Receptors have several key properties: 1. Specificity - Each sensory pathway is labeled to identify its origin and modality. 2. Strength of stimulus - Stronger stimuli activate more receptors, including those with lower thresholds. 3. Adaptation - Sensitivity decreases over long stimulation, like a hot shower feeling comfortable after feeling hot initially. Receptors adapt through sodium channel inactivation.

1. Properties of Receptors
Dr. Sara Sadiq
(MBBS, M.Phil)

2. Properties of Receptors
 Specificity
 Strength of stimulus
 Excitability
 Adaptation
 Neural coding of sensory information
 Sensory unit and receptive field

3. 1. Specificity
Labelled-line Principal
 Each nerve pathway from sensory cells to
the brain is labeled to identify its origin, and
the brain uses these labels to interpret what
modality the signal represents

4. 2. Effect of Strength of Stimulus
Increase strength of stimulus
 More receptors are stimulated
 Activates receptor with low threshold values

5. 3. Excitability
Receptor Potential
 Have short neurons that synapse with first
order sensory neurons.
 Causes an increase or decrease in
exocytosis from synaptic vesicles.

6. Stimulus to AP

7. Time
-
70
-
55
0
+3
5
Thresh
old
mV
Resting
potential
Action potential
More Na+
channels
open Na+
floods
into
neurone
Na+
voltage-
gated
channels
open

8. -70
-55
0
+35
Threshol
d
m
V
Time
Resting
potential
Action potential
Na+ channels close
and K+ channels
open, K+ floods out
of neurone
Resting potential

9. -70
-55
0
+35
Threshol
d
Time
mV
Resting potential Resting
potential
Action potential
Active pumping
of Na+ out and
K+ in during the
refractory period
Hyperpolarisation
of the membrane

10. 4. Adaptation
 A change in sensitivity (usually a decrease)
over a long stimulation.
 EX: A hot shower feels hot a first, then feels
comfortable.

11. Receptors Adaptation
 Rapidly Adapting Receptors
Associated with pressure, smell and touch;
adapt quickly.
 Slowly Adapting Receptors
Associated with pain, body position and
chemicals in the blood; adapt slowly.

12. Why receptors adapt???
 Inactivation of Na channels

13. Sensory Adaptation
1. Tonic Receptors
Produce constant rate of firing as long as stimulus
is applied
e.g: Pain, Proprioception, Chemoreceptor
2. Phasic Receptors
Burst of activity but quickly reduce firing rate
(adapt) if stimulus maintained
e,.g: Touch, Smell

14. 5. Neural coding of Sensory
Information
Receptors encode four elements of stimuli
 Modality
 Location
 Intensity
 Duration

15. 6. Sensory Unit & Receptive Field
 Sensory Unit
Single primary afferent nerve fiber including all
its peripheral branches
 Receptive Field
The area of the body whose sensory nerve
supply comes from one sensory unit