Lecture #2 Flashcards
Characteristics of muscles
- Excitability (responsiveness)
- Conductivity
- Contractility
- Extensibility
- Elasticity
Types of muscles
- Skeletal
- Cardiac
- Smooth
Myofilaments – the functional contractile unit
- Muscles shorten b/c their individual sarcomeres shorten
Neither thick nor thin filaments change length during shortening - Only the amount of overlap changes
Sliding Filament Thoery
Thick and thin filaments slide over one another = sliding filament theory
Elastic filaments (titin) stabilize thick filament and allows recoil
Myofilaments - Thick
Made of several hundred myosin molecules, shaped like a golf club
Heads directed outward in a helical array around the bundle

Myofilaments - Thin Filaments
- Fibrous (F) actin: two intertwined strands
• String of globular (G) actin subunits each with an active site that can
bind to head of myosin molecule 2. Tropomyosin
• Blocks active sites on G actin subunits - Troponin
• Calcium-binding protein on each tropomyosin molecule
2 kinds of muscles
- Striated Muscles - have sarcomeres, and alternating light and dark bands
- Smooth Muscle
lack sacromeres
Striations
Dark = A band -- thick (myosin) and thin (actin) overlap Light = I band -- thin filaments (actin) only
Nerve Relationship
skeletal muscles never contracted unless stimulated by a nerve
Muscle fibers of one motor unit
- contract in unison
- dispersed throughout muscle (large SA = weaker contraction)
- long term contraction
Excitation
nerve action potentials = muscle action potentials
Excitation-contraction coupling
link action potentials on sacrolemma to activation of the myoflimates … preparing them to contract
Contraction
muscle fibers develop tensions and shortens
Relaxation
relaxes and turns to resting length
The process of Excitation
- Voltage-gated Ca+ channels open in synaptic knob
- Ca+ enters, which causes the release of ACh
- ACh binds to receptor
- Na enters = end plate which opens and creates action potential
The process of Excitation-contraction Coupling
- Action potential spreads down T tubules
- Open voltage-gated ion channels in T tubules and Ca channels in SR
- Ca leaves SR and
enters cytosol, binds to troponin = exposure of active sites on actin
The process of Contraction
- ATPase in myosin head hydrolyzes ATP
- Activates the head “cocking” it in an extended position
• ADP + Pi remain attached - Head binds to actin active site forming a myosin–actin cross- bridge
- Myosin releases ADP and Pi, and flexes pulling thin filament with it = power stroke
Latent Period
delay between stimulus and contraction
Contraction Phase
time when muscle generates external tension
Relaxation phase
—time when tension declines to baseline
Recruitment or multiple motor unit (MMU) summation
Occurs according to the size principle
Isometric Contraction
Muscle produces internal tension but external resistance causes it to stay the same length – Stablizing
Isotonic Contraction
Muscle changes in length with no change in tension
Sensory Receptors and its general properties
a structure specialized to detect a stimulus
- Transduction—the conversion of stimulus energy into nerve signals
- Receptor potential—small local electrical change on a receptor
cell
Sensation
a subjective awareness of the stimulus
Sensory Receptores
- Afferent neurons
- Epithelial Cells
both send signal to integrating centre
Phasic receptors
adapt rapidly, smell, hair movement
Tonic Receptors
adapt slowly, body position, joint movement
Free nerve endings
for pain and temperature
located in skin and mucous membrane
Tactile (Merkel discs)
for light touch and tecture
Hair receptors
monitor movement of the hair
Somatosensory Projection Pathways
from receptor to brain
1st order neuron
2nd order neuron
3rd order neuron
The Chemical Senses
Taste (Gustation): • stimulants on taste buds • Tastants must dissolve in saliva • Smell (Olfaction): • Response to odorants
The Five Primary sensations of taste
1. Salty: • by metal ions 2. Sweet: • associated with carbohydrates 3. Sour: • acids such as in citrus fruits 4. Bitter: • associated with spoiled foods 5. Umami: • “meaty” taste of amino acids
Hearing and Equilibrium
Hearing - a response to vibrating air molecules
Equilibrium- the sense of motion, body orientation, and balance
- Sound
- Loudness
- Pitch
1.any audible vibration of molecules
- the perception
of sound energy, intensity, or amplitude of the vibration in decibels (dB) - sense of whether a sound is “high” or “low”
vibration frequency: hertz (Hz) or cycles/second
