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)