Musculoskeletal Reflexes Flashcards
Dorsal white matter
Contains ascending tracts to the cortex of the brain
Lateral white matter
Ascending and Descending corticospinal tracts
Primarily pathway of cerebellum receiving and sending signals
Anteriorlateral
Ascending and Descending tracts that modulate pain, temperature and maintain muscular posture.
Lamina 1
Found in dorsal horn
Dorsal root fibers that mediate pain, touch and temperature
Lamina 2
Found in dorsal horn
Substantia gelatinous neurons that modulate pain, muscular activity and temperature.
Lamina 3 and 4
Found in dorsal horn
Contains Proper sensory nucleus and spinothalamic tracts
Receives information from lamina 2 and mediates temperature, pain and crude touch.
Lamina 5
Found in dorsal horn
Receives descending tracts from corticospinal and rubrospinal areas.
Site of corticospinal tract development
Receives proprioception fibers and regulates movement
Lamina 6
Found in dorsal horn
Lateral portion: Receives descending corticospinal and rubospinal fibers
Medial portion: receives Afferent from muscle spindles and joint Afferents
receives majority of proprioception fibers and regulation of movement
*ONLY present in cervical and lumbar segments for limb modulation
Jaw muscle stretch reflex includes what nerve and what segmental innervation?
Pons= segmental innervation
Mandibular and trigeminal branches = Nerves
Biceps muscle stretch reflex includes what segmental innervation and what nerve?
C5-6 = segmental innervation
Musculocutaneous = nerve
Brachioradialis muscle stretch reflex includes what segmental innervation and what nerve?
C5-6 = segmental Innervation
Radial = nerve
Triceps brachi deep muscle reflex includes what segmental innervation and nerve?
C7-8 = segmental innervation
Radial = nerve
Finger muscle stretch reflex includes what segmental innervation and nerve?
C8 and T1 = segmental innervation
Median = nerve
Knee muscle stretch reflex includes what segmental innervation and nerve?
L3-4 = segmental innervation
Femoral = nerve
Ankle muscle stretch reflex includes what segmental innervation and nerve?
S1-2 = segmental innervation
Tibial = nerve
Upper abdominal superficial reflex includes what nerves and center modalities?
Afferent nerve center and efferent nerve = T7-10
Lower abdominal superficial reflexes includes what nerves and center modalities?
Afferent and efferent nerves and center = T10-12
Cremasteric superficial reflex includes what nerves and center modalities?
Afferent nerve = femoral
Efferent nerve = genital branch of genital femoral
Center = L1
Plantar superficial reflex includes what nerve and center modalities?
Afferent nerve = tibial
Efferent nerve = tibial
Center = S1-2
Perineal (anal wink) superficial reflexes include what nerve and center modalities?
Afferent nerve = pudendal
Center = S4-S5
Efferent nerve = pudendal
Ventral horn somatotopic organization of neuron bodies.
Posterior section of ventral horn = flexors
Anterior section of ventral horn = extensors
Medial section of ventral horn = axial and limb girdle
Lateral section of ventral horn = distal extremities.
Alpha vs gamma motor neurons
Alpha: large A type motor neurons that synapse on extrafusal fibers (bulk of muscle not muscle spindle)
- receive input from upper motor neurons and muscle spindles
- generate contractile force
Gamma: small A type motor neurons that synapse on intrafusal fibers (muscle spindle in the middle of the muscle belly)
- receive input from upper motor neurons
- control basic muscle tone and reset sensitivity of a muscle
Lateral inhibition explanation
Three steps
- alpha motor neuron is excited
- alpha motor neuron stimulates renshaw cells and other neurons (if present) via cholinergic signals
- Stimulated renshaw cells inhibit motor neurons via GABA
Renshaw cells
Regulate firing of alpha motor neurons “sharpen the signal”
Types of muscle sensory receptors
Muscle spindles and golgi tendon organs
Muscle spindles
Sense the stretch and velocity of contractions in muscle fibers.
Organized via nuclear bag (centrally located nuclei) or nuclear chain (nuclei arranged in single file) in the intrafusal fibers.
- contain primary Afferent fibers in both bag and chain organization
- contain secondary afferent fibers in only nuclear chain form
Primary Afferent fibers (1a) vs secondary afferent fibers (2)
Primary = found in nuclear bag or chain intrafusal fibers within muscle spindles
- respond to slow changes in length and rapid changes in length (static and dynamic responses)
Secondary = found only in nuclear chain intrafusal fibers within muscle spindles
- respond to slow changes in length only (static responses)
Golgi tendon organs
Found on tendons and send information regarding tensile load of the tendon.
- critical for resisting forces exerted to resist imposed loads or gravity acting on body.
- also maintain posture
Spinal reflexes general information
Involve an efferent motor neuron response via an afferent neruon stimulation.
- not modulated by CNS and instead modulated via supraspinal mechanisms.
- reflexes still remain intact below lesion levels if spinal cord is cut/damaged.
Steps in the stretch reflex
- muscle is stretched via force and activates via muscle spindles
- intrafusal fibers deform and stimulate 1a afferents
- 1a afferents synapse on alpha motor neurons eliciting contraction and also stimulate inhibitor interneurons.
- inhibitory interneurons stimulate Innervation of the antagonist muscle via lateral inhibition.
- 2 types: static and dynamic*
- prevents oscillation or jerkiness of body*
Dynamic vs static stretch reflexes
Dynamic: elicited by rapid change in length via primary afferents. Very quick change in muscle length
Static: elicited by continuous static receptor signals AFTER a dynamic stretch reflex via primary and secondary afferents. Causes muscle tone
Steps in the inverse stretch reflex (inverse myotonic or golgi tendon reflex)
- activation of golgi tendon bodies sends info via 1b afferents to inhibitory interneuron
- interneuron inhibits alpha motor neruon of the muscle being stretched.
- muscle stops contracting
- prevents overstretching*
Steps in the Flexion (withdrawal) reflex
Mediated by nociceptors to get away from a noxious stimulus
Steps
- noxious stimulus is applied to skin of deeper structures
- stimulates free nerve endings and conveys info to spinal cord
- spinal cord fibers synapse with 3-4 excitatory interneurons which stimulate multiple alpha motor neurons
- alpha motor neurons contract ipsilateral flexors and relaxes ipsilateral extensors to pull away from noxious stimuli
Crossed extension reflex steps
In conjunction with flexion reflex but on the contralateral side of the noxious stimuli.
Steps
- afferent nerve endings that carry noxious stimuli to spinal cord to elicit flexion also stimulate interneurons through anterior commissure.
- commissure stimulates alpha motor neurons contralateral to the noxious stimuli and elicit relaxation of flexor muscles and stimulation of extensor muscles of contralateral side of noxious stimuli
How do you elicit muscle Stretch and superficial reflexes?
Muscle stretch = hard external stimulus
Superficial = soft scraping of the skin or cornea
Lamina 7
- known as the intermediate zone*
- contains nucleus dorsalis of Clarke (segments C8-T2 only though)
- receives muscle and tendon afferents and allows communication between dorsal and ventral horns of segments.
- origin of dorsal spinocerebellar tracts
- includes intermediolateral cell column (lateral horn in T1-L2
- Lateral portion contains preganglionic parasympathetic neurons and renshaw cells
Lamina 8
Found in ventral horn
- contains motor interneurons and coordinates lower motor neurons.
- receives input from descending motor tracts.
Lamina 9
Found in ventral horn
- contains lower motor neuron columns
Lamina 10
Central zone of gray matter
- site of convergence for somatic and visceral afferents.
What lamina control cutaneous sensation?
1-4
