The rising phase of the action potential is produced mainly by:

Influx of sodium ions through voltage-gated channels

Which non-invasive technique measures brain activity through changes in blood oxygenation?

Functional MRI (the BOLD signal)

Assertion (A): The intensity of a stimulus is coded by the frequency of action potentials rather than by their size. Reason (R): An action potential obeys the all-or-none law: once threshold is reached, its amplitude is the same regardless of stimulus strength. Choose the correct option.

Both A and R are true, and R is the correct explanation of A

Both A and R are true, but R is not the correct explanation of A

Which of the following are INVASIVE methods of physiological psychology? Select all that apply.

Single-unit microelectrode recording

Biological Basis of Behavior I: Sensory Systems, Neurons and the Neural Impulse, Synaptic Transmission and Neurotransmitters, the Central and Peripheral Nervous Systems, Neuroplasticity, and the Methods of Physiological Psychology

Unit 4 opens with the machinery: "Sensory systems: General and specific sensations, receptors and processes. Neurons: Structure, functions, types, neural impulse, synaptic transmission. Neurotransmitters. The Central and Peripheral Nervous Systems – Structure and functions. Neuroplasticity. Methods of Physiological Psychology: Invasive methods – Anatomical methods, degeneration techniques, lesion techniques, chemical methods, microelectrode studies. Non-invasive methods – EEG, Scanning methods." Questions here reward exact biology — the resting potential, the ions of the action potential, which transmitter does what and which disorder follows its loss — so this chapter gives each fact precisely and pairs each brain structure with its function.

1. Sensory systems: general and special senses, receptors and transduction

The general senses have receptors spread through the body — touch, pressure, vibration, temperature, pain, and the body senses of proprioception and kinaesthesis (position and movement) and interoception. The special senses have dedicated organs: vision, hearing, the vestibular sense (balance), taste and smell. Every receptor performs transduction, converting physical energy into a receptor potential and then neural impulses, and most show sensory adaptation to constant stimulation. Müller's doctrine of specific nerve energies holds that the quality of a sensation depends on which nerve is stimulated, not on the stimulus.

Receptors and pathways
System	Receptors and key facts
Touch and pressure	Meissner's corpuscles (light touch), Merkel's discs (sustained pressure, texture), Pacinian corpuscles (vibration and deep pressure), Ruffini endings (skin stretch); free nerve endings for pain and temperature. Melzack and Wall's gate-control theory (1965): a spinal "gate" modulates pain signals.
Vision	About 120 million rods (dim light, periphery, rhodopsin, no colour) and about 6 million cones (bright light, colour, concentrated in the fovea). Pathway: retina → optic nerve → optic chiasm (nasal fibres cross) → lateral geniculate nucleus of the thalamus → primary visual cortex in the occipital lobe. Colour is trichromatic at the receptors (Young–Helmholtz) and opponent-process beyond them (Hering).
Hearing and balance	Hair cells on the basilar membrane in the organ of Corti (cochlea); pathway via the medial geniculate nucleus to the temporal lobe. Pitch: place theory (von Békésy's travelling wave) for high frequencies, frequency theory with Wever's volley principle for low ones. The semicircular canals and otolith organs of the vestibular system sense rotation and linear acceleration.
Taste and smell	Taste buds signal five basic tastes: sweet, sour, salty, bitter and umami. Olfactory receptors project to the olfactory bulb and then to the piriform cortex and amygdala — smell is the only sense not relayed first through the thalamus.

2. Neurons, the neural impulse and synaptic transmission

A neuron has dendrites (receiving), a soma (cell body), an axon hillock where impulses are initiated, an axon often wrapped in myelin (made by Schwann cells in the peripheral and oligodendrocytes in the central nervous system) with gaps called nodes of Ranvier, and terminal buttons. Functionally neurons are sensory (afferent), motor (efferent) or interneurons; structurally unipolar, bipolar (as in the retina) or multipolar (most neurons). Glial cells — astrocytes, microglia, oligodendrocytes and Schwann cells — support, insulate and defend.

The action potential
Phase	What happens
Resting potential	About −70 mV, inside negative; maintained by the sodium–potassium pump (3 Na⁺ out for 2 K⁺ in) and by membrane permeability to K⁺.
Depolarisation to threshold	At about −55 mV voltage-gated Na⁺ channels open and sodium rushes in.
Action potential peak	The inside reaches about +30 to +40 mV.
Repolarisation and hyperpolarisation	Na⁺ channels inactivate and K⁺ flows out, briefly overshooting below rest.
Refractory periods	Absolute (no new spike possible) then relative (a stronger stimulus needed) — which limits firing rate and makes impulses travel one way.

The action potential obeys the all-or-none law: its size does not depend on stimulus strength, so intensity is coded by firing frequency and by the number of neurons recruited. In myelinated axons the impulse jumps from node to node — saltatory conduction — which is much faster. At the synapse, arrival of the impulse opens voltage-gated Ca²⁺ channels; calcium entry triggers vesicles to release transmitter into the cleft; it binds ionotropic (fast, ion-channel) or metabotropic (slower, second-messenger) receptors and produces an excitatory (EPSP) or inhibitory (IPSP) postsynaptic potential. Potentials sum spatially and temporally at the axon hillock. Transmission ends by reuptake, enzymatic breakdown (acetylcholinesterase for ACh) or diffusion. Otto Loewi's frog-heart experiment (1921) first showed chemical transmission.

3. Neurotransmitters

Neurotransmitters and their functions
Transmitter	Main functions	Clinical links
Acetylcholine (ACh)	Neuromuscular junction (muscle contraction), parasympathetic system, attention and memory	Loss of cholinergic neurons (nucleus basalis) in Alzheimer's disease; myasthenia gravis attacks ACh receptors; curare blocks them; botulinum toxin blocks ACh release
Dopamine	Reward and motivation (mesolimbic pathway), voluntary movement (nigrostriatal pathway)	Parkinson's disease from loss of substantia nigra neurons; the dopamine hypothesis of schizophrenia (excess mesolimbic activity); addiction
Serotonin (5-HT)	Mood, sleep, appetite, impulse control	Depression and anxiety; SSRIs block its reuptake
Norepinephrine	Arousal, vigilance, the sympathetic response	Depression (monoamine hypothesis), anxiety and stress
GABA	The main inhibitory transmitter of the brain	Anxiety; benzodiazepines and alcohol enhance GABA-A activity; seizures when inhibition fails
Glutamate	The main excitatory transmitter; learning and long-term potentiation through NMDA receptors	Excitotoxicity in stroke and neurodegeneration
Endorphins; substance P	Endogenous opioids that reduce pain; substance P transmits pain signals	Runner's high, placebo analgesia; morphine mimics endorphins

⚠️ Parkinson's vs schizophrenia

Too little dopamine in the nigrostriatal pathway gives Parkinson's; too much activity in the mesolimbic pathway is linked to the positive symptoms of schizophrenia. This is why L-dopa can produce psychotic symptoms and older antipsychotics can produce Parkinson-like side effects.

4. The central and peripheral nervous systems, and neuroplasticity

The central nervous system: structure and function
Structure	Function
Medulla	Breathing, heart rate, blood pressure, reflexes such as swallowing
Pons	Relay between cerebrum and cerebellum; sleep and arousal
Cerebellum	Coordination, balance, timing and procedural (motor) learning
Reticular formation	The reticular activating system maintains arousal and wakefulness
Thalamus	Relay station for all senses except smell
Hypothalamus	Homeostasis — hunger, thirst, temperature, sexual behaviour, circadian rhythm (suprachiasmatic nucleus) — and control of the pituitary
Basal ganglia	Initiation and smoothing of voluntary movement; habit learning
Frontal lobe	Primary motor cortex, Broca's area (speech production, usually left), prefrontal executive functions, planning and personality
Parietal lobe	Primary somatosensory cortex, spatial attention
Temporal lobe	Primary auditory cortex, Wernicke's area (language comprehension), memory with the hippocampus
Occipital lobe	Primary visual cortex
Corpus callosum	Connects the hemispheres; Sperry and Gazzaniga's split-brain studies revealed lateralisation

The peripheral nervous system comprises 12 pairs of cranial and 31 pairs of spinal nerves, divided into the somatic system (voluntary muscles, sensory input) and the autonomic system. The autonomic system has a sympathetic division — thoracolumbar, "fight or flight": it dilates the pupils, speeds the heart, relaxes the airways and inhibits digestion — and a parasympathetic division — craniosacral, "rest and digest", which does the reverse.

Neuroplasticity is the nervous system's capacity to change with experience. Hebb (1949) proposed that neurons that fire together strengthen their connection; long-term potentiation (Bliss and Lømo, 1973) is its cellular form. Rats reared in enriched environments develop a thicker cortex (Rosenzweig); London taxi drivers show larger posterior hippocampi (Maguire, 2000); adult neurogenesis occurs in the dentate gyrus of the hippocampus; cortical maps reorganise after amputation, producing phantom-limb sensations (Ramachandran); and there are sensitive periods, as Hubel and Wiesel showed with visual deprivation in kittens. Constraint-induced movement therapy after stroke (Taub) exploits plasticity in rehabilitation.

5. Methods of physiological psychology

Invasive and non-invasive methods
Method	What it involves
Anatomical methods (invasive)	Staining of fixed tissue — the Golgi stain shows whole individual neurons, the Nissl stain cell bodies; tract tracing.
Degeneration techniques	Cutting an axon and tracing the pathway by the degeneration (Wallerian) that follows, historically with the Marchi method.
Lesion techniques	Destroying a region by aspiration, radio-frequency current or excitotoxins (placed with stereotaxic surgery), or reversibly by cooling or drugs; sham lesions serve as controls.
Chemical methods	Injecting agonists, antagonists or selective neurotoxins (6-hydroxydopamine for dopamine neurons); 2-deoxyglucose autoradiography of active areas; microdialysis to sample transmitters.
Microelectrode studies	Single-unit recording (Hubel and Wiesel's orientation-selective cells in visual cortex), intracellular recording, and electrical stimulation (Penfield's cortical mapping; Olds and Milner's reward centres, 1954).
EEG (non-invasive)	Scalp electrodes record summed cortical activity (Hans Berger, 1929): beta (13–30 Hz, alert), alpha (8–13 Hz, relaxed with eyes closed), theta (4–8 Hz, drowsy, light sleep), delta (below 4 Hz, deep sleep). Averaged event-related potentials such as the P300 track cognition with millisecond timing.
Scanning methods	CT (X-ray structure), MRI (detailed structure), fMRI (activity through the blood-oxygen-level-dependent signal), PET (activity through radioactive tracers such as labelled glucose), SPECT, diffusion tensor imaging (white-matter tracts); TMS stimulates cortex through the skull.

🧠 Time versus space

EEG and ERPs have excellent temporal resolution (milliseconds) but poor spatial resolution; fMRI and PET have good spatial resolution but track slow blood-flow changes over seconds. Questions about "when" favour EEG; questions about "where" favour fMRI.

Key takeaways

Receptors transduce energy into impulses; rods serve dim light and cones colour; vision relays through the lateral and hearing through the medial geniculate nucleus, and smell alone bypasses the thalamus.
The resting potential is about −70 mV; Na⁺ influx depolarises and K⁺ efflux repolarises; the spike is all-or-none, intensity is coded by frequency, and myelin allows saltatory conduction.
ACh (muscle, memory; Alzheimer's), dopamine (reward, movement; Parkinson's, schizophrenia), serotonin (mood; SSRIs), GABA (main inhibitory) and glutamate (main excitatory, LTP) are the core transmitters.
The hypothalamus governs homeostasis, the cerebellum coordination, Broca's area speech production and Wernicke's comprehension; the sympathetic system mobilises and the parasympathetic restores.
Plasticity runs from Hebb and LTP to enriched environments, adult neurogenesis and cortical remapping; methods range from lesions, stains and single-unit recording to EEG, fMRI and PET.

Practice questions (10)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

The main inhibitory neurotransmitter of the brain, whose action is enhanced by benzodiazepines, is:
1. Glutamate
2. Acetylcholine
3. Dopamine
4. GABA
Show answer
Answer: D — GABA
GABA is the principal inhibitory transmitter, and benzodiazepines increase the effect of GABA at GABA-A receptors, which is why they reduce anxiety. Glutamate is the principal excitatory transmitter.
Parkinson's disease results chiefly from the degeneration of dopamine-producing neurons in the:
1. Hippocampus
2. Suprachiasmatic nucleus
3. Substantia nigra
4. Nucleus basalis
Show answer
Answer: C — Substantia nigra
Loss of substantia nigra neurons depletes dopamine in the nigrostriatal pathway to the basal ganglia, producing tremor, rigidity and slowness. The nucleus basalis is the cholinergic source lost in Alzheimer's, and the suprachiasmatic nucleus is the circadian clock.
The rising phase of the action potential is produced mainly by:
1. Influx of sodium ions through voltage-gated channels
2. Influx of chloride ions
3. The sodium–potassium pump
4. Efflux of potassium ions
Show answer
Answer: A — Influx of sodium ions through voltage-gated channels
At threshold, voltage-gated Na⁺ channels open and sodium rushes in, driving the inside positive. K⁺ efflux repolarises the membrane; Cl⁻ influx hyperpolarises (inhibits); and the pump maintains the resting gradients rather than generating the spike.
What is the approximate resting membrane potential of a typical neuron, in millivolts? Type a number, including its sign.
Numerical answer — type the value.
Show answer
Answer: -70
The inside of a resting neuron is about −70 mV relative to the outside, kept there by the sodium–potassium pump and the membrane's greater permeability to potassium.
Which of the following are effects of SYMPATHETIC activation? Select all that apply.
1. Increased heart rate
2. Stimulation of digestion
3. Dilation of the pupils
4. Relaxation of the airways
Show answer
Answer: A — Increased heart rate; C — Dilation of the pupils; D — Relaxation of the airways
The sympathetic "fight or flight" system dilates the pupils, speeds the heart and opens the airways, while inhibiting digestion. Stimulating digestion is a parasympathetic ("rest and digest") effect.
Which sense is NOT relayed through the thalamus before reaching the cortex?
1. Hearing
2. Touch
3. Smell
4. Vision
Show answer
Answer: C — Smell
Olfactory signals go from the olfactory bulb directly to the piriform cortex and amygdala. Vision relays in the lateral geniculate nucleus, hearing in the medial geniculate nucleus, and touch in the ventral posterior nuclei of the thalamus.
Which non-invasive technique measures brain activity through changes in blood oxygenation?
1. Computerised tomography
2. Functional MRI (the BOLD signal)
3. Electroencephalography
4. Golgi staining
Show answer
Answer: B — Functional MRI (the BOLD signal)
fMRI detects the blood-oxygen-level-dependent signal that follows neural activity. EEG records electrical activity, CT images structure with X-rays, and Golgi staining is an invasive anatomical method on fixed tissue.
Match the EEG rhythm with the state.
(A) Alpha
(B) Delta
(C) Beta
(D) Theta — (1) alert, active thinking (2) relaxed wakefulness with eyes closed (3) deep sleep (4) drowsiness and light sleep
1. A-2, B-3, C-1, D-4
2. A-1, B-3, C-2, D-4
3. A-2, B-4, C-1, D-3
4. A-4, B-3, C-1, D-2
Show answer
Answer: A — A-2, B-3, C-1, D-4
Alpha (8–13 Hz) marks relaxed wakefulness, delta (below 4 Hz) deep slow-wave sleep, beta (13–30 Hz) alert activity, and theta (4–8 Hz) drowsiness and light sleep.
Assertion (A): The intensity of a stimulus is coded by the frequency of action potentials rather than by their size. Reason (R): An action potential obeys the all-or-none law: once threshold is reached, its amplitude is the same regardless of stimulus strength. Choose the correct option.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true, but R is false
4. A is false, but R is true
Show answer
Answer: A — Both A and R are true, and R is the correct explanation of A
Both are true and R explains A: since every spike has the same size, the only ways left to signal a stronger stimulus are more spikes per second and more neurons firing.
Which of the following are INVASIVE methods of physiological psychology? Select all that apply.
1. Scalp EEG
2. Single-unit microelectrode recording
3. Microdialysis
4. Stereotaxic lesions
Show answer
Answer: B — Single-unit microelectrode recording; C — Microdialysis; D — Stereotaxic lesions
Lesions, microelectrode recording and microdialysis all require entering the brain. Scalp EEG records from the surface of the head and is non-invasive, as are MRI and fMRI.