Nervous System and Sensation

The 3 Types of Muscles in the Eye:

Ciliary Muscles Iris Extra-ocular Muscles

Taste (Gustation)

- It provides info about what is entering the digestive system. -The receptor cells for taste are located in roughly 10,000 TASTE BUDS, which are distributed across the tongue and other parts of the mouth and throat.The taste buds wear out and are replaced every 10 days or so. -Tongue is also called the PAPILLAE. Four Primary Taste Qualities: 1) Sweet 2) Salt 3) Sour 4) Bitter Umami is not qualified as a taste it is still on the list (deals with meat taste)

Sending the Message from the Eye to the Brain

- Stimulation of the nerve cells in the eye triggers a neural response that is transmitted to other nerve cells in the retina called BIPOLAR CELLS and GANGLION CELLS. Bipolar Cells receive info directly from the rods and cones and communicate that info to the ganglion cells. Ganglion Cells collect and summarize visual info, which is then moved out the back of the eyeball and sent to the brain through a bundle of ganglion axons called the OPTIC NERVE. - Because the opening for the optic nerve passes through the retina, there are no rods or cones in the area, and that creates a blind spot. Once beyond the eye itself, the neural impulses relating to the image move through the optic nerve.

Smell (Olfaction)

- The sense of smell is sparked when the molecules of a substance enter the nasal passages and meet OLFACTORY CELLS, which are the receptor neurons of the nose, which are spread across the nasal cavity. - It has long been known that nonhumans release PHERMONES, chemicals they secrete into the environment that produce a social response in other members of the same species. Pheromones transmit messages such as alarm ("danger-predators are close by!") or sexual availability ("I'm interested in sex"). For one thing, it is not clear what specific sense organ is receptive to pheromones. In humans the organ appears to recede during the fetal development. (We lose when we are in the womb.)

Hearing Defects

Conduction Deafness: Due to the structure problems in or on the outer or middle ear. Nerve Deafness: Happens when the nerve cells inside the cochlea start to die. Eventually leading to the loss of hearing. Prebyacusia: In the aging process, the nerve endings in the inner ear start to deteriorate causing them to become less flexible. Tinnitus: The constant ringing of the ears .The most common cause of tinnitus is damage and loss of the tiny sensory hair cells in the cochlea of the inner ear. This tends to happen as people age, and it can also result from prolonged exposure to excessively loud noise. Hearing loss may coincide with it.

The Structure of the Eye

Cornea- A transparent, protective window. Because of its curvature, bends (or refracts) light as it passes through, playing a primary role in focusing the light more sharply. -After moving through the cornea, the light traverses the pupil. Pupil: The dark hole in the center of the iris. The size of the pupil opening depends on the amount of light in the environment. The dimmer the surroundings are, the more the pupil opens to allow more light to enter-but at the expanse of visual detail. A small pupil greatly increases the range of distances at which objects are in focus. Iris: The colored part of the eye. Can range from dark brown to light blue. The muscles in the iris determine the diameter of the pupil. The causes of the iris to work there has to be a certain amount of light, could be affected by drugs, and is connected to certain emotions and stress. -Once light passes through the pupil, it enters the lens. Lens: Directly behind the pupil. The lens acts to bend the rays of light so that they are properly focused on the rear of the eye. The lens focuses light by changing its own thickness, a process called accommodation: It becomes flatter when viewing distant objects and rounder when looking at closer objects. It loses elasticity when older. -After the image travels through the pupil and the lens, it reaches its ultimate destination- the retina. Retina: The part of the eye that converts the electromagnetic energy of light to electrical impulses for transmission to the brain. There are two kinds of light-sensitive receptor cells: rods and cones. They are distributed unevenly throughout the retina. - Rods: These are generally used for dimmer lighting compared to the cones. They are also not affiliated with color, they are achromatic (no color). Rods are not in the fovea or connected to it. They are more rods than cones. Rods play a key role in PERIPHERAL VISION-seeing objects that are outside the main center of focus-and in night vision. - Cones: These are generally used for brighter light. They are affiliated with color. Cones are more concentrated to the fovea. There are less cones in the retina than rods. - Fovea: It is a particularly sensitive region of the retina. If you want to focus on something of particular interest, you will automatically try to center the image on the fovea to see it more sharply.

Adaptation

It is an adjustment in sensory capacity after prolonged exposure to unchanging stimuli. In a sense, our brain mentally turns down the volume of the stimulation that it's experiencing. The apparent decline in sensitivity to sensory stimuli is due to the inability of the sensory nerve receptors to fire off messages to the brain indefinitely. Because these receptor cells are most responsive to CHANGES in stimulation, constant stimulation is not effective in producing a sustained reaction. Example: Although jumping into a cold lake may be temporary unpleasant, eventually you probably will get used to the temperature.

Visual Defects

Nearsightedness- It is also called myopia. It is caused when the cornea or the lens is too curved to the length of the eyeball. Farsightedness- It is also hyperopia. It is caused when the eye is too short, when the cornea is not curved enough, and when the lens sits farther in the back of eye than normal. Color Blindness

Skin Senses

Skin Senses- Touch, pressure, temperature, and pain-play a critical role in survival, making us aware of potential danger to our bodies. Provides info about physiological stimuli in the environment. Senses: 1) Pressure/Touch 2) Pain 3) Cold 4) Warmth 5) Itchiness 6) Tickling 7) Vibration Structures: Pacinian Corpuscle: Pressure, vibration, tickle (very fast) Merkel's Discs: Light touch (slow) Ruffini Endings: Heat Meissner's Corpuscle: Touch, vibration, and flutter Kraus' Bulb: Cold - Pain is a response to a great variety of different kinds of stimuli. When a cell is damaged, regardless of the source of damage, it releases a chemical called SUBSTANCE P that transmits pain messages to the brain. Clearly, then, pain is a perceptual response that depends heavily on our emotions and thoughts. Gate-control Theory of Pain is the theory that particular nerve receptors in the spinal cord lead to specific areas of the brain related to pain. When these receptors are activated because of an injury or problem with a part of the body, a "gate" to the brain is opened, allowing us to experience the sensation of pain.

Structure and Function of the Ear

THE OUTER PART OF THE EAR: Pinna: The external part of the ear and it funnels sound waves into head leading to the auditory canal. Auditory Canal: A tube-like passage that leads to the eardrum. When the sound hits it, it resonates (amplifies) the intensity of the waves entering the ear to pass to the tympanic membrane. Tympanic Membrane: When the sound resonates due to the auditory canal, it then causes the eardrum to vibrate when the sound comes in. Eustachian Tube: When the sound hits the tube it causes it to keep pressure to equalize the sound by allowing air into the middle ear. THE MIDDLE PART OF THE EAR: -These vibrations are then transferred into the middle ear, a tiny chamber containing three bones: the malleus (hammer), the incus (anvil), and the stapes (stirrup) that transmit vibrations to the oval window, a thin membrane leading to the inner ear. Because the three bones act as a set of levers, they not only transmit vibrations but also increase their strength. The middle ear, then, acts as a tiny mechanical amplifier. THE INNER PART OF THE EAR: -The inner ear is the portion of the ear that changes the sound vibrations into a form in which they can be transmitted to the brain. When sound enters the inner ear through the oval window, it moves into the COCHLEA. Cochlea: A coiled tube that looks something like a snail and is filled with fluid that vibrates in response to sound. Inside the cochlea is the BASILAR MEMBRANE. Basilar Membrane: A vibrating structure that runs through the center of the cochlea, dividing it into an upper chamber and a lower chamber and containing sense receptors for sound. They are two theories which incorporate themselves with the membrane: place theory of hearing and frequency theory of hearing. - Place theory of hearing is that different areas of the basilar membrane respond to different frequencies. - Frequency theory of hearing is that the entire basilar membrane acts like a microphone, vibrating as a whole in response to a sound. Hair Cells: Tiny cells covering the basilar membrane that, when bent by the vibrations entering the cochlea, the cells send a neural message to the brain.

Psychophysics

The study of the relationship between the physical aspects of stimuli and our psychological experience of them. It elaborated the question of how different types of stimuli activate different sense organs based on the intensity of the stimulus. It is divided into two sub groups: Absolute and Difference Threshold. Absolute Threshold is the smallest intensity of a stimulus that must be present for the stimulus to be detected. Difference Threshold is the smallest level of added or reduced (difference) stimulation required to sense that a change in stimulation has occurred. It is also known as the Just Noticeable Difference. Both thresholds are connected to Weber's Law: a basic law that a just noticeable difference is a constant proportion to the intensity of an initial stimulus (rather than a constant amount).

Trichromatic Theory of Color Vision

The theory that there are three kinds of cones in the retina, each of which primarily to a specific range of wavelengths. One is most responsive to blue-violet colors, one to green, and the third to yellow-red.

Balance Associated with the Inner Ear

Vestibular System: Which responds to the pull of gravity and allows us to maintain our balance. It is mainly formed by the SEMICIRCULAR CANALS. Semicircular Canals: Three tube-like structures of the inner ear containing fluid that sloshes through them when the head moves, signaling rotational or angular movement to the brain. - The pull on our bodies caused by the acceleration of forward, backward, or up-and-down motion, as well as the constant pull of gravity, is sensed by OTOLITHS. Otoliths: Tiny, motion-sensitive crystals in the semicircular canals. When we move, these crystals shift as sands do on a windy beach, contacting the specialized receptor hair cells in the semicircular canals.