Chapter 3The Brain, Biology, and Behavior

Neuron: Individual nerve cell Dendrites: Receive messages from other neurons Soma: Cell body; body of the neuron Axon: Carries information away from the cell body Axon Terminals: Branches that link the dendrites and

soma of other neurons Myelin sheath – speeds up transmission Terminal Buttons – end of axon; secrete

neurotransmitters Neurotransmitters – chemical messengers

Synapse – point at which neurons interconnect

Neuron and its parts

Figure 3.1 An example of a neuron, or nerve cell, showing several of its important features. The right foreground shows a nerve cell fiber in cross section, and the upper left inset gives a more realistic picture of the shape of neurons. The nerve impulse usually travels from the dendrites and soma to the branching ends of the axon. The neuron shown here is a motor neuron. Motor neurons originate in the brain or spinal cord and send their axons to the muscles or glands of the body.

Figure 3.3 The inside of an axon normally has a negative electrical charge. The fluid surrounding an axon is normally positive. As an action potential passes along the axon, these charges reverse, so that the interior of the axon briefly becomes positive.

Figure 3.5 A highly magnified view of the synapse. Neurotransmitters are stored in tiny sacs called synaptic vesicles. When a nerve impulse arrives at an axon terminal, the vesicles move to the surface and release neurotransmitters. These transmitter molecules cross the synaptic gap to affect the next neuron. The size of the gap is exaggerated here; it is actually only about one millionth of an inch. Transmitter molecules vary in their effects: Some excite the next neuron, and some inhibit its activity.

Chemicals that alter activity in neurons; brain chemicals. Some examples: Acetylcholine: Activates muscles Dopamine: Muscle control Serotonin: Mood and appetite control

Messages from one neuron to another pass over a microscopic gap called a synapse

Receptor Site: Areas on the surface of neurons and other cells that are sensitive to neurotransmitters or hormones

Neurotransmitters

Neural Peptides: Regulate activity of other neuronsEnkephalins: Relieve pain and stress

Neural Regulators

Central Nervous System (CNS): Brain and spinal cord. Peripheral Nervous System: All parts of the nervous system outside

of the brain and spinal cord. Somatic System: Links spinal cord with body and sense organs.

Controls voluntary behavior Autonomic System: Serves internal organs and glands. Controls

automatic functions such as heart rate and blood pressureSympathetic: Arouses body- Go (fight-or-flight)Parasympathetic: Quiets body- Stop

Afferent = toward the CNS Efferent = away from the CNS

Neural Networks

Figure 3.6(a) Central and peripheral nervous systems. (b) Spinal nerves, cranial nerves, and the autonomic nervous system.

Figure 3.7 Subparts of the nervous system.

Figure 3.8 Sympathetic and parasympathetic branches of the autonomic nervous system. Both branches control involuntary actions. The sympathetic system generally activates the body. The parasympathetic system generally quiets it. The sympathetic branch relays through a chain of ganglia (clusters of cell bodies) outside the spinal cord.

Figure 3.9 A simple sensory-motor (reflex) arc. A simple reflex is set in motion by a stimulus to the skin (or other part of the body). The nerve impulse travels to the spinal cord and then back out to a muscle, which contracts. Reflexes provide an “automatic” protective device for the body.

Electroencephalograph (EEG): Detects, amplifies and records electrical activity in the brain

Computed Tomographic Scanning (CT): Computer-enhanced X-Ray of the brain or body

Magnetic Resonance Imaging (MRI): Uses a strong magnetic field, not an X-Ray, to produce an image

Functional MRI: MRI that also records brain activity

Positron Emission Tomography (PET): Computer-generated color image of brain activity, based on glucose consumption in the brain.

Researching the Brain

Hindbrain – vital functions – medulla, pons, and cerebellum

Midbrain – sensory functions – dopaminergic projections, reticular activating system

Forebrain – emotion, complex thought – thalamus, hypothalamus, limbic system, cerebrum, cerebral cortex

Brain Regions and Functions

Outer layer of the cerebrum Cerebrum: Two large hemispheres that cover upper part of the brain Cerebral Hemispheres: Right and left halves of the cerebrum

Left hemisphere – verbal processing: language, speech, reading, writing

Right hemisphere – nonverbal processing: spatial, musical, visual recognition

Corpus Callosum: Bundle of fibers connecting cerebral hemispheres

Cerebral Cortex

Figure 3.15 An illustration showing the increased relative size of the human cerebrum and cerebral cortex, a significant factor in human adaptability and intelligence.

Figure 3.17 The corpus callosum is the major “cable system” through which the right and left cerebral hemispheres communicate. A recent study found that the corpus callosum is larger in classically trained musicians than it is in nonmusicians. When a person plays a violin or piano, the two hemispheres must communicate rapidly as they coordinate the movements of both hands. Presumably, the size of the corpus callosum can be altered by early experience, such as musical training.

Occipital: Back of brain; vision center Parietal: Just above occipital; bodily sensations

such as touch, pain, and temperature Temporal: Each side of the brain; auditory and

language centers Frontal: Movement, sense of smell, higher

mental functionsContains motor cortex; controls motor

movement

Central Cortex Lobes

Basic nerve pathways of vision. Notice that the left portion of each eye connects only to the left half of the brain; likewise, the right portion of each eye connects to the right brain. When the corpus callosum is cut, a “split brain” results. Then visual information can be directed to one hemisphere or the other by flashing it in the right or left visual field as the person stares straight ahead.

 Many of the lobes of the cerebral cortex are defined by larger fissures on the surface of the cerebrum. Others are regarded as separate areas because their functions are quite different.

Aphasia: Speech disturbance resulting from brain damage Broca’s Area: Related to language and speech production.

If damaged, person knows what s/he wants to say but can’t say the words

Wernicke’s Area: Related to language comprehension. If damaged, person has problems with meanings of words,

NOT pronunciation Agnosia: Inability to identify seen objects Facial agnosia: Inability to perceive familiar faces

When the brain fails to function properly

Figure 3.21Language processing in the brain. This view of the left hemisphere highlights the location of two centers for language processing in the brain: Broca’s area, which is involved in speech production, and Wernicke’s area, which is involved in language comprehension.

 Language is controlled by the left side of the brain in the majority of right- and left-handers.

A direct brain-computer link may provide a way of communicating for people who are paralyzed and unable to speak. Activity in the patient’s motor cortex is detected by an implanted electrode. The signal is then amplified and transmitted to a nearby computer. By thinking in certain ways, patients can move an on-screen cursor. This allows them to spell out words or select from a list of messages, such as “I am thirsty.”

Hindbrain (brainstem) Medulla: Connects brain with the spinal cord and

controls vital life functions such as heart rate and breathing

Pons (Bridge): Acts as a bridge between brainstem and other structures.Influences sleep and arousal

Cerebellum: Located at base of brain.Regulates posture, muscle tone and muscular

coordination

Subcortex

Reticular Formation (RF): Inside medulla.Associated with alertness, attention and some

reflexes Reticular Activating System (RAS): Part of RF that

keeps it active and alert.Its alarm clockActivates and arouses cerebral cortex

Subcortex: Reticular Formation (RF)

Structures are part of Limbic System: System within forebrain closely linked to emotional

responseThalamus: Relays sensory information on the way to

the cortex; switchboardHypothalamus: Regulates emotional behaviors and

motives e.g. sex, hunger, rage, hormone releaseAmygdala: Associated with fear responsesHippocampus: Associated with storing memories

Forebrain

 Parts of the limbic system are shown in this highly simplified drawing. Although only one side is shown, the hippocampus and the amygdala extend out into the temporal lobes at each side of the brain. The limbic system is a sort of “primitive core” of the brain strongly associated with emotion.

 This simplified drawing shows the main structures of the human brain and describes some of their most important features. (You can use the color code in the foreground to identify which areas are part of the forebrain, midbrain, and hindbrain.)

Glands that pour chemicals (hormones) directly into the bloodstream or lymph system Pituitary Gland: Regulates growth via growth hormone

Too little means person will be smaller than averageToo much leads to giantism:

Excessive body growthAcromegaly: Enlargement of arms, hands, feet and

facial bones.Too much growth hormone released late in

growth periodAndre the Giant

Endocrine System

< Low Pituitary

Acromegaly >

< Giantism

Pineal Gland: Regulates body rhythms and sleep cycles. Releases hormone melatonin, which responds to

variations in light Thyroid: In neck; regulates metabolism

Hyperthyroidism: Overactive thyroid; person tends to be thin, tense, excitable, nervous

Hypothyroidism; Underactive thyroid; person tends to be inactive, sleepy, slow, obese

Adrenals: Arouse body, regulate salt balance, adjust body to stress, regulate sexual functioning

Endocrine System Continued

Figure 3.27 Locations of the endocrine glands in the male and female.

Behavioral genetics = the study of the influence of genetic factors on behavioral traits Basic terminology:

Chromosomes – strands of DNA carrying genetic information

Human cells each contain 46 chromosomes in pairs (sex-cells – 23 single)

Each chromosome – thousands of genes, also in pairs

Dominant, recessive

Genes and Behavior: The InterdisciplinaryField of Behavioral Genetics

Genotype/Phenotype and Polygenic inheritance

Homozygous, heterozygous

Plasticity: Brain’s capacity to change its structure and functions

Neurogenesis: Production of new brain cells

Neurogenesis and Plasticity

 Neuroscientists are searching for ways to repair damage caused by strokes and other brain injuries. One promising technique involves growing neurons in the laboratory and injecting them into the brain. These immature cells are placed near damaged areas, where they can link up with healthy neurons. The technique has proved successful in animals and is now under study in humans.

Molecular Genetics = the study of the biochemical bases of genetic inheritanceGenetic mapping – locating specific genes

Behavioral GeneticsThe interactionist model

Richard Rose (1995) – “We inherit dispositions, not destinies.”

Modern Approaches to the Nature vs. Nurture Debate

Based on Darwin’s ideas of natural selectionReproductive success key

Adaptations – behavioral as well as physicalFight-or-flight responseTaste preferences

Evolutionary Psychology: Behavior in Terms of Adaptive Significance