1.5 Explain the interrelationship between the nervous system and movement, including structure and function
About the dot point
The nervous system is the body’s control and communication network. It uses electrical and chemical signals to coordinate how muscles contract and how the body responds to what is happening inside and around it. Movement is not produced by muscles working in isolation. It depends on messages travelling between the brain, spinal cord and peripheral nerves, and on continuous sensory information that tells the body where it is in space, how fast it is moving, and whether adjustments are needed.
How to approach it
In this dot point, the directive verb is explain, which means you must show how and why the nervous system and movement are linked, not just describe each one. As you work through this page, focus on cause-and-effect relationships, such as how the CNS initiates and coordinates movement, how the PNS carries commands and returns feedback, and how changes in sensory input lead to changes in muscle action for accuracy, balance and safety.
1. The interrelationship between the nervous system and movement
Movement happens because the nervous system runs a constant two-way loop between control and feedback.
First, the central nervous system (CNS) plans and initiates movement. Next, the peripheral nervous system (PNS) carries commands to skeletal muscles so they contract. At the same time, the PNS sends sensory information back to the CNS so the movement can be adjusted for accuracy, balance and safety. This loop keeps running during all movement, from posture to complex sport skills.
Example: When you balance on one foot, your CNS sends commands to activate stabilising muscles at the ankle, knee and hip. As you sway, receptors in the ankle and inner ear send feedback to the CNS, which adjusts muscle activation to keep you upright. Without this feedback loop, balance would be unreliable.
Example: When you catch a ball, your eyes detect its speed and direction. Your brain predicts where it will arrive, and motor commands are sent to your arm and hand muscles. As your fingers contact the ball, touch and stretch receptors provide feedback so your grip can tighten or reposition if needed.
2. Structure of the nervous system for movement control
The nervous system is organised so movement can be controlled centrally, but carried out and adjusted throughout the body.
2.1 Central nervous system (CNS)
The CNS consists of the brain and spinal cord. It is protected by the skull and vertebrae because damage can seriously disrupt movement.
The brain coordinates movement through several regions working together:
- The primary motor cortex sends the main commands for voluntary movement.
- The premotor cortex and supplementary motor area help plan sequences and coordinate complex patterns.
- The basal ganglia help start movement and reduce unwanted movement. This helps control movement smoothness and force.
- The cerebellum fine-tunes timing, balance and precision. It uses sensory feedback to correct errors.
- The brainstem supports posture, balance and basic movement pathways.
- The prefrontal cortex supports decision-making about what action to take. The parietal lobes help combine spatial and sensory information about where the body is in space.
The spinal cord links the brain to the body and plays a major role in fast movement responses. It carries information through ascending tracts (sensory information to the brain) and descending tracts (motor commands to the body). It also branches into 31 pairs of spinal nerves, which connect the CNS to much of the body.
2.2 Peripheral nervous system (PNS)
The PNS includes all nerves outside the brain and spinal cord. It connects the CNS to effectors (such as skeletal muscle) and to sensory receptors that detect what is happening inside and outside the body.
The PNS has two main functional divisions:
- The somatic nervous system, which controls voluntary skeletal muscle movement and carries sensory input from skin, muscles and joints.
- The autonomic nervous system (ANS), which controls involuntary functions that support movement, including heart rate, blood vessel diameter, breathing patterns at rest, digestion, and temperature regulation. The ANS includes the sympathetic branch (prepares the body for action) and the parasympathetic branch (supports recovery).
Some sensory input used for movement is carried by cranial nerves, including visual input and balance input from the inner ear. Both are essential for coordination and posture.
2.3 Neurons
The nervous system works through specialised cells called neurons. Neurons transmit signals as electrical impulses and chemical messages.
A neuron has a cell body (with the nucleus), branching dendrites that receive signals, and a long axon that carries impulses away from the cell body. Many axons are covered by myelin, a fatty insulating layer that increases signal speed. In the brain and spinal cord, areas rich in myelinated axons form white matter.
Example: A motor neuron that carries movement commands from the spinal cord down to the muscles in the foot has a very long axon. Because the signal travels quickly along this single long fibre (especially when myelinated), the CNS can activate the toes rapidly.
Neurons communicate at synapses, which are small gaps between cells. When an impulse reaches the axon terminal, neurotransmitters are released and bind to receptors on the next cell. At the neuromuscular junction (between a motor neuron and a muscle fibre), the neurotransmitter acetylcholine triggers muscle contraction.
Neurons involved in movement include:
- Sensory neurons, which carry information from receptors to the CNS.
- Motor neurons, which carry commands from the CNS to muscles. A single motor neuron and the muscle fibres it controls form a motor unit.
- Interneurons, which connect neurons within the CNS and help processing and coordination, including reflex pathways.
3. Function in movement: from stimulus to response and feedback
Movement control depends on how the nervous system processes information and produces coordinated muscle action.
3.1 Voluntary movement
Voluntary movement begins with the brain selecting and planning an action. Commands then travel down the spinal cord to motor neurons that activate skeletal muscles. A key pathway is the corticospinal tract, which carries signals from the motor cortex to the spinal cord.
Force and precision depend on how many motor units are recruited and how often motor neurons fire. The nervous system also coordinates muscles across joints so movement is smooth and targeted. It also reduces unnecessary activation in opposing muscles that would resist the movement.
Example: When you pick up a cup, your brain plans the reach and grip. Motor commands activate shoulder, elbow, wrist and finger muscles in a timed sequence. Sensory feedback from the fingertips then adjusts grip pressure if the cup is heavier, slippery, or shifting.
3.2 Reflexes
A reflex is a rapid, automatic response to a stimulus that does not need conscious brain input to begin. Reflexes are processed mostly in the spinal cord, which makes them faster.
Example: When a goalkeeper’s hand touches a hot goal post in summer, a withdrawal reflex pulls the hand away before the brain consciously registers pain. The sensory signal reaches the spinal cord, which immediately sends motor commands to arm flexor muscles.
Reflexes support movement by protecting tissues and helping stabilise posture. Protective reflexes can limit excessive stretch and help manage sudden changes in load. The spinal cord can also coordinate multi-limb responses to maintain balance.
Example: When a basketball player lands from a rebound and one knee starts to buckle inward, stretch receptors in the quadriceps detect rapid lengthening. A protective reflex immediately increases muscle activation to resist the collapse and protect the knee ligaments.
The spinal cord can also help with rhythmic movement through central pattern generators (CPGs). These help produce basic repeated patterns, while the brain adapts the pattern to the environment.
Example: During freestyle swimming, the rhythmic arm strokes and flutter kick are partly coordinated by spinal CPGs. This allows the swimmer to concentrate on breathing timing, turn technique, and race tactics, without having to consciously think about each arm pull or leg kick.
3.3 Sensory feedback
Efficient movement depends on continuous sensory feedback carried by the PNS to the CNS.
Proprioception provides information about body position and movement. Receptors in muscles and tendons detect stretch and tension, and receptors in joints detect position and pressure. This helps the nervous system adjust movement even when you are not looking at your limbs.
Touch and pressure receptors in the skin help you control grip and contact force.
Example: If the ball starts to slip as a rugby league player is being tackled, touch and pressure feedback can trigger a rapid increase in grip force before they consciously think about it.
Vision and balance input from the inner ear also guide movement by informing the brain about body orientation, head movement and stability. If this information is disrupted, coordination becomes less reliable.
Example: After an intermediate gymnast completes a series of fast spins on the balance beam, the vestibular system can misjudge head and body position. The CNS receives less reliable balance input, so the gymnast may wobble or step off the beam unless visual and proprioceptive feedback quickly corrects posture.
4. Why this interrelationship improves movement efficiency and safety
The nervous system improves movement by making actions faster, smoother, more accurate, and more adaptable to changing conditions.
|
Aspect |
How the Nervous System Supports Movement |
Example |
|---|---|---|
|
Speed and Efficiency |
Fast processing and signal transmission through myelinated nerves enable quick reaction times when sensory information is detected and processed effectively. |
Elite sprinters can react to a start signal in about 0.15 seconds, showing very fast sensory-to-motor processing. |
|
Coordination |
The cerebellum adjusts timing and force across multiple joints by comparing intended movement with actual movement and correcting errors. Damage causes ataxia (clumsy, poorly timed movement). |
A tennis player adjusts the timing and angle of the racquet mid-swing after slightly misjudging a fast serve, using cerebellar error-correction to still make clean contact. |
|
Posture and Balance |
The brainstem and cerebellum combine sensory input and adjust muscle activation through constant, mostly unconscious adjustments to maintain stability. |
In surfing, a surfer makes constant, automatic postural adjustments as the board tilts on the wave, using vestibular (inner ear) and proprioceptive feedback to stay balanced. |
|
Learning and Neural Memory |
Movement becomes more efficient with practice as the nervous system strengthens useful neural pathways and reduces unnecessary processing through neural memory. |
When learning a basketball free throw, early attempts require conscious focus on stance, grip and release. With repetition, the shot becomes more automatic as neural pathways are strengthened. |
|
Internal Regulation |
The autonomic nervous system (ANS) increases heart rate, redirects blood flow, adjusts breathing, and maintains thermoregulation during exercise. |
During a hard run on a hot day, the nervous system increases skin blood flow and activates sweating to prevent hyperthermia. |
|
Injury Prevention |
Fast protective reflexes, stable posture control, and rapid corrections to unexpected changes reduce injury risk. |
Landing awkwardly on uneven ground triggers proprioceptive feedback and spinal reflexes that increase ankle muscle activation within a fraction of a second, reducing sprain risk. |
Damage to nervous system structures disrupts movement. A severe spinal cord injury can block messages between the brain and body below the injury level, causing loss of movement and sensation. Damage to peripheral nerves can weaken or paralyse the muscles they supply, even when the CNS is intact. Conditions that damage myelin, such as multiple sclerosis, can slow signal conduction and impair coordination.
Brief Summary
About the dot point and how to approach it
- The nervous system is the body’s control and communication network that coordinates how muscles contract using electrical and chemical signals.
- Movement depends on messages between the brain, spinal cord and peripheral nerves and continuous sensory information to adjust movement.
- Explain requires showing how and why the nervous system and movement are linked, including cause-and-effect relationships.
1. The interrelationship between the nervous system and movement
- Movement relies on a constant two-way loop between control and feedback.
- The CNS plans and initiates movement, and the PNS carries commands to muscles and returns sensory feedback to adjust accuracy, balance and safety.
2. Structure of the nervous system for movement control
- The CNS (brain and spinal cord) coordinates movement and sends information via ascending and descending tracts.
- The PNS links the CNS to effectors and sensory receptors (including vision and balance input), using somatic and autonomic (ANS) pathways.
- Movement signalling depends on neurons and synapses, with faster conduction through myelin and muscle activation at the neuromuscular junction via acetylcholine.
3. Function in movement: from stimulus to response and feedback
- Voluntary movement is planned in the brain and sent down the spinal cord (including the corticospinal tract) to recruit motor units for force and precision.
- A reflex is a rapid, automatic response to a stimulus, processed mostly in the spinal cord for fast protection and adjustment.
- Continuous sensory feedback (especially proprioception, touch, vision and inner ear balance input) allows coordination, balance and precision.
4. Why this interrelationship improves movement efficiency and safety
- The nervous system makes movement faster, smoother, more accurate, and more adaptable through rapid processing, myelinated signalling, and coordination (especially via the cerebellum).
- It improves safety through posture control, protective reflexes, and rapid corrections, and supports exercise by regulating internal conditions via the ANS (including thermoregulation).
- Damage (for example spinal cord injury, peripheral nerve damage, or conditions affecting myelin such as multiple sclerosis) disrupts movement and coordination.