Nervous System Flashcards
Collection of nerve cell bodies and nerve axons (fibers) in the CNS and PNS
CNS
cell bodies - nucleus
fibers - tract
PNS
cell bodies - ganglion
fibers - peripheral nerve
Cranial nerves
12 pairs of nerves CN I-XII
Most arise from the brain
ALL exit the cranial cavity via foramina
Organization of spinal nerves
31 pairs total
C8 (BUT only 7 vertebrae) T12 L5 S5 Co
Where do spinal nerves exit?
C1 spinal nerve exits between skull and C1 so there are 8 cervical nerves but only 7 cervical vertebrae.
All other nerves exit through intervertebral foramina.
Parts of a spinal nerve
Nerve arises from spinal cord via rootlets.
Rootlets converge to form ventral / dorsal root.
Roots converge to form spinal nerve.
Nerve divides into ventral / dorsal rami.
Somatic NS
Motor to skeletal muscle
Sensory from skin (pain, temperature, touch)
Sensory from joints, muscles, and tendons (proprioception)
Autonomic NS (aka Visceral motor)
Motor to smooth muscle (organs), cardiac muscle, and glands
Visceral Sensory
Sensory from organs (ischemia, stretch)
Somatic motor pathway
Location of motor cell body: ventral horn
Motor fiber EXITS spinal cord via ventral root, spinal nerve, and ventral or dorsal ramus
Somatic sensory pathway
Location of sensory cell body: dorsal root ganglia
Sensory fiber travels via ventral or dorsal rami, spinal nerve, and ENTERS spinal cord through dorsal root
Ventral rami and dorsal rami innervate what regions?
Ventral rami innervate majority of body wall
Dorsal rami innervate small region of skin/muscle along dorsal midline
Carry what kind of fibers?
Ventral root - motor fibers only
Dorsal root - sensory fibers only
Ventral ramus, dorsal ramus, and spinal nerve - both
Brachial plexus
Network of ventral rami to upper extremity
Lumbosacral plexus
Network of ventral rami to lower extremity and perineum
Sympathetic NS
“Fight or flight”
Innervates tissues in the body wall (sweat glands, arrector pilli muscles, peripheral blood vessels) and body cavities
Parasympathetic NS
“Rest and digest”
Innervates tissues in the body cavities, head, and external genitalia
How many neurons in autonomic NS?
2 neurons
preganglionic cell body and fiber
postganglionic cell body and fiber
Location of preganglion cell bodies in sympathetic and parasympathetic
Sympathetic - lateral horn of thoracolumbar segments of spinal cord
Parasympathetic - craniosacral (brain and sacral segments of spinal cord)
Location of postganglion cell bodies in sympathetic and parasympathetic
Sympathetic - prevertebral ganglia and paravertebral ganglia
Parasympathetic - ganglia in the head or walls of organs
How many paravertebral ganglia are associated with each spinal nerve?
Usually one per nerve. But there are only 3 paravertebral ganglia associated with the 8 cervical spinal nerves.
Sympathetic trunk
Paravertebral ganglia on each side are linked to form the sympathetic trunk that extends length of vertebral column.
Although all preganglionic sympathetic cell bodies originate in a confined area (thoracolumbar spinal cord), the sympathetic trunk allows for the distribution of sympathetic fibers throughout the body.
How does the sympathetic trunk attach?
Sympathetic trunks are tethered to the ventral rami via the white and gray rami communicans. White is entrance and gray is exit.
Sympathetic pathway - body wall
- Lateral horn
- Ventral root
- Spinal nerve
- Ventral ramus
- White ramus communicans
- Sympathetic trunk
- Paravertebral ganglia (synapse)
- Gray ramus communicans
- Ventral or dorsal ramus
- Body wall - blood vessels, sweat glands, arrector pilli muscles
Sympathetic pathway - thoracic organs
- Lateral horn
- Ventral root
- Spinal nerve
- Ventral ramus
- White ramus communicans
- Sympathetic trunk
- Paravertebral ganglia (synapse)
- Cardiac / pulmonary nerves
- Heart or lungs
Sympathetic pathway - abdominal organs
- Lateral horn
- Ventral root
- Spinal nerve
- Ventral ramus
- White ramus communicans
- Sympathetic trunk
- Splanchnic nerve
- Prevertebral ganglia (synapse)
- Abdominal and pelvic viscera
Visceral Sensory
Sensory from organs, e.g. ischemia, stretch
Single neuron
Enters dorsal root
Travels to spinal cord along sympathetic OR parasympathetic fibers
Referred pain
Phenomenon of visceral (organ) pain being perceived as somatic (body wall) pain
Mechanism is unclear. Visceral and somatic sensory neurons enter the spinal cord via the same dorsal roots and have cell bodies located in the same dorsal root ganglia.
The CNS appears to misinterpret an incoming visceral signal as somatic sensory.
