37. Sense Organs Flashcards
How do sensory receptor types vary?
By modality (what they react to), by distribution, and by origin of stimuli (internal/external)
Where are special sense receptors located?
Where are general sense receptors located?
In the head
Widely distributed, may be clustered in areas
How do sensory receptors transduce stimuli into potentials?
Through the opening of ion-gated channels
What is the concept of graded potentials?
The magnitude of the receptor potential varies with the strength of the stimulus
How is stimulus intensity encoded?
How is stimulus duration encoded?
Number of receptors activated and rate of APs
Duration of APs in sensory neurons
How do special sense receptors differ structurally from general sense receptors?
Synapse on ganglion cells, have high specificity
Which sensory systems axons do not decussate?
Olfactory and gustative systems
What is the purpose of the thalamus in the role of special senses?
Serves as a sensory relay, sends to different parts of cortex for processing
What areas of the body experience sensory magnification?
Mouth, tongue, tip of index finger
Fovea of eye
What are olfactory receptors?
Bipolar neurons
What is the organisation of olfactory receptor cells?
Randomly distributed in nasal mucosa, multiple cells synapse only the same glomeruli in the olfactory bulb
How do odorant molecules stimulate the olfactory sense?
Bind to G protein on cilia, depolarises cell and sends AP to olfactory bulb
What is the purpose of mitral cells in the olfactory bulb?
Forward the signal from olfactory receptor cells to the primary olfactory cortex
What is cranial nerve I?
Olfactory nerve
Which structures make up the primary olfactory cortex?
Piriform, enthorinal cortex, amygdala
What is the purpose of the orbitofrontal cortex?
Associate olfactory info with gustatory info
How many receptor cells make up a taste bud?
50-150, plus support cells
How are different tastes sensed?
Each has its own receptors based on shape and ion charges
Where is flavour integrated?
Where is this information sent?
Secondary gustatory cortex
Hypothalamus and amygdala
Where do the taste receptors send signals to?
The gustatory nucleus in the brain stem, onto the thalamus
Which photopigments are contained in rods?
Which photopigments are contained in cones?
Rhodopsin
Opsin
What type of vision are rods responsible for?
Where are they located?
Low light/night vision and grey shades
Located peripherally in the retina
Why are photoreceptors hyperpolarised by light?
Reduces noise in the final image
How are neurons arranged in the retina?
Photoreceptors - bipolar cells - retinal ganglion cells
Which cells send APs along the optic nerve?
Retinal ganglion cells only
Which structures receive visual information?
Primary visual cortex - through the LGN
Superior colliuculus - control of eye movements, coordination with auditory info
Suprachiasmatic nucleus - control of body clock and circadian rhythms
Which optical fibres decussate?
Half of the fibres coming from one eye decussate at the optic chiasm, and project in the contralateral LGN. The other half remain ipsilateral
Which type of receptors detect auditory stimuli?
Mechanoreceptors (hair cells)
How are sound waves transduced in the ear?
Distortion of the basilar membrane causes stereocilia of the hair cells to bend and discharge APs
How are different frequencies of sound differentiated?
Different regions of the basilar membrane vibrate for different frequencies
How are APs transmitted from the cochlea to the brain?
Vestibulocochlear nerve (CN-VIII) sends to cochlear nucleus, send to inferior colliculus then thalamus, then auditory cortex
What region of the cochlea do low frequency sounds vibrate?
The inner spiral
Where are high frequency sounds processed in the auditory cortex?
Deeper into the brain, further from the skull
How is head position sensed?
How is head motion sensed?
Utricle and saccule
Semi-circular canals
What type of motion do saccule and utricle respond to?
Acceleration in a straight line, ie gravity
What are contained within the saccule and utricle?
Otoliths which displace the gelatine and bend stereocilia
What is contained within the semi-circular canals?
Hair cells in a gelatinous cup which shifts due to angular acceleration or deceleration
How are different directions of head rotation transduced?
One direction causes excitation of nerve, many APs, and the other direction causes inhibition, firing less APs
Where are vestibular info projected to?
The vestibular nucleus in the brainstem, into spinal cord, cerebellum, superior colliculus, and primary somatosensory cortex
