Sensory Systems Chapter 45. 2 Overview of Sensory Receptors Axon nerve endings respond to...

Sensory Systems

Chapter 45

2

Overview of Sensory ReceptorsAxon 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 pressure2. Chemoreceptors detect chemicals or chemical changes3. Energy-detecting receptors react to electromagnetic and thermal energy

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Overview of Sensory ReceptorsSensory information is conveyed

to the CNS and perceived in a

four-step process

1. Stimulation

2. Transduction

3. Transmission

4. Interpretation

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Mechanoreceptors

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

Afferent Nerve undergoing depolarization & “local current

flow”

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Receptors in the skin contain sensoryCells with ion channels that open in Response to mechanical distortion...

Touch detectors

-Phasic = Intermittently activated -Tonic = Continuously activated

Mechanoreceptors

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MechanoreceptorsProprioceptors 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

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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

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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

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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

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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

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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!!!)

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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

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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

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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

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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

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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

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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

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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

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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.

Taste

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SmellIn 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

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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

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VisionVision 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

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VisionThe 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.

-

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Retina

Opticnerve

Fovea

VeinArtery

Iris

CorneaLens

Lens

Suspensoryligament

Suspensory ligament

Sclera

Ciliary muscle

Pupil

Ciliary muscle

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

Structure of the Vertebrate Eye

Ciliary Muscle bends lens

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Outer segmentInner segmentSynapticterminal

Nucleus Mitochondria Pigmentdiscs

Rod

Cone

Connecting cilium


Rhodopsin

Photopsin

The Vertebrate Retina contains two types of Photoreceptors:

black-and-white vision

color vision

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100

80

60

40

Lig

ht

ab

so

rpti

on

(p

erc

en

t o

f m

axi

mu

m)

Bluecones420 nm

Greencones530 nm

Redcones560 nm

Rods500 nm

400 500 600 700

Wavelength (nm)


Each cone possesses a

photopsin consisting of

a cis-retinal bound to a

protein with slightly different

amino acid sequences

Humans have three kinds of cones

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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 neurotransmitteronto bipolar cells

Sensory Transduction in the Eye

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Axons tooptic nerve

Bipolarcell

Choroid

Horizontalcell

Amacrinecell

RodConeGanglioncell

Light


...Bipolar cells fire and then ganglion cells send signal to optic nerve and

brain

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AND THEN YOU SEE THE LIGHT

Sensory Systems Chapter 45. 2 Overview of Sensory Receptors Axon nerve endings respond to...

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