somatosensory Pt1 Flashcards
- Describe the compound action potential and what it tells you. For example, how is an unmyelinated nerve fiber (axon) designated in terms of the compound action potential?
Compound Action Potentials are recordings OF THE SUMMED ACTION POTENTIALS AND measured over time at particular sites o the nerve
• the further along the nerve, the more the potentials seperate by velocity
• peaks correspond to axpon closters with different velocities and dedgrees of myelination
• Types I or A are the most myelinated
and conduct the fastest;
Types IV or C the slowest
- What is meant by intensity coding?
Increased stimulus intensity enhances the amplitude of the receptor potential increasing the FREQUENCY of the AP
- What impact do slow vs fast adapting receptors have on the message sent to the brain?
Rate of change of a stimulus or status of a sensation
rapid onset/ offset of the stimulus alerting
the CNS “that it occurs”
• Mechanisms include rapid ion channel inactivation and decreasing receptor potential
MEISSNER, PACINIAN, hair follicles
- slow adapting is a gradual decrease in receptor activity, ‘“what is occurring”
- Mechanism is gradual reduction of receptor potential
MERKEL, RUFFINI
- What are cutaneous receptive fields and how do they contribute to tactile localization?
area of skin innervated by single sensory neuron
• Receptive of mechanoreceptors vary in size
for fordegrees of acuity.peripheral RFs densely innervated and small;proximal ones less innervated and bigger
Discriminative touch
Small RF
• Meissner and Merkel- small and conc.
IN THE FINGERTIPS
LargeRF
• Ruffini,Pacinian- large and located over most of region
- Pacinian located along median and ulnar nerve
- Ruffini detects stretch in specific directions
- How are sensory modalities distinguished by the peripheral nerves?
Axons have membrane receptors that respond to specific stimuli–>indirectly thru CT capsules, modified epithelial cells, hairs
–>Directly thru membrane of the free nerve endings
Sensory receptor proteins are TRPs (transient receptor) type ion channels. Each responds maximally to ONE STIMULUS (“adequate stimulus”) and less to others
The “adequate stimulus” is the energy that elicits the greatest response and determines which neurons will be responsible for the perception of the sensory “modality”
–>pain can elicit burning hot/cold
- Describe some examples of the kinds of information that slow and fast adapting exteroceptors mediate.
FAST Meissner: movement across skin Pacinian: high vibration hair: touch SLOW Merkel: form/ texture ruffini:stretch
- What type of axons mediate pain, temperature and non-discriminative touch?
slower conducting, slower adapting smaller A -gamma and C fibers (epidermis, stratum granulosum)
NON DISCRIMINATIVE TOUCH
• high threshold sense of touch, poor localization
- Describe the dorsal column lemniscal system in terms of:
• Modalities
• Location, projection and decussation of first, second and third order neurons
in dorsal column-lemniscal system Discriminative touch and proprioception. Fast AP conduction
3rd order: internal capsule. To primary somatosensory cortex in postcentral gyrus. homunculus
2nd order: decussate in medulla. Axons form medial lemniscus which synapse onto thalamus neurons. synapse onto anterolateral system
1st order: sensory, A-beta, Form dorsal columns (cuneate..)
synapse onto dorsal column nuclei in the medulla
- Describe the anterolateral system in terms of:
• Pathways,
• Location of second order neurons
Non-discriminative touch, pain, temp 2nd order neurons neospinalthalamic tract paleospinothalamic tract 3rd order neurons (lateral, medial thalamic)
- Compare the neo- and paleospinothalamic pathways
NEOSPINOTHALAMIC Projects to lateral thalamus and somatosensory cortex • Localization of sensation PALEOSPINOTHALAMIC Projects to reticular formation,medial thalamus and cortex • Qualitative aspects of pain,temperature and non-discriminative touch
- Give a general description of the reticular formation
Median column a.k.a. the raphe nuclei.
Medial column a.k.a. magnocellular nuclei.(because of larger size of the cells)
Lateral column a.k.a. parvocellular nuclei.(because of smaller size of the cells.)
- Compare the medial and lateral projections of the anterolateral system third order neurons in terms of location and perception
Lateral thalamic neurons
• project to primary somatosensory cortex
• homunclulus for stimulus localization
Medial thalamic neurons • project to cynuglate gyrus and insula • Affective qualitiesof pain/temp • Differentmedial thalamic nuclei make alerting respinses or dull pain
- Account for the peculiar symptoms of syringomyelia a
Syringomyelia
• Cysts form in center of cervical grey matter interrupting decussation of anterolateral (spinothalamic)
and 2nd order neurons
affects both sides–>bilateral loss of pain/temp but not discriminative touch or proprioceptin (cervicothoracic area)
- Describe the sensory projections of the trigeminal nerve.
Sensory innervation to face from PONS.enters face via various foramina
Opthalmic-orbital cavity, forehead, nose dorsum
Maxillary: nasal cavity, cheecks
Mandibular:oral cavity,chin sides of face,ear, EAM,tympanic membrane.
MOTOR to masticators and soft palate
What are the different nuclei of the trigeminal nerve that mediate the different modalities ?
• PRINCIPAL (Main, Chief) Sensory Nucleus Discriminative touch from face • SPINAL Trigeminal Nucleus Pain Temperature from face • MESENPHALIC Nucleus Proprioception from masticators mediate muscle reflexes • MOTOR Nucleus Motor to masticating muscles
