Ch 11 - Nervous System & Nervous Tissue Fundamentals Flashcards
Functions of the Nervous System
1) Sensory Input
2) Integration
3) Motor output (response)
Cell types in Nervous System
1) Neurons
2) Neuroglia (glial cells)
Types of Neuroglia
1) Astrocytes (CNS)
2) Microglial cells (CNS)
3) Ependymal cells (CNS)
4) Satellite cells (PNS)
5) Oligodendrocytes (CNS)
6) Schwann Cells (PNS)
Star-shaped glial cell that supports and protects neurons in the CNS
Astrocytes
functions:
A) Provide nutrient supply for neuron cells
B) Allows migration of young neurons
C) “Clean up” outside neuron cells (leaked K+ ions, neurotransmitters, etc)
Glial cell that monitors the health of neuron cells, and phagocytizes them when theyre unhealthy.
Microglial cells (CNS)
Glial cell that lines central cavities of the CNS to circulate CSF within
Ependymal cells (CNS)
Glial cells that support and protect neuron cells in PNS only
Satellite cells (PNS)
Glial cells that wrap around nerve fibers in CNS creating an insulating covering called the myelin sheath
Oligodendrocytes (CNS)
Glial cell that wraps around nerve fibers in PNS that creates an insulating covering called the myelin sheath
Schwan Cells (PNS)
Cluster of cell bodies in CNS
Nuclei
Cluster of cell bodies in PNS
Ganglia
Bundles of axons in CNS
Tracts
Bundles of axons in PNS
Nerves
Functional classifications of neurons
Functional classification groups neurons according to direction in which nerve impulses travel relative to the CNS
1) Sensory (afferent) neuron - transmits signals from body towards CNS
2) Motor (efferent) neuron - transmits response from CNS to body
3) Interneuron - pass signals throigh CNS pathways, where integration occurs
Resting Membrane Potential
-70 mV
Selective Transport Protiens (involved in changing membrane potential)
1) Leakage (non-gated) chanels - always open
2) Chemically gated - protien opens due to binding of a specific chemical (neurotransmitter, etc)
3) Voltage-gated - open/close in response to changing membrane potentials
4) Mechanically gated - open in response to physical deformation
Change in Membrane Potential Voltage due to the opening of ion channels can result in:
1) Depolarization - Excitation of a neuron, more likely to reach threshold (less negative)
2) Hyperpolarization - Inhibition of a neuron, less likely to reach threshold (more negative)
What is needed to reach an action potential
Cumulative sum of graded potentials (EPSPs and IPSPs) reach a threshold voltage of -55 mV. At this point, depolarization becomes self-generating (voltage-gated channels open, flooding cell with Na+)
2 gates of Na+ channel
1) Activation gate: voltage-sensitive, opens at depolarization
2) Inactivation gate: blocks channel to prevent Na+ movement
Process of Generating Action Potential
1) Rest - all voltage-gated channels are closed at the resting state (-70 mV)
2) Depolarization - voltage-gated Na+ channels open at the axon (reach threshold of -55 mV, go all the way to +30 mV at peak)
3) Repolarization - action potential “ends,” Na+ gates close, voltage-gated K+ channels open
4) Hyperpolarization - excess K+ leaves cell, then Na+-K+ pump re-establishes normal concentrations outside and inside the cell - brings membrane potential back to -70 mV
1) During Rest, all leakage channels are still open!!!
3) Repolarization - K+ leaves the cell, restoring internal negative charge, Na+ does not move
How does the nervous system differentiate between strong/weak stimulus
Frequency!!
* Strong stimuli: impulses are sent more frequently
* Weak stimuli: impulses sent less frequently
Types of Refractory Periods:
1) Absolute Refractory Period - When Na+ gated channels open though to when Na+ channels reset
2) Relative Refractory Period - Due to hyperpolarization, weak stimuli cannot stimulate an AP, but strong stimuli can
Importance of the Absolute Refractory Period
1) Ensures each AP is a separate, all-or-none event
2) Enforces one-way transmission of the AP
Variables for Neuron Conduction Speed
1) Axon diameter: larger axon = faster conduction
2) Degree of myelination: more myelination = faster conduction
Types of Conduction
1) Continuous conduction: propagation in unmyelinated fibers - voltage-gated ion channels are adjacent
2) Saltatory conduction: propagation in myelinated fibers - voltage-gated ion channels found only in myelin sheath gaps (leaps from node of ranvier to node of ranvier)
Process of transmitting signas from one neuron to another:
1) AP arrives at axon terminal of presynaptic neuron
2) Voltage-gated Ca2+ channels in axon terminal open in response to AP
3) Synaptic vesicles in axon terminal fuse with membrane in response to Ca2+ influx - vesicles contain neurotransmitters
4) Neurotransmitter crosses cleft, binds to proteins on postsynaptic neuron
5) Neurotransmitter binds receptors on the postsynaptic neuron membrane - binds to receptor, causing ion channels to open, generating a graded potential
6) Neurotransmitter in synaptic cleft is disposed of - either by 1) reuptake, 2) degredation, or 3) diffusion
How are neurotransmitters disposed of in Synaptic Cleft
1) Reuptake of neurotransmitter by an astrocyte or by the pre-synaptic neuron
2) Degredation of neurotransmitter by an enzyme
3) Diffusion of neurotransmitter out of the synapse
Variables that affect graded potential strength
1) Amount of neurotransmitter released
2) How long neurotransmitter stays in the synaptic cleft
3) Whether the binding causes excitatory or inhibitory effects
Types of EPSP summation
1) Temporal summation - postsynaptic neuron receives multiple EPSPs in rapid-fire order
2) Spatial summation - postsynaptic neuron receives multiple EPSPs at the same time (summated simultaneously)
A single EPSP cannot induce an AP alone, must summate
How many neurotransmitters do each neuron produce/release
Produce: at least 2
Release: one, some may release more at a time
Types of Neurotransmitter Receptors
1) Channel-linked receptors - fast synaptic teansmission (receptors are ligand-gated ion channels)
2) G-Protein Coupled Receptors - indirect and prolonged response
G-Protein Coupled Receptor Mechanism:
1) Neurotransmitter binds to receptor
2) G-Protein is activated inside neuron
3) G-Protein activates adenylate cyclase
4) Adenylate cyclase produces cyclic AMP (cAMP)
5) cAMP released into cell, produces outcome
Actions of cAMP
1) Change membrane permeability by opening or closing ion channels in membrane
2) Activate specific genes in the cell nucleus - cell can produce more or less proteins, overall a metabolic change
3) Activate kinase enzyme - kinase begins to catalyze reactions - overall a metabolic change as well
