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Chapter 4

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Kathy Foxall

Chapter 4: The Brain: Source of Mind and Self The Nervous System: A Basic Blueprint The Central Nervous System  Portion of the nervous system consisting of the brain and the spinal cord  Receives, processes, and stores sensory information  Spinal cord o Collection of neurons and supportive tissue running from the base of the brain down the centre of the back, protected by a column of bones o Spinal reflexes  Automatic, require no conscious effort (hot iron)  Reflexes influenced by thoughts and emotions (e.g. erection)  Neural circuits underly many spinal reflexes linked to neural pathways that run up and down spinal cord, to and from brain The Peripheral Nervous System  Handles central nervous system input and output  Contains portions of the nervous system outside the brain and spinal cord  Sensory nerves o Carry messages from receptors in skin, muscles, and other internal and external sense organs to the spinal cord, which sends them to the brain  Motor nerves o Carry orders from central nervous system to muscle, gland, and internal organs o Cause glands to secrete hormones  Somatic nervous system o Subdivision of peripheral nervous system that connects sensory receptors to skeletal muscles  Autonomic nervous system o Subdivision of peripheral nervous system that regulates internal organs and glands  Sympathetic nervous system o Subdivision of the autonomic nervous system that mobilizes bodily resources and increases output of energy during emotion and stress  Parasympathetic nervous system o Subdivision of nervous system that operates during relaxed states and conserves energy Communication in the Nervous System  Neurons o Cell that conducts electrochemical signals, basic unit of the nervous system, called a nerve cell o Transmit info through central nervous system  Glia o Cells that support, nurture, and insulate neurons, remove debris, and enhance formation and maintenance of neural connections  Estimate 100 billion neurons in brain The Structure of the Neuron  Dendrites o Neuron’s branches that receive info from other neurons and transmit it towards the cell body  Cell body o Part of the neuron that keeps it alive and determines whether or not it will fire  Axon o Neuron’s extending fibre that conducts impulses away from the cell body and transmits them to other neurons  Myelin sheath o Fatty insulation that may surround the axon o Prevent signals in adjacent cells from interfering with each other, speeds up conduction of neural impulses  Nerve o Bundle of nerve fibres in the peripheral nervous system (axons and dendrites)  Cranial nerves o Connect directly to the brain Neurons in the News  Neurogenesis o The production of new neurons from immature stem cells  Stem cells o Immature cells that renew themselves and have the potential to develop into mature cells; given encouraging environments, stem cells from early embryos can develop into any cell type o ES cells useful, differentiate into any type of cell How Neurons Communicate  Synapse o Site where transmission of a nerve impulse from one nerve cell to another occurs o Includes the axon terminal, synaptic clef, and receptor sites in the membrane  Action potential o Brief change in electrical voltage that occurs between the inside and outside of an axon when a neuron is stimulated o In unmyelin sheath, gives rise to new action potential at next point o In myelin sheath, action potential hops from one node to the next at a faster rate, causes regeneration of action at each node  Neurotransmitter o Chemical substance released by a transmitting neuron at the synapse, alters activity of receiving neuron at tip o Molecules bind briefly with receptor sites  Excitatory o Shift in positive direction  Inhibitory o Voltage shift in negative direction The Plastic Brain  Plasticity o Brains ability to change and adapt in response to experience, reorganize neural connections  Unused connections pruned away as cells or branches die, leave more efficient neural network, explain critical development periods Chemical Messengers in the Nervous System Neurotransmitters  Serotonin affects neurons involved in sleep, appetite, perception, suppression  Dopamine affects movement, memory, learning, emotion (parkinsons loss of dopamine)  Acetylcholine affects muscle action, cognitive functioning, memory, function (Alzheimer’s can’t produce it)  Norepinephrine affects heart rate and intestinal activity  GABA is major inhibitory in the brain (sleep/eating disorders/EPILEPSY)  Glutamate major excitatory in brain (multiple sclerosis overproduce)  DISORDER MAY LEADS TO ABNORMAL NEUROTRANSMITTER RATHER THAN OTHER WAY AROUND Endrophins  Chemical substances in the nervous system that are similar in structure and action to opiates; involved in pain reduction, pleasure, memory, and are known technically as endogenous  Endorphin levels seem to shoot up when an animal or person is afraid or under stress/pain Hormones  Chemical substances secreted by organs called glands, that affect the functioning of other organs  Endocrine glands o Internal organs that produce hormones and release them into the bloodstream  Melatonin o Secreted by pineal gland, involved in daily regulation of biological rhythms  Oxytocin o Secreted by pituitary gland, stimulates contraction, milk, promotes trust in sexes  Adrenal hormone
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