1. The Sensory System 9 Chapter
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2. Introduction A stimulated sensory receptor sends a signal to the brain
Signals are interpreted in the brain

3. 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

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

5. Fig 9.1

6. 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

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

9. 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

10. 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

11. 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

13. 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

14. 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

16. 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

17. 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

18. Fig 9.5a

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

20. 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

21. Fig 9.6

22. 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

23. 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

25. 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

27. 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

29. 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

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

33. 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

34. 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

36. 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

37. 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

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

41. 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

42. 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