security threat meaning, security threat definition | English Cobuild dictionary. security. 1 n-uncount Security refers to all the measures that are taken to protect a place, or to ensure that only people with permission enter it or leave it.
A muscle expands when it relaxes. The muscles in our bodies are attached to bones. They help the bones move, much like strings help a puppet move. But muscles can pull in only one direction. They cannot push.Each bone is usually attached to a pair of muscles.ones and muscles work like  ropes and levers. The muscles can only pull against the bone not  push it. So to bend your arm at the elbow, the â¦ bicep pulls the  lower arm up. To streighten your arm, the tricep pulls the lower  arm back out. the muscles have to work in pairs opposite each other  to make movement.
The joints between bones allow movement, some allowing a wider range of movement than others, e.g. the ball and socket joint allows a greater range of movement than the pivot joint at the neck. Movement is powered by skeletal muscles, which are attached to the skeleton at various sites on bones.t is composed of 270 bones at birth â this total decreases to 206 bones by adulthood after some bones have fused together. The bone mass in the skeleton reaches maximum density around age 30.