Chapter 39
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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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Chapter 39

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Chapter 39

Chapter 39


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


Chapter 39

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


Chapter 39

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

  • 5 basic types

    • Mechanoreceptors

    • Photoreceptors

    • Chemoreceptors

    • Thermoreceptors

    • Nociceptors

  • Some animals have receptors that detect electrical or magnetic fields


Sensory perception

Sensory Perception

  • 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

  • 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 Tactile and Spatial Senses

  • Receptors for touch and pressure occur throughout the body

  • Proprioceptors provide information about movements and position of the body


Mechanoreceptors

Mechanoreceptors

  • 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 Tactile and Spatial Senses

  • Receptors for touch and pressure occur throughout the body

  • Proprioceptors provide information about movements and position of the body


Mechanoreceptors1

Mechanoreceptors

  • 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 Tactile 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

  • Detect mechanical energy

    • Touch, pressure, acceleration, vibration

  • Touch and pressure receptors

    • Free nerve endings

    • Encapsulated nerve endings of sensory neurons


Chapter 39

Shaft of hair inside follicle

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

  • 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


Chapter 39

Vestibular apparatus

Anterior semicircular canal

Posterior semicircular canal

Utricle

Saccule

Lateral semicircular canal

Fig. 39.5a, p. 890


Chapter 39

Ampulla of a semicircular canal

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 Golgi Tendon Organs


Hearing

Hearing

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


Terrestrial vertebrate ear 1

Terrestrial Vertebrate Ear (1)

  • 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)

  • 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


Chapter 39

Semicircular canals

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

  • 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


Chapter 39

Retina

Cornea

Lens

Pupil

Iris

Fig. 39.11, p. 895


Photoreceptors of the eye

Photoreceptors of the Eye

  • 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)

  • 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)

  • Lens

    • Focuses image on the retina

  • Retina

    • Lines the back of the eye

    • Photoreceptors and neurons integrate information detected by photoreceptors


Chapter 39

Sclera

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

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


Chapter 39

Fig. 39.13a, p. 896


Chapter 39

Fig. 39.13b, p. 896


Chapter 39

Region of overlap of the two visual fields

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

  • Rods

    • Specialized for detection of low-intensity light

  • Cones

    • Specialized for detecting light of different wavelengths (colors)


Photopigment molecules

Photopigment Molecules

  • 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


Chapter 39

a. Structure of cones and rods

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


Chapter 39

b. How rhodopsin functions

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

  • 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

  • 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).


Retina initial integration

Retina: Initial Integration


Chemoreceptors

Chemoreceptors

  • 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

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

  • Are used primarily to identify foods


Chapter 39

Taste bud

Papilla (cutaway)

Sensory hair of taste receptor

Papillae

Tongue

Afferent nerve

Taste buds

Papilla

Fig. 39.20, p. 902


Chapter 39

Olfactory tract from receptors to the brain

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

  • Thermoreceptors occur in warm and cold forms

  • Nociceptors protect animals from potentially damaging stimuli


Nociceptors

Nociceptors

  • 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 Found in Some Vertebrates

  • Electroreceptors

    • Detect electrical currents and fields

  • Magnetoreceptors

    • Detect magnetic fields


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