Nervous System

Efferent means “outgoing”. Outgoing information travels from the brain to the body carrying motor information to an effector – a muscle or gland.

The autonomic NS, which in turn is one part (the somatic NS is the other part) of the efferent division of the peripheral NS.

The superior colliculi receive input from the lateral geniculate nuclei. The inferior colliculi receive auditory sensation.

The brainstem is at the end of the spinal cord, just inferior to the diencephalon which is surrounded by the cerebrum. The cerebellum is dorsal to the brainstem and inferior to the cerebrum.

The brainstem consists of the midbrain, the pons and the medulla oblongata.

The corneal (blink) reflex and pharyngeal (gag) reflex are mediated by cranial nerves V and IX, respectively. These nerves are attached to the brainstem. In an unconscious person who is brain dead, even the brainstem is unresponsive.

The eye’s lens is convex and flexible. So its degree of curvature (convexity) and hence its “focal length” can be altered so that light from objects at almost any distance can be made to come to a focus on the retina.

The ear canal is about 2.7 cm long, and a tube of this length, closed at one end, resonates at about 3000 Hz (resonates means that a “standing wave” is set up).

This answer is not a complete description of the BBB as it does not include astrocytes, but it is the best of the four choices.

The second neuron runs from ganglion to effector. The first neuron runs from the CNS to a ganglion and then synapses with the cell body of the second neuron.