5 sense organs, classification and Functions
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| 5 sense organs, classification and Functions |
Table of contents
1.Introduction of sensory nerves.
2.CLASSIFICATION OF SENSATIONS
3.SENSE OF SMELL OR OLFACTION
4.THE SENSE OF TASTE
5.SENSE OF HEARING
6.WHICH IS THE LARGEST ORGAN OF THE BODY?
7.THE SENSE OF VISION (SIGHT)
8.Accessory Organs
9.What is Olfaction?
10.Which part of the human ear is responsible for maintaining body balance?
INTRODUCTION
The sensory nerves reaching the CNS have their beginnings in various peripheral structures such as:
1. Skin
2. Muscles
3. Joints
4. Special organs like eye and ear
Structures concerned in the production of sensations are:
1. An end organ or a sensory receptor
2. Afferent nerve fibre
3. Thalamus
4. Cerebral cortex.
CLASSIFICATION OF SENSATIONS
1. Special senses-sight, hearing, smell, taste and equilibrium
2. Somatic senses-pain, touch, pressure
, vibration.
SENSE OF SMELL OR OLFACTION
Mechanism
The mechanism of smell depends upon.
1. Olfactory receptor cells lying in the epithelial lining
of the olfactory mucosa of nasal cavities.
2. Olfactory nerves, olfactory bulb and olfactory tract which convey the impulses to brain.
3. The limbic lobe, situated in the medial surface of cerebral hemisphere.
The olfactory receptor cells are situated in the epithelium lining the olfactory mucosa. Each receptor cell consists of a cell body and 2 processes i.e. it is a bipolar cell). The dendrite reaches the surface of the olfactory epithelium and ends in a small , to which a number of cilia are attached. The central process or axon forms one fibre of the olfactory nerve. These fibres form 13 to 20 bundles forming olfactory nerves; they pass through the cribriform plate of ethmoid to reach the anterior cranial fossa and terminate in the olfactory bulb. The olfactory bulb has important neurons called mitral cells. The axons
of the mitral cells form the olfactory tract. These fibres pass to primary olfactory cortex. It has connections with the limbic system.
The stimulus for the sense of smell are usually minute particles which are soluble in the secretions of nasal mucous membrane.
The sense of smell is closely related to the sense of taste. So, in common cold, there will be loss of sense of smell and altered taste. Loss of sense of smell is called anosmia.
THE SENSE OF TASTE
The true sense of taste is localised in the tongue. There are 4 basic tastes-bitter, sweet, sour and salt (all other flavours are appreciated by the sense of smell).
The tongue is covered by a mucous membrane. There are numerous elevations called papillae, on the tongue (see, Digestive system-Tongue). The end organs for the sense of taste are called taste buds. They are situated most densely at the tip, sides and base of the tongue. Taste buds are also present in the walls of the circumvallate papillae, on the palate, epiglottis and oropharynx.
The taste buds consist of collections of receptor cells and supporting cells, together with the sensory nerve endings. The taste bud has a pore which opens on the epithelial surface of the tongue. A number of hairs project from the receptor cells into the pore.
SENSE OF HEARING
The hearing or auditory apparatus consists of:
1. The external ear
2. The middle ear
3. Cochlea of the internal ear
4. The cochlear nerve
5. Auditory area of temporal lobe.
Functions
The ear has two functions-balance and hearing. The external and middle ears are mainly concerned with conduction of sound to the internal ear; the inner (internal) ear contains the vestibulocochlear organ that is essential for equilibrium and hearing.
External Auditory Meatus
The external auditory meatus is 2.5 cm long. Its outer 1/3 is cartilaginous and inner 2/3 is bony. Lateral third is lined with skin; contains hair follicles and ceruminous glands (modified sweat glands). The ceruminous glands produce a waxy exudate called cerumen (wax). The medial 2/3 is lined with very thin skin, which is continuous with the external layer of tympanic membrane.
The external auditory meatus is not a straight passage. It shows an S-shaped bend. In order to make it straight (while examining the tympanic membrane), the pinna should be pulled upwards and backwards in adults (in children, pinna should be pulled downwards and backwards).
THE SENSE OF VISION (SIGHT)
The eye or the organ of sight is situated in the orbital cavity of the skull and it is well protected by its bony walls. The orbit also contains the muscles of the eyeball, their nerves, vessels, the lacrimal gland and fat.
The Living Eye
When examined from the anterior aspect, most of the eyeball appears to be in the orbit, but from the side, it is seen to be protruding between the eyelids (palpebral fissure). The "white of the eye" is the anterior aspect of the sclera. The anterior, transparent part of the eye is the cornea. At the margins, the cornea is continuous with the sclera. The dark, circular aperture that is seen through the cornea is the pupil. This opening is surrounded by a circular, pigmented diaphragm, the iris. The sclera is covered by a thin, moist, transparent mucous membrane, the bulbar conjunctiva. It does not cover the cornea. From the sclera, the bulbar conjunctiva is reflected
onto the deep surface of the eyelids or palpebrae, lining them, up to their margins. This is the palpebral conjunctiva. When the eyelids are closed, the bulbar and palpebral conjunctivae form a closed sac.
Essential Organs
Essential organs of visual apparatus are;
1. The eyeballs
2. The optic nerves
3. The visual centres in the brain (occipital lobe).
Accessory Organs
Accessory organs for the protection and smooth functioning of the eyes are;
1. The eyebrows
2. The eyelids or palpebrae
3. The conjunctiva
4. The lacrimal apparatus
5. Muscles of the eye.
FAQS
Q1.What is Olfaction?
Ans.Olfaction is the term mainly referred to as the sense of smell.
Q2.Which part of the human ear is responsible for maintaining body balance?
Ans.The inner part of the human ear called semicircular canals is responsible for maintaining body balance.
Q3. WHICH IS THE LARGEST ORGAN OF THE BODY?
Ans. Skin
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