-Length: 45cm (17-18in); Ends at level L1-2 in adults.

-Enlargements: in cervical (C4-T1) and lumbar (T11-L1) regions for innervation of upper and lower limbs.

-Conus Medullaris: pointed cone-shaped end of spinal cord L1-2.

-Cauda Equina: Collection of dorsal & ventral nerve roots at inferior ends of spinal cord filling in the vertebral canal.

Brain/spinal cord covered by 3 layers of CT (meninges):
Epidural space lies between vertebrae & dura mater; contains fat.

1. Dura Mater: Outermost layer; very thick and tough.

2. Arachnoid Mater: Middle layer; delicate membrane with numerous fine branching fibers (spiderweb-like appearance); space between arachnoid and pia =

Subarachnoid space: contains cerebral spinal fluid.

3. Pia Mater: inner most layer; very thin; adherent to spinal cord except for:

Denticulate Ligaments-20-22 pairs along length of cord which hold cord in place within vertebral column and Filum Terminale- a thin, thread-like extension of pia that holds spinal cord to sacrum. 

31 pairs; leave vertebral column through appropriate intervertebral foramina; formed by 2 adjacent vertebrae

-Cervical: 8 pairs (C1-C8); cords leave above corresponding vertebrae; ex: C1 in between skull & C1.

-Thoracic: 12 pairs (T1-T12); cords leave below coresponding vertebrae; ex: T1 in between T1 & T2.

-Lumbar: 5 pairs (L1-L5); also exit inferior to corresponding vertebrae.

-Sacral: 5 pairs (S1-S5); exit through correct sacral foramina.

-Coccygeal: 1 pair (CO)

Contain both afferent & efferent fibers;

-Ventral Roots: arrise from anterior side of spinal nerve; contains outgoing or efferent (motor) information; sends info to innervate skeletal muscles.

-Dorsal Roots: arrise from posterior side of spinal nerve; contains incoming or afferent (sensory) information; causes impulses from periphery located receptors to spinal cord.

Roots almost immediately unite after passing through dura mater to form a mixed spinal nerve which will then divide again to form a ventral ramus (to anterior/lateral trunk & extremities) and dorsal ramus (to deep back).

Meningeal Branch: innervates meninges and smaller branches of ANS called Rami Communicantes.

Posterior Body Trunk: muscles and skin by dorsal rami

Anterolateral Thorax & Abdomen Wall: muscles and skin by ventral rami

Gray Matter: contains dorsal (sensory neurons) and ventral horns (motor neurons).

White Matter: contains motor fibers/tracts descending from brain and sensory fibers/tracts ascending to brain.

-An area of skin innervated by the cutaneous (sensory) branch of a single spinal nerve;

-All except C1 participate in dermatomes;

-Adjacent dermatomes on body wall are fairly uniform in width and arranged horizontally; those in extremites are longitudinally arranged.

-Trunk dermatomes regions overlap

-Limbs less obvious overlap

Upper Limbs: ventral rami C5-T1

Lower Limbs: ventral rami L1-S2

-Braid or network of several spinal nerves which come together to supply the upper extremities

Ventral Rami (5): C5-T1; can have postfix or prefix brachial plexus-contribution from C4 or T2 (one level higher/lower)

Trunks (3): formed from rami; Upper Trunk- C5-6; Middle Trunk- C7; & Lower Trunk- C8-T1.

Divisions (2): formed from trunks; Anterior Division- Flexor compartments; Posterior Division: Extensor compts.

Cords (3): formed from divisions; Lateral Cord- anterior division of upper & middle trunks; Medial Cord- anterior division of lower trunk; Posterior Cord- posterior divisions of all 3 trunks

Branches (5): formed from cords; Axillary Nerve- smaller branch of posterior cord; Radial Nerve- larger branch of posterior cord; Musculocutaneous Nerve- 1 branch of lateral cord; Ulnar Nerve- 1 branch of medial cord; Median Nerve- 1/2 branch of both lateral and medial cord

-A network of nerves which supply the lower extremities; 

Lumbar Plexus: L1-4 (contributions from T12); forms 2 major branches- Femoral Nerve (iliacus/anterior thigh) & Obturator Nerve (medial thigh)

Sacral Plexus: L4-S4; major branch= Sciatic Nerve which splits into Tibial Nerve (hamstrings/posterior leg) & Common Fibular Nerve (lateral/anterior leg)

-Other branches: Superior Gluteal Nerve (gluteus medius & minimus/tensor fascia lata), Inferior Gluteal Nerve (gluteus maximus), & Pudendal Nerve (skin of perineum)

Protrusion of nucleus pulposus into the annulus fibrosus of an intervertebral disc;

Pushes on nerve root exiting from cord;

Common in lumbar region of back (L4-5 or L5-S1);

Sciatic nerve affected- causes pain in lower back, weakened hamstrings, and weakness of posterior leg muscles (sciatica)