Introduction to the Senses

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Chapter 13

• Introduction to the Senses

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Outline

• Types of Sensory Receptors
• Sense of Taste
• Sense of Smell
• Sense of Vision
• Focusing
• Integration of Visual Signals
• Abnormalities of the Eye
• Sense of Hearing
• Sense of Equilibrium

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Sensory Receptors and Sensations

• Sensory receptors are specialized to detect
  certain types of stimuli.
• Exteroceptors detect stimuli outside the body.
• Taste, smell, vision.
• Not invovled in homeostasis send messages to CNS
• Interoceptors detect stimuli inside the body.
• Blood pressure, blood volume, pH.
• Directly involved in homeostasis

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Types of Sensory Receptors

• Chemoreceptors.
• Respond to chemical substances in the immediate
  vicinity.
• Taste buds and odorant receptors
• Photoreceptors
• Respond to light energy
• Rods and cones
• Pain Receptors/Nociceptors
• Respond to chemicals released by damaged tissue.
• Mechanoreceptors.
• Stimulated by mechanical forces.
• Sterocilia in the cochlea of the ear
• Thermoreceptors.
• Stimulated by changes in temperature.
• Warm and cold receptors in the skin and
  hypothalamus

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How Sensation Occurs

• Sensation occurs when nerve impulses arrive at
  the cerebral cortex of the brain.
• Perception occurs when the cerebral cortex
  interprets the meaning of sensations.
• All sensory receptors initiate nerve impulses
  the sensation that results depends on the part of
  the brain receiving the nerve impulses.

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Proprioceptors

• Proprioceptors are mechanoreceptors that help
  determine limb position in space by detecting the
  degree of muscle relaxation, stretch of tendons,
  and movement of ligaments.
• Muscle spindles act to increase the degree of
  muscle contraction, while Golgi tendon organs act
  to decrease it.

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Muscle Spindle
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Cutaneous Receptors

• The dermis contains cutaneous receptors, which
  include
• Mechanoreceptors.
• Sensitive to touch.
• Pain Receptors/Nociceptors.
• Sensitive to pain.
• Thermoreceptors.
• Sensitive to temperature.

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Cutaneous Sensory Receptors in Human Skin
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Chemical Senses Taste Buds- Our Taste Receptors

• Sense of Taste.
• Location primarily embedded in tongue
  epithelium.
• Taste Responses sweet, salty, bitter, sour,
  umame (MSG)

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Sense of Smell

• Sense of smell is dependent on olfactory cells
  located within olfactory epithelium high in the
  roof of the nasal cavity.
• Olfactory bulbs have direct connections with the
  limbic system and its centers for emotions and
  memory.
• Sense of taste and smell work together to create
  a combined effect.

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Olfactory Cell Location and Anatomy
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Sense of Vision

• The eyeball has three layers.
• Sclera protects and supports the eyeball
• Choroid absorbs stray light
• Retina contains sensory photoreceptors
• Rods
• Cones

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Anatomy of the Human Eye
Refer to Table 13.2 in your Text for Summary
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Focusing

• When looking at an object, light rays pass
  through the pupil and are focused on the retina.
• Focusing starts with the cornea and continues as
  the rays pass through the lens and the humors.

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Photoreceptors

• Vision begins once light has been focused on the
  photoreceptors in the retina.
• Rods are very sensitive to light and therefore
  are suited to night vision.
• Cones allow detection of fine detail and color.
• Color vision depends on three different kinds of
  cones which contain blue, green, and red pigments.

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Photoreceptors in the Eye
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Integration of Visual Signals in the Retina

• The retina has three layers.
• Layer closest to choroid contains rod cells and
  cone cells.
• Middle layer contains bipolar cells.
• Innermost layer contains ganglion cells.
• Only rod and cone cells are light-sensitive, thus
  light must penetrate to the back of the retina
  before they are stimulated.

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Structure and Function of the Retina
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Integration of Visual Signals in the Brain

• The visual pathway begins in the retina and
  passes through the thalamus before reaching the
  primary visual cortex in the occipital lobe of
  the cerebral cortex.

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Abnormalities of the Eye

• Color blindness.
• Particular type of cone is lacking.
• Distance Vision
• Nearsighted.
• Elongated eyeball.
• Farsighted.
• Shortened eyeball.
• Astigmatism.
• Uneven cornea.

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Sense of Hearing

• Anatomy of the Ear.
• Outer ear consists of the pinna and the auditory
  canal.
• Middle ear begins at tympanic membrane and ends
  at bony wall with a round window and oval window.
• Ossicles found between tympanic membrane and the
  oval window.
• Inner ear consists of semicircular canals,
  vestibule, and cochlea.

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Human Ear
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Mechanoreceptors for Hearing
Hearing Basilar membrane (spiral organ)
vibrates, stereocilia of the hair cells bend,
and nerve impulses are transmitted to the brain.
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Sense of Equilibrium

• Cupula movement within the semicircular canals
  detects rotation and/or angular movement of the
  head.
• Rotational Equilibrium.
• Movement of the otolithic membrane within the
  utricle and the saccule detects movement of the
  head in the vertical and horizontal planes.
• Gravitational Equilibrium.