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Spinal Cord Overview

  • Central part of the nervous system, consists of numerous neurons.
  • Major functions:
    • Relay of information to and from the body and brain (ascending and descending pathways).
    • Processing of information within the spinal cord.
    • Responsible for certain reflex actions.

Structure of the Spinal Cord

  • Extends from the skull exit (foramen magnum) to the cauda equina.
  • Contains enlargements:
    • Cervical enlargement (serves upper limbs).
    • Lumbar enlargement (serves lower limbs).
  • Contains 31 pairs of spinal nerves.

Reflex Pathways

Patellar Tendon Reflex

  • A monosynaptic reflex triggered by tapping the patellar tendon.
  • Sensory information travels through the dorsal root.
  • Motor information sent out via the ventral root to quadriceps muscle.

Cross Extensor Reflex

  • Important for maintaining balance, involves multiple steps:
    • Sensory neuron synapses with an interneuron in the spinal cord.
    • Interneuron activates motor neurons on the same side (withdrawal) and inhibits extensors.
    • Interneurons cross to the other side, activating extensors and inhibiting flexors for balance.

Neuron Types

  • Sensory neurons: Unipolar, receive stimuli and send action potentials to the spinal cord.
  • Motor neurons: Multipolar, transmit signals from the spinal cord to muscles and glands.

Communication Pathways

Ascending Tracts

  1. Dorsal Column: Carries sensory information (skin, muscles, tendons) to the brain.
  2. Spinocerebellar Tract: Delivers information from the spine to the cerebellum for motor coordination.
  3. Spinothalamic Tract: Transmits sensory information from the spinal cord to the thalamus.

Descending Tracts

  1. Corticospinal Tract: Motor control from the motor cortex to spinal cord.
  2. Rubrospinal Tract: Facilitates learned motor movements.
  3. Reticulospinal Tract: Maintains muscle tone and posture, regulates autonomic functions (sweat glands).