spinal cord Flashcards
each spinal cord segment gives rise to a pair of ____ ____ that are entering or exiting from that segment
spinal nerves
spinal cord ends below L1 vertebrae as the:
conus medullaris
lumbar and sacral nerves travel far before emerging from the vertebral column, this is called:
cauda equina
how many spinal cord segments are in the dog
36
what is the dorsal root ganglion
contains somas of sensory afferents entering the cord
what is the dorsal root
sensory (somatic and visceral afferents)
what is the ventral root
motor (somatic and visceral efferents)
what are spinal nerves
mixed sensory and motor
what is grey matter
nerve cell bodies, dendrites and axons
what is white matter
bundles of myelinated axons organized into tracts or fasciculi (pathways)
what are the different fasiculi
- dorsal funiculus (fasiculus gracilis, cuneatus)
- lateral funiculus
- ventral funiculus
where are there increased innervation segments in the spinal cord
- cervical enlargement
- lumbar enlargement
how do the different levels of spinal cords vary
- in size and shape
- in configuration of gray matter
- in relative amounts of gray and white matter
- white matter decreases from rostral to caudal
what are the divisions of gray matter
- dorsal horn
- intermediate gray
- ventral horn
- lateral horn
dorsal horn
mainly neurons responding to sensory input
intermediate gray
some sensory neurons, some motor neurons, interneurons
ventral horn
mainly motor neurons whose axons exit the spinal cord
lateral horn
- T1-L2
- cell bodies of preganglionic sympathetic neurons
- send axons out ventral root to innervate smooth muscle, cardiac muscle and glands
what nerves innervate skeletal muscle
alpha and gamma motor neurons
what is a motor unit
one alpha motor neuron and all the muscle fibers it innervates
what is a motor neuron pool
the collection of alpha motor neurons that innervates a single muscle
what specific types of neurons are in the vental horn
alpha and gamma motor neurons that innervate skeletal muscle
what type of neurons are in the intermediolateral cell column
- visceral efferents
- preganglionic sympathetic (lateral horn, T1-L2)
- preganglionic parasympathetic (sacral level) neurons
voluntary contraction of skeletal muscle requires an interaction of 2 neurons:
- an upper motor neuron (UMN)
- a lower motor neuron (LMN)
neurons that synapse on striated muscle clinically referred to as:
lower motor neurons
what is the function of the corticospinal tract (pyramidal tract)
voluntary refined movements of the distal extremities
the corticospinal tract is in what area of the spinal cord
lateral funiculus
descending spinal pathways from the brain do:
- modulate spinal reflexes or directly drive motor output
- clincially referred to as “upper motor neurons”
- especially corticospinal tract
lateral pathways
- voluntary movement of distal musculature
- under direct cortical control
- innervate distal musculature
ventromedial pathways
- control of posture, locomotion, orienting and balance
- under brainstem control
- innervate axial and proximal musculature
sensory afferents entering the dorsal roots are segregated according to degree of myelination, conduction velocity and ____ ____
sensory submodality
dorsal column-medial lemniscal system
a 3 neuron path that carries proprioception (limb position sense) fine touch, pressure and vibratory sense to the cortex
first neuron of the DC-ML
large myelinated axons of dorsal roots that carry proprioception and touch modalities into the cord
axon collaterals of the heavily myelinated afferents enter:
dorsal columns
2nd neuron in ____ medulla axon crosses in medulla
DC-ML
ipsilateral
fasiculus gracilis
body map
hindlimb - S,L
fasiculus cuneatus
body map
forelimb - T,C
what are the 2 dorsal column nuclei
- nucleus gracilis
- nucleus cuneatus
spinothalamic tract
a 3 neuron pathway that carries pain and temperature sensations to the cortex
first neuron of spinothalamic tract
- small diameter axons of dorsal roots that carry pain and temperature modalities into the cord
- all synapse with sensory neruons in the dorsal horn
2nd neuron in spinothalamic tract
- in ipsilateral spinal spinal cord
- axon crosses in the cord ascends contralaterally
spinocerebellar systems
convey unconscious proprioception to ipsilateral cerebellum
dorsal spinocerebellar
lower limb (1) -> clarke’s nucelus (2)
cuneocerebellar tract
upper limb (1) -> accessory cuneate nucelus (2)
pathways to neocortex for conscious proprioception/touch/pain/temp
- dorsal column - medial lemniscal tract (proprioception/touch/vibration/pressure)
- spinorthalamic tract (pain/temperature)
pathways to the cerebellum for unconscious proprioception
- dorsal spinocerebellar tract
- cuneocerebellar tract
parallel pathways of ascending information
somatosensory input is split into separate submodalities and carried up to brain on separate paths
if there is a meisection of spinal cord T10 what occurs
- contralateral loss of pain and temperature (ascending, crossed spinothalamic tract)
- ipsilateral loss of vibration, proprioception, light, touch, below lesion (ascending uncrossed fibers in dorsal columns)
- ipsilateral impaired motor function below lesion, increased tendon reflexes (UMN) (descending corticospinal tract, already crossed)
