1. Anatomy and Physiology Mission Hills High School
The Sensory System
Anatomy and Physiology
Mission Hills High School

2. SENSORY FUNCTIONS
A sensation is a state of awareness of a particular stimulus
Vital for survival
Provide brain information necessary to maintain homeostatic balance

3. Sensory Pathways
Ouch!
All sensory pathways begin with a receptor and travel toward the central nervous system.
The receptor receives a stimulus from the environment (internal or external)
The stimulus is converted by the receptor to a nerve impulse
The nerve impulse is conducted along a sensory neuron to the CNS

4. General senses
Touch and Pressure: cutaneous sensations. They are detected by mechanoreceptors which located in the skin. They.include
Meissner's corpuscles, sensitive to fine touch; abudndant in the fingers, palms, soles, lips and external genitilia
Merkel’s disc, less common, it’s dendrites end in the skin’s epidermis
Pacinian corpuscles, sensitive to deep pressure.

5. General senses
Temperature (thermoreceptors) Changes in temperature are detected by receptors probably located in the skin.
Pain (nociceptors): is detected by receptors that are free nerve endings. Pain receptors make us aware of danger to the body.
Free nerve endings (mechanoreceptors) for both temperature and pain are located in the skin, muscle and most visceral organs

6. General senses
Body Position: detected by receptors called proprioreceptors
Proprioreceptors provide awareness on the degree of muscle contraction, the tension in tendons, and head position relative to the ground.
Primary receptors of body positions are
muscle spindles in skeletal muscles
Gogi tendon organs between tendon and muscle.

7. Special senses
Smell, taste, sight, and hearing are each detected by complex organs.
These sense organs are properly called the sensory organs
Each organ has special sensory receptors

8. smell sense of smell is also known as olfaction,
functions by means of sensory receptors within olfactory organs located in the upper wall of the nasal cavity.
The olfactory organs contain olfactory hairs, which respond to dissolved chemicals.
Olfactory Pathway Olfactory hairs generate the action potential
Action potential passes to the olfactory bulbs and on to the frontal lobes of the cerebral cortex.

9. Smell
The olfactory pathway is closely linked to the limbic system of the brain.
Olfactory sensations are long-lasting
Form part of our memories and emotions
A particular smell sensation sometimes has enough impact to sweep us back to a memory of an experience thought to be long-forgotten!

10. Taste sense of taste is also known as gustation
Its location depends on receptors in organs known as taste buds within papillae on the tongue and in other areas of the mouth.
The receptors are called gustatory cells, and they respond to dissolved chemicals.
Gustatory Pathway Gustatory cells stimulate an action potential in sensory neurons at their bases.

11. taste
There are four primary taste sensations. Each is associated with a particular type of taste bud
Sweet
Sour
Bitter
Salty

12. Sight
The sense of sight, or vision, depends on photoreceptors in the eye or eyeball

13. Accessory structures Structures associated with the eye include
eyelids
lacrimal apparatus
extrinsic muscles of the eyeball.

14. Eyelids Protect the anterior surface of the eyes
Margins of the eyelids contain eyelashes
Eyelids consist of four layers of tissues
Outer skin layer
Inner skeletal muscle (orbicularis oculi)
Connective tissue layer
Inner mucous membrane called the conjunctiva
Conjunctiva folds back to cover much of the anterior surface of the eye as well. It also secretes mucus to help moisten and lubricate the eyeball

15. Conjunctivitis
What is Conjunctivitis? (Pink Eye)

16. The lacrimal apparatus
Consists of
Lacrimal gland (A)
Lacrimal canals (B)
Lacrimal sac (C)
Nasolacrimal duct (D)

17. In Your Notes: What is the purpose of tears?
Where are tears made and where do they flow?

18. Structure of the Eye
The walls of the eye consist of three layers, or tunics:
Fibrous Tunic (C)
Vascular Tunic (B)
Nervous Tunic (A)

19. Fibrous tunica The thick outermost layer of the eyeball. It contains…
WHITE SCLERA: Composed of white fibrous connective tissue. It provides protection and shape of the eyeball
TRANSPARENT CORNEA: Window of the eye. Its transparency is due to its lack of blood vessels and its regular arrangement of protein fibers. Light is first refracted (bent) here to direct it to the iris.

20. Vascular tunica
Middle vascular layer (rich supply of blood vessels) which has three parts…
Choroid (B) Dark brown membrane, lines most of the sclera. The brown pigments minimize reflection of light in the eye (reflection distorts images)
Ciliary body (H): Anterior to the choroid, becomes thickest part and modified to become smooth muscle which connects to the lens by way of suspensory ligament (M).
Iris (L). The beautifully colored part of the eye the can be seen from the exterior. It is suspended between the cornea and the lens. Contraction of the eye is due to a reflex from intensity of the light (Cranial nerve III) and visual focus (accommodation). The higher the intensity of light, the stronger the contraction; the close-up of an object will cause contraction.
Pupil (J): The opening in the center of the iris. Contraction of the doughnut shaped muscles of the iris causes constriction (closing) and relaxation causes dilation (opening) of the pupil

21. Vascular tunica
Lens: Located behind the pupil and iris is held in position behind the suspensory ligament. It is transparent, made of cytoplasm extensions from epithelial cells. Its transparency is lost with advancing age (cataract)
suspensory ligaments (M) attached to the ciliary body. Tension on the lens can be varied by ciliary muscles, stretching or relaxing the lens to accommodate for near and far vision.
Chambers: Between the cornea and the lens is a cavity divided in half by the iris: between the cornea and iris it is called the anterior chamber (I);
between the iris and lens it is the posterior chamber.
The space behind the lens is the posterior cavity (G).
Humor:
The anterior and posterior chambers contain aqueous humor which is a clear watery fluid secreted by the ciliary body is continuously recycled with blood plasma through canal of Schlemm near the cornea at the sclera,
posterior cavity contains vitreous humor. It is a gel-like fluid that helps support the eye structure.

22. Nervous tunic
The inner layer of the eyeball, consisting of the retina.
Retina: lines the posterior cavity and contains the photoreceptor cells (rods and cones) and its own vascular system
Rods: Are elongated cylindrical bipolar neurons that are sensitive to very small levels of white/grey light (black and white)
Cones: Tapered bipolar neurons that are sensitive to color but requier a higher instensity of light than the rods. They provide a sharper image.
fovea centralis: contains many cone cells and is the area of sharpest vision.

24. Audition

25. Sound Energy waves that travel through the air
The ear is specialized to detect and direct these sound waves
Healthy young humans hear frequencies of 20 – 20,000 hertz (vibration per second)
Average middle-aged adult humans hear frequencies of 12,000 – 14,000 hertz

26. External auditory canal
Ear
The ear is organized into three functional categories
Outer Ear
Middle Ear
Inner Ear
External auditory canal
Tympanic
Membrane
(eardrum)
Round window
Auditory (Eustachian) tube
Bone
Cochlea
Auditory (Vestibulocochlear) Nerve
Semicircular canals
Oval window
Stapes
Incus
Malleus
Vestibule
Auricle

27. Outer Ear Auricle: Visible portion of the ear External Auditory Canal
Directs sounds waves into the external auditory canal
External Auditory Canal
Channels the sound to the eardrum
Contains glands in skin lining that secrete cerumen (ear wax)
Auricle
External Auditory Canal

28. Middle Ear Tympanic Membrane (eardrum) Auditory ossicles
Transfers sound waves into vibrations which it transfers to the auditory ossicles
Auditory ossicles
Malleus, Incus, and Stapes
Amplifies vibrations from the tympanic membrane and transfers them to the oval window
Stapes
Incus
Oval window
Malleus
Tympanic
cavity
Auditory (Eustachian) tube
Tympanic
membrane
(eardrum)

29. Middle Ear Oval Window Tympanic cavity Auditory tube
Transfers vibrations to the cochlea
Tympanic cavity
Cavity contains the auditory ossicles and connects to the…
Auditory tube
Allows air to flow from the throat to the tympanic cavity to balance air pressure
Stapes
Incus
Oval window
Malleus
Tympanic
cavity
Auditory (Eustachian) tube
Tympanic
membrane
(eardrum)

30. Inner Ear Semicircular canals Vestibule
Three loops at right angles to each other
Effects equilibrium
Vestibule
Area between the semicircular canals and the cochlea
Semicircular canals
Vestibule
Cochlea

31. Inner Ear
Cochlea
Vibrations transfer from the oval window to the perilymph, a liquid found in the cochlea
Specialized auditory hair receptors called the organ of Corti transfer the flow of the perilymph into a nerve impulse
The impulse is carried to the brain by the Auditory Nerve
Semicircular canals
Vestibule
Cochlea

32. How are the organ of corti found in the cochlea of the inner ear and the retina found lining the inside of the back of the eye analogous?