1 Biological Bases of Behavior

A person may have a predisposition toward a characteristic, while education, family experience, or another environmental condition affects how strongly it appears. Psychologists compare twins, biological relatives, and adopted family members to estimate how heredity and shared or different environments relate to behavior. These designs reveal patterns of association; they do not prove that one gene or one experience is the sole cause. The evolutionary perspective adds a population-level explanation: natural selection can favor behavioral tendencies that increased survival or reproductive success.

Reaching for a cup is voluntary, so the outgoing control is classified as somatic PNS activity. Regulation of an involuntary process such as heart activity is classified as autonomic PNS activity. In both cases, peripheral pathways communicate with the CNS; ‘peripheral’ describes the connection network, not unimportant processing.

A spinal reflex shows CNS and PNS neurons working as one pathway: (1) a sensory neuron carries information from a stimulus toward the spinal cord; (2) an interneuron in the spinal cord connects and processes the signal; (3) a motor neuron carries the response command toward the body. Because the spinal cord coordinates this pathway, a response can begin without waiting for deliberate conscious processing.

Neural transmission follows an ordered cycle. A neuron begins at resting potential. If incoming stimulation reaches threshold, depolarization produces an action potential according to the all-or-none principle: the neuron fires fully rather than partially. A refractory period follows before the neuron can fire normally again. At the next cell, chemical messengers influence whether another action potential becomes more or less likely; reuptake removes released neurotransmitter back into the sending cell.

The corpus callosum connects the hemispheres. In split-brain research, severing it—often to treat severe epilepsy—allows researchers to present information to different visual fields and test contralateral hemispheric specialization. Language is typically left-lateralized: Broca’s area supports speech production and Wernicke’s area supports speech comprehension; damage can produce aphasia. Localization is not completely fixed, however. Brain plasticity allows connections to be modified or created across development and may allow another area to assume a damaged area’s function.

Disrupted sleep can reduce physical and cognitive performance during wakefulness. Treatment and regular sleep schedules can improve waking performance and well-being. The AP list is limited to insomnia, narcolepsy, REM sleep behavior disorder, sleep apnea, and somnambulism.

Sensory systems do not operate in isolation. Sensory interaction occurs when systems work together to shape experience. Synesthesia is a distinct experience in which stimulation of one sensory system is experienced through another.

The lens focuses visual stimuli onto the retina by accommodation. The retina is the photosensitive surface at the back of the eye; its cells transduce captured information into signals for the brain. Where the visual nerve exits, the retina has a blind spot, so the captured image is incomplete and the brain fills the gap. Altered accommodation can produce nearsightedness or farsightedness.

Sound localization is the process of identifying where an environmental sound originates. Hearing difficulty may result from aging or damage to auditory structures. AP Psychology distinguishes conduction deafness from sensorineural deafness as different categories of hearing loss.

Experienced flavor depends on sensory interaction. Gustatory signals supply basic taste information while olfactory signals contribute smell; when smell is unavailable, taste sensations may be muted or absent.

The sensation described as ‘hot’ illustrates combination rather than a single one-to-one receptor label: it is produced by activation of both warm and cold receptors in the skin.