Study Chart |
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- Retina stuff:
The retina is a thin layer of tissue that lines the back of the eye on the inside. It is located near the optic nerve. The purpose of the retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition.
The retina processes light through a layer of photoreceptor cells. These are essentially light-sensitive cells, responsible for detecting qualities such as color and light-intensity. The retina processes the information gathered by the photoreceptor cells and sends this information to the brain via the optic nerve. Basically, the retina processes a picture from the focused light, and the brain is left to decide what the picture is.
Due to the retina's vital role in vision, damage to it can cause permanent blindness. Conditions such as retinal detachment, where the retina is abnormally detached from its usual position, can prevent the retina from receiving or processing light. This prevents the brain from receiving this information, thus leading to blindness.
STIMULI - something that incites to action or exertion or quickens action, feeling, thought, etc.:
2: Stimulus is a word often used in biology — something that causes a reaction in an organ or cell, for example.
3: a thing or event that evokes a specific functional reaction in an organ or tissue.
"areas of the brain which respond to auditory stimuli
- Sensory System:
The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for vision, auditory (hearing), somatic sensation (touch), gustatory(taste), olfaction (smell) and vestibular (balance/movement).- mechanoreceptors (touch and sound):
Please take a moment and notice how your fingertips sense the tabletops. Notice the different mechanisms for sensing location, roughness, table edge, table temperature. And, try to pay attention to how you use your fingers to detect certain signals, such as roughness or temperature.
One important characteristic of the sensors in your skin is referred to as the Rate of Adaptation. Most human mechanoreceptor cells respond to a change in the external stimulus (pressure, temperature, etc) by producing voltage pulses across neurons. Immediately after the change in external stimulus, these pulses begin to appear. Over some time, the pulse rate declines and eventually returns to the original passive level. The rate of adaptation is the rate at which the mechanoreceptor pulse rate returns to normal after a change in stimulus. Simply put, sensors with adaptation do not provide information about static signals - only about changing signals. To use such a sensor to sense a static quantity, like roughness, it is necessary to make the roughness produce a time-varying contact force on the tactile sensors in the fingers.
The mechanoreceptors in your skin may be separated into distinct categories:Fast Adaptation
Pacinian Corpuscles are rapidly adapting mechanoreceptors in your skin and are often the most sensitive cells to very small changes in the stimulus, such as the tactile force. These rapidly adapting cells return to a normal rate of pulses in less than 0.1 second. These delicate mechanoreceptors are generally found in the subcutaneous layer of the skin, where they are protected from the abuses which may occur at the surface. These receptors are used in human perception to detect surface roughness as the fingertips are dragged across a surface, or very small vibrations in machines. Because of their location far below the surface and the role of the skin in transmission of signals, it is not necessary or useful to have a high areal density of these receptors. The skin acts to distribute the applied forces over relatively large areas (maybe 10x the thickness of the skin), so spacing closer than tenths of a millimeter would not add any additional sensitivity.Moderate Adaptation
Meissner's Corpuscles and hair follicle receptors are good examples of mechanoreceptors with moderate adaptation rates. These receptors can be located near the surface of the skin, and adapt to changes on time periods of order 1 second. Some experiments with the hair on your arm should confirm these adaptation rates. Think about the sorts of things such sensors (located around hair follicles) would be useful for in an outdoor setting. If you've been camping recently, you might recall that these sensors are the ones you use most effectively to detect insects on your skin (mosquitoes, ticks, flies, etc). Since these insects are a threat to human survival at some level, evolving a capability to detect and remove such insects would be of obvious value.Slow Adaptation
Ruffini Endings, Merkel's Cells, and Tactile Disks are examples of slow adapting mechanoreceptors. These receptors are generally located near the surface of the skin, and are responsible for much of the static perceptive capabilities. For example, the sensitivity to temperature at the skin is generally of a slow-adapting type, as are many tactile sensors useful for maintaining grip on an object. The adaptation time scale for these cells can be from 10 to more than 100 seconds. Experiment with grasping of an object in the air, like a pencil or a cup of coffee. Close your eyes and think about how it is that you overcome the adaptation in these sensors to avoid dropping objects.
In fact, it is interesting to give some thought to the whole process of grasping objects in the air. You have all developed a set of skills for holding drinks in your hand with a minimum of effort. Think about how often you mistakenly crush the coffee cup in your hand, or about how often the cup slips completely through your fingers. Aside from falling asleep, these events are extremely rare. However, the task of holding a cup of liquid is an extremely complicated one. Think about all the forces that must be balanced and maintained, and remember that the sensors used in this task have very odd temporal response, and that ALL of them eventually stop sending information about the forces on the fingertips if those forces are constant. Nevertheless, all of you are able to accomplish this task without much direct feedback control being applied - in fact it might be completely unconscious!
- Smell:
- The Sense of Smell
Smell depends on sensory receptors that respond to airborne chemicals. In humans, these chemoreceptors are located in theolfactory epithelium — a patch of tissue about the size of a postage stamp located high in the nasal cavity. The olfactory epithelium is made up of three kinds of cells:- sensory neurons each with a primary cilium
- supporting cells between them
- basal cells that divide regularly producing a fresh crop of sensory neurons to replace those that die (and providing an exception to the usual rule that neurons seldom are replaced).
How does your sense of smell work?
Your sense of smell—like your sense of taste—is part of your chemosensory system, or the chemical senses.
Your ability to smell comes from specialized sensory cells, called olfactory sensory neurons, which are found in a small patch of tissue high inside the nose. These cells connect directly to the brain. Each olfactory neuron has one odor receptor. Microscopic molecules released by substances around us—whether it’s coffee brewing or pine trees in a forest—stimulate these receptors. Once the neurons detect the molecules, they send messages to your brain, which identifies the smell. There are more smells in the environment than there are receptors, and any given molecule may stimulate a combination of receptors, creating a unique representation in the brain. These representations are registered by the brain as a particular smell.
Smells reach the olfactory sensory neurons through two pathways. The first pathway is through your nostrils. The second pathway is through a channel that connects the roof of the throat to the nose. Chewing food releases aromas that access the olfactory sensory neurons through the second channel. If the channel is blocked, such as when your nose is stuffed up by a cold or flu, odors can’t reach the sensory cells that are stimulated by smells. As a result, you lose much of your ability to enjoy a food’s flavor. In this way, your senses of smell and taste work closely together.
Without the olfactory sensory neurons, familiar flavors such as chocolate or oranges would be hard to distinguish. Without smell, foods tend to taste bland and have little or no flavor. Some people who go to the doctor because they think they’ve lost their sense of taste are surprised to learn that they’ve lost their sense of smell instead.
Your sense of smell is also influenced by something called the common chemical sense. This sense involves thousands of nerve endings, especially on the moist surfaces of the eyes, nose, mouth, and throat. These nerve endings help you sense irritating substances—such as the tear-inducing power of an onion—or the refreshing coolness of menthol.- Hyposmia [high-POSE-mee-ah] is a reduced ability to detect odors.
- Anosmia [ah-NOSE-mee-ah] is the complete inability to detect odors. In rare cases, someone may be born without a sense of smell, a condition called congenital anosmia.
- Parosmia [pahr-OZE-mee-ah] is a change in the normal perception of odors, such as when the smell of something familiar is distorted, or when something that normally smells pleasant now smells foul.
- Phantosmia [fan-TOES-mee-ah] is the sensation of an odor that isn’t there.
What causes smell disorders?
Smell disorders have many causes, with some more obvious than others. Most people who develop a smell disorder have experienced a recent illness or injury. Common causes of smell disorders are:- Aging
- Sinus and other upper respiratory infections
- Smoking
- Growths in the nasal cavities
- Head injury
- Hormonal disturbances
- Dental problems
- Exposure to certain chemicals, such as insecticides and solvents
- Numerous medications, including some common antibiotics and antihistamines
- Radiation for treatment of head and neck cancers
- Conditions that affect the nervous system, such as Parkinson’s disease or Alzheimer’s disease.
Some interesting facts:- Humans possess around 12 million olfactory receptor cells that can detect approximately 10,000 odours. Dogs, on the other hand, have anything from 100 to 200 million plus receptor cells, depending on the breed. The bloodhound is thought to have more receptor cells than any other dog (as many as 300 million) and can detect 40,000 different odours!- The higher concentration of an odour, the stronger the signal sent by the receptor cells to the olfactory bulb. - sensory neurons each with a primary cilium
BACKGROUND:
A tissue is a group of cells that have a similar shape and function. Different types of tissues can be found in different organs. In humans, there are four basic types of tissue: epithelial, connective, muscular, and nervous tissue. There may be various sub-tissues within each of the primary tissues.
Epithelial tissue covers the body surface and forms the lining for most internal cavities. The major function of epithelial tissue includes protection, secretion, absorption, and filtration. The skin is an organ made up of epithelial tissue which protects the body from dirt, dust, bacteria and other microbes that may be harmful. Cells of the epithelial tissue have different shapes as shown on the student's worksheet. Cells can be thin, flat to cubic to elongated.
Connective tissue is the most abundant and the most widely distributed of the tissues. Connective tissues perform a variety of functions including support and protection. The following tissues are found in the human body, ordinary loose connective tissue, fat tissue, dense fibrous tissue, cartilage, bone, blood, and lymph, which are all considered connective tissue.
There are three types of muscle tissue: skeletal, smooth, and cardiac. Skeletal muscle is a voluntary type of muscle tissue that is used in the contraction of skeletal parts. Smooth muscle is found in the walls of internal organs and blood vessels. It is an involuntary type. The cardiac muscle is found only in the walls of the heart and is involuntary in nature.
Nerve tissue is composed of specialized cells which not only receive stimuli but also conduct impulses to and from all parts of the body. Nerve cells or neurons are long and string-like.
In tissues the simplest combination is called a membrane, or a sheet of tissues which cover or line the body surface or divide organs into parts. Examples include the mucous membrane which lines body cavities. Tissues combine to form organs. An organ is a part of the body which performs a definite function. The final units of organization in the body are called systems. A system is a group of organs each of which contributes its share to the function of the body as a whole.
Last edited by Callous on Wed Aug 10, 2016 5:41 pm; edited 3 times in total
