The Sensory System 9 Chapter Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Introduction A stimulated sensory receptor sends a signal to the brain Signals are interpreted in the brain

Introduction Five types of sensory receptors Mechanoreceptors – stimulated by changes in pressure or body movement Thermoreceptors – stimulated by changes in the external or internal temperature Pain receptors – stimulated by damage or oxygen deprivation to the tissues Chemoreceptors – stimulated by changes in the chemical concentrations of substances Photoreceptors – stimulated by light energy

General Senses Proprioceptors Mechanoreceptors involved in reflex actions Maintain equilibrium and posture

Fig 9.1

General Senses Cutaneous Receptors Located in the deepest layer of the epidermis and the entire dermis Make skin sensitive to touch, pressure, pain, and temperature

General Senses Pain Receptors (nociceptors) Somatic nociceptors Skin and skeletal muscle Respond to mechanical, thermal, electrical or chemical damage

Senses of Taste and Smell Chemical senses Sensitive to molecules in food and in the air Other chemoreceptors in the body Govern respiratory rate Sensitive to the hydrogen ion concentration of the blood

Senses of Taste and Smell Sense of Taste Sensory receptors located in the taste buds Primarily on the tongue Also present on the hard palate, the pharynx, and the epiglottis Types of taste sensations Sweet Sour Salty Bitter Umami – meat

Senses of Taste and Smell How the brain receives taste information Molecules in food bind with receptor proteins on microvilli on taste cells Nerve impulses are generated and go to the brain Sensory receiving and memory areas for taste are located in the insula

Senses of Taste and Smell Sense of Smell Dependent on olfactory cells Located in olfactory epithelium in the roof of the nasal cavity Modified neurons Olfactory cilia have receptor proteins for odor molecules How the brain receives odor information

Senses of Taste and Smell How the brain receives odor information Nerve fibers lead to the olfactory bulb Combinations of activated receptor proteins account for different odors An odor’s signature is determined by which neurons are stimulated in the olfactory bulb Neurons send signals through the olfactory tract to the olfactory areas of the cerebral cortex in the temporal lobe

Senses of Taste and Smell Sense of taste and sense of smell Both work together Smell can enhance taste Part of what is referred to as smell may actually be taste

Sense of Vision Accessory Organs of the Eye Eyebrows, eyelids, and eyelashes Eyebrows shade the eyes from the sun and protect eyes from perspiration or debris Eyelids are continuations of the skin Eyelashes can block debris from entering the eye Secretions from sebaceous glands associated with eyelashes lubricate the eye Eyelids help keep the eye lubricated

Fig 9.5a

Sense of Vision Lacrimal apparatus Lacrimal gland produces tears Tears collect in lacrimal sac Tears drain into the nose by the nasolacrimal duct

Sense of Vision Extrinsic muscles Contractions move the eyes Superior rectus rolls eye upward Inferior rectus rolls eye downward Lateral rectus turns eye outward Medial rectus turns eye inward Superior oblique rotates eye counterclockwise Inferior oblique rotates eye clockwise Three cranial nerves control these muscles

Fig 9.6

Sense of Vision Anatomy and Physiology of the Eye Three layers Sclera White and fibrous Cornea is transparent Choroid Middle, vascularized layer Becomes the iris towards the front Regulates the size of the pupil Colored portion of eye The ciliary body is behind the iris Contains the ciliary muscle Controls the shape of the lens

Sense of Vision Lens – divides the eye into two compartments Retina Anterior compartment contains aqueous humor Posterior compartment contains the retina and the vitreous humor Retina Contains photoreceptors Rod cells – night vision and peripheral vision Cone cells – distinguish colors Fovea centralis – area of retina where cone cells are densely packed Optic nerve – formed from sensory fibers from the retina

Sense of Vision Function of the lens Focuses images on the retina Image produced is smaller than the object Image on retina is inverted and reversed Accommodation Maintaining focus on a distant and then near object Lens must change shape Controlled by the ciliary muscle Ciliary muscle is relaxed for a distant object Ciliary muscle contracts to view a near object

Sense of Vision Vision pathway Color vision Light is refracted by cornea, aqueous humor, lens, vitreous humor Image is formed on the retina Nerve impulses travel to the visual area of the cerebral cortex Color vision Depends on three kinds of cones Color blindness is caused by the inherited absence of the color pigments in the cones

Sense of Vision Function of the retina Blind spot Rod cells and cone cells are located in the deepest layer Light must penetrate to the back of the retina Blind spot No rods and cones where the optic nerve leaves the retina No vision is possible in this area

Sense of Vision From the retina to the visual cortex The right and left visual cortex rebuilds and rights image

Sense of Hearing Two sensory functions of the ear Sensory receptors located in the inner ear Consists of hair cells Sensitive to mechanical stimulation (mechanoreceptors) Anatomy of the Ear Sound Pathway

Sense of Hearing Anatomy of the Ear Outer ear Middle ear Inner ear Pinna Auditory canal Lined with hair Modified sweat glands secret cerumen Middle ear Begins at the tympanic membrane Ends at bony wall with two small openings Oval window Round window Three small bones (ossicles) Malleus Incus Stapes Auditory tube (eustachian tube) extends from the middle ear to the nasopharynx Inner ear Filled with fluid Three areas Semicircular canals Vestibule Cochlea

Sense of Hearing Sound pathway Through the auditory canal and middle ear Sound travels by the vibrations of air molecules Sound waves strike the tympanic membrane causing it to vibrate Pressure from the tympanic membrane causes the malleus, the incus, and then the stapes, to vibrate The stapes strikes the oval window Vibrations from the oval window are passed to the fluid within the cochlea of the inner ear

Sense of Hearing Impulses travel From the cochlea to the auditory cortex The spiral organ (organ of Corti) is the sense organ for hearing Located in cochlear canal Pressure waves cause the hair cells to bend Nerve impulses begin in the cochlear nerve and travel to the brain stem and then the auditory cortex

Sense of Equilibrium Mechanoreceptors in the semicircular canals are responsible for rotational equilibrium Mechanoreceptors in the vestibule are responsible for gravitational equilibrium

Sense of Equilibrium Rotational Equilibrium Pathway Involves the three semicircular canals Motion sickness Continuous movement of fluid within the semicircular canals Sensory input from the inner ear that is different from visual sensations Vertigo is dizziness and a sensation of rotation

Effects of Aging The lens of the eye does not accommodate as well Three visual disorders seen frequently: Cataracts Age-related macular degeneration Glaucoma The need for a hearing aid increases with age Presbycusis (age-related hearing decline) Otosclerosis is the most frequent cause of conduction deafness in adults Dizziness and the inability to maintain balance