CH. 19 Senses: General and Special

Question 1

What are the functional characteristics of sensory receptors?

Answer 1

1. Act as transducers; transducers change one form of energy into a different form - specific to type of receptor but is always transduced to electrical energy
2. Receptive field: the entire area through which the sensitive ends of the sensory receptor cell are distributed - some are small while some are big and used more generally
3. Tonic and phasic receptors: all sensory receptors become less sensitive to a constant stimulus, adaptation. difference in adaptation is used to categorize sensory receptors as either tonic or phasic receptors
   - Tonic receptors: constant stimulus, continuously generate nerve impulses and only slowly decrease the number relayed to the CNS
   - Phasic receptors: exhibit rapid adaptation to a constant stimulus; generate nerve impulses only in response to a new stimulus and quickly decrease the number of nerve impulses related to the CNS

Question 2

What are the 3 ways in which you classify sensory receptors?

Answer 2

1. Sensory receptor distribution: General sense receptors are distributed throughout the body and are simple in structure
   - subdivided into somatic sensory receptors and visceral sensory receptors

Special sense receptors: located only within the head and are specialized, complex sense organs - olfaction (smell), gustation (taste), vision (sight), hearing (audition), and equilibrium (head position and acceleration)

2. Stimulus origin: based upon where stimulus originates
   - 3 types: 1) Exterorecptors: detect stimuli from external environment 2) Interoreceptors: detect stimuli in internal organs 3) Proprioceptors: located in muscles, tendons, and joints; detect body and limb movements, skeletal muscle contraction and stretch, and changes in joint capsule structure
3. Modality of stimulus: classification according to stimulus they perceive
   - 5 groups of sensory receptors: 1) Chemoreceptors 2) Thermoreceptors 3) Photoreceptors 4) Mechanoreceptors 5) Nocireceptors

Question 3

What are the clinically significant types of pain?

Answer 3

1. Phantom pain: sensation associated with a body part that has been removed
2. Referred pain: when impulses from a certain viscera are perceived as originating not from the organ, but in dermatomes of the skin

Question 4

What are the 3 different types of unencapsulated tactile receptors?

Answer 4

1. Free nerve endings: terminal branches of dendrites; reside closest to the surface of the skin
2. Root hair plexuses: specialized free nerve endings that form a weblike sheath around hair follicles in the reticular layer of the dermis
3. Tactile disks: flattened nerve endings that function as tonic receptors for fine touch; tactile cells are the only specialized receptor cells - other tactile receptors are simply the dendritic endings of primary sensory neurons

Question 5

What are the 4 different types of encapsulated tactile receptors?

Answer 5

1. End bulbs: dendritic endings of sensory neurons ensheathed in connective tissue; located in the dermis of the skin near the border of the stratified squamous epithelium and in mucous membranes - detect light pressure and low frequency vibration
2. Lamellated corpuscles: composed of several dendritic endings ensheathed with an inner core of neurolemmocytes and outer concentric laters of connective tissue; occur deep within reticular layer of the dermis of skin
3. Bulbous corpuscles: dendritic endings of sensory neurons ensheathed within connective tissue that are housed within the dermis and subcutaneous layer, as well as in joint capsules - detect deep pressure and distortion in skin and are tonic receptors that do not exhibit adaptation
4. Tactile corpuscles: large, encapsulated oval receptors that are formed from highly intertwined dendrites enclosed by modified neurolemmocytes which are then covered with dense irregular CT - phasic receptors for disciminative touch to determine textures and shapes of an object and for light touch

Question 6

What are the 4 types of papillae on the tongue?

Answer 6

1. Filiform papillae: short and bristlelike; assist in detecting texture and manipulating food
2. Fungiform papillae: blocklike projections primarily located on the tip and sides of the tongue; contains a few taste buds
3. Vallate papillae: arranged in inverted V shape on the posterior dorsal surface of the tongue; most taste buds are housed within the walls of these papillae along side facing depression
4. Foliate papillae: extend as ridges on the posterior lateral side of the tongue and house only a few taste buds during infancy and early childhood

Question 7

What are the 3 distinct cell types of taste buds?

Answer 7

1. Gustatory cells: detect tastants in our food
2. Supporting cells: sustain the gustatory cells
3. Basal cells: function as neural stem cells to continually replace the relativey short lived gustatory cells

Question 8

What are the 5 basic taste sensations?

Answer 8

1. Sweet
2. Salt
3. Sour
4. Bitter
5. Umami

Question 9

What are the 3 distinct cell types of the olfactory epithelium?

Answer 9

1. Olfactory receptor cells: detect odors
2. Supporting cells: sandwich olfactory neurons and sustain receptors
3. Basal cells: function as neural stem cells that continually replace olfactory receptor cells

Question 10

What are the external accessory structures of the eye?

Answer 10

1. eyebrows
2. eyelashes
3. eyelids

Question 11

What are the internal accessories of the eye?

Answer 11

1. conjuctiva: specialized stratified columna epithelium that forms a continuous lining over the external, anterior surface of the eye (ocular conjuctiva) and internal surface of the eyelid (palpebral conjuctiva)
2. lacrimal glands: located within the superolateral depression of each orbit and continuously produces tears

Question 12

What are the three principal layers that form the wall of the eye?

Answer 12

1. fibrous tunic (outermost layer): composed of the anterior cornea and the posterior sclera
2. vascular tunic (middle layer): houses an extensive array of blood vessels, lymph vessels, and intrinsic muscles of the eye - subdivided into three parts (choroid, ciliary body, and iris)
3. retina (innermost layer): internal layer of the eye wall; composed of two layers (outer pigmented layer and an inner neural layer)

Question 13

What are the 3 distinct layers of cells that form the neural layer of the retina?

Answer 13

1. photoreceptor cells: outermost layer of the neural layer; two types (rods that pick up contrasting dark and light tones and cones that provide precise visual acuity and color recognition)
2. bipolar cells: immediately internal to photoreceptor layer; rods and cones form synapses on the dendrites of bipolar cells - sandwiched between the photorecptor layer and the bipolar cells is a thin web of horizontal cells
3. ganglion cells: forms the innermost layer in the neural layer

Question 14

What are the cavities within the eye?

Answer 14

1. anterior cavity: space anterior to the lens and posterior to the cornea; iris of the eye subdivides the anterior cavity further into anterior chamber and posterior chamber
   - contains fluid called aqueous humor which is a filtrate of plasma that resembles CSF and removes waste products and helps maintain chemical environment within chambers
2. posterior cavity: posterior to the lens and is surrounded laterally, superiorly, inferiorly, and posteriorly by the retina; flattened structure where many of the optic nerve axons decussate to the other side

Question 15

What are the 3 distinct anatomic regions of the ear?

Answer 15

1. external ear: skin-covered, primarily cartilaginous structure called the auricle; serves to protect entry into ear and direct sound waves into external acoustic meatus
2. middle ear: contains an air-filled tympanic cavity; maintains an open connection with the atmosphere through the auditory tube
   - houses three smallest bones called auditory ossicles (malleus, incus, and stapes)
   - also contains two skeletal muscles (stapedius and tensor tympani)
3. inner ear: located within the petrous part of the temporal bone, where there are spaces called the bony labyrinth; winthin are membrane-lined, fluid filled tubes and spaces called the membranous labyrinth (where receptors for equilibrium and hearing are housed)

Question 16

Explain the nerve pathway that relays sensory input from the vestibular apparatus.

Answer 16

1. sterocilia of either maculae or crista ampullaris distory, nerve impulses are initiated through the vestibular branch of the vestibulochlear nerve

2, sensory axons of vestibular branch terminate at either the medulla oblongata or cerebellum. paired vestibular nuclei within superior region of medulla oblongata integrate the stimuli from the vestibular apparatus to reflectively control movements of the eye and skeletal muscle contraction for balance

3. nerve impulses are sent from the vestibular nuclei and cerebellum to the thalamus and eventually the cerebral cortex for further processing and for our awareness of body position

Question 17

Explain the nerve pathway of the auditory pathway that initiates nerve impulses that travel through in the brain.

Answer 17

1. when basilar membrane moves, the sterocilia on spiral organ hair cells distory. this initiates nerve impulses that are transmitted through the cochlear nerve branches that attach to hair cells, sensory axons of cochlear nerve terminate in the cochlear nucleus within brainstem; sensory neurons synapse with secondary neurons housed within nucleus
2. secondary neurons in cochlear nucleus take on of two pathways - a) axons of some secondary neurons project directly to inferior colliculi of midbrain or b) axons from other secondary neurons project to the superior olivary nucleus within pons and synapse with other sensory neurons that then project to inferior colliculi
3. nerve impulses transmitted from inferior colliculus to medial geniculate nucleus of thalamus for initial processing and filtering of auditory sensory info
4. axons from tertiary neurons in thalamus extend to the primary auditory cortex within temporal lobe, where nerve impulses are perceived as sounds