Study the brain, neurons and neurotransmitters

The Brain

From the brainstem that keeps you breathing to the cortex that plans your day.

Life support: the brainstem and cerebellum

• Brainstem: Keeps you alive without you thinking about it: breathing, heart rate and blood pressure. The stalk at the base of the brain, joining it to the spinal cord.
• Medulla (medulla oblongata): Runs the body's automatic processes: breathing, blood pressure and heart rate. In the brainstem, in the hindbrain, which looks like an extension of the spinal cord.
• Pons: Connects the hindbrain to the rest of the brain. In the brainstem, part of the hindbrain.
• Reticular formation (reticular activating system): Alertness and arousal: it regulates the sleep–wake cycle. Centered in the midbrain, reaching up into the forebrain and down into the hindbrain.
• Cerebellum: Coordinates movement and balance, and handles some procedural learning (learning skills). At the back of the brain, tucked beneath the occipital lobe.

Deep inside: the limbic system

• Limbic system: Emotion, memory and motivation. A group of structures beneath the cortex and above the brainstem.
• Thalamus: The sensory relay station: every sense except smell passes through it on the way to the cortex. Deep in the center of the brain. Thalamus relays the senses; the hypothalamus keeps the body in balance.
• Hypothalamus: Keeps the body in balance (homeostasis): body temperature, appetite and blood pressure. It also controls the pituitary gland. A small cluster of nuclei in the center of the brain. Hypothalamus keeps the body in balance; the thalamus relays the senses.
• Pituitary gland: Releases hormones that control other glands (the thyroid and adrenal glands), growth and reproduction, on orders from the hypothalamus. Hanging from the base of the brain.
• Hippocampus: Forms new memories: it makes experiences last (consolidation). Curled along the inner edge of the temporal lobe. The hippocampus makes memories; the amygdala ties emotion to them.
• Amygdala: Emotion, especially fear: it learns what to fear and sets off the body's defenses. An almond-shaped cluster deep in the temporal lobe, just in front of the hippocampus.
• Reward center (nucleus accumbens): Wanting and motivation: dopamine from the ventral tegmental area arrives here. Deep in the brain, in the lower part of the striatum.

The cerebral cortex and its four lobes

• Cerebral cortex: Higher-level processes: awareness, thinking, feeling, logic, speech and recall. The brain's outer surface, divided into a left and a right hemisphere.
• Corpus callosum: The thick band of nerve fibers that carries signals between the left and right hemispheres. Deep on the midline, between the two hemispheres.
• Frontal lobe: Thinking, planning, judgment and language, with the control of movement at its back edge. Just behind the forehead.
• Prefrontal cortex: Executive functions and higher-order thinking: planning ahead, foresight and judgment. The front of the frontal lobe.
• Motor cortex: Sends out the commands for voluntary movement of the skeletal muscles. A strip at the back of the frontal lobe. Motor cortex (back of the frontal lobe) moves you; the somatosensory cortex, just behind it in the parietal lobe, feels touch.
• Parietal lobe: Touch and the body's senses, plus association areas that process and organize information. Near the back crown of the head.
• Somatosensory cortex: Feels touch, pressure, temperature, pain and the position of your limbs. A strip at the front of the parietal lobe, just behind the motor cortex. Somatosensory cortex feels; the motor cortex, just in front of it, moves.
• Association areas: Process and organize information. AP Psychology places them in the parietal lobes.
• Temporal lobe: Hearing and understanding language, and also memory and emotion. On the sides of the brain.
• Occipital lobe: Vision: it holds the primary visual cortex. At the very back of the brain.

Language and the two hemispheres

• Broca's area: Speech production: putting words together to speak. In the frontal lobe of the language side of the brain, usually the left. Broca's area produces speech; Wernicke's area understands it. Broca builds the words, Wernicke works out the meaning.
• Wernicke's area: Understanding speech (comprehension). In the temporal lobe of the language side of the brain, next to the auditory cortex. Wernicke's area understands speech; Broca's area produces it.
• Aphasia: A loss of language ability caused by damage to the brain's language areas.
• Hemispheric specialization (lateralization): The left and right halves of the brain may specialize in different jobs; language is typically on the left.
• Contralateral control: Each side of the brain runs the opposite side of the body: your left motor cortex moves your right arm and leg.
• Split brain: After the corpus callosum is cut to treat severe epilepsy, the two hemispheres stop sharing information, revealing what each does on its own.
• Neuroplasticity: The brain's ability to change and rewire itself; a healthy area can take over the job of a damaged one.

How we study the brain

• EEG (electroencephalography): Records the brain's electrical activity (brainwaves) through electrodes placed around the head. EEG measures electrical activity; fMRI tracks blood flow.
• fMRI (functional MRI): Shows which areas are active, and how that changes over time, by tracking blood flow and oxygen. fMRI tracks blood flow; EEG measures electrical activity.
• Case studies and lesioning: Learning what a part does from one person with damage to it, or from damaging it surgically.

Neurons and Neurotransmitters

The cells, how one fires, the messengers they use, and what drugs do to them.

The nervous system

• Central nervous system (CNS): The brain and the spinal cord.
• Peripheral nervous system (PNS): The nerves that carry messages between the brain and spinal cord and the rest of the body.
• Somatic nervous system: Voluntary actions: it carries the sensory and motor messages for the movements you choose to make. Somatic is voluntary; autonomic runs on its own.
• Autonomic nervous system: Involuntary control of the internal organs and glands.
• Sympathetic nervous system: Arouses the body for "fight or flight": heart rate and blood pressure rise, the pupils widen, and digestion slows. Sympathetic speeds you up (fight or flight); parasympathetic calms you down (rest and digest).
• Parasympathetic nervous system: Calms the body back to normal after stress: heart rate slows and digestion picks up again. Parasympathetic calms you (rest and digest); sympathetic arouses you (fight or flight).

Two kinds of cell

• Neuron: A nerve cell: it transmits information.
• Glial cells (glia): The support cells: they provide structure, insulation, communication and waste transport.

Parts of a neuron

• Dendrites: Branches that receive signals from other neurons and carry them in to the cell body.
• Cell body (soma): Adds up all the incoming signals, and holds the nucleus.
• Axon: The long cable that carries the signal away from the cell body, out to the terminals and the next cells.
• Myelin sheath: Fatty insulation around the axon, made by glial cells, that makes the signal travel much faster.
• Nodes of Ranvier: Gaps in the myelin where the signal is rebuilt, so it leaps from gap to gap.
• Axon terminals (terminal buttons): The axon's ends: they hold vesicles of neurotransmitter and release it into the synapse.
• Synapse: Where one neuron passes its message to the next, across a tiny gap called the synaptic cleft.
• Receptors: Sites on the receiving neuron where a neurotransmitter binds, like a key in a lock.

How a neuron fires

• Resting potential: The neuron's charge at rest, ready to fire: negative inside, about −70 mV.
• Threshold: The level of charge that must be reached for the neuron to fire.
• Action potential: The electrical signal that travels down the axon when the neuron fires.
• Depolarization: Sodium channels open, sodium rushes in, and the charge inside shoots up: the start of the action potential.
• All-or-none principle: A neuron fires at full strength or not at all.
• Refractory period: A brief moment after firing when the neuron can't fire again.
• Reuptake: The sending neuron pumps the neurotransmitter back in, clearing the synapse.
• Excitatory and inhibitory: The two kinds of message: one makes the next neuron more likely to fire, the other less likely.

Three kinds of neuron, and the reflex

• Sensory neurons: Carry messages from the senses in to the spinal cord.
• Motor neurons: Carry commands out from the spinal cord to the muscles.
• Interneurons: In the spinal cord, they pass the message from the sensory neuron to the motor neuron.
• Reflex arc: An automatic response the spinal cord handles on its own: sensory neuron → interneuron → motor neuron.

The eight neurotransmitters AP names

• Glutamate: The brain's main excitatory ("go") signal; thought to be involved in storing memories. Glutamate is go; GABA is stop.
• GABA: One of the brain's major inhibitory ("stop") signals. GABA is stop; glutamate is go.
• Dopamine: Learning, movement, reward and emotion; losing the neurons that make it is part of Parkinson's disease.
• Serotonin: Tunes many mental processes; it's implicated in depression, and many psychiatric drugs act on it.
• Norepinephrine: Tied to wakefulness: the cells that supply it fire most when awake, and almost not at all in REM sleep (in rats).
• Acetylcholine: Carries the signal from nerve to muscle.
• Endorphins: The body's own opioids: they ease pain and help explain exercise euphoria. Endorphins ease pain; substance P signals it.
• Substance P: Best known for its role in feeling pain. Substance P signals pain; endorphins ease it.

When it goes wrong

• Multiple sclerosis: The myelin around nerve fibers is lost, so signals slow and serious neurological problems follow.
• Myasthenia gravis: Antibodies attack the acetylcholine receptors where nerves meet muscles, so the muscles weaken.

Drugs at the synapse

• Agonist: Encourages neural firing, often by mimicking a neurotransmitter at its receptor.
• Antagonist: Discourages neural firing, often by blocking a receptor without switching it on.
• Reuptake inhibitor: Blocks a neurotransmitter from being taken back into the sending cell.
• Stimulants: Typically increase neural activity. Examples: caffeine and cocaine.
• Depressants: Typically decrease neural activity. Example: alcohol.
• Hallucinogens: Typically distort perception or thinking. The AP course's example: marijuana.
• Opioids: Typically relieve pain. Example: heroin.
• Tolerance: Needing more of a drug to get the same effect.
• Addiction: An overpowering desire to use a drug despite the harm it does.
• Withdrawal: The symptoms that come when someone who's addicted stops taking the drug.