Anatomy of Acupuncture Important Pathways for Pain Control & Acupuncture Relief

Spinal Cord A. Spinal cord anatomy 1. Protection and coverings a. Vertebral column b. Meninges 2. External anatomy of the spinal cord 3. Internal anatomy of the spinal cord B. Spinal cord physiology 1. Reflexes 2. Reflex arc and homeostasis a. Physiology of the stretch reflex b. Physiology of the flexor (withdrawal) reflex and crossed extensor reflexes C. Spinal nerves 1. Composition and coverings 2. Distribution of spinal nerves 3. Dermatomes

The Spinal Cord 1. is continuous with brain 2. mediates spinal reflexes 3. is site for integration 4. provides the pathways

Protection and Coverings 1. vertebral canal 2. meninges 3. cerebrospinal fluid

Meninges and Spaces 1. epidural space 2. dura mater 3. subdural space 4. arachnoid membrane 5. subarachnoid space 6. pia mater -- denticulate ligaments

External Anatomy 1. cylindrical 2. flattened A-P 3. foramen magnum to L2 4. differential growth 5. cervical enlargement 6. lumbar enlargement 7. conus medullaris 8. filum terminale 9. cauda equina 10. functional segments

Internal Anatomy 1. gray matter 2. white matter 3. gray commissure 4. central canal 1. gray matter 2. white matter 3. gray commissure 4. central canal

Gray Matter 1. nuclei 2. horns a. dorsal -- sensory b. ventral -- motor c. lateral -- autonomic

Spinal Cord Grey Matter Spinal Layers Spinal grey matters divided into 10 layers Substantia Gelatinosa Composed of a layer of cell bodies running up and down the dorsal horns of the spinal cord Receive input from A and C-fibers Activity in SG inhibits pain transmission

Spinal Nerve Roots 1. dorsal root (axons of sensory neurons) -- dorsal root ganglion (cell bodies of sensory neurons) 2. ventral root (axons of motor neurons) Dorsal roots Dorsal root ganglion Ventral roots

White Matter 1. columns a. anterior b. posterior c. lateral 2. tracts a. ascending b. descending Posterior columns Lateral columns Lateral columns Anterior columns

Tracts of the Spinal Cord

The Spinal Cord Has Two Essential Functions 1. convey impulses between the periphery and the brain 2. provide integrating centers for spinal reflexes

Reflexes are… 1. inborn 2. unlearned 3. unconscious

Somatic Reflexes Versus Visceral Reflexes Somatic reflexes involve the somatic nervous system. Visceral reflexes involve the autonomic nervous system.

Reflex Arc 1. receptor 2. sensory neuron 3. integration center sensory receptor 1 2 3 4 5 sensory (afferent) neuron center of integration with association neuron motor (efferent) neuron effector 1. receptor 2. sensory neuron 3. integration center 4. motor neuron 5. effector sensory receptor 2 3 4 5 sensory (afferent) neuron center of integration with association neuron motor (efferent) neuron effector

THE REFLEX ARC AS A FEEDBACK SYSTEM CONTROLLED CONDITION RETURN TO HOMEOSTASIS The action of the effector returns the body process to within its normal homeostatic range A stimulus or stress disrupts membrane homeostasis by altering some controlled condition EFFECTORS The motor neurons initiate some response by an effector (muscle or gland) to counteract the stimulus that originally disrupted homeostasis RECEPTOR The receptors in a reflex are sensory neurons associated with a receptor device (transducer) and which relay nerve impulses to a central control center CONTROL CENTER The control center is an integrating center of neurons in the CNS. It relays the information to motor neurons

Stretch Reflex 1. monosynaptic 2. muscle spindle 3. muscle tone 4. ipsilateral 5. reciprocal innervation

The Flexor and Crossed Extensor Reflex Intersegmental Polysynaptic Ipsilateral Pain receptor Role of association neurons Reciprocal innervation Intersegmental Polysynaptic Contralateral Pain receptor Role of association neurons Reciprocal innervation excitatory neurons inhibitory neurons

The Nervous System and Pain Somatosensory System Brain Cortex Thalamus Spinal Cord Ventral Root Dorsal Horn PNS Efferent Neuron Afferent Neuron A-delta Fibers C-Fibers

Pain Pathways – Going Up Pain information travels up the spinal cord through the spinothalamic track (2 parts) PSTT Immediate warning of the presence, location, and intensity of an injury NSTT Slow, aching reminder that tissue damage has occurred

Pain Pathways – Going Down Descending pain pathway responsible for pain inhibition

The Neurochemicals of Pain Pain Initiators Glutamate - Central Substance P - Central Brandykinin - Peripheral Prostaglandins - Peripheral Pain Inhibitors Serotonin Endorphins Enkephalins Dynorphin

Theories of Pain Specificity Theory Gate Control Theory Began with Aristotle Pain is hardwired Specific “pain” fibers bring info to a “pain center” Refuted in 1965 Gate Control Theory

Gate-Control Theory – Ronald Melzack (1960s) Described physiological mechanism by which psychological factors can affect the experience of pain. Neural gate can open and close thereby modulating pain. Gate is located in the spinal cord. It is the SG

Opening and Closing the Gate When the gate is closed signals from small diameter pain fibres do not excite the dorsal horn transmission neurons. When the gate is open pain signals excite dorsal horn transmission cells

Three Factors Involved in Opening and Closing the Gate The amount of activity in the pain fibers. The amount of activity in other peripheral fibers. Messages that descend from the brain.

Conditions that Open the Gate Physical conditions Extent of injury Inappropriate activity level Emotional conditions Anxiety or worry Tension Depression Mental Conditions Focusing on pain Boredom

Conditions That Close the Gate Physical conditions Medications Counter stimulation (e.g., heat, massage) Emotional conditions Positive emotions Relaxation, Rest Mental conditions Intense concentration or distraction Involvement and interest in life activities

Mechanisms that Regulate AP Inhibitor of AP Cholecytokinin Enhancer of AP L-phenylalanine

Conclusion Knowledge of the functional anatomy of the nervous system may be useful in determining how acupuncture works since all evidence suggests that the effects acupuncture can be explained only by its affects on the nervous system.