Finish whole muscle physiology Start hormones / endocrinology

Tension Vm ‘twitch’ Muscle AP Time latency 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

Contractile component Series elastic component Parallel Elastic Component

Rest Contraction initiated Sarcomere shortens Series elastic component stretches but no muscle shortening Tension generation Sarcomere shortens further muscle shortens Text fig 10-26

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’

Muscle plasma membrane Dystrophin Actin cytoskeleton (not actin thin filaments)  Dystroglycan  Dystroglycan Grb2 Acetylcholine receptor Potential protein associations of dystrophin Extracellular matrix

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.Autocrine – affects the secreting cell 2.Paracrine – affects neighbouring cell 3.Endocrine – secreted into bloodstream 4.Exocrine – secreted onto body surface, including surface of gut

Mechanisms of Secretion Neuron Neurosecretory cell Simple Endocrine Cell Ca++ Capillary Ca++ Intracellular Ca stores

Neurosecretory cells –Work like all neurons Sensory Input  APs  secretion –Except secrete into bloodstream

Secretory Pathway in Endocrine cells Nucleus Rough ER Golgi Exocytosis Ca++ Like synaptic vesicle secretion, these steps also require SNARE proteins Secretory vesicle

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 Transcription & Translation long lasting effects Nuclear receptor Cytoplasmic receptor Carrier molecule Hormone molecule Nucleus

Two types of hormones 2.Lipid-insoluble Cellular effects Hormone molecule Plasma membrane receptor Second Messenger Effector Protein

Signal Transduction Signal Reception, Transduction Amplification Second Messengers Regulators Cellular Response Specific Effectors