2. Nervous System Flashcards
What is membrane potential?
Voltage difference across cell membrane
Is resting membrane potential positive or negative and why?
resting membrane potential (MP) is negative (-ve), with intracellular fluid (ICF) more negative than extracellular fluid (ECF).
What is an action potential?
Rapid, changing electrochemical impulses in excitable cells (e.g., nerve, muscle) used to transmit messages.
Which other cells use action potentials besides nerves and muscles?
Fertilized egg cells and hormone-secreting cells.
What two conditions are required to establish a potential difference across a membrane?
- A concentration gradient for an ion
- A membrane permeable to that ion.
What is the relationship between concentration and electrical gradients in membrane potentials?
Ions move down their concentration gradient, creating an electrical gradient. The electrical force eventually balances the concentration gradient, so ion movement in equals ion movement out.
How does K+ contribute to membrane potential?
K+ moves out of the cell due to its concentration gradient, creating a negative charge inside the membrane, which then attracts K+ back into the cell due to the electrical gradient.
What is equilibrium potential (E of ion)?
The potential difference across a membrane at equilibrium for a specific ion, also called reversal potential.
What happens when the voltage difference exceeds the equilibrium potential?
The direction of ion movement changes.
What occurs if the membrane potential becomes more negative than -60 mV for K+?
More K+ would move from outside to inside the cell, against its concentration gradient
How do the ions affect the overall cell/cytoplasm
The number of ions moving is very small, and they stay close to the membrane, not affecting the overall cell/cytoplasm.
What is the Nernst potential (NP)?
The diffusion potential across a membrane that opposes the net diffusion of a specific ion, determined by the concentration ratio of the ion on either side of the membrane.
How does the concentration ratio affect the Nernst potential?
The greater the concentration ratio, the higher the Nernst potential required to stop net diffusion of the ion.
How does ion charge affect the sign of EMF?
EMF is positive if a negative ion diffuses from inside to outside, and negative if a positive ion diffuses from inside to outside.
What does the Goldman equation calculate?
The equilibrium potential for all relevant ions when the membrane is permeable to multiple ions.
What factors affect the Goldman equation?
Ion polarity, membrane permeability (P_ion), and ion concentrations inside (C_i) and outside (C_o) the cell.
What is the resting membrane potential for a nerve?
-90 mV.
How does the Na+/K+ pump contribute to the resting membrane potential?
It pumps 3 Na+ out for every 2 K+ in, creating a negative potential inside the cell and maintaining a large concentration gradient.
How does membrane permeability differ between K+ and Na+?
Leaky channels are 100 times more permeable to K+ than Na+.
SAVING FOR MEMBRANE POTENTIAL QUESTION
A. Only K+
* Nernst: + 61 X log (35) = -94 mV
B. add slight Na+ perm. through leaky
channels
* permeability of the membrane to
K is about 100 times that of Na
* Therefore, only reduced to -86 mV
C. Na+ - K+ pump
* adds - 4 mV
* Overall net membrane potential =
-90 mV
What are the stages of a nerve action potential?
- Resting
- depolarization
- repolarization.
What is the resting stage of a nerve action potential?
The membrane is polarized at -90 mV.
What happens during depolarization?
The membrane becomes very permeable to Na+, and Na+ diffuses into the axon.
What happens during repolarization?
Na+ channels close, K+ channels open, and K+ diffuses out, reestablishing polarization.
What are the two gates of a voltage-gated Na+ channel?
The activation gate (outside) and the inactivation gate (inside).
What is the state of Na+ channels at resting membrane potential (-90 mV)?
The activation gate is closed, preventing Na+ entry.
What happens to the Na+ channel as the membrane potential changes from -70 to -50 mV?
The activation gate opens, increasing Na+ permeability 500-5000 fold.
Why does Na+ stop entering the cell after depolarization?
The inactivation gate closes, though more slowly than the activation gate, allowing brief Na+ entry.
When can the inactivation gates of Na+ channels reopen?
They only reopen when the membrane potential returns to the original resting potential (-90 mV).
When do voltage-gated K+ channels open?
They open as the membrane potential moves toward zero, slightly delayed, coinciding with the closing of Na+ channels.
How do K+ channels contribute to repolarization?
Decreased Na+ entry and increased K+ exit speed up repolarization, restoring the negative membrane potential.
What triggers the initiation of an action potential?
Any factor causing sufficient Na+ to diffuse inward, starting the positive feedback cycle of Na+ channel opening.
What are the three types of stimuli that can initiate an action potential?
- Mechanical (e.g., sensory neurons in skin)
- chemical (e.g., neurotransmitters)
- electrical (e.g., heart and intestine cells).
What is the threshold for excitation?
Approximately -65 millivolts.
How does an action potential propagate along the membrane?
It spreads in all directions from the stimulus until the entire membrane is depolarized, known as the nerve impulse.
What is the “all-or-nothing” principle of action potential propagation?
Once initiated, the action potential propagates fully across the membrane, or not at all.
What is the absolute refractory period?
A period during which a second action potential cannot be generated, even with a strong stimulus, because Na+ channels are inactivated.
How are sodium-potassium gradients re-established after an action potential?
The Na+/K+ pump uses ATP to restore ionic gradients, with pump activity increasing proportionally to the intracellular Na+ concentration.
What is saltatory conductance in myelinated nerve fibers?
It refers to the process where ions flow only through the nodes of Ranvier, increasing conduction velocity.
How much does saltatory conductance increase nerve impulse speed?
It increases velocity 5 to 50-fold.
How does saltatory conductance affect energy use?
It reduces the energy needed to re-establish Na+ and K+ concentrations and allows re-polarization with minimal ion transfer
Whats the speed of nerve impulses
- Small unmyelinated fibers - slow
- Very large myelinated fibers - fast
Channels vs Pump
C: diffusion
P: active transport
What does conductance measure in relation to ion movement?
Conductance measures the movement of charge across the membrane.
What does permeability indicate about ions and membranes?
Permeability measures the capability of ions to flow across the membrane, regardless of whether they are actually moving.
What comprises the Central Nervous System (CNS)?
The brain and spinal cord.
What does the Peripheral Nervous System (PNS) include?
Cranial nerves and spinal nerves going to somatic structures, as well as the autonomic nervous system (ANS) that goes to visceral structures.
What is the function of sensory neurons (afferent neurons)?
They transmit sensory information from receptors throughout the body to the CNS.
What do motor neurons (efferent neurons) do?
They control various body functions.
What are association neurons (interneurons)?
Neurons that connect afferent and efferent neurons and comprise 90% of all neurons, performing integrative functions.
What are the two main divisions of the nervous system?
Central Nervous System (CNS) and Peripheral Nervous System (PNS).
Where is the CNS located?
In the bony casing of the cranium and vertebrae.
What does the PNS connect?
The periphery with the brain and spinal cord, innervating muscles, skin, and glands.
What are the two functional divisions of the PNS?
Autonomic nervous system and somatic nervous system.
What does the somatic nervous system control?
Voluntary control of muscles.
What functions does the autonomic nervous system regulate?
Involuntary functions such as control of smooth muscle, cardiac muscle, and glands.
- Control the most visceral functions of the body
What are the three components of the autonomic nervous system?
1) Sympathetic nervous system (stress response)
2) Parasympathetic nervous system (homeostatic functions)
3) Enteric nervous system (gastrointestinal regulation)
Where are the cell bodies for the parasympathetic system located?
In select regions of the brain and in sacral levels of the spinal cord.
Where are the cell bodies for the sympathetic system located?
In the thoracic and lumbar regions of the spinal cord.
What is the enteric nervous system?
A subdivision of the ANS located in the walls of the gastrointestinal tract that can function independently while being influenced by both sympathetic and parasympathetic systems.
How do sympathetic and parasympathetic neurons typically interact?
They tend to have opposite actions when innervating the same structure.
What is the primary role of the parasympathetic system?
Normal maintenance of the internal environment, acting during “rest and digest” states.
What is the primary role of the sympathetic system?
Response to external environmental stressors, acting during “fight or flight” or “freeze” responses.
Name some organs that receive both sympathetic and parasympathetic input.
Salivary glands, heart, bladder, and sex organs.
What are some structures that only receive sympathetic input?
Sweat glands, most blood vessels, and piloerector muscles of the skin.
What are neurons?
Nerve cells that transmit information throughout the nervous system.
Afferent processes vs afferent process
Dendrites and axon
What is a nuclei
Groups of nerve cell bodies within the CNS
What is a ganglia
Groups of nerve cell bodies outside the CNS
What are tracts/fasciculi
Bundles of nerve processes within the CNS
What are nerves?
Bundles of processes outside the CNS
What are glia?
Non-neuronal cells that don’t produce impulses, they provide support and protection
What are some functions of glial cells?
K⁺ and Ca²⁺ buffering, neurotransmitter reuptake, axonal guidance during regeneration, and CSF production.
What are the 2 types of macroglia?
- Astrocytes
- Oligodendroglia
What are astrocytes?
A type of macroglia found throughout the CNS, involved in forming the blood-brain barrier and providing support.
What role do oligodendroglia play in the CNS?
They are involved in the formation of myelin sheaths.
What are microglia?
Resident macrophages in the CNS that act as immune responders.
What are terminal or synaptic boutons?
Swellings at the distal end of the axon that contain neurotransmitter-filled vesicles and form chemical synapses with other neurons.
What are en passant boutons?
Boutons found along the length of the axon in some types of neurons
What are the different types of synaptic connections?
Axo-dendritic: Between axons and dendrites.
Axo-somatic: Between axons and cell bodies.
Axo-axonic: Between axons and the initial segment of another axon or synaptic boutons.
Dendro-dentritic: Between dendrites.
Neuromuscular junction: Between neurons and muscles, as well as other organs like the heart.
What is the resting membrane potential of a spinal motor neuron?
Approximately -65 mV, which is less negative than peripheral nerves and skeletal muscle fibers.
What is the change in membrane potential during an EPSP?
Resting potential changes from -65 mV to -45 mV; EPSP = +20 mV.
What occurs during an inhibitory postsynaptic potential (IPSP)?
Hyperpolarization occurs, increasing negativity beyond the normal resting potential, primarily through opening chloride and potassium channels.
What is presynaptic inhibition
The release of an inhibitory substance (often GABA) onto presynaptic nerve fibers, which opens anion channels and allows chloride ions to enter, inhibiting synaptic transmission.
What is spatial summation?
The process where multiple presynaptic terminals simultaneously discharge to achieve the firing threshold.
What is temporal summation?
The summation of successive discharges from a single presynaptic terminal that occur rapidly enough to reach the firing threshold and cause an action potential.
Describe the efferent component of the sympathetic nervous system.
Preganglionic neuron: Soma in the brain stem or spinal cord.
Postganglionic neuron: Soma in ganglia outside the CNS.
How is the frequency of action potentials related to receptor potential?
Frequency of action potentials is proportional to receptor potential, allowing sensitivity to weak stimuli and peak firing only at extreme stimuli.
What happens when a continuous sensory stimulus is applied to receptors?
Receptor firing decreases or ceases, especially in mechanoreceptors.
What is convergence from a single source?
It provides spatial summation, where input signals from the same source are combined.
What is convergence from multiple sources?
It allows correlation, summation, and sorting of different types of information from various sources.
What is the function of the spinal cord in reflexes?
The spinal cord is involved in reflexes, sensory processing, and motor outflow. Reflexes typically involve receptor structures, afferent neurons, and efferent neurons.
- A reaction without using the brain
What is the stretch reflex?
When a muscle is stretched, excitation of the muscle spindles causes reflex contraction of the same muscle and related muscles, using a monosynaptic pathway involving type 1A nerve fibers.
What is the role of type 2 fibers in the stretch reflex?
Most type 2 fibers from muscle spindles terminate on interneurons, which slow down the signal.
What is the flexor (withdrawal) reflex?
This reflex involves excitation of muscles, such as in the upper arm, with information passed to the spinal cord’s interneuron pool, activating necessary muscles while inhibiting antagonists and causing after-discharge.
