Flashcards in TBL 3 - Somatic and Autonomic Nervous Systems, Spinal Nerves, and Ganglia Deck (45):
CNS vs PNS
Brain and spinal cord vs. spinal nerves, cranial nerves, and autonomic nerves
motor - multiple dendrites with one single axon that could have collateral branches. Efferent axons - signals go away from CNS
sensory - cell body with double process: a peripheral process that brings signals from receptor organs into cell body and a central process that goes from the cell body to the CNS. Afferent axons - signals come to the CNS
Dorsal root ganglion
PNS - where the sensory neurons reside. Aka spinal ganglion. Here the sensory impulse goes from the long peripheral axon to the short central axon which is also the posterior roots of the spinal nerve
Describe what interneurons are and what synapses with them
Mulltipolar, unmyelinated neurons. Synapse with posterior roots that bring in sensory impulse and they either convey information to the motor neurons in anterior horn or to the brain
Which neurons are affected by amyotrophic lateral sclerosis (ALS) and why is the disease ultimately fatal?
Motor neurons are affected. Eventually the respiratory muscles are affected and the person can no longer breathe
What constitutes the somatic nervous system
Cranial and spinal nerves that innervate all parts of the body except the organs, glands, and smooth muscles
What does the autonomic nervous system consist of
Pairs of multipolar neurons that involuntarily regulates the organs, glands, and smooth muscle. Also called visceral nerves. First neuron is in the CNS and the second is in the autonomic ganglion. Sympathetic and parasympathetic
Where do interneurons reside in the spinal cord?
Are the roots and DRG in the vertebral canal or outside of it?
Which spinal nerve roots are compressed by disc herniations between vertebrae L4 and L5 and between vertebrae C4 and C5?
L5 and C5
Describe nomenclature of spinal nerves in the cervical and inferior portions
Cervical - named after vertebrae inferior to the IV foramina of exit
Inferior (T, L, S, Co) - named after the vertebrae forming superior margin of exit
Where do posterior and anterior rami form and where do they go?
Immediately after emerging from the IV foramina, the nerves divide into posterior and anterior rami. Posterior to the posterior body wall, anterior to the anterolateral body wall and extremities
Describe the somatic reflex process
Sensory impulse comes to the DRG and then through the posterior rami and into the posterior horn when it synapses with the interneuron. Interneuron synapses directly to the motor neuron generating a response. A second signal is sent to the brain to feel pain
Where are the presynaptic neurons of the sympathetic nervous system located and describe their course until synapse
Intermediolateral (lateral) horns of the spinal cord between T1 and L2. Exit the spinal cord through the anterior rami where the motor neurons exist and synapse in the sympathetic ganglia
What is the paravertebral ganglia
The linkage of the sympathetic ganglia that forms bilateral sympathetic trunks along the vertebral column. The paravertebral column has 3 segments along the 8 cervical vertebrae and than one for each vertebrae through the sacral spinal segment
What goes through the white communicating rami and what goes through the gray communicating rami and what do they do.
Presynaptic sympathetic fibers go from anterior rami into the white communicating rami to the paravertebral ganglia. The postsynaptic sympathetic fibers go from the paravertebral ganglia into the gray communicating rami back into the anterior rami to their destination. Postsynaptic fibers also go into the posterior rami to their destination.
Do all presynaptic fibers go to their corresponding paravertebral ganglia? If not, where to they go and what happens to the postsynaptic fibers.
They can ascend or descend in the cervical or lumbar/sacral paravertebral ganglia. Gray communicating rami send the postsynaptic fibers back to the anterior and posterior rami
Why are white communicating rami only associated with para-vertebral sympathetic ganglia at T1-L2?
T1-L2 is where the presynaptic neurons from the lateral horns arise
What causes “goose bumps”?
The arrestor pili muscles are contracted by the postganglionic sympathetic nerve fibers
What do spinal nerves consist of?
Somatic motor fibers, somatic sensory fivers, and visceral motor fibers bundled together with connective tissue
What is the epineurium
Outer sleeve of dense connective tissue. Strong cylindrical sheath around the whole nerve and bundles fascicles of mixed axons together
What is the perineurium
Bundles the fascicles together and consists of tight junctions creating the nerve blood barrier regulating the inner environment around the nerves where the capillaries are.
Are the fibers in the fascicles myelinated?
Most are but not all
What is the endoneurium?
Loose connective tissue between fibers
How is myelin formed?
It is a lipoprotein rich sheath formed by Schwann cells. Gaps between the cells create the nodes of Ranvier.
Describe how the myelin is in the PNS?
Schwann cells wrap individual axons like jelly rolls.
What are some axons that are myelinated
Somatic motor, somatic sensory, and presynaptic axons of white communicating rami
How do Schwann cells assist in regenerating damaged nerve fibers?
Basement membrances invest the Schwann cells and the Schwann cells aid in debris removal and guidance for the regenerating axons
What are some axons that are unmyelinated (surrounded by Schwann cells but not myelin sheath)
Postsynaptic axons of gray communicating rami, axons of interneurons, somatic sensory neurons for pain and temperature
Compare the speeds of impulse conduction for myelinated vs unmyelinated and how do nodes of Ranvier help with saltatory conductance?
5 to 100 m/s versus 0.2 to 2 m/s. Saltatory conductance is where the pulse jumps by skipping the myelinated areas and only going to the nodes.
What do oligodendrocytes do and how are they different from Schwann cells
CNS. They envelope multiple axons to form myelin sheaths. They do not envelope unmyelinated fibers and the basement membranes do not invest in them
Why can MS affect both afferent and efferent axons?
It affects the CNS and degrades myelin and plaques appear randomly in the white matter affecting both motor and sensory neurons
What is the clinical significance of the histological observation that Schwann cells but not oligodendrocytes are invested by basement membranes?
The CNS does not heal well compared to the PNS because there is no investment by basement membranes.
Why does a cutting nerve injury but not a crushing nerve injury require surgery?
Crushing injury leaves cell bodies and connective tissue intact allowing axons to regenerate and be guided. Cutting injury cuts everything so there is no guidance for regrowing the axons so surgery is necessary
in the CNS, axons synapse with motor neuron dendrites. Neurotransmitters are released from the axon terminal into the synaptic cleft and bind to the dendrite of the postsynaptic cell
Describe ganglia and what covers it
Aggregates of neurons covered by a dense connective tissue capsule continuous with the epineurium of the entering and emerging nerves.
What are satellite cells
Cells that enclose the sensory neurons of DRG. The postsynaptic neurons are not completely invested by satellite cells allowing for synapses to form with presynaptic fibers
What creates the bilateral neural folds and what happens to the folds
indentation by the neural groove on the neural plate, a part of the dorsal surface ectoderm. The edges of the fold form the neural crest which fuses to form the neural tube
What lines the lumen of the neural tube
What do the neuroepithelium-derived neuroblasts form as the tube differentiates into the spinal cord?
Somatic motor neurons, interneurons, and presynaptic sympathetic motor neurons
What separates the neural tube from the covering surface ectoderm
The neural crest
What do ectoderm-derived neural crest cells become?
Neuroblasts that form somatic sensory neurons of the DRG and postsynaptic visceral motor neurons of the paravertebral sympathetic ganglia. Schwann cells are derivative of neural crest cells and satellite cells are derivatives of Schwann cells
When do neuroblasts lose their ability to divide and what is the clinical consequence of this loss?
Once the neuroblast undergoes its final differentiation and becomes a neuron, it can no longer divide.