Chapter 47 Flashcards
What are the three tactile senses?
- Touch
- Pressure
- Vibration
What is the only tactile receptor that sends alpha-gamma signals? what do the rest send?
- Free nerve endings
- the rest send alpha-beta signals
What is the tactile sense of Meissner corpuscle? Where is it most prevelent?
- touch
- the non-hairy parts of the skin (fingertips and lips)
What touch receptor is most common in the hairy parts of the skin and allows for determination of continuous touch of objects against the skin?
Merkel disc
What is stimulated by slight movement of any hair on the body?
hair-end organs
Where are raffini ending receptors found and what do they sense?
- found in the deep skin and the deeper internal tissues as well as the joints
- heavy prolonged touch and pressure
What receptor is responsible for vibration sense?
Pacinian corpuscles which are immediately beneath the skin and in the deep fascial tissues
What type of information is carried by the dorsal columns/medial lemniscus pathway?
- fine touch
- vibration
- joint position
- fine degree of pressure judgement
Where are the snapses for the dorsal column pathway?
FIrst order–>second order in the nuclei gracilis and cuneatus
Decussation
Second–>third order in VPL of thalamus
Thrird order travels to the prmary sensory cortex (post-central gyrus)
What information is carried by the anterolateral system (ALS)?
-pain
–temperature
- crude touch
- tickle and itch
- sexual sensations
Where are the synapses for the ALS?
First order–> second order in the dorsal horn of gray matter
Decussation within a segment or two
Second–>third order in the VPL of the thalamus
Third order continues on to the primary sensory cotex
What is most medial on the somatropic representation of the somatosensory cortex? What is most lateral?
- genitals are most medial
- Pharynx and intrabdominal are most lateral
After the genitals, moving laterally and inferiorly what is the general layout of the somatropic representation of the somatosensory cortex?
Toes, foot, leg, hip, trunk, neck, head, shoulder, arm, elbow, forearm, wrist, hand, fingers, thumb, eye, nose, face, lips, teeth gums and jaw, tongue
Is the information in the primary sensory cortex from the ipsilateral or contralateral body?
contralateral
What is the function of somatosensory area I?
- localize different sensations in the different parts of the body and judge the degrees of information.
- Allows for judgement of shapes or forms of objects (Astereognosis is when this sense is absent)
What is the function, location and name of the somatosensory association areas?
- Brodmann area 5 and 7 which are located in the parietal cortex behind the somatosensory area I
- play an important role in deciphering deeper meanings of sensory information from the prmary sensory cortex
What is the affect of a lesion to the somatosensory area I?
inability to:
- localize discretely the different sensations
- judge pressure
- judge weight
- judge shapes or form (astereognosis)
- judge texture
What happens if the somatosensory association area is lesioned?
- the person will lose the ability to recognize complex objects and forms on the OPPOSITE SIDE OF THE BODY.
- AMORPHOSYNTHESIS
- Will lead to them forgetting to use the affected side for motor function
How many layers are there in the somatic seonsory cortex?
6
Which layer does the incoming sensory signal excite first?
Layer IV
After entering layer IV where does the signal spread?
towards the surface (I, II, III) and towards the deeper layers (V, VI)
Which layers are in communication with the opposite side of the brain though the corpus collosum?
Layers II and III
Which layer controls the overal excitability of the brain while receiving diffuse, non-specific input signals?
Layers I and II
What are the differences in function between layers V and VI of the somatic sensory cortex?
Layer V sends axons to the deeper parts of the nervous system (basal ganglia, spinal cord and brainstem)
Layer VI extends to the thalamus to help control excitatory levels of incoming information
How is a 2 point discrimination test performed?
-Two needles are placed within close proximity to allow the patient to differentiate between the feeling of one or two needles
What is the role of surround inhibition?
-in almost all sensory pathways, sensory neurons inhibit neurons on either side (laterally) to block the lateral spread of the excitatory signal and increase the amount of sensory contrast perceived by the cortex
What is the principle of the Weber-fechner principle?
-gradations of stimulus strength are discriminated approximately in proportion to the log of the stimulus stregnth
What is the ratio for the change in stimulus required for detection?
About 1:30
at 30g, a 1g addition is not noticed and at 300g a 10g addition is not noticed.
But at 30g, a 10g addition will be noticed
What are the two types of propioception?
- Static position sense: conscious propioception
- Rate of movement sense: Kinesthesia or dynamic propioception
What is the most important sense for propioception at the midrange of joint angulation?
-muscle spindles helping to control muscle movement
What receptors and senses are most important for propioception at extreme joint angulation?
- stretch of the ligaments and deep tissues around the joints is important
- pacinian corpuscles, Ruffini endings. receptors similar to golgi tendon receptors
Which receptors are most important for detecting rapid rates of changing joint angulation?
Pacinian corpuscles and muscle spindles
What is the role of the thalamus in somatic sensing?
-has a slight ability to discriminate tactile sensation (this has been seen in people who have a somatosensory cortex that is destroyed)
