special senses

What are the five traditionally listed special senses?

Vision (Sight), Smell (olfaction), Taste, Touch, Hearing.

What additional sense, found in the ear, is also considered a special sense?

Equilibrium (Balance).

Where are taste buds primarily found?

In papillae on the tongue mucosa.

What are the three types of papillae found on the tongue?

Filiform, fungiform, and circumvallate.

Which types of tongue papillae contain taste buds?

Fungiform and circumvallate papillae.

Approximately how many taste buds are there, and how many cells does each contain?

Approximately 10,000 taste buds; each has 40-100 epithelial cells.

What are the 3 major types of epithelial cells within a taste bud and their functions?

Supporting Cells: Separate and insulate receptor cells. Receptor (Gustatory) Cells: Deal with taste detection. Basal Cells: Stem cells that produce new receptor cells.

What are the five basic taste sensations?

Sweet, Salt, Sour, Bitter, Umami.

What types of substances typically elicit a SWEET taste?

Sugars, saccharin, alcohol, and some amino acids.

What types of substances typically elicit a SALT taste?

Metal ions (like sodium chloride).

What types of substances typically elicit a SOUR taste?

Hydrogen ions (acids).

What types of substances typically elicit a BITTER taste?

Alkaloids such as quinine and nicotine.

What typically elicits an UMAMI taste?

The amino acid glutamate (found in savory foods like meat broth, aged cheese).

What must happen for a chemical to be tasted (activation)?

It must be dissolved in saliva, diffuse into the taste pore, and contact the gustatory hairs of receptor cells.

How quickly does taste adaptation occur?

Adapts rapidly in 3-5 seconds and completely in 1-5 minutes.

What is taste transduction?

The process where the stimulus energy (chemical taste) is converted into a nerve impulse, usually involving an influx of ions into the receptor cell.

Which two cranial nerves carry taste information, and from which parts of the tongue?

Facial Nerve (VII): Anterior two-thirds of the tongue. Glossopharyngeal Nerve (IX): Posterior one-third of the tongue.

What digestive reflexes can taste trigger?

Increasing secretion of saliva and gastric juice.

How significant is the sense of smell to the perception of taste?

Taste is heavily influenced by smell (often cited as 80%). Blocked olfactory receptors make food taste bland.

What other sensory receptors in the mouth influence taste perception?

Thermoreceptors (temperature), mechanoreceptors (texture), and nociceptors (pain/irritation).

What is the primary organ of smell, and where is it located?

The olfactory epithelium, covering the superior nasal concha.

What type of neurons are olfactory receptor cells, and what key feature do they have?

They are bipolar neurons with radiating olfactory cilia (which contain the receptors).

What types of cells are found in the olfactory epithelium besides receptor cells?

Supporting cells (cushion receptors) and Basal cells (stem cells for regeneration).

What does the olfactory epithelium detect? What covers it to aid this?

Detects chemicals in solution. It's covered by mucus which traps airborne molecules and dissolves them.

What two physical states/properties must a substance have to be smelled?

Must be in a gaseous state (volatile) to enter the nasal cavity and must be water-soluble to dissolve in the olfactory epithelium mucus.

Briefly describe the physiology of smell detection.

An odorant molecule binds to protein receptors on olfactory cilia -> opens ion channels -> generates an action potential -> signal sent to the olfactory bulb.

Describe the olfactory pathway after the olfactory bulb.

Impulses travel down the olfactory tract to the thalamus -> frontal lobe (for conscious interpretation) OR to the hypothalamus/limbic system (for emotional responses to odor).

What is anosmia, and what is a common cause?

Loss of the sense of smell ('without smells'). Can be caused by head injuries that damage olfactory pathways.

What are uncinate fits?

Olfactory hallucinations (experiencing smells that aren't actually present), often preceding epileptic seizures.

What are the functions of the eyebrows?

Shade the eyes from sunlight and prevent perspiration from dripping into the eyes.

What is another term for eyelids? What muscle opens the eye?

Palpebrae. The levator palpebrae superioris muscle raises the upper eyelid.

What is the function of eyelashes?

Trigger reflexive blinking when touched, protecting the eye.

What is the conjunctiva? Where is it found? What causes 'bloodshot' eyes?

A transparent mucous membrane. Lines the eyelids (palpebral conjunctiva) and covers the anterior surface (white part) of the eyeball (bulbar conjunctiva). It's vascular; irritation or inflammation causes its blood vessels to dilate, resulting in bloodshot eyes.

What does the lacrimal apparatus consist of?

The lacrimal gland and the ducts that drain lacrimal secretions (tears).

What do lacrimal glands secrete? What protective substances are in tears?

Secrete tears. Tears contain mucus, antibodies, and lysozyme (an enzyme that destroys bacteria).

Describe the path of tears across and out of the eye.

Secreted by lacrimal gland -> released via superolateral excretory ducts -> spread across eye -> enter lacrimal puncta medially -> drain into the nasolacrimal duct -> empty into the nasal cavity.

What is the outermost layer of the eye called? What are its two parts?

The Fibrous Tunic. Composed of the posterior, opaque Sclera and the anterior, transparent Cornea.

What are the functions of the sclera?

Protects the eyeball and provides an anchoring site for the extrinsic eye muscles.

What is the primary function of the cornea?

Allows light to enter the eye; major part of the eye's light-bending apparatus.

What is the middle layer of the eye called? What are its three regions?

The Vascular Tunic (Uvea). Regions: Choroid, Ciliary Body, and Iris.

Describe the choroid. What is its main function?

A dark brown, vascular membrane forming the posterior part of the uvea. Its blood vessels supply nutrients to all eye tunics, and its pigment helps absorb excess light.

Describe the ciliary body. What muscle does it contain, and what structure does it control?

A thickened ring of tissue surrounding the lens. Contains smooth muscle bundles (ciliary muscles). It anchors the suspensory ligaments that hold the lens in place; ciliary muscle contraction/relaxation changes lens shape for focusing.

What is the iris? What is the pupil?

The iris is the colored part of the eye. The pupil is the central opening in the iris that allows light to enter the inner eye.

How does the iris control the amount of light entering the eye?

In bright light/close vision: Circular muscles contract, pupil constricts. In dim light/distant vision: Radial muscles contract, pupil dilates.

How can emotional states affect pupil size?

Pupils can dilate when observing appealing subject matter or during problem-solving/high mental effort; often linked to sympathetic nervous system activity.

What is the innermost layer of the eye? What are its two main layers?

The Sensory Tunic, or Retina. Composed of an outer Pigmented layer and an inner Neural layer.

What is the function of the pigmented layer of the retina?

Absorbs light that passes through the neural layer, preventing it from scattering and reflecting back, which would cause visual confusion. Also stores Vitamin A for photoreceptors.

What key cell types are found in the neural layer of the retina?

Photoreceptors (rods and cones) that transduce light energy, Bipolar cells, Ganglion cells, and interneurons (Amacrine and Horizontal cells) that process visual information.

Where do ganglion cell axons run, and what structure do they form when leaving the eye?

They run along the inner surface of the retina and converge to leave the eye as the Optic Nerve.

What is the optic disc? Why is it called the 'blind spot'?

The site where the optic nerve exits the eyeball. It lacks photoreceptors (rods and cones), so light focused on this spot cannot be seen.

What are the two types of photoreceptor cells in the retina?

Rods and Cones.

Describe the function of Rods.

Respond to dim light (high sensitivity), used for peripheral and night vision. Perceive input only in gray tones. Many rods converge onto a single ganglion cell, resulting in fuzzy, less detailed images.

Describe the function of Cones.

Respond to bright light (low sensitivity), provide high-acuity color vision. Found in the macula lutea, concentrated in the fovea centralis. Each cone (or few cones) synapses with a single ganglion cell, resulting in detailed vision.

What structure divides the internal eye into anterior and posterior segments?

The Lens.

Describe the lens. What is a key property related to focusing? Is it vascular?

A transparent, biconvex, flexible structure. It can change shape (accommodation) to precisely focus light on the retina. It is avascular (lacks blood vessels).

How does the lens change with age? What condition can result?

It becomes thicker, denser, and less elastic with age, impairing its ability to focus on close objects (presbyopia).

What is a cataract? What are common causes?

Clouding of the lens that obstructs vision. Can be caused by aging (lens thickening), diabetes mellitus, heavy smoking, or prolonged exposure to intense sunlight.

What fills the posterior segment of the eye (behind the lens)? What are its functions?

Vitreous humor (a clear, gel-like substance). Functions: transmits light, supports the posterior surface of the lens, holds the neural retina firmly against the pigmented layer, contributes to intraocular pressure.

What fills the anterior segment of the eye (in front of the lens)? What are its two chambers?

Aqueous humor (a clear fluid similar to blood plasma). Chambers: Anterior chamber (between cornea and iris) and Posterior chamber (between iris and lens).

What are the functions of aqueous humor? How is it drained?

Supplies nutrients and oxygen to the lens and cornea, carries away metabolic wastes. Drains continuously via the Canal of Schlemm (scleral venous sinus).

What happens to light when it passes from one transparent medium to another at an angle?

Its speed changes, and it refracts (bends).

How does a convex lens (like the eye's lens) affect parallel light rays?

It bends the light rays so they converge at a single point called the focal point.

What is the orientation of an image formed on the retina by the eye's lens system?

It is upside down and reversed left to right. (The brain interprets it correctly).

What is photoreception?

The process by which the eye detects light energy.

What do rods and cones contain that allows them to detect light? How are these arranged?

They contain visual pigments (photopigments, e.g., rhodopsin in rods) located within stacked, disk-like infoldings of the plasma membrane. These pigments change shape when they absorb light.

From where does the neural retina receive its blood supply?

Two sources: The outer third (including photoreceptors) receives blood from the Choroid. The inner two-thirds receives blood from the Central Artery and Central Vein of the retina, which enter/exit through the optic nerve.

How many extrinsic (extraocular) muscles control the movement of each eye? Name the two groups.

Six muscles: Four Rectus muscles (Superior, Inferior, Lateral, Medial) and Two Oblique muscles (Superior, Inferior).

Which three cranial nerves innervate the extrinsic eye muscles?

Oculomotor (III), Trochlear (IV), and Abducens (VI).

What are the three major areas of the ear?

Outer Ear, Middle Ear, and Inner Ear.

Which parts of the ear are involved only with hearing?

Outer Ear and Middle Ear.

Which part of the ear functions in both hearing and equilibrium?

Inner Ear.

What is the external, visible part of the ear called? What is its function and composition?

Auricle or Pinna. Composed of elastic cartilage covered by skin. Function is to direct sound waves into the external auditory canal.

What is the tube extending from the auricle to the eardrum? What lines it and what glands are present?

External auditory meatus (canal). Lined with skin containing hairs, sebaceous (oil) glands, and ceruminous glands (which secrete cerumen/earwax).

What structure forms the boundary between the outer and middle ear?

Tympanic membrane (eardrum).

What is the middle ear also known as? Describe its general characteristics.

Tympanic cavity. It's a small, air-filled, mucosa-lined cavity within the temporal bone.

What structures border the middle ear laterally and medially?

Laterally: Tympanic membrane (eardrum). Medially: Bony wall containing the Oval Window and Round Window (openings to the inner ear).

What is the superior portion of the middle ear cavity called?

Epitympanic recess.

What tube connects the middle ear to the nasopharynx? What is its crucial function?

Pharyngotympanic (Auditory or Eustachian) tube. Its function is to equalize the pressure in the middle ear cavity with the external air pressure, allowing the eardrum to vibrate freely.

Name the three tiny bones (ear ossicles) found in the middle ear, in order from the eardrum to the oval window.

Malleus (hammer), Incus (anvil), Stapes (stirrup).

What is the function of the ear ossicles?

To transmit the vibratory motion of the eardrum to the oval window, amplifying the pressure/force of the sound waves.

Which two small skeletal muscles are found in the middle ear, and what is their function?

Tensor tympani (attached to malleus) and Stapedius (attached to stapes). They contract reflexively in response to loud sounds to dampen vibrations and protect the inner ear.

What is the complex system of tunnels within the temporal bone called? Name its three regions. What fluid fills it?

Bony (osseous) Labyrinth. Regions: Vestibule, Cochlea, and Semicircular Canals. Filled with Perilymph.

What structure lies suspended within the bony labyrinth? What fluid fills it?

Membranous Labyrinth (a series of interconnected sacs and ducts). Filled with Endolymph (a potassium-rich fluid).