Video 2-Auditory Transduction (in detail)

[Note: Mr. Friend, you told us not to go into detail and I understand that it is not on the syllabus. But the content of the second video was quite interesting and the pieces sort of fit together a bit better with some detail so I went into a little bit of detail. ]

The sense of hearing is accomplished by a process known as auditory transition. (transmitting sound waves)

the ear converts sound waves in the air into electrical impulses which can be interpreted by the brain. 

As sound enters the ear it asses through the external auditory canal where it meetings the tympanic membrane. 

The tympanic membrane then vibrates in response to the sound. 

Sounds of a lower frequency produce a slower rate of vibration and sounds of a lower volume or amplitude produce a less dramatic vibration. 

higher frequency sounds produce FASTER vibrations. 

the tympanic membrane is cone shaped and is connected to 3 bones collectively known as the auditory ossicles. They consist of the malleus, the incus and the stapes.  

The movement of the tympanic membrane causes the ossicles to vibrate passing on the information of the sound wave (frequency of amplitude). 

The three bones pivot together on an axis. The pivotal axis is due to a series of ligaments which hold the bones in place within the middle ear cavity (space). The two main ligaments are the malleal ligament and the posterior costal ligament. 

The vibrations are transmitted eventually to the footplate of the stapes. 

The stapes moves with a piston like action which sends vibrations into a bony labyrinth. 

The labyrinth is filled with a fluid called perilymph. It is important because if the bony structure was closed and inflexible then the stapes movement would be unable to displace the perilymph and vibrations would be unable to be sent. 

Due to the flexibility of a membrane called the oval window. The stapes movement can displace the perilymph allowing vibrations to enter the labyrinth. 

The corridor leading to the round window (one of the two openings of the inner ear) is found within the spinal portion of the bony labyrinth (called the cochlea). --> snail shaped structure. 

Vibrations are produced by the stapes and are drawn into the spiral system and is sent through the round window for the vibrations to dissipate in the inner ear.

Portion of the passage by which vibrations travel have names:

-vibrations ascend via the scale of vestibule 

-vibrations descend via the scale of timpani. 

in between is the cochlea duct-filled with a fluid called endolymph. The membrane within the duct is flexible and thus respond to vibrations and send the vibrations back down the scale of timpani where it is directed to be dissipated via the round window.

There are two portions of membrane in the cochlea duct. The top part is called the reissner's membrane and the bottom portion of the membrane is known as the basilar membrane. 

Within the basilar membrane sits the organ of corti. 

The nerve impulses are actually generated by specialized cells WITHIN the organ of corti called hair cells. The hair cells are covered by a membrane called the tectorial membrane. As the basilar membrane vibrates the hair cells are pushed up against the tectorial membrane causing the hair cell to generate an AP or nerve impulse to the brain via the auditory nerve. 

The entire basilar membrane does not vibrate evenly it depends on the frequency of the sound waves. A high frequency will result in the lower portion of the basilar membrane near the base of the cochlea to vibrate and a lower frequency will result in the higher portion (near the apex) of the basilar membrane to vibrate. 

Source: Auditory Transduction- YouTube-flv

The Human Brain

Homework: (It is very unclear so I will type out what is written on the diagram-starting from the very top label and working in a clockwise direction + with the noted functions of each section of the human brain) 

The human brain

Cerebral hemispheres- Composed of two parts of the cerebrum. The cerebrum is the part of the brain that is responsible for the integration (processing) of sensor and neural (relating to the nervous system) functions and the initiation of co-ordination and voluntary activity. 

Cerebellum-it is the part of the brain below the back of the cerebrum. It regulates balance, posture, movement and muscle co-ordination. 

Medulla oblongata- the lowest section of the brainstem, it controls automatic (involuntary-in other words it is not in our control) functions like heartbeat and breathing. 

Pituitary gland- it is an endocrine (relating to glands which secrete hormones into the blood system) glands about the size of a pea. It is a gland that is attached to the base of the brain and secretes hormones which are associated with homeostasis. 

Hypothalamus- the region of the brain that co-ordinates both the automic nervous system (part of the nervous system which cannot be controlled by us e.g heartbeat, breathing and digestion) and controls the activity of the pituitary gland. 

Corpus Callosum- a large bundle of nerve fibres that connect the left and right cerebral hemisphere's together. 

Source: http://www.enchantedlearning.com/subjects/anatomy/brain/label/lateralbrain/label.shtml

Clearer diagram of the brain

Source: http://www.enchantedlearning.com/subjects/anatomy/brain/label/lateralbrain/label.shtml

Notes from video 1- introduction to the ear

Diagram of an ear: 

Source: http://www.enchantedlearning.com/subjects/anatomy/ear/earanatomy.GIF

Introducing the different parts of the ear and an introduction as to how sound is introduced into the ear: 

-the oracle (visible part of the ear) collects sound waves and directs them to the auditory canal or ear canal which is lined with cilia and ceruminous glands. The ear wax (which is produced by the ceruminous gland) and the cilia (tiny hairs) trap and prevent foreign matter from getting deep into the ear. 

The thin membrane that separates the outer ear from the middle ear cavity is called the ear drum or the tympanic membrane. 

The sound waves cause the tympanic membrane to vibrate which in turn causes 3 other bones to vibrate:

-(in order): the malleus (hammer), anvil (incus), stapes (sterum). They pick up vibrations form the outer ear and transmit them to the inner ear. 

-The eustachian tube of the inner ear opens into the pharynx (part of the nose that is behind the mouth and nasal cavity-nose space). It allows air pressure to equalize between the ear and the outside air. 

The inner ear consisting membranous structure and bony structures surrounded by fluid. 

Semicircular canals are fluid with fluid, they are bony loops that help us maintain balance. 

The cochlea is a fluid filled snail shaped structure that contains the organ of corti- which is basically the 'true' organ of hearing. 

They change the vibration (actually the hair cells in the organ of corti do this) of nerve impulses into nerve impulses that are picky up by the auditory nerve and then sent to the brain for interpretation.

Introduction to: how are sounds perceived? 

Sound waves are collected by the oracle or outer ear and sent through the auditory canal, the tympanic membrane, ear bones and then to the cochlea. Where the vibrations are changed by the organ of corti to nerve impulse and transmitted by the auditory or cochlea nerve to the temporal lobe (this is a part of the brain) for interpretation. 

Source: Process of Hearing- YouTube.flv

More detailed notes on the organ of corti:

They are the organ that is the space between the two fluid filled tubes, the fluid filled tubes because they are liquid membranous structures they are able to be compressed (how much depends on the amplitude and frequency of the sound waves). Within the organ of corti there are hair cells which then pick up these compressions and depending on it's frequency and amplitude convert those sound waves into nerve impulses which are then sent to the temporal lobe of the brain for interpretation via the auditory or cochlea nerve. Each impulse is not the same as the impulse will be for that specific amplitude and frequency of that particular sound wave.