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1. PHYSIOLOGY
Sensory neuron function
Dr. Izza javaid
Ms Diagnostics Ultrasound
lecturer

2. Objectives
1.Sensory Receptors, Neuronal Circuits for Processing
Information
2.Somatic Sensations: General Organization, the
Tactile and Position Pain and Thermal Sensations

4. Afferent division of the nervous
System
 Receptors
 Sensory neurons
 Sensory pathways

13. Receptors adaptation
 The duration of a stimulus is coded by duration of action
potentials.
 A longer stimulus generates longer series of APs.
 If a stimulus persists, some receptors adapt or stop responding
 There are 2 classes of receptors according to how they adapt:
 Tonic receptors – slowly adapting – they fire rapidly when first
activated, then they slow and maintain firing as long as the
stimulus is present (baroreceptors, proprioceptors)
 Phasic receptors – rapidly adapting receptors – rapidly firing
when first activated but stop firing if the strength of stimulus
remains constant
 This type of reaction allows the body to ignore information
that was evaluated and found not to be a threat to
homeostasis (smell)

14. Sensory receptors properties
• Sensory transduction convert stimulus energy
into nerve energy (action potential)
• Receptor potential (excitable tissue)
• Adaptation (high and low ) conscious
sensation declines with continued stimulation

16. Processing at the Receptor Level
 The receptor must have specificity for the stimulus energy
 The receptor’s receptive field must be stimulated
 The stimulus need to be converted to a nerve impulse
 Receptors have different levels of adaptation
 Information is encoded in the frequency of the stimuli –
the greater the frequency, the stronger is the stimulus.

17. The somatic sensory system
 Sensory stimuli that reach the conscious level of
perception
 Specialized cells that monitor specific conditions in the
body or external environment
 General Senses:
 Temp, pain, touch, pressure, vibration, proprioception
 Simple receptors located anywhere on body
 Special Senses:
 Are located in sense organs such as the eye or ear
 Olfaction, vision, gustation, hearing, equilibrium
 Complex receptors located in specialized sense organs

18. 1
2
3
Receptor level
(sensory reception
and transmission
to CNS)
Circuit level
(processing in
ascending pathways)
Spinal
cord
Cerebellum
Reticular
formation
Pons
Muscle
spindle
Joint
kinesthetic
receptor
Free nerve
endings (pain,
cold, warmth)
Medulla
Perceptual level (processing in
cortical sensory centers)
Motor
cortex
Somatosensory
cortex
Thalamus
Processing of the sensory information

19. Association Motor
Sensory
Sensory area for
impulses from
eyes

20. cerebrum/cerebral hemispheres
•Sensory areas of the cerebral hemispheres receive impulses from sense organs and
transmit them to the association areas
•The association areas of the cerebral hemispheres receive impulses - interpret them
in the light of similar past experiences and transmit impulses to motor areas
•The motor areas transmit impulses to the effectors
•The size of the sensory and motor areas is related to the number of receptors in that
area
•The left and right cerebral hemispheres control the opposite sides of the body

21. Mapping of the sensory & motor
areas to the body
shoulder
w
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a
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f
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g
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r
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eye
face
lips
jaw
tongue
s
w
a
l
l
o
w
i
n
g
c
h
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w
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g
legs
toes
n
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c
k
e
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b
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t
r
u
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k
ankle
hip
Motor
Cortex
shoulder
w
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s
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f
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r
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a
r
m
h
a
n
d
f
i
n
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s
t
h
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eye
face
nose
lips
gums
jaw
tongue
p
h
a
r
y
n
x
a
b
d
o
m
e
n
legs
toes
genitalia
e
l
b
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w
t
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foot
hip
Sensory
Cortex