Tamim Ahmed
Tamim Ahmed
24 Jan 2023 (1 week ago)
Araihazar, Narayanganj, Dhaka, Bangladesh
learn psychology for beginners (part- 03)

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Biological Foundations of Behavior

Introduction (Prologue):

Biological life is dependent on psychological life. If humans didn’t have hands, they couldn’t write, draw or play racquetball. If the eyes we have had no ability to detect any color, we would see everything in the world in black and white.

The brain , an important part of the body, is intimately connected with the psychological life . Dr. Penifield , a Canadian brain surgeon/surgeon, explained this in 1930 with an important experiment. Dr. Penifield performed surgery on the upper cerebral cortex of a patient while he was almost awake .

Pennyfield placed a small rod of gentle current against the brain. Then the patient felt that he was in the kitchen. He is more; He heard his little son playing in the yard and cars driving down the street.

Dr. Pennyfield’s experiments prove that the cerebral cortex is involved in our psychological experience. In addition to this, in many other ways we learn that our brain and psychological life are intimately connected.

In this chapter, various topics are directly relevant to understanding human behavior; For example, brain and nervous system, genetic mechanisms etc. are discussed. We will study this biological method; Because we are psychological beings and live in a biological machine !

Just as electronic devices are made up of electrical wires, transistors and other components; Similarly, the nervous system is made up of special cells called neurons . Through billions of neurons exchanging information in a complex process; Our body has developed a nervous system like a computer and communication network . The biological control center of this nervous system is the brain ! Although different parts of the brain handle different functions; The nervous system is managed by the brain in a coordinated way.

Figure: Human Nervous System

The human nervous system

The human nervous system consists of two major parts. One part is called the brain and the other is the Spinal Cord ; which is the cranial nerve; which is located behind the crown and inside the vertebrae of the spine.

Many nerves extend outside the brain and form the second part of the spinal nervous system; Which extends to the end of the body, this part is called the peripheral nervous system (peripheral nervous system).

Brain communicates with different organs spread in the body through nerves . The brain also uses endocrine glands to maintain communication with the body . These glands act as carriers of secret chemicals called hormones . Hormones travel through the body’s bloodstream.

Hormones regulate our behavior by stimulating the functions of various organs of the body. Hormones are a powerful substance in the brain; But it influences or controls us in a more sporadic way than in a definite way.

Nervous System: Biological Control Center:

The nervous system is a very powerful body’s communication medium, like a computer. The brain not only thinks and calculates like a computer but can also control emotions and desires! The brain is attached to the spinal cord ; A bunch of long nerves lie inside the spinal cord. Each nerve leaves or enters the brain and spinal cord and connects the brain to every part of the body. Some of its nerves send messages from the body to the brain about what is happening in the body.

Other nerves carry messages/instructions from the brain to body functions and control the person’s behavior. Without the nervous system, the body would have become a numb object without consciousness; Unfeeling and unable to do anything. In other words; Without the nervous system there would be no psychological life .

Neurons: Primary Units of the Nervous System

Computers, telephone systems, and other electronic devices are made up of wires, microphones, transistors, and other electronic components that can conduct and conduct electricity. The nervous system is made of exactly the same material.

The important individual unit of the nervous system is the nerve cell or neuron.
In 1900, the scientist Santiago (Santiago) discovered the neuron. Since then, many studies have been done on this component of the nervous system.

Parts of Neurons

Neurons range in size from less than a millimeter to more than a meter in length; But all neurons are divided into three important parts:

Parts of Neurons
  1. The cell body: The round or oval part of the neuron consisting of nucleus, plasma membrane, cytoplasm is called cell body The cell body stores the material and also contains nutrients for the cell.
  2. Dendrites: Branches that extend from the cell body and receive messages from other neurons; It is called dendrite .
  3. Axon (Axons): The long fiber-like part originating from the cell body is called axon. The thin covering around this axon is called neurilemma. Between these axons and neurilemma is a layer called myelin! The end of the axon, the branch, divides into the axon terminal . It is through these terminals that nerve impulses or messages are sent by synapses to the dendrites of other neurons .

Neurons together form a complex control system like a child’s toy. The human nervous system consists of 100 million neurons! That’s almost more than all the stars in our galaxy.

Each neuron can send or receive messages with other neurons anywhere from 1,000 to 10,000 times. It is said that our body has trillions of trillions of neurons. This number is not the main thing; The important point is that neurons make us intelligent people by creating a network of powerful connections.

We have to take special care that neuron and nerve are not the same. Many people make this mistake. Actually, a nerve is a group of numerous or sometimes thousands of neurons.

Neural Transmission

Neurons are the conducting wires of the nervous system—the telephone lines that transmit our speech; Similarly, neurons also send messages (Neural Transmission). But; Neurons are living wires; Which has the ability to provide electricity by itself! It also has batteries that provide power to the nervous system.

Neurons can act as batteries and conductors because; Like all other living cells, it is wet. The inside of the neuron is filled with one type of fluid and the outside is soaked in a different type of fluid! Different chemicals, ions, different particles are dissolved in this liquid juice which carry either positive or negative electronic/electrical charge.

But rather than the positive (+) ions inside the neuron; Because of the high amount of negative (-) air; Turns all neurons into a negative charge . This negative charge inside the neuron is attracted by the positive charge outside; Just as the negative end of a magnet is attracted to the positive end of another magnet.

Thus the neuron cell membrane becomes saturated with positive ions, especially sodium (Na+) ions! When neurons are at rest, there are 10 times more positively charged sodium ions outside the neuron membrane than inside ! This is the source of the neutron’s electrical energy; Where the neuron membrane has a positive charge on one side and a negative charge on the other side.

in salty seawater to remember which side of the neuron’s membrane has more sodium ions; Being high in sodium can be noted. Because the fluid outside the neuron; Like seawater, it contains large amounts of sodium, along with other chemical elements.

Why is that? The reason for this – according to the theory of evolution, all organisms were born in the sea water and then the organisms emerged from the ocean! As a result, they brought the salt water of the sea with their bodies. This salty fluid resides in the spaces between the body’s cells.

Many ions can move freely through the cell membrane of a neuron But other ions such as sodium ions cannot move freely ! For this reason, the normal state of this membrane is called semipermeable; However, some substances can pass through all membranes.

This is why the inner negative ion is equal to the outer positive ion. So neurons are electrically polarized in normal/resting state .

When the membrane is stimulated by its adjacent neuron, the permeability of the neuron membrane immediately closes. Important positively charged sodium ions rush towards the neuron at high speed. As a result; The neuron is no longer negative (-), a process called depolarization.

Depolarization creates an eccentric current chain; Which is called action potential (action potential).

Once started from the resting membrane potential until fully returned to the resting potential; That electrical signal is created, so a complete action potential! Through this, the neuron stimulation contains, nature, intensity, time etc. all the information; Coordinates information transmitted or received by the central nervous system.

Ramon y Cajal ( Ramon y Cajal) thought; Neural transmission was always based on the all – or -none principle ! This means that nerve impulses flow from one neuron to another; When the depolarization is strong enough to drive an action potential .

He also thought that; Once action potentials are initiated they are all the same. Neuroscientists have believed in this idea for 100 years; But now it is known that messages of neurons always flow through graded electrical potentials .

Myelin Sheath and Neural Transmission

The white covering of the axon is called the myelin sheath. It covers the axon with a layer of jelly! Axons emerge from this layer of myelin; And this layer increases the speed at which the axon conducts the neuron’s impulses. The thickness of the myelin sheath increases with puberty.

Interestingly, from childhood to adulthood, the thickness of myelin in some parts of the brain is greater in girls than in boys. As a result, girls are ahead in many areas in the neurological process of the brain.

  1. Central nervous system
  2. Peripheral nervous system
  3. Divisions of the Peripheral Nervous System
  4. Division of the Autonomic nervous system
Divisions of the Nervous System

Figure 1 above shows that our complex nervous system is divided or arranged into different parts. The two main parts of the nervous system are 1. Central nervous system and 2. Peripheral nervous system.

Central Nervous System:

The central nervous system consists of the brain and spinal cord . The brain controls the functioning of the nervous system. The main function of the spinal cord is to exchange messages between the body and the brain. But the spinal cord can also provide basic information on its own. For example; If it suddenly touches a hot object, it withdraws itself. When the hot object causes neural stimulation, the interneuron sends the message to another neuron, thereby moving the body/organ through muscle contraction and relaxation.

Peripheral Nervous System :

Nerves that branch out from the brain and spinal cord to all parts of the body are called the peripheral nervous system . The peripheral nervous system transmits messages from the body to the central nervous system. Again it functions according to the central nervous system to different parts of the body such as; Also sends messages to muscles, glands .

Messages can only flow in one direction through a synapse. Therefore, the part of the neuron through which the message from all the body returns to the central nervous system is called afferent neuron (Afferent neurons); Again, the separate part or set of neurons through which the message returns from the central nervous system to the body is called efferent neurons.

Divisions of the Peripheral Nervous System :

The peripheral nervous system is again divided into two parts. 1. Somatic nervous system and 2. Autonomic nervous system
Somatic nervous system carries messages from the central nervous system to the brain to control the body. It transports messages for both our voluntary actions and involuntary actions. The carotid-spinal nerve also transports messages from sensory receptors to the central nervous system .

Autonomic nervous system consists of nerves that send messages to the heart, stomach, intestines, etc. The synaptic nervous system plays an important role in performing two main functions. That is:

1. Essential body function (Essential body function): Synaptic nervous system synergistically accelerates the function of many organs of the body. Various functions such as heartbeat, breathing, digestion, sweating, sexual arousal are controlled by this synaptic nervous system .

2. Emotions: The synaptic nervous system plays an important role in emotions. For example, if someone has a headache, diarrhea, stomach ache, he becomes very worried or agitated. It is the synaptic nervous system that causes such sensations.

We actually have no control over the synthetic nervous system! Because; The autonomic nervous system conducts its work autonomically .

Divisions of the Autonomic nervous system:

The autonomic nervous system consists of two types of nerves: sympathetic and parasympathetic . Both these types of nerves work differently according to the type of work and the situation.

Sympathetic nerves enable the body to heal physical or emotional conditions. Increases the ability of our organs to heal under sympathetic nerve stimulation . Function of sympathetic nerves:

  1. Eyes open to light.
  2. Reduces redness.
  3. Increases heart rate .
  4. Expands the thorax and increases air pressure in the lungs .
  5. Digestion inhibits the digestive system.
  6. Releases glycogen or sugar from the liver .
  7. Epinephrine is released from the adrenal gland .
  8. Prevents urethral stricture [results in urination]
  9. Increases muscle tension and blood flow .

The function of the parasympathetic nervous system is similar to that of the sympathetic nervous system; But the opposite kind. The parasympathetic nervous system slightly reduces our body’s ability to respond to stimulation. Function of Parasympathetic Nerve:

  1. Closes the eyelids .
  2. Helps in digestion by increasing salivation.
  3. Reduces heart rate .
  4. Reduces air pressure in the lungs by compressing the thorax .
  5. Digestion activates the digestive system.
  6. It helps in the digestion of fat by secreting bile from the liver .
  7. Inhibits the secretion of epinephrine from the adrenal gland .
  8. Constricts the urethra. [results in no urination]
  9. Reduces large muscle tension and blood flow .

Structure and Function of the Brain

Brain is the basic foundation of psychological life . Different functions are carried out by different parts of the brain. We have to remember that all mental activities require the coordination of multiple parts of the brain. No task can be handled by just one part of the brain. The brain is divided into 3 main parts – 1) Forebrain; 2) Midbrain; 3) Hindbrain . These main sections are further subdivided into different sections.

Structure and function of the brain

Hindbrain and Midbrain: Housekeeping Chores and Reflexes

The hindbrain is the rearmost part of the brain located at the base of the crown/skull . The primary function of the hindbrain is to properly regulate all of the body’s regular major activities. The medulla, pons and cerebellum are the 3 main parts of the hindbrain .

The medulla is the most posterior part of the brain ie the spinal cord through which the brain enters; Just above it is the medulla. The medulla controls our breathing, our ability to stand upright, and our reflexes! Just above the medulla is the pons. The pons controls balance, hearing, and some parasympathetic functions.

The cerebellum consists of two spherical lobes and lies just superficial to the pons. in complex organ circulation; And where coordination is achieved by knowing and remembering different information, the cerebellum plays a very important role.

Numerous neurons together form the reticular formation that pervades the medulla and pons! Although the reticular formation is thought to be a single nervous system, it is actually composed of many nervous systems ; which are used in various nerve impulses. These different parts of the reticular formation are influenced by different parts of the brain.

Above the hindbrain lies the midbrain ! The midbrain helps control such functions related to the senses . For example; The midbrain plays an important role in vision (seeing) and hearing . Again , the midbrain plays an important role in the coordination and balance of various muscles!

Forebrain: Cognition, Motivation, Emotion and Action

For psychologists, the most interesting part of the brain is the forebrain. Structurally, the forebrain consists of 2 distinct regions. One of these regions includes the thalamus, hypothalamus, and most of the limbic system, located above the hindbrain and midbrain (see Figure 1) . The other region consists of the cerebral cortex. These 2 regions of the forebrain are not only structurally different; Rather, their activities are also different.

Thalamus, hypothalamus and limbic system

The thalamus sends the impulses from the sensory organs of the body to the appropriate parts of the brain and connects them with the upper and lower centers of the brain .

It is clearly known through a recent research that; The thalamus plays a major role in processing incoming sensory information along with the upper brain structures.

Although the hypothalamus is small, it is an important part of the brain! The hypothalamus is located below the thalamus and just in front of the midbrain. The hypothalamus is intimately involved with our motives and emotions. Also; The hypothalamus also plays an important role in regulating body temperature, sleep, endocrine gland activity, and immunity .

The hypothalamus also controls the secretion of gastric and intestinal juices; And helps maintain the normal speed and rhythm of body functions such as blood pressure and heartbeat ! So the hypothalamus is directly connected with the function of the synaptic nervous system of the brain.

The limbic system is made up of 3 important parts.

  1. Amygdala (The amygdala) : The amygdala plays a key role in emotions and aggression! It plays a major role in forming memories about emotionally charged events.
  2. The hippocampus: The hippocampus brings important cognitive components to the processing of emotional information! The hippocampus also plays a major role in forming new memories. That’s why; If the hippocampus is damaged, people’s memory can be lost or damaged.
  3. The cingulate cortex: The cingulate cortex works with the hippocampus to process cognitive information related to emotion.

Cerebral Cortex: Sensory, Cognitive and Motor Functions:

The word cortex means “bark or skin”. The largest part of the forebrain is the cerebral cortex . Associated with many aspects of the cerebral cortex , such as; Conscious experience, voluntary action; Language, intelligence, etc. are what make us human.

Its upper or outer thin layer is made up of a dense covering of millions of neurons. Therefore; According to the color of the cell body, its outer color is gray which is known as gray matter .

On the other hand, the area of ​​the cerebrum below the cortex is identified as white matter! Because it is mainly composed of axons of cortical neurons. These neurons appear white because of their fatty myelin coating! Which is known as white matter.

Lobes of the Cerebral Cortex

Because of the great importance of the cerebral cortex in human psychological functioning , there is a need for a more detailed understanding of the cerebral cortex. The cerebral cortex has four parts or lobes . 4 parts are:

  1. Frontal lobe (Frontal Lobes) ; The frontal lobe extends from the part of the skull behind our forehead to the middle of the head! It plays a key role in our thinking! Besides remembering, deciding, speaking; Predicts future outcomes, controls actions, controls movement, and senses.
  2. Parietal lobe (Parietal Lobes) ; Right behind the frontal lobes of the head are the parietal lobes. Different parts of our body like; The parietal lobe can understand and control what the hands and feet are doing.
  3. Temporal lobes (Temporal Lobes) ; Temporal lobes are located between the base of the brain below the frontal and parietal lobes. That is; It is located near the ear and inside the skull! As it is located near the ear, the temporal lobes are involved in hearing.
  4. Occipital Lobe (Occipital Lobes) ; The occipital lobes are located at the base of the back of the head! It takes information through the eyes and analyzes it.
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