Neuron Notes Flashcards
Neurons
Arise from the ventricular layer of the neural tube
Neurofilaments are sparse in young neurons and cilia and centrioles are found
Very little rna in developing neurons
Neuron growth
Increase in RER and golgi
Precursors to Nissl bodies on nucleus and cytoplasmic glycogen reduced
Proliferation of mitochondria and ribosomes
Microtubules and neurofilaments increase forming axonal volume
Growth cones
Tips of the initial neural outgrowth and branches
Axonal growth
Non random process
Grow out in consistent directions, initial overproduction of axons
Intrinsic factors determine axonal termination
CNS and termination
Chemical affinity
Dendritic ramification
Believed to be associated with activity sensory stimulation and developing cognitive facility
CNS
Brain and spinal cord
PNS
Ganglia and peripheral nerves
Sensory neurons
Detect events in periphery through receptors
Located in dorsal root ganglion of spinal cord
Cell body, peripheral nerve innervate receptor and central axon conveys signal to spinal cord or brain
Motor neurons
CNS gray matter of spinal cord and brain
Axons enter PNS through spinal or cranial nerves and innervate striated muscle
Innervated by postganglionic axons
Interneurons
Majority of neurons in brain and spinal cord
Projection neurons
Interneurons that leave one brain region and travel to another
Many are excitatory
Upper motor neurons
Projection neurons that strongly influence motor neuron
Local interneurons
Axons that ratify in immediate vicinity of their cell body
Most local release inhibitory neurotransmitters
Neuroglia
Non neuronal CNS cells
Supportive function for neurons
Ependymal cells
Line the ventricles which contain CSF
Meninges
Connective tissue in CNS that envelops the ventricle system
PNS derivation
From embryonic neural crest
Dorsal root ganglion and autonomic postganglionic cells
Supporting cells are satellite cells and Schwann cells analogous to neuroglia
Dorsal root ganglion
Primary sensory neurons in PNS
Autonomic postganglionic cells
Innervate smooth muscles and glands, PNS
Motoneuron
Innervates skeletal muscle
Nucleus with single nucleotide and cytoplasm with organelles
Cell body, soma and perikaryon are contained in nucleus of neuron
Cell body
Metabolic center of the cell
Membrane surrounds entire cell including cytoplasmic processes- axons and dendrites
Dendritic spines
Projections off dendrites
Axons
Each neuron has only 1 axon
Axon collaterals are the branches of axons
Axon originates from axon hillock in cell body
Initial segment
Region between axon hillock and myelin sheath
Initiation of action potential
Boutons
Specialized to form functional contacts with other cells
Contact areas are synapses if interact with muscle are neuromuscular junctions
Nissl bodies
Cytoplasm of neurons filled with clumps of intensely staining bodies
Aggregates of RER in nucleus and proximal parts of dendrites
Axons have no ER so no stain so if numerous axons appear white
Silver stain
Has affinity for neurofibrils , nuclear membrane and nucleolus attract
Shows axons and cell bodies
Golgi stain
Only stain which shows neuron will all processes, entire trajectory and dendritic spread
Neuron plasma membrane
Three layers, differs in thickness in region of synapse where membrane is thickened and ER is elaborate
Two abundant filamentous structures
Microtubules in dendrites and neurofilaments in axons
Transport and forms scaffolding to maintain neuron complexity
Chemical synapses
Most common in mammalian nervous system
Presynaptic complement of membrane bound vesicles
Aggregations in cytoplasm adjacent to membrane
Distinct synaptic cleft or intercellular space
Mitochondria
Synaptic vesicles
Feature of chemical synapse
Contain neurotransmitters and shape can vary
Synaptic density can be on one or both sides
Synaptic cleft
Distinct gap between pre and post synaptic cell membranes
Clear or striated
Contains glycoproteins and can be involved in specificity
Mitochondria presynaptic and use ATP for energy
Electrical synapse
Rarer
Close apposition of pre and postsynaptic membranes
No intracellular cleft
Neuroglia cell types
Astrocytes, oligodendrocytes, and microglia
Differ from neurons because unpolarized, proliferate, no synapses and do not transmit action potentials
Astrocytes
Star shaped
Processes extend around neural cell bodies and fibers
Irregular nucleus
Fibrous in white matter and protoplasmic is grey matter
Regulate blood flow, vasodilation and constriction and neurotransmitter action
Form scar tissue
Oligodendrocytes
Myelin in CNS, predominant cell type in white matter
In grey matter are perineuronal satellite cells
Extensive cytoplasmic processes
Chief function= maintenance of myelin sheath around axons, segments of myelin are nodes of ranvier
Internode
Myelin segment between two nodes
Ependyma
Microvilli and cilia form specialized junctions with one another
Vascular regions known as choroid plexus, associated with meninges
Tanycyte
Tanycyte
Cell with basal processes through nervous tissue to blood vessels or Pia
Hypothalamic hormones to pituitary
Microglia
Macrophages of the Brain
First line of defense
From hematopoietic stem cells
Ganglia
PNS neuron cell body aggregates
Dorsal root ganglia
Unipolar, connected to spinal cord by dorsal root which is purely sensory
Motor fibers from ventral root and form peripheral nerves by joining in intervertebral foramen
Schwann cells in PNS
Neural crest derivation
Produce myelin
In CNS oligodendroglial cells will myelinate
Myelinate sensory then as reach CNS oligo myelinates
Endoneurium
Schwann cells here in connective tissue matrix
Wrapped with perineurium which have tight junctions and are wrapped by epineurium which contains fat and blood vessels
Retrograde degeneration
Of cut nerve fibers simultaneously from both ends
Peripheral nerves within 7 days regenerate and grow into scar, Schwann cells remylinate
Regenerative nerve fibers
Can grow into mass if misdirected- neuromas
CNS NEURONS
No neuronal replacement
