Week 4: Nervous System Intro I Flashcards
Describe how the embryonic origin of the CNS and PNS relates to the organization of the adult NS
The PNS originates from the neural crest cells, which proliferate after dorsal/ventralization of the neural tube. The neural crest cells extend ventrally, spreading out to form the PNS axons.
The CNS comes from the neural tube, and organizes into compartments along the rostral/caudal axis based on Hox gene levels and signaling, with more Hox genes being expressed caudally, and fewer being expressed rostrally.
Discuss the general anatomy and function of the NS and its major subcomponents (CNS and PNS)
The CNS is the “control center” made up of the brain (fore/mid/hindbrain) and spinal cord (cervical (8 vertebrae), thoracic (12), lumbar (5), sacral (5) and coccygeal (1)) segments
The PNS is composed all the nerves outside of the CNS, and connects the CNS to the limbs/organs. It acts as a relay between the CNS and the remainder of the body. There are three subcomponents:
Somatic (skeletal muscles)
Visceral/autonomic (para/sympathetic)
and Enteric (GI function)
What is the relationship of the CNS subdivisions to one another? How is the ventricular system involved in coordinating these subdivisions?
The fore/mid/hindbrain elements of the CNS develop rostrally to caudally. This is the early 3 Vesicular Phase.
The later 5 Vesicular Phase is composed of the:
Telencephalon
Diencephalon
Mesencephalon
Metencephalon
and Myelencephalon
The rostral/caudal organization of the brain is also connected via ventricles, or cavities where CSF is produced and circulated. The ventricles help the various brain regions communicate.
Explain what organizing centers and molecules are involved in developing the dorsal-ventral and rostral-caudal axes of the CNS
The head develops the prosencephalon and mesencephalon (derive from the prechordal plate and anterior visceral mesoderm) using Otx-2
The notochord uses Shh to signal development of the rhombencelphalon and spinal cord regions
The isthmic organizer produces the rostral prosencephalon and mesencephalon and the caudal rhombencephalon and spinal cord.
The spinal cord activates different Hox genes via the retinoic acid and FGF gradients, which increase from rostral to caudal end. Hox 5/6 separate cervical and thoracic and Hox 9/10 separate thoracic and lumbar
…FINALLY…BMP is produced by the roof plate/ectoderm, and diffuses into the dorsal/alar plate of the neural tube. Shh is produced by the notochord and diffuses into the ventral/basal plate of the neural tube. The sulcus limitans forms the transition zone between the two plates. The alar region becomes sensory afferent neurons and the basal region becomes motor efferent neurons
What are the inductive events and processes that establish the organization of the spine?
Spinal nerves are segmented into anterior/posterior segments due to the varied expression of EphB2 receptors located on neural crest cells and motor axons.
Ephrin-B1/2, the ligand for the EphB2 receptor is only expressed posteriorly. This allows for the segmental organization of the vertebral column and spinal nerves. The Ephrin-B1/2 ligand is a cell surface marker and binds to the Eph B2 receptor located on nearby cells–this controls cell migration and axonal development. Contact with the ligand causes cytoskeleton collapse, so neural crest cells/motor axons only migrate through the anterior compartment.
Describe the functional division of the NS and explain the function of each group
There are two major divisions: the sensory (afferent) and motor (efferent)
Somatic sensory nerves feel touch, pain, pressure, vibration, temperature, proprioception in the skin, body wall and limbs
Visceral sensory feels stretch, pain, temperature, chemical changes, nausea, and hunger
Somatic motor are the voluntary skeletal muscles and
Visceral motor (ANS) innervate smooth & cardiac muscles, glands, and the general ANS components
How does spina bifida occulta and anencephaly occur, and how do these issues relate to the closing of the neural tube?
Spina bifida occurs due to a failure of the neural tube to close properly at the caudal end of the embryo. Anencephaly is the result of a failure of neural tube closure at the cranial end of the neural tube.
The neural tube begins closing at the cervical (upper) region of the axis, then moves both caudally and cranially in a zipperlike fashion. Folic acid is one of the many signaling molecules that can prevent proper closure of the tube.
Explain the ventral/dorsal differentiation of the neural tube as it relates to signaling molecules
BMPs and Wnts from the overlying primitive ectoderm diffuse ventrally towards the neural tube, binding with cell receptors and causing dorsalization of the neural tube region there. This process is halted once a sufficient [BMP] threshold is reached to produce noggin, which feeds back negatively on the ectoderm cells, signaling a cease of BMP release. This forms the roof/future alar plate.
On the ventral side, the notochord releases Shh, which rises towards the ventral neural tube and forms the ventral neural tube cells, which will eventually become the basal plate of the developoing neural tube.
The neural crest cells of the primitive ectoderm will, once BMP secretion has ceased, work together with mesodermal somites to spread laterally and form the muscles and nerves of the abdomen/PNS.
What are the structures that arise from the CNS and PNS?
The CNS forms the fore/mid/hindbrain and the regions of the spinal cord, which include the cervical, thoracic, lumbar, sacral, and coccygeal regions. These are formed from neural tube cells.
The PNS forms from the neural crest cells, and develops the somatic NS (innervates muscles from the somites), the visceral/autonomic NS (innervates visceral muscles of the parasymp/symp-related structures), and the enteric NS (innervates gut tissues)
What are the regions of the brain and their subdivisions?
Prosencephalon (forebrain): telencephalon and diencephalon
Mesencephalon (midbrain): pons and tectum
Rhombencephalon (hindbrain): cerebellum and medulla
What are the major regions and derivations that help form/differentiate the brain regions?
The anterior visceral endoderm (endoderm) and prechordal plate (mesoderm) help develop the pro/mesencephalon regions of the brain.
What helps develop the hindbrain and the spinal cord? What divides the pro/mesencephalon from this region?
The Shh secreted by the notochord help differentiate and develop the rhombencephalon and spinal cord regions. The constricted region at the isthmic organizer helps differentiate the pro/mesencephalon from the rhombencephalon and spinal cord.
What cells line the inner aspect of the neural tube?
The neuroectoderm cells
What is the dividing line between the alar and basal plates, and how does it form?
The sulcus limitans forms from the ventral movement of BMPs from the alar plate and the dorsal movement of Shh from the basal plate. These signals “cancel one another out” in this region, and help differentiate the sensory and motor neurons of the developing NS
What is the significance of the dorsal and ventral regions of the spinal cord, as it relates to future development of the body’s PNS? What do the cells lining the future central canal become, and what do they produce?
The dorsal cells of the alar plate will become the sensory neurons (incoming) that receive PNS signals, and the ventral cells of the basal plate become the motor neurons (outgoing) that send signals to the PNS. The neuroectodermal cells lining the central canal differentiate into radial glia that will eventually be wrapped in neuroblast (nerve progenitor )cells. The neuroblasts will migrate/move outwards from the ventricular zone to the intermediate zone and pial zones.
What are the different regions of the embryonic brain, and what regions of the adult brain do they give rise to? What is their associated ventricular space?
SEE ATTACHED
Prosencephalon:
Telencephalon: cerebral cortex, basal ganglia, hippocampus, olfactory bulb, basal forbrain (lateral ventricles)
Diencephalon: dorsal thalamus, hypothalamus (third ventricle)
Mesencephalon:
Midbrain (cerebral aqueduct)
Rhombencephalon:
Metencephalon: cerebellum, pons (fourth ventricle)
Myencephalon: medulla (fourth ventricle)
What are the ventricles of the mature brain, and what brain regions are they associated with?
The Telencephalon is associated with the most rostral lateral ventricles
The Diencephalon is associated with the third ventricle
The Mesencephalon is associated with the cerebral aqueduct
The Metencephalon and Myelencephalon are associated with the fourth ventricle
and the spinal cord is associated with the central canal
The ventricular system is where cerebrospinal fluid (CSF) is produced
Name each of the labeled sections of the diagram. Explain the derivations of D-H, and what ventricles they are associated with.
(A) Prosencephelon
(B) Mesencephalon
(C) Rhombencephalon
(D) Telencephalon - Cerebrual cortex, basal ganglia, hippocampus, olfactory bulb (lateral vent.)
(E) Diencephalon - Dorsal thalamus, hypothalamus (3rd vent.)
(F) Mesencephalon - Midbrain (cerebral aqueduct)
(G) Metencephalon - Cerebellum, pons (4th vent.)
(H) Myencephalon - Medulla (4th vent.)
What are the twelve cranial nerves, and how do we remember them?
Oh - Olfactory (I)
Oh - Optic (II)
Oh - Oculomotor (III)
To - Trochlear (IV)
Touch - Trigeminal (V)
And - Abducens (VI)
Feel - Facial (VII)
Virgin - Vestibulocochlear (VIII)
Girls’ - Glossopharyngeal (IX)
VJ - Vagus (X)
Ah - spinal Accessory (XI)
Heaven - Hypoglossal (XII)
How do you remember the either sensory, motor, or “both” status of the cranial nerves?
S = Sensory, M = Motor, B = Both
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What cranial nerves are associated with the myencephalon?
Part of the Vestibulocochlear, the Glossopharyngeal, Vagus, part of the spinal Accessory and the Hypoglosseal (part of VIII and XI, all of IX, X, and XII) are associated with the myencephalon. XI (Spinal Accessory) is partially associated with both the medulla and the spinal cord.
