Your hand jerks off a hot pan before you decide to. What moved it?

Two main divisions

• The central nervous system (CNS) is the brain and the spinal cord.
• The peripheral nervous system (PNS) is all the nerves outside the CNS. It carries messages between the CNS and the rest of the body.
• The PNS has two parts. The somatic nervous system controls voluntary movement and carries information from the senses.
• The autonomic nervous system controls automatic functions, such as heart rate, breathing and digestion.

What the CNS does

• The CNS receives information from the senses, processes it and sends instructions to muscles and glands.
• The brain is the control centre. It makes decisions and controls thinking, memory, emotion and voluntary movement.
• The brain also keeps you alive: its lowest part, the brain stem, controls breathing and heartbeat.

The spinal cord

• The spinal cord runs down your back, protected by the spine.
• It carries messages between the brain and the body: up from the senses, down to the muscles.
• It can also control simple reflexes by itself. The message comes in and goes straight back out to the muscle, which is faster than waiting for the brain.
• The brain finds out a moment later.

The autonomic nervous system and fight or flight

• The autonomic system has two branches: the sympathetic branch arouses the body; the parasympathetic branch calms it ("rest and digest").
• Sensing a threat, the sympathetic branch triggers the fight or flight response and the adrenal glands release adrenaline.
• Heart rate and breathing rise, pupils widen, you sweat and digestion slows, ready to fight or run.
• When the threat passes, the parasympathetic branch returns the body to normal.

The James-Lange theory of emotion

• Common sense says: you feel afraid, so your heart races.
• James-Lange says the order is the other way round: event → physical arousal → you notice the arousal → emotion.
• The body reacts first (fight or flight); the emotion comes from interpreting that body change. "I'm trembling, so I must be afraid."
• No physical change means no emotion.

Brain signals are electrical, until they hit a gap. How do they cross?

Inside a neuron

• A neuron is a nerve cell that carries messages as electrical impulses.
• Dendrites receive messages from other neurons. The cell body contains the nucleus.
• The impulse travels along the axon, which is often wrapped in a fatty myelin sheath that speeds it up.
• At the end of the axon are axon terminals, where the message is passed on to the next neuron.

Three types of neuron

• In a reflex, the message goes sensory → relay (spinal cord) → motor.

Crossing the synapse

• The tiny gap between two neurons is the synapse (synaptic gap). The impulse can't jump it.
• When the impulse reaches the axon terminal, vesicles release a chemical, a neurotransmitter, into the gap: this is release.
• The neurotransmitter crosses the gap and binds to receptors on the next neuron, passing the message on.
• Leftover neurotransmitter is taken back into the first neuron to be reused: reuptake.

Excitation and inhibition

• A neurotransmitter's function is to carry the message across the synapse and affect the next neuron.
• Excitatory neurotransmitters (e.g. glutamate) make the next neuron more likely to fire an impulse.
• Inhibitory neurotransmitters (e.g. GABA) make it less likely to fire.
• One neuron receives messages from many synapses. It adds up the excitatory and inhibitory signals and fires only if excitation is strong enough.

Hebb's theory of learning and neuronal growth

• Hebb said that when we learn, groups of neurons fire together. Each time they do, the synapses between them get stronger.
• With practice, these neurons form a cell assembly: a network that fires easily, so the skill or memory becomes easier.
• Neuronal growth: learning makes neurons grow new connections (synaptic knobs) and strengthens existing ones. Unused connections weaken.
• So the brain is plastic: experience (nurture) changes its structure.

Your eyes are at the front. Which part of your brain does the seeing?

The lobes and the cerebellum

• The wrinkled outer layer of the brain is the cerebral cortex. It has two halves (hemispheres), each divided into four lobes.
• Frontal lobe: at the front, behind the forehead.
• Parietal lobe: at the top, behind the frontal lobe.
• Temporal lobe: at the side, near the ears.
• Occipital lobe: at the back.
• The cerebellum sits underneath, at the back, below the occipital lobe.

What each part does

The cerebellum

• The cerebellum ("little brain") sits at the back, underneath the occipital lobe.
• It coordinates movement: balance, posture and smooth, accurate movements.
• It doesn't start movements. It fine-tunes them, so you can walk in a straight line or reach for a cup without missing.
• It helps you learn movement skills, such as riding a bike or typing, until they become automatic.

Localisation of function

• Localisation of function means specific areas of the brain carry out specific jobs.

A rod went through his skull. He walked and talked. So what changed?

What neurological damage is

• Neurological damage is damage to the brain or nerves. Dead brain cells are not replaced.
• A stroke happens when the blood supply to part of the brain is blocked or a vessel bursts, so cells there are starved of oxygen and die.
• An injury is physical damage, e.g. a blow to the head.
• Effects depend on where the damage is: one ability can be lost while others are untouched.

Damage, movement and behaviour

• Damage to the motor area in one hemisphere causes weakness or paralysis on the opposite side of the body, e.g. after a stroke.
• Damage to the cerebellum causes clumsy, poorly coordinated movement and problems with balance.
• Damage to Broca's area makes speaking slow and difficult.
• Damage to the very front of the frontal lobe mainly changes behaviour rather than movement (next screen).

The prefrontal cortex and behaviour

• The prefrontal cortex is the very front of the frontal lobe.
• It is involved in planning, decision-making, controlling impulses and controlling emotions and social behaviour.
• Damage can leave movement, speech and memory working, yet the person becomes impulsive, takes risks, makes poor decisions and may seem to have a different personality.

People once read minds from bumps on the skull. What changed?

From skull bumps to evidence

• Around 1800, phrenology claimed each mental ability had its own brain area, shown by bumps on the skull.
• The idea of areas with different jobs survived; skull-reading did not, as skull thickness varies.
• 1800s: studying people with brain damage, e.g. Gage (1848) and Broca's patient who lost speech (1861).
• 1900s: stimulating the brain during surgery; split-brain studies (1960s).
• 1970s on: brain scanning shows the living brain.

Cognitive neuroscience

• Cognitive neuroscience studies how the structure and function of the brain relate to behaviour and cognition (thinking, memory, perception, language).
• It asks: which brain areas are active when we remember, recognise a face or make a decision?
• Its evidence comes from comparing people with brain damage, measuring what happens when the brain is stimulated, and scanning healthy brains while people do tasks.

CT and PET scans

• CT (computerised tomography): X-rays are taken from many angles and a computer builds up slice images. It shows structure, e.g. tumours, bleeding or stroke damage. Quick and widely available, but uses radiation and shows no activity.
• PET (positron emission tomography): a radioactive tracer (often a form of glucose) is injected. Active areas use more glucose, so they show up. It shows function (activity), but is radioactive, expensive and less detailed.

fMRI scans

• fMRI (functional magnetic resonance imaging) uses a strong magnetic field to detect changes in blood oxygen. Active areas need more oxygen-rich blood.
• It shows function: which areas are active during a task, with good detail.
• No radiation, so it can be repeated. But it is expensive, noisy, needs the person to lie very still, and shows activity a few seconds after it happens.

Big ideas

• The nervous system has two divisions: the CNS (brain and spinal cord) and the PNS (nerves linking the CNS to the body).
• The CNS receives, processes and sends out information; the spinal cord carries messages and handles simple reflexes.
• The autonomic nervous system controls automatic functions; its sympathetic branch produces fight or flight. James-Lange says emotion comes from noticing these body changes.
• A neuron carries an electrical impulse along its axon; at the synapse, the message is carried across by a chemical neurotransmitter.
• Neurotransmitters are released, bind to receptors and are removed by reuptake; excitatory ones make the next neuron more likely to fire, inhibitory ones less likely.
• Sensory, relay and motor neurons carry messages to, within and out of the CNS; Hebb: neurons that fire together strengthen their connections, so learning physically changes the brain.
• The cortex has four lobes in each hemisphere (frontal, parietal, temporal, occipital), with the cerebellum underneath at the back.
• Each structure has main functions: frontal (planning, movement, speech), parietal (touch), temporal (hearing, memory, language), occipital (vision), cerebellum (balance and coordination).
• Localisation of function: motor, somatosensory, visual, auditory and language (Broca's, Wernicke's) areas; Penfield's stimulation of the temporal lobe (interpretive cortex) is evidence for it.
• Neurological damage (from a stroke or injury) affects whichever functions the damaged area carries out, leaving others intact.
• Damage to the prefrontal cortex can change behaviour and personality: impulsive actions, poor decisions and less emotional control.
• Damage to the motor area causes weakness or paralysis on the opposite side; cerebellum damage affects coordination and balance.
• Understanding of the brain moved from phrenology to evidence: brain damage case studies, stimulation, split-brain research and brain scanning.
• Cognitive neuroscience links brain structure and function to behaviour and cognition. CT shows structure; PET and fMRI show activity. Tulving's 'gold' study found episodic and semantic memories linked to different brain areas.