Cells of the Nervous System (Week 1--Micevych) Flashcards
Anatomical organization of nervous system
CNS: brain and spinal cord
PNS: cranial nerves, spinal nerves and associated ganglia
Functional organization of nervous system
Sensory (afferent) for receiving signals
Motor (efferent) component for transmitting impulses to effector organs throughout the body
Basolateral and apical sides of neuron
Basolateral: cell body and dendrites
Apical: axon and terminals
Cell body/soma of a neuron
Actively synthesizing proteins!
Prominent nucleus (pale) and nucleolus (dark) with dispersed chromatin (because actively being transcribed)
Lots of rough ER and polysomes called Nissl bodies
Golgi complex synthesizes receptors, enzymes, peptide transmitters
Numerous mitochondria
Inclusions (not organelles, just aggregations of things) including melanin granules, lipofuscin pigment (older people have more), lipid droplets
Neurosecretory cells in hypothalamus also have secretory vesicles in cell body
Dendrites of a neuron
Cytoplasmic projections of cell body with same organelles (except nucleus)
Specialized for receiving impulses
Highly branched
Specialized zones that receive inputs are equipped with membrane receptors, gap junctions, and associated signal transduction machinery
Some dendrites have spines for input
Dendritic spines
CNS dendritic specialization for receiving input/synapses (axon terminals make contact with spine)
Little bumps on dendrite shaft that look like mushrooms
Spines help focus the signal (to small area of dendrite)
Axon of a neuron
Single process (can branch AFTER leaving cell body)
Often myelinated (CNS by oligodendrocytes and PNS by Schwann cells)
Axon begins as axon hillock (initial segment) which has no Nissl bodies and is not myelinated; this area initiates action potentials
Axon shaft has smooth ER, mitochondria, vesicles, actin filaments, microtubules, intermediate filaments (neurofilaments), MAPs (1,3,5), motoric proteins (kinesin anterograde and dynein retrograde)
Axon ends with terminal bouton (end bulb or axon terminal) which converts electrical impulses into release of chemical messengers (NTs)
Tau proteins
Stabilize microtubules
Pathologically contribute to neurodegenerative diseases (tauopathies include Alzheimer’s disease and frontotemporal dementia)
Types of axon damage
Closed head injury (concussion) can cause axon damage via:
Stretching
Twisting
Compression
Reaction to damage
Axonal transport
Need transport to get things up and down the axon which can be up to 100cm long!
Fast transport: vesicles move 50-400mm/day, propelled by molecular motor proteins
Kinesin moves to + end, anterograde (toward axon terminal/synapse)
Dynein moves to - end, retrograde (toward cell body)
Slow transport: nonmembrane organelles (proteins, ribosomes, cytoskeletal components) move 0.3-8mm/day because intermittent and bidirectional movement
Chemical synapse vs. electrochemical synapse
Chemical synapse: where NTs released; space that separates terminal bouton from receiving cell dendrite, cell body or axon
Electrochemical synapse: gap junction
Morphology of neurons
Unipolar: single process, only during development
Bipolar: two processes from cell body (one dendrite and one axon); in olfactory epithelium and vestibular and cochlear ganglia
Pseudounipolar neurons: have only one process emanating from cell body that divides into peripheral and a central branch which are BOTH axonal; terminal portion of peripheral end often branched and contains secretory vesicles; in cranial sensory and spinal (dorsal root) ganglia
Multipolar neurons: most common type; pyramidal, motoneuron, Purkinje cells
Classification of neurons based on function
Sensory (afferent): primarily in PNS, for transmission of sensory input
Motor (efferent): originate in CNS and activate peripheral effectors (muscles, glands)
Interneuron: only in CNS; integrators that establish networks of neuronal circuits
Glia
Provide metabolic and mechanical support for neurons and are active participants in nervous system (synthesize and release NTs, sop up NTs to clean area)
In CNS, have astrocytes, oligodendrocytes, microglia and ependymal cells
In PNS have Schwann cells, satellite cells
Astrocytes
Found in both gray and white matter
Protoplasmic astrocytes more prevalent in gray matter
Fibrous astrocytes more prevalent in white matter
Reactive astrocytes activated by injury and create glial scar
Elaborate process that extend between blood vessels and neurons and ends of processes form end feet that cover large areas of surface of blood vessels
Astrocytes coupled by gap junctions
Contain GFAP
Help form BBB (regulate tight junctions between endothelium of brain capillaries)
Move metabolites away from neurons
Regulate ion concentrations (membranes have high gK so buffer extracellular K+ during repititive activity)
Regulate NT concentrations (have uptake machinery for NTs)
Synthesize neurosteroids (role in reproduction, neuroprotection)
