THE SENSORY ORGANS

1. THE SENSORY ORGANS Anatomy & Physiology

2. Sensations • Result from stimuli that initiate afferent impulses • Eventually reach a conscious level in the cerebral cortex • All sensations involve receptor organs • Simplest receptor organs are bare nerve endings

3. Sensations • Pain • Temperature • Pressure • Touch • Special Senses • Sight • Hearing • Taste • Smell • Orientation in space

4. Receptors • Exteroceptors • Detect stimuli near outer body surface • Interoceptors • Detect stimuli from inside the body • Proprioceptors • Detect stimuli deep within the body

5. Exteroceptors • Cold • Warmth • Touch • Pressure • Special senses • Hearing • Vision

6. Interoceptors • Taste • Smell • pH • Distension • Spasm • Flow

7. Proprioceptors • Located in skeletal muscles, tendons, ligaments, and joint capsules. • Provide information to CNS on posture, orientation in space, pressure, etc. • Fibers are heavily myelinated for rapid transmission.

8. Sensory Receptor • Peripheral component of an afferent axon and the centrally located nerve cell body of that axon. • Convert different types of energy into nerve signals (sound, light, thermal, chemical, and mechanical). • Generally receptors are specific and only respond to one form of energy.

9. Graded Responses • Subject to graded responses depending on the intensity of the stimulus. • Receptor can be regarded as a generator in which the amount of voltage produced is determined by stimulus. • Increasing stimulus increases firing rate of receptor.

10. Adaptation • Receptors adapt to continued stimulus. • Receptors vary in their degree of adaptation. • Adaptation involves slowing of firing rate. • Burst of action potentials at a high frequency followed by a decrease in ratethat quickly returns to zero.

11. Phasic Receptor Organ • Quickly accommodates to prolonged stimulation • Example is pacinian corpuscles (sensitive to pressure). • These receptors are best suited for signaling sudden change in environment.

12. Tonic Receptor • Application of a prolonged stimulus elicits a brief volley of action potentials at high frequency followed by an action potential rate that slows to a lower level and is maintained.

13. Pain Reception • Receptors are termed nociceptors • Bare nerve endings of pain neurons • Pain stimulus causes cell damage resulting in firing of the neuron • Essentially a chemoreceptor • Either myelinated or unmyelinated • Myelinated fibers have a short lag time between stimulus and reaction “bright quality”

14. Pain Reception • Unmyelinated fibers have a longer lag time, pain is more diffuse, dull, and throbbing • Pain fibers are grouped in a specific tract in the spinal cord • Reaction threshold varies considerably across individuals • Diversion of attention reduces pain reception (e.g. twitch)

15. Visceral Pain • Pain can arise from organs in abdominal cavity (viscera) • Peritonitis and pleuritis are two examples • Intestinal pain is another • Heart can also be a source of pain

16. Referred Pain • Usually felt on surface of the body, but source is deep within viscera • Caused by convergence of cutaneous and visceral pain afferent fibers on the same neuron in the sensory pathway • Example (traumatic pericarditis) hardware • Pressure applied to withers causes pain response

17. Taste • Sense of taste is called gustation • The receptor organ is the taste bud • Taste buds are found on the tongue, palate, pharynx, and larynx. • Taste buds have gustatory cells and supporting cells. • Gustatory cells are receptors for taste.

18. Taste Reception • Taste bud pit communicates with the oral cavity by way of the pore. • Any substance tasted must get into solution and enter the pore of the taste bud. • Hair of the gustatory cell is affected causing stimulation of the gustatory cell. • The impulse is transmitted by cranial nerves VII and IX to the brain.

19. Taste Sensations • Classified as salty, sweet, bitter, or sour. • Each taste sensation is some combination of the above. • Taste perception by animals is based on preference. • Considerable variation within a species

20. Temperature and Taste • In humans, the temperature of a beverage or food markedly affects its taste. • In humans, the temperature of a beverage or food markedly affects its taste.

21. Smell • As evolution progressed, nerve cell bodies migrated centrally so that only the nerve fibers remained in a peripheral position. • This provided protection for nerve cells, which do not regenerate. • Central migration did not occur for the nerve cell bodies of Cranial Nerve I (olfactory). • Cell bodies of Cranial Nerve I are found in the mucous membrane of the nasal cavity.

22. Smell • This location is known as the olfactory region. • The size of this region is directly related to the development of the sense of smell. • Dogs can detect substances 1:1000 of that detectable by humans. • Sensation of smell is known as olfaction.

23. Smell • Animals with greatly developed sense of smell are macrosmatic. • Animals with less developed sense are microsmatic. (e.g. humans and monkeys) • Animals with no sense of smell are anosmatic. (many aquatic animals)

24. Smell • Each olfactory receptor has a cell body and a nerve fiber extending from each end. One is an axon and the other a dendrite. • The dendritic process of the olfactory cell extends to the outside of the olfactory region membrane in crevices between sustentacular cells.

25. Smell • Sustentacular cells provide major support to the dendritic processes and shield the nerve cell body from the olfactory cavity. • Dendritic processes form hair-like structures (olfactory cilia) that extend into the nasal cavity. • Cilia are covered with secretions from the glands of Bowman.

26. Smell • Ducts from the glands of Bowman lead through the epithelium of the nasal cavity to its surface. • Secretions constantly refresh the thin layer of fluid bathing the olfactory cilia. • Sniffing allows for back-and-forth movement of air, providing a greater chance for substances to go into solution.

27. Smell • Once the compound is in solution it binds to olfactory cilia and provides a stimulus for the impulse to be transmitted. • Axons of the olfactory cells join and proceed as fibers and branches of the olfactory nerves. • Basal cells divide and become sustentacular cells or olfactory cells replacing those lost.

28. Smell • It is unlikely that a specific olfactory cell exists for each smell. • It is probable that the basic smells combine to provide the sensation of a particular odor. • Only one odor can be perceived at any one time. • Olfactory cells adapt to odors.

29. Phermones • Animals use odors to communicate with each other. • A chemical secreted by one animal which influences the behavior of another is called a pheromone. • Pheromones are used to identify species, mark territories, emit alarms, mark food location, and identify animals in estrus.

30. ANATOMY OF THE EYE

34. Muscles of the Eye

36. Integumentary System

37. Objectives: 1- Describe the functions of the integumentary system. 2- Identify the major structures found in the three layers of the skin. 3. Describe the anatomy and physiology of hair and nails 4. Define some common dermatopathological disorders.

38. This system is divided into: 1- skin 2- hair 3- glands 4- nails 5- nerve endings I) Skin Skin is an organ because it consists of different tissues that are joined to perform a specific function.Largest organ of the body in surface area and weight. Dermatology is the medical specialty concerning the diagnosing and treatment of skin disorders.

40. Anatomy (structure) Epidermis (thinner outer layer of skin) Dermis (thicker connective tissue layer) Hypodermis (subcutaneous layer or Sub-Q) Muscle and bone Physiology (function) 1- Protection - physical barrier that protects underlying tissues from injury, UV light and bacterial invasion. - mechanical barrier is part non specific immunity (skin, tears and saliva).

41. 2- Regulation of body temperature - high temperature or strenuous exercise; sweat is evaporated from the skin surface to cool it down. - vasodilation (increases blood flow) and vasoconstriction (decrease in blood flow) regulates body temp. 3-Sensation - nerve endings and receptor cells that detect stimuli to temp., pain, pressure and touch.

42. 4- Excretion - sweat removes water and small amounts of salt, uric acid and ammonia from the body surface 5- Blood reservoir - dermis houses an extensive network of blood vessels carrying 8-10% of total blood flow in a resting adult. 6- Synthesis of Vitamin D (cholecalciferol) -UV rays in sunlight stimulate the production of Vit. D. Enzymes in the kidney and liver modify and convert to final form; calcitriol (most active form of Vit. D.) Calcitriol aids in absorption of calcium from foods and is considered a hormone.

43. Epidermis: keratinized stratified squamous epithelium with four distinct cell types and five distinct layers.

44. Cells in the epidermis: - keratinoytes - melanocytes - Merkel cells - Langerhans’ cells 1- Keratinocytes: most abundant - produce keratin (fibrous protein) - protective; waterproofing the skin - continuous mitosis - form in the deepest layer called the stratum basale - cells push their way up to the surface where they are dead cells filled with keratin; will slough off. Regenerates every 25-45 days.

45. 2- Melanocytes: - cells produce brownish/black pigment called melanin. (8% of epidermal cells) - stratum basale - branching processes (dendrites) - melanin accumulates in melanosomes and transported along dendrites of the melanocytes to keratinocytes. - melanin accumulates on the superficial aspect of the keratinocyte shielding its nucleus from harmful UV light. - lack of melanin: albino

47. 3- Merkel cells: - stratum basale - epidermis of hairless skin - attach to keratinocytes by desmosomes - make contact with a sensory neuron ending called a Merkel disc (touch). 4- Langerhans’ cells: - star-shaped cells arising from bone marrow that migrate to epidermis. - epidermal dendritic cells (macrophages) - interact with a WBC called a T- helper cell - easily damaged by UV light.

49. Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Stratum basale

50. 5 layers of the epidermis: 1- Stratum corneum (horny layer) - layer has many rows of dead cells filled with keratin - continuously shed and replaced (desquamation) - effective barrier against light, heat and bacteria - 20-30 cell layers thick - dandruff and flakes - 40 lbs. of skin flakes in a lifetime (dust mites!)