Spinal Nerves Intro Flashcards
Describe how mechanoreceptors often open.
A force applied to the membrane causes indentation of the cytoskeleton bridge associated with the ionophore. This causes the ionophore to open, allowing sodium or potassium to cross the membrane.
Describe the impulses caused by sodium or potassium crossing the membrane when the ionophore is altered.
A graded potential is first created which has varying intensity associated with the strength of stimulus. These graded receptor potentials are converted to APs, which confer info about the strength of stimulus via AP firing frequency.
Describe the purpose of large fiber sensory receptors.
Are for fine touch and proprioceptive information, and include meissner, merkel, pacinian, ruffini, and hair fibers. They all use A-beta fibers with a large diameter, fast conduction velocity, and myelination.
Describe the difference between fast and slow adapting receptors.
Slow (tonic)- Merkel and Ruffini, generate graded potentials proportionate to amplitude AND DURATION of signal.
Fast (physic)- Meissner, Pacinian, and hair. Produce on-response and off-response signals to define temporal boundary of the signal.
Note this adaptation is due to the encapsulation type, not the nerve ending itself.
What large fiber types are used for proprioception?
Ia and II fibers of muscle spindles, and Ib fibers of golgi tendon organs.
Describe the muscle spindle fiber types.
Ia- Sensitive to muscle length and its rate of change. Provide information about speed of movement and position.
II- Active during steady state phase of stretch, provide information about the muscle length and position.
Describe the golgi tendon organ muscle fiber type.
Ib- At the junctions between the muscle and tendon. Monitor muscle tension.
Describe the small fiber types.
A-delta: Sharp pain and cold.
C: Dull pain and warmth.
Both have small diameter and are slightly myelinated (a-delta) or unmyelinated (C). Conduction velocity is slow.
List and describe the medial deviation fibers of the dorsal root fibers.
Ia, Ib, II, and a-beta.
Are large and myelinated with fast conduction velocity. All send collaterals into the dorsal column, and project on specific laminae of the spinal cord to interact with sensory modalities and cause reflex circuits.
List the lateral division dorsal root fibers.
A-delta and C fibers
List and describe the ventral root fibers.
Alpha motor- Control extrafusal fibers. All fibers innervated by one a-motor neuron comprise a motor unit.
Gamma motor- Innervate and control the sensitivity of intrafusal fibers (muscle spindles) that are thin stretch receptors. Are attached to extrafusal fibers, so when the main muscle is stretched, they are as well.
What are the main symptoms of a peripheral neuropathy?
Numbness, paresthesia, radiating pain, muscle weakness/wasting, reflex loss, and autonomic dysfunction.
Describe the difference between a peripheral neuropathy and a myelopathy.
Peripheral- Damage of peripheral nerve (complex branching pattern affected) or spinal nerve root (radiculopathy, follow dermatomes and myotomes innervated by that root).
Myelopathy- Damage inside the spinal cord. Symptoms may be hyperreflexia or spastic paralysis. Are present at AND BELOW level of the lesion.
Describe where disc herniations occur that lead to cervial or lumbosacral radiculopathies.
Cervical- IVD herniation at level of dorsal root exit above the specific vertebrae.
Lumbosacral- IVD herniation also above the root exit level, which is now below the respective vertebrae.
What are the cervical radiculopathies of note?
C5- Numbness and pain in shoulder, upper arm. Weakness in delts, and biceps.
C6- Numbness and pain in lateral forearm, thumb, and index finger. Weakness in bicep and wrist extensor.
C7- Numbness and pain in middle finger. Weakness in triceps.
C8- Numbness and pain in medial forearm, ring finger, and little finger. Hand muscle weakness.
