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Chapter 3

Ch. 3 notes - Neuroscience Part 1.docx

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Christopher Teeter

Neuroscience • Don’t actually experience anything directly – stimulus from environment triggers series of events in CNS – then we become aware of these processes, not the direct stimuli itself • Structural questions – what is the brain made of? How is it constructed? What are the different parts and how are they connected? - give us a map/blueprint of the brain’s structure • Functional questions – what do all the parts do? – if you don’t know what a part does, you will never understand why it is there – understand the whole picture • Brain makes up 2% of body weight but consumes a large proportion of the energy supply – burns 20% of our oxygen intake at rest • 2 basic cell types: glial cells and neurons • Glial cells – provide structure and perform “housekeeping” tasks in the brain – far more glial cells than neurons • Neuron – typically referred to as the ‘brain cell’ – 100 billion in an adult human brain – may form synapses with thousands of other neurons – result in brain with a thousand trillion different connections • Organelles – smaller parts of biological machinery in the cells that perform a specific function • Reductionist problem – can’t really explain all aspects of human behaviour just based on activity of the neurons - psychologists need to examine the brain from different levels/perspectives Consciousness and Awareness • Widespread belief that mind is separate from physical nature possibly arises from what seems like irreconcilable differences between thoughts, memories, sensations and the physical operation of our bodies • Rene Descartes (1596-1650) – dualist – body is a machine that follows laws of physics and is distinct form the mind/mind is a non-physical entity and does not follow the laws of physics • Believed that the seat of the soul was in the pineal gland – somehow affected control of body through nerves • These ideas encouraged others to investigate how the body operates – neurobiology and neuropsychology developed – inc. successful at explaining mental phenomena • So far there has not been any successful challenges to the idea that it is impossible for the mental state of a person to change without some physical change in their brain • Epilepsy and the Split Brain • Interesting demonstration of the relationship between consciousness, awareness and the underlying physical structure of the brain is found by studying behaviour of people who have undergone surgery for treatment of epilepsy • Epilepsy – chronic disorder characterized by recurring seizures caused by abnormal brain activity • Known as “falling sickness” in the middle ages • Most individuals can be made seizure-free with drug therapy – about 20% cannot be helped • Surgery targets exact area of the brain where seizures originate • Split-brain surgery – in patients with severe epilepsy, the seizure started on one side of the brain then crossed over to the other side – performed corpus callosotomies – severed some/all nerve fibers connecting 2 hemispheres – had adverse effects on the brain’s normal functioning so after the 1960s, very few were performed • Experiments performed on the split-brain patients revealed info about hemispheric specialization – different sides of the brain perform different functions  A patient with a split brain that was shown an image in his left visual field (projects to right side of the brain) would be unable to name what he saw – left side of brain controls speech function  A patient shown a picture of an object to the right visual field (projects to left brain) would be able to name the object but not pick it up using their left hand – left hand controlled by right side of brain  Sometimes 2 brains seemed to take on almost completely independent existences – one patient (an accountant) was asked to write out what he would like to do for a living – wrote “accountant” with right hand and “racing driver” with left Divisions of the Nervous System – The Central and Peripheral Nervous Systems • This part just talks briefly about what the CNS and PNS consist of – divided by structure • The Somatic and Autonomic Nervous Systems • PNS divided further – based on function • Somatic – receives sensory info and controls voluntary muscle movement • Autonomic – involuntary – regulates smooth muscle, cardiac muscle, and glands  Divides further into sympathetic and parasympathetic  Sympathetic – fight/flight – dilate pupils, dilates internal structures of the lungs, and inhibits digestion, contraction of the bladder and contraction of the rectum º all happen at once º also causes release of E form adrenal gland into blood – ensures response reaches organs not connected directly to nerves  Parasympathetic – opposite in nature – slowing of the heart, dec. in BP, constrict pupils, inc. activity in GI tract, and secretion of digestive juices º Return body functions to normal after sympathetic stimulation º Conserve and inc. body’s energy stores The Nerve Cell and the Action Potential • The Neuron • All animals incl. humans are eukaryotes – cells have complex structure – a number of elements have distinct roles in its operation • Each cell has a cell body (soma) surrounded by membrane – nucleus inside contains DNA (regulates much of the cells operation and other membrane-bound organelles such as mitochondria and ribosomes) • Organelles act as chemical factories – responsible for synthesizing various substances for operation of the cell • Neuron – specialized cell for integrating and communicating info – transmits info via chemical and electrical signals • STRUCTURE OF THE NEURON  Dendrites – receive and integrate incoming info  Axons – pass info to other cells  May branch several times to carry the impulse to multiple destinations  Destination may be another neuron/another cell (ex. muscle/gland) capable of receiving and responding to a nerve impulse (effectors)  Sequence of electrical activity: dendrites (info is gathered)cell body (info from multiple dendrites is integrated)axon (signal transmission)other neurons/effector cells (info is acted upon) • THE DENDRITE  Branched projections that conduct nerve impulses received from other cells to the cell body are usually fairly short (few hundred microns away from the cell)  Covered in tiny spines – connections from other neurons on the spines are made at a synapse (gap that message must cross to get from one neuron to the next)  Bring together impulses occurring across many thousands of synapses to their final destination at the cell body • THE CELL BODY  Soma of a neuron in a human  Ranges from 4 microns in the smallest type of neuron (granule cell) to about 100 microns for a motor neuron in the sc  The axon exits the cell body from a large elongated portion known as the axon hillock • THE AXON  Carries info to the terminal boutons/end terminals – where connections to other neurons are made  Basic message carried by the axon is the AP  Surrounded by a myelin sheath – tube of fatty tissue (part of glial cell) – insulates axon from other axons and speeds up conduction of AP  White matter in brain (more than half of the brain volume) made up of myelinated axons – some are short (1-3mm) and other are longer (up to 170mm) running through corpus callosum  Longest axons run through sciatic nerve (bundle of axons)  Trigeminal nerve contains 150,000 axons • NEURON SUBTYPES  Info from environment is sent to rest of NS by sensory neurons - some responsible from gathering info directly form environment (ex. sensing pressure on surface of skin)/some responsible for converting/transducing physical stimuli from outside world to specialized receptor cells (ex. cells of inner ear converting sound vibrations to nerve impulses) – in this case receptor cells connect directly to sensory neurons  Effector neurons (most common ones are motor neurons) activate muscle of the body controlling movement  Between sensory and motor neurons are interneurons – majority of neurons in the NS – come in different varieties each with different dendrite and axon sized and shapes  Most common type is the multipolar neuron – multiple dendrites extending form cell body and 1 axon  Bipolar neuron – 1 dendrite exiting the side of the cell body and 1 axon exiting the other  Unipolar neuron – 1 process leaving the cell body and branches into 2 directions (1
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