IB MYP 4-5 Biology-Nervous system- Study Notes - New Syllabus
IB MYP 4-5 Biology-Nervous system- Study Notes – New syllabus
IB MYP 4-5 Biology-Nervous system- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Central vs peripheral nervous system
- Neuron structure and function
- Reflex arcs and involuntary responses
- Synaptic transmission
The Human Nervous System
What is the Nervous System?
The nervous system is the control and communication system of your body. It helps you:
- Sense your surroundings
- React to stimuli
- Control movement
- Think, learn, and remember
It works by sending electrical messages (nerve impulses) between the brain, spinal cord, and body parts.
Nervous system organization:
Two Main Parts of the Nervous System
- Central Nervous System (CNS)
- Peripheral Nervous System (PNS)
1. Central Nervous System (CNS)
Includes: Brain and Spinal Cord
The Brain: Controls thoughts, senses, emotions, memory, and voluntary actions.
The Spinal Cord: Sends signals between brain and body. Also controls reflexes.
2. Peripheral Nervous System (PNS)
Includes: All the nerves outside the brain and spinal cord
Sensory nerves: Carry information to the brain
Motor nerves: Carry commands from the brain
The PNS acts like your body’s wiring linking the brain and spinal cord to every part of you.
Comparison Table – CNS vs PNS
| Feature | CNS | PNS |
|---|---|---|
| Main parts | Brain & spinal cord | Nerves outside CNS |
| Function | Processes and controls | Connects CNS to body |
| Location | Skull and spine | All over body |
| Role | Decision maker | Message carrier |
| Type of control | Voluntary & reflex | Voluntary + automatic |
How They Work Together
Example: You touch a hot object
- PNS: Sensory nerve detects heat and sends signal to spinal cord
- CNS: Spinal cord processes it and sends back a response
- PNS: Motor nerve tells muscles to move hand away
Why Is the Nervous System Important?
- Helps sense and respond to the environment
- Controls voluntary and involuntary actions
- Supports thinking, memory, emotion, and balance
- Maintains homeostasis (internal balance)
Neuron – Structure and Function
What is a Neuron?
A neuron is the basic unit of the nervous system. It carries electrical signals called nerve impulses that allow the body to:
- Sense surroundings
- Think and make decisions
- React to stimuli
- Control movements
Think of neurons as the body’s electrical wiring – connecting and powering everything.
Main Parts of a Neuron
- Cell Body (Soma): Contains the nucleus and controls the neuron’s function
- Dendrites: Receive signals from other neurons or receptors and carry them to the cell body
- Axon: A long fiber that sends signals away from the cell body to other cells
Other important parts:
- Myelin Sheath: A fatty layer that insulates the axon and speeds up signal transmission
- Axon Terminals: Ends of the axon that pass the signal to the next cell
- Synapse: The tiny gap where the message is transferred to another neuron or muscle
Summary Table – Neuron Parts and Functions
| Part | Function |
|---|---|
| Cell body (soma) | Contains nucleus, controls cell function |
| Dendrites | Receive signals from other cells |
| Axon | Sends signals away from cell body |
| Myelin sheath | Speeds up impulse transmission |
| Axon terminals | Pass signals to next neuron/muscle |
| Synapse | Tiny gap between neurons for signal transfer |
How Do Neurons Work?
- A stimulus (e.g., light, heat, touch) is detected
- Dendrites receive the signal
- The impulse travels through the axon
- At the axon terminal, it crosses the synapse
- Reaches another neuron, muscle, or gland
Types of Neurons
| Type | Function | Location |
|---|---|---|
| Sensory neuron | Carries signals from sense organs to CNS | Skin, eyes, ears |
| Motor neuron | Carries signals from CNS to muscles/glands | Brain, spinal cord to body |
| Relay neuron | Connects sensory and motor neurons | Brain and spinal cord |
Why Are Neurons Important?
- Enable fast communication in the body
- Control every reaction and movement
- Help you sense, think, remember, and stay alive
Reflex Arcs and Involuntary Responses
What Is a Reflex?
A reflex is a quick, automatic response to a stimulus it happens without thinking, often to protect the body from danger.
What Is an Involuntary Response?
An involuntary response is a reaction that happens without conscious control. Reflexes are a special type of involuntary response.
Steps in a Reflex Arc
- Stimulus: Change in environment (e.g. something sharp touches the skin)
- Receptor: Detects the stimulus (touch/temperature receptor)
- Sensory Neuron: Sends signal to spinal cord
- Relay Neuron: Passes signal inside spinal cord
- Motor Neuron: Sends signal to a muscle
- Effector: Muscle or gland carries out the response
- Response: Immediate action – like pulling hand away
Reflex Arc Example – Touching Something Hot
| Stage | What Happens |
|---|---|
| Stimulus | Hot surface touches hand |
| Receptor | Temperature/pain receptors detect heat |
| Sensory Neuron | Sends message to spinal cord |
| Relay Neuron | Processes signal in spinal cord |
| Motor Neuron | Carries response signal to muscle |
| Effector | Muscle contracts — hand pulls away |
Reflex vs Voluntary Action
| Feature | Reflex Action | Voluntary Action |
|---|---|---|
| Speed | Very fast | Slower |
| Control | Involuntary | Voluntary |
| Pathway | Spinal cord | Brain |
| Example | Blinking, sneezing, withdrawal | Walking, writing, talking |
Why Are Reflexes Important?
- Provide fast protection from danger
- Prevent injury (e.g., burns, cuts)
- Do not require conscious thought – saves time
Synaptic Transmission
What Is Synaptic Transmission?
Synaptic transmission is the process by which a nerve impulse passes from one neuron to the next across a tiny gap called a synapse.
What Is a Synapse?
A synapse is the tiny gap between two neurons – specifically between the axon terminal of one neuron and the dendrite of the next.
Key Parts Involved
| Part | Role in Transmission |
|---|---|
| Axon terminal | End of the sending neuron |
| Synaptic cleft | Gap between neurons |
| Neurotransmitters | Chemicals that carry the signal across the gap |
| Receptors | Detect neurotransmitters on the next neuron |
Step-by-Step: Synaptic Transmission
- Impulse reaches the axon terminal of the first neuron
- Vesicles release neurotransmitters into the synaptic cleft
- Neurotransmitters diffuse across the gap
- They bind to receptors on the second neuron’s dendrite
- This triggers a new electrical impulse in the next neuron
Why Use Neurotransmitters?
- Electrical signals can’t cross the synapse directly
- Neurotransmitters convert the signal to chemical form
- Ensures one-way transmission and accurate control
Examples of Neurotransmitters
| Neurotransmitter | Function |
|---|---|
| Dopamine | Linked to pleasure and reward |
| Serotonin | Affects mood and emotions |
| Acetylcholine | Helps control muscle movement |
| Adrenaline | Prepares body for “fight or flight” |
Why Is Synaptic Transmission Important?
- Enables communication between billions of neurons
- Controls muscle actions, thinking, reflexes, and learning
- Regulates emotions, memory, attention, and mood