Unbeknown to us, the tone of our somatic muscles is varied through muscle spindles, which is why we get tension headaches unexpectedly.

Lateralised headaches have followed the use of mobile ‘phones, perhaps due to activation of muscle spindles by magnetic fields, from internal hardware and from radio frequency signals.

Symmetrical headaches have followed the use of computers, perhaps due to activation of muscle spindles by magnetic fields.

Autonomously, sympathetic and parasympathetic nerves enable our viscera to function in sympathy with each other.

Sensory stimulation may occur without realisation, through the diffuse network of nerves called the reticular formation.

Subliminal advertising is illegal on television in the United Kingdom, which acknowledges that visual perception and auditory perception occur in two stages.

Stimuli pass respectively to the superior and inferior colliculi of the midbrain, wherefrom collicular nerves can activate the reticular formation, and, potentially, the septal nuclei, the three-layered hippocampal allocortices, the four-layered cingulate mesocortices, and the amygdalae; stimuli also pass respectively to the lateral and medial geniculate bodies of the thalami, wherefrom they can activate respectively the six-layered occipital cortices and the six-layered temporal cortices: the additional two layers of cortex may be the anatomical basis for self-consciousness.

The two stages of visual perception and of auditory perception are captured theatrically in the double take.
The eyeblink startle response to lightning and the acoustic startle response to thunder confirm the subcortical stages of visual perception and of auditory perception.

The decussation, that is crossing over, of sensory nerves enables bilateral perception by each eye, each ear, and each side of the brain.
Sensory nerves that cross over parallel motor nerves that cross over.

The spinothalamic tracts decussate on entry to the spinal cord, whereas the gracile fasciculi and the cuneate fasciculi decussate in the brainstem, which means that in the event of a partial spinal injury, sensation is retained below the injury on the damaged side.

Intentional movements become automatic, because, with practice, control moves from the cerebral cortex to the basal ganglia.

There are descending nerves from the cerebral cortex to the sensory nerves that enable sensory activation to be gated, that is inhibited: these nerves likely evolved to enable predators, like bats, to focus on prey, like insects.
Descending nerves from the cerebral cortex to the sensory nerves may be activated to produce the mind’s eye and the mind’s ear.

Contraction of the tensor tympani muscles reduces movement of the tympanic membranes, and thus enables sleep.

The intention to vocalise is followed by contraction of the stapedius muscles, which reduces vibrations of the stapes (stirrup) bones, and thus the transmission of sound waves through the oval windows to the inner ears.