sensory system

sensory transduction

physical and chemical stimuli converted into neuronal signals which can be transmitted to the CNS for processing and interpretation

sensory transduction: steps

• receptor protein opens/closes ion channels in response to a specific stimulus

• there is a change in membrane permeability to ions that alters the receptor cell’s membrane potential (receptor potential)

• this triggers an action potential in the receptor cell or stimulates it to release neurotransmitter so signals can travel longer distances

receptor potential

graded membrane potentials spread over only short distances

special sense organs

• stimuli exist in different energy forms

• afferent neurons have sensory receptors at their peripheral end which respond to stimuli

• receptors convert these energy forms into electrical signals (signal transduction)

classification of sensory receptors

• classified depending on what they respond to

• messages from different kinds of sensory cells arrive at different places in the CNS so that different responses are stimulated

• sensory adaptation - some sensory receptors give gradually diminishing responses to maintained or repeated stimulation

the ear

• 3 parts: external, middle, inner

ear: external

• consists of pinnae and auditory canal

• pinnae direct sound waves into auditory canals

• ear drum covers auditory canal and vibrates in response to pressure waves

• pressure waves converted into physical forces in middle ear

• ear wax lubricates skin to prevent entry of foreign substances

ear: eustachian tube

• connects middle ear to nasopharynx

• filled with air so equalizes air pressure between the middle ear and outside

• pseudostratified respiratory epithelium

• numerous goblet cells

• dilates during swallowing and yawning

ear: tympanum membrane (ear drum)

• attached to ossicles

• external cuticular layer - thin, hairless epidermis and dermis

• middle fibrous layer - mixture of type II and III collagen fibrils with small amount of type I

• inner mucous layer - single layer of cuboidal cells, cilia and goblet cells, continuation of respiratory epithelium of eustachian tube

• allows conduction of sound

middle ear