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Spinal Cord, Spinal Nerves, and Somatic Reflexes - Anatomy & Physiology

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  • Where does the spinal cord begin and how long is it?
    The spinal cord begins at the foramen magnum and is about 45 cm (~18 inches) long.
  • How many pairs of spinal nerves are there?
    There are 31 pairs of spinal nerves.
  • What are the two longitudinal grooves on the spinal cord?
    The anterior median fissure and the posterior median sulcus.
  • What are the cervical and lumbar enlargements of the spinal cord for?
    The cervical enlargement contains nerves for the upper limbs; the lumbar enlargement contains nerves for the pelvic region and lower limbs.
  • What is the conus medullaris?
    The tapered end of the spinal cord.
  • What is the cauda equina?
    A bundle of nerve roots at the end of the spinal cord, resembling a horse's tail.
  • Name the three meninges of the spinal cord.
    Dura mater (tough outer membrane), arachnoid mater (middle layer with cerebrospinal fluid in subarachnoid space), and pia mater (delicate inner membrane touching nervous tissue).
  • What is the function of the denticulate ligaments?
    They anchor the spinal cord laterally to the dura mater.
  • Describe the gray matter in the spinal cord.
    Gray matter is butterfly-shaped, contains somas and dendrites, and includes dorsal, ventral, and lateral horns.
  • What is the role of the dorsal horns in the spinal cord?
    They contain axons of incoming sensory neurons and interneurons.
  • What is the function of the ventral horns?
    They send motor information via ventral roots to skeletal muscles.
  • What is the significance of the lateral horns?
    They contain neurons of the sympathetic nervous system regulating cardiac muscle, glands, and smooth muscle.
  • What is the difference between a nerve and a tract?
    A nerve is a bundle of axons in the PNS; a tract is a bundle of axons in the CNS.
  • What are ascending and descending tracts?
    Ascending tracts carry sensory information up the spinal cord; descending tracts carry motor information down.
  • What is decussation in spinal tracts?
    The crossing of nerve fibers from one side of the spinal cord to the other.
  • Define contralateral and ipsilateral in spinal tracts.
    Contralateral means origin and destination are on opposite sides; ipsilateral means they are on the same side.
  • What are the three orders of neurons in sensory pathways?
    1st order neurons detect stimuli and transmit to spinal cord; 2nd order neurons carry signals to thalamus; 3rd order neurons carry signals to cerebral cortex.
  • What is the function of the gracile fasciculus?
    Carries sensory signals (touch, proprioception, vibration) from T6 and below to the gracile nucleus.
  • What does the cuneate fasciculus carry?
    Sensory signals from T6 and above, similar to the gracile fasciculus.
  • What sensations are carried by the spinothalamic tracts?
    Anterior spinothalamic tract carries crude touch and pressure; lateral spinothalamic tract carries pain and temperature.
  • What is the role of the spinocerebellar tracts?
    They carry subconscious proprioception signals to the cerebellum.
  • What is the corticospinal pathway responsible for?
    It controls precise, fine, or skilled voluntary movements, especially of distal limbs.
  • What is the function of the tectospinal tract?
    Mediates reflexive head and eye movements in response to sight and sound.
  • What do the reticulospinal tracts control?
    Gross movements of the neck, trunk, and proximal limb muscles.
  • What is the function of the vestibulospinal tracts?
    Maintain posture and balance in response to head movement.
  • What are the three connective tissue layers surrounding a nerve?
    Epineurium (around entire nerve), perineurium (around nerve fascicles), and endoneurium (around individual nerve fibers).
  • What is a ganglion?
    A cluster of neuron cell bodies (somas) in the peripheral nervous system.
  • How many pairs of spinal nerves are in each region?
    8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal pair.
  • What is a dermatome?
    An area of skin innervated by sensory fibers from a single spinal nerve.
  • What are the four properties of a reflex?
    Require stimulation, quick, involuntary, and stereotyped (predictable).
  • What is the stretch reflex?
    A muscle contracts in response to being stretched to resist the stretch.
  • What is the function of the Golgi tendon reflex?
    It inhibits muscle contraction in response to excessive tension to prevent injury.