Special Senses....Anatomy...

Special Senses

I). Sense Pathway

STIMULUS Peripheral nervous system Sensory receptors Receptor Proteins Ion Channels Open Nerve Impulse Sensory Nerve Fiber (afferent) Central Nervous System Spinal Cord
Reflex Arc (efferent nerve fiber) Motor unit Muscle response	Brain Stem Thalamus Sensory Area In the cerebral cortex Sensory association area Sensation Perception

II. Sensory Receptors
 

A).  Receptors are specialized to receive a certain type of stimuli which will result in sensation in the cerebral cortex

B).  Types of senses

  1.  Somatic

 2.  Special Senses

C.  Types of sensory receptors

1. Chemoreceptors

 

2. Pain Receptors

3. Mechanoreceptors
4. Thermoreceptors

5. Photoreceptors

III) Pain

  Free Nerve Endings

A). Damaged tissues signal that action must be taken

B).  Pain receptors are responsive to different stimuli:

	Temperature
	Mechanical damage
	Chemicals
	Ischemia
	Hypoxia
	Mechanical Sensitive

C).  Pain receptors do not adapt

D).  Pain receptor become more sensitive to pain producing chemicals thus lowering the pain threshold.

E).  Pain Pathways

1).  Acute Pain Fibers

 

2).  Chronic Pain Nerve Fibers

Pain can become debilitating even if the stimuli is no longer present

F. Pain Travels

Free nerve ending Spinal nerve (some cranial nerves) peripheral nervous
Reflex Arc (efferent nerve fiber) Motor unit Muscle response	Terminate in the reticular formation Hypothalamus Thalamus Awareness of pain Cerebral cortex Mechanical and emotional response

IV.  Temperature

A). Receptors

  Thermoreceptors

  Free nerve endings

 

B).  Warm receptors

C).  Cold receptors

V.  Touch & Pressure

Mechanical Receptors
Sense mechanical forces that deform or displace tissues

A). Free Nerve Endings
B). Meissner’s Corpuscles
C). Pacinian Corpuscles

VI). Vision

A). Accessory structures of the eye
1). Eyebrows: Protect from sunlight and stop perspiration from entering the eye.
2). Eyelids:

	Sweat and sebaceous glands (produce sandman=s sand)
	Muscles that open and close eye causing reflex blinking which protects and lubricates the eye.
	Eyelashes with nerve endings trigger blinking if anything touch

3). Conjunctiva

Lines interior of the eyelid and folds over the eye.

4). Lacrimal apparatus

Contains the lacrimal gland or tear ducts drain into the nasal cavity.

Lacrimal puncta: red dots on margin of each eyelid.

B). Eyeball Anatomy

1). Lens: Transparent biconvex, focusing apparatus of the eye & divides anterior & posterior segments.
2). Humors: fluids that fill internal cavity
3). Layers
a). Outer tunic: 

i). Sclera: Fibrous white dense connective tissue seen as white of the eye.
ii). Cornea: Transparent fibrous connective tissue that allows light to enter. (bulges anteriorly)

b). Middle Tunic

i). Iris: Visible colored part; with pupil that allows the light to enter.

c).  Inner Tunic

i).  Retina (sensory area) Posterior interior layer extends to the cilliary body

Blind spot or optic disc where optic nerve passes through.

C). Photoreceptors

1). Rods:

	Low light and peripheral vision receptors.
	Black and white vision.

2). Cones

Operate in bright light and provide color vision and visual acuity.

      Types of cones

	Pigment B (blue)
	Pigment G (green)
	Pigment R (red)

Various combinations of cones are stimulated by in-between colors

D). Light, Vision and Perception

1). Light travels in waves and consists of small packets called photons.
2). The objects absorb some wavelengths and reflects back others.
3). The color we perceive is the color that the object reflects.

4). The real image is formed on the retina & it is upside down and reversed.

5).  Photoreceptors in back hyperpolarize.

6).  The signal is feed forward to the bipolar neurons and the ganglion cells.

7). Down the optic nerve.

8).  At the optic chiasma the nerves cross right to left & left to right but also continue on right to right and left to left.

9). To the thalamus.

(All cerebral cortex signals go through thalamus first)

10). To the visual cortex in the occipital lobes.

11). Visual cortex sensory and association areas fuses the images resulting in depth  perception or 3 dimensional vision so we perceive the entire field right side up.

VII.  Hearing

A).  Properties of sound

Sound is a pressure disturbance originating from a vibrating object and propagated by molecules in the air  or other medium.

A sound wave moves outward in all directions, but the molecules in the air just vibrate against each other.

1).  Frequency:  tone or pitch.  (units:  Hertz) 

  Number of waves that pass a given point. 

  Short wavelength (distance between waves) higher the sound.

2).  Amplitude:  intensity or loudness  (units: Decibels)

   Height of the waves

B). Anatomy

A). Outer ear (external)

1). Pinna or Auricle: shell shaped cartilage projection
2). External auditory canal: tube that extends to eardrum
3). Tympanic membrane: ear drum

B). Middle Ear

1). Tympanic cavity: Separates external & internal ears
2). Ossicles: 

	Malleus (hammer)
	Incus (anvil)
	Stapes (stirrups)

3). Oval Window with secondary tympanic window
4). Auditory tube or Eustachian tube: Continuous with pharynx opens to equalize pressure

C). Inner Ear

1). Bony or Osseous Labyrinth

i). Vestibule: central cavity; houses equilibrium receptors.
ii). Semicircular Canals:
iii). Cochlea: fluid filled; spiral chamber houses

Organ of Corti: receptor for hearing.

2). Membranous Labyrinth: series of sacs & ducts within the bony labyrinth.

D). Properties of Sound

1). Sound is a pressure disturbance originating from a vibrating object and propagated by molecules of the medium.

The molecules in the air just vibrate against each other.

2). Frequency: tone or pitch. (units: Hertz)

	Number of waves that pass a given point.
	Short wavelength (distance between waves) higher the sound.

3). Amplitude: intensity or loudness (units: Decibels)

Height of the waves

E). Process of Hearing

 Steps
Sound waves are propagated through the air.
The pinna and the auditory canal focus the waves.
Sound wave strikes the tympanic membrane and starts it vibrating.
The malleus is secured to the membrane and passes the same total forces through the stapes and into the oval window.
The oval window is smaller so the force becomes concentrated. (pressure is related to area)
The wave is passed on to the cochlea and the fluid filled chamber vibrates. It also causes the fluid to vibrate the round window.

	Fluids cannot be compressed.
	So when the stapes moves in and out and the membrane moves up and down the round or cochlear window will also move in and out.

Hair cells in the Organ of Corti are stimulated by activity in the membrane

High pitch activates cells near oval window and low pitch activates cells further away.

 Stimuli are sent to the spiral ganglia and the cochlear nerve.
To the auditory reflex center of the midbrain.
To the thalamus.
To the auditory cortex in the temporal lobe.
Each auditory cortex receives input from both ears.
Cortical processing distinguishes wavelengths and sounds.

B).  Distinguishing sounds

1)  Pitch

Specific cochlear cells are stimulated for different pitch and the cortex has a tonotopic map of the regions of the organ of Corti.

2).  Detection of loudness

Some cochlear cells have a higher threshold.

3).  Localization of sound

Determined by relative timing and relative intensity. (ie. overhead: both ears received sound waves at the same time)

VIII). Equilibrium (Mechnoreceptors)

Responds to position of the head plus vision and position of the limbs.

A). Static Equilibrium:

	Maculae in the cochlea and the semicircular canal respond to linear motion of the head but not on unchanging head position.
	A change in the position of the vertical hairs in the maculae results in nerve impulses down the vestibular nerve

B). Dynamic Equilibrium
1). Crista ampullaris: Hair cell receptors in the semicircular canals
2).  Semicircular canals are located in all 3 planes and rotational movement of the head will affect a receptor.
3).  Respond to changes in velocity of rotatory movement.As the hairs are bent they depolarize and send impulses
4). Pathway

i). Hair cells send impulse to the vestibular nerve.
ii). To the brain stem or cerebellum integrate information from vision and somatic receptors and sends reflex actions to the brain stem motor center.
iii). Skeletal muscle activity, posture and head position are adjusted.

IX. Taste: Gustation

 (Chemoreceptors)

A). Anatomy

1). Papillae

Surface structures on the tongue contain taste buds.

2). Taste buds

10,000 taste buds on the tongue, and soft palate.

Contain
i). supporting cells,
ii). receptor (gustatory) cells

with sensitive gustatory hairs

iii). basal cells: act as stem cells replacing needed parts.

C). Taste Sensation
Categories

1). Sweet

Responds to sugars and some amino acids (and lead)

2). Sour

Responds to H+

3). Salty

Responds to metal ions & NaCl

4). Bitter

Responds to alkaloids

D). Regions on the tongue
E). Activation of Taste

1). Chemical is dissolved in saliva. We can not taste material that does not dissolve.
2). Molecules bind to receptor proteins.
3). Nerve impulses are generated in associated nerve fibers.

	Different cells have different threshold for activation.
	Bitter is most sensitive than sour than sweet & salty
	Each taste opens up different ion channels.

4). Impulses travel to the medulla and than the thalamus
5). To the gustatory cortex in the parietal lobe.
6). Reflexes for digestion are triggered.

F). Other factors that affect taste

1). Smell
2). Thermoreceptors, pain receptors, mechanoreceptors record the temperature and texture of food.
3). Vision: what food looks like.

X.  Sense of Smell: Olfactory

 (Chemoreceptors)

Located on the roof of the nasal cavity covering the superior nasal conchae

We distinguish at least 10,00 chemicals

A). Anatomy

1). Olfactory receptor cells with cilia

Surrounded by:

2). Supporting cells: produce mucus to capture and dissolve airborne odor molecules.
3) Basal cells

B). Physiology of smell

1). Odor must be volatile (gaseous state) and water soluble.
2). Chemicals bind to protein receptors and open ion channels.
3). Synapse in the distal end of the olfactory tracts.
4). Signals are integrated at the glomeruli and the mitral cells.
Only highly excitable olfactory impulses are transmitted resulting in olfactory adaptation.
5). Impulse from olfactory to the thalamus to the olfactory cortex of the frontal lobe.
Also to the limbic system eliciting an emotional response. (ie. Danger, safety, etc)