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What are the principles of sensory system function?

Sensory receptors
receptors are energy filters
receptive fields


Sensory receptors general function

specialized cells that transduce or convert sensory energy into neural activity. All the sensory receptors connect to the cortex through a sequence of intervening relay neurons.


Receptive fields

specific part of the world to which a sensory receptor responds.
provides a unique view of the world for each sensory system.
Helps to locate sensory events in space.


Receptors as energy filters

response only to a narrow band of energy (within each modality energy spectrum)


What is the basic organization of sensory system?

After transduction, sensory information is encoded by action potentials.
A present stimulus is encoded by increase or decrease in the discharge rate of the neuron.
The amount of increase can encode the stimulus intensity.
Qualitative changes are encoded by activity in different neurons, or activity in the same neuron.


What are the main sensory pathways?

Dorsal pathway/stream it is the where stream.
Ventral pathway/stream it is the what stream.


Which sensory system does not relay through the thalamus?

Olfactory (Smell)


What do sensory system subsystems do?

Perform distinct and specific roles and are independent
Each sensory system has distinct wiring with certain behaviors.


What is the role of neural relays

Receptors connect to the cortex through a sequence of three or four intervening neurons.
Relays allow sensory systems to interact
Relays allow sensory systems to produce relevant actions.
Also message modification happens at the neural relays.


What is the process of energy transduction in vision?

light is converted to chemical energy in the photoreceptors, and this is converted into action potentials.


What are the photoreceptors and their location and functioning?

Rods: sensitive to dim light, night vision. Located in the peripheral retina.
Cones: Sensitive to bright light, day vision and color vision. Densely packed in the fovea


What is color-deficient?

People who lack one or more types of photoreceptors for parts of the usual visual spectrum.


Anatomy of the eye and visual processes

Ray of light enter the eye through the cornea, which bends them slightly, then go through the lens, which bends them to a much greater degree to focus the visual image, upside down and backwards, on the receptors at the back of the eye. Many of the fibers forming the optic nerve bend away from the retina's central part of fovea, so as not to interfere with the passage of light through the retina.


Visual Pathways

Geniculostriate pathway & Tectopulvinar pathway


Explain the streams of the Geniculostriate pathways

Bipolar cells synapse with the rods and cons (induce graded potentials)
Send information to Retinal Ganglion Cell (RGC)
Send axons to the brain (optic nerve)
Optic nerves leave the eye and cross at the optic chiasm. The right half of each eye's visual field is transmitted to the left hemisphere, the left half of each eye's visual field is transmitted to the right hemisphere. Information relays the lateral geniculate nucleus (LGN) of the thalamus. LGN projects to the primary visual cortex or striate cortex (or V1). V1 contains a retinotopic map of the visual field.


What is the Geniculostriate pathways role?

This pathway takes part in pattern recognition and conscious visual functions.


What happens if there is a damage to Geniculostriate pathways?

Damage to this system can produce impairments in pattern, color, and motion perception.
Visual-form agnosia which is the inability to recognize objects.


Explain the streams of the Tectopulvinar Pathway

Optic nerve projects to the superior colliculus (midbrain). Reaches visual association areas in the temporal and parietal lobes through relays in the lateral posterior-pulvinar complex of the thalamus. This is more of a basic level pathway.


What is the Tectopulvinar pathways role?

Detects stimuli and helps orient us to stimuli. Sophisticated in fish, amphibians and reptiles. In mammals, there is additional projection from colliculus to cortex via the pulvinar nucleus. Provides information about absolute spatial location of objects.


What happens if there is a damage to Tectopulvinar pathways?

Visual ataxia.


Damage to ventral and dorsal stream can cause...? (Secondary visual processing)

Can cause more complex perceptual problems
e.g. agnosias


Anton's syndrome

It is a visual anosognosia, Objectively blind but lack awareness into blindness and confabulate what they see. hypothesis that occipital lobe damage disconnects incoming information from association with the speed-language areas of the brain. Visual imagery is received but cannot be interpreted, the brain confabulates a response.



It is a cortical blindness. No conscious vision due to lesions to primary visual cortex (striate), but able to detect, localize and discriminate visual stimuli better than chance. Hypothesis that other pathways (not through striate) are intact leading to non-conscious processing of visual information.


What is the process of energy transduction in hearing?

Air pressure waves are converted into mechanical energy, which activates the auditory receptor cells which in turn produce action potentials.


The process of hearing

auditory receptors detect the frequency, amplitude, and complexity of air pressure waves. Humans rapidly lose high-frequency hearing (age and exposure)


What are the most important frequencies to humans?

those of speech in the lower frequencies.


Projections of Retinotopic map

Right visual field projects to left visual cortex. Central visual field projects to the peripheral visual cortex. Peripheral visual cortex projects to medial cortex. Upper visual field projects onto the lower visual cortex. Lower visual field projects onto upper visual cortex.


What are the physical dimensions of sound waves? Explain.

Frequency (pitch): the rate at which waves vibrate. Corresponds to our perception of pitch.
Amplitude (loudness): The intensity of sound. Corresponds to our perception of loudness.
Complexity (timber): most sounds are a mixture of frequencies. The particular mixture determines the sound's timber or perceived uniqueness. Timber provides information about the nature of sounds.


List the main anatomy of the ear

Outer ear: Pinna and external ear canal
middle ear: Eardrum and the ossicles, the hammer, anvil and stirrup.
inner ear: Oval window and cochlea (contains hair cells that convert sound to electrical impulses).


What is the tonotopic representation?

different points on the basilar membrane and the cortex present different sound frequencies. Also maintained in cortex.


Auditory pathways

Axons of hair cells from the auditory nerve (8th cranial nerve) . Auditory nerve projects to the dorsal or ventral cochlear nuclei or to the superior olivary nucleus (brainstem). Next, axon project to the inferior colliculus (midbrain) and then relay through the medial geniculate nucleus ( thalamus)
One pathway projects to the primary auditory cortex, the other projects to the secondary auditory cortex.

Medial geniculate= M for music
Lateral geniculate= L for light


Cross of over of information in auditory system and how is this cross over helpful?

most of the information cross over. About 60% crossover and 40% are ipsilateral. So helps when you have a brain damage you can still process information through the other ear.


What happens if there is a damage to the primary auditory pathway?

Can cause hearing loss. However, some auditory information is passed ipsilaterally.


Secondary auditory pathway/processing location and role?

Near the semantic temporal area "what" stream.
ID sounds and language. (in the right hemisphere-- discrimination of non-speech sounds, in the left hemisphere discrimination of speech sounds)


Vestibular system general function and location?

Motion and balance. Allows us to perceive our own motion and to maintain balance (done by the hair cells that bend when we move.) It is located in the inner ear, with a semicircular canals which can respond to any movement of the head. Otolith organs respond to head's linear acceleration and it is sensitive to changes in the position of the head with respect to gravity.


What are the vestibular system pathway?

Hair cells project over the 8th cranial nerve to nuclei in the brainstem. Connection to the midbrain and cerebellum.


What is the process of energy transduction in somatosensory?

mechanical energy (touch, pressure) activates mechanoreceptors that generate action potentials. Tissue damage release neurotransmitters that activate pain fibers and produce action potentials.


Name four major somatosensory submodalities and what they are?

Nociception: perception of unpleasant stimuli-- pain, temperature, itch.
Haps is: tactile perception of objects using fine touch and pressure.
Proprioception: perception of body location, movement
4th submodality mediates balance.


Name the two somatosensory pathways

Posterior spinothalamic tract.
Anterior spinothalamic tract.


Posterior spinothalamic tract

Hapsis and proprioception.
Sensory receptior in the body project into spinal cord. Ascends to contralateral ventrolateral thalamus---which is the somatosensory cortex (S1 and S4).


Anterior spinothalamic tract

smaller less myelinated, more slowly adapting. Send information across to the other side of the cord, where they form the anterior spinothalamic tract.
Anterior fibers eventually join posterior hapsis and proprioception fibers in medial lemniscus (brainstem/medulla). Also terminate primarily in ventrolateral thalamus, as well as in posterior thalamus. Then message is relayed to areas 3,2,1 of the cortex.


What is Taste and Olfaction

Transduction of energy, chemical molecules in the air and in food fit into receptors and activate action potentials.


Taste and smell pathways

Gustatory pathway
Olfactory pathway


Explain gustatory pathway

cranial nerves 9, 10, 7 carry information from the tongue and enter the solitary tract (pons). Two pathways emerge from the solitary tract, one route projects to S1 and S2 via the ventroposterior medial nucleus of the thalamus. Other routs leads to pontine taste are which in turn projects to the amygdala and lateral hypothalamus.


Explain olfactory pathways

Axons of olfactory receptor relays synapses in the olfactory bulb. Bulb's major output is lateral olfactory tract it passes ipsilateral to the pyriform cortex the amygdala and the entorhinal cortex. Pyriform cortex project to dorsomedial nucleus in the thalamus, it in turn projects to orbitofrontal cortex considered the primary olfactory neocortex.
Single cell recordings from this pathway suggests two general classes of neurons, some responsive to specific odors and some more broadly tuned.


What is perception?

Sensory impression are affected by contexts, emotion states and experiences.


What is synesthesia?

Involves sensory mixing, ability to perceive a stimulus of one sense as the sensation of a different sense. More than 100 kinds and can run in the family. Most common type is colored hearing.


What is self-perception?

Body image is product of both the brain's representation and sensory information provided by the body to the brain. Moment to moment updating of the brain's representation through sensory experience ensures that reality and inborn body representations are congruent.


Exteroceptive receptors

Response to external stimuli.


Interoceptive receptors

Responses to internal stimuli, help interpret meaning of external stimuli , The ones in muscles and joints and in vestibular organs of inner ear tell us about our position and movement


Optic flow

Visual stimuli seem to stream past when you run


Auditory flow

Distinguishes changes in intensity of sound because of our changing location.