1. Lecture 21 Major Senses

2. Sensory Perception
The sensory nervous system tells the central nervous system what’s happenin’!
Sensory receptors
Specialized sensory cells that detect changes inside and outside the body
Sensory organs
Complex sensory receptors
Eyes, ears, taste buds

3. The path of sensory information
Stimulation
Physical stimulus activates a sensory receptor
Transduction
Converting the stimulus into an action potential
Stimulus-gated ion channels in sensory neuron are opened or closed
An action potential is generated
Transmission
Nerve impulse is conducted to the CNS
Two main types of sensory receptors
Extroreceptors sense stimuli in external environment
Introreceptors sense stimuli in internal environment

4. Sensing the Internal Environment
Vertebrates use many different sensory receptors to respond to changes in internal environment
Temperature Change
Two nerve endings in the skin
One stimulated by cold, the other by warmth
Blood chemistry
Receptors in arteries sense blood CO2 levels
Pain
Special nerve endings within tissues near the surface

5. Sensing Pressure & Strectch
Muscle contraction
Sensory receptors called proprioceptors embedded within muscle & tendons sense stretch of muscle
Touch
Pressure receptors buried below skin
Blood pressure
Neurons called baroreceptors in major arteries

6. Sensing Chemicals: Taste
Taste buds are located in raised areas called papillae
Food chemicals dissolve in saliva and contact the taste cells

7. Sensing Chemicals: Smell
Olfactory receptor cells are embedded in the epithelium of the nasal passage
These are far more sensitive in dogs than in humans

8. Evolution of Balance & Hearing
Lateral Line and the fish’s sense of hearing
Fish are able to sense objects that reflect pressure waves and low-frequency vibrations
The system consists of canals running the length of the fish’s body under the skin
Canals have sensory structures containing hair cells projecting into a gelatinous cupula
Vibrations produce movements of the cupula
Hair cells bend and depolarize associated sensory neurons

9. Human Sensation of Gravity and Motion
Receptors in the ear inform the brain where the body is in three dimensions
Balance
Gravity is detected by shifting of otolith sensory receptors
These are located in a gelatin-like matrix in the utricle and saccule chambers of the inner ear
Motion
Motion is detected by the deflection of hair cells by fluid in a direction opposite to that of motion
These hair cells are found in the cupula, tent-like assemblies in the three semicircular canals

10. Properties of Sound Sound is:
A pressure disturbance (alternating areas of high and low pressure) originating from a vibrating object
Composed of areas of rarefaction and compression
Represented by a sine wave in wavelength, frequency, and amplitude
Frequency – the number of waves that pass a given point in a given time
Pitch – perception of different frequencies (we hear from 20–20,000 Hz)
Amplitude – intensity of a sound measured in decibels (dB)
Loudness – subjective interpretation of sound intensity

11. Sensing Sounds: Hearing
When a sound is heard, air vibration is detected
Eardrum membrane is pushed in and out by waves of air pressure
Three small bones (ossicles) located on other side of eardrum increase the vibration force
Amplified vibration is transferred to fluid within the inner ear
Inner ear chamber is shaped like a tightly coiled snail shell and is called cochlea

12. Sensing Sounds: Hearing
Cochlea are hair cells that rest on a membrane running up and down the chamber
They are covered by another membrane
Sound waves entering the cochlea cause this membrane “sandwich” to vibrate
Bent hair cells send nerve impulses to brain
Pitch is determined by different frequencies causing different parts of the membrane to vibrate
Different sensory neurons are fired
Sound intensity is determined by how often the neurons fire
PLAY
Transduction of Sound Waves

13. The Evolution of Vision
Vision begins with the capture of light energy by photoreceptors
Many invertebrates have simple visual systems
Photoreceptors are clustered in an eyespot
Perceive light direction but not a visual image
Members of four phyla have evolved well-developed, image-forming eyes
Annelids
Mollusks
Arthropods
Vertebrates
The eyes are strikingly similar in structure but are believed to have evolved independently

14. Eyes in Three Phyla of Animals

15. Structure of the Vertebrate Eye
The vertebrate eye works like a lens-focused camera
Cornea – Transparent covering that focuses light
Lens – Completes the focusing
Ciliary muscles – Change the shape of the lens
Iris – Shutter that controls amount of light
Pupil – Transparent zone
Retina – The back surface of the eye
Contains two types of photoreceptors: rods and cones
Fovea – Center of retina
Produces the sharpest image

16. How Rods and Cones Work Rods are extremely sensitive to dim light
Cannot distinguish colors
Do not detect edges
Produce poorly defined images
Cones can detect color
Detect edges well
Produce sharp images

17. How Light is Converted to a Nerve Impulse
Pigment in rods and cones are made from carotenoids
cis-retinal is attached to a protein called opsin
This light-gathering complex is called rhodopsin
When light is absorbed by cis-retinal, it changes shape to trans-retinal
This induces a change in the shape of the opsin protein
A signal-transduction pathway is initiated leading to generation of a nerve impulse

18. Color Vision
Three kinds of cone cells exist, each with its own opsin type
Differences in opsin shape, affect the flexibility of the attached cis-retinal
This shifts the wavelength at which it absorbs light
420 nm – Blue
530 nm – Green
560 nm – Red

19. Colorblindness
Colorblindness is a condition in which a person cannot see all three colors
Caused by a lack of one or more types of cones
It is inherited as a sex-linked trait and is more likely to affect males

20. Conveying the Light Information to the Brain
Rods and cones are at the rear of the retina, not front!
Light passes through four types of cells before it reaches them
Photoreceptor activation stimulates bipolar cells, and then ganglion cells
Nerve impulse travels through the optic nerve to the cerebral cortex

21. Focusing the Eye Focusing for Distant Vision:
Light from a distance needs little adjustment for proper focusing
Far point of vision – the distance beyond which the lens does not need to change shape to focus (20 ft.)
Focusing for Close Vision:
Accommodation – changing the lens shape by ciliary muscles to increase refractory power
Constriction – the pupillary reflex constricts the pupils to prevent divergent light rays from entering the eye
Convergence – medial rotation of the eyeballs toward the object being viewed

22. Problems of Refraction
Normal eye (Emmetropic) – with light focused properly
Nearsighted (Myopic) – the focal point is in front of the retina
Corrected with a concave lens
Farsighted (Hyperopic) – the focal point is behind the retina
Corrected with a convex lens

23. Muscles That Move the Eye
Six strap-like extrinsic eye muscles
Enable the eye to follow moving objects
Maintain the shape of the eyeball
Four rectus muscles originate from the annular ring
Two oblique muscles move the eye in the vertical plane

24. Binocular Vision
Primates and most predators have eyes on front of the head
The two fields of vision overlap allowing the perception of 3-D images and depth
Prey animals generally have eyes located on sides of the head
This prevents binocular vision but enlarges the perceptive field

25. Lacrimal Apparatus Consists of the lacrimal gland and associated ducts
Lacrimal glands secrete tears
Tears
Contain mucus, antibodies, and lysozyme
Enter the eye via lacrimal excretory ducts
Exit the eye medially via the lacrimal punctum & lacrimal canal
Drain into the nasolacrimal duct

26. Other Types of Sensory Reception
Heat
Pit vipers can locate warm prey, using infrared radiation
Heat-detecting pit organs
Electricity
Used by aquatic vertebrates to locate prey and mates
Magnetism
Eels, sharks and many birds orient themselves in relation to the Earth’s magnetic field