Lecture 17: Senses Flashcards
Senses
What are 3 Levels of Processing of Sensory Information?
- Receptor level
- Circuit level
- Perceptual level
1.
Generating Signal at Receptor Level
stimulus energy must match receptor specificity (touch receptors do not respond to light)
graded potentials must reach threshold in first-order sensory neuron
1
Adaptation at Receptor Level
Adaptation is the change in sensitivity in the presence of a constant stimulus.
The receptor membranes become less responsive and the receptor potentials decline in frequency or stop.
1
Peripheral Adaptation at Receptor Level
Level of the receptor and reduces how much information is sent to the CNS
Central adaptation is at the level of the neural pathway to the brain and involves brain nuclei
1
Phasic Receptors
Phasic receptors send signals when there is a phase change, so the start of something or end of something.
1
Tonic Receptors
Adapt slowly or not at all.
1
Phasic Receptor Example
Receptors for touch; you notice when you change your clothes or take them off but you don’t really think about them while you have them on.
1
Tonic Receptor Example
Nociceptors and most proprioceptors.
2.
Processing at the Circuit Level (Function)
to get information to the correct area of the cortex so that one is aware(perception) and can localize source of stimulus
2.
Serial Processing
1st order neuron —> 2nd order neuron —-> 3rd order neuron
ex. skin receptor (for pain) —-> dorsal horn of spinal cord
—-> thalamus —-> cortex
2 Curcuit Level Processing
1.
Ascending pathways carry impulses to appropriate regions of cerebral cortex
2 Curcuit Level Processing
2.
First order brings signal to spinal cord
2 Curcuit Level Processing
3.
Synapse with second order neurons in cord or medulla UNLESS reflex- then doesn’t go to brain, just synapses directly with motor neuron
2 Curcuit Level Processing
4.
Second order carries impulse to thalamus or cerebellum
2 Curcuit Level Processing
5.
Synapses with third order in thalamus
2 Curcuit Level Processing
6.
Transmits signals to somatosensory cortex or cerebrum
2 Curcuit Level Processing
7.
goes to perceptual level
Three main pathways for somatosensory information to ascend the spinal cord
1.Dorsal column-medial lemniscal pathways
2.Spinothalamic pathways
3.Spinocerebellar pathways
1 Dorsal column-medial lemniscal pathways
target is the thalamus; usually a single type of receptor (or a few related types) that can be localized precisely on the body surface (discriminative touch, vibrations; also proprioceptors);decussation at the level of the medulla
2 Spinothalamic pathways
- target is also the thalamus; input from several types of receptors with information pertaining to pain, temperature, coarse touch and pressure; don’t localize source as precisely; decussation at level of spinal cord
3 Pinocerebellar pathways
- target is the cerebellum; information about muscle or tendon stretch so cerebellum can coordinate skeletal muscle activity; ipsilateral, so do not decussate; we are not consciously aware
Processing at the Perceptual Level
- Information has to get to the right place to be understood and localized; using the correct neural pathway to permit arrival at the correct destination is key
- Notion of sensation (aware of changes in internal/external environment) versus perception (conscious interpretation of those changes); perception determines how you will respond
Properties of Sensory Perception
- Perceptual detection
- Magnitude estimation
- Spatial discrimination
- Feature abstraction
- Quality discrimination
- Pattern recognition
1 Perceptual detection
Simply put, one is aware; need to sum inputs from several receptors to achieve detection
2 Magnitude estimaton
Intensity of the stimulus; encoded by action potential frequency
3 Spatial discrimination
Localize the stimulus; notion of “two-point discrimination test” as a measure of how precise that localization can be; can vary between 5 and 50 mm, depending on body area
4 Feature abstraction
Each neuron tuned to one feature or property of a stimulus - often several features come together for the sensory experience (temperature, texture, firmness, & dimensions of something you are touching)
5 Quality discrimination
Distinguish submodalities of a particular sensation (e.g. submodalities of taste)
6 Pattern recognition
E.g. recognition of a familiar face, a letter, a piece of music
Pain
- Can be helpful - warns of tissue damage and motivates us to take action
- Pain is very personal – can’t really be measured
- Extreme temperature or pressure
- Pain chemicals include histamine, K+, ATP, acids, bradykinin
Pain suppression
Endogenous opioids are endorphins and enkephalins; their release can be triggered by the activation of the SNS.
Pain Tolerence
Pain threshold (amount of stimulus needed to generate sensation of pain) is the same for everyone, but tolerance (ability to withstand high levels of pain) varies and can be influenced by genetics as well as mental state, even gender, social isolation, stress.
Somatic Pain
Musculoskeletal pain; often described as aching, gnawing, throbbing or cramping; usually easy to localize because the bones and muscles are well innervated
Visceral pain
Pain associated with organs of the thorax and abdominal cavity – aching, burning, gnawing – can be the result of extreme stretching of tissues, ischemia, irritating chemicals, muscle spasms – uses same pathways as somatic pain making it possible to have referred pain
Referred Pain
Pain arising from one part of the body appears to come from somewhere else; (e.g. heart attack and pain along medial aspect of left arm – both are spinal nerves T1 to T5)
Phantom Pain
A type of hyperalgesia (pain amplification) which involves NMDA receptors making it a “learned” pain – if limb amputated under general anesthesia, then spinal cord still experienced the pain of amputation; better to use epidural anaesthetics to block spinal cord during the surgery
