Download Nervous System III – Senses

Nervous System III - Senses
Anatomy and Physiology | Tutorial Notes
Nervous System III – Senses
LEARNING OBJECTIVES
After study of this chapter, the student should be able to:
1.
Differentiate between general senses and special senses
2.
Distinguish between Sensation and Perception
3.
Name five types of receptors and state the function of each
4.
Explain how receptors trigger sensory impulses
5.
Explain sensation and sensory adaptation
6.
Describe the differences among receptors associated with the senses of touch, pressure, temperature,
and pain.
7.
Describe how the sensation of pain is produced.
8.
Explain the importance of stretch receptors in muscles and tendons.
9.
Explain the relationship between the senses of smell and taste.
10.
Describe how the sensations of smell and taste are produced and interpreted.
11.
Name the parts of the ear and explain the function of each part.
12.
Distinguish between static and dynamic equilibrium
13.
Describe the roles of the accessory organs to the eye.
14.
Name the parts of the eye and explain the function of each part.
15.
Explain how the eye refracts light.
16.
Distinguish between rods and cones, and discuss their respective visual pigments.
17.
Explain how the brain perceives depth and distance
18.
Describe the visual nerve pathways.
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Nervous System III - Senses
TUTORIAL OUTLINE
I.
Introduction
A.
Receptors
1.
Detect stimuli from the external and internal environments
2.
May be the dendritic end of a neuron or a specialized cell or multicellular structures.
3.
Types of receptors
a. Chemoreceptors = Detects changes in chemicals
o
Smell, taste, blood pH, ect
b. Pain receptors “nociceptors” – responds to tissue damage
c. Thermoreceptors – respond to temperature changes
d. Mechanoreceptors – respond to physical deformation

Proprioceptors – sense position of limbs in space

Baroreceptors – detects changes in pressure (eg. Blood pressure)

Stretch receptors – detects stretching (eg lung expansion)
e. Photoreceptors – respond to light energy
B.
Divisions of Senses
1.
2.
C.
General Senses

Distributed throughout the body

Associated with skin, certain organs, and joints

Includes touch, pressure, temperature, pain, etc.
Special Senses

Contain specialized receptors

Confined to the head

Olfaction, Taste, Smell, Hearing, Equilibrium
Sensory Processing
1.
Sensation

The bottom-up process, by which our senses receive and relay outside stimuli to
the brain.

Sensation refers to the feeling that occurs when the brain becomes aware of the
incoming sensory information.

Example: Sensation occurs when action potentials make the brain aware of a
sensory event (such as pain)
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Nervous System III - Senses
2.
3.
4.
II.
Perception

The top-down way our brain organizes and interprets the sensory information and
puts it into context.

Example: Perception occurs when the brain interprets sensory impulses (realizing
that the pain is a result of stepping on a tack).
Projection

Process in which cerebral cortex interprets sensation as being derived from certain
pain receptors.

Brain projects the sensation back to apparent source.

Projection allows a person to pinpoint the region of stimulation.
Sensory Adaptation

Ability to ignore unimportant or continuous stimuli

Involves a decreased response to a particular stimulus from either:
o
Receptors – sensory adaptation
o
Along the CNS – central adaptation

Sensory impulses become less frequent with adaptation and may cease.

Stronger stimulus is then required to trigger impulses.

Adaptation best accomplished by olfactory receptors and thermoreceptors.

Pain receptors (nociceptors) adapt poorly or not at all.
General Senses
A.
Groups of General Receptors
1.
Exteroceptive senses – associated with body surface

2.
Interoreceptive senses – associated with visceral organs

3.
Touch, pressure, temperature, etc.
pH, Blood Pressure, Heart Rate, O2/CO2 concentrations, etc.
Proprioceptive senses – associated with position of limbs and tension of skeletal
muscles
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Nervous System III - Senses
Smell
Flavor: Smell + Taste
80% of flavor is attributed to smell
I.
Structures
a. Olfactory epithelium
i. Olfactory receptor cells = bipolar neurons
ii. Supportive columnar epithelium
b. Olfactory bulb
c. Ofactory tract
II.
Adult Neurogenesis
a. Special adult neurogenesis continually forms new neurons in adulthood
b. Most other neurons do not regenerate
III.
Limbic System
a. Responsible for moods, memories, and emotions
b. Receives input from olfactory tract
c. Associates smell with memory:
i. Smell of warm cookies reminds you of a childhood memory in the kitchen
ii. Fresh cut grass reminds you of summer day
Eyes
I.
II.
3 Tunics “coats”
a. Inner “neural” tunic
i. Retina = photoreceptors
b. Middle “vascular” tunic
i. Choroid coat – blood vessels
ii. Ciliary Body + suspensory ligaments = suspends lens in place
iii. Iris
1. Radial muscles – dilate pupil
2. Circular muscles – constrict pupil
c. Outer “fibrous” layer
i. Sclera = tough connective tissue
ii. Cornea = transparent
Visual Nerve Pathways
a. Optic chiasm
i. Fibers from medial half of each retina decussate
ii. Fibers from lateral half of each retina do not
b. Optic tract leads to thalamus
c. Meyer’s loop
i. Optic fibers radiate outward into the temporal lobe before reaching their destination
in the visual cortex in the occipital lobe.
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