Spinal Cord Anatomy and Reflex Arcs - Anatomy and Physiology
- At about which vertebral level does the spinal cord end in adults?
- Around L1 to L2, where it tapers as the conus medullaris.
- Why are there cervical and lumbar enlargements of the spinal cord?
- They contain extra neurons serving the upper and lower limbs, respectively.
- Why is the patellar (knee-jerk) stretch reflex called monosynaptic?
- The sensory neuron from the muscle spindle synapses directly on the motor neuron, with no interneuron in between.
- What is reciprocal inhibition in a stretch reflex?
- Interneurons inhibit motor neurons to the antagonist muscle, so it relaxes while the stretched muscle contracts.
- In which spinal cord regions are lateral horns present, and what do they contain?
- T1 to L2. They contain the cell bodies of sympathetic preganglionic neurons.
- What is the crossed extensor reflex?
- When one limb withdraws from a painful stimulus, the opposite limb extends to support body weight, via interneurons crossing the cord.
- Which part of the spinal cord gray matter contains somatic motor neuron cell bodies?
- The ventral (anterior) horn. Their axons leave through the ventral root to skeletal muscle.
- What does the dorsal root ganglion contain?
- The cell bodies of sensory (afferent) neurons, whose axons enter the cord through the dorsal root.
- How many pairs of spinal nerves do humans have?
- 31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal.
- How is gray and white matter arranged in the spinal cord?
- Gray matter forms a central H- or butterfly-shaped core, surrounded by white matter tracts, the reverse of the cerebral cortex.
- What is the cauda equina?
- The bundle of lumbar and sacral nerve roots that continues down the vertebral canal below the end of the spinal cord.
- What are the five components of a reflex arc, in order?
- Receptor, sensory neuron, integration center, motor neuron, and effector.