Chapter 13: The Spinal Cord and Spinal Nerves BIO 210 Lab Instructor: Dr. Rebecca Clarke

Spinal Cord Structurally and functionally integrated with brain Occupies upper two-thirds of vertebral column (adult: 1.5 ft long, 0.5 in. wide) Ends between vertebrae L1 and L2

Gross Anatomy of the Spinal Cord Divided into 4 regions (like vertebrae): Cervical (C) Thoracic (T) Lumbar (L) Sacral (S) 31 Pairs of spinal nerves Named for regions Cervical numbered for vertebra below Rest numbered for vertebra above Figure 13-2

Gross Anatomy of the Spinal Cord: Distal End Conus medullaris (medullary cone): Conical structure at T-L junction Filum terminale (terminal filum): Thin strand of fibrous tissue at end of conus medullaris Cauda equina (“horse tail”): Bundle of elongated nerve roots extending below conus medullaris (L2-S5) Note: After age 4, vertebral column continues to elongate but spinal cord does not therefore roots elongate) Figure 13-2

Sectional Anatomy of the Spinal Cord Posterior median sulcus: Groove on posterior side Anterior median fissure: Deeper, wider groove on anterior side Gray matter covered by thick layer of white matter Figure 13–5a

Sectional Anatomy of the Spinal Cord: Gray Matter Neuron cell bodies, neuroglia, unmyelinated axons H- or butterfly-shape with horns (projections) Gray commissure – where axons connect R/L sides Central canal in middle; contains CSF Figure 13–5a

Sectional Anatomy of the Spinal Cord: Gray Matter Cell bodies organized in nuclei in horns of gray matter: Somatic and visceral Sensory (dorsal) and motor (ventral) Figure 13–5a

Sectional Anatomy of the Spinal Cord: White Matter Spinal tracts (bundles of myelinated axons) arranged in columns Have similar distribution as nuclei in gray matter Relay same type of info (sensory or motor) in same direction (ascending or descending) to brain Figure 13–5a

Gross Anatomy of a Spinal Nerve Forms 2 branches on each side of spinal cord: Dorsal root: Contains axons of sensory (afferent) neurons coming from receptors Ventral root: Contains axons of motor (efferent) neurons going to effectors Dorsal root ganglion: Contains cell bodies of sensory neurons Figure 13-2

Mixed Nerves Carry both sensory (afferent) and motor (efferent) fibers Spinal nerves are mixed nerves

Spinal Nerves and Plexuses

Spinal Nerves and Plexuses

Nerve Plexus Complex interwoven network of nerve fibers of adjacent spinal nerves Formed during development Nerves arising at a plexus: Are mixed nerves (like spinal nerves) Control skeletal muscles of neck, upper torso, limbs

4 Major Nerve Plexuses Cervical plexus Brachial Lumbar Sacral  Neck, thoracic cavity, diaphragm  Phrenic nerve Brachial  Shoulder/pectoral girdle and upper limbs  Radial and ulnar nerves Lumbar  Pelvic girdle and lower limbs  Femoral nerve Sacral  Sciatic nerve Figure 13–9

Brachial Plexus

Meninges Specialized, protective membranes Separate, isolate, protect soft tissue of: Spinal cord from bones of vertebra (spinal meninges) Brain from bones of skull (cranial meninges) Spinal meninges continuous with cranial meninges Have 3 layers: Dura (“hard”) mater – outermost covering Arachnoid mater – middle layer Pia (“delicate”) mater – innermost layer

Gross Anatomy of Spinal Cord and Meninges Spinal cord located in vertebral foramen Epidural space Between vertebra and dura mater Contains loose connective tissue, blood vessels, adipose tissue Epidural block Injection of anesthetic Used to control pain Figure 13–3

Gross Anatomy of Spinal Cord and Meninges Dura mater Arachnoid mater Subarachnoid space Between arachnoid membrane and pia mater Filled with CSF Acts as shock absorber Carries dissolved gases, nutrients, chemical messengers, waste products Spinal tap Withdrawal of CSF for diagnostic purposes when CNS infection suspected, for back pain, headaches, disc problems, etc. Pia mater Figure 13–3

Meningitis Meningitis: Viral or bacterial infection of meninges

Sympathetic Chain Ganglia String of ganglia alongside spinal cord Figure 16–5

Sympathetic Chain Ganglia Figure 16–4a