Welcome to the Nervous System!
Ever wondered how a sprinter reacts instantly to the sound of a starter pistol, or how a goalkeeper dives to make a fingertip save? It all comes down to your body's master communication network: the Nervous System.
In this chapter of "The Body at Work" for CCEA GCSE PE, we will break down how your brain, spinal cord, and nerves work together to control every single movement, reaction, and skill in sport. Don't worry if this seems tricky at first—we will take it step-by-step with clear examples!
---1. Role and Core Functions in Physical Activity
The nervous system acts as the ultimate command, control, and communication centre of your body.
In sports and physical activity, it has four crucial roles:
1. Detecting stimuli: It constantly senses changes in your environment, both internal (e.g. muscle tension) and external (e.g. seeing a pass incoming or hearing the referee's whistle).
2. Transmitting signals: It carries electrical signals called nerve impulses across the body at rapid speeds.
3. Coordinating movement: It processes sensory information to make decisions and execute both conscious voluntary skills (like shooting a basketball) and automatic reflex actions (like dodging an unexpected ball).
4. Stimulating muscle contraction: It activates and recruits motor units so your muscles can contract with the right force and timing.
Analogy to remember: Think of the nervous system as a team's manager and broadband network combined. It spots what is happening on the pitch, makes tactical decisions, and sends instant instructions directly to the players (the muscles).
Key Takeaway:
The nervous system detects changes (stimuli), sends electrical nerve impulses, processes information, and tells muscles when and how hard to contract.
---2. Structural Divisions: CNS vs. PNS
The nervous system is divided into two main parts. You need to know the components and jobs of each:
A. The Central Nervous System (CNS)
• Components: The Brain and the Spinal Cord.
• Function: This is the main processing and decision-making headquarters. It receives sensory information, makes sense of it, decides what to do, and sends out movement commands.
B. The Peripheral Nervous System (PNS)
• Components: All the nerves radiating outside the CNS throughout the rest of the body (including cranial nerves and spinal nerves).
• Function: It acts as the two-way wiring system connecting your CNS to your limbs, sense organs, and muscles. It carries incoming sensory signals toward the CNS and outgoing motor signals away from the CNS to your muscles.
Memory Trick:
• Central = Centre of the body (Brain and Spine).
• Peripheral = On the Periphery / outer edges (Nerves reaching out to hands, feet, and limbs).
Key Takeaway:
The CNS (Brain & Spinal Cord) is the decision-maker; the PNS (all other nerves) is the wiring network that delivers messages to and from the CNS.
---3. Nerve Cells (Neurones) and How Signals Travel
The basic building block of the nervous system is a specialised nerve cell called a neurone.
Structure of a Neurone
• Dendrites: Branch-like structures that receive incoming impulses from other neurones or sensory receptors.
• Cell Body (Soma): Contains the nucleus and keeps the cell alive and functioning.
• Axon: A long fibre that conducts the electrical impulse away from the cell body toward target tissues (like muscles) or other neurones.
The Three Types of Neurones in Movement
To produce movement, three types of neurones work together in sequence:
1. Sensory (Afferent) Neurones: Carry impulses from sensory receptors (e.g. your eyes, skin, or muscle receptors) inward to the CNS.
2. Relay Neurones (Interneurones): Found inside the CNS (brain and spinal cord). They connect sensory neurones to motor neurones and process information.
3. Motor (Efferent) Neurones: Carry movement commands outward from the CNS to effectors (the muscles) to cause contraction.
Common Exam Pitfall to Avoid:
Candidates often mix up sensory and motor neurones! Remember:
• Sensory = Senses the environment \(\rightarrow\) goes IN to the CNS.
• Motor = Movement \(\rightarrow\) goes OUT to the muscles.
Synaptic Transmission: Crossing the Gap
Neurones do not physically touch each other. There is a tiny microscopic gap between them called a synapse (or a neuromuscular junction when a motor neurone connects to a muscle fibre).
• When an electrical impulse reaches the end of an axon, it triggers the release of chemical messengers called neurotransmitters.
• These chemicals diffuse across the synaptic gap.
• They bind to receptors on the next neurone or muscle fibre, regenerating the electrical impulse so the message continues.
Key Takeaway:
Sensory neurones carry signals to the CNS, relay neurones link them inside the CNS, and motor neurones carry commands to muscles. Chemical neurotransmitters carry messages across the microscopic gap called a synapse.
---4. Motor Control and Information Processing in Sport
A. Pathway of a Voluntary Movement
A voluntary movement is a conscious, deliberate sports action (for example, a netballer seeing a teammate and choosing to throw a chest pass).
The pathway follows this exact step-by-step sequence:
1. Stimulus / Environment: A change in the sporting environment (e.g. hearing the starter pistol).
2. Receptor: Sensory organ detects the stimulus (e.g. ears detect the sound).
3. Sensory Neurone: Transmits the electrical impulse towards the CNS.
4. Central Nervous System (Brain/Spinal Cord): Interprets the signal and makes a decision.
5. Motor Neurone: Sends the motor impulse away from the CNS.
6. Effector: The working skeletal muscle receives the impulse (e.g. leg muscles).
7. Response: The muscle contracts, producing the action (e.g. pushing off the starting blocks).
\(\text{Stimulus} \rightarrow \text{Receptor} \rightarrow \text{Sensory Neurone} \rightarrow \text{CNS} \rightarrow \text{Motor Neurone} \rightarrow \text{Effector} \rightarrow \text{Response}\)
B. Reflex Actions (Involuntary)
A reflex action is a rapid, automatic, and involuntary response designed for safety and injury prevention (e.g. instantly pulling your hand away from a hot surface, or blinking when an object flies toward your eyes).
• Key difference: Reflexes bypass conscious brain decision-making.
• The signal travels through a direct spinal Reflex Arc: \(\text{Receptor} \rightarrow \text{Sensory Neurone} \rightarrow \text{Relay Neurone in Spinal Cord} \rightarrow \text{Motor Neurone} \rightarrow \text{Effector}\).
• Because the brain is not needed to make a conscious choice, the response is ultra-fast!
Examiner Tip:
Do NOT confuse sports skills with reflexes! A goalkeeper making a save from a penalty kick is performing a fast voluntary response using their brain, not a spinal reflex arc.
C. Proprioception and Sensory Feedback
How do you know where your arms and legs are when doing a backflip without looking at them? That is proprioception.
• Special sensory receptors (proprioceptors / muscle spindles) located in your muscles, tendons, and joints constantly detect body position, muscle stretch, and joint angle.
• They send real-time feedback to the CNS to adjust balance, posture, and movement precision during complex athletic skills.
Key Takeaway:
Voluntary actions involve conscious processing in the brain (\(\text{Stimulus} \rightarrow \text{Receptor} \rightarrow \text{Sensory} \rightarrow \text{CNS} \rightarrow \text{Motor} \rightarrow \text{Effector} \rightarrow \text{Response}\)), while reflex actions travel through the spinal cord for fast protection.
---5. Short-Term and Long-Term Effects of Exercise
Just like your muscular and cardiovascular systems, your nervous system responds during a workout and adapts over time with regular training.
Short-Term Responses (During a Single Workout)
• Increased rate of nerve impulse firing: The CNS sends impulses much faster to recruit the required motor units and muscle fibres for work.
• Heightened alertness and focus: Rapid processing of visual and auditory tactical stimuli (e.g. tracking player movements and reacting to game situations).
Long-Term Adaptations (After Weeks/Months of Training)
• Improved neural pathways: Faster reaction times and smoother coordination. Motor skills become "automated" (muscle memory), allowing athletes to perform complex skills effortlessly.
• More efficient neuromuscular recruitment: Greater synchronisation of motor units and increased firing rates, meaning muscles can contract with significantly more strength, speed, and power.
Key Takeaway:
During exercise, nerve impulses fire faster to recruit muscles. Over months of training, neural pathways become faster and more efficient, leading to sharper reaction times, smoother skill execution, and increased muscular power.
---Quick Exam Review & Summary Checklist
Before moving on to exam questions, check that you can:
✓ Name the 2 parts of the CNS (Brain & Spinal Cord) and describe the PNS (Nerves outside CNS).
✓ Identify the 3 parts of a neurone (Dendrites, Cell Body, Axon).
✓ Outline the path of a voluntary movement: \(\text{Stimulus} \rightarrow \text{Receptor} \rightarrow \text{Sensory Neurone} \rightarrow \text{CNS} \rightarrow \text{Motor Neurone} \rightarrow \text{Effector} \rightarrow \text{Response}\).
✓ Explain the role of neurotransmitters at the synapse.
✓ State why a reflex arc is faster than a voluntary action (bypasses conscious brain processing).
✓ Use technical terms in long-answer questions (e.g. "motor neurone sending nerve impulses to effector muscles" instead of "the brain tells the muscle to move").