Chapter 4: Biology of Behavior A. The brain is the most complex organ that we know. It is responsible for many of the behaviors that humans are capable of I. The Brain and Its Components A. Basic Structure of the Nervous System 1. The brain has 3 functions: a. Controlling behavior b. Processing and retaining the information we receive from the environment c. Regulating the body s physiological processes 2. The nervous system consists of two divisions: a. Central Nervous System (CNS)-the brain and the spinal cord and retina i. Spinal Cord-a long, thin, collection of neural cells attached to the base of the brain and running the length of the spinal column b. The central nervous system communicates with the rest of the body through the peripheral nervous system (PNS), the cranial and spinal nerves i. The PNS consists of nerves, a bundle of fibers that transmit information between the central nervous system and the body s sense organs, muscles and glands ii. Cranial nerves-a bundle of nerve fibers attached to the base of the brain; it conveys sensory information from the face and head and carries messages to muscles and glands iii. Spinal nerves-a bundle of nerve fibers attached to the spinal cord; conveys sensory information from the body and carries messages to muscles and glands 3. The human brain consists of three major parts: a. The brain stem (Medulla oblongata)-primarily controls the physiological functions and automatic behaviors b. Cerebellum-attached to the back of the brain stem, primarily controls and coordinates movements c. Cerebral hemispheres-the largest part of the brain, it is involved in perceptions, memories and behaviors of particular interest to psychologists d. The brain is convoluted (wrinkly) which allows us to feel consciousness 4. The brain is protected by the skull. The spinal cord is encased in the vertebrae 5. Meninges-the three-layered set of membranes that enclose the brain and the spinal cord 6. The brain and spinal cord float in a clear liquid called cerebrospinal fluid (CSF). It provides a cushion, and reduces damage to the brain if the organism is being harmed 7. Cerebral Ventricles-one of the hollow spaces within the brain, filled with cerebrospinal liquid 8. The brain has capillaries but they do not have openings so it is not assaulted by chemicals a. This impediment is known as the blood-brain barrier-a barrier between the blood and the brain produced by the cells in the walls of the brain s capillaries; prevents some substances from passing from the blood into the brain 9. The surface of the cerebral hemispheres is covered by the cerebral cortex a. There is a part in the cerebral cortex called gray matter which contains billions of neural cells b. It is here where memories are stored, plans are formulated and executed B. Cells of the Nervous System 1. Neurons are the basic units of the nervous system 2. They receive, process, and send information throughout the body depending on the environment 3. Glia-cells of the central nervous system that provide support for neurons and supply them with some essential chemicals
4. Dendrites-treelike parts of neurons on which other neurons form synapses 5. Soma-a cell body; the largest part of a neuron a. It contains the mechanisms that control the metabolism and maintenance of the cell 6. Axon-a long, thin part of a neuron attached to the soma; divides into a few or many branches 7. Terminal buttons-the rounded swelling at the end of the axon of a neuron 8. Terminal buttons release neurotransmitters, chemicals that causes the post synaptic neuron to be excited or inhibited 9. Myelin sheath-the insulating material that encases most large axons a. The primary function of the sheath is to prevent the scrambling of messages by insulating the axons. Another function (not mentioned in the book) is it helps transmits messages faster 10. Multiple Sclerosis is a disorder in which a person s immune system attacks its own cells. During this process, the myelin sheaths on the axons deteriorate and victims of the disease suffer numerous neurological disorders C. The Excitable Axon: The Action Potential 1. The action potential is a brief electrochemical event that is carried by an axon from the soma of the neuron to its terminal buttons; causes the release of a neurotransmitter a. Action potential is basically the firing of an axon 2. When the neuron is not transmitting messages it has an electrical charge known as the resting potential, the membrane potential of a neuron when it is not producing an action potential a. This happens because of an unequal distribution of ions both in and out of the cell 3. What happens is that a neuron is a rest. However a certain stimulus causes some activation gates on the sodium ion channels to open allowing Na+ to move into the cell. This causes an increase in the voltage of a cell 4. The way a neuron controls its voltage is by the use of ion transporters or ion channels both of which control how and what ions get in and out of the cells 5. Once the voltage reaches the threshold (about -65 mv), all of the activation gates on the sodium ion channels open causing the neuron to reach the action potential in which case an impulse is fired 6. In order for the cell to reduce its voltage, the cell releases K+ ions from the cell (at around 15 mv). Getting rid of a positive charge makes the cell more negative 7. The sodium is pumped outside the cell and potassium is brought back into the cell and the neuron is ready to fire another impulse if necessary 8. The action potential continues down the axon in a wave of excitation 9. It is important to note that action potentials all have the same strength. No action potential is stronger than the other. This follows the all-or-nothing law, the principle that once an action potential is triggered an axon, it is propagated without becoming smaller to the end of the axon 10. The way that the nervous system identifies the type of stimulus is not by the strength of the impulses but rather the number of impulses that are being fired D. Communication with Other Cells: Synapses 1. Neurons communicate with other cells through synapses, junctions between the terminal button of one neuron and the membrane of a muscle fiber, a gland, or another neuron 2. Information is passed from the presynaptic neuron (the one with the terminal buttons) to the postsynaptic neuron (the one receiving the message) 3. There are two major types of synapses: a. Excitatory-excites postsynaptic neurons to increase the rate of firing b. Inhibitory-lower the rate of firing 4. Once the action potential reaches the terminal button it causes several synaptic vesicles to fuse with the presynaptic membrane, burst open, and spills their contents into the synaptic cleft
5. The contents (known as the neurotransmitter) then bind to proteins (known as neurotransmitter receptors) on the postsynaptic membrane and open ion channels that allow Na + ions to excite the postsynaptic neuron and fire an impulse 6. It is important to note that this process (action potential and neurotransmitter reception) takes less than a fraction of a second. At most synapses, the effects are terminated by a process called reuptake the process by which a terminal button retrieves the molecules of a neurotransmitter that it has just released; terminated the effect of the neurotransmitter on the receptors of the postsynaptic neuron II. Drugs and Behavior A. Drugs alter the mechanisms of the nervous system B. Effects of Drugs on Synaptic Transmission 1. Drugs affect our perceptions, emotions, and behaviors by affecting the activity of neurons in the brain 2. Drugs can affect the activity of neurons in many different ways: 3. Stimulating or Inhibiting the Release of Neurotransmitters a. Some drugs stimulate certain terminal buttons to constantly release neurotransmitters even when the axon is not firing b. Other drugs can prevent terminal buttons from releasing neurotransmitters from being released even when the axon fires 4. Stimulating or Blocking Postsynaptic Receptors a. Some drugs stimulate postsynaptic receptors and cause the postsynaptic neuron to continually fire, while others can block the postsynaptic receptors from opening 5. Inhibiting Reuptake a. Some drugs inhibit the process of reuptake so that molecules of the neurotransmitter continue to stimulate the postsynaptic receptors for a long time. This increases the effect of the neurotransmitter 6. Agonists- stimulates the increased reception of neurotransmitters a. Some can bind directly to receptors of neurotransmitters (direct agonists) b. Other cans block the reuptake mechanism which will cause an increase binding in the receptors 7. Antagonists-inhibits the reception of neurotransmitters C. Neurotransmitters, Their Actions, and Drugs that Affect Them 1. Different types of neurotransmitters have different effects on synaptic communication 2. Glutamate-the most important excitatory neurotransmitter in the brain and spinal cord a. All sensory organs transmit information to the brain through axons whose terminals release glutamate (except those that transmit pain) b. Glutamate is also critical in the effects of environmental stimulation on the developing brain and responsible for the synaptic connections that are responsible for learning c. This neurotransmitter is turned off by alcohol 3. GABA-the most important inhibitory neurotransmitter in the brain a. Barbiturates-a drug that causes sedation b. Antianxiety drugs-reduce anxiety; part of the benzodiazepines which tranquilize subjects c. These drugs effect the GABA neurotransmitter receptors 4. Acetylcholine (ACh)-involved in muscular movement a. The primary neurotransmitter secreted by the axons of motor neurons b. The axons and terminal buttons of acetylcholinergic neurons are found all over the body c. There are three systems that are involved with acetylcholine: REM sleep, activates neurons in the cerebral cortex and facilitate learning
d. Botulinum toxin can prevent the release of ACh, causes paralysis of the muscles e. Black widow spider venom stimulates the release of ACh f. Nicotine is the best known drug that affects acetylcholine receptors. Because it is an addictive drug many believe it plays an important role in reinforcement mechanisms in the brain g. Curare-blocks acetylcholine receptors and causes paralysis 5. Monoamines a. Neurons with these neurotransmitters serve to modulate the function of widespread regions of the brain, increasing or decreasing the activities of particular brain functions b. Dopamine (DA) serves several important functions including movement, attention, learning, and the reinforcing effects of drugs. A disease that destroys the set of DA neurons is called Parkinson s Disease which is a movement disorder that results in tremors, rigidity of the limbs, poor balance, and difficulty in initiating movements. We treat this disease with LDopa c. Norephinephrine (NE) appears to cause an increase in vigilance; attentiveness d. Serotonin plays a role in the regulation of mood; control of eating, sleep, and arousal; serotonin release becomes deficient with alcoholism, this can cause depression, anxiety, and OCD 6. Peptides-a category of neurotransmitters and neuromodulators that consist of two or more amino acids, linked by peptide bonds a. Neuromodulators-a substance secreted in the brain that modules the activity of neurons that contain the appropriate receptors b. Most neuromodulators are peptides c. Endogenous opioids stimulates special opioid receptors located on neurons in several parts of the brain. Effects include decreased sensitivity to pain 7. Cannabinoids a. Cannabis, the plant that is used to synthesize hemp and marijuana contains THC b. THC mimics the effects of endogenous cannabinoids-chemicals produced and released by neurons in the brain III. The Study of the Brain A. Experimental Ablation 1. Creates a brain lesion, an injury to a particular part of the brain 2. When something occurs to the brain, it changes behavior of the subject 3. The effects in the lesion on an animal s behavior are studied 4. Animal laboratories use a stereotaxic apparatus in which the animal does not move its head and the researcher is able to temporarily destroy parts the brain at various points and study the behavior B. Visualizing the Structure of the Brain 1. CT Scan (CAT Scan) a. The scanner sends a narrow beam of x-rays through a person s head b. The computer creates a model of the brain by calculating the amount of radiation that passes through it at various points along each angle c. It creates a two-dimensional model of a slice of the brain 2. MRI scan a. Putting a person s head in a magnetic field which causes the molecules to orient to them around the brain. A radio signal is sent into the brain and causes the molecules to vibrate and produce a picture of the brain b. MRIs produce a higher resolution picture of the brain than CT scans C. Measuring Brain Activity 1. EEG
a. Electrodes around the head pick up the brain activity b. It is used to diagnose various seizure disorders and monitor various stages of sleep 2.MEG a. Detects small magnetic fields within in the brain b. This technology is used to figure which part of the brain causes specific seizures 3.PET scans a. Radioactively tag a molecule that will make it to the brain b. Those part of the brains that are more active will require the molecule and will radiate more than those parts of the brain that will not 4. fmri a. Modifies the MRI to measure the rate of metabolism in regions of the brain by detecting levels of oxygen in the brain s blood vessels D. Stimulating the Brain s Activity 1. Intracranial Stimulation a. Put an electrode into the brain and stimulate the brain 2. Intracranial Self-Stimulation (ICSS) a. Stimulate the brain to reinforce a certain behavior 3. Transcranial Magnetic Stimulation (TMS) a. Magnetic fields machines which uses coils of wires to stimulate neurons in the human cerebral cortex E. Altering Genetics 1. Targeted mutation a. Inactivates a gene by producing a particular neurotransmitter or a particular receptor 2. Researchers can also insert genes that may affect the development of the brain of a particular organism and observe if that changes its behaviors F. Focus On: Neural Plasticity and Neurogenesis 1. Neural Plasticity-the production of changes in the structure and functions of the nervous system, induced by environmental events a. The type of environment that you live in literally changes the physical appearance of brain as to better adapt to that specific situation 2. Neurogenesis-the process responsible for the production of a new neuron a. It was believed that neuron production ceases early in life and that new neurons could not be produced b. However, it is now believed that we have certain stem cells within our brain that allow us to produce new neurons IV. Control of Behavior and the Body s Physiological Functions A. Organization of the Cerebral Cortex 1. The cerebral cortex contains a large groove called the central fissure which provides an important dividing line between the anterior and posterior parts of the cerebral cortex 2. The names of the four lobes of the brain are: frontal lobe, parietal lobe, temporal lobe, and occipital lobe 3. Regions of Primary Sensory and Motor Cortex a. There are 3 areas of the cerebral cortex that receive information from the sensory organs: primary visual cortex, primary auditory cortex, and the primary somatosensory cortex b. The three regions of the primary sensory cortex in each hemisphere receive information from the opposite side of the body (contralateral-residing in the body opposite the reference point) 4. Association cortex
a. The rest of the cerebral cortex accomplishes what is done between sensation and action: perceiving, learning, etc. This occurs in the association parts of the cortex b. The anterior region is involved in movement-related activities c. Each of the primary sensory cortexes sends information to adjacent regions known as the sensory association cortex i. Neurons analyze the information there. It is here where perception takes place and memories are stored d. The frontal association cortex is involved in perceiving and planning the execution of movements e. The anterior part of the frontal lobe is known as the prefrontal cortex which contains the motor association cortex which controls the primary motor cortex 5. The Thalamus-a region of the brain near the center of the cerebral hemispheres a. The thalamus lies between both cerebral hemispheres and is divided into two parts, one for each hemisphere b. The thalamus performs two functions: receives sensory information to assist other parts of the brain with motor movement and to relay information for the cortex B. Lateralization of Function 1. The cerebral hemispheres do not perform identical functions a. The left side participates in the analysis of information as well as recognizing serial behavior. It also plays a role in speech and understanding of language (mathematical) b. The right side is specialized in synthesis; putting things together (artistic) c. Although the hemispheres act differently of one another, they are unified by the corpus callosum, which is a large band of axons that connect the two hemispheres C. Vision 1. Vision occurs as a result of the lower temporal and occipital lobe 2. Damage to this part of the brain can cause visual agnosia, a deficit in visual perception D. Audition 1. The audition center is located on the temporal lobe which contains both the primary auditory cortex and the auditory association cortex 2. Damage to the primary auditory cortex results in hearing loss. However, damage to the auditory association cortex causes language deficits E. Somatosensation and Spatial Perception 1. The parietal lobe allows for the perception of our own body and the location of objects in the world around us. Damage to parts of the parietal lobe will cause interference in people s ability to perceive and remember the location of items in their environment F. Planning and Moving 1. The Frontal Lobes a. The frontal lobes are primarily involved with movement but they it is also involved in planning strategies making changes if necessary b. Damage to this part of the brain will cause paralysis in the opposite side of the body G. The Cerebellum 1. The cerebellum knows the sensory information especially about the position of body parts and what the frontal lobes are trying to do. The cerebellum is the control center for movements. It allows the movements to become more graceful and quick, rather than spastic and uncoordinated 2. Case study summary: Mr. P. damaged his cerebellum and as a result was not able to control quick movements H. The Basal Ganglia-a group of nuclei in the brain interconnected with the cerebral cortex, thalamus, and brain stem; involved in control of slow movements and movements of large muscles 1. Involved in the control of slow movements 2. The basal ganglia are also involved in learning skilled motions I. Episodic and Spatial Memory: Role of the Hippocampus
1. Hippocampus-a part of the limbic system of the brain located deep in the temporal lobe; damage causes changes in emotional and aggressive behavior 2. The hippocampus is also involved with episodic memory, our ability to learn and remember experiences from our daily lives J. Emotions: Role of the Amygdala 1. Amygdala is located in the middle of the temporal lobe 2. Controls feelings in negative situations K. The Brain Stem: A Control Internal Functions and Automatic Behavior 1. The brain stem and hypothalamus are involved in homeostasis within the body 2. The Brain Stem a. Contains 3 structures: medulla, pons, midbrain b. The hypothalamus and pituitary gland are located in the front of the brain stem c. Medulla controls heart rate, blood pressure, and rate of respiration. For simpler creatures, this includes locomotion d. Pons-sleeping and wakefulness e. Midbrain-controls movements used in fighting and sexual behavior and decreased sensitivity to pain while a person is engaged in these activities 3. Hypothalamus a. Participates in homeostasis b. It receives information from the sensory neurons c. Hypothalamus controls the pituitary gland ( the master gland ) d. Hormones are chemical messengers through the body and access certain target cells and produce a specific response e. The hypothalamus controls the endocrine system f. Autonomic Nervous System-is controlled by the hypothalamus and controls functions of the glands and internal organs i. Sympathetic branch-fight or flight response ii. Parasympathetic branch-controls quiet activities such as digestion of food g. Somatic Nervous System-acts as a mediator between the central nervous system and muscles/sense organs 4. Thalamus a. Above the hypothalamus b. It is the first synapse (except smell) to receive information from the sensory neurons