Spinal Cord and Reflexes Quiz

Spinal Cord, Spinal Nerves, and Spinal Reflexes

• Spinal reflexes are rapid, automatic nerve responses triggered by specific stimuli.
• They are controlled by the spinal cord, not the brain.
• The spinal cord is approximately 18 inches (45 cm) long and 1/2 inch (14 mm) wide.
• It extends between vertebrae L1 and L2.
• The spinal cord has bilateral symmetry.
• Grooves divide it into left and right sides.
• The posterior median sulcus is a groove on the posterior side.
• The anterior median fissure is a deeper groove on the anterior side.

Spinal Cord Enlargements

• Enlargements are caused by the amount of gray matter in a segment, and the involvement of the sensory and motor nerves of the limbs.
• The cervical enlargement contains nerves for the shoulders and upper limbs.
• The lumbar enlargement contains nerves for the pelvis and lower limbs.

Three Meningial Layers

• The dura mater is the outermost layer of the spinal cord.
• The arachnoid mater is the middle layer.
• The pia mater is the innermost layer.

Dura Mater

• The dura mater is tough and fibrous.
• Cranially, it fuses with the periosteum of the occipital bone.
• It's continuous with the cranial dura mater.
• Caudally, it tapers to a dense cord of collagen fibers that attach to the coccygeal ligament.

Epidural Space

• Located between the spinal dura mater and the walls of the vertebral canal.
• It contains loose connective tissue and adipose tissue.
• It's a common site for anesthetic injection.

Arachnoid Mater

• It's the middle meningeal layer.
• The arachnoid membrane is a simple squamous epithelium.
• It covers the arachnoid mater.
• The subdural space is between the arachnoid and dura mater.
• The subarachnoid space contains a network of collagen/elastin fibers (arachnoid trabeculae).
• The space is filled with cerebrospinal fluid (CSF).

Cerebrospinal Fluid (CSF)

• CSF carries dissolved gases, nutrients, and waste products.
• Lumbar puncture (spinal tap) withdraws CSF.

Pia Mater

• The pia mater is the innermost meningeal layer.
• It's a mesh of collagen and elastic fibers that adheres to the underlying neural tissue.

Sectional Anatomy of the Spinal Cord

• White matter is superficial and contains myelinated and unmyelinated axons.
• Gray matter surrounds the central canal of the spinal cord and contains neuron cell bodies, neuroglia, and unmyelinated axons.
• It has projections called gray horns.

Organization of Gray Matter

• Posterior gray horns contain somatic and visceral sensory nuclei.
• Anterior gray horns contain somatic motor nuclei.
• Lateral gray horns are located in the thoracic and lumbar segments and contain visceral motor nuclei.
• Gray commissures connect axons from one side of the spinal cord to the other side.

Organization of White Matter

• Posterior white columns are located between the posterior gray horns and the posterior median sulcus.
• Anterior white columns are between the anterior gray horns and the anterior median fissure.
• Anterior white commissure contains axons that cross to the other side of the spinal cord.
• Lateral white columns are on each side of the spinal cord.

Spinal Nerves and Plexuses

• Peripheral neuropathy is a regional loss of sensory or motor function, due to trauma or compression.

Paraplegia vs. Quadriplegia

• Paraplegia affects both legs and is caused by injury to the thoracic, lumbar, or sacral regions of the spinal cord.
• Quadriplegia affects both arms and legs, and is caused by injury to the cervical region of the spinal cord.

Neuronal Pools

• Neuronal pools are functional groups of interconnected neurons (interneurons).
• They have limited input sources and output destinations.
• They can stimulate or depress parts of the brain or spinal cord.

Five Patterns of Neural Circuits

• Divergence: Spreading stimulation to multiple neurons or pools.
• Convergence: Providing input to a single neuron from multiple sources.
• Serial processing: Neurons or pools working sequentially.
• Parallel processing: Neurons or pools processing the same information simultaneously.