Chapter 12: The Somatic Sensory System Flashcards
Enables body to feel, ache, sense temperature and pressure (communication to external world)
somatic sensation
somatic sensation is responsible for ()
touch and pain
unique characteristics of the somatic sensory system (compared to other senses)
- receptors are found all over the body
- responds to multiple (at least 4) types of stimuli
somatic sensation responds to the ff. stimuli
- touch
- temperature
- pain
- body position
types of skin
hairy and glabrous (i.e. hairless: palm)
Most somatosensory receptors are () -> Present in unmyelinated axon branches sensitive to stretching, bending, pressure or vibration
mechanoreceptors
Specialized structures of mechanoreceptor nerve endings
Pacinian corpuscles
Ruffini’s endings
Meissner’s corpuscles
Merkel’s disks
mechanoreceptor nerve ending structures that have small receptive fields (only a few millimeters wide)
Meissner’s corpuscles and Merkel’s disk
mechanoreceptor nerve ending structures that have large receptive fields (an entire finger or half of palm)
Pacinian corpuscles and Ruffini’s endings
mechanoreceptor nerve ending structure: most sensitive to vibration of about 200-300 Hz
Pacinian corpuscles
mechanoreceptor nerve ending structure: respond best around 50 Hz.
Meissner’s corpuscles
The selectivity of a mechanoreceptive axon depends primarily on the ().
structure of its special ending
Larger onion-like capsules allow for increased ()
adaptivity
- Onion shells (corpuscles) have () in response to pressure on the structure
viscous fluid-filled structures that flow
For striped corpuscles, adaptation is ()
slow -> slow AP
Mechanoreceptors have (myelinated/unmyelinated) axon terminals.
unmyelinated
() convert mechanical force into a change of ionic current.
Mechanosensitive ion channels
Mechanical stimuli may trigger release of ().
second messengers
mechanosensitive ion channels can be sensitive to one of the ff. types of stimuli
- stretching of lipid membrane
- Force Applied to Extracellular Structures
- Deformation and Stress on Cell’s Cytoskeleton
Minimum distance for specific tissues for the successful discrimination of 2 points
Two-Point Discrimination
smaller 2-point discrimination -> (higher/lower) density of mechanoreceptors, (larger/smaller) receptive field size
higher, smaller
types of primary afferent axons (axon fibers) in the somatic sensory system
A(alpha), A(beta), A(delta), C
() fibers mediate pain, temperature, and itch
C
() fibers mediate touch sensation
A(beta)
spinal nerves within four divisions of spinal cord
spinal segments
()—one-to-one correspondence with spinal segments
Dermatomes
Divisions of spinal gray matter: ()
dorsal horn, intermediate zone, ventral horn
The neurons that receive sensory input from primary afferents: () (mostly in the dorsal horns)
second-order sensory neurons
A(beta) axons get branched to connect with the:
- (1) for rapid and unconscious reflexes)
- (2) for perception and judgments about the stimuli
- second-order sensory neurons
- brain
The pathway serving touch is called the ().
dorsal column-medial lemniscal pathway
From (), the somatic sensory system of one side of the brain is concerned with sensations originated from the other side of the body. (contralateral)
medial lemniscus
Somatosensory information from face is supplied by the (1), which enter the brain at the (2)
- large trigeminal nerves
- pons
also called S1/area 3b; Lesions here impair somatic sensation
primary sensory cortex
the primary sensory cortex receives dense inputs from the ()
VP nucleus of the thalamus
The thalamic inputs to S1 terminate mainly in layer ().
4
S1 neurons with similar inputs and responses are () that extend across the cortical layers.
stacked vertically into columns
(): usually evoked for the amputees by stimulating skin regions whose somatotopic representation border those of the missing limb.
Phantom limb sensation
the () cortex is involved in somatic sensation, visual stimuli, movement planning, attentiveness
posterior parietal
Damage to posterior parietal areas causes neurological disorders: (examples)
- agnosia
- neglect syndrome
(): the inability to recognize objects even though simple sensory skills seem to be normal
Agnosia
(): a part of the body or a part of the world is ignored or suppressed.
Neglect syndrome
(): a sensory neuron with free nerve ending that responds to damaging or potentially damaging stimuli (distinct from the path taken by mechanoreceptors)
Nociceptors
()—feeling of sore, stinging, aching, throbbing sensations
Pain
()—sensory process that provides signals that trigger pain
Nociception
ion channels on nociceptors can be opened by:
- direct stimulation (1)
- indirect stimulation (2)
- Direct and strong mechanical stimulation, temperature extremes, oxygen deprivation, chemicals
- Indirect substances released by damaged cells
examples of substances that indirectly open ion channels on nociceptors
- proteases, ATP, K+
- Histamine
kininogen cleaved -> () : increase ionic conductances, stimulates nociceptors
bradykinin
Types of nociceptors—most are (1), but show (2) in their responses to different stimuli
- polymodal nociceptors
- selectivity
(): tissues that have been already damaged are unusually sensitive to additional stimuli
Hyperalgesia
primary hyperalgesia occurs at ()
within area of damaged tissues
Surrounded damaged area may become supersensitive as well
secondary hyperalgesia
() (from the enzymatic breakdown of lipid membrane) induces hyperalgesia.
Inflammation soup, including Bradykinin, and Prostaglandins
(1), a peptide produced by the nociceptors causes vasodilation and (2) release from the mast cells -> One cause of secondary hyperalgesia.
- Substance P
- histamine
TRPV1 (transient receptor potential V1) as a () receptor
capsaicin
() can be activated by several natural pain inducers as well as high temperature
TRPV1 (transient receptor potential V1)
There are more TRPs that regulate many different pain stimuli as well -> () as cold detection
TRPM8
Disagreeable sensation that induces desire or reflex to scratch; Usually brief, minor annoyance—can become chronic, debilitating condition
Itch
Since Aδ and C fiber have different rates of action potential conduction velocities, the activation of skin nociceptors produces ()
two distinct perceptions of pain
two distinct perceptions of pain -> First pain by (1) and second pain by (2) fiber
- Aδ
- C
() -> signals from actual source have same paths as signals from other sources -> brain is confused and identifies source incorrectly
Referred pain
angina as an example of referred pain
Source is from lack of oxygen in heart, but pain is felt in upper chest wall
The neurotransmitter of the pain afferents: ()
glutamate
Within the spinal cord, there is (): cause the phenomenon of referred pain
mixing of information from nociceptors in skin and viscera
Touch and pain pathways differ: Nerve endings in the skin
specialized structures for touch vs free nerve ending for pain
Touch and pain pathways differ: Diameter of axons
large Aβ vs small Aδ or C fiber
touch sensation is (faster/slower) than pain sensation
faster
Touch and pain pathways differ: Connections in spinal cord
Touch—ascends ipsilaterally
- Decussation further up in brain
Pain—ascends contralaterally
- Decussation in spinal cord
decussation in the touch pathway occurs specifically at ()
medial lemniscus
The pathway serving pain is called the ()
spinothalamic pathway
in the spinothalamic pathway, axons of the second-order neurons () and ascend through the spinothalamic tract running along the ventral surface of the spinal cord.
immediately decussate
The relay of nociceptive signals by the projection neuron is gated by the activity of an ().
inhibitory interneuron
If the large sensory neuron is activated concurrently, the interneurons inhibit the pain signals from reaching spinothalamic tract
gate theory of pain
(): Electrical stimulation of PAG in the midbrain cause a profound pain insensitivity by depressing activity of nociceptive neurons.
descending regulation
() - area in midbrain involved in descending regulation
periaqueductal gray matter (PAG)
() are highly concentrated in areas that process nociceptive information, where they suppress nociceptive signal transduction.
Opioid or endorphin receptors
() channels are involved in detecting temperature
Thermoreceptor TRP
Thermoreceptors also have adaptations to ()
continuous stimulation
Sudden () generate most intense neural and perceptual responses to temperature
changes in quality of stimulus
Organization of temperature pathway is similar to the ()
pain pathway
Cold receptors coupled to () fibers
A(delta) and C
Hot receptors coupled to ()
C fibers
