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Spinal Cord, Human
Reflex
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Gross Anatomy of the Adult Spinal
Cord
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Anatomy of the Spinal Cord
 Extends from the foramen magnum to L1 or L2
 Conus medularis - it is the end of the spinal
cord
 Denticulate ligaments – pia mater attaching the
spinal cord t the vertebral wall
 Filum terminale – pia mater extension from the
conus medularis to the coccix
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Anatomy of the Spinal Cord
 Lumbar tap – removal of CSF from the vertebral
canal bellow L3
 Cervical and lumbar enlargements
 31 pairs of spinal nerves leave the spinal cord
 Cauda equina – collection of spinal nerves at
the end of the spinal cord
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The Spinal Cord and Spinal Meninges
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Spinal meninges
 Three layers
Dura mater
Single layer
Epidural space – between the vertebra
and dura. Filled with fat and blood
vessels
Arachnoid
Subarachnoid space – between
arachnoid and pia. Filled with CSF
Pia mater
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The Spinal Cord and Spinal Meninges
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Sectional Organization of the Spinal
Cord
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Structures of the spinal cord
 Gray Matter
 Cell bodies, unmyelinated axons,
dendrites and neuroglia
Posterior or dorsal horns – interneurons
and sensory fibers coming from the
dorsal root ganglion
Anterior or ventral horns – cell bodies of
the somatic motor neurons that send
their axons to the ventral root
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Gray matter
 Lateral gray horns contain visceral motor
neurons
 Gray commissures contain axons that cross
from one side to the other
 Central canal – filled with CSF
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White matter
 Divided into six columns (funiculi) containing
tracts
 Posterior funiculi
Posterior median sulcus
 Anterior funiculi
Anterior median fissure
 Lateral funiculi
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Spinal Nerves
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31 pairs of spinal nerves (mixed)
 8 pairs of cervical
Above C7 all nerves emerge above the
corresponding vertebra
C8 emerge between C7 and T1
 12 pairs of thoracic
 5 pairs of lumbar
 5 pairs of sacral
 I pair of coccygeal
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Spinal nerves
 Origin
Dorsal root and dorsal root ganglion
Ventral root
 Dorsal ramus
sensory and motor innervation to the skin
and muscles of the back
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Spinal nerves
 Ventral ramus
sensory and motor to the ventrolateral
body surface, body wall and limbs
T2 – T12 form intercostal nerves
All other will form plexuses
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Nerve plexus
 Complex interwoven network of nerves
 Four large plexuses
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
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Peripheral Nerves and Nerve Plexus
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The Cervical Plexus
 Ventral rami of spinal nerves C1 to C5
 Innervate muscles of the neck
 Innervate the diaphragm
Phrenic nerve (C3, C4,C5)
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Cervical Plexus
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Brachial Plexus
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Brachial Plexus
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The Brachial Plexus
 Axillary nerve
Shoulder
 Musculocutaneous nerve
 Anterior brachial area
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The Brachial Plexus
 Radial nerve
 Posterior arm and hand
 Median nerve
 Anterior antebrachial area
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The Brachial Plexus
 Ulnar nerve
 Anterior antebrachial area
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The Lumbar and Sacral Plexuses
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Lumbar Plexus
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The Lumbar Plexus
 Lower abdominopelvic region and the
anterior thigh
 L1 – L4
 Femoral Nerve
Anterior muscles of femoral area
 Obturator Nerve
Adductors of leg
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The Sacral Plexus
 Posterior thigh, gluteal region, leg and foot
 L4 – S4
 Sciatic nerve
Tibial nerve
Common fibular nerve
 Pudendal nerve
Muscles and skin of perineum
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Spinal Reflexes
 Reflexes are rapid and predictable automatic
responses to stimuli
 Neural reflex involves sensory fibers to CNS
and motor fibers to effectors
Reflex arc
 Five components
 Receptor – it is the site of the stimulus
 Sensory neuron – transmits the stimulus
Integration Center
Monosynaptic reflex
Polysynaptic reflex
 Motor neuron - conducts the impulse to
the effector
 Effector – muscle or gland
Arc Reflex Components
Reflex classification
 Somatic Reflexes
Spinal Reflexes
Patellar (knee-jerk)
Achilles
Triceps
Biceps etc.
The Babinski Reflexes
Reflex classification
Superficial reflexes
Plantar reflex
• Normal response – curling the toe
• Abnormal response – Babisnki’s sign
Corneal reflex - Cranial nerve V
Gag reflex
• Cranial nerves IX and X
Reflex classification
 Autonomic Reflexes
Pupillary reflex
Ipsilateral constriction of the pupil
Consensual reflex
Contralateral constriction of the pupil
Ciliospinal reflex
Pupil dilation when pinching the neck
Salivary reflex