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Types, distribution, and functions of receptors: location and stimulus detected

• Free nerve ending: a form of peripheral ending of sensory nerve fibers in which the terminal filaments end freely in the tissue.

Synonyms: terminationes nervorum liberae (40)• Root Hair Plexuses: free nerve endings associated with hair follicle

- very sensitive to touch which moves the hair (41)• Merkel Disks: Merkel's disks are located in the epidermis, where

they are precisely aligned with the papillae that lie beneath the dermal ridges. They account for about 25% of the mechanoreceptors of the hand and are particularly dense in the fingertips, lips, and external genitalia. (42)

• Meissner Corpuscle: enclosed in connective tissue capsule, just below epidermis in hairless areas of skin such as lips, finger tips, nipples, external genitalia, palms of hands and soles of feet - fine touch and pressure (41)

• Pacinian Corpuscles: enclosed in multilayered connective tissue capsule, in deeper skin and tendons, sensitive to deep pressure and high pressure vibrations (41)

• Muscle Spindles: small sensory organs that are enclosed within a capsule. They are found throughout the body of a muscle, in parallel with typical muscle fibers. There are several small, specialized muscle fibers known as intrafusal fibers. (43)

• Golgi tendon Organs: are in series with muscle fibers, located in the tendons that attach muscle to bone. The sensory dendrites of the Golgi tendon organ afferent are interwoven with collagen fibrils in the tendon. (43)

Structure

44

SPECIAL SENSES

Smell (give diagram of nose indicating receptors) Describe each

SMELL

(1) smell, also called Olfaction, the detection and identification by sensory organs of airborne chemicals. The concept of smell, as it applies to humans, becomes less distinct when invertebrates and lower vertebrates (fish and amphibians) are considered, because many lower animals detect chemicals in the environment by means of receptors in various locations on the body, and no invertebrate possesses a chemoreceptive structure resembling the vertebrate nasal cavity. For this reason, many authorities prefer to regard smell as distance chemoreception and taste as contact chemoreception.

Left receptor bulb

Right receptor bulb

(20)

Smell diagram!(7)

Olfactory receptors

OLFACTORY RECEPTOR BULB

olfactory receptor, also called smell receptor, of binding odour molecules that plays a central role in the sense of smell (olfaction). In terrestrial vertebrates, including humans, the receptors are located on olfactory receptor cells, which are present in very large numbers (millions) and are clustered within a small area in the back of the nasal cavity, forming an olfactory epithelium. (2) (20

)

The sense of smell can create a powerful and long lasting memories. These memories couples with unique sensory inputs especially ordor, often persist from early child hood to death. New car, baby, kitchen and people odors are all olfactory triggers that often bring back memories of events that have occurred from the past. There is a huge relationship between the olfactory and gustatory pathways because our sense of smell and taste are closely related. (8)

Olfactory pathways

Olfactory straie (yellow)

OLFACTORY RECEPTOR BULB (blue)

(20)

(5)Taste bud organ located on the tongue in terrestrial vertebrates that functions in the perception of taste. In fish, taste buds occur on the lips, the flanks, and the caudal (tail) fins of some species and on the barbells of catfish. In most animals, including humans, taste buds are most prevalent on small pegs of epithelium on the tongue called papillae The taste receptor cells of other animals can often be characterized in ways similar to those of humans, because all animals have the same basic needs in selecting food.

Com paring human and canine olfaction

(4)

The gustatory sensations or taste are closely associated with olfaction. Taste receptors are located inside structures called taste buds that line the surface of the tongue, and are found on the soft palate, pharynx, and larynx. Nervous impulses generated in the anterior two thirds of the tongue travel over the facial nerve where they are generated from the posterior one third are conducted by fibers of the glossopharynegal.(10)

Neural pathway

(9)

The taste buds are embedded in the epithelium of the tongue and make contact with the outside environment through a taste pore.

Taste Buds are small organs located on the tongue in terrestrial vertebrates that functions in the perception of taste

TasteTaste buds: bitter, sweet, sour, salty

papillaeh

Taste buds are composed of groups of between 50 and 150 columnar taste receptor cells bundled together like a cluster of bananas. The taste receptor cells within a bud are arranged such that their tips form a small taste pore, and through this pore extend microvilli from the taste cells. The microvilli of the taste cells bear taste receptors.

(20)

Hearing

(51)

When one hears a sound or someone speaking, then an image comes to mind that is called the cartilaginous tissue, or the pinna. The pinna directs the sound energy into the ear canal. The eternal meatus is about one inch in length and is closed at the inner end near the ear drum; it forms a passage way in which sound energy may be transmitted into the inner reaches of the ear. (30)

The Mechanism of Hearing

(45)

Cochlear N. to the brain stem interneurons to multi-neuron pathway to the thalamus then to the auditory cortex

The Organ of Corti with its sound-sensitive hair cells and basilar membrane are important parts of the sound transducing system for hearing. Mechanical vibrations of the basilar membrane generate membrane potentials in the hair cells which produce impulse patterns in the cochlear portion of the vestibulocochlear nerve (cranial nerve VIII). (53)

Neuronal pathway of Hearing

Balance

(49)

The vestibule has a round open space that accesses various passageways, it is the central structure within the inner ear. The outer wall of the vestibule contains the oval and round windows (which are the connection sites between the middle and inner ear). Internally, the vestibule contains two membranous sacs, the utricle and the saccule, which are lined with tiny hair cells. (47)

The semicircular canals have three bony tubes that form loops. Each tube ends in a bulge, or ampulla, containing sensors that detect the movement of fluid in the loop—which depends on your body’s movement. Similar receptors called maculae detect how upright you are. Your brain uses these signals to correct your balance. (48)

The vestibular system serves the bodily functions of balance and equilibrium. It accomplishes this by assessing head and body movement and position in space, generating a neural code representing this information, and distributing this code to appropriate sites located throughout the central nervous system. Vestibular function is largely reflex and unconscious in nature. (46)

Vestibule and semicircular canals

The semicircular canals are three pretzel-like curved tubes arranged at angles roughly perpendicular to each other, with the two vestibular sacs located at their base. Both the canals and sacs contain fluid and tiny hair cells, which act as receptors. When a person's head moves, the fluid disturbs the hair cells, which stimulate a branch of the auditory nerve, signaling the brain to make adjustments in the eyes and body. A movement at any given angle will have its primary effect on one of the three canals. Overstimulation from extreme movements will produce dizziness and nausea. (32)

Having a sense of balance is…

The special sense which interprets balance when one is moving, or at least the head is moving; the semicircular canals contain the receptors for dynamic equilibrium; within each semicircular canal is a complex mechanoreceptor called a crista ampullaris which contains the mechanoreceptors (Hair cells) for dynamic equilibrium; when the perilymph in one of the semicircular canals moves, the hair cells in the crista ampullaris are stimulated to send nerve impulses to the brain; this advises the brain of whether or not a person has their balance during body movements or if their body is in motion, such as moving their head side-to-side.(50)

Dynamic Equilibrium…

Vision

• Humors- is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. It is often referred to as the vitreous body or simply "the vitreous".

• Cavities of the eye- the anterior cavity is actually divided into two subcategories.

• the anterior chamber ( from iris to cornea)

• the posterior chamber ( from iris to lens)

Cavities and humors of the eye

Since only the fovea provides sharp distinct vision, the eye must move to follow a target. It must be precise and fast. This is seen in scenarios like reading, wherein the reader must shift gaze constantly, or following a small object like a golf ball, in which the extraocular muscles must lead the eye to follow the head movements. Although under voluntary control, most movement is done without thinking, such as those based on head or other body movement, or movement of objects in the area. Researchers still have some work in order to find the parallel nature of the environment-based (involuntary) and voluntary control

Muscles of the eye

The site of accessory structures of the eye are as follows: eyebrows, eyelashes, eyelids, conjunctiva, and lacrimal apparatus.

accessory structures

The photopigments that absorb light all have a similar structure, which consists of a protein called an opsin and a small attached molecule known as the chromophore. The chromophore absorbs photons of light, using a mechanism that involves a change in its configuration. In vertebrate rods the chromophore is retinal, the aldehyde of vitamin A1

Photopigments

formation of focused images on the photoreceptors of the retina depends on the refraction (bending) of light by the cornea and the lens . The corna is responsible for most of the necessary refraction, a contribution easily appreciated by considering the hazy out-of-focus images experienced when swimming underwater. Water, unlike air, has a refractive index close to that of the cornea; as a result, immersion in water virtually eliminates the refraction that normally occurs at the air/cornea interface.

Retinal image

Rods are responsible for vision at low light levels (scotopic vision). They do not mediate color vision, and have a low spatial acuity.

Cones are active at higher light levels (photopic vision), are capable of color vision and are responsible for high spatial acuity. The central fovea is populated exclusively by cones. There are 3 types of cones which we will refer to as the short-wavelength sensitive cones, the middle-wavelength sensitive cones and the long-wavelength sensitive cones or S-cone, M-cones, and L-cones for short

Rods & cones

Why don't deer see Hunters who wear Bright orange?

Deer have no red-sensitive cone cells in their eyes, so they can't tell red or orange from green and brown.

What is the difference between "nearsighted" and "farsighted"? How are each of these corrected?

There are several differences between being nearsighted and being farsighted, as these are two different vision problems. Nearsightedness is called myopia, and farsightedness is known as hyperopia. The main biological difference in the two is that in myopia, the images seen are focused in front of the retina, rather than directly on the retina. In hyperopia, the images are focused behind the retina, rather than on top of it. You can fix these problems by simply getting eye glasses

Questions