Sensory Organs

Sensory organ

• sensory organ = neuron + accessory tissues

Sensory receptor

• sensory receptors - monitors external/internal environment

  • exteroceptors - environment

  • interoceptors - internal body

• free sensory receptors detect pain, extreme cold/heat

Target organ

• somatic sensors - provide info from somatic tissues (skeletal muscles, skin)

• visceral sensors - provide info from internal organs

Meissner’s corpuscle

an encapsulated sensory receptor that detects touch

Pacinian corpuscle

an encapsulated sensory receptor that detects pressure

Merkel disk

an encapsulated sensory receptor that detects pressure

Corpuscle of Ruffini/Ruffini organ

an encapsulated sensory receptor that detects warmth

End-bulb of Krause

an encapsulated sensory receptor that detects cold

Associated sensory receptors

nerve endings wrapped around another organ - hair follicles, proprioceptors

Stretch reflex

• Golgi tendon organs - sense force of muscle; stress and pressure

• Joint capsule receptors - sense joint angle stress and pressure

• afferent sensory nerve - sense tensions and stimulate motor neurons to cause muscle contraction

Chemoroceptors

specific chemical presence induces electrical impulse

Olfaction

detection of scent in nasal passage, vomeronasal organ, etc

Nasal passages phylogeny

• reptiles

  • vestibule (anterior) and nasal chamber (posterior)

  • lateral wall (turbinate)

  • nasopharyngeal duct - exit

• mammals - extensive turbinates

• fish - well developed senses in nasal sacs

• tetrapods - external and internal naris (choana)

• amphibians - nasolabial groove

Nasal turbinates

• warms, slows, and filters air

• lined with chemoreceptors

Vomeronasal organ

• accessory olfactory sense only in some tetrapods

• absent - fish, turtles, crocodiles, birds

• reptiles - prominent structure in snakes, lizards (tongue flicking)

• mammals - isolated area olfactory membrane in nasal cavity connected to mouth by nasopalatine duct

  • recognizes chemicals associated with social, reproductive pheromones

  • separate pathway from other olfactory info

  • pheromones

    • ex. Feliway, calm, FurAppease (for calves)

• contains microvilli cells (not cilia) on secretory cells

Taste buds

• 5 basic tastes - sweet, sour, salty, bitter, umami (savory)

• amphibians, reptiles, avian - mouth, pharynx

• mammals - tongue

• cranial nerve innervation - facial (7), glossopharyngeal (9), vagus (10)

• fungiform papilla (mushroom)

• filiform papilla

Pineal complex/gland

• anamionte - photoreception

• amniotes - endocrine gland

  • melatonin - involved in circadian rhythm (bright light = awake)

Ear

• External - external auditory meatus

  • fish, amphibians - absent

  • birds, mammals - elongated

  • pinna - elastic cartilage

• Middle

  • tympanic membrane

  • ossicles - malleus, incus, stapes

• Inner

  • vestibular apparatus

  • innervated by vestibulocochlear nerve (7)

Vestibular apparatus

• inner ear

• organ of balance - “membranous labyrinth”

• semicircular canals - respond to rotation/turn of head

  • endolymph - fills semicircular canals

  • perilymph - surrounds endolymph

  • cristae ampullae within the semicircular canals sense rotational movement

• sacculus, utriculus - otolith receptors that respond to change in orientation in gravitational field

Eye

• radiation receptors - receive stimuli from various wavelengths of electromagnetic radiation

• wavelengths seen - 380nm - 760 nm

• UV - fishes, reptiles, birds

• infrared - vampire bats, pythons, pit vipers

Eye anatomy

• sclera - outer tough capsule

• uvea - middle layer

  • choroid - vascular

  • ciliary body - smooth muscle

  • iris - thin layer forming pupil

• retina - photreceptors

Accommodation

• terrestrial - cornea focuses, lens refines the image

• aquatic - cornea does little focusing, lens moves

Photoreception

• rods - absent in fovea - low light vision

• cones - color vision in bright light

Depth perception - eye placement

• monocular - separate vision fields for each eye

• binocular - various degrees of overlap between visual fields