1.2 Spinal Cord and Autonomic Nervous System Flashcards
In the adult the spinal cord ends as a tapered portion termed the … at the L1 vertebral level.
- In newborns it ends at L3 vertebral level)
conus medullaris
Due to the discrepancy between the spinal cord and the vertebral column, the more caudal spinal nerves are longer and more vertical forming the…
cauda equina
“horse tail”
What are the 3 layers, meninges, surrounding the spinal cord?
- Dura mater
- Arachnoid mater
- Pia mater
What connection of pia mater, connects the conus medullaris to the coccyx?
filum terminale
tethering to keep the coccyx in place
In the CNS, what forms the gray matter?
neuronal cell bodies
In the CNS, what forms the white matter?
interconnecting nerve fiber tracts
In the CNS, what is a discrete group of neuronal cell bodies called?
Nucleus
In the PNS, what is a discrete group of neuronal cell bodies called?
Ganglion
What are spinal nerves responsible for?
Conveying information to/from the gray mater horns of the spinal cord
- DO NOT supply internal structures (viscera within thoracic or abdominopelvic cavities)
- DO NOT supply structers of the head
What is the Dorsal (posterior) horn of the CNS gray matter responsible for?
Receives Sensory Information
What is the Ventral (anterior) horn of the CNS gray matter responsible for?
Transmits Motor Information
What is the Lateral horn of the CNS gray matter responsible for?
Transmits Motor Information
Where do the 8 cervical paired spinal nerves recieve their name from?
- C1 - C7 named for vertebra inferior to their exit
- C8 exits between C7 and T1 vertebrae
Where do the 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal paired spinal nerves recieve their names from?
Named by vertebra superior to their point of exit
i.e. T2 exits between vertebrae T2 and T3
Fibers emerge from the spinal cord as what?
rootlets
What do rootlets converge to form?
2 Nerve Roots
- Anterior (ventral) - motor fibers from the ventral horn of the spinal cord
- Posterior (dorsal) - sensory fibers from the dorsal horn of the spinal cord
What do the anterior and posterior roots converge to form?
Mixed Spinal Nerve
- Contains both motor and sensory fibers (mixed fibers)
Where does the formation of the mixed spinal nerve occur?
At or near the intervertebral foramen
What does the mixed spinal nerve immediately divide into?
Anterior and Posterior Rami
Each ramus carries both sensory and motor fibers
*rami = branch
What does the posterior (dorsal) rami supply and what fibers does it carry?
- Deep (true) muscles of the back
- Somatic Motor
- Overlying skin
- Somatic sensory
- Vasculature (arteries) structures supplying these structures
- Postganglionic Sympathetic Fibers
What does the anterior (ventral) rami supply?
- Anterior and lateral trunk
- Upper and lower limbs
- Generally partcipating in plexus formation
What fibers does the anterior (ventral) rami carry?
- Somatic motor
- Somatic sensory
- Postganglionic sympathetic fibers
Where are the cell bodies located in the sensory (afferent) subdivision of the PNS?
Outside, but close to the CNS
Where are the cell bodies located in the motor (efferent) subdivision of the PNS?
Gray matter of CNS
How do the sensory (afferent) fibers enter the CNS?
Via the posterior (dorsal) root) of spinal or cranial nerves
Where do the motor (efferent) fibers exit the CNS?
Anterior (ventral) roots of spinal or cranial nerves
What does the somatic subdivision of the PNS do?
Conveys info to/from CNS, and body wall and extremities (skeletal muscle)
What does the visceral subdivision of the PNS do?
Conveys info to/from CNS and, internal organs and blood vessels
How many neurons are between the CNS and the end organ (target) in the Somatic Motor System?
1 neuron
What is the target organ of the somatic motor system?
ALWAYS skeletal muscle
How many neurons are between the CNS and the end organ (target) in the visceral motor system (ANS)?
2 neuron system
Where is the cell body of the preganglionic neuron of the visceral motor system (ANS) located?
grey matter of CNS
What are the target organs of the visceral motor system (ANS)?
- Smooth muscle (non-striated, involuntary)
- Glands
- Modified cardiac muscle
- SA and AV nodes
Where do you find preganglionic sympathetic cell bodies?
- Forms the intermediolateral cell column (IML)
- Composes the lateral horn of the spinal cord from T1 - L2
IML is the only place preganglionic sympathetic cell bodies exist
Where do preganglionic sympathetic fibers exit the CNS?
Anterior (ventral) roots
becoming components of the mixed spinal nerve and entering the anterior ramus
Where do the preganglionic sympathetic fibers exit the spinal nerve?
White Ramus Communican
Communicating branch between spinal nerves T1 - L2 (same as IML) only and the sympathetic trunk
What is the sympathetic trunk composed of?
paravertebral ganglia
What is the course the preganglionic sympathetic fibers take if the target structures are located within the body wall of T1 - L2 OR within the thoracic cavity?
Synapses with a postganglionic cell body within a paravertebral ganglia of the sympathetic trunk at the SAME level it entered the sympathetic trunk.
What is the course the preganglionic sympathetic fibers take if the target structures are located above T1?
the preganglionic sympathetic fibers will ascend within the sympathetic trunk to synapse with a postganglionic cell body located in a paravertebral ganglia in the cervical region.
What is the course the preganglionic sympathetic fibers take if the target structures are located below L2?
Descend within the sympathetic trunk to synapse with a postganglionic cell body located in a paravertebral ganglia in the lower lumbar or sacral region.
What is the course the preganglionic sympathetic fibers take if the target structures are located in the abdomen or pelvic cavities?
- Only involves fibers involved in the sympathetic innervation of the abdominopelvic viscera (below the diaphragm)
They will pass through the sympathetic trunk WITHOUT synapsing.
- Once the preganglionic sympathetic fibers leave the sympathetic trunk they are called thoracic or lumbar splanchnics.
What is the branch of postganglionic fibers that arises from the paravertebral ganglia of the sympathetic trunk, traveling laterally, called that targets: smooth muscle and glands of body wall and limbs aka structures supplied by Spinal Nerves?
Gray ramus communicans
What is the branch of postganglionic fibers that arises from the paravertebral ganglia of the sympathetic trunk called that targets: the head, since no spinal nerves go to the head?
Cephalic arterial rami
surround arteries going to the head forming a periarterial plexus to reach their targets
What is the branch of postganglionic fibers that arises from the paravertebral ganglia of the sympathetic trunk, running medially, called that targets: innervate the viscera of the thoracic cavity?
Cardiopulmonary splanchnics
What is the path of the thoracic splanchnic nerves?
- Preganglionic sympathetic fibers arise from the thoracic region of the sympathetic trunk
- They do NOT synapse with the sympathetic trunk
- Pass into abdominal cavity near the aorta
- Synapse within a prevertebral ganglia on a postganglionic cell body
- postganglionic fibers travel on arteries to their targets
What are the main differences between the thoracic splanchnics and the lumbar splanchnics?
- Arise from lumbar portion of sympathetic trunk (L1 -L2)
- Innervate pelvic viscera
What are the 2 locations of preganglionic parasympathetic cell bodies?
- Cranial - gray matter of brainstem
- Sacral - gray matter of S2 - S4 spinal cord
How do the preganglionic parasympathetic fibers exit?
- Cranial - as CNs III, VII, IX, X
- Sacral - via anterior roots of spinal nerves S2 - S4 as pelvic splanchnic nerves
Where are the postganglionic parasympathetic cell bodies of the sacral division located?
Within the wall (tissue) of the target organ located in an intramural ganglia
Where are the postganglionic parasympathetic cell bodies in the head located?
Any of the 4 pairs of parasympathetic ganglia that are located close to their target.
C.O.P.S.
Describe the postganglionic parasympathetic fibers
They are very short and within the wall of an organ, since the postganglionic cell bodies are already in the target tissue.
What do parasympathetics NOT innervate?
Structures of the body wall or limbs
ONLY INNERVATES:
- specific structures in the head
- thoracic, abdominal, and pelvic viscera
What is the job of the somatic sensory system?
Input to CNS from skin or skm
Where is the cell body located in the somatic sensory system?
Dorsal root (spinal) ganglion
How does the somatic sensory system work?
- 1 neuron system
- The neuron has a distal (peripheral) process to the target, and a central process to the CNS
- NO SYNAPSE occurs in a sensory ganglion
What is the job of the visceral sensory system?
Carry information from viscera to CNS (pain, distension)
How do the distal (peripheral) fibers in the visceral sensory system get to the sympathetic trunk?
Hitching a ride on splanchnic nerves (cardiopulmonary, thoracic, or lumbar)
What is the path of the visceral sensory system once it arrives at the sympathetic trunk?
Exits the trunk via white ramus communican at the appropriate spinal cord level to travel back to their cell body, located in the dorsal (spinal) root ganglion.
