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Wilfrid Laurier University
Jim Mc Cutcheon

10/27/2013 8:30:00 AM The Nervous System Two main parts: Central nervous system (CNS): receives, processes, interprets, & stores incoming sensory information; sends out messages to muscles, glands, organs Peripheral nervous system (PNS): handles input & output from the CNS; all portions of the nervous system outside the brain & spinal cord Central Nervous System Two Components: Brain and Spinal Cord Spinal cord is a bridge between the brain and parts of the body below the neck Spinal nerves protected by the spinal column Enables spinal reflexes Peripheral Nervous System Contains two subdivisions (messages carried through sensory and motor nerves): 1. Somatic Nervous System: nerves connected to sensory receptors and skeletal muscles 2. Autonomic Nervous System: regulates functioning of blood vessels, glands, & internal organs contains the sympathetic and parasympathetic nervous system Communication in the Nervous System Nervous system is made up of: Neurons: cells that conduct electromagnetic signals, basic unit of the nervous system Glia: cells that support, nurture, and insulate neurons, remove debris when neurons die, enhance the formation & maintenance of neural connections, and modify neural functioning Structure of the Neuron Approximately 100 billion neurons in the brain Neurons vary in size and shape Dendrites Branch-like fibres that receive information from other neurons and transmit towards cell body Cell body Keeps neuron alive and plays key role in determining whether neuron will “fire” Axon Extending fibre that conducts impulse away from cell body and transmit to other cells Branches at end called axon terminal May be collected together in bundles called nerves Myelin Sheath Many axons are insulated by surrounding layer of fatty called myelin sheath In the CNS, this is made up of glial cells Constrictions in covering (nodes) divide myelin into segments Purpose to speed conduction of neural impulses & prevent interference from neighboring signals Neurons in the News Neurogenesis: production of new neurons from immature stem cells Stem cells: immature cells that renew themselves and have potential to develop into mature cells stem cells from early embryos develop into any cell type Stem-cell Research Embryonic stem cells can differentiate into any type of cell; adult stem cells limited Use is controversial and surrounded by ethical debates regarding extraction* Most promising in developing treatments for cancer, blood, organ, and brain disorders (e.g., Parkinson’s) Canadian researchers have had some success with adult stem cells transforming to brain cells How Neurons Communicate No direct contact between neurons Communicate through the synapse Includes the axon terminal, synaptic cleft, and receptor sites in the membrane of the receiving cell Communication occurs through electrical and chemical signals Stimulation causes change in charge between inside and outside of cell Inflow of sodium ions causes an action potential Synaptic vesicles release chemicals called neurotransmitters Neurotransmitters bind to receptor sites on receiving neuron and causes changes in the cell membrane Excitatory changes – a voltage shift in a positive direction Increases probability of receiving neuron firing Inhibitory changes – a voltage shift in a negative direction Decreases probability of receiving neuron firing Brain Plasticity Plasticity The brain’s ability to change and adapt in response to experience (e.g., reorganizing or growing new neural connections) Behavioural deficits that occur as a result of brain damage may be lessened by enriching environment people live in Chemical Messengers Neurotransmitters A chemical substance that is released by a transmitting neuron at the synapse and that alters the activity of a receiving neuron Major neurotransmitters: Serotonin, dopamine, acetylcholine, norepinephrine, GABA, glutamate Each neurotransmitter has different effects Serotonin: sleep, appetite, sensory perception, temperature regulation, pain suppression, mood Dopamine: voluntary movement, learning, memory, emotion, pleasure or reward, response to novelty Acetylcholine: muscle action, cognitive functioning, memory, and emotion Norepinephrine: increased heart rate, slowed intestinal activity during stress, learning, memory, dreaming, waking , emotion GABA: major inhibitory neurotransmitter Glutamate: Major excitatory neurotransmitter in brain The synapse: When a neural impulse reaches an axon’s terminal buttons, it triggers the release of chemical messengers called neurotransmitters. The neurotransmitter molecules diffuse across the synaptic cleft and bind to receptor sites on the postsynaptic neuron. A specific neurotransmitter can bind only to receptor sites that its molecular structure will fit into, much like a key must fit a lock. Endorphins Chemical substances in the nervous system that are similar in structure and action to opiates Involved in pain reduction, pleasure, and memory Technically known as endogenous opioid peptides Hormones Chemical
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