Chapter - I

 

Anatomy (from the Greek word meaning to cut up, cut open) is the branch of biology that deals with the structure and organization of living things. It can be divided into animal anatomy (zootomy) and plant anatomy (phytonomy). Major branches of anatomy include comparative anatomy, histology, and human anatomy.

 

Anatomy from point of Medicine consists of a knowledge of the exact form, position, size and relationship of the various structures of the healthy human body, and to this study the term descriptive or topographical human anatomy is given, though it is often, less happily, spoken of as anthropotomy.

 

So intricate is the human body that only a small number of professional human anatomists, after years of patient observation, are complete masters of all its details; most of them specialize on certain parts, such as the brain or viscera, contenting themselves with a good working knowledge of the rest.

 

 

Major Body Systems:

 

Some Major Organs:

 

Bones in the Human Skeleton:

 

Glands:

  

Tissus:

 

Externally visible parts of the human body:

 

Other anatomic terms (not classified):

 

 

Human anatomy or anthropotomy is a special field within anatomy. It studies gross structures and systems of the human body, leaving the study of tissues to histology and cells to cytology. The human body, like the bodies of all animals, is made up of systems that are made up of organs that are made up of tissues that are made up of cells.

 

 

External body features:

Common names of well known parts of the human body, from top to bottom:

 

Skin

Head -- Forehead -- Eye -- Ear -- Nose -- Mouth -- Tongue -- Teeth -- Jaw -- Face -- Cheek -- Chin

Neck -- Throat -- Adam's apple -- Shoulders

Arm -- Elbow -- Wrist -- Hand -- Fingers -- Thumb

Spine -- Chest -- Breast -- Ribcage

Abdomen -- Belly button -- Sex organs (Penis/Scrotum or Clitoris/Vagina) -- Rectum -- Anus

Hip -- Buttocks -- Leg -- Thigh -- Knee -- Calf -- Heel -- Ankle -- Foot -- Toes

 

Common names of internal organs (in alphabetical order):

 

Adrenals

Appendix

Bladder

Brain

Duodenum

Eyes

Gall bladder

Heart

Intestines

Kidney

Liver

Lungs

Ovaries

Pancreas

Parathyroids

Pituitary

Prostate

Spleen

Stomach

Thymus

Thyroid

Testicles

Womb

 

Amygdala -- Brainstem -- Cerebellum -- Cerebral cortex -- Hypothalamus -- Limbic system -- medulla-- midbrain -- Pituitary gland -- pons

 

Certain professions, especially medicine and physiotherapy, require the study of human anatomy in depth. Textbooks usually split the body into the following regional groups:

 

Head and Neck - includes everything above the thoracic inlet

 

Upper limb - includes everything from your hand, forearm, arm, shoulder, axilla, pectoral region and scapular region.

 

Thorax - contains the region of the chest from the thoracic inlet to the thoracic diaphragm.

 

Abdomen - everything from the thoracic diaphragm to the pelvic brim or to the pelvic inlet.

 

The back - about the spine and its components, the intervertebral disks and bodies

 

Pelvis and Perineum - the pelvis consists of everything from the pelvic inlet to the pelvic diaphragm. The perineum is everything below the pelvic diaphragm.

Lower limb - the lower limb is usually everything below the inguinal ligament, including the thigh, the hip joint, the leg, and the foot.

 

 

First let us understand more about the human skeleton as it forms the framework of human body about which all organs and systems function and perform.

 

The human skeleton is made of bones, some of them joined together, supported and supplemented by a structure of ligaments, tendons, muscles, and cartilage.

The skeleton changes composition over a lifespan. Early in gestation, a fetus has no hard skeleton — bones form gradually during nine months in the womb. When a baby is born it has more bones than it will as an adult. On average, an adult human has 206 bones in their skeleton (the number can vary slightly from individual to individual), but a baby is born with approximately 270. The difference comes from a number of small bones that fuse together during growth. These include the bones in the skull and the spine. The sacrum (the bone at the base of the spine) consists of six bones, which are separated at birth but fuse together into a solid structure in later years.

 

There are 6 bones (three on each side) in the middle ear that articulate only with themselves, and one bone, the hyoid bone, which does not touch any other bones in the body.

 

The longest bone in the body is the femur and the smallest is the stapes bone in the middle ear.

 

The skeleton functions not only as the support for the body but also in hematopoiesis, the manufacture of blood cells that takes place in bone marrow (which is why bone marrow cancer is very often a terminal disease). It is also necessary for protection of vital organs and is needed by the muscles for movement. Not only does the skeleton serve to help manufacture blood cells, but it also serves as a mineral storage deposit in which nutrients can be stored and retrieved.

 

One way to group the bones of the human skeleton is to divide them into two groups, namely the axial skeleton and the appendicular skeleton. The axial skeleton consists of bones in the midline and includes all the bones of the head and neck, the vertebrae, ribs and sternum. The appendicular skeleton consists of the clavicles, scapulae, bones of the upper limb, bones of the pelvis and bones of the lower limb.

 

There are many differences between the male and female human skeletons. Men tend to have slightly thicker and longer limbs and digit bones while women tend to have larger pelvic bones in relation to body size. Women also tend to have narrower rib cages, smaller teeth, less angular mandibles, and less pronounced cranial features such as the brow ridges and occipital protuberance (the small bump in the cranium's posterior). Most striking is the difference in hip bones owing to differences related to the process of reproduction, and very likely also to the biological process of sexual selection. There are also a number of smaller differences between human male and female skeletons.

 

The skeleton can be affected by many diseases that compromise physical mobility and strength. Skeletal diseases range from minor to extremely debilitating. Bone cancer and bone tumors are extremely serious and are sometimes treated by radical surgery such as amputation of the affected limb. Various forms of arthritis attack the skeleton resulting in severe pain and debility. Osteoporosis can increase the likelihood of fractures and broken bones, especially among post-menopausal women and the elderly. Scoliosis is another, when the spine curves from side to side.

 

A typical adult human skeleton consists of the following 206 bones. (Numbers in bold refer to the diagram at right.)

 

In the skull (22):

 

1. Frontal bone

2. Parietal bone (2)

3. Temporal bone (2)

4. Occipital bone

Sphenoid bone

Ethmoid bone

 

5. Zygomatic bone (2)

6. Superior and inferior maxilla

9. Nasal bone (2)

7. Mandible

Palatine bone (2)

Lacrimal bone (2)

Vomer bone

inferior nasal conchae (2)

 

Malleus (2)

Incus (2)

Stapes (2)

 

 

Hyoid bone

 

 

25. Clavicle or collarbone (2)

29. Scapula or shoulder blade (2)

 

 

10. Sternum

28. Ribs (2 x 12)

 

 

8. Cervical vertebrae (7) incl. Atlas & axis

14. Lumbar vertebrae (5)

Thoracic vertebrae (12)

 

 

11. Humerus (2)

26. Condyles of humerus

12. Ulna (2)

13. Radius (2)

27. Head of radius

 

 

Wrist (carpal) bones:

Scaphoid bone (2)

Lunate bone (2)

Triquetrum bone (2)

Pisiform bone (2)

Trapezium (bone) (2)

Trapezoid bone (2)

Capitate bone (2)

Hamate bone (2)

 

Metacarpal bones (5 × 2)

 

Proximal phalanges (5 × 2)

Intermediate phalanges (4 × 2)

Distal phalanges (5 × 2)

In the pelvis (4):

 

15. Ossa coxa (hip bones or innominate bones) (2)

16. Sacrum

Coccyx

 

 

17. Femur (2)

22. Greater trochanter of femur

23. Condyles of femur

19. Patella (2)

20. Tibia (2)

21. Fibula (2)

 

 

Ankle (tarsal) bones:

Calcaneus (heel bone) (2)

Talus (2)

Navicular bone (2)

Medial cuneiform bone (2)

Intermediate cuneiform bone (2)

Lateral cuneiform bone (2)

Cuboidal bone (2)

 

Metatarsal Bone (5 × 2)

 

Proximal phalanges (5 × 2)

Intermediate phalanges (4 × 2)

Distal phalanges (5 × 2)

 

The infant skeleton has the following bones in addition to those above:

 

1.        Sacral vertebrae (4 or 5), which fuse in adults to form the sacrum.

2.        Coccygeal vertebrae (3 to 5), which fuse in adults to form the coccyx.

3.        Ilium, ischium and pubis, which fuse in adults to form the pelvic girdle

 

 

Skull

Middle ear

Throat

Shoulder girdle

Ribcage

Vertebra

Arms

Hands

Pelvis

Legs

Feet

 

 

Now let us study in detail about each bony organization in detail.

 

A skull, or cranium, is a bony structure of Craniates, which serves as the general framework for a head. The skull supports the structures of the face and protects the brain against injury.

In humans, the adult skull is normally made up of 28 bones. Except for the mandible, all of the bones of the skull are joined together by sutures, rigid articulations permitting very little movement.

Eight bones form the neurocranium (braincase), a protective vault of bone surrounding the brain and medulla oblongata. Fourteen bones form the splanchnocranium, the bones supporting the face. Encased within the temporal bones are the six ear ossicles of the middle ear. The hyoid bone, supporting the larynx, is usually not considered as part of the skull, as it does not articulate with any other bones.

 

The skull is a complex structure; its bones are formed both by intramembranous and endochondral ossification. The bones of the splanchnocranium and the sides and roof of the neurocranium are formed by intramembranous (or dermal) ossification, while the bones supporting the brain (the occipital, sphenoid, temporal, and ethmoid) are largely formed by endochondral ossification.

 

At birth, the human skull is made up of 45 separate bony elements. As growth occurs, many of these bony elements gradually fuse together into solid bone (for example, the frontal bones). The bones of the roof of the skull are initially separated by regions of dense connective tissue called "sutures". There are five sutures: the frontal suture, sagittal suture, lambdoid suture, coronal suture, and squamosal suture. At birth these regions are fibrous and moveable, necessary for birth and later growth. This growth can put a large amount of tension on the "obstetrical hinge," which is where the squamous and lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the great cerebral vein of Galen. Larger regions of connective tissue where multiple sutures meet are called fontanelles. The six fontanelles are: the anterior fontanelle, the posterior fontanelle, the two sphenoid fontanelles, and the two mastoid fontanelles. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone. The posterior fontanelle usually closes by eight weeks, but the anterior fontanelle can remain up to eighteen months. The anterior fontanelle is located at the junction of the frontal and parietal bones; it is a "soft spot" on a baby's forehead. Careful observation will show that you can count a baby's heart rate by observing his or her pulse pulsing softly through the anterior fontanelle.

 

If the brain is bruised or injured it can be extremely serious. Normally the skull protects the brain from damage through its hard unyieldingness, but in some cases of head injury, there can be raised intracranial pressure through mechanisms such as a subdural hematoma. In these cases the raised intracranial pressure can cause herniation of the brain out of the foramen magnum ('coning') because there is no space for the brain to expand; this can result in significant brain damage or death unless an urgent operation is performed to relieve the pressure. This is why patients with concussion must be watched extremely carefully.

 

The skull also contains the sinus cavities. The meninges are the membranes that separate the brain from the skull.

 

 

Frontal bone

Parietal bone (2)

Temporal bone (2)

Occipital bone

Sphenoid bone

Ethmoid bone

 

Mandible

Maxilla (2)

Palatine bone (2)

Zygomatic bone (2)

Nasal bone (2)

Lacrimal bone (2)

Vomer bone

Inferior nasal conchae (2)

 

Malleus (2)

Incus (2)

Stapes (2)

 

In addition to the usual centers of ossification of the cranium, others may occur, giving rise to irregular isolated bones termed sutural or Wormian bones.

 

 

Most sutures are named for the bones they articulate, but some have special names of their own.

 

Sagittal suture - along the midline, between parietal bones

Coronal suture - between the frontal and parietal bones

Lambdoidal suture - between the parietals and the occipital bone

Squamosal suture - between the parietal and the temporal bone

Metopic suture - between the two frontal bones, prior to the fusion of the two into a single bone

 

The following is a list of holes, or foramina, in the base of the skull and what goes through each of them.

 

 

Foramen caecum - emissary veins to superior sagittal sinus

Foramina of cribriform plate - olfactory nerve bundles

Posterior ethmoidal foramen - posterior ethmoidal artery, vein and nerve

Optic canal - optic nerve (II), ophthalmic artery

Superior orbital fissure

Oculomotor nerve (III)

Trochlear nerve (IV)

Lacrimal, frontal and nasociliary branches of ophthalmic nerve (V1)

Abducens nerve (VI)

Superior ophthalmic vein

Foramen rotundum - maxillary nerve (V2)

Foramen ovale

Mandibular nerve (V3)

Accessory meningeal artery

Lesser petrosal nerve (occasionally)

Foramen spinosum

Middle meningeal artery and vein

Meningeal branch of mandibular nerve

Foramen lacerum

Internal carotid artery

Internal carotid nerve plexus

Hiatus of canal of lesser petrosal nerve

Hiatus of canal of greater petrosal nerve

Internal acoustic meatus

Facial nerve (vii)

Vestibulocochlear nerve (VIII)

Labyrinthine artery

Jugular foramen

Inferior petrosal sinus

Glossopharyngeal nerve (IX)

Vagus nerve (X)

Accessory nerve (XI)

Sigmoid sinus

Posterior meningeal artery

Internal jugular vein

Hypoglossal canal - hypoglossal nerve (XII)

Foramen magnum

Medulla oblongata

Vertebral arteries

Meningeal branches of vertebral arteries

Spinal roots of accessory nerves

 

 

An ear is an organ used by an animal to detect sound waves. The term may refer to the entire system responsible for collection and early processing of sound (the beginning of the auditory system), or merely the externally-visible part.

 

Mammals, including humans, have two ears, one on each side of the head.

 

EXTERNAL EAR: The outer ear is the external portion of the ear and includes the eardrum.

The visible part is called the pinna, or auricle, and functions to collect and focus sound waves. Many mammals can move the pinna in order to focus their hearing in a certain direction in much the same way that they can turn their eyes. Humans have generally lost this ability. From the pinna the sound pressure waves move into the ear canal, a simple tube running to the middle ear. This tube amplifies frequencies in the range 3 kHz to 12 kHz.

 

The human ear has earlobes at the bottom, which are vestigial but are used by many people to provide an attachment point for earrings. The earlobe is usually formed cleft from the side of the face and hangs from the rest of the ear but occasionally will be found looking fused and "lobeless" due to a recessive gene. The helix is the outer edge of the outer ear.

 

MIDDLE EAR: The middle ear includes the ossicles (three tiny bones), two muscle tendons (of the stapedius and tensor tympani muscles), and two nerve bundles (the horizontal portion of the facial nerve and a branch of the facial nerve called the chorda tympani). The Latin names of the ossicles are the malleus, incus, and stapes, but they are also referred to by their English translations: the hammer, anvil, and stirrup respectively.

 

Mammals are unique in having three ear bones. The incus and stapes are derived from bones of the jaw, and allow finer detection of sound. These bones form the linkage between the tympanic membrane and the oval window that leads to the inner ear. The tympanum converts vibrations of air in the ear canal into vibrations of the ossicles. The ossicles in turn transmit the vibrations through the membrane of the oval window into the fluid of the inner ear. The ratio in area between the tympanic membrane and the oval window results in an effective amplification of approximately 14 dB, peaking at a frequency of around 1 kHz. The combined transfer function of the outer ear and middle ear gives humans a peak sensitivity to frequencies between 1 kHz and 3 kHz. The tensor tympani muscle and stapedius muscles of the middle ear contract in response to loud sounds, thereby reducing the transmission of sound to the inner ear. This is called the acoustic reflex.

 

The middle ear is hollow. If the animal moves to a high-altitude environment, or dives into the water, there will be a pressure difference between the middle ear and the outside environment. This pressure will pose a risk of bursting or otherwise damaging the tympanum if it is not relieved. This is one of the functions of the Eustachian tubes, evolutionary descendants of the gills, which connect the middle ear to the nasopharynx. The Eustachian tubes are normally pinched off at the nose end, to prevent being clogged with phlegm, but they may be opened by lowering and protruding the jaw; this is why yawning helps relieve the pressure felt in the ears when on board an aircraft.

 

INNER EAR: The inner ear comprises both the organ of hearing (the cochlea) and the labyrinth or vestibular apparatus, the organ of balance located in the inner ear that consists of three semicircular canals and the vestibule.

 

The cochlea (Latin for "snail") is a spiralled, hollow, conical chamber of bone filled with perilymph and endolymph (in the scala media), a fluid medium that receives the sound vibrations transmitted from the air to the oval window through the ear drum and ossicles of the middle ear (see above). Running through its centre is the cochlea duct, which contains the spiral Organ of Corti, the receptor organ responsible for hearing. The bony cavity of the cochlea is divided into three separate chambers: the scala vestibuli, which lies superior to the cochlea duct and abuts the oval window; the scala media, which is the membranous cochlea duct containing endolymph and the organ of Corti; and the scala tympani, which lies inferior to the scala media and terminates at the round window. The two bony chambers (scala vestibuli and scala tympani) both contain perilymph and join together at the cochlear apex, a region called the helicotrema. Separating the scala vestibuli from the scala media is the Reissner's membrane. The basilar membrane separates the scala media from the scala tympani. Sitting on top of the basilar membrane is a cellular layer known as the Organ of Corti, which is lined with hair cells — sensory cells topped with hair-like structures called stereocilia.

 

As the stapes oscillates against the oval window in response to sound, the perilymph within the scala vestibuli also oscillates. For very low frequencies (below 20Hz), the pressure waves propagate along the complete route of the cochlea - up scala vestibuli, around helicotrema and down scala tympani to the round window. Frequencies this low do not activate the organ of Corti and are below the threshold for hearing. Higher frequencies do not propagate to the helicotrema but are transmitted through the endolymph in the cochlea duct to the perilymph in the scala tympani. The hair cells in the organ of Corti are tuned to certain sound frequencies, being responsive to high frequencies near the oval window and to low frequencies near the apex of the cochlea.

 

All excited hair cells send nerve impulses to the brain, which are perceived as a sound of whatever pitch the hair cell is associated with. A very strong movement of the endolymph due to very loud noise may cause hair cells to die. This is a common cause of partial hearing loss and is the reason why anyone using firearms or heavy machinery should wear earmuffs or earplugs.

 

The vestibular apparatus is filled with the same endolymph as the cochlea, but instead of detecting sound, it detects rotation of the head. If a line is drawn through the middle of each of the three semicircular canals, perpendicular to the plane in which the canal lies, the three lines would be perpendicular. They would represent three axes of rotation. Any rotation could be represented as three simultaneous rotations about the three axes.

 

 

Problems with the ear or auditory processing system in the brain can lead to deafness. Other disorders related to auditory system are:

 

Acoustic neuroma

Balance disorders

Barotrauma

Benign Paroxysmal Positional Vertigo

Cholesteatoma

Ear infections

Conductive hearing impairment

Labyrinthine hydrops

Labyrinthitis

Ménière's disease

Meningitis

Neurofibromatosis Type 1

Neurofibromatosis Type 2

Noise-induced hearing loss

Nonsyndromic hereditary hearing impairment

Otitis externa

Otitis media

Otosclerosis

Perilymph fistula

Presbycusis

Sensorineural hearing loss

Sudden deafness

Tinnitus

Usher syndrome

Vestibular neuronitis

 

 

Acoustic neurinoma - tumor, usually benign, which may develop on the hearing and balance nerves and can cause gradual hearing loss, tinnitus, and/or dizziness. (sometimes called vestibular schwannoma). Also see Neurofibromatosis Type 2.

 

Acquired deafness - loss of hearing that occurs or develops some time during the lifespan but is not present at birth.

 

Ageusia - loss of the sense of taste.

 

Albinism - lack of normal pigment in the skin, eyes, and hair.

 

Alport syndrome - hereditary condition characterized by kidney disease, sensorineural hearing loss, and sometimes eye defects.

 

American Sign Language (ASL) - manual language with its own syntax and grammar, used primarily by people who are deaf.

 

Anosmia - absence of the sense of smell.

 

Aphasia - total or partial loss of the ability to use or understand language; usually caused by stroke, brain disease, or injury.

 

Aphonia - complete loss of voice.

 

Apraxia - inability to execute a voluntary movement despite being able to demonstrate normal muscle function.

 

Articulation disorder - inability to correctly produce speech sounds (phonemes) because of imprecise placement, timing, pressure, speed, or flow of movement of the lips, tongue, or throat.

 

Assistive devices - technical tools and devices such as alphabet boards, text telephones, or text-to-speech conversion software used to aid individuals who have communication disorders perform actions, tasks, and activities.

 

Audiologist - health care professional who is trained to evaluate hearing loss and related disorders, including balance (vestibular) disorders and tinnitus, and to rehabilitate individuals with hearing loss and related disorders. An audiologist uses a variety of tests and procedures to assess hearing and balance function and to fit and dispense hearing aids and other assistive devices for hearing.

 

Auditory Brainstem Response test (ABR test) - a test for brain functioning in comatose, unresponsive, etc., patients, and for hearing in infants and young children; involves attaching electrodes to the head to record electrical activity from the hearing nerve and other parts of the brain.

 

Auditory nerve - eighth cranial nerve that connects the inner ear to the brainstem and is responsible for hearing and balance.

 

Auditory perception - ability to identify, interpret, and attach meaning to sound.

 

Auditory prosthesis - device that substitutes or enhances the ability to hear.

 

Augmentative devices - tools that help individuals with limited or absent speech to communicate, such as communication boards, pictographs (symbols that look like the things they represent), or ideographs (symbols representing ideas).

 

Aural rehabilitation - techniques used with people who are hearing impaired to improve their ability to speak and communicate.

 

Autoimmune deafness - individual's immune system produces abnormal antibodies that react against the body's healthy tissues.

 

Autism - brain disorder that begins in early childhood and persists throughout adulthood; affects three crucial areas of development: communication, social interaction, and creative or imaginative play.

 

 

Balance - biological system that enables individuals to know where their bodies are in the environment and to maintain a desired position. Normal balance depends on information from the labyrinth in the inner ear, from other senses such as sight and touch, and from muscle movement.

 

Balance disorder - disruption in the labyrinth, the inner ear organ that controls the balance system, which allows individuals to know where their bodies are in the environment. The labyrinth works with other systems in the body, such as the visual and skeletal systems, to maintain posture.

 

Barotrauma - injury to the middle ear caused by a reduction of air pressure.

 

Benign Paroxysmal Positional Vertigo (BPPV) - balance disorder that results in sudden onset of dizziness, spinning, or vertigo when moving the head.

 

Brainstem implant - auditory prosthesis that bypasses the cochlea and auditory nerve. This type of implant helps individuals who cannot benefit from a cochlear implant because the auditory nerves are not working.

 

Captioning - text display of spoken words, presented on a television or a movie screen, that allows a deaf or hard-of-hearing viewer to follow the dialogue and the action of a program simultaneously.

 

Central auditory processing disorder - inability to differentiate, recognize, or understand sounds; hearing and intelligence are normal.

 

Chemosensory disorders - diseases or problems associated with the sense of smell or the sense of taste.

 

Cholesteatoma - accumulation of dead cells in the middle ear, caused by repeated middle ear infections.

 

Cochlea - snail-shaped structure in the inner ear that contains the organ of hearing.

 

Cochlear implant - medical device that bypasses damaged structures in the inner ear and directly stimulates the auditory nerve, allowing some deaf individuals to learn to hear and interpret sounds and speech.

 

Cognition - thinking skills that include perception, memory, awareness, reasoning, judgment, intellect, and imagination.

 

Conductive hearing impairment - hearing loss caused by dysfunction of the outer or middle ear.

 

Cued speech - method of communication that combines speech reading with a system of handshapes placed near the mouth to help deaf or hard-of-hearing individuals differentiate words that look similar on the lips (e.g., bunch vs. punch) or are hidden (e.g., gag).

 

Cytomegalovirus (Congenital) - one group of herpes viruses that infects humans and can cause a variety of clinical symptoms, including deafness or hearing impairment; infection with the virus may be either before or after birth.

 

Decibel - unit that measures the intensity or loudness of sound.

 

Dizziness - physical unsteadiness, imbalance, and lightheadedness associated with balance disorders.

 

Dysarthria - group of speech disorders caused by disturbances in the strength or coordination of the muscles of the speech mechanism as a result of damage to the brain or nerves.

 

Dysequilibrium - any disturbance of balance.

 

Dysfluency - disruption in the smooth flow or expression of speech.

 

Dysgeusia - distortion or absence of the sense of taste.

 

Dyslexia - learning disability characterized by reading difficulties. Some individuals may also have difficulty writing, spelling, or working with numbers.

 

Dysosmia - distortion or absence of the sense of smell.

 

Dysphagia - difficulty swallowing.

 

Dysphonia - any impairment of the voice or speaking ability.

 

Dyspraxia of speech - in individuals with normal muscle tone and speech muscle coordination, partial loss of the ability to consistently pronounce words.

 

Dystonia - abnormal muscle tone of one or more muscles.

 

Ear infection - presence and growth of bacteria or viruses in the ear.

 

Ear wax - yellow secretion from glands in the outer ear (cerumen) that keeps the skin of the ear dry and protected from infection.

 

Endolymph - fluid in the labyrinth (the organ of balance located in the inner ear that consists of three semicircular canals and the vestibule).

Gustation - act or sensation of tasting.

 

Hair cells - sensory cells of the inner ear, which are topped with hair-like structures, the stereocilia, and which transform the mechanical energy of sound waves into nerve impulses.

 

Haptic sense - sense of physical contact or touch.

 

Haptometer - instrument for measuring sensitivity to touch.

 

Hearing - series of events in which sound waves in the air are converted to electrical signals, which are sent as nerve impulses to the brain, where they are interpreted.

 

Hearing aid - electronic device that brings amplified sound to the ear. A hearing aid usually consists of a microphone, amplifier, and receiver.

 

Hearing disorder - disruption in the normal hearing process that may occur in outer, middle, or inner ear, whereby sound waves are not conducted to the inner ear, converted to electrical signals and/or nerve impulses are not transmitted to the brain to be interpreted.

 

Hereditary hearing impairment - hearing loss passed down through generations of a family.

 

Hoarseness - abnormally rough or harsh-sounding voice caused by vocal abuse and other disorders such as gastroesophageal reflux, thyroid problems, or trauma to the larynx (voice box).

 

Hypogeusia - diminished sensitivity to taste.

 

Hyposmia - diminished sensitivity to smell.

 

Inner ear - part of the ear that contains both the organ of hearing (the cochlea) and the organ of balance (the labyrinth).

 

Kallmann's syndrome - disorder that can include several characteristics such as absence of the sense of smell and decreas