Material After Quiz (midterm) Flashcards
(29 cards)
Adequate stimulus
Form of energy to which a sensory receptor is most responsive
- each sensory receptor has an adequate stimulus (thermoreceptors more sensitive to temperature change than pressure)
- a blow to the eye may cause us to see stars if mechanical energy great enough to stimulate photoreceptors
Threshold
Minimum stimulus required to activate a receptor (just as the minimum depolarization required to trigger an AP is called a threshold too)
What is receptor potential
Change in sensory receptor membrane potential (graded potential)
-receptor potential may initiate an AP or influence NT release by the receptor cell and alters electrical activity in an associated sensory neuron
Transduction
Conversion of stimulus energy into electrical energy (info that can be processed by the NS)
Receptive field
An area where stimulus falls in order for sensory neurons to respond to the stimulus (specific physical area)
- fingertips(more sensitive areas) have smaller receptive fields than the arms
- receptive fields of three primary sensory neurons can overlap to form one big secondary receptive field
- two stimuli that fall within one secondary receptive field are perceived as a single point because only one signal goes to the brain
What are the four properties of a stimulus the CNS must distinguish between in order to tell what type of stimulus it is? Heat or pressure, in the hand or the foot?
Modality
Location
Intensity
Duration
What is the modality of a stimulus
The nature of it
- indicated by which sensory neurons are activated and where the pathways of the activated neuron end in the brain
- each receptor type is most sensitive to a particular modality of a stimulus
Lateral inhibition
Enhances contrast and makes a stimulus easier to perceive.
Secondary sensory neuron closest to where the stimulus hit the receptive field will inhibit the sensory neurons beside it that are also in the same secondary receptive field (makes this neuron fire more APs and creates contrast between it and the other neurons beside it)
How is the intensity of a stimulus determined?
By the number of receptors activated and the frequency of APs
-longer or stronger stimulus release more NTs
How is th duration of a stimulus determined?
However long the receptors are activated
-a longer stimulus generates a longer series of APs in the primary sensory neuron (however, if a stimulus persists, some receptors adapt and stop responding )
What are tonic and phasic receptors (vary in how fast they adapt to continuous stimulation)
Tonic receptors- adapt slowly and fire rapidly when first activated then fire slowly and maintain their firing as long as the stimulus is present
-parameters that must be monitored continuously by the body
Phasic receptors- rapidly adapting and fire when they first receive a stimulus but stop firing when the strength of the stimulus remains constant (reaches a steady intensity)
- allows body to ignore information that has been found not to threaten homeostasis or well being
- can concentrate on what is new or important
Somatic senses
Touch
Proprioception
Nociception
Temperature
Where are sensory tracts perceived in the brain?
In the primary somatic sensory cortex (each tract has a corresponding region in the somatosensory cortex)
-the amount of space on the somatosensory cortex devoted to each body part is proportional to the sensitivity to that part
Describe pathway of olfaction
Olfactory sensory neurons -> axons form olfactory nerve and synapse with secondary sensory neurons in olfactory bulb -> secondary sensory neurons project through olfactory tract to olfactory cortex
Describe how odorant molecules can lead to an action potential in an olfactory sensory neuron
- odorant molecule binds to its receptor
- this may activate G protein (Golf) which increases cAMP
- an increase in cAMP opens cAMP gated cation channels and Na and Ca come in depolarizing the cell and Cl leaves
- if graded receptor potential is large enough, AP is fired and travels to olfactory bulb to synapse with secondary sensory neurons
Describe the pathway of the taste ligands to the brain
Primary sensory neurons (gustatory neurons) are activated from the chemical signals (NTs) released from the taste receptor cells
- gustatory neuron axons run through 3 cranial nerves to medulla and then to thalamus then to the gustatory cortex
- each taste receptor cell sensitive to only one taste
Compare umami, bitter and sweet receptor taste cells (type 2) with sour and salty receptor taste cells (type 111)
Umami, bitter and sweet taste receptor cells have G proteins (gustducin) which opens ion channels once activated (when ligand binds to receptor) then ATP is released onto primary gustatory neuron (bc Ca signal)
-G protein coupled receptors (metabotropic)
Salty and sour receptor cells have ionotropic receptors. Ligand bind to receptor and positive ions flow in now open channel which triggers NT release(serotonin) onto primary gustatory neuron and AP fired.. goes to gustatory cortex
What do amplitude and frequency of sound waves determine
Loudness and pitch
Describe how sound gets to the brain
Sound waves in air are collected by the pinna and channeled to ear canal
-sound waves at particular frequency then hit the eardrum and it vibrates (sound waves become vibrations)
-this vibration moves the 3 middle ear bones (at the same frequency)
-movement of these bones hit oval window and triggers wavelike movement of fluid in cochlea (fluid filled inner ear)
(Pressure of sound waves amplified in middle ear)
-fluid waves push on flexible membranes (basilar and tectorial) of the cochlear duct that surround the organ of corti
-hair cells bend and ion channels open (creates electrical signal that alters NT release)
-NT release into sensory neurons creates action potentials that travel through vestibulocochlear nerve to brain
-energy from the waves transfers into tympanic duct and is dissipated back into the middle ear at the round window
Describe the three fluid filled channels in the cochlea
- Vestibular duct
- perilymph (similar ion composition to plasma) - Cochlear duct
- endolymph (is extracellular fluid that is more like intracellular fluid with high concentrations of K+ and low conc. of Na+ - Tympanic duct
- perilymph (similar ion composition to plasma)
When do hair cells cause depolarization or hyperpolarization
When waves deflect the tectorial membrane so that stereocilia bend towards the tallest members of a hair bundle, tip links pop more cation channels open (K+ enters cell) and cell depolarizes releasing NTs onto sensory neuron which increases its firing rate
-when stereocilia bend towards shortest stereocila, the cell hyperpolarizes, less NT released and less AP firing of sensory auditory neuron
What are the three kinds of hearing loss?
Conductive: sound waves not adequately conducted through the external and middle ear portions
-plugged ear canal, fluid in middle ear from infection, disease or trauma to ear bones that impede vibrations
Sensorineural: sound waves are not translated into nerve signals that are interpreted by the brain as sound sensations (due to damage to structures of the middle ear, including death of hair cells)
Central: damage to the nerve pathways between the ear and auditory cortex (or to the cortex itself)
- maybe from a stroke
- uncommon
What is the function of the pigment epithelial cells in the retina
Absorb any light rays that escape the photoreceptors, preventing distracting light from refracting inside the eye and distorting the visual image
Also act as phagocytes by consuming dying photoreceptors
-stores vitamin A
Compare rods and cones
Rods:
- Vision in shades of grey
- high sensitivity
- low acuity
- night vision
- more numerous in periphery
- much convergence in retinal pathways (Ex. 3 rods go to one bipolar cell)
Cones:
- 3 times more of them in retina
- colour vision
- low sensitivity
- high acuity
- day vision
- concentrated in fovea and macula lutea
- little convergence in retinal pathways
