1. Establish how sensory neurons interpret specific
2. How is this sensory information processed
in the PNS and CNS?
3. Discuss some of the conditions that result from malfunction of sensory
A. Primary functions of the Peripheral Nervous System (PNS)
1. Sensory input
2. Motor output
B. Types of sensory neurons
C. General characteristics of sensory neurons
1. Graded response results in an action potential
2. Receptor and Generator Potentials
a. Dendritic action potentials
3. Tonic verses Phasic firing
4. Lateral inhibition
5. Receptive fields
D. Introduction to sensory pathways to brain
1. Sensory systems often map to specific cortical locations
A. Nociceptor structure and function
1. Similarities between nociceptors and thermoreceptors
B. Fast and slow pain
1. Myelinated and unmyelinated fibers
C. Pain pathway projections in the CNS
D. The brain's analgesic system
1. Periaqueductal gray, raphe, and pain suppression
a. Role of endogenous opioids, such as enkephalin
2. Referred pain
III. TASTE AND SMELL
A. How are taste and smell related?
1. Summary of functional similarities
2. Functional differences
1. How a chemical stimulus activates its taste receptor?
a. Signal transduction for taste
1) Second messengers (e.g., Ca++) have a central role
2. Integration of taste
1. Functional organization of the olfactory epithelium
2. Odor is a "lock and key" association
3. Integration of olfaction
IV. HEARING AND BALANCE
A. Introduction to the ear
1. Relationship between hearing and balance
2. Ear is divided into outer, middle, and inner ear
B. How does the ear hear?
1. Role of hair cells in basilar membrane
a. Importance of K+ influx
2. Hearing frequency and loudness
a. A tonotopic map exists in the auditory cortex
3. Summary (Animation on how we hear)
C. Balance and sensing movement and position
1. Roles of semicircular canals, cupula, kinocilium
2. Motion of the head and body
3. Position of the head
a. Role of ototliths in the utricle and saccule
A. Structure/Function of the eye
a. Refraction and accomodation by the lens
b. Nearsightedness and farsightedness
a. Structure and function of rods and cones
1) color vision
b. Fovea is packed with cones
1) Dysfunction: Macular degeneration
B. Neuronal organization and integration in retina
a. Rods and cones, bipolar, ganglion cells, etc.
b. Function of each
1. Phototransduction: Light activates rhodopsin (Animation)
a. Signal transduction mechanism
b. Hyperpolarization of photoreceptor
c. Light disinhibits bipolar neurons
d. Ganglion cell fires an action potential
2. Receptive fields of ganglion cells (Animation on visual processing)
3. Integration beyond the retina
a. Projection to lateral geniculate nucleus (LGN) and visual cortex
Review of sensory input and motor output
Please read Chapter 11 and the first part of Chapter 12 for the next lecture.
I will start to lecture on muscle physiology next Thursday.
STUDY QUESTIONS ON SENSORY PHYSIOLOGY (CHAPTER 10)
BASIC FACTS AND TERMS
Compare the slow and fast pain pathways with respect to 1) characteristics
of the sensory neurons (type of fiber, etc.), 2) the ascending pathways
to the brain, and 3) analgesic modulation of the pain pathways by
- You place the point of a pencil on the back of your hand. Trace the
path that the sensory input takes from your hand to the cerebral cortex.
In correct order list all of the structures that the signal passes through.
List all of the synapses that occur en route.
- What is referred pain? Explain the neuronal basis for referred pain.
- Define and give the physiological significance (how or why it is
important) for the following terms:
- Organ of Corti
- Olfactory glomeruli
- Semicircular canals
- Oval and Round windows
- Periaqueductal gray (PAG)
- Basilar membrane of the cochlea
- Phasic receptor firing
- Tonic receptor firing
- Receptive field (of a ganglion cell)
- List six neuronal cell types which make up the retina. Where is each
located? How does each function?
- Using a flow chart format, outline the correct order of cellular
events associated with light transduction (=signal transduction
pathway) in a rod.
- What is the optical basis for nearsightedness (myopia) and farsightedness
(hyperopia)? How do glasses adjust these conditions? (See Fig. 10-33)?
- What roles do the bones of the middle ear play in hearing? --roles
of the oval and round windows? How does the cochlea sense differences
in the 1) frequency and 2) loudness of a sound? Be sure to look at this
on how the ear works, especially how sound activates the hair cells
in the Organ of Corti. You are responsible for knowing the information
presented in this animation.
- In what ways are receptor potentials similar to Excitatory Post-synaptic
Potentials (EPSPs)? Explain.
- What is the receptive field of a ganglion cell? What are On-center
Cells and Off-center Cells, and how do they function in vision? (see
Text.) See this very good animation
on how these cells work. You are responsible for knowning the information
presented in this animation.
- Diagram the visual paths from light input (rods and cones) to the
primary visual cortex. What happens to this visual input at each step?
How is light information coded at each step? See this animation
for more details.
- You are looking at a image that is far away. Where and how is the
image altered as it passes through the eye to the retina? What change
occurs in the eye that let you focus on a very close image (Read about
accomodation in Silverthorn)? What is the default state for the lens?
- When you first enter a dark room you can not see well, but with time
your vision becomes better. What is the physiological basis for light
adaptation? See Silverthorn.
- What is the physiological basis for the following conditions?
- night blindness
- color blindness
- Transduction of a stimulus usually causes depolarization of a sensory
receptor. What is the cellular basis for depolarization of a sensory
receptor? One exception to this rule is the photoreceptor which is hyperpolarized
in the presence of light. Explain how this hyperpolarization is eventually
realized as an action potential leaving the retina (See Fig. 10-39).
- Explain pre-synaptic inhibition. Give an example and explain how
- How does the "lock and key" relationship between odorants and sensory
receptors in the olfactory epithelium explain the multitude of complex
smells that we can sense? Explain.
- What are the cellular mechanisms for transduction of taste stimuli
(salt, sweet, bitter, and sour)? You do not have to memorize these mechanisms,
but look for generalizations, such as 1) how Ca++ is involved in signal
transduction and neurotransmitter release, 2) how membrane depolarization
is accomplished (Note that there is more than one way), and 3) how these
mechanisms compare with what was covered in Figures 6-11, 6-12, and
- How is the internal structure of a rod and cone related to its function?
Then, contrast rods and cones with respect to: 1) distribution in the
retina, 2) sensitivity to light, 3) adaptation to light, and 4) visual
acuity. At what point on the retina is vision the sharpest? Explain
why this is case.
- What is the neuronal basis for our ability to perceive subtle differences
in the color spectrum?
- How are mechanoreceptors involved in 1) hearing and 2) balance/head
position? Draw each of these receptors. How are they alike in structure
- Which part of the cerebral cortex integrates 1) visual input, 2)
auditory input, 3) gustatory input, 4) olfactory input, 5) somatosensory
input, and 6) speech production and speech understanding. Which of these
cortical areas have "point to point maps" for sensory input? Why have
such "maps" in the cerebral cortex? Which sensory system apparently
lacks a "point to point" map?
- Afferent neurons often modulate their firing pattern to code specific
sensory informaton. Give two different examples of how the nervous system
encodes information about the intensity of a sensory input. What
type of information does tonic firing convey? --phasic firing? Describe
sensory adaptation and explain how it is used as a method of information
coding. Describe lateral inhibition and explain how it is used as a
method of information coding.
- How does the vestibular apparatus sense 1) initiation of movement
in a forward or backward direction and 2) turning the head?
REASONING AND PROBLEM SOLVING
- Pain results from tissue destruction. What chemical stimuli at the
tissue level excite pain receptors? Aspirin is an analgesic. Given your
knowledge of how the pain pathways work, give three different avenues
by which aspirin might inhibit pain. Click
here for the correct answer.
- Ganglion cells consist of either ON-CENTER CELLS (=firing increases)
or OFF-CENTER CELLS (=firing decreases) when white light appears
in the "center" of the receptive field. When white light appears in
the "surround area" (rather that center) of the receptive field, the
opposite response occurs for both the ON (=decreases) and OFF cells
(=increases). Can you expand on this general principle to explain how
color-senstive ganglion cells might code for color vision?
- A person training for a marathon is often said to be "addicted" to
running. Further, not running often leads to "withdrawal-like" symptoms.
Given your knowledge of how endogenous opioids (e.g., enkephalin) act
in the CNS, what might be happening interally that could explain these
- The endolymph, which surrounds both the the inner hair cells in the
inner ear and the cupula in the semicircular canals, is rich in K+,
rather than Na+. This difference in ionic concentration is unique to
these fluids. Given your general understanding of how ion flux leads
to depolarization, how might K+ current play a role in depolarization
of the inner hair cells and the cupula?
Last revised: February 7, 2008