Chapter 8 Flashcards
sensory receptors
- connect to the cortex through a sequence of intervening relaying neurons that allow each sensory system to mediate different responses and to interact with other sensory systems
- transduce or convert energy to neural activity, light, photons
vision sensory receptors
light energy is converted to chemical energy into further receptors of the retina, which actually is part of the brain, and this chemical energy is in turn converted to action potentials
auditory system conversion
air pressure waves are converted first to mechanical energy, which eventually activates the auditory receptors that produce action potentials
somatosensory sensory system
mechanical energy activates receptor cells that are sensitive to touch or pressure → receptors generate action potentials
pain
tissue damage releases chemicals that act like neurotransmitter to activate pain fibers and produce action potentials
taste and olfaction
chemical molecules carried on the air or contained in food, fit themselves into receptors of various shapes to activate action potentials
*
auditory receptors
- respond to sound wave frequencies between 20 and 20,000 Hertz
- elephants can actually hear and produce sounds below 20 Hertz
- bats can hear and produce sounds as high as 120,000 Hertz
color deficient
lack one or more types of photoreceptors for color vision, the red, blue, and green cones
can see many colors, but not the same colors as people with all three cones can
action potentials
- dendrite of a somatosensory neuron is wrapped around the base of the hair
- when the hair is displaced in a certain direction, the dendrite is stretched by the displacement
- sodium channels in the dendrites’ membrane are stretch sensitive, so they open in response to scratching
- if the influx of sodium ions in the stretch-sensitive channels is sufficient, the resulting voltage change will depolarize the dendrite to its threshold, or an action potential, and the voltage-gated, sensitive, K plus, and sodium channels, will open, resulting in a nerve impulse heading to the brain
receptive fields
and ex
- area from which a stimulus can activate a sensory receptor
- not only sample sensory information, but also help locate sensory events in space and facilitate different actions in space
- localize sensations
- ex: Our lower visual receptive field facilitates the use of our hands in making skilled actions. Whereas, our upper visual field facilitates our movements through our more distant surroundings.
rapidly adapting receptors
+ ex x2
- receptor that responds at the onset of stimulus on the body
- easy to activate, but stop responding after very short time
- ex: if you touch your arm very lightly, you will immediately detect a touch, but if you keep your finger still, the sensation will fade as receptors adapt → detect the movement of objects
- ex: rods - respond to visible light of any wavelength and have lower response threshold than do the slowly adapting cone shaped receptors which are instead sensitive to color and position
slowly adapting receptors
ex
- receptor that responds for the duration of a stimulus on the body
- react to stimulation slowly
- ex: if you push a little harder when you first touch your arm, you will feel the touch longer
exteroceptive receptors
ex
receptor that responds to external stimuli
ex: optic and auditory flow -> useful in telling us how fast we are going, whether we are going in a straight line, or up or down, and whether we are moving, or an object in the world is moving
optic flow
(exteroceptive receptors)
stimulus configuration - when you run, visual stimuli appear to stream past
auditory flow
(exteroceptive receptors)
when you move past the sound source, you hear changes in sound intensity that take place because of your changing location
interoceptive receptor
ex
- receptor that responds to internal stimuli
- position and movement of our bodies
- interpret meaning from external stimuli
- ex: learn from interoceptive receptors in our muscles and joints, and in the vestibular organs of the inner ear
receptor density
- receptor density determines a sensory system’s sensitivity
- ex: tactile receptors on the fingers are numerous compared with those on the arm
two point sensitivity
You can prove this by moving the tips of two pencils apart to different degrees, as you touch different parts of your body. The ability to recognize the presence of two pencil points close together, is highest on the parts of the body having the most touch receptors
interneurons
(sensory system)
- all receptors connect to cortex through sequence of 3 or 4 interneurons
first relay for pain receptors
- first relay for pain receptors in the spinal cord is related to reflexes that produce withdrawal from a painful stimulus
- Even after damage to the spinal cord that cuts it off from the brain, a limb will still withdraw from a painful stimulus, why? Because rapidly drawing your fingers from a hot stove is a reflex produced at the spinal level.
pain pathway
- spinal cord - reflex
- relays in the brainstem, esp in midbrain PAG
- neocortex
- ex: pain you feel
periaqueductal gray matter
- surround cerebral aqueduct
- prompt many complex responses to pain stimuli
- behavioral activation and emotional responses
- enduring pain that you feel long after touching a hot stove may be related to neural activity in the periaqueductal gray matter nuclei
neocortex
- not only localize pain in a body part, but also identify the felt pain, its external cause, and possible remedies
- cortex can also adapt to our experience with hot stoves so that we know in advance not to touch one
gating
with ex
- inhibition of sensory information produced by descending signals from the cortex
- the messages sensory systems carry can be modified at neural relays
- descending impulses from the cortex can block or amplify pain signals at the level of the brainstem and at the level of the spinal cord
- ex: when excited or playing a sport
- can also amplify sensory signal
- ex: when we think about the injury, it might feel much more painful because a descending signal from the brain now amplifies the pain signal from the spinal cord
- ex: attention: form of gating that takes place in the cortex, one that allows us to move efficiently from one action to another
- hierarchical code sent from sensory receptors, through neural relays, is interpreted in the brain, especially in the neocortex, and eventually translated into perception, memory, and action
sensory coding
- firing rate/activity
- amount of increase or decrease can encode the stimulus intensity
- ex: qualitative visual changes (ie red to green) an be encoded by activity in different neurons or even by different levels of discharge in the same neurons
- more activity by a neuron might signify a redder, and less activity greener
- also related to what other neurons are doing
- ex: ability to perceive colors as constant under a wide range of sensory conditions is a computation made by the brain
- color constancy
color constancy
enables us to see green as green under a wide range of illumination → brain is not simply recording sensory stimuli, but rather is manipulating sensory input so that it is behaviorally useful
how do we percieve touch, smell, and sound as different from one another?
- different sensations are processed in distinct regions of the cortex
- we learn through experience to distinguish them
- each sensory system has a preferential link with certain behaviors constituting a distinct neural wiring that helps keep each system distinct at all organizational levels
sensory systems have subsystems that are surprisingly independent in the behaviors with which they are associated
name them
- suprachiasmic nucleus
- pretectum
- pineal gland
- superior colliculus
- accessory optic nucleus
- visual cortex
- frontal eye fields
suprachiasmatic nucleus
circadian rhythm in response to light and feeding
pretectum
pupils constrict in bright light and dilate in dim light
pineal gland
- long term circadian rhythm
- release of the chemical melatonin in the pineal gland
superior colliculus
head orientation
accessory optic nucleus
eye movement in response to head movement
visual cortex
- pattern and depth perceptions, color vision, visual tracking
- ex: pathways for pattern perception, color vision, depth perception, and visual tracking
frontal eye fields
voluntary eye movement
topographic organization
neural-spatial representation of the body or areas of the sensory world a sensory organ detects
light hitting eye process
When rays of light enter the eye through the cornea, which bends them slightly, they pass through the lens which bends them to a much greater degree to focus the visual image upside down and backward on the receptors at the back of the eye.
lights having to pass through the layer of retinal cells, poses little obstacle to our visual acuity for reasons:
- the cells are transparent and the photoreceptors are extremely sensitive
- can be excited by a single photon
- fibers forming the optic nerve bend away from the retina central part or fovea, so as not to interfere with the passage of light through the retina
photoreceptive cells in retina
rods and cones
- induce action potentials in retinal ganglion cells
- other retinal cell including horizontal and amacrine cells contribute to the readiness processing of visual information
- each photoreceptor points in a slightly different direction, and so, has a unique receptive fields
rods
- sensitive to dim light
- night vision
- distribution: absent entirely from the fovea and more sparsely distributed over the rest of the retina
- in bright light, acuity is best when looking directly at things and dim light acuity is best when looking slightly away
cones
- transduce bright light
- daytime vision
- distribution: packed together densely in the fovea region
- three types: each type maximally responsive to a different set of wavelengths, red or blue or green mediate color vision
optic chiasm and on
- just before entering the brain, the two optic nerves, one from each eye meet and form the optic chasm
- At this point, about half the fibers from each eye cross, so the right half of each eye’s visual field is represented in the left hemisphere. And the left half of each eye’s visual field is represented in the right hemisphere.
- Having entered in the brain proper, the optic tract still consisting of retinal ganglion cells, axons diverges to form two main pathways.
geniculostriate pathway
main
- runs from the retina to the lateral geniculate nucleus LGN, a nucleus of the thalamus to the primary visual cortex in the occipital lobe
- takes part in pattern, color, and motion recognition and includes conscious visual functions
lateral geniculate nucleus (LGN)
layers
- layers 2, 3, 5
- receive fibers from the ipsilateral eye on the same eye, on the same side
- layers 1, 4, 6
- receive fibers from the contralateral eye
lateral geniculate nucleus (LGN)
visual field
- topography of visual field is reproduced in each LGN layer
- central parts → central part of visual field
- peripheral parts → peripheral field
- LGN cells → layer 4 of primary visual cortex (aka V1)
- V1/striate cortex - very large in primates and appears striped
- visual field is upside down, inverted, and reversed in V1
- V1/striate cortex - very large in primates and appears striped
damage to tectopulvinar pathway
visual ataxia: inability to recognize where objects are located
damage to geniculostriate system
- impairments in pattern, color and motion perception as well as visual-form agnosia
- agnosia: inability to recognize objects
sound localization
identifying source of air pressure waves
echolocalization
identifying and locating objects by bouncing sound waves off them as well as the ability to detect the complexity of pressure waves
why auditory system is complex:
- many transformations of pressure waves take place within the ear before action potentials are generated in the auditory nerve
- the auditory nerve projects to many targets in the brain stem and cortex
frequency
- speed of pressure changes = changes in pitch
- frequency of a sound is transduced by the longitudinal and structure of the basilar membrane
- Higher sound frequencies cause maximum peaks near the cochlear base that is near the oval window
- Lower sound frequencies cause maximum peaks near the apex, farthest from the oval window
amplitude
intensity of pressure changes = loudness
timbre
complexity of pressure changes = perceived uniqueness of tonal quality of a sound
pinna
outer ear
external structure, which catches waves of air pressures and directs them into the external ear canal, which amplifies them somewhat and directs them to the eardrum at its inner end
middle ear
- inner side of eardrum
- air-filled chamber that contains the three smallest bone in the human body connected in a series
- includes ossicles and ear drum
eardrum
Sound waves striking the eardrum, vibrate it at frequency varying with the wave’s frequency
ossicles
- hammer, anvil and stirrup
- attach the ear drum to the oval window of the inner ear
- amplify and convey vibrations to the oval window
cochlea
- contains the auditory sensory receptors called hair cells
- rolled up into the shape of a snail shell
- filled with fluid and floating in the middle of this fluid is the basilar membrane
- hair cells are embedded in a part of the basilar membrane called the organ of Corti
- hair cells maximally disturbed at the point at which the wave peaks producing their maximal neural discharge at that place
basilar membrane
narrow and thick at its base near the round window and thinner and wider at its apex within the cochlea
perception of sound
- sounds are caught in the outer ear and amplified by the middle ear
- pressure waves in the air are amplified and transformed a number of times in the ear, by deflection in the pinna, by oscillation of the travel through the external ear canal and by the movement of the bones of the middle ear to the cochlea
- In the inner ear, they are converted to action potentials on the auditory pathway going to the brain and we interpret the action potentials as our perception of sound.
- When sound waves strike the ear drum also termed the tympanic membrane, this membrane vibrates.
tonotopic organization
- different points on the basilar membrane represent different sound frequencies also applies to the auditory cortex
- projections from hair cells of the organ of Corti form a representation of the basilar membrane in the neocortex
- receptive field of a hair cell is not a point in space, but rather a particular sound frequency
- composes the auditory systems
pathway connecting cochlea to primary auditory area in the superior temporal gyrus
- The axons of hair cells leave the cochlear to form the major part of the auditory nerve, the eighth cranial nerve. This nerve, first projects to the medulla in the hindbrain.
- Synapse in either in the dorsal or ventral cochlear nuclei, or in the superior olivary nucleus. The axons of neurons in these areas form the lateral lemniscus, which terminates in discrete zones of the inferior colliculus in the midbrain
-
Two distinct pathways emerge from the colliculus, crossing to the ventral and the dorsal medial geniculate nuclei in the thalamus.
- The ventral region: -> core auditory cortex, A1 or Brodmann’s area 41
- identifies the sound
- The dorsal region: -> secondary auditory regions
- indicates its spatial source
- The ventral region: -> core auditory cortex, A1 or Brodmann’s area 41
vestibular system
information from the vestibular system allows us not only to balance, but also to record and replay actively in the mind’s eye, the movements we have made
inner ear
contains the organs that allow you to perceive your own motion, and to stand upright without loosing your balance
hair cells in vestibular system
bend when the body moves forward, or when the head changes position relative to the body
semicircular canals
- oriented in the three planes that correspond to the three dimensions in which we move
- collectively, they can represent any head movement
otholith organs
sensitive to the head’s static position in space - balance
fibers from balance receptors
- project over the eighth cranial nerve to a number of nuclei in the brain stem
- nuclei interact in the hind brain to help keep us balanced while we move
- also aid in controlling eye movements at the mid-brain
exteroceptive function
enables us to feel the world around us
interoceptive function
monitoring internal bodily events and informing the brain about the position of body segments relative to one another and about the body in space
submodalities of somatosensory system
- 1,2,3: mediate our perceptions of sensations, such as pain, touch, and body awareness
- 4: mediate balance
- composed of a set of interoceptive receptors within the inner ear
somatosensory receptors
types
nociception, hapsis, proprioception
nociception
- noxious perception → perception of pain, temp, and itch
- most consist of free nerve endings
- CNS (esp in cortex) - where pain is perceived
- phantom limb pain
- Many internal organs, including the heart and kidney and blood vessels, have pain receptors but the ganglion neurons carrying information from these receptors lack pathways to the brain
- instead they synapse with spinal cord neurons that receive no susceptive information from the body’s surface
neurons in spinal cord that relay pain, temp, and itch messages to the brain recieve two sets of signals:
- from the body’s surface
- other from the internal organs
- cannot distinguish between the two sets of signals → pain in body organs is often felt as referred pain coming from the body surface
hapsis
- our tactile perception of objects
- hapsis receptors enable fine touch and pressure, allowing us to identify objects we touch and grasp
- occupy both superficial and deep skin layers and are attached to body hairs as well
- When touch is lost, not only do we lose the information that it normally provides about the objects we handles or the movements we make, but movement is affected as well.
proprioception
- the perception of body location and movement
- proprioceptors encapsulated nerve endings sensitive to the stretch of muscles and tendons and to joint movements
major somatosensory pathways:
- posterior spinothalamic tract
- anterior spinothalamic tract
posterior spinothalamic tract
major spinothalamic tract
- for hapsis, pressure, and proprioception, body awareness
- fibers of somatosensory neurons that make up the hapsis and proprioception system are relatively large, heavily myelinated, and for the most part, rapidly adapting
- cell bodies are located in the posterior root ganglion
- dendrites project to sensory receptors in the body and their axons project into the spinal cord
posterior
anterior spinothalamic tract
major somatosensory pathway
- for nociception
- fibers are somewhat smaller, less myelinated, and more slowly adapting than those of the haptic and proprioception pathway
- follow the same course to enter the spinal cord but once there project to relay neurons in the more central regions of the spinal cord, the substantia gelatinosa
- second relay cells then send their axons across to the other side of the cord where they form the anterior spinothalamic tract
- anterior fibers eventually join the posterior hapsis and proprioception fibers in the medial lemniscus
anterior
brown-sequard syndrome
- unilateral spinal cord injury that cuts the somatosensory pathways in that half of the spinal cord
- results in the bilateral symptoms
- loss of hapsis and proprioception occurs unilaterally on the side of the body where damage occurred
- loss of nociception occurs contralaterally on the side of the body opposite to the injury
- unilateral damage to the points where the pathways come together, that is to the posterior roots, brainstem, and thalamus, affects hapsis, proprioception, and nociception equally because these parts of the pathways are in proximity
homonculus
(penfield 1930s)
Wilder Penfield first stimulated the sensory cortex in the conscious epilepsy patients and asked them to report the sensation they felt he created a topographic map that represents the body surface on the primary somatosensory cortex, S1
The results show that the primary somatosensory cortex contains a number of homunculi, one for each of its subregion, 3a, 3b, 1, and 2.
taste receptors
taste buds
- bumps on the tongue called papillae are probably there to help the tongue grasp food → taste buds lie buried around them
- chemicals in food dissolve in the saliva that coats the tongue, and disperse through the saliva to reach the taste receptors
- If the tongue is dry, the taste buds receive few chemical signals and food is difficult to taste
- taste receptors also found in gut and other places
- may play a role in food absorption, metabolism and appetite
types of taste receptors
- 5 main types:
- each responds to different chemical component in food
- Sweet, Sour, Salty, Bitter and Umami
super tasters
perceived certain tastes as strong and offensive, whereas others are indifferent to them
underlying basis for species, and individual difference in taste
stems from differences in the genes, for taste receptors
smell receptors
- axons projecting from the olfactory receptors -> glomeruli mitral cells in olfactory bulb -> form the olfactory tract (Cranial nerve one) -> pyriform cortex -> hypothalamus, the amygdala, the entorhinal cortex of the temporal lobe and the orbital frontal cortex, the area of the prefrontal cortex (located behind the eye sockets)
three cranial nerves carry information from the tongue:
- glossopharyngeal nerve, the vagus nerve, and the chorda tympani branch of the facial nerve
- all three enter solitary tract
gustatory
solitary tract
main gustatory pathway
divides into two routes:
- red
- goes to the VPM of the thalamus → which in turn sends out two pathways:
-
s1
- sensitive to tactile stimuli
- probably responsible for localizing tastes on the tongue
- region just rostral to s2, in the insular cortex
- probably dedicated entirely to taste, because it is not responsive to tactile stimulation
- blue
- leads to the pontine taste area→ projects to thelateral hypothalamusandamygdala
olfactory pathway
olfactory pathways
- major output of olfactory bulb: lateral olfactory tract, which passes ipsilateral to the pyriform cortex, the amygdala and the entorhinal cortex
- pyriform cortex primary projection goes to the central part, of the dorsal medial nucleus in the thalamus → projects to the orbital frontal cortex. Which can be considered the primary olfactory neocortex
- two classes of neurons
- responsive to specific orders
- broadly tuned
sensory synergies
- sensory systems exist at all levels of the nervous system and their interactions are mediated by these sensory connections
- connect to the cortex through a sequence of intervening relaying neurons that allow each sensory system to mediate different responses and to interact with other sensory systems
- transduce or convert energy to neural activity, light, photons
sensory receptors
- unilateral spinal cord injury that cuts the somatosensory pathways in that half of the spinal cord
- results in the bilateral symptoms
- loss of hapsis and proprioception occurs unilaterally on the side of the body where damage occurred
- loss of nociception occurs contralaterally on the side of the body opposite to the injury
- unilateral damage to the points where the pathways come together, that is to the posterior roots, brainstem, and thalamus, affects hapsis, proprioception, and nociception equally because these parts of the pathways are in proximity
brown-sequard syndrome
(penfield 1930s)
Wilder Penfield first stimulated the sensory cortex in the conscious epilepsy patients and asked them to report the sensation they felt he created a topographic map that represents the body surface on the primary somatosensory cortex, S1
The results show that the primary somatosensory cortex contains a number of homunculi, one for each of its subregion, 3a, 3b, 1, and 2.
homonculus
tectopulvinar pathway
- takes part in detecting and orienting to visual stimulation
- eye -> superior colliculus -> visual areas
- reaches the visual areas in the temporal and parietal lobes through relays in the lateral posterior-pulvinar complex of the thalamus
- mammals - additional projection from the colliculus to the cortex via this thalamic pulvinar nucleus provides information to the cortex about the absolute special location of objects
pain gate
- we often rub the area around an injury or shake a limb to reduce the pain sensation → increase the activity in fine touch and pressure pathways and can block information transmission in spinal cord relays
- interneuron in spinal cord recieves excitatory input from fine touch and pressure pathway and inhibitory input from the pain and temp pathway
- the activity of the interneuron determines whether pain and temp info is sent to the brain
- we often rub the area around an injury or shake a limb to reduce the pain sensation → increase the activity in fine touch and pressure pathways and can block information transmission in spinal cord relays
- interneuron in spinal cord recieves excitatory input from fine touch and pressure pathway and inhibitory input from the pain and temp pathway
- the activity of the interneuron determines whether pain and temp info is sent to the brain
- how inhibitory interneuron in the spinal cord can block transmission in the pain pathway
- activating this inhibitory neuron via collaterals from the fine touch and pressure pathway provides the physical substrate through which rubbing an injury or each can gate sensation
pain gate
what is the neuromuscular junction?
the location where motor neurons make contact with muscle fibers
complex cognition and planning is directed mostly by which part of the frontal lobes?
- premotor cortex
- lateral prefrontal cortex
- frontopolar cortex
- primary motor cortex
lateral prefrontal cortex
