Flashcards in A&P Chapters 12, 13, 14 Nervous System; Signaling, ANS Deck (88):
What are ligand gated ion channels?
Ion channels that require a ligand in order for them to open and cause depolarization.
What are voltage gated ion channels?
Ion channels that require a change in membrane voltage to open and cause depolarization.
What is electrophysiology?
The study of how the flow and location of charged ions across a cell's membrane affect its function and activity.
What is the charge inside of a resting cell? What about outside?
Negative Inside, Positive Outside.
The Na+/K+ ATPase pump totals how much of the nervous systems ATP usage?
Where does the action potential of a neuron originate?
Typically at the dendrites, they contain ligand-gated Na+ channels.
What is a LOCAL POTENTIAL?
The depolarization of a neuron at the dendrite. The LOCAL POTENTIAL must travel down the neuron through the soma to the Trigger zone to propagate an action potential to the axon. If stimulation at the dendrite isn't sufficient an action potential will not occur.
How is a LOCAL POTENTIAL initiated?
By the opening of ligand gated Na+ ions channels which depolarizes the membrane of the dendrite.
Describe LOCAL POTENTIALS
They are variable in strength, more/less ligand= more/less Na+ flow.
They are reversible, the removal of stimulus stops local potential. The Na+ channels close and K+ channels open resulting in repolarization.
They can be EXCITATORY OR IHIBITORY. Some ligands can cause the neuron to become HYPERPOLARIZED which prevents an action potential from occurring. INHIBITORY doesn't block the Na+ channels, instead they open other channels allowing other ions to enter or exit, such as Cl- or K+. This is done to counter act a change in potential.
Describe step by step the process of creating an action potential within a neuron.
1. Neurotransmitter binds to ligand-gated Na+ channels on the dendrite.
2. Na+ rushes in and depolarizes the membrane near the dendrite (LOCAL POTENTIAL).
3. Na+ diffuses away from the dendrite towards the soma and trigger zone.
4. If concentrations of Na+ is high enough it causes Voltage gated Na+ ion channels in the trigger zone to open.
5. Opening of the Voltage gated Na+ channels causes depolarization of the membrane near the trigger zone (ACTION POTENTIAL).
6. This triggers a wave of action potentials that proceed down the length of the axon.
Where is the VERY HIGH CONCENTRATION of Voltage Gated Na+ channels in a Neuron?
The Trigger Zone
What maintains the resting membrane potential?
The Na+/K+ ATPase Pump
Describe the flow of Ions during action potential
1. Ion channels are closed, resting membrane potential is maintained.
2. Opening of Na+ channels causes depolarization, the inside of the cell becomes less negative.
3. Na+ channels close, THEN the K+ channels open, causing inside of the cell to regain negative charge.
4. K+ channels close, astrocytes absorb excess K+, and the Na+/K+ ATPase pump actively restores resting membrane potential.
What does it mean to say an action potential is "all or none"?
That as long as the local potential reaches or exceeds threshold, the neuron will fire an action potential at maximum voltage and the strength of the action potential will be the same along the entire axon.
Do action potentials change strength at any time during propagation along an axon?
Can an action potential be stopped once it has begun?
What is a NERVE SIGNAL?
A NERVE SIGNAL refers to the wave of MANY action potentials that travel down the axon.
Explain the difference between an ACTION POTENTIAL and a NERVE SIGNAL
An action potential is the individual "wave" of depolarization at a given point along the cell membrane which results in local depolarization and repolarization.
A NERVE SIGNAL is the combined result of many "waves" of action potential travelling down an axon.
What is the REFRACTORY PERIOD? What does it result in?
The REFRACTORY PERIOD is the area directly behind an action potential that is in the process of returning to a resting state but isn't resting yet.
This results in the action potential only being allowed to travel in ONE DIRECTION.
What are the NODES OF RANVIER?
The small spaces between myelin along a myelinated axon that remain UNMYELINATED.
What are the INTERNODES?
The areas along a myelinated axon that ARE COVERD IN MYELIN.
Why does depolarization occur more easily at the Nodes of Ranvier?
Because they don't have myelin covering them which allows the Na+ ions to get to the cell membrane, if the Na+ cannot get to the cell membrane no action potential can be produced.
ALSO, the voltage gated ion channels are much more concentrated in the Nodes of Ranvier.
How does an action potential get from one Node of Ranvier to the next if the myelin is in the way?
The incoming Na+ ions diffuse down the axon to the next Node of Ranvier triggering an action potential.
What is SALATORY CONDUCTION?
The "jumping" of action potentials down an axon from one Node of Ranvier to the next.
What is the PRE-SYNAPTIC NEURON?
The neuron that releases the neurotransmitter and is located before the synapse.
What is the POST-SYNAPTIC NEURON?
The neuron that receives the neurotransmitter and is after the synapse.
Where can the axon of a pre-synaptic neuron synapse with another neuron?
The Dendrites, Soma, or Axon.
What is the SYNAPTIC CLEFT?
The small gap between the axon releasing neurotransmitter and the neuron accepting the neurotransmitter.
What is a NEUROTRANSMITTER?
The signaling molecule used to bind to ligand gated ion channels on the dendrite, soma or axon which will open Ligand gated Na+ ion channels triggering depolarization.
What are the four classes of chemical neurotransmitters?
Acetylcholine, Amino acids, Monoamines, and Neuropeptides.
Are all neurons stimulated by Neurotransmitters? If not what other things trigger neurons?
No, some are stimulated by light, heat, mechanical force. Eyes, ears, and stretch receptors are examples.
It is used by motor neurons to communicate with muscle fibers.
Describe Amino Acids as they relate to Neuron communication
Some neurons store and release individual amino acids to communicate
They are basically amino acids that have their carboxylic acid groups removed.
Examples; Epinephrine (adrenaline), histamine, dopamine.
They are very short proteins that are synthesized in the SOMA and then transported down the axon to the synaptic bulb where they are stored until needed.
Describe the steps of Excitatory Synapse
1. Arrival of a nerve signal to the PRE-synaptic bulb triggers the opening of Ca2+ channels.
2. The entry of Ca2+ triggers the exocytosis of ACh from the bulb.
3. ACh travels across the synaptic cleft and binds to ligand-gated ion channels on the POST-synaptic cell.
4. ACh causes ion channels to open allowing Na+ to rush into the cell causing depolarization and initiation of a LOCAL POTENTIAL.
5. IF the stimulation is strong enough the Na+ will diffuse away and depolarize other parts of the membrane. This triggers the opening of VOLTAGE GATED ion channel throughout the rest of the neuron.
Describe the use of Second Messengers and their function
A neurotransmitter binds to a receptor which releases a protein that will bind to another receptor releasing a 2nd Messenger, like cAMP inside the cell which can effect cell function in many ways.
What happens to the cell during an INHIBITORY stimulus?
The result is the inhibiting it's ability to become stimulated.
What are GABA-ergic synapses?
They are inhibitory molecules that bind to receptor sites that open Cl- or K+ ion channels. The entry of Cl- or exit of K+ makes the interior of the cell MORE NEGATIVE resulting in HYPERPOLARIZATION and more difficult or impossible to stimulate.
Why is the ability to regulate nerve signals important?
Because the inability to turn off the signal leads to constant activation (or inhibition).
The ability to regulate nerve signals is critical to maintaining homeostasis.
What are the methods of removing a neurotransmitter from the receptor sites?
Diffusion, the neurotransmitter simply diffuses away from the synapse and are taken up by astrocytes.
Reuptake, the neurotransmitter is taken back up by the presynaptic neuron via ENDOCYTOSIS
Degradation/metabolism, the neurotransmitter is broken down by enzymes. Ex. is Acetylcholine is broken down by acetylcholinesterase at the neuromuscular junction.
What are NEUROMODULATORS?
Specialized molecules that can modify a neuron's ability to communicate.
They can: increase/decrease receptors on the post synaptic neuron making it more or less sensitive.
Increase/decrease production of neurotransmitters, more or less able to stimulate.
Increase/decrease metabolism of neurotransmitters which alters the length of stimulation.
What is NEURAL INTEGRATION?
The COMBINED signals of many neurons that will tell a POST-synaptic neuron whether or not to fire an action potential.
What is SUMMATION?
The process by which nerve signals "add up" to stimulate another neuron.
Remember that many neurons send inhibitory and stimulatory signals to a post synaptic neuron, it is the combined total that determines if an action potential will fire.
What is TEMPORAL SUMMATION?
ONE neuron sending signals fast enough to trigger an action potential in another neuron. (strong signal from one pre-synaptic neuron)
What is SPATIAL SUMMATION?
MANY neurons sending slower signals so that their combined effect is to trigger an action potential. (weak signal from many presynaptic neurons)
What are the PROPERTIES of a Reflex?
1. Requires stimulation.
2. Quick, very rapid short lived responses.
3. Involuntary, cannot control reflexes.
4. Predictable, they occur in the same way every time.
What are the two categories of reflexes?
SOMATIC and VISCERAL
Describe SOMATIC reflexes
They typically involve reactions to some sort of physical stimulus on skin, muscles, or tendons.
Describe VISCERAL reflexes
They involve altering the function of visceral organs in response to a stimulus. (Increasing heart rates in response to low blood pressure)
Describe the FIVE steps of a REFLEX ARC
1. Sensory Receptors detect a stimulus, change in stretch, pressure, temp, ect...
2. Afferent nerve fibers carry the information TO the CNS.
3. Integration center, the afferent neurons synapse with interneurons in the CNS. This is where the decision is made whether or not to send a signal via the efferent neuron.
4. Efferent Neurons carry information AWAY from the CNS to a target tissue/neuron.
5. Effector, skeletal muscles carry out the response.
What is the Autonomic Nervous System? How does it carry out it's Actions?
It is the MOTOR system that REGULATES the actions of visceral organs like the heart, lungs, many glands and smooth muscle, ect...
The ANS carries out it's actions UNCONSCIOUSLY.
The ANS REGULATES man organs and gland activities but is not necessarily needed for FUNCTION. The ANS can speed up or slow down heart rates, breathing rates, gland secretion however these organs can still operate without the ANS we just can't control them.
The AUTONOMIC NERVOUS SYSTEM is a subdivision of what?
The Peripheral Nervous Systems Motor Division, specifically the VISCERAL Motor Division broken into the Sympathetic and Parasympathetic Divisions.
What are the two divisions of the ANS?
Sympathetic and Parasympathetic Divisions
Describe the Sympathetic Division of the ANS
Responsible for the "Fight or Flight" response. Adapts the body for strenuous activity, increases blood pressure, blood flow to the heart and skeletal muscle. Decreases blood flow and function of "Non-Essential" tissues and organs like skin, digestive system and waste elimination.
Important during times of stress, anger, fear, sexual arousal, ect..
Describe the Parasympathetic Division of the ANS
Responsible for the "Rest and Digest" response, has more of a calming effect on the body. Reduces use of energy and prepares the body for "maintenance" functions like digestion and waste elimination.
Describe COOPERATIVE RESPONSES with the Sympathetic and Parasympathetic Divisions of the ANS
When BOTH the Sympathetic and Parasympathetic divisions illicit the SAME response. Salivary glands are an example of a cooperative response.
What is an example where the Parasympathetic Division speeds something up?
Digestion and Waste Elimination
What does the ANS use to regulate organ functions?
Describe the steps of a VISCERAL REFLEX arc
1. Sensory receptors detect a change, stretch, chemicals, temp, pH, ect...(these sensors are located inside or close to an organ)
2. Afferent neurons carry information back to the CNS
3. Interneurons in the CNS that process this information and determine what action is needed (In integration centers)
4. Efferent neurons carry the signal away from the CNS to the effector.
5. The Effector is the organ or tissue who's function is being regulated is stimulated.
What parts of the brain are control centers for the ANS?
Hypothalamus, midbrain, pons, and medulla oblongata.
How many neurons does the ANS use to get from the spinal cord to a target? How many does a Somatic motor neuron use?
The ANS uses 2 neurons to get from the spinal cord to a target. A PRE GANGLIONIC neuron and a POST GANGLIONIC neuron.
Somatic motor division uses only 1 neuron to get from the CNS to a target tissue (skeletal muscles)
What is the THORACOLUMBAR DIVISON of the ANS?
This is the name sometimes used for the SYMPATHETIC division because the nerve fibers EXIT the spinal cord with the spinal nerves T1-L2 and then branch off and enter the SYMPATHETIC chain via COMMUNICATING RAMI.
The Preganglionic fibers that enter the sympathetic chain can 1. synapse with a postganglionic fiber (in the Sympathetic chain) and then travel to the target organ or 2. pass right through the sympathetic chain and synapse with a post ganglionic fiber just beyond the sympathetic chain.
Where do SYMPATHETIC division fibers exit the CNS?
Through the spinal cord inside spinal nerves T1-L2 then they branch off into the Communicating Rami.
Where do the PARASYMPATHETIC division fibers exit the CNS?
Either the brain via cranial nerves or the sacral region of the spinal cord (S2-S4)
What is the CRANIOSACRAL division of the ANS? Where do the preganglionic neurons travel and where do they synapse with the post ganglionic fibers?
The Parasympathetic division that exits in the cranial nerves or in the sacral region of S2-S4.
The PREGANGLIONIC fibers travel with cranial or sacral nerves and synapse with POSTGANGLIONIC fibers NEAR OR INSIDE the target organ or tissue
Which Cranial Nerve carries the VAST majority of preganglionic parasympathetic fibers? What do they innervate? What other Cranial nerves carry preganglionic sympathetic fibers?
Cranial Nerve 10 the VAGUS nerve carries 90% of the preganglionic parasympathetic fibers and they innervate the heart, lungs, and digestive organs to slow down heart rate, breathing rate and speed up digestion. Cranial nerves 3,7, and 9 carry fibers that control saliva, tear production, swallowing and pupil constriction.
How does the Parasympathetic division decrease contraction of cardiac muscle and at the same time increase the contraction of smooth muscle?
The neurons use or have receptor sites for DIFFERENT neurotransmitters. So the cardiac muscle fibers might be inhibited while the smooth muscle in the digestive system is stimulated.
What are the two PRIMARY neurotransmitters of the ANS used to communicate between pre and post ganglionic neurons as well as with the target tissues or organs?
Acetylcholine and Norepinephrine (noradrenaline)
What neurotransmitter do ALL PREGANGLIONIC neurons of the ANS release?
What neurotransmitter do the POST GANGLIONIC nerve fibers of the ANS release?
Norepinephrine (the mist common) and Acetylcholine.
What are CHOLINERGIC Fibers?
Neurons that RELEASE ACh
What are ADRENERGIC Fibers?
Neurons that Release Norepinephrine.
What are the two types of CHOLINERGIC receptors?
Nicotinic Receptors and Muscarinic Receptors
Describe Nicotinic Receptors
A type of CHOLGERGINIC receptor that is stimulated by ACh. This type is found at the neuromuscular junction of skeletal muscle.
Describe Muscarinic Receptors
A type of CHOLINERGIC receptor that could be found on a cell that might be stimulate or inhibited by ACh.
What are the two types of ADRENERGIC receptors?
Alpha-Adrenergic receptors and Beta-Adrenergic receptors.
Describe Alpha-adrenergic receptors
They bind NE (norepinephrine) and typically result in an EXITATORY response.
Describe Beta-adrenergic receptors
They bind NE (norepinephrine) and typically result in an INHIBITORY response.
How does the release of Norepinephrine by the ANS result in Vasoconstriction and Bronchodilation at the same time?
Because the receptor sites on the blood vessels are Alpha-adrenergic receptors while the receptor sites on the Bronchioles are Beta-adrenergic receptors resulting in relaxation or inhibition of contraction.
Explain what it means to have ANTAGONISTIC EFFECTS on an organ from the ANS
Most organs are innervated by BOTH the sympathetic and parasympathetic nerve fibers resulting in DUAL innervation. When the sympathetic and parasympathetic nervous systems have OPPOSITE effects on an organ it is said to have ANTAGONISTIC EFFECTS.
Explain what is means to have COOPERATIVE EFFECTS on an organ by the ANS
When the Sympathetic and Parasympathetic nerve fibers have SIMIAL effects on an organ. Such as the stimulation of salivary production in salivary glands.
What does it mean to have DUAL innervation from the ANS and what about SINGLE?
DUAL innervation means that the target organ has fibers from both the sympathetic and parasympathetic nervous systems. SINGLE means an organ is only innervated by ONE division of the ANS.
All PREGANGLIONIC Neurons in the ANS are __________ and they release __________.
Cholerginic and they release Acetylcholine
All POSTGANGLIONIC neurons in the ANS have __________ receptors and they bind __________.
Nicotinic/Cholerginic and they bind Acetylcholine
A Nicotinic receptor binds _______ and is found on _________.
Acetylcholine and is found on POST GANGLIONIC neurons.
Most tissues that are controlled by the Parasympathetic division contain _________ receptors for ACh except for skeletal muscle which have _________receptors.