Neuroscience Basics Quiz

Basics of the Nervous System

• Division
• Types of cells
• Anatomy

Early Embryonic Development

• Gastrulation
• Somitogenesis
• Neural induction/neurulation
• Neural crest cells
• Neural tube defects

Development of the Brain Vesicles

• Development of the Primary Brain Vesicles
• Development of the Secondary Brain Vesicles

Nervous System Overview

• Enclosed by meninges (Dura Mater, Leptomeninges - Arachnoid & Pia Mater)
• Central Nervous System (CNS): Brain and Spinal cord
• Receives and processes sensory information, initiates responses, stores memories, generates thoughts, and emotions (brain) Conducts signals to and from the brain, controls reflex activities (spinal cord)
• Peripheral Nervous System (PNS): Cranial nerves, Spinal nerves, Sensory neurons, Motor neurons, Sensory ganglia, and Autonomic ganglia
• Cell body of neurons
• Somatic nervous system- Controls voluntary movements
• Autonomic nervous system- Smooth muscle, cardiac muscle and glandular epithelium
  • Sympathetic division ("Fight or Flight")- T1 - L2/3
  • Parasympathetic division ("Rest or Digest")- Cranial nerves III, VII, IX, X, S2-S4 Pelvic splanchnic nn
• Gray Matter- Cell body of neurons (within nuclei), Glia cells,
• White Matter- Axons (tracts), Glia cells

Cells of the Nervous System

• Neurons: the main cells of the nervous system (NS), their cell bodies are located in the gray matter of the CNS (central nervous system) and within the ganglia of the PNS (peripheral nervous system)
• Glial Cells:
  • CNS: Astrocytes, Oligodendrocytes, Ependymal cells, Microglia, and Radial Glia cells (embryonic)
  • PNS: Schwann cells (PNS), and Satellite cells (PNS)

Types of Neurons (Morphological Classification)

• Bipolar
• Multipolar
• Pseudounipolar

Types of Neurons (Functional Classification)

• Sensory neuron
• Interneuron
• Motor neuron

The Spinal Cord

• Ventral horn (Anterior gray column)
• Dorsal horn (Posterior gray column)
• Central canal
• Ventral groove
• Motor neurons are located in the ventral horn, while sensory neurons are located outside the spinal cord, inside dorsal root ganglia

Autonomic Nervous System

• Functional components: Somatic afferent (skin, muscle, tendon, joint capsule); Visceral afferent (smooth muscle, glands); Visceral Efferent (autonomic ganglia); Somatic Efferent (skeletal muscles)
• SA, VA, and SE run the full length of the cord.
• VE - T1 – L2/3 (Sympathetic)
• S2 - S4 (Parasympathetic)

Autonomic Nervous System

• Two efferent neurons in series:
  • Preganglionic neuron (inside CNS)
  • Postganglionic neuron (outside CNS, in autonomic ganglion)

Autonomic Nervous System

• Sympathetic and parasympathetic divisions

The Brain (Prosencephalon)

• Telencephalon: Cerebral cortex, basal ganglia, coordination of voluntary movements,
• Diencephalon: Thalamus, hypothalamus, epithalamus
• Midbrain (Mesencephalon): Colliculi (visual & auditory processing), Pons (neuron pathways), Cerebellum (motor control), Medulla (many autonomic functions)

The Brain (Rhombencephalon)

• Metencephalon: pons, cerebellum
• Myelencephalon: medulla

Ventricles of the Brain

• Spaces filled with cerebrospinal fluid (CSF)
• Lateral Ventricles (right and left)
• Third ventricle
• Fourth ventricle
• Passageways connecting internal brain vesicles and subarachnoid space surrounding the brain and spinal cord
• Communications between CSF-filled spaces and blood-filled dural venous sinuses through arachnoid granulations

Cranial Nerves

• 12 pairs (motor/sensory/mixed) Most arise in the brainstem (except CN I & II)
• Motor: nuclei located in the brain
• Sensory: neurons located outside the brain (sensory ganglia)
• Parasympathetic fibers carried along with some cranial nerves (III, VII, IX, X)

Gastrulation

• Formation of the primitive streak
• The first epiblast cells to migrate to the primitive streak become endoderm
• Epiblast cells that migrate further into the primitive streak become mesoderm
• The remaining epiblast becomes ectoderm

The primitive streak doesn't reach the most anterior region of the embryo. Why?

• Wnt3 and Brachyury induce formation and anterior extension of the primitive streak
• The future head region has a signaling center called Anterior Visceral Endoderm (AVE).
• AVE blocks Wnt3 and brachyury signaling, preventing cranial expansion of the primitive streak

Gastrulation and Cell Fates

• Hypoblastic cells move toward the oropharyngeal membrane, creating the prechordal plate

Prechordal Plate

• Location: rostral to notochord, posterior to the oropharyngeal membrane and AVE
• Function: signaling center that induces brain development

Notochord

• Epiblast cells form the notochord along the embryo's midline
• Forms a midline axis, basis of axial skeleton
• Induces formation and folding of the neural plate
• Contributes to dorso-ventral patterning of the neural tube

After Gastrulation

• Remaining epiblast cells differentiate into surface ectoderm, neural plate, neural crest cells, and ectodermal placodes (olfactory, nasal, lens, otic, and epiphyrangeal)
• Placodes assist neural cells in forming sensory ganglia of cranial arches (V-VII-IX-X)

Neural Induction

• Notochord secretes BMP (Bone Morphogenetic Protein) antagonists (Chordin, Noggin, Follistatin, and Nodal)
• These block BMP signaling in the undifferentiated ectoderm, allowing neural tissue to form

Neurulation

• Neurogenic factors released by the notochord induce the overlying ectoderm to form the neural plate.
• Neural plate folds to form the neural tube.
• Neural crest cells undergo epithelial-mesenchymal transitions and delaminate from the neural plate.

Neural Crest and Derivatives

• Migratory, pluripotent cells
• Contribute to structures in the head and neck
• Neural derivatives: sensory ganglia of spinal nerves, sensory ganglia of cranial nerves, sympathetic ganglia, parasympathetic ganglia, adrenal medulla (chromaffin cells)

Neural Crest Cells: Non-neural derivatives

• Glia cells in PNS: Schwann cells and satellite cells
• Melanocytes, odontoblasts, cementoblasts
• Skeletal components in the pharyngeal arches (cartilage & bones)
• Ciliary and pupillary muscles
• Leptomeninges: arachnoid and pia mater
• Migration guided by signals from non-neuronal tissue (somites)

Somitogenesis

• Neurulation and somitogenesis occur concomitantly
• Cells migrating through the node (posteriorly) and cranial part of the primitive streak form paraxial mesoderm
• Paraxial mesoderm cells coalesce to form somites.

Fate of the Somite

• Dermomyotome (dermatome: forms dermis, myotome: forms muscles)
• Sclerotome (forms vertebrae and intervertebral disc (IVD))

Neural Plate Formation and Neurulation

• Neural tube begins folding and fusing in the occipito-cervical region
• Forms cranial and caudal neuropores

Neural Tube Defects

• NTDs: diverse set of birth defects that involve the neural tube and/or associated structures
• Result from failure of neural tube or neuropores to close properly
  • Spina bifida: defects in the spinal cord/caudal neuropore
  • Anencephaly: defects in the cranial neuropore (fatal)
• Causes: folic acid deficiency, genetic predisposition, teratogens (other factors: obesity, smoking, hyperthermia)
• Diagnosis: high levels of alpha-fetoprotein in amniotic fluid

Skull defects and encephaloceles

• Defects in skull bone ossification can result in meningoceles, encephalomeningoceles, and encephalomeningohydroceles.
• The squamous part of the occipital bone is most often involved
• Severity depends on the size of the bony defect

Development of the Primary Brain Vesicles

• Following neural induction, the cephalic end of the neural tube shows three dilations: prosencephalon, mesencephalon, and rhombencephalon

Development of the Secondary Brain Vesicles

• At 5 weeks, the primary vesicles develop into 5 secondary vesicles: telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon

Development of the Secondary Brain Vesicles

• The lumen of the developing spinal cord is continuous with the brain vesicles.
• They become filled with cerebrospinal fluid (CSF) produced by choroid plexus.

Hydrocephalus

• Accumulation of CSF in the brain
• Enlarges ventricles
• Common cause: aqueduct blockage

Summary

• Sequential development of brain vesicles