December 2 Lecture - December 2 2008 Test 64 average Range...

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December 2, 2008 Test: 64% average Range: 20% - 94% Nerve Tracts - When referring to a nerve, it is generally actually a nerve tract - A nerve tract (a collective group of neurons), it is surrounded by a connective tissue covering known as the epineurium o Binds together all of the internal components - Individual axons and myelin sheath (if present), are grouped together in bundles which is referred to as a fascicle or fasciculous - Connective tissue that surrounds a bundle of neurons is the perineurium o It is through this portion of the fibre tract that the blood vessels penetrate - The finer connective tissue that surrounds individual nerve’s is the endoneurium The Reflex Arc - Any movement within the body is dependent upon the contraction of skeletal muscle - There are two types of movement that may be involved: o Reflex contraction o Voluntary contraction - Can involve glandular tissue, not just skeletal muscle o Ex. when eye is touched, tears are secreted by reflex - Reflex responses do not depend on the brain, instead they are controlled by the spinal cord and a nerve pathway or circuitry - Reflex arc has a number of essential components o Some type of a receptor (can be organized or simple – ex. free nerve endings of a neuron) o Sensory fibre (sensory neuron) Afferent fibre o Interneuron Also known as: internuncial neuron or interconnecting neuron o Motor neuron
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Efferent neuron o Effector organ or tissue Will respond to stimuli associated with the nerve circuitry The Reflex Arc - Receptor is connected to afferent neuron which will carry information to the central nervous system o Receptor will pickup stimulus and convert it into a potential which will transmit to the afferent neuron - Afferent neuron will enter the dorsal root ganglion and into the grey matter of the spinal cord o Dendrite of neuron will run from the receptor to the dorsal root ganglion, the axon is considerably shorter, will move information from the dorsal root ganglion to the dorsal horn (dendrites are longer than axon – and exception from normal) - Interneuron will synapse at the dorsal horn and transmit information to the ventral horn o A relatively short neuron o Interconnecting neurons are found only in the central nervous system o Cell body is located in the grey matter, while the axon extends into the ventral horn to synapse with the efferent (motor) neuron - Motor neuron has relatively short dendrites, cell body located within the ventral horn and axon will extend from the spinal cord out to the outer regions of the arm to synapse with muscle fibres in the upper arm o Signals will bring about contraction of muscles in the upper arm
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December 2 Lecture - December 2 2008 Test 64 average Range...

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