Difficulty: Introductory | Prerequisites: None
This unit is the biological foundation for the entire course. Every topic that follows, from memory to mental illness, depends on understanding how the nervous system is organised, how neurons communicate, and what different brain structures do. The material covers the divisions of the nervous system, the anatomy of neurons and action potentials, the major neurotransmitters, the lobes of the cerebral cortex, and key subcortical structures. Expect this to be one of the most heavily tested areas on the final.
The nervous system divides into the central nervous system (brain and spinal cord) and the peripheral nervous system (somatic and autonomic branches). Neurons communicate through electrical impulses (action potentials) and chemical signals (neurotransmitters). Specific brain regions handle specific functions, from the hippocampus forming long-term memories to the parietal lobe processing sensation.
Central nervous system (CNS)
The brain and spinal cord. This is the command centre of the body.
In simple terms, it is the part of your nervous system that is protected by bone (skull and vertebrae).
Peripheral nervous system (PNS)
Everything outside the brain and spinal cord, including the somatic and autonomic nervous systems.
Somatic nervous system
The division of the PNS that controls voluntary movements and carries sensory information from the body to the brain.
Think of it as the system you use when you feel a fly on your arm and then consciously move to swat it.
Autonomic nervous system
The division of the PNS that controls involuntary functions (heart rate, digestion, breathing). It divides into the sympathetic and parasympathetic branches.
Sympathetic nervous system
The "fight or flight" branch. It activates when you face a threat: heart rate increases, breathing quickens, digestion slows.
In simple terms, this is your body's emergency response system.
Parasympathetic nervous system
The "rest and digest" branch. It returns the body to baseline after a threat has passed: stores nutrients, repairs the body, and returns internal organ activity to resting levels.
In simple terms, it is the calm-down system that undoes what the sympathetic system started.
Neuron
A nerve cell that transmits information through electrical and chemical signals.
Axon
The long fibre extending from the cell body that carries electrical impulses (action potentials) away from the cell body and down the length of the neuron.
In simple terms, it is the neuron's output cable.
Dendrites
Branch-like extensions that receive signals from other neurons and carry them toward the cell body.
Myelin sheath
A fatty coating around axons that speeds up signal transmission.
Action potential
A brief electrical charge that travels along the axon of a neuron. It follows an all-or-nothing principle.
Depolarization
The phase of the action potential in which sodium ions rush into the cell, causing a sharp increase in electrical charge. This is the rising phase of the action potential.
In simple terms, the neuron "fires" as positive ions flood in.
Repolarization
The phase in which potassium ions flow out of the cell, returning the membrane potential back toward its resting level.
Hyperpolarization
A brief overshoot below the resting potential that occurs after repolarization, during which the neuron is less likely to fire.
Threshold
The minimum level of stimulation needed to trigger an action potential.
Neurotransmitter
Chemical messengers released at the synapse that carry signals from one neuron to the next.
Endorphins
Neurotransmitters that act as natural painkillers. They are released during vigorous exercise, explaining why runners sometimes forget their pain during marathons.
In simple terms, endorphins are your body's built-in morphine.
Acetylcholine (ACh)
A neurotransmitter involved in muscle movement and memory. Drugs that increase acetylcholine production may help boost memory in Alzheimer's patients.
Norepinephrine
A neurotransmitter involved in alertness and the body's stress response. It is released during unexpected or alarming events (e.g. a fire alarm).
Dopamine
A neurotransmitter involved in reward, motivation, and movement.
Serotonin
A neurotransmitter that regulates mood, appetite, and sleep.
Hippocampus
A subcortical structure essential for forming new long-term memories. Damage to the hippocampus prevents new memory formation but does not erase old memories.
In simple terms, it is the brain's "save" button for new experiences.
Nucleus accumbens
A structure in the brain's reward circuit. It activates during pleasurable experiences and feelings of contentment and satisfaction.
Amygdala
A structure involved in processing emotions, particularly fear.
Hypothalamus
Regulates temperature, thirst, hunger, biological rhythms, and sexual behaviour. It sits below the thalamus.
Thalamus
The brain's sensory relay station. Almost all sensory information (except smell) passes through the thalamus on its way to the cortex.
Corpus callosum
The large bundle of nerve fibres connecting the left and right cerebral hemispheres. Cutting it (split-brain procedure) prevents the two hemispheres from communicating directly.
Cerebellum
Located at the back of the brain, responsible for coordination, balance, and fine motor control.
Brainstem
The lowest part of the brain, connecting to the spinal cord. Includes the medulla, pons, and midbrain.
Medulla
Part of the brainstem responsible for heart rate, blood pressure, and breathing.
Pons
Part of the brainstem responsible for sleep, arousal, and relaying signals between the cerebellum and cortex.
Midbrain
Part of the brainstem responsible for sensory reflexes (such as visual and auditory reflexes).
Reticular formation
A network within the brainstem that regulates sleep and arousal.
CNS = brain + spinal cord
PNS = somatic nervous system + autonomic nervous system
Somatic: voluntary movement and sensory input (feel a fly, move your arm)
Autonomic: involuntary functions, splits into:
Sympathetic: fight or flight (arousal, increased heart rate)
Parasympathetic: rest and digest (returns body to baseline, stores nutrients, repairs body)
Dendrites receive signals → cell body integrates → axon carries signal away
The axon carries information down the length of a single neuron
Action potential sequence: resting potential → threshold reached → depolarization (sodium rushes in, sharp rise) → repolarization (potassium flows out) → hyperpolarization (brief overshoot below resting level) → return to resting potential
Multiple excitatory signals cause a neuron to depolarize
Endorphins: natural pain relief (runners forgetting pain in marathons)
Acetylcholine: memory and muscle movement (Alzheimer's drugs target this)
Norepinephrine: alertness, stress response (fire alarm goes off, body produces more of this)
Dopamine: reward, motivation, movement
Serotonin: mood, appetite, sleep
Frontal lobe: planning, decision-making, personality, voluntary movement (primary motor cortex)
Parietal lobe: sensation and touch (primary somatosensory cortex). If Max hits his head and has trouble experiencing sensation, the parietal lobe is injured.
Temporal lobe: hearing, language comprehension
Occipital lobe: vision. If Caleb has an accident and wakes up blind, the occipital lobe was damaged.
Hippocampus: forming new long-term memories. A lesion here means trouble forming new memories, but old ones remain.
Amygdala: fear and emotion processing.
Nucleus accumbens: reward, pleasure, contentment.
Hypothalamus: regulates temperature, thirst, hunger, biological rhythms, sexual activity.
Thalamus: sensory relay station (all senses except smell).
Basal ganglia: voluntary motor control, procedural learning.
Medulla: heart rate, blood pressure, breathing.
Pons: sleep and arousal.
Midbrain: sensory reflexes. Contains endorphin receptors (a tumour here could impair sensory reflexes and pain perception).
Reticular formation: regulates sleep and arousal (damage leads to problems with sleep regulation).
The amygdala is NOT part of the brainstem (this is a common trick answer).
fMRI (functional magnetic resonance imaging): tracks blood flow and oxygen use with magnets to show active brain areas. This is the answer when the question says "tracking the flow of oxygen with magnets."
PET (positron emission tomography): uses radioactive tracers to show brain activity.
EEG (electroencephalogram): measures electrical activity on the scalp surface.
Students often confuse the somatic and autonomic nervous systems. The somatic system handles voluntary movement and sensory input. The autonomic system handles involuntary functions.
The amygdala is not part of the brainstem. It is a subcortical limbic structure. The exam uses this as a distractor.
Depolarization is the rise in the action potential (sodium rushing in), not the fall. Repolarization is the return toward resting potential.
The hippocampus is for forming new long-term memories. Damage does not erase memories already formed before the injury.
⚠️ Know which lobe handles sensation (parietal) vs. vision (occipital). These appear in scenario questions.
⚠️ Be able to identify fMRI from the description "tracking oxygen flow with magnets."
⚠️ The hippocampus question (trouble forming long-term memories) appears at least three times across the review.
⚠️ Know that the parasympathetic system does ALL of the following: stores nutrients, repairs body, returns organs to baseline.
⚠️ Depolarization = sodium in = sharp rise. This is the single most tested action-potential concept.
⚠️ Endorphins = pain relief during exercise. This question appears twice.
⚠️ The corpus callosum is the fibre bundle cut in a split-brain procedure.
Fill in the blank: The __________ nervous system activates during a threat and increases heart rate. Sympathetic.
True or False: The hippocampus is responsible for processing fear. False. That is the amygdala. The hippocampus forms new long-term memories.
Fill in the blank: The sharp increase in an action potential when sodium rushes into the cell is called __________. Depolarization.
True or False: The amygdala is part of the brainstem. False. It is a limbic structure.
Fill in the blank: The primary somatosensory cortex is located in the __________ lobe. Parietal.
Q: Which structure is responsible for forming new long-term memories?
A: The hippocampus. A lesion on the hippocampus prevents the formation of new long-term memories, though memories formed before the damage remain intact.
Q: Chris sometimes forgets he is in pain while running marathons. Which neurotransmitter is most likely responsible?
A: Endorphins. They are the body's natural painkillers and are released in large quantities during sustained exercise.
Q: Which brain imaging technique tracks the flow of oxygen using magnets?
A: Functional magnetic resonance imaging (fMRI). It detects changes in blood oxygenation to map brain activity.
Q: Which branch of the autonomic nervous system returns the body to baseline after a stressful event?
A: The parasympathetic nervous system. It stores nutrients, repairs the body, and returns organ activity to resting levels.
Q: The axon carries information in which direction relative to the cell body?
A: Away from the cell body. The axon transmits the action potential down the length of the neuron toward the axon terminals.
The hippocampus reappears in the Memory unit. Understanding its role here makes memory encoding, storage, and retrieval much easier to follow.
The sympathetic nervous system is central to the Stress and Coping unit, where it drives the fight-or-flight response and connects to the HPA axis.
Neurotransmitters link directly to both the Psychoactive Drugs section (Consciousness unit) and the Psychological Disorders unit (dopamine hypothesis of schizophrenia, serotonin in depression).
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