Physiology 2130 Lecture Notes - Lecture 7: Lamellar Corpuscle, Postcentral Gyrus, Spinothalamic Tract

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Module #7- Sensory Systems
Objectives
Define a sensory receptor and its adequate stimulus
List 4 characteristics of generator potentials
List receptors responsible for touch, vibration, temperature, pain, and
proprioception
Define receptive field of a neuron. Name the two major ascending sensory
pathways and describe their anatomy and the information they carry.
List the somatotopic organization on the postcentral gyrus, going from medial to
lateral on the cortex
Draw and label a picture of the visual system and the eye
List the cell types in retina and draw a diagram of their anatomical arrangement
List the functional characteristics of the rod and cone systems
Draw a flow diagram of the sequence of steps in the retina by which light is
transduced to AP
List 4 types of eye movements, describe when they occur, and describe their
overall function
Draw a simple diagram of the auditory system
List three ways in which the outer and middle ear act to transmit pressure waves
from air to fluid
Describe how different frequencies of sound are transduced into AP
Draw a simple diagram of a single semicircular canal with hair cells and cupula
and utricle and saccule with otoliths
List major functions of the vestibular system
Name the movement detected by the semicircular canal receptors and the two
detected by otolith organs
Describe how angular motion of the head is transduced into AP
Changes to the sensory system
Important to maintain homeostasis because the body needs to detect changes in
the external environment so it can react properly
List of sensory systems humans have:
- Somatosensory (touch) system
- Visual system
- Auditory and vestibular system
- Olfactory system (smell)
- Gustatory (taste) system
Focus on how events in the outside world are detected and converted to AP,
travel to the brain and perceived
Transduction of environmental information
Is how information from external environment is turned into language the brain
understands (AP)
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Environmental stimuli (energy) like heat, light, touch, or sound must be detected
by sensory receptors and the information must be converted to AP
Environmental Stimuli
Environmental stimuli come in different forms and require different receptors to
detect the stimulus and convert it into AP
1) Mechanical stimulus (e.g. vibration of skin, touching): stretches sensory
receptors in the skin and open ion channels, causing depolarization of the
sensory neuron and producing AP
2) Chemical stimulus (e.g. sour taste, odor): binds with a receptor, causing
depolarization and then an AP
3) Light energy is absorbed by photoreceptors of the eye (rods and cones in
retina) and eventually produces AP
4) Gravity and motion: detected by hair cells in the vestibular system, converting
it from environmental stimulus to AP
Adequate Stimulus for the receptor
Some receptors are able to detect >1 type of stimulus
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Adequate stimulus- particular form of environmental stimulus to which the
sensory receptor is most sensitive to
- Example: adequate stimulus for rod and cone cells in retina is light; they also
respond to pressure but not optimally
Generator potential/Receptor Potential
Steps:
1) Sensory receptor is stimulated by an environmental stimulus, inducing ion
permeability change and leading to local depolarization (called generator
potential)
2) The receptor does not contain voltage-gated ion channels therefore it must
spread to an area on sensory neuron that do contain it- the first node of Ranvier
on the axon
3) The action potential is then generated and propagated along the axon and into
the spinal cord
4) In receptors with no axons (e.g. hair cells in inner ear), the depolarization has to
spread to the synapse to result in release of a neurotransmitter
EPSP/IPSP vs. Generator Potentials: Similarities
1. Generally depolarizing but can be hyperpolarizing
2. Caused by an increase in ion permeability to sodium ions in depolarization or
potassium in case of hyperpolarizing stimulus
3. Local and do not propagate down the neuron like AP but spreads like EPSP, is a
graded potential (diminishes with time and space)
4. Proportional to the strength of the stimulus; stronger stimulus causes larger
receptor potential and more likely to fire AP
Receptor Potential and Neural Coding
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