The lower CNS, spinal cord nerves and cranial nerves, operate as reflexes with little control from descending systems. Sensory inputs connect within the CNS through one or more synapses to form a rapid response of extensor or flexor muscle groups or to produce gland secretions.

• The lower CNS, spinal cord nerves and cranial nerves, operate as reflexes with little control from descending systems. Sensory inputs connect within the CNS through one or more synapses to form a rapid response of extensor or flexor muscle groups or to produce gland secretions.