Music is a medium of entertainment which can also make many types of emotions in our brain. Some music will give us happiness, but some give us sadness. Sometimes we listen to our favourite genre of music to make ourselves relaxed. Now think about your favourite music and observe what kind of emotion is perceived by your brain!!
Fig: Brain GIF: Man listening to music
Not only music, whatever we listen to is actually going to our brain as different signals and it gets processed over there. So how is this happening? This happens with the help of receptors present inside our ears. Hearing is one of the five senses present in our body. What about the other senses? All the other senses like vision, touch, smell and taste are processed finally by the brain. Do all these senses work with a similar principle? How do the external stimuli reach internally? To answer all these questions we have to know more about the sensory perceptions which give us the stimulus for every sense. So we are going to discuss more about sensory perception in this article.
Table of contents
Sensory perception is the capacity of an individual to detect, experience or sense the stimuli in their environment. Different sense organs in the human body such as eyes, ears, nose, tongue and skin helps in this process through vision, hearing, smell, taste and touch respectively. So this process involves the detection of stimuli, characterising and recognising it.
Fig: Sense organs
The major five stimulus involved in the sensory perception are as follows:
The coordination of sense organs and the brain brings sensory perception. Anything which affects their coordination will result in the loss of sensory perception.
Fig: Stimulus transmitting to brain through neurons
When there is a change in the stimuli in your surroundings, then sensory perception happens. There are three major steps for the process of sensory perception and they are as follows:
Sensory receptors are a group of cells present in various sense organs of the human body which can detect the stimulus. They help in sensory perception.
The various types of sensory receptors present are classified into five on the basis of the stimuli to which they respond. The location and functions of each sensory receptors varies accordingly. The major sensory receptors are as follows:
Chemoreceptors are those which detect and respond to any chemical stimulus. On the basis of the location, there are two classes of chemoreceptors and they are as follows:
These are present in the medulla oblongata and detect the changes in the pH.
Fig: Medulla oblongata of human brain
These are present in the carotid and aortic bodies and detect the changes in the oxygen levels in the blood.
Photoreceptors are those which detect and respond to changes in the light. They are present in the retina of the eye. A pigment called rhodopsin is responsible for detecting the changes in the light.
Fig: Retina of human eye
Thermoreceptors are those which detect and respond to changes in temperature in the environment. Thermosensors are the thermoreceptors present in the skin. The organism can allow their body to adjust according to the external temperature with the help of thermosensors.
Baroreceptors are those which detect and respond to the changes in the pressure. They regulate the systemic blood pressure levels. The baroreceptors are located on the following areas:
Mechanoreceptors are those which detect and respond to changes in mechanical stimulus. The locations of these receptors are as follows:
Some properties are common in all types of sensory receptors and they are as follows:
The area of a body where a stimulus affects the sensory receptors is called the receptive field. This property is important to encode the accurate location of a stimulus. Examples of receptive field are as follows:
Both these areas have a higher density of tiny receptor fields which can achieve spatial resolution.
The labelled line principle reserves the specificity of a receptor class in encoding a sensory message. This message will be specific to the designated brain area. The somatosensory systems as well as more specialised systems like the auditory and visual are all impacted by this principle.
If stimulus repeatedly excites the receptor there will be a decline in the rate of action potentials. This change in the stimulus or its intensity can be easily adapted by the receptors. This property is common in most of the sense receptors.
The starting point of all sensory impulses are receptor potentials. The action potential of the receptor cell membrane must rise above a threshold level in order to generate a receptor potential. This is triggered by the stimuli which are received. The neurotransmitter is released as a result of the receptor potential and it stimulates the neurons which are specific.
These receptors transfer the information to the brain via sensory neurons. The two centres for processing the sensory impulse in the brain are hypothalamus (main centre) and cerebral cortex (second centre).
Fig: Hypothalamus and cerebral cortex
The five sense organs present in the human body are capable of detecting all the changes happening in the surroundings. Each sense organ responds in different ways. Let’s discuss the mechanism of sensory perception in each sense organ.
The visual sense organ our body uses for vision or ophthalmoception is called eyes. They are located inside a bony socket in the skull called ‘orbit’. They are sensitive to light images.
The three layers of the wall of the eyeball are:
Sensory receptors are present in the retina and it has two parts as follows:
The inner nervous part is sensitive and it is made up of three layers as follows:
Fig: The layers of retina
The ability of the eyes and brain to detect the electromagnetic radiation in certain wavelengths (visible region) is called sight or vision. Different photoreceptors are present in the retina for the perception of colour and perception of brightness. Retina is light sensitive.
1. Light passes through the layers of eyes in the order - Cornea (clear protective layer) → Pupil (Opening of iris) → Biconvex lens (Transparent).
2. Muscles attached to the biconvex lens changes shape of the lens and along with the cornea it helps the light to focus on the retina by bending the light rays.
3. Chemical changes occur on the photosensitive (Rods and cones) cells of the retina when light hits it.
4. The pigment that absorbs the energy from different wavelengths of light is present in the cone cells and it initiates the nerve impulses.
5. The brain combines the nerve impulses from the cone cells and perceives the world in all the colours of the visual spectrum.
Fig: Path of light sensation
The sense organ used for hearing or audioception is called the ears. They help to perceive sound by sensing the vibrations in the air. These vibrations are turned into sounds. This is known as hearing or audio captioning.
The major three parts of the ear are as follows:
It consists of pinna (visible folds of cartilage), a short external auditory canal and a tympanic membrane or ear drum.
Fig: External ear
It holds three tiny bones named malleus (hammer shaped), incus (anvil shaped), and stapes (stirrup shaped). They are collectively called ear ossicles.
Fig: Middle Ear
It is composed of a membranous labyrinth present inside the bony labyrinth. It has two functional units and they are the vestibular apparatus and cochlea. The cochlea has auditory receptors that help in hearing.
Fig: Inner ear
The sense of sound perception due to the movement of tiny hair fibres inside the inner ears is called hearing.
1. Sound waves are gathered by the pinna and channelled down to the auditory canal.
Fig: Sound waves collected by pinna
2. Sound waves end at the eardrum or tympanum and hit on it. This will cause the vibration of the eardrum.
3. The vibrations from eardrum travel across the ear ossicles and they will amplify the sound and transfer the vibration to a membrane called an oval window which separates the inner ear from the middle ear.
4. Now the vibrations pass from the oval window to the perilymph of the internal ear.
Fig: Sound waves passes from auditory canal to cochlea
5. From the perilymph the vibrations are transferred to the scala media through Reissner’s membrane, where they generate waves in the endolymph.
6. The vibration of endolymph induces a ripple in the basilar membrane.
7. These movements in the basilar membrane bend the hair cells, pressing them against the tectorial membrane.
8. This stimulates thousands of auditory receptors that are mechanoreceptors and they release neurotransmitters.
6. This impulse is carried to the auditory cortex of the brain through the cochlear branch of the auditory nerve.
Fig: Impulse transmitting from auditory nerve to brain
The sense organ which is used for smell or olfalcoception is called nose. It helps to detect different odours.
Bones and cartilages give proper shape to the nose. Nose has two nasal cavities separated by the nasal septum. The nose is lined by mucous membrane. The curved bony plates on each side of the nose are called turbinates. The hollow and air filled chambers of the bone around the nose are called sinuses.
Fig: Structure of nose
The term used for the sense of smell is olfaction. It is a chemical sense and the receptors are called olfactory receptors and they are specific. There are about 40 million olfactory receptor neurons present in the nasal passage. Smell is an interactive sense too. Olfactory receptor neurons die and regenerate on the regular basis. Olfactory epithelium is the area where all the olfactory receptors are present.
Fig: Olfactory region of nose
1. Air enters the nasal cavity through breathing.
2. Olfactory cells on the roof of the nasal cavity have protein receptors called chemoreceptors which can detect minute changes in chemicals.
3. Olfactory cells have nerve fibres and cilia where chemicals bind.
4. The sensory information from the cilia is transmitted to the brain.
5. The brain then converts these impulses into an interpretable fragrance.
Fig: Impulses transmitting from nose to brain
The sense organ which helps in the perception of different tastes and flavours and used for gustaoception is called tongue. Taste buds present in the tongue helps in the perception of taste.
Different taste buds are working for the perception of different tastes located at particular places in the tongue. The different types of tastes are as follows:
Fig: Locations of tastes
Tongue is located in the oral cavity. Embryologically the tongue can be divided into anterior (oral or presulcal part) and posterior part (pharyngeal or post sulcal part). It can be divided into three parts as follows:
The three components that form a tongue are as follows:
Taste buds are located between the papillae of the tongue. Papillae are also called bumps.
Fig: Structure of tongue
The term used for taste is gustation. The sensations of taste and smell frequently work together. Chemoreceptors on the tongue perform the same function as those in the nasal cavity. 100 to 150 types of receptors are present in the human tongue. Taste buds (bundle of taste cells) are the chemoreceptors of the mouth.
1. While eating food, the chemoreceptors in the taste cells detect minute change in chemicals.
2. This will stimulate the neurons in the taste cells.
3. The nerves responsible for the taste sensation are the glossopharyngeal nerve and the chorda tympanic branch of the facial nerve.
4. The sensory information from the glossopharyngeal nerve begins an action potential that alerts the brain.
5. The brain then converts these impulses into specific taste.
The other sensations like temperature, spiciness, hotness, fattiness, and coolness that are not included in the taste can be felt by the tongue. Both the olfactory receptors and taste receptors contribute to the flavour of any food.
The biggest organ in the human body is the skin. It is used for touch or tactioception. It helps to perceive the sensation of touch. The sensations detected by the skin are as follows:
The three layers present in the skin are as follows:
Fig: Layers of skin
The sensation of touch is called somatosensation. The sense of pressure that is felt in skin is the touch. Different pressure receptors respond to various tension and pressure. Mechanical, chemical and thermal receptors are present in the skin.
1. The touch, pressure or temperature on the skin is perceived through skin receptors.
2. The impulse generated at sensory nerves in the skin are transmitted to the neurons of the spinal cord.
3. The signals from the spinal cord are then transmitted to the thalamus which passes the information to the rest of the brain.
Q1. Which is the sensory receptor which detects and responds to changes in temperature?
Solution: Sensory receptors are a group of cells present in various sense organs of the human body which can detect the stimulus. Thermoreceptors are those which detect and respond to changes in temperature in their environment. Thermosensors are the thermoreceptors present in the skin. The organism can allow their body to adjust according to the external temperature with the help of thermosensors. Hence the correct option is c.
Q2. Which is the correct order of stimulus passing through the eye?
A. Cornea → pupil → biconvex lens → retina → cone cells → brain
B. Cornea → pupil → biconvex lens → retina → rod cells → brain
C. Cornea → biconvex lens → pupil → retina → cone cells → brain
D. Cornea → retina→ biconvex lens → pupil → rod cells → brain
Solution: Light passes through the layers of eyes in the order - Cornea (clear protective layer) → Pupil (opening of iris) → Biconvex lens (transparent). Muscles attached to the biconvex lens change shape of the lens and along with the cornea. This helps the light to focus on the retina by bending the light rays. Chemical changes occur on the photosensitive (rods and cones) cells of the retina when light hits it. The pigment that absorbs the energy from different wavelengths of light is present in the cone cells and it initiates the nerve impulses. The brain combines the nerve impulses from the cone cells and perceives the world in all the colours of the visual spectrum. Hence the correct option is a.
Q3. Which of the following is wrong about the sensory perception in the ear?
A. Sound waves are gathered by the pinna and channelled down to the auditory canal
B. Sound waves end at the eardrum or tympanum and hit on it.
C. Oval window release neurotransmitters
D. Impulse from the ear is carried to the brain through the cochlear branch of the auditory nerve
Solution: Sound waves are gathered by the pinna and channelled down to the auditory canal. Sound waves end at the eardrum or tympanum and hit on it. This will cause a vibration. The vibrations from the eardrum travel across the ear ossicles and they will amplify the sound and transfer the vibration to a membrane called an oval window which splits inner ear from middle ear. Now the vibrations pass from the oval window to the perilymph of the internal ear. From the perilymph the vibrations are transferred to the scala media through Reissner’s membrane, where they generate waves in the endolymph. The vibration of endolymph induces a ripple in the basilar membrane. These movements in the basilar membrane bend the hair cells, pressing them against the tectorial membrane. This stimulates thousands of auditory receptors that are mechanoreceptors and they release neurotransmitters. This impulse is carried to the auditory cortex of the brain through the cochlear branch of the auditory nerve. Hence the correct option is c.
Fig: Sound waves passes from auditory canal to cochlea
Q4. Which of the following sense organs transmit the impulses mainly to the spinal cord and then to the brain?
Solution: The touch, pressure or temperature on the skin is perceived through skin receptors. The impulse generated at sensory nerves in the skin are transmitted to the neurons of the spinal cord. The signals from the spinal cord are then transmitted to the thalamus which passes the information to the rest of the brain. Except skin, all the sense organs are directly connected to the brain. Hence the correct option is a.
Q1. Why can dogs smell more than humans?
Answer: The number of scent receptors are more in dogs than humans. More than 100 million sensory receptor sites are present in the nasal cavity of a dog. The area of the canine brain which can analyse odours is about 40 times larger than in humans.
Q2. What is umami?
Answer: Umami is the fifth receptor for taste sensation. The major component of umami is tomato. The receptors for umami detect the amino acid glutamate that can cause savoury flavour in foods.
Q3. What are nociceptors?
Answer: The unspecialised nerve cell endings which can initiate sensation of pain are called nociceptors. So they are pain receptors. They can be found in the skin, cornea, muscles, mucous membranes, joints and some internal organs.
Q4. Which are the nerves that transmits the signals from sense organs to the brain or spinal cord?
Answer: Cranial nerves and spinal nerves help in the transmission of signals from the sense organs. Sensory information like vision, taste, hearing and smell are carried by cranial nerves. Most of the other body parts (including skin) and brain communicate through spinal nerves.
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