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Chapter 9
Term | Definition |
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Hormones | are chemical substances secreted into body fluids by a gland. These substances have specific effects on the activities of target cells, tissues, or organs. |
Primary ossification centers | areas in the midportion of the shafts of long bones where bones cells are formed so that the cartilage-model bones of the fetal skeleton begin ossifying, from the center outward, to form bone shafts. |
Twitch | is a brief period of contraction of a muscle fiber (cell) followed by relaxation. |
Slow twitch | muscles that have slower contraction relaxation cycle and greater endurance. |
Fast twitch | muscles that have fast contraction relaxation cycle and lower endurance. |
Neurons | are the cells of the nervous system that receive and transmit information. |
Synapse | is a connection between two neurons; it is made by the release of chemicals called neurotransmitters from an axon. These neurotransmitters cross a small gap between neurons, then permeate the cell wall at the dendrite, or cell body, of receiving neuron to |
Secondary ossification centers or epiphyseal plates | areas near the ends of long bones where new bone cells are formed and deposited so that the bones grow in length. Active secondary oddification centers are indicated on X rays by a line (an area not opaque) that is a layer of cartilage cells. Such an area |
Appositional bone growth | involves the addition of new layers on previously formed layers so that a bone grows in girth. |
Glia | are the cells of the nervous system that support and nourish the neurons. |
Myelin | is an insulating sheath around the axons. |
Cerebral cortex | is the wrinkles surface of the brain containing millions of neurons and regulating many human functions and behaviours. |
Myelination | the process whereby the axons of the neural cells are insulated when insulating myelin sheaths formed by Schwann (glial) cells wrap themselves around the axon. |
Nerve tracts | major neurological pathways. There are two major motor tracts |
Neurogenesis | the division and propagation of neurons. |