🧠 Biopsychology: The Connection Between Body and Mind
Hello future psychologists! This chapter, Biopsychology, is where we merge Biology with Psychology. It's fascinating because it helps us understand *how* the physical structures in our body—like our brain and nervous system—actually create our thoughts, feelings, and behaviours.
Don't worry if this sounds intimidating! We will break down complex systems into simple parts. Think of your body as the world's most sophisticated communication network, and we are going to learn how its wires (nerves) and chemical signals (hormones) work.
1. The Divisions of the Nervous System
The nervous system is the body's main internal communication system. It’s responsible for everything you do, from blinking your eyes to solving complex equations.
The Central Nervous System (CNS)
- CNS Components: The Brain and the Spinal Cord.
- Function: This is the control centre—the 'Commander-in-Chief'. It processes information received from the senses and coordinates all motor responses.
The Peripheral Nervous System (PNS)
The PNS is made up of all the nerves extending out from the CNS. It acts as the messenger system, carrying information to and from the CNS.
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1. The Somatic Nervous System:
Controls voluntary actions, like moving your arm. It also carries sensory information (touch, taste, etc.) to the CNS.
Analogy: This is the system you use when you consciously decide to pick up your phone. -
2. The Autonomic Nervous System (ANS):
Controls involuntary (automatic) functions necessary for life, like heart rate, digestion, and breathing.
The ANS has two crucial sub-divisions that work in opposition:
- Sympathetic Nervous System: The body's accelerator. Prepares the body for action, specifically the Fight or Flight response (more on this later). Increases heart rate, stops digestion.
- Parasympathetic Nervous System: The body's brake. Calms the body down after an emergency. Responsible for 'Rest and Digest' functions. Decreases heart rate, restarts digestion.
Quick Review: CNS (control) vs. PNS (communication). PNS splits into Somatic (voluntary) and Autonomic (automatic). Autonomic splits into Sympathetic (stress) and Parasympathetic (peace).
2. The Structure and Function of Neurons
A neuron is the basic building block of the nervous system. It is a specialised cell that transmits electrical and chemical signals.
Neuron Structure
- Cell Body (Soma): Contains the nucleus and genetic material; the life-support centre.
- Dendrites: Branch-like structures that receive nerve impulses from other neurons. (Think of 'D' for 'Detect').
- Axon: A long, slender fibre that carries the electrical impulse away from the cell body toward other neurons or muscles.
- Myelin Sheath: A fatty layer covering the axon. It protects the axon and speeds up the electrical transmission.
Types of Neurons (The Three Musketeers)
- Sensory Neurons: Carry messages from the PNS receptors (skin, eyes, etc.) to the CNS. Example: When you touch a hot stove, the sensory neurons fire first.
- Motor Neurons: Carry messages from the CNS to effectors (muscles and glands) to produce movement or action. Example: The impulse that tells your hand to pull away from the stove.
- Relay Neurons (Interneurons): Found only within the CNS (brain and spinal cord). They connect sensory neurons to motor neurons or other relay neurons. They are responsible for processing and analysis.
Key Takeaway: Sensory goes IN, Motor comes OUT, Relay stays IN the centre.
3. Synaptic Transmission (How Neurons Talk)
Neurons don't actually touch each other. They communicate across a tiny gap called the synapse. This process is called synaptic transmission.
The Step-by-Step Process
- An electrical impulse reaches the end of the axon (the pre-synaptic terminal).
- This impulse triggers the release of tiny chemical messengers called neurotransmitters.
- The neurotransmitters cross the synaptic gap.
- They bind to receptor sites on the dendrite of the next neuron (the post-synaptic neuron), converting the chemical message back into an electrical impulse.
Excitation and Inhibition: The Gas and Brake Pedals
Neurotransmitters don't just send messages; they instruct the next neuron what to do. They can either excite it or inhibit it.
- Excitation: An excitatory neurotransmitter (like adrenaline) increases the positive charge of the post-synaptic neuron. This makes the neuron more likely to fire an electrical impulse. (Hitting the gas pedal).
- Inhibition: An inhibitory neurotransmitter (like GABA) increases the negative charge of the post-synaptic neuron. This makes the neuron less likely to fire an electrical impulse. (Hitting the brake).
Did you know? The nervous system works by constantly adding up all the excitatory and inhibitory messages. Only if the net sum is high enough (reaching the 'threshold') will the neuron fire.
4. The Endocrine System and Fight or Flight
While the nervous system uses electrical signals for rapid, short-term communication, the endocrine system uses chemical messengers called hormones for slower, long-term communication.
Glands and Hormones
- The endocrine system is a network of glands (like the pituitary or thyroid) that produce and secrete hormones directly into the bloodstream.
- Hormones travel through the blood until they reach a target organ with the corresponding receptors, regulating processes like mood, metabolism, and reproduction.
The Fight or Flight Response (Role of Adrenaline)
When you face a significant threat, the nervous system and the endocrine system work together in a sudden, powerful reaction known as the Fight or Flight response.
Step-by-Step Emergency Response:
- Threat Detected: The brain perceives a threat (e.g., seeing a dangerous animal).
- Sympathetic Activation: The hypothalamus (in the brain) triggers the Sympathetic Nervous System (SNS).
- Adrenaline Release: The SNS stimulates the adrenal medulla (part of the adrenal gland), which releases the hormone adrenaline into the bloodstream.
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Body Changes: Adrenaline causes immediate physiological changes to prepare the body for intense physical action:
- Heart rate and breathing increase (to pump oxygenated blood fast).
- Digestion and saliva production stop (not needed right now).
- Pupils dilate (to take in more light).
- Blood is diverted from the skin/stomach towards the major muscles.
- Return to Normal: Once the threat has passed, the Parasympathetic Nervous System takes over, slowing the heart rate, and restoring bodily functions to their relaxed state.
Key Takeaway: Adrenaline is the hormone of preparation—it gets your body ready to run away (flight) or face the danger (fight).
5. Localisation of Function in the Brain
The idea of Localisation of Function suggests that different areas of the brain are responsible for specific behaviours, processes, or activities. Our brain is divided into two hemispheres (left and right), and four main lobes (frontal, parietal, temporal, occipital).
Specific Centres in the Cortex
- Motor Cortex (Frontal Lobe): Responsible for voluntary movement. The motor cortex on the left hemisphere controls the right side of the body, and vice versa.
- Somatosensory Cortex (Parietal Lobe): Processes sensory information from the skin (touch, temperature, pain). The amount of cortex dedicated to a body part relates to its sensitivity (e.g., fingers get more space than your back).
- Visual Cortex (Occipital Lobe): Processes visual information. Information from the left visual field is processed in the right visual cortex, and vice versa.
- Auditory Cortex (Temporal Lobe): Analyses speech-based information and sound. Damage here can cause hearing loss.
Language Centres
Damage to specific areas of the left hemisphere often reveals the strong localisation of language:
- Broca’s Area (Frontal Lobe): Critical for speech production. Damage leads to Broca’s aphasia, causing slow, non-fluent, and difficult speech.
- Wernicke’s Area (Temporal Lobe): Critical for speech understanding (comprehension). Damage leads to Wernicke’s aphasia, where speech is fluent but often meaningless, and the person struggles to understand others.
6. Hemispheric Lateralisation and Split Brain Research
Hemispheric Lateralisation is the concept that the two halves (hemispheres) of the brain are functionally different; certain mental processes are mainly confined to one side.
Example: For most people, the Left Hemisphere controls language and logic, while the Right Hemisphere controls creativity and spatial tasks.
Split Brain Research (Sperry)
This research examined patients whose corpus callosum (the thick bundle of fibres connecting the two hemispheres) had been cut, usually to treat severe epilepsy. This effectively separates the two halves of the brain.
- Findings: If a patient was shown an object in their right visual field (processed by the left, language hemisphere), they could easily name it.
- However, if shown the object in their left visual field (processed by the right, non-verbal hemisphere), they could not name it, but they could correctly identify it by touch.
- Conclusion: This confirmed that communication between the hemispheres is crucial and provided dramatic evidence that certain functions, especially language processing (naming), are strongly lateralised to one side of the brain (the left).
7. Plasticity and Functional Recovery
For a long time, scientists believed the brain developed fully in childhood and was largely fixed. We now know the brain is constantly adapting.
Brain Plasticity
Plasticity refers to the brain’s ability to change its structure and function throughout life due to learning, experience, or trauma.
Example: If you learn to play a musical instrument, the motor cortex area dedicated to your fingers actually expands and creates new synaptic connections.
Functional Recovery After Trauma
Functional Recovery is a specific type of plasticity. It refers to the recovery of abilities and mental processes that have been compromised as a result of brain injury or disease.
Don't worry, the brain has a clever way of fixing itself! Undamaged areas of the brain can compensate for damaged areas. This can happen in several ways:
- Axonal Sprouting: New nerve endings grow and connect with undamaged nerve cells to form new pathways.
- Recruitment of Homologous Areas: The opposite, undamaged hemisphere takes over specific tasks. For instance, if the left Broca’s area is destroyed, the corresponding area on the right hemisphere might take over language production (though often less efficiently).
Important Point: Functional recovery tends to happen quickly right after the trauma (spontaneous recovery) but then slows down. Rehabilitation therapy is often necessary to maximise long-term recovery.
KEY TAKEAWAY: The brain isn't rigid; it is incredibly plastic, allowing it to adapt and recover functions lost due to injury.