Structure and Function of Neurons

Ever wondered how your brain processes information faster than the most advanced computer? The nervous system is your body's primary internal communication network, using electrical and chemical signals to keep everything running smoothly.

The system has two main jobs: collecting and responding to environmental information, plus coordinating all your organs and cells. It's split into the central nervous system (CNS) - your brain and spinal cord - and the peripheral nervous system (PNS) - all the nerves throughout your body.

Neurons are the star players here - specialised nerve cells that transmit messages through electrical and chemical signals. With 100 billion neurons in your nervous system (80% packed into your brain), they're constantly chatting to keep you functioning.

Quick Fact: You have more neurons in your brain than there are stars in the Milky Way galaxy!

Types of Neurons and Their Structure

Think of neurons as tiny messengers with specific parts designed for communication. Each neuron has dendrites that receive messages, a nucleus containing genetic material, and an axon that transmits signals onwards.

The myelin sheath acts like insulation around electrical wires, preventing signal loss and speeding up transmission. Axon terminals at the end pass messages to the next neuron in line.

There are three main types you need to know: sensory neurons carry messages from your body to your brain (long dendrites, short axons), relay neurons connect different neurons in your brain (short dendrites and axons), and motor neurons carry signals from your brain to muscles and glands (short dendrites, long axons).

Understanding these differences helps explain how information flows through your nervous system - from sensing something hot, processing that information, and triggering your hand to pull away.

Memory Tip: Think SRM - Sensory receives, Relay connects, Motor moves!

Electrical and Synaptic Transmission

Here's where things get fascinating - neurons use both electrical and chemical signals to communicate. When resting, a neuron is negatively charged inside compared to outside. When activated by a stimulus, it briefly becomes positively charged, creating an action potential that fires along the axon like electricity through a wire.

But neurons don't actually touch each other. When the electrical signal reaches the end of one neuron, it triggers the release of neurotransmitters - chemical messengers that float across the tiny gap called a synapse.

These neurotransmitters work like a lock and key system, fitting into specific receptor sites on the next neuron. Only the right neurotransmitter can unlock each receptor, ensuring messages get delivered accurately.

The process switches from electrical (within neurons) to chemical (between neurons) and back to electrical again. This might seem complex, but it allows for incredibly precise control over which messages get passed along.

Real-world Connection: This is exactly what happens when you take medication - drugs work by affecting neurotransmitter activity!

Excitation, Inhibition and Summation

Not all neurotransmitters have the same effect - some are like the accelerator pedal, others like the brakes. Excitatory neurotransmitters (like adrenaline) increase the positive charge in the receiving neuron, making it more likely to fire. Inhibitory neurotransmitters (like serotonin) increase negative charge, making firing less likely.

Here's the clever bit: each neuron receives multiple influences simultaneously. Through summation, the neuron adds up all the excitatory and inhibitory signals it receives. If the combined effect reaches a certain threshold and is more excitatory than inhibitory, the neuron fires.

Think of it like voting - if you receive 4 serotonin signals (inhibitory) and 6 adrenaline signals (excitatory), the excitatory signals win and the neuron is more likely to fire. But 8 serotonin plus 2 adrenaline? The inhibitory signals dominate.

This system allows for incredibly sophisticated information processing, explaining how your brain can weigh up complex decisions and responses.

Exam Tip: Remember that summation explains why mental health medications can take time to work - they gradually shift the balance of neurotransmitter activity.

The Endocrine System

While your nervous system handles rapid communication, the endocrine system works as your body's slower, longer-lasting messaging service. Instead of electrical signals, it uses hormones - chemical messengers released into your bloodstream that affect any cell with the right receptors.

Key players include the pituitary gland (the 'master gland' that controls others), thyroid gland (regulates metabolism through thyroxine), adrenal glands $trigger fight-or-flight responses$, and pancreas (produces insulin for blood sugar control).

When things go wrong, you get conditions like hypothyroidism (not enough thyroid hormone, causing weight gain and depression), hyperthyroidism (too much, causing hyperactivity and nervousness), or diabetes (problems with insulin production or response).

The endocrine system works alongside your nervous system but operates much more slowly - think minutes or hours rather than milliseconds. This makes it perfect for coordinating long-term changes in your body's functioning.

Health Connection: Understanding hormones explains why teenagers experience mood swings - changing hormone levels directly affect brain function and behaviour!

Fight or Flight Response

When you perceive danger, your body has an amazing automatic response system. The fight-or-flight response kicks in when your hypothalamus detects a threat and activates your sympathetic nervous system.

This triggers a cascade of changes: your heart rate increases, breathing speeds up, pupils dilate for better vision, digestion stops (who needs to digest lunch when running from danger?), and saliva production decreases. Adrenaline flooding your bloodstream powers all these changes.

Once the threat passes, your parasympathetic nervous system takes over - the 'rest and digest' response. This acts like a brake, reversing all those sympathetic changes and returning your body to its calm, resting state.

The whole system is antagonistic - sympathetic and parasympathetic branches have opposite effects, allowing your body to switch between high alert and relaxation as needed.

Modern Problem: Our fight-or-flight system evolved for physical threats, but now activates for psychological stress like exams - your body can't tell the difference!

Acute vs Chronic Stress Responses

Your body handles short-term and long-term stress very differently. Acute stress uses the sympathomedullary pathway (SAM) - the rapid fight-or-flight response you just learned about. It's quick, intense, and designed to handle immediate threats.

Chronic stress requires a different approach: the hypothalamic-pituitary-adrenal (HPA) system. When stress persists, your hypothalamus releases CRF, which signals your pituitary gland to release ACTH into your bloodstream. This travels to your adrenal cortex, triggering cortisol release.

Cortisol provides long-term energy supplies to cope with ongoing stress, but there's a downside - it can suppress your immune system, making you more vulnerable to illness. Thankfully, the HPA system self-regulates through a negative feedback loop, monitoring cortisol levels and adjusting production accordingly.

Understanding these two systems explains why short bursts of stress can be helpful (like before an exam), but chronic stress becomes problematic for both physical and mental health.

Study Application: This is why managing long-term academic stress is crucial - chronic cortisol elevation can actually impair memory formation!

Localisation of Function - Motor and Sensory Areas

Your brain isn't just one big thinking blob - different areas specialise in specific functions. Localisation of function theory suggests that particular brain regions control specific behaviours and processes, challenging earlier 'holistic' views.

The motor cortex in your frontal lobe controls voluntary movements, with different regions mapped to specific body parts. Remarkably, it controls the opposite side of your body - your left motor cortex moves your right hand. Hitzig and Fritsch discovered this by electrically stimulating dogs' motor areas and watching specific muscles contract.

Your somatosensory area in the parietal lobe processes touch, pressure, pain, and temperature from different body parts. The amount of brain space devoted to each body part reflects its sensitivity - your hands and face get over half the area because they're incredibly sensitive.

Damage to these areas causes predictable problems: motor cortex damage affects movement control, while somatosensory damage affects sensation. This precise mapping provides strong evidence for localisation.

Fascinating Fact: The famous 'brain homunculus' shows a distorted human figure with huge hands and lips - representing how much brain space these sensitive areas occupy!

Visual, Auditory Areas and Brain Plasticity

Your visual cortex in the occipital lobe processes everything you see, with different parts handling colour, shape, and movement. Information from your right visual field goes to your left hemisphere and vice versa - damage to one side can cause partial blindness in the opposite visual field.

The auditory cortex in your temporal lobe analyses sound, processing features like volume, tempo, and pitch. Like vision, information crosses over - your left ear connects primarily to your right hemisphere. Wernicke's area, also in the temporal lobe, specifically handles language comprehension.

The famous case of Phineas Gage dramatically demonstrated localisation. After a metal rod shot through his frontal lobe in 1848, Gage's personality completely changed from calm and reserved to quick-tempered and rude, showing how specific brain areas control personality traits.

But here's the exciting bit - your brain shows plasticity. Robertson found that Braille readers develop larger somatosensory areas for their fingertips, proving that brain areas can adapt and reorganise based on use.

Hope for Recovery: Brain plasticity explains why stroke patients can sometimes recover functions - other brain areas can take over damaged regions' roles!

Language Centres and Evaluation

Language processing happens primarily in your brain's left hemisphere, with two crucial areas discovered by pioneering researchers. Broca's area in the frontal lobe handles speech production - damage causes Broca's aphasia, where people understand language but struggle to speak fluently.

Wernicke's area in the temporal lobe manages language comprehension. Damage here causes Wernicke's aphasia - people can speak fluently but produce meaningless words called neologisms.

The evidence for localisation is compelling. Brain scans show Wernicke's area activating during listening tasks and Broca's area during reading. Successful neurosurgery for mental disorders like OCD (targeting the cingulate gyrus) suggests that even complex behaviours can be localised.

However, modern research suggests the reality is more complex than simple localisation. Many functions involve networks of brain areas working together rather than single regions operating in isolation.

Exam Success: Remember the key evidence - Petersen's brain scans, Phineas Gage's personality change, and the success of localised neurosurgery treatments!