Physiology Flashcards
What is common between all three types of muscle?
All can develop tension and produce movement through contraction
Skeletal and cardiac muscle are striated- how is this viewed under a light microscope?
Alternating dark and light bands.
Skeletal muscles are innervated by______
somatic nervous system so are under voluntary control
Difference between contraction in skeletal and cardiac muscle?
Skeletal muscle needs neurogenic initiation of contraction, there are motor units and a NM junction.
Cardiac muscle has a pacemaker potential which spreads via gap junctions.
Is there calcium induced calcium released in skeletal muscle?
No- only in heart muscle, in skeletal muscle all the Ca come from the sarcoplasmic reticulum.
What is the neurotransmitter at the neuromuscular junction?
Acetylcholine
Define a motor unit
A single alpha motor neurone and all the skeletal muscle fibres it innervates
What does the number of fibres per motor unit depend on?
The functions served by the muscle
Muscles which serve fine movements e.g. _______ will have ______ fibres per motor
external eye muscles
muscles of facial expression
muscles in fingers
FEWER
A muscle fibre =
A muscle cell
A skeletal muscle consists of ______1_______ bundled by connective tissue. The fibres usually extend ____2_______
1) fibres/cells
2) whole length of the muscle
What are myofibrils?
Each muscle cell contains these which are specialised contractile intracellular structures
Myofibrils have alernating segments of thick __1____ which appear dark and thin __2______ filaments which appear light
1) myosin
2) actin
Within each myofibril actin and myosin are arranged into_____
sarcomeres
What is a functional unit? What is the functional unit of muscle
Sarcomeres- smallest components capable of forming all the functions of that organ
Where is a sarcomere found?
Between 2 Z lines
Z lines connect________
the thin filaments of two adjoining sarcomeres
Describe the four zones of the sarcomere
I band- part of thin filament not in the A band
M line- line extends vertically down
H band- middle area where thin filament doesn’t reach
A band- area were thick and thin filament are overlapping
What produces muscle tension?
Sliding of actin filaments on myosin filaments
What is ATP required for?
Both contraction and relaxation 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 the contractile structures of the muscle fibre
Describe the seven steps of muscular contraction
1) Ach released by axon of motor neurone crosses cleft and binds to receptors on motor end plate
2) Action potential generated in response to binding of Ach and end plate potential is propagated across surface membrane and down T tubules of muscle cell
3) Action potential in t tubules triggers Ca release from SR
4) Ca released binds to troponin on actin filaments resulting in tropomyosin being moved aside to uncover cross-bridge binding sites on actin
5) Myosin cross bridges attach to actin and bend, pulling actin filaments toward centre of sarcomere powered by energy from ATP
6) Ca is actively taken up by sarcoplasmic reticulum when there is no longer local action potential
7) With Ca no longer bound to troponin, tropomyosin slips back to its blocking position over binding sites on actin contraction ends and actin passively slides back to original resting position
Where is end plate potential sent down?
T tubules
Gradation of skeletal muscle tension depends on two primary factors which are?
1- number of muscle fibres contracting within the muscle
2- tension developed by each contracting muscle fibre
If a skeletal muscle is stimulated once a _____1____ is produces this produces little __2____
1) single contraction called a twitch
2) tension
Tension developed by skeletal muscles increases with increasing ________
frequency of stimulation
A sustained much longer contraction will be produced is skeletal muscle if stimulated _______
very rapidly with no opportunity to relax between stimuli
Difference between tension in skeletal and cardiac muscle?
Cardiac muscle has a refractory period and cannot be tetanised as this would stop it being able to pump, skeletal muscle can have sustained tension and be tetanised
When is skeletal muscle approximately at its optimal length?
At rest
What are the two types of skeletal muscle contraction?
Isotonic
Isometric
Describe isotonic contraction
Used for body movements and moving objects. Muscle tension remains constant as the muscle length changes
Describe isometric contraction
Used for supporting objects in a fixed position and for maintaining body posture. Muscle tension develops at constant muscle length.
What are three types of muscle fibre?
Slow oxidative type 1
Fast oxidative type 2a
Fast glycolytic type 2x
Describe slow oxidative type muscle fibres?
Used mainly for prolonged relatively low work aerobic activities e.g. posture and walking
Describe fast oxidative fibres?
Use anaerobic and aerobic metabolism for prolonged moderate work e.g. jogging
Describe fast glycolytic fibres?
Use anaerobic metabolism and used for short high intensity e.g. jumping
Purpose of the stretch reflex?
Negative feedback that resists passive change in muscle length to maintain optimal resting length.
What does the stretch reflex help maintain?
Posture whilst walking
Where is the sensory receptor for the stretch reflex?
In the muscle spindle and is activated by muscle stretch
What are the three types of joint?
Synovial, cartilaginous and fibrous
Describe fibrous joints?
These have limited mobility but are quite stable
Two types
Syndemoses- unite bones with a fibrous sheet e.g. tibia and fibula
Sutures- joins between the bones of the skull
Describe cartilaginous joints?
These have fairly limited mobility but are relatively stable
Two types
Primary cartilaginous- syndochroses, bones joined by hyaline cartilage permitting growth
Secondary cartilaginous- joints between vertebra
Describe synovial joints?
Range of movement. Joint cavity with synovial fluid, tendons and ligaments, a capsule wraps around the joint.
5 subsets:
1) Pivot - shaking of the head
2) Ball and socket - circumduction of the shoulder
3) Plane- minimal movement in one plane e.g. acromioclavicular
4) Hinge- good range of movement in one plane e.g.the elbow or knee
5) Biaxial/ SADDLE- reasonable range of movement in one plane and lesson another e.g. metacarpophalangeal
Bones separated by a cavity (containing synovial fluid) and united by a _________1____________
The inner aspect of fibrous capsule is lined with _____2______
The synovial membrane is _________3___________
The synovial membrane contains________4__________
The articular surfaces of bones are covered with ____5_____
1) fibrous capsule (and other extra-articular structures e.g. ligaments, tendons, and bursae)
2) synovial membrane
3) vascular connective tissue with capillary networks and lymphatics
4) synovial cells (fibroblasts) which produces the synovial fluid
5) cartilage
Difference between simple and compound synovial joints?
Simple- one pair of articular surface e.g. fingers
Compound- more than one pair of articular surfaces e.g. elbow joint
Describe what three things joint lubrication is provided by
Cartilage interstitial fluid
Synovium - derived hyaluronic acid (mucin) - a polymer of disaccharides
Synovium-derived lubrcin - a glycoprotein
As well as lubrication and joint movement the synovial fluid also ….
Supplies the chondrocytes (cartilage cells) with O2 and nutrients and remove CO2 and waste products
The synovial fluid Fills the joint cavity volume ___________1____________
The synovial fluid is continuously _______2__________
The synovial fluid has a high viscosity - mainly due to the presence of ____________3_____________
The viscosity of the synovial fluid varies with _____4______
Other constituents of the synovial fluid (for example uric acid) are derived by _______5__________
Normally, the synovial fluid contains ______6_____
1) < 3.5 ml in adult knee
2) replenished and absorbed by the synovial membrane - i.e. not a static poole
3) hyaluronic acid (mucin) produced by the synovial cells
4) Joint movement
5) dialysis of blood plasma
6) few cells (mainly mononuclear leucocytes)
The viscosity and elasticity of synovial fluid change________1________
Rapid movement is associated with ______2_______
These properties of synovial fluid become defective in a _____3____ joint
1) during joint movement
2) decreased viscosity and increased elasticity
3) diseased
The normal synovial fluid is _______1________
The synovial fluid WBC count ____2____ in inflammatory and septic arthritis
The synovial fluid turns ___3____ in traumatic synovial tap and in haemorrhagic arthritis
1) clear and colourless
2) increases
3) red
Two main functions of articular cartilage?
Provides a low friction lubricated gliding surface. This helps prevent wear-and-tear of joints
Distributes contact pressure to subchodral bone
Main function of water in ECM of cartilage?
Maintain the resiliency of the tissue and contribute to the nutrition and lubrication system
Main function of collagen in ECM of cartilage?
Provides tensile stiffness and strength
Main function of proteoglycan in ECM of cartilage?
Responsible for the compressive properties associated with load bearing
Markers of cartilage degradation?
Serum and synovial keratin sulphate
Increased levels indicate cartilage breakdown
Level increases with age and patients with osteoarthritis
Type II collagen in synovial fluid
Increased levels indicate cartilage breakdown
Useful in evaluating cartilage erosion e.g. in osteoarthritis and rheumatoid arthritis
Definition of pain
“An unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage”
Explain the four distinct processes in the physiology 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 is the name of the specific primary sensory afferent neurones normally activated by intense noxious stimuli (e.g. mechanical, thermal or chemical)?
Nociceptors
__________ are first order neurones that relay pain information to second order neurones in the CNS by chemical synaptic transmission
Nociceptors
Two subtypes of Nociceptors?
A delta fibres
C fibres
Describe A delta fibres?
mechanical/thermal nociceptors that are thinly myelinated (conduction velocity of 6 – 30 ms-1 ) - respond to noxious mechanical and thermal stimuli. Mediate ‘first’, or fast, pain.
Lacinating, stabbing, pricking sensations.
Describe C fibres?
Nociceptors that are unmyelinated (conduction velocity of 0.5 – 2.0 ms-1) – collectively they respond to all noxious stimuli (e.g. they are polymodal). Mediate ‘second’, or slow, pain.
Burning, throbbing, cramping or aching sensations.
Four categories of pain by mechanism?
Nociceptive, Inflammatory, Pathological (neuropathic), Pathological (dysfunctional)
Describe nociceptive pain?
This represents normal response to injury of tissues by noxious (damaging) stimuli
Only provoked by intense stimulation of nociceptors by noxious stimuli (e.g. mechanical, chemical, thermal)
Nociceptive pain is adaptive
Functions as early warning physiological protective system to detect and avoid noxious stimuli
What is one of the most important characteristics of nociceptive and inflammatory pain?
The pathways are adaptive, as the injury heals the pain goes away
Describe inflammatory pain?
- Caused by activation of the immune system by tissue injury or infection
- Pain activated by a variety of mediators released at the site of inflammation by leucocytes, vascular endothelium and tissue resident mast cells
- Causes heightened pain sensitivity to noxious stimuli (hyperalgesia) and pain sensitivity to innocuous stimuli (Allodynia). Harmless stimuli e.g. touching can cause you pain.
- This discourages physical contact (with the affected part) and also discourages movement (e.g. of a joint)
- Inflammatory pain is adaptive. It promotes repair until healing occurs
Describe pathological neuropathic pain?
Neuropathic pain is caused by damage to neural tissue
Examples of neuropathic pain include (but not limited to): compression neuropathies, peripheral neuropathies, central pain (following stroke or spinal injury), postherpetic neuralgia, trigeminal neuralgia, phantom limb
Can be perceived as burning, shooting, numbness, pins and needles. May be less localized
Describe pathological dysfunctional pain?
In dysfunctional pain there is no identifiable damage or inflammation
Examples of dysfunctional pain include (but not limited to): fibromyalgia, irritable bowel syndrome, tension headache, temporomandibular joint disease, interstitial cystitis
Pathophysiology of dysfunctional pain is not fully understood
Simple analgesics usually not very effective in pathological pain (neuropathic or dysfunctional)
Pathological pain is sometimes treated by drugs not originally developed for pain (e.g. antidepressants or anti-epileptics)
Pathological pain is not protective, but maladaptive
Skeletal muscle is innervated by ________1____________
Near the muscle the axon divides into _____2_______ that innervate an individual muscle fibre
Individual branches further divide into _____________3____________________
Action potentials arising in the cell body are conducted via the axon to the boutons causing ____4_________
1) alpha motor neurons with myelinated axons and cell bodies in the spinal cord or brain stem
2) unmyelinated branches
3) multiple fine branches that end in a terminal bouton that forms a chemical synapse with the muscle membrane at the neuromuscular junction
4) the release of Ach
Explain how an action potential is generated?
- Acetyl choline binds and opens Sodium potassium channel
- When the gate is open Na+ enters the muscle cell (influx) whilst K+ exits (efflux) simultaneously through nAChRs
- Because the driving force for Na+ is greater than for K+ at resting membrane potential influx of Na+ is greater than efflux of K+: a depolarizing end plate potential (e.p.p.) is generated by the simultaneous opening of many nAChRs
Explain the key steps in muscular contraction and spread of impulse from NM junction
- Transmission at the NMJ is mediated by quantal release of ACh which acts on post-junctional nicotinic ACh receptors (nAChRs) to increase membrane cation conductance generating an e.p.p.
- The e.p.p. initiates a muscle action potential (AP) that invades the T-tubule system causing contraction by electromechanical coupling
- The action of ACh is terminated its hydrolysis by acetylcholinesterase (AChE)
5 things that relate to dtysfunctioning NM junction?
- Neuromyotonia (NMT, or Isaac’s syndrome)
- Eaton Lambert Syndrome
- Myaesthenia gravis
- Botulinum toxin (botox)
- Curare-like’ compounds
Describe Neuromyotonia/ Isaacs syndrome?
abnormal voltage activated potassium channels, dysfunctioning MSK system
Describe Eaton Lambert Syndrome/ LEMS
antibodies againt voltage activated Ca channels causes muscle weakness
Describe Myaesthenia Gravis?
antibodies against Ach receptors so reduction in functional channels
Describe Botulinum toxin?
toxin produced by bacteria clostridium botunlinum irreversibly inhibits Ach release. Infection has high death rate. The toxin has clinical uses though as botox.
Describe curare like compounds
Interfere with the postsynaptic action of acetylcholine by acting as competitive antagonists of the nicotinic ACh receptor (e.g. vecuronium, atracurium), Are used clinically to induce reversible muscle paralysis in certain types of surgery
What is the action of Ach terminated by?
hydrolysis by acetylcholinesterase (AChE)
