General Principles of Sensory Processing, Touch, and Pain Flashcards
Sensory receptor organs
Organs specialized to detect a certain stimulus
Receptor cells within the organ convert the stimulus into an electrical signal
Adequate stimulus
The type of stimulus to which a sensory organ is particularly adapted
Ex: photic light energy for the eye
Transduction
Converting information to neural signals
The doctrine of specific nerve energies says:
receptors and neural channels for different senses are independent
Labeled lines
The concept of labeled lines says that the brain recognizes distinct senses because action potential travels along separate nerve tracts
Lines are: sound, smell, and touch
Receptors in skin
Touch receptor associated w hair follicles
Pacinian corpuscle
A skin receptor that detects vibration and pressure
A stimulus to the corpuscle…
opens stretch-sensitive sodium channels made of a protein called Piezo, and produces a graded receptor potential (or generator potential)
When the potential is big enough, the receptor reaches _______ and generates an action potential
threshold
You can only detect the touch if…
an action potential is generated
Structure and function of the Pacinian Corpuscle
- Cell membrane stretches, channel opens, sodium comes in
- Stimulus is touch to corpuscle
- Causes structural change in ion channel to allow sodium to come in
- Influx of sodium ions causes a change in the membrane of the cell
- If enough come in, cell fires an AP and that’s how we detect the touch that comes in
Stimulus location is determined from…
the position of the activated receptors
The action potentials produced by a sensory neuron always have the same size and duration, so one way the intensity of sensory events are encoded is…
in number and frequency of action potentials
Some sensory systems employ multiple sensory receptor cells that specialize in one part of a…
range of intensities
as strength of a stimulus increases…
more neurons sensitive to higher intensities are recruited
Range fractionation
Each of the traces represents a nerve cell with a different threshold (a different response to different stimuli)
Adaptation
Phasic receptors and tonic receptors
Phasic receptors
Display adaptation and decrease the frequency of action potentials
Tonic receptors
Show slow or no decline in action potential frequency
Why does adaptation do this?
Sensory systems emphasize change in stimuli, as that is more important for survival
This prevents the nervous system from being overwhelmed by too much info coming in
Other ways to control sensory info
Accessory structures: such as eyelids
Top-down processing: higher brain centers suppress some sensory inputs and amplify others
Sensory info path in the brain
Sensory information enters the CNS through the spinal cord or brain stem and then reaches the thalamus
The ________ transmits info to the cerebral cortex
thalamus
Then, the cortex directs the thalamus to…
suppress some sensations
Primary sensory cortex
Swaps information with the
secondary sensory cortex
Delivers touch info to the brain
The dorsal column system
Dorsal column system
The stimulus triggers the receptive field of a neuron
These receptors send projections via the dorsal column of the spinal cord where they synapse on dorsal column nuclei in the medulla (brain stem)
Axons from neurons in the medulla cross the midline and go to the thalamus for initial processing, and then on to the primary somatosensory cortex
So, the brain processes touch information from the contralateral side of the body
Receptive field
The receptive field is the region in which a stimulus will alter a sensory neuron’s firing rate
Receptive fields differ in size, shape, and response to types of stimulation
What does the larger size of a region indicate?
The amount of neurons is different
The more neurons in the cortex dedicated to an area…
the smaller the receptive field and the better that body part is detecting touch
If we touch within a receptive field (two pokes close to each other)…
neuron is only triggered one time; one action potential
The somatosensory cortex is plastic
Intentional stimulation of a specific body region can be changed by experience
Loss of use will cause it to shrink
Phantom limb
When D3 and D2 expand, the cells themselves don’t move, but their projections do
Phantom limb touch happens because of neurons taking over area
Ex: face neurons take over hand area, so when you touch the face some of the neurons still think you’re responding to hand
Pain
An unpleasant experience associated with tissue damage
Pain helps us to withdraw from its source, engage in recuperative actions, and to signal others
Human pain can be measured
The McGill Pain Questionnaire describes three aspects of pain:
1. Sensory-discriminative quality (e.g., throbbing, gnawing, shooting)
2. Motivational-affective (emotional) quality (e.g., tiring, sickening, fearful)
3. Cognitive evaluative quality (e.g., no pain, mild, excruciating)
Why is pain so hard to measure?
Everyone’s pain tolerance is different
Level of experience with pain
Expecting the pain or not
Nociceptors
Peripheral receptors that respond to painful stimuli
Free nerve endings
in the dermis; have specialized receptor proteins on the cell membrane that respond to various signals
The free nerve endings produce different receptor proteins, so they respond to different stimuli like temperature changes, chemicals, and pain
Peripheral mediation of pain
Usually stems from damaged tissue
The anterolateral (or spinothalamic) system
Transmits the sensations of pain and temperature
Receptors synapse on spinal neurons in the ___________
dorsal horn
Pain information __________________ in the spinal cord before ascending to the brain
crosses the midline
Phantom limb (neuropathic) pain
Microglial cells release chemicals that make the dorsal horn neurons hyperexcitable and cause chronic pain
Visual system can change the brain’s processing of info
Social rejection activates brain regions for affective pain
Activation of anterior cingulate cortex
People who took Tylenol experienced less distress and showed less activation in these brain regions
Analgesia
The absence or reduction in pain sensation
Opioids
are endogenous opiate-like peptides in the brain
Opiates
Drugs that reduce pain
Three classes of endogenous opioids
Endorphins
Enkephalins
Dynorphins
Opioid receptors
respond to opiates or opioids
Stimulation of mu opioid receptors
relieves pain more effectively in
men than women
Stimulation of k opioid receptors
relieves pain more effectively in women
Periaqueductal gray (PAG)
An area in the midbrain involved in pain perception
Electrical stimulation of the PAG produces potent analgesia
