NEUROSCIENCE AND BEHAVIOR I – NEURON - a nerve cell; the basic building block of the nervous system
Everything Psychological is Simultaneously Biological
Dendrite: Branching extensions of a neuron that receive impulses from other neurons or from sensory organs and conduct them toward the cell body.
Axon: Extension of a neuron, ending in branching terminal fibers through which messages pass to other neurons or to muscles or glands.
Myelin sheath: Layer of fatty tissue surrounding fibers of many neurons; insulates and increases the speed of transmission of neural impulses; impulse hops from one node/segment to the next; speed of transmission varies from 2 mph to 200 mph; measured in milliseconds (1000th of a second) vs. computers (nanoseconds – 1 billionth of a second).
Action potential: A neural impulse; a brief electrical charge that travels down an axon; generated by the movement of positively charged atoms in and out of channels in the axon’s membrane; triggers by stimulation for sensory organs or other neurons.
Resting potential: Neuron has more negatively charged ions inside (selective permeability); when the neuron fires, positively charged ions and the impulse spreads down the neuron (depolarization); during the refractory period, neuron pumps the positively charged ions back out.
Threshold: Minimal level of stimulation required to trigger a neural impulse; excitatory impulses must exceed inhibitory impulses and achieve threshold for the neuron to fire.
Action potential (AP) is all-or-none – either the neuron fires or not (stronger stimulation does not affect strength or speed of the AP). However, stronger stimulation triggers more frequent firing and more neurons firing.
II – HOW NEURONS COMMUNICATE AND INFLUENCE BEHAVIOR
Synapse: junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or cleft.
Neurotransmitters: Chemical messengers that traverse the synaptic gaps from the sending neuron and bind to receptor sites on the receiving neuron, influencing whether that neuron will generate a neural impulse. Overall: Most neurons have a resting rate of random firing, which either increases or decreases with input from other neurons and from chemicals that affect their sensitivity. If the neuron receives more excitatory than inhibitory messages, it fires often. More electrical impulses flash down its axon, releasing more packets of neurotransmitters, which diffuse across their synaptic gaps to other neurons.
Major Neurotransmitters and their Functions
Acetylcholine (ACh): Enables muscle action, learning, and memory Deficiency implicated in Alzheimer’s disease.
Dopamine: Influences movement, learning, attention, and emotion
Excess dopamine receptor activity linked to schizophrenia; starved of dopamine, the brain produces the tremors and decreased mobility of Parkinson’s disease.
Serotonin: Affects mood, hunger, sleep, and arousal
Undersupply linked to depression; Prozac and some other antidepressant drugs raise serotonin levels.
Norepinephrine: Helps control alertness and arousal Undersupply can depress mood.
GABA (gamma-aminobutyric acid): A major inhibitory neurotransmitter Undersupply linked to seizures, tremors, and insomnia.
Glutamate: A major excitatory neurotransmitter; involved in memory
Oversupply can over stimulate brain, producing migraines or seizures (which is why some people avoid MSG, monosodium glutamate).
Endorphins: “morphine within”- natural, opiate-like neurotransmitters linked to pain control and to pleasure
III – HOW DRUGS AFFECT BEHAVIOR (Preview)
Long-term: Drugs suppress the natural production of the neurotransmitter (withdrawal effects)
Agonists excite : A drug molecule similar enough to the neurotransmitter to mimic its effects or block a neurotransmitter’s reuptake (e.g., opiates)
Antagonists inhibit : A drug molecule that inhibits a neurotransmitter’s release, or is similar enough to occupy its receptor site and block its effect but not similar enough to stimulate the receptor (e.g., curare).
IV – THE NERVOUS SYSTEM (NS) – an electrochemical communication system, consisting of all the nerve cells of the peripheral and central nervous systems.
Central NS (CNS): Brain and spinal cord
Peripheral NS (PNS): Sensory and motor neurons that connect the CNS to the rest of the body. Nerves - neural “cables” containing many axons; these bundles of axons connect CNS with muscles, glands, and sense organs.
Sensory neurons: Carry incoming information from sense receptors to the CNS. - a few million
Interneurons: CNS neurons that internally communicate and intervene between the sensory inputs and motor outputs. Billions – responsible for complexity.
Motor neurons: Carry outgoing information from the CNS to muscles and glands. - a few million. V- PERIPHERAL NS
S
omatic nervous system : Controls skeletal muscles (also called skeletal NS).
Autonomic nervous system (ANS): Controls glands and the muscles of the internal organs (such as the heart); involuntary activities.
Sympathetic division of ANS: Arouses; mobilizes energy for stressful situations; fight or flight response (increases heart rate, slows digestion, raises blood sugar, dilate arteries and pupils). Parasympathetic division of ANS: Calms; conserves energy (slows heart rate, etc.)
VI – CENTRAL NS
Spinal Cord: Connects peripheral nervous system to the brain. Ascending neural tracts send up sensory information, and Descending tracts send back motor-control information.
Reflexes: Simple, automatic, inborn response to a sensory stimulus, such as the knee-jerk response; simplest consists of one sensory, one interneuron and one motor neuron.
Brain: 30 billion neurons, each having roughly 10,000 contacts with other neurons - 300 trillion cortical synaptic connections.
Neural networks: Interconnected neural cells; with experience, networks can learn, as feedback strengthens or inhibits connections that produce certain results. Computer simulations of neural networks show analogous learning.
Networks are interconnected, resulting in still more complexity. VII – TOOLS FOR STUDYING THE BRAIN
Clinical Observations of people with brain disease or injury. Change the brain by stimulation or lesion.
Recording brain structures and activity
EEG: Electroencephalogram: Amplified recording of the waves of electrical activity that sweep the brain.
CT (computed tomography) scan: A series of x-ray photographs taken from different angles and combined by computer into a composite representation of a slice through the brain (CAT scan). To see structures.
PET (positron emission tomography) scan: A visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a given task.
MRI (magnetic resonance imaging): A technique that uses magnetic fields and radio waves to
produce computer-generated images that distinguish among different types of soft tissue; allows us to see structures within the brain; allows seeing changes in blood flow with brain activity (functional MRI).
VIII – PARTS OF THE BRAIN
Brainstem: Oldest part and central core of the brain, beginning where the spinal cord swells as it enters the skull; responsible for automatic survival functions.
Medulla: Base of the brainstem; controls heartbeat and breathing.
Reticular formation: A nerve network in the brainstem that plays an important role in controlling arousal.
Thalamus: The brain’s sensory switchboard, located on top of the brainstem; it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla.
Cerebellum: The “little brain” attached to the rear of the brainstem; it helps coordinate voluntary movement and balance.
Limbic System: A doughnut-shaped system of neural structures at the border of the brainstem and cerebral hemispheres; associated with emotions such as fear and aggression and drives such as those for food and sex. Includes the hippocampus, amygdala, and hypothalamus.
Amygdala: Two almond-shaped neural clusters in the limbic system that are linked to emotion, especially to fear and aggression (producing, perceiving, processing emotional memories). Note: many brain regions are involved in emotions and other behaviors.
Hypothalamus: A neural structure lying below (hypo) the thalamus; directs several maintenance activities (hunger, thirst, sex, body temperature), helps govern the endocrine system via the pituitary gland, and is linked to emotion; monitors blood chemistry; triggers ANS activity; a link between the Nervous System and Endocrine System; “pleasure” or “reward” centers located here.
Cerebral cortex: The intricate fabric of interconnected neural cells (20-23 billion) that covers the cerebral hemispheres; the body’s ultimate control and information-processing center; also contains 9X as many glial
Two hemispheres (left and right), each divided into 4 regions or LOBES.
Frontal lobes (behind forehead): Speaking and muscle movements; making plans and judgments. Parietal lobes (top and rear): Processing somatosensory information (touch).
Occipital lobes (back): Processing visual information.
Temporal lobes (just above ears): Processing auditory information.
MOTOR CORTEX (MC): An area at the rear of the frontal lobes that controls voluntary movements; left MC controls right side of body and right MC controls left side of body; larger area of MC devoted to areas of the body that require finer control (e.g., fingers vs. forearm); just thinking about movement produces electrical activity in the MC.
SENSORY CORTEX (SC): An area at the front of the parietal lobes that registers and processes body sensations; left SC receives information from right side of body and right SC receives
information from left side of body; larger areas of SC are devoted to more sensitive areas (lips) of the body (e.g., lose a finger, then more SC area gets devoted to adjacent fingers; pianists have more auditory cortex, deaf people more visual cortex).
ASSOCIATIVE CORTEX (AA): The remaining 2/3 of the cortex involved in higher mental functions such as learning, remembering, thinking, and speaking; integrate and act on information received and processed by the sensory area; unlike MC and SC, stimulating specific areas of the AC does not result in specific responses so functions cannot be neatly specified.
Frontal lobes: AA enables us to judge, plan, and process new memories, moral behavior. Damage to frontal lobes – cannot make plans (e.g., a meal), may change personality (e.g., Phineas Gage), loss of moral compass.
Parietal lobes: Mathematical and spatial reasoning. Temporal lobe (right): Face recognition.
NOTE: Most complex mental functions such as learning and memory don’t reside in any one place but are distributed throughout the brain.
IX – LANGUAGE
Aphasia: Impairment of language, usually caused by left hemisphere damage either to Broca’s area (impairing speaking) or to Wernicke’s area (impairing understanding).
Broca’s area : An area of the frontal lobe, usually in the left hemisphere, that directs the muscle movements involved in speech production/expression, not comprehension.
Wernicke’s area: An area in the left temporal lobe involved in speech comprehension and expression.
Angular gyrus: Receives visual information from the visual cortex and recodes it into the auditory form, which Wernicke’s area then uses to derive its meaning.
How we understand language:
When you read aloud words it (1) registers in the visual area, (2) is relayed to the angular gyrus that transforms the words into an auditory code that is (3) received and understood in the nearby Wernicke’s area and (4) sent to Broca’s area, which (5) controls the motor cortex, creating the pronounced word.
Depending on which link in this chain is damaged, a different form of aphasia occurs. Damage to the angular gyrus leaves the person able to speak and understand but unable to read. Damage to Wernicke’s area disrupts understanding. Damage to Broca’s area disrupts speaking.
NOTE: Complex abilities result from intricate coordination of many brain areas! SPECIALIZATION and INTEGRATION –neural networks coordinate their work
X - BRAIN REORGANIZATION
Plasticity: The brain’s capacity for modification, as evident in brain reorganization following damage (especially in children) and in experiments on the effects of experience on brain development. Brain can rewire itself with new synapses or select new uses for its prewired circuits (e.g., hearing areas become seeing areas; hemispherectomy). New brain cells can develop from stem cells.
Split Brain Research:
Corpus callosum: Large band of neural fibers connecting the two brain hemispheres and carrying messages between them.
“Two minds:” Hemispheres act independently. Left brain interprets the right brain’s behavior. “Alien hand syndrome:” A neurological disorder in which people experience one hand as operating with a mind of its own.
Hemispheric Specialization in Normal Brains
Right hemisphere: Perceptual tasks (face/picture recognition), subtleties/nuance, intuitive, spatial, parallel processing, emotional
Left hemisphere: Speech, math, speaks or calculates, word recognition, language (including sign language), logical, sequential processing, analytic.
Handedness and Brain Organization
90% right-handed; 95% process speech in left hemisphere (bigger) 10% left-handed; 25% process in right, 25% use both hemispheres;
Lefties (Southpaws) more likely to have reading disabilities, allergies, and migraine headaches, but also more likely to be musicians, mathematicians, professional baseball and cricket players, architects, and artists.
Left-handed – shorter lives.
XI – THE ENDOCRINE SYSTEM: the body’s second communication system, interconnected with the nervous system; its glands secrete another form of chemical messengers, hormones, which travel through the bloodstream, and affect other tissues, including the brain. Some hormones are identical to neurotransmitters.
Adrenal glands: A pair of endocrine glands just above the kidneys; secrete the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline), which help to arouse the body in times of stress.
Pituitary gland: Pea-sized, at base of brain, under the influence of the hypothalamus, the pituitary regulates growth and controls other endocrine glands.
Thyroid gland: Regulates metabolism. Parathyroids: Regulates calcium levels. Pancreas: Regulates sugar levels.
