Physiology 1 and 2 Flashcards
What are the striated muscles
Skeletal and cardiac
What makes the muscles striated?
Alternating dark thick myosin bands and light thin actin bands
What are skeletal muscles innervated by
the somatic nervous system - subject to voluntary control
What are cardiac and smooth muscles innervated by
Autonomic nervous system - involuntary
How does initation of contraction come about in skeletal and cardiac muscle
Neurogenic by skeletal muscle, and myogenic by cardiac
How does calcium enter cells in skeletal and cardiac muscle
In skeletal muscle, entirely from SR - in cardiac muscle from ECF and SR (Calcium induced Ca release)
What is the transmitter at the neuromuscular junction
Acetylcholine
What is a motor unit
A single alpha motor neurone and all the skeletal muscle fibres it innervates
Where is precision more important than power
Extra ocular muscles, few muscle fibres per motor unit
What exists inside a muscle fibre (one cell)
Myofibril and sarcomere
How are skeletal muscles usually attached to bones
by tendons
What are the functional units of muscle
Sarcomeres
What are myofibrils
Specialised contractile intracellular structures
What is a functional unit of any organ defined as
the smallest componenet capable of performing all the functions of that organ
Where is the sarcomere found
between two Z lines
What is the A band
made up of thick filaments along with portions of thin that overlap in both ends of thick filaments
What is the H Zone
lighter area within middle of A band where thin filaments don’t reach
What is the M line
Extends vertically down middle of A band within the centre of H zone
What is the I Band
Consists of remaining portion of thin filaments that do not project in A Band
How is muscle tension produced
By sliding of actin filaments on myosin filaments
What is force generation dependent upon
ATP dependent interaction between thick and thin filaments
What is ATP required for
both contraction (to power cross bridges) and relaxation (release cross bridges and pump calcium back into SR) of muscle
What is Calcium required for
to switch on cross bridge formation
What is excitation contraction coupling
the process whereby the surface action potential results in activation of contractile structures of the muscle fibre
Where is calcium released from in skeletal muscle fibres
Lateral sacs of the sarcoplasmic reticulum
When is calcium released from skeletal muscle fibres
When the surface action potential spreads down the transverse T tubules
What are T tubules
Invaginations of the surface membrane that dip into the muscle fibre
What is motor unit recruitment
a stronger contraction achieved by stimulation of more motor units
What are the two primary factors which changes the gradation of skeletal muscle tension
Number of muscle fibres contracting within the muscle and tension developed by each contracting muscle fibre
In skeletal muscle, what relation does the duration of the action potential have to the resulting twitch
the duration of the action potential is much shorter than the duration of resulting twitch
Why can cardiac muscle not be tetanised
The long refractory period prevents generation of tetanic contraction
What is tetanus
A maximal sustained contraction achieved by summation of action potentials
Is a single twitch useful in bringing about meaningful muscle activity
No its not
How can maximal tetanic contraction be achieved
When the muscle is at its optimal length before the onset of contraction
When in the body are skeletal muscles at their optimal length
At their resting length
What are the two types of skeletal muscle contraction
Isotonic and isometric
What is isotonic contraction used for and what is it
Body movements and moving objects, muscle tension remains constant as the muscle length changes
What is isometric contraction and whats it used for
Muscle tension develops at a constant muscle length, used for supporting objects in fixed position and maintaining body posture
What happens to the velocity of muscle shortening as the load increases
It decreases
What are the 3 main metabolic pathways that supply ATP in muscle fibre
Transfer of high energy phosphate from creatine phosphate to ADP, oxidative phosphorylation, glycolysis
What is an immediate source for ATP
Transfer of high energy phosphate from creatine phosphate to ADP
What is the main source for ATP when oxygen is present
oxidative phosphorylation
What is the main source for ATP when oxygen is not present
Glycolysis
What are the 3 types of skeletal muscle fibres
Slow-oxidative, fast-oxidative, fast glycolytic
What are slow oxidative type 1 fibres (slow twitch) used for
prolonged relatively low work aerobic activities eg. posture, walking
What are fast oxidative type 2a (intermed twitch) fibres used for
prolonged relatively moderate work activities eg jogging (use both aerobic and anaerobic)
What are fast glycolytic type 2x fibres (fast twitch) used for
anaerobic metabolism, short term high intensity activities eg. jumping
What is a reflex action
a stereotyped response to a specific stimulus - the simplest form of coordinated movement
What is the simplest monosynaptic spinal reflex
Stretch reflex
Sum up a stretch reflex
Serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle
Where is the sensory receptor located in musc;e
in the muscle spindle, activated by muscle stretch
What effect does stretching the muscle spindle have
increases firing in the afferent neurones, which synapse in the spinal cord with alpha motor neurones (efferent) - activation of the reflex results in contraction of stretched muscle
What are muscle spindles
the sensory receptors for stretch reflex, collection of specialised muscle fibres
What are muscle spindles also known as
intrafusal fibres
what can ordinary muscle fibres be known as
extrafusal fibres
Where are intrafusal fibres found in the muscle
The belly
What are annulospiral fibres
the sensory nerve endings on muscle spindles
What is the efferent motor nerve supply to muscle spindles called
gamma motor neurones
does the contraction of intrafusal fibres contribute to the overall strength of muscle contraction
no
What is the role of gamma motor neurones
They adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shorten during muscle contraction
Some useful investigations in neuromuscular disease
Electromyography, nerve conduction studies, muscle enzymes CK, inflammatory markers, muscle biopsy
What is myalgia
muscle pain
What is myotonia
Delayed relaxation after voluntary contraction
What are two main causes of intrinsic muscle disease
Genetically determined, acquired
