CIE iGCSE Biology-14.1 Coordination and response- Study Notes- New Syllabus
CIE iGCSE Biology-14.1 Coordination and response- Study Notes – New syllabus
CIE iGCSE Biology-14.1 Coordination and response- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
- State that electrical impulses travel along neurones
- Describe the mammalian nervous system in terms of:
(a) the central nervous system (CNS) consisting of the brain and the spinal cord
(b) the peripheral nervous system (PNS) consisting of the nerves outside of the brain and spinal cord - Describe the role of the nervous system as coordination and regulation of body functions
- Identify in diagrams and images sensory, relay and motor neurones
- Describe a simple reflex arc in terms of: receptor, sensory neurone, relay neurone, motor neurone and effector
- Describe a reflex action as a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands)
- Describe a synapse as a junction between two neurones
Supplement
- Describe the structure of a synapse, including the presence of vesicles containing neurotransmitter molecules, the synaptic gap and receptor proteins
- Describe the events at a synapse as:
(a) an impulse stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap
(b) the neurotransmitter molecules diffuse across the gap
(c) neurotransmitter molecules bind with receptor proteins on the next neurone
(d) an impulse is then stimulated in the next neurone - State that synapses ensure that impulses travel in one direction only
Electrical Impulses and Neurones
Key Statement:
Electrical impulses travel along neurones to transmit information rapidly around the body.
🔍 What Are Electrical Impulses?
- Tiny electrical signals generated by neurones (nerve cells).
- Used by the nervous system to send messages quickly and precisely.
🧠 Neurones – The Signal Carriers
| Feature | Description |
|---|---|
| Neurones | Specialised cells that carry nerve impulses. |
| Axon | The long part of a neurone where the impulse travels. |
| Direction | Impulses travel in one direction: from dendrites → cell body → axon terminals. |
⚙️ Function of Electrical Impulses
- Allow quick communication between:
- Receptors (e.g. in skin)
- Spinal cord/brain (processing centre)
- Effectors (muscles or glands)
- Enable rapid responses to changes in the environment (stimuli).
Neurones = nerve cells
Impulses = electrical messages
Travel fast to coordinate actions
Allow reactions like pulling away from hot objects
The Mammalian Nervous System
Overview:
- The nervous system is the body’s fast communication system.
- It detects stimuli, processes information, and coordinates responses through electrical impulses.
(a) Central Nervous System (CNS)
| Component | Function |
|---|---|
| Brain | Acts as the control centre, processes information, stores memories, and makes decisions. |
| Spinal Cord | Connects the brain to the rest of the body and coordinates reflex actions. |
🧠 The CNS:
- Is protected by the skull (brain) and vertebrae (spinal cord).
- Processes all incoming sensory information and sends out responses via motor neurones.
(b) Peripheral Nervous System (PNS)
| Component | Function |
|---|---|
| Nerves outside the CNS | Carry impulses to and from the brain and spinal cord. Includes: – Sensory neurones: carry messages to the CNS – Motor neurones: carry commands from the CNS to effectors |
🟢 The PNS:
- Connects the CNS to the limbs and organs.
- Allows the body to respond quickly to stimuli.
- Plays a role in both voluntary and involuntary responses.
📘 Summary:
| System | Includes | Main Role |
|---|---|---|
| CNS | Brain + Spinal cord | Processes and coordinates responses |
| PNS | All nerves outside CNS | Sends messages to and from the CNS |
CNS = Brain + Spinal cord (control centre)
PNS = Nerves (communication network)
Together, they detect, process, and respond to stimuli
Role of the Nervous System: Coordination and Regulation
Key Function:
The nervous system is responsible for the coordination and regulation of body functions by detecting changes (stimuli), processing information, and producing appropriate responses.
🔍 What is Coordination?
Coordination means making sure that all body parts work together smoothly.
The nervous system ensures that different organs and systems respond in a controlled and balanced way.
🧠 Example:
If you touch something hot, your hand quickly pulls away – muscles, skin receptors, spinal cord, and brain all work together instantly.
⚙️ What is Regulation?
Regulation means keeping internal body conditions stable and functioning properly.
The nervous system helps control:
- Heart rate
- Breathing rate
- Movement
- Reflexes
- Voluntary and involuntary actions
How the Nervous System Works:
| Step | Action |
|---|---|
| 1 | Stimulus (e.g., pain, temperature) is detected by receptors. |
| 2 | Electrical impulses are sent through sensory neurones to the CNS. |
| 3 | Brain or spinal cord processes the information. |
| 4 | A response is sent through motor neurones to effectors (muscles or glands). |
| 5 | The effector produces the appropriate response (e.g., muscle contraction, hormone release). |
Types of Neurones & How to Identify Them
1. Sensory Neurone
Function: Carries electrical impulses from receptors (e.g., skin) to the central nervous system (CNS)
| Feature | How to Identify |
|---|---|
| Cell body | Located off to the side (in a swelling called the dorsal root ganglion) |
| Direction | From receptor → CNS |
| Structure | Long dendron (from receptor), short axon (to CNS) |
2. Relay Neurone (Interneurone)
Function: Carries impulses within the CNS, usually between sensory and motor neurones
| Feature | How to Identify |
|---|---|
| Cell body | In the middle of the neurone |
| Direction | From sensory neurone → motor neurone |
| Structure | Short axons and dendrites, found only in brain and spinal cord |
3. Motor Neurone
Function: Carries impulses from the CNS to effectors (muscles or glands)
| Feature | How to Identify |
|---|---|
| Cell body | Located at one end (within the spinal cord) |
| Direction | From CNS → effector |
| Structure | Long axon, short dendrites |
| Neurone Type | Direction of Impulse | Cell Body Location | Connected To |
|---|---|---|---|
| Sensory | Receptor → CNS | Side (ganglion) | Receptor to CNS |
| Relay | CNS → CNS | Centre | Between sensory & motor |
| Motor | CNS → Effector | Start of neurone | CNS to muscle/gland |
Simple Reflex Arc
Definition:
A reflex arc is the pathway taken by a nerve impulse during a reflex action — a quick, automatic response to a stimulus that protects the body from harm.
🔄 Steps in a Simple Reflex Arc:
| Step | Description |
|---|---|
| 1. Stimulus | A change in the environment is detected (e.g., touching a hot object). |
| 2. Receptor | A sensory receptor in the skin detects the stimulus (e.g., heat or pain). |
| 3. Sensory Neurone | Carries the impulse from the receptor to the spinal cord. |
| 4. Relay Neurone | Located in the spinal cord (CNS), passes the impulse from sensory to motor neurone. |
| 5. Motor Neurone | Carries the impulse from the spinal cord to the effector. |
| 6. Effector | A muscle or gland that carries out the response (e.g., the muscle contracts to pull your hand away). |
🧠 Key Feature of Reflexes:
- Very fast (no brain involvement in the decision).
- Helps prevent injury by producing immediate protective actions.
Stimulus → Receptor → Sensory neurone → Relay neurone → Motor neurone → Effector
Reflex actions are involuntary and bypass the brain for faster response.
Reflex Action – Definition and Description
What is a Reflex Action?
A reflex action is an automatic and rapid response to a stimulus, designed to protect the body from harm.
🔄 Key Features:
| Feature | Description |
|---|---|
| Automatic | Happens without conscious thought (involuntary). |
| Rapid | Involves minimal nerve pathway – no delay from brain processing. |
| Protective | Helps avoid injury or harm (e.g., blinking, pulling hand away from heat). |
| Coordination | Connects stimulus with the appropriate effector quickly. |
🧠 How It Works:
- Receptors detect the stimulus (e.g. pain).
- Sensory neurones carry the impulse to the spinal cord.
- Relay neurones in the spinal cord transfer the signal.
- Motor neurones carry the impulse to the effectors (muscles/glands).
- Effectors carry out the response (e.g. muscle contracts, gland secretes).
🧷 Example:
Touching a hot object
→ Skin receptors detect heat
→ Sensory neurone sends impulse to spinal cord
→ Relay neurone passes message
→ Motor neurone sends impulse to biceps
→ Muscle contracts → hand pulls away
Reflex = Fast + Involuntary + Protective
Stimulus → Response via spinal cord
Effectors = Muscles or glands
What is a Synapse?
Definition:
A synapse is a tiny gap or junction between two neurones, where nerve impulses are transmitted chemically from one neurone to the next.
🧠 Key Points:
| Feature | Description |
|---|---|
| Structure | A synapse is the gap between the axon terminal of one neurone and the dendrite of the next. |
| Transmission | The impulse is passed across the gap using chemical messengers called neurotransmitters. |
| Direction | Impulses only travel in one direction across a synapse. |
🔄 How It Works:
- An electrical impulse reaches the end of the first neurone (axon terminal).
- This triggers the release of neurotransmitters into the synaptic gap.
- The neurotransmitters diffuse across the gap.
- They bind to receptors on the second neurone.
- A new electrical impulse is generated in the second neurone.
Synapse = Gap between neurones
Neurotransmitters = Chemicals that cross the gap
Direction = Always one-way
Structure of a Synapse
Definition:
A synapse is a tiny gap between two neurones where nerve impulses are transmitted chemically using neurotransmitters.
🔍 Key Components of a Synapse:
| Part | Description |
|---|---|
| Presynaptic neurone | The neurone sending the signal. Its axon terminal contains vesicles filled with neurotransmitters. |
| Synaptic vesicles | Small sacs that store and release neurotransmitter molecules (e.g. acetylcholine). |
| Synaptic cleft | The tiny gap (20–40 nm) between the presynaptic and postsynaptic neurones where neurotransmitters diffuse. |
| Postsynaptic neurone | The receiving neurone with receptor proteins that bind neurotransmitters. |
| Receptor proteins | Located on the postsynaptic membrane; they detect neurotransmitters and trigger a new impulse. |
🔄 Transmission Process:
- Electrical impulse arrives at presynaptic terminal.
- Vesicles release neurotransmitters into the synaptic cleft.
- Neurotransmitters diffuse across the gap.
- They bind to receptor proteins on the postsynaptic neurone.
- This stimulates a new electrical impulse.
Synapse = Presynaptic neurone + Synaptic cleft + Postsynaptic neurone
Vesicles = Store neurotransmitters
Receptors = Detect neurotransmitters and trigger response
Events at a Synapse
What is a Synapse?
A synapse is the junction between two neurones, where signals are passed from one neurone to the next using chemical messengers called neurotransmitters.
🔄 Step-by-Step Events at a Synapse:
| Step | Description |
|---|---|
| (a) Impulse arrival and neurotransmitter release | When an electrical impulse reaches the axon terminal of the first (presynaptic) neurone, it triggers vesicles to move to the membrane and release neurotransmitter molecules into the synaptic gap. |
| (b) Diffusion across the synaptic gap | The neurotransmitter molecules then diffuse across the synaptic cleft (the small gap between the two neurones). |
| (c) Binding to receptor proteins | The neurotransmitters bind to specific receptor proteins on the membrane of the postsynaptic neurone. |
| (d) New impulse generated | This binding stimulates a new electrical impulse in the next neurone, allowing the signal to continue. |
📌 Summary:
- Transmission across a synapse is chemical (neurotransmitters)
- Direction is one-way: from presynaptic → postsynaptic neurone
- Synapses slow down impulses slightly but allow flexibility in response
One-Way Transmission at Synapses
Key Statement:
Synapses ensure that impulses travel in one direction only.
Explanation:
A synapse is the gap between two neurones, where information is passed using chemical messengers called neurotransmitters.
- Only the presynaptic neurone has vesicles that store and release neurotransmitters.
- Only the postsynaptic neurone has receptor proteins to detect and respond to neurotransmitters.
Because of this arrangement, impulses can only pass from the presynaptic → postsynaptic neurone, and not in reverse.
📘 Summary Table:
| Structure | Found in | Role |
|---|---|---|
| Neurotransmitter vesicles | Presynaptic neurone | Releases signal |
| Receptor proteins | Postsynaptic neurone | Detects and responds to signal |
Synapses are built for one-way flow
Vesicles → neurotransmitters → receptors
This ensures signals only move forward