Unit 1_Neural Communication Part 1 Flashcards
What do the following help us with?
Helps us to understand the flexibility/adaptability the CNS has for normal function.
Helps us understand what underlies normal learning processes across the life span.
Helps us understand processes in response to disease and trauma that are important to rehabilitation.
Helps us develop an understanding of how we as rehabilitation and other health professionals can treat without drugs or surgery.
Understanding Neural Communication
What generate impulses and serve as the major means of communication within the nervous system and between the nervous system and the body parts?
Neurons
What is the metabolic center of the cell and an important area to receive signals (postsynaptic) from other neurons?
Cell body
What receive signals from other neurons (postsynaptic)?
Dendritic branches or dendrites
What conducts signals away from the cell body to communicate with other neurons?
A single axon
What release neurotransmitters at the end of axons?
Presynaptic terminals
What are 3 primary classifications of neurons?
Pseudounipolar
Bipolar
Multipolar
What cell bodies do we see most in our nervous system?
Bipolar cell
In addition to electrical signals, what do the axons transport from the cell body to the synaptic terminals (anterograde transport) and back from the synaptic terminal to the cell body (retrograde transport) to provide nourishment, structural changes, and materials needed at synapses?
Materials
The axon arises from a specialized region of the cell body referred to as what?
axon hillock
It is the axon that will convey information within the nervous system from one cell to another by transmitting an electrical signal that is called what?
Action potential
What is started at the initial segment or trigger zone which is distal to the axon hillock?
Action potential
What is just distal to the axon hillock where action potentials are generated?
The “trigger zone” or “initial segment”
Near its end, an axon will divide into fine branches that have specialized swellings called what? By means of these terminals, one neuron will transmit information that it is carrying to the receptive post-synaptic surface of other neurons (usually dendrites but also on cell bodies or axons).
pre-synaptic terminals
What is the site of communication between excitable cells (neuron to neuron or neuron to effector cell (muscle, gland, etc.))? This cell is one that can undergo changes in its electrical charge in response to stimulation.
Synapse
What are two types of synapses?
Electrical and chemical
What type of synapse is most common in the CNS and specialized neurotransmitters convey information from one cell to the other?
Chemical synapse
What typically occur between the axon terminal of one neuron and the cell body or dendrite of a second neuron?
Neuronal synapses
What is the neuron conducting impulses towards the synapse referred to as?
Pre-synaptic neuron
What is the neuron conducting impulses away from the synapse referred to as?
Post-synaptic neuron
What is a narrow gap that separates the pre-synaptic and post-synaptic cells?
Synaptic cleft
How are signals transmitted across the synaptic cleft that is released from the presynaptic terminal?
Neurotransmitter
Neurotransmitters can have either an excitatory effect or an inhibitory effect on the post-synaptic cell based on what?
Post synaptic receptor
(ex. Dopamine, which can be either excitatory or inhibitory depending on the post-synaptic receptor it binds with)
If a threshold level of stimulation is reached, what will carry the signal from the post-synaptic cell to the next cell?
An action potential
Synapses occur on all parts of neuron, but most are on what followed by cell body (soma)?
Dendrites
What allows information to be widely spread to other neurons and other parts of the nervous system?
Divergence
What allows information from various parts of the nervous system to be integrated at single or groups of neurons?
Convergence
What signal is pre-synaptic?
Sensory signals
What signal is pre and post-synaptic?
Motor signals
What signal is post-synaptic?
Muscle signals
What allows the nervous system to carry out its functions including the action potential for communication?
Special membrane properties
What are the following properties of?
Has passive properties based on basic physics
Responds to voltage changes
Responds to various chemicals (neurotransmtters)
Special membrane properties that allow the nervous system to carry out its functions
What is the difference in electric potential (Voltage) between the interior and the exterior of a cell (neuron)?
Membrane Potential (Vm)
What refers to how hard it is for ions to flow through membrane?
Membrane resistance (Rm)
What refers to how easy it is for ions to flow through membrane?
Membrane conductance (g)
What refers to the ability for membrane to store charge (think of a ditch or water tank)? Myelin decreases membrane capacitance.
Membrane capacitance (Cm)
What refers to resistance to flow of ions within the cell, particularly the axon? Dependent on diameter of axon.
Axoplasmic (cytoplasmic) resistance (Ra)
What is dependent on Membrane capacitance and membrane resistance, but more on membrane capacitance? Important for temporal summation.
Membrane time constant
What refers to how far a membrane potential can maintain its height? Dependent on membrane resistance and axoplasmic resistance. Important for spatial summation.
Length (space) constant
What is dependent on axoplasmic resistance and membrane resistance?
Conduction Velocity
What decreases membrane capacitance reducing the time constant and increasing the conduction velocity?
Myelin
What do neurons have that makes up a cell membrane and is made of fat?
Lipid bilayer
What is the area outside of the neuron known as?
Extracellular space
What does resting membrane potential of a neuron refer to?
Negative
When we mention values of membrane potential, what are we reporting?
What is the inside of the cell relative to the outside of the cell
What move ions across the neuron’s membrane?
electrical and chemical gradients
What is a mosaic of membrane channels (windows) with transmembrane channels of various types that live right next to each other?
A neuron
Some synapses involve depolarization (or less negative/positive charge, more sodium) which we call what?
Excitation
Some synapses involve hyperpolarization (or negative charge, more potassium) which we call what?
Inhibition
What requires adenosine triphosphate (ATP) that is responsible for maintaining the concentration gradients for continuous diffusion of ions and, therefore, a continual charge separation or membrane potential?
Sodium-Potassium Pump
The local graded alterations in the resting membrane potential of the post-synaptic cell are referred to as what? These result from changes in ion permeability due to the effect of the neurotransmitter.
post-synaptic potentials
What determine whether a synapse is excitatory or inhibitory?
The receptors
If the neurotransmitter causes excitation, what will the result be, which will depolarize the post-synaptic cell membrane and bring it closer to threshold?
Excitatory post-synaptic potential or EPSP
If the neurotransmitter causes inhibition, what will the result be, which will hyperpolarize the post-synaptic cell membrane and move it further from threshold?
inhibitory post-synaptic potential or IPSP
What will determine whether or not a given post-synaptic cell reaches a threshold of stimulation that will result in an action potential?
The summation of EPSP’s and IPSP’s
What is an autoimmune disease that destroys receptor sites (junctional folds) for acetylcholine at Neuromuscular junction (NMJ) on muscle cells which are post-synaptic cells? Patients have signs and symptoms related to cortical bulbar pathways, cranial nerve pathways so weakness in the face and can sometimes have difficulty swallowing.
Myasthenia Gravis
What is is the initial segment or trigger zone of axon where SUMMATION occurs?
Activity of all EPSPs/IPSPs are summed and decision of cell to generate action potential or not is reached.
All EPSPs and all IPSPs passively move around the cell and via the axon hillock to initial segment/trigger zone.
All are summated. If there is sufficient depolarization to reach threshold an action potential will be generated.
Integrative Component
What occurs when a single neuron has many excitatory and inhibitory synapses on it with some out on dendrites and cell body with a few near the axon terminals?
For example, a single motor neuron in the ventral horn of the spinal cord may have 10,000 synapses with other neurons.
Convergence
What is a summation of post-synaptic potentials from a single stimulus location occurring at high frequencies?
At high frequencies a new EPSP occurs before membrane potential can return to baseline. Therefore, a single sub-threshold synapse may drive neuron to threshold when it fires at high frequency.
Temporal summation
What is combined action of 2 of more post-synaptic potentials from different points on the neuron (dendrite, cell body and sometimes axon terminal)? Synapses need to be close enough for summation to occur.
Spatial summation
What ultimately affect initial segment/trigger zone?
Temporal and spatial summation
Capacitance adds a time element to passive properties during what type of summation?
Temporal summation
What determines amount of capacitance?
Separation of charges
Less separation = more capacitance
More separation = less capacitance (myelin separates charges)
What affect how far a potential can move without disappearing and are the basis of the length (space) constant which is important for Spatial Summation?
Axonal (within cell) and Membrane (through membrane) resistances
Larger diameter axons have what?
Less resistance
What degrades signal?
Length
What have greater impact than those out on tips of dendrites all else being equal?
Synapses closer to trigger zone
When is there greater chance for spatial summation?
If the length constant is longer
What is dependent on passive properties, but active properties underlay spiking an action potential?
Summation
How do neurons communicate with each other?
Via action potentials
What is a rapid change in membrane polarity observed in excitable cells that allows for the transmission of electrical information from one cell to another?
Action potential
What involves a positive feedback cycle and is time-limited?
Spiking an action potential
As soon as the critical threshold of depolarization caused by the summation of post- synaptic potentials is reached, what channels open allowing Na+ to rush into the cell along both its concentration and electrical gradient?
These channels also open but more slowly and take longer to close.
During this time more positive charges (Na+) enter the cell than leave (K+). The membrane potential thus decreases (becomes more positive) and eventually reverses as the inside becomes more positive than the outside. This constitutes the depolarization phase of the action potential which is short lived (<1 millisecond).
voltage gated sodium channels
What channels close rapidly as the membrane becomes more positive and voltage gated potassium channels remain open long to allow K+ to diffuse quickly out of the cell? This K+ efflux brings the membrane potential back to its resting level and is called the repolarization phase.
The K+ channels remain open long enough to cause a brief period of hyperpolarization.
Sodium channels
What underlies generation of an action potential?
Positive feedback
What channels do the following:
Open quickly
Close quickly
Are refractory
Voltage gated Na+ channels
What is responsible for refractory period?
Inactivation of voltage gated Na channels
What is the axon itself?
The conductive component
In regards to an atom, what do the following relate to:
- diameter (Axoplasmic resistance)
- if it is myelinated or not (Membrane 3. capacitance and resistance)
- If myelinated, how much myelin.
How fast an axon conducts
What is inversely related to Axonal resistance (Ra) and Axonal Capacitance (Cm)?
Axonal conduction velocity
If axons have the following, what speed is their conduction velocity?
- Small diameter axons have high resistance
- Unmyelinated axons have high capacitance
Slower
If axons have the following, what speed is their conduction velocity?
- Large diameter axons have low resistance
- Myelinated axons have low capacitance
Faster
Not all axons are myelinated, but those that are myelinated conduct action potentials how?
Faster
What process reduces the ability of passive current to leak out of the axon, increases the distance along the axon that a given local current can flow passively and decreases the capacitance of the axon reducing time to charge membrane allowing action potentials to conduct faster?
Myelinated axons at the Nodes of Ranvier
What appear to occur only at the “nodes of Ranvier” where there are gaps in myelin, but they are traveling whole axon?
Action potentials
What separate charges so they are less attracted to each other?
Myelin
What varies with diameter of axon, and presence and thickness of myelin?
Velocity
What are faster than smaller diameter because less axoplasmic resistance?
Large diameter myelin
What are faster than unmyelinated because myelin reduces membrane capacitance?
Myelinated
What disease affects the conductive component and is autoimmune?
It destroys myelin in PNS-affects motor, sensory and autonomic functions of peripheral nerves-subsequent to infection-rapid progression.
Initial symptoms are often tingling/numbness and weakness.
Progressive muscle weakness that may result in full paralysis within days or weeks.
Guillain Barre
What disease affects the conductive component and is autoimmune?
It destroys myelin in CNS-cerebrum, brainstem and spinal cord.
Visual, motor, sensory, bowel and bladder, cognition, emotions, speech, swallowing, autonomic, etc.
Progressive – speed/severity may vary
Multiple Sclerosis
