physiology Flashcards
which muscles are striated
skeletal
cardiac
what are motor units
single alpha motor neurone and all the skeletal muscle it innervates
> skeletal muscle fibres are organised into motor units
how many muscle fibre cells in a motor unit
depends on the functions served by the skeletal muscle ie strength or precision
> muscles which serve fine movements eg external eye muscles or muscle of facial expression have fewer intrinsic fibres than muscles that need power ie vastus medialis
what is a functional unit
sarcomere is the functional unit of skeletal muscle
-the smallest component capable of performing all the functions of that organ
functions of skeletal muscle
posture
movement
breathing
heat prod.
whole body metabolism
3 types of muscle tissue
skeletal
cardiac
smooth
what is the ‘voluntary’ muscle
skeletal
how can striation be visualised
myosin and actin filaments
what innervates skeletal
somatic -
what innervates cardiac and smooth
-
initiation and propagation of skeletal muscle
neurogenic
motor units
neuromuscular junction present
No gap junctions
calcium comes entirely from sarcoplasmic reticulum
> no continuity of cytoplasm between nerve and skeletal muscle cells
initiation and propagation of cardiac muscle
myogenic
no neuromuscular junction
gap junctions present
calcium comes from ECF and sarcoplasmic reticulum
what is a myofibril
specialised intracellular structure involved in contraction and is organised into sarcomeres
how many bands does the sarcomere have
4 bands :
A band
H zone
M line
I band
what is excitation contraction coupling
where is calcium released from in skeletal muscle fibres
lateral sacs of sarcoplasmic reticulum
why is calcium required
to switch on cross bridge formation
-it is the link between excitation and contraction
-is entirely derived from sarcoplasmic reticulum in skeletal muscles
what is the difference between actin myosin / excitation /calcium contraction in cardiac muscle and skeletal muscle
?
what is skeletal muscle contraction initiated by
neurogenic initiation
what is the transmitter at the neuromuscular junction
acetylcholine
why is ATP needed
contraction: to power cross bridges
relaxation:
release cross bridges and to pump Ca back into sarcoplasmic reticulum (rigor mortis)
what are the two influences that act on tension developed by skeletal muscle
-the no of muscle fibres contracting
-the tension developed by each contracting muscle fibres
how does frequency of stimulation and summation of contractions brings about increased tension in skeletal muscle
describe the two primary types of skeletal muscle contraction
what can develop at optimum muscle length
maximum muscle tension
what is a reflex action
stereotyped response to a specific stimulus
they are the simplest form of coordinated movement
why might you get impairment of muscle function
intrinsic muscle disease
neuromuscular junction disease
pathology of lower motor neurons
disruption of input to motor nerves
what allows for simultaneous contraction of a number of muscle fibres
motor units
what allows for simultaneous contraction of a number of muscle fibres
motor units
how might a stronger contraction be achieved
motor unit recruitment
what helps prevents muscle fatigue during sub maximal contraction
asynchronous motor unit recruitment
what are the factors affecting tension developed by each contraction muscle fibre
-thickness
-length of muscle fibre
-frequency of stimulation and summation
twitch summation and tetanus in skeletal muscle
what happens when skeletal muscle is stimulated once
a single contraction called a twitch is produced
what happens when skeletal muscle receives a second stimulation before it had time to completely relax
the second response is much greater…
T or F : the resting length of skeletal muscle is the optimal length
T
what are the 2 types of skeletal muscle contraction
isotonic = muscle tension remains constant as the muscle length changes, useful for body movements and moving objects
isometric = muscle tension develops at constant muscle length , useful in supporting objects in fixed position and for maintaining body posture
what are the main differences between skeletal muscle fibres
- enzymatic pathways for ATP synthesis
- resistance to fatigue (muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue)
- activity of myosin ATPase - this determines the speed at which energy is made available - the speed of contraction
how many types of fibres does a motor unit usually have
one
the three types of skeletal muscle fibres
slow oxidative - slow twitch ie walking , aerobic
fast oxidative - intermediate twitch ie aerobic and anaerobic , jogging
fast glycolytic - fast twitch ie sprinting , anaerobic
why are neural pathways for reflexes important
can help to localise lesions
the stretch reflex
negative feedback mechanism
that resists p
passive changes in muscle length to maintain optimal resting length of muscle
helps maintain posture
the sensory receptor is the muscle spindle and is activated by muscle strength
stretching the muscle spindle increases firing in the afferent neurons
where do the afferent neurons synapse
in the spinal cord
intrafusal vs extrafusal
what are muscle spindles
collection of specialised muscle fibres
causes of intrinsic muscle disease
genetically determined myopathies :
congenital
chronic degeneration - dystrophy
abnormalities in muscle membrane ion channels - myotonia
acquired :
inflammatory
non-inflammatory
endocrine
toxic - alcohol
symptoms of muscle disease
muscle weakness / tiredness
stiffness
-
useful investigation
creatinine kinase
nerve conduction studies
inflammatory marker
biopsy
EMG
what are the joints of the body
synovial
fibrous
cartilaginous
do fibrous joints allow movement
doesn’t allow movement
do cartilaginous joints allow movement
allow limited movement ie intervertebral discs , pubic symphysis
features of the synovial joints
the bones are separated by a cavity - filled with synovial fluid -
and united by a fibrous capsule
what is the inner aspect of fibrous capsule (of synovial joints) lined with
synovial membrane
what is the synovial membrane
vascular connective tissue (with capillary networks and lymphatics)
-contains synovial cells (fibroblasts) which produces the synovial fluid
- about 60um thick in the human knee
what is a simple synovial joint
one pair of articular surfaces ie metacarpophalangeal
what is a compound synovial joint
more than one pair of articular surfaces eg elbow joint
purposeful function of joints
stress distribution
confer stability
joint lubrication ie cartilage interstitial fluid
synovial fluid features
> continuously replenished and absorbed by synovial membrane ie not a static pool
> has a high viscosity - due to presence of hyaluronic acid produced by the synovial cells
> viscosity and elasticity varies with joint movement
what happens to viscosity and elasticity in rapid movements
viscosity decreases
elasticity increases
what happens to synovial fluid when in a traumatic synovial tap (and also in haemorrhagic arthritis)
turns red
what should normal synovial fluid look like
clear colourless and viscous
normally has less than 200WBC
what does synovial fluid look like from a severely inflamed joint
thin and opaque
main functions of articular cartilage
prevents wear and tear - low friction lubricated gliding surfaces
distributes contact pressure to subchondral bone
the composition of the cartilage ECM and interaction between the fluid and solid phase of the cartilage determines the mechanical properties of cartilage
structural properties of articular cartilage
> elastic and sponge like - usually hyaline
> covers articular surfaces of bones
> has special ECM made predominantly of water and collagen , also proteoglycans
water: maintains resiliency of tissues and contribute to the nutrition and lubrication system
collagen: provides tensile stiffness and strength
proteoglycan: provides compressive properties associated with load bearing
specialised ECM of articular cartilage
synthesised, organised and degraded by chondrocytes
avascular - so has poor healing
in normal joints the rate at which the ECM is degraded doesn’t exceed the rate at which it is replaced
(joint disease can occur if the rate of ECM degradation exceeds the rate of its synthesis)
catabolic factors of ECM synthesis
they stimulate proteolytic enzymes and inhibit proteoglycan synthesis
what may go wrong in a joint
cartilage and synovial composition and function deteriorate with age and repeated wear and tear giving rise to osteoarthritis
synovial cell proliferation and inflammation > arthritis
deposition of salt crystals
injury and inflammation to periarticular structures cause soft tissue rheumatism
anabolic factors of ECM synthesis
stimulate proteoglycan synthesis and counteract effects of interleukin-1
