Special Senses Flashcards
What is the sensory system?
Portion of the nervous system composed of
1. Sensory receptors
2. Nerve pathways that conduct sensory info from receptors to CNS
3. Parts of the brain that process sensory information
What are the two types of sensory receptors?
- One with a receptor membrane
- One with a receptor cell, which releases vesicles containg neurotransmitters
In response to a stimulus, what do receptors generate?
Graded potentials that can initiate APs, which travel into CNS
What is an adequate stimulus?
A form of energy to which a sensory receptor is most responsive
What are the major classes of sensory receptors? (5)
- Chemoreceptors (O2, CO2, glucose)
- Mechanoreceptors (pressure, cell stretch, sound, vibration)
- Photoreceptors (photons of light)
- Thermoreceptors (degrees of heat)
- Nociceptors (pain)
What are the four properties of all stimuli?
- Modality
- Location
- Intensity
- Duration
What is modality?
The type of stimulus; there is a specialized receptor for each type of stimulus modality
What is location?
Identified by receptive fields
What is lateral inhibition?
- Increase of contrast between active receptive fields and inactive neighbours
- Exact localization which increases the brain’s ability to localize the input
What is intensity?
Coded by number of receptors activated, and frequency of APs
What is duration?
Coded by duration of APs
What is the difference between phasic and tonic receptors?
Phasic Receptors: Quick to respond, but adapt rapidly to constant stimuli, sensitive to changes.
Tonic Receptors: Sustain a response to constant stimuli, less prone to rapid adaptation, maintain sensitivity over time.
What is somatic sensation?
Sensation from the skin, skeletal muscles, bones, tendons, and joints initiated by a variety of sensory receptors
What is the somatic sense pathway?
What does viscual perception require? (2)
- The eye; an organic which focuses the visual image and responds to light
- Neural pathways, which interpret the signals and transform the visual image into a pattern of graded and action potentials
What are major components of the human eye? (3)
- Optic disk (blind spot): where neurons join into the optic nerve
- Macula: round area at the center of retina, at the back of the eyeball
- Fovea: the center part of the macula, which is the region of sharpest vision
What is the retina?
The layer of photoreceptors cells and glial cells within the eye that captures incoming photons and transmits them
What are the optics of vision?
Relies on refraction
What part of the eye is responsibe for refraction?
Cornea
What is the roles of the lens?
Focusing the visual image on the retina
What is accommodation?
The process by which the eye adjusts the shape of the lens to keep objects in focus
What is myopia?
Difficulty seeing far objects; corrected with concave lenses
What is hyperopia?
Difficulty seeing near objects; corrected with convex lens
What is presbyopia?
The loss of elasticity of the lens resulting in the inability to accommodate for near vision
What is astigmatism?
When the surface of the lens or cornea is not smoothly spherical, resulting in distorted images
What is glaucoma?
Damage to the retina due to increased intraocular pressure
What are cataracts?
Clouding of the lens
What is the pathway for sight?
- Ganglion cells
- Bipolar cells
- Photoreceptors
What are rods?
Photoreceptors that function in low light conditions
What are cones?
Photoreceptors that function best in bright light; responsible for colour vision
What does a photoreceptor look like?
What is the sense of hearing based on? (4)
- Physics of sound
- Physiology of external, middle, and inner ear
- Nerves that travel to the brain
- The brain regions involved in sensing and perceiving acoustic information
What are the three bones in the middle ear?
- Malleus
- Inces
- Stapes
What is the pathway of sound transmission in the ear?
- Ttmpanic membrane deflects
- Middle ear bones move
- Membrane in oval window moves
- Pressure waves travel through perilymph of scala vestilbuli and return to round window through scala tympani
- Membrane in round window moves
What does the round window lead to?
Cochlea
Where are the hair cells found in the auditory system?
On the organ of corti
What do the vibration caused by sound waves do?
Bends the stereocilia on these hair cells via an electromechanical force
Where do the primary sensory neurons in auditory pathways project to?
The medulla oblongata in the brainstem
What is the auditory pathway for secondary sensory pathways?
- Project to both sides of the brain so both sides get signals from both ears
- Synapse in nuclei in midbrain and thalamus
- Finally projects into the auditory cortex
What does the localization of a sound source require?
Simultaneous input from both ears
What is conductive hearing loss?
No transmission through either external or
middle ear (ear wax)
What is central hearing loss?
Damage to neural pathway between ear and cerebral
cortex or damage to cortex itself (uncommon, stroke)
What is the sensorineural hearing loss?
damage to structures of inner ear (most common, old age, damage to hair cells, loud noises)
How do hearing aids work?
Amplifier placed in the auditory canal which activates existing auditory “machinery”
How do cochlear implants work?
Externally located audio sensor receives input and activates electrodes which physically stimulate cochlear nerve.
The organ of Corti sends electrical signals about sound to the brain. The perceived pitch of a sound is determined by the
- Location of the activated hair cells on the basilar membrane
- Different frequencies of sound stimulate different regions of the basilar membrane
