Nerves and Stimuli - Frostburg State UniversityNerves and Stimuli Bundles of nerve cells called...
Transcript of Nerves and Stimuli - Frostburg State UniversityNerves and Stimuli Bundles of nerve cells called...
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Nerves and Stimuli Bundles of nerve cells called
neurons Nerves receive and transmit signals Stimuli signal changes in the
environment Types of stimuli:
Chemical Odorants and tastants Particles that are smelled or tasted
Thermal Changes in temperature HotCold or ColdHot
Mechanical stimuli Touch Pain Vibration Movement
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Nervous Systems Central Nervous System
(CNS) Brain and Spinal Cord
Stimuli received from and sent to the PNS
Peripheral Nervous System (PNS) Nerves throughout body
Stimuli received from the environment and the CNS
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Types of Neurons Interneurons-
Found in CNS
Responsible for processing and responding to stimuli
Sensory neurons- Found in PNS
Pick up and translate stimuli
Motor neurons- Found in PNS
Carry signals that cause movement
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Neuron Structure Dendrites- Receive
stimuli
Cell body- Houses the nucleus
Axon- Relays signals to the next neuron
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Sensory Receptors and Stimuli Transport Found on the end of
dendrites
Detect and transport stimuli to CNS
Stimuli travels through the neuron
Stimuli are passed from one neuron to the next
Stimuli are transported to the CNS
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Touch Receptors Allow us to detect
mechanical stimuli
Types of Touch Receptors Merkel’s Discs
Meissner’s Corpuscles
Krause’s End Bulbs
Ruffini Endings
Pacinian Corpuscles
Hair follicle receptors
Free nerve endings
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Somatosensory Cortex Headband shaped region of the
brain Stimuli from touch receptors
processed Neurologist mapped out the cortex
Electrically stimulating spots on cortex
Causing illusions of stimulation
Area in the cortex is proportional to number of touch receptors Lips have a large area on the cortex Trunk of body has very small area
on the cortex
Motor neurons carry the response away from the brain
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Sensory Fields Area in which any one
neuron detects stimuli
Dendrite branches extend across this area
Dendrite branches have sensory receptor that detects stimuli in its sensory field
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Density and Sensory Field Size Small, dense sensory
fields
More densely packed neurons
More sensitive to stimuli
Large, less dense sensory fields
Less densely packed neurons
Less sensitive to stimuli
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Measuring Sensory Fields Two-Point Touch
Discrimination Tests
Medical test used to determine extent of nerve damage
Measures distance between two sensory fields
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Two-Point Discrimination Test Caliper with two blunt needles
Measured distance between needles
Needles placed simultaneously against skin
Subject may feel 1 or 2 points Feels 1 point- activated 1
sensory field Feels 2 points- activated 2
sensory fields
Two-Point Discrimination Threshold is the minimum distance between two sensory fields
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Preliminary Findings Two-Point Touch Discrimination Lab
Test regions included fingers, palms, forearm, neck and shins
Smaller two-point threshold sizes on fingertips
Smaller, more dense sensory fields on fingertips
Findings match the Somatosensory Cortex map developed by neurologist
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Research on Hands and Stimuli Sathiamoorthy et al. (1994)
Fingertips to push machine buttons
Visual and auditory stimuli reaction time measured
Left handed women responded faster to auditory stimuli
Since left handed females responded faster to auditory stimuli, how does handedness relate to other stimuli such as touch?
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Handedness Preferred use of left or right hand
Dominant hand is the preferred hand
Often the hand used to write
10% of population is left handed
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Dominant Hands Preferred use
Are faster, stronger, and more precise for manual tasks
Writing
Cutting with scissors
Screwing lids on a jar
Hammering nails
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Purpose Determine if sensory field sizes differ on dominant
and non-dominant hands.
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Hypotheses Null: Sensory field sizes are the same on both
dominant and non-dominant hands
Alternate: Sensory field sizes will differ between dominant and non-dominant hands
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Study Site and Subjects Frostburg State University
July 1, 2015
Two test groups
Left Handed- 9 individuals
Right Handed- 9 individuals
Males and females in each group
Ages ranged from 13-50 years old
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Calipers Plastic Calipers
(General/National No. N-141 me)
Measured in millimeters
Modified- hot glued metal blunt sewing needles to caliper prongs
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Using the Calipers Needles glued in slightly
different places
Rulers were used to measure distance between needle points
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Finding Two-Point Thresholds Calipers were opened and
needles separate Needles placed simultaneously
against skin Subject would state if they felt 1
or 2 points 1-increase distance between
needles 2- slightly decrease distance
between needles
Measured distance with a ruler Sample multiple locations in a
region Recorded the two-point
threshold
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Caliper Sample Sites Sampled Left and Right
arms of each subject
Found minimum two-point threshold in five regions
Tip of index finger
Tip of thumb
Palm
Forearm
Upper arm
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Data Analysis Microsoft Excel
Calculate averages for both groups
Average Two-Point Threshold
95% Confidence Intervals
For the five regions
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Right Handed Group Smaller thresholds on left
thumb, forearm, and upper arm
Smaller thresholds on right index fingers
Same size thresholds on palms
All 95% confidence intervals overlapped
Averages between left and right hands are not different
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
Index Thumb Palm Forearm UpperArm
Ave
rage
2-P
oin
t D
iscr
imin
atio
n T
hre
sho
ld (
mm
)
Arm Regions
Right Handed Group
Left
Right
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Left Handed Group All 5 regions had smaller
thresholds on left hands
All 95% confidence intervals overlapped
Averages between the left and right hand are not different
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
Index Thumb Palm Forearm UpperArm
Ave
rage
2-P
oin
t D
iscr
imin
atio
n T
hre
sho
ld (
mm
)
Arm Regions
Left Handed Group
Left
Right
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Left and Right Handed Groups Both had overlapping 95% confidence intervals for all regions with no difference between dominant and non dominant hands
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Hypotheses Accept Null: Sensory field sizes are the same on both
dominant and non-dominant hands
Reject Alternate: Sensory field sizes will differ between dominant and non-dominant hands
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Purpose Revisited Do sensory field sizes differ on dominant and non-dominant hands?
Sensory field sizes did not differ between dominant and non-dominant hands
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Right Handed Group All averages were very
similar
Sensory field sizes, density and sensitivity were not different between left and right hands
Both hands may have similar neuron density and space on the somatosensory cortex
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
Index Thumb Palm Forearm UpperArm
Ave
rage
2-P
oin
t D
iscr
imin
atio
n T
hre
sho
ld (
mm
)
Arm Regions
Right Handed Group
Left
Right
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Left Handed Group Larger difference between
averages, but overlapping CIs.
Sensory field sizes, density and sensitivity were not different between left and right hands
Both hands may have similar neuron density and space on the somatosensory cortex
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Left Handed Group Trend-left hands
consistently had smaller thresholds on all five regions
Implications-difference may exist if we could improve upon limitations of our study
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Sample Size Limitations and Improvements Low sample size in groups, N=9
Number too low for statistical analysis
Number of subjects in each group should be increased
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Gender Limitations and Improvements Gender of subjects
varied
Only 2 left handed females
Number of left handed females should be increased
Comparisons can be made between genders
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Equipment Limitations and Improvements Calipers were imprecise
due to being homemade
Medical grade equipment is very expensive
Future studies could use medical grade equipment
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Sampling Method Limitations and Improvements Sampling regions lacked
consistency
Lack of practice and experience
Regions for sampling should be more specific
Researchers should have more training or checks to see if they are measuring the same
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Test Environment Limitation and Improvements Location of testing
varied from lab, hallway, and cafeteria
Cold room temperatures may impact results
Select one location with comfortable temperature for testing
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New Questions What are the normal size ranges for sensory fields in
various body locations?
Do sensory field sizes differ between genders?
Does temperature impact two-point touch discrimination thresholds?
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Special Thanks RMSC staff and directors
Volunteer test subjects
Frostburg State University
Biology Department
Office of Information Technology
Parents, teachers, and guests
RMSC seniors and fellow students
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Questions