Download - Anatomy -Spinal Cord & Spinal Nerves
The Nervous SystemThe Nervous SystemSpinal Cord & Spinal Spinal Cord & Spinal
NervesNerves
The Nervous SystemThe Nervous SystemSpinal Cord & Spinal Spinal Cord & Spinal
NervesNervesAnatomy Anatomy
Dr. Edita RevayDr. Edita Revay
The Central Nervous System
Meninges – Connective tissues that surround and protect the brain and spinal cord
The CNS is well protected by bone, CT, and fluid
Dura Mater – tough, fibrous outer layer; 2 layers thick around brain with creation of dural sinuses between layers; 1 layer around spinal cord with epidural space external
Arachnoid – “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 laterally
Subarachnoid space – between arachnoid & pia mater; contains cerebral spinal fluid (CSF)
Lumbar cistern – area of subarachnoid space below the conus medularis; site for lumbar puncture (“spinal tap”)
Lumbar cystern
The Spinal Cord Begins at foramen magnum & ends at L2 vertebral level by forming conus medularis
Made up of 31 spinal cord segments
Has 2 thickened areas-
cervical enlargement - supplies nerves to upper extremity
lumbar enlargement - supplies nerves to lower extremity
•Each spinal cord segment has a pair of
• dorsal roots with their associated dorsal root ganglia (DRG)
• ventral roots
Dorsal root ganglion (DRG)
Dorsal root
Ventral root
• Each dorsal root contains the axons of sensory neurons
• Each dorsal root ganglion contains the cell bodies of these sensory neurons
• Each ventral root contains the axons of motor neurons
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. These spinal nerves make up the cauda equina
Cauda equina
Sectional Anatomy of the Spinal cord
Anterior median fissure
Posterior median sulcus
Lateral gray horn (T1-L2, S2-S4) - autonomic
Anterior gray horn - motor
Central canal
Gray commissure
Anterior column
Lateral column
Posterior column
Posterior gray horn - sensory
Key Note
The spinal cord has a narrow central canal surrounded by “horns” of gray matter connected by a commissure. Gray matter horns contain sensory & motor nuclei (groups of cell bodies).
Gray matter is surrounded by white matter “columns” which are made up of groups of myelinated axons creating organized ascending & descending tracts.
Tracts (Motor & Sensory Pathways)
• Groups of axons found in the white matter columns of the spinal cord that carry specific information
• Ascending tracts - carry sensory information up the spinal cord to areas of the brain (cerebrum or cerebellum)
• Descending tracts – carry motor information from the brain down to specific levels of the spinal cord
Ascending Tracts (Pathways)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 tractsAnterior spinothalamic tract (ASTT) – crude touch & pressure
Lateral spinothalamic tract (LSTT) – pain & temperature
THALAMUS
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 PathwaysThree major pathways carry motor signals from conscious & unconscious areas of the brain, down the spinal cord to control contraction of skeletal muscles
Corticospinal tracts
Medial pathways
Lateral pathways
Corticospinal (Pyramidal) Tracts Corticobulbar tracts – voluntary control of skeletal muscles of head & neck
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 commissure
Medial & Lateral PathwaysIntegrated with corticospinal pathways to allow for coordination of motor activity, maintenance of posture and muscle tone
Medial pathways – unconscious control over trunk & proximal limb muscles for gross muscle movements
Lateral pathways – unconscious control over distal limb muscles for precise muscle movements
Tracts include: vestibulospinal, tectospinal, reticulospinal & rubrospinal
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
Dorsal ramus – transmits sensations from skin of back & neck; provides motor control of deep muscles of back
Once formed, spinal nerves will branch into Rami
Ventral ramus – provides motor control to muscles of extremities, anterior & lateral trunk; transmits sensations from all but skin of back
Rami communicantes – carry autonomic motor fibers (ANS) to smooth muscles & glands in ventral body cavity; transmit visceral sensations
Nerve Plexuses
Adjacent ventral rami will form complex interwoven networks of nerve fibers known as a nerve plexus
Emerging from each plexus will be specifically named peripheral nerves, which will contain fibers from multiple spinal cord levels
Cervical plexus (C1-C5) Phrenic nerve (C3-C5)
Brachial plexus (C5-T1)
Axillary nerve (C5-C6)
Musculocutaneous nerve (C5-7)
Radial nerve (C5-T1)
Median nerve (C6-T1)
Ulnar nerve (C8-T1)
Lumbar plexus (T12-L4)
Femoral nerve (L2-L4)
Iliohypogastric nerve (T12-L1)
Obturator nerve (L2-L4)
Sacral plexus (L4-S4)
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
Dermatomes
Dorsal & ventral rami of spinal nerves provide control of skeletal muscle contraction & carry sensory input from the skin
Dermatomes – segmental sensory “map” of the body related to spinal nerve levels