TBL 3 Objectives Flashcards
Which neurons are affected by ALS and why is the disease ultimately fatal?
progressive neuromuscular disorder caused by destruction of of motor neurons, which leads to degeneration and atrophy of muscles. Respiratory muscles are affected, and death is due to inability to breath
Compare alphanumeric designations of the segmental spinal nerves
For cervical: nerve is ABOVE the corresponding vertebra
For thoracic and downward: the nerve is BELOW the corresponding vertebra
Distinguish anterior and posterior rami of the spinal nerves
Immediately after emerging from the intervertebral foramina, spinal nerves divide into anterior and posterior rami
- posterior rami supply the posterior body wall
- anterior rami supply the anterolateral body wall and extremities
Summarize a somatic reflexive response
Touching a hot surface:
- pain is conducted via posterior sensory neurons
- interneuron transmits impulse to motor neuron
- motor neuron sends message to move hand away from surface
** not from TBL, but from prior knowledge. The nerve that sends pain information to your brain conducts slower than the motor neuron, so you pull your hand away before you realize it hurts
Define spinal cord segmental origins of presynaptic sympathetic neurons
They are located in the intermediolateral (lateral horns) of the spinal cord (T1-L2 only)
Distinguish the CNS and PNS
The CNS (central nervous system) includes the brain and the spinal cord. The PNS (peripheral nervous system) consists of the spinal nerves, cranial nerves, and autonomic nerves.
Compare multipolar (motor) and pseudounipolar (sensory) neurons
Multipolar (motor) neurons:
- all the motor neurons that control skeletal muscle and comprise the ANS (autonomic NS)
- contain one axon and many dendrites
- axons are called “efferent” because they activate skeletal muscle, glands, cardiac muscle, smooth muscle, etc.
Pseudounipolar (sensory) neurons:
- all the sensory neurons of the PNS with cell bodies located in the dorsal root ganglia, exceptions: olfaction and vision
- contain one axon that splits into two branches: central and peripheral
- axons are called “afferent” because they convey sensations of touch, pain, and temp from muscles, bones, and skin of the body wall/extremities into the CNS
Define the interneurons
Interneurons are neurons that form connections between other neurons. They are neither motor nor sensory.
Example: neurons coming from the dorsal root ganglion synapse with neurons in the posterior horn of the spinal cord. These neurons that are synapsed on are interneurons that convey the sensory impulses to motor neurons in the adjacent anterior horn or help convey the sensory impulses to the brain.
Cite the nerves that constitute the SNS (somatic NS)
Multipolar motor neurons and pseudounipolar sensory neurons
*can someone double check this and let me know?? i’m not 100% sure. thanks! -catherine
Describe the pair of multipolar neurons that constitute the ANS (autonomic NS)
Pair: presynaptic and postsynaptic neuron
Presynaptic neuron starts from the CNS and synapses within the autonomic ganglion on the postsynaptic neuron, which synapses on viscera, glands, and smooth muscles.
Name the divisions of the ANS (autonomic NS)
Sympathetic NS (fight or flight) and Parasympathetic NS (rest and digest)
Sympathetic division: cardiopulmonary splanchnic nerves and abdominopelvic splanchnic nerves
Parasympathetic: cranial nerves III, VII, IX, X and pelvic splanchnic nerves
Bilateral sympathetic trunks
Formed by linked paravertebral ganglia. Divided in 12 thoracis, 5 lumbar, 5 sacral and 3 cervical segments.
White and gray communication rami
White: formed by presynaptic sympathetic fibers, they arise from the anterior rami of spinal nerves T1-L2 and terminate in corresponding paravertebral ganglia.
Gray: Arise in the ganglia, formed by postsynaptic sympathetic fibers returning to the anterior rami of spinal nerves T1-L2.
Types of axons in every spinal nerve
somatic motor fibers, somatic sensory fibers and visceral motor fibers.
Epineurium, endoneurium, perineurium
Perineurium: Encloses bundles of axons.
Endoneurium: Loose conective tissue between axons
Epineurium: Encloses perineurium bundles.
Myelinated and unmyelinated axons
Myelinated: Motor axons, presynaptic axons of white rami, and somatic sensory conductin sensations of touch.
Unmyelinated: Postsynaptic fibers of gray rami, interneurons and somatic sensory of temperature and pain.
Schwann cells and oligodendrocytes
Schwann cell are located in PNS. They myelinate axon when wraped around then. When associate with axons without wrapping them they become unmyelinated.
Oligodendrocytes locate in CNS. Myelinate multiple axons
Distinguish the neural plate and neural tube
The neural plate becomes the neural tube when the plate begins to fold at the neural fold, these folding cells become the neural crest cells. The neual tube is formed once the neural plate completely folds to form the neural tube.
Compare locations of neuroepithelium and the neural crest
The neuroepithelium line the inside of the neural tube and the neural crest cells are posterior to the neural tube and anterior to the ectoderm that eventually makes the dermis of the back.
Compare derivatives of neuroblasts derived from neuroepithelium and neural crest cells
Neuroepithelium: multipolar motor neurons of the anterior horn, multipolar presynaptic motor neurons of the lateral horn, multipolar interneurons of the posterior horn.
Neural Crest: psuedounipolar sensory neurons of the dorsal root ganglia and postsynaptic visceral motor neurons of the paravertebral sympathetic ganglia.
Cite origins of Schwann cells and ganglionic satellite cells
Schwann cells are derived from neural crest cells and satellite cells are modified Schwann cells
When do neuroblasts lose their ability to divide?
What is the consequence of this?
Neuroblasts lose their ability to divide when they differentiate into neurons. This means limited capacity for wound healing. (Limited to axon repair in peripheral nervous system).
Describe axodendritic synapses.
Synapses are sites of communication between neurons.
The axon of the presynaptic neuron is carrying an AP (action potential). The AP stimulates vesicles of neurotransmitter to be released from the axon terminal into the synaptic cleft (space between pre- and post-synaptic neuron). The neurotransmitter diffuses across the synaptic cleft and is received by membrane receptors on the postsynaptic neuron, and effects an AP down the axon of that neuron.
Note- in the CNS, most synapses are between axons and dendrites—ex: axons from interneurons of SC posterior horn and dendrites of MN in adjacent interior horn.
Why can multiple sclerosis affect both afferent and efferent axons?
In multiple sclerosis, T cells at the white matter mediate an inflammatory response which causes a loss of oligodendrocytes. Because oligodendrocytes myelinate and support CNS axons, there is a loss of myelination in the CNS axons. Both afferent and efferent axons (of the CNS – brain and spinal cord) are myelinated by oligodendrocytes; thus, both are affected.
Schwann cells, but not oligodendrocytes, are invested by basement membrane. What is the clinical significance of this fact?
Schwann cells (PNS) are invested by basement membrane, which enables regeneration and repair of axons after injury. Oligodendrocytes (CNS), however, are not invested by basement membrane. This means CNS axons have poor regeneration capacity after injury.
Why does a nerve-cutting injury require surgery while a nerve-crushing injury does not?
A crushed nerve still has intact connective tissue (epineurium) to help guide re-growing axons along the right track. A cut nerve means the connective tissue is cut too, so the epineurium must be stitched back together and the nerve bundles aligned in order to ensure the proper re-growth trajectory.
Define ganglia in the PNS.
Ganglia are discrete aggregations of neuron bodies outside of the CNS. They are covered by a dense connective tissue capsule, which is continuous with the epineurium of entering and emerging nerve fibers.
Ganglia are derived from neural crest.
Compare neurons of the sympathetic ganglia and the DRG
DRG (sensory neurons):
Are not in synapses.
Are enclosed by a ring of satellite cells.
Contain neuron bodies of pseudo-unipolar neurons, which are comprised of a central and peripheral axon that converge at the neuron body (which comprise the ganglia).
Thus, it is the same neuron entering (central axon) and exiting (peripheral axon) the DRG.
Sympathetic ganglia neurons:
Contain synapses between pre- and post-ganglionic neurons. In other words, the sympathetic ganglia is comprised of neuron bodies belonging to postganglionic neurons, whose bodies are synapsing with axon terminals of the pre-ganglionic neurons.
Have no satellite cells – allows pre-ganglionic fibers to form synapses with postsynaptic neurons that occupy the ganglia.
Are multipolar- a neuron comprised of a body with one axon (can have multiple branches) that synapses onto another neuron body.
Compare satellite cells investments in the sympathetic ganglia and DRG.
DRG: satellite cells invest neuron bodies.
Sympathetic: no satellite cells – helps synapses happen.
