A&P Chp. 11: Fundamentals fo the Nervous System and Nervous Tissue Flashcards
Functions of the Nervous System
Sensory input: from millions of specialized receptors; receive stimuli
Integration: process stimuli; interpret stimuli
Motor output: cause response; at many effector organs
Central Nervous System
The brain and spinal cord
Process and integrate information, store information, determine emotions
Initiate commands for muscle contraction, glandular secretion and hormone release (regulate and maintain homeostasis)
Connected to all other parts of the body by the peripheral nervous system
Peripheral Nervous System
Anatomical connections: spinal nerves are connected to the spinal cord; cranial nerves are connected to the brain
Two Functional subdivisions: Sensory (afferent) divisions and Motor (efferent) divisions
Motor (efferent) divisions
Somatic Nervous System (SNS): voluntary motor neurons
Autonomic Nervous System (ANS): involuntary visceral motor neurons; output to smooth muscle, cardiac muscles and to glands; two cooperative
Sympathetic Division
for muscular exertion and for “fight or flight” emergencies
Parasympathetic Division
for metabolic/ physiologic “business as usual” (“feed” or “breed”)
Astrocytes
Neuroglia in Central Nervous System
star shaped with many processes
connect to neurons; help anchor them to nearby blood capillaries
control the chemical environment of the neurons
Microglia
Neuroglia in Central Nervous System
oval with thorny projections
monitor the health of neurons
if infections occurs, they change into macrophages
Ependymal Cells
Neuroglia in Central Nervous System
barriers between brain tissue of fluid sacs (cerebrospinal fluid)
range in the shape from squamous to columnar: many are cilated
line the dorsal body cavity housing the brain and spinal cord
form a barrier between the neurons and the rest of the body
Oligondendrocytes
Neuroglia in Central Nervous System
have a few processes
line up along neurons and wrap themselves around axons
form the myelin sheath - an insulating membrane
speeds up rate of action potentials
Satellite Cells
Neuroglia in the Peripheral Nervous System
similar to astrocyte
surround neuron cell bodies in the periphery
maintain the extracellular environment
Schwann Cells (neurolemmocytes)
Similar to oligodendrocytes except they can only wrap one axon.
Surround axons/dendrites and form the myelin sheath around larger nerve fibers in the periphery
Insulators
Neurons
highly specialized cells which conduct electrochemical signals (nerve impulses)
Amitotic: cant perform mitosis; once they are gone they’re gone
high metabolic rate
Neuron Cell Body (Soma)
site of most metabolism
Nuclei: clusters of neuron cell bodies in the CNS
Ganglia: clusters of neuron cell bodies in the PNS
Neuron: Dendrites
lead to axon terminal
short, tapering, highly branched processes of the soma
Not myelinated
transmit graded potentials, not action potentials
Neuron: Axon
Transmits action potentials from the soma
Originates from “axon hillock:” where action potential is created in neurons
Axonplasm
Cytoplasm of the axon
Axolemma
The cell membrane of the axon, specialized to initiate and conduct action potentials (nerve impulses)
Myelin Sheath
lipid wrapping of an axon multiple layers of the cell membrane dendrites are never myelinated protects and electrically insulates increases the speed of nerve impulses
Myelinating Cells
Neurolemmocytes (Schwan Cells) in the PNS
Oligodendrocytes in the CNS
Myelination
Myelinating cell wraps around an axon up to 100 times, squeezing its cytoplasm and organelles to the periphery
Myelinated Fibers
Myelin Sheath Neurofibril nodes (Nodes of Ranvier): periodic gaps in the myelin sheath between the neurolemmocytes (Schwann Cells)
Unmyelinated Fibers
surrounded by Schwann cells
May enclose up to 15 axons
Schwann cells do not wrap successfully
Interneurons (Association Neurons)
Carry nerve impulses from one neuron to another allowing for higher decision making
99% of the body’s neurons
Most located in CNS
Voltage
The measure of potential energy generated by separated changes
Current
Movement of an ion
flow of charged particles from point to another
due to the movement of charged ions: concentration gradient
Resistance
Prevents the flow of charged particles (ions)
property of the structure through which the ions flow (cell membrane)
Resting Membrane Potential
Plasma membrane has limited permeability to Na+ and K+ ions
Ion concentrations on either side of the plasma membrane are due to the action of the Na+/K+ ATPase pumps
Graded Potentials
Stimulus strength determines size of the potential
As they move along the cell membrane they get smaller and smaller (propagated with decrement)
ACh receptor causes graded potential at motor end plate
Depolarzing: make the inside less negative; decrease membrane polarity
Hyperpolarizing: make the inside more negative; increase membrane polarity
Electrotonic propagation
charges move down the membrane
Action Potentials
In response to graded potentials of significant strength
Signal over long distances
All or nothing
when graded potentials are transmitted to the axon hillock
If stimuli reach a threshold level, voltage gated Na+ channels open generating an action potential
Sequence of Events in Action Potentials
- Depolarizaiton: graded potential depolarizes the axon hillock to the threshold; v-gated Na+ channels open and Na+ moves into the cell while more V-gated Na+ channels open (positive feedback)
- Repolarization: Inactivation gates of V-gated Na+ channels close and V-gated K+ channels open
- Hyperpolarization: Inactivation and activation gates are reset on Na+ channels; cell hyperpolarizes until K+ channels close, causing the relative refractory period.
Absolute Refractory Period
Time period during which second action potential cannot be initiated
due to closure of inactivation gate on V-gated Na+ channel
Due to closure of inactivation gate on V-gated Na+ channel
Prevents action potential from going backward
Refractory = does not respond
Relative Refractory Period
Time period during which a second action potential cannot be initiated with a suprathreshold (goes above the necessary stimulus threshold) stimulus
K+ channels are open, Na+ channels are reset
the membrane remains hyperpolarized
Contiguous Propagation of Action Potentials
Movement of an action potential down a non-myelinated axon
influx of sodium ions
depolarizes nearby membrane: opening V-gated Na+ channels
Saltatory Conduction
Energy efficient: membrane only has to depolarize and repolarize at the nodes
“jumping” depolarization
Not a continuous process of region to region depolarization
myelinated axons transmit an action potential differently
Conduction Velocity
Heat increases conduction velocity
Cold decreases conduction velocity
Two structural ways to increase impulse velocity
Increase axon diameter: decreases resistance
Insulate the axon: myelin sheath
Electrical Synapse
Gap Junction: found in cardiac muscle and in some smooth muscle tissues
Direct, rapid electrochemical connections between neurons
mostly in infants
Chemical Synapse
Specialized for synthesis, release, reception, and removal of neurotransmitters
Chemical Presynaptic Events
An action potential reaches the axon terminal and depolarizes the terminal.
Exocytosis
Neurotransmitter diffuses across the cleft
Chemical Postsynaptic Events
Neurotransmitter diffuses across the cleft
Neurotransmitter binds to a receptor
Ion channels open as a result: metabotropic (receptor is activated to separately open anion channels) or ionotropic (receptor is ion channel like ACh receptor)
Neurotransmitters are removed quickly
EPSP
Excitatory Postsynaptic Potential
Provides a small local depolarization
IPSP
Inhibitory Postsynaptic Potential
Provides a small local hyperpolarization
Summation of Postsynaptic Potentials
Temporal: rapid repeated stimulation from 1 or more presynaptic neurons
Spatial: simulataneous stimulation at 2 or more different places on the neuron by presynaptic neurons
EPSPs and IPSPs counteract each other
