Biological Bases of Behavior

by

Carmen Mejia

Physiological Techniques

• Techniques used to examine the interrelationship between the brain and behavior.

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

• Cat scans (Computerized Axial Tomography) – generate cross-sectional images of the brain through X-ray-like techniques.

• MRI (Magnetic Resonance Imaging) – generates more highly detailed pictures of the brain which capture “snapshots” of the brain.

• Pet scans (Positron Emission Tomography) – techniques that allow scientist to view the brain as it is working. Provides images via diffusion of radioactive glucose in the brain.

Physiological Techniques (continued)

• Glucose – the primary “fuel” of brain cells; the more glucose being used in the given brain are, the more that area is in active use.

• The procedure allows psychologist to observe what brain areas are at work during various tasks and psychological events.

Neuroanatomy

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

1. Hindbrain2. Midbrain (limbic system)3. Forebrain (cerebral cortex)

The Hindbrain

• Oldest part of the brain.• 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).• Pons – Latin for “bridge”, the Pons is a way station, passing neural

information from one brain region to another.• Thalamus – relays sensory information; receives and directs sensory

information from visual and auditory systems; and conveys information about balance and pain.

The Midbrain• Second-oldest part of the brain in evolutionary terms.• Widely referred to as the limbic system, or emotional center of he

brain.• Composed of the hippocampus, amygdala, and hypothalamus.• Hippocampus – involved in learning and memory formation. Damage

prevents the formation of new memories (anterograde amnesia).• 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; it can be divided into the lateral hypothalamus and ventromedial hypothalamus, the combination of which regulates eating behaviors and body weight.

The Forebrain

• The most recent to develop in evolutionary terms.• Cerebral cortex (wrinkled outer layer of the brain).• Receives sensory input (sensory cortex) and sends out

motor information (motor cortex).• Consists of the two sides of the brain -> left and right

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

Left Hemisphere

• Specialized for language processing, as first noticed by Paula Broca, who observed that brain damage to the left hemisphere in stroke patients resulted in expressive aphasia (loss of the ability to speak).

• Carl Wernicke – Discovered an are in the left temporal lobe that, when damaged in stroke patients, resulted in receptive aphasia (inability to comprehend speech)

Right Hemisphere

• Process certain kinds of visual and spatial information.• Roger Sperry – demonstrated that the two hemispheres of

the brain can operate independently of each other. He did so by performing experiments on split-brain patients, had corpus callosums severed to control their epileptic seizures.

Cortex• Frontal Lobe – responsible for higher-level thought and reasoning.

Contains the primary motor cortex, which is the area responsible for making plans, forming judgments, and performing movements.

• Parietal Lobe – handles somatosensory information and is the home of the primary somatosensory cortex. Receives information about temperature, pressure, texture, and pain.

• Temporal Lobe – handles auditory input and is critical for processing speech and appreciating music.

• Occipital Lobe – processes visual input. • Much of the brain is compose of association areas (responsible for

associating information in the sensory and motor cortices). Damage can lead to:

• apraxia - the inability to organize movement.• agnosia - difficulty processing sensory input.• alexia - the inability to read.

Functional Organization of the Nervous System

• Can be divided into 2 distinct subsystems 1. Central Nervous System (CNS) - comprising the brain and the spinal cord.

2. Peripheral Nervous System (PNS) – comprising all other nerves in the body.

The brain is the central processing center for thoughts, motivations, and emotions.Nerves sending information to the brain are sensory (afferent) neurons; those

conveying information to the brain are motor (efferent) neurons.• A certain small subset of movements are controlled by direct transmission from

afferent to efferent cells at the level of the spinal cord.These responses are known as reflexes (quick and involuntary responses to

environmental stimuli).

Peripheral Nervous System• Comprises all of the nerve cells in the body with the exception of those in the CNS

(the brain and spinal cord).• Can be subdivided into; • the somatic nervous system – responsible for voluntary movement of large skeletal

muscles. • the autonomic nervous system – controls the non-skeletal or smooth muscles, such

as those of the heart and digestive tract. Can be further divided into the sympathetic and parasympathetic nervous system.1. Sympathetic Nervous System – associated with processes that burn energy.

Also responsible for the heightened state of psychological arousal known as the fight-or-flight reaction (an increase in heart rate and respiration, accompanied by a decrease in digestion and salivation).

2. Parasympathetic Nervous System – complementary opposite system responsible for ample, digestion ceases, blood transfers to skeletal muscle, and heart rate increases.

When the fight ends the parasympathetic system becomes active, sending blood to the stomach for digestion and slowing the heart rate and conserving energy.

Neural Transmission

• Nerves – bundles of neurons, the basic unit of the nervous system.• Neurons – cells with a clearly defined, nucleated cell body, soma.• Dendrites- branch out from the soma which receive input from other

neurons through receptors on their surface.• Axon – a long, tube like structure that responds to input from the

dendrites and soma. Transmits a neural message on to other cells. Neurons have a fatty coating known as myelin sheath surrounding

the axon. Myelin sheath – serves as insulation for the electrical impulses

carried down the axon and also speeds up the rate at which electrical information travels down the axon.

Neural Transmission (continued)

• Nodes of Ranvier – small gaps between the “beads.” Help speed up neural transmission.

• Terminal buttons – knobs on the branched end of the axon. • The terminal buttons come very close to the cell body and dendrites

of other neurons, but they do not touch. The gap between them is known as a synapse.

• The terminal buttons release neurotransmitters, chemical messengers, across the synapse, where they bind with receptors on subsequent dendrites.

Neural Transmission (continued)

• Neuronal communication occur both within and between cells.• Communication within cells is electrochemical.• In order for communication to occur, a cell must reach a certain level

of stimulation known as the threshold of excitation.• Threshold => action potential (nerve impulse).• Action potential travels down the axon to terminal buttons, where it

causes the release of a neurotransmitter.

(continued)

• Communication between cells happen via neurotransmitters, which bind the receptors on the dendrites of the adjacent neurons.

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

• Inhibitory messages inhibit (or stop) cell firing.• After a neurotransmitter is released and has conducted the

impulse to the next cell or cells, it is either broken down by enzymes or absorbed back into the cell that released it in a process called reuptake.

Key Neurotransmitters

• Acetylcholine – affects memory function, as well as muscle contraction, particularly in the heart.

• Serotonin – related to arousal, sleep, pain sensitivity, and mood and hunger regulation.

• Dopamine – associated with movement, attention, and reward; dopamine imbalance may play a role in Parkinson’s disease and in schizophrenia.

• GABA – an inhibitory neurotransmitter.• Norepinephrine – affects levels of alertness; a lack of

norepinephrine is implicated in depression.• Endorphins – the body’s natural painkillers.

Endocrine System• Endocrine system – provides another way by which various parts of our bodies

relay information to another.• This system works through groups of cells known as glands, which release

substances called hormones.• Hormones affect cell growth and proliferation. • Pituitary gland – master gland. Releases hormones, which in turn control

hormonal release by many glands. Controlled by the hypothalamus.• 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.

Genetics• Behavioral genetics is the application of the principles of evolutionary theory to the

study of behavior.• Traits are distinctive characteristics of 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 that is a recessive

trait. • A genotype comprises all of the possible combinations of genes. Whenever a

dominant gene is paired with a recessive gene, the dominant one typically will shoe in the phenotype, the observable result.

• The phenotype typically shows the recessive trait only when two recessive genes are paired together.

• Humans have 46 chromosomes, with one set of 23 inherited from each parent, so that half of our genetic makeup comes from each parent.

Conclusion

• Many physical and psychological characteristics are inherited.• Genes do not determine everything about us.• Our psychological, makeup is largely the result of the interaction of

the two forces => nature vs. nurture debate.- Down’s syndrome -> when there’s a break in the twenty-first

chromosomal pair, which generally cause a degree of mental retardation.

- Huntington’s chorea -> genetic disorder that results in muscle impairment that does not typically occur until after age 40. It is cause by the degeneration of the structure of the brain known as the basal ganglia.