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Chapter 3

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PSYC 100
Jens Pruessner

Chapter 3 Basic units of the nerve system are called the neurons. These cells receive, integrate, and transmit information in the nervous system. They form neural networks which are not random or arbitrary. The entire nervous system is divided into two functional units: 1. The central nervous system (CNS) which consists of the brain and the spinal cord which consist of nerve cells. 2. The peripheral nerve system (PNS) which consists of all other nerve cells in the rest of the body. These two units are anatomically separate but their functions are highly interdependent. The PNS transmits signals to the CNS where the CNS organizes and evaluates the information and then direct the PNS to perform specific behaviours and make movements. Nerve cells are excitable (unlike other cells) and are specialized for communication. They’re powered by electrical impulses and communicate with other nerve cells through chemical signals. Reception phase: take up chemicals from other neighbouring cells Integration phase: assess incoming signals Transmission phase: pass their signals to another receiving neurons Three basic types of neurons: 1. sensory neurons – detect information from neighbouring neurons and pass information to the brain usually via the spinal cord (aka afferent neurons) 2. motor neurons – direct muscles to contract or relax thereby producing movement (aka efferent neurons which means they transmit information from the brain to the muscles) 3. interneurons communicate within local or short-distance circuits. They integrate neural activity within a single area rather than transmitting information or signal to the brain. Together, sensory and motor neurons control movement. Reflexes are automatic. Neuronal structure: - dendrites: short, branchlike appendages that increase the neuron’s receptive field and detect chemical signals from their neighbours - cell body: also known as the soma, the information received from thousands of other neurons is collected and integrated - axon: where electrical impulses travel - nerve: is a bundle of axons - terminal buttons - synapse: where chemical communication occurs between neurons - synaptic cleft: tiny gap - myelin sheath allows the electrical signals to travel quickly; it encases the neuron; made up of glial cells or neuroglia - Nodes of Ranvier: gaps of exposed neuron where there are ion channels The resting membrane potential is negatively charged. Action potentials cause neuronal communication. Two types of signals are: excitatory and inhibitory. Excitatory signals depolarize cell membranes, increasing the likelihood that a neuron will fire. Inhibitory signals hyperpolarize cells, decreasing the likelihood that the neuron will fire. When a neuron fires, the sodium channels open and depolarize the neuron. The influx of sodium makes the neuron positively charged. After, potassium channels open to let the potassium rush out. Through natural restoration, the membrane repolarizes itself. Earliest symptoms of MS include blurry vision and numbness in limbs. This neurological disorder is characterized by the myelin sheath deterioration, which in turn slows down action potentials. Motor actions become jerky and people lose the ability to coordinate motor movements. Over time, movement, sensation, and coordination are severely impaired. Neuron either fires or it does not which implies the all or none principle. It is the sum of inhibitory and excitatory signals received by the neuron which determines whether the neuron fires or not. Neurotransmitters bind to receptors across the synapse. The three major events that terminate the neurotransmitter influence in the synaptic cleft are: 1. reuptake – neurotransmitter is taken back into the presynaptic terminal buttons 2. enzyme deactivation – occurs when an enzyme destroys the neurotransmitter in the synaptic cleft 3. autoreception – monitor how much neurotransmitter has been released into the synaptic cleft, when excess is detected, the autoreceptors signal the presynaptic neuron to stop releasing neurotransmitter. Drugs and toxins can alter a neurotransmitter’s action in 3 ways: 1. can alter how a neurotransmitter is synthesized 2. they can raise or lower the amount of neurotransmitter released from the terminal buttons 3. by blocking reuptake, they can change the way a neurotransmitter is deactivated in the synaptic cleft and therefore can affect the concentration of the neurotransmitter Drugs that enhance the actions of neurotransmitters are called agonists. They essentially increase how much neurotransmitter is made, so there is more inside each vesicle and can block the reuptake of neurotransmitters. Drugs that inhibit these actions are called antagonists. They decrease the amount of neurotransmitters, so there are fewer in each vesicle and they also help destroy neurotransmitters in the synapse. Drugs and toxins can also mimic neurotransmitters and bind with their receptors. Heroin and cocaine act similarly to the neurotransmitters. Neurotransmitter Functions Acetylcholine Motor control over muscles, learn
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