INTRODUCTION TO BIOLOGY AND BEHAVIOR

• Physiological psychology is the study of behavior as influenced by biology.

• It draws its techniques and research methods from biology and medicine to examine psychological phenomena.

IMAGING TECHNIQUES

• Imaging techniques allow researchers to map the structure and/or activity of the brain and correlate this data with behavior.

• An EEG (electroencephalogram) measures subtle changes in brain electrical activity through electrodes placed on the head.

• Computerized axial tomography scans, better known as CAT scans, generate cross-sectional images of the brain using a series of X-ray pictures taken from different angles.

• MRI (magnetic resonance imaging) uses extremely powerful electromagnets and radio waves to get 3-D structural information from the brain.

• Functional MRI (fMRI) and PET scans (positron emission tomography) do allow scientists to view the brain as it is working.

FUNCTIONAL ORGANIZATION OF THE NERVOUS SYSTEM

• The nervous system can be divided into two distinct subsystems:

  • Central nervous system (CNS)—comprising the brain and the spinal cord

  • Peripheral nervous system (PNS)—comprising all other nerves in the body.

• The brain is located in the skull and is the central processing center for thoughts, motivations, and emotions.

• The brain, as well as the rest of the nervous system, is made up of neurons, or nerve cells.

• Nerves sending information to the brain are sensory (or afferent) neurons; those conveying information from the brain are motor (or efferent) neurons.

• Reflexes are quick and involuntary responses to environmental stimuli.

• The PNS can be subdivided into the somatic nervous system and the autonomic nervous system.

  • The somatic nervous system is responsible for voluntary movement of large skeletal muscles.

  • The autonomic nervous system controls the nonskeletal or smooth muscles, such as those of the heart and digestive tract.

• The sympathetic nervous system is associated with processes that burn energy.

  • This is the system responsible for the heightened state of physiological arousal known as the fight-or-flight reaction—an increase in heart rate and respiration, accompanied by a decrease in digestion and salivation.

• The parasympathetic nervous system is the complementary system responsible for conserving energy.

NEUROANATOMY

• The brain is divided into three distinct regions that have evolved over time.

• These are the hindbrain, the midbrain, and the forebrain (limbic system and cerebral cortex).

The Hindbrain

• The oldest part of the brain to develop, in evolutionary terms

• Composed of the cerebellum, medulla oblongata, reticular activating system (RAS), and pons

• Cerebellum—controls muscle tone and balance

• Medulla oblongata—controls involuntary actions, such as breathing, digestion, heart rate, and swallowing (basic life functions)

• Reticular activating system (RAS)—controls arousal (wakefulness and alertness).

  • This is also known as the reticular formation.

• Pons—Latin for “bridge,” the pons is a way station, passing neural information from one brain region to another.

  • The pons is also implicated in REM sleep.

The Midbrain

• The midbrain is a region of the brain that helps to control vision, hearing, and other functions related to movement.

• It also plays an important role in processing sensory information from the body and sending it back to other parts of the brain.

• The midbrain is located between the forebrain and hindbrain, forming a bridge between them.

• Major components of the midbrain are the tectum and the tegmentum

  • These two act as the brain’s roof (tectum) and floor (tegmentum).

• The tectum and tegmentum govern visual and auditory reflexes, such as orienting to a sight or sound.

The Forebrain

• The forebrain is the part of the brain located at the front of the head, consisting mainly of the cerebrum.

• The forebrain is responsible for higher-level thinking such as abstract thought and decision making.

• It also plays a role in learning, memory formation, and language processing.

  • Additionally, it controls many bodily functions like movement and coordination.

• Contains the limbic system, or emotional center of the brain

• Composed of the thalamus, hippocampus, amygdala, and hypothalamus

• Thalamus—relays sensory information; receives and directs sensory information from visual and auditory systems

• Hippocampus—involved in processing and integrating memories.

• Amygdala—implicated in the expression of anger and frustration

• Hypothalamus—controls the temperature and water balance of the body; controls hunger and sex drives; orchestrates the activation of the sympathetic nervous system and the endocrine system; and it can be divided into the lateral hypothalamus and ventromedial hypothalamus, the combination of which regulates eating behaviors and body weight.

• Also contains the cerebral cortex, or the wrinkled outer layer of the brain

• This area receives sensory input (sensory cortex) and sends out motor information (motor cortex).

• The cortex covers two symmetrical-looking sides of the brain known as the left and right cerebral hemispheres.

  • These hemispheres are joined together by a band of connective nerve fibers called the corpus callosum.

• The left hemisphere is typically specialized for language processing, as first noticed by Paul Broca, who observed that brain damage to the left hemisphere in stroke patients resulted in expressive aphasia, or loss of the ability to speak.

  • This area of the brain is known as Broca’s area.

• Another researcher, Carl Wernicke, discovered an area in the left temporal lobe that, when damaged in stroke patients, resulted in receptive aphasia, or the inability to comprehend speech.

  • This is called Wernicke’s Area.

• Roger Sperry demonstrated that the two hemispheres of the brain can operate independently of each other.

  • He did this by performing experiments on split-brain patients who had their corpus callosums severed to control their epileptic seizures.

• Damage to these association areas can lead to a variety of dysfunctions, including apraxia, the inability to organize movement; agnosia, a difficulty processing sensory input; alexia, the inability to read; and agraphia, the inability to write.

NEURAL TRANSMISSION

• Nerves are bundles of neurons, the basic unit of the nervous system.

  • Neurons are cells with a clearly defined, nucleated cell body, or soma.

  • Branching out from the soma are dendrites, which receive input from other neurons through receptors on their surface.

  • The axon is a long, tubelike structure that responds to input from the dendrites and soma.

• Some neurons have a fatty coating known as a myelin sheath surrounding the axon.

• The myelin looks like beads on a string; the small gaps between the “beads” are known as the nodes of Ranvier.

• The axons end in terminal buttons, knobs on the branched end of the axon.

  • The gap between them is known as a synapse.

• A terminal button releases neurotransmitters, chemical messengers, across the synapse, where they bind with receptors on subsequent dendrites.

• Leak channels are channels that are open all the time and that simply allow ions to “leak” across the membrane according to their gradient.

• An action potential, also referred to as a nerve impulse, is a disturbance in this membrane potential.

• Excitatory neurotransmitters serve to excite the cell or cause the neuron to fire.

• Inhibitory neurotransmitters inhibit (or stop) cell firing.

• Michael Gazzaniga has not only done pioneering research in this area, focusing on split-brain patients, but also published works in cognitive neuroscience for the general reader.

ENDOCRINE SYSTEM

• The endocrine system provides another way by which various parts of our bodies relay information to one another.

  • This system works through groups of cells known as glands, which release substances called hormones.

• The primary gland is the pituitary gland, which is also known as the master gland.

• Stressful situations cause the pituitary to release adrenocorticotropic hormone (ACTH), which stimulates the adrenal glands, resulting in fight-or-flight reactions.

• The adrenal glands secrete epinephrine (adrenaline) and norepinephrine (noradrenaline).

• The thyroid gland, located at the front of the neck, produces thyroxine, which is important for regulating cellular metabolism.

HEREDITY AND ENVIRONMENT: BEHAVIORAL GENETICS

• Traits are distinctive characteristics or behavior patterns that are determined by genetics.

• Genes are the basic biological elements responsible for carrying information about traits between successive generations.

• A dominant trait is more likely to be expressed in offspring than is a recessive trait.

• A genotype is the genetic makeup of a cell or of an organism.

  • The genotype is distinct from the expressed features, or phenotype, of the cell or organism.

• Down syndrome occurs when there are three copies of the 21st chromosome, which generally causes some degree of intellectual disability.

• Huntington’s chorea is a genetic disorder that results in muscle impairment that does not typically occur until after age 40.

Next Chapter: Biological Bases: Consciousness