BIOC32H3 Lecture Notes - Lecture 13: Withdrawal Reflex, Lateral Inhibition, Nociception
BIOC32
LECTURE 13
Sensory Physiology I
Processing of Sensory Stimuli
● Special senses (always conscious)
○ Vision
○ Hearing
○ Taste
○ Smell
○ Equilibrium (balance)
General Properties of Sensory Systems
1. Activated by a stimulus (physical energy)
2. Stimulus activates sensory receptor
● Converts stimulus to intracellular signal
● Signal transduction
● Changes in membrane potential (Vm) known
as generator or receptor potential (same as
graded potential)
3. If threshold is reached, conduction of action
potential to CNS
4. Integration of signal in the CNS
● somatosensory cortex (conscious)
● brain stem (unconscious)
Types of Sensory receptors: Classified by Structure
Types of Sensory Receptor: Classified by the
Stimulus that they are Most Sensitive To
●Chemoreceptors: respond to chemical
stimuli that bind to receptors e.g taste, smell,
O2, glucose, pH
●Mechanoreceptors: mechanical stress or
mechanical strain such as pressure
(baroreceptors), vibration, gravity, cell
stretch (osmoreceptors), acceleration
(proprioceptors), sound
●Thermoreceptors: temperature
●Photoreceptors: light
●Nociceptors: respond to painful stimuli
●Adequate stimulus: the form of energy to
which that receptor is most responsive
● Sensory receptors can respond to other
forms of energy if stimulus intensity is high
enough e.g photoreceptors respond to
pressure
BIOC32
LECTURE 13
1. Determination of Location of Stimulus
→ (Somatic and Vision sensory neurons have
receptive fields)
● Somatic and visual stimuli are activated by
stimuli that falls within physical area : the
receptive
field
● 1 receptive field may be associated with 1
secondary sensory neuron
● Receptive fields may overlap
○ Several primary neurons converge
onto one secondary neuron
● Convergence decreases ability to locate the
stimulus accurately
→ Two-Point Discrimination: Convergence
● Stimulation of 2 primary neurons
● Convergence onto 1 secondary neurons
● Receptive field is large – less sensitive
● OUTCOME: will seem like compass only
pricked one area on skin
● e.g arms, legs, back
→ Two-Point Discrimination: Small receptive Field
● Stimulation of 2 primary neurons
● 2 secondary neurons activated
● Receptive fields small: more sensitive
● OUTCOME: allows 2 separate pin to be
decoded as 2 separate touches
● e.g fingertips
Coding of Auditory Info Doesn’t Require receptive
Fields to Locate Stimulus
● Ear sensitive to different frequencies of
sound waves
● No receptive fields in ear
● Instead timing of stimulation used to
compute location
● Time difference taken for sound stimuli to
reach the 2 sides of auditory cortex is
registered and used to locate the sound
source
●OUTCOME: source is on left side of body
Document Summary
General properties of sensory systems: activated by a stimulus (physical energy, stimulus activates sensory receptor. Changes in membrane potential (vm) known as generator or receptor potential (same as graded potential) threshold is reached, conduction of action. 3. potential to cns: integration of signal in the cns somatosensory cortex (conscious) brain stem (unconscious) Adequate stimulus : the form of energy to which that receptor is most responsive. Sensory receptors can respond to other forms of energy if stimulus intensity is high enough e. g photoreceptors respond to pressure. Mechanoreceptors : mechanical stress or stimuli that bind to receptors e. g taste, smell, O 2 , glucose, ph mechanical strain such as pressure (baroreceptors), vibration, gravity, cell stretch (osmoreceptors), acceleration (proprioceptors), sound. Lecture 13: determination of location of stimulus. (somatic and vision sensory neurons have receptive fields) Somatic and visual stimuli are activated by stimuli that falls within physical area : the receptive field.
