Senses and automatic nervous system (Chp. 16-17)

Question 1

Sensory receptors:
* Structures specialized to detect a stimulus
* Can be:
* Free nerve endings (simple) or
* Sense organs (complex)

Question 2

Classification of receptors:
1. By modality:
1. Thermoreceptor: Senses heat/cold
2. Photoreceptor: light
3. Chemoreceptor: respond to chemicals (e.g. odor taste)
4. Nociceptors: pain receptors, response to damage, ischemia, excess
stimulation
5. Mechanoreceptors: physical deformation

Question 3

By origins of stimuli:
1. Exteroceptors: external to body
2. Interoceptors: internal organs
3. Proprioceptors: position, movement of body parts

Question 4

1. General Senses:
   * Employ simple receptors in skin, muscle, tendons, joint and viscera;
   * Modalities:
   * Touch
   * Pressure
   * Stretch
   * Temperature
   * Pain
2. Special senses:
   * Employ more complex sense organs;
   * Vision
   * Hearing & equilibrium
   * Taste and smell

Question 5

• Receptors (nerve endings) are relatively simple
• Receptors classified into:
• Unencapsulated: dendrites lacking connective tissue wrapping
• Encapsulated: dendrites wrapped in glial cells/connective tissue

Question 6

Types of unencapsulated nerve endings:
1. Free nerve endings: senses warm, cold and pain
2. Tactile discs: light touch & pressure
3. Hair receptors (aka root hair plexuse): movement & bending of hairs

Question 7

Encapsulated nerve endings:
* Modified by connective tissues/glial cells, more selective to type of stimulus
1. Tactile corpuscles: in sensitive skin regions, e.g. finger-tip, palm, eyelids, lips
2. End bulbs: in mucous membranes
* Both respond to light touch and texture

Question 8

• Encapsulated receptors (con’t)
  3. Bulbous Corpuscles: heavy touch, pressure, joint movements
  4. Lamellar Corpuscles: deep pressure, stretch, tickle, vibration
  Both found in dermis and joints; combine to feel shape and texture of objects

Question 9

Encapsulated receptors (con’t)
5. Muscle spindles: in skeletal muscles, near tendon; senses muscle tensions
6. Tendon organs: in tendons; sense tendon tensions
Both sense stretch and tension

Question 10

Receptive field:
* The area supplied by a
single sensory neuron
* Smaller receptive field
higher density of
receptors
 much sensitive to
sensation
finer two-point touch
discrimination

Question 11

Whole picture of Sensory projection
pathway:
* Pain received by nociceptors (free nerve
endings)
* Nerve impulse transduced by first-order
neuron
* Synapse at gray matter of spinal cord;
* Second-order neuron decussate in the
spinal cord, nerve impulse sent via axons in
the ascending tracts;
* Second synapse with third-order neurons in
reticular formation (brainstem) or thalamus;
* Signal sent to primary somatosensory
cortex by third-order neurons;
* Pain sensation interpreted by
somatosensory association area

Question 12

Chemical senses: detect environmental chemicals
* Gustation (taste): respond to chemicals in food and
drinks
* Olfaction (smell): respond to chemicals in air

Question 13

Lingual papillae:
* Visible bumps on tongue
* Taste buds:
* Clustered in lingual papillae
* Found on tongue, and oral cavity (cheeks and soft palate, pharynx and epiglottis)
* Taste cells (sensory cells):
* Clustered in taste
buds
* Respond to chemicals

Question 14

Types of lingual papillae:
1. Filiform:
- Tiny spikes
- No taste buds
- Sense texture of food
2. Foliate:
- Leaf-like
- taste buds degenerate after 3
years old

Question 15

Types of taste bud (con’t)
3. Fungiform:
- Mushroom-like
- Each has about 3 taste buds
- for both taste and texture
4. Vallate:
- Large papillae
- arranged in a V at rear tongue
- Deep circular trench
- contains half of the taste buds

Question 16

Taste Buds:
* Sense organ for gustation
* Contains:
* Taste cells:
* as taste hairs, as receptor surfaces for taste
molecules
* Epithelial cells, not neurons; synapse with nerve
fibers
* Each lives for 7-10 days
* Basal cells:
* Stem cells to replace taste cells
* Supporting cells: unclear role

Question 17

Five primary taste sensation:
* Sweet
* Salty
* Sour
* Bitter
* Umami (Meaty taste, stimulated by
certain amino acids, glutamate and
aspartate)
* All primary taste can be detected
throughout the tongue
* Flavor is the result of combining primary
tastes, smell, food texture, temperature,
appearance

Question 18

Cranial nerves and gustation:
* CN VII facial nerve: taste of anterior 2/3 of tongue
* CN IX glossopharyngeal nerve: taste of posterior 1/3 of tongue
* CN X Vagus nerve: taste from taste buds of palate, pharynx and epiglottis
* Sensory signals set to medulla, then to
* Hypothalamus and amygdala: autonomic reflexes
* Thalamus and insula: interpret taste

Question 19

Chemical Senses: Olfaction
* Airborne chemicals detected by
receptor cells in the olfactory mucosa
* Receptor cells:
* The only neurons directly exposed to the
external environment
* Lives for about 60 days, replaced by basal
stem cells
* Has cilia (olfactory hairs), with olfactory
receptors for odor molecules
* CN I: collection of axons of receptor cells

Question 20

Receptor cells with same
receptor type (i.e.
respond to a particular
odor) send axons to a
same structure called
glomerulus
* They synapse with 2
other types of neurons:
mitral and tufted cells;
signal sent through these
cells to the brain via
olfactory tract

Question 21

• Olfactory tract sends signals to Primary
  olfactory cortex directly (not through
  thalamus)
• From primary olfactory cortex, signals
  sent to
• Insula
• Limbic system (amygdala and
  hippocampus)
• Smell may trigger emotion directly (e.g. bad
  smell)

Question 22

Anatomy of the Ear
* Three sections of ear: outer, middle and inner
ear
* Outer and middle: conducting sound to inner ear
* Inner: sense organ for hearing and equilibrium
* Outer Ear:
* Begins with auricle, supported by elastic cartilage
* Direct sound into auditory canal (external acoustic
meatus)
* Protected by guard hairs and cerumen

Question 23

Middle Ear:
* Begins with tympanic membrane,
attached to three ear-bones (auditory
ossicles)
* The 3 ossicles:
* Malleus: hammer like
* Incus: Anvil like
* Stapes: stirrup like; attach to oval window
* Connected to nasopharynx with
auditory tube (eustachian tube)
* Two muscles (tensor tympani and
stapedius) inserts on malleus and
stapes respectively, dampen vibration
if needed

Question 24

• Inner ear:
• Housed in bony labyrinth (maze) of
  cranium
• Membranous labyrinth in bony labyrinth:
  tube-in-tube structure
• Begins at oval window, lead to:
• Vestibule
• Semicircular canals
• Cochlea

Question 25

Cochlea
* Sense organ for hearing (i.e.
Spiral organ) located in
cochlear duct (blue)
* Above cochlear duct:
* vestibular membrane and scala
vestibule
* Below cochlear duct:
* Basilar membrane and scala
tympani

Question 26

Spiral organ
* Thick epithelium, generates auditory nerve
signals
* Structures:
* Hair cells, with stereocilia
* Inner hair cells: arranged in a row, supplies 90-
95% of sensory fibers of cochlear nerve
* Outer hair cells: 3 rows, adjust response to
different frequencies
* Stereocilia covered by tectorial membrane

Question 27

Auditory function
* Sound waves vibrate tympanic membrane
* Auditory ossicles transfer the vibrations
* Fluid in the inner ear vibrated, moves basilar
membrane vibrate up and down
* Hair cells are thrust up and down
* Rocking of stereocilia opens makes potassium ions
go into the hair cells and excite the cells
* Neurotransmitter from hair cells creates nerve
signal

Question 28

Saccule and
Utricle
* Sense organ for static equilibrium and
linear acceleration
* Macula: 2 X 3 mm patch of hair cells and
supporting cells
* Macula Sacculi: vertical
* Macula utriculi: horizontal
* Hair cells in macula:
* Stereocilia embedding in otolithic membrane
* Otolith: calcium carbonate and protein
* Movement of head
→ move otolithic membrane
→bending stereocilia
→ generate nerve signals
→ interpret head orientation by combining
signals from saccule and utricle

Question 29

Semicircular ducts
* Sense organ of angular
acceleration
* Filled with endolymph
* Have dilated sac called ampulla
* Inside an ampulla:
* Hair cells with stereocilia embedded
in cupula, gelatin-like structure
* Supporting cells
* Detection of angular movement:
* Head turns → semicircular ducts
rotate → endolymph lags behind →
push cupula → bends stereocilia and
stimulate hair cells → nerve signal to
the cranial nerve

Question 30

Accessory structures of Orbit
* Orbit: bony socket housing the eyeball
* Structures of orbit:
* Eyebrows: shield the eyes from glare/perspiration
* Eyelashes: guard hairs
* Eyelid (palpebrae):
* moisten eyes, block foreign objects/lights
* Separated by palpebral fissure; meet at
medial/lateral commisusures
* Tarsal plate: fibrous margin
* Tarsal glands: oily secretion, prevent tear
evaporation

Question 31

• Conjunctiva:
• Transparent, mucous membrane covers inner
  surface of eyelid and anterior eyeball
• Two contact surfaces:
• Palpebral conjunctiva: to eyelid
• Bulbar conjunctiva: to eyeball
• Prevent eyeball from drying

Question 32

Lacrimal apparatus:
* Produce and drain tears into nasal cavity
* Direction of tear flow:
* Lacrimal gland secret tears
→Conjunctiva (cleaning and lubricate)
→Lacrimal caruncle near medial commissure
→Lacrimal punctum
→Lacrimal canaliculus
→Lacrimal sac
→Nasolacrimal duct
→Nasal cavity

Question 33

Extrinsic eye muscles:
* For movement of eyes
* Rectus (straight) muscle X4, Oblique muscles X 2
* Rectus:
* superior, inferior, medial, lateral
* Move eyeballs in 4 directions
* Oblique:
* Superior: tendon passes through a loop called trochlea
* Inferior
* Rotate the eyeballs

Question 34

Three principal components:
1. Three layers (tunics), form the wall
2. Optical components, admit and focus light
3. Neural components, retina and optic nerve, produce and transduce neural
signals

Question 35

Three tunic layers:
1. Outer fibrous layer
* Sclera and cornea
* Sclera: dense collagenous connective tissue,
protect eyeball
2. Middle vascular layer (aka uvea)
* Choroid: vascular, pigmented layer
* Ciliary body: supports the lens via ciliary muscle
* Iris: adjustable diaphragm, control amount of
light through pupil by pupillary constrictor/dilator
3. Inner layer: Retina

Question 36

1. Cornea: anterior region admits light
2. Aqueous humor:
   * Serous fluid secreted by ciliary processes
   * Flows from posterior to anterior chamber
3. Lens:
   * suspended by suspensory ligament
   * Focus of image
   * 4. Vitreous body:
   * Transparent jelly filling vitreous chamber
   * Maintain intraocular pressure

Question 37

• Neural components consists retina and optic nerve
• Retina:
• Attach to wall of eyeball at
• Optic disc: where optic nerve leaves;
• Ora serrata: anterior margin
• Layered structure:
• Pigment epithelium: absorb stray light
• Photoreceptor cells:
• Convert light signal to nerve signal
• Rods: night, monochromatic vision
• Cones: day, trichromatic vision

Question 38

Retina (con’t)
* Bipolar cells:
* Interneurons, send signals from photoreceptors to
ganglion cells or amacrine cells
* Ganglion cells:
* Axons form optic nerve
* Contains melanopsin, for circadian rhythm
* Other cell types in retina:
* Amacrine cells: connecting bipolar cells (receives
rod input) to ganglion cells
* Horizontal cells: diverse roles, e.g. in perception of
contrast
* Muller glial cells: structural and metabolic support

Question 38

First-order neuron: bipolar cells
* Second-order neuron: retinal ganglion cells
* Axons of ganglion cells form optic nerve,
form optic chiasm with hemidecussation
* Most axons from optic tract end at the
thalamus (lateral genicular nucleus),
synapse with third-order neuron]
* Third-order neurons form the optic
radiation, project to the primary visual
cortex
* Melanopsin-containing ganglion cells: to
pretectal nucleus and superior colliculus,
for visual reflex

Question 39

Autonomic Nervous system (ANS)
Regulate fundamental life processes, e.g. heart rate, blood
pressure, temperature, digestion etc. unconsciously
* Works through visceral reflexes

Question 40

Visceral reflex
* Unconscious, automatic, stereotyped responses to stimulation
* Involves visceral receptors and effectors
* Somewhat slower response
* Receptors detect
* Stretch
* Tissue damage
* Blood chemicals
* Body temperature
* Other internal stimuli
* Afferent neurons leading to CNS, interneurons in the CNS, efferent

Question 41

visceral reflex
* Example: high blood pressure
activates visceral baroreflex

Question 42

Neural Pathways of ANS
* Motor pathways different
between ANS and somatic
motor system
* Presence of autonomic
ganglion in ANS
* Preganglionic neuron
* Soma in brainstem or spinal
cord
* Axon terminates in ganglion
* Postganglionic neuron
* Soma in ganglion
* Axon extends to target

Question 43

Division of the ANS
* Traditionally ANS divided into sympathetic and parasympathetic
divisions
* Sympathetic:
* Prepare for ‘’fight-or-flight’’
* Increase alertness, heart rate, blood pressure, etc
* Parasympathetic:
* Calming effect: ‘’rest and digest’’
* Reduce energy expenditure and for bodily maintence

Question 44

Motor pathway of Sympathetic Division
* Thoracolumbar
division:
* Nuclei arise at
thoracic and lumbar
spinal cords
* Relatively short
preganlionic fibers
* Relatively long
postganglionic fibers
* Sympathetic chain
ganglia (paravertebral
ganglia)

Question 45

Motor pathway of Parasympathetic
Division
* Craniosacral division
* Motor pathway arise from
cranial/sacral spinal cord
* Long preganglionic fibers
* End in terminal ganglia in
or near the target organ
* Very short postganglionic fibers
* Innervation to head
* Oculomotor nerve (III)
* Facial nerve (VII)
* Glossopharyngeal nerve (IX)
* Innervation to viscera
* Vagus nerve (X)