Spinal Cord, Spinal Nerves, and Reflexes Flashcards
Anterior boundary of vertebral canal
vertebral bodies, intervertebral discs, and posterior longitudinal ligament
Posterior boundary of the vertebral canal
vertebral laminae and the ligamentum flavum
Lateral boundaries of the vertebral canal
vertebral pedicles and the intervertebral foramina
Contents of the vertebral canal
the canal contains neural tissue and other structures associated with the protection and metabolic support of the neural tissue
What does the spinal cord include?
gray and white matter
What type of spinal nerve rootlets/roots are there?
left and right, dorsal and ventral
Spinal meninges are separated into 3 parts
pia mater, arachnoid mater, and dura mater
What other contents are found in the vertebral canal?
epidural fat, cerebrospinal fluid, and blood vessels
Superior end of spinal cord
ends at foramen magnum, continous with brainstem
Inferior end of spinal cord
conus medullaris, L1-2 in adults, L3-4 in newborn, 18in long
Shape of spinal cord
irregularly cylindrical
Cervical enlargement
supplies upper limbs, spinal cord segments C5-T1
Lumbosacral enlargement
supplies lower limbs, spinal cord segments L1-S3
Longitudinal grooves
help to delineate left, right, and column sections
Ventral (anterior) median fissure
wide groove on the anterior midline
Dorsal (posterior) median sulcus
narrow groove on the posterior midline
Ventral lateral sulci and dorsal lateral sulci
lateral grooves at site of respective rootlet attachments (dorsal more prominent)
White matter is primarily formed by _____with minimal cell bodies. The _____are bundled to form _____.
axons, axons, tracts
Tracts are organized within 3 columns
dorsal, lateral, and ventral columns that are delineated by the external longitudinal grooves
Ascending tracts relay information where?
the brain
Descending tracts relay information where?
inferiorly, the periphery
Dorsal columns are formed by which fibers and transmit what?
formed by primary ascending fibers and transmit ipsilateral fine touch and proprioception
fasciculus gracilis
subset of dorsal column, carries lower body information
fasciculus cuneatus
subset of dorsal column, carries upper body info (only found in upper spinal cord, more lateral)
Where does the dorsal column synapse?
synapse with secondary fibers within nuclei of medulla, which then cross the midline (decussate) and ascend as the medial lemniscus to the third order neurons in the thalamus and eventually terminate in the contralateral brain
Where is the spinothalamic tract found and what forms it?
found in both the lateral and ventral columns of white matter, formed by secondary ascending fibers
Peripheral primary sensory fibers synapse on the secondary cells where?
the dorsal gray horn, ipsilaterally
Where does secondary fibers cross?
the midline, then ascend within the tract
What does the lateral tract of the spinothalamic tract transmit?
contralateral pain and temperature !!!
What does the anterior tract of the spinothalamic tract transmit?
crude touch and pressure
Where is the lateral corticospinal (pyramidal) tract found and what forms it?
found in the lateral column of white matter and formed by descending upper motor neurons which originate in the motor cortices of the crebrum (brain)
Where do upper motor neurons cross?
they cross the midline in the medulla at the pyramids, thus run contralaterally in the spinal cord
Where does the lateral corticospinal tract synapse with the lower motor neurons?
in the ventral gray horn for eventual distribution to skeletal muscle for voluntary motor control
Gray matter is formed by what?
neural cell bodies, axon terminal branches and dendrites
Ventral horns
cut surface of ventral columns of gray matter, found at all levels of spinal cord, contains somatic motor neuron cell bodies, aka LMN, that innervate skeletal muscle
Dorsal horns
cut surface of dorsal columns of gray matter, found at all levels of spinal cord, contains central processes of sensory neuron axons and interneurons which integrate various sensory and motor neurons
Lateral horns
found only at spinal cord segments T1 to L2, contains preganglionic sympathetic neuron cell bodies (general visceral efferent)
Gray commissure
found at all levels of spinal cord, deepest/central region of spinal cord, contains central canal, connects to the left and right gray columns
Central canal location
continuous with the 4th ventricle of the brain, found thru entire length of spinal cord
Central canal is the most central feature found within what?
the gray commissure
What does the central canal contain?
cerebrospinal fluid
What could be occluded in the aged or diseased spinal cord?
the central canal
Ventral nerve roots
a series of ventral (motor) roots respective to each spinal cord segment, individually are a collection of motor axons going to the periphery
A single ventral root is formed by a series of rootlets from where?
a single spinal cord segment level that is symmetrical bilaterally
Where is a ventral rootlet formed?
along the ventral lateral sulcus
What type of fibers does ventral nerve roots contain?
motor fibers only
Dorsal nerve roots
a series of dorsal (sensory) roots respective to each spinal cord segment, individually are a collection of sensory axons going to the spinal cord
A single dorsal nerve root is a collection of central axonal processes from pseudounipolar neuron cell bodies located where?
the dorsal root ganglion
Where is the spinal ganglion found?
near the intervertebral foramina
A single dorsal root splits into a series of dorsal rootlets which enter the spinal cord where?
the dorsal lateral sulcus, symmetrical bilat
What type of fibers do dorsal nerve roots contain?
sensory fibers only
Typical spinal nerve layout
spinal cord - rootlet - root - spinal nerve - rami
A single spinal nerve
formed near the intervertebral foramen, formed by the joining of the dorsal and ventral nerve roots, and contain both motor and sensory fibers
How many pairs of spinal nerves are there?
31 pairs
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
The spinal cords ends at the L1/L2 vertebral level, thus the dorsal and ventral roots of levels L2 to Co continue within the vertebral canal to their respective exit points. What is the collection of rootlets/roots called?
cauda equina
Dorsal rami
innervate skin, muscles, and joints of the vertebral column and nearby structures
Ventral rami
innervate all the structures anterior to the vertebral column and including the limb structures/embryological derivatives (these are much larger than dorsal rami)
Spinal cord segmentation
a spinal cord segment is defined by the spinal nerve it produces, 31 spinal cord segments
Dermatome
the area of skin innervated by a single spinal cord segment
Dermatome T4, T10, C6, C8, S5 (high yield spots)
nipples, umbilicus, pad of thumb, pinky, anus
Why is the dermatome pattern of the limbs much more complex?
- the ventral rami of the cervical and lumbosacral regions form plexuses, which feed to the upper and lower limbs
- this allows nerve fibers from various spinal cord segments to form the peripheral nerves
- this the dermatome pattern of the limb does not match the peripheral nerve distrubution
What is the general rule for segmental muscle innervations? (particularly the limbs)
most muscles are innervated via two or more spinal nerves and that one spinal nerve helps to supple many muscles
The most exterior and densest meninge, forms a sac that closes inferiorly at S2, open superiorly and continuous with the cranial dura mater at the foramen magnum enclosing the entire CNS, continues laterally around the dorsal and ventral roots of the spinal nerves, bony anchors, and continues beyond the sac at S2 as the external filum teminale
spinal dura mater
What are bony anchors?
attaches to the bony ramework of the foramen magum and the intervertebral foramen
What does the external filum terminale do?
anchors the sac to the coccyx
The intermediate layer that is more delicate than dura mater, lines the entire dural sac down to its termination at S2 and extends into the sleeves surrounding the dorsal and ventral roots, forms fine strands of tissue (trabeculae) between the layers resulting in a web-like appearance
spinal arachnoid mater
The most internal and most delicate layer; envelops the spinal cord, associated blood vessles, rootlets, and dorsal/ventral roots; forms the denticulate ligament reinforced with dense connective tissue, ends inferiorly at the conus medullaris
spinal pia mater
Denticulate ligament
expanse of tissue found between the dorsal and ventral rootlets bilat with tooth-like projections that pierce the arachnoid into the dura at about 21 locations on each side (this attachment helps to stabilze the cord within the center of the dural sac)
Prolongation of the spinal pia mater
internal filum terminale- extends from the tip of the conus medullaris
Epidural (extradural) space
located external to the dural sac, contents include a cushioning layer of adipose tissue and extensive pelxus of veins
Subdural space
located between the spinal dura mater and arachnoid mater (potential space)
Subarachnoid space
located between the arachnoid and pia mater layers filled with CSF
Lumbar cistern
expanded area of the subarachnoid space below the conus medullaris (site of LP)
Vertebral artery (blood supply to spinal cord)
3 main arteries
- single anterior spinal artery
- paired posterior spinal artery
Single anterior spinal artery
located in the anterior median fissue which supplies twice as much as the smaller posterior spinal arteries
Paired posterior spinal arteries
pass longitudinally near posterolateral sulci
Secondary supplies (arterial supply to spinal cord)
Segmental spinal arteries that branch from various vessels and enter through each intervertebral foramen
Segmental spinal arteries give rise to what?
anterior and posterior radicular arteries that course along the anterior and posterior spinal roots/rootlets AND anterior and posterior segmental medullary arteries wihch periodically reinforce the main spinal arteries
Venous drainage
dorsal and ventral spinal veins directly drain the spinal cord and generally distribute similar to spinal arteries, they drain into the internal vertebral pelxus which lies in the epidural space
Internal vertebral pelxus
a valveless system of venous channels in the epidural space that connects the dural sinuses in the cranium, the external vertebral plexus surround the vertebral column and with major veins in the thorax, abdomen, and pelvis
Each spinal nerve provides 2-4 small ______.
recurrent meningeal branches
Recurrent meningeal branches return to the vertebral canal via the intervertebral foramina to supply what?
- sensory fibers for the peristeum of the vertebra, the pos. longitudinal ligament, the outer portion of the annulus fibrosis, and the meninges
- autonomic fibers to the vessels to aid in regulation of blood flow, sensory and sympathetic fibers to meninges, ligaments, and IV discs
Spinal reflex
a fast, automatic, hard-wired muscular reaction to a stimulus
Reflex arc
the neural pathway from the stimulus to the effector
What are the five components in a typical spinal reflex?
receptors, sensory neurons, synapsing (integration, communication, and processing), motor neurons (alpha), and effectors (muscles and glands)
What ranges from a simple dendrite to a complex sense organ, specialized to sense or receive a specific range or status in the environment?
receptors
Exteroreceptive receptors are aroused by changes in what?
the external environment
What receptor is excited by changes in skeletal position, thus important for movement control?
proprioceptive
Proprioception provides knowledge of what two things?
body position and body movement (this is the most dominate proprioceptive receptor in the muscle spindle)
1a neuron from muscle spindle to spinal cord characteristics and yields
- sensitive to length change and velocity of length change of the muscle
- proprioception, T-reflex, recipricol inhibition
II neuron from muscle spindle to spinal cord characteristics and yields
- sensitive to length change only
- proprioception
1b neuron from Golgi tendon organ to spinal cord characteristics and yields
- stimulated by stress/strain on the GTO at muscle/tendon junction
- proprioception, autogenic inhibition
Alpha M.N. fro spinal cord to muscle characteristics and yields
- is a lower motor neuron, affected by sensory fibers, interneurons, and upper motor neurons
- contraction of the muscle
Gamma M.N. from spinal cord to muscle spindle characteristics and yeilds
- is a lower motor neuron, affected by interneurons and upper motor neurons
- resets the spindle regulates muscle tone
GTO (Golgi Tendon Organs)
A proprioceptor that is sensitive to strain/stress on a muscle that is embedded within the muscle/tendon junction in series with muscle fibers. It provides a phasic signal via Ib sensory fibers and leads to inhibition of the stimulation of the same muscle it is found in
Afferent (sensory) neuron
A pseudounipolar neuron (t-shaped) whose cell body is located in the dorsal root ganglia. The axon is divided into the peripheral process that is outside the cell body and a central process that is central to the cell body. The receptor stimulates the peripheral process
