Download - Anatomical Review of Muscle Cell anatomy
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Anatomical Review of Muscle Cell anatomy
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Fig. 12.1
Whole muscle = many muscle cells + CT
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Fig. 12.15
Individual Muscle Cell—Anatomy Review
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Fig. 12.6
Organization of actin and myosin filaments--Alternating and overlapping
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Fig. 12.7
Organization of a sarcomere
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Muscular System
• Skeletal Muscles and associated connective tissue– Skeletal muscle cells=muscle fibers
FUNCTIONS• Produces movement
– (through contraction of cells)– Important in verbal and non-verbal communication
• Stabilizes joints and maintains posture – (through contraction of cells)
• Produces body heat – (through high levels of cellular respiration)
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OVERVIEW OF SKELETAL MUSCLE ACTIVITY
BrainMotor Neurons, synaptic activity--ACh
Action Potential & propagation
sliding of actin & myosin filaments
Ca+ channel activity
production of force and movement (sometimes)
ATP production/consumption
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CONTROL OF SKELETAL MUSCLES
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Voluntary Motor Activity Originates in Frontal Lobe of cerebral cortex
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13-10
Voluntary Muscle Contraction:
Neuron Activity Begins Frontal Lobe:
Upper motor neuron
• Decussates in medulla (~80%)
• Travels down spinal cord through anterior or lateral corticospinal tracts to lower motor neuron
• Synapse with lower motor neuron
•Lower motor neuron travels through nerve to effector muscle
•Forms synapse—Neuromuscular Junction—with muscle
•NT= Ach binds to nicotinic receptors
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Neurological Control of Skeletal Muscle
• CNS (brain and spinal cord): generate motor commands that will signal muscle cells to contract
• Voluntary Activity
– Frontal lobe: initiates voluntary muscle activity
– Basal nuclei: coordinates voluntary muscle activity
– Thalamus: involved with coordination of voluntary muscle activity
– substantia nigra: coordinates muscle activity (inhibits antagonistic muscles)
– Cerebellum: coordinates muscle activity (makes adjustments based on current body position)
• Cranial reflexes– Generate involuntary, reflexive muscle use to specific stimuli. Integrating center is in brain
• Spinal Cord– Spinal reflexes
• Generate involuntary, reflexive muscle use to specific stimuli. Integrating center is in spinal cord
• Lower motor neurons (PNS) directly innervate muscle cells– CNS initiated commands are relayed (through synapses) to lower motor neurons which carry
A.P.s from CNS to the individual muscle cells they innervate.
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Neurological Control of Skeletal Muscle
• All Skeletal Muscle cells are directly innervated by a motor neuron
• Neuromuscular Junction:– The chemical synapse between a motor neuron and a
muscle fiber (cell)– Chemical synapse, always excitatory
• Motor Units: a motor neuron and all the muscle cells it innervates– Multiple fibers innervated by same neuron– They contract together as a unit
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Fig. 12.4
This neuron is also a lower motor neurons
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Fig. 12.3
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Key NMJ concepts
• Chemical synapses (as described in neuron physiology unit)
• Neurotransmitter: ACh
• Receptor: nicotinic
• Receptor Action: ACh opens ligand gated Na+ channel, Na+ enters cells depolarizing itend plate potential
• Short-lived due to action of ACh’ase
• NMJ are always excitatory
• A single AP almost always releases enough ACh to bring the motor end plate/muscle cell to threshold
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Structure and events that occur at a NMJ
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Another representation of the events at a neuromuscular junction
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EXCITATION-CONTRACTION COUPLING: from AP formation at synapse to actin-myosin interaction
• AP propagates across PM (sarcolemma of muscle cell)
– VG Na+ channels
– Just like an AP in axon
• AP travels down T-tubels
• VG Ca+ channels (aka DHP receptors) open– DHP receptors are coupled/linked to Ca+
release channels
• Ca+ release channels (aka ryanodine receptors) open
• Ca+ floods into cytoplasm
• Ca+ binds actin filament allowing actin-myosin interaction
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Fig. 12.16
Visual representation of excitation-contraction coupling
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Fig. 12.17
Flow Chart of excitation-contraction coupling
events
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• REVIEW OF MYOFILAMENT ANATOMY AND FUNCTION
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Fig. 12.13
Ca+ binds
Covers up binding sites for myosin heads, can
move to expose binding sites
Has binding sites of myosin head, will be
bound by myosin during interaction/contraction
ACTIN FILAMENTS
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Fig. 12.10
Myosin Head:• Binds Actin• Have binding site for ATP• Will grab, pull on, and detach from actin
MYOSIN FILAMENT STRUCTURE
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Fig. 12.9
Filament Interaction:•Myosin grabs and pulls on actinfilaments slide across one another•Zone of filament overlap increases•Sarcomeres get shorter cell shortens=contraction
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FILAMENT INTERACTION: SLIDING FILAMENT THEORY OF MUSCLE CONTRACTION
• Myosin and actin filaments interact
• Myosin pulls on actin• Filaments slide past one
another increasing zone of overlap
• Sarcomeres get smaller• Results in contraction of
muscle and production of tension (i.e., pulling force)
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Fig. 12.14
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When Ca+ binds troponin, tropomyosin moves to expose myosin binding sites as shown in diagram
NOTE:This is show as if you were viewing the filaments along their short axis—different perspective then other diagram
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Fig. 12.10
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Fig. 12.11
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Fig. 12.12
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Table 9.02
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Table 12.2
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Figure 9.12
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Production and Control of Tension• Contraction produces
pulling force known as tension
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Twitch: a single contraction. The result of a single AP/excitation contraction coupling event
Latent: •AP propagation, Ca release, Ca build up in sarcoplasm
Contraction:• Active cross bridging/contraction, Ca+ available
Relaxation:• Ca+ decreasing in sarcoplasm, diminished and eventual lack of crossbridging/contraction
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Figure 9.41
Relationship between time of stimulus, AP, and tension
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Factors that influence tension (i.e., strength of contraction)
• Action Potential (stimulus) frequency
• Number of active fibers/number of motor units activated
• Fiber length (amount of actin-myosin overlap)
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Figure 9.19
Green: single twitches, complete relaxation between
Orange: partial relaxation between two stimuli stimuli
wave summation—second contraction stronger than first
Purple: two stimuli with no relaxation between
contraction stronger than that with a single stimulus
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Summation (temporal/frequency)
• Increased stimulation rate increased tension/strength– Build up/availability of Ca+ in cytoplasm
• Incomplete/unfused tetanus—stimulation frequency allows partial contractions
• Complete/fused tetanus – stimulation frequency does not allow any relaxation phase.
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Figure 9.20
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• Recruitment = strength of contraction proportional to number of motor units activated
– E.g., ↑ motor unit = ↑ tension/strength
• Rotating through motor units allows prolonged contraction with reduced fatigue
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• Optimal resting length = optimal overlap of filaments ↑ cross bridging ↑ tension
• Too long = too little overlap not enough crossbridging ↓ tension
• Too short = no room left to contract & fiber mis-alignment ↓ tension
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• Energetics
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Energetics
ATP needed for:
• Energizing head
• Detaching head from myosin
• Power Ca+ pumps that transport Ca+ into SR (from cytoplasm)
ATP production through:
• Aerobic respiration
• Anaerobic respiration
• Creatine Phosphate
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Stored energy sources and how much muscle contraction they can sustain.
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Resting Muscle• Primary substrate plasm fatty acids
• ATP production ˃ ATP consumption/demand
• Surplus ATP used to:
– Creatine CP
– Glucose glycogen
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Fig. 12.24
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Moderate activity• Substrates = plasm fatty acids & glucose/glycogen
• ATP production can meet ATP consumption/demand
• Aerobic respiration dominates
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Heavy/intense activity• Primary substrate glucose (from glycogen)
• Aerobic respiration is insufficient to meet needs
• Anaerobic respiration occurs– Produces lactic acid
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Cori Cycle• Lactic acid from anearobic activity of muscle blood liver
• Liver uses ATP (produced aerobically) to synthesize glucose from lactic acid
• Liver glucose blood skeletal muscle** liver cells = only type that can release glucose
5-15
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Figure 9.22
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Fig. 12.22
Intensity-substrate use patterns (short duration)• As intensity increases:
– Fatty acids glycogen– Plasma borne substrate intracellular substrates
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Intensity-substrate use patterns (long duration)• As intensity increases:
– Fatty acids glycogen
– Plasma borne substrate intracellular substrates
– Why no graph for Heavy exercise of 90-120 min duration?
Fig. 12.22
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SUBSTRATE USE AT ACTIVITY ONSET
• Stored ATP• CP• Anaerobic Respiration
• Aerobic Respiration (if mild to moderate intensity)
“instant” energy that is available immediately
Ongoing activity + cardiopulmonary response-- increased O2 delivery
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There are 3 types of muscle fibers
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Table 12.3
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Fig. 12.26
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Table 12.4
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Figure 9.13
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Figure 9.24
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