Chapter 3: Physiological Bases of Human BEhavior

Chapter 3

PHYSIOLOGICAL BASES OF HUMAN BEHAVIOR

INTRODUCTION

                Organism as diverse as humans and other creatures share many biological processes. However, their unique behavioral capacities depend on the differences in their physiological make- up.

                You and I have a larger repertoire of behavior different from the other grades of beings because we come equipped with a more complex brain and nervous system. The activity of the human brain is so complex that no one has ever come close to duplicate it.

                Your nervous system contains many cells that are busy integrating and relaying information. This could be the reason why many psychologists dedicated their time in exploring the biological bases of human behavior (Weiten, 2008).

                In this section, we take a closer look at the communication in the nervous system.

NERVOUS TISSUE: The Basic Hardware

                Your nervous system is a living tissue composed of cells. The cells in the nervous system fall into two major categories: GLIA AND NEURONS or NERVE CELL.

Neuron

It is the individual cells in the nervous system that receive, integrate and transmit information.  The basic unit of the nervous system is of differing shapes, sizes and function. There are approximately trillion of neurons throughout the body which primarily involved in the control of body activities and behavior.

Parts of Neuron

                CELL BODY/SOMA - contains the nucleus which provides              nourishment and insulation.

                DENDRITES- receive signals from the neighboring neurons and carry them back to the cell body.

                AXONS- relatively longer than the other neurons which                carries messages to the other neuron. Axons terminate in       small bulges called TERMINAL BUTTONS that send messages      to other neurons.

Myelin sheath- these are fatty tissues and proteins surrounding the axons. It prevents interference from electrical signals generated in adjacent axons. You may have heard that the brain consists of the gray and white matter. Gray is the color of the cell bodies and white is the color of myelin sheaths.

Kinds of Neuron According to Speed

                Impulses in the fastest neuron move at a rate of 110 meters per second; in the slowest, 0.5 meters per second. The speed of condition is matched by the thickness of the myelin sheath. The more myelin sheath, the faster the conduction. (Kahayon, 2004)

Kinds of Neuron According to Basic Function

1. Sensory (Afferent neurons)- conveys information from the body’s sense organs to the brain and spinal cord. This is initiated by the receptors- specialized cells in the sense organs, muscles, skin and joints that detect physical or chemical changes and convert these into impulses that pass along the sensory neurons.
2. Motor (Efferent neurons) carry impulses away from the brain and spinal cord to the reacting organs, the muscles and glands.
3. Association/Interneurons- connect the neurons together and and combine the activities of the sensory and motor neurons.

GLIAL CELLS- (Greek word “glia” means glue) these are the non-neural cells that surround the neurons and ensure that it can perform its functions while holding them in place.

                When the neural impulse reaches an axon’s terminal buttons, it triggers the release of chemical messengers called neurotransmitters. The neurotransmitter molecules diffuse across the synaptic cleft and binds through receptor sites on the postsynaptic neuron. A specific neurotransmitter can bind only to receptor sites that its molecular structure will fit into, much like a key must fit the lock (Weiten, 2008).

HOW THE NEURONS FIRE

ALL-or-NONE-LAW

                The firing of neurons occurs at either in full strength or not at all. After each firing, the neuron needs time to recover called the refractory period. During this period, action potential is much less likely to occur ( Miranda, 2008).

                Various neurons transmit impulses at different speeds. Most often, thicker axons transmit neural impulses faster than the thinner ones.

RESTING STATE

        This is the state of the neuron when not firing a neural impulse and when the message arrives, gates in the cell membrane open briefly to allow positively charged ions to rush in rates as high as 100million ions per second (Feldman, 2010).

ACTION POTENTIAL

                This is the time when there is a release of the neural impulse consisting of a reversal of the electrical charge within the axon. After it has occurred, the neuron cannot fire again no matter how much stimulation it receives.

THE SYNAPSE: SENDING THE MESSAGE TO OTHER CELLS

                Two neurons do not actually meet. They are separated by the synaptic cleft which is a microscopic gap between the terminal button of one neuron and the cell membrane of another neuron.

                In this situation, the neurons that send a signal across the gap is called pre-synaptic neuron and the neurons that receive the signals is called the post-synaptic neuron.

NEUROTRANSMITTERS: MESSENGERS OF THE NETWORK

                These are chemicals that carry messages across the synapse or cell body of a receiving neuron.

                It may vary on how intense its concentration that can cause a neuron to fire when it is secreted in one part of the brain and can inhibit the firing of neurons when it is produced by another part (Apruebo, 2009).

                Miranda (2008) presented the five key neurotransmitters according to location and functions.

Neurotransmitter Functions	Location	Functions
1. Acethylcholine	Brain, spinal cord ANS, selected organs	Releases at neuromuscular junctions; involved in memory
2. Norephinephrine	Brain, spinal cord, selected organs	Regulates physical logical arousal; learning, memory and emotion
3. Dopamine	Brain	Linked to muscle activity, emotional arousal, learning memory
5. Gamma Amino	Brain, Spinal cord	Involved in motor behavior and arousal           Butyric Acid (GABA)

ORGANIZATION OF THE NERVOUS SYSTEM

                It is important to understand the organization and functions of the nervous system and its mutually dependent systems and divisions.

A.      Central Nervous System (CNS): Brain-Spinal Cord

  

  BRAIN- Protection: Skull                                                                                  SPINAL CORD-     

                                                                                                                     Protection: Vertebrae

   

                                B. Peripheral Nervous System (PNS):  Extension of CNS

 

                 Somatic System                                  Autonomic System

           Reacts to outside stimuli                          Maintains homeostasis

 

                                                                 Sympathetic System              Parasympathetic System

Response: Involuntary                Response: Normal

 

THE PERIPHERAL NERVOUS SYSTEM

                It is made up of all those nerves that lie outside the brain and spinal cord. The peripheral nervous system can be divided into somatic nervous system and the autonomic nervous system.

The Somatic Nervous System

                This is made up of nerves that connect to voluntary skeletal muscles and to sensory receptors. These nerves are the cables that carry information from receptors in the skin, muscles and joints to the central nervous system to the muscles.

These functions require two kinds of nerve fibers:

ü      AFFERENT nerve fibers are axons that carry information inward to the central nervous

        system from the periphery of the body.

ü  EFFERENT nerve fibers are axons that carry information outward from the central nervous system to the periphery of the body (Weiten, 2009).  

The Autonomic Nervous System

                It is concerned with parts of the body that keeps us alive- the heart, blood vessels, glands, and other organs that operate involuntarily without our awareness.

                The autonomic nervous system mediates much of the physiological arousal when people experience emotions. Based on the above discussion, it is divided into sympathetic and parasympathetic division.

The Sympathetic Division

                It is primarily located on the middle of the spinal column—running from near the top of the ribcage to the waist area.  It is usually called as the “fight-or-flight system” because it allows people and animals to deal with different kinds of stressful events.              Emotions during these events might be anger (hence, the term fight) or fear (the term flight, obviously) or extreme joy and excitement. Yes, even joy can be stressful. The sympathetic division’s job is to get the body ready to deal with the stress (White, 2009).

The Parasympathetic Division

                If the sympathetic division can be called the fight-or-flight system, the parasympathetic division might be called the eat-drink-and-rest system.

                 The neurons of this division are located at the top and bottom of the spinal column, on either side of the sympathetic division neurons (para means “beyond” or “next to” and in this sense refers to the neurons located on either side of the sympathetic division neurons).

                The parasympathetic division’s job is to restore the body to normal functioning after a stressful situation ends. It slows the heart and breathing, constricts the pupils and reactivates digestion and excretion.

                Signals to the adrenal glands stop because the parasympathetic division is not connected to the adrenal glands. In a sense, the parasympathetic division allows the body to put back all the energy it burned—which is why people are often hungry after the stress is all over. It also functions on most ordinary, day-to-day functioning such as regular heartbeat, normal breathing and digestion (White, 2009).

THE CENTRAL NERVOUS SYSTEM

Brain

                This is the true core of nervous system. It takes information from senses, processes it, makes decisions and sends commands to the rest of the body (White, 2009).

Modern Brain Scanning Techniques: Providing Snapshots of its Internal Works

1. Electroencephalogram (EEG)- records electrical activity in the brain through electrodes placed on the outside of the skull. The device is used to assess brain damage, epilepsy and other problems.
2. Positron Emission Tomography (PET)- scans show the biochemical activity within the brain while hearing, seeing, thinking and speaking.

        It measures the amount of glucose in various areas of the   

      brain, and then sends this information to a computer for 

      analysis.

3. Functional Magnetic Resonance Imaging (fMRI)- scans provide a detailed, three-dimensional computer-generated image of the brain structures and activity by aiming a powerful magnetic field at the body. Through fMRI, it is possible to produce a vivid, detailed image of the functioning of the brain.
4. Computerized/Computed Tomography (CT) scan- produces a three-dimensional image obtained from X-rays of the head that are assembled into a composite image by a computer. It provides valuable information about the location and extent of damage involving stroke, language disorder or loss of memory.
5. Transcranial Magnetic Stimulation (TMS)- one of the newest types of scan. By exposing a tiny region of the brain to a strong magnetic field, TMS causes a momentary interruption of electrical activity. The procedure is sometimes called a “virtual lesion” because it produces effects analogous to what would occur if areas of the brain were physically cut. The enormous advantage of TMS, of course, is that the virtual cut is only temporary (Fedman, 2010,/Santrock,2005,/ White, 2009).

MAJOR PARTS OF THE BRAIN

                A human brain which can easily be held in one hand, weighs about 1,350 grams or 3 pounds, and has the consistency of a firm Jell-O. The brain is protected by a thick skull and covered with thin, tough, plastic -like membranes.

                 If shot in the head, he may or may not die depending on which area is damaged. For example, damage to an area in the forebrain would result in paralysis, damage to an area in the midbrain would result in coma but damage to an area in the hindbrain would certainly result in death (Plotnik,et.al., 2008).

                Let’s begin to explore the brain by looking into the major areas: the forebrain, the midbrain and the hindbrain.

The Hindbrain

                It is located at the skull’s rear, which is the lowest portion of the brain. The hindbrain has three identified structures: the medulla, the pons and the cerebellum.

• Medulla- it controls some sensitive body functions such as breathing, heartbeat, blood pressure and body posture. Medulla begins where the spinal cord enters the skull.

• Pons- joining two halves of the cerebellum, this lies adjacent to it containing large bundles of nerves, the pons acts as neurotransmitter of motor information, coordinating muscles and integrating movement between the right and left halves of the body. It is involved in regulating sleep ( Feldman, 2010).

• Cerebellum- extends from the rear of the hindbrain, just above the medulla and behind the pons. It consists of two-rounded structures thought to play important roles in motor coordination (Santrock, 2005).  It is also involved in several intellectual functions ranging from the analysis and coordination of sensory information to problem solving (Feldman, 2010).

                The cerebellum is also involved in performing timed motor responses such as those needed in playing games or sports, and in automatic or reflexive learning, such as blinking the eye to a signal which is called as classical conditioning (Plotnik et al., 2008).

The Midbrain

                It is located between the hindbrain and the forebrain. It is an area in which many nerve-fiber systems ascend and descend to connect the higher and lower portions of the brain.

                In particular, the midbrain relays information between the brain and the eyes and ears. The ability to attend to objects visually, for example, is linked to one bundle of neurons in the midbrain.

                Parkinson’s disease, deterioration of movement that produces rigidity and tremors, damages a section near the bottom of the midbrain (Santrock, 2005).

               

Two systems of the midbrain that are of special interest:

Reticular Formation- diffused collection of neurons involved in stereotyped patterns of behavior such as walking, sleeping or turning to attend to a sudden noise.

Small groups of neurons that use the neurotransmitter serotonin, dopamine and norepinephrine. Although these two groups contain relatively few cells, they send their axons to a remarkable variety of brain regions, perhaps explaining their involvement in high-level, integrative factors (Santrock,2005).

The Forebrain

                The forebrain is the largest part of the brain, has left and right sides that are called hemispheres.

                The hemispheres, connected by a wide band of fibers, are responsible for an incredible number of functions, including learning and memory, speaking and language, having emotional responses, experiencing sensations, initiating voluntary movements, planning and making decisions (Plotnik et al., 2008).

THE CEREBRAL CORTEX: Our New Brain

                In Latin, cortex means “cover” which is referred to as the new brain because of its relatively recent evolution.

                It consists of a mass of deeply folded, rippled, convoluted tissue.

                Although only about one-twelfth of an inch thick, if flattened out, cover an area more than two feet square (Feldman, 2010).

                It is the highest region of the forebrain where the highest mental functions, such as thinking and planning takes place (Santrock, 2005).

                The cortex is divided into two hemispheres called CEREBRAL HEMISPHERES, which are connected by a thick, tough band of neural fibers (axons) called CORPS CALLOSUM (literally means “hard bodies” as calluses on the feet are hard (White, 2009).

               

The cortex has four major sections called LOBES.

1. Frontal lobe-(Broca’s Area) lies at the front center of the cortex; involved with personality, emotions and motor behaviors.
2. Parietal lobe- area at the top of the head functions with perception and memory experiences; also involved in spatial location, attention and motor control.
3. Temporal lobe- (Wernickes’s Area) found in the lower center portion of the cortex just above the ears which involved with hearing, language processing and memory.            
4. Occipital lobe- found at the back of the head which is involved with vision.

                The four sets of lobes are physically separated with deep grooves called SULCI.

               

                There are three main areas in the cerebral cortex: (1) the motor areas, (2) the sensory areas, and (3) the association areas.

1. Motor Areas- Located just behind the frontal lobes which are largely responsible for the body’s voluntary movement. 

        For example, the control movements that is relatively large        scale and requires little precision, such as the movement of            a knee or hip, is centered in a very small space in the motor        area.

                        In contrast, movements that must be precise and            delicate, such as facial expressions and finger movements               are controlled by a considerably larger portion of the motor        area. (Feldman, 2010)

2. Association Areas- Areas within each lobe of the cortex is responsible for the coordination and interpretation of information as well as higher mental processes such as thought, language, memory and speech. (White, 2009).
3. Sensory Areas- Areas of the cerebral cortex that includes three regions: (1) processes information about body sensations including touch and pressure, (2) relating to sight and (3) relating to sound (Feldman, 2010).

THE LIMBIC SYSTEM:  Old Brain

                The limbic system (the word limbic means, marginal) and its structures are found in the inner margin of the upper brain which includes the thalamus, hypothalamus, and amygdale. In general, the limbic system is involved in emotions, motivation and learning (White, 2009).

                The limbic system is often referred to as our primitive, or animal brain because its same structures are found in the brains of animals that are evolutionarily very old, such as alligators (Plotnik et al.,2008).

Thalamus (inner chamber)

                The part of the brain located in the middle of the central core that acts primarily to relay information about senses (Feldman, 2010).

Hypothalamus (below the inner chamber)

                The hypothalamus regulates body temperature, thirst, hunger, sleeping and waking, sexual activity and emotions. It seats right above the pituitary gland, which is called as the “master gland” because it controls the functions of all the other endocrine glands that will be discussed later in this chapter. ]

                The hypothalamus controls the pituitary, so the ultimate regulation of hormones lies with the hypothalamus (White, 2009).

Hippocampus (Greek word for sea horse)

                Curved structure located inside the temporal lobe which is responsible for the formation of long-term memories and the storage of memory for location of objects (White, 2009).

Amygdala (almond)

                It is the area of the brain located near the hippocampus. Amygdala receives input for all the senses.

                It plays a major role in evaluating the emotional significance of stimuli and facial expressions, especially those involving fear, distress and threat (Plotnik et al., 2008).

THE CHEMICAL CONNECTION: THE ENDOCRINE GLANDS

               

Another body’s communication system is the endocrine system. ENDORINE SYSTEM is a chemical communication network that sends messages throughout the body via the bloodstream (Feldman, 2010).

                Glands are organs in the body that secrete chemicals. Some glands, such as salivary glands and sweat glands secrete their chemicals directly onto the body’s tissues through tiny tubes, or ducts. This kind of gland affects the functioning of the body but doesn’t really affect behavior.

                Other glands called ENDOCRINE GLANDS, which have no ducts and secrete their chemicals directly into the bloodstream. The chemicals secreted by this type of gland are called HORMONES (White, 2009).

A. Pituitary Gland: The Master of Hormonal Universe (White, 2009)

Pituitary gland is located in the brain itself, just below the hypothalamus.

It is called as the master gland because it is the one that controls or influences all of the other endocrine glands.

                The pituitary gland is divided into the anterior (front) and posterior (back) sections.

·               Anterior Pituitary

It regulates growth through secretion of growth hormones and produces hormones that control the adrenal cortex, pancreas, thyroid and gonads.

·                                 Posterior Pituitary 

                The rear portion of the pituitary gland that regulates water         and salt balance

B. Pineal Gland (White, 2009)

                Pineal gland is also located in the brain near the back. It secretes hormones called MELATONIN, which regulates the sleep-wake cycle.

C. Thyroid Gland (White, 2009)

                The thyroid gland is located inside the neck and secretes hormone called THYROXIN that regulates metabolism.

D. Pancreas (White, 2009)

                The pancreas controls the level of blood sugar in the body by secreting INSULIN and GLUCAGONS.  If the pancreas secretes too little insulin, it results in diabetes. If it secretes too much insulin, it results to hypoglycemia or low blood sugar, which causes a person to feel hungry all the time and often become overweight as a result.

E. Gonads (White, 2009)

                The gonads are sex glands, including the ovaries in the female and testes in the male. They secrete hormones that regulate sexual behavior and reproduction. They do not control all sexual behavior, though. In a very real sense, the brain itself is the master of the sexual system—human sexual behavior is not controlled totally by instincts and the actions of the glands as in the animal world but also by psychological factors such as attractiveness.

F. Adrenal Glands (White, 2009)

                Everyone has two adrenal glands, one on top of each kidney. By etymology, renal comes from the Latin word meaning “kidney”, and ad is Latin for “to”, so adrenal means “to or on the kidney”.

                Each adrenal gland is divided into two sections, the ADRENAL MEDULLA and the ADRENAL CORTEX.

 It is the adrenal medulla that releases ephinephrine and norepinephrine when people are under stress and that aids in sympathetic arousal.

                The adrenal cortex produces over 30 different hormones called CORTICOIDS (also called steroids) that regulate salt intake, help initiate and control stress reactions and also provides a source of sex hormones in addition to those provided by the gonads.

                One of the most important of these adrenal hormones is CORTISOL, released when the body experiences stress both physical stress (illness, surgery, or extreme heat or cold) and psychological stress (such as emotional upset)