Physiology Flashcards
How do muscles produce movement?
Through contraction
Cardiac muscle
Striated
Involuntary - regulated by ANS
Smooth muscle
Non-striated
Involuntary - regulated by ANS
Skeletal muscle
Striated
Voluntary - regulated by somatic nervous system
Multi-nucleated (nuclei at periphery)
Needs nervous stimulation to initiate contraction
Motor units present
What is the transmitter of the neuromuscular junction?
ACh
What is a motor unit?
Single alpha motor neurone which innervates many muscle fibres.
The number of muscle fibres per motor unit varies depending on the functions of the muscle
Muscles which serve fine movements (facial expression, intrinsic hand muscles) have LOTS/FEW fibres per motor unit?
Few
When power (e.g. thigh muscles) is more important than precision, there are LOTS/FEW fibres per motor unit?
Lots
Skeletal muscle organisation
Muscle fibres are held together by loose connective tissue.
Each muscle fibre = 1 muscle cell
Contractile units within muscle fibres?
Myofibrils contain actin (thin, light) and myosin (thick, dark) filaments
Functional units of skeletal muscles?
And where are they found?
Sarcomeres
Found between 2 Z-Z lines
Z lines
Connect the thin filaments of 2 joining sarcomeres
A band
Made up of thick filaments
H zone
Lighter area in the middle of A band
M line
Extends vertically down the middle of an A band
I band
Remaining portion of thin filaments
How do muscles contract?
Sliding of actin filaments on myosin filaments.
ATP and calcium are needed
Cross bridge formation - muscle contraction
Calcium binds to troponin causing a conformational change.
This exposes the actin and myosin binding site so cross bridging occurs
Muscle relaxation
Calcium unbinds from Troponin and cross bridges between actin and myosin break.
ATP is required
If the muscle is stimulated continuously, it produces a STRONGER/WEAKER contraction
Stronger
Skeletal muscle action potential
The tension increases with increasing frequency of stimulation.
(if a skeletal muscle is stimulated once, a single twitch is produced. but if a skeletal muscle receives a second stimulation before it has time to completely relax, then greater muscle tension is developed.
What is tetanus?
A sustained contraction which occurs if a skeletal muscle is stimulated rapidly and it doesn’t have an opportunity to relax
Skeletal muscle optimum length
Resting length
Isotonic contraction of skeletal muscle
Length of muscle changes
Muscle tension remains constant
eg: body movements
Isometric contraction of skeletal muscle
Length of muscle constant
Muscle tension changes
eg: maintaining body posture
ATP production in skeletal muscle fibres
Transfer of high energy phosphate from creatinine phosphate to ADP (immediate source of ATP)
Oxidative phosphorylation produces an abundance of ATP (when O2 present)
Gycolysis produces ATP (when O2 absent)
Slow oxidative skeletal muscle fibres (type 1)
Low myosin ATPase activity, so contraction is slow
Lots of mitochondria -> lots of oxidative phosphorylation
Used for prolonged relatively low work aerobic activities (e.g.: walking)