Divisions of the Nervous System (AQA A-Level Psychology): Revision Notes
Divisions of the Nervous System
The human nervous system is organised into distinct divisions that work together to control behaviour and maintain bodily functions. Understanding these divisions is essential for grasping how biological structures influence psychological processes.
Overview of nervous system organisation
The nervous system divides into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). These interconnected divisions form a complex network that enables communication throughout the body and controls both voluntary and involuntary behaviours.
The CNS includes the brain and spinal cord, whilst the PNS encompasses all nervous tissue beyond these central structures. From these primary divisions, the system branches further into specialised subsystems, each with distinct functions.
The beauty of nervous system organisation lies in its interconnected nature - no division works in isolation. The CNS and PNS constantly communicate, creating a seamless network that coordinates everything from conscious thought to automatic breathing.
Central nervous system (CNS)
The central nervous system consists of the brain and spinal cord, forming the body's primary control centre for psychological and physiological processes.
The brain
The brain serves as the command centre for psychological processes and maintains essential life functions. It coordinates complex behaviours including problem-solving, planning, and higher-order thinking. Different brain regions handle various functions, from basic survival processes to sophisticated cognitive abilities.
The brain processes information from throughout the body, integrates this data, and generates appropriate responses. This integration allows for complex behaviours and the coordination of multiple bodily systems simultaneously.
The spinal cord
The spinal cord acts as a communication highway between the brain and the rest of the body. It facilitates the transfer of messages travelling to and from the brain via the peripheral nervous system. Additionally, the spinal cord coordinates reflex actions independently, such as the startle response, which occur without direct brain involvement.
This dual function makes the spinal cord crucial for both conscious control and automatic protective responses.
Peripheral nervous system (PNS)
The peripheral nervous system extends beyond the CNS boundaries and transmits information between the central structures and the entire body. The PNS divides into two distinct systems: the somatic nervous system and the autonomic nervous system.
Somatic nervous system
The somatic nervous system handles voluntary movements and sensory information processing. Its primary responsibility involves transmitting messages between the senses and the CNS, as well as controlling conscious muscle movements.
This system processes sensory input such as visual information from the eyes and auditory signals from the ears. It also directs voluntary muscle movements, enabling deliberate actions like walking, writing, or speaking. The somatic system essentially manages our conscious interactions with the environment.
Autonomic nervous system
The autonomic nervous system controls involuntary bodily functions, particularly those involving internal organs. This system operates largely without conscious awareness, maintaining vital processes that sustain life.
The autonomic system transmits information between internal organs and the CNS, helping regulate processes such as heart rate, breathing, and digestion. It divides further into two complementary branches that work in opposition to maintain bodily balance.
The autonomic nervous system's two branches - sympathetic and parasympathetic - work in constant opposition to each other. This balance is crucial for survival: too much sympathetic activity leads to chronic stress, whilst insufficient sympathetic response prevents appropriate reactions to danger.
Sympathetic nervous system
The sympathetic nervous system represents the body's activation branch, increasing physiological activity when heightened arousal is required. This system prepares the body for action during stressful or demanding situations.
When activated, the sympathetic system increases heart rate, dilates pupils, releases stress hormones, and redirects blood flow to muscles. These responses collectively prepare the organism for fight-or-flight situations, enhancing physical performance during emergencies.
Parasympathetic nervous system
The parasympathetic nervous system serves as the body's conservation branch, decreasing activity levels and promoting rest and recovery. This system maintains the body's baseline functioning during calm periods.
The parasympathetic system slows heart rate, constricts pupils, stimulates digestive processes, and promotes energy conservation. These responses support rest, digestion, and recovery, allowing the body to maintain and repair itself during peaceful periods.
Functional integration
These nervous system divisions work together seamlessly to coordinate behaviour and maintain homeostasis. The CNS processes information and makes decisions, whilst the PNS carries out these commands and relays sensory feedback. The balance between sympathetic and parasympathetic activity ensures appropriate responses to changing environmental demands.
This hierarchical organisation allows for both conscious control and automatic regulation, enabling complex behaviours whilst maintaining essential life functions without conscious effort.
Key Points to Remember:
- The nervous system divides into the CNS (brain and spinal cord) and PNS (everything else)
- The somatic nervous system controls voluntary movements and processes sensory information
- The autonomic nervous system manages involuntary functions through two opposing branches
- The sympathetic system increases activity (fight-or-flight), whilst the parasympathetic system decreases activity (rest-and-digest)
- All divisions work together to coordinate behaviour and maintain bodily functions