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Four Special Characteristics of Muscle

-Excitability: (responsiveness), can receive/respond to stimuli.
-Contractility: can shorten forcibly when stimulated.
-Extensibility- can extend or stretch.
-Elasticity- can recoil and resume resting length after stretching.

Muscle Connective Tissue Sheaths Hierarchy

Epimysium (Surround muscle)
-Perimysium (Surround Fascicles)
-Endomysium (surround each muscle fiber)

Muscle Attachments

-Origin is the immovable or less movable bone, Insertion is the movable bone.
-Direct attachments: Muscle cartilage is fused to periosteum of bone or perichondrium of cartilage
-Indirect attachments: connective tissue extensions of muscle: Rope like (tendon) or sheet like (aponeurosis).

Inducing a muscle contraction (4 steps):

1. Change of membrane potential induced by nerve ending stimulation
2. Action potential generated in sarcolemma of muscle fiber
3. Action potential automatically propagates along sarcolemma
4. Intracellular Calcium ions rise briefly, providing final trigger for contraction.

Regulatory proteins of thin filament

Troponin- Small protein on tropomyosin-troponin complex, undergoes a conformational change when binding with calcium ions, moves tropomyosin off active sites, allowing for myosin head binding (crossbridge formation)
Tropomyosin- elongated protein which covers active sites when muscle is relaxed.

Regulatory proteins of thin filament

Troponin- Small protein on tropomyosin-troponin complex, undergoes a conformational change when binding with calcium ions, moves tropomyosin off active sites, allowing for myosin head binding (crossbridge formation)
Tropomyosin- elongated protein which covers active sites when muscle is relaxed.

Action potential in muscle fiber

Threshold is reached after AcH binds to receptors (channel for Na+)
Na+ voltage gated channels open and the cell depolarizes due to Na+ entry.
At peak potential Na+ channels close and K+ channels open
Repolarization occurs due to K+ exit (loss of positive charge)
Sodium-potassium pump works to maintain resting membrane potential in order to receive next signal.

Events at Neuromuscular junction (summary)

Events at Neuromuscular junction (summary)
1. AP reaches terminal impulse (action potential depolarization)
2. Release of AcH into synaptic cleft by exocytosis
3. AcH binds to AcH receptor, which increases membrane permeability to sodium ions
4. Sodium ion increase induces action potential which spreads
5. Calcium ions are released from the sarcoplasmic reticulum
6. Actin myosin interaction results in contraction

Calcium and ATP roles in muscle contraction

-Calcium binds to troponin (a small protein on tropomyosin), conformational change occurs, causes complex to shift position, leading to exposure of myosin binding sites.
-ATP attaches to myosin and weakens the link between myosin and actin, detaching the crossbridge

Sarcomere parts

A bands come closer together but do change size
I bands shorten, bringing z discs (do not change size) closer together
As the Z discs move closer together and the I bands shorten, the H zone disappears

Muscle Twitch physiology

Muscle twitch is a motor units response to a single action potential of its motor neuron
-Latent period: cross bridges begin to cycle, no measureable tension
-Period of contraction: tension peaks, if tension>resistance of load, muscle shortens
-Period of relaxation: Initiated by reentry of Ca2+ into the SR, muscle tension decreases to 0. Muscle returns to initial length.

Temporal (Wave) Summation and Recruitment (Multiple Motor unit summation)
Effects on Muscle Contraction

-Temporal Summation: if two identical stimuli are delivered to a muscle in rapid succession, the second twitch will be stronger because the second contraction occurs before the muscle has completely relaxed, therefore the contractions are added together.
-Recruitment (multiple motor unit summation)-Controls force of contraction more precisely, delivery of shocks in increasing voltage to muscle cells bring more and more muscle fibers into play.

Subthreshold Stimulus Vs. Threshold Stimulus Vs. Maximal Stimulus

-Subthreshold stimuli produce no observable contraction
- Threshold stimuli are at the point in which the first observable contraction occurs.
-Maximal stimuli is the point at which all the muscle motor units are recruited (strongest)

How muscles generate graded responses

-Strength of force is dependent on frequency of stimuli, achieved by increase in firing rate of motor neurons.
-Motor units with smallest muscle fibers are activated first, and as motor units with larger and larger muscle fibers begin to be excited, contractile strength increases.

Main categories of muscle contractions

Isotonic- Tension develops muscle length shortens and moves a load.
Isometric- Tension develops but load is too heavy and muscle does not shorten
Concentric- Increases tension/Muscle shortens
Eccentric- Increases tension/Muscle lengthens

Sources of ATP to support muscle contraction during exercise

-Store of ATP to get things going
-Direct phosphorylation of creatine phosphate and ADP (energy source: CP, 1 ATP per CP, duration of energy: 15 seconds) No oxygen used
-Anaerobic pathway: glycolysis and lactic acid formation from pyruvic acid (2 ATP per glucose, lactic acid by-product; duration of energy: 30 secs-2mins) No oxygen used
-Aerobic Pathway: Aerobic cellular respiration, energy source: glucose from glycogen breakdown or blood, pyruvic acid from glycolysis, fatty acids from adipose tissue; duration of energy: hours. 32 ATP per glucose, CO2, H2O)

Types of muscle fibers

Slow oxidative fibers: (energy from aerobic pathway) Fatigue resistant, endurance, recruited first
Fast oxidative fibers: (energy from aerobic pathway) Moderate fatigue resistant: Sprinting, recruited second
Fast glycolytic fibers: (energy from anaerobic glycolysis): Fast Fatigue: Lifting heavy weight, recruited third.

Determining factors of strength:

1. # of motor units activated, especially fast twitch
2. Size of muscle-cross sectional area (# of muscle fibers/size of muscle fibers, increased by exercise)
3. Frequency of firing (wave summation)
4. Degree of Muscle stretch- muscle can generate the most force at 80-120% resting length

Events at neuromuscular junction flowchart

1. AP in motor neuron
2. Release of acetylcholine from the axon terminal (exocytosis induced by an increase of calcium)
3. Acetylcholine binds to its receptor on the myofiber, produces an action potential in the myofiber, causing calcium release from S.R.
4. Contraction

Where do action potentials occur in nerve cells and muscle cells?

Axon and Axon hillock in neurons and anywhere in the muscle cell.

Threshold definition and information

The membrane potential required to open voltage gated Na channels,

Events at the peak of the action potential

-Once the peak is reached Na channels close and K+ channels open

Graded potential vs Action potential

Graded potentials are proportional to how much sodium comes into the cell (amount of stimulus) Graded potentials can be added together and will spread further greater chance of reaching threshold at axon hillock)

Speed of contraction

how fast a muscle contracts depends on the load

Calculation of power

Work/time

Calculation of Work

Distance x weight

Differences in smooth muscle excitation-contraction coupling

-Cross bridge formation: What is binding the calcium because there is no troponin
-How filaments are arranged (thick filaments are fewer but have myosin heads along their entire length, thick and thin filaments are arranged diagonally)

How crossbridges are formed in smooth muscle

1. Inactive calmodulin binds calcium
2. Calmodulin activates the myosin light chain kinase enzymes
3. Activated kinase enzymes catalyze the transfer of phosphate to myosin.
4. Activated myosin forms cross bridges

CNS components/function

-brain, spinal cord
-interprets sensory input, dictates motor output based on reflexes, current conditions, and past experiences

PNS components/function

-Nerves (bundles of axons) extending from the brain to the spinal cord

Functional divisions of the PNS

-Sensory (afferent) Impulses to CNS
Somatic sensory fibers- from skin, skeletal muscles, joints
Visceral sensory fibers- Convey impulses from the skin to
-Motor (efferent) Impulses from CNS to effector organs
Somatic nervous system- (voluntary) voluntary control of skeletal muscles
Autonomic nervous system- (involuntary) regulation of smooth muscles

CNS neuroglia

-Astrocytes, microglial cells, ependymal cells, Oligodendrocytes

PNS neuroglia

-Satellite Cells
-Schwann Cells

Astrocyte/Satellite

-Involved in making changes between capillary neurons, helping determine capillary permeability

Microglial cells function

-Transform into macrophages in case of infection

Oligodenrocytes/ Schwann cells

Produce an insulation covering called the myelin sheath

Ependymal Cells function

Brain and spinal cord and provide a fairly permeable barrier between the CSF and nervous tissue

Differentiate between depolarization and hyperpolarization

depolarization is a decrease in membrane potential
hyperpolarization is an increase in membrane potential

Graded potentials vs Action potentials

graded potentials are incoming signals over short distances
action potentials are long distance signals of axons

Conduction velocity is determined by

-Axon diameter
-Degree of myelination

Saltatory conduction

Aps are only triggered at the gaps due to myelination, the more myelinated, the faster.

Absolute refractory vs. relative refractory

-Absolute refractory period is the period from when the Na+ channels until the Na+ channels begin to reset. It ensures that each AP is a separate "all or none" event and enforces the one way of transmission of the AP.
-The relative refractory period is the interval following the absolute refractory period, during this time a stimulus that would normally generate a stimulus is inefficient, another AP can be generated by an exceptionally strong stimuli

Differentiate between chemical and electrical synapses

-Electrical are specialized to allow the release and reception of chemical neurotransmitters.
-Chemical synapses- membrane bound sacs called synaptic vesicles

Synaptic transmission

1. AP arrives at synapse
2. Voltage gated Ca2+

Processes by which Neurotransmitter effects are terminated

-Reuptake by astrocytes, neurotransmitter is stored or destroyed
-Degradation- by enzymes
-Diffusion- away from synapse

common strategy for drugs

A common strategy of drugs is to block the reuptake of certain neurotransmitters, prevent degration, in order to prolong polarization caused by neurotransmitter.

Types of synapses

-axodendritic synapses- synapses between and dendrites of another
-axosomatic synapses- between cell bodies and dendrites
-presynaptic neuron- the neuron transmitting the electrical signal away
-postsynaptic neuron- the neuron transmitting the electrical signal from the synapse

IPSPs vs EPSPs

IPSPs are hyperpolarizing changes in potentials, binding of neurotransmitters reduces a postsynaptic neurons ability to generate an action potential
EPSPs trigger an action potential

Integration and modification of post synaptic events

No summation
temporal summation: two excitatory stimuli close in time, add together
Spatial summation: two simultaneous stimuli cause EPSPs that add together.
(summation of EPSPs and IPSPs).

Neurotransmitter agonists and antagonists

agonists promote effect (depolarization)
antagonists inhibit effect (hyperpolarization)

Excitatory vs inhibitory neurotransmitters

Excitatory cause depolarization
Inhibitory cause hyperpolarization

Neuromodulator vs. Neurotransmitter

Neuromodulator is a chemical messenger that effects the strength of synaptic transmission and does not cause ESPSs or ISPSs directly

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