1. Sensory Systems
Chapter 46

2. Sensory Systems All nerve impulses arrive to CNS as Action Potential
They reach different brain regions so different senses sensed
Intensity depends upon number of action potentials received.

3. Categories of Sensory Receptors
Sensory information is conveyed to the CNS and perceived in a four-step process.

4. 3 Main Classes of Sensory Receptors
Mechanoreceptors – Pressure, Gravity, Inertia, Sound, Touch, Vibration
Chemoreceptors – Taste,
Smell, Humidity
Photoreceptors – Light, Heat, Electricity, Magnetism

5. Categories of Sensory Receptors
Sensory receptors transduce stimuli into graded depolarizations which stimulates the production of action potentials.
Exteroceptors sense stimuli that arise in the external environment.
Interoceptors sense stimuli that arise from within the body.

6. Sensory Transduction
Sensory cells respond to stimuli because they possess stimulus-gated ion channels in their membranes.
Sensory stimulus produces a change in the membrane potential.
receptor potential
greater the sensory stimulus, the greater the depolarization of the receptor potential and higher frequency of action potentials

7. Events in Sensory Transduction

8. Cutaneous receptors Thermoreceptors – naked dendritic nerve endings
Cold – stimulated by fall – inhibited by increase
Heat –
Nociceptors – transmit pain signal to brain
Some sense tissue damage others more sensitive
Mechanoreceptors – Fine touch – face and fingertips
hair follicle receptors - with hair
Meissner’s corpulse – no hair – fingers, palms, nipples
Ruffini endings - duration and extent of touch
Merkel cells - duration and extent
Pacinian Corpuscle – deep subcutaneous - pressure
Mechnoreceptors – measure force applied to membrane
Proprioreceptors – measure stretch – reflex Knee-jerk
Baroreceptors – measure stretch in arteries adjust B.P.

9. Muscle Spindle

10. Sensing Taste, Smell, and Body Position
Chemoreceptors contain membrane proteins that can bind to particular chemicals in the extracellular fluid.
Taste
Taste buds mediate taste in vertebrates.
located in epithelium of tongue and oral cavity within raised papillae

11. Taste

12. Sensing Taste, Smell, and Body Position
Olfaction involves chemoreceptors located in the upper portion of the nasal passage.
New research suggests there may be as many as a thousand different genes coding for different receptor proteins for smell.
Internal chemoreceptors
detect variety of chemical characteristics of blood or fluid derived from blood

13. Smell

14. Sensing Taste, Smell, and Body Position
Lateral line system
made up of sensory structures within a longitudinal canal in the fish’s skin
hairlike processes at their surface project into gelatinous membrane (cupula)
vibrations in the environment produce movements of the cupula, which cause hairs to bend
stimulates sensory neurons

16. Sensing Taste, Smell, and Body Position
Gravity and angular acceleration
statocyst – invertebrates generally consists of ciliated hair cells with the cilia embedded in a gelatinous membrane containing crystals of calcium carbonate
Cilia bend with change in position
Tilt to the right cilia on right side bend activate sensory neurons

17. Sensing Taste, Smell, and Body Position
In vertebrates – fluid filled membranous chamber – labyrinth = organ of equilibrium and hearing
Gravity receptors = two chambers utricle and saccule – possess hair cells similar to the lateral line system

18. Sensing Taste, Smell, and Body Position
Inner ear
Receptors consist of utricle and saccule.
hairlike processes embedded within a gelatinous membrane containing calcium carbonate crystal (otolith membrane)
utricle more sensitive to horizontal acceleration
saccule more sensitive to vertical acceleration

19. Sensing Taste, Smell, and Body Position
Utricle and saccule are continuous, with three semicircular canals oriented in different planes. - Detect angular acceleration at any angle
ampullae - swollen chambers at end of canals
group of cilia protrude into ampullae
tips of cilia embedded within wedge of cupula that protrudes into the endolymph fluid of each semicircular canal

20. Utricle and Saccule

21. Structure of Semicircular Canals

22. The Ears and Hearing
Structure of the ear
In terrestrial vertebrates, vibrations in air may be channeled through the ear canal to the eardrum (tympanic membrane).
Vibrations of the tympanic membrane cause movement of three small bones (ossicles) in the middle ear.
malleus
incus
stapes

23. Outer ear
Middle
ear
Inner
ear
Auditory canal
Pinna
Eustachian tube

24. Malleus
Incus
Stapes
Semicircular
canals
Skull
Auditory
nerve
to brain
Tympanic
membrane
Oval
window
Cochlea
Round
window
Eustachian tube

25. The Ears and Hearing
The middle ear is connected to the throat by the Eustachian tube which equalizes the air pressure between the middle ear and the external environment.
Inner ear is composed of the cochlea.
The cochlear duct is located in the center of the cochlea.
The area above is the vestibular canal and the area below is the tympanic canal.

26. Bone
Cochlear
duct
Vestibular
canal
Auditory
nerve
Tympanic
canal
Organ of Corti

27. The Ears and Hearing
Transduction in the cochlea
bottom of the cochlear duct, basilar membrane, quite flexible and vibrates in response to pressure waves
cilia of sensory hair cells project into tectorial membrane
organ of Corti
cilia of hair cells bend in response to the movement of the basiliar membrane relative to the tectorial membrane

28. Tectorial
membrane
Hair cells
Sensory
neurons
Basilar
membrane
To auditory
nerve

29. The Ears and Hearing
Frequency location in cochlea
When a sound wave enters the cochlea from the oval window, it initiates a traveling motion of the basilar membrane.
Flexibility of the basilar membrane limits the frequency range of human hearing to between approximately 20 and 20,000 cycles per second (in children).

31. High frequency (20,000Hz) Medium frequency (2000Hz)
Stapes
Oval window
Incus
Basilar
membrane
Malleus
Vestibular canal
Cochlear
duct
Tympanic
membrane
Apex
Round
window
Base
Tympanic canal
High frequency (20,000Hz)
Medium frequency (2000Hz)
Low frequency (500Hz)

32. Sonar
Some mammals such as bats emit sounds and then determine the time it takes for the sound to return.
locate themselves in relation to other objects such as prey

33. Evolution of the Eye
Structure of the vertebrate eye
sclera - white portion of the eye, formed of tough connective tissue
iris - colored portion of the eye
Contraction of the iris muscles in bright light decreases pupil size.

34. Evolution of the Eye
Light enters the eye through a transparent cornea which begins to focus the light.
Light then passes through the pupil to the lens, a transparent structure that completes the focusing of light onto the retina.
lens attached by suspensory ligament to the ciliary muscles

35. Human Eye

36. Vertebrate Photoreceptors
Vertebrate retina contains two photoreceptors.
rods - black and white vision
photopigment - rhodopsin
cones - sharpness and color vision
Both have an inner segment rich in mitochondria, with numerous vesicles filled with neurotransmitter molecules.
photopigment - photopsins
red, blue, and green cones

37. Color Vision

38. Vertebrate Photoreceptors
Sensory transduction in photoreceptors
Inverse to the usual way stimuli are detected
In the dark, photoreceptors release inhibitory neurotransmitter the hyperpolarizes the neurons
Light inhibits the photoreceptors from releasing their inhibitory neurotransmitter, and thus stimulates the bipolar cells and the ganglion cells, which transmit action potentials to the brain.

39. Structure of the Retina

40. Visual Processing in the Vertebrate Retina
Action potentials propagated along the axons of ganglion cells are relayed through the lateral geniculate nuclei of the thalamus and projected to the occipital lobe of the cerebral cortex.
The brain interprets this information as light in a specific region of the eye’s receptive field.

41. Visual Processing in the Vertebrate Retina
Color blindness
inherited lack of one or more types of cones
more common in men due to sex-linkage
Binocular vision
ability to perceive three-dimensional images and sense depth
each eye sees object at a slightly different angle

42. Pathway of Visual Information

43. Diversity of Sensory Experiences
Heat
pit vipers
Pits have membrane
that is warmed by
infrared radiation
stimulating
thermal receptors
Electricity
Elasmobranchs – ampullae of Lorenzini
Magnetism
eels, sharks, bees, and birds – navigate in magnetic field of earth