Unit 4 Flash Cards
Nervous System
Central Nervous System (CNS)
think brain and spinal cord; integrate and process sensory info and coordinate motor response
Peripheral Nervous System (PNS)
sensory receptors of sense organs, nerves connect nervous system w/other systems, deliver sensory info to the CNS and carry motor commands to peripheral tissues and system
functions of Central Nervous System
integrates, processes, and coordinates sensory data + motor commands; motor commands control or adjust peripheral organs like skeletal muscles
functions of Peripheral Nervous System
sensory receptors again, but you have different branches within the PNS which are Afferent Division, and Efferent Division. Efferent Division has the Autonomic and Somatic Nervous System within it
Afferent Division
Carries info from PNS to CNS
Efferent Division
carries motor commands from CNS to PNS muscle glands and effectors
Autonomic Nervous System (within Efferent and PNS)
controls subconscious actions, contraction of smooth muscle + cardiac muscle, and glandular secretions
sympathetic- “fight or flight”
parasympathetic- “resting and digesting”
Somatic Nervous System (within Efferent and PNS)
controls VOLUNTARY and sometimes involuntary reflexes such as skeletal contractions
Presynaptic Cell
neuron that sends a message via neurtransmitter
Postsynaptic cell
cell that receives the message
Schwann Cells
surrounds axons in the PNS, responsible for their myelination
Satellite cells
(PNS) surround neuron cell bodies, regulate O2 + CO2, nutrient and neurotransmitters levels around ganglia
Ependymal Cells
makes cerebral fluid in CNS
Astrocytes
helps w/Brain blood barrier
Microglia
removes cell debris, wastes, and other pathogens by phagocytosis
Ogliodendrocytes
myelinate CNS axons; provide structural framework
White Matter
regions dominated by myelinated axons of the CNS
Grey Matter
areas containing neuron cell bodies, dendrites, and unmyelinated axons
Three important concepts regarding Membrane Potential
1) extracellular fluid and intracellular fluid differ greatly in ionic composition
2) Cells have selectively permeable membranes
3) Membrane permeability varies by ion
Graded Potentials
1) any stimulus that opens a chemically or mechanically gated channel that allows ions to move across the membrane
2) IF stimulus is strong enough, it can lead to an action potential at the axon hillock, for example neuromuscular junction and postsynaptic potentials are GP
Action Potential
propagated changes in transmembrane potential
Generation of Action Potential
you need an initial stimulus that is caused by a graded depolarization of axion hillock that is big enough (10-15 mV) to change resting membrane potential (-70 mV) to threshold level of voltage gated sodium channels
Each Step of Action Potential
1) Depolarization to Threshold (via graded potential): basically stimulus initiates AP and that opens up the sodium channels
2) Activation of Na+ channels: basically the sodium channels open and the membrane depolarizes/becomes more positive because sodium ions are going INTO the membrane
3) Inactivation of Na+ channels and ACTIVATION of K+ channels: the membrane gets positive enough to the point that the voltage gated sodium channels close and the potassium one opens, releasing K+ out of the membrane and repolarizing it, making it more negative relatively.
4) Return to normal Permeability: potassium channels are slow to close which can lead to hyperpolarization, but basically they start to close at -70mV
Sodium-Potassium Pump role in Action Potential
after sodium has entered the cell and potassium has left the cell, the sodium-potassium pump restores sodium and potassium to their original concentration
more sodium OUTside the cell
more potassium INside the cell
Refractory Period
the time period from the beginning of action potential to the return to resting state where the membrane will not respond to additional stimuli
Absolute Refractory period
sodium channels cannot reopen no matter how strong the stimuli is, no action potential possible
Relative Refractory Period
membrane potential almost normal, very large stimulus can initiate action potential
Conduction Velocity of an AP is based on 2 factors
1) axon diameter: the larger the diameter, the faster it will be
2) degree of mylenation: the more myelin you have, the faster the AP will be
Continuous Propagation
done through UNmyelinated axons
Saltatory Propagation
done through Mylenated axons, much faster than continuous propagation, and it’s where the current jumps from node to node between Schwann cells so PNS
Removal of Neurotransmitters from the Synapse
1) NT is degraded (ACh into acetate and choline)
2) NT diffuses away from synapse
3) NT may be taken back up by the presynaptic neuron
Neurotransmitter
chemical messengers that bind to a receptor either on the presynaptic cell or postsynaptic cell; there are two types either Excitatory or Inhibitory
Excitatory NT
causes depolarization of postsynaptic membranes, promotes action potentials, and stimulates EPSP (excitatory postsynaptic potentials)
Inhibitory NT
causes hyperpolarization or postsynaptic membranes, suppresses AP, stimulates (IPSP) inhibitory postsyaptic potentials
Temporal Summation
multiple times, rapid, repeated stimuli at once
Spatial Summation
multiple locations, many stimuli, arrives at MULTIPLE synapses
Presynaptic Inhibition
decreases the NT released by presynaptic membrane
Presynaptic Factilitation
Increases the NT released by presynaptic membrane
