BSC 2086 1st Edition Lecture 4 Outline of Last Lecture I. Accessory Structures of the Eye II. Visual Physiology III. Structures of the Ear Outline of Current Lecture I. Equilibrium and HearingII. Intro to Endocrine SystemIII. Intercellular Communication in the Endocrine System Current LectureI. Equilibrium and Hearing a. Receptors allowing for Equilibriumi. Hair cells 1. When stimulated can send signal to auditory cortex to give information about movement or sound2. Used in hearing alsoii. Semicircular ductsiii. Utricle and Saccule1. Maculae: where hair cells cluster2. Otolith (ear stone): gel solution containing many calcium carbonate crystals 3. Movement of these structures causes a stimulation of the hair cells by the otolith lagging behind and moving the stereocilia b. Pathways for Equilibrium Sensationsi. Vestibular receptors activate sensory neurons in the vestibular ganglia ii. Vestibular branch of vestibulocochlear nerve (VIII) is formed by axonsiii. Synapse is made within vestibular nuclei 1. Vestibular nuclei has 4 functions:a. Combine sensations from both sides of the head about equilibrium and balanceb. Help coordinate movement by sending information from vestibular complex to cerebellumc. Give a conscious sense of how fast your accelerating and inwhat direction (head position and movement) by sending information from vestibular complex to cerebral cortexd. Sends commands to motor neurons in brain stem and spinal cord i. Reflexive motor commands regarding the eye, headand neck movements are dispersed to the motor nuclei for the cranial nervesii. Peripheral muscle tone, neck, and head movement commands are sent down vestibulospinal tracts of spinal cord iv. Eye movements 1. Sensation directed by superior colliculi of midbrain2. Try to keep focus on one point3. Nystagmus: eyes always moving back and forth, cant control their movementsa. Due to brain stem damage or inner ear damage c. Hearingi. Sense of hearing = cochleaii. Auditory ossicles increase the pressure fluctuation in the perilymph of cochlea by:1. Frequency of sound: how fast it vibrates or taps on oval window a. Depends on which part of the cochlear duct is stimulated2. Intensity: how many hair cells stimulated iii. Sound components:1. Pressure waves: regions where air molecules are grouped 2. Wavelength: space between 2 adjacent wave troughs3. Frequency: measured in hertz (hz) it is the number of waves that pass a fixed reference point at a given timea. (1/wavelength) 4. Pitch: our sensory response to frequency 5. Amplitude: reported in decibels (dB), it is the intensity of the sound wave which says how high pitched or loud something isiv. Cochlear duct receptors:1. Basilar membrane: separated cochlear duct and tympanic ducta. Hair cells lack kinociliab. Stereocilia is in contact with tectorial membrane v. Sound transduction:1. Tympanic membrane “tapped” by air pressure.2. Vibration of tympanic membrane = vibration of auditory ossicles3. Vibration of tympanic membrane pushes perilymph through scala vestibule, which causes pressure. Once it reaches scala tympani the pressure is relieved by the round window.4. Movement in scala tympani distorts basilar membrane, either moving it closer to the oval window (high frequency sounds) or farther (low frequency sounds).5. Hair cells move due to other movements taking place, which causes hairs of the hair cells to bend which releases a neurotransmitter.6. Sensory neurons are stimulated and send action potentials through the cochlear branch of the vestibulocochlear nerve.vi. Auditory Pathways 1. Cochlear branch: made by afferent fiber of ganglion neurons2. Arrives at medulla oblongata3. Synapse is made at dorsal and ventral cochlear nerve4. Information crosses to other side of the brain5. Ascending auditory sensations synapse in medial geniculate nucleus in the thalamus 6. Information delivered to auditory cortex by projection fibers vii. Hearing range1. Softest loudest = trillionfold increase in power2. Greatest in young kidsII. Intro to Endocrine Systema. Functions:i. Long term processes1. Development2. Growth3. Reproductionii. Uses chemical messengers to send information and instructions III. Intercellular Communication in the Endocrine Systema. Direct communicationi. Highly specialized and rare communication between 2 cells of the same type ii. Ions and molecules exchanged across gap junctionsb. Paracrine communicationi. Most common form communication between nearby cellsii. Chemical signals transfer data within a single tissue between cellsc. Endocrine communication i. Long distance communicationii. Endocrine cells release hormones which change metabolic activities of tissues and organs at the same time iii. Target Cells- Possess the receptors needed for cells to react to hormones iv. Hormones- chemical messengers sent through the blood 1. Stimulate or inhibit the making of enzymes and proteins 2. Turn enzyme or membrane channels “on” or “off”d. Synaptic communicationi. Used for fast reactions in time of crisisii. Limited to very specific area, the chemical message (neurotransmitter) only travels a short distance to reach the target cell1. Nervous system is a lot faster than endocrine systemiii. Response doesn’t last
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