LESSON-2.1.1_The-Neurological-basis-of-Behavior_-The-Neuron.pdf

CHAPTER 2 BIOLOGICAL BASIS OF BEHAVIOR Intended Learning Outcomes: At the end of this chapter, students should have: 1. Described the essential functions and structures of biological-psychologic...

CHAPTER 2 BIOLOGICAL BASIS OF BEHAVIOR Intended Learning Outcomes: At the end of this chapter, students should have: 1. Described the essential functions and structures of biological-psychological systems as the basis of human behavior; 2. analyzed the relationship between physiology, mental processes, and behavior; and 3. related to the body's neural, hormonal, and genetic mechanisms toward behavior and mental processes. What is Biological Psychology? Biological psychology has ancient roots, dating back to around 3000 BCE when people practiced Trepanation—drilling holes in the skull—to treat neurological and mental issues. However, it wasn't until the 20th century that the field became truly scientific, thanks to advances in brain research and technological advancement. This led to the discovery of important concepts like neurons and synapses to name a few. As our understanding grew, researchers began to combine various scientific approaches, including studies of animal behavior, to better explain the biological-psychological aspects of human behavior. Biological psychology is also known as biopsychology, psychobiology, physiological psychology, or behavioral neuroscience. It studies the evolutionary, physiological, and developmental processes of behavior and experience. (Kalat, 2017). Specifically, it studies the cells, genes, and organs of the body and the physical and chemical changes involved in behavior and mental processes. For example, everything you do is a result of your brain at work. It’s not your eyes that actually see—it's the visual cortex in your brain. The eyes simply send visual information to the brain, and the visual cortex interprets it so you can "see" things, like an apple. The brain and other organs play a big role in shaping behavior too. For instance, if your brain has low serotonin levels, you might feel depressed or anxious. This way of understanding behavior through biology is known as the biological approach. In this study, we’ll focus on three key biological systems that control our feelings, thoughts, actions, and overall body functions: the neural system, the nervous system, and the endocrine system. Let's begin with understanding the neurological basis of behavior through the neurons and synapses. Lesson 2.1 THE NEUROLOGICAL BASIS OF BEHAVIOR: Neurons and Synapses Intended Learning Outcomes: At the end of the session, students should have: 1. described the structures and functions of a neuron and  2. discussed the relationship between neural communication and behavior Lesson 2.1.1. The Neurons ABSTRACTION The Neuron It is necessary to understand the neuron to understand one's mind and that of others. The nervous system is composed of two types of cells: neurons and glial cells. The concept of a neuron can be traced back to the work of Sir Santiago Ramón y Cajal, a Spanish histologist who is distinguished from his significant accomplishments. He established the neuron as the basic unit of nervous structure. He is also the father of Neuron Theory, which asserts that neurons are discrete (or distinct), autonomous cells that interact but are not physically connected. Neurons send electrical signals to communicate with one another. Just think of these neurons as a plug and a socket. Plugging in triggers the socket a signal along the wire and produces some effects, such as turning the light on. The word neuron comes from the Greek word nevronas, which means a sinew, cord, or nerve. Just like the muscle cells are used for movement, neurons (or nerve cells) perform executive functions such as reception, conduction, and transmission of nerve reactions or impulses as a response to a stimulus (such as touch, pain, heat, cold, odor, or light). There are approximately 90 billion nerve cells, 100 trillion neural connections, billions of nerve fibers, and where brain information travels 268 miles per hour in the human brain. They come in two major types, namely, neurons and glia. We will focus more on the neurons as the basic functional units of the nervous system. Structures and Functions of the Neurons. A neuron is like a tree that has roots (axon), trunk (soma), and branches (dendrites). These parts represent the main structural components for transmitting those signals to other cells. a. Dendrites. It is a Greek word for “tree”. These branching fibers receive signals from other cells. b. Cell body, or soma. It is a Greek word for “body”; plural: so- mata. It contains the nucleus, ribosomes, and mitochondria responsible for biochemical processes and integration of synaptic input received before transmitting the signal by the axon. c. Axon. It is a Greek word for "axis". It is a thin fiber of constant diameter that conveys an impulse toward other neurons, an organ, or a muscle. d. Myelin Sheath. It is the axon's insulating material. Patients with multiple sclerosis have vision, arm or leg movement, sensation, or balance problems caused by damage in the myelin sheath. e. Nodes of Ranvier (RAHN-vee-ay). It facilitates the rapid conduction of nerve impulses. f. Presynaptic terminal. It is a French word for “button”. It is also known as an end bulb or bouton), where the axon releases chemicals that cross through the junction between that neuron and another cell. Types of Neurons. Neurons come in various forms, shapes, sizes, and locations. They can be categorized structurally and according to the location of the cell body concerning the axon and dendrites, as well as the number of dendrites and axon branches. a. Unipolar neuron. It is a neuron with uni or one process (axon only) extending from its cell body, composed of an axon. These neurons are  found in spinal and cranial nerve ganglia (cluster of cell bodies in the peripheral nervous system) b. Bipolar neuron. It is a neuron with "bi" or two processes (one axon and one dendrite) extending from its cell body. These neurons are found in the retina, the roof of the nasal cavity, and the inner ear. c. Multipolar neuron. It is a neuron with multiple or many processes (many dendrites and one axon) extending from the cell body. These neurons are found in the cortex of the brain and the spinal cord. Functional Variations of the Neurons. Neurons are categorized according to their functions. a. Sensory neurons. The type of neuron that receives sensory input is susceptible to certain kinds of stimulation, like light, sound, or touch. An afferent (letter "a" as admit) axon of the sensory neuron brings information to the interneuron. These are unipolar neurons. b. Interneuron or intrinsic neuron. It is when the cell's dendrites and axons are entirely contained within a single structure. For instance, an intrinsic neuron in the thalamus has both its axon and all of its dendrites contained entirely within the thalamus.It connects the sensory neuron to the motor neuron and is located between the sensory and motor neuron (inter, means between) by transmitting the information. These are multipolar neurons. c. Motor neuron. Usually, its soma is located in the spinal cord. It receives excitation through its dendrites and conducts impulses along its axon to a muscle. An efferent axon of the motor neuron carries information away from a structure; efferent starts with “e” as in exit. These neurons are multipolar. Nerve Impulse. This section describes how information is transferred from neuron to neuron through nerve impulses and synaptic transmission. We have identified the basic unit of the nervous system, the neuron. Now, let me introduce you to how those cells receive and send electrochemical signals throughout the nervous system or the nerve impulse. This will lead to knowing how neurons communicate, an essential step in understanding complex behaviors. The nerve impulse is a tiny, brief "spike" of electricity traveling through the neurons via the axon. It consists of chemical particles moving across the cell's outer membrane from one side to the other. It can be likened to electrical conductivity, where the axons use electrical conduction (movement of positive and negative ions) to transmit information at a velocity from 1 to 120 meters per second, depending on the type of nerve carrying them. Let's first review the membrane channels. There are proteins embedded in an axon's cell membrane that serve many functions, such as channels, gates, and pumps to permit ion movement. Many kinds of ions move in and out of the membrane; let's focus on only two: sodium ions and potassium ions, which carry positive electrical charges. These features contribute to a neuron's ability to convey information. Mechanisms of Nerve Impulse Let us describe the three primary mechanisms of nerve impulse conduction: a. Resting Potential. The membrane potential is at rest in the absence of stimulation or when the neuron is not currently receiving or sending messages (e.g., sleepiness or lack of energy). Using a microelectrode recording that measures electrical charges in the membrane, one tip of the electrode is attached inside the neuron, and the tip of another electrode outside the neuron in the extracellular fluid. The record will show a steady potential of about −70 millivolts (mV) less than outside the cell membrane. It is more  negative inside than outside. Specifically, there are more Na+ ions outside the cell than inside and more K+ ions inside than outside; this is also called polarization. b. Action Potential. Now, in the presence of stimulation sent by the axon or when a neuron is receiving messages (e.g., participating in games or exercise), it decreases the negativity of charge inside the membrane towards zero, called Depolarization, or from negative to positive. When the stimulation of the neuron reaches beyond the excitation threshold (around -55mV to -65mV), it produces a massive membrane depolarization. It generated a complete response regardless of the intensity of the stimulus (All-or-None Law). The action potential opens the membrane's sodium channels (+ion), lets sodium ions flow into the cell, and travels at less than 1 meter/second. c. Saltatory Conduction. After an action potential occurs at a node of Ranvier, sodium ions enter the axon and diffuse, pushing a chain of positive charge along the axon to the next node. The action potential "jumps" from node to node, where they regenerate it. Saltatory conductions are fastest in myelinated axons. d. Refractory Period. At the peak of the action potential, an absolute refractory period occurs where the axon resists the production of further action potentials regardless of the stimulation, the sodium ion channel is shut up, and the potassium ion leaks out, causing hyperpolarization. It is followed by a relative refractory period when a stronger-than-usual stimulus is necessary to initiate an action potential.