Unit 2 Flashcards
CNS
Central nervous system. Made up of the brain and spinal cord.
Neurons
Generate and transmit electrical impulses often over long distances.
Neurotransmitter
Chemical messengers released by neurons.
Dendrites
Slender processes that receive information (transmit electrical signals towards the soma).
Axon Terminals
The end of the axon (the connection between the neuron and other cells). Participate as part of the synapse (presynaptic).
Myelin
Layers of membrane around the axon that acts as an electrical insulator.
Node of Ranvier
Located between myelinated axons (the unmyelinated portion that can conduct an action potiental).
Efferent Neurons
Motor neurons. Receive information from the interneurons. The efferent neuron cell bodies are located within CNS. Cytoplasmic extensions transmit information to effectors.
Synapse
The gap between neurons.
Postsynaptic Neuron
The neuron that receives the signal.
Microglia
Small specialized immune cells (macrophage-like). Their function is to remove damaged cells and foreign invaders. They stop damage from spreading in the CNS but result in scar tissue.
Depolarization
A decrease in the membrane potential difference (cell membrane potential becomes less negative).
Repolarization
An increase in the membrane potential difference (cell membrane potential becomes more negative).
Graded Potentials
Short distance signals (those that travel short distances). Can be depolarizations or hyperpolarizations. Triggered by the opening or closing of ion channels (the number of channels opened increase the magnitude of the response). The amplitude of the potential is proportional to the strength of the triggering event.
All-or-None
A way to describe action potentials. They are all identical and do not diminish in strength as they travel long distances. Occur once the membrane potential hits -55 mV at the trigger zone.
Absolute Refractory Period
At the beginning of the refractory period. Lasts approximately 1 millisecond. Na+ channels are closed by inactivation gate. No action potentials can be triggered at all no matter how large the stimulus.
Saltatory Conduction
Conduction that occurs in myelinated axons.
Synaptic Vesicle
Contains the neurotransmitter.
Spatial Summation
Graded potentials are reliant over space/distance.
Norepinephrine (NE)
Released by most post-ganglionic sympathetic neurons onto adrenergic receptors.
Epinephrine
A neurotransmitter released by chromaffin cells.
Muscarinic Cholinergic Receptor
Coupled to G proteins which may close or open different ion channels (slower response). May be excitatory OR inhibitory. ACh is the primary ligand while muscarine is the agonist.
PNS
Peripheral nervous system. Part of the nervous system outside of the brain and spinal cord. Consists of sensory (afferent) and motor (efferent) neurons.
Glial Cells
Are associated with neurons. Do not carry electrical signals (information) over long distances but they do communicate with each other and with nearby neurons using electrical and chemical signals.
Cell Body/Soma
Contains the nucleus and all biosynthetic machinery. Is the center of the chemical processes (keeps cell functioning and alive).
Axon
Cytoplasmic extension that sends out information (transmit electrical signals away from the soma).
Initial Segment/Trigger Zone
Where the action potential begins. Must reach -55 mV.
Schwann Cells
Special glial cells that are wrapped around axons in the PNS. One Schwann cell creates one sheet of myelin.
Afferent Neurons
Sensory neurons. Receive information from the receptor cells (peripheral/outside). They transmit sensory information to the CNS. Cell bodies are located outside the CNS. Long cytoplasmic extensions transmit information to cells (interneurons) within the CNS.
Receptor
Where the signal binds.
Presynaptic Neuron
The neuron that releases the signal.
Astroglia/Astrocytes
Are small star shaped cells that contact blood vessels and neurons. They maintain neuron microenvironment which helps maintain homestasis in the extracellular fluid around neurons (regulates what’s in the extracellular fluid).
Oligodendria/Oligodendrocytes
Are the CNS version of the Schwann cell (forms the myelin). Can wrap around multiple axons. Have gap junctions.
Ependymal Cells
Part of the blood-brain barrier. They produce cerebral spinal fluid (CSF). They create selectively permeable barriers between compartments of the brain. Are stem cells.
Hyperpolarization
An increase in the membrane potential difference (cell membrane potential becomes more negative).
Action Potentials
Long distance signals (those that travel long distances).
Threshold Potential
The minimum depolarization necessary to trigger an action potential (-55 mV).
Relative Refractory Period
The second half of the refractory period. A large suprathreshold stimulus is required to bring forth an action potential during this phase.
Temporal Summation
Graded potentials are reliant over time/frequency.
Adrenergic Receptor
Two classes (α and β). Are coupled to G proteins. Are used for norepinephrine.
Nicotinic Cholinergic Receptor
Receptor operated channels that allows Na+ to enter the cell (faster response). Is always excitatory. ACh is the primary ligand while nicotine is the agonist.
Receptor Types
1) Adrenergic Receptors
—> α1 Receptors
—> β1 Receptors
—> β2 Receptors
2) Cholinergic Receptors
—> Nicotinic Receptors
—> Muscarinic Receptors
Ion Receptors
Ligand-gated channels.
GPCR Receptors
G-Protein Coupled Receptors.
Electrical Gradient
A difference in charge.
Chemical Gradient
A difference in concentration.
Electrochemical Gradient
A difference in charge and concentration.
Resting Membrane Potential
The charge difference between the inside and outside of a cell at rest. For a typical neuron, the resting membrane potential is -70 mV.
Nernst Equation
Looks at what the membrane potential would be if the membrane was permeable to only one ion.
Goldman-Hodgkin-Katz (GHK) Equation
An equation that predicts membrane potential using multiple ions.
Gated Ion Channels
Regulate the movement of ions.
Positive Feedback in Action Potential
The opening of voltage-gated sodium channels.
Refractory Period
When an action potential either can’t occur or needs a really strong stimulus to occur (a state of recovery).
Neurotransmitters in the PNS
1) Acetylcholine (ACh)
2) Norepinephrine
3) Epinephrine
The Nervous System
1) Receives Information (using sensory neurons (receptors) to receive from external environment).
2) Integrates Information (organizes the information and brings it together with already stored information).
3) Transduces Information (sends appropriate signals to the appropriate target (mostly muscles or glands)).
Types of Cells in the Nervous System
1) Neurons
2) Glial Cells
Parts of a Neuron
1) Soma/Cell Body
2) Dendrites
3) Axon
4) Axon Terminals
Nuclei
A cluster of cell bodies in the CNS.
Ganglia
A cluster of cell bodies in the PNS.
Tracts
Bundles of axons in the CNS forming a pathway.
Nerves
Bundles of axons in the PNS forming a pathway (only neurons found in the PNS can be called nerves).
Pseudounipolar
Somatic sensory neurons/afferent neurons (the axon and dendrites are connected in a chain with the soma/cell body branching out of the middle of the axon).
Bipolar
Smell/vision sensory neurons/afferent neurons (contain a single axon and dendrite with the cell body/soma in the middle of the axon). In neuron development, bipolar neurons become pseudounipolar neurons.
Multipolar
CNS and efferent neurons. Standard neuron structure (one axon and two or more dendrites).
Interneurons
Neurons located inside the CNS. Makes up 96% of all neurons. Transmit information signals within CNS either laterally within the spinal cord or vertically to the brain. Integrates information received from afferent neurons and previous information and transmit signals to efferent neurons.
Effectors
Carry out the message ex. muscles, glands, and etc.
How Glial Contribute to the Function of Neurons
1) Aid in nerve impulse conduction.
2) Maintain the microenvironment around neurons.
Satellite Cells
Non-myelinating Schwann cells that support nerve cell bodies (soma).
Nervous System Breakdown
Nervous System
1) CNS
—> Brain
—> Spinal Cord
1) PNS
—> Sensory
—> Motor
2) Motor
—> Somatic
—> Autonomic
3) Autonomic
—> Sympathetic
—> Parasympathetic
Sympathetic Nervous System
Controls the fight or flight response.
Parasympathetic Nervous System
Controls the rest and digest response.
Cell Membrane
An electrical insulator (allows for the separation of electrical charge).
ICF
Intracellular fluid. Has a net negative charge.
ECF
Extracellular fluid. Has a net positive charge.
Ion Channels
Allow electrical charge to move through the membrane.
Membrane Potential
The difference of the electrical potential between the inside and outside of the cell. Measured in millivolts (mV). All cells have membrane potential but not all cells are excitable (only nervous and muscle).
Excitable Tissues
Nervous and muscle tissues. Use rapid changes of membrane potential when they are excited which allows neurons to conduct an electrical signal and muscle cells to contract.
Anions
Large, negatively charged intercellular proteins that are highest concentration in the ICF. Due to their size, anions do not move across the membrane.
Na+/K+ Pump
Maintains concentration differences of Na+ and K+ (uses ATP for energy to drive ions against the gradient).
Ion With the Most Leaky Channels
K+. It is easier for K+ to move passively due to the large number of passive channels for K+ compared to Na+ (makes the cell more negative, important for neurons).
Equilibrium Potential (Eion)
The membrane potential that exactly opposes the concentration gradient of an ion. This is where the electrical and chemical forces acting on the ion are equal and opposite ex. Na+ wants to go into the cell due to the concentration gradient but it also wants to go out of the cell due to electrochemical gradient (cell is now positive from Na+ going into the cell).
Equilibrium Potential (K+)
-90 mV. The flow of K+ at equilibrium makes the cell negative.
Equilibrium Potential (Na+)
+60 mV. The flow of Na+ at equilibrium makes the cell positive.
Types of Gated Ion Channels
1) Mechanically Gated
2) Ligand-Gated
3) Voltage-Gated
Mechanically Gated
Found in sensory neurons (afferent neurons). They open in response to physical forces ex. stretch.
Ligand-Gated
Respond to ligands such as neurotransmitters.
Voltage-Gated
Respond to changes of voltage. Important in initiation and conduction of electrical signals along the axon.
4 Major Types of Selective Ion Channels in Neurons
1) Na+ Channels (Na+ Entry - Depolarizing)
2) K+ Channels (K+ Exit - Hyperpolarizing)
3) Ca^2+ Channels (Ca^2+ Entry - Depolarizing)
4) Cl- Channels (Cl- Entry - Hyperpolarizing)
Afferent Pathway
Input/afferent signal.
Efferent Pathway
Output/efferent signal.
Autonomic Nervous System
Controls involuntary movement. Consists of a 2 neuron chain. It goes to smooth muscle, cardiac muscle, glands, and some adipose tissue.
Somatic Nervous System
Controls voluntary movement via the skeletal muscles. Consists of a single neuron chain. Causes only muscle excitation. Cannot inhibit muscle function.
Events After Neurotransmitter Binding
1) Ion channels open.
2) Ions move into or out of the neuron along their electrochemical gradient.
3) A wave of depolarization or hyperpolarization spreads through the cell.
Excitatory Post Synaptic Potentials (EPSPs)
Depolarizing graded potentials that increase the chance of exciting the axon to fire thus they can bring the cell closer to firing an action potential (cause an action potential).
Inhibitory Post Synaptic Potentials (IPSPs)
Hyperpolarizing graded potentials that decrease the chance of exciting the axon to fire thus they inhibit the cell to fire an action potential (prevent an action potential).
Phases of an Action Potential
1) Resting membrane potential (-70 mV).
2) Depolarizing stimulus.
3) Membrane potential reaches threshold (-55 mV). Voltage-gated Na+ channels open immediately while voltage-gated K+ channels open much more slowly.
4) Depolarization occurs (-55 mV to +30 mV).
5) Peak in action potential (+30 mV). Na+ channels close and K+ channels fully open.
6) Repolarization occurs (+30 to -70 mV).
7) Hyperpolarization occurs (-70 mV to -80 mV).
8) Voltage-gated K+ channels close.
9) Membrane potential returns to resting membrane potential (-70 mV) via leak channels.
Activation Gate (Voltage-Gated Na+ Channel)
Opens and closes to allow Na+ to follow into the cell.
Inactivation Gate
Only on voltage-gated Na+ channels. Blocks the channel by a ball and chain structure to prevent Na+ to follow into the cell. It stops the positive feedback loop initiated by the cascade of opening voltage-gated Na+ channels due to the activation gates opening in response to the increasing membrane potential.
Refractory Period Phases
1) Absolute Refractory Period
2) Relative Refractory Period
Suprathreshold Stimulus
A very large stimulus.
Factors That Effect the Speed of an Action Potential Along a Neuron
1) Diameter of the axon (larger diameter leads to faster action potential).
2) Resistance of the axon membrane to ion leakage out of the cell (insulating the axon reduces that amount of ion flow out of the cell since the signal only occurs in certain areas and doesn’t have to travel the full length of the axon).
Parts of a Synapse
1) Presynaptic Cell
2) Synaptic Cleft
3) Postsynaptic Cell
Presynaptic Cell
The axon terminal.
Synaptic Cleft
The space between cells (ECF).
Postsynaptic Cell
The membrane.
Electrical Synapses
Gap junctions that allow direct electrical signalling between cells (information can flow in both directions). These synapses are uncommon and occur mainly in the CNS. They exist between neurons and between neurons and glial cells. They are important in nervous system development and transmission in adult brain.
Chemical Synapses
The vast majority of synapses. Information from one cell is carried to the next cell by a neurotransmitter. Peripheral neurons use chemical synapses. They exist between neurons or between a neuron and an effector.
Neuroeffector Junction
A chemical synapse between a neuron and an effector (involves a varicosity).
Neuromuscular Junction
The synapse between a somatic motor neuron and a skeletal muscle fiber. There is a sheath of Schwann cells around the terminal boutons at the synapse. There are nicotinic ACh receptor channels on the muscle that are non-selective channels where Na+ goes in and K+ leaves but more Na+ enters than K+ exits.
Voltage-Gated Ca^2+ Channels
Triggers the release of neurotransmitters.
The Events at the Synapse
1) The action potential travels down the axon and depolarizes the axon terminal in the presynaptic cell.
2) Depolarization wave triggers the opening of voltage-gated Ca^2+ channels in the presynaptic cell membrane.
3) Calcium entry signals the synaptic vessels in the presynaptic cell to release the neurotransmitter.
4) The neurotransmitter then diffuses across the synaptic cleft and binds with specific receptors on the postsynaptic cell membrane.
5) Binding of the neurotransmitter initiates a response in the postsynaptic cell (a graded potential).
Direct Response
Also known as fast synaptic potential. The response is quick and does not last long by interaction with an ion channel.
Indirect Response
Also known as slow synaptic potential. It takes longer to create the response but it is a longer lasting response (usually involves G proteins).
Acetylcholine (ACh)
A neurotransmitter synthesized from choline and acetyl CoA and catalyzed by enzyme choline acetyl transferase (CAT). The synthesis of ACh occurs in the axon terminal and is packaged into vesicles. It is released by all pre-ganglionic neurons (both sympathetic and parasympathetic) onto cholinergic nicotine receptors. It is also released by most post-ganglionic parasympathetic neurons onto cholinergic muscarinic receptors.
Cholinergic
Neurons that secrete or have receptors for ACh.
Amines
Derived from single amino acids. Are synthesized in the axon terminal and are packaged into vesicles.
Catecholamines
Amine neurotransmitters.
Adrenergic
Neurons that secrete norepinephrine.
Acetylcholinesterase
Degrades ACh. Is found on either the presynaptic or postsynaptic membrane or both.
Preganglionic
Cells leading from the CNS to the ganglion.
Postganglionic
Cells leading from the ganglion to the effector.
Targets of Autonomic Pathway
1) Smooth Muscle
2) Cardiac Muscle
3) Exocrine Glands
4) Endocrine Glands
5) Adipose Tissue
Varicosity
Located in the middle of the axon (action potential still travels through to the synapse) and releases neurotransmitter into interstitial fluid (tissue fluid). The distance of the synapse is greater than between neurons.
α1 Receptors
Found on most tissues. Increases Ca^2+ levels in the cytoplasm. Responds best to NE > E.
β1 Receptors
Found on heart muscle and kidney. Stimulates cAMP production. Responds to NE = E.
β2 Receptors
Found on blood vessels and smooth muscle. Stimulates cAMP production. Responds to NE < E.
Adrenal Gland Parts
1) Adrenal Cortex
2) Adrenal Medulla
Adrenal Cortex
Secretes steroid hormones.
Adrenal Medulla
Associated with the sympathic division. Is a modified sympathetic ganglion.
Chromaffin Cells
Part of the adrenal gland. Secretes epinephrine which travels in the blood.
Varicosity Synapse Stages
1) Action potential arrives at the varicosity.
2) Depolarization opens voltage-gated Ca^2+ channels.
3) Ca^2+ entry triggers exocytosis of synaptic vesicles.
4) NE binds to adrenergic receptor on target.
5) Receptor activation ceases when NE diffuses away from the synapse.
6) NE is removed from the synapse.
7) NE can be taken back into synaptic vesicles for re-release.
8) NE is metabolized by monoamine oxidase (MAO).
