Exam 3: Muscles, Intro to Nervous system Flashcards
What are the 3 types of muscles?
Skeletal muscle, smooth muscle, cardiac muscle
What are the functions of skeletal muscle?
locomotion (physical movement), posture, respiration
describe Skeletal muscle
voluntary (stimulated by motor neuron)
striated
What are the functions of smooth muscle?
contraction of hollow organs, vasoconstriction, vasodilation
describe smooth muscle
most widely distributed muscle type (in hollow organs & blood vessels)
involuntary (enteric and autonomic nervous system regulation - not controlled consciously)
Some are autorhythmic (initiate contraction w/o external nervous stimulation - muscles can self-contract)
what are the functions of cardiac muscle?
contraction of heart chambers
describe cardiac muscle
only found in heart
involuntary (regulated by autonomic nervous system)
Autorhythmic
striated
What are the connective tissues of muscles?
fascicles and coverings
what are fascicles?
bundles of muscle fibers
what are the coverings of muscles?
endomysium - around the fiber
perimysium - around the fascicle
epimysium - around the muscle
Muscular fascia - superficial to to the epimysium, separates/ compartmentalizes muscles
what do connective tissues of muscles do?
extend to form tendons
What are the parts of innervation and vasculature of muscles
nerve stimulation
blood vessels
how does nerve stimulation occur
motor neurons (like the sciatic nerve)
describe the blood vessels of muscles
capillary beds around muscle fibers
muscle blood vessels are supplied and drained by arteries and veins
what are the cells of muscles
myofibrils
Parts of myofibrils
actin myofilaments (thin)
myosin myofilaments (thick)
actin and myosin form sarcomeres
what are sarcomeres
functional unit of skeletal muscle
what do sarcomeres form
striations
Describe light bands
I bands (isotropic, uniform) that extends to ends of myosin myofilaments
Describe dark bands
A bands (anisotropic, not uniform) that extends the length of myosin
what do light and dark bands make
striations
Describe the H zone of striations
only myosin is present
describe m line of striations
holds myosin in place
Parts of Actin
F actin (“fibrous”) - forms “strands” of actin
Tropomyosin - dark line of actin
G actin (globular) - forms “beads” of actin: there are 2 strands of beads (proteins) twisted together in actin
Troponin - has 3 subunits
1. binds to G actin
2. binds to calcium ions (Ca++)
3. binds to tropomyosin
what is the function of myosin heads
binds to actin molecules = cross bridge
contraction of muscle (hinge region bends and straightens)
Have ATPase (enzyme) to break down ATP & power movement
Describe the sliding filament model
Actin myofilament sliding over the myosin myofilament:
-shortening of sarcomere
-shortening leads to muscle contraction
Relaxation=lengthening of sarcomere
Describe the resting membrane potential
Voltage (charge) difference across cell membrane when cell is at rest
(inside of cell is more negatively charged than outside of cell)
what is a resting membrane potential caused by
more positive (+) ions outside cell
fewer positive (+) ions inside the cell (some + ions leak out of cell)
so there is a negative charge inside the cell when at rest
How does membrane permeability occur?
Via channels in the plasma membrane
Describe how voltage-gated ion channels work
open or close in response to a certain membrane potential (charge in cell)
Describe how Ligand-gated ion channels work
open or close in response to presence/absence of a chemical signal
describe an inactive site of a ligand-gated ion channel
no ligand is present
channel is closed
describe an active site of a ligand-gated ion channel
ligand bound
channel is open
Sodium ions (Na+) enter cell
What is an action potential (AP)
temporary reversal of voltage (charge) inside cell —> voltage within cell becomes temporarily positive
“signal firing”
What are the stages of an action potential
- Resting Membrane Potential
-no ion channels open
Stimulus
-some Na+ channels open
-Na+ starts to move into cell (start of depolarization)
- Depolarization (2nd part)
-Voltage-gated Na+ channels are open
-Na+ rushes into cell - Repolarization
-Na+ channels close
-voltage-gated K+ channels open
-K+ rushes out of cell - Hyperpolarization
-“undershoot”
-excess K+ moving out of cell - Back to resting membrane potential
what are some action potential concepts
all-or-nothing principle
-if threshold is reached (-55 millivolts), entire process of AP occurs
-if threshold is not reached, nothing happens
Propagation of AP
-triggers APs all along axon toward axon terminals
Strength of signal
-strong stimulus=increased AP frequency (not larger APs)
What do axon terminals do
will release neurotransmitter (chemical signal) —> stimulates muscle
What is a neuromuscular junction
site of transmission of action potential from motor neuron to muscle fiber
synapse of neuron on muscle fiber
Acetylcholine (Ach), important neurotransmitter released
describe what occurs at a neuromuscular junction
- Action potential arrives at axon terminal
- Voltage-gated calcium (Ca++) channels open
-Ca++ rushes IN to axon terminal - Calcium ions (Ca++) triggers vesicles to release acetylcholine (Ach) into synaptic cleft
- Acetylcholine (Ach) diffuses across synaptic cleft
- Acetylcholine (Ach) binds to receptors on muscle fiber
- Na+ (sodium) channels open
-Na+ moves into muscle fiber
-triggers action potential (AP) in muscle fiber
…. —-> Muscle contraction
How is acetylcholine rapidly cleared?
Acetylcholinesterase
-breaks down Acetylcholine (Ach) in synaptic cleft —>
-ensures Ach does not accumulate & constantly stimulate muscle
-Broken down parts are recycled within axon after metabolism
what is excitation-contraction coupling
conversion of neural signals into physical process of contraction
Neuron action potential —> Muscle action potential —> contraction
what are T-tubules
transverse tubules
-infoldings of sarcolemma
what is the sarcoplasmic reticulum
modified smooth ER
-stores Calcium ions (Ca++)
-releases Ca++ into sarcoplasm (muscle fiber cytoplasm) in response to muscle action potential
What is the sarcolemma
plasma membrane of muscle fiber
Describe the process of neurotransmitter release to muscle contraction
- Acetylcholine secretion from motor neuron, Ach binds to receptors on muscle fiber (detailed steps at neuromuscular junction)
- Increased influx of sodium ions (Na+) into muscle fiber —> triggers muscular action potential
- Propagation of action potential across muscle fiber
- Depolarization of membrane and release of calcium ions (Ca++) from sarcoplasmic Reticulum (SR)
-due to: travelling of action potential into the inside of the fiber (T-tubules) - Cross-bridge formation & sliding filaments (or muscle contractions)
-due to: Ca++ binding to troponin
-troponin-tropomyosin complex moves out of the way, revealing active (binding) sites for myosin to bind on actin - Calcium ions (Ca++) goes back into sarcoplasmic reticulum (SR)
-restoration of filaments to original positions
describe cross-bridge cycling
repeated interaction of myosin head & actin myofilament
-cross-bridge formation
-sliding myofilaments
-release…and repeat
Happens many times in a single muscle contraction
Needs ATP for movement/contraction to occur
what does relaxation require
energy
Describe muscle relaxation process
-No more release of acetylcholine (Ach) at neuromuscular junction —->
stops action potentials along sarcolemma —->
stops Ca++ release from Sarcoplasmic reticulum (SR)
-movement of Ca++ back into SR
—->
energy-dependent process
-Ca++ actively pumped back into SR (requires ATP)
-Restoration of membrane potential (negative charge) —->
Na+/K+ pumps to do this (requires ATP)
What is a motor unit
motor neuron and ALL the muscle fibers it innervates (synapses to)
Allows muscles to contract as a single unit
What is a muscle twitch
A single contraction of muscle in response to stimulus
-due to action potential in one or more muscle fibers from motor neuron
what are the phases of muscle twitch
lag/latent - time between stimulus & start of contraction
contraction - start of contraction to peak of tension in muscle
Relaxation - from peak of muscle tension back to fully relaxed
NOT AN AP
how do muscles respond
in a graded fashion=greater stimulus on muscles produces greater strength of contraction
what is recruitment
increased number of motor units stimulated (produces higher force of contraction)
Number of fibers in motor unit vary based on motion generated
Describe Recruitment example of playing banjo
delicate, precise movement –> more motor units –> but fewer fibers per motor unit
Describe recruitment example of kicking something big over
large, less precise movement –> fewer motor units –> but lots of fibers per motor unit
Define summation
additional twitches before muscle has fully relaxed (also produces higher force of contraction)
Define Incomplete Tetanus
partial relaxation of muscle between contraction
Define complete tetanus
no relaxation of muscle
*rapid frequency of stimuli
*sustained contraction!
what leads to tetanus
high frequency stimulation
-this can cause fatigue, Additional Ca++ in muscle fiber causes greater force of contraction
Define treppe
“staircase” of increased frequency of stimulation
-increasing force of contraction in response to same level of stimulation
-eventually reach the maximum level
Think of warming up before full exercise/workout
-increases muscle efficiency with progressive force
Describe isometric contraction
no change in muscle length, no movement of limbs
increase of tension/force in muscle during contraction
what is an example of isometric contraction
maintenance of posture
Describe Isotonic contraction
change in muscle length, movement of limbs
tension produced by muscle is constant
change in length of muscle
Example of isotonic contraction
moving arms or fingers like when doing a bicep curl
what are the 2 types of Isotonic contraction
concentric contraction
eccentric contraction
define concentric contraction
working muscle shortens
tension of muscle great enough to overcome the weight load
(ex. curling bicep up)
define eccentric contraction
working muscle lengthens
Tension being maintained against the load
(ex. releasing bicep curl down with control)
define muscle tone
constant tension produced by muscles for long periods
-small percentage of motor units contracting asynchronously
Maintenance of posture
define fatigue
the diminished ability for muscles to generate force
psychological leads to physiological effect
physiologically: accumulation of metabolites & lack of glycogen may interfere with Ca++ release from Sarcoplasmic Reticulum
Describe slow twitch/ Type I muscle fibers
-smaller fiber diameter
-slower response to nervous stimulation
-extensive vasculature
-higher mitochondria & myoglobin (oxygen storing molecule) concentrations
——>darker red appearance due to myoglobin
-slow ATP breakdown
-good for long sustained movements, not great for big powerful movements
Example of when slow twitch fibers are used
ultramarathon running
Describe fast twitch/ Type II fibers
-larger fiber diameter
-faster response to nervous stimulation
-less vasculature
-less myoglobin & mitochondria
—->lighter (pink) color
-Fast ATP breakdown
-higher glycogen (reserve of glucose) content
-more susceptible to fatigue, but good for large powerful movements
Example of when fast twitch fibers are used
Olympic powerlifting
What are the 2 major subdivisions of the nervous system
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
What are the parts of the central nervous system
brain
spinal cord
functions of central nervous system
-integration of information
-generate memories
-control of various system
-mentation (thinking, learning, understanding)
what 2 kinds of nerves have we discussed?
cranial
spinal nerves
where do cranial nerves originate from
the brain
where do spinal nerves originate from
spinal cord (they then extend laterally)
how many pairs of cranial nerves do humans have
12 pairs
how many pairs of spinal nerves do humans have
31 pairs
What are the parts of the peripheral nervous system
-sensory receptors
-nerves
-ganglia
-plexuses
What is the function of sensory receptors
detection of various sensations
what is the function of nerves
links between sensory receptors and central nervous system
what are ganglia
cluster of neuron cell bodies located outside of the central nervous system
what are plexuses
“braids” of neurons and axons located outside of the central nervous system
what are the subdivisions of the peripheral nervous system?
Afferent (sensory) division
Efferent (motor) division
What does the afferent (sensory) division of the PNS do
-transmission of signals from sensory receptors TO the CNS via sensory neurons
-entry point to the CNS (dorsal horn of the spinal cord)
what does the efferent (motor) division of the PNS do
-transmission of signals AWAY from the CNS to the organs via motor neurons
-exit point from CNS (ventral horn of the spinal cord)
What is the division of the efferent (motor) division of the PNS
Autonomic Nervous System (ANS)
what is the function of the autonomic nervous system (ANS)
involuntary regulation of functions in the body
Ex: heart rate, pupil diameter, blood pressure, blood vessel diameter, etc.
what are the 2 branches of the Autonomic Nervous system
sympathetic branch (“fight-or-flight”)
parasympathetic branch (“rest-and-digest”)
what does the enteric part of peripheral nervous system do
regulation of the GI tract function
*plexuses on walls of GI tract
What neural tissue exists in nervous system
neuron
neuroglial cells
what is the function of a neuron
generate, send, and receive neural signals
What is the function of neuroglial cells
support and protection for neurons/nervous system
what are the parts of a neuron
neuron cell body
dendrites
axon
axon terminals
myelin sheaths
nodes of Ranvier
what is the function of dendrites
receive signals from other neurons
what is the function of axons
transmit signals
what is the function of axon terminals
send signals to other neurons (or organs like the muscles)
how does transmission of neural signal occur
across the entire length of the axon
-only moves from trigger zone to axon terminals, not backwards
what are the neuroglia of the CNS
Oligodendrocytes
what are the neuroglia of the PNS
Schwann cells
what is the function of Oligodendrocytes and Schwann cells
produce myelin sheaths that surround axons of some neurons
what is myelin
lipid-rich insulation
does myelination of axon speed up action potential function
yes
how does myelination of axon speed up action potential function
Saltatory conduction
what is saltatory conduction
it means “jump”
-APs only occur at node of Ranvier
-voltage-gated Na+ and K+ channels concentrated at the nodes; myelinated regions of axon have almost no channels
-unmyelinated axons have channels along its length —> slower propagation of APs
Myelinated axons=
faster conduction
thicker myelin sheaths=
faster conduction
greater axon diameter=
faster conduction bc there is a greater surface area for Na+ channels
Large myelinated axons conduct at
120 m/s (ex. skeletal muscle neuron)
small unmyelinated axons conduct at
0.7 m/s (ex. GI tract neuron)
what is AP speed of conduction related to
urgency of information
Ex. response for digestion vs. tripping and falling
