Physiology Flashcards
What is Rheumatology
Concerns the diagnosis and treatment of diseases of joints and soft tissues
Primarily inflammatory conditions
What is orthopaedics
Surgical discipline concerned specifically with musculoskeletal system
Includes elective and emergency surgery
What are the physiological functions of skeletal muscles
Maintain posture Purposeful movement Respiratory movement Heat production Contribute to whole body metabolism
What are the 3 types of muscles
Skeletal
Cardiac
Smooth
What is achieved through muscle contraction
Developing tension
Producing movement
What causes striation of muscle tissue
Alternating bands of myocin thick filaments (dark) and actin thin filaments (light)
What branch of the nervous system innervates cardiac and smooth muscle
Autonomic nervous system
Involuntary
Do skeletal muscles have gap junctions
NO
This is a feature of cardiac muscle
Which type of muscles have neuromuscular junctions present
Skeletal
What is a neuromuscular junction
where the somatic nerve connects to the muscle to cause it to contract
Where does the calcium come from in skeletal muscle contraction
Entirely from the sarcoplasmic reticulum
What is the transmitter at neuromuscular junctions?
Acetylcholine
Why are neurotransmitters required at the neuromuscular junction
There is no continuity of cytoplasm between nerve and skeletal muscle cells
A single motor unit can supply more than one muscle fibre - true or false
TRUE
Which muscles have high numbers of fibres per unit
Muscles where power is important
E.g. thighs
What is the functional unit of skeletal muscle
Sarcomere
Made up of actin and myosin
How do skeletal muscles attach to bones
Via tendons
How far does a single muscle fibre usually extend
the entire length of muscle
What are myofibrils
Specialised contractile intracellular structures
Made up of actin and myosin organised into sarcomeres
What is the Z line
Where two sarcomeres meet
Connects the thin filaments of 2 adjoining sarcomeres
What is a functional unit
the smallest component capable of performing all the functions of that organ
What is required for muscle contraction
ATP - energises the myosin head
Calcium - switches on cross bridge formation
Is it ATP or calcium that is required for muscle relaxation
ATP
needed to break down the crossbridges and pump Ca back into SR
What is excitation contraction coupling
the process whereby the surface action potential results in activation of the contractile structures of the muscle fibre
When is Ca released from the SR in skeletal muscles
When the surface action potential travels down the transverse tubules (T-tubules)
What are T tubules
Extensions of the surface membrane that dip into the muscle fibre
Bring AP much closer to SR
What initiates skeletal muscle contraction
Stimulation of alpha motor neurons
This is neurogenic initiation
What factors affect the tension developed by each contracting muscle fibre
Frequency of stimulation
Summation of contractions
Length and thickness of muscle fibre
What lasts longer, the action potential or the muscle twitch
The AP is short lived
The contraction continues for a while after
What type of muscle cannot be tetanised
Cardiac
Due to long refractory period
What causes tension of the muscle to increase
Increasing the frequency of stimulation
How is sustained muscle contraction produced
If the muscle is stimulated rapidly with no opportunity to relax between stimuli
Contraction will also be stronger
What happens when a skeletal muscle is stimulated once
A twitch is produced
Not useful for meaningful muscle activity
How is muscle tension transmitted to bone
Via the elastic components of muscle
Tendon or connective tissue
What are the main differences between different types of skeletal muscle fibres
The pathway used for ATP synthesis
The level of resistance to fatigue
The activity of myosin ATPase
Each motor unit contains more than one type of muscle fibre - true or false
False
Usually only contains one type
Which metabolic pathways can supply ATP in a muscle fibre
Transfer of phosphate from creatine phosphate to ADP
Oxidative phosphorylation - when O2 present
Glycolysis - when O2 not present
Describe slow oxidative type 1 fibres
Slow twitch fibres
Used for prolonged, low aerobic activity
Resistant to fatigue
produces lots of ATP
Describe fast oxidative, type IIa fibres
Intermediate twitch fibres
Use both aerobic and anaerobic metabolism
Useful in prolonged activity with moderate work - jogging
Describe fast glycolytic type IIx fibres
Fast twitch fibres
Uses anaerobic metabolism
Used for short-term, high intensity activity
Fatigue easily - produce less ATP
What is a reflex action
A stereotyped response to a specific stimulus
Simplest form of coordinated movement
Which nerve is stimulated by the knee jerk reaction
L3, 4
Femoral nerve
Which nerve is stimulated by the ankle jerk reaction
S1, S2
Tibial nerve
Which nerve is stimulated by the biceps jerk reaction
C5, 6
Musculocutaneous Nerve
Which nerve is stimulated by the brachioradialis jerk reaction
C5-6
Radial nerve
Which nerve is stimulated by the Triceps jerk reaction
C6-7
Radial nerve
What are annulospiral fibres
The sensory nerve ending of muscle spindles
Where are muscle spindles found
Within the belly of muscles
They run parallel to ordinary muscle fibres (
Describe the nerve supply to muscle spindles
They have their own (efferent) motor nerve supply
Called gamma neurons
What factors may impair skeletal muscle functions
Intrinsic muscle disease
Disease of NMJ
Disease of the lower neurons that supply the muscle
Disruption of input to motor neuron - e.g. MND
What are some general symptoms of muscle disease
Muscle weakness/tiredness
Delayed relaxation - myotonia
Muscle pain - myalgia
Stiffness
List some useful investigations in neuromuscular disease
Electromyography Nerve conduction studies Muscle enzymes - CK Inflammatory markers - CRP, PV Muscle biopsy
What is defined as chronic pain
Lasting over 3 months
What is the definition of pain
An unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage
What are the 4 processes in the experience of pain
Transduction - stimuli turned into electrical impulse
Transmission - signal passes through nervous system
Modulation - signal is modified or hindered by system
Perception - finishes with the conscious experience of pain
What are nociceptors
Sensory afferent neurons - first order
they are activated by intense noxious/harmful stimuli
Describe the pain pathway
Noxious stimuli is picked up by free nerve ending of nociceptors
Pass along the nerve and synapse with second order in spinal cord send signal to brain
Where are second order neurons found
They ascend the spinal cord in the anterolateral system
Terminate in the thalamus
What is the spinothalamic tract
Part of second order neuron system
Involved in pain perception - location and intensity
What is the spinoreticular tract
Part of second order neuron system
Involved in responses to pain, arousal, emotion etc
What types of stimuli can be noxious
Mechanical
Thermal
Chemical
What are the two types of nociceptors
A delta-fibres
C fibres
What are A delta fibres
mechanical/thermal nociceptors so respond to those stimuli
Thinly myelinated so transmit fast
What are C fibres
respond to all types of noxious stimuli
Non-myelinated so slow transmission
What type of pain in transmitted by A delta fibres
Stabbing, pricking sensation
Immediate pain
What type of pain in transmitted by C fibres
burning, throbbing, cramp sensations
slower
How can you classify pain
Mechanism
Time course - acute/chronic
Severity
Source of origin
What is nociceptive pain
Normal response to injury of tissue by damaging stimuli
Only occurs with intense stimulation
Has a protective function
What is inflammatory pain
Caused by activation of the immune system
Variety of mediators can be the cause
Discourages contact and movement of the affected area
This is protective as it promotes healing
What is neuropathic pain
Caused by damage to neural tissue
Pathological pain
Can present as burning, shooting, numbness etc
What is dysfunctional pain
type of pathological pain
no identifiable cause
Not well understood and hard to treat
What is referred pain
Pain developed in one part of the body felt in another structure
Most common in deep, visceral pain
What causes referred pain
convergence of nociceptive visceral and skin afferents upon the same spinothalamic neurons at the same spinal level
What are the 3 types of joints
Synovial
Fibrous
Cartilaginous
Describe fibrous joints
Where bones are united by fibrous tissue
Doesn’t allow movement
E.g. skull in adults
Describe cartilaginous joints
Where bones are united by cartilage
Allow limited movement
E.g. intervertebral discs
Describe synovial joints
Bones that are separated by a cavity and united by a fibrous capsule
Also involves ligaments, tendons etc
Allow a wider range of movement
What is the synovial membrane
the lining of the fibrous capsule in a synovial joints
Its a vascular connective tissue - with capillaries and lymphatics
What produces synovial fluid
synovial cells that are found in the synovial membrane
What covers the articular surfaces of bones
Cartilage
What supports a joint
extra-articular structures such as ligaments, tendons and bursa
What are the physiological functions of a joint
structural support
purposeful motion - help distribute stress, confer stability
What provides joint lubrication
Interstitial fluid
Synovium and synovium derived lubricin
Synovial fluid has high viscosity - true or false
True
Due to presence of hyaluronic acid produced by synovial cells
Does the synovial fluid contain cells
Normally contains a few
Mainly mononuclear leucocytes (WBC)
Is the synovial fluid a static pool in the joint
No
It is continuously replenished and absorbed by the synovial membrane
When would the synovial fluid WBC count rise
In inflammatory and septic arthritis
It becomes more opaque due to increased cell count
When would synovial fluid turn red
Traumatic synovial tap and in haemorrhagic arthritis
What are the main functions of articular cartilage
Provides a low friction surface for joints - reduces wear and tear
Distributes pressure in the bone
What determines the mechanical properties of cartilage
composition of the cartilage extracellular matrix
What is the function of the water in the cartilage
Maintains resiliency of the tissye
Contributes to nutrition and lubrication
Different amounts in different areas of the joints
What is the function of the collagen in the cartilage
Maintains cartilage architecture
Provides tensile stiffness and strength
What is the function of the proteoglycan component of cartilage
Responsible for the compressive properties associated with load bearing
Concentration varies in different areas
How do chondrocytes receive nutrients
Via the synovial fluid
The cartilage itself is avascular
Describe the turnover of cartilage ECM
Chondrocytes produce enzymes that help degrade the components
Also lay down the cells
In normal joints the two processes are in balance
What changes in the cartilage could lead to disease
Changes in the relative amounts of the three major components
Rate of ECM degradation exceeding the rate of synthesis
What does repeated wear and tear of joints lead to
Osteoarthritis
Common in increasing age
What causes rheumatoid arthritis
Synovial cell proliferation and inflammation
What are some effects of cartilage wear and tear on the subchondral bone
Cyst formation
Sclerosis in the bone
Osteophyte formation
These may be seen in X-ray
What innervates skeletal muscle
motor neurones
Describe the motor neurones to skeletal muscle
Cell bodies are found in the brain or spinal cord
Myelinated axon for fast transmission
The axon branches into many fine branches which lose the myelin sheath as they approach the target muscle
The axon ends with a terminal bouton at the NMJ
What neurotransmitter is used in all skeletal muscle contractions
Acetylcholine
What is a motor unit
The neurone and the number of fibres that it innervates
What surrounds the terminal bouton of a motor neuron
A cap of Schwann cells
What are active zones at the NMJ
The point at which the neurotransmitter can be released
The vesicles cluster near these areas and will fuse in the zone when needed
How is acetylcholine synthesised
Choline is brought into the terminal by a choline transporter
ACh is then synthesised in the cytosol from the choline and acetyl coenzyme A
It is then transported into a vesicle by vesicular ACh transporter
Describe how ACh is stimulated to leave the vesicle
Action potential arrives at the terminal and triggers the opening of Ca channels
Ca flows in and binds to vesicles which allows them to fuse with the presynaptic membrane
Acetylcholine is released by exocytosis
What is the end plate potential
The depolarisation generated by nicotinic ACh receptors at the post-synaptic membrane
Caused by influx of Na+ (which exceeds K+ efflux)
This movement of ions is caused by ACh binding to receptor and opening the pore in the centre
Each vesicle contains roughly the same amount of neurotransmitter - true or false
True
This amount is known as a quantum
Why are the voltage gated Na channels in the muscle fibre so important
Although the initial stimulation (e.p.p) is generated by the nicotinic receptor, it would not be enough on its own to trigger contraction
The additional Na+ channels allow the action potential to spread the length of the fibre and cause the contraction
What are transverse (T) tubules and their function
These tubules are formed by invaginations of the muscle fibre membrane (sarcolemma)
They allow the AP to pass deep into the fibre, closer to the SR
This brings about the release of calcium that causes contraction
Why does the duration of muscle twitch exceed that of the AP
There is a delay of Ca release from the SR - contraction period
And also takes extra time to reuptake the Ca - relaxation phase
What is the function of acetylcholinesterase
Breaks down the ACh in the synaptic cleft so that a single epp cannot trigger a run of AP
How can you treat Neuromyotonia
Anti-convulsants - carbamazepine
Block voltage gated Na+ channels
What drugs may be used in the treatment of LEMS
Anticholinesterases - pyridostigmine
These decrease the breakdown of ACh so more likely to get contraction
K+ channel blockers -
LEMS may improve on exertion
TRUE
Activity can help symptoms
What drugs are used to treat Myasthenia Gravis
Anticholinesterases
Immunosuppressants - azathioprine
How does the botulinum toxin work
Acts on motor neurone terminals to irreversible inhibit ACh release - prevents exocytosis
The effects are only overcome when the toxin is cleared and new vesicles have been synthesized – takes many weeks to recover
Death rate is high
What are the clinical uses of botulinum toxin
Low doses can be given as IM injection to treat overactive muscles (twitches)
Used cosmetically as botox to reduce wrinkles
What are curare-like compounds
Act as competitive antagonists of nicotinic receptors - interfere with ACh action
Reduce the amplitude of e.p.p. to below the threshold - no contraction
How are curare-like compounds used clinically
Used to induce reversible muscle paralysis in certain types of surgery
Name 2 examples of curare-like compounds
Vecuronium
Atracurium
How does the angle of the legs change throughout childhood
All babies are bow legged
Then straightens up at 1-2 years
Angle out slightly over 2
Then back to straight or ‘normal’ alignment from 4 onwards
What are some common ‘abnormalities’ in children that usually correct themselves
Overlapping toes
Internally rotated feet
Flat feet
How do bones grow longitudinally
From the growth plate by enchondral ossification
This is where you start with a cartilage model that eventually becomes bone
How does bone grow in circumference (get wider)
From the periosteum by appositional growth
Which part of the bone is most vulnerable to trauma
Growth plates
What factors affect the growth plate of bone
Hormones Diet/nutrition Sunshine - vitamins Injury Illness
What is meant by varum knee alignment
Knees bend out the way
Bow legged
Normal in under 2s
What is meant by valgum knee alignment
Knees bend in the way
Knock kneed
When is genu varum abnormal
If unilateral
If very severe
If it is causing pain
Causes include, skeletal dysplasia, rickets, Blount’s disease and tumours
What is Blount’s disease
Rare condition where growth is stopped in the tibial physis unilaterally
Get a typical beak-like protrusion on x ray
What pathologies can cause genu valgum
Tumours – enchondroma, osteochondroma
Rickets
Neurofibromatosis
Idiopathic
More likely if asymmetrical, painful or severe
