HUMAN ANATOMY & PHYSIOLOGY II

1. BIOL 2020 HUMAN ANATOMY & PHYSIOLOGY II Dr. Tyler Evans Email: tyler.evans@csueastbay.edu Office: S Sci 350 Office Hours: F 8:30-11:30 or by appointment Website: http://evanslabcsueb.weebly.com/ Phone: 510-885-3475

2. LAST LECTURE ORGANIZATION OF THE NERVOUS SYSTEM Fig 11.2 pg 388

3. LAST LECTURE CELL TYPES OF THE NERVOUS SYSTEM • although highly complex, the nervous system is made of two principal cell types: • 1. NEURONS: excitable cells capable of transmitting electrical signal • 2. NEURGOGLIA: supporting cells that surround more delicate neurons TYPES OF NEUROGLIA: • ASTROCYTES: support, brace and anchor neurons • called SATELLITE CELLS in the PNS • MICROGLIA: repair damages neurons and prevent against infection • EPENDYMAL CELLS: line cavities of the central nervous system separating cerebrospinal fluid from nervous tissue • can be ciliated to help circulate the fluid • OLIGODENDROCYTES: wrap around neurons to produce an insulating cover called MYELIN SHEATH • in the PNS, SCHWANN CELLS produce myelin sheath Fig 11.3 pg 390

4. LAST LECTURE FUNCTION OF REGIONS OF THE BRAIN • recall, CNS consists of the BRAIN and SPINAL CORD and is the integrating and control center for the nervous system • four regions in the adult brain: • CEREBRAL HEMISPHERES • DIENCEPHALON • BRAIN STEM • CEREBELLUM (includes midbrain, pons and medulla oblongata) Fig 12.2 pg 430

5. LAST LECTURE THE SPINAL CORD • the spinal cord is enclosed in the vertebral column and provides a two-way conduction pathway to/from the brain • surrounded by a protective membrane called DURA MATER and CEREBROSPINAL FLUID • it terminates at a structure called the CONUS MEDULLARIS • 31 pairs of spinal nerve fibers attach via foramen (holes) in vertebrae • these fibers connect to motor and sensory neurons that control movement and the senses Fig 12.28 pg 467 Fig 12.26 pg 465

6. THE PERIPHERAL NERVOUS SYSTEM CHAPTER 13 SENSORY RECEPTORS • the PERIPHERAL NERVOUS SYSTEM (PNS) provides links from and to the world outside our bodies • the PNS includes all neural structures outside the brain and spinal cord including sensory receptors, peripheral nerves and motor endings • input into the PNS comes from SENSORY RECEPTORS that are specialized to respond to changes in their environment • receptors can be classified in three different ways: • STIMULUS THEY DETECT • MECHANORECPTORS: respond to mechanical force such as touch and pressure • THERMORECEPTORS: respond to temperature changes • PHOTORECEPTORS: respond to light and found in the retina of the eye • CHEMORECEPTORS: respond to chemicals in solution and involved in smell and taste • NOCICEPTORS: responds to damaging stimuli that result in pain

7. THE PERIPHERAL NERVOUS SYSTEM SENSORY RECEPTORS • Receptors can be classified in three different ways: • 2. LOCATION IN THE BODY • EXTERORECEPTORS: are sensitive to stimuli originating outside the body, so most of these receptors occur near the surface for example in the skin and special sense • INTERORECEPTORS: also called VISCERORECEPTORS, respond to stimuli within the body such as viscera and blood vessels. • respond to chemical changes, temperature and tissue stretch • usually unaware of their activities • PROPRIORECEPTORS: also respond to internal stimuli, but occur only in skeletal muscles, tendons, ligaments, joints • these receptors constantly relay information about our movement to the brain

8. THE PERIPHERAL NERVOUS SYSTEM SENSORY RECEPTORS • Receptors can be classified in three different ways: • 3. RECEPTOR STRUCTURE • NONENCAPSULATED (FREE) NERVE ENDINGS: typically nothing more that swellings at the end of a nerve fiber • are present throughout the body and in abundance in epithelia (especially the skin) and connective tissue • Table 13.1 list examples of non-encapsulated receptors • they include the Merkel disks in the skin and hair follicle receptors we have already described (ROOT HAIR PLEXUS)

9. THE PERIPHERAL NERVOUS SYSTEM SENSORY RECEPTORS • Receptors can be classified in three different ways: • 3. RECEPTOR STRUCTURE • ENCAPSULATED NERVE ENDINGS: terminals of sensory neurons enclosed in connective tissue • virtually all are mechanoreceptors involved in touch and pressure detection • vary greatly in shape, size and distribution in the body • found in joints, muscle, tendons and deeper parts of the skin • require stronger stimulus to become activated

10. THE PERIPHERAL NERVOUS SYSTEM SENSORY RECEPTORS • regardless of detected, stimulus, location or structure of the receptor, each sensory receptor takes incoming stimuli and converts them into changes in membrane potential • typically, specialized receptor proteins in the cell membrane absorb energy of the incoming stimulus and undergo a conformation change • this conformational change triggers a signal transduction pathway that opens or closes ion channels in the membrane and creates an ACTION POTENTIAL

11. THE PERIPHERAL NERVOUS SYSTEM CREATING STIMULUS MODALITY • just said that whatever the stimulus, different types of sensory receptors convert the signals to action potentials • but if all action potentials are the same how can integrating centers (e.g. like our brain) distinguish signals coming from different types of receptor?

12. THE PERIPHERAL NERVOUS SYSTEM DETERMINING STIMULUS LOCATION • sensory systems must also encode the location of the stimulus • one main factor determining stimulus location is the location of the stimulated receptor on the body • e.g. NEURONS INVOLVED IN TOUCH • sensory neurons involved in touch have a RECEPTIVE FIELD, referring to a region of the skin that triggers a particular set of sensory neurons • however, information from a particular set of sensory neurons can only determine whether a signal has occurred in the receptive field and cannot provide more precise locations • can be problematic because neurons can have very small or very large receptive fields or differences in ACUITY How could organisms gain more precise information about the location of a stimulus?

13. THE PERIPHERAL NERVOUS SYSTEM DETERMINING STIMULUS INTENSITY • because action potentials will not change their signal intensity (recall this is an all-or-nothing response), stimulus intensity is determined by the number of activated receptors on the membrane of a sensory cell • the weakest stimulus that will produce an action potential is called the THRESHOLD OF DETECTION • e.g. some photoreceptors can detect a single photon of light • In contrast, at RECEPTOR SATURATION all of the receptors on a sensory cell are activated and an increase in stimulus intensity will have no effect • difference between threshold of detection and receptor saturation is called the DYNAMIC RANGE, which is depicted in this graph

14. THE PERIPHERAL NERVOUS SYSTEM DETERMINING STIMULUS DURATION • sensory receptors, regardless of the stimulus they detect, can come in two forms that allow information to be conveyed about stimulus duration • TONIC RECEPTORS: • fire action potentials as long as the stimulus is present • while most tonic receptors will continue to fire action potential, the frequency usually declines substantially over time, called RECEPTOR ADAPTATION • receptor adaptation is critically important as it allows us to tune out unimportant information

15. THE PERIPHERAL NERVOUS SYSTEM DETERMINING STIMULUS DURATION • sensory receptors, regardless of the stimulus they detect, can come in two forms that allow information to be conveyed about stimulus duration • PHASIC RECEPTORS • fire an action potential only when the stimulus begins, even if the stimulus persists

16. TODAY’S LECTURE: THE SPECIAL SENSES CHAPTER 15 • most people think of five basic senses: vision, taste, smell, hearing and touch • your textbook considers touch a general sense and doesn’t include a discussion in this chapter, but we have briefly described sense of touch in the integumentary system lecture (e.g. root hair plexus) • the remaining four senses plus EQUILIBRIUM are considered SPECIAL SENSES • SPECIAL SENSORY RECEPTORS are distinct because these receptors are confined to the head region and are housed within complex sensory organs (e.g. eyes, ears) of epithelial structures (e.g. taste buds) • keep in mind that we perceive the world through the simultaneous use of several special senses

17. THE SPECIAL SENSES THE EYE AND VISION: ACCESSORY STRUCTURES • vision is our dominant sense and some 70% of sensory receptors in the body are in the eyes and 50% of cerebral cortex involved in visual processing • most structures are not actually involved in photoreception and there are several important accessory structures in the eye: • EYEBROWS: shades eyes from UV light and prevent sweat form entering eye • EYELIDS: provides protection and moisture • eyelids are associated with LACRIMAL CARUNCLE that contains sebaceous and sweat glands that moisturize the eye when eyelids blink • eyelashes are heavily innervated so that anything that contacts eyelashes causes a reflexive blink Fig 15.1 pg 545

18. THE SPECIAL SENSES THE EYE AND VISION: ACCESSORY STRUCTURES • 3. CONJUNCTIVA: mucous membrane that lines the eyelid and part of eyeball • produces a lubricating mucus that prevents the eyes from drying out • 4. LACRIMAL APPARATUS: consists of LACRIMAL (TEAR) GLAND and ducts which drain the gland. • the lacrimal gland continually releases LACRIMAL SECRETION (i.e. tears), which contain mucus, antibodies and lysozyme, an enzyme that destroys bacteria • tears move across the eye and drain into the LACRIMAL PUNCTA which leads into the nasal cavity (cause of sniffles when tear production is high) Fig 15.2 pg 546

19. THE SPECIAL SENSES THE EYE AND VISION: ACCESSORY STRUCTURES • 5. EXTRINSIC EYE MUSCLES: six strap-like muscle control the movement of each eye • four RECTUS MUSCLES insert into the eyeball and each moving the eye in the superior, inferior, lateral and medial directions • SUPERIOR OBLIQUE MUSCLE rotates eye downward and laterally, while the INFERIOR OBLIQUE MUSCLE rotates eye upward and laterally. • DIPLODIA (double vision) or STRABISMUS (cross-eyes) can result from weakened eye muscles Fig 15.3 pg 547

20. THE SPECIAL SENSES THE EYEBALL • composed of three regions: the outermost FIBROUS LAYER, the VASCULAR LAYER and the innermost INNER LAYER • FIBROUS LAYER • SCLERA: seen externally as “whites of eye” provides anchor points for muscles • CORNEA: transparent structure that acts as window to bend and focus light entering the eye • interestingly, cornea has no blood supply or immune response • the cornea can be transplanted without possibility of rejection WHY?

21. THE SPECIAL SENSES THE EYEBALL • composed of three regions: the outermost FIBROUS LAYER, the VASCULAR LAYER and the innermost INNER LAYER • VASCULAR LAYER (middle of eyeball) • CHOROID: contains blood vessels that supply the eye and also produces melanin that assists in absorbing light • CILIARY BODY: circle the lens and houses muscles that control the lens shape • IRIS: visible colored part of the eye and has an opening at the center called the PUPIL • associated muscles contract or relax to control the diameter of the pupil and thereby regulating the amount of light entering the eye • iris diameter is under the control of the autonomic nervous system Fig 15.5 pg 549

22. THE SPECIAL SENSES THE EYEBALL Fig 15.4 pg 548

23. THE SPECIAL SENSES THE EYEBALL • Composed of three regions: the outermost FIBROUS LAYER, the VASCULAR LAYER and the innermost INNER LAYER • the INNER LAYER is the RETINA: contains millions of photoreceptors that transduce light energy. The retina has two main divisions: • 1. PIGMENTED LAYER OF RETINA: absorbs light and prevents it from scattering • 2. NEURAL LAYER OF RETINA: contains three major types of neurons: • PHOTORECEPTORS: sensory cells that detects incoming light • BIPOLAR CELLS and GANGLION CELLS: transduce light information to optic nerve (which eventually leads to the brain) Fig 15.6 pg 550

24. THE SPECIAL SENSES PHOTORECEPTORS • PHOTORECEPTORS: are sensory cells that detect incoming light. A quarter billion are found in the retina and come in two forms: • RODS: used for dim-light and peripheral vision because they are more numerous and more sensitive to light. • however, rods do not provide sharp vision or color vision • CONES: are photoreceptors for bright light and provide high resolution color vision Fig 15.6 pg 550

25. THE SPECIAL SENSES EYE HUMORS • HUMOR refers to the liquid that fills and supports the eye ball. There are two main types that occur in different locations of the eye • VITREOUS HUMOR: covers the lens are cornea and helps transmit light and maintain intraocular pressure • AQUEOUS HUMOR: covers posterior eye and is continually circulated because is assists in supplying oxygen and nutrients to eye while draining metabolic wastes • GLAUCOMA occurs when aqueous humor fails to drain and pressure builds in the eye compressing the retina and optic nerve Fig 15.8 pg 552

26. THE SPECIAL SENSES LENS • the LENS is a convex and transparent structure that can bend to precisely focus light on the retina (ciliary muscle control its shape) • like the cornea, it lacks a blood supply (it must to be transparent) • is composed primarily of CRYSTALLIN proteins • CATARACTS result from clouding of the lens. Cataracts are triggered by oxidative damage that promotes the clumping of crystallin proteins which makes the lens less transparent. Cataracts, a clouding of the lens Fig 15.9 pg 553

27. THE SPECIAL SENSES LIGHT AND OPTICS • eyes respond to the part of the ELECTROMAGNETIC SPETRUM called VISIBLE LIGHT ( approx. 400-700 nm wavelengths) • color is given to objected by the wavelengths they reflect. For example, an apple reflects mostly red wavelengths of light between 650-700 nm • Light travels in a straight line, but slows down when traveling through objects of differing density which causes REFRACTION Fig 15.10 & 15.11 pg 554

28. THE SPECIAL SENSES LIGHT AND OPTICS • light is refracted three times before contacting the photoreceptors in the retina: entering the cornea, entering the lens and leaving the lens • changing the curvature of the lens ensures that light converges on the retina • CILIARY MUSCLES contract to cause the lens to become more rounded in order to focus on close objects • to focus on distant objects, ciliary muscles relax causing the lens to flatten • this process is called ACCOMODATION

29. THE SPECIAL SENSES VISUAL PROBLEMS • MYOPIA: occurs when distant objects do not focus on the retina and cannot be viewed clearly. Commonly called nearsightedness and can be fixed with flattened contact lenses that better focus distant objects • HYPEROPIA: or farsightedness occurs when light from close objects do not focus on the retina, but can be corrected with convex corrective lenses. Fig 15.14 pg 557

30. THE SPECIAL SENSES PHOTOTRANSDUCTION • PHOTOTRANSDUCTION is the process of converting light energy into changes in membrane potential • photoreceptors are arranged into outer and inner segments • the outer segments contain the PHOTOPIGMENTS that absorb incoming light. • inner segments contain the synaptic terminals that connect photoreceptors to other retinal neurons that lead to the nervous system • rods are very sensitive and function in low light conditions • cones contain one of three different photopigments, each of which absorb a different wavelength of color (red, green or blue) and thus provide color vision Fig 15.15 pg 558

31. THE SPECIAL SENSES PHOTOTRANSDUCTION • photopigments are a combination of a light absorbing molecule called RETINAL (a derivative of VITAMIN A) and an OPSIN protein • for example, RHODOPSIN is the photopigment found in rods • when retinal is struck by light it undergoes a conformational (shape) change: • photoexcitation causes 11-CIS-RETINAL to change to 11-TRANS-RETINAL • same process occurs in cones, but using different photopigments Fig 15.16 pg 560

32. THE SPECIAL SENSES PHOTOTRANSDUCTION • the conformational change in retinal, triggers the opsin protein to change shape, which in turn triggers a G-PROTEIN SIGNALING CASCADE that ultimately leads to the opening or closing of ion channels that changes membrane potentials (not necessary to memorize the steps in this signaling pathway) Fig 15.17 pg 561

33. THE SPECIAL SENSES PHOTORECEPTOR PATHOLOGIES • deficiencies in vitamin A occurs in countries where malnutrition is common • lack of vitamin A in the diet prevents the synthesis of the photopigmentRETINAL • this leads to rod degeneration which seriously hampers vision in low light, more commonly called NIGHT BLINDNESS • eat your carrots if you want to see at night! • genetic conditions that affect the CONES cause color blindness

34. THE SPECIAL SENSES CHEMICAL SENSES: OLFACTION (SMELL) • although our sense of smell is far less acute than other animals, humans can still distinguish a very large number of odors • the organ of smell is a small patch of pseudostratified epithelium located in the nasal cavity called the OLFACTORY EPITHELIUM • the olfactory epithelium contains millions of OLFACTORY SENSORY NEURONS • mucus helps capture chemical odors Fig 15.20 pg 566

35. THE SPECIAL SENSES CHEMICAL SENSES: OLFACTION (SMELL) • there are about 400 “smell” genes active only in the nose, each encoding a different olfactory receptor (in combination can discriminate about 10,000 scents) • chemical must be volatile (gas) and be capable of dissolving in mucus to reach receptor, otherwise it will be undetectable OCTANOIC ACID OCTANOL carboxylic acid hydroxyl • smells like roses or oranges • smells rancid or sweaty

36. THE SPECIAL SENSES CHEMICAL SENSES: OLFACTION (SMELL) • olfaction follows the same type of transduction pathway as was described for photoreceptors • binding of an ODORANT to an OLFACTORY RECEPTOR triggers a conformational change in the receptor that opens ion channels and creates an action potential that transmits this information to the OLFACTORY BULBS of the brain • some “emotional” odors are eventually processed by the LIMBIC SYSTEM • dangerous odors like smoke can trigger fight or flight response • food odors can trigger salivation and stimulate digestion

37. THE SPECIAL SENSES PATHOLOGIES OF SMELL • most olfactory disorders result from head injuries that tears the olfactory nerves or neurological disorders like Parkinson’s disease • some people can have UNCINATE FITS, olfactory hallucinations in which they experience a particularly bad smell (e.g. rotting meat) • for example, can occur in epileptics just prior to a seizure

38. THE SPECIAL SENSES CHEMICAL SENSES: GUSTATION (TASTE) • the sensory organs for taste are TASTE BUDS, most of which are located on the tongue (a few are scattered around the inside of the mouth) • taste buds are located on the top of FUNGIFORM PAPILLAE, mushroom shaped bumps scattered over the surface of the tongue • a few FOLIATE PAPILLAEare found on the edges of the tongue and fewer still VALLATE PAILLAEare found at the back of the tongue Fig 15.22 pg 568

39. THE SPECIAL SENSES CHEMICAL SENSES: GUSTATION (TASTE) • taste buds contain GUSTATORY EPITHELIAL CELLS that are the receptors for taste • these cells have long microvilli called GUSTATORY HAIRS that project into the taste bud through a pore and act as the sensitive portions of the cell • coiling around each gustatory epithelial cell are nerve fibers that provide a link to the nervous system Fig 15.22 pg 568

40. THE SPECIAL SENSES CHEMICAL SENSES: GUSTATION (TASTE) • normally, taste occurs as a complicated mixture of qualities • can be grouped into five categories: • SWEET: elicited by organic substances including sugars, amino acids and alcohols • SOUR: produced by acids and their high hydrogen ion content • SALTY: produced by metal ions like sodium and chloride • BITTER: elicited alkaloids like caffeine, morphine, quinine, nicotine • these tastes have an important nutritional function, by signaling foods we require for survival, for example: • sugar indicates carbohydrates • salts indicate minerals • sour and bitter indicate things we should not eat

41. THE SPECIAL SENSES ACTIVATION OF TASTE RECEPTORS • for a chemical to taste, it must dissolve in saliva, diffuse through taste bud pores and contact the gustatory hairs • each taste is detected in a different way. For example, salty and sour do not actually use receptors instead effects ion channels directly • SALTY-triggered by Na+ influx through Na+ion channels present in gustatory hairs • SOUR-triggered by H+ influx through H+ion channels present in gustatory hairs • thus salty and sour do not require receptors, but can alter membrane potential directly • SWEET-triggered by the binding of sugars to a receptor protein called GUSTDUCIN • BITTER-also requires receptors, but bitter receptors are much more complex and humans have at least 25 different genes encoding for bitter taste receptors

42. THE SPECIAL SENSES PATHOLOGIES OF TASTE • causes of taste disorders include: upper respiratory tract infections, head injuries, chemicals or medications and neck radiation for cancer treatment • disorders of taste are rare because taste can be detected over a larger area than smell and is transduced through multiple neuronal pathways

43. FOR REVIEW TONIGHT • Understand the different types of sensory receptor and how they are distinguished • Understand how action potentials can be varied to create different signals • Understand the structure and function of various parts of the eye • Understand the role of rods and cones in the process of phototransduction • Understand the process of olfaction • Understand how different tastes excite sensory cells (i.e. receptors vs. direct effects on ion channels)

44. NEXT LECTURE • NERVOUS SYSTEM II • Hearing, equilibrium and the Autonomic Nervous System