAL ANATOMY OF THE SPINAL
CORD
 Grey Matter – It is organized into an H- shaped body of cell
bodies. The anterior horn comprises motor nuclei while the
posterior horn comprises sensory nuclei.
 White Matter – It is organized into anterior, posterior and lateral
columns (funiculi), from neuronal axons organized into tracts that
convey neural messages back and forth the CNS (the ascending
and descending tracts).
 The anterolateral columns carry temperature and pain
information, while the dorsal column communicates the sense of
touch, proprioception, vibration. The cervical and thoracic spinal
segments present an intermediolateral gray horn which give off
preganglionic sympathetic fibers onto the sympathetic trunk on
both sides of the spinal cord.
 The spinal cord's central canal is an extension of the 4th
ventricle. It contains CSF, surrounding it is the gray commissure
and the anterior white commissure. Decussation of the tracts of
the white columns occurs at the anterior white commissure.
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10.  Central area of gray matter shaped like a
butterfly and surrounded by white matter in 3
columns
 Gray matter = neuron cell bodies with little
myelin
 White matter = myelinated axons
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11. GRAY MATTER IN THE SPINAL CORD
 Pair of dorsal or posterior horns
 dorsal root of spinal nerve is totally sensory fibers
 Pair of ventral or anterior horns
 ventral root of spinal nerve is totally motor fibers
 Connected by gray commissure punctured by a
central canal continuous above with 4th
ventricle
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12. WHITE MATTER IN THE SPINAL CORD
 White column = bundles of myelinated axons
that carry signals up and down to and from
brainstem
 3 pairs of columns or funiculi
 dorsal, lateral, and anterior columns
 Each column is filled with named tracts or
fasciculi (fibers with a similar origin, destination
and function)
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13. SPINAL TRACTS
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14.  Ascending and descending tract head up or
down while decussation means that the fibers
cross sides
 Contralateral means origin and destination are
on opposite sides while ipsilateral means on
same side
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15. BLOOD SUPPLY AND LYMPHATIC
 Anterior spinal artery - branch of the vertebral artery,
supplies the anterior 2/3 of the spinal segment
 Left and right posterior spinal arteries - The pair
posterior branches of the vertebral artery supply the
posterior 1/3 of the spinal segment
 Radiculo-medullary branches from the anterior and
posterior spinal arteries and the costocervical trunk
anastomose to supply the cervical region of the spinal
cord. The thoracolumbar segments of the spinal cord
receive extra arterial blood supply through radiculo-
medullary branches of segmental arteries from the
aorta; of note is the great radicular artery called
Adamkiewicz artery. It has a variable origin arising
anywhere between T9 and L5 vertebra.
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16. NERVES
 There are 31 spinal nerve pairs (mixed) that arise from the intervertebral
foramen on both sides of the vertebral column.
1. 8 Cervical nerves - C1 - C7 nerves arising from above corresponding
cervical vertebra except for C8 which exits from between C7 and T1
Vertebrae
2. 12 Thoracic nerves
3. 5 Lumber nerves
4. 5 Sacral nerves
5. 1 Coccygeal segment
 Nerves from the lower spinal segment exit terminal to the conus medullaris
and form the cauda equina.
 Ventral spinal nerve roots - make up the motor component of the spinal
innervation with rootlets arising from the anterior horn of the spinal segment,
sending motor impulses to muscles and joints, etc
 Dorsal spinal nerve roots - make up the sensory component, with the dorsal
ganglia sending sensory impulses via nerve rootlets to the posterior horn of
spinal segments.
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17. THE SPINAL NERVES
 Proximal branches
 dorsal root is sensory input to spinal cord
 ventral root is motor output of spinal cord
 cauda equina is roots from L2 to C0 of the cord
 Distal branches
 dorsal ramus supplies dorsal body muscle and skin
 ventral ramus to ventral skin and muscles and limbs
 meningeal branch to meninges, vertebrae and ligaments
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18. BRANCHES OF A SPINAL NERVE
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19. DORSAL COLUMN ASCENDING PATHWAY
 Deep touch,
 visceral pain, vibration, and proprioception
 Fasciculus gracilis and cuneatus carry signals
from arm and leg
 Decussation of 2nd order neuron in medulla
 13-14
 3rd order neuron in thalamus carries signal to
cerebral cortex
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20. SPINOTHALAMIC PATHWAY
 Pain, pressure, temperature, light touch, tickle
and itch
 Decussation of the second order neuron occurs
in spinal cord
 13-15
 Third order neurons arise in thalamus and
continue to cerebral cortex
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21. SPINORETICULAR TRACT
 Pain signals from tissue injury
 Decussate in spinal cord and ascend with
spinothalamic fibers
 End in reticular formation (medulla and pons)
 3rd and 4th order neurons continue to thalamus
and cerebral cortex
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22. SPINOCEREBELLAR PATHWAY
 Proprioceptive signals from limbs and trunk
travel up to the cerebellum
 Second order nerves ascend in ipsilateral
lateral column
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23. CORTICOSPINAL TRACT
 Precise, coordinated limb movements
 Two neuron pathway
 upper motor neuron in cerebral cortex
 lower motor neuron in spinal cord
 13-18
 Decussation in medulla
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24. DESCENDING MOTOR TRACTS
 Tectospinal tract (tectum of midbrain)
 reflex turning of head in response to sights and
sounds
 Reticulospinal tract (reticular formation)
 controls limb movements important to maintain
posture and balance
 Vestibulospinal tract (brainstem nuclei)
 postural muscle activity in response to inner ear
signals
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25. NERVE PLEXUSES
 Ventral rami branch and anastomose repeatedly
to form 5 nerve plexuses
 cervical in the neck, C1 to C5
 supplies neck and phrenic nerve to the diaphragm
 brachial in the armpit, C5 to T1
 supplies upper limb and some of shoulder and neck
 lumbar in the low back, L1 to L4
 supplies abdominal wall, anterior thigh and genitalia
 sacral in the pelvis, L4, L5 and S1 to S4
 supplies remainder of lower trunk and lower limb
 coccygeal, S4, S5 and C0
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26. CUTANEOUS INNERVATION AND DERMATOMES
 Each spinal nerve receive sensory input from a
specific area of skin called dermatome
 Overlap at edges by 50%
 a total loss of sensation requires anesthesia of 3
successive spinal nerves
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27. NATURE OF SOMATIC REFLEXES
 Quick, involuntary, stereotyped reactions of
glands or muscle to sensory stimulation
 automatic responses to sensory input that occur
without our intent or often even our awareness
 Functions by means of a somatic reflex arc
 stimulation of somatic receptors
 afferent fibers carry signal to dorsal horn of spinal
cord
 one or more interneurons integrate the information
 efferent fibers carry impulses to skeletal muscles
 skeletal muscles respond
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28. THE STRETCH (MYOTATIC) REFLEX
 When a muscle is stretched, it contracts and
maintains increased tonus (stretch reflex)
 helps maintain equilibrium and posture
 head starts to tip forward as you fall asleep
 muscles contract to raise the head
 stabilize joints by balancing tension in extensors and
flexors smoothing muscle actions
 Very sudden muscle stretch causes tendon reflex
 knee-jerk (patellar) reflex is monosynaptic reflex
 testing somatic reflexes helps diagnose many
diseases
 Reciprocal inhibition prevents muscles from
working against each other
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29. SPINAL CORD TRAUMA
 10-12,000 people/ year are paralyzed
 55% occur in traffic accidents
 This damage poses risk of respiratory failure
 Early symptoms are called spinal shock
 Tissue damage at time of injury is followed by
post-traumatic infarction
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30. SPINAL CORD INJURY (SCI) PATTERNS
1. Descriptive
 Tetraplegia
 Cervical spine injury resulting in impaired arm/trunk/leg/pelvic
organ function Paraplegia
 Thoracic/lumbar/sacral spinal injury leading to impaired
trunk/leg/pelvic organ function Preserved arm function
 Complete injuries
 By definition, a complete SCI yields no sparing of the motor or
sensory function below the injured level
 The patient must have already recovered from the acute phase of
spinal shock (usually 48 hours from presentation)
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31.  Spina bifida - Neural tube defect in which the
neural tube does not completely close leaving a
dorsal defect. Folate deficiency in early pregnancy
is a risk factor. The severity of symptoms depends
on the extent of the defect; myelomeningocele is
the most severe variant with the spinal cord,
meninges both exposed. Other variants include
meningocele, which exposes only the meninges,
and spina bifida occulta which is the mildest.
 Symptoms include loss of lower limb sensations,
lower limb weakness, urinary incontinence, bowel
incontinence
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32. COMPLETE / INCOMPLETE INJURIES
 A complete spinal cord injury means that there is a total blockage
of signals from the brain to your sacral nerves. An incomplete
spinal cord injury means there is some preservation of nerves
from the brain to the lowest part of the spinal cord, the sacral
level. The amount of movement and feeling that is lost is different
for each person as it depends on the extent of your spinal cord
damage.
 Every spinal nerve activates certain muscles, and this is tested at
intervals following injury by medical staff, physiotherapists and
nurses. Every spinal nerve also transmits the sensation from a
particular patch of your skin to the brain, and this is tested with
various types of sensation.
 Every person with spinal cord damage will be different in how
much they can move or feel. How your injury affects you will be
unique to you.
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33. SPINAL SHOCK
 Initially after spinal cord damage there is a period of
spinal shock when your reflexes are not present.
These reflexes can return anytime up to 3 months,
usually between 1 to 6 weeks. Until your reflexes
return there is a ‘flaccid’ effect.
 The loss of spinal reflexes results in flaccid
paralysis below the level of your injury. This also
results in lower blood pressure and heart rate, slow
gut motility, and reduced urine output.
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34. CHANGES TO REFLEXES AFTER SPINAL CORD
INJURY
 Depending on your level and extent of neurological injury reflexes may or may
not be present as outlined below:
 Above T12/L1 reflexes should be present below the level of your injury (this is
known as ‘reflexic’)
 At T12/L1 may have some reflexes intact below the level of your injury
 Below T12/L1 will generally have no reflexes below the level of your injury
(this is known as “flaccid”)
 If reflexes are present after your SCI, you will probably experience involuntary
muscle movement to a stimulus. The response to the stimulus will not be the
same as before your injury. The message that goes to the brain telling it what
has just happened is blocked by your spinal cord injury.
 Furthermore, your brain can’t send a message back to cancel the muscle
movement.
 Spasm is an exaggerated reflex response to a stimulus. Spasm can be useful
because it helps to keep your muscle tone and improve circulation. However,
sometimes spasms can be very severe, and may need to be controlled by
medication.
 Reflexes can also be used for such things as emptying your bladder and
bowel after SCI. This is not under voluntary control, because of the
disconnection of the body’s communication system to the brain, but can
nevertheless be useful.
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35. CARRYING SIGNALS
 Your body registers the stimulus i.e. stubbing your
toe.
 The message moves up the nerves into the spinal
cord.
 The reflex is activated as the message comes out
of the spinal cord causing the limb to move
involuntary.
 Finally the message is sent up the spinal cord to
the brain to register the action.
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36. REFLEXIC/FLACCID
Reflexic (reflexes present) Flaccid (no reflexes present)
Has spasm. Some muscle wastage No spasms therefore more muscle
wastage
May be able to use a reflex to trigger
bladder emptying
Loss of bladder tone. Need to self-
catheterise
Can use a reflex to trigger bowel
evacuation with suppositories and/or
stimulation
Slower gut motility. Can evacuate
bowel by straining, pushing or manual
evacuation
Tight bladder and bowel sphincters Flaccid bladder and bowel sphincters
May get reflexic erections Does not have reflexic erections.
It is important to know whether your reflexes are intact as this affects
many body functions and therefore management options.
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37. PHYSICAL EFFECTS OF SPINAL CORD INJURY ON
YOUR BODY
 As well as changes in movement and sensation to your
body, effects on skin, bladder, bowel and sexual function
below the level of your SCI, other body systems and
functions may also be affected.
 Breathing and Coughing
People with tetraplegia and high level paraplegia lose spinal
nerve supply to the chest and abdominal muscles. Your
ability to cough is affected, and assistance to cough may be
required. Chest physiotherapy is important, especially in the
initial stages after injury. People with high level tetraplegia
may also lose innervation to the diaphragm, which is the
band of muscle at the bottom of the rib cage which allows
us to breathe. In some cases a ventilator may be required
for you to breathe.
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38.  Heart Rate, Blood Pressure and Circulation
Changes to your body’s autonomic nervous system after
SCI especially in people with lesions above T6 result in
altered control of your heart rate, blood pressure and
circulation,. Your blood pressure is lowered, your heart
rate is slower, and blood circulation slows. Together with
reduced mobility this results in blood pooling in your
legs, increasing the risk of blood clots. The fall in blood
pressure can also result in you becoming dizzy and
feeling faint when sitting upright quickly. This tends to
resolve over time as your body gets used to its new
physiology. In the initial stages wearing an abdominal
binder, anti-embolic stockings, or having someone raise
your legs and tilting the wheelchair backwards (with
brakes on) helps.
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39.  Temperature Regulation
After SCI, especially in people with tetraplegia, it can be
difficult for your body to regulate its temperature
effectively, as sweating (to cool the body) and shivering
(to heat the body) is impaired. Wearing appropriate
clothing is important as you will be prone to taking on
the temperature in the environment around you.
 Autonomic Dysreflexia
This is a medical emergency, which affects people with
SCI above T6. Autonomic dysreflexia is a rise in blood
pressure in response to a stimulus below the level of
your injury. If left untreated the blood pressure can
continue to rise to dangerous levels. It is vital that all
spinal cord injured people with a lesion above T6 know
how to treat this emergency. (See section on Autonomic
Dysreflexia).
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40. THANK YOU !