Chapter 2: The Biology of Mind — Comprehensive Study Notes
Neural and Hormonal Systems
Biological psychology: Everything psychological is biological; psychologists study the links between biological (genetic, neural, hormonal) and psychological processes.
A wrongheaded theory: Phrenology proposed that bumps on the skull reveal mental faculties and character traits; now considered a pseudoscience. However, the general idea that different parts of the brain control different aspects of behavior has some truth, as suggested by contemporary neuroscience.
Plasticity: The brain’s ability to change throughout life by reorganizing after damage or by building new pathways based on experience. New neural pathways reflect personal experiences.
Example spotlight: Dr. Marian Diamond’s factors influencing brain development (5 factors): Diet, Exercise, Challenge, Newness, Love.
Dr. Diamond: Professor Emerita of Integrative Biology and a foundational figure in modern neuroscience.
Neuron: The basic building block of the nervous system; electrical and chemical signaling underlie brain and body communication.
Dendrites: Extensions that receive messages and conduct them toward the cell body.
Axon: Long projection that conducts messages away from the cell body; some axons are covered by the myelin sheath to speed transmission.
Myelin sheath: Fatty layer around many axons that speeds signal transmission.
Glial cells (glia): Supportive cells that nourish, protect, and sometimes modulate learning and memory; they also participate in myelination.
Synapse: Junction between the axon tip of a sending neuron and the dendrite or cell body of a receiving neuron.
Refractory period: A brief period after firing during which a neuron is less able to fire again.
Threshold: Level of stimulation required to trigger a neural impulse.
All-or-none response: A neuron fires at full strength or not at all; the strength of a stimulus changes the rate of firing, not the size of the spike.
Neurotransmitters: Neuron-produced chemicals that cross synapses to carry messages to other neurons or cells; their binding at receptors influences whether the receiving neuron will generate a neural impulse.
Reuptake: Reabsorption of neurotransmitters by the sending neuron.
Action potential: A neural impulse that travels down an axon; the signal is an electrochemical wave.
Acetylcholine (ACh): A neurotransmitter that affects muscle action, learning, and memory.
Endorphins: Natural opiates released in response to pain and exercise; part of the body’s own analgesic system.
Agonist: Molecule that increases a neurotransmitter’s action.
Antagonist: Molecule that inhibits or blocks a neurotransmitter’s action.
Nervous system: The body’s speedy electrochemical communication network, consisting of the CNS and PNS.
Central nervous system (CNS): Brain and spinal cord.
Peripheral nervous system (PNS): The network of nerves outside the CNS; subdivides into:
Somatic nervous system: Controls the body’s skeletal muscles; voluntary movement.
Autonomic nervous system: Regulates glands and internal organs; involuntary functions; subdivides into:
Sympathetic nervous system: Arouses the body, mobilizing energy in stressful situations.
Parasympathetic nervous system: Calms the body, conserving energy.
Sensory neurons: Carry messages from tissues and sensory receptors inward to the spinal cord and brain.
Motor neurons: Carry instructions from the CNS out to the body’s muscles.
Interneurons: Within the brain and spinal cord; communicate with one another and process information between sensory input and motor output.
Endocrine system: Glands that secrete hormones into the bloodstream; hormones travel through the body and affect tissues, including the brain.
Pituitary gland: The master gland that influences hormone release by other glands (e.g., adrenal glands).
Hypothalamus: Influences the pituitary gland; part of a feedback system linking the brain and endocrine system.
What do phrenology and biological psychology have in common?
Both are concerned with brain-behavior relationships, but phrenology’s specific claims are unsupportable; modern biology shows that different parts of the brain have specialized functions.
When a neuron fires an action potential, the information travels through the axon, the dendrites, and the cell body, but not in that order. Place these three structures in the correct order.
Correct order: Dendrites → Cell body (soma) → Axon.
How does our nervous system allow us to experience the difference between a slap and a tap on the back?
Differences arise from the magnitude and pattern of neural activation along somatosensory pathways, including receptor density, speed of conduction, and the brain’s interpretation of the sensory signals.
Serotonin, dopamine, and endorphins are all chemical messengers called: neurotransmitters.
Curare poisoning paralyzes its victims by blocking ACh receptors involved in muscle movements. Morphine mimics endorphin actions. Which is an agonist, and which is an antagonist?
Morphine is an agonist (activates endorphin receptors).
Curare is an antagonist (blocks ACh receptors).
Why is the pituitary gland called the “master gland”?
It releases hormones that regulate other glands, including adrenal glands; it is regulated by the hypothalamus in a feedback system.
How are the nervous and endocrine systems alike, and how do they differ?
Both coordinate body’s responses to the environment; nervous system uses fast electrochemical signaling; endocrine system uses chemical hormones that travel through the bloodstream and typically have longer-lasting effects.
Tools of Discovery, Older Brain Structures, and the Limbic System
Methods neuroscientists use to study the brain’s connections to behavior and mind:
Electroencephalogram (EEG): measures electrical activity of large populations of neurons.
Magnetoencephalography (MEG): measures magnetic fields produced by neural activity.
Positron emission tomography (PET): measures brain metabolic activity using injected tracers.
Magnetic resonance imaging (MRI): provides high-resolution images of brain structure.
Functional MRI (fMRI): measures brain activity by detecting changes associated with blood flow.
Older Brain Structures:
Medulla: at the base of the brainstem; controls heartbeat and breathing.
Pons: above the medulla; helps coordinate movement.
Thalamus: directs sensory messages to the cortex and transmits replies to the cerebellum and medulla.
Reticular formation: nerve network through the brainstem and thalamus; plays an important role in controlling arousal.
Cerebellum: coordinates voluntary movement and supports functions such as time, texture discrimination, and emotional control; helps process and store information outside of awareness.
The Brainstem is the oldest and innermost brain region; it is an extension of the spinal cord.
The Limbic System:
Sits between the brain’s older parts and its cerebral hemispheres; neural centers include the hippocampus, amygdala, and hypothalamus.
Functions: linked to emotions, memory, and drives; controls nearby pituitary gland; involved in reward.
Amygdala: two lima-bean–sized clusters linked to emotion (fear, aggression).
Hypothalamus: below the thalamus; directs maintenance activities (hunger, thirst, body temperature); helps govern the endocrine system via the pituitary and is linked to emotion and reward.
Hippocampus: processes conscious memories; involved in forming explicit memories; tends to decrease in size and function with age.
The hypothalamus controls the pituitary (the “master gland”) by stimulating it to trigger hormone release.
The Cerebral Cortex:
Thin layer of interconnected neurons covering the cerebral hemispheres; the brain’s ultimate control and information-processing center.
Frontal lobes: located behind the forehead; involved in speaking and muscle movements, planning and judgments.
Parietal lobes: located at the top of the head toward the rear; receives sensory input for touch and body position.
Occipital lobes: located at the back of the head; include areas that receive information from the visual fields.
Temporal lobes: located roughly above the ears; include areas that receive information from the ears.
Motor cortex: located at the rear of the frontal lobes; controls voluntary movements.
Somatosensory cortex: located in the parietal lobes; registers and processes body touch and movement sensations.
Association areas: found in all four lobes; involved in higher mental functions such as planning, judgment, and memory; damage leads to various deficits.
Corpus callosum: large bundle of neural fibers connecting the two hemispheres.
Split brains: condition in which the corpus callosum is severed, isolating each hemisphere.
The Cerebral Cortex is topographically mapped; a disproportionate amount of cortex is devoted to sensitive or precise control (e.g., fingers and lips) in both the motor and somatosensory cortices.
Brain–Computer Interfaces (BCI):
Electrodes in motor cortexes can record signals that map to intended movements of a robotic arm.
Monkeys and humans have learned to control robot arms to grasp and deliver food (Collinger et al., 2013).
Clinical trials are exploring cognitive neural prosthetics for paralysis or amputations.
Machine learning techniques decode brain signals to control assistive devices.
The Cortical representation:
Visual cortex (occipital lobe) processes visual input; auditory cortex (temporal lobe) processes hearing input.
Functional MRI studies show connectivity changes under altering states (e.g., LSD vs placebo) indicating complex network interactions.
Association areas:
Involve higher-level processing such as judgment, planning, and memory formation; damage can result in specific deficits while basic sensory or motor functions remain.
Phineas Gage: classic case illustrating the brain's involvement in personality and executive function.
The Brain’s Plasticity in detail:
Brain damage often leads to limited regeneration of severed neurons; some brain functions are preassigned, but neural tissue can reorganize after damage.
Plasticity may allow other brain areas to take over functions after injury.
Constraint-induced therapy aims to rewire brain and improve dexterity after brain damage.
Sensory loss (blindness or deafness) can free up unused brain areas for other uses; neurogenesis can be promoted by factors such as exercise, sleep, and stimulating environments.
The Corpus Callosum and Split-Brain findings:
The corpus callosum enables inter-hemispheric communication; cutting it can prevent information sharing between hemispheres, leading to a split-brain condition.
Right–Left differences in intact brains:
Left hemisphere: excels at language, quick, exact interpretations.
Right hemisphere: excels at inferring, modulating speech, and self-awareness.
Split Brain Syndrome: experiments show that when split, each hemisphere can operate independently with distinct processing styles and responses (e.g., commands, recognition tasks).
The Cerebral Cortex: Structure and Function
The cerebral cortex consists of four lobes with distinct yet interconnected roles:
Frontal lobes: planning, judgments, motor control; motor cortex maps fine motor control to specific body parts; Brodmann areas and motor homunculus demonstration through electrical stimulation.
Parietal lobes: somatosensory processing; body position and touch.
Occipital lobes: visual processing; visual cortex.
Temporal lobes: auditory processing; understanding language.
Motor cortex and somatosensory cortex representation:
The amount of cortical area dedicated to a body part is not proportional to its size; highly sensitive or precisely controlled parts (e.g., fingers, lips) have larger cortical representations.
The left/right hemisphere specialization:
Language and rapid processing on the left; spatial, holistic processing and self-awareness on the right.
The Brain’s Plasticity and Development
Plasticity: The brain’s capacity to change in response to experience, learning, and injury.
After damage, some brain functions can be redistributed to other areas; plasticity can be enhanced by experience, training, and environment.
Neurogenesis: The growth of new neurons; supported by factors such as exercise, sleep, and stimulating environments.
Constraint-induced therapy and reorganization: Therapies that promote use of affected limbs to rewire neural circuits.
Neurotransmission in Action: A Step-by-Step View
Neuron is the basic element of the nervous system; communication happens as signals are transmitted within neurons and across synapses.
Action potential process (simplified):
Resting potential: membrane potential is at rest until stimulation reaches threshold.
Threshold: the critical level that must be reached to trigger an action potential; approximate value referenced in many texts is around .
Depolarization: stimulation opens voltage-gated sodium channels; $Na^+$ ions flood into the neuron, causing the membrane potential to become more positive.
Repolarization: potassium channels open, and $K^+$ ions flow out, restoring the resting state.
Propagation: the action potential travels down the axon; signals move like a wave but via ion movement, not a linear electrical current.
Refractory period: after firing, there is a brief period during which a neuron cannot fire again immediately.
Resting potential restoration: sodium–potassium pumps help restore the original ion distribution.
All-or-none: once the threshold is crossed, the neuron fires at full strength; stronger stimuli do not produce a stronger action potential but may trigger more frequent firing.
Communication across the synapse:
Neurotransmitters are released from the sending neuron’s axon terminal into the synapse.
They bind to receptor sites on the receiving neuron, influencing whether that neuron will fire.
Reuptake returns neurotransmitters to the sending neuron for reuse.
Ion movement and direction of signal during an action potential: the signal travels toward the axon terminals; the wave of depolarization moves along the axon.
The speed of neural transmission: neural signals travel about depending on myelination and fiber type; electrical signals in wires travel much faster, but chemical signals offer the advantage of stability over distance.
Myelin and disease: multiple sclerosis involves degeneration of the myelin sheath, interfering with neural communication.
The neuron’s overall process summary:
Neurons receive signals via dendrites, integrate them in the soma, and transmit signals via the axon.
Myelin increases conduction speed; glial cells provide myelin and support.
A sufficiently strong collective input triggers an action potential; the signal travels via the axon in an all-or-none fashion.
Neurotransmitters, Drugs, and Behavioral Effects
Neurotransmitters travel along designated pathways to influence specific behaviors and emotions.
Common neurotransmitters and functions:
Acetylcholine (ACh): affects muscle action, learning, and memory.
Endorphins: natural opioids linked to pain relief and pleasure; modulate pain and stress.
Drug effects on neurotransmission:
Agonist: molecule that increases a neurotransmitter’s action.
Antagonist: molecule that blocks a neurotransmitter’s action.
Drugs can alter brain chemistry at synapses by acting as agonists or antagonists, changing the likelihood of neuron firing and downstream behavior.
The Nervous and Endocrine Systems: Quick Comparisons
Nervous system: fast, electrochemical communication; precise in timing; often short-lived effects.
Endocrine system: slower communication via hormones released into the bloodstream; effects may be longer-lasting; coordinated with the brain through feedback loops involving the hypothalamus and pituitary gland.
Similarities:
Both transmit information and regulate body functions.
Differences:
Speed, duration, and distance of effect; one uses electrical signals in neurons, the other uses hormones in the blood.
The Endocrine System in Action
Endocrine glands secrete hormones into the bloodstream.
Hormones influence various tissues, including the brain, and can modulate mood, metabolism, growth, and stress responses.
The hypothalamus–pituitary axis:
The hypothalamus signals the pituitary gland, which in turn releases hormones that regulate other endocrine organs (e.g., adrenal glands).
This forms a feedback loop that coordinates hormonal release with brain activity and environmental demands.
Modern Methods for Studying the Brain
Electroencephalography (EEG): records electrical activity of the brain via scalp electrodes.
Magnetoencephalography (MEG): detects magnetic fields produced by neural activity.
Positron emission tomography (PET): measures brain activity by detecting radioactive tracers.
Magnetic resonance imaging (MRI): provides high-resolution images of brain structure.
Functional MRI (fMRI): measures brain activity by detecting changes in blood flow.
Table 5.1 (referenced in course materials) summarizes additional methods and details.
The Brain’s Basic Organization: The Brainstem, Cerebellum, and Limbic System
Brainstem (older brain structures):
Medulla: controls heartbeat and breathing.
Pons: coordinates movement.
Thalamus: routes sensory information to cortex and transmits replies to cerebellum and medulla.
Reticular formation: regulates arousal and alertness.
Cerebellum: coordinates movement, time, discrimination of sounds and textures, emotional control; helps with nonconscious processing.
The Limbic System: structures and roles defined earlier; crucial for emotion, memory, and drives; interacts with the pituitary to influence hormones.
The Cerebral Cortex: Structure, Function, and Connectivity
Cortex: thin layer of neural tissue covering the hemispheres; the brain’s processing and control center.
Four lobes:
Frontal lobes: speaking, movement, planning, decision-making.
Parietal lobes: touch and body position.
Occipital lobes: vision.
Temporal lobes: hearing and language.
Motor cortex: is the rear portion of the frontal lobes; controls voluntary movements; mapped by researchers:
Fine motor control (e.g., fingers, mouth) occupies large cortical areas.
Somatosensory cortex: located in the parietal lobes; registers and processes body touch and movement sensations; similarly mapped with larger regions for sensitive body parts.
Association areas: areas of the cortex involved in higher-level processing, planning, and decision-making; they are active in many tasks beyond primary sensory and motor functions.
Corpus callosum: large bundle of neural fibers that connects the two hemispheres and enables interhemispheric communication.
Split brains: condition resulting from severing the corpus callosum; each hemisphere can operate independently on certain tasks; evidence that the hemispheres have specialized functions but normally work together to create unified experience.
Left vs. right hemisphere specializations in intact brains:
Left: language, quick, exact interpretations.
Right: inferences, modulation of speech, self-awareness.
Brain–Computer Interfaces (BCIs) and Brain Connectivity
Recording signals from the motor cortex allows control of a robotic arm or other assistive devices.
Research examples:
Colinger et al. (2013): brain signals used to control a robotic arm that can grasp and deliver food.
Monkeys and humans have learned to operate a robotic arm to interact with the environment using brain signals (advancements in neural prosthetics).
Clinical implications: cognitive neural prosthetics for paralysis or amputations are being explored in ongoing trials.
Technology and machine learning: the decoding of brain signals to predict motor commands or cognitive states.
Functions of the Cortex: Sensory and Motor Areas
Sensory cortices:
Visual cortex: located in the occipital lobe; processes visual input.
Auditory cortex: located in the temporal lobe; processes hearing input.
Other sensory areas process smell, taste, etc. (not detailed in this transcript).
Visual and auditory processing can be visualized with functional imaging studies showing increased connectivity during task performance or under certain altered states (e.g., LSD experiments).
Association areas and higher functions:
Involved in planning, judgment, and memory storage.
Damage to association areas can lead to deficits that affect complex tasks even when basic senses and motor control remain intact.
Phineas Gage: a famous case illustrating how frontal lobe damage can alter personality and social behavior.
The Brain’s Plasticity, Experience, and Neurogenesis
Plasticity and experience: the brain’s ability to reorganize and form new connections throughout life; essential for learning and recovery from injury.
Neurogenesis: generation of new neurons; influenced by lifestyle factors such as exercise, sleep, and stimulating environments.
Exercise, sleep, and low-stress but stimulating environments promote neurogenesis and brain health.
Practical and Ethical Implications
Understanding brain plasticity supports educational approaches and rehabilitation strategies after brain injury.
Knowledge of neural substrates underpins therapies like constraint-induced therapy and rehabilitation after stroke.
Brain–computer interfaces hold promise for restoring motor function and communication for people with paralysis or amputations; this raises questions about accessibility, safety, and long-term impact.
Quick Review Questions (from the transcript)
What do phrenology and biological psychology have in common?
When a neuron fires an action potential, the information travels through the axon, the dendrites, and the cell body, but not in that order. Place these structures in the correct order.
How does our nervous system allow us to experience the difference between a slap and a tap on the back?
Serotonin, dopamine, and endorphins are all chemical messengers called:
Curare poisoning blocks ACh receptors; Morphine mimics endorphin actions. Which is the agonist, and which is the antagonist?
Why is the pituitary gland called the “master gland”?
How are the nervous and endocrine systems alike, and how do they differ?
What are the three key structures of the limbic system, and what functions do they serve?
The left hemisphere is good at: a) rapid language processing; The right hemisphere is good at: b) inferring, modulating speech, and self-awareness.
What is the role of the corpus callosum in normal brain function? How does split-brain surgery illuminate lateralization of function?
How does plasticity enable recovery after brain injury? What roles do neurogenesis and environmental factors play?
Notes on Key Terms (quick reference)
Biological psychology, plasticity, neuron, dendrites, axon, myelin sheath, glial cells (glia), synapse, refractory period, threshold, all-or-none, neurotransmitters, reuptake, action potential, acetylcholine (ACh), endorphins, agonist, antagonist, nervous system, CNS, PNS, somatic nervous system, autonomic nervous system, sympathetic nervous system, parasympathetic nervous system, sensory neurons, motor neurons, interneurons, endocrine system, pituitary gland, hypothalamus, lamination of the cortex (frontal, parietal, occipital, temporal), limbic system, amygdala, hippocampus, hypothalamus, thalamus, cerebellum, medulla, pons, reticular formation, corpus callosum, split brains, brain–computer interfaces, neurogenesis, constraint-induced therapy.