Ch. 10 Sensory Physiology Flashcards
Sensory Receptors
Transduce (convert energy into a different form) different forms of energy in the “real world” to nerve impulses.
Different modalities of sensations (sound, light, pressure) arise from differences in neural pathways and synaptic connections
–ex: If the optic nerve delivers an impulse, the brain interprets it as light even though the impulse is the same as for hearing
Functional Sensory Receptors: Chemoreceptors
Sense chemicals in the environment (taste, smell) or blood
Functional Sensory Receptors: Photoreceptors
Sense light
Functional Sensory Receptors: Thermoreceptors
Respond to cold or heat
Functional Sensory Receptors: Mechanoreceptors
Stimulated by mechanical deformation of the receptor (touch, hearing)
Information Sensory Receptors: Proprioceptors
Found in muscles, tendons, and joints. Provide a sense of body position and allows fine muscle control
Information Sensory Receptors: Cutaneous (skin)
Touch, pressure, heat, cold, and pain
Information Sensory Receptors: Special Senses
Vision, hearing, taste, smell, equilibrium
What are the 2 origins of sensory receptors?
Exteroceptors and Interoceptors
Exteroceptors
Respond to stimuli from outside the body; includes cutaneous receptors and special senses
Vision, hearing, taste, smell
Interoceptors
Respond to internal stimuli; found in organs; monitor BP, pH, and oxygen concentrations
Cardiovascular system: sense BP
Phasic
Respond w/ a burst of activity when stimulus is first applied but quickly adapt to the stimulus by decreasing response
–sense something and fire response/signal
Allow sensory adaptation - cease to pay attention to constant stimuli
–ex: live near airport hearing constant noise –> adaptation and it becomes background activity
Ex: smell, touch, temperature
Tonic
Maintain a high firing rate as long as the stimulus is applied
Ex: pain
Phasic Receptor
Fast-adapting
Fire less frequently –> consistency of signal
Tonic Receptor
Slow-adapting
What is the only special sense that bypasses the Thalamus?
Olfaction (smell)
Describe Olfaction’s Sensory Pathway
Olfaction goes from nose to Olfactory cortex, not relayed through Thalamus
Directly process smell, all other senses relayed through Thalamus to be processed and sent to where it needs to go
What are the 2 types of Chemoreceptors?
Taste (gustation)
Smell (olfaction)
Taste (gustation)
Responds to chemicals dissolved in food and drink
Smell (olfaction)
Responds to chemical molecules from the air; olfaction influences gustation
Gustation
Receptors are called taste buds - consist of 50 to 100 specialized epithelial cells w/ long microvilli that extend out through the pore in the taste bud
- -each taste bud has taste cell sensitive to each category of 5 tastes: salty, sour, sweet, umami (meaty), bitter
- -microvilli come into contact w/ chemicals
- -cells behave like neurons by depolarizing and producing action potentials
- -cells release neurotransmitters onto sensory neurons
Olfactory Receptors
Bipolar neurons w/ ciliated dendrites projecting into nasal cavity
Proteins in the cilia bind to odors
~380 genes code for ~380 different olfactory receptors
One odorant molecule stimulates one protein
Vestibular Apparatus
Provides sense of equilibrium
Located in inner ear
Consists of:
- Otolith organs
- ->Utricle and Saccule - linear acceleration (ex: running toward door)
- Semicircular canals - rotational acceleration (ex: rotating body)
Inner Ear
Consists of a body labyrinth surrounding a membranous labyrinth
Between the 2 is fluid called Perilymph
W/in the membranous labyrinth is fluid calls Endolymph, which has an unusually high K+ concentration, which will produce depolarization
Why is the Perilymph important?
The multiple layers of membrane and fluid allow us to detect subtle movements
This wouldn’t be possible if the membrane was against bone w/o fluid
Sensory Hair Cells
Modified epithelial cells w/ 20-50 hairlike extensions called Stereocilia (not true cilia) and one Kinocilium (true cilium)
When the stereocilia bend toward the kinocilium, K+ channels and K+ rushes into the cell and depolarizes the cell
–K+ concentration high on outside of cell, so when channels open it rushes in and depolarizes cell
Cells release a neurotransmitter that depolarizes sensory dendrites in vestibulocochlear nerve
Which has more structural support: stereocilia or microvilli?
Stereocilia
What causes the stereocilia to move?
Fluid moving causes stereocilia to bend (won’t bend w/o fluid movement)
What is the tympanic membrane?
The eardrum
Which part of the ear (outer, middle, or inner) is the fluid filled cavity?
The inner ear
Middle Ear
Air-filled cavity between Tympanic Membrane and Cochlea
Contains 3 bones called Ossicles:
-Malleus, Incus, Stapes
Vibrations are transmitted and amplified along the bones
The stapes is attached to the Oval Window, which transfers the vibrations into the cochlea
What is the purpose of the 3 ossicles (malleus, incus, stapes)?
Transmit sound waves that passed through tympanic membrane to the cochlea via the oval window
Cochlea
Hearing part of inner ear
3 chambers:
- -upper chamber is portion of bony labyrinth called Scala Vestibule (Perilymph)
- -lower bony chamber called Scala Tympani (Perilymph)
- -cochlea also contains a membranous labyrinth called Cochlear Duct (Scala Media) filled w/ Endolymph
What’s special about Endolymph?
There’s a high K+ concentration outside of the cell; contains stereocilia
How does the ear prevent echoing?
Sound waves are dissipated back into the middle ear from the inner ear at the Round Window
Is the Cochlea fluid filled?
Yes (part of inner ear)
Hearing: Mechanism
When sound waves enter the scala media, the tectorial membrane vibrates, bending stereocilia in the hair cells of the Organ of Corti.
- -opens K+ channels that are facing endolymph
- -K+ rushes in, depolarizing cell (b/c it’s high concentration on outside)
- -releases glutamate onto sensory neurons
- -K+ returns to perilymph at base of stereocilia
Hearing: Neural Pathways
Sensory neurons in inner ear –> integrated in Thalamus –> auditory cortex
Vision
Comes from light energy transduced into nerve impulses
Only a limited part of the electromagnetic spectrum can excite photoreceptors
Where is the blind spot in the eye?
At the optic disc
Is the eye highly vascularized?
Yes
Path of Light (I’m sorry, but you need to know this)
- Light passes through cornea and into anterior chamber of eye
- Passes through pupil, which can change shape (due to pigmented iris muscle) to allow more/less light in
- Passes through lens, which can change shape to focus image
- Passes through posterior chamber and the vitreous body
- Finally, it hits the retina, where photoreceptors are found and then absorbed by the pigmented choroid layer
Pupil and Iris
Iris can increase or decrease the diameter of the pupil
- Constriction: contraction of circular muscles via parasympathetic stimulation
- Dilation: contraction of radial muscles via sympathetic stimulation
Iris also has pigmented epithelium for eye color
Lens
Composed of layers of living cells that are normally completely clear (must be transparent to do its job)
Avascular
Cell metabolism is anaerobic (lens is a group of cells!)
Attached to muscles called Ciliary Bodies
Suspended from Suspensory Ligaments
Visual Fields
Part of the external world projected onto the retina
Right side is projected onto the left side of retina
Left side is projected onto right side of retina
(see ch. 10 p. 36 notes for a good picture of how this works)
Lens Accommodation
Accommodation is the ability of the lens to keep an object focused on the retina as the distance between the eye and the object moves
Contraction of the ciliary muscle causes the lens to thicken and roundup (close vision)
Relaxation of the ciliary muscle causes the lens to thin and flatten (distant vision)
Retina
Extension of the brain, so the neural layers face outward toward incoming light (have to face outward in order to receive light)
Neuron axons in retina are gathered at a point called the Optic Disc (blind spot) and exit as the Optic Nerve; blood vessels also enter/leave here
Photoreceptors (rods and cones) are in the inner layer (toward vitreous body)
These synapse on a middle layer of bipolar cells, which synapse on the outer layer of ganglion cells
There are also horizontal cells and amacrine cells w/in the layers
Rods and Cones: Outer and Inner Segments
Outer segment: full of flattened discs with photopigment molecules
Inner segment: contains the cell organelles
Rods
Black and white vision in low light; contain rhodopsin
Cones
Color vision and acuity, contain photopsin which vary depending upon cone
Vision: Mechanism
Stimulation of photoreceptor cells is outlier
Stimulation results in hyperpolarization (instead of depolarization)
Bipolar cells activate ganglion cells that transmit action potentials to brain
