lecture three: lifespan perspective of the sensory system Flashcards
sensory system overview
receptors —> sensory pathways —> central nervous system (CNS) —> motor system
- receptors: receive stimulus
- sensory pathways: nerve axons and afferent pathways; transmit signals
- CNS: interpret or integrate sensory inputs
- motor system: efferent pathways; produce response
what are the two types of receptors?
nerve cell and specialized-epithelial cell
receptor activation
- stimulus specific
- transform an external stimulus to an electrical signal
sensory pathways describe the _____ and ______ of the sensory stimulus
type, location
type of sensory stimulus
dependent on what type of receptor is activated
location of sensory stimulus
each receptor has a specific location on the sensory map in the brain
dorsal root ganglion (DRG)
- collection of cell bodies of the afferent sensory fibers
- associated with posterior or dorsal root of spinal nerve
what do the dorsal roots contain?
- sensory fibers from the skin
- subcutaneous and deep tissues
- viscera
primary afferent fibers of the dorsal roots are either _____________ or ____________
myelinated, unmyelinated
- cutaneous, joint, and visceral afferents are composed of myelinated
perception
the integration of sensory impressions into psychologically meaningful information
(involves peripheral sensory mechanisms and higher-level processing)
sensory maps
location of sensory receptors in the brain
(sensory homunculus: shows the somatic sensory projections from the body surface)
sensory integration
ability to use sensory information efficiently
(combining several sensory inputs to produce a desired movement; examples include drawing and writing)
what systems are involved in stable standing balance?
- somatosensory system (proprioception)
- vision
- vestibular system
sensory pathways
transmits electrical signal to area of brain that corresponds with receptor location
somatosensory system receptors
receptors include
- mechanoreceptors (touch, pressure, vibration, proprioception)
- thermoreceptors (heat and cold)
- nociceptors (pain)
somatosensory system
- provides sensory information about the body
- cutaneous sensation of touch (exteroception)
- proprioceptive sensation from ligaments, muscles, joints, and tendons
- function
- transmits information about senses of touch, pain, temperature, and body position from sensory receptors to CNS to regulate behavior
interoception
perception of sensation from inside the body
propioception
perception of one’s body in space
somatosensory system (prenatal)
- order of sensory system development: touch —> vestibular —> smell —> hearing —> vision —> taste —> proprioception
- proprioceptive receptors (muscle spindles and golgi tendon organs) are well developed by mid-fetal life
_____ is the first system to function in utero
touch (allows for communication and attachment)
prenatal timeline for somatosensory system
7 weeks: fetus responds to touch around mouth
12 weeks: muscle spindles formed
16 weeks: golgi tendon organs formed
17 weeks: cutaneous sensation spreads to entire body
somatosensory system (infancy and childhood part one)
- all sensory systems are ready to function at birth (not matured)
- peripheral nervous system is completely myelinated
- complete structural maturation of sensory pathways occurs throughout childhood
- increased nerve conduction velocity
- redistribution of axon branching
- increased synaptic efficiency
somatosensory system (infancy and childhood part two)
- touch
- used by infant to locate food (e.g. rooting reflex)
- crucial role in parent-infant attachment, sociability, and cognitive development
- further structural and functional changes occur as infant and child interact with the world
infancy and childhood timeline for somatosensory system
12-16 months: specific touch localization
5 years: identify objects by touch
7 years: two-point discrimination
somatosensory system (infancy and childhood part three)
- proprioception
- used very early after birth
- execution of purposeful movements such as imitation, reaching, and locomotion
- ability to achieve and maintain upright postures
- muscle spindles mature as early as 3 years old
- proprioceptive acuity for movements improves between age 5-12
- allows for beginning mastery of skills such as hopping, dancing, and gymnastics
- integration of sensation and movement occurs during childhood and continues to develop through adolescence
- used very early after birth
somatosensory system (adolescence)
- tactile and proprioceptive senses are further refined
- maturation and integration of somatosensory system processing guide motor abilities and skill refinement
- sensory system is keenest during late adolescence into early adulthood
somatosensory system (adulthood)
- sensory function begins to decline in adulthood
- sensory receptor functions decline in middle age
- peripheral and central changes are small and gradual (do not always correlate with decline in function)
- skin becomes dry and less elastic —> compromised precision of cutaneous receptors
reaction time peaks in ________, then slows by ______ during middle adulthood
mid-20’s, 20%
somatosensory system (aging part one)
- gradual decline in sensory functioning
- decrease in number of sensory neurons
- decline in functioning of remaining sensory neurons
- structural and physiological changes within CNS
- impact on tactile system
- skin receptors decrease in number and undergo structural changes
- decrease in number of receptors —> decline in fine touch, pressure, and vibration sense
- impact on proprioceptive system
- atrophy of muscle spindles, joint receptors, and GTO’s —> decreasing feedback that CNS normally receives during movement
loss of up to ______ of sensory fibers innervating peripheral receptors leads to _________ ___________
30%, peripheral neuropathy
_________ changes affect the ability of joint receptors to detect _______ _______
arthritic, joint motion
somatosensory system (aging part two)
- redundancy of sensory information is decreased by age-related changes —> older adults are forced to compensate more
- functional consequences
- postural instability
- exaggerated body sway
- balance problems
- gait disturbances
- diminished fine motor coordination
- tendency to drop things held in hands
- difficulty recognizing body or limb positions in space
what is the dominant sensory modality in humans?
- visual system
- vision provides individuals information about
- the external world
- identification of external objects and determination of their movement
- where the body is in space, relationship of one’s body parts, and motion of one’s body
- vision provides individuals information about
vision is vital in control of ________, _________, _______, and ______ ________
posture, locomotion, balance, hand function
visual system anatomy overview
- peripheral anatomy
- structures and receptors in the eyeball
- 6 extraocular muscles
- central anatomy
- optic nerve
-carries nerve impulses - optic chiasm
- optic tract
- optic radiations
- occipital cortex
- visual cortex
- optic nerve
visual system eye movements
- head position and head control are important elements leading to visual function
- 4 types of eye movements are controlled by 6 extraocular muscles
saccades
quick, simultaneous movement of both eyes in the same direction
slow pursuit or tracking
- slow, smooth eye movements
- allow the eyes to closely follow moving object
vestibulo-ocular reflex (VOR)
- reflex eye movement that stabilizes images on retina
- produces eye movement in opposite direction to head movement
vergence
- simultaneous movement of both eyes in opposite direction
- convergence: eyes rotate towards each other
- divergence: eyes rotate away from each other
visual system (prenatal)
- derived from thalamus in diencephalon
- most peripheral structure develops into the eyeball
- 4th week: eye forms
- 13th week: myelinated begins
- once formed, visual system extends to occipital poles and forms horizontal axis of brain
- neurons in the occipital cortex are organized into their adult layers during 2nd half of gestation and ready to receive input by birth
- 6 months of gestation: reflexive eye blinking
visual system (newborns)
- central visual pathways develop postnatally
- complete maturation of sensory pathways occur after birth
- visual development
- visual acuity is 20/800
- initially see in black and white
- sustained ocular fixation on an object observed at birth
- pattern preference, especially for a human face
for newborns, the best distance for fixation is _______ inches away from eyes
7 to 9
visual system (infancy and childhood part one)
2 months
- see 2 colors (red and yellow)
- track vertically, horizontally, and in circular path
3 months
- preference for a colored object
- perception of form
4 months
- full color vision
- binocular vision matures between 3-5 months; adult-like binocular vision occurs by 2 years old
12 months
- adult levels of visual acuity achieved (20/20)
visual system (infancy and childhood part two)
- postural control promotes visual interest
- head control facilities visual fixation on objects
- postural adjustments allow child to maintain a position in space to visually explore environment
- greatest requirement for visual feedback during first 3 months after child begins sitting and standing
- visual perception becomes increasingly more accurate during preschool years
children between ______ years old are highly dependent on visual feedback for upright postural control and balance
4 to 6
visual system (adolescence)
- visual system matures and becomes sophisticated
- eye-hand coordination and perception-action coupling
- smooth tracking of small objects in activities such as baseball, pinball, and computer games
- age 11: perceptual judgements regarding size of objects
- age 12: adult levels of depth perception achieved
visual system (adulthood)
- changes in visual acuity
- increases in 20s and 30s and remains stable during 40s and 50s
- most rapid decline occurs between 60-80 years old
- age related changes
- cataracts begin to form in individuals over 30
- after age 40, decline in ability to quickly adapt from light to dark environments
at what age does presbyopia develop?
age 45
visual system (older adults)
- decrease in visual acuity
- increased visual threshold with older age —> more light required to see; decreased ability to adapt from dark to light environments
- field of vision diminishes —> loss of depth perception
- contrast sensitivity decreases between 65 to 75
- slowed peripheral and central processing impairs postural control, balance, safety, and independence
cataract formation in _____ of adults over 65
60%
macular degeneration in ____ of adults over 75
28%
vestibular system
function
- provides information regarding position of head in space
- detects sudden changes in direction of movement of head
- linear (otolith organs) and rotational (semicircular canals) accelerations
- vestibular inputs integrate visual and proprioceptive information to coordinate motor responses
- assists with eye stabilization and static and dynamic postural stability during standing and walking
vestibular system (prenatal)
- vestibular structures begin as a thickening of the ectoderm within primitive ear in the 4th week of gestation
- 10 weeks: semicircular canals, utricle, and saccule completely formed
- as fetus moves in utero, vestibular apparatus provides information about that movement
- fetus show a generalized body response to changes in body position, including ability to right the head
vestibular system (infancy and childhood)
- vestibular system completely myelinated at birth
- movement behavior developed by movement experience and acquiring postural control against gravity
- leads to development of trunk righting and equilibrium reactions
- rocking and spinning contribute to maturation of vestibular system
- movement behavior developed by movement experience and acquiring postural control against gravity
- develop ability to relate eye movements to head movements
- increase vestibular sensitivity from birth to a peak between 6 and 12 months of age; gradually decline from 2.5 years to puberty
normal vestibular ocular reflex present by ____ months of age
2 months
vestibular system (adolescence)
- full maturity of vestibular system achieved between 10 and 14 yrs of age
- contributes to healthy body scheme and gravitational security
- vestibular, visual, and somatosensory systems coordinate to control balance
- 9 to 12 yrs: gains in static balance
- 12 yrs: gains in dynamic balance
- sports and dancing contribute to further maturation and refinement
vestibular system (adulthood)
- age relegated changes: begin at 40s
- decreased number of sensory cells and nerve fibers in the peripheral nervous system
- neural changes possible in the vestibular nerve
vestibular system (older adults)
- vestibular system shows a decline in function with aging
- common issues for over 50: dizziness and vertigo
- 40% reduction in hair cells and 36% reduction in peripheral nerve fibers in adults over 70
- deterioration in central vestibular integrative functions —> impaired balance
- increased thresholds of excitation of vestibular nuclei
- vestibular system becomes unreliable when visual and proprioceptive input conflicts
somatosensory, visual, and vestibular systems develop concurrently to allow growth in ________, ________, and _______
balance, motor coordination, upright postural control
