What is the role of the ear in the sensing of sound?

The ear is the main body part responsible for sensing sound. It is made up of a number of different structures which allow humans and other animals to hear. The structure of the external ear (the part of the ear which one can see), is shaped in a way that it can amplify sound waves that it receives from the environment. 

The actual sensing of sound waves occurs in the middle and inner ear...

The ear is the main body part responsible for sensing sound. It is made up of a number of different structures which allow humans and other animals to hear. The structure of the external ear (the part of the ear which one can see), is shaped in a way that it can amplify sound waves that it receives from the environment. 

The actual sensing of sound waves occurs in the middle and inner ear. The middle ear is a small compartment filled with air and small bones to carry sound waves. When a sound wave hits the ear drum, the barrier between the external ear and middle ear, it causes a vibration. This vibration from the sound wave resonates through the malleus which is attached to the ear drum. The wave then travels through the malleus to the attached incus, and finally, to the stapes which is attached to the incus. Interestingly, these three bones are the smallest three in the body. 

The stapes is attached to the inner ear. This attachment is to a small "oval window" that serves as the barrier for the inner ear to the middle ear. Pushing and pulling of the stapes on the window then sends the sound waves through the fluid filled cochlea. Inside the cochlea, a large amount of small hairs cells are present. Once a wave is detected, these hair cells fire much like neurons and send signals to the brain. Based on how many hair cells fire, and where they are located, the brain is able to use this information to determine the frequency, and pitch of the sound. Specifically, signals are sent to the "superior olivary nucleus, the inferior colliculus, the medial geniculate nucleus, and the auditory cortex." It is here that processing occurs. It is also here that sound wave information from both ears meets and is processed. This allows the person or animal hearing to determine the location of the sound. Hope this helps!