lecture 19

Anatomy of the Spinal Cord

• The spinal cord is structured in segments, with significant landmarks essential for identification and understanding.

• The lumbar region's conus medullaris ends around the L1-L2 vertebrae, where spinal nerves continue as cauda equina.

Cross-Sectional Anatomy

• Anterior Median Fissure: A longitudinal groove marking the anterior side of the spinal cord.

• White and Gray Matter: Opposite arrangement compared to the brain; white matter is on the outside, gray matter on the inside.

  • Gray Matter: Contains densely packed cell bodies of neurons (horns).

  • White Matter: Composed of myelinated axons (columns).

Major Components of the Spinal Cord

• White Matter Columns: Classified as dorsal (posterior), ventral (anterior), and lateral columns.

• Gray Matter Horns: Composed of anterior, lateral, and posterior horns, resembling projections or "horns."

• Central Canal: Contains cerebrospinal fluid (CSF), essential for cushioning and protecting the spinal cord.

Nerve Functions

• Spinal nerves branch off into ventral and dorsal roots:

  • Dorsal Root: Contains sensory neurons, bringing information to the spinal cord from body receptors.

  • Ventral Root: Contains motor neurons enabling movement from the spinal cord to skeletal muscles.

• Damage at specific points in the spinal cord can lead to different paralysis types (e.g., flaccid vs. spastic paralysis).

Types of Paralysis

• Flaccid Paralysis: Loss of motor control due to damage in the ventral horn of the spinal cord.

• Spastic Paralysis: Caused by damage to the brain where messages originate, maintaining the spinal cord's integrity.

• Quadriplegia: Paralysis of all four limbs caused by high spinal cord damage.

• Paraplegia: Paralysis of the lower body due to lower spinal cord injury.

Meningeal Layers and Epidural Space

• The spinal cord is surrounded by three meningeal layers similar to the brain, with an epidural space containing fat for cushioning.

• Epidural Space: Commonly used for administering anesthesia during procedures such as childbirth.

Spinal Cord Trauma

• Traumatic injuries can lead to significant loss of function; examples include ALS (Amyotrophic Lateral Sclerosis), where motor neurons progressively degrade.

Diagnostic Tools

• Techniques such as reflex testing can assess the integrity of the spinal cord and nervous system. A common reflex includes the knee-jerk reflex, indicating functionality.

• Functional Imaging: MRI and PET scans provide insight into brain activity and structure without invasive procedures.

• Cerebral Angiography: Used to examine blood flow in the brain to detect possible blockages or strokes.

Reflex Activity

• Reflex Arc Components: Includes receptor, sensory neuron, interneuron (integration center), motor neuron, and effector (muscle).

• Types of Reflexes:

  • Stretch Reflex: Example is the knee-jerk reflex, involving direct activation of muscle and inhibition of the opposing muscle.

  • Withdrawal Reflex: Quick removal of body part from harm, involving sensory neurons directly connecting to motor neurons for immediate response.

Cranial Nerves Overview

• There are 12 pairs of cranial nerves, each with specific functions:

  • Olfactory Nerve (I): Sensory, sense of smell.

  • Optic Nerve (II): Sensory, sense of vision.

  • Oculomotor Nerve (III): Motor, movement of eye muscles.

  • Trochlear Nerve (IV): Motor, innervates one eye muscle.

  • Trigeminal Nerve (V): Mixed, sensory for face, motor for jaw.

  • Abducens Nerve (VI): Motor, lateral eye movement.

  • Facial Nerve (VII): Mixed, taste and facial expressions.

  • Vestibulocochlear Nerve (VIII): Sensory, hearing and balance.

  • Glossopharyngeal Nerve (IX): Mixed, taste and swallowing.

  • Vagus Nerve (X): Mixed, controls heart and digestive tract.

  • Accessory Nerve (XI): Motor, muscles of neck.

  • Hypoglossal Nerve (XII): Motor, tongue movement.

Spinal Nerves and Plexus

• Spinal nerves are categorized based on regions:

  • Cervical, Thoracic, Lumber, Sacral Plexus: Plexuses are networks that interconnect nerve branches for coordinated body functions.

  • Major Nerves to Remember:

  • Phrenic Nerve: Innervates the diaphragm.

  • Axillary, Radial, Ulnar, and Median Nerves: Related to arm movement.

  • Femoral and Sciatic Nerves: Key to leg movement.

Femoral Nerve:

• Location: Comes from the L2-L4 spinal nerves in the lower back.

• Path: Runs down the front of the hip and thigh, under a ligament (inguinal ligament).

• Function: Controls movement for the quadriceps (front thigh muscle) and provides feeling to the front of the thigh and inner leg.

Sciatic Nerve:

• Location: Arises from L4-S3 spinal nerves in the lower back and pelvis.

• Path: Travels down the back of the thigh and splits into two nerves near the knee.

• Function: Helps with movement in the hamstrings (back thigh muscles) and lower leg, and senses feeling in the back of the leg and foot.

Dermatomes

• Dermatomes are maps of skin segments innervated by specific spinal nerves, allowing for localizing sensory information from the body areas connected to those nerves.