Physiology of Nervous System Flashcards
What is depolarization. what is it represented by
short positive changes in the membrane potential. represented by action potentials (nerve impulses) are generated in the cell body (axon hillock) and carried down the axon.
What are the three overlapping functions of the nervous system
- Sensory input
- Integration
- Motor output
What is the sensory input part of the nervous system
uses its sensory receptors to monitor changes occurring both inside and outside the body. the info gathered is called the sensory input
What is the integration part of the nervous system
the system processes and interprets sensory input and decides what should be done at each moment
What is the motor output part of the nervous system
the nervous system activates effector organs (the muscles and glands) to cause a response called motor output
What are the two main types of membrane ion channels
- Leakage or nongated channels
- Gated channels
What are leakage or nongated channels
membrane ion channels that are always open.
What are gated channels
membrane ion channels that open and close the channel in response to specific signals. There are three main types:
1. Chemically gated
2. Voltage gated
3. Mechanically gated
What is a chemically gated channel
aka: ligand-gated channel. open when the appropriate chemical binds. (NT bings to membrane protein and opens the channel)
What is a voltage-gated channel
open and close in response to changes in the membrane potential. No receptor
What are mechanically gated channels
open in response to physical deformation of the receptor (as in sensory receptors for touch and pressure)
What are the two things that generating a resting membrane potential depends on
- differences in K+ and Na+ concentrations inside and outside cells
- differences in permeability of the plasma membrane to these ions (3 K+ out, 2 Na+ in to maintain RMP)
the term depolarization and hyperpolarization describe changes in…
membrane potentials relative to resting membrane potential
Changes in membrane potential can produce two types of signals. what are they?
- graded potentials and 2. action potentials
What is depolarization
incoming signals operating over short distances that have variable (graded) strength
What is an action potential
long-distance signals of axons that always have the same strength
The resting membrane potential is approx ___mV in neurons
-70 (inside negative)
What is depolarization? Explain how it works
a decrease in membrane potential.
The inside of the membrane becomes less negative (moves closer to zero) than the resting potential. For instance, a change in resting potential from −70mV to −65mV is a depolarization.
What is hyperpolarization? Explain how it works
an increase in membrane potential
The inside of the membrane becomes more negative than the resting potential. A change from −70mV to −75mV is hyperpolarization. Reduces nerve impulses
What does depolarization do
Increases the probability of producing nerve impulses
What does hyperpolarization do
Decreases the probability of producing nerve impulses
Graded potentials are _____-lived, localized changes in membrane potential, usually in _______ or the _______.
short lived, dendrites or cell-body
Why are graded potentials called “graded”
because their magnitude varies directly with stimulus strength. The stronger the stimulus, the more the voltage changes and the farther the current flows.
APs-voltage gated ion channels are _____, _____-distance signals within a neuron
brief and long-distance
Where do action potentials occur
Occur only in muscle cells and axons of neurons (only found in the membranes of excitable tissues)
How does the CNS tell the difference between a weak stimulus and a strong one
CNS tells difference between a weak stimulus and a strong one by frequency of impulses (the number of AP received per second)
Higher frequency means stronger stimulus
Rate of AP propagation depends on 2 factors:
- Axon diameter
Larger-diameter fibers have less resistance to local current flow, so have faster impulse conduction - Degree of myelination
Two types of conduction depending on presence or absence of myelin
What is continuous conduction of an impulse
slow conduction that occurs in nonmyelinated axons
What is the saltatory conduction of an impulse
occurs only in myelinated axons and is about 30 times faster
What are some conditions that occur when an impulse is saltatory instead of continuous
Myelin sheaths insulate and prevent leakage of charge
Voltage-gated Na+ channels are located at myelin sheath gaps
APs generated only at gaps
Electrical signal appears to jump rapidly from gap to gap
What are the three categories of Nerve fibers
Group A, Group B, Group C
Describe Group A nerve fibers
Largest diameter
Myelinated somatic sensory and motor fibers of skin, skeletal muscles, and joints
Transmit at 150 m/s (~300 mph) (FASTEST)
Describe group B nerve fibers
Intermediate diameter
Lightly myelinated fibers
Transmit at 15 m/s (~30 mph)
Describe group C nerve fibers
Smallest diameter
Unmyelinated
Transmit at 1 m/s (~2 mph)
B and C groups of nerve fibers include _______ motor and sensory fibers that serve _______
ANS visceral, serve visceral organs
what is the presynaptic neuron
The neuron conducting impulses toward the synapse
What is the post-synaptic neuron
the neuron transmitting the electrical signal away from the synapse
Outside the central nervous system, the postsynaptic cell may be either another_______ or an _______
another neuron or an effector cell (a muscle cell or gland cell)
What are the two most common synapses
- Axodendritic synapses
- Axosomatic synapses
What are axodendritic synapses
Synapses between the axon endings of one neuron and the dendrites of other neurons.
What are axosomatic synapses
Synapses between axon endings of one neuron and the cell body (soma) of another neuron.
What are Axoaxonal synpases
synapses between axons
what are Dendrodendritic synapses
synapses between dendrites
What are Somatodendritic synapses
synapses between cell bodies and dendrites
What are the two types of synapses
- Electrical
- Chemical (neuromuscular junction)
Transmission of nerve impulses along an axon is an electrical or chemical event
electrical
Explain the 6 steps involved in converting an electrical impulse to a chemical impulse at a synapse
- Action Potential Arrives at axon terminal
- Voltage-gated Ca2+channels open and Ca2+enters the axon terminal
- Ca2+entry causes synaptic vesicles to release neurotransmitter by exocytosis
- Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane.
- Binding of neurotransmitter opens ion channels, creating graded potentials
6.Neurotransmitter effects are terminated
What are the three ways the postsynaptic cleft is cleaned after NT release
- Reuptake
- Degradation
- Diffusion
What is reuptake
Reuptake by astrocytes or the presynaptic terminal, where the neurotransmitter is stored or destroyed by enzymes (as with the neurotransmitter norepinephrine)
What is degradation of NT
Degradation by enzymes associated with the postsynaptic membrane or present in the synaptic cleft (as with acetylcholine
What is diffusion of NT
Diffusion away from the synapse
ACh is released by all neurons that stimulate________ and by many neurons of the autonomic nervous system. ACh-releasing neurons are also found in the _____
skeletal muscles. CNS
The function of a neurotransmitter is determined by ____________
by the receptor to which it binds.
If a IPSP was released, the result of K and Na would be…
Makes postsynaptic membrane more permeable to K+ or Cl–
If K+ channels open, it moves out of cell
If Cl– channels open, it moves into cell
If an EPSP is released, the result of K and Na would be…
allows simultaneous flow of Na+ and K+ in opposite directions
Na+ influx greater than K+ efflux,
Explain No Summation
When two EPSPs are far apart in time, they do not influence each other. It’s like if someone says “fire!” every so often—it doesn’t really grab your attention because it’s not frequent enough to cause concern.
Explain Temporal Summation
When two EPSPs occur close together in time, they can add up (summate), potentially bringing the neuron to the threshold needed to fire an AP. It’s like someone shouting “fire!” repeatedly in quick succession—you’re more likely to respond immediately.
Explain Spatial Summation
This happens when two EPSPs are generated at the same time but come from different locations on the neuron. If the combined depolarizations bring the neuron to threshold, an AP will fire. It’s similar to multiple people shouting “fire!” at the same moment, which gets your attention quickly.
Explain Spatial Summation of EPSPs and IPSPs:
If an EPSP and an IPSP occur at the same time, they will counteract each other. This is akin to one person shouting “fire!” while another shouts “don’t fire!” at the same time, causing confusion and no clear action.
Explain a direct action NT
neurotransmitter binds directly to and opens ion channels
Promotes rapid responses by altering membrane potential
Examples: ACh and amino acids
Explain an indirect action of NT
neurotransmitter acts through intracellular second messengers, usually G protein pathways
Broader, longer-lasting effects similar to hormones
Biogenic amines, neuropeptides, and dissolved gases
What are the two main types of receptors involved in neurotransmission
channel-linked receptors and G protein–coupled receptors.
What is the difference between channel-linked receptors and Gprotein receptors
Channel-linked receptors are responsible for fast synaptic transmission. When a neurotransmitter binds to these receptors, they change shape and open a channel directly, allowing specific ions to pass through quickly, which changes the membrane potential.
G protein–coupled receptors (GPCRs) oversee slower synaptic responses. They don’t directly open ion channels. Instead, when a neurotransmitter binds to a GPCR, it activates a G protein inside the cell. This G protein can then trigger a series of events
Describe the two types of zones within the simple neuronal pool
Discharge Zone: Neurons at the discharge zone are more likely to fire action potentials due to receiving more synapses.
Facilitated Zone: Neurons at the facilitated zone receive fewer synapses and are less likely to fire but are “primed” and can be easily activated by additional stimuli.
What are two types of neural processing pathways
- Serial: signals travel along a straight, predetermined path, one neuron activating the next in a sequence.
- Parallel: the input can travel along multiple pathways simultaneously. This allows different parts of the nervous system to deal with the same information at the same time, promoting complex responses and higher-level functions like memory and learning.
What is an example of serial processing pathway
An example is the spinal reflex arc, where a specific stimulus causes a predictable response. Reflex arcs typically include:
Receptor: Senses the stimulus.
Sensory neuron: Transmits the signal to the CNS.
CNS integration center: Processes the signal and forms a response.
Motor neuron: Carries the response signal from the CNS.
Effector: Acts in response to the signal (e.g., muscle or gland).
What are circuits
The patterns of synaptic connections in neuronal pools, called circuits, determine the pool’s functional capabilities.
What are the 4 types of circuits
Diverging, Converging, Reverberating, Parallel after-discharge
What is a diverging circuit. Give an exam
One input, many outputs. An Amplifying circuit.
Ex// a single neurons in the brain can activate 100 or more motor neurons in the spinal cord and thousands of skeletal muscle fibers
What is a Converging circuit
Many inputs, one output. A concentrating circuit
Ex//Different sensory stimuli can all elicit the same memory
What is a reverberating circuit
Signal travels through a chain of neurons, each feeding back to previous neurons. An oscillating circuit that controls rhythmic activity.
Ex// involved in breathing, sleep-wake cycle, and repetitive motor activities such as walking
What is a parallel after-discharge circuit
signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell. Impulses reach output cell at different times, causing a burst of impulses called an “after-discharge”
Ex// may be involved in exacting mental processes such as mathematical calculations
