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Chapter 4

Psyc100-Ch4 - Neurons & Nervous System.docx

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PSYC 100
Jaime Palmer- Hague

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Psychology 100 Chapter 4: The brain and Behaviour N EURONS  specialized cells  building blocks of the nervous system  estimated 100 billion nerve cells in the brain and spinal cord Structure of a Neuron: Each has three main parts: a cell body, dendrites and an axon. (P.93)  Soma (cell body): contains biochemical structures needed to keep the neuron alive and its nucleus carries the genetic information that determines how the cell develops and functions.  Dendrites: receive and collect messages from neighboring neurons and send them to cell body  Axon: conducts electrical impulses away from the cell body to other neurons, muscles or glands  Axon branches out at its end to form axon terminals, as many as several hundred in some cases. Each AT may connect with dendrites from numerous neurons, making it possible for a single neuron to pass messages to as many as 50,000 other neurons.  Myelin Sheath: Fatty insulation layer derived from glial cells. Interrupted by nodes of Ranvier, where myelin is extremely thin. If damaged, it will interrupt the timing for action potential.  Glial Cells: support Neurons. They do not send or receive nerve impulses, but surround neurons and hold them in place. Also manufacture nutrient chemicals that neurons need and absorb toxins and wastes. Two Types: ○ Astrocyte ○ Oligadendrocyte Neuron Function #1: Electrical Impulses (p.94) Outside: Na (Sodium) and Cl (Chloride) Inside: K+ (potassium) and A- (or anions, protein molecules)  Cell membrance have ion channels (potassium and sodium)  Membrane potential – difference in charge between inside and outside of a cell 1. Resting potential:  10:1 concentration of sodium (Na+) ions outside the neuron and the negative protein (A-) inside contribute to a resting potential of -70mV.  Inside of cell is more negative  neuron is in a state of polarization 2. Action potential (Nerve Impulse)  if stimulated = shift in electrical charge from -70mV to +40mV  Lasts approximately 1 millisecond  Na+ channels open, and Na+ flood into axon (Inside is more positive, cell is depolarized)  To restore resting potential, the cell closes its Na+ and K+ channels on membrane open, K+ flows out of cell (Inside of cell restores negative state, cell is repolarized)  After impulse passes a point along the axon, there is an Absolute refractory period: while the cell is restoring negative state, the membrance is not excitable and cannot discharge another impulse.  Impulse (Na+) flows down axon to axon terminals and escaped K+ ions are recovered.  All or Nothing : action potentials occur at maximum intensity, or they do not occur at all. Only occurs if neuron is sufficiently stimulated. Neuron Function #2: Synaptic Transmission (p.96)  Neurons do not actually touch each other.  Synaptic space: a tiny gap between the axon terminal and the next neuron.  They communicate via neurotransmitters: chemical substances that carry messages cross the synaptic space to other neurons FIVE STEPS: Synthesis → Storage → Release → Binding → Deactivation or Reuptake 1. In the synthesis stage, the transmitter molecules are formed inside neuron. 2. The neurons are stored in synaptic vesicles: chambers within the axon terminals. 3. When action potential comes down the axon, these vesicles move to surface of the axon terminal and the molecules are released into the fluid-filled space between the axon of the presynaptic (sending) neuron and the membrane of the postsynaptic (receiving) neuron. 4. The molecules cross the synaptic space and bind themselves to receptor sites: large protein molecules embedded in the receiving neron’s cell membrane. Each receptor site has a specifically shaped surface that fits a specific transmitter molecule, like a lock and key.  When transmitter molecule binds to a receptor site, a chemical reaction occurs. This reaction can have two different effects on the receiving neuron.  When an excitatory transmitter is at work, the chemical reaction causes the receiving neuron’s sodium channels to open, ions flow through and depolarize, creating action potential  An inhibitory neurotransmitter will do opposite. Cause positive K+ to flow out of neuron, increasing negative potential and making it harder to fire the neuron. 5. Once binded to receptor, it continues to excite/inhibit the neuron until it is shut off. Can happen in two ways:  Some transmitter molecules are deactivated by other chemicals located in the synaptic space that breaks them down into their chemical components.  the deactivation mechanism is reuptake in which the transmitter molecules are taken back into the presynaptic axon terminals. Specialized Neurotransmitter Systems (p.97) Excitatory Inhibitory Excite postsynaptic neuron - Depolarization Inhibits postsynaptic neuron - Increases negative membrane  Acetylcholine potential  Dopamine  GABA  Serotonin  Endorphin (neuromodulator)  Norepinephrine  Norepinephrine Acethcholine (ACh): a neurotransmitter involved in muscle activity and memory.  Alzheimer’s disease (undersupply), paralysis (absence), violent muscle contrations (oversupply) Dopamine: E: involved in voluntary movement, emotional arousal, learning, memory and experiencing pleasure/pain  Parkinson’s disease and depression (undersupply), schizophrenia (overactivity) Serotonin: E/I in mood, sleep, eating and arousal, and may be an important transmitter underlying pleasure and pain.  Depression, sleeping/eating disorder (undersupply), OCD (overactibity) Norepinephrine: E/I functions are various sites; controlling learning, memory, wakefulness and eating  Depression (undersupply), stress/panic (overactivity) GABA: inhibitory transmitter in motor system  Destruction of GABA-producing neurons in Huntington’s disease produces tremors and loss of motor control, as well as personality changes Endorphin: inhibits transmission of pain impulses  Insentivity to pain (oversupply), pain hypersensitivity (undersupply) Most neurotransmitter have their effects only on specific neurons that have receptors for them. Others are called neuromodulators: have a more widespread and generalized influence on synaptic transmission. Eg endorphin Psychoactive Drugs (p.99) chemicals that produce alternations in consciousness, emotion, and behavior.  Alter the synthesis, storage, release, binding, or deactivation of neurotransmitters. Agonist: a drug that increase activity of neurotransmitters Antagonist: a drug that inhibits or decreases the action of  Enhances synthesis, storage, release a neurotransmitter  Mimic a neurotransmitter by binding with and  Reduces synthesis, storage, release, or binding stimulating postsynaptic receptor sites  Prevents binding by blocking receptor sites on  Bind to/stimulate postsynaptic sites postsynaptic neuron  make it more difficult for neurotransmitters to be deactivated, eg inhibiting reuptake Alcohol Nicotine  Depressant Caffeine  an agonist for Acetylcholine.  GABA agonist  an Adenosine anatognist (excites neurons)  Glutamate antagonist  Adenosine inhibits  stimulates Dopamine  overall neural slow-down excitatory transmission (increase energy and and  By reducing adenosine, pleasure), which explains  Inhibits: Rational thinking, excitation is increased, more addiction Emotional control, Motor energy is available. coordination Amphetamines Cocaine  increase Dopamine and Norepinephrine activity by: o cause presynaptic neurons to release more  also increases Dopamine and Norepinephrine activity neurotransmitters by: o Inhibit reuptake, allowing excitatory o Inhibit reuptake of neurotransmitter neurotransmitters to keep stimulating  Causes feelings of excitation, increased muscular postsynaptic neurons strength, and euphoria  Boost arousal and mood Date Rape Drugs (Rohypnol, GHB)  Enhance the activity of GABA  Extremely potent  Causes: Respiratory slowing, Loss of consciousness, Coma, Death, Loss of memory Psychology 100 Chapter 4: The brain and Behaviour N ERVOUS S YSTEM Sensory neurons: carry input message from the sense organs to the spinal cord and brain Motor neurons: transmit output impulses from the brain and spinal cord to the body’s muscles and organs Interneurons: perform connective or associative function within the nervous system  Summary: The major divisions are the CNS and PNS. The peripheral system is divided into the somatic system (responsible for sensory and motor functions) and the autonomic nervous system (which directs the activity of the body’s internal organs and glands). PERIPHERAL NERVOUS SYSTEM (p101) Contains all the neural structures that lie outside of the brain and spinal cord. 1. Enables us to sense events in and out of the body (input functions) eg hunger 2. Enables us to responds to events with muscles and glands (output functions) 1. Somatic Nervous System (sense and respond to environment)  transmit messages from sensory organs to brain (Sensory nerves)  send messages from the CNS to the muscles that control voluntary movements (Motor nerves) 2. Autonomic Nervous System  Regulate body’s internal environment  Controls involuntary functions eg respiration, circulation and digestion, stress responses  Two subdivisions: a) Sympathetic nervous system: activation or arousal function, mobilizes body, and tends to act as total unit b) Parasympathetic nervous system: slows down bodily processes, reduce arousal, more specific in its action o Together they maintain equilibrium or homeostasis: a delicately balanced or constant internal state E.g. Fight-or-flight response (p102 chart)  Under stress, system will: Speed up heart rate (more blood to muscles, increase oxygen); Dilates pupils (enhanced vision); Slows down digestive system (more blood to muscles); Increase respiration rate (more oxygen); Contract vessels (increased blood pressure)  After stress, system will: Contract pupils, constricts bronchi (lungs), slows heartbeat, stimulates activity in stomach, dilates vessels CENTRAL NERVOUS SYSTEM (p102) Contains the brain and spinal cord, which connects most of the PNS with the brain 1. Spinal Cord  Conducts spinal reflexes (do not require brain)  Contains s
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