pathophys2 final: The Spinal Cord ppt

The Spinal Cord

• Lies within the vertebral column, covered by the meninges, and originates in the medulla oblongata
• Carries two types of information:
  • Efferent motor neuron outputs from the brain
  • Afferent sensory neural inputs to the brain from the body
• In the adult, the spinal cord extends to the lower border of L1
• Conus medullaris: ~L1/L2, end of the spinal cord
• Cauda Equina: nerve fibers projecting from end of spinal cord > S5
• 31 pairs of spinal nerves, all containing both efferent motor and afferent sensory fibers

Gray Matter Horns

• Dorsal Horn: axons/interneurons of sensory (afferent) neurons (cell bodies live in dorsal root ganglion)
• Ventral Horn: cell bodies for motor (efferent) pathways leaving spinal cord

Spinal Cord Organization

• Superficial white matter tracts surround deeper gray matter
• Somatotopic organization within central gray matter and surrounding white matter tracts

Upper and Lower Motor Neurons

• Upper Motor Neurons:
  • Cell bodies live in motor cortex of the brain with axons reaching down to a certain vertebral level in corticospinal tract
  • Crosses from one side of the body to the other at the level of the brain stem
  • Uses glutamate as neurotransmitter
• Lower Motor Neurons:
  • Cell bodies live in ventral horn of the spinal cord with axons reaching out into PNS
  • Uses acetylcholine as neurotransmitter at neuromuscular junction

Spinal Reflexes

• Definition: involuntary, near-instant response to a stimulus that does not involve input from the brain
• Types of reflex arcs:
  • Autonomic – visceral organs
  • Somatic
  • Stretch – plays a major role in maintaining posture
  • Golgi Tendon Reflex – senses if there is too much muscle tension
  • Crossed extensor – helps body compensate for a stimulus on one side of the body
  • Flexor/Withdrawal – withdrawal in response to noxious stimulus

Reflex Arc

• Stretch Reflex Arc:
  • Four processes: monosynaptic response, reciprocal innervation, synergistic muscle recruitment, ascending information

Clinical Correlation

• Stretch Reflex operates as a protective mechanism to prevent strain/tear of muscles and tendons
• Clinically, we can get information about the spinal cord, peripheral nerves, and muscle tone/strength by checking reflexes

Spinal Cord Organization

• Dermatomes & Myotomes:
  • Sensory: dermatomes
  • Motor: myotomes
• Ascending and Descending Tracts:
  • In the spinal cord, certain types of information are carried within specific tracts that are physically separated
  • By knowing which type of info lives in which tract, we can understand the type and degree of injury based on clinical exam

Afferent Pathways (Ascending)

• Spinothalamic:
  • Vague touch
  • Pain (nociception)
  • Temperature
  • Fibers decussate (cross over) immediately at their level of entry into spinal cord
• Dorsal Columns:
  • Basic (normal) perception of touch
  • Proprioception
  • Vibration
  • Fibers cross at the medulla

Efferent Pathways (Descending)

• Corticospinal Tracts:
  • Efferent/motor control below the head
  • Contain upper motor neurons
  • Some fibers stay ipsilateral and travel in the anterior corticospinal tract
  • Mostly innervate very proximal muscles in extremities

Spinal Cord Injuries

• Complete vs Incomplete Spinal Cord Injury:
  • Complete spinal cord transection: will interrupt all three tracts with complete loss of motor/sensory function below the level of injury
  • Incomplete spinal cord injury: variable degree of dysfunction due to only part of the spinal cord being affected

Types of Spinal Cord Injury

• Cord concussion
• Cord contusion
• Cord compression
• Transection
• Hemorrhage
• Infarct/Obstruction of blood supply
• Can be "complete" or "incomplete"

Evolution of Spinal Cord Injury

• Primary cord injury: the actual trauma/compression/transaction etc itself
• Secondary cord injury: cascade of events leading to swelling and tissue destruction
• Resolution of symptoms: weeks, months, maybe never

This quiz cover the structure and function of the spinal cord, including its location, protection, and role in transmitting information between the brain and body.