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Chapter 39. Learning Objectives. Describe sensory circuit List five basic type of sensory receptors Define sensation in neurological terms Identify the role of each of the various mechanoreceptors for pressure, vibration, etc.

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Learning objectives
Learning Objectives

  • Describe sensory circuit

  • List five basic type of sensory receptors

  • Define sensation in neurological terms

  • Identify the role of each of the various mechanoreceptors for pressure, vibration, etc.

  • Explain the function of proprioceptors, electroreceptors and magnetoceptors


Learning objectives1
Learning Objectives

  • Describe how the ear transmits sound

  • Describe the morphology and function of the human eye

  • Define chemoreceptors

  • Map the human tongue and the process of taste

  • Diagram the human nasal cavity and the process of olfaction

  • Describe the function of nociceptors


Sensory receptors 1
Sensory Receptors(1)

  • Formed by endings of afferent neurons or specialized cells adjacent to neurons

  • Detect stimuli (various forms of energy)

    • Mechanical pressure

    • Sound waves

    • Light

    • Specific molecules or chemical conditions


Sensory receptors 2
Sensory Receptors(2)

  • Sensory transduction

    • Axons of afferent neurons carry action potentials generated by receptors to pathways leading to specific parts of the brain

  • Brain processes signals into sensory sensations


a. Sensory receptor formed by dendrites of an afferent neuron

Stimulus

Stimulus opens gated ion channels

In sensory receptors formed by the dendrites of afferent neurons, a stimulus causes a change in membrane potential that generates action potentials in the axon of the neuron. Temperature and pain receptors are among the receptors of this type.

Action potential

Afferent neuron (to CNS)

Dendrites forming sensory receptor

Fig. 39.1a, p. 886


b. Sensory receptor formed by a cell that synapses with an afferent neuron

Stimulus

Sensory receptor cell or structure

In sensory receptors consisting of separate cells, a stimulus causes a change in membrane potential that releases a neurotransmitter from the cell. The neuro-transmitter triggers an action potential in the axon of a nearby afferent neuron. Mechanoreceptors, photoreceptors, and chemoreceptors are examples of receptors of this type.

Action potential

Neurotransmitter or first messenger opens gated ion channels

Diffusion of neurotransmitter or first messenger

Fig. 39.1b, p. 886


Types of receptors
Types of Receptors afferent neuron

  • 5 basic types

    • Mechanoreceptors

    • Photoreceptors

    • Chemoreceptors

    • Thermoreceptors

    • Nociceptors

  • Some animals have receptors that detect electrical or magnetic fields


Sensory perception
Sensory Perception afferent neuron

  • Routing of information from sensory receptors to particular brain regions identifies a specific stimulus as a sensation

  • Intensity of a stimulus is determined by

    • Frequency of action potentials along neural pathways

    • Number of afferent neurons carrying action potentials


Sensory adaptation
Sensory Adaptation afferent neuron

  • In many systems, frequency of action potentials decreases while a stimulus remains constant

  • Some sensory receptors (those related to tissue damage) show little or no sensory adaptation


39 2 mechanoreceptors and the tactile and spatial senses
39.2 Mechanoreceptors and the afferent neuronTactile and Spatial Senses

  • Receptors for touch and pressure occur throughout the body

  • Proprioceptors provide information about movements and position of the body


Mechanoreceptors
Mechanoreceptors afferent neuron

  • Detect mechanical energy

    • Touch, pressure, acceleration, vibration

  • Touch and pressure receptors

    • Free nerve endings

    • Encapsulated nerve endings of sensory neurons


39 2 mechanoreceptors and the tactile and spatial senses1
39.2 Mechanoreceptors and the afferent neuronTactile and Spatial Senses

  • Receptors for touch and pressure occur throughout the body

  • Proprioceptors provide information about movements and position of the body


Mechanoreceptors1
Mechanoreceptors afferent neuron

  • Detect mechanical energy

    • Touch, pressure, acceleration, vibration

  • Touch and pressure receptors

    • Free nerve endings

    • Encapsulated nerve endings of sensory neurons


39 2 mechanoreceptors and the tactile and spatial senses2
39.2 Mechanoreceptors and the afferent neuronTactile and Spatial Senses

  • Receptors for touch and pressure occur throughout the body

  • Proprioceptors provide information about movements and position of the body


Mechanoreceptors constant feedback on tactile senses
Mechanoreceptors: constant feedback on tactile senses afferent neuron

  • Detect mechanical energy

    • Touch, pressure, acceleration, vibration

  • Touch and pressure receptors

    • Free nerve endings

    • Encapsulated nerve endings of sensory neurons


Shaft of hair inside follicle afferent neuron

Skin surface

Epidermis

Dermis

Myelinated neuron

Free nerve endings around hair root plexus

Free nerve endings: light touch

Pacinian corpuscle: deep pressure and vibrations

Ruffini endings: deep pressure

Meissner’s corpuscle: light touch, surface vibrations

Fig. 39.2, p. 888


Proprioceptors constant feedback on spatial position
Proprioceptors: constant feedback on spatial position afferent neuron

  • Proprioceptors provide information about movements and position of the body

  • The vestibular apparatus of the human ear

  • Stretch receptors in muscles (muscles spindles)

  • Proprioceptors of tendons (Golgi tendon organs) for balance


Vestibular apparatus afferent neuron

Anterior semicircular canal

Posterior semicircular canal

Utricle

Saccule

Lateral semicircular canal

Fig. 39.5a, p. 890


Ampulla of a semicircular canal afferent neuron

Direction of body rotation

Endolymph pulls cupula in this direction

Cupula

Sensory hair cells

Afferent neurons

Fig. 39.5b, p. 890


Muscle spindles and golgi tendon organs
Muscle Spindles and afferent neuronGolgi Tendon Organs


Hearing
Hearing afferent neuron

  • Hearing relies on sensory hair cells in organs that respond to the vibrations of sound waves


Terrestrial vertebrate ear 1
Terrestrial Vertebrate Ear (1) afferent neuron

  • Outer ear (pinna)

    • Directs sound to the eardrum

  • Eardrum (tympanic membrane)

    • Transmits vibrations through one or more bones in the middle ear to the fluid-filled inner ear


Terrestrial vertebrate ear 2
Terrestrial Vertebrate Ear (2) afferent neuron

  • Middle ear

    • Malleus, incus, stapes

    • Oval window

  • Inner ear

    • Transmits vibrations through structures that bend stereocilia of hair cells

    • Cochelea, organ of Corti, round window

    • Bursts of action potentials determine frequency of sound waves


Semicircular canals afferent neuron

Oval window (behind stapes)

Stapes

Auditory nerve

Bone of skull

Pinna

Incus

Malleus

Eustachian tube leading to throat

Round window

Auditory canal

Eardrum

Cochlea

Location of the human ear in the head

Middle ear

Inner ear

Outer ear

Internal structures of the outer, middle, and inner ear

Fig. 39.8a, p. 893


39 4 photoreceptors and vision
39.4 Photoreceptors and Vision afferent neuron

  • Vision involves detection and perception of radiant energy

  • Mammalian retinas contains rods and cones and a complex neuronal network

  • Three kinds of opsin pigments underlie color vision

  • The visual cortex processes visual information


Retina afferent neuron

Cornea

Lens

Pupil

Iris

Fig. 39.11, p. 895


Photoreceptors of the eye
Photoreceptors of the Eye afferent neuron

  • Contain pigment molecules

    • Absorb energy of light

    • Generate changes in membrane potential

  • Retinal

    • Light-absorbing pigment in all animals


The vertebrate eye 1
The Vertebrate Eye (1) afferent neuron

  • Cornea

    • Transparent, admits light

  • Iris

    • Behind the cornea

    • Controls diameter of pupil

    • Regulates amount of light that strikes the lens


The vertebrate eye 2
The Vertebrate Eye (2) afferent neuron

  • Lens

    • Focuses image on the retina

  • Retina

    • Lines the back of the eye

    • Photoreceptors and neurons integrate information detected by photoreceptors


Sclera afferent neuron

Retina

Choroid

Ciliary body

Fovea

Iris

Blind spot

Lens

Pupil

Cornea

Part of optic nerve

Aqueous humor

Ciliary muscle

Vitreous humor

Fig. 39.12, p. 896


Focus
Focus afferent neuron

  • In birds, mammals, and most reptiles, light is focused on the retina by the combined effect of the cornea and adjusting lens shape


Fig. 39.13a, p. 896 afferent neuron


Fig. 39.13b, p. 896 afferent neuron


Region of overlap of the two visual fields afferent neuron

Visual field of left eye

Visual field of right eye

Region of overlap of two visual fields

Right eye

Left eye

Optic nerve

Optic chiasm

Lateral geniculate nucleus of the thalamus

Visual cortex

Fig. 39.17, p. 900


Photoreceptors of the retina
Photoreceptors of the Retina afferent neuron

  • Rods

    • Specialized for detection of low-intensity light

  • Cones

    • Specialized for detecting light of different wavelengths (colors)


Photopigment molecules
Photopigment Molecules afferent neuron

  • Absorb light in photoreceptor cells

    • Consist of retinal combined with an opsin protein

    • 3 photopigments (photopsins)

      Pigment absorbs light, retinal changes form

    • Reactions alter amount of neurotransmitter released by photoreceptor cells


a. Structure of cones and rods afferent neuron

Cone

Rod

Discs

Back of retina

Light-absorbing photopigment

Outer segment

Outer segment

Discs

(houses discs that contain light-absorbing photopigment)

Inner segment

Inner segment

(houses cell’s metabolic machinery)

Synaptic terminal

Synaptic terminal

(stores and releases neurotransmitters)

Front of retina

Fig. 39.14a, p. 897


b. How rhodopsin functions afferent neuron

Rhodopsin in the dark (inactivated)

Rhodopsin in the light (activated)

Light absorption

Retinal changes shape

Enzymes

cis-Retinal

trans-Retinal

Fig. 39.14b, p. 897


The retina and visual processing
The Retina and Visual Processing afferent neuron

  • Rods (low light) and cones( bright and color)

    • Linked to neurons in the retina

    • Perform initial integration and processing of visual information

  • Processed signal is sent via the optic nerve through the lateral geniculate nuclei to the visual cortex


Color blindness
Color-blindness afferent neuron

  • Genetic disorder

  • 8% males, 0.5% females

  • Red-green is most common

  • Type of color deficiency depends on wavelength of light that is not being detected (long, medium, or short wavelength detecting cone).



Chemoreceptors
Chemoreceptors afferent neuron

  • Chemoreceptors respond to the presence of specific molecules in the environment

  • In vertebrates, they form parts of receptor organs for taste (gustation) and smell (olfaction)


Taste receptors
Taste Receptors afferent neuron

  • Detect molecules from food or other objects that come into direct contact with the receptor

  • Are used primarily to identify foods


Taste bud afferent neuron

Papilla (cutaway)

Sensory hair of taste receptor

Papillae

Tongue

Afferent nerve

Taste buds

Papilla

Fig. 39.20, p. 902


Olfactory tract from receptors to the brain afferent neuron

Olfactory bulb

Nasal cavity

Bone

Olfactory receptors

Supporting cells

Sensory hairs of olfactory receptors

Mucus

Fig. 39.21, p. 902


39 6 thermoreceptors and nociceptors
39.6 Thermoreceptors and Nociceptors afferent neuron

  • Thermoreceptors occur in warm and cold forms

  • Nociceptors protect animals from potentially damaging stimuli


Nociceptors
Nociceptors afferent neuron

  • Detect stimuli that can damage body tissues

  • Located on body surface and interior

  • Information from receptors is integrated in the brain into the sensation of pain


Other sensory receptors found in some vertebrates
Other Sensory Receptors afferent neuronFound in Some Vertebrates

  • Electroreceptors

    • Detect electrical currents and fields

  • Magnetoreceptors

    • Detect magnetic fields


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