spinal cord segmental organization Flashcards
Where is the posterior median sulcus?
posterior/dorsal surface
Where is the posterior lateral sulcus?
dorsal root entry zone (sensory)
Where isq the anterior median fissure?
anterior/ventral midline
Where is the anterior lateral sulcus?
exit anterior (motor) roots
What is the dorsal (posterior) root ganglion?
give rise to central and peripheral nerve fibers.
Where is the central canal located?
In the gray commissure
Where can we find lateral gray horn?
in thoracic & upper lumbar segments of the cord
Into what is the white matter divided?
columns or funiculi
What are the columns of the spinla cord?
dorsal (posterior) column
lateral column
ventral (anterior) column
identify
cervical
identifyq
thoracic
identify
lumbar
identify
sacral
What are the type of neurons in the gray matter?
Local interneurons
Commissural neurons
Propriospinal neurons
What are local interneurons?
axons remain on ipsilateral (same
side) gray matter within a cord
segment
What are commissural neurons?
axons cross midline to
terminate in contralateral
(opposite side) gray matter
What are propriospinal neurons?
axons project rostrally (superiorly) or caudally (inferiorly) in surrounding
white matter for several segments before terminating in gray matter
What are interneurons?
-Majority of spinal neurons
-Receive information from primary sensory afferents, dorsal horn neurons, motor neurons, & descending pathways
-Integrate segmental activity that
controls spinal sensory processing &
motor and autonomic outputs
-May have excitatory or inhibitory effects on other spinal neurons
(excitatory neurons are glutamatergic)
(inhibitory neurons are GABAergic or glycenergic)
What are second order sensory neurons?
Projection neurons:
neurons which are glutamatergic and project axons from the dorsal and
intermediate gray horn to the thalamus, brainstem or cerebellum
What are cholinergic (acetylcholine) motor neurons?
Projection neurons:
located in the ventral horn and project
to skeletal muscle
What are cholinergic autonomic preganglionic neurons?
located in the intermediate gray matter and project to autonomic ganglia.
Where is the dorsomarginal nucleus found?
all cord levels in lamina I
What type of sensations does dorsomarginal nucleus has?
light touch (non-specific), pain and temperature sensations
What does dorsomarginal nucleus contain?
contains somas of 2nd-order sensory neurons that project to the thalamus
Where is the substantia gelatinosa found?
found at all cord levels (mostly in
lamina II
What type of sensations does substantia gelatinosa has?
mostly pain, some touch and
temperature sensations
What does substantia gelatinosa contain?
somas of 2nd-order sensory local
interneurons that integrate inputs
from primary sensory neurons to
modulate sensations; projects to
other lamina, thalamus and other
parts of brain
Where is the nucleus propius found?
found at all cord levels (mostly
in laminas III & IV)
What type of sensations does nucleus propius has?
light touch, pain & temperature
sensations
What deos nucleus propius contains?
contains somas of 2nd-order sensory neurons that project to the thalamus and other parts of brain
Where is the Nucleus Dorsalis of Clarke (posterior thoracic nucleus) located?
Lamina VII; found at spinal levels (C8)T1-L2 (L3), at the base of dorsal horn or the
intermediate gray matter
What is the function of the nucleus dorsalis?
associated with unconscious propioception (muscle spindles & gogli tendon organs)
Whar does the nucleus dorsalis contain?
contains somas of 2nd-order sensory
neurons that project to the cerebellum
Where is intermediolateral nucleus located?
found at spinal levels ~T1-L2 (Lamina VII)
what does intermediolateral nucleus contain?
-contains somas of preganglionic
sympathetic motor neurons (GVE)
that project to sympathetic ganglia
-contains, at T1-T2, the ciliospinal
nucleus (center of Budge), source
of sympathetic innervation of eye
Where are somatic motor nuclei found?
Lamina VIII & IX; Found at all spinal levels
wHAT DOES SOMATIC MOTOR NUCLEI INCLUDE?
Include nuclei for specific motor nerves,
such as the:
1. Spinal Accessory Nucleus –extends
from C1-C6 and gives rise to the spinal
root of the spinal accessory nerve
(Cranial nerve XI)
2. Phrenic Nucleus –extends from C3 to C6
and gives rise to the phrenic nerve
Where is the sacral parasympathetic nucleus found?
- found at spinal levels S2-S4
- contains cell bodies of preganglionic parasympathetic motor neurons
(GVE) that project to ganglia of the pelvic viscera
Explain the distribution of somatic motor nuclei in terms of innervation
-More dorsal nuclei in ventral horn innervate flexor muscles
-More ventral nuclei in ventral horn innervate extensor muscles
-medial nuclei innervate axial (proximal) muscles or trunk musculature
-lateral nuclei innervate appendicular (extremities) or distal musculature
What are the dorsal columns ascending pathways?
Fasciculus Gracillis
Fasciculus Cuneatus
What are the lateral columns ascending pathways?
Dorsal Spinocerebellar tract
Ventral Spinocerebellar tract
Lateral Spinothalamic tract
What are the lateral columns descending pathways?
Lateral Corticospinal tract
Rubrospinal tract
What are the ventral columns ascending pathways?
Ventral Spinothalamic tract
What are the ventral columns descending pathways?
Ventral Corticospinal tract
Reticulospinal tract
Vestibulospinal tract
Tectospinal tract
What are the two pathways in spinal cord for somatic sensation?
-posterior column pathway (propioception,
vibration, fine/epicritic, discriminative touch);
-anterolateral pathway (pain, temperature & crude touch).
Explain the descending tracts generally
-Control of skeletal muscle via
descending pathways (e.g. corticospinal
tract) include:
Upper motor neurons (UMNs): cell
body is in brain (i.e. cortex or
cerebellum) that projects via axons
through white matter to brain stem and
spinal cord.
UMNs synapse onto lower motor
neurons (LMNs) in anterior horns of
the central gray matter of brainstem
motor nuclei or in spinal cord.
Axons of LMNs project out of CNS via
anterior spinal roots or cranial nerves
to reach muscle in periphery.
Explain the somatosensory afferent fiber type Ia
Aa thick; fast 70-120m/sec; propioception (muscle spindles)
Explain the somatosensory afferent fiber type Ib
Aa thick; fast 70-120m/sec; propioception (golgi tendon organs)
Explain the somatosensory afferent fiber type II
AB moderate; moderate 30-70m/sec; Touch, pressure, stretch, vibration (cutaneous mechanoreceptors), propioception (muscle spindles and joint capsule)
Explain the somatosensory afferent fiber type III
Ag; thin; moderate 12-30m/sec; touch , pressure, stretch, fast pain and temperature
Explain the somatosensory afferent fiber type IV
C (unmyelinated); very thin; slow (0.5-2m/sec); slow pain and temperature
Explain the visceral afferent fiber type III
Ag: thin; moderate (12-30m/sec); visceral sensation (stretch, pain, chemoreception, ischemia)
Explain the visceral afferent fiber type IV
c (unmyelinated); very thin, slow (0.5-2m/sec); visceral sensation (stretch, pain, chemorception, ischemia)
Explain the somatic efferent fiber LMN Alpha
Aa; thick; moderate to fast (15-120m/sec); innervate extrafusal muscle fibers
Explain the somatic efferent fiber LMN Gamma
Ay; Thin; moderate (10-45m/sec); innervate intrafusal muscle fibers
Explain the visceral efferent fiber LMN B
Myelinated; thin -very thin; moderate to slow (3-5m/sec); pregangionic autonomic fibers
Explain the visceral efferent fiber LMN C
Unmyelinated; very thin; slow 2m/sec; postganglionic autonomic fibers
What do Alpha LMN do?
generates force with contraction
What does Gamma LMN do?
mechanosensory to detect stretch
WHst is the motor end plate?
Where alpha motor neurons project the axons to extrafusal fibers forming a specialized synapse
What are motor units?
An alpha (⍺) motorneuron, its axon and all the muscle fibers it innervates
What do small motorunits innervate?
motorneuron innervates few muscle fibers (i.e. 10-100) for small muscles (e.g. extraocular muscles)
What do large motorunits innervate?
motorneuron innervates many muscle fibers (i.e. 600-1000) for large muscles (e.g. quadriceps muscles)
What are intrafusal fibers?
muscle spindles and specialized sensory organs embedded in skeletal muscle
What are the two components of the intrafusal fibers and by what are they innervated?
◦ Nuclear bag fiber (innvervated by Ia
sensory fiber)
◦ Nuclear chain fiber (innvervated
largely by II sensory fiber)
What does the intrafusal fibers responds to?
Responds to stretch/length change provding signal to CNS
Which part of intrafusal fibers are contractile?
polar ends; central regions are non-contratile
Where do Ia & II sensory endings originate?
center region of intrafusal fibers
What innervates contractile polar ends of intrafusal fibers?
Gamma y-motor neurons
explain what happens when muscle is stretched
When muscle is stretched, muscle
spindle intrafusal fibers & sensory
endings are also stretched, resulting in
increased activity in afferent fibers
What is a spinal reflex?
involves excitation of a motor neuron in response to afferent
stimulation. They become exaggerated when there is damage to descending pathways. (UMN)
What is the golgi tendoon relfex?
inverse myotatic reflex; Resist sustained contraction of a
muscle to protect tendon from
damage during contraction of the
muscle
how is the contrcation of the golgi tendon reflex?
Ipsilateral: contraction of a
muscle results in inhibition of
contraction of same
(homonymous) muscle on same
side
What is the afferent limb for golgi tendon reflex?
Ib sensory neurons
What is the efferent limb for golgi tendon reflex?
alpha (a) motor neuron
What is the effcetor of golgi tendon relfex?
extrafusal fibers of skeletal
muscle where activated GTO is
found
WHich fibers work in the afferent sense for the golgi tendon and how?
Ib fibers from GTO project to spinal
cord where they excite inhibitory
interneurons to inhibit α-motor
neurons for that muscle (modulation of cortivospinal and bulbospinal pathways)
WHat is the flexor withdrawal reflex?
Quickly withdraw a limb from a
painful or noxious stimulus (i.e.
withdrawal reflex).
Reception of painful or noxious
stimulus results in contraction of
flexor muscles on same side
sensory information is received
Which sensory neurons detect noxious stimuli y flexor withdrawal reflex AFFERENT LIMB/SENSORY?
III (Aδ) and IV (C) sensory neurons
detect noxious stimuli
Which sensory neurons detect noxious stimuli y flexor withdrawal reflex EFFERENT LIMB/SENSORY?
⍺-motor neuron
What is the effector of the flexor withdrawal reflex?
excite extrafusal fibers of
flexor muscles on limb where
nociceptors have been activated, and
inhibit extensor muscles. Modulation – corticospinal &
bulbospinal pathways
What happens when there is activiation of inhibitory interneurons in the flexor withdrawal reflex?
Inhibition of motor neurons that innervate
extensor muscles
What happens when there is activiation of non-inhibitory interneurons in the flexor withdrawal reflex?
Excitation of motor neurons that innervate
flexor muscles (agonist & synergist)
What is the crossed extension reflex?
Postural support & balance during
withdrawal of limb due to painful
stimulus
Contraction of extensor muscles in
opposite limb counteracts
increased load caused by
withdrawing limb.
By what is the crossed extension reflex mediated?
Mediated via interneurons that
send collaterals through the ventral
gray commissure to make
connections with α-motor neurons.
Explain the crossed extension reflex
Excitation of motor neurons
innervating CONTRALATERAL
extensor muscles
Inhibition of MNs innervating
CONTRALATERAL flexor muscles
WHta is the alpha gamma coactivation?
Since muscle spindles are organized in parallel with extrafusal muscle
fibers, during voluntary movement it is necessary to activate gamma
fibers simultaneously to maintain tension in intrafusal fiber; able for intrafusal fibers to detect muscle length change
what is the gamma loop?
refers to movements initiated by descending supraspinal
influences (i.e. cortical spinal tract) that activate gamma motor neurons
