Mechanisms of Perception: Hearing, Touch, Smell, Taste & Attention
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Transcript Mechanisms of Perception: Hearing, Touch, Smell, Taste & Attention
MECHANISMS OF PERCEPTION:
HEARING, TOUCH, SMELL,
TASTE & ATTENTION
1.
2.
3.
4.
5.
5 exteroceptive sensory systems
Visual
Auditory (hearing)
Somatosensory (touch)
Olfactory (smell)
Gustatory (taste)
SOMATOSENSORY SYSTEM
1.
Somatosensations: sensations from your body
3 separate but interacting systems
Exteroceptive system
Senses external stimuli interacting with the skin
2.
Proprioceptive system
Monitors body position
Receptors in the muscles, joints & organs of balance
3.
Interoceptive system
General info on the internal body conditions
Ex: temp, BP
EXTEROCEPTIVE SYSTEM
3 distinct divisions for perceiving different types
of stimuli
1.
2.
3.
Mechanical (touch)
Thermal (temperature)
Nociceptive (pain)
CUTANEOUS RECEPTORS
Receptors in the skin; many types
Free nerve endings
Pacinian corpuscles
Largest & deepest
Adapt rapidly
Respond to sudden displacements of skin, not constant
pressure
Merkel’s disks
Simplest; neuron endings with no specialized structures
Sensitive to temperature change & pain
Adapt slowly
Respond to gradual skin indentation
Ruffini endings
Adapt slowly
Respond to gradual skin stretch
CUTANEOUS RECEPTORS
When constant pressure is applied to the skin,
there is a burst of firing in all of the receptors,
corresponding to the sensation of touch.
But after a bit, only the slowly adapting receptors
stay active & the sensation changes (often becoming
unnoticeable)
So to maintain constant input, you move &
manipulate objects in your hands
Stereognosis: identification of objects by touch
CUTANEOUS RECEPTORS
Each type has its own unique structure, but they
all basically work the same way
Stimuli to the skin changes the chemistry of the
receptor, which changes the permeability of the
receptor cell membrane to ions, which sends a
neural signal
DERMATOMES
Nerve fibers from cutaneous receptors come
together and enter the spinal cord at the doral
root
The area of the body
innervated by the
left & right dorsal
root at a given
spinal segment is a
dermatome
2 MAJOR SOMATOSENSORY PATHWAYS
1.
Dorsal-column medial-lemniscus system
2.
Anterolateral system
Info about touch & proprioception
Info about pain & temperature
However, there is overlap in the type of info
each pathway carries
PG. 176 & 177
1.
Dorsal-column medial-lemniscus system
2.
Anterolateral system
Ipsilateral, decussates at the dorsal column nuclei,
contralateral
Neurons of this path that start in the toes are the
longest neurons in the human body!
Spinothalamic tract
Neurons decussate immediately upon entering the
spinal cord & travel up contralaterally
If both paths are cut by a spinal cord injury,
there will be no sensation from below that point.
CORTICAL AREAS OF SOMATOSENSATION
The primary somatosensory cortex is located on
the postcentral gyrus
Most input is contralateral
It is organized somatotopically; according to a
map of the body surface
Referred to as the homunculus (“little man”)
*my fave!*
CORTICAL AREAS OF SOMATOSENSATION
Secondary somatosensory cortex is just ventral to
the primary
Association cortex is in the posterior parietal lobe
SOMATOSENSORY AGNOSIAS
Astereognosia
Inability to recognize objects by touch
Rare
Asomatognosia
Inability to recognize parts of your own body
Usually only affects the left side of the body after
damage to the right posterior parietal lobe
PERCEPTION OF PAIN
Pain is the response to any kind of harmful
stimulation
Serves as a warning system
There is no clear cortical area involved in pain
Although the anterior cingulate cortex is
activated during the emotional reaction to physical
pain
Amazingly, we can exhibit a lot of control over
our perception of pain
Gate-control theory: descending cognitive signals
from the brain can activate neural gate circuits in the
spinal cord to block incoming pain signals
DESCENDING PAIN-CONTROL CIRCUIT
Activity in the periaqueductal gray has
analgesic (pain blocking) effects
Also has specialized receptors for opioids, including
endorphins
Potentially involves stimulation of serotonergic
neurons
NEUROPATHIC PAIN
Severe chronic pain in the absence of a
recognizable pain stimulus
Often after an injury has healed & there should
be no more reason for pain
THE CHEMICAL SENSES: SMELL
& TASTE
These senses respond to chemicals in our
environment
Smell for airborne chemicals
Taste for those that dissolve in our oral cavity
Smell & taste are highly integrated
Together they produce what we know as flavor
We use these senses primarily to recognize
flavor, but many other species use it for
communication, via pheromones
OLFACTORY SYSTEM: SMELL
Receptor cells are in the upper part of your nose,
within the olfactory mucosa
The axons of these neurons actually project
through the cribriform plate in your skull &
enter the olfactory bulbs, which go via the
olfactory tracts to the brain
Your olfactory receptor neurons can be
regenerated throughout your life
Primary olfactory cortex: piriform cortex
Medial temporal cortex next to the amygdala
Only sensory system that does not first go
through the thalamus!!
GUSTATORY SYSTEM: TASTE
Taste receptors are on the tongue & elsewhere in
the oral cavity
Occur in clusters of 50 called taste buds
So each taste bud sends out many axons and many
individual neural signals
1.
2.
3.
4.
5.
The 5 traditional tastes
Sweet
Salty
Sour
Bitter
Umami
But not every taste we experience can be made from
any combo of those 5…
GUSTATORY PATHWAY
Afferent neurons leave the mouth as the facial,
glossopharyngeal & vagus cranial nerves; which
terminate in the solitary nucleus of the medulla,
to the ventral posterior nucleus of the thalamus,
to the primary gustatory cortex
Primary cortex: near the face area of the
somatosensory homunculus
DAMAGE TO THE CHEMICAL SENSES
Anosmia: inability to smell
Caused by blows to the head that rip the olfactory
nerves as they pass through the cribriform plate
Symptom along with several other neurological
disorders
Ageusia: inability to taste
Rare
SELECTIVE ATTENTION
SELECTIVE ATTENTION
At any instance, we are receiving a LOT more
sensory input than we consciously perceive
Selective attention is the process by which we
are able to “ignore” the rest
Works to essentially enhance the signals that we
are focusing on & get rid of interference caused
by the signals we’re ignoring
Cocktail-party phenomenon
Change blindness