Module 3: Behavioral Neuroscience PDF

# Module 3: Behavioral Neuroscience ## Module 3: Outline - The Neuron: Types of neurons, structure and functions of the neuron - Neurotransmitters and Hormones: Types and Functions - Note: Hormones for self-study - The Brain and Nervous System: Structures and Function - Common neurological dis...

# Module 3: Behavioral Neuroscience ## Module 3: Outline - The Neuron: Types of neurons, structure and functions of the neuron - Neurotransmitters and Hormones: Types and Functions - Note: Hormones for self-study - The Brain and Nervous System: Structures and Function - Common neurological disorders and diseases - Note: This section has been covered under different sections of the chapter: Parkinson's diseases, Alzheimer's Disease and Multiple Sclerosis; along with psychological disorders - depression, anxiety and schizophrenia) ## The Nervous System ### The Central and Peripheral Nervous System - **Sensing (Via Receptor)** - **Processing (Typically by the Brain)** - **Responding (Message sent to muscles to produce a response)** ### The Peripheral Nervous System - Connects outer portions, peripheries of the body with the CNS - **Somatic Division** - Sensory (afferent) nerves - Motor (efferent) nerves - **Autonomic Division** - **Sympathetic nervous system (Prepares body for "fight or flight")** - **Parasympathetic nervous system (Resume normalcy to a calm state)** ### The Central Nervous System - **Brain** - Hemispheres and contralateral conduction - Hindbrain - Midbrain - Forebrain - **Spinal Cord** - Surrounded by protective jacket of the vertebral column, made up of 24 bones called vertebrae - Sensory neurons enter (back) and motor neurons leave the spinal cord (front) - Serves as an information superhighway - **Interneurons**: Connect neurons to each other - Send info directly to motor neurons - Send info up spinal cord for further processing by the brain - Automatic behaviors (reflexes) have a "shorter journey" and hence rapid responses (evolutionary advantage) ## The Neuron - **Types of neurons, structure and functions of the neuron** ### Structure of the neuron - **Dendrites**: Receives messages from other neurons/receptors - **Cell Membrane**: - Surrounds the entire neuron, giving it shape and keeping the cell's internal fluids inside. - Is semipermeable: It allows some-but not all-substances to pass through it. - **Cell body/Soma**: - Contains the nucleus - Keeps the entire cell alive and functioning. - **Axon**: - Long slim, tube-like extension, attached to the soma. - Carries (electrical) messages out to other cells. - Only one axon which branches out to several other neurons. - These messages move in only one direction. - Considerably longer than the rest of the neuron from several millimeters to as long as three feet. - Covered by a protective layer of fat and protein that prevents messages from "short circuiting" each other. - **Terminal button**: Communicates with other nerve cells. ### Parts of a neuron - **Dendrites**: Receive signals from other neuroscols. - **Cell Body**: Contains the nucleus. - **Nucleus**: Contains the genetic material of the neuron cell. - **Axon**: Conducts electrical impulses along the neuron cell. - **Myelin sheath**: Insulates to protect the neuron cell & speed up transmission. - **Axon terminal**: Responsible for transmitting a signal to the next neuron. ## Glia or Glial Cells - Another kind of cell found in the nervous system, more numerous than neurons. - They affect the structure and functioning of neurons. ### Types of Glial Cells - **Oligodendrocytes (CNS: brain and spinal cord) and Schwann cells (PNS)** - They generate a layer of fatty protein substance called myelin that wraps around the shaft of the axon and has a whitish appearance. - Bundles of myelin-coated axons travel together as "cables" - tracts (CNS) or nerves (PNS). ### Myelin sheath insulates and protects the neuron and speeds up transmission down the axon. #### **How does the myelin sheath help speed up transmission?** - Myelin bump up next to each other on the axon at spaces called nodes (Nodes of Ranvier). - Nodes are not covered in myelin. - When the electrical impulse/neural message travels down an axon coated with myelin, it is regenerated at each node and appears to "jump" or skip rapidly from node to node down the axon. - This makes the message go much faster (100xX) down the coated axon than it would down an uncoated axon of a neuron in the brain. ### **DID YOU KNOW?** - Axons that carry the most important and urgently required info have the greatest concentrations of myelin. - Myelin from Schwann cells (but not oligodendrocytes) has a unique feature that can serve as a tunnel through which damaged nerve fibers can reconnect and repair themselves. - What do you think is the implication for oligodendrocytes in the CNS which don't have this unique feature? ## How do neurons fire? - **Resting potential**: Inside and outside the neuron is a semi-liquid solution containing ions (charged particles) - At rest when a neuron is neither sending nor receiving a signal - a neuron is negatively charged (-70 mV difference in electric charge between the inside and outside of a neuron at rest is the resting potential.) - **Depolarization**: Occurs when the inside of the neuron becomes less negative, or even positive, compared to the resting membrane potential. - **Hyperpolarization**: It is the opposite of depolarization. It occurs when the inside of the neuron becomes more negative than the resting membrane potential. - **Action potential**: The axon quickly reverses its electrical charge. This reversal in electrical charge is known as the action potential. - **Absolute refractory period**: The neuron cannot fire. - **Relative refractory period**: A specific time interval during which a neuron, having just undergone an action potential, exhibits increased resistance to being triggered for another action potential (a heightened threshold for excitation.) ## Sending the Message to Other Cells - Although messages travel in electrical form within a neuron, they move between neurons through a **chemical transmission system**. - **Neurotransmitters**: Can either have an excitatory **(turn "on" the cell - make it more likely to generate an action potential)** or inhibitory effect **(turn "off" the cell - reduce the likelihood of action potential generation)** - **Synaptic vesicles**: Little sac-like structures which contain, chemicals suspended in fluid, which are molecules of substances called neurotransmitters. - **Neurotransmitter**: Chemical substances stored in terminal buttons and released into the synapse between two neurons to carry signals from one neuron to the next. - **Receptor sites**: Proteins that allow only particular molecules of a certain shape to fit into it. - **Synaptic gap**: Fluid-filled space between the terminal buttons of one axon and the dendrites of the next axon ### **Getting Ready to Send the Next Message** - The neurotransmitters have to get out of the receptor sites before the next stimulation can occur. - **Diffusion**: Some neurotransmitters drift away. - **Reuptake**: Process in which a neurotransmitter produced by a terminal button is reabsorbed by the terminal button. - **Enzymatic degradation**: Enzymes breakdown NT in the synapse. Rapid breakdown of ACh is important for producing the rapid motor responses required to play the piano, type, or use a calculator. ## How do Neurons Fire? - Neurons fire in an all or none manner - Threshold for firing - Firing rate and stimulus intensity - Refractory period - Speed of transmission ## Neurotransmitters: Multitalented Chemical Couriers - Chemical substances stored in terminal buttons and released into the synapse between two neurons to carry signals from one neuron to the next. - They can have either an excitatory **("fire")** or an inhibitory **("don't fire")** effect on the post-synaptic membrane. - They play a vital role in brain and body functioning and their deficiency/excess could produce severe behavior disorders. - **Agonists**: Drugs can either promote or enhance the operation of a neurotransmitter, whereas antagonists oppose or inhibit the operation of a neurotransmitter. ### Acetylcholine - Excitatory and Inhibitory - Stimulates muscle cells to contract - Arousal, attention, learning and memory - ACh found in the hippocampus ### Dopamine - Controls arousal levels; movement, attention, and learning. - Dopamine is involved in brain pathways that are responsible for reward and punishment. - **Implications**: - **Low levels of dopamine**: Parkinson's disease - **L-dopa**: A chemical precursor of dopamine (a building block that certain brain neurons use to manufacture dopamine) - **High levels of dopamine**: Schizophrenia, Addiction/Dependence on drugs (amphetamines, cocaine), Pathological gambling (impulse control issues) ### GABA - Inhibitory - Helps to calm anxiety - General inhibition of the nervous system ### Glutamate - Excitatory neurotransmitter - Plays an important role in learning and memory, and may also be involved in the development of the nervous system and in synaptic plasticity (brain changes connections among its neurons). - Excessive levels of glutamate may cause neurons to become overexcited, and they may die as a consequence. ### Norepinephrine - Generally excitatory - Induces physical and mental arousal and heightens our mood. - It is found in the autonomic nervous system and is part of the power behind the fight-or-flight response. ### Serotonin - Inhibitory or excitatory - It is associated with sleep, mood, anxiety, and appetite. - Low levels of serotonin activity have been linked to depression. ### Neuropeptides - Serve as neurotransmitters, hormones, or influence the action of other neurotransmitters. - **Endorphins**: Pain-controlling chemicals in the body. - When hurt, endorphins released block the receptors that open ion channels along the axon - making it unable to fire a pain signal - the intensity of the pain subsides with time. - Like "Endogenous morphine" (native to the body); morphine, heroin (opiates) bind to the same receptor site as endorphins. - Explains addiction to pain med - "everything hurts" once the pain meds stop - since the body neglects to produce endorphins. ## The Brain: Structure and Function ### Hindbrain - The oldest parts of the brain, has important survival functions. - **Medulla**: Regulates automatic responses (life-sustaining functions) such as breathing, swallowing, heart rate and blood circulation - **Pons**: Latin for "bridge" (a bridge between the lower and the upper sections of the brain) - Crossover of motor nerves carrying messages from the brain to the body. - Connects two halves of the brain. - Role in sleep, dreaming and arousal. - **Cerebellum**: "Little brain" - Deal with involuntary, rapid, fine motor movement and coordinates voluntary movements that have to happen in rapid succession (walking, skating, dancing, playing a musical instrument, and even the movements of speech). - Learned reflexes, skills, and habits. - Fine tunes gross motor signals that come from the upper brain. - Output is entirely inhibitory. ### Midbrain - Reticular formation: Network of neurons running through the middle of the medulla and the pons and slightly beyond. - **RAS**: Nerve fibers passing through the midbrain that control arousal and alertness. - Blocks out constant, unchanging information, maintains alertness over unfamiliar, changing stimuli. - Role in ADHD. - Destruction of RF - implicated in comas; stimulation of RF results in waking up. - **Brain stem**: Hindbrain and midbrain together form the brain stem. - The oldest part of the brain; begins at the top of the spinal cord and contains brain centers responsible for basic survival activities. ### Forebrain - The forebrain is divided into two distinct halves with duplicate structures in each half. - **Corpus callosum**: Wide band of neural fibers that connects the two hemispheres of the brain allowing the two hemispheres to communicate with each other. - **Subcortical structures**: Are located beneath the other main division of the forebrain, the cerebral cortex (aka cerebrum) or outer covering of the brain. - **Basal Ganglia**: A series of interconnected structures that play a significant role in motor movement (slow voluntary movements, such as standing, sitting, and walking) and are connected to other areas of the brain involved in motor movement. - **Limbic system**: A group of interrelated subcortical structures involved in the regulation of emotions and motivated behaviours (hunger, thirst, aggression, sexual behaviour). - **Thalamus**: "Inner chamber" - Relay station - sends sensory information (vision, taste etc, except smell) to appropriate area in the cortex and other areas of the brain. - **Hypothalamus**: "Below inner chamber" - Regulates body temperature, thirst, hunger, sleeping and waking, sexual activity, and emotions. - **Hippocampus**: "Seahorse" - Located in the medial temporal lobe in each side of the brain - Role in memory consolidation (long-term memory, declarative memories, but stored elsewhere). - **Amygdala**: "Almond" - Fear response and memory of fear. Respond to feared stimuli before conscious awareness - Damage/Removal of amygdala - unafraid/decreased fear response (Klüver-Bucy syndrome). - **Cingulate cortex**: Emotional and cognitive processing (frontal and parietal) above corpus callosum. ### Cerebral Cortex - Cortex ("rind" or outer covering) is the outermost part of the brain. - Made up of tightly packed neurons. - Wrinkling of the cortex allows a much larger area of cortical cells to exist in the small space inside the skull. - The brain gets more and more wrinkled as the brain increases in size and complexity. - This increase in wrinkling is called "corticalization." #### Lobes - Divided into cerebral hemispheres, connected by the corpus callosum. - Each hemisphere is divided into four lobes based on the fissures in its surface.: frontal, parietal, occipital and temporal lobes. - **Frontal lobe**: The brain's "executive arm": Involved in higher order mental functions: language (left hemisphere), movement, reasoning, planning, problem solving, and personality. - The frontal lobe also helps in controlling emotions by means of its connection to the limbic system. - **Parietal lobe**: Thought of as a sensory integrator because they are responsible for body position as well as our sensory cortex or somatosensory strip. - **Occipital lobe**: Processing of visual information - Processes visual information from the eyes in the primary visual cortex. - The visual association cortex, also in this lobe and in parts of the temporal and parietal lobes, helps identify and make sense of the visual information from the eyes. - Neuron specialized for specific kinds of visual inputs. - **Temporal lobe**: Contains the primary auditory cortex and the auditory association areas. - Processing of auditory information; in most people the left side interprets the meaning of speech (Wernicke's area - speech comprehension). #### Association Areas - Association areas are made up of neurons in the cortex that are devoted to making connections between the sensory information coming into the brain and stored memories, images, and knowledge. In other words, association areas help people make sense of the incoming sensory input. Much of the brain's association cortex is in the frontal lobes. ## Language and the Brain - Aphasia: Refers to an inability to use or understand either written or spoken language. - **Broca's Aphasia (Non-fluent aphasia)**: Broca's area: Left Frontal lobe - Person unable to get words out in a smooth, connected fashion - Speech production issues, however can understand speech - Speech is halting and words are often mispronounced, such as saying "cot" instead of "clock" or "non" instead of "nine." Some words may be left out entirely, such as "the" or "for." - **Wernicke's Aphasia (Fluent Aphasia)**: Wernicke's' area: Left temporal lobe - Appears to be involved in understanding the meaning of words - Pt. speaks fluently and pronounce words correctly, but the words would be the wrong ones entirely. - Have trouble understanding what others are saying. - **In the vast majority of the population, the left hemisphere is dominant for language, and speech is generated only from the left hemisphere.** ## Damage to the Right Hemisphere - Apraxias are deficits in nonverbal skills, involve damage to the right hemisphere. - Depending on the site of the damage, one might observe a dressing apraxia, in which a person has trouble putting clothing on one side of the body, or a constructional apraxia, in which a person cannot copy a simple drawing. - The right hemisphere controls prosody, the ability to express emotion. People suffering from motor aprosodia speak in a flat monotone regardless of their real feelings. Such people simply cannot display emotions. ## Hemispheric Specialization - Left and right hemisphere specialize in different activities and functions. - **Sperry's work with patients with epilepsy (commissurotomy) leading to "two brains" in one body**: Implications of Split brain procedure: People with a severed corpus callosum, the two hemispheres appeared to be doing different things. It was as if there were two minds in one head! For example, the right hand might unbutton the patient's shirt, while the left hand buttoned it! Such conflicts typically occur shortly after surgery and tend to subside as the separated hemispheres learn to work together. - **Levy, Trevarthen and Sperry (1972) - Bilateral nature of the hemispheres**: A split brain patient was asked to look at a fixation point at the centre of the screen. Two faces were combined where half was a man and the other half was a woman. The face was briefly flashed on the screen. The participant did not report anything unusual about the composite, even though each hemisphere received a different face. When asked to describe the face, the participant verbally described a man's features, supporting the verbal nature of the left hemisphere. However, when asked to recognise the face from an array of photographs, the participant picked the woman's photo supporting the pictorial nature of the right hemisphere. ### Specializations of the Two Hemispheres - **Left Hemisphere**: Controls the right hand, Spoken language, Written language, Mathematical calculations, Logical thought processes, Analysis of detail, Reading - **Right Hemisphere**: Controls the left hand, Nonverbal, Visual-spatial perception, Music and artistic processing, Emotional thought and recognition, Processes the whole, Pattern recognition ## Neuroplasticity - Neuroplasticity is the ability of the neocortex to acquire new functions as a result of interacting with the environment. - Various activities can result in the growth of new neurons; this process is known as neurogenesis. - Training in a specific ability will result in brain differences — the organization of cortical neurons of musicians and non-musicians is different. - Humans do not come into this world with a fully developed, hard-wired brain. The evolutionary process did not have to produce a brain with specialized circuits that performed specialized tasks. Instead, it could simply produce a larger brain with an abundance of neural circuits that could be modified by experience. ## Mirror Neurons - Although all neurons operate through the firing of action potentials, there is significant specialization among different types of neurons. For example, neuroscientists have discovered the existence of mirror neurons, neurons that fire not only when a person enacts a particular behavior but also when a person simply observes another individual carrying out the same behavior (Spaulding, 2013; Brucker et al., 2015; Bonini, 2017). - Mirror neurons may help explain how (and why) humans have the capacity to understand others' intentions. Specifically, mirror neurons may fire when we view someone doing something, helping us to predict what their goals are and what they may do next. - The discovery of mirror neurons suggests that the capacity of even young children to imitate others may be an inborn behavior. Furthermore, mirror neurons may be at the root of empathy — those feelings of concern, compassion, and sympathy for others — and even the development of language in humans (Ramachandra, 2009; Rogalsky et al., 2011; Lim & Okuno, 2015). - Some researchers suggest an even broader role for mirror neurons. For example, mirror neurons, which respond to sound, appear to be related to speech perception and language comprehension. Furthermore, stimulating the mirror neuron system can help stroke victims as well and may prove to be helpful for those with emotional problems by helping them to develop greater empathy (Gallese et al., 2011; Hoenen, Lübke, & Pause, 2017).