Midterm Flashcards
2 major cell types of the nervous system
Neurons and glia
- Glia are more numerous (1 trillion glia vs. 100 billion neurons)
Central Nervous System (CNS)
- Functions: Analyze and integrate information
- Has a blood-brain barrier
- Cannot regenerate (usually)
- Myelination: oligodendrocytes
- Terminology: nuclei, tracts
Peripheral Nervous System (PNS)
- Functions: receive sensory info, muscle movement
- No blood-brain barrier
- Regenerates
- Myelination: Schwann cells
- Terminology: ganglia, nerves
Gyrus, sulci, & fissures
- Gyrus: surface of brain
- Sulci: grooves
- Fissures: deep grooves
Gray matter
- Cortex, Nuclei or Ganglia (groups of nerve cell bodies and neuropil) generally of similar function
- Neuropil - neuronal processes, synapses and glia
White matter (& bundles vs. tracts)
- Bundles: (groups of myelinated axons [see below]) that course in the same direction
-
Tracts: also groups of axons - myelinated and un-myelinated but indicates origin, destination and therefore function
- e.g., corticospinal tract
Cerebrospinal fluid, dura matter, and arachnoid matter
- Made in the ventricles
- Circulates between all the cells and their processes and in the space between a membrane on the brain surface (pia matter) and a membrane next to the skull or spine (arachnoid matter)
- called the subarachnoid space
Blood vessels and coverings of the brain
Blood vessels:
- Arteries, capillaries, veins and venous sinuses
Coverings (meninges):
- Dura mater (tough mother)
- Arachnoid mater (spider web like)
- Pia mater (tender/affectionate)
Types of neurons
- Stellate (star-like)
- Pyramidal (conical/triangular)
- Correspond to function
- Multiple dendrites, only one axon
- Neurons named after famous guys (Purkinje, Betz, Cajal, Retzius, Mauthner)
- Purkinje cell:
- One complex dendrite that resembles a sea fan
- Many synapses
Golgi stain vs. Nissl stain
- Golgi stain: fills processes of some cells with black precipitates of heavy metals
- Nissl stain: stains all nuclei and neuronal cytoplasm blue
Synapse types
Asymmetrical = type 1
- Postsynaptic membrane is thicker than presynaptic membrane; spherical clear vesicles
- These are excitatory synapses - on
Symmetrical = type 2
- Postsynaptic membrane same as presynaptic membrane; flattened clear vesicles
- These are inhibitory synapses - off
3 types of glia
- Astrocytes: Maintains appropriate chemical environment for neuronal signaling (only in CNS)
- Oligodendrocytes: Lay down myelin around some (not all) axons (only in CNS)
- Microglial cell: Scavenger cells that remove cellular debris from sites of injury or normal cell turnover
3 principle germ bands
- Ectoderm: forms skin, neurons
-
Mesoderm: forms notocord, muscle, kidney, bone, blood
- Underlies (neuro) ectodrm, and induces the neural plate
- Endoderm: forms lining of gut, lungs, placenta in mammals
Neural crest cells, notocord, and neural floor plate
- Neural crest cells: make PNS, endocrine, pigment cells, connective tissues, and is source of ganglia
- Migrate into somites to form the PNS
- Derived from leading edge of neural folds
- Notocord: induces floor plate (helps polarize dorsal to ventral)
- Neural floor plate: rich source of neuronal porphogens & axonal cues
Apoptosis
Programmed Cell Death
Instrinsic and extrinsic factors
Features: membrane blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation
Requires ATP
Systematic and clean
- Can be beneficial
Necrosis
- Premature death of living cells
- Extrinsic factors only
Features: cell swelling, disruption of membranes, cell lysis, release of intracellular content (causing inflammation)
Detrimental
Often leads to buildup of dead tissue
Nerve growth factor (NGF)
- One example of a neurotrophin (NT)
- Supplied by target, promotes cell growth (instead of apoptosis)
- Signals through tyrosine kinase (Trk) receptors
- Viktor Hamburger, Rita Levi-Montalcini, Stanley Cohen
Bcl-2 gene
- This gene encodes an integral outer mitochondrial membrane protein that blocks the apoptotic death of some cells such as lymphocytes
- Overexpression of this causes B-Cell Leukemia
- Example of how cell death can be blocked by overexpression of a gene (as in Leukemia)
Ced-4
Pro-apoptotic protein expressed primarily during embryogenesis of C. elegans, homologous to the human Apoptosis activity factor (Apaf)
Apaf
- This scaffold protein binds to Cytochrome c and dATP to form a 7-spoke apoptosome complex
Cytochrome C
- This freely-diffusible molecule is well known for it’s role in cellular respiration but it also functions to activate a caspase cascade, which commits the cell to the death process
Caspase
- This family of proteins exists as inactive proenzymes that only become active after undergoing proteolytic processing and plays a central role in the execution-phase of cell apoptosis
Mitochondria
In response to a variety of apoptotic stimuli (i.e. DNA damage, ischemia, oxidative stress, etc.) it releases apoptogenic proteins to the cytoplasm that initiates the execution of apoptosis
TrKA
High affinity receptor for nerve growth factor (NGF)
NGF
- This molecule that promotes the survival and differentiation of neurons was discovered by Rita Levi-Montalcini and Stanley Cohen in the 1950s while faculty members at Washington University in St Louis
Selective aggregation
- If you put dissociated embryonic tissures (vertebrate and invertebrate) in a dish, you will get formation of different animal embryos
- This suggests ancient (surface) adhesion molecules
- Cell adhesion gene = N-cadherin
Lamellipodium
The primary morphological characteristic is a sheetlike expansion of the growing axon at its tip
filopodia
- The fine processes that extend from the lamellapodium
Microtubule cytoskeleton
- Responsible for the elongation of the axon itself
Integrins
- A broad class of cell surface receptors that bind specifically to the extraceullular matrix cell adhesion molecules
- They do not have any kinase or direct signaling capacity
Netrins
- Secreted molecules that can attract or repel axons by binding to their receptors DCC (attract) and UNC5 (repulse)
- Opposing activities of netrin and slit occur at the ventral midline of the spinal cord. This guidance system ensure the axons relaying pain and termperature cross the midline at appropriate levels of the spinal cord and remain on the correct side until they reach their thalamic targets
Slits
- Secreted proteins that normally repel growth cones by engaging Robo class receptors
- Secreted factor important for preventing an axon from straying back over the midline once it has crossed initially
Ephrins
- Cell surface molecules used to recognize appropriate pathways for growth and appropriate sites for synaptogenesis
- Found on growing axons and growth cones. Function via homophilic binding. Have been associated with fasciculation of axons
Semaphorins
- Chemorepellent bound to cell surfaces or extracellular matrix that prevent extension of nearby axons
Cell adhesion molecules
- Integral membrane proteins that utilize homophilic binding that have been associated with the bundling of groups of axons
Calcium-dependent cell adhesion molecules
A family of diffusible molecules that act as attractive or repulsive cues to guide growing axons. First vertebrate gene identified was called Unc
Pioneer Neurons and Guidepost Cells
The first nerve cells to appear in limb buds of embryonic grasshoppers are a pair that lie at the distal tip and project axons along the length of the limb to the central nervous system
- The stereotyped route navigated by these pioneer axons is followed by other neurons and eventually becomes that of a major adult nerve trunk
- The guidance cues that delineate the route come from a set of nonadjacent guidpost cells along with the pioneers grow
Horizontal Gaze Palsy with Progressive Scoliosis
- Caused by mutation in ROBO3 gene.
- Robo3 ensures that motor and sensory nerve pathways cross over the midline by inhibiting Robo1/2-mediated repulsion.
- Drosophila robo disrupts longitudinal tract formation
- Mutation prevents axons in the corticospinal tract and trochlear nerve from growing past the midline, so the hindbrain and spinal cord undergo abnormal growth
Neurotrophins and their Receptors
- Signaling via Trk receptors can lead to a variety of cellular responses depending on the signaling cascade involved. The possibilities include cell survival, neurite growth, and activity dependent plasticity
- Signaling through p75 receptors can lead to neurite growth, cell cycle arrest, and cell death.
- Neurotrophins have distinct effects on different target neurons
Topographic mapping
Posterior retinal axons project to the anterior tectum, and anterior retinal axons project to the posterior tectum
Sperry experiment
- When the optic nerve of a frog is surgically interrupted, the axons regenerate with appropriate specificity. Even when rotated the axons regenerate to the original position in the tectum
Rhombencephalon develops into:
- Medulla
- Pons
- Cerebellim
- Metencephalon
- Myencephalon
- I.e., rhombencephalon develops into brainstem
Prosencephalon develops into:
- Cerebrum
- Diencephalon
- Telencephalon
- Diencephalon and telencephalon develop into cerebrum
- Hypothalamus
- Hippocampus
- Thalamus
- Optic cups
Mesencephalon developes into:
- Midbrain
Neural tube deveopes into:
- Spinal cord
Hox genes
- Encode transcription factors
- Are present in humans
- Are also present in flies