COORDINATION SYSTEM

THE SENSES

Ch.9/XI bil

Sensory system

• Sense organs or receptors are receptors, it functions to receive information

• These organs are designed to receive stimuli which make us aware of changes taking place in our environment

• Receptor is an external stimulus receiver• Senses, which have special receptor cells to identify

changes in the external environment, have function to provide information ( heat, cold,pressure, touch etc)

• Stimulus from external environment is carried by the somatic nerve.

Sensory system

• All the senses have highly specialized receptors enabling them to respond to stimuli– Chemoreceptors : chemical– Photoreceptors : light– Phonoreceptors : sound– Tangoreceptors : touch/pressure

• Exteroreceptors = detects stimuli originating outside the body• Interoreceptors = detects stimuli originating inside the body• Proprioreceptors = located within the body muscles, joints

and bones (kinestetic)

Sense of touch

• The sense organ for touching and pressure is skin.

• The skin is richly supplied with nerve endings and these enable it to act as a sense organ

• Stimulation of nerve endings in the skin produces sensations related to temperature, pain and touch which are important for survival

Skin

• Type of receptors in skin Merkel : touch corpusclePaccini : pressure

corpuscleRuffini : heat

(thermoreceptor)Meissner : cold

corpuscleFree nerve endings :

pain

Sense of taste

• The tongue is covered by projections called papillae on the surface.

• The papillae contain taste receptors – taste buds

• The taste receptor is a chemoreceptor because it can be stimulated by various chemical substances

• Sense of taste depends to the sense of smell

Tongue• There are 4 main kinds of

tastes :Bitter : on the backSweet : on the tipSour : on the side to tipSalty : on the sides

Sense of hearing

• The sense of hearing is concerned with the perception of sound

• The ear is the only organ of hearing and it is also concerned with balance

• There is a close relationship between the sense of hearing and speech

Ear structure• Three parts of ear :

Outer ear (external)oAuricle/Pinna/flap : receive and collect the soundsoAuditory canal : is a canal, covered by hair, sebaceous

and ceruminous glands – secretes cerumen (ear wax) Middle ear

o Tympanic membraneo Ear bones (ossicles): responsible for the transmission

Malleus (hammer) Incus ( anvil) Stapes (stirrup)

o Eustachian tube : connect middle ear and pharynx

Ear structure

Inner ear (internal)oOval windowo Semicircular canal : balance organ

• Sacculus• Utriculus• Ampula

oCochlea : Sound receptor

Ear

• Middle ear

The inner ear

• Semicircular canal • Cochlea

Anatomy of inner ear

• Within the cochlea, there is a fluid called perilymph and endolymph– Scala vestibuli– Scala media– Scala tymphani

Sound transmission

Sense of smell

• Smelling rods (olfactory rods) – bipolar cells – are located on the surface of the nasal cavity (upper part)

• The nose is both an organ of the respiratory system and sensory system

• The odor dissolves in the layer of moist mucous membrane covering the receptors in the upper nasal cavity. The impulses are transmitted to the brain for interpretation

The nose

Sense of sight

• This sense organs responsible for vision.• Eye is the vision organ that composed of photoreceptor

cells that receive light (intensity and colour) – visual receptors in the retina are highly sensitive to light

• Two different receptors– Cone cells : for vision in bright day and colours– Rod cells : for vision in low light /night

• Accomodation power = ability to change lens shape and focal length that enables the eye to receive clear images of objects

Eye structure

The eye

• External structure

The eye

• Internal structure

Photoreceptors

Physiology of vision

Light transmission

The senses(summary)

Sense organ receptors Type of receptors

Type of stimulus

location

Sense of touch Nerve endings exteroreceptor touch skin

Sense of taste Taste buds exteroreceptor chemical tongue

Sense of smell Olfactory cell exteroreceptor chemical nose

Sense of hearing

Organ of corti exteroreceptor sound ear

Sense of sight Rod and Cones exteroreceptor light eye

Disorders and disturbances