The Nervous System and Brain Structure
The Nervous System and Brain Structure
Understanding the nervous system and brain structure is essential for explaining how biology influences behaviour. This topic links biology to psychology.
The Nervous System
The nervous system is the body's communication network — it transmits signals between the brain and the rest of the body.
Structure of the Nervous System
| Division | Components | Function |
|---|---|---|
| Central Nervous System (CNS) | Brain and spinal cord | Processes information; makes decisions; coordinates responses |
| Peripheral Nervous System (PNS) | All nerves outside the CNS | Transmits messages between the CNS and the rest of the body |
The PNS has two subdivisions:
| Subdivision | Function |
|---|---|
| Somatic nervous system | Controls voluntary movements (muscles you consciously control, e.g. walking, writing) |
| Autonomic nervous system (ANS) | Controls involuntary functions (things that happen automatically, e.g. heart rate, digestion, breathing) |
The ANS has two branches:
| Branch | Function | Activated When |
|---|---|---|
| Sympathetic nervous system | Prepares the body for action — the fight-or-flight response (increases heart rate, dilates pupils, releases adrenaline) | Threat or stress is detected |
| Parasympathetic nervous system | Calms the body down — the rest-and-digest response (slows heart rate, promotes digestion) | The threat has passed |
Neurons
Neurons are nerve cells that transmit electrical signals (nerve impulses) throughout the nervous system.
| Type | Function | Location |
|---|---|---|
| Sensory neurons | Carry signals from sense organs to the CNS | Connect receptors (eyes, ears, skin) to the brain/spinal cord |
| Relay neurons (interneurons) | Connect sensory and motor neurons within the CNS; process information | Brain and spinal cord |
| Motor neurons | Carry signals from the CNS to muscles and glands (effectors) | Connect the brain/spinal cord to the body |
The Synapse
- A synapse is the tiny gap between two neurons
- Electrical signals cannot jump across the gap — instead, neurotransmitters (chemical messengers) are released from one neuron, cross the gap and bind to receptors on the next neuron
- This triggers a new electrical signal in the receiving neuron
- Key neurotransmitters: serotonin (mood), dopamine (pleasure and reward), adrenaline (fight-or-flight)
Brain Structure
The brain is the most complex organ in the body. Different areas are responsible for different functions.
| Brain Area | Location | Function |
|---|---|---|
| Frontal lobe | Front of the brain | Higher thinking, planning, decision-making, personality, speech production (Broca's area), voluntary movement |
| Temporal lobe | Sides of the brain (behind the temples) | Hearing, language comprehension (Wernicke's area), memory |
| Parietal lobe | Top of the brain | Processing sensory information (touch, temperature, pain), spatial awareness |
| Occipital lobe | Back of the brain | Processing visual information |
| Cerebellum | Lower back of the brain | Balance, coordination, fine motor control, procedural memory |
| Brain stem | Base of the brain (connects to spinal cord) | Basic life functions: breathing, heart rate, sleeping, swallowing |
| Hippocampus | Deep within the temporal lobe | Forming new long-term memories; spatial navigation |
| Amygdala | Deep within the temporal lobe | Processing emotions, especially fear; emotional memory |
How Do We Know What Brain Areas Do?
- Brain damage case studies — e.g. Phineas Gage (1848): an iron rod went through his frontal lobe; he survived but his personality changed dramatically — he became impulsive, rude and irresponsible. This showed the frontal lobe is involved in personality and decision-making
- Brain scans — fMRI, PET and CT scans show which areas are active during different tasks
- Electrical stimulation — directly stimulating brain areas during surgery can trigger specific responses
Exam Tips
- Know the divisions of the nervous system — CNS, PNS, somatic, autonomic, sympathetic, parasympathetic
- Know the three types of neuron and their functions
- Know the main brain areas and what each does — this is frequently tested
- Use Phineas Gage as a key example of how brain damage affects behaviour
- For AO3: case studies of brain damage provide detailed evidence but are unique cases — hard to generalise
- Link brain structure to other topics — e.g. hippocampus to memory, amygdala to anxiety and EWT