Nervous Organisation (AQA A-Level Biology): Revision Notes
Nervous Organisation
Overview of the nervous system
The nervous system controls how organisms respond to changes in their environment. Understanding how millions of neurones work together requires knowledge of how the nervous system is organised structurally and functionally.
The coordination of millions of neurones working together represents one of the most complex biological systems, requiring precise structural and functional organisation to enable rapid and appropriate responses.
The nervous system divides into two main parts that work together to coordinate responses throughout the body.
Central nervous system (CNS)
The central nervous system forms the main control centre of the nervous system. It consists of two key components:
- Brain - the primary processing centre for information
- Spinal cord - the main pathway connecting the brain to the rest of the body
These structures process incoming information and coordinate appropriate responses.
Think of the CNS as the "headquarters" of your nervous system - the brain makes the decisions while the spinal cord acts as the main communication highway to carry messages throughout the body.
Peripheral nervous system (PNS)
The peripheral nervous system includes all nervous tissue outside the brain and spinal cord. It consists of pairs of nerves that connect either the brain or spinal cord to other parts of the body.
The PNS divides into two functional types based on the direction information travels:
Sensory neurones
Sensory neurones transport nerve impulses (electrical signals) from receptors towards the central nervous system. These neurones detect stimuli from the environment and carry this information to the brain and spinal cord for processing.
Motor neurones
Motor neurones carry nerve impulses away from the central nervous system to effectors (muscles and glands). These neurones transmit commands from the brain and spinal cord to produce responses.
Remember the direction: Sensory neurones carry signals TO the CNS (inward), while motor neurones carry signals FROM the CNS (outward). This directional flow is crucial for coordinated responses.
Motor system organisation
The motor nervous system subdivides further based on the type of control:
Voluntary nervous system
The voluntary nervous system carries nerve impulses to body muscles under conscious control. This system allows deliberate movements like walking, writing, or speaking.
Autonomic nervous system
The autonomic nervous system carries nerve impulses to glands, smooth muscle, and cardiac muscle. This system operates without conscious control - it is involuntary and manages subconscious functions like heart rate, breathing, and digestion.
The key distinction: Voluntary = conscious control (you decide to move), Autonomic = unconscious control (your heart beats automatically). This division allows your brain to focus on complex tasks while essential life functions continue automatically.
Spinal cord structure
The spinal cord forms a column of nervous tissue running along the back, protected within the vertebral column. Pairs of spinal nerves emerge at regular intervals along its length.
The spinal cord contains both sensory and motor neurones organised in specific regions. Sensory neurones are located in areas that receive incoming signals, while motor neurones occupy regions that send outgoing commands to effectors.
This organised structure isn't random - sensory and motor pathways are strategically positioned to enable efficient processing and rapid response times.
This organisation allows the spinal cord to process simple responses independently of the brain, forming the basis for reflex arcs - rapid, automatic responses to stimuli.
Key Points to Remember:
- The nervous system divides into CNS (brain + spinal cord) and PNS (all other nerves)
- Sensory neurones carry signals TO the CNS, motor neurones carry signals FROM the CNS
- The voluntary system controls conscious movement, the autonomic system manages unconscious functions
- The spinal cord contains organised pathways for both sensory input and motor output
- This organisation enables both complex processing and rapid reflex responses