Anatomy & Physiology II: Lecture Notes PDF

Anatomy & Physiology II: Lecture Exam \# 1 Chapters 17 & 18 - Filled with **[crystallins]**, which provide clarity and focusing power. **17-4 The Focusing of Light on the Retina Leads to the Formation of a Visual Image.** **An Introduction to Light** Light energy is a form of radiant energ...

Anatomy & Physiology II: Lecture Exam \# 1 Chapters 17 & 18 - Filled with **[crystallins]**, which provide clarity and focusing power. **17-4 The Focusing of Light on the Retina Leads to the Formation of a Visual Image.** **An Introduction to Light** Light energy is a form of radiant energy that travels in waves. **Wavelength and Color: visible spectrum acronym: ROY G BIV (red, orange, yellow, green blue, indigo, violet)** R: red (740-625nm) longest visible wavelength V: violet (435-380nm) shortest visible wavelength Visible light is also described as being made up of photons, small energy packets with characteristic wavelengths. Photons of red light carry the least energy and have the longest wavelength, whereas photons of violet carry the most energy and have the shortest wavelength. **Refraction and Focusing of Light** Light is **[refracted (bent)]** as it passes through cornea and lens. - **[Focal point:]** specific point of intersection of light rays on retina. - **[Focal distance:]** distance between center of lens and focal point. **[Astigmatism:]** condition where light passing through cornea and lens is not refracted properly, visual image is distorted. **[Accommodation:]** automatic adjustment of eye to provide clear vision. - Lens becomes rounder to focus on [nearby] objects. - Flatter lens allows focus on [distant] objects. **Image Formation and Reversal** Image arriving at retina is miniaturized, upside down, and reversed from left and right and the brain compensates for this. **Visual Acuity** **[Visual acuity:]** clarity of vision. - Standard rating is 20/20. This means a person can see at 20 feet what should normally be seen at 20 feet. 20/15 is better than normal vision, while 20/30 is slightly worse. A person is legally blind when their vision with assistance is 20/200 or worse (person needs to be at 20 feet to see what can normally be seen at 200 feet). **[Scotoma:]** abnormal, permanent blind spot. - May result from compression of optic nerve, damage to photoreceptors, or central damage. **[Emmetropia:]** normal vision. **[Myopia:]** nearsightedness. **[Hyperopia:]** farsightedness. **[Photorefractive keratectomy (PRK):]** computer-guided laser shapes the cornea to exact specifications. - LASIK is a variation of PRK. **17-5 Photoreceptors Transduce Light into Electrical Signals that are then Processed in the Visual Cortex.** **Physiology of Vision** The rods and cones of the retina are called photoreceptors because they detect photons, the basic units of visible light. **Anatomy of Photoreceptors: Rods and Cones** **[Rods:]** detect pressure or absence of photons. **[Cones:]** provide information about wavelengths of photons. Both rods and cones have... - Inner segment containing major organelles. - Outer segment with membranous discs that contain visual pigments. **Physiology of Photoreceptors** **[Visual pigments:]** absorb pigments. - First step in photoreception. - Derivatives of rhodopsin. - Opsin (protein) plus retinal (pigment). - Retinal is synthesized from vitamin A. **[Color vision:]** provided by blue cones, green cones, and red cones. - Each type has a different form of opsin. **[Color blindness:]** inability to distinguish certain colors. **Steps in Photoreception** - Absorption of a photon changes retinal from 11-cis to 11-trans form. - This activates opsin. - Opsin activates transducin (G-protein). - Which activates phosphodiesterase (PDE). - PDE reduces levels of cyclic GMP - Chemically gated sodium ion channels close. - Dark current is reduced. - Rate of neurotransmitter release declines. **Bleaching and Regeneration of Visual Pigments** **[Bleaching ]** - After absorbing a photon, rhodopsin splits into retinal and opsin. - 11-trans retinal is converted back to 11-cis retinal. - Requires ATP. - Retinal then recombines with opsin. **Synthesis and Recycling of Visual Pigments** **[Night blindness (nyctalopia):]** results from deficiency of vitamin A. **Light and Dark Adaption of Visual Pigments** **[Dark-adapted state:]** visual pigments are fully receptive to stimulation. **[Light-adapted state:]** rates of bleaching and reassembly of visual pigments are balanced. **[Retinitis pigmentosa (RP):]** inherited disease characterized by progressive retinal degeneration. **The Visual Pathways** - Begin at photoreceptors, - End at visual cortex of cerebral hemispheres. - Messages must cross two synapses before moving toward brain. - Photoreceptor to bipolar cell, - Bipolar cell to ganglion cell. **Processing by the Retina** **Ganglion Cells** **[Ganglion cells:]** monitor specific portions of field of vision. **[M cells:]** ganglion cells that monitor rods. - Relatively large. - Provide information about... - General form of an object. - Motion. - Shadows in dim lighting. **[P cells:]** ganglion cells that monitor cones. - Smaller and more numerous than M cells. - In fovea, ratio of cones to ganglion cells is 1:1. - Provide information about... - Edges. - Fine detail. - Color. **[On-center neurons:]** excited by light arriving in center of receptive field. - Inhibited when light strikes edges. **[Off-center neurons:]** excited by light at edges. - Inhibited by light in central zone. **Central Processing of Visual Information** - Axons from ganglion cells converge on optic disc. - Penetrate wall of eye. - Proceed toward diencephalon as optic nerve (II). - Two optic nerves reach diencephalon after partial crossover at **[optic chiasm]**. - Information travels to visual cortex in occipital lobe. - **[Optic radiation:]** bundle of projection fibers linking lateral geniculates with visual cortex. **The Field of Vision** **[Field of vision:]** combined visual images from left and right eyes. - **[Depth perception:]** obtained by comparing relative positions of objects between images received from both eyes. **Brainstem and Visual Processing** **[Circadian rhythm:]** daily pattern of activity tied to day-night cycle. - Established from visual information. - Affects metabolic rate, blood pressure, etc. **17-6 Equilibrium Sensations Monitor Head Position and Movement, while Hearing Involves the Detection and Interpretation of Sound Waves.** **Anatomy of the Ear** The ear is divided into three anatomical regions... - External ear - Middle ear - Internal ear **The External Ear** **[Auricle (pinna):]** surrounds and protects external acoustic meatus (EAM). - Provides directional sensitivity. **[Tympanic membrane (eardrum):]** thin, semitransparent sheet at the end of EAM that separates the external ear from the middle ear. **[Ceruminous glands:]** integumentary gland along EAM that secrete **[cerumen]** (ear wax). - Helps keep out foreign objects and insects. - Slows growth of microorganisms. **The Middle Ear** **[Middle ear (tympanic cavity) ]** - Air-filled chamber. - Communicates with nasopharynx through auditory tube. - Permits equalization of pressure on either side of tympanic membrane. - Contains 3 tiny ear bones called auditory ossicles. - **[Malleus (hammer)]** - **[Incus (anvil)]** - **[Stapes (stirrup) ]** When sound waves vibrate tympanic membrane, auditory ossicles conduct vibrations to internal ear. **Muscles of the Middle Ear** - Two small muscles protect the ear from very loud noises. - **[Tensor tympani ]** - Pulls on malleus and stiffens tympanic membrane. - **[Stapedius ]** - Reduces movement of stapes at oval window. **The Internal Ear** **[Labyrinth:]** winding passageway. **[Bony labyrinth]** surrounds and protects **[membranous labyrinth]**. - Perilymph flows between the two labyrinths. - Endolymph is within membranous labyrinth. Bony labyrinth can be subdivided into... - Vestibule - Semicircular canals - Cochlea **[Vestibule:]** encloses saccule and utricle. - Receptors detect gravity and linear acceleration. **[Semicircular canals:]** contains three semicircular ducts. - Receptors stimulated by rotation of head. **[Cochlea:]** contains cochlear duct of membranous labyrinth. - Receptors provide sense of hearing. **[Round window:]** thin, membranous partition that separates perilymph from air spaces of middle ear. **[Oval window:]** connected to base of stapes by collagen fibers. **Equilibrium** **[Equilibrium:]** state of physical balance. **The Vestibular Complex and Physiology of Equilibrium** - Sensations provided by receptors of vestibular complex (vestibule and semicircular canals). - **[Hair cells:]** sensory receptors of internal ear. - Provide information about direction and strength of mechanical stimuli. **The Semicircular Ducts: Rotational Movements** **[Anterior, posterior, and lateral semicircular ducts:]** continuous with utricle. - Each duct contains an expanded region (ampulla). - With gelatinous **[ampullary cupula]**. - **[Ampullary crest]** contains hair cells. - Each hair cell in vestibular complex has... - 80-100 stereocilia (resembles long microvilli). - A single large kinocilium. **The Utricle and Saccule: Position and Acceleration** - Hair cells provide sensations of position and linear movement. - Connected with **[endolymphatic duct]**, which ends in **[endolymphatic sac]**. **[Maculae:]** oval structures where hair cells cluster. - **[Macula of utricle:]** sense horizontal movement. - **[Macula of saccule:]** senses vertical movement. **[Otoliths (ear stones):]** densely packed calcium carbonate crystals on surface of gelatinous mass. **Pathways for Equilibrium Sensations** Sensory neurons in **[vestibular ganglia]**. - Monitor hair cells of vestibular complex. - Fibers from ganglia form **[vestibular nerve]** of vestibulocochlear nerve (VIII). - Synapse within **[vestibular nuclei]** at boundary between pons and medulla oblongata. There are four functions of vestibular nuclei... - Integrate sensory information about balance and equilibrium from both sides of head. - Relay information from vestibular complex to cerebellum. - Relay information from vestibular complex to cerebral cortex. - Providing conscious sense of head position. - **Send commands to motor nuclei in brainstem and spinal cord.** **Reflexive Motor Commands from Vestibular Nuclei** - Distribute to motor nuclei for cranial nerves involved with eye, head, and neck movements. - Instructions descending in vestibulospinal tracts of spinal cord. - Adjust peripheral muscle tone. - Complement reflexive movements of head and neck. **Automatic Movements of Eyes** - Directed by superior colliculi of midbrain in response to sensations of motion. - Attempt to keep gaze focused on a specific point. - If spinning rapidly, eyes make jerky movements. - **[Nystagmus:]** trouble controlling eye movements when body is stationary. - Caused by damage to brainstem or internal ear **Hearing** - Sound waves are converted into mechanical movements by vibration of tympanic membrane. - Auditory ossicles conduct vibrations to internal ear. - Vibrations are converted to pressure waves in fluid. - Detected by hair cells in cochlear duct. - Information is sent to auditory cortex of brain. **An Introduction to Sound** **[Pressure wave:]** sine wave (S-shaped curve). - Consists of a region where air molecules are crowded together, - And adjacent zone where they are farther apart. **[Wavelength:]** distance between two adjacent wave crests. **[Frequency:]** number of waves (cycles) that pass a fixed reference point in a given time. - Measured in **[hertz (Hz):]** number of cycles per second. **[Pitch:]** our sensory response to frequency. **[Amplitude:]** height of a sound wave. **[Intensity:]** amount of energy in a sound wave, determines how loud it seems. - Measured in **[decibels]**. **Anatomy of the Cochlear Duct** **[Cochlear duct (scala media)]** lies between **[scala vestibuli (vestibular duct)]** and **[scala tympani (tympanic duct)]**. - Hair cells lie in **[spiral organ (organ of Corti).]** - Rests on **[basilar membrane]**. - Separates cochlear duct from scala tympani. - Hair cells lack kinocilia. - Stereocilia contact overlying **[tectorial membrane]**. **Auditory Discrimination** - Range from softest to loudest tolerable sound represents trillion-fold increase in power. - Young children have greatest hearing range. - With age, damage accumulates... - Tympanic membrane gets less flexible. - Articulations between ossicles stiffen. - Round window may begin to ossify. **The Physiology of Hearing** There are six basic steps in process of hearing... - Sound waves arrive at tympanic membrane. - Movement of tympanic membrane displaces auditory ossicles. - Movement of stapes at oval window produces pressure waves in perilymph in perilymph of scala vestibuli. - Pressure waves distort basilar membrane on their way to round window of scala tympani. - Vibration of basilar membrane causes hair cells to vibrate against tectorial membrane. - Information about stimulation is relayed to CNS over cochlear nerve. - Spiral ganglion contains cell bodies of bipolar sensory neurons that monitor cochlear hair cells. **Auditory Pathways** - Afferent fibers of sensory neurons in spiral ganglion form cochlear nerve. - Axons enter medulla oblongata and synapse at cochlear nucleus. - Information ascends to... - Superior olivary nuclei of pons. - Inferior colliculi of midbrain. - Midbrain coordinates unconscious motor responses. - Ascending auditory sensations synapse in medial geniculate body of thalamus. - Projection fibers deliver information to auditory cortex of temporal lobe.