11-37. THE VESTIBULAR NERVE
The vestibular nerve (cranial nerve VIII) carries all this information from the
maculae and cristae to the brain. The vestibular and auditory nerves are contained in
the same fibrous sheath from the membranous labyrinth to the brain. Within the brain,
the vestibular and auditory nerves separate into different pathways.
Section XII. CONTROLS IN THE HUMAN NERVOUS SYSTEM
11-38. GENERAL CONCEPT
The human nervous system can be thought of as a series of steps or levels.
Each level is more complex than the level just below. No level is completely
overpowered by upper levels, but each level is controlled or guided by the next upper
level as it functions.
11-39. LEVELS OF CONTROL
a. Reflex Arc. The simplest and lowest level of control is the reflex arc (see
para 11-15c). The reflex arc operates essentially on the level of the sensory input.
b. Segmental Reflexes. Segmental reflexes produce a wider reaction to a
stimulus than the reflex arc. For this purpose, the nervous system is organized more
complexly. Thus, information spreads to a wider area of the CNS. We can observe a
greater reaction to the stimulus.
c. Medullary Hindbrain. In the hindbrainstem are to be found a number of
nuclei (collections of neuron cell bodies) which monitor and control the activities of the
visceral functions of the body, such as respiration, heartbeat, etc.
d. Reticular Formation. Within the substance of the brainstem is a diffuse
system called the reticular formation.
RETICULAR = network
This reticular formation has a facilitatory (excitatory) area and an inhibitory area. These
areas monitor and control general body functions, including sleep.
e. Thalamus. In the forebrainstem is a major collection of nuclei, all together
called the thalamus. The thalamus is a primary relay for information going to and from
the cerebrum and cerebellum. In the lowest animals, the thalamus represents the
highest level of nervous control.