General Sensory Mechanisms Flashcards
(63 cards)
1
Q
What are the two “types” of mechanoreceptors?
A
-free and encapsulated
2
Q
What are the free/expanded tip ending mechanoreceptors? Skin tactile sensibilities
A
-Merkel’s discs
3
Q
What are the encapsulated ending mechanoreceptors? Skin tactile sensibilities
A
- Meissner’s corpuscles
- Kraus’ corpuscles
4
Q
What are the deep tissue sensibility mechanoreceptors? What are examples of each?
A
-free and expanded tip
-spray endings
+Ruffini’s corpuscles
-encapsulated endings
+Pacinian corpuscles
5
Q
What are the 4 receptor characteristics?
A
- differential sensitivity: sensitive to one type if stimulus and is almost non responsive to other types
- modality: refers to each of the principle types of sensation
- labeled line principle: specificity of nerve fibers for transmitting only one modality of sensation
- adaptation of receptors
6
Q
What are the 4 mechanisms of stimulation for receptors?
A
Mechanical deformation
Application of a chemical
Temperature change
Electromagnetic radiation
7
Q
What are tonic receptors and what are some examples?
A
- slow adapting
- detect continuous stimulus strength
- transmit impulses as long as stimulus is present
Examples:
- muscle spindles
- macula and vestibular receptors
- Golgi tendon organs
- baroreceptors
- chemoreceptors
8
Q
What are phasic receptors?
A
- fast adapting
- do not transmit a continuous signal
- stimulated only thing when stimulus strength changes
- transmit info regarding rate of change
9
Q
What are the different nerve fiber types?
A
- type A
- type C
- group Ia
- group Ib
- group II
- group III
- group IV
10
Q
What are type A nerve fibers?
A
- further subdivided into alpha, beta, and delta
- large and medium-sized myelinated fibers of spinal nerves
11
Q
What are type C nerve fibers?
A
- small, unmyelinated fibers
- conduct signals at low velocity
- make up more than half of all sensory fibers in most peripheral nerves and all postganglionic autonomic fibers
12
Q
What are group Ia fibers?
A
-fibers from annuli spiral endings of muscle spindles
13
Q
What are group Ib fibers?
A
-fibers from Golgi tendon organs
14
Q
What are group I fibers?
A
-from cutaneous tactile receptors and flower spray
15
Q
What are group III fibers?
A
-carry temp, crude touch, and pricking pain
16
Q
What are group IV fibers?
A
Carry pain, temp, and crude touch
17
Q
What is spatial summation?
A
- increasing signal strength is transmitted by using progressively greater number of fibers
- entire cluster of nerve ending from pain fiber covers an area so skin referred to as the receptor field for that fiber
- number of endings is large in center of field but is reduced in periphery
- nerve endings from one pain fiber overlap those of other pain fibers
18
Q
What is temporal summation?
A
-increase signal strength by increasing frequency of nerve impulses in each fiber
19
Q
What is the stimulators field of a neuronal pool?
A
- neuronal area within the pool stimulated by each incoming never fiber
- terminals for. Each input fiber lie on the nearest neuron its field
- fewer terminals for each input lie on neurons further away
20
Q
What is the discharge zone of the neuronal pool?
A
-includes all output fibers stimulated by the incoming fiber
21
Q
What is the facilitated/inhibition zone of the neuronal pool?
A
- neurons further from the discharge zone that are facilitated but not excited
- may be inhibitory or excitatory depending on the input fiber
22
Q
What is the difference between diverging and converging neuronal pathways?
A
Diverging
- may result in amplification of initial signal
- may allow transmission of original signal to separate areas
Converging
- multiple input fibers converge onto a single output neuron
- input fibers may be from a single source or from multiple separate sources
23
Q
What are reverberatory circuits?
A
- aka oscillatory circuits
- caused by positive feedback within neuronal circuit
- circuit once stimulated may discharge repetitively for a long time
24
Q
What are the two types of senses?
A
-somatic senses
+collect sensory info from all over the body
+include mechanoreceptors, thermoreceptors, and nocireceptors
-special senses
+vision, hearing, smell, taste, and equilibrium
25
What are the three types of sensation?
- exteroreceptive sensation: from surface of body
- proprioceptive sensation: physical state of body (position, muscle and tendon sensations, pressure sensations, ad equilibrium
- deep sensations: deep pressure, pain, and vibrations
26
What are the 5 basic sensory receptors?
- mechanoreceptors
- thermoreceptors
- nocireceptors
- electromagnetic receptors
- chemoreceptors
27
What are exteroreceptive sensations?
-sensation from the surface of the body
28
What are proprioceptive sensations?
```
-refer to physical state of the body
+position sensations
+muscle and tendon
+pressure
+equilibrium
```
29
What are deep sensations?
-deep pressure, pain, and vibrations
30
In terms of ascending pathways, what are the three neuron pathways?
-primary sensory neurons
+from external receptors
+travel through dorsal roots of spinal cord
+synapse with secondary neurons
-secondary neurons
+make up tracts in spinal cord and brainstem
+usually terminate in thalamus
+synapse with tertiary neurons
-tertiary neurons
+from thalamus to primary sensory cortex
+travel through internal capsule
31
What are the systems utilized for conscious and unconscious perception?
Conscious:
- spinothalamic system
- medial Lemniscal system
Unconscious:
- spinocerebellar
- spino-olivary
- spinotectal
- spinoreticular
32
What are the two subdivisions of the spinothalamic system?
- lateral spinothalamic tract
| - anterior spinothalamic tract
33
What does the lateral spinothalamic tract do? How does it travel?
-carries pain and temperature
- primary fibers ascend or descend 1-2 spinal cord segments before synapsing with secondary fibers
- secondary axons decussate through anterior gray and white commissures
- secondary axons make up the lateral spinothalamic tract traveling in the lateral column of the spinal cord
- secondary fibers are joined in brainstem by fibers of the trigeminothalamic tract (pain and temp from face and teeth)
- secondary fiber collaterals project to reticular formation (stimulate wakefulness and consciousness)
- secondary fibers project to ventral posterolateral nucleus of thalamus
- secondary fibers synapse with tertiary fibers in VPL nucleus
- tertiary fibers synapse in post central gurus (somatic sensory area 3,1,2)
- tertiary fibers form part of internal capsule
34
What does the anterior spinothalamic tract do? How does it travel?
-carries light touch, pressure, tickle, itch
- primary neurons may ascend 8-10 spinal cord segments before synapsing with secondary neurons
- secondary fibers decussate in anterior gray or white commissures
- secondary fibers ascend to synapse with tertiary fibers in VPL nucleus of thalamus
- tertiary fibers ascend through internal capsule to primary sensory cortex
35
What is the medial Lemniscal system? How does in travel in the spinal cord?
- aka posterior column system
- carries sensations for two point sensation (fine touch), pressure, and vibration
- primary fibers ascend entire length of spinal cord and synapse with secondary neurons in medulla (fasciculus gracilis and fasciculus cuneatus)
- fiber of the gracilis synapse in nucleus gracilis (convey sensations from below mid thoracic level)
- fibers of cuneatus synapse with nucleus cuneatus (convey sensations from above midthoracic level and proprioceptive sensation from arms to cerebellum)
- secondary fibers decussate
- secondary fibers ascend in VPL of thalamus
- tertiary fibers ascend through internal; capsule to primary sensory cortex
36
What makes up the primary somatosensory area and the somatosensory association area?
- Brodmann's areas 1,2,3
| - Brodmann's area 5 and 7
37
What is the sensory homunculus?
-areas of the brain that receive the sensory information for various body parts
38
What would a widespread excision of somatosensory area I cause?
- loss of ability to localize the different sensations in the different parts of the body, crude localization possible
- loss of ability to judge critical degrees of pressure against the body
- loss of ability to judge weights of objects
- loss of ability to judge shapes or forms (astreognosis)
- loss of ability to judge textures of material
- pain and temp sense is still preserved but poorly localized
39
Where does somatosensory area II receive signals from?
- brain stem, transmitted upward from both sides of the body
- secondarily from somatosensory area I
- other areas of the body, including visual and auditory
40
Projections from somatosensory area ___ are required for function of somatosensory area ____. The opposite is not true.
I, II
41
What are the layers of the somatosensory cortex? What do each of these layers do?
-Layers I and II (superficial):
+receive input signals from lower brain centers
-Layers II and III:
+send information through corpus callosum to opposite hemisphere
-Layers V and VI (deep):
+large neurons in V project to distant areas such as basal nuclei, brain stem, and spinal cord
+axons from layer VI project to the thalamus
-Layer IV:
+received incoming sensory input
42
How are potentials created?
Opening "modality" gated channels (eg. Na channels) that are opened in response to membrane deformation caused by touch or pressure
43
What type of potential do receptors create?
-local decremental poterntial
44
Most pathways are made up of three neurons. What are these three neurons utilized in sensory pathways?
-primary neurons: originate from peripheral receptors such as Merkel receptors
+enter spinal cord/brain via dorsal roots of spinal/cranial nerves
+cell bodies are located in the dorsal root ganglia
+synapse in spinal cord with secondary neurons
-secondary neurons: originate in spinal cord gray matter
+travel through spinal cord in one of the myelinated columns
+decussate
+synapse in thalamus with tertiary neurons
-tertiary neurons: travel through internal capsule (myelinated pathway between thalamus and some basal nuclei)
+synapse in somatosensory cortex
45
What does two point touch refer to?
-the ability to distinguish two separate points as close as 2mm apart
46
What pathway does two point discrimination travel?
-dorsal column-medial lemniscal pathway
47
What is lateral inhibition?
-important in blocking the lateral spread of excitatory signals of two point discrimination
-increases the degree of contrast in the cerebral cortex
-occurs at each synaptic level:
+dorsal column nuclei
+ventrobasal nuclei of thalamus
+somatosensory cortex
48
Trace the dorsal column-medial lemniscal pathway.
- primary neurons (peripheral sensory neurons) travel through a spinal nerve and through the dorsal root ganglia
- primary neurons continue into the spinal cord and travel up the spinal cord through the dorsal columns
- secondary up through the medulla and synapse with tertiary in the ventrobasal complex of the thalamus
- the tertiary goes to the postcentral gyrus (homunculus)
49
How do axons from the lower limbs and upper limbs in the dorsal column-medial lemniscal pathway differ?
-lower limbs travel in the medial portions of the two dorsal columns -> gracilis
+synapse in lower medulla in gracilis
-upper limbs travel in the lateral portions of the dorsal columns -> cuneatus
+synapse in the lower medulla in cuneatus
50
What are the characteristics of fast pain? (ON EXAM)
- felt within 0.1sec after stimulus is applied
- not felt in most deep tissues
- elicited by mechanical and thermal stimuli
- typically carried by A(gamma) pain fibers
- pain fiber terminate in lamina I of the dorsal horns of the spinal cord
51
What are characteristics of slow pain? (ON EXAM)
- begins about 1sec after stimulus is applied and increases with time
- aching, slow burning, throbbing, nausea, and chronic
- elicited by mechanical, thermal, and chemical stimuli
- carried by C fibers which terminate in layers II and III (substantia gelatinous a) of the dorsal horns of the spinal cord
52
Describe how pain travels and differentiate between slow and fast pain pathways.
- pain travels through ANTEROLATERAL pathways
- primary pain fibers synapse in the dorsal horns of the spinal cord (layers 1,2,3) with the secondary fibers
- secondary fibers decussate and make up anterolateral pathways
FAST:
- make up neospinothalamic tracts and synapse terminate in the ventrobasal nuclei of thalamus -> ascend to somatosensory cortex
- use Glu as neurotransmitter
SLOW:
- make up paleospinothalamic pathway
- secondary fibers terminate throughout the brainstem, some pass all the way to the thalamus
- release both Glu and substance P (slower than Glu)
53
What is Brown-Sequard syndrome?
- occurs when there is a hemisection of the spinal cord
- motor functions are blocked on the side of the transection in all segments below the level of the transection
- sensation of pain, heat, and cold are lost on opposite sides of the body in dermatomes 2-6 segments below the transection
- kin esthetic and position sensations, vibration sensation, discrete localization, and two point discrimination are lost on the side of the transection in all dermatomes below the transection
54
What does the analgesia system consist of?
- periaquaductal gray and periventricular regions of brainstem and third ventricle
- Raphe magnus nucleus and reticular nuclei in medulla
- pain inhibitory complex in dorsal horns of spinal cord
55
Describe the analgesia system.
- enkephalins has an ability to suppress pain by synapsing directly onto a pain receptor turning it off
- body's natural painkiller system
- doesn't always work, typically in extreme situations
56
What are the three receptors that discriminate thermal gradations?
- cold
- warmth
- pain
57
Describe the warm nerve endings.
- free nerve ending
| - mainly transmitted over C type fibers
58
Describe cold receptors.
- 3-10x more numerous than warm nerve receptors
| - small type A(gamma) myelinated endings
59
How are cold and warm receptors thought to be stimulated?
- changes in their metabolic rate
| - transmitted in pathways parallel to pain signals
60
What is referred pain?
- occurs when visceral fibers are stimulated and stimulate some of the pain fibers that conduct pain signals from the skin
- severe pain results when there is diffuse stimulation of pain nerve endings throughout the viscera
- can result from ischemia
- transmitted via C pain fibers
61
What essentially causes referred pain?
-crossed visceral and skin nerve fibers
62
What is a prominent example of referred pain?
-headache
63
How can you get headaches when the brain is insensitive to pain?
-membranes and meninges surrounding the brain
