Spinal Cord, Spinal Nerves, and ANS LO
What is a dermatome? What is a myotome clinically?
A dermatome is a strip of skin supplied by sensory branches of dorsal and ventral rami from one spinal cord level A myotome is a group of muscles innervated by a single spinal nerve-can be tested clinically to help you localize a legion to a root or peripheral nerve
What is a splanchnic nerve? What fiber types can a splanchnic nerve contain?
A splanchnic nerve goes to an internal organ. Splanchnic nerves can contain sympathetic or parasympathetic fibers
What is the denticulate ligament?
A tooth-like lateral extension of pia mater off the spinal cord tacking to the dural sac. It stabilizes the cord side-to-side within the dural sac.
What do visceral motor (autonomic) neurons innervate?
Smooth muscle, cardiac muscle, and glands
What do visceral sensory neurons innervate? Where are their cell bodies of origin located? How many neurons link the CNS to the target?
Smooth muscle, cardiac muscle, and glands Cell bodies of origin located in dorsal root ganglion One neuron link between viscera and CNS
What do somatic motor neurons innervate? Where are their cell bodies of origin located? How many neurons link the CNS to the target?
Somatic motor neurons innervate the skeletal muscle of trunk or limbs Cell bodies of origin are in a nucleus (collection of cell bodies inside the CNS) in the ventral horn of the spinal cord One neuron system from the target to CNS
At which vertebral level does the spinal cord terminate?
L1-L2
Describe the names and locations of the sulci and fissure of the external surface of the spinal cord. What do these grooves separate?
ANTERIOR MEDIAN FISSURE deep, middle of the anterior side; separates right from left POSTERIOR MEDIAN SULCUS Less deep, middle of the posterior side, separates right from left LATERAL SULCI On either side of the median fissure/sulcus about 30 degrees away; separates posterior and lateral funiculi in white matter POSTERIOR INTERMEDIATE SULCI On either side of the posterior median sulcus about 15 degrees away; separates fasciculus gracilis and cuneatus of posterior funiculi of white matter
What are Rexed's laminae?
Alternative classification scheme for the gray matter organization with layers of neurons which have different fxns
How are 8 cervical spinal nerves related to 7 cervical vertebrae?
C1-7 spinal nerves named for vertebra inferior to their exit C8 exits between C7 and T1
Which cranial nerve is responsible for the majority of the parasympathetic supply to the viscera of the thorax and abdomen?
CN X (Vagus)
What fills the subarachnoid space?
CSF (cerebrospinal fluid)
How does gray and white matter of the spinal cord differ cranial to caudal?
Cervical: most white matter because more axons are needed near the brain Thoracic: small amount of gray matter Lumbar: most gray matter because more neurons are needed in the regions that innervate arms, legs, hands, etc.
Define the following: Conus medullaris Filum terminale Cauda equina
Conus medullaris=the tapered end of the spinal cord Filum terminale= pia mater that comes together at the bottom of the conus medullaris, goes all the way down to the coccyx and anchors the spinal cord Cauda equina= more caudal nerves, longer and more vertical, suspended in subarachnoid space filled with CSF (lumbar cistern)
List the 3 meninges that wrap the spinal cord, from superficial to deep
Dura mater-arachnoid mater-pia mater
What does the dorsal/ventral ramus innervate?
Each dorsal ramus takes motor and sensory (and sympathetic) to supply the skin, muscles, and vasculature of the back Ventral rami may either remain segmental, or unite with other ventral rami to form a plexus. They take sensory and motor fibers to muscles, joints, and skin of lateral and ventral body walls and extremities
List the names of key nuclei of each horn of the spinal cord, along with their general fxn
GRAY MATTER Dorsal Horn a) Substantia gelatinosa (pain sensation) b) Nucleus proprius (pain/temperature) c) Dorsal nucleus of Clarke (proprioceptive info) Lateral Horn a) Intermediolateral nucleus (sympathetics T1-L2, parasympathetics S2-4): Motor neurons to smooth muscle, cardiac muscle, glands Ventral Horn a) Medial nuclei (muscles of trunk; flexors are posterior to extensors) Lateral nuclei (muscles of limbs, flexors are posterior to extensors)
Preganglionic cell bodies for the sympathetic division of the ANS are localized where?
In the intermediolateral grey horn (cell column) of the spinal cord from segments T1-L2 only Referred to as being "thoracolumbar" in distribution
Which ganglion type is involved in the parasympathetic innervation of the thorax and abdomen? How far distal does its innervation extend into the abdomen? What takes over once the vagal innervation terminates?
Intramural ganglia is involved in the parasympathetic innervation of the thorax and abdomen.
Which 2 of the 3 types of autonomic ganglia are associated with the sympathetic synapse in the ANS? Which is strictly involved in the parasympathetic system? Where is each of the 3 types of autonomic ganglia found?
Paravertebral ganglia: sympathetic division; lie next to vertebrae (one set on either side) from the base of the skull to bottom of coccyx; innervate targets in body wall, limbs, thoracic viscera Prevertebral ganglia: sympathetic division; anterior to vertebral column, close to major abdominal arteries; innervate targets in abdomen and pelvis Intramural ganglia (terminal ganglia): parasympathetic division; located close to, or within the wall of the effector organ; innervate targets in thorax, abdomen, and pelvis
Generalize the differences between the two divisions of the ANS: origin, fiber lengths, and ganglia used for synapse
SYMPATHETIC Origin: Intermediolateral gray horn from T1-L2 Fiber Lengths: Short preganglionic and long postganglionic Ganglia: prevertebral and paravertebral ganglia PARASYMPATHETIC Origin: nuclei of the brain stem and S2-4 Fiber Lengths: Long preganglionic and short postganglionic Ganglia: Intramural ganglia (external surface of organs)
What do somatic sensory neurons innervate? Where are their cell bodies of origin located? How many neurons link the CNS to the target?
Somatic sensory neurons give input to the CNS from skin or skeletal muscle The cell bodies of origin are in a dorsal root or spinal ganglion One neuron system from the target to the CNS **No synapses in sensory ganglia**
What vertebral levels exhibit "typical" (segmental) spinal nerves?
T2-T12, because this is where there are no plexuses and both dorsal and ventral rami exhibit "typical" anatomy
What are the two divisions of the autonomic nervous system and what are their general fxns?
The ANS (visceral motor) has two divisions: sympathetic=fight/flight parasympathetic=rest/digest
Is the autonomic nervous system (ANS) a sensory or motor system, or both? How many neurons link the CNS to the target?
The ANS is a motor system and is composed of sympathetic and parasympathetic nervous systems Each division of the ANS is a two neuron motor system, consisting of a: preganglionic neuron and postganglionic neuron **Autonomic ganglia DO have synapses**
Where is the epi(extra) dural space and what is found within it?
The area between the dura mater and the vertebral wall which contains fat and small blood vessels
List the enlargements of the spinal cord. Why do these enlargements exist? What is the specific function of each enlargement?
The cervical and lumbar enlargements exist because the upper and lower limbs develop from these areas- we need more neurons because they have to innervate areas further away from the trunk Cervical enlargement: C3-T1, corresponds to brachial plexus which innervates the upper limb Lumbar enlargement: L1-S2, corresponds to lumbosacral plexus which innervates the lower limb
List the autonomic ganglia of the head associated with the parasympathetic division of the ANS. With which cranial nerve is each associated?
The cranial ganglia connect the preganglionic parasympathetic axons traveling from the nuclei of the brainstem along the cranial nerve (CN III, VII, IX, X) to postganglionic parasympathetic cell bodies.
How do ventral/dorsal roots differ from ventral/dorsal rami?
The dorsal and ventral roots from the spinal cord fuse to form the true spinal nerve that exits the intervertebral foramen. Once the spinal nerve passes through this bony opening, it immediately branches into two main portions: the dorsal and ventral rami. Dorsal rami innervate the back while ventral rami innervate the anterolateral aspects of the body wall.
What types of fibers (modality) are found in the dorsal/ventral roots?
The dorsal root contains sensory fibers, while the ventral root contains motor fibers
What is the difference between the somatic and visceral nervous systems?
The somatic nervous system gives input to CNS from skin or skeletal muscle, two components: motor and sensory The visceral nervous system links the CNS to a gland, internal organ, or blood vessel and has two components: motor and sensory Visceral sensory neurons relay information from the body viscera Visceral motor neurons=Autonomic Nervous System
How do white and gray rami communicans differ? What is the fxn of each ramus communicans? Which is more numerous and why?
The white rami communicans is a linker between the true spinal nerve and the sympathetic trunk(myelinated). The gray rami communicans is the exit ramp from the sympathetic trunk back onto the true spinal nerve (non-myelinated) The gray rami are more numerous because they are found at every vertebral level that exhibits a sympathetic ganglion White rami input sympathetic innervation and are restricted to T1-L2 where the sympathetic preganglionic cell bodies are located-the preganglionic fiber ascends or descends within the sympathetic trunk to synapse in a sympathetic ganglion at a level other than that at which it entered the trunk
Where are the neuron cell bodies of origin for each division of the ANS located in the CNS? Based on this location, what are the anatomical-based names for each division?
There are three types of autonomic ganglia: 1) paravertebral ganglia (sympathetic trunk ganglia) used only for synapses of the sympathetic division of the ANS-innervate targets in body wall, limbs, thoracic viscera 2) prevertebral ganglia (anterior to the vertebral column, close to major abdominal arteries. Used only for synapses of the sympathetic division of the ANS- innervate targets in abdomen and pelvis 3) intramural ganglia (terminal ganglia) located close to, or within the wall of the effector organ. These are sites of parasympathetic synapse, innervate targets in thorax, abdomen, and pelvis 4) cranial...will learn about later
For complete cutaneous sensory loss, how many spinal nerves would have to be lesioned? Why?
Three spinal nerves would have to be lesioned because there is actually considerable overlap between any two adjacent dermatomes
What is the fxn of the sympathetic trunk?
To distribute postganglionic sympathetic innervation throughout the body since preganglionic sympathetic cell bodies are only found in the spinal cord segments T1-L2
Identify the white matter funiculi, along with their associated tracts. Know the general fxn of the tracts.
WHITE MATTER Posterior/dorsal funiculi (sensory info about position, vibration, and touch) a) Fasciculus gracilis (legs) b) Fasciculus cuneatus (arms) Lateral funiculi (sensory and motor) a) Spino-cerebellar (balance info to cerebellum) b) Spino-thalamic (pain and temp info to thalamus) c) Lateral cortico-spinal (motor output from brain to skeletal muscles) Anterior/ventral funiculi a) Anterior cortico-spinal tract (motor output from brain to skeletal muscles)
Where is the first point where a nerve becomes "mixed" (ie contains motor and sensory innervation)?
true spinal nerve