Spinal Cord, Spinal Nerves, and Reflexes I & II Flashcards
What are the anterior, posterior, and lateral boundaries of the vertebral canal?
anterior: vertebral bodies, intervertebral discs, and posterior longitudinal ligament
posterior: vertebral laminae and the ligament flavum
lateral: vertebral pedicles and the intervertebral foramina
What are the six contents of the vertebral canal?
- spinal cord
- spinal nerve rootlets/roots
- spinal meninges - pia, arachnoid, and dura
- epidural fat
- CSF
- blood vessels
What opening is at the superior end of the spinal cord?
foramen magnum
What structure is at the inferior end of the spinal cord and at what vertebrae?
conus medullaris at L1/L2 (adults); L3/L4 (newborns)
The spinal cord is __ inches long
18
The spinal cord has a cervical enlargement that supplies upper limbs. The enlargement occurs at what segment?
C5-T1
The spinal cord as a lumbosacral enlargement that supplies the lower limbs. This enlargement occurs at what segment?
L1-S3
The ventral lateral selves and dorsal lateral sulcus are lateral grooves at the site of respective rootlet attachments. Which one is more prominent?
dorsal
The following structures are in the correct order, true or false?
spinal cord - rootlet - root - spinal nerve - rami
true
True or false?
The white matter is deeper, while the gray matter is found more superficial.
false; white matter is superficial, gray matter is deeper, forming an H-like shape
The central canal is the most central within the middle of the gray matter and contains what?
CSF
White matter is primarily found where?
neural fiber processes (axons), with minimal cell bodies
Axons bundle to form ___, which relay information to the brain (ascending) or inferiorly/peripherally (descending)
tracts
____ columns are formed by primary ascending fibers (central processes of sensory fibers)
dorsal
primary sensory neurons start at the receptor and synapse with secondary sensory neurons either in the ___ ___ or ___, leading to tertiary sensory neurons which end in the cerebral cortex
spinal cord, medulla
dorsal columns transmit what?
ipsilateral fine touch and proprioception
This is a subset of dorsal column, which carries lower body information
fasciculus gracilis
What is fasciculus cuneatus?
subset of dorsal column, carries upper body info (only found in spinal cord)
What is the name of the pathway that sensory neurons carrying fine touch and proprioception take as they ascend to the thalamus and eventually terminate in the contralateral brain?
medial lemniscal
True or false?
The spinothalamic tract is found in both the lateral and ventral columns of white matter
true
The spinothalamic tract is formed by ___ ascending fibers
secondary
The lateral spinothalamic tract transmits what?
contralateral pain and temperature
The anterior spinothalamic tract transmits what?
crude touch and pressure
The spinothalamic tract passes through the medulla without crossing, then secondary fibers terminate in the ___ before continuing to the ___
thalamus; cortex
The lateral corticospinaltract is found where?
in the lateral column of white matter
The lateral corticospinal tract is formed by descending ___ ___ ___, which originate in motor cortices of the cerebrum
upper motor neurons (UMN)
In regards to the lateral corticospinal tract, UMN fibers cross the midline (decussate) in the medulla at the ____, thus run contralaterally in the spinal cord
pyramids
note: the left side of the brain controls the right side of the body. this is why
The lateral corticospinal tract synapses with lower motor neurons in the ventral gray horn for eventual distribution to skeletal muscle for voluntary ___ ____
motor control
Lesions in what tract lead to paralysis below the level of the damage?
lateral corticospinal tract
____ matter is primarily formed by neural cell bodies, axon terminal branches and dendrites. It is shaped like an “H”.
gray
Ventral horns are found at all levels of the spinal cord. True or false?
true
Ventral horns contain somatic motor neuron cell bodies which innervate what?
skeletal muscle
Dorsal horns are found only in the thoracic and cerebral segments of the spinal cord. True or false?
false; all levels
Dorsal horns contain what?
central process of sensory neuron axons and interneurons
What do interneurons do?
integrate various sensory and motor neurons
Lateral horns are found only at spinal cord segments ___ to ___
T1 - L2
Lateral horns contain what?
parasympathetic neuron cell bodies
This part of gray matter is found at all levels of the spinal cord, is the deepest/central region of spinal cord, contains central canal, and connects the left and right gray columns
gray commissure
The central canal is continuous with the ___ ventricle of the brain, found through entire length of the spinal cord
4th
A ventral rootlet is formed along the ___ ____ sulcus and is a collection of axons from motor neurons in the lateral and ventral gray horns
ventral lateral
Ventral nerve roots contain ___ fibers only
motor
A single dorsal nerve root is a collection of central axonal processes from pseudo unipolar neuron cell bodies located in the what?
dorsal root ganglion
The spinal ganglion is found near the ___ foramina. It is important to note that all spinal nerve sensory neuron cell bodies are found within this ganglia.
intervertebral
A single dorsal root splits into a series of dorsal rootlets which enter the spinal cord at the ____ ____ sulcus
dorsal lateral
Dorsal nerve roots contain only ___ fibers
sensory
A spinal nerve is formed near the ____ foramen
intervertebral
A spinal nerve is formed by the joining of a dorsal and ventral nerve root and contains both sensory and motor fibers. True or false?
true
C1-C7 spinal nerves exit ___ C1-C7 vertebrae, while C8 spinal nerve exits ___ the C7 vertebra
above; below
Thoracic and lumbar regions - spinal nerves exit the vertebral canal ___ to the pedicles of the vertebra with the same number
inferior
example: T6 spinal nerve exits below the right pedicle of the 6th thoracic vertebra
Spinal nerves are successively ____ the further inferior, thus having an oblique to vertical trajectory to exit
longer
The sacral spinal nerves (S1-S4) are found within the ___ ___ and do not exit as a spinal nerve
sacral canal
note: each must branch into their dorsal and ventral rami to exit through dorsal and ventral sacral foramina
S5 and coccygeal spinal nerves exit through what?
sacral hiatus
The spinal cord ends at the ____ vertebral level
L1/L2
The ventral roots of levels L2 to C0 continue within the vertebral canal to their respective exit points. This collection of rootlets/roots is called what?
cauda equina
Dorsal rami innervate what?
skin, muscles, and joints of the vertebral column and nearby structures
Ventral rami innervate what?
all the structures anterior to the vertebral column and including the limb structures.
True or false? Dorsal rami are much longer than ventral rami
false; ventral rami are longer than dorsal rami
note: think about it, ventral rami cover everything anterior of the vertebral column and go to limbs - have more distance to cover, therefore have to be longer
A spinal cord segment is defined by what?
the spinal nerve it produces
31 spinal nerves result in ___ spinal cord segments
31
The segments of the spinal cord do not directly correspond with the same named vertebra, especially in the lower spinal cord. For each of the following spinal segments, give the vertebra that it is aligned with
C3
T5
L5
C3: C2
T5: T3
L5: L1
Sensory cell bodies for each dermatome are located where?
in the dorsal root ganglia of the paired spinal nerves
Match the following spinal cord segment with its dermatome (area of innervation): T4 T10 C6 C8 S5
T4: nipples T10: umbilicus C6: pad of thumb C8: pinky S5: 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 - the dermatome pattern of the limb does not match the peripheral nerve distribution
True or false?
The limbs rotate during development
true
___ ____ is the most exterior and densest meninge
dura mater
The spinal dura mater forms a sac which closes inferiorly at which sacral vertebral level?
S2
True or false? The dura mater is continuous with the cranial dura mater at the foramen magnum, enclosing the entire CNS
true
The dura mater continues beyond the sac at S2 as the ___ ___ ____
external film terminale
___ mater is the intermediate layer, more delicate than dura mater and lines the entire dural sac down to its termination at S2
arachnoid
The arachnid mater forms fine strands of tissue called ____ between two layers resulting in a web-like appearence
trabeculae
___ mater is the most internal and most delicate layer of the meninges
pia
Pia mater envelops the spinal cord, its associated blood vessels, the roolets, and dorsal/ventral roots, finally merging with the ___ of the spinal nerves
epineurium
The pia mater forms the ___ ligament, reinforced with denser connective tissue. This is an expanse of tissue found between the dorsal and ventral rootlets, bilaterally. These tooth-like projections pierce the arachnoid into the dura at about 21 locations on each side. This attachment helps to stabilize the cord within the center of the dural sac
denticulate
The pia mater ends inferiorly at the conus medullaris except for its prolongation, the _____ ____ ______, which extends from the tip of the conus medullaris
internal filum terminale
What space is located external to the dural sac? Its contents include a cushioning layer of adipose tissue and an extensive plexus of veins
epidural space
What space is located between the spinal dura mater an the arachnoid mater? This is a potential space.
subdural space
Which space is located between the arachnoid and pia mater, and is filled with CSF. Below the conus medullaris, there is an expanded area of this space called the lumbar cistern which contains CSF surrounding the cauda equina - making it an excellent location for a lumbar puncture/ spinal tap
subarachnoid
The 3 main arteries that supply the spinal cord are branches of the ___ arteries within the cranium
vertebral
single ___ spinal artery located in the anterior median fissure, supplies twice as much as the smaller posterior spinal arteries
anterior
segmental spinal arteries branch from various vessels and enter through each intervertebral foramen to 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
note: radicular means roots
The great anterior segmental medullary artery typically arises from one of the lower intercostal arteries on which side?
left
Dorsal and ventral spinal veins vary in number, are found on the surface of the spinal cord - enveloped in spinal pia mater, and drain into the internal vertebral plexus which lies in the ___ space
epidural
The valveless system of the internal vertebral plexus and its high interconnection allows for the spread of infection and neoplastic cells. True or false?
true
Each spinal nerve provides 2-4 small ___ meningeal branches which return to the vertebral canal via the intervertebral foramina to supply sensory fibers and autonomic fibers
recurrent
Clinical: intervertebral disc rupture and meningitis may irritate these recurrent branches leading to what?
increased reflective tone and referred pain
Define spinal reflex
a fast, automatic, hard-wired muscular reaction to a stimulus
Define reflex arc
the neural pathway from the stimulus to the effector (receptors - sensory neurons - synapsing - motor neurons - effectors)
Exteroceptive receptors are aroused by changes in what?
the external environment
ex: the skin for touch, vibration, pain, or temp; eyes for vision; vestibular apparatus for acceleration
Proprioceptive receptors are excited by changes in skeletal position, thus important for ___ ___.
movement control
The most dominate proprioceptive receptor is the ___ ____
muscle spindle
Muscle spindles are sensitive to what?
muscle length and the velocity of changes in muscle lenght
Muscle spindles provide a tonic signal via which fibers?
Ia and II sensory fibers
Muscle spindles contain their own intrafusal muscle fibers within the capsule which are stimulated by which type of motor neurons?
gamma - yield 2 functions: sensor reset and muscle tone
The following characteristics describe what?
- a proprioceptor that is sensitive to strain/stress on a muscle
- embedded within the muscle/tendon junction, in series with muscle fibers
- provides a phasic signal via Ib sensory fibers
golgi-tendon organ
An afferent (sensory) neuron is a pseudounipolar neuron (t-shaped) whose cell body is located where?
in the dorsal root ganglia
A sensory neuron that synapses directly with a motor neuron is called what? A synapse that incorporates internuerons is considered what?
a monosynaptic reflex; polysynaptic
The interneuron is usually a multipolar neuron whose cell body and dendrites are located in the dorsal gray horn and the very short axon terminates on the efferent neurons. Interneurons will most typically have an ___ influence on its target
inhibitory
Motor neurons are ___ neurons whose cell bodies and dendrites are located in the gray matter and their axons pass out the ventral rootlets to the ventral root to spinal nerves, to rami, and finally to an effector
multipolar
Lower motor neurons that stimulate skeletal muscles are termed what?
alpha motor neurons
An alpha motor neuron and all the muscle fibers it innervates is called a what?
motor unit
True or false?
A motor unit contains only one type of muscle fiber (slow or fast twitch), while the entire muscle may have a unique mixture of fiber types
true
General somatic efferent neurons which stimulate muscle spindle fibers (intrafusal) are what type of motor neurons?
gamma
Visceral motor neuron cell bodies in lateral gray horn are found at which levels of the spinal cord
T1-L2
General visceral efferent neurons originating inside the spinal cord are _____ neurons, these fibers course out the ventral root through the white rams communicants to sympathetic trunk ganglion
preganglionic
What is the effector structure for the following types of neurons:
General somatic efferent neuron (GSE)
General visceral efferent neuron (GVE)
GSE: skeletal muscle or intrafusal fiber
GVE: smooth muscle, cardiac msucle, arrector pili muscle, glands
Describe the following reflexes and give an example of each one
- somatosomatic reflex
- somatovisceral reflex
- viscersomatic reflex
- viscerovisceral reflex
- somatosomatic reflex: somatic sensory sources stimulate motor output to somatic tissue, ex: pin prick to finger -> withdrawal of hand
- somatovisceral reflex: somatic sensory sources stimulate a motor output to visceral tissue, ex: foot smashed by stone -> increased heart rate
- viscersomatic reflex: visceral sensory sources stimulate the motor output to somatic tissues, ex: ischemic heart muscle -> increased tone of paraspinal muscles
- viscerovisceral reflex: visceral sensory sources stimulate the motor output to viscera, ex: noxious material in the gut -> increased gut motility
The ___ reflex is the most fundamental spinal reflex. It is a monosynaptic reflex that is elicited by tapping a tendon
stretch
Quickly stretched muscle spindles stimulate their ___ afferent neurons
Ia
The Ia afferent neurons propagate their action potentials through the dorsal spinal nerve system to directly terminate on the ___ motor neurons within the ventral gray horn of the spinal cord
alpha
These efferent neurons (alpha motor) travel through the ventral spinal nerve system to terminate at the ___ ____
neuromuscular junction
Extrafusual muscle fiber stimulation leads to what?
muscle contraciton
The monosynaptic stretch reflex also has a disynaptic reflex response which is called reciprocal inhibition. Describe what happens
the same Ia afferent stimulates a Ia-interneuron which in turn inhibits the alpha motor neuron of the antagonistic muscle. This activity results in relaxation of the antagonistic muscle - reduced tone
What are the two purposes of the gamma loop?
drive muscle tone; reset muscle spindle to a new, shorter length
Gamma motor neurons are stimulated by higher brain centers and interneurons. They innervate what?
muscle spindles, leading to 2 outcomes:
1. reset muscle spindle
2. drive muscle tone
the loop regulates length and tone
Major loss of inhibitory signal from the brain (spinal cord lesion) may result in ___ (rigidity) or spasticity.
hypertonicity
Hypertonicity causes damage to upper motor neurons or lower motor neurons. Describe the result of this.
UMN damage: spastic paralysis (reflexes still work)
LMN damage: flaccid paralysis (reflexes don’t work)
Describe the route of the gamma loop.
Brain -> UMN -> gamma mn -> MS -> Ia -> multiple alpha mn -> skeletal muscle tone
