1. Sensory Systems
Chapter 45

2. Overview of Sensory Receptors
Axon nerve endings respond to stimuli...Axon nerve endings are not dendrites!!! And they can be afferent or efferent
-Exteroceptors
-Interoceptors
1. Mechanoreceptors are stimulated by mechanical forces such as pressure
2. Chemoreceptors detect chemicals or chemical changes
3. Energy-detecting receptors react to electromagnetic and thermal energy

3. Overview of Sensory Receptors
Sensory information is conveyed
to the CNS and perceived in a
four-step process
1. Stimulation
2. Transduction
3. Transmission
4. Interpretation

4. Afferent Nerve undergoing depolarization & “local current flow”
Mechanoreceptors
Afferent Nerve undergoing depolarization & “local current flow”
Nociceptors = pain receptors
-Free nerve endings,
are located where
damage is most likely to occur
Temperature extremes affect the transient receptor potential (TRP) ion channel
-Produces depolarization by an inward flow of Na+ and Ca2+, which in turn causes the sensory neuron to fire
-Leads to a release of glutamate and an EPSP in neurons in spinal cord, which ultimately produces the pain response

5. Mechanoreceptors Receptors in the skin contain sensory
Cells with ion channels that open in
Response to mechanical distortion...
Touch detectors
-Phasic = Intermittently activated
-Tonic = Continuously activated

6. Mechanoreceptors Proprioceptors become activated when muscle
is stretched
-Provide information about
the relative position or
movement of animal’s
body parts
-Examples:
-Muscle spindles sensory neuron
innervates thin group of muscle fibers
-Golgi tendon organs Monitors tension
in tendons

7. Mechanoreceptors Baroreceptors monitor blood pressure
-A highly branched network of afferent neurons located in the carotid sinus (blood to the brain) aortic arch (near the heart)
-Detect tension or stretch in the walls of these blood vessels
-When blood pressure decreases, the frequency of impulses produced by baroreceptors decreases...Sympathetic Division of Autonomic Nervous system Creates Vasoconstriction

8. Hearing Hearing is the detection of sound waves
-Sound is the result of vibration, or waves, traveling through a medium
Auditory stimuli travel farther and more quickly than chemical ones
Auditory receptors provide better directional information than chemoreceptors

9. Lateral Line System in Fish “Distant Touch”
Canals running the length of the fish’s body
-Contain hair cells with cilia that project into a gelatinous cupula(moves around)...Detect pressure waves. Allows fish to swim in schools, hunt...
Bend cilia toward kinocilium = stimulate

10. Ear Structure of Land Vertebrates
Air vibrations are channeled through the auditory canal of the outer ear
-Vibrations reach the tympanic membrane causing movement of three small bones (ossicles) in the middle ear...
-Malleus (hammer), incus (anvil) and stapes (stirrup)
-The stapes vibrates against the oval window, which leads into the inner ear... The inner ear consists of the cochlea, a bony structure

11. Ear Structure of Land Vertebrates
Pressure vibrations enter into the oval window...
which opens into vestibular canal crosses through the cochlear duct into the tympanic canal...All three chambers are filled with fluid
-Pressure waves travel down the tympanic canal to the round window, which is another flexible membrane
-Transmits pressure back to middle ear (So no echo!!!)

12. But How do We Get Sound to the Brain??
The organ of Corti, which transduces sound in the cochlea,
consists of:
-Basilar membrane: Bottom of cochlear duct
-Hair cells with associated sensory neurons & stereocilia
-Tectorial membrane: Overhanging, gelatinous membrane
(holds top of stereocilia in place) Stereocilia of hair
cells bend in response to vibrations of the basilar membrane
-Hair cells are depolarized or hyperpolarized and signals are sent
to brain via afferent auditory nerve... You hear a sound

13. Navigation by Sound
A few mammals have the ability to perceive presence and distance of objects by sound
-Bats, shrews, whales, dolphins
-They emit sounds and then determine the time it takes these sounds to return
-This process is called echolocation
The invention of sonar (sound navigation and ranging) relied on echolocation principles

14. Detection of Body Position
Most invertebrates can orient themselves with respect to gravity due to a sensory structure called a statocyst
-Consists of ciliated hair cells embedded in a gelatin with calcium carbonate stones called statoliths (the stones are called statoliths)
In vertebrates, the gravity receptors consist of two chambers in the membranous labyrinth
-Utricle and saccule

16. Detection of Body Position
Within the utricle and saccule are hair cells with stereocilia and a kinocilium
-Embedded in the calcium carbonate-rich otolith membrane
Utricle more sensitive to horizontal acceleration
Saccule more sensitive to vertical acceleration
-Both types of accelerations cause cilia to bend, thus producing an action potential in an associated sensory neuron

17. Detection of Body Position
The utricle and saccule are continuous with three semicircular canals that detect angular acceleration in any direction
-At the ends of the canals are swollen chambers called ampullae
-Groups of cilia protrude into them
-Tips of cilia are embedded within a gelatinous cupula, that protrudes into the endolymph fluid of each canal

18. Detection of Body Position
When the head rotates, the semicircular canal fluid pushes against the cupula, causing the cilia to bend
-Bending in the direction of the kinocilium causes a receptor potential
-Stimulates an action potential in the associated sensory neuron
Saccule, utricle and semicircular canals are collectively called the vestibular apparatus

20. Chemoreception Used in Taste & Smell
Chemoreceptors
-Membrane of sensory neuron becomes depolarized and produces action potentials
Taste (gustation)
-Broken down into five categories:
-Sweet, bitter, and umami sensations are transmitted via G-protein coupled receptors on receptor cells...Salty tastes are detected via ion channels that take in Na+...Sour tastes are detected through H+ ion channels

21. Taste
Flies taste with hairs in their feet and fish can taste from all over their body surface
In land vertebrates, taste buds are located in the epithelium of the tongue and oral cavity within raised areas called papillae... That contain taste buds that are a epithelial cells associated with afferent neurons.

22. Smell In land vertebrates, the sense of smell (olfaction) involves
neurons located in the upper
portion of the nasal passages....
Chemoreceptor neurons have dendrites,
with G-protein coupled receptors & cilia
Projecting into nasal mucosa.
Axons synapse with Olfactory
bulb that project into cerebral cortex
Humans can discern thousands
of different smells

23. pH Peripheral chemoreceptors -Found in the aortic and carotid bodies
-Sensitive primarily to the pH of plasma
Central chemoreceptors
-Found in the medulla oblongata of the brain
-Sensitive to the pH of cerebrospinal fluid

24. Vision
Vision begins with the capture of light energy by photoreceptors
-Visual information is used to determine both the direction and distance of an object
Invertebrates have simple
visual systems with
photoreceptors clustered
in an eyespot
-Flatworms can perceive
the direction of light but
cannot construct a visual image

25. Vision
The members of four phyla have evolved well-developed, image-forming eyes that use the same light-capturing molecule
-Annelids, mollusks, arthropods, and chordates
Although these eyes are similar in structure, they have evolved independently
-An example of convergent evolution. -

26. Structure of the Vertebrate Eye
Retina
Optic
nerve
Fovea
Vein
Artery
Iris
Cornea
Lens
Suspensory
ligament
Suspensory ligament
Sclera
Ciliary muscle
Pupil
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Sclera = White
portion of the eye, formed
of tough connective tissue
Cornea = Transparent
portion through which
light enters;
begins to focus light
Iris = Colored portion of the eye
-Contraction of iris muscles
in bright light decreases
the size of its opening, the pupil
Lens = A transparent structure
that completes focusing of
light onto the retina
Ciliary Muscle bends lens

27. The Vertebrate Retina contains two types of Photoreceptors:
Outer segment
Inner segment
Synaptic
terminal
Nucleus
Mitochondria
Pigment
discs
Rod
Cone
Connecting cilium
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The Vertebrate Retina contains two types of Photoreceptors:
black-and-white vision
color vision
Rhodopsin
Photopsin

28. Humans have three kinds of cones
Each cone possesses a
photopsin consisting of
a cis-retinal bound to a
protein with slightly different
amino acid sequences
100 80 60 40
Light absorption (percent of maximum)
Blue
cones
420 nm
Green
530 nm
Red
560 nm
Rods
500 nm
400
500
600
700
Wavelength (nm)
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Humans have three kinds of cones

29. Sensory Transduction in the Eye
When rhodopsin absorbs light,
11 cis-retinal is isomerized into
all-trans-retinal
-Activates a G protein that
stimulates the enzyme
phosphodiesterase, which
converts cGMP to GMP
-Na+ channels close, leading
to a hyperpolarization of the membrane
-Prevents the release of the
inhibitory neurotransmitter
onto bipolar cells

30. ...Bipolar cells fire and then ganglion cells send signal to optic nerve and brain
Axons to
optic nerve
Bipolar
cell
Choroid
Horizontal
Amacrine
Rod
Cone
Ganglion
Light
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31. AND THEN YOU SEE THE LIGHT