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PS102 (318)
Chapter 3


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Carolyn Ensley

CHAPTER 3: Nervous System Nervous System- complex communication networks in which signals are constantly being transmitted, received and integrated - behaviour depends on rapid information processing The 2 types of Nervous System Cells are… - Glia- “glue”; provide structural support, nourishment and insulation for neurons o involved in the removal of waste o helps maintain the chemical environment of the neurons - Neurons- the individual cells in the Nervous System that receive, integrate (put together) and transmit information o basic links that permit communication Soma- or cell body; contains the cell nucleus and much of the chemical machinery common to most cells - used for handling information Dendrites- the parts of a neuron that are specialized to receive information (branch-like) Axon- a long, thin fibre that transmits signals away from the soma, to other neurons or to muscles or glands - branch off to communicate with a number of other cells Myelin Sheath- an insulating material, derived from glial cells, that encases some axons - serves to speed up the transmission of signals that move along axons Terminal Buttons- located at the axon end; small knobs that secrete chemicals called neurotransmitters - neurotransmitters- serve as messengers that may activate neighbouring neurons; chemicals that transmit information from one neuron to another Synapses- a junction where information is transmitted from one neuron to another The General Pathway of Information… (visual on pg 79 – Fig.3.1) - dendrites receive information - information is passed to the soma - along the axon - transmitted to synapses of adjacent neurons - neurotransmitters are released to activate neuron (triggered by terminal button) - information is now in new neuron, and being passed to the dendrites (which are then connected to other axon  new neuron) Neural Impulse- complex electrochemical reaction  energy used to send information (pg 81– Fig.3.2) + - positively charged on the outside (K ) - - negatively charged on the inside (Na) - they do not cross the membrane at the same time  creates overall charge - neuron therefore, carries potential energy and acts as a tiny battery - resting potential- of a neuron is its stable, negative charge when the cell is inactive - when the neuron is stimulated, channels in its cell membrane open (sodium gates open) Action Potential- is a very brief shift in a neuron’s electrical charge that travels along the axon - created at the point when the neuron’s charge is less negative - firing action channels in the cell membrane that opened to let in sodium close up Absolute Refractory Period- the minimum length of time after an action potential during which another action potential cannot begin All-or-None Principle: - neuron fires or it doesn’t - action potential is all the same size - weaker stimuli do not produce smaller action potentials - the stronger the stimulus, will cause the cell to fire more rapidly (rate) THE SYNAPSE: where neurons meet 1. Sending Signals: Synaptic Cleft- a microscopic gap between the terminal button of one neuron and the cell membrane of another neuron - presynaptic neuron- sends the signal across the gap to… - postsynaptic neuron- receives the signal - synaptic vesicles- where the chemicals released by the neurotransmitter are stored (in the terminal button) Neurotransmitters- are triggered when the presynaptic cell and its contents spill into the synaptic cleft - after they are released, they diffuse across the synaptic cleft to the membrane of the receiving cell and find their appropriate receptor site 2. Receiving Signals: (pg 83 – Fig.3.4) Postsynaptic Potential (PSP)- a voltage change at a receptor site on a postsynaptic cell membrane - they do not follow the all-or-none principle, but are graded - vary in size  increase or decrease the probability of a neural impulse - Sends two types of messages… o Excitatory PSP- the positive voltage shift that increases the likelihood that the postsynaptic neuron will fire action potentials o Inhibitory PSP- a negative voltage shift that decreases the likelihood that the postsynaptic neuron will fire action potentials Some neurotransmitters do not bind and drift away or are inactivated… - reuptake- a process in which neurotransmitters are sponged up from the synaptic cleft by the postsynaptic membrane o recycles their material 3. Integrating Signals: Integrate- to bring together as a whole - must be done before it ‘decides’ whether to fire a neural impulse - electrical currents add up  voltage to reach the threshold (an action potential will be fired) - neuron state is weighted on balance between excitatory and inhibitory influences Our perceptions, thoughts and actions depend on patterns of neural activity in elaborate neural networks Synaptic Pruning- a process by which the nervous system gradually eliminates less active synapses - this is key in the formation of the neural networks that are crucial to communication in the nervous system Cell Assemblies- a complex network of neurons, which are linked to each other  influence behaviour NEUROTRANSMITTERS AND BEHAVIOUR… - there are nine, well established, transmitters - lock-and-key theory: just as a key has to fit a lock to work, a transmitter has to fit into a receptor site for binding to occur o reduces cross-talk  making the nervous systems communication more precise Acetylcholine (ACh) – the transmitter between motor neurons and voluntary muscles Agonist- a chemical that mimics the action of a neurotransmitter - example: ACh synapses will be stimulated by nicotine that arrives in your brain (fools the brain)  nicotine is the agonist Antagonist- a chemical that opposes the action of a neurotransmitter; blocks the action of the natural transmitter by occupying its receptor sites, making them unusable Monoamines- regulate many aspects of everyday behaviour; they include 3 neurotransmitters… - dopamine (DA): controls voluntary movement; pleasurable emotions - norepinephrine (NE): contributes to modulation of mood and arousal - serotonin: involved in regulation of sleep and wakefulness, eating and aggression GABA (gamma-aminobutyric acid) – serves as widely distributed inhibitory transmitter; regulates anxiety Endorphins- resemble opiate drugs in structure and effects - morphine – exerts its effects by binding to specialized receptors in the brain - endorphins – internally produced chemicals that resemble opiates in structure and effects THE NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM BRIAIN SPINAL CORD SOMATIC AUTONOMIC (voluntary) (involuntary) SYMPATHETIC PARASYMPATHETIC PERIPHERAL NERVOUS SYSTEM: …is made up of all those nerves that lie outside the brain and spinal cord Nerves- the bundles of neuron fibres (axons) that are routed together - the part that extends outside the central nervous system The Somatic Nervous System- made up of nerves that connect to voluntary skeletal muscles and to sensory receptors - Afferent Nerve Fibres- carry information from receptors (skin, muscle, joints)  CNS - Efferent Nerve Fibres- carry information from the CNS  muscles The Autonomic Nervous System (ANS)- is made up of nerves that connect to the heart, blood vessels, smooth muscles and glands - controls involuntary, intuitive functions that people don’t normally think about - fight-or-flight response: organisms generally respond to threat by preparing physiologically for attacking (fight) or fleeing (flight) from the enemy Sympathetic- the branch of the ANS that mobilizes the body’s resources for emergencies - signal adrenal glands to secrete hormones that ready the body for exertion Parasympathetic- the branch of the ANS that generally conserves bodily resources - allow body to save and store resources THE CENTRAL NERVOUS SYSTEM: … consists of the brain and the spinal cord The Spinal Cord- connects the brain to the rest of the body through the PNS - houses bundles of axons that carry the brain’s commands to peripheral nerves and relay sensations from the periphery of the body to the brain The Brain- contains billions of interacting cells that integrate information from the body, coordinates body actions, and enables humans to speak, think, and remember  behaviour - Cerebrospinal fluid (CSF)- nourishes the brain and provides a protective cushion for it THE BRAIN The Brain can be divided into 3 major regions… (pg 96 – Fig.3.15) 1. Hindbrain: included the cerebellum and two structures found in the lower part of the brainstem (medulla and the pons) - medulla – attaches the brain to the spinal cord; charge of the largely unconscious but vital functions - pons – includes the bridge of fibres that connects the brainstem with the cerebellum - cerebellum – “little brain”; a relatively large and deeply folded structure located adjacent to the back surface of the brainstem o coordinates movement o equilibrium o organizes sensory info that guides muscular movements 2. Midbrain: the segment of t
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