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Chapter 3

PSYC 1000 Chapter 3: Brain and Behaviour 3.2,3.3,3.4

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PSYC 1000
Dan Meegan

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1. Brain and Behaviour (3.2,3.3,3.4) Sept 18, 2016 3.2 Neural Communication  Neurons –(cells) found in the nervous system, responsible for sending and receiving messages throughout the body  Billions of these receive and send messages every day Neurons  Cells fire messages to other cells, which eventually leads to some type of behaviour  All neurons have a cell body (aka soma) – part of a neuron that contains the nucleus that houses the cell’s genetic material  Genes in cell body make proteins which form chemicals and structures which allow the cell to function  Activity of these gens can be influenced by input coming from other cells o Input is received by dendrites (small branches radiating from the cell body that receive messages from other cells and transmit those messages toward the rest of the cell)  Neuron will get many inputs from other cells, and will travel across neuron to the base of cell body known as the axon hillock  If axon hillock gets enough input, it will start a chemical reaction that will flow down to the rest of the neuron  This reaction is the initial step in a neuron communicating with other cells  Axon – transports info in the form of electrochemical reactions from the cell body to the end of the neuron  When activity reaches the end of axon, it will arrive at axon terminals, a bulb-like extensions filled with vesicles  These vesicles contain neurotransmitters – the chemical that function as messengers allowing neurons to communicate with each other o Allows the neural communication to take place  Sensory neurons receive info from the bodily senses and bring it toward the brain  Motor neurons carry messages away from the brain and spinal cord and toward muscles in order to control their flexion and extensions Glial cells  Specialized cells of the nervous system that are involved in mounting immune responses in the brain, removing waste, and synchronizing the activity of the billions of neurons that constitute the nervous system  Outnumber neurons 10-1  Myelin – fatty sheath that insulates axons from one another, resulting in increased speed and efficiency of neural communication  Speed difference between axon with myelin and without is large o With, 150 m/s o Without, 0.5 to 10 m/s  Most neurons in brain have myelin  When myelin sheath is damaged, the efficiency of axon decreases tons o Ex. Multiple sclerosis is a disease in which the immune system does not recognize myelin and attacks it which affect communication between cells The neuron’s electrical system: resting and action potentials  Neural activity is based on changes in the concentrations of charged atoms called ion  Resting potential – relatively stable state during which the cell is not transmitting messages  Seemingly stable resting state involves a great deal of tension o Because the electrostatic gradient and concentration gradient o Electrostatic gradient (inside and outside of the cell have different charges – neg+pos) o Concentration gradient (different types of ions are more densely packed on one side of the membrane than the other – ex. There are more sodium ions outside than inside cell)  If enough positively charged ions reach the axon hillock to push its charge past that cell’s firing threshold, the neuron will then initiate an action potential o Action potential – a wave of electrical activity that originates at the base of the axon and rapidly travels down its length o When action potential occurs, the cell changes from negative to positively charged  Refractory period – brief period in which a neuron cannot fire  When action potential reaches axon terminal, triggers the release of that cell’s neurotransmitters into the synapses  Synapses- microscopically small spaces that separate individual nerve cells  Cell releases the chemical is known as presynaptic cell (“before the synapse”) whereas the cell that receives this input is known as postsynaptic cell (after)  All-or-none principle- individual nerve cells fire at the same strength every time an action potential occurs The Chemical Messengers: Neurotransmitters and Hormones  Synaptic cleft- the minute space between the axon terminal (terminal button) and the dendrite o Process is almost as important as action potential o Prolonged stimulation of the receptors makes it more difficult for the cell to return to its resting potential (necessary for neuron to fire again) o Once neurotransmitters have detached from the receptors and float back into the synapse, they are either broken down by enzymes or go through reuptake  Reuptake- process whereby neurotransmitter molecules that have been released into the synapse are reabsorbed into the axon terminals of the presynaptic neuron  Serves as a natural recycling system for neurotransmitters  Also process that is modified by many commonly used drugs  Ex. Antidepressants Types of neurotransmitters  Most common neurotransmitter in brain are glutamate and GABA o Glutamate- most common excitatory neurotransmitter in the brains of vertebrates  Involved in a number of processes, including our ability to form new memories  Abnormal functioning of glutamate-releasing neurons has also been implicated in a number of brain disorders including the triggering of seizures in epilepsy o GABA – primary inhibitory neurotransmitter of the nervous system, meaning that it prevents neurons from generating action potentials  Acetylcholine- one of the most widespread neurotransmitters within the body, found at the junctions between nerve cells and skeletal muscles; it is very important for voluntary movement o Releases neurons connected to the spinal cord binds to receptors on muscles o Link between nervous system and muscles is known as neuromuscular junction o Acetylcholine activity in the brain is associated with attention and memory o Altered levels of this neurotransmitter have also been linked to cognitive deficits associated with aging and Alzheimer’s disease o Group of transmitters known as monoamines include dopamine  Dopamine- neurotransmitter involved in such varied functions as mood, control of voluntary movement, and processing of rewarding experiences  Norepinephrine- monoamine synthesized from dopamine molecules that is involved in regulating stress responses, including increasing arousal, attention, and heart rate – works alongside epinephrine (adrenaline)  Serotonin- involved in regulating mood, sleep, aggression, and appetite  Known for its role in depression  Many antidepressants block the reuptake of serotonin which results in mood increase and decrease in symptoms of depression Drug effects on neurotransmission  Agonists- drugs that enhance or mimic the effects of a neurotransmitter’s action o Well-known drug nicotine is an acetylcholine agonist meaning it stimulates the receptor sites for this neurotransmitter o Drugs can behave as agonists either directly or indirectly o Drug that acts as an indirect agonist facilitates the effects of a neurotransmitter but doesn’t physically bind to the same part of the receptor as the neurotransmitter  Ex. Drug that blocks reuptake would be indirect o Antagonists- inhibit neurotransmitter activity by blocking receptors or preventing synthesis of a neurotransmitter  Botox Hormones and the endocrine system  Hormones- chemical secreted by the glands of the endocrine system  Hypothalamus- a brain structure that regulates basic biological needs and motivational systems o Releases specialized chemicals called releasing factors that stimulate the pituitary gland o The master gland of the endocrine system that produces hormones and sends commands about hormone production to the other glands of the endocrine system  Adrenal glands- pair of endocrine glands located adjacent to the kidneys that release stress hormones, such as cortisol and epinephrine  Endorphin- hormone produced by the pituitary gland and the hypothalamus that functions to reduce pain and induce feelings of pleasure 2. 3.3 Structure and organization of the nervous system Divisions of the Nervous system  The central nervous system o Ability to answer questions (thinking) involves different parts of your central nervous system o Central nervous system consists of the brain and the spinal cord o CNS runs from neck to base of spinal cord o Signals are sent down which go out to rest of body which causes movement o Two structures are critical for survival  The peripheral nervous system o This is a division of the nervous system that transmits signals between the brain and the rest of the body and is divided into two subcomponents  The somatic system consists of nerves that control skeletal muscles, which are responsible for voluntary and reflexive movement, as well as consists of nerves that receive sensory input from the body (reading, walking)  automatic nervous system is the portion of the peripheral nervous system responsible for regulating the activity of organs and glands  includes 2 subcomponents which increase our ability to make rapid responses and another returns back to normal levels of emotional arousal which include:  sympathetic nervous system is responsible for fight or flight of an increased heart rate, decrease of saliva (responses to action)  parasympathetic nervous system helps maintain homeostatic balance in the presence of change (following sympathetic arousal)  The brain and its structures  Brain is divided into halves called cerebral hemispheres o The hindbrain  Critical to controlling basic, life-sustaining processes  Brain stem: bottom of the brain and consist of two structures; the medulla and the pons  Nerve cells in medulla connect with body to do basic functions
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