Muscle Anatomy & Physiology Flashcards
What are the 3 types of muscle ?
- skeletal
- cardiac
- smooth
Define skeletal muscle
moves muscles attached to bone, voluntary & striated
Define cardiac muscle
heart muscle, involuntary, striated & auto-rhythmicity
Define smooth muscle
non-striated, involuntary, elements of auto-rhythmicity
What are the properties of muscular tissue ?
- excitability
- extensibility
- contractility
- elasticity
What are some basic functions of muscles ?
- body movement
- postural stability
- storage & movement of substances
- heat generation
Define Extensibility
- stretch without being damaged –> smooth muscle experiences this in the stomach as it fills
Define Excitability
- action potentials via innervation of muscle
- triggered by auto rhythmic nature of the heart & chemical stimuli via neurotransmitters
Define contractility
- generation of force as an output from an action potential
- contraction generates tension as the muscle pulls on its attachment points
Define elasticity
ability to return to original shape and conformation following muscle contraction
How is skeletal muscle developed ?
- zygote cleaved into an 8 stage cell
- 8 stage cell is cleaved into a blastula
- Blastula under goes gastrulation to create blastopore
What are the 3 layers of an embryo ?
Outer = Ectoderm
Middle = Mesoderm
Inner = Endoderm
Describe the ectoderm
- epidermis skin & its derivatives (sweat glands & hair follicles)
- nervous & sensory systems
- pituitary gland & adrenal medulla
- jaws & teeth
- germ cells
Describe the mesoderm
- skeletal & muscular systems
- circulatory & lymphatic
- excretory & reproductive systems
- dermis of skin
- adrenal cortex
Describe the endoderm
- epithelial lining of digestive tracts & associated organs
- thymus, thyroid & parathyroid glands
- epithelial lining of respiratory, excretory & reproductive tracts/ducts
How are skeletal muscles organised ?
muscle (epimysium)
fascicle (perimysium)
muscle fibre (sarcolemma)
myofibril (sarcomere)
myofilaments (actin & myosin)
Define epimysium
layer covering the whole muscle
Define perimysium
surrounds 10-100 fibres
What is a fascicle ?
a bundle of fibres
Describe the nerve & blood supply in skeletal muscle tissue
- artery with 1/2 veins accompany each nerve that penetrates the muscle
- each fibre is innervated to form an NMJ (neuromuscular junction)
- blood supply via capillary network, supply of oxygen & nutrients
What is the microscopic anatomy of skeletal muscle tissue ?
- diameter = 10-100 um
- length = 10-30cm
- multi-nucleated
- fibre number is set at birth
Define hypertrophy
- increase in fibre size,
- HGH and testosterone promotes muscle growth
Define atrophy
reduction in fibre size , typically caused by disease, disuse and ageing
What is the sarcolemma ?
the plasma membrane of the muscle cell
What are T-tubules ?
invagination of the sarcolemma, involved in AP propagation
What is the sarcoplasm?
cytoplasm of the muscle fibre
What are myofibrils ?
- contractile machinery of muscle -2mM in diameter
- comprised of myosin & actin
Describe the sarcoplasmic reticulum
network of ER which is specialised for skeletal muscle in Ca 2+ handling
Describe the sarcomere
- each myofibril has a striated pattern = sarcomere
- basci unit of striated muscle tissue
- repeating unit between 2 Z discs
- ends of actin filaments are attached to a Z disc
- length of sarcomere changes upon contraction
What are the components of the sarcomere ?
- contractile proteins
- regulatory proteins
- structural proteins
Describe contractile proteins
- generate force during contraction
- example = actin & myosin
Describe regulatory proteins
- helps switch the contraction process on/off
- troponin & tropomyosin = example
Describe structural proteins
- maintain the structure integrity of the sarcomere
- examples = Titin, alpha actin and myomesin
Describe the process of muscle contraction
- action potential travels along the nerve axon
- ends at the synaptic terminal
- synaptic terminal releases neurotransmitter acetylcholine into the synaptic cleft
Describe a motor unit
- consists of a somatic motor neurone plus all the skeletal muscle fibres it stimulates
What is the process of muscle contraction ?
- ACh is released, binding to reception on the motor end plate
- action potential reaches the T tubule
- sarcoplasmic reticulum releases Ca2+
- active site exposure, cross bridge formation
- contraction begins
What is the process of muscle relaxation?
- Aceltycholine is broken down by AChE
- Sarcoplasmic reticulum recaptures Ca2+
- active sites are covered, no cross bridge interaction
- contraction ends
- relaxation occurs, passive return to resting length
Describe muscle contraction in regards to myosin & actin
- myosin heads hydrolyse ATP and become reoriented & energised
- myosin heads bind to actin, forming cross bridges
- myosin cross bridges rotate centre of the sarcomere
- as myosin heads bind ATP the cross bridges detach from actin
Where does energy for muscle contraction come from?
- muscle contraction is a cyclical process which relies on a supply of key substrates = ATP & Ions (Ca2+)
What are the 3 types of skeletal muscle fibres ?
- slow oxidative - type 1
- fast oxidative/glyolytic - type 2a
- fast glycolytic - type 2b
What are the 2 main types of smooth muscle ?
- multi-unit smooth muscle
- unitary smooth muscle
What are the functions of smooth muscle ?
- vascular tone
- peristalsis
- pupil constriction/dilation
Define peristalsis
movement of food down the digestive tract
Describe the general structure of smooth muscle
- single, centrally places nucleus
- spindle (fusiform) shape
- not-striated
- actin filaments attached to dense bodies
- myosin filaments are interspersed in the actin
Describe the structure of multi-unit smooth muscle
- composed of discrete, separate smooth muscle fibres
- each fibre operates independently of the others, innervated by a single nerve ending
- covered by a thin basement membrane composed of fine collagen & glycoproteins
- controlled by nerve signals
What are some examples of multi-unit smooth muscle ?
- iris muscle of the eye
- piloerector muscle - erection of hairs upon sympathetic NS stimulation
Physiology of Smooth Muscle
- principles of contraction are similar to SKM = Ca2+
- smooth muscle contracts & relaxes in response to action potentials from the ANS
- responsive to changes in hormones, pH, temp and ion conc. at a local level
What 3 types of cardiac muscle make up the heart?
- atrial muscle
- ventricular muscle
- excitatory & conductive muscle fibres
How do excitatory & conductive muscle fibres contract ?
- feebly due to few contractile fibrils
Describe the structure of the cardiac muscle
- fibres arranged in a latticework
- striated appearance
- dark area crossing fibres = intercalated disc
What are intercalated discs ?
cells that separate individual cardiac muscle cells
- at each intercalated disc cell membrane fuse together
- gap junctions allow for rapid diffusion of ions
What are the 2 syncytiums of the heart ?
- atrial - 2 walls of the atria
- ventricular - 2 walls of the ventricles
What does the 2 syncytiums allows ?
they allow atria to contract a short time ahead of the ventricular contractions
