SPINAL CORD, SPINAL NERVE and SPINAL PLEXUSES

Continuation of the medulla oblangata (bulbus), the caudal part of the brain stem. 42-45 cm long Foramen magnum-L2 (L1-L3) Medullary cone 2 enlargements: cervical, lumbosacral

33 segments, 31 paired spinal nerves 8 cervical 12 thoracic 5 lumbar 5 sacralis 3 cocygeal (1 pair of spinal nerve) 1st cervical spinal nerve: between atlas and occipital bone 8th cervical cervical spinal nerve: between C7-T1 1st thoracic spinal nerve : betwen T1-T2

Distal End Conus medullaris: Cauda equina: Filum terminale: thin, conical end of the spinal cord Cauda equina: nerve roots extending below conus medullaris Filum terminale: thin thread of fibrous tissue at end of conus medullaris attaches to coccygeal ligament

Spinal Meninges Specialized membranes isolate spinal cord from surroundings protect spinal cord carry blood supply continuous with cranial meninges Pia mater-arachnoid mater –dura mater

Spinal Dura Mater tough and fibrous Cranially: fuses with periosteum of occipital bone continuous with cranial dura mater Caudally: tapers to dense cord of collagen fibers joins filum terminale in coccygeal ligament (for longitudinal stability)

The Epidural Space Between spinal dura mater and walls of vertebral canal (above the dura) No such space in the brain Contains loose connective and adipose tissue Anesthetic injection site

Inter-Layer Spaces – just like in the brain Subdural space: between arachnoid mater and dura mater Subarachnoid space: between arachnoid mater and pia mater filled with cerebrospinal fluid (CSF) Spinal Tap withdraws CSF from inferior lumbar region (below conus medularis) for diagnostic purposes. Where do they get the CSF?

Roots 2 branches of spinal nerves: Dorsal root ganglia: ventral root: contains axons of motor neurons dorsal root: contains axons of sensory neurons Dorsal root ganglia: contain cell bodies of sensory neurons Pseudounipolar neurons

White Matter fiber tracts for transmission of information ascending (sensory) tracts descending (motor) tracts Posterior funiculus Lateral funiculus Anterior funiculus

Some fiber tracts in the different funiculi Posterior funiculus: Faciculus cuneatus and gracilis Ascending sensory Lateral funiculus Spinothalamic tract Corticospinal tract Descending motor Anterior funiculus

Reflex Arc 1) Receptor - reacts to stimulus 2) Sensory Neurons - afferent impulses to CNS 3) Integration centers - synapses in CNS 4) Motor Neurons - efferent impulses from Integration centers to effector 5) Effector - muscle or glands

Spinal Cord Trauma: Transection Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut Paraplegia – transection between T1 and L1 Quadriplegia – transection in the cervical region; how high determines the extent of the damage