Lecture 3-spinal cord pt 3 Flashcards
what does gray matter contain
what does white matter contain
- cell bodies and their dendritic processes and synaptic connections
- myelinated fibers/axons going longitudinally
what is a tract/fasciculus
collectoin of axons w/ a common origin, course, and termination
what is a funiculus/column
2 or more fasciculi
what does the dorsal funiculus contain?
fasciculus gracilis (all lvls) fasciculus cuneatus (C1-T6)
what do the ventral funiculus contain?
the ventral white commissure
where is the dorsal intermediate sulcus found
midthoracic segments and above (C1-T6)
-notably absent in lumbar regions, only found where there is fasiculus cuneatus
which fissure/sulci is very deep?
ventral median fissure unlike the dorsal median sulcus
what receives dorsal roots white
dorsal lateral
where do ventral roots emerge white
ventral lateral
what does the dorsal horn gray contain
sensory
what does the ventral horn gray contain
motor nuclei
waht does the lateral horn gray contain? where is it present at?
autonomic motor
only present w/ symp pre gang cell body (T1-L3 only)
what is the substantia gelatinosa homologous to?
spinal trigeminal nucleus
where is clarke’s nucleus found?
T1-L3
what information does substantia gelatinosa carry?
senosry in function, temperature
substance P
these are nuclei
where is clarke’s nucleus prominent at
lower thoracic levels
where is clarke’s nucleus located? why is it located there?
dorsal horn gray bc of its function in sensory prcoessing
waht does substance P act liek a cap to
dorsal horn
what does the ventral horn contain
cell bodies for lower motor neurons and found at all levels of the cord
what are the two types of lower motor neurons
alpha motor neurons: innervate extrafusal striated skeletal muscle fibers (“do work” when lifting)
gamma motor neuron: innervate intrafusal muscle fibers of muscle spinkles (keeps muscle spindle receptor sensitive to new changes in lenght)
what happens when alpha motor neurons are lesioned
cant contract skeletal muscle which leads to paralysis
why do alpha motor neurons have enormous cell bodies and dendritic trees?
bc everyone wants to influence them. there are lots of descending tracts and reflex pathways that will want to synapse on them in order to influence their final decision as to whether to “fire” to contract msucle
how do alpha motor neurons leave the ventral horn gray? what do they eventually merge w/ and innervate?
via ventral roots and will eventually merge into the spinal nerve and go out to the periphery to innervate skeletal muscle
what do alpha motor neurons that are located more medially tend to innervate
axial muscles or ones that are considered proximal like shoulder and arm
in the chunk of ventral horn that is located more lateral, what do those alpha motor neurons tend to innervate/
the appendicular or distal muscles like the forearm and hand (limbs)
where are flexor motor neurons located at in the ventral horn ?
where are extensor motor neurons located in the ventral horn?
more dorsally in the ventral horn
more ventral in the ventral horn
where is the intermediolateral cell column found
what do they contain
lateral horns
preganglionic sympathetic fibers
where does the oculosympathetics originate from? and wehre at
the ciliospinal center of budge at C8-T2
how are the cervical regions shaped? and why?
oval shaped and contain the largest absolute amount of white matter.
-all of the descending tracts, destined for cervial, thoracic, lumbar, and sacral have to go through the cervical region
-sensory ascending tracts starting in the sacral region go up, from lumbar and adding on thoracic, adding on cervical, etc.
SO…dorsal columns are more fully present at the cervical levls
why is the cord enlarged in the lower cervical and lumbosacral regions
to accommodate innervation of the arms and legs
In C5-T1, why is there more gray matter than just above or below those levels?
bc gray matter has to service the upper extremity (the arms) and we need more gray matter to service the lower extremity (L2-S3)
where is the lateral horn present
T1-L3
what is the origin of the brachial plexus?
lumbosacral plexus?
cervical enlargement (C5-T1) lumar enlargement (L2 - S3)
in the afferent limb, what does it start out w/ ?
what is this specialized receptor aligned in parallel to?
sensory stretch receptor IN THE MUSCLE ITSELF
-muscle spindle: reports on muscle length
what are the largest and fastest nerve fibers in the nervous system called
how are they so fast
where are their cell bodies located
Ia.
- large diameter and highly myelinated for fast conduction velocity
- these afferent fibers going to the cord have their cell bodies in the dorsal root ganglion and they enter the cord through the dorsal roots
in the efferent limb after arriving in the cord, where does it make its ONE synapse?
what kind of reflex is this?
what do they innervate?
alpha motor neuron aka lower motor neuron
monosynaptic reflex
homonymous muscle that was stretched in the first place
what happens when someone taps your patellar tendon
- you quickly and efficiently stretch the muscle
- this simultaneously stretches the stretch receptor buried inside it
- you get a burst of activity, a direct excitatory synapse on the alpha motor neuron
- this results in contraction of the extrafusal fibers of the same muscle that was stretched
what are the small muscle fibers at the extreme ends of the spindle called
intrafusal fibers
they change the lengthof the spindle apparatus itself to keep the receptor “taut” so that it’s always responsive to changes in muscle length or increased loads
.;……basically make the spindle receptor a better receptor, making it more sensivitve
what innervates intrafusal fibers
what innervates extrafusal fibers
own innervation-by gamma motor neurons which are located in the same place in the cord as the alphas
alpha motor neurons
when you use your muscles voluntarily, what do you activate to shorten the muscle
what are you keeping the same length
alpha motor neurons and gamma motor neurons to shorten the poles of the spindle receptor so you keep the central region the same lenght
what are stretch reflexes important for
maintaining appropriate muscle tone
what does the extra stretch on your bicep increase
the activity of your Ia’s causing an instantaneous monosynaptic connection w/ efferents to shorten the length of that bicep and overcome the unexpected load
waht is hyporeflexia
waht is hyperreflexia
sometimes, due to pathology tapping the tendon doesn’t do much
-othertimes, due to other types of pathology, reflexes are exaggerated or display hyperreflexia (from a loss of inhibitory influence on these pool of cells
what is another type of sensory muscle receptor that is not a length receptor
wehre is it located
force receptor-the golgi tendon organ (GTO) and is located not w/in the msucle but w/in the tendon
why do skeletal muscles and tendons have proprioceptors
to give information about body sense
they use fast fibers
what does the dorsal column medial lemiscus pathway use for proprioceptors
what about anterolateral system?
larger diameter fibers having faster conduction velocity
-uses the second 2, smaller diameter fibers w/ slower conduction velocity
what is the withdrawal reflex
polysynaptic. its a protective reflex in helping you withdraw a limb from a painful stiumus
what cause the withdrawal reflex
nociceptive (pain) receptors in the skin
what is crossed extension reflex
also increase extensor tone on the opposite leg via interneurons that cross the midline to have the opposite effect in the other leg so the pt has something to stand on
- active extensor on the other leg and inhibit those flexors
- involves the entire lumbar cord
-adpated, won’t see this reflex in the upper limbs
what are the 3 destintions that a single incoming axon will supply
reflex, cerebellum, and cerebral cortex
what else do afferents do other than reflexes
send info up the cord to the brain
