Sensory Systems in Animals

All animals have some kind of anxious system that can get and interpret information about its interior and external environment. Sensory organs provide a means for communication from the external environment to the internal. Sensory receptors contain receptor cells that are specialised to react to specialised stimuli. These sensory organs may be found all around the body or in localised areas. Afferent neurons hold the sensory information from the periphery toward and in to the central stressed system while the efferent neurons hold information from the central stressed system. Sensations arising when signals initiated in sensory receptors are sent in certain regions of the brain, producing signals using parts of the mind. (Hickman, Roberts, & Eager, 2009)

Stimulus types have features that may be distinguished in one another. In the torso of an animal the sensory receptor skin cells are usually revised. For example, certain receptors detect pressure, heat, chemicals, light and even pain. The stimulus for light detection and chemical diagnosis is different and likewise, the same type of stimulus may possess different features. This can be seen, set for example the recognition of blue and red light, both being regarded as a stimulus of light.

In the first part of the sensible the sensory structures of lots of invertebrate organisms were studied and in comparison to each other. Mainly chemoreception, photoreception and mechanoreception were analyzed. Chemicals in the animals surrounding is recognized by lots of chemoreceptors. Chemoreceptors may be divided into two main categories; olfactory (smell), which respond to airborne substances and gustatory (taste), responding to dissolved molecules.

Mechanoreceptors are made of undifferentiated nerve endings within connective tissues on the periphery of the pet such as the skin. More complex accessory buildings have accessory constructions that transfer mechanical energy to the receptive membrane. These mechanoreceptors are also able to filter the mechanical energy plus they may also are the muscle stretch receptors

Photoreception contains transducing photons of light into electro-mechanical signals that can be interpreted by the nervous system and photoreceptive organs including the eyes.

These sensory structures in different pets or animals have taken a variety of sizes and shapes that contain been modified to this environment best for them. Although quite different all the sensory composition of particular receptor has the same function of collecting information from the surroundings and responding in the best way possible to enhance its success.


  • Light Microscope cardboard
  • Stereomicroscope 1g-5g, 10 g, 20 g, 50, 100 g weights
  • Pencil x3 500 mL drinking water bath
  • Pointed forceps heater/Bunsen to heat water
  • Stop watch thermometer
  • X3 5 c coins


Refer to fastened sheet


  • The plastomounts were located under a stereomicroscope for better browsing of small body features
  • The same couple of forceps was used to use the stimulus since different tools could result in different outcomes.
  • As much as you can the gold coin was located in the test place for everyone things since different area may have another amount of receptors.
  • The temperature in this baths was assessed before the experiment was conducted. This was done so that the initial temp of this particular for all the subjects could be the same. Thus the results would be more comparable.

Sources of Error

  • Due to the clothing worn the test of tactile response using the forceps had to be carried out on the clothing. This thus developed an extra covering that could reduce the response of the nerve.
  • Not all the sensory set ups of the organisms might have been identified.
  • The experiments on each subject were only carried out once. More appropriate results would have been obtained if completed at least 3 times

Results Part A

Refer to fastened diagrams


For all 3 subject matter the cold water was almost painful, while the normal water at 45 certifications was calming. On positioning the hand in water at room temperature the right hands felt this inflatable water warm as the left side (previously in the warm water) felt water cold.


Part A: Invertebrates

These sensory set ups in different pets or animals have taken a variety of shapes and sizes that have been modified to this environment best for them. These mainly have evolved from simple to more technical sensory organs that improve the ability of the animal in collecting information from the surroundings and responding in the simplest way possible to enhance its success.

The Cnidarian Hydra, has not at all hard sensory cells spread all around the body among the list of other epidermal cells, especially the mouth area and tentacles. It is of utmost importance for sensory set ups to be located all over the body due to the fact that the animal is radially symmetrical and can find stimuli from all path, including the recognition of predators. The free end of each sensory cell bears a flagellum, which is the sensory receptor for chemical substance and tactile stimuli. The other end branches into fine techniques, which synapse with nerve skin cells. On the surface of the dog is a changed cilia called a Cnidocil, that whenever simulated by any mechanised stimulation releases a nematocyst that is toxic to the predator. (Barnes & Cawlow, 2002)

These sense organs then lead into a diffuse nerve network, building two interconnected nerve nets. It really is very important for sensory set ups to be located all around the body due to the fact that the pet is radially symmetrical and can detect stimuli from all route, including the recognition of predators. (Hickman, Roberts, & Keen, 2009)

From the radially symmetrical Cnidarian you can move on to the bilaterally symmetrical Platyhelminthes that is represented here by the Planaria. Here the nervous system is organised into two longitudinal nerve chords that end in the anterior of the pet. This sorts an anterior mind and cephalisation is launched. (Hickman, Roberts, & Eager, 2009) The Planaria, unlike the Hydra are seen with an eye place and auricles. The auricles are lobe like and are located on the sides of the top. The auricles become a means of chemoreception while the eye spot acts as photoreceptor discovering light. Like the Hydra, it could also include a statocyst for equilibrium and rheoreceptors for sensing water currents. Cephalisation allowed the pet to develop a bilaterally symmetrical condition. The animal migrated onward and can find changes in the environment with the part of the body with the most sensory organs, its anterior region. (Leineschh, 2007)

The Pulmonate gastropod, owned by the course Gastropoda is seen to help expand develop its sensory in the anterior of the body. In the anterior of the body the animal is seen to have combined eyes that work as photoreceptors, even though they are not capable of forming a graphic. Also the labial and cephalic tentacles are mechanoreceptors, delicate to tactile stimuli, and are probably also chemoreceptive. (Hickman, Roberts, & Willing, 2009)

The basic body surface is also very sensitive to chemical substance and mechanical stimuli. The gastropod also offers a framework that operates as both a mechanical and chemoreceptor. This is seen to be the osphradium which is positioned in the inhalant respiratory drinking water current where it displays water on the way to the gill. One common composition with the previously studied animals is the statocyst which functions as a detector of gravity. (Hickman, Roberts, & Willing, 2009)

The next three types studied all participate in the phylum Arthropoda, but are found in various classes. The first to be examined was the Tarantula within the category Arachnida (order Aranea). This creature has locks like receptors called sensory setae that work as mechanoreceptors all around the body of the pet. Also, additionally they have small, extremely delicate tactile hairs called trichobothria that are sensitive to even airborne vibrations, including acoustics frequencies. Chemoreception is associated with fine hairs encircling the oral cavity, on the pedipalps. (Hickman, Roberts, & Willing, 2009)

The tarantula also has 8 simple sight that are made up of a lens, optical rods, and a retina. Even though most only can detect activity like the recently studied pets, some are able to form images. Because the spider is more accustomed to capturing victim within webs, perspective is relatively unimportant and so in most stay simple. (Underwood, 2009)

Another person in the phylum Arthropoda is the scorpion, classified in the class Scorpionida. Although they are equipped with venom for defence the scorpion continues to be seen to be the prey of several other pets or animals, thus they might need specialised sensory structures for recognition of risk. This animal is seen to possess a distinctive sensory composition know as a pectine. This can be used primarily in detecting vibrations which are used for capturing victim. (Gaoge & Smith, 2000)

This is seen to be the principal chemosensory organs of scorpions. The pectines are located in the ventral medial part of body and are seen to be combined appendages that brush the substrate as the scorpion walks. Comb-like organ includes a supportive spinal column and an array of teeth. Each tooth supports a huge selection of setaform sensilla called pegs. The neuronal cell layer within the teeth sometimes appears to be further split into inner and outer sub-larninae, comprised of chemosensory and mechanosensory neurons. (Melville, 2000)

Similar to the arachnids defined recently, the scorpion has sensory hairs called setae that function as tactile and chemosensory hairs. These sensory hairs are also on the pedipalps of the animal to sense air-borne vibrations. Also, thicker setae are found all around the body to find direct touch. As opposed to the spiders the scorpions own six pairs of eyes within their photoreceptor composition.

The previous arthropod group to be explained is the centipede, labeled in to the sub-phylum Myiapoda and order Centipedes. These pets or animals have emerged to own one couple of antennae rather than the most common two paid within other arthropods. The antennae are sensory appendages within the top of the pet that are sensitive to airborne chemicals and also possibly dampness. Similar to the planaria, Centipedes also bears a set of simple eyes made up of ocelli. (Barnes & Cawlow, 2002)

Part B: Sensory function in Mammals


Somatosensory system has a large number of receptrors which range in location and type. Receptors are situated in the superfial epidermis, dermal, epidermal and depper in dermis, and in subcutaneous structure. Meissner's corpusles are positioned in the dermal papillae, Merkel's receptors in the dermal papillae, and bare nerve endings. Subcuateous receptors, beneath both previously mentiones levels, have pacinian and Rufflin corpusles. Pacinian may be both cutaneous and subcutaneous. (Wang, 2007)

The Pacinian corpusles can be found in the skin, muscles, mesentery, tendons, and bones of mammals that are swiftly adapting. Each Pacinian corpuscle consists of a region of receptor membrane that is hypersensitive to mechanised stimuli that is certainly surrounded by concentric lamellae of connective muscle structures (Anonymous, 2007)

Pressure on the corpuscle transmits mechanically through the layers to the delicate membrane of the receptor neuron. The receptor membrane normally responds with a brief, transient depolarization at both onset and the offset of the deformation. The mechanised properties of the intact corpuscle, which preferentially move immediate changes in pressure, confer on the receptor neuron its normally phasic response. (Randall, Berggren, & France, 1997)

This behaviour points out why the feeling of the gold coin was lost after a couple of seconds. The added gold coin did not produce enough mechanised make to excite the Pacinian corpustle once again, thus it had not been felt. Enough time considered for the coin to avoid being felt assorted from individual to individual. This could be due to the several amount of tissue between the skin area and the nerve. The thicker the less the coin is experienced and the quicker is feeling is lost.

A mechanoreceptor's receptive field is the area within which a stimulus can excite the cell. If your skin is handled in two individual points within a single receptive field, the subject will be unable to feel both separate items. If both points touched course greater than a solo receptive field then both will be felt. How big is mechanoreceptors' receptive fields in a given area determines the degree to which precise stimuli can be resolved: small plus more densely clustered the receptive domains, the higher the resolution. Because of this, the density of the Merkel nerve endings and Meissner's corpuscles determine the awareness of the particular area. (Wang, 2007)

From the results obtained the fingertip sometimes appears to be the most hypersensitive and thus will have a higher density of Merkel nerve endings and Meissner's corpuscles. Alternatively the fore arm sometimes appears to be one of minimal sensitive and thus will have a little density of the nerves

Besides physical contact detected by mechanoreceptors, more complex accessory structures have the ability to transfer mechanical energy to the receptive membrane. These most intricate accessory structure associate with mechanoreceptive skin cells is the vertebrate midsection and inner ear canal.

Hair cells are located in every vertebrate pets or animals including humans, and are really sensitive mechanoreceptors. They may be responsible for transducing mechanical stimuli to electrical power signals.

They are found in a number of locations. For example, in vertebrate fish and amphibians, an exterior set of receptors are called the lateral brand system. This technique is based on series of hair cells that find motion in the encompassing water so when activated produces an action potential as with the mammalian ear canal. This lateral lines is, however, not present in mammals. (Hickman, Roberts, & Keen, 2009)

The ears of vertebrates perform two sensory functions. The organs of equilibrium perform like the statocysts in invertebrates that allow the animal to discover its position with respect to gravity. The organ of experiencing provides formation about vibrational stimuli in the surroundings, thus detecting audio. (Hickman, Roberts, & Eager, 2009)

Sound waves enter into the external ear of your vertebrate aided by the pinna and the tragus. The complete external structure has a function similar compared to that of any funnel, amplifying and then focusing acoustics waves. Vibrations from audio waves cause changes in air pressure, which travel from the exterior hearing, down the auditory canal, and then move the eardrum.

The ear converts energy of audio into nerve impulses. The vibration of the eardrum causes the liquid of the cochlea to go. The basilar membrane formulated with the floor of the cochlea, and the scala advertising, containing the organ of corti is where these vibrations undergo the alteration to neuronal impulses. The body organ of corti contains sensory hair skin cells, and the waves of substance in the cochlea press the mane cells against an overhanging tectorial membrane, and then yank them away. These locks cells are just across synapses from sensory neurons, which action provides a stimulus that starts sodium programs in the sensory cell membranes. This gives for an action potential in the environment of high potassium concentrations that the endolymph has. Auditory nerves situated in a spiral ganglion carry the action probable to the brain. (Randall, Berggren, & People from france, 1997)

Invertebrates, including the bugs have 'ears' situated on their thoracic lower limbs and are associated with respiratory passages, called the trachea. The ear tympanum has an analogous function to the tympanic membrane of the mammalian ear canal. Similar to a mammal, sound waves energize the membrane to vibrate, however in the insect, this directly activates nerve impulses. (Barnes & Cawlow, 2002)

Some insects likewise have a related tracheal system that directs information on air pressure changes, inside the insect, to the eardrum. When the right tympanum is stimulated, it will send the indication through the tracheae left tympanum. The wait in stimulus between your remaining and the right ear canal helps the insect locate the path from which the sound came up.

Weber's law expresses that the percentage of the difference threshold to the value of stimulus is constant. Regarding to this romance, doubling the worthiness of the stimulus will cause a doubling of the difference in the threshold. As observed in the results the just visible difference or power difference for the 50 g and 100 g was seen to be regular for all the subjects.


Vertebrates, including humans discover chemicals using standard receptors and two types of particular receptors, gustatory and olfactory. Many aquatic vertebrates have generalized chemical substance receptors spread over their body surface. Vertebrates usually complete chemoreception by moving chemically rich air or water into a canal or sac that contains the substance receptors. Mammals as well as other vertebrate have style receptor cells positioned in taste buds that are reinforced by basal skin cells.

Chemoreception is a lot different in invertebrates than in vertebrates. For instance, planarians find food by following chemical gradients in their surroundings. Their simple chemoreceptors are located in pits on their bodies, over which they move water with cilia. Insects have chemoreceptors in their body surface, mouthparts, antennae, forelegs, and, in some instances, the ovipositor. Moths, for example, smell with a large number of sensory hairs on their antennae. (Barnes & Cawlow, 2002)


In vertebrates such as humans, the top of eyeball comprises of the sclera, a white connective cells, and under that a thin pigmented part called the choroid. The sclera provides the cornea which is clear, which is where light initially enters the eye, and the choroid contains the iris which contracts and expands to regulate the amount of light coming into the hole in its centre, known as the pupil. The trunk inner surface of the attention is the retina, which contains the actual photoreception skin cells. Within the retina, there are two types of receptor skin cells, rods and cones. Rods and cones contain visual pigments consisting of light absorbing retinal substances. (Randall, Berggren, & People from france, 1997)

Compound sight of arthropods are image forming sight made up of many optic models called ommatidia. They are able to identify a very small fraction of the spectrum of light that the eye as a whole is subjected to; like the rods and cones of the vertebrate eyesight. In compound sight, the photoreception cells are called retinular cells, and they encircle a single eccentric cell. Because the receptive field of each device in a substance eyes is relatively large, chemical substance eyes have lower visible acuity than vertebrates. (Randall, Berggren, & French, 1997)


Temperature is an important environmental adjustable, and many organisms acquire sensory information about temperatures from the action of professional nerve endings known as thermoreceptors, in the skin. Both the exterior skin and higher surface of the tongue of mammals contain 'warmness' and 'chilly' receptors. the 'warmth' receptors discover a rise in temperatures in the environment by increasing the firing rate transient. On the contrary frigid receptors increase its firing rate transient whenever a cool environment is discovered. (Randall, Berggren, & People from france, 1997)

These receptors are quite delicate. Their firing rate is seen to improve the more the temperatures of the external environment varies from the inner body temperature around 37 OC. when the temps becomes sufficiently different the patter changes for both types of receptors and the regularity of the action probable is seen to drop. The response of the thermoreceptors consists of a big transient change in firing rate, followed by a longer-lasting, steady-state stage.

Other sensory buildings that are not within humans also can be found. For example, snakes have thermoreceptors that are able to detect emitted warmth energy. This is advantageous to allow them to detect warm-blooded victim. Also fish have the ability to use very low frequency electrical signs to communicate in murky drinking water, thus they are able to locate each other. (Hickman, Roberts, & Keen, 2009)


From this test it was concluded that different microorganisms have different sensory constructions adapted with their unique modes of life. One could also not that as family pets become more sophisticated, their sensory set ups are also seen to become more developed. This can be seen from the development of the easy eye location in planaria to the complex eye within humans. Not merely are humans seen to be able to detect movement but also coloring. However, you can also remember that humans do not always possess the most advanced sensory structures. This is seen in for example, the ability of reptile snakes to discover infrared radiation. This being absent in humans.

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