The Divisions of the Nervous System (College Board AP® Psychology): Revision Note

The central nervous system (CNS)

• The nervous system is the body's primary communication network, responsible for:

  • collecting information from the internal and external environment

  • processing this information

  • coordinating appropriate responses

• The nervous system is divided into two major interconnected divisions that work together:

  • The central nervous system (CNS)

  • The peripheral nervous system (PNS)

• These two systems are not independent as they communicate constantly

  • The PNS relays information to and from the CNS to enable behavior and mental processes

• The CNS consists of the brain and the spinal cord, and interacts with all processes in the body

• The brain is the body's central processing center for behavior, thoughts, motivations, and emotions

  • It regulates a wide range of functions including:

    • body temperature, heart rate, and breathing

    • language production and comprehension

    • coordinating movement

    • problem-solving and planning

    • processing sensory information from the environment

• The spinal cord is a bundle of nerves housed within the protective bones of the spine (the vertebrae)

  • It transmits signals between the brain and the rest of the body via the PNS

  • It also plays a role in producing rapid, automatic responses to stimuli

• Because the CNS is responsible for integrating and processing all incoming information and generating responses, damage to the CNS can have profound effects on behavior and mental processes

  • E.g. damage to spinal cord can disrupt the transmission of motor signals from the brain to the body, resulting in paralysis

The peripheral nervous system (PNS)

• The PNS consists of all the nerves outside the brain and spinal cord

  • It relays messages between the CNS and the rest of the body

• Sensory (afferent) neurons carry information from the body and environment toward the CNS

• Motor (efferent) neurons carry instructions from the CNS out to muscles and organs

• The PNS is divided into two subsystems:

  • The somatic nervous system

  • The autonomic nervous system

The somatic nervous system

• The somatic nervous system governs voluntary processes

  • These are movements and actions that are under conscious control

    • E.g. choosing to pick up a pen, throw a ball, or stand up from a chair

• It controls the movement of skeletal muscles in response to instructions from the motor cortex of the brain

• The somatic nervous system also transmits sensory information from the body to the brain, such as touch, sound, smell, and taste

  • E.g. the sensation of texture when touching a surface, or the flavor of food on the tongue

The autonomic nervous system

• The autonomic nervous system (ANS) governs involuntary processes

  • These are bodily functions that occur automatically without conscious control

    • E.g. heart rate, breathing, digestion, and the stress response

• The ANS is further divided into two complementary subsystems:

  • The sympathetic nervous system

  • The parasympathetic nervous system

The sympathetic nervous system

• The sympathetic nervous system prepares the body for physical activity in response to a perceived threat or stressor

• The hypothalamus detects the stimulus and triggers the release of adrenaline from the adrenal glands

• This produces rapid physiological changes that enable a fast, automatic response

  • E.g. accelerated heart rate, widened airways for increased breathing capacity, pupil dilation, and sweating

• This response can also be triggered by excitement or intense positive arousal, not only by threat

The parasympathetic nervous system

• The parasympathetic nervous system conserves the body's energy and returns it to a resting state after the sympathetic response has been activated

  • It slows heart and breathing rates, lowers blood pressure, and promotes digestion

• The more time spent in a parasympathetic state, the more efficiently the body can recover and maintain health

• The sympathetic and parasympathetic systems work in opposition to one another, but together they maintain the body's overall equilibrium

  • This is a state known as homeostasis