EXAM 3: Neurons and Muscles Flashcards
Do neurons have a resting membrane potential
Yes
Can neurons rapidly change membrane potentials
yes
Where are things presynaptic
before the response cell
Where does presynaptic send signals through
through the postsynaptic cell, which is the second cell
What is the key axon property
each cable has resistance
What are channels
how things move across the membrane (gates)
What states can channels be in?
open, closed and inactivated
What do cable properties allow for
ions like sodium to move
What does the movement of sodium and potassium generate
the signal
What is Olm’s law
when you change current flow, you change the velocity
(moving sodium and potassium changes the voltage
What are opposite charges attracted too
eachother
What is required to keep opposite charges seperated across a membrane
energy
When does the system has potential energy
when opposite charges are separated
Voltage defination
measure of potential energy generated by separated charge
Potential difference
charge difference across plasma membrane results in potential
Currents
flow of electrical charge (ions) between two points
What is flow dependent on
voltage and resistance
resistance
hindrance to charge flow
insulator
substance with high electrical resistance
conductor
substance with low electrical resistance
Ohm’s law
gives relationship of voltage, current, resistance
Is depolorization occur first or second?
first
does repolorization occur first or second
second
Sensory adaption
made aware but brain no longer cares; stimulus is not strong enough
does sensory adaption apply to pain
no it does not
Membrane potential
voltage difference across the membrane of a neuron
What is typical membrane potential of a neuron
-70mV
How does membrane potential change
they can become more or less negative
Deplorization
inside of a mem becomes less negative then the RMP (upward)
Hypoerpolorization
inside membrane becomes more negative then RMP (downward)
what are the two types of signals
graded and action potentials
What happens when Na channels open
Na+ goes into cell and the 2 forces are charges and gradients
What opens and closes first, Na+ voltage gates or K+ channels
Na+ voltage gates opens and closes first (lemons)
K+ last to open and then slow to close (Lemons husband)
What triggers an action potential to fire
- Small membrane depolorizes by 15-20mv (-70->-50)
- Neuron becomes excited
- Triggers the voltage gated channels to open (due to the voltage change)
What does all or none mean?
Action potentials either happen fully or not at all
If action potentials are all or none how does the brain differentiate between weak and strong stimulis
by the frequency of the action potentials
Absolute Refractory Periods
AP absolutely cannot be fired
- Prevents the neuron from generating an AP
- Enforces one way transmission of nerve impulses
What does Absolute Refractory Periods ensure
that AP’s are separate
Relative Refractory Period
- Follows the absolute refractory
- sodium channels have returned to resting states
- some K+ gates are open
- Repol and hyperpolorization are occuring
Can another AP be fired with a relative refractory period
Yes but you need a very strong stimulus
Conduction velocity
speed of axon potential traveling down an axon
What influences Conductive velocity
axon diameter and presence of a myelin sheath (more= faster)
When do ions move
when there is a change in voltage
What are eddy currents
flow of currents; current moves, charges moves; voltage changes
Where do AP’s occur
ONLY in the axon, no where else
The rate of AP propagation depends on two factors
- Axon diameter
- Degree of myelination
Axon diameter
larger diameter fibers have less resistance to local current flow
Degree of myelination
2 types of conduction depending on presence/absence of myeline
CC and SC
What is continuous conduction
slowest, you need to excite every area (nonmyelin)
What is Saltatory Conduction
leap frogging, fastest speed myelinated (30X faster)
What do myelin sheaths do
insulate and prevent leakage or charge
What occurs first, absolute or relative refractory
absolute: with depolarization
relative: with repolarization
Where are voltage gated Na+ channels located
at myelin sheath gaps
What are graded potentials
Short lived, localized changes in the membrane potentials
- The stronger the stimulus the more voltage channels and the further current flows
What is tetrodotoxin
found in puffer fish, blocks Na receptors(channels) and since everything runs on sodium, youll die
Where are graded potentials located
in receptors of sensory neurons
Where are junctional potentials
in neuromuscular junction
where are postsynaptics
neuron to neuron
What are the differences between GP’s and AP’s
GP’s: cell body and dendrites; only travel localily; different sizes, decay quickly
AP’s: Axon, travels long distance; allows same size, doesn’t degrade
Temporal summation
only 1:1 connections; greater frequency of NT release, greater the chance of signal
Spacial Summation
Many neurons to one; can be both temporal and spacial
- Many people yelling fire, quickly reach the threshold
Are 1:1 neuron connections found in the brain
rarely, the most common is 10:1
If you have an inhibatory neuron and excitatory what is the outcome
inhibatory it only takes 1 inhib to make the whole thing inhibatory
Why does the nervous system work
Works because it flows from neuron to neuron
What is a synpase
junctions that mediate information transfer
What will occur as long as NAP’s are traveling down an axon
have a release of NT’s and have action potential
What does ACHesterase do
cuts ACH off the receptors and follows the process in teh synapse
Synaptic potentiation
repeated use of synpase increases ability of pre-synaptic cell to excite post synaptic neuron
What causes Ca++ voltage gates to open
Potentiation
When Ca++ activates kinase enzymes what does it lead too
more effective response to subsequent stimuli
Learning and memory is what?
Long term potentiation
Presynaptic inhibition
release of excitatory NT’s by 1 neuron is inhibited by another neuron via axoaxonal synpase
Synaptic connections
axodendritic
axosomatic
axodendritic
b/w axon terminals of 1 neuron and dendrites of others
axosomatic
b/w axon terminals of 1 neuron and cell body of others
What are the two main types of synapses
chemical and electrical
Electrical synapses
- less common then chemical
- Neurons are electrically coupled
- joined by gap junctions that connect cytoplasm of adjacent neurons
- communication is very rapid
- found in some brain regions responsible for eye movement
NT’s to know
ACH
Dopamine
Norepi
epi
Serotonin
Histamine
how are NT’s classified
by chemical structure and function
What are imbalances of NT’s associated with
mental illnesses
Proven AA NT’s
- Glutamate (Excitatory)
- Aspartite (Excitatory)
- Glycine (Inhib)
- GABA
Peptides
- String of AA’s that have diverse functions
- Substance P and endorphines
What are endorphins
something the brain releases to reduce pain feelings
What are the effects of NT’s
they can be excitatory or inhib
determined by where it binds
ACH binds to ___ to be excitatory
neuromuscular junctions in skeletal muscles
ACH binds to ___ to be inhibatory
cardiac muscle
how did we find out that ACH and norepi are both E and I
from tabacco and muscorine (mushrooms)
placed them on and watched the effects
Direct actions
NT binds directly to and opens ion channels, promotes rapid responses by altering mem potential
Indirect actions
NT acts through intracellular 2nd messengers typically g-protein pathways
What are the 3 muscle tissue types
skeletal smooth and cardiac
Sarcolemma
muscle plasma mem
sarcoplasm
cytoplasma of muscle cell
Skeletal muscle tissue
- packaged in skeletal muscles that attach to and cover the skeleton
- Has striations
- Voluntary control
- contracts rapidly, fatigue easy
- Responsible for body motility
- exert forces from an oz to 250 lbs
Cardiac muscle tissue
- occurs in the heart
- striated
- nonvol
- conracts at steady rate set by hearts pacemaker
Smooth muscle tissue
- found in walls of hollow visceral organs (Bladder, stomach)
- forced food and other substances through
non-striated and invol
Functional characteristics of muscles
excitability
extensibility
elasticity
contractility
excitability
ability to receive and respond to stimuli
extensibility
ability to be stretched or extended
elasticity
ability to recoil and resume the original resting length
contractility
ability to shorten forcably
Function of skeletal myo
responsible for all locomotion and maintaining posture, stability of joints and generating heat
Function of cardiac muscle
responsible for coursing the blood through the body
Function of smooth muscle
helps to maintain BP and squeezes substances through organs
What is each muscle served by
1 nerve, artery, 1or more veins
What do contracting fibers require
continuous delivery of O2 and nutrients via arteries
Does dead muscle ever come back
Nope
what are the steps that occur for skeletal muscle to contract
- Events at NMJ
- Myo fiber excitation
- Excitation-contraction coupling
- Cross bridge cycling
what is excitation always coupled with
contraction
What is myasthenia gravis
- disease characterized by drooping eyelids, difficulty swallowing, talking and myo weakness
- Involves a shortage of ACH receptors
Indolamines
serotonin: made from the AA trytophan (turkey stuff)
Catecholamines
Domaine; epi, norepi: made from AA tyrosine
purines
monomers of nucleic acids that have an effect in both CNS and PNS
What does caffeine block?
adenosine receptors
endocannabinoids
acts the same as THC; most common g-protein linked receptors in brain
What do connective sheaths do
support cells and reinforce the whole muscle
- each skeletal muscle and myo fiber is covered in CT
What surrounds the entire muscle
epimusium
Surrounds fascile and joins with CT at the bone
perimysium
What is a fascicle
make up 10-15 myo fibers
the smallest group of muscle fibers that can be seen
CT surrounding the muscle fiber
endomysium (sarcolemma)
what happens when Ca binds to troponin
theres a change in confirmation and troponin gets pulled away from actin, the tropomyosin gets pulled too, the actin binding sites get exposed and the paddle heads get excite and allows for connection
Cross bridge steps
- Crossbridge formation: high energy myosin head attaches to actin thin filament active site
- Working (power stroke): myosin head pivots and pulls thin filament toward M line
- Cross bridge detachment: ATP attaches to myosin head, causing cross bridge to detatch
- Cocking of myosin head: energy from hydrolysis at ATP cocks myosin head into high energy state
Rigor Mortis
- 2-3 hrs post death myo stiffen
- Intracellular levels of Ca increases bc ATP isnt be synthesized (Ca cannot be pumped back into SR)
- Myos stay connected until myo proteins break down (bacteria eating them)
- Ca then leaks out causing A and M to attach but they cannot be undone
When does contraction end
when the CB becomes inactive
Do thick/thin filaments overlap at all in resting state
yes only slightly at ends
What is an H-zone
space where A slides; actin becomes against Z-disc
What is a motor unit
a motor neuron and all the myo fibers it supplies
How many myofibers are in each motor unit
4-several hundred
What is a myo twitch
response of a myo to a single, brief threshold stimulus
what are five reasons for myo fatigue
- ATP production fails to keep pace with ATP use
- There is a reletive deficit of ATP, causing contractions
- Lactic acid accumulates in myo
- ionic imbalances are present
- Calcium deficiency
Why do contractions increase
- theres increasing Ca++ in SR
- Myo enzyme systems become more efficient bc heat is increased
What is muscle tone
constant, slightly contracted state of all muscles
- keeps myos firm and healthym ready to respond to stimuli
What affects the force of contraction
- The number of myo fibers contracting
- The relative size of the muscle
- Degree of myo stretch
Isotonic contractions
pick up the load your muscle shortens
Isometric contractions
- generates lots of force, doesn’t shorten
can myos be both isometric and isotonic
yes, but they must be isometric before they become isotonic
What determines the speed of contraction
the soeed by which ATPases split ATP
What are the three muscle fiber types
- Type 1/Slow oxidative
- Type 2A/Fast oxidative Glycolytic
- Type2B/Fast Glycolytic
Type 1/Slow oxidative fibers
contract slowly, have slow acting myosin ATPases, are fatigue resistant (lots of BS, O2 and capillaries)
Type 2A/Fast oxidative Glycolytic
contract quickly, have fast myosin ATPases and have moderate fatigue resistance (thicker; int. cap dense, flucuate b/w ana and areobic)
Type2B/Fast Glycolytic
contract quickest, have very fast myosin ATPases and are easily fatigued
Smooth muscle
composed of spindle fibers with 2-10 micometer diameter
- lack CT sheaths have a fine endomyosium
- has the same contractile mech as skeletal myo
how many contraction cycles in smooth myo per min
12-15 at a speed of 1-5 seconds
Peristalsis
alternating rhythm
What happens when the longitudial layer contracts
the organ dialates and contracts
what happens when the circular layer contraction
the organ elongates
What drives vasod and vasoc
vasod- relaxation driven by ach
vasoc-contraction driven by epi
Does smooth muscle have a t tubule or sarcomers
nope
Is the ratio of thick to thin filaments in smooth myo lower or higher then in skeletal
lower
in smooth myo how are the thick and thin filaments arranged
diagonally so they cause smooth myo to contract in a corkscrew manner
How does skeletal myo contract
in unison which reflects hte electrical coupling with gap junctions
What is the contraction mech for smooth myo
with an increase of Ca, it binds with calmodulin and with myosin light chain kinase, in presence of Ca the myosin combines with ATP+ actin making AMATP–> AM ADP+Pi + energy
When does smooth muscle relax
when intracellular Ca++ levels drop
What are some unique features of smooth muscle
- smooth myo tone
- slow, prolonged contractile activity
- low energy requirements
- response to stretch
Hyperplasia
- Smooth muscles can divide and increase their numbers by undergoing hyperplasia
- Shown by estrogen in the uterus: hormone that increases smooth myo cells
Sarcopenia
the loss of muscle mass, by age 80, 50% is lost
What myos can regenerate
- skeletal and cardiac can lengthen and thicken but can’t regen
- smooth myo can regen
Skeletal myo mass in womens
36% of their body mass is skeletal myo
Skeletal myo mass in men
42% of their body mass is skeletal myo
