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Chapter 3

textbook note Chapter 3

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Steve Joordens

3 Neuroscience and Behaviour The electrical and chemical activities of neurons are the starting point of all behaviour, thought, and emotion. Neurons: Origin of Behaviour  Approximately 100 billion cells in your brain perform a variety of tasks to allow a person to function  Neurons are cells in the nervous system that communicate with one antoher to perform information-processing tasks. Discovery  In the 1800s scientists studied the mechanics of limbs, lungs and livers in order to study the harder-to-observe brain.  Believed the brain was composed of many lattices of fine threads.  Late 1880s Spanish physician, Santiago Ramon y Cajal found that the cells came in different shapes and sizes.  Cajal concluded that neurons are the information-processing units of the brain Components of the Neuron(pg 79) 3 basic parts:  Cell Body (Aka soma) -Largest component of the neuron -Functions such as protein synthesis, energy production, and metabolism -contains a nucleus; this structure houses chromosomes that contain your DNA -surrounded by a porous cell membrane that allows molecules to flow in and out (There are 2 types of specialized extensions of the cell membrane)  Dendrite -recieve information from other neurons and relay it to the cell body -dendrites and axons do not touch  Axon -transmits info. To other neurons, muscles or glands -each neuron has a single axon that stretches up to 1metre -covered by a myelin sheath(insulation) which is made of glial cells(support cells and has 10-50x more than neurons) (Refer to fig. 3.6) GLIAL CELLS -digests parts of dead neurons, others provide physical and nutritional support for neurons, and others form myelin to help the axon Components of the Neuron(pg 81)  Sensory neurons – receive information from the external world and convey this information to the brain via the spinal cord.  Motor Neurons- carry signals from the spinal cord to the muscles to produce movement  Interneurons- connect sensory neurons, motor neurons, or other interneurons. Neurons by location Purkinje cells- carries info from cerebellum to rest of brain and spinal cord Pyramidal cells (triangular)- found in the cerebral cortex has a long dendrite among many smaller dendrites Electrochemical Actions of Neurons: Info. Processing  Neurons communication of information happens in 2 stages(conduction and transmission)  Conduction-sends electrical signal over long distances within neurons, from the dendrites to the cell body then throughout the axon  Transmission- transmitting chemical signals between neurons over the synapse  Together they’re referred to as electrochemical action of neurons Resting potential(pg83) the difference in electric charge between the inside and outside of a neuron’s cell membrane  Works much like the ‘+’ and ‘-‘ of a battery Action Potential(pg84-85)an electric signal that is conducted along a neuron’s axon to a synapse  Always occurs with the same characteristics  Occurs when there is a change in the state of the axon’s membrane channels.  When it reaches maximum, the membrane channels revert to their original state and K+ ions flows out until axon returns to the resting potential.  Refractory period:The time following an action potential during which a new action potential cannot be initiated. Chemical Signaling:Transmission between Neurons Axons usually end in terminal buttons, which are knoblike structures that branch out from an axon. A terminal button is filled with tiny vesicles, or ‘bags that contain neurotransmitters, chemicals that transmit information across the synapse to a receiving neuron’s dendrites. The dendrites of the receiving neuron contain receptors, parts of the cell membrane that receive neurotransmitters and either initiate or prevent a new electrical signal. (86) Acetylcholine(Ach), Dopamine, Glutamate, Norepinephrine, Endorphins (definitions all on page 87) Prozac, a commonly used drug to treat depression is an agonist. Prozac blocks the reuptake of the neurotransmitter serotonin, making it a part of a category of drugs called selective serotonin reuptake inhibitors or SSRIs Agonists(refer to figure 3.8):are drugs that increase the action of a neurotransmitter. (antonym:Antagonists) An antagonist with important medical implications is a drug called propranalol, one of a class of drugs called beta-blockers that obstruct a receptor site for norepinphrine in the heart. Organization of the Nervous System  There are 2 major divisons of the nervous system: the central(CNS) and peripheral nervous system(PNS) CNS  Controls where information goes.  At the top rests the brain which contains structures that support the most complex perceptual, motor, emotional, and cognitive functions. PNS  2 subdivisions, -the Somatic nervous system: conveys info in and out of the CNS -the Autonomic nervous system: carries involuntary and auto commands that control blood vessels, body organs and glands. 2sub-categories Sympathetic nervous system: a set of nerves that prepares the body for action in threatening situations Parasympathetic nervous system: helps the body return to a normal resting state Components of the CNS  Consists of the spinal cord and the brain  The spinal cord keeps you breathing, respond to pain, move muscles and allows you to walk  The spinal cord is just as important as the brain, it carries out the commands of the brain, the brain and spinal cord work side-by-side  Spinal reflexes are simple pathways in the nervous system that rapidly generate muscle contraction BRAIN STRUCTURE:  Simple tasks are done near the bottom of the brain whereas more complex tasks at the top.  Separated into 3 parts from bottom to top(Hindbrain, Midbrain, and Forebrain) Hindbrain coordinates info. Coming in and out of spinal cord.(96) -Medulla extension of the spinal cord into the skull that coordinates heart rate,circulation and respiration -Reticular formation located in the medulla;regulates sleep, wakefulness and arousal Midbrain(relatively small) important for orientation and movement(96) -Tectum orients an organism in the environment (e.g. you hear a sound to the left behind you, your body starts turning towards that direction) -Tegmentum involved with movement and arousal Forebrain:important for complex cognitive, emotional, sensory and motor functions. It is divided into 2 parts: cerebral cortex and underlying subcortical.(97) -Cerebral cortex(Outer) -responsible for complex aspects of perception, emotion, movement and thought. 3 levels of organization Level 1: -the raised part are called gyri(singular is called gyrus) -the fissures or indentations are called sulci(singular is sulcus) -each hemisphere controls the opposite of the body, this is called contralateral control -The hemispheres are connected by commissures, bundles of axons -The largest of these commissures is the corpus callosum which connects large areas of the cerebral cortex on each side of the brain Level 2: 4 lobes from back to front, occipital lobe, parietal lobe, temporal lobe, and frontal lobe Occipital processes visual information. Sensory receptors in the eyes send and receive info from thalamus Parietal processes info about touch.It contains the somatosensory cortex, a strip of brain tissue running from top of the brain to the sides, the motor cortex is parallel to the somatosensory.(refer to fig. 3.22) T
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