During middle age, the ability to hear higher-pitched sounds declines first. Presbycusis is the aging-hearing loss that occurs as a result of the aging process. It is a slow process that affects botrh ears equally thus difficult to notice, the first signs is the inability to understand speech in noisy environments and high frequency sounds.
The nervous system sends electrical impulses to certain cells receptors that stimulate the immune system to produce antibodies to fight foreign bodies.
