Spinal Cord, Human Reflex

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Gross Anatomy of the Adult Spinal Cord

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Extends from the foramen magnum to L1 or L2Conus medularis - it is the end of the spinal

cord Denticulate ligaments – pia mater attaching the

spinal cord t the vertebral wallFilum terminale – pia mater extension from the

conus medularis to the coccix

Anatomy of the Spinal Cord

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Lumbar tap – removal of CSF from the vertebral canal bellow L3

Cervical and lumbar enlargements31 pairs of spinal nerves leave the spinal cordCauda equina – collection of spinal nerves at

the end of the spinal cord

Anatomy of the Spinal Cord

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The Spinal Cord and Spinal Meninges

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Spinal meninges

Three layersDura mater

Single layerEpidural space – between the vertebra

and dura. Filled with fat and blood vessels

ArachnoidSubarachnoid space – between

arachnoid and pia. Filled with CSFPia 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 neurogliaPosterior 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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Lateral gray horns contain visceral motor neurons

Gray commissures contain axons that cross from one side to the other

Central canal – filled with CSF

Gray matter

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White matter

Divided into six columns (funiculi) containing tracts

Posterior funiculiPosterior median sulcus

Anterior funiculiAnterior median fissure

Lateral funiculi

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Spinal Nerves

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8 pairs of cervicalAbove C7 all nerves emerge above the

corresponding vertebraC8 emerge between C7 and T1

12 pairs of thoracic5 pairs of lumbar5 pairs of sacralI pair of coccygeal

31 pairs of spinal nerves (mixed)

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OriginDorsal root and dorsal root ganglionVentral root

Dorsal ramus sensory and motor innervation to the skin

and muscles of the back

Spinal nerves

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Spinal nerves

Ventral ramus sensory and motor to the ventrolateral

body surface, body wall and limbsT2 – T12 form intercostal nervesAll other will form plexuses

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Complex interwoven network of nervesFour large plexuses

Cervical plexusBrachial plexusLumbar plexusSacral plexus

Nerve plexus

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Peripheral Nerves and Nerve Plexus

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The Cervical Plexus

Ventral rami of spinal nerves C1 to C5Innervate muscles of the neckInnervate 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 nerveShoulder

Musculocutaneous nerve Anterior brachial area

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The Brachial PlexusRadial 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 – L4Femoral Nerve

Anterior muscles of femoral areaObturator Nerve

Adductors of leg

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The Sacral Plexus

Posterior thigh, gluteal region, leg and footL4 – S4Sciatic nerve

Tibial nerveCommon fibular nerve

Pudendal nerveMuscles and skin of perineum

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Reflexes are rapid and predictable automatic responses to stimuli

Neural reflex involves sensory fibers to CNS and motor fibers to effectors

Spinal Reflexes

Five components Receptor – it is the site of the stimulus Sensory neuron – transmits the stimulusIntegration Center

Monosynaptic reflexPolysynaptic reflex

Motor neuron - conducts the impulse to the effector

Effector – muscle or gland

Reflex arc

Arc Reflex Components

Somatic ReflexesSpinal Reflexes

Patellar (knee-jerk)Achilles Triceps Biceps etc.

Reflex classification

The Babinski Reflexes

Reflex classification

Superficial reflexes Plantar reflex

• Normal response – curling the toe• Abnormal response – Babisnki’s sign

Corneal reflex - Cranial nerve VGag reflex

• Cranial nerves IX and X

Autonomic ReflexesPupillary reflex

Ipsilateral constriction of the pupilConsensual reflex

Contralateral constriction of the pupilCiliospinal reflex

Pupil dilation when pinching the neckSalivary reflex

Reflex classification