BMS129 Lecture Notes - Lecture 10: Sensory Neuron, Referred Pain, Receptive Field
NERVOUS SYSTEM
Lecture 10 - Sensory receptors, taste and smell
Recommended readings
: Saladin, CH 16 pp 579-591
1. Define sensation & discuss the process of sensation
2. List the 4 kinds of information that sensory receptors transmit & describe how the
CNS encodes each one
3. Outline 3 ways in which receptors can be classified
4. List & identify the different types of somatosensory receptors
5. Differentiate between somatic pain, visceral pain & referred pain
6. Describe the receptors for taste & explain how they are stimulated
7. List the 5 primary taste sensation & state their location on tongue
8. Describe the projection pathways for taste
9. Describe the receptors for smell & explain how they are stimulated
10.Describe the projection pathways for smell
Define sensation & discuss the process of sensation
Sensation can be defined as the conscious or subconscious awareness of changes in
the external or internal environment
1. Stimulus must occur within the receptive field of the receptor
2. The sensory receptor transduces energy in a stimulus (e.g. mechanical, thermal,
chemical) into a graded/receptor potential (electrochemical energy)
3. If graded potential reaches threshold an action potential is triggered which
propagates to CNS via 1st order neurons
4. Integration of sensory input takes place in a particular region of the CNS via 2nd
& 3rd order neurons with conscious sensation perceived in cerebral cortex only.
List the 4 kinds of information that sensory receptors transmit & describe how
the CNS encodes each one
Information
CNS encoding
Modality
Type of stimulus encoded by labelled line code
Location
Sensory receptor receives input from its receptive field
Sensory projection - brain identifies site of stimulation
The area of the cortex dedicated to sensations from specific body
parts is proportional to the sensitivity of that body part
Intensity
1. Frequency of action potentials can increase or decrease
2. Number of nerve fibres stimulated rises with increases in
intensity
3. Which fibres are activated depends on weak or strong stimuli
as nerve fibres can differ in their sensitivity and hence the
threshold for which an action potential is generated
4. Firing rate of sensory receptor neuron or release rate of
transmitter from the sensory receptor cell to activate the second
order neuron
Duration
Changes in firing frequency over time
If the stimulus is prolonged then the firing of the neuron will get slower
over time
1. Phasic - burst of activity and quickly adapt
2. Tonic - adapt slowly, generates impulses continually
Outline 3 ways in which receptors can be classified
Classification
Examples
Modality
Chemo-, thermo-, mechano-, photo- receptors and
nociceptors
Origin of stimuli
1. Interoceptors - detect internal stimuli (from organs)
2. Proprioceptors - sense body position and movements
3. Exteroceptors - detect external stimuli
Distribution
1. General senses - widely distributed (somatic)
2. Special senses - limited to head, innervated by CNs
List & identify the different types of somatosensory receptors
Classified according to whether the dendrites are wrapped in CT or glial cells
(encapsulated nerve endings) or not (unencapsulated nerve endings)
Document Summary
Lecture 10 - sensory receptors, taste and smell. Recommended readings : saladin, ch 16 pp 579-591: define sensation & discuss the process of sensation, list the 4 kinds of information that sensory receptors transmit & describe how the. Define sensation & discuss the process of sensation. If graded potential reaches threshold an action potential is triggered which propagates to cns via 1st order neurons. Integration of sensory input takes place in a particular region of the cns via 2nd. & 3rd order neurons with conscious sensation perceived in cerebral cortex only. List the 4 kinds of information that sensory receptors transmit & describe how the cns encodes each one. Type of stimulus encoded by labelled line code. Sensory receptor receives input from its receptive field. Sensory projection - brain identifies site of stimulation. The area of the cortex dedicated to sensations from specific body parts is proportional to the sensitivity of that body part.
