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54 Cards in this Set

  • Front
  • Back
Cell body
metabolic center of cell
Info conveyed by AP
determined by pathway signal travels in brain
Predominate neurons in NS vertebrates
Simplest neurons
unipolar: have single primary process giving rise to many branches
Predominate neurons in invertebrates NS
Unipolar (in autonomic NS in verbtebrates)
Pseudo-unipolar cells
receptor neurons convey touch, pressure, pain signals to spinal cord
wrap axons of neurons in CNS
Schwann cells
Wrap axons of neurons in PNS
Star shaped, large end feet, provide nourishment, insulation, regulate K+
the neuron doctrine
the NS is composed of cells
Jan Evangelista Purkyne
first to represent cells in the brain
Deiter's (1865)
First observed neurons after dissection (spinal cord)
Staining techniques
Developed in 1860s; revealed tangle dendrites & axons of neurons but most anatomists in 60-90s thought NS was reticulum (fused cells)
Camilio Golgi 1843-1926
Method revolutionized neuroanatomy: growth of silver chromate crystals within 2 neurons
Cajal's evidence for contact but not connection
basket cells in a kitten cerebellum, purkinje cells: made use of Camillo Golgi's silver dichromate staining technique in 1887: reazione nera (black rxn) stained 1% of neurons completely black while 99% left unstained: neurons completely separated from one another & did not fuse
Corollaries of neuron doctrine
Neuron is basic unit of the nervous system, each w independent anatomy, development & biochemistry, is independent unit of metabolism, dynamically polarized, independent units of development, independent units of information processing
Dynamic polarization (1 way flow of info or signal)
In retina, signals which originate in the pigmented receptor cells always progress from dendrites - cell body - axon - terminals
Which part of the neuron is responsible for dynamic polarization?
Ramon y Cajal 1909 & 1911
Neurons in the cortex are units of information processing: AP & centralization reduces cost of cytoplasm
Electrical properties of neurons
Ion channels generate local electric signals on cell membrane
Propagated AP required
Voltage-activated ion channels
Evolution of voltage-gated channels
Came mostly from potassium channels
Release & receptor (diverse): electrical or chemical
Sir Charles Scott Sherrington (1859-1952)
Nobel in Med w Edgar Adrian for reflexes in spinal cord as way of understanding function of neural circuits, coined term "synapses"
Law of reciprocal innervation
For every excitatory connection to a muscle, there is a corresponding inhibitory connection to an opposing muscle
Cutaneous receptor stimulates leg flexes to withdraw, cutaneous afferent fiber from nociceptor to motor neuron to extensor muscle, opposite leg extends to support
Neurons are found in
all animals except sponges (porifera)
Polyp NS
Ectoderm, Gastroderm, mesoglea, gastrovascular cavity, tentacle, spermary with sperm, ovary with ovum, hydra bud
Nerve nets
Hydra and jellyfish (cnidaria)
platyhelminthes: nerve cords, primitive brain vs. bilateral nerve cords
Possible origin of NS-related genes, possible neurotransmission-related genes constituted the major category
540 MYA
Emergence of CNS: basis genes (neurotransmission, neural network, morphogenesis/differentiation, sensory system) -> divergence by gene loss, gene recruitment, gene duplication, horizontal gene transfer, mutation
Central Nervous system
Specific genes in each species: deuterostomia, ecdysozoa, lophotorochozoa
multidisciplinary effort to understand how NS controls behavior: how we & other animals perceive, act, learn, remember
Nervous system complexity
Human NS has 100 bill neurons or nerve cells & thousands diff types neurons, 140 trillion synapses, many modified & regulated so function in multiple diff ways, unknown # neural circuits
Scientific method used to study brain & behavior
Empirical data collected by observations & measurement, hypotheses formulated on basis of reasonable interpretation of the data, hypotheses tested by experimentation & further observation
Electrically excitable cells w highly varied elongated processes suitable for transmitting elec signals rapidly to other cells @ distance, responsive to elec & ligand-depend inputs from environment/other cells, recognized by elongate branching extensions from cell body
Elec signals travel @ great speed in neurons
Permitted our metazoan ancestors to get larger & larger but still move & respond quickly
Glial cells
Surround & support neurons but not directly involved in elec signalling. Provide: insulation, clean up after injury, guidance during development, regulation extracell chem, & formation blood/brain barrier
1954 using electron microscopes
Cell biologists confirmed that neurons were not fused & synapses mere contacts, not connections
The neuron is the basic unit of anatomy, development & biochem: with neuron doctrine anatomists could
define the NS in terms of types of cells rather than neural net postulated by reticularists
Neuron is the unit of metabolism
Like all cells, neurons control own biosynth & metabolic breakdown, reg gene expression, growth, transport intracell materials, transmembrane trafficking metabolites & other substances, initiating change in response to external cmpds & conditions: nucleus synth enzymes that control metab processes including uptake energy cmpds related to physiological activity of cell
Wallerian degeneration
Severing an axon leads to death of terminals
Nerve cell specialized intracell transport mech
Provide nutrients & metabolites to distal parts of axons
Support for dynamic polarization
Anatomical studies of retina & physiological studies of spinal cord by Sherrington (synapse is responsible)
Neurons are units of development
Neurons cannot divide because of shape but because they form connections w specific & distant targets, must first divide then differentiate & have a means for axon guidance to targets
Neurons are units of info processing
Communicate w other nerve cells via propagated AP
allowed researchers to make intracell recordings of APs: knowledge of complex neural circuits has to be built up from studies of individual cells & microelectrodes allow recording of spikes, synap potent, quantized synap events, & activity of ion channels
Ion channels arose
Early in evolution of life on earth (in bacteria) where used for regulating internal ion conc & pH
First synapse to arise in evolution likely
Electrical synapse: formed by connexins forming pore-like connections from one cell to another: cytoplasms fuse & charged ions (elec currents) & some small mlcs pass thru junctions in both directions
Chem synapses
one-way transmission - prob evolved in animals by first co-opting existing membrane bound receptors used for sensing small mlcs such as amino acids like glutamate
DNA sequence analysis of glutamate receptors
basic chem receptor in place in eukaryotes well before divergence of plants & animals - binding domain traces ancestry as far back as bacteria
Once glutamate receptor was established
animals evolved mechanisms to release near other cells carrying receptor & chem synapse became functional
Genes for receptor proteins were then duplicated & mutated to create families of similar receptors
Some chem synapses allowed pos ions to enter while others neg ions, causing synaptic inhibition - thru nat selection functional synapses applied to genetic specification of neural circuits