Anatomy Exam 1

Which axis system is most common for clinical work in humans?

The anterior-posterior-superior-inferior system, especially for the cerebrum. For deeper structures, especially the spinal cord, a mixture of terms is in widespread use. It's best to know both.

Cranium (skull)

A composite of several bones. The junctions between these bones (articulations) are fixed or flexible.

Lobes of the brain

The cerebral cortex has two hemispheres. Each is commonly divided into four lobes, named after the overlying cranial bones:

Frontal; Parietal; Temporal; Occipital

Temporal bone (general)

-Has multiple divisions (parts) and articulates with other cranial bones.

-The peripheral auditory structures (external, middle & inner ear) are housed within or attached to the temporal bone.

-Developmental and acquired pathologies that affect the peripheral auditory system may involve one or more parts of the temporal bone.

Temporal bone articulations

Parietal bone; Sphenoid bone; Occipital bone; Zygomatic bone; Mandible

Four major parts of the temporal bone

-Squamous

-Mastoid

-Petrous

-Tympanic

Squamous part of temporal bone

(Squamous = flat) Thin circular plate above the external acoustic meatus (EAM) (external ear canal)

Mastoid part of temporal bone

Porous region posterior and inferior to the EAM

Petrous part of temporal bone

-(Petrous = hard)

-Medial to the other 3 parts

-contains inner ear, nerves, arteries, veins.

-Extends about 5 cm toward the center of the head

-Very dense bone.

Petromastoid

The Petrous and Mastoid divisions of the temporal bone, often considered together

Tympanic part of temporal bone

Thin curved plate that forms the walls of the EAM

Temporal bone fractures

Usually secondary to blunt trauma or compression of skull. Can cause hearing loss, facial nerve injury, brain injury, infection (e.g., meningitis), or even death (severe closed head injury -> rapid death).

Two general types of temporal bone fracture

-Oblique (transverse/oblique angle across temporal bone)

-Longitudinal (parallel to long axis of petrous pyramid)

Temporal bone fracture: tympanic part (external ear canal)

May be associated with tympanic membrane tear

Temporal bone fracture: mastoid part

Hemorrhaging (bruising) may cause Battle's sign

Battle's sign

Bruising of the postauricular mastoid area (postauricular artery). Bluish tint of the tympanic membrane, hemorrhage in tympanum.

Temporal bone fracture: mastoid/petrous parts (middle ear)

-Otorrhea (CSF leakage into tympanum, EAC)

-Ossicular discontinuity

-Facial nerve weakness or paralysis (partial, complete)

Temporal bone fracture: petrous part

Cochlear or vestibular damage:

-sensory-neural hearing loss

-vertigo and other vestibular disturbances

Temporal bone fracture: zygomatic process

Temporal mandibular joint (TMJ) dysfunction (less common)

Paget's disease (osteitis deformans)

-Progressive bone disease involving the skull and temporal bones in about 2/3 of patients.

-Males more often affected than females.

-Viral and hereditary causes are known.

-Bone is broken down and/or remodeled (bone loss and addition of new bone).

-In the temporal bone, alterations of petrous pyramid, external canal, middle ear and inner ear capsule may occur.

-May cause sensory-neural hearing loss (~30-50% of cases) and/or vestibular dysfunction (~20-25%).

Congenital malformations of the temporal bone

-During embryonic development, the temporal bone and other bones of the face and skull may develop abnormally or fail to form.

-Temporal bone malformations are a prominent cause of congenital hearing loss.

Mastoiditis

-Inflammation of the mastoid bone caused by infections and/or tumors (e.g., cholesteatoma).

-Such infections may accompany long-standing (chronic) otitis media that has spread from the middle ear to the surrounding bone.

-The mastoid is most commonly involved as it is continuous with the tympanum (middle ear space) through an opening, known as the aditus ad antrum.

Mastoiditis: symptoms and risk

Ear pain (otalgia) and swelling behind the ear are common symptoms. There is a risk of the infection spreading and involving the intracranial structures (meninges, brain).

Tumors

-Malignant and benign tumors of several types (e.g., cholesteatoma).

-Relatively rare. May spread from external or middle ear.

-Otalgia (ear pain), hearing loss, tinnitus, and vertigo are among the symptoms.

Pendred syndrome

-The most common form of childhood syndromal deafness.

• 5-10% of hereditary hearing loss (severe to profound).

• Bilateral sensory-neural hearing loss at birth and often progressive.

• Onset of hearing loss may be sudden, or delayed until early adulthood.

-Autosomal recessive (chromosome 7; mutation of SLC26A4 gene called pendrin). Some other genes can be involved.

-Thyroid gland goiter (neck), hypothyroidism, kidney dysfunction, vestibular problems

Pendred syndrome: temporal bone abnormalities (2 consistent findings)

-Cochlear hypoplasia

• Cochlear turns reduced from 2.75 to ~1.5, apex.

• Primary cause of the hearing loss.

• Aka: cystic apex, Mondini malformation, incomplete partition Type II.

-Enlarged vestibular aqueduct (EVA)

• Always present, but does not appear to be the main cause of hearing loss.

• Possible disruption of inner ear homeostatis (ionic balance).

• Rather, EVA presence on imaging signals the developmental defect.

Major functions of the external ear

-Collect and channel acoustic signals to the middle ear

-Enhance reception of higher frequency signals

-Protection of middle and inner ear structures

Scapha (scaphoid fossa)

Aka scaphoid fossa = boat shaped ditch. Curved depression between helix and antihelix.

Fossa triangularis

Depression between crura superior and inferior

Antihelix

Curves around the concha. Divides into crura superior and inferior branches.

Concha (Conchae)

Divided into two parts by the crus helicus: cymba conchae and cavum conchae

Auricle: cartilage and skin

-Except for the lobule, the auricle is composed of thin cartilage (0.5 to 1 mm thick) covered by a layer of skin that adheres closely to the cartilage surface.

-The cartilage gives shape to the auricle.

-The lobule has no cartilage. It is composed of areolar and adipose tissue.

Auricle: intrinsic muscles

Rudimentary in humans. Useful in rotating and changing shape of auricle to localize sound (well developed in some animals).

Auricle: extrinsic muscles

Connect auricle with skin and scalp. Move auricle as a whole. (ability to wiggle ears)

Auricle: extrinsic ligaments

Connect auricle with the side of the head (skull)

Auricle: intrinsic ligaments

-Link various portions of the cartilage together.

-Link auricle to external acoustic meatus.

Auricle: sensory innervation

-Branches of CN V, VII, IX, X + Greater auricular n. Includes:

• auricular branch of CN X (Vagus n.)

• greater auricular and lesser occipital nerves (from cervical plexus, spinal nerves 2 and 3)

• auriculotemporal nerve, branch of CN V (trigeminal), supplies anterior auricle

• branch of CN VII (facial)

• branch of CN IX (glossopharyngeal)

Auricle: motor innervation

Temporal and auricular branches of CN VII (facial)

Auricle: blood supply

-Posterior auricular artery (branch of external carotid artery)

-anterior auricular artery (branch of superficial temporal artery)

-auricular branch of occipital artery (not shown)

Head-Related Transfer Function (HRTF)

-Refers to the difference in sound pressure level (dB SPL) to some sound (e.g., pure tone, noise band) measured in the free field and some other location:

• the entrance of the ear canal, in the concha

• or at the tympanic membrane.

-The difference in SPL between the two locations is due to resonance and filtering effects of the head and auricle as measured just inside the external ear canal

HRTF equation

Ear canal SPL - Free field SPL = HRTF

High frequency resonance of the auricle

-Measured at the opening of the ear canal (concha), intensity gain/enhancement (aka: amplification, resonance) peaks at approximately 5000 Hz.

-The gain is due to the shape of the auricle, especially the concha region (e.g., satellite dish).

HRTFs of 7 different ears recorded from the ear canal opening (wider frequency range)

-Significant gain between 1 and 8 kHz, peaking at ~5 kHz.

-Large secondary peak at ~12 kHz.

-Note large individual differences between 5 and 10 kHz.

Spectral filtering in the vertical plane

-Sound source localization in the vertical plane (elevation) depends on perception of small changes in the spectrum (balance of frequencies) of the acoustic signal.

-A general observation is that intensity at frequencies above about 4000 Hz are enhanced at progressively higher elevations (relative to horizontal).

-Detailed observations support the general observation, but also reveal a progressive shift in the "notch frequency", where there is negative gain (filtering, loss). The "notch" moves to higher frequencies with increased elevation.

-More complexity: the effects of elevation vary with azimuth (horizontal angle of the sound source).

External auditory (acoustic) canal (meatus) (EAC, EAM): anatomical features

-Approximately 2.5 cm to 3.5 cm (1 to 1.5 inches) long; 6 to 9 mm diameter in adults.

-Slightly longer inferiorly due to angle of tympanic membrane.

-medial two thirds of canal is skin over bone (i.e., the tympanic portion of temporal bone).

• This portion curves anteriorly and inferiorly.

• At its midpoint is a narrowing known as the isthmus.

• Near the tympanic membrane the skin becomes thinner (5 to 7 cells thick) … greater risk of bleeding.

-lateral one third of the canal is skin over cartilage.

• This cartilage is firmly attached to tympanic and squamous portions of the temporal bone, but is flexible.

• The skin here contains numerous hair follicles, sebaceous glands, and ceruminous glands.

  • The secretions of sebaceous (oil) and ceruminous glands combine to form cerumen.

  • Cerumen forms a coating over the skin that mixes with the migrating layer (keratin). The cerumen coating forms a protective surface with antibacterial, antifungal, and insect repellent properties.

Migration of the outer skin layer (EAC and TM)

The outer skin layer (keratin layer) of the tympanic membrane and bony portion of the EAC migrates outward toward the cartilaginous portion. Migration is most rapid at the eardrum, slowing toward the external meatus. The migration cleans the ear canal of cerumen and dead skin cells.

Shape of the EAC

The EAC is NOT a straight tube in most people. Usually curved anteriorly and inferiorly (protective feature). There are exceptions!!!

EAC: sensory innervation

-Similar to auricle (branches of CN V, IX, X).

-The branch of CN X is known as Arnold’s nerve. Stimulation by touching the skin of the EAC (e.g., cleaning, earmold impression) can elicit a cough reflex in some people.

-Stimulation of CN X branches may also affect cardiovascular rhythms and circulation that can result in fainting.

EAC: blood supply

Similar to auricle. Branches of external carotid artery.

EAC: physiological features

-Mid-frequency resonance

• The gain produced by resonance in the ear canal peaks at about 2500 to 3500 Hz (average 2800 Hz). This increases amplitude by about 10 dB.

• This resonance peak can be estimated from the length of the EAC:

  • An air-filled tube closed at one end resonates at a frequency with a wavelength 4 times the length of the tube.

  • Example: 3.0 cm X 4 = 12 cm (wavelength). Frequency (Hz) = velocity of sound / wavelength; Frequency = 340 m/sec / 0.12 m/cycle = 2833 cycles/sec.

Combined HRTF (auricle + EAC)

The combined effects of the auricle and EAC on the sound intensity represent the difference between the intensity of the free field response and sound intensity measured at the tympanic membrane.

Combined resonance effects of the auricle and EAC

-Very generally, increase the intensity of frequencies primarily between 2000 and 8000 Hz (range).

-The greatest effects (peak) amount to amplification of about 15 dB between 2500 and 5000 Hz. -Additional peaks are found above 10 kHz.

-Important note: precise HRTF values vary between ears and direction of sound source.

Head baffle effect

-Refers to an increase in sound intensity for the ear turned toward a sound source (relative to 0 or 180 degrees azimuth, straight ahead).

-The gains are greatest at 45-90 degrees azimuth to the near ear in the horizontal plane (no elevation) due to auricle resonance.

-The effect is greatest for the mid-high frequencies (~2000 to 8000 Hz).

Head shadow effect

Refers to a decrease in sound intensity for the ear turned away from a sound source (relative to 0 or 180 degrees azimuth).

-The effect is greatest for frequencies above 2000 Hz.

-High frequencies are most affected because their wavelength is short compared to the diameter of the head, and are therefore blocked. Longer wavelength sounds are not significantly blocked by the head, so the head shadow effect is minimal.

Interaural differences

Interaural differences in timing and intensity are the principal cues used to determine the location of a sound source in the horizontal plane.

Interaural time (phase) difference (ITD, IPD)

-At 0 and 180 degrees azimuth, sound from a single source reaches both ears at the same time.

-Otherwise, sound reaches the near ear before it reaches the far ear, due to the finite speed of sound (~340 meters/second, ~1100 feet/second)

-For an average head size (8.5 cm radius), the maximum ITD is about 600 µs (0.6 ms) with the sound source at 90 degrees azimuth to the near ear.

Interaural level (intensity) difference (ILD, IID)

-At 0 and 180 degrees azimuth, sound from a single source reaches both ears at the same intensity.

-At other angles, sound levels are higher at the ear nearest the sound source and lower at the ear opposite the sound source due to head baffle and head shadow effects.

-The ILD is greatest for higher frequencies (> 2000 Hz) and varies by the angle of incidence of the sound source (greatest ILDs between 45 and 135 degrees).

Where ITDs and ILDs are encoded

-In the brainstem.

-ITD and ILD information can be resolved by the circuitry of the central auditory pathways, and then encoded into neuronal signals used to determine the location of a sound source in the horizontal plane.

-Additional information from auricle/pinna filtering in the vertical plane is combined to create 3-dimensional representations of sound space.

Auricle clinical: Trauma

-Hematoma:

• Trauma from a blow to head, boxing, wrestling, rugby

-keloid fibroma:

• Abnormal tissue healing following laceration, piercing

Auricle clinical: frostbite

-Common in northern climates.

-Auricles lack adipose tissue to insulate blood vessels.

-Prolonged ischemia can lead to necrosis of the tissue.

Auricle clinical: infections

Various bacterial types. May follow injury.

Auricle clinical: skin disorders

Dermatitis; Psoriasis, eczema

Auricle clinical: tumors and cysts

-Periauricular cysts

-Carcinoma

• basal or squamous cell

• age and sun exposure are factors

Auricle clinical: acquired malformation

-creased lobule

• Appear later in life

• Correlated with obstructive coronary artery disease

Auricle clinical: congenital deformity

Range from complete absence to microtia

EAC clinical correlations

-Cerumen accumulation

-Foreign bodies

-External otitis (otitis externa)

• Symptoms include itching, pain.

• Pain is exacerbated by movement of the cartilaginous canal, as in chewing.

• Swelling and exudate accumulation can produce hearing loss.

  • Exudate (discharge) is initially watery, but becomes thick when mixed with pus and desquamated cells.

  • In chronic forms, the discharge is minimal due to coagulum, which is usually foul smelling because of bacterial or fungal activity.

• Bacterial and fungal causes.

Exostoses (EAC)

-Most common tumors of the EAC.

-Formed of outgrowths of bone.

-Most common in those who swim in cold water.

-Not problematic unless accumulation of debris blocks the eardrum or leads to infection.

Other EAC tumors

Granuloma; Papilloma; Polyp; Ceruminoma; Carcinoma

EAC stenosis

-Narrowing or blockage of EAC.

-Acquired type:

• secondary to trauma, swelling, infection.

-Congenital type:

• developmental malformation

3 major functions of the middle ear

-Transduction of airborne acoustic vibrations into mechanical vibrations

-Transmission of the mechanical representation of sound to the cochlea

-Impedance matching between the air (external ear) and fluid-filled (internal ear) structures

Middle ear cavity

-Air-filled; ~2 cc average volume.

-Comprised of 3 interconnected regions: tympanum (main cavity), epitympanum, antrum.

Epitympanum (epitympanic recess, attic)

-The portion of the tympanum above the level of the eardrum

-Main part of the ossicles located here (e.g., head of malleus), hence pathology affecting this part of the tympanum can be devastating to hearing.

-The roof is formed by petrous and squamous portions of the temporal bone

• otherwise, it is surrounded by mastoid bone air cells.

-Close proximity to middle cranial fossa.

• Dehiscences (fistula, opening) in the bone create direct contact between the middle ear mucosa and dura.

Antrum

-Posterior extension of the epitympanum

-Larger in size (kidney shaped), and surrounded by pneumatized bone (i.e., mastoid portion of the temporal bone).

-Access to the antrum is via a small opening known as the aditus

Middle ear structures: 6 sided box model (right ear)

The middle ear cavity can be modeled as a cube with 6 inner walls: lateral, medial, inferior, superior, anterior, posterior.

Lateral wall of the middle ear (pars membranacea)

Tympanic membrane; Bony frame

Medial wall of the middle ear (pars labyrinthica)

-Separates the middle ear from the bony labyrinth. Contains:

• promontory

• oval window

• round window

• facial nerve (CN VII) canal

• tympanic branch of CN IX (Jacobson's branch)

• canal of tensor tympani; bulge of lateral (horizontal) semicircular canal.

Promontory

Bulging area of dense bone formed by the lateral wall of the basal turn of the cochlea.

Oval window (fenestra ovalis; fenestra vestibuli)

Insertion point of the stapes footplate into the cochlea (scala vestibuli portion). Shaped like the sole of a foot (~3 mm x 1.5 mm).

Round window (fenestra cochleae; fenestra tympani)

-Opens into scala tympani

-Moves in opposition to oval window to compensate for displacement of cochlear fluids.

-Surrounded by a bony opening known as the round window niche.

-The round window membrane is located in the depth of the niche.

Facial nerve (CN VII) canal (medial wall)

-Enters above the oval window within a bony canal.

-Makes a ~90 degree turn onto the posterior wall, then descends.

• Small motor branch supplies the stapedius muscle.

• Sensory branch (chorda tympani) supplies the tongue.

• Main motor branch exits the skull through the stylomastoid foramen to supply the facial muscles.

Tympanic branch of cranial nerve IX (Jacobson's branch, tympanic nerve)

Main function: sensory innervation of middle ear mucosa. Other branches to parotid gland.

Canal of tensor tympani (muscle and tendon)

Attaches to the manubrium of the malleus bone. Adjacent to the Eustachian tube opening.

Bulge of lateral (horizontal) semicircular canal

Primary site of warming/cooling during caloric stimulation, as in ENG testing.

Inferior wall of the middle ear (floor; pars jugularis; hypotympanic recess)

-Lies about 2.5 to 3.0 mm below the inferior rim of the eardrum.

-Possible for fluid to accumulate in the tympanum before it becomes visible through the eardrum during an otoscopic examination.

-Contains jugular bulb, tympanic artery, nerve, and vein

Jugular bulb (middle ear floor)

-On the floor is a bony protrusion that may extend well into the inferior tympanum. This protrusion contains the superior bulb of the jugular vein. The protrusion is usually larger in the right ear.

-Dehiscence of the bony covering of the jugular bulb is common, and in some cases the jugular bulb may be in direct contact with the mucous membrane of the tympanum.

Superior wall of the middle ear (roof, tegmen tympani)

-The tegmen tympani is the bony roof of the epitympanum and antrum.

-It is also the floor of the middle cranial fossa (skull base).

-Formed primarily by petrous and squamous portions of the temporal bone.

Anterior wall of the middle ear (pars carotica)

-Shortest of the 6 walls, comprising inferior half of tympanum.

-Contains: carotid canal; Eustachian tube opening; chorda tympani exit.

Carotid canal

Lies just anterior to the tympanum. A bony protrusion can mark the location of the carotid canal, surround by numerous air filled cells in the bone.

Eustachian tube opening (anterior wall)

Canal connecting the nasopharynx and tympanum. Superior portion/half of anterior wall.

Chorda tympani (branch of CN VII)

-Sensory innervation to anterior 2/3 of the tongue.

-Parasympathetic innervation of salivary glands.

-Enters the middle ear space from the posterior wall of tympanum.

-Passes across the superior aspect of the tympanic membrane between the long process of the incus and manubrium of the malleus bones!!!

-Exits through the anterior wall near the Eustachian tube opening.

Posterior wall of the middle ear (pars mastoidea)

Contains: pyramidal eminence; chorda tympani branch of facial nerve (canal opening); facial nerve canal (posterior segment); aditus ad antrum.

Pyramidal eminence

-Houses stapedius muscle.

-Stapedial tendon extends to the neck of the stapes.

• Contraction pulls the ossicular chain posteriorly.

• Muscle innervation is stapedial branch of CN VII.

Facial nerve canal (posterior segment)

Located medial to the pyramidal eminence. Represents an extension of the facial canal originating on the medial wall of the tympanum.

Aditus ad antrum (posterior wall)

Opening to the mastoid antrum

Tympanic membrane (TM; eardrum): shape and size

-Oval in shape and concave (as viewed from external ear).

• Long axis of the oval is about 8.5 to 10 mm across, corresponding to the angle of the manubrium of the malleus (allows for easy identification of left and right in photos).

• Surface area is 55 to 90 mm2; this is much larger than the surface area of the oval window, averaging 3.2 mm2.

• Relative to vertical (90 degrees), the angle of the TM is at about 50 degrees, with the superior portion tilted toward the ear canal.

• The point of greatest inward concavity is called the umbo, located at the tip of the manubrium.

TM major subdivisions

Pars tensa; Pars flaccida (Shrapnell's membrane)

Pars tensa

Comprises most (~7/8) of the surface area of the TM. Fibrous layers present throughout and thicker than the pars flaccida.

Pars flaccida (Shrapnell's membrane)

Relatively small area in the superior/posterior quadrant of the TM. Lacks the central fibrous layers, and is under less tension than the pars tensa. Bulges outward slightly (mallear prominence) due to lateral process of the malleus bone.

TM membranous composition

Composed of four layers (about 0.1 mm thick total): outer layer; inner layer; 2 central (fibrous) layers.

TM outer layer

Very thin; represents a continuation of the migrating skin of the ear canal.