Somatosensory System Flashcards
Area of skin innervated by a single neuron; tend to be smaller distally and larger proximally; Distal regions of the body have a greater density of receptors than proximal areas
Receptive field
What are the two reasons to have overlapping of receptive fields?
- protective mechanism - if there’s an injury to one nerve, there is only a small area of sensation lost
- Helps with localization of touch - activates more than one neuron indicating a different area of the body
Touch is categorized as fine or cars. Which touch includes a variety of receptors and sensations, and can localize sensation very well? which touch is mediated by free endings throughout the skin, with no specialized receptor, and is not as localizable, including sensations of tickle, itch, slow pain, and sexual sensations?
Fine (discriminative); Coarse
What are the two types of intrafusal fibers?
- Nuclear bag fibers
2. Nuclear chain fibers
What are the two different sensory endings in the muscle spindle?
Primary endings of type Ia
Secondary endings of type II
neurons wrap around the central region of each intrafusal fiber
Type Ia (phasic and tonic)
end mainly on nuclear chain fibers adjacent to the primary endings
Type II (tonic)
maintain sensitivity of Muscle spindles during all muscle lengths
Gamma efferents
Sensitive to changes in tension on a tendon; Respond to active contraction and passive stretch
GTO
respond to quick and prolonged stretches of the muscle
Muscle spindles
signal the force generated by the muscle contraction or by a passive stretch of the tendon
Tendon organs
respond to mechanical deformation of joint capsules and ligaments
Joint receptors
What axon type innervates muscle spindles? what is its stimulus?
Ia and II; muscle stretch
What axon type innervates GTO? what is its stimulus?
Ib; Tendon tension
What axon type innervates ligament receptors? what is its stimulus?
Ib; Ligament tension
What axon type innervates Paciniform and ruffini type receptors in joint capusles? what is its stimulus?
II; joint movement
What axon type innervates free nerving that sense fast pain? what is its stimulus?
A delta; cold
What axon type innervates free nerving that sense slow pain? what is its stimulus?
C; hot, itch and tickle
What axon type innervates Meissner’s and Pacinian receptors in skin? what is its stimulus?
A beta; touch, vibration
What axon type innervates ruffni’s receptors in the skin? what is its stimulus?
A beta; Skin stretch
What axon type innervates merkle’s and hair follicles in the skin? what is its stimulus?
A beta; pressure
Have high-fidelity transmission that provides accurate details regarding the location of the stimulation
Pathways to the brain
- When describing pathways in the nervous system, only the neurons with long axons that connect distant regions of the nervous system (projection neurons) are counted
The bundle of axons with the same origin and a common termination
Tract
What are the three types of pathways that bring sensory info to the brain?
- Conscious relay
- Divergent (diffuse systems)
- Unconscious relay
Transmit information to many locations in the brainstem and cerebrum and use pathways with varying numbers of neurons (though usually three); transmitted with high fidelity; helps make fine distinctions about stimuli
Conscious relay pathways
Information is transmitted to many locations in the brainstem and cerebrum and use pathways with varying numbers of neurons; Sensory information is used at both the conscious and unconscious levels; Aching pain is a form of sensation that is transmitted in the CNS
Divergent pathways
Unconscious proprioceptive and other movement-related information is carried to the cerebellum (Does not reach consciousness); Information plays an essential role in automatic adjustments of our movements and posture.
Unconscious relay pathways
What are two routes the pathways to consciousness travel upward in the spinal cord?
- Dorsal columns (discrete touch, conscious proprioception)
2. Anterolateral tracts (pain and temp, crude touch)
Where is the first neuron in conscious pathways located for sensation of the body? sensation of the face?
DRG; Trigeminal ganglia;
For the DC-ML pathway, where does the second neuron cross the midline? ALS pathway?
Caudal medulla; spinal cord
Where is the 3rd neuron in conscious pathways located for the body? face?
VPL; VPM
the localization of touch and vibration and the ability to discriminate between two closely spaced points touching the skin
Discriminative touch
the awareness of the movements and relative position of body parts
Conscious proprioception
the ability to use touch and proprioceptive information to identify an object; for example, a key in the hand can be identified without vision
Stereognosis
What senses follow this pathway?
Primary conveys information from the receptors to the medulla.
Secondary conveys information from the medulla to the thalamus.
Tertiary conveys information from the thalamus to the cerebral cortex
Discriminative touch and conscious proprioception
The most medial part of the dorsal column of the spinal cord carries info from what part of the body? What is it called?
Lower extremity; Gracile Fascicle
- 2nd order neuron = Nucleus gracilis
The most lateral part of the dorsal column of the spinal cord carries info from what part of the body? What is it called?
Upper extremity; Cuneate fascicle
- 2nd order neuron = nucleus cunateus
Where do the cuneate and gracile fascicles terminate?
Caudal (lower) medulla
Where would sensation be lost in an injury occurring above the medial lemniscus? below?
Contralateral side; ipsilateral side
What is the pathway for discriminative touch and conscious proprioception for the body? for the face?
DCML; Trigeminalthalmic pathway
If information reaches the _____, it reaches consciousness.
thalamus; may not be able to discriminate where, but you will feel it somewhere
the initial and immediate sharp sensation that indicates the location of the injury
Fast pain AKA spinothalamic pain
the dull, throbbing ache following fast pain that is not well localized
Slow pain AKA spinolimbic pain
- onset is later due to impulses traveling on smaller, unmyelinated axons
- occurs if tissue is damaged
Where does fast pain info from the face travel?
Spinal trigeminal pathway
a single lesion can cause pain sensation to be lost on the side of the face ipsilateral to the lesion and the contralateral side of the body
Crossed analgesia
- injuries to medulla or pons
- AKA Wallenber
divergent ascending network of neurons carrying pain information; Uses several pathways with variable numbers of projection neurons; Activity of the medial pain system elicits affective, motivational, withdrawal, arousal, and autonomic responses; not somatotopically organized, so slow pain cannot be precisely localized
Medial pain system
Where do medial pain systems synapse in the thalamus?
Intralaminar nuclei
Where is the first neuron in medial pain systems?
DRG (via small unmyelinated C fiber)
What happens to C fiber nerve endings in medial pain systems when there is repeated stimulation?
Becomes sensitized (pain response increases to stimulus
What are the three tracts in the anterolateral spinal cord that carry info for medial pain systems?
Spinomesencephalic
Spinoreticular
Spinolimbic - one that actually makes people feel pain
Carries nociceptive information to the superior colliculus and periaqueductal gray of the mid brain; involved in turning the eyes and head toward the source of noxious input and in activating descending tracts that control pain
Spinomesencephalic tract
A neural network in the brainstem that includes the reticular nuclei and their connections
Reticular formation
These ascending neurons synapse in the reticular formation; Modulates arousal, attention, and sleep-waking cycles
Spinoreticular tract
Axons of this tract transmit slow pain information to the medial and intralaminar nuclei in the thalamus; provide information that produces automatic movements and autonomic and emotional responses to noxious stimuli; connects emotional and physical aspects of who we are
Spinolimbic tract
Activity in the ______ and _____ tracts result in arousal, withdrawal, autonomic, and affective responses to pain
spinoreticular; spinolimbic
Slow pain information is transmitted via this pathway from the face; i.e., toothache
Trigeminoreticulolimbic pathway
Information is transmitted in phylogenetically older pathways to the following:
- Reticular formation
- Nonspecific nuclei of the thalamus
- Subcortical nuclei
- Hypothalamus
What does info that does not reach conscious awareness contribute to?
- arousal
- provides gross localization
- contributes to autonomic regulation
Transmit information from proprioceptors and information about activity in spinal interneurons; Relay information critical for adjusting movements; Inadequate proprioceptive input can cause ataxia because the loss of sensory feedback disrupts movement control
Unconscious relay tracts to the cerebellum
What are the two high-fidelity pathways? (receive precise proprioceptive information)
- Posterior spinocerebellar pathway
2. Cuneocerebellar pathway
High-fidelity pathway that transmits information from the legs and the lower half of the body
Posterior spinocerebellar pathway
High-fidelity pathway that begins with primary afferents from the arm and upper half of the body; the central axons travel via the posterior columns to the lower medulla
Cuneocerebellar pathway
What are the two internal feedback tracts? (information about how our brain wants our body to move)
- Anterior spinocerebellar tract
2. Rostrospinocerebellar tract
What internal feedback tract transmits information about the thoracolumbar spinal cord? Cervical spinal cord?
- Anterior spinocerebellar tract
- Rostrospinocerebellar tract
- start in the SC and go to cerebellum on same side
What are the functions of the spinocerebellar tracts?
- Information in the spinocerebellar tracts comes from the proprioceptors, spinal interneurons, and descending motor pathways.
- Information, which does not reach conscious awareness, contributes to automatic movements and postural adjustments
Where are the superior colliculi located? what is their function?
Tectum; carries the visual map of the world, orients the eyes to the stimulus
Where are the periaqueductal gray located? what is their function?
around cerebral aqueduct; modulates pain as part of the descending pain control system
Although intact sensory and parietal cortex is required for the localization of pain, crude awareness of slow pain can be achieved in many cortical areas and possibly in the _______ and _______
thalamus and basal ganglia
Monitor the activity of spinal interneurons and of descending motor signals form the cerebral cortex and brainstem
Internal feedback tracts (anterior spinocerebellar and rostrospinocerebellar tracts)
