12 Nervous System Flashcards
What are the functions of the nervous system?
-collect information (internal/external receptors respond to stimuli)
-process and evaluate informations (brain and spinal cord determine response)
-initiate response to information (relayed along neurons to effectors)
What are the five characteristics of neurons?
-exitability-responsiveness to a stimulus
-conductivity-electrical charges propagate along membrane
-secretion-release neurotransmitters
-extreme longevity-most formed before birth and function in advanced age
-amitotic-can’t form new cells by cell division, except olfactory epithelium and ocassionally hippocampus
Multipolar neuron
most common, many dendrites and one axon, all motor neurons, many interneurons
Bipolar neuron
Two processes extend directly from the cell body, one dendrite and one axon, limited locations, some special sense neurons
Unipolar neuron
single short process extends directly from the cell and looks like a T, most sensory neurons
Interneuron
AKA association neuron
lie entirely within the CNS
facilitate communication between sensory and motor neurons
99% of our neurons are interneurons
either multipolar (mostly) or anaxonic (dendrites no axons) neurons
What is the structure of a nerve?
Epineurion (thick layer dense irregular CT for pretection/support)
-holds bundles of fascicles together
Perineurion (dense irregular CT for protection/support)
-wraps around bundles of axons creating fascicles, supports blood vessels
Endoneurion (areolar CT)
-surrounds/insulates each axon
What are the 4 types of glial cells found in the CNS?
astrocytes - most abundant
ependymal - ciliated simple cuboidal or columnar epithelium with slender branching processes that contact other glial cells
microglial - small cells with slender branches, smallest percent of glial cells, phagocytic
oligodendrocytes - large cells with bulbous body and slender cytoplasmic extensions wrap around and insulate axons within the CNS to form the myelin sheath (one cell wraps around multiple axons)
What are the functions of astrocytes?
1) BBB where perivascular feet wrap around capillaries
2)regulate tissue/interstitial fluid composition by controlling movement of substances b/n blood and interstitial fluid
3)assist neuronal development in fetal brain by secreting chemicals that regulate the formation of connections between neurons
4) occupy the space of dying neurons
5) structural support via cytoskeleton
6)alter synaptic activity by adding and eliminating synapses and influencing communication at existing synapses
What are the two types of glial cells found in the PNS?
-satellite cells - flattened cells arranged around neuronal cell bodies in a ganglion, physically separate cell bodies from surrounding fluid, regulate the exchange of nutrients and waste.
-neurolemmocytes (schwann cells) - elongated flattened cells wrap aroudn and insulate axons to form the myelin sheath
What are the functional segments of a neuron and what type of channels/pumps are found in each?
What are the important points about graded potentials?
-occur in the receptive segment
-the degree of change in the RMP that is caused by a graded potential is dependent upon the amount of neurotransmitter bound/time
-can be weak or strong but relatively short live
-gets weaker with distance and time (temporal summation and spatial summation in initial segment to create AP)
-multidirectional
-can be either excitatory EPSP (Na+ in, depolarization) or inhibitory IPSP (Cl- in or K+ out, hyperpolarization)
Explain an action potential
-if enough Na+ flows from adjacent regions into the initial segment to reach the threshold and change the membrane potential from -70mV to -55mV then voltage gated Na+ channels open
-depolarization occurs (Na+ flows into the cell) and the membrane potential changes from -55mV to +30mV
-repolarization occurs when the sequential opening of voltage gated K+ channels allow K+ out of the cell, returning the membrane potential to -70mV
-hyperpolarization (-80mV) occurs when the K+ channels are open slightly longer than needed to establish the RMP
-RMP is reestablished by leak channels and Na/K pumps
Describe refractory periods
-only allows the signal to move away from the cell body
-absolute refractory period - (~1ms) not stimulus can initiate an AP because Na+ channels are open and then inactivated
-relative refractory period - another AP is possible because Na+ channels have reset but the minimum stimulus strength is now greater because the cell is hyperpolarized
What are the 3 ways neurotransmitters can be removed from the synaptic cleft?
degradation
reuptake
diffusion
Compare Graded Potential versus Action Potential
