• Finish whole muscle physiology
• Start hormones / endocrinology
‘twitch’
Tension
Muscle AP
Vm
latency
Time
• Why latency?
– In part due to time for all biochemical
reactions
– Also due to elastic components of the muscle
• Tendons, connective tissue, cross-bridge links
Parallel Elastic
Component
Contractile
component
Series elastic
component
Text fig 10-26
Rest
Contraction initiated
Tension generation
•Sarcomere shortens further
•Sarcomere shortens
•Series elastic component
stretches
•but no muscle shortening
•muscle shortens
Whole muscle summary
• 4 types of skeletal muscle fibers
• Neural control of contraction
– Twitches and tetanus
– Motor units & size principal
• Generation of muscle force
– Elastic components of muscle
• Non-twitch muscles
– Graded contractions
Muscle Diseases
• Duchenne muscular dystrophy
– Muscle wasting disease
– Affects 1 in 3500 boys
– Life expectancy ~20 years
• Genetic disease
– Complete absence of the protein ‘dystrophin’
Potential protein associations of dystrophin
Extracellular matrix
 Dystroglycan
 Dystroglycan
Muscle plasma membrane
Acetylcholine receptor
Dystrophin
Actin cytoskeleton
(not actin thin filaments)
Grb2
• There are many effects of dystrophin
absence including:
– Altered calcium handling (too much inside)
– Membrane destabilization (too permeable)
– Susceptibility to mechanical damage
• Effects on neuromuscular physiology
– Altered nACH receptor clusters
– Reduced mepp size
• Cardiac & Smooth muscle
– Contractile mechanisms (actin & myosin) the
same as skeletal muscle
– Structural and organizational differences
• Cardiac muscle
– like skeletal muscle
• Striated
• Uses troponin/tropomyosin control
• Well developed SR and T-tubule network
– Muscle cells are joined end-to-end,
• electrically connected by gap junctions
– Contraction initiated within the muscle
(myogenic) not by neural innervation
Gap junctions
Striated
Skeletal muscle
Smooth muscle
Cardiac
Skeletal muscle
• Smooth muscle
– Less like skeletal muscle
• No visible striations
• No troponin/tropomyosin
• No SR or T-Tubules
– Contraction regulated by calcium in several
different ways
• End of muscle!
Hormones
• Robert Wadlow
– 8’-11” tall
– 496 pounds
– Size 37 shoe
• Too much growth
hormone
Hormones
Topics:
• Types of hormones
• Signal transduction pathways
• Major Hormone systems
• Hormonal control of physiological
processes
Hormones
•
Another form of communication
•
Types of Secretion
1.
2.
3.
4.
Autocrine – affects the secreting cell
Paracrine – affects neighbouring cell
Endocrine – secreted into bloodstream
Exocrine – secreted onto body surface,
including surface of gut
Mechanisms of Secretion
Ca++
Neuron
Ca++
Neurosecretory cell
Ca++
Simple Endocrine Cell
Ca++
Intracellular Ca stores
Capillary
• Neurosecretory cells
– Work like all neurons
Sensory Input  APs  secretion
– Except secrete into bloodstream
• Secretory Pathway in Endocrine cells
Exocytosis
Ca++
Secretory vesicle
Golgi
Rough ER
Nucleus
Like synaptic vesicle
secretion, these
steps also require
SNARE proteins
Two types of hormones
• Lipid Soluble
– Steroid hormones (eg estrogen, testosterone)
– Thyroid hormones
• Lipid Insoluble
– Peptides and Proteins (eg insulin)
– Catecholamines (eg adrenalin)
Two types of hormones
1. Lipid-soluble
Carrier molecule
Hormone molecule
Cytoplasmic receptor
Nuclear receptor
Transcription &
Translation
long lasting effects
Nucleus
Two types of hormones
2. Lipid-insoluble
Hormone molecule
Plasma membrane receptor
Second Messenger
Effector Protein
Cellular effects
Signal Transduction
Signal
Reception, Transduction
Amplification
Second Messengers
Regulators
Specific Effectors
Cellular Response