• Finish whole muscle physiology

• Start hormones / endocrinology

Te

nsio

n

Vm

‘twitch’Muscle AP

Timelatency

• 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 elasticcomponent

Parallel ElasticComponent

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

Grb2Acetylcholine receptor

Potential protein associations of dystrophinExtracellular 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

StriatedSkeletal muscle

Smooth muscle

CardiacSkeletal 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 Secretion1. 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++

Ca++

Ca++

Intracellular Ca stores

• Neurosecretory cells– Work like all neurons

Sensory Input APs secretion

– Except secrete into bloodstream

• Secretory Pathway in Endocrine cells

NucleusRough 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 hormones1. 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 TransductionSignal

Reception, Transduction

Amplification

Second Messengers

Regulators

Cellular Response

Specific Effectors