Spinal Cord and Nerves Anatomy

• The objective is to learn the anatomy of the spinal cord and spinal nerves and reflexes

Introduction

• The main functions of the spinal cord include conveying information between neurons connecting peripheral structures to the brain, and processing information.
• The spinal cord is encased in a hard bony structure called the vertebral column.
• It is a continuous structure starting at the foramen magnum and terminating at the L1 and L2 intervertebral column.
• Thirty-one pairs of spinal nerves emerge from the spinal cord.

Anatomy of Spinal Region

• Meninges are the outermost protective membrane of the brain and spinal cord, made of connective tissue and continuous with cranial meninges.
• The dura mater is the outermost tough protective layer.
• The epidural space is the space between the dura mater and the vertebral column, filled with adipose tissue for cushioning and blood vessel network.
• The subdural space is the space between the dura mater and the arachnoid mater.
• The arachnoid mater is the middle layer with a spider web-like appearance.
• The subarachnoid space is the space between the arachnoid and pia mater filled with cerebrospinal fluid (CSF).

Central Gray Matter

• It has a butterfly or "H" shape and appears gray due to neuron cell bodies (somas) and non-myelinated axons, dendrites, synapses, and neuroglia.
• It is divided into dorsal, lateral, and ventral horns, which contain cell bodies of motor neurons, interneurons, and endings of sensory neurons.
• Dorsal horns process sensory information.
• Lateral horns process autonomic information.
• Ventral horns process motor information.

Peripheral White Matter

• It is located in the periphery surrounding the gray matter and appears white due to myelinated axons.
• Ascending and descending tracts pass through this region carrying sensory and motor information.
• Similar to gray matter it is divided into dorsal, lateral, and anterior (ventral) columns.
• The central canal is a centrally located canal continuous with the brain ventricles, allowing CSF flow.

Spinal Nerve Anatomy

• Spinal nerves carry both motor and sensory axons for a single spinal segment.
• Dorsal and ventral roots briefly join to form spinal nerves.
• The dorsal root ganglion contains cell bodies of sensory neurons.
• Ventral roots exit the vertebral column and divide into dorsal and ventral rami (ramus) that communicate with the spinal cord.

Spinal Tracts

• Spinal tracts are bundles of axons with the same origin and common termination.
• Ascending fiber tracts convey sensory information from cutaneous receptors, proprioceptors (muscle and joint senses), and visceral receptors.
• Descending tracts convey motor information from the brain to effectors.

Spinal Reflexes - Stretch Reflex

• Spinal reflexes are rapid, preprogrammed, involuntary responses to a stimulus that do not require brain involvement.
• They are generally protective to prevent damage or injury.
• Reflexes occur within the spinal cord like the monosynaptic reflex, which involves one sensory neuron synapsing to one motor neuron.
• The patellar reflex (knee jerk) is an example of spinal reflexes.

Spinal Reflexes - Withdrawal Reflex

• The withdrawal reflex is a spinal reflex intended to protect the body by removing it from potential damage.
• It rapidly coordinates flexor muscle contractions and extensor muscle relaxations, causing limb withdrawal from a damaging stimulus and involves 3 neurons
• Reflex arc components include: Receptor (Stimulus) > Sensory neuron > (Interneuron) > Motor neuron > Effector.

Disorders associated with the spinal region

• Meningomyelocele: failure of the inferior neuropore to close properly (spina bifida); creates an open area in the bony vertebrae where the meninges and spinal cord protrudes through; it may result in inability to control bowels and bladder, problems with movement of the legs
• Spastic Cerebral Palsy: developmental, congenital brain disorder; increase in muscle tone which causes stiff, jerky movements
• Multiple Sclerosis: autoimmune disorder where the body attacks the myelin sheath in the CNS; depending on progression of disease may experience numbness, weakness, gait problems and can progress to inability to walk
• Spinal Region Tumors: abnormal growth of tissue that surrounds the spinal cord, can be cancerous or benign; depending on whether the tumor is within the spinal cord itself or under the dura mater or epidural space can affect whether surgery can be performed to remove the tumor
• Myelopathy due to Cervical Spondylosis: degenerative joint disease affecting the cervical vertebrae intervertebral discs and vertebrae facets; compression of the cervical vertebrae; can be painful or not; numbness of limbs, stiff neck, neck pain, coordination problems
• Lumbar Stenosis: narrowing of the spinal canal in the lumbar region, can press upon spinal nerves and blood vessels in this area; pain, tingling, numbness of lower back and legs
• Syringomyelia: cyst in the spinal cord (fluid filled); can damage the spinal cord over time as it grows; can cause weakness, stiffness, pain, loss of sensations