Final answer:
The statement that all sensory signals are consciously perceived is false. Sensory signals go through sensory transduction, a process that is not always within our conscious awareness, such as with olfactory cells for smell and hair cells for hearing. The cranial nerves do carry sensory information to the CNS, and the parasympathetic nervous system is part of the autonomic nervous system, not the CNS.
Step-by-step explanation:
The statement that all sensory signals are consciously perceived is false. Sensory signals involve the detection of physical or chemical stimuli by sensory receptors, which then undergo a process called sensory transduction to convert these stimuli into electrical signals. However, not all these signals reach our conscious awareness; many are processed subconsciously. For example, the senses of smell and hearing use their respective sensory receptor cells - olfactory receptor neurons for smell, and hair cells for hearing. Olfactory receptors are chemoreceptors that detect chemical substances in the air we breathe, whereas hair cells are mechanoreceptors that respond to mechanical vibrations in the ear caused by sound waves.
Sensory information from the olfactory, gustatory (taste), and auditory (hearing) systems is indeed carried to the central nervous system (CNS) by cranial nerves. Moreover, the action potential in neurons, which includes those in sensory pathways, is an 'all-or-none' event, meaning that once the threshold is reached, the neuron fires and the action potential is the same magnitude regardless of the strength of the stimulus. The effect of a neurotransmitter as excitatory or inhibitory depends on the type of receptors present on the post-synaptic cell and the overall integration of signals in the CNS.
As for the nervous system divisions, the parasympathetic nervous system is a division of the autonomic nervous system, not the central nervous system. The autonomic nervous system is a part of the peripheral nervous system that controls involuntary functions.