THE SENSES

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THE SENSES

• CHAPTER 9

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OUR SENSES

• Detect changes in the external or internal
  environment enable the body to respond
  appropriately in order to maintain homeostasis
• Stimulus-some change that initiates a nerve
  impulse, which travels to the CNS by way of a
  neuron. These are detected at or near the
  surface of the body

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RECEPTORS

• Detect changes and generate impulses
• It then generates a nerve impulse

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SENSORY NEURONS

• Transmit impulses from the receptors to the CNS
  for interpretation

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SENSORY TRACTS AREAS

• Tracts are the white matter in the CNS
• Sensory areas are mostly in the cerebral cortex
  where the sensation is actually felt and
  intrepretated

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CHARACTERISTICS OF SENSATIONS

• Adaptation becoming UNAWARE of a continuing
  stimulus because the stimulus remains constant,
  there is not a change for the receptors to detect
• After image the sensation remains in the
  consciousness after the stimulus has stopped

• Projection the sensation seems to come from
  where the area where the receptors were
  stimulated
• Intensity the degree to which the sensation is
  felt strong stimulus affect more receptors
• Contrast the effect of a previous or
  simultaneous sensation on a current sensation as
  the brain compares them

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TYPES OF SENSES

• The receptors for pain, heat cold are free
  nerve endings
• The receptors for touch pressure are
  encapsulated nerve endings
• See fig 9-1

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CUTANEOUS SENSES

• Provide information about the external
  environment and the skin itself
• Example heat, pain, cold, touch and pressure
• Referred Pain pain that is occuring in an
  internal organ may be felt in a cutaneous area
• Example pain from a heart attack may be felt in
  the left arm or shoulder due to the brains
  activity

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MUSCLE SENSE

• Knowing where our muscles are without looking at
  them
• Example walking up stairs, we dont have to
  visually look at our feet to make sure that they
  are stepping on the steps

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SENSE OF TASTE

• Chemoreceptors taste buds on the tongue
• Tastes are sweet, sour, salty, bitter, savory
• Nerves of taste include the facial and the
  glossopharyngeal cranial nerves
• figure 9-2

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SENSE OF SMELL

• Chemoreceptors in the upper nasal cavities
  detect vaporized chemicals
• Sniffing brings odors up into the nose
• Olfactory nerves to olfactory bulbs to olfactory
  areas in the temporal lobes
• Closely related to taste
• figure 9-2

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HUNGER AND THIRST

• HUNGER
• Receptors in the hypothalamus, detect changes
  in the GI hormones nutrient levels in the
  blood hunger is projected to the stomach
  adaptation does occur

• THIRST
• Receptors in the hypothalamus detect changes
  in the body water ( water-salt proportions)
  thirst is projected to the mouth and pharynx
  adaptation does not occur

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THE EYE

• EYELIDS EYELASHES keep dust out of the eyes
• CONJUNCTIVA lines the eyelids cover the white
  of the eye
• LACRIMAL GLANDS produce tears to wash the
  anterior eyeball contain lysozymes to inhibit
  bacterial growth

• EYE SOCKET protects the soft eyeball structure
• 6 EXTRINSIC MUSCLES- provide movement for the
  eyeball
• SCLERA outermost layer of the eyeball anterior
  portion is the transparent cornea

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THE EYE

• CHOROID LAYER middle layer of the eyeball
  absorbs light to prevent glare
• CILIARY BODY OR MUSCLE SUSPENSORY LIGAMENTS
  change shape of the lens to refract light

• IRIS colored part of the eye that regulates the
  diameter of the pupil in order to regulate the
  amount of light that enters the eye strikes the
  retina
• RETINA innermost layer of the eyeball which
  contains rods cones

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THE EYE

• RODS detect light
• CONES detect color
• OPTIC DISC contains no rods or cones, also
  known as the blind spot
• OPTIC NERVE a continuation of the optic disc
  that passes through the wall of the eyeball
  transmits impulses to the brain

• POSTERIOR CAVITY contains the vitreous humor
  which is semisolid that keeps the retina in place
• ANTERIOR CAVITY contains aqueous humor which
  nourishes the lens cornea it is made by the
  capillaries of the ciliary body flows through
  the pupil is reabsorbed to blood at the canal
  of Schlemm

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PHYSIOLOGY OF VISION

• As light enters the eye it is refracted or bent
  focused following this pathway cornea, aqueous
  humor, lens, vitreous humor
• Light then strikes the retina stimulates the
  rods cones

• A nerve impulse is generated passes through the
  wall of the eyeball via the optic disc
• Optic chiasma is the site where the optic nerves
  from the eyes cross over, permitting binocular
  vision
• Nerve impulses continue on to the visual areas
  of the occipital lobes in the brain where they
  are merged to create one image turned right
  side up

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THE EAR

• Sensory organ for hearing and equilibrium
  (balance)
• Divided into 3 main sections
• outer ear
• middle ear
• inner ear

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OUTER EAR STRUCTURES

• AURICLE OR PINNA serves no real function for
  humans
• EAR CANAL curves forward down into the
  temporal bone

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STRUCTURES OF THE MIDDLE EAR

• EARDRUM at the end of the ear canal. It
  vibrates when sound waves strike it.
• AUDITORY BONES malleus, incus, stapes
  transmit vibrations to the inner ear at the oval
  window
• EUSTACHIAN TUBE extends from the middle ear to
  the nasopharynx allows air in and out of the
  middle ear to permit the eardrum to vibrate

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STRUCTURES OF THE INNER EAR

• BONY LABYRINTH contains lymph that vibrates
  with sound waves
• COCHLEA shaped like a snail shell contains
  hearing receptors
• ORGAN OF CORTI contains hair cells that bend
  help with the sense of balance

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STRUCTURES OF THE INNER EAR

• UTRICLE SACCULE contain hair cells that are
  affected by gravity
• NERVE IMPULSES TRAVEL FROM THERE TO THE BRAIN FOR
  INTERPRETATION
• SEMICIRCULAR CANALS also contain hair cells
  that function in nerve impulse transmission to
  the brain to be interpreted as body movement,
  speed change of the body stopping or starting.

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ARTERIAL RECEPTORS

• AORTIC ARCH AND RIGHT LEFT CAROTID ARTERIES
  EACH CONTAIN
• PRESSORECEPTORS which detect changes in blood
  pressure
• CHEMORECEPTORS detect changes in pH or oxygen
  CO2 levels in the blood
• THIS INFORMATION IS USED BY THE BODY TO MAKE
  CHANGES IN RESPIRATION OR CIRCULATION TO MAINTAIN
  NORMAL BP, 02 CO2 LEVELS