General Senses and Spinal Cord Anatomy and Physiology

Introduction

• Chapter Learning Outcomes:
  • Describe structures and functions of the spinal cord
  • Explain major sensory and motor tracts of the spinal cord
  • Detail structures and functions of spinal nerves
  • Discuss peripheral nerves of nerve plexuses
  • Define sensation, general senses, and their receptors
  • Understand reflex arcs and types of neurological exams

Spinal Cord Anatomy

• Central Nervous System (CNS): Composed of the brain and spinal cord
• Meninges: Protective 3-layered covering
  • Pia Mater: Delicate inner layer
  • Arachnoid Mater: Middle spider-web-like layer
  • Dura Mater: Tough outer layer
• Spaces in Meninges:
  • Subarachnoid Space: Contains cerebrospinal fluid (CSF)
  • Epidural Space: Filled with fat and blood vessels
• Spina Bifida: A condition due to underdeveloped vertebrae, linked to folic acid deficiency

Spinal Cord Structure

• Divided into Segments:
  • Spinal nerves exit through intervertebral foramen
  • Ends at L1/L2 in adults, L3/L4 in children
  • Conus Medullaris: Pointed end of spinal cord
  • Cauda Equina: Bundle of nerve roots

Cross-section of Spinal Cord

• Gray Matter: Butterfly-shaped, contains cell bodies and interneurons
• White Matter: Surrounds gray matter, contains ascending and descending pathways
• Dorsal and Ventral Horns:
  • Dorsal Horns: Contain sensory neuron cell bodies
  • Ventral Horns: Contain lower motor neuron cell bodies

Spinal Cord Pathways

• Motor Pathways:
  • Corticospinal Tract: Controls skeletal muscle movements
  • Extrapyramidal Pathways: Include rubrospinal, reticulospinal, vestibulospinal tracts
• Sensory Pathways:
  • Spinothalamic Tract: Carries pain and temperature info
  • Dorsal Column-Medial Lemniscus Pathway: Carries touch and proprioception info

Spinal Nerves

• Structure and Function:
  • Mixed motor and sensory nerves
  • 31 pairs of spinal nerves (cervical, thoracic, lumbar, sacral, coccygeal)
• Connective Tissue Coverings:
  • Epineurium: Surrounds entire nerve
  • Perineurium: Surrounds fascicles
  • Endoneurium: Surrounds individual axons
• Nerve Plexuses:
  • Cervical Plexus: Includes phrenic nerve
  • Brachial Plexus: Includes axillary, radial, median, ulnar nerves
  • Lumbar and Sacral Plexuses: Include femoral, obturator, sciatic nerves

Sensation and Perception

• Sensory Modality: General and special senses
• Receptors: Types and Functions:
  • Mechanoreceptors, Thermoreceptors, Nociceptors: For touch, temperature, and pain
• Sensory Adaptation: Reduction in response to constant stimuli

Reflexes

• Types of Reflexes:
  • Stretch Reflex, Tendon Reflex, Flexor Withdrawal, Crossed Extensor Reflexes
• Reflex Arc Components:
  • Sensory receptor, sensory neuron, integration center, motor neuron, effector

Spinal Cord Injury and Neurological Exams

• Types of Injuries:
  • Quadriplegia, Paraplegia, Hemiplegia
• Neurological Testing:
  • Two-point discrimination, reflex examination
  • Assessing motor function and proprioception

This summary provides a high-level overview of the anatomy and physiology of general senses and the spinal cord, highlighting the main structures, functions, and associated clinical aspects.