Download Biology 212: January 30, 2002

Biology 212: January 26, 2004
Sensory systems
I.
Introduction to sensory processes
A. Key concepts
1. Transduction
2. Amplification
3. Transmission
4. Integration
B. Receptor types: categorized by types of energy they transduce
1. Mechanoreceptors
2. Thermoreceptors (type of mechanoreceptor?)
3. Chemoreceptors
4. Electromagnetic receptors
II. Vision/human eye
A. Anatomy of the eye [Fig. 49.9]
1. Three major tissue layers of the eye
a. Sclera
b. Choroid
c. Retina
2. Lens/ciliary body (muscular)
a. Anatomy
b. Focusing [Fig. 49.10]
 Near vision.
 Distance vision
3. “Humors” of the eye
a. Aqueous humor
b. Vitreous humor
4. Review: Pathway of light from outside eye to the retina
B. The functioning of the retina
1. Introduction: basic structures
2. Transduction in rods (simplified!) [Figs 49.11, 49.12, 49.13, 49.14]
a. Location/basic structure of rhodopsin in rods
b. Effect of light on retinal/rhodopsin molecule
c. Signal transduction pathway (briefly!)
d. Membrane permeability change membrane potential change (know the
specifics here…)
e. Effects on neurotransmitter release from rod to bipolar cell
3. Integration of visual signals is quite complex; begins at retina [Fig. 49.15]
a. Vertical pathways (direct)
b. Lateral pathways
C. Pathway of visual input after transduction [Fig. 49.16]
III. Hearing
A. Overview
B. Structure of ear/function of parts [Fig. 49.17]
1. External ear
2. Tympanic membrane
3. Earbones (in middle ear): malleus, incus and stapes
4. Cochlea [Fig. 49.18]
a. Unwound version showing orientation of canals and structures
b. Organ of Corti
 Basilar membrane: focus on tonotopic organization
 Hair cells
 Tectorial membrane
 Specifics of transduction
C. Putting it all together (reception to transduction)
1. Pathway of sound/pressure wave until transduction
2. Pitch vs. amplitude (loudness)
3. Nerve pathway: Auditory nerve (crosses midline) thalamusauditory cortex
(temporal lobe)
Study questions
1. Explain what is meant by transduction, amplification, transmission and integration as it
relates to sensory systems. Describe where they occur (as specifically as possible) for the
auditory and visual systems.
2. List and give examples of the major types of receptors (i.e. mechanoreceptors, etc...)
3. Be able to identify the major structures of the eye and describe their functions. Also, for a
slightly different approach to this question, describe the path of light through the eye, from
the cornea to the optic nerve, being sure to indicate the function of each structure, as well as
of closely associated structures (i.e. if you mention the pupil you better also mention the iris)!
4. Explain how the eye adjusts between near and far vision, being sure to describe the role of all
major structures involved.
5. Where does transduction occur in the eye (general location and specific cell types)?
6. Describe the basics of transduction as it occurs in rod cells. [Note: You need not explain
every step of the signal transduction pathway, but you should be able to describe what
initiates the pathway, and describe final step of that pathway and its effects on ion
movement, membrane potential and neurotransmitter release.]
7. What is the blind spot? What is the fovea?
8. Describe the visual pathway from the optic nerve to the primary visual cortex. Be sure to
indicate where crossing occurs.
9. What is the function of the external ear? Is the external ear absolutely necessary for hearing
in mammals?
10. What is the function of the tympanic membrane?
11. Name the earbones and their location. What are the two functions of these bones?
12. How is sound transmitted from the middle ear to the inner ear?
13. What structure within the cochlea responds differently to different pitches (frequencies) of
sound? How is this structure organized?
14. Where are the hair cells located? Name the two membranes between which they are
basically “sandwiched”. How are they stimulated? What occurs when they are stimulated?
Answer in terms of ions and permeability change.
15. Putting it all together, the pathway of sound in the ear: Follow the vibrational energy of a
sound wave as it travels from the external ear until it is transduced into an action potential.
Be sure you name all relevant structures, and be clear as to the function/movement of each of
those parts (or of fluid within them).
16. How is information about loudness (amplitude) coded in the auditory neurons?
17. Describe the auditory pathway from the auditory nerve to the auditory cortex. Where does
crossing occur?
NOTE: When the hair cell bends, K+ enters the cell because K+ is higher in the fluid of the
cochlear duct than in the hair cell. Be sure you realize this is an unusual situation. Remember
that in neurons, K+ is higher inside the cell than outside of it, and it is Na+ that is high outside
and low inside!