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Human physiology part 5

Human physiology part 5






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    Human physiology part 5 Human physiology part 5 Presentation Transcript

    • Sensory System
      John Paul L. Oliveros, MD, DPPS
    • Section A
      General principles
    • General Principles
      Awarenesss of our external and internal world is brought about by neural mechanisms that process afferent information
      Stimulus energy  receptor potentials (graded potentials)  action potentials (Nerve fibers)
      Sensory system
      Part of the nervous system that consists of
      sensory receptors
      Neural pathways
      Processing areas of the brain
      Sensory information
      Information processed by a sensory system
      May or may not lead to conscious awareness of the stimulus
      Sensory information that reaches consciousness
      A persron’s understanding of the sensation’s meaning
    • Receptors
      Sensory Receptors
      Initiates neural activity at the border betwee the nervoussystem and the outside world
      Change stimulus energy (pressure, temperature, light, soundwaves, etc)
      Can either be:
      Specialized ending s of afferent neurons
      Separate cellthat affect the ends of afferent neurons
      Energy that impinges upon and activates a sensory receptor
      Stimulus transduction
      The process by which stimulus is transformed into an electrical response
      Adequate stimulus
      The type of energy to which a receptor responds in normal functioning
      Receptors respond best to only a very narrow range of stimulus energy (lowest threshold)
    • Receptor Potential
      Transduction process in all sensory receptors involve the opening and closing of ion channels that receive information about the outside world
      Receptor potential
      A change in the membrane potential on a specialized receptor membrane
      It is a Graded potential
      separate receptors:
      graded potential causes release of neurotransmitter
      Receptors on afferent neuons:
      A local current must flow to a part of an axon that can produce an action potential
      1st node of Ranvier
      Part of myelinated afferent neurons capable of producing action potentials
    • Receptor Potential
      Graded potential magnitude determines action potential frequency but not action potential magnitude
      Factors controlling receptor potential magnitude
      Stimulus strength
      Rate of change of stimulus strength
      Temporal summation of successive receptor potentials
      Decrease in receptor sensitivity
      Results in decrease in frequency of action potentials in an afferent neuron despite maintenance of the stimulus at a constant strength
    • Neural pathways in sensory system
      Sensory pathway
      A bundle of parallel 3-neuron chains
      Sensory units
      A single afferent neuron with all its receptor endings
      Receptive field
      Portion of the body that when stimulated leads to activity in a particular afferent neuron
    • Ascending pathways
      Central processes
      Part of afferent neurons that enter the brain or spinal cord and synapse with interneurons
      2nd order neurons
      Interneurons that synapse with afferent neurons
      Synapse with 3rd, 4th, etc interneurons until the cerebral cortex is reached
    • Ascending pathways
      Specific ascending pathways
      Ascending pathways in the brain and spinal cord that carry information about single types of stimuli
      Somatosensory cortex
      Lies in the parietal lobe of the brain behind the junction of the parietal and frontal lobes
      Where information from somatic recepotrs are transmitted
      Information from skin, skeletal muscles, tendon and joints
      Visual cortex
      At the occipital lobe
      Where spefic pathways from the eyes transmit
      Auditory cortex
      Where specific pathways from the ears transmit
      Loacted at the temporal lobe
    • Ascending pathways
      Nonspecific ascending pathways
      Activated by sensory units of several different types
      Signal general information
      Polymodal neurons
      2nd order neurons that respond to inputs from several afferent neurons, each activated by a different stimulus
    • Association Cortex and Perceptual Processing
      Cortical Association Areas
      Areas of the brain outside the primary cortical sensory areas but are adjacent to them
      Elaborates perception information from the primary sensory cortical areas
      Regions closests to the primary sensory cortical areas process information in fairly simple ways and serves basic sensory function
      Regions farther from the primary sensory cortical areas process information in more complicated ways
      Emotional and motivational significance (frontal lobe/ limbic system)
    • Association Cortex and Perceptual Processing
      Factors that affect perception
      1.Afferent information is influenced by sensory receptor mechanisms and by processing of the information along afferent pathways
      2. Factors such as emotions, personality, experience and social background can influence perceptions so that 2 persons can witness the same events and yet perceive them differently
      3. Not all informationentering the CNS give rise to conscious sensation
      * e.g. carotid/aortic bodies
      4. We lack suitable receptors for many energy forms
      * x-ray, radio and TV waves
      5. Damaged neural networks may give rise to faulty perceptions
      * phantom limb phenomenon
      6. Some drugs alter perceptions
      * drugs
      * diseases
      In summary:
      *3 processes needed for perception to occur
      1. transducing stimulus energy into action potentials by receptor
      2. transmitting data through the CNS
      3. Interpreting the data
      • 3 iportant organizational principles of the sensory system
      • 1. there is heirarchical processing of afferent information along individual pathways
      • 2. information is processed by parallel pathways, each of which handles a limited aspect of neural signals generated by the sensory transducers
      • 3. information at each stage along the pathway is modified by “topdown” influences serving emotions, attention, memory and language
    • Primary sensory coding
      The sensory system codes 4 aspects of a stimulus
      Stimulus type
      Stimulus type
      AKA stumulus modality (temp, sound, pressure)
      A receptor type is particularly sensitive to one stimulus modality (adequate stimulus)
      Due to the signal transduction mechanisms and ion channels in the receptor’s plasma membrane
      e.g. Vision receptors have pigments whose shape is transformed by light
    • Primary sensory coding
      Stimulus intensity
      Distinguishing intensity
      Frequency of action potentials
      Inc. Stimulus strengthinc. Receptor potential  inc. Action potential frequency
      single receptor
      Other receptors of the same neuron
      Calling in of receptors on additional afferent neurons
    • Primary sensory coding
      Stimulus location
      Main factor: Site of the stimulated receptor
      amount of convergence of neuronal input in ascending pathways: inversely related to acuity/precision
      Size of the receptive fieldcovered by a receptor
      Overlap of nearby receptive fields
    • Primary sensory coding
    • Primary sensory coding
      Lateral inhibition
      More important in localization than the different sensitivites of receptors throughout the receptor field
      Information from afferent neurons whose receptors are at the edge of the stimulus is inhibitted compared to information from the stimulus’ center
      Increases contrast between relevant and irrelevant information
      May occur at any levels of the pathway but mostly on the early stages
    • Primary sensory coding
      Stimulus duration
      Receptors differ in the way they respond to a constantly maintained stimulus adaptation
      Rapidly adapting receptors:
      Important in signaling rapid change
      On response
      On-off response
      Slowly adapting receptors:
      Maintain response at or near the initial level of firing regardless of the stimulus duration
      For prolonged events (posture)
    • Central control of afferent information
      Reticular formation and cortex: main control
    • Section B
      Specific Sensory Systems
    • Somatic sensation
      Somatic sensation:
      Activation gives rise to sensations
      awareness of the position of the parts and their movement
      Each sensation has a specific receptor type
      Information enters both specific and non-specific pathways
      Specific pathways cross to the opposite side of the brain (somatosensory cortex
    • Somatic sensation
    • Somatic sensation
      Somatosensory cortex
      Endings of axons of the specific pathways are grouped according to the location of the receptors giving rise to the pathways
    • Touch-pressure
      Skin mechanoreceptors
      Rapidly adapting receptors
      Slowly adapting receptors
    • Sense of posture and movement
      Receptors for postures and movement
      Muscle-spindle stretch receptors
      Vision and vestibular organs
      Mechanoreceptors in joints, tendons, ligaments, skin
      Sense of movement at a joint
    • Temperature
      Warmth receptors
      Respond to temp between 30c-43c
      Increase discharge rate upon warming
      Cold receptors
      Stimulated by small decrease in temperature
    • Pain
      Detect stimulus that causes tissue damage
      Respond to intense mechanical deformation, excessive heat, and many chemicals (several secreted by damaged cells)
      Increased sensitivity to painful stimuli
      Last for hours after the stimulus is over
      Referred pain
      Sensation of pain is experienced at a site other than the injured/diseased part
      Due to activation of intrneurons by incoming nociceptive afferents
      Visceral and somatic afferents often converge in the same interneurons in the pain pathway
      Selective suppresion of pain without effects on consciousness or other sensation
      Stimulation-produced analgesia
      Electrical stimulation
      Transcutaneous electric nerve stimulation
      Electrodes are placed on the surface of the skin above the painful site or nerves leading from it
      Stimulation of non-pain, low threshold fibers leads to inhibition of neurons in the painful pathway
      Needles are introduced into specific parts of the body to stimulate afferent fibers which causes analgesia
      It ivolves endogenous opiod neurotransmitters
    • Vision
      Receptors of the eyes are only sensitive to visible light
      Distance between 2 successive wave peaks of the electromagnetic radiation
      Measured in hertz (cycles per second)
      Varies inversely with wavelength
      Visible spectrum
      Between 400-700nm
      Light of different wavelength is percieved as colors
    • Vision
      Optics of vision
      Focuses the image being viewed
      Thin layer of neural tissue lining the back of the eyeball
      Lens and cornea
      Optical system that focus the impinging light rays into an image upon the retina
      Surface are curved to bend light rays coming from different directions and focus them into a single point at the retina
      Fovea centralis
      Area in the retina with the greatest visual clarithy
      Area where light rays from the cornea/lens are focused
      Image is upside down and reversed right to left
    • Vision
      Optics of vision
    • Vision
      Optics of vision
      Process of focusing and adjusting image on the retina
      Greater part of focusing image on the retina
      Adjustments for distance made by changing its shape
      Cilliary muscles
      Controls the shape of the lens
      Stimulated by parasymphatetic
      Sphincter like and draws lens towards it as it contracts
      Accomodation for viewing near objects
      Zonular fibers
      Attaches the ciliary muscles to the lens
      Pulls lens to flatten it to focus distant objects
      Relaxes to make lens more spherical to focus near objects
    • Vision
      Include the following mechanisms
      To view near objects
      Moving of lens slightly towards the back of the eye
      Turn the eyes inward and towards the nose (convergence)
      Constrict the pupil
      To view far objects
      Opposite of the above mechanisms
    • Vision
      Normal part of aging process
      Increasing stiffness of the lens making accomodation difficult
      Opacity of the lens
      Usually due to changing color due to age
      Nearsightedness / myopia
      Unable to see distant objects clearly
      Eyeball is too long
      Far images focus at a point in front of the retina
      Farsightedness / hyperopia
      Eye is too short
      Near objects are focused behind the retina
      Near vision is poor
      Lens and cornea doesn’t have a smoothly spherical surface
      Aqueous humor is formed faster than it is removed
      Increase intraocular pressure
      Leading cause of irreversible blindness
      Axons of the otic nerve die
    • Vision
      Controls the amount of light entering the eye
      Ringlike pigmented muscular tissue
      Color is not significant
      Sympathetic innervation
      Radial muscles contract
      Pupils enlarge
      Parasymphatetic innervation:
      Sphincter muscles contract
      Pupils contract
      Whole in the center of the iris
      Where light enters the eye
    • Vision
      Photoreceptor cells
    • vision
      Photoreceptor cells
      Extremely sensitive to very low levels of illumination
      Less sensitive and respond to bright light
      Pigmented layer behind the retina
      Absorbs light and prevents reflection back to the rods and cones
      Inside photoreceptors
      Absorb light
      4 types:
      Rods (1): rhodopsin)
      Cones (3)
      Each contains:
      Group of integral proteins that surround and binds a chromophore molecule
      Differs in each of the 4 photopigments
      Light filters differently in each photopigments and thus absorbs light most effectivly at different spectrum
      Light sensitive part of the photopigment
      Same in all 4 photopigments
      A derivative of vit. A (retinal)
    • Vision
    • Vision
      Light retinal changes shape  photoreceptor hyperpolarization decrease release of neurotransmitter (glutamate)  hyperpolarization of bipolar cell
      In the dark:
      Retinal has resting shape
      Photoreceptor cell partially depolarized
      More neurotransmitter is transmitted
      Dark adaptation
      Temporary blindness when one steps into a darkend room from bright sunlight
      At brighlight: rhodopsin completely activated
      At dark: at least 10mins needed to restore rhodopsin to resting state
      Neural Pathways of vision
    • Vision
      Color vision
      The colors we perceived are related to the wavelengths of light that are reflected, absorbed, or transmitted by the pigments in the objects of our visual world
      White light
      Mixture of all colors
      Absence of all light
      Begins with the activation of the photopigments of the cone receptor cells(red, green, blue)
    • Vision
      Color vision
      Ganglion cells
      general brightness: receives input from all 3 colors
      Opponent color cells:
      Code for specific color
      Excitatory input from one type of receptor and inhibitory from another
      Color blindness
      AKA color deficiency
      Lack red or green pigments entirely or have them in abnormal form
      Trouble perceiving red vs green
    • Vision
      Eye movement
      Controlled by 6 skeletal muscles
      2 basic movements
      Fast movements
      AKA saccades
      small jerking movements
      Rapidly bring eye from one fixation point to another
      Allow search for visual field
      Prevent adaptation
      Move during certain periods of sleep (watching visual imagery of dreams)
      Slow movements
      Involve in tracking visual objects moving throught the visual field
      Compensation during movements of the head
    • Hearing
      Sound energy:
      Medium: gaseous, liquid, or solid medium
      Vibration of the mediums’ molecules
      Vibrating objects can serve as a sound source
      Sound wave:
      Zones of compression
      Molecules close together
      Pressure is increased
      Zones of rarefaction
      Molecules are far apart
      Pressure is less
      Sound wave (cont)
      Consists of rapidly alternating pressures
      Determined bydifference between the 2 zones
      Related to the loudness of the sound
      Number of zones in a given time
      Determines the pitch we hear
      Keenly audible frquency: 1000-4000hz
      Audble frquency: 20-40,000hz
    • Hearing
    • Hearing
      Sound transmission in the ear
      External auditory canal
      Help amplify and direct sound
      Tympanic membrane
      Vibrate at the same frequency of the sound waves
      Middle ear cavity
      Air filled cavity in the temporal bone
      Auditory/eustachian tube
      Connects the middle ear to the pharynx
      Exposes the middle ear to atmospheric pressure
      Normally close but opens during yawning, sneezing, swallowing to equal middle ear pressure to atmospheric pressure
      Pain during sudden change of altitude because of pressure difference between middle ear and atmosphere
    • Hearing
      Middle ear
      Sound waves amplified by chain of bones that act as pistons and couple the motions of the tympanic membrane to the oval window
      Force of sound waves transferred from tympanic membrane to oval window
    • Hearing
    • Hearing
      Inner Ear/Cochlea
      Fluid filled, spiral shaped passage in the temporal bone
      Where the receptors cells are located
      Cochlear duct
      Fluid filled membranous tube
      Follows the cochlear spiral
      Divides the cochlea lengthwise
      Scala vestibuli
      On side of cochlear duct and ends on the oval window
      Scala tympani
      Below the cochlear duct and ends on the round window
      Oval window
      Separates inner ear from middle ear
      Basilar membrane
      Forms one side of the cochlear duct
      Organ of corti
      Sits on the basilar membrane
      Contains receptor cells
      Hair cells
      Mechanoreceptors with hairlike stereocilia
      Transform pressure waves in the cochlea into receptor potentials
      Movements of basilar membrane stimulate hair cells
      Tectorial membrane
      Move in relation to haircells
      Bend sterocilia to open ion channels
      Efferent nerve fibers
      From brainstem
      Dampen response for protectionr
      Afferent neurons
      Forms cochlear portion of cranial nerve VIII
    • Hearing
      Neural pathways of hearing
      Cochlear N.  brainstem interneurons  multineuron pathway  thalamus  auditory cortex
      Hearing aids
      Amplify incoming sounds
      Cochlear implants
      Used when there is extensive damage
      Restore functional hearing
      Directly stimulate the cochlear nerve with tiny electric currents
      Bypass the cochlea
    • Vestibular system
      Vestibular apparatus
      Series of fluid filled membranous tubes that connect with each other and with the cochlear duct
      Contains hair cells that detect changes in the motion and position of the head
      Consists of:
      3 semicircular canals
      Bony canals of the inner ear that contains the vestibular apparatus and cochlea
    • Vestibular system
      Semicircular canals
      Detect angular acceleration during rotation of the head along 3 perpendicular axes
      Nodding head up and down (yes)
      Turning head from side to side (no)
      Tipping the head so ear touches shoulder
      Receptor cells
      Also contains hairlike stereocilia
      Gelatinous mass that ensheaths the stereocilia
      Slight bulge in the wall of each duct
    • Vestibular system
      Utricle and saccule
      Mechanoreceptors with stereocilia
      Utricle: horizontalposition
      Saccule: vertical position
      Tiny calcium carbonate stones
      Embedded in gelatinous substance together with stereocilia
      Makes gelationous substance heavier than surrounding fluid
      Moves according to the force of gravity
      Provide information on:
      Linear acceleration
      Up and down
      Back and forth
      Changes in head position in relation to gravity
    • Vestibular system
      Vestibular information and dysfunction
      Hair cell  vestibular branch of cranial N. VIII  brainstem  multineuronal pathway  vestibular centers of parietal lobe
      3 uses of vestibular information:
      1. Control eye muscles to fix eye in the same point in spite of head movement
      nystagmus: large jerky back and forth movement of the eye in response to unusual vesdtibular input
      2. To maintain upright posture
      3. To provide conscious awareness of the position and acceleration of the body
      Illusion of movement (usually spinning)
      Accompanied by feelings of nausea and lightheadedness
      Occurs when there is a mismatch in the information from the various sensory systems
      e.g. Looking down from the building
      Motion sickness
      Unfamiliar patterns of linear and rotational acceleration are experienced and adaptation to them has not occured
      Meniere’s disease
      Involves the vestibular system
      Episodes of abrupt and severe dizziness, ringing of ears, bouts of hearing loss
      Due to increase fluid pressure in the membranous duct sytem of the inner ear
    • Chemical senses
      Receptors: chemoreceptors
      Specialized organs for taste
      10,000 + present
      4 basic groups
      Pathways end up in mouth region of the somatosensory cortex
    • Chemical Senses
      80% of flavor of food is contributed by smell
      Odor of a substance is related to its chemical structure
      Olfactory receptor cells
      Lie in the olfactory epithelium in upper part of the nasal cavity
      Specialized afferent neurons
      With single enlarged dendrite that extends to the surface of the epithelium
      Processes of dendrites
      Bath in mucus
      Containreceptor proteins for olfactory stimuli
      1000 or so different plasma membrane odorant receptor types
      Axons (cranial N. I) olfactory bulbs  olfactory cortex (limbic system)
      Limbic system:
      Emotional behavior
      Fodd getting behavior
      Sexual behavior
      Olfactory discrimination
      Increased in hunger
      More keen in women
      Smokig decrease sensitivity
      Decreases with age
      Decreases with nasal congestion
    • Chemical senses
    • Good luck sa exam!!!