Regulation of Contraction I. How do nerves stimulate muscle contraction? II. Factors influencing muscle tension III. How does contraction of smooth/cardiac muscle differ from skeletal?

Innervations of Muscle Fiber SR Sarcolemma

Neuromuscular Junction AP to synaptic terminal of motor neuron

Neuromuscular Junction AP to synaptic terminal of motor neuron Release of Ach

Neuromuscular Junction AP to synaptic terminal of motor neuron Release of Ach AP spreads across sarcolemma

Neuromuscular Junction AP to synaptic terminal of motor neuron Release of Ach AP spreads across sarcolemma

Skeletal Muscle Contraction Sarcolemma

Skeletal Muscle Contraction AP passes down T tubules Sarcolemma

Skeletal Muscle Contraction AP passes down T tubules Release of Ca + from the ____________

Skeletal Muscle Contraction AP passes down T tubules Release of Ca + from the ____________ Ca + binds to Troponin

Skeletal Muscle Contraction AP passes down T tubules Release of Ca + from the ____________ Ca + binds to Troponin Sliding Filament Animation

Regulation of Contraction I. How do nerves stimulate muscle contraction? II. Factors influencing muscle tension III. How does contraction of smooth/cardiac muscle differ from skeletal?

Factors Influencing Muscle Tension 1.Frequency of stimulation 2.Fiber length at onset of contraction 3.Number of muscle fibers contracting 4.Muscle fatigue

Frequency of Muscle Fiber Stimulation Incomplete

Incomplete

Maximum Tension Incomplete

Complete Tetanus Sustained maximum muscle tension

Tetanus Infection Clostridium tetani Muscles contract severely Respiratory failure

Factors Influencing Muscle Tension 1.Frequency of stimulation 2.Fiber length at onset of contraction 3.Number of muscle fibers contracting 4.Muscle fatigue

Muscle Tone & L-T Relationship Relaxed muscles are slightly contracted

Muscle Tone & L-T Relationship Relaxed muscles are slightly contracted Tension during contraction depends on sarcomere length of optimum length

Muscle Tone & L-T Relationship Too much tone yields a weak contraction of optimum length

Muscle Tone & L-T Relationship Too much tone yields a weak contraction Too little tone also yields a weak contraction of optimum length

Length-Tension Relationship % of resting length Tension (% of maximum) Tension (% of maximum)

Northern Leopard Frog

Factors Influencing Muscle Tension 1.Frequency of stimulation 2.Fiber length at onset of contraction 3.Number of muscle fibers contracting Each fiber can contract or not (all or none) More fibers means a stronger contraction

Factors Influencing Muscle Tension

4. Muscle fatigue Muscle fibers cannot contract strongly until Ca + is sequestered Delay is “fatigue”

Regulation of Contraction I. How do nerves stimulate a muscle contraction? II. Factors influencing muscle tension III. How does contraction of smooth/cardiac muscle differ from skeletal?

Smooth & Cardiac Muscle Contraction Contain actin & myosin Use ATP to power cross-bridge cycling

Smooth & Cardiac Muscle Contraction Contain actin & myosin Use ATP to power cross-bridge cycling Differences in muscle excitation Differences in muscle contraction

Smooth Muscle Contraction Myosin and Actin lattice Slow, wavelike contraction Relaxed Contracted

Smooth Muscle Contraction Myosin and Actin lattice Slow, wavelike contraction Influx of Ca + from ECF Self-excitable Relaxed Contracted

Smooth Muscle Contraction Differs from skeletal and cardiac muscle: –Lacks troponin and tropomyosin –Ca + binds to calmodulin (similar to troponin)

Smooth Muscle Contraction Differs from skeletal and cardiac muscle: –Ca + - calmodulin complex phosphorylates Myosin, increases its affinity for Actin –Ca + removal causes Myosin-Actin dissociation Relaxed Contracted

Cardiac Muscle

Has characteristics of both skeletal and smooth Skeletal Similarity: Troponin & tropomyosin Smooth Similarity: Self-excitable Unique Feature: Long AP’s

Skeletal Muscle Cardiac Muscle AP in Cardiac Muscle Long AP prevents tetanus

Summary Motor neurons stimulate muscle contraction. The AP then passes along the sarcolemma and down the T tubules, deep into the muscle fiber. This allows all myofilaments within the cell to be stimulated. Release of Ca + from the SR binds to troponin, causing tropomyosin to shift and expose the myosin head binding sites on actin. Sliding filament process then takes over. Muscle fiber length, fatigue, and the number of fibers stimulated can all influence the strength of contraction. Smooth/Cardiac contraction differs from Skeletal contraction.