Exam II Flashcards
Muscle spindles
detect changes in LENGTH of a muscle. located in parallel with the extrafusal muscle fibers
Are muscle receptors intrafusal or extrafusal?
Intrafusal.
Primary annulospiral (Type 1A) Muscle Spindle
Sensory innervation, respond to SUDDEN changes in length. Wrap around mid portion of nuclear bags and chains. Branches come off the 1A & synapse on interneuron to inhibit the antagonist muscles.
Secondary (Type II) Muscle Spindle
Sensory Innervation. Wraps around distal end of chains. Responds to SLOW CHANGES in length.
Gamma Motor neurons
Stimulate nuclear bag and nuclear chain fibers (intrafusal). Keep the muscle on a constant slight stretch to enhance the muscle spindles ability to respond to stretches of the muscle at all parts of the range.
Alpha motor neurons
stimulate the extrafusal muscle fibers (actin & myosin), when stimulated the entire fiber shortens.
Explain how gamma motor neurons work.
cause the muscle spindle to lengthen while the muscle is contracting & shortening. This maintains the sensitivity of the spindle throughout the range of the muscle length.
Alpha-gamma coactivation
Spindle lengthens while the muscle shortens. Provides constant feedback to the CNS to stimulate alpha motor neurons
Monosynaptic reflex (myotatic)
1A primary annulospiral synapse DIRECTLY on alpha motor neurons. The muscle spindle are stretched, stimulating the 1A, causing the alpha motor neurons to fire, causing contraction of the muscle.
Flexor (withdrawal) reflex
NOT monosynaptic. Sensory neuron synapses on a pool of interneurons. Example: free nerve endings synapse on interneurons which synapse on alpha motor neurons which remove the extremity from the object.
Tonic Muscle Stretch Reflex
Only w/ UMN lesions. Reflex muscle contraction continues as long as a stretch is maintained. Typically the sensory afferents send info from muscle spindles to interneurons in spinal cord (LMN), in normal pts this is inhibited but with LMN lesion the inhibition is lost thus the reflex is present.
Golgi tendon organs
Sensory type 1B. located at myotendinous junction, detects tension in the tendon. Connected in series (perpendicular with the extrafusal fibers) Active when extrafusal fibers contract or are lengthened to end range.
Traditional sequence of GTO
tension in tendon –> AP in type 1B fibers –> inhibitory signal to alpha motor neuron (muscle relaxes). Also stimulates the antagonist muscle.
Autogenic inhibition
Inhibition of alpha motor neurons that innervate the muscle in which the GTO resides.
Current theory of GTO function?
Contribute to proprioception by causing stimulation and inhibition of motor neurons during functional activities. Like walking for example (facilitates gastroc during stance contracts it during swing)
What is the reliability of testing skin sensation dependent on?
Cognitive state & level of arousal.
Testing pain sensation
nociceptive free nerve endings. prick them with something sharp.
Testing temperature sensation
free nerve endings/krause bulbs
Testing touch sensation
free nerve endings, hair follicles, krause end bulbs
generalized (crude) - cotton ball over diffuse area or along dermatome or peripheral nerve distribution
localized (fine) - specific area of skin
Efferent peripheral nerves
Aa (large myelinated, innervate extrafusal fibers), Ay (innervate intrafusal fibers), B (preganglionic autonomic nervous system, C (postganglionic fibers)
Afferent peripheral nerves
1a (muscle spindle), 1b (GTO), II (muscle spindle), III (fast pain), C [type IV] slow pain, A-beta (“close the gate”)
neuropraxia (class I)
traumatic myelinopathy - no axonal disruption, repair within 3 weeks
axotmesis (class II)
traumatic axonopathy - axon disrupted but not endoneurium, still contained so better chance of recovery. normal EMG changes 2-3 weeks, recovery 6 weeks to 6 months, maybe longer.
neurotmesis (class III)
severance - axon and endoneurium disrupted, need surgery
Synkinesis
totally disrupted nerve reconnects with another nerve so theres an abnormal connection when that nerve fires.
Axons re-grow….
at a rate of 1-4 mm/day (1 in per month)
What nerves are affected first in compression injuries?
large myelinated neurons
Sequence of sensory loss
conscious proprioception & fine discriminatory touch –> cold sensation –> fast sharp pain sensation –> heat sensation –> dull (slow) pain sensation (return of sensation is reverse)
Wallerian degeneration
disconnected distal stump undergoes swelling, fragmentation and phagocytosis
Central chromatolysis
degenerative changes of clusters of rER (nissl bodies) that can result in death of the cell
Axonal regrowth connecting the proximal and distal stump
schwann cells from the proximal stump secrete NGF, proliferate and fill the space within the endoneurium and form an intact tunnel between the proximal and distal stumps.
Collateral sprouting
denervated post-synaptic cells are reinnervated by branches of intact neighboring neurons
Regenerative sprouting
regenerating axon innervates a new post-synaptic cell
What is neuropathic pain?
pain arising as a direct consequence of nerve injury
Symptoms of neuropathic pain
paresthesia, dysesthesia, allodynia, secondary hyperalgesia
paresthesia
painless abnormal sensations such as tingling
dysesthesia
Unpleasant abnormal sensations such as shooting or burning
Allodynia
pain evoked by stimulus that would not normally cause pain (light touch)
Secondary hyperalgesia
hypersensitivity to mildly painful stimulus to uninjured tissue
Ectopic foci
increased production and insertion of ion channels in demyelinated areas, becomes an area capable of generating action potentials
Ephaptic transmission
a “cross-talk” of APs from one demyelinated axon to another demyelinated axon
Central sensitization
increased production of NT’s and receptors in neurons in spinal cord and brain. Excessive neural activity disproportionate to incoming nociceptive signals. (fibromyalgia, barre virus, lots of diffuse pain)
What is a lower motor neuron?
alpha motor neuron cell body and its axon.
What is Henneman’s size principle?
The body recruits slow twitch first, then fast twitch recruitment.
S/S of LMN
flaccid paralysis or weakness, diminished/absent reflexes, fasciculaitons (spontaneous contractions - muscle cells have more AcH receptors and are hypersensitive), atrophy, sensory loss/paresthesias
Mononeuropathy
involves one peripheral nerve
Polyneuropathy
symmetrical involvement of more than one nerve in the same region (diabetic neuropathy, guillan-barre)
Radiculopathy
Damage to nerve root
Multiple Mononeuropathy
asymmetrical involvement of 2 or more nerves often due to ischemia of individual nerves
Common causes of peripheral neuropathies
Infections, immune disorders, trauma, vitamin deficiencies, diabetes, impaired glucose tolerance, idiopathic
Clinical signs to detect peripheral neuropathies
absence or asymmetrical decrease of a reflex (ankle jerk reflex), impaired pallesthesia, impaired proprioception, paresthesias, muscle weakness
Diabetic Neuropathy
glove and stocking distribution, axons and myelin damaged
S/S - pain, dysesthesias, impaired pallesthesia, hyporeflexia
long term - motor loss, bone resorption
Pain can be treated with lyrica (pregabalin) (binds to voltage gated Ca2+ channels and blocks release of substance P)
Bell’s Palsy
etiology unknown (maybe viral), inflammation of CN 12, pain behind the mandible 24-48 hrs before one sided facial paralysis. 2/3 of cases spontaneously recover within 3 months.
Deep peroneal nerve pathology
MOI usually pressure on head of fibula
S/S - weakness or dorsiflexion, decreased sensation in area between great and second toe.
Herniated NP
C5/C6 disc (C6 nerve root), C6/C7 disc (C7 nerve root)
L4/L5 disc (L5 nerve root)
L5/SI disc (S1 nerve root)
Guillian-Barre Syndrome
possibly autoimmune (antibodies attack schwann cells), possibly triggered by viral or bacterial infection. S/S: ascending paralysis distal to proximal, decreased reflexes, ANS dysfunction (decreased CO, arrythmias, peripheral edema, urinary retention), demyelination (medical emergency)
Polio/post-polio syndrome
Eventual degeneration of collateral branches of surviving neurons resulting in new onset of progressive weakness/fatigue, muscle cramping and joint pain.
Charcot-Marie-Tooth Disease
Also known as hereditary motor and sensory neuropathy, genetic mutations cause damage to axons and myelin
S/S - paresis below the knee resulting resulting in foot drop w/ steppage gait pattern, pain, pes cavus/ hammer toes/claw toes, decreased touch sensation, muscle atrophy, hand and forearms may be affected.
Spinal cord
from foramen magnum to L1/L2 in adults
Cervical Enlargement
C4-T1
Lumbar Enlargement
L2-S2
Thecal (Dural) Sac
Dura and arachnoid together = dural sac, coccygeal ligament attaches teh dural sac to the sacrum
Epidural Space
space b/t the thecal sac and teh bony vertebral canal , filled w/ blood vessels and fat
Dorsal Gray Horn
Substantia gelatinosa (II), lamina V (T-cells, transmitting the sensations of pain and temperature), nucleus proprius ( III/ IV, origin of contralateral ventral spinothalamic tract - general crude touch)
Ventral Medial Gray Horn
motor neurons to the trunk musculature, at ALL levels of the spinal cord
Ventral Lateral Gray Horn
motor neurons to the extremities, only at the cervical and lumbar enlargements.
Interomediolateral cell column
T1-L3 (preganglionic sympathetics cell bodies) & S2-S4 (preganglionic parasympathetics cell bodies)
Dorsal nucleus of Clarke
Ipsilateral dorsal spinocerebellar tract for concious nad unconscious proprioception of LE
Other things in the ventral gray horn
Spinal Accessory nucleus (C1-C5), phrenic nucleus (C3,4,5), Onuf nucleus (S2, S3, S4 –> voluntary control of the urethral and anal sphincters)
Sacral Sparing
indicates incomplete SCI, central lesion affects proximal muscles first. The sacral innervated legs/feet affected last, perianal sensation and toe flexion intact.
Anterior Spinal artery
supplies a lot of the anterior part of the spinal cord (ventral gray matter)
Posterior spinal artery
Posterior spinal cord
Segmental and medullary arteries
auxiliary blood to SC. Travel with the spinal nerves
Reciprocal Inhibition
Inhibit motor neurons of antagonistic muscles during voluntary motion, inhibits antagonist during reflex testing, can be suppressed by: co-contraction, anxiety, learning new activity, anticipating uncontrolled movements
Non-reciprocal Inhibition
Inhibit motor neurons of agonists, antagonists, and synergists throughout the limb to allow smooth movement.
Recurrent inhibition
inhibits agonist motor neuron and synergists. “Renshaw cell”, dampens muscle activation to allow smooth movement
Stepping Pattern Generators
POOLS of interneurons that are normally activated during the initiation of walking (in the gray matter), help produce the rhythmic movements of walking.
Why is the White matter of the spinal cord white
because most of the axons are myelinated and teh high fat content in myelin gives it a whitish appearance.
Dorsal funiculus
Ascending tracts - White matter - R & L sides separated by the dorsal median septum. Contains Fasciculus gracilus & cuneatus.
Fasciculus gracilus & Fasciculus cuneatus
located throughout the spinal cord (gracilus), located at spinal cord segments T6 and above (cuneatus). TRANSMIT: 2 point discrimination, vibration, fine discriminatory touch and position sense from IPSILATERAL lower trunk/LE (gracilus) & upper trunk/UE (cuneatus)
Tabes dorsalis
a disease process of the dorsal spinal cord –> syphilis, degeneration of dorsal column axons, loss of previously indicated sensations, be losing 2 point discrim, vibration, fine discrim touch.
Lateral funiculus
descending tracts –> lateral corticospinal tract, raphe spinal tract, hypothalamospinal tract.
Lateral corticospinal tract
descending axons from CL pre-motor, pre-central gyri to motor neurons of extremity muscles
Raphe spinal tract
Descending axons from brainstem that synapse on neurons in dorsal gray horn to modify pain perception
Hypothalamospinal tract
descending axons from hypothalamus to autonomic neurons in spinal cord
Components of Spinal Nerves
ventral rootlets/roots, dorsal roots/rootlets, spinal nerves
Ventral roots/rootlets
Axons of alpha and gamma motor neurons, axons of pre-ganglionic sym. (T1-L3) and pre-ganglionic parasym. (S2-S4 )
Dorsal roots/rootlets
central processes of sensory neurons
Spinal Nerves
Ventral and dorsal roots converge → through IV foramen→ split into dorsal and ventral primary rami
dermatomes
Sensory innervation of skin from one spinal cord segment
myotomes
Skeletal musculature innervated by motor neurons from one spinal cord level
