Somatosensory Processing Flashcards
______ is the sense of oneself
Proprioception
-Receptors in the skeletal muscle joint capsules, and the skin provide information about the posture and movements of our own body
______ – the sense of direct interaction with the external world
-Exteroception
-Receptors embedded under the skin convey sensations of contact, pressure, stroking, motion, vibration, temperature, pain
______ the sense of the function of the major organ systems of the body and its internal state
-Interoception –
-Receptors in the viscera convey non-conscious sensations involved in regulation autonomic functions: the cardiovascular, respiratory, digestive, and renal systems
Explain this image
4 types of sensory nerve fibers
Conduction velocity of myelinated peripheral nerve fibers is approximately six times the fiber of the diameter, smaller = faster conduction
How does proprioception work in limb position sense?
Muscle spindles: intrafusal fibers
- Aligned and parallel with muscle
- Enclosed within a capsule
- Detect muscle stretch
- Signal limb positioned (signaled by the mean rate of discharge in the muscle spindles) & change in position (the response of the primary ending increases in the direct t proportion of the rate of length change)
What is located between skeletal muscle and tendon, enclosed within a capsule that detects muscle tension and force?
Golgi tendon organs
Explain this image?
Spindles encode muscle stretch, only on triceps muscle
What is the point?
Our sense of where our body is is encoded jointly by an ensemble activity from many receptors and nerves to understand where our body is
What are the 4 types of exteroception: tactile perception receptors
Pacinian corpuscles, Merkel disc, Meissner corpuscles, Free nerve endings, Ruffini endings,
What are the characteristic s of Meissner’s corpuscle?
ØMost numerous
ØLocated close to skin surface
ØSensitive to dynamic skin deformation of relatively high frequency (~5–50 Hz)
ØDetect changes in texture (activated by lateral motion)
ØFA1: fast adapting
What are the characteristics of Merkel disc/cell?
ØLocated at the tip of epidermal sweat edges
ØSensitive to low-frequency dynamic skin deformations (<~5 Hz)
ØDetect sustained touch and pressure (activated by edge, points): important for detecting surface features, eg reading Braille
ØSA1: slowly adapting firing proportional to pressure
What are the characteristics of pacinian corpuscles?
ØLocated in dermis deep tissue
ØImportant for using tools (activated by vibration)
ØFA2: fast adapting
ØRespond to high frequencies
What are the characteristics of Ruffini endings?
ØLocated in dermis
ØDetect tension (activated by skin stretch, eg when manipulating large objects
ØSA2: Slowly adapting
Explain this image
Receptive fields on human hadn are smallest in fingertips
Explain this image
Results of an experiment measuring the minimal (threshold) amplitude of vibration at the fingertip that people can detect, as a function of the vibratory frequency
Threshold amplitude of vibration at different frequencies
What is the point of this image?
Responses of touch receptors to braille dots scanned by the fingers
- Receptors code different features to help us perform tasks, ie, SA1 is the best here
Explain this image
Sensory information from the hand during grasping in lifting
all 4 receptors are working throughout this task, RA2 would be good for the prediction
Explain this pathway
Dorsal Column-Medial Lemniscus Pathway: -> transmits touch & position sense (kinesthesis)
Explain this pathway
Anterolateral path -> transmits temperature, pain and itch
What are the 4 sub-areas that makeup S1 in the somatosensory cortex?
S1 – comprised of sub-areas
3a – proprioceptive inputs
3b – cutaneous
1 – cutaneous – larger RFs
2 – cutaneous (complex touch) / proprioceptive
Know the receptor fields
3a muscle tissue (deep)
3b (SA1, RA1 skin)
1 (RA1, RA2 skin)
2 (proprioception deep, complex touch skin)
5 (active touch skin)
Explain this image
Columnar organization of the somatosensory cortex
- Organized in columns
- Separate body maps in each subregion of S1
- Feedforward signals from thalamus – layer IV
- Feedback: recurrent signals from other SS areas, as well as PPC, motor, limbic and medial temporal cortex: sensory gating
Explain 3 characteristics of area 1
- RFs compared to area 3b
- ~ 10% respond to stimuli in 1 direction only
- involved in sensing the details of surface texture
Explain the characteristics of area 2
- large RFs
- integration of cutaneous & proprioceptive inputs
- convergence of inputs from areas 3a, 1 and thalamus
- cells respond to moving stimuli in preferred directions
- cutaneous responses may be conditional on proprioceptive cue
What are the characteristics of the secondary somatosensory area (S-II)
- large, bilateral RFs
- emphasis on discrimination of texture, and size
- processing modulated by attention
Explain Diagram
Attention enhances the response of a neuron in the S-II
A: Dual-task, tactile task, ask to indicate whether the orientation of bars was the same or different. The visual task, detect a change in brightness of square displayed
B: Mean firing rate was higher when animal attended to the tactile task than when the stimulus was ignored by the visual task
C. Stimulus stronger in tactile task
What make of the posterior parietal cortex (PPC)
Area 5, Area 7
What are the 3 characteristics of area 5?
- bilateral RFs
- respond to combinations of joint manipulations through different angles
- posture specific
What happens during lesions of area 5?
•clumsy movements
•
•movements of contralateral limbs made imprecise
•
•may produce perceptual loss of the affected parts
What are the characteristics of area 7?
•somatosensory information integrated with visual information
•
•aligns body schema with visual scene
•
•neurons may respond to stroking a particular body region or if an observed object passes over it without touching
•
•Processing modulated by attention
•
•Lesions: misguidance of limb movement in space (optic ataxia)
•SS input controlled by pre- & post-synaptic inhib. at each______
synaptic junction
True or False: in DC-ML pathway – axons from SI & motor cortex can block information at the DCN or thalamus
True
How does movement-related gating occur in regards to SS information?
- Psychophysical thresholds for detecting tactile stimulation are different during movement
- No attenuation…
- Somatosensory-evoked potentials in human cerebral cortex are also modulated during movement
- Greater attenuation during self motion
Air puffs were applied to the center of the receptive field (ulnar forearm in this case) either at a variable delay or with the animal at rest (right, control trial). The evoked potential traces are averages of 38 trials, aligned on the onset of the air puff stimulus (negative up). The corresponding displacement traces and EMG were averaged either on the onset of displacement (left), to show where the air puffs were applied relative to the motor task, or on the onset of the trial (right). F, flexion; X, extension.
Explain this image
•How can you tell the difference between u moving and something move you? comparison between predicted sensory feedback and actual sensory feedback
How does pre-synaptic inhibition work?
- Axo-axonic synapses
- 1 mechanism – ↑ Cl- permeability
- Shunts depolarizing current of AP
- ↓ Influx of Ca2+ into presynaptic terminal
- ↓ Neurotransmitter release
