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95 Terms
1
Neuron
Transmit and translate electrical impulses into chemical signals.
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2
Which type of cell does not have a nucleus?
Mature red blood cells
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What is the structure and function?
Cell Body / Soma
Where the nucleus is located.
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4
What is the structure and function?
Axon Hillock
Integrates incoming signals and plays an important role in action potentials.
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5
What is the structure and function?
Dendrites
Receive messages from other cells.
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6
What is the structure and function?
Schwann Cells
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7
What is the structure and function?
Nodes of Ranvier
Small breaks in the myelin sheath with exposed areas of axon membrane. Critical for rapid signal conduction.
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8
What is the structure and function?
Myelin Sheath
Maintains the electrical signal within one neuron.
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9
What is the structure and function?
Axon
Terminates in close proximity to a target structure.
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10
What is the structure and function?
Nerve / Axon Terminals (aka. Synaptic Bouton / Knob)
Enlarged and flattened to maximize transmission of the signal to the next neuron and ensure proper release of neurotransmitters.
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What produces myelin (around axons)?
Oligodendrocytes (CNS)
Schwann Cells (PNS)
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Soma / Cell Body is also the location of…
The endoplasmic reticulum and ribosomes.
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13
Action Potential
Transmission of electrical impulses down the axon.
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Myelin
A fatty membrane that insulates (most) mammalian nerve fibers to prevent signal loss or crossing of signals.
Increases speed of conduction in the axon.
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Neurotransmitters
The chemicals that transmit information between neurons.
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Synaptic Cleft
Space into which the terminal portion of the axon releases neurotransmitters that bind to the dendrites of the adjacent neuron (postsynaptic neuron)
Neurons are not physically connected to each other.
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Synapse
Made up of:
Nerve terminal, synaptic cleft, postsynaptic membrane
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Nerve
Multiple neurons bundled together in the PNS.
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Types of nerves…
Motor
Sensory
Mixed
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Mixed Neurons
Carry both sensory and motor information.
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Sensory Neurons
Carry sensory information.
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Motor Neurons
Carry motor information.
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Ganglia
Cell bodies of neurons of the same type that are clustered together.
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Tracts
Axons bundled together in the CNS. The cell bodies of neurons in the same ____ are grouped into nuclei.
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Nerves vs. Tracts
Tracts (unlike nerves) only carry one type of information.
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Axons carry neural signals ____ the soma
Away from
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27
Dendrites carry neural signals ____ the soma
Toward
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28
Glial Cells / Neuroglia
Neurons need to be supported and myelinated by other cells for both structural and supportive roles.
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Astrocytes
Nourish neurons and form the blood-brain barrier, which controls the transmission of solutes from the bloodstream into nervous tissue.
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Ependymal Cells
Line the ventricles of the brain and produce cerebrospinal fluid, which physically supports the brain and serves as a shock absorber.
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Microglia
Phagocytic cells that ingest and break down waste products and pathogens in the CNS.
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Action Potential
All or nothing messages that relay electrical impulses down the axon to the synaptic bouton. Ultimately cause the release of neurotransmitters into the synaptic cleft.
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Resting Membrane Potential
Net electrical potential difference that exists across the cell membrane. It is created by movement of charged molecules across the membrane.
-70 mV (for neurons)
The inside of the neuron is negative relative to the outside.
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(Transmembrane) Potassium Leak Channels
Facilitate the outward movement of potassium.
As potassium leaks out of the cell:
The cell loses a small amount of positive charge —> leaves behind a small negative charge = outside of the cell has slight positive charge.
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Equilibrium Potential of Potassium
Point when there is no more net movement of the ion since the cell is at equilibrium with respect to potassium.
Around -90 mV (negative sign assigned because K+ - pos ion - is leaving the cell.
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36
Sodium’s concentration gradient is ____ of potassium’s
The reverse
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Sodium Leak Channels
Driving force pushing sodium into the cell. The movement is facilitated by these channels.
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Equilibrium Potential of Sodium
Around +60 mV (positive since sodium is moving into cell).
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Resting Membrane Potential
-70 mV, the balance between sodium and potassium’s equilibrium potentials. Closer to potassium’s equilibrium since the cell is much more permeable to potassium.
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40
Why is Na+/K+ ATPase needed?
The continual ion leaking at the membrane means that sodium and potassium ions should be moved back against their gradients so resting potential (-70 mV) can be maintained.
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41
Na+/K+ ATPase
Continually pumps sodium and potassium back to where they started. Potassium into cell and sodium out of the cell (pumpKin)
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42
What types of input can neurons receive?
Excitatory and inhibitory.
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Depolarization
Raising the membrane potential (Vm) from its resting potential (-70 mV). Caused by excitatory input. Makes neuron more likely to fire an action potential.
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Hyperpolarization
Lowering the membrane potential from its resting potential (-70 mV). Caused by inhibitory input. Makes neuron less likely to fire an action potential.
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45
Threshold (Value)
Axon Hillock receives enough excitatory input to be depolarized to range of -55 mV to -40 mV - action potential triggered.
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46
Summation
The additive effect of multiple signals. Includes information from multiple presynaptic neurons (some of which are excitatory and some of which are inhibitory).
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Types of Summation
Temporal
Spatial
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48
Temporal Summation
Multiple signals are integrated during a short period of time. A lot of small excitatory signals fire at (nearly) the same time causing an action potential.
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Spatial Summation
Based on number and location of the incoming signals. A lot of inhibitory signals firing directly on cell body cause more profound hyperpolarization than the depolarization caused by a few excitatory signals fired on the dendrites of a neuron.
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50
Action Potential Time vs. Membrane Potential Graph
Depolarization (Na+ ions in)
Action Potential
Repolarization (K+ ions out)
Hyperpolarization
Resting Membrane Potential
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51
Voltage-Gated Sodium Channels
If the cell is brought to threshold, channels open in the membrane. Open in response to the change in potential of the membrane (depolarization) and allow for the passage of sodium ions.
Vm approaches +35 mV —> Sodium channels inactivated (brought back near resting potential to be deactivated).
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Electrochemical Gradient
Promotes the migration of sodium into the cell (in relation to voltage-gated sodium channels).
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53
The interior of the cell is more ____ than the exterior of the cell (from an electrical standpoint)
Negative
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54
There is a higher concentration of ____ outside the cell than inside (from a chemical standpoint)
Sodium (also favors the movement of sodium inside the cell).
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States of Sodium Channels
Closed
Open
Inactive
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Closed Sodium Channels
Before the cell reaches threshold and after inactivation has been reversed.
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Open Sodium Channels
From threshold to about +35 mV.
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Inactive Sodium Channels
From +35 mV to the resting potential.
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Voltage-Gated Potassium Channels
Open when there is positive potential inside the cell (voltage-gated sodium channels are inactive).
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Repolarization
Restoration of the negative membrane potential as positively charged potassium cations are driven out of the cell.
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Types of Refractory Periods
Absolute Refractory Period
Relative Refractory Period
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Absolute Refractory Period
No amount of stimulation can cause another action potential to occur.
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Relative Refractory Period
Greater than normal stimulation needed to cause action potential since the membrane is starting from a potential that is more negative than its resting value.
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Impulse Propagation
The movement of the action potential down the axon and the subsequent release of neurotransmitters.
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65
What impacts the speed at which action potentials move?
Length of the axon
Cross - sectional area of the axon
Increased length = higher resistance, slower conduction
Increased cross sectional area = decreased resistance, faster propagation.
Cross sectional area has more significant effect than the effect of length.
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Saltatory Conduction
Signal hops from node to node since the myelin sheath is such a good insulator that the membrane is only permeable to ion movement at the nodes of Ranvier.
Saltar = to jump
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Presynaptic Neuron
The neuron preceding the synaptic cleft.
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Postsynaptic Neuron
The neuron after the synaptic cleft.
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Effector
Neuron that signals to a gland or muscle (rather than another neuron). In relation to postsynaptic neurons.
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70
Most synapses are ___ in nature; they use molecules called ___ to send messages from one cell to the next.
chemical; neurotransmitters.
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71
Where are neurotransmitters stored prior to release?
In membrane bound vesicles in the nerve terminal.
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72
What causes the release of the neurotransmitter?
When the action potential reaches the nerve terminal, voltage-gated calcium channels open, allowing calcium in the cell. The increase of calcium triggers the fusion of the membrane-bound vesicles with the cell membrane (at the synapse) resulting in exocytosis.
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73
Ways to Remove Neurotransmitters from Synaptic Cleft…
Breakdown by enzymatic reactions
Reuptake Carriers
Simple diffusion out of synaptic cleft
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74
Example of Neurotransmitter breakdown.
The Breakdown of Acetylcholine (ACh).
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75
Example of Neurotransmitter Reuptake
Reuptake of Serotonin (5-HT) . Dopamine (DA) and Norepinephrine (NE) also use reuptake carriers.
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Example of Neurotransmitter Diffusion
Nitric Oxide (NO) - gaseous signaling molecule.
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77
Nervous System Functions:
Sensation and Perception
Motor Function
Cognition and Problem Solving
Executive Function and Planning
Language Comprehension and Creation
Memory
Emotion and Emotional Expression
Balance and Coordination
Regulation of Endocrine Organs
Regulation of Heart Rate, Breathing Rate, Vascular Resistance, Temperature and Exocrine Glands
Maintaining Homeostasis
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Sensory Neurons (Afferent Neurons)
Transmit sensory information from sensory receptors to the spinal cord and brain.
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Motor Neurons (Efferent Neurons)
Transmit motor information from the brain and spinal cord to muscles and glands.
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80
Interneurons
Found between other neurons. Most numerous of three types. Located (predominantly) in the brain and spinal cord - linked to reflexive behavior.
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Nervous System Organization
Autonomic = automatic
Sympathetic = fight or flight
Parasympathetic = rest and digest
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Central Nervous System (CNS)
Composed of brain and spinal cord. Brain has white matter and gray matter.
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White Matter
Axons encased in myelin sheaths. Deeper in the brain.
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Grey Matter
Unmyelinated cell bodies and dendrites. More superficial in the brain.
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Brainstem
Basic life functions (ie. breathing)
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Regions of the Spinal Cord
Cervical
Thoracic
Lumbar
Sacral
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Peripheral Nervous System (PNS)
Made up of nerve tissue and fibers outside the brain and spinal cord. Includes all 31 pairs of spinal nerves and 10 out of 12 pairs of cranial nerves.
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Somatic Nervous System
Made up of sensory and motor neurons distributed throughout the skin, joints and muscles. Sensory neurons transmit information through afferent fibers. Motor neurons transmit information through efferent fibers.
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Autonomic Nervous System (ANS)
Regulates
Heartbeat
Respiration
Digestion
Glandular Secretions
Body Temperature - sweating or piloerection
Manages involuntary muscles associated with internal organs and glands.
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Parasympathetic Nervous System
Conserve Energy. Associated with resting states and acts to reduce heart rate and constrict the bronchi. Acetylcholine (ACh) is the neurotransmitter responsible for the parasympathetic responses.
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Sympathetic Nervous System
Activated by stress. Fight or flight response.
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Reflex Arcs
Neural circuits that control reflexive behavior.
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Types of Reflexive Arcs
Monosynaptic
Polysynaptic
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94
Monosynaptic Reflex Arc
There is a single synapse between the sensory (afferent) neuron the receives the stimulus and the motor (efferent) neuron that responds to it.
Ex. Knee-jerk reflex
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Polysynaptic Reflex Arc
There is at least one interneuron between the sensory (afferent) neuron the receives the stimulus and the motor (efferent) neuron that responds to it.
Ex. Withdrawal reflex
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