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Study guide for spine quiz 1 SE

1. Movements Related to Planes of the Body

  • Sagittal Plane (divides body into left and right halves):
    • Flexion: Decreasing the angle between bones (e.g., bending elbow, bringing chin to chest).
    • Extension: Increasing the angle between bones (e.g., straightening elbow, looking up).
    • Dorsiflexion: Bending the foot upward at the ankle.
    • Plantarflexion: Bending the foot downward at the ankle.
  • Frontal (Coronal) Plane (divides body into front and back halves):
    • Abduction: Moving a limb away from the midline of the body (e.g., raising arm out to the side).
    • Adduction: Moving a limb toward the midline of the body (e.g., bringing arm back to side).
    • Lateral Flexion/Bending: Bending the trunk or neck to the side.
    • Inversion: Turning the sole of the foot inward.
    • Eversion: Turning the sole of the foot outward.
  • Transverse (Horizontal) Plane (divides body into upper and lower halves):
    • Rotation: Turning a body part around its long axis.
      • Medial/Internal Rotation: Turning toward the midline.
      • Lateral/External Rotation: Turning away from the midline.
    • Pronation: Rotating the forearm so the palm faces posteriorly (or inferiorly if arm is flexed).
    • Supination: Rotating the forearm so the palm faces anteriorly (or superiorly if arm is flexed).
    • Horizontal Abduction/Adduction: Moving a limb horizontally away from or towards the midline, typically from a flexed position (e.g., flying motion).
    • Circumduction: A circular movement combining flexion, abduction, extension, and adduction (e.g., circling the arm); technically occurs in multiple planes.

2. Pre-synaptic and Post-synaptic Sympathetic Fibers Related to Ventral Roots and Rami

  • Pre-synaptic (Preganglionic) Sympathetic Fibers:

    • Cell bodies located in the intermediolateral cell column (IML) (lateral horn) of the spinal cord from levels T1 to L2/L3.
    • These myelinated fibers exit the spinal cord via the ventral root.
    • They join the spinal nerve briefly.
    • They then leave the spinal nerve to enter the white rami communicantes to reach the sympathetic trunk (paravertebral ganglia).
    • From the sympathetic trunk, they can:
      1. Synapse at the same level in a paravertebral ganglion.
      2. Ascend or descend the sympathetic trunk to synapse at a different level.
      3. Pass through the sympathetic trunk without synapsing to form splanchnic nerves and synapse in prevertebral (collateral) ganglia (e.g., celiac, superior mesenteric ganglia).

  • Post-synaptic (Postganglionic) Sympathetic Fibers:

    • Cell bodies are located in the sympathetic ganglia (paravertebral or prevertebral).
    • If synapsed in a paravertebral ganglion, unmyelinated postganglionic fibers exit the sympathetic trunk via gray rami communicantes.
    • They rejoin the spinal nerve (ventral or dorsal ramus) to be distributed to target organs (e.g., smooth muscle of blood vessels, sweat glands, arrector pili muscles in the body wall and limbs).
    • If synapsed in a prevertebral ganglion, postganglionic fibers typically travel along blood vessels to reach visceral organs in the abdomen and pelvis.

3. Surface Anatomy Landmarks for Dermatomes/Myotomes

  • Dermatomes: Areas of skin supplied by a single spinal nerve (or more specifically, by afferent fibers from a single dorsal root).

    • C_2: Posterior half of skull cap.
    • C_3: Supraclavicular fossa.
    • C_4: Top of acromioclavicular joint.
    • C_5: Lateral side of antecubital fossa (elbow crease).
    • C_6: Dorsal surface of proximal phalanx of thumb.
    • C_7: Dorsal surface of proximal phalanx of middle finger.
    • C_8: Dorsal surface of proximal phalanx of little finger.
    • T_1: Medial side of antecubital fossa.
    • T_2: Apex of axilla.
    • T_4: Nipple level.
    • T_{10}: Umbilicus level.
    • L_1: Just above inguinal ligament.
    • L_2: Middle of anterior thigh.
    • L_3: Medial femoral condyle.
    • L_4: Medial malleolus.
    • L_5: Dorsum of foot at the 3rd metatarsophalangeal joint.
    • S_1: Lateral heel.

  • Myotomes: Groups of muscles innervated by a single spinal nerve segment (or more specifically, by efferent fibers from a single ventral root).

    • C_5: Elbow flexion (biceps, brachialis).
    • C_6: Wrist extension (extensor carpi radialis).
    • C_7: Elbow extension (triceps).
    • C_8: Finger flexion (flexor digitorum profundus).
    • T_1: Finger abduction (abductor digiti minimi).
    • L_2: Hip flexion (iliopsoas).
    • L_3: Knee extension (quadriceps).
    • L_4: Ankle dorsiflexion (tibialis anterior).
    • L_5: Great toe extension (extensor hallucis longus).
    • S_1: Ankle plantarflexion (gastrocnemius, soleus).

4. Locations of Sensory/Motor Cell Bodies

  • Sensory Neuron Cell Bodies:

    • Pseudounipolar neurons: Located in the dorsal root ganglia (DRG), which are swellings on the dorsal roots outside the spinal cord. These transmit general somatic (touch, pain, temperature, proprioception) and general visceral afferent information.
    • Bipolar neurons: Located in special sense ganglia (e.g., cochlear, vestibular, olfactory, retinal) for special senses, not typically discussed in standard spinal cord quizzes.

  • Motor Neuron Cell Bodies:

    • Somatic Motor Neurons (Lower Motor Neurons): Located in the ventral horn of the spinal cord gray matter. These innervate skeletal muscle.
    • Pre-ganglionic Autonomic Motor Neurons:
      • Sympathetic: Located in the intermediolateral cell column (IML) (lateral horn) of the spinal cord from T1 to L2/L3.
      • Parasympathetic: Located in the lateral gray matter from spinal cord levels S2-S4 (sacral parasympathetic nucleus) for the pelvic viscera, and in brainstem nuclei for cranial nerves (not in spinal cord).

5. Types of Fibers in Cauda Equina

  • The cauda equina ("horse's tail") is a bundle of spinal nerves and nerve rootlets extending inferiorly from the conus medullaris. It contains:
    • Spinal nerves (L2-Co1), which are mixed nerves. Therefore, it contains:
      • Somatic afferent (sensory) fibers: Transmitting sensation from the lower limbs, perineum, and pelvic organs.
      • Somatic efferent (motor) fibers: Innervating skeletal muscles of the lower limbs and some pelvic floor muscles.
      • Autonomic (preganglionic sympathetic and parasympathetic, and postganglionic sympathetic) fibers: Innervating smooth muscle, cardiac muscle, and glands in the lower body, especially the pelvic viscera.

6. 'End' of Spinal Cord

  • The spinal cord terminates inferiorly as a conical tapering structure called the conus medullaris.
  • In adults, the conus medullaris typically ends around the vertebral level of L1/L2.
  • Attached to the inferior tip of the conus medullaris is the filum terminale, a non-neural fibrous extension of the pia mater that anchors the spinal cord to the coccyx.
  • The space below the conus medullaris (from L2 downwards) within the vertebral canal is where the cauda equina resides and is a common site for lumbar punctures.

7. Visceral vs. Somatic Sensory Information

  • Somatic Sensory Information:

    • Origin: From the body wall, limbs, and head; includes skin, skeletal muscles, tendons, joints.
    • Types of Sensation: Pain, temperature, touch (light touch, pressure, vibration), proprioception (sense of body position and movement).
    • Consciousness: Generally perceived consciously and localized precisely.
    • Pathways: Typically involves a three-neuron pathway ascending to the cerebral cortex (e.g., dorsal column-medial lemniscus pathway, spinothalamic tracts).

  • Visceral Sensory Information:

    • Origin: From internal organs (viscera) within the thoracic and abdominopelvic cavities (e.g., heart, lungs, gastrointestinal tract, bladder).
    • Types of Sensation: Stretch, ischemia (lack of blood flow), inflammation, chemical irritation, pressure, nausea, hunger, fullness. Primarily related to the internal state of the body.
    • Consciousness: Often not perceived consciously (e.g., blood pressure regulation), or poorly localized and diffuse when conscious (e.g., visceral pain,