Physiological Flashcards
What three types of muscle tissue is there?
Cardiac
Skeletal
smooth
Which muscle tissue are striated?
Skeletal and cardiac
What are the dark bands in striated muscle caused by?
Myosin thick filaments
what are the thin bands in striated muscle caused by?
Actin thin filaments
Which muscle tissue are involunatry?
smooth and cardiac - ANS
what is the difference between cardiac and striated muscle?
with regards to initiation and propagation of contraction?
- Skeletal muscle - neurogenic initiation of contractionCardiac muscle - myogenic initiation of contraction
- Skeletal muscle has neuromuscular junction cardiac muscle doesn’t
- Skeletal muscle does not have gap junctions cardiac muscle does
- skeletal muscles have motor units cardiac muscle does not
what is the difference between cardiac and striated muscle?
with regards to Excitation Contraction Coupling?
- skeletal: Ca++ entirely from sarcoplasmic reticulum
2. Cardiac: Ca++ from ECF and sarcoplasmic reticulum (Ca++ induced Ca++ release)
what is the difference between cardiac and striated muscle?
with regards to gradation of contraction?
Skeletal: depends on
(1) motor unit recruitment (2) summation of contractions
cardiac: depends on extent of preload (amount of blood filled in heart chambers)
What neurotransmitter is used in a neuromuscular junction for skeletal muscles?
ACh (acetylcholine)
what do skeletal muscle fibres organise into?
motor units
What is a motor unit?
a single alpha motor neuron and all the skeletal muscle fibres it innervates
Which muscle may have less motor units?
muscles which serve fine movement e.g. external eye muscle and intrinsic hand muscles
Discuss the organisation of a whole muscle.
- sarcomere
- Many sarcomeres make up a MYOFIBRIL
- Many myofibrils make up a MUSCLE FIBRE
- Many muscle fibres make up a WHOLE MUSCLE
what is a muscle fibre?
a skeletal muscle cell
what is the arrangement of muscle fibres in skeletal muscle?
they are parallel to each other
also bundled by connective tissue
skeletal muscle fibres usually extend the entire length of what?
muscle
What joins bone and muscle together?
tendons
What are actin and myosin arranged into in myofibrils?
sarcomere
What is the length of a sarcomere?
one z line to the next one
What does the M line of a sarcomere show?
the midpoint of the sarcomere. within the centre of H zone
what does the A band of a sarcomere show?
Made up of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments
What does the I band of a sarcomere show?
Consists of remaining portion of thin filaments that do not project in A-band
what does the H zone of a sarcomere show?
Lighter area within middle of A-band where thin filaments don’t reach
what occurs in the contraction cycle?
- Energised muscle filament myosin with Ca 2+ presence binds to actin filament (BINDING stage). Removes the troponin
- overlapping of both filaments causes release of energy in the form of ADP and Pi ( Power stroke/BENDING)
- Available ATP allows the detachment of myosin from actin ( DETACHMENT)
- Myosin now energised again
what is the definition of excitation contraction coupling
the process whereby the surface action potential results in activation of the contractile structures of the muscle fibre
In skeletal muscle fibres when is Ca 2+ released from the lateral sacs of the sarcoplasmic reticulum?
When the surface action potential spreads the transverse tubules
What are transverse tubules? (T-tubules)
extensions of the surface membrane that dip into the muscle fibre
Describe the process of skeletal cells contracting and relaxing.
- Acetylcholine is released by the axon of the motor neuron and crosses the synaptic cleft and binds to receptors on the more end plate
- Action potential generated in response to bind of ACh and subsequent end plate potential is propagated across cell surface membrane and down T tubules of muscle cell
- Action potential in T tubules stimulate release of Ca 2+ from sarcoplasmic reticulum
- Calcium ions released from lateral sacs bind to troponin on actin filaments. Tropomyosin is moved revealing binding sites on actin
- Myosin cross bridges attach to actin and bend pulling actin filaments towards centre of sarcomere powered by energy supplied by ATP
- Ca2+ is taken up by sarcoplasmic reticulum when there is no local action potential
- No more Ca 2+ causes tropomyosin back to its original position blocking actin binding sites. contraction ends
gradation of skeletal muscle tension depends on which two main factors?
- Number of muscle fibres contracting in the muscle
2. The tension created by each of the contracting muscle fibres
What is motor unit recruitment?
The stimulation of more motor units leading to a stronger contraction
what do asynchronous motor units recruitment during submaximal contraction help prevent?
muscle fatigue
What are the three main factors which determine the extent of the tension created by contracting muscle fibres?
depends on frequency of stimulation and summation of contractions and
length of muscle fibre at the onset of contraction
thickness of muscle fibre
How do you summate twitches which causes stronger contractions of skeletal muscle?
repetitive fast stimulation of skeletal muscle
what happens if a muscle fibre is restimulated after it has completely relaxed?
second twitch is the same magnitude as the previous one
what happens if a muscle fibre is restimulated before it has completely relaxed?
second twitch is added to the first one causing summation
what happens if a muscle fibre is restimulated before it hasn’t relaxed at all?
A tetanus forms - maximal sustained contraction
Cardiac muscle can be tetanised true or false?
false - long refractory period prevents generation of tetanic contraction
what is a twitch?
a single contraction caused by stimulation of a skeletal muscle
How can maximal tetanic contractions be achieved?
when the muscle is at its optimal length before the onset of contraction
The resting length of a skeletal muscle is aproximately what?
optimal length
what are the two types of skeletal muscle contractions?
- Isotonic contraction
2. Isometric contraction
What is isotonic contraction used for?
ii. what happens to the muscle tension?
(1) body movements
(2) moving objects.
ii. Muscle tension remains constant as the muscle length changes
what is isometric contraction used for?
ii. what happens to the muscle tension?
1) supporting objects in fixed positions.
(2) maintaining body posture.
ii. Muscle tension develops at constant muscle length
In both isotonic and isometric contractions how is muscle tension transmitted to the bone?
via the elastic components of muscle
when does the velocity of muscle shortening decrease?
as the load increases
what are the main differences between the different types of skeletal muscle fibres?
- the enzymatic pathways for ATP synthesis;
- the resistance to fatigue - muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue; and
- the activity of myosin ATPase - this determines the speed at which energy is made available for cross bridge cycling i.e. the speed of contraction
What are three main steps involved in metabolic pathways that supply ATP in muscle fibres?
- Transfer of high energy phosphate from creatine Phosphate to ADP - immediate source for ATP
- Oxidative phosphorylation: main source when O2 is present
- Glycolysis: main source when O2 is not present
What three main types of skeletal muscle fibres are there?
- Slow oxidative type I fibres (also known as slow-twitch fibres) are used mainly for prolonged relatively low work aerobic activities e.g. maintenance of posture, walking
- Fast oxidative (Type IIa) fibres (also known as intermediate-twitch fibres) use both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities e.g. jogging
- Fast glycolytic (Type IIx) fibres (also known as fast-twitch fibers) use anaerobic metabolism and are mainly used for short-term high intensity activities e.g. jumping
What is a reflex?
stereotyped response to a specific stimulus
What type of reflex is the stretch reflex?
monosynaptic spinal reflex
What type of feedback mechanism is the stretch reflex?
negative feedback-resists passive change in muscle length to maintain optimal resting length of muscle
What is the sensory receptor in the stretch reflex?
ii. how is it stimulated?
the muscle spindle
ii. muscle stretching
What does stretching the muscle spindle in the stretch reflex cause?
increases firing in the afferent neurones
where do the afferent neurones synapse at in the stretch reflex?
The afferent neurons synapse in the spinal cord with the alpha motor neurons (efferent limb of the stretch reflex)
what is the result of the stretch reflex?
causes contraction of stretched muscle
How can a doctor stimulate the stretch reflex?
Tapping the muscle tendon with a rubber hammer - causes muscle to rapidly stretch leading to contraction
What nerve is stimulated by the knee jerk reflex?
ii. what spinal segment is the nerve from?
Femoral nerve
ii. L3-4
What nerve is stimulated by the Ankle jerk reflex?
ii. what spinal segment is the nerve from?
Tibial nerve
ii.S1-2
What nerve is stimulated by the Biceps jerk reflex?
ii. what spinal segment is the nerve from?
Musculocutaneous Nerve
ii. C5-6
What nerve is stimulated by the Brachioradialis jerk reflex?
ii. what spinal segment is the nerve from?
Radial nerve
ii. C5-6
What nerve is stimulated by the Triceps jerk reflex?
ii. what spinal segment is the nerve from?
Radial nerve
C6-7
What is a muscle spindle?
collection of specialised muscle fibres
they are the sensory receptors for stretch reflexes
What are muscle spindles also known as?
intrafusal fibres
What are normal muscle fibres (Non muscle spindles) known as?
extrafusal fibres
where are muscle spindles found in the muscle?
within the belly of muscles and run parallel to ordinary muscle fibres
What are the muscle spindle’s nerve endings called?
annulospiral fibres
What happens to the muscle spindle’s discharge when the muscle stretches?
it increases
What is the name to the efferent neurons which supply muscle spindles?
gamma (y) motor neurons
What is the role of gamma motor neurons?
adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shorten during muscle contraction
The contraction of intrafusal fibres does not contribute to the overall strength of muscle contraction
true or false?
true
what are the main causes of Impairment of skeletal muscle function?
- Intrinsic disease of muscle
- Disease of NMJ
- Disease of lower motor neurons
which supply the muscle
4.Disruption of input to motor
nerves (e.g. upper motor neuron disease
What are the main causes of intrinsic muscle disease?
- genetically determined myopathies
- Acquired myopathies
e.g. Inflammatory myopathies e.g. polymyositis, inclusion body myositis
Non-Inflammatory myopathies e.g. fibromyalgia
Endocrine mypoathies e.g. Cushing syndrome, thyroid disease
Toxic myopathies e.g. alcohol, statins
What are the three main types of joints in the body?
- synovial
- Fibrous
- Cartilaginous
What is the function of fibrous joints?
doesn’t allow for any movement
Give an example of a fibrous joint
Bones of skull in adults
How are bones joined together in fibrous joints?
Fibrous tissue
What is the function of cartilaginous joints?
Allows limited movement
Give examples of cartilaginous joints.
Intervertebral Discs
Pubic symphsis
Part of the sacroiliac joints
Costochondral joints
How are bones joined together via cartilaginous joints?
Via cartilage
what is a synovial joint?
Bones separated by a cavity (containing synovial fluid) and united by a fibrous capsule (and other extra-articular structures e.g. ligaments, tendons, and bursae)
what is a synovial joint?
Bones separated by a cavity (containing synovial fluid) and united by a fibrous capsule (and other extra-articular structures e.g. ligaments, tendons, and bursae)
What is the inner aspect of the fibrous capsule lined with?
Synovial membrane
what is the synovial membrane?
ii. what cells does this contain?
vascular connective tissue with capillary networks and lymphatics
ii. contains synovial cells (fibroblasts)
what do fibroblasts produce?
produces the synovial fluid
What are the articular surfaces of synovial joints covered in ?
Cartilage
what are the two types of synovial joints?
simple
compound
what are the differences between the two main subtypes of synovial joints?
simple synovial joints have one pair of articular surfaces e.g. metacarpophalangeal joints
compound synovial joints have more than one pair of articular surfaces e.g. elbow joints
What is the role of joints in purposeful motion?
Stress distribution (note that the greatest share of loading energy is taken up within the muscles and tendons crossing each joint)
Confer stability
Shape of the articular component e.g. the hip joint
Ligaments provide a second major stabilising influence
Synovial fluid acts as an adhesive seal that freely permits sliding motion between cartilaginous surfaces
Joint lubrication provided by
Cartilage interstitial fluid
Synovium - derived hyaluronic acid (mucin) - a polymer of disaccharides
Synovium-derived lubrcin - a glycoprotein
what is the role of synovial fluid?
Lubricates Joint
Facilitates joint movements - reduces friction
Helps minimise wear-and-tear of joints through efficient lubrication
Aids in the nutrition of articular cartilage
Supplies the chondrocytes (cartilage cells) with O2 and nutrients and remove CO2 and waste products
Why is the synovial fluid described as not being static in the synovial joint?
as it is constantly being absorbed by the synovial membrane and also being produced
Why has synovial fluid got high viscosity?
due to the presence of hyaluronic acid (mucin) produced by the synovial cells
what cells does the synovial fluid contain?
contains few cells (mainly mononuclear leucocytes
what are the two main properties of synovial fluid which changes during movement?
elasticity
viscosity
What happens to the two main properties of synovial fluid during rapid movement?
elasticity increases
viscosity decreases
what is the normal colour of synovial fluid?
clear and colourless
What is the normal WBC count in synovial fluid?
<200 WBC/mm3
of which polymorphs are usually <25/mm3
What is the colour of synovial fluid in traumatic spinal tap and haemorrhagic arthiritis?
Red
What is the WBC in synovial fluid in inflammatory synovial fluid?
2000-75000
What is the WBC in synovial fluid in septic synovial fluid?
> 100,000
polymorph usually >75
what is the colour of synovial fluid in inflammatory synovial fluid?
straw coloured
what is the function of articular cartilage in a synovial joint?
Provides a low friction lubricated gliding surface. This helps prevent wear-and-tear of joints
Distributes contact pressure to subchodral bone
The composition of the cartilage ECM and the interaction between the fluid and solid phase of the cartilage plays a significant role in determining the mechanical properties of cartilage
What are the layers of articular cartilage from superficial to deep?
- articular surface
- superficial zone (10-20%)
- Mid zone (40-60%)
- deep zone (30%)
- calcified zone
Zones differ in: organization of collagen fibres and relative content of cartilage components
What is the articular cartilage mainly made out of?
Hyaline
What is the Extracellular matrix of the articular cartilage consist of?
water (70%),
collagen (20%) -mainly type II contributes most to the elastic behaviour of cartilage,
proteoglycans (10%)
what is the role of water in the ECM of articular cartilage?
Maintain the resiliency of the tissue and contribute to the nutrition and lubrication system
what is the role of collagen in the ECM of articular cartilage?
Provides tensile stiffness and strength
what happens to water and collagen as people get older?
levels decrease in the ECM
what is the role of Proteoglycan
in the ECM of articular cartilage?
Responsible for the compressive properties associated with load bearing
where is proteoglycan mainly found in the ECM of articular cartilage?
the middle and deep zone
what is the proteoglycan mainly made out of?
glycosaminoglycan e.g. chondroitin sulphate
what is the ECM is synthesized, organised, degraded and maintained by?
chondrocytes
In normal joints which is faster, ECM synthesis or ECM degradation?
ECM synthesis
what do chondrocytes secrete to break down ECM?
Metalloproteinase proteolytic enzymes e.g. collagenase and stromelysin
What are the catabolic factors of cartilage matrix turnover?
Stimulate proteolytic enzymes and inhibit proteoglycan synthesis
e.g.
Tumour necrosis factor (TNF)-
Interleukin (IL)-1
What are the anabolic factors of cartilage matrix turnover?
Stimulate proteoglycan synthesis and counteract effects of IL-1
e.g.
Tumour growth factor (TGF)-β
Insulin-like growth factor (IGF)-1
What are the two main signs of cartilage degradation?
- increased levels of Serum and synovial keratin sulphate
Level increases with age and patients with osteoarthritis
- increased levels of Type II collagen in synovial fluid
Useful in evaluating cartilage erosion e.g. in osteoarthritis and rheumatoid arthritis
what is pain?
When she doesn’t message you back
or
” An unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage”
What are the 4 main physiological processes of pain?
Transduction: translation of noxious stimulus into electrical activity at the peripheral nociceptor
Transmission: propagation of pain signal as nerve impulses through the nervous system
Modulation: modification/hindering of pain transmission in the nervous system e.g. by inhibitory neurotransmitters like endogenous opioids
Perception: Conscious experience of pain. Causes physiological and behavioural responses
What are nociceptors?
Nociceptors are specific primary sensory afferent neurones normally activated by intense noxious stimuli (e.g. mechanical, thermal or chemical)
What type of order neurone is a Nociceptor?
first order neurone - relay information to second order neurones in the CNS by chemical synaptic transmission
In which system do second order neurones ascend the spinal cord?
the anterolateral system
terminates at thalamus
what does the anterolateral system consist of?
The spinothalamic tract (STT): Involved in pain perception (location, intensity)
The spinoreticular tract (SRT): Involved in autonomic responses to pain, arousal, emotional responses, fear of pain
What happens at the the thalamus?
sensory information is relayed (third order neurones) to the primary sensory cortex
what are the two main types of nociceptors?
A-fibres
C-fibres
What type of nociceptor is the A-fibre?
ii. what stimuli do they respond to?
Mechanical/thermal nociceptors that are thinly myelinated . respond fast to pain
ii. mechanical and thermal stimuli
What type of nociceptor is the C-fibre?
what stimuli do they respond to?
nociceptors that are unmyelinated. respond slowly to pain
ii. all noxious stimuli -polymodal
What are three main types of pain classified by mechanism?
- inflammatory
- nociceptive
- pathological
what is nociceptive pain?
ii. what provokes it?
normal response to injury of tissues by noxious (damaging) stimuli
ii. only intense stimulation of nociceptors
Nociceptive pain adaptive true or false?
true
what is inflammatory pain?
ii. what provokes it?
activation of the immune system by tissue injury or infection
ii. variety of mediators released at the site of inflammation by leucocytes, vascular endothelium and tissue resident mast cells
what does inflammatory pain cause?
discourages physical contact and movement
inflammatory pain adaptive true or false?
true
what are the two main subtypes of pathological pain?
Neuropathic and dysfunctional
what is neuropathic pain caused by?
damage to neural tissue
Give some examples of neuropathic pain.
compression neuropathies, peripheral neuropathies, central pain (following stroke or spinal injury), postherpetic neuralgia, trigeminal neuralgia, phantom limb
feels like burning/pins and needles
What is dysfunctional pain?
no identifiable damage or inflammation
Give some examples of dysfunctional pain.
fibromyalgia,
irritable bowel syndrome,
tension headache,
temporomandibular joint disease, interstitial cystitis
Pathological pain is adaptive true or false?
false- it is maladaptive
What is refered pain caused by?
convergence of nociceptive visceral and skin afferents upon the same spinothalamic neurons at the same spinal level
What is the principal role of the ACL?
To prevent abnormal internal rotation of the tibia
What is the principal role of the posterior cruciate ligament (PCL)?
Prevents hyperextension and anterior translation of the femur
What is the principal role of the medial cruciate ligament (MCL)?
Resists valgus force
What is the Principal role of the Lateral cruciate ligament (LCL)?
Resists varus force and abnormal external rotation of the tibia
