Physiology Flashcards
What are the main functions of skeletal muscles?
Maintain posture
Purposeful movement
Respiration
Heat production (e.g. shivering)
Contribution to whole body metabolism
What are the three main types of muscles in the body?
skeletal
cardiac
smooth
What types of muscle are striated?
Cardiac
skeletal
What causes striated muscles to look like alternating dark and light bands under a light microscope?
Thick Myocin filaments (dark)
Thin Actin filaments (light)
If skeletal muscles are under voluntary control, what nervous system is therefore responsible for its movement?
Somatic NS
What nervous system controls cardiac and smooth muscle?
The autonomic nervous system
=> actions are involuntary
Describe the difference between the initiation and propagation of a contraction in skeletal muscle compared to that of cardiac muscle
Skeletal = neurogenic
=> arranged in motor units
=> neuromuscular junctions
Cardiac = myogenic (pacemaker potential)
=> GAP junctions
What neurotransmitter can be found at the neuromuscular junction?
Acetylcholine (ACh)
How is a single motor unit defined?
a single alpha motor neuron
and all the skeletal muscle fibres it innervates
A muscle contains motor units if it has the responsibility of carrying out fine movements (e.g. external eye muscle, intrinsic hand muscles) TRUE/ FALSE?
FALSE
muscles which serve fine movements have fewer fibres per motor unit
Name the progression of structures from a whole muscle down to its smallest functional unit
Whole Muscle
Muscle Fibre
Myofibril
Sarcomere
TRUE/FALSE - Skeletal muscle fibres (cells) usually extend the entire length of muscle
TRUE
How are skeletal muscles usually attached to bone?
attached to skeleton by means of tendons
What is the functional unit of any organ?
smallest component capable of performing all the functions of that organ
=> for muscle this is a sarcomere
Between where can a sarcomere be found?
found between two Z-lines - connect the thin filaments of 2 adjoining sarcomeres
What is found in the sarcomere zone known as the A-Band?
A-band:
Made up of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments
What is found in the H-Zone of a sarcomere?
H-Zone:
Lighter area within middle of A-band where thin filaments don’t reach
Where in a sarcomere can the M-Line be found?
M-Line:
Extends vertically down middle of A-band within the centre of H-zone
What can be seen in the I-Band of sarcomeres?
I-Band:
Consists of remaining portion of thin filaments that do not project in A-band
How do muscles shorten and produces force?
Muscle tension is produced by sliding of actin filaments on myocin filaments
=> decreasing the length of the muscle and producing contraction
What compound is extremely important for contraction and relaxation of muscle?
ATP
Describe the process of contraction by cross-linking
1) ACh released by axon to motor end plate => binding
2) AP generated and spread across surface membrane and down T-Tubules
3) AP in T-Tubules induces Ca release from SR
4) Ca ions bind to troponin on actin filaments
=> tropomyosin moved aside to reveal cross bridge binding site on actin
5) Myosin cross bridges bind to Actin, bending and pulling them towards centre of sarcomere
Describe the process of relaxation in a skeletal muscle
1) No more APs => Ca taken back up by SR
2) Ca no longer bound to troponin => tropomyosin can move back over and block cross bridge binding site on actin
=> RELAXATION
What part of the sarcoplasmic reticulum is stimulated to release calcium when an action potential travels down a T-Tubule?
lateral sacs of SR
What two primary factors does gradation of skeletal muscle tension depend on?
Number of muscle fibres contracting within muscle
Tension developed by each contracting muscle fibre
What does asynchronus motor unit recruitment suring submaximal contraction help to prevent?
prevent muscle fatigue
=> not all motor units are being used for activities which aren’t extremely strenuous
What factors can influence the tension produced by a muscle fibre?
- frequency of stimulation
- summation of contractions
- length of muscle fibre at the onset of contraction
- thickness of muscle fibre
If the action potential of a muscle is significantly shorter than the twitch it brings about, what does this imply we can do to the muscle?
Repetitively stimulate the muscle with action potentials to bring about a stronger contraction
What is it called when we continuously stimulate a muscle for constant contraction?
Tetanic contraction or Tetanus
What feature of the muscle in the heart resists tetanic contraction?
The long refractory period prevents generation of tetanic contraction
A single twitch produces sufficient tension to bring about meaningful skeletal muscle activity. TRUE/FALSE
FALSE
A single twitch produces little tension and is not useful in bringing about meaningful skeletal muscle activity
When can maximal tetanic contraction be achieved?
when the muscle is at its optimal length (lo)
before the onset of contraction
(where most Myocin and actin is overlapping)
How is skeletal muscle tension transmitted to bone?
via stretching and tightening of muscle connective tissue and tendon (elastic component)
What are the two types of skeletal muscle contraction?
Isotonic contraction
Isometric contraction
Describe what is meant by an Isotonic contraction and what it is used for
Muscle tension remains constant
muscle LENGTH CHANGES
USED FOR:
- body movements
- moving objects
Describe what is meant by an Isometric contraction and what it is used for
Muscle TENSION DEVELOPS
constant muscle length
USED FOR:
- supporting objects in fixed positions
- maintaining body posture
The velocity of muscle shortening decreases as the load increases
TRUE/FALSE
TRUE
as load increases, contraction takes longer
WHat are the main differences between seperate types of skeletal muscle fibre
1) The enzymatic pathways for ATP synthesis
2) The resistance to fatigue
(greater capacity to synthesise ATP are more resistant to fatigue)
3) Activity of myosin ATPase - determines speed of
contraction
Each motor unit usually contains one type of muscle fibres TRUE/FALSE?
TRUE
By which 3 ways can muscles make ATP?
1) Transfer of high energy phosphate from creatine phosphate to ADP to make ATP (immediate source)
2) Oxidative phosphorylation
3) Glycolysis
Describe what type of activity each type of skeletal muscle fibre would be used for
Slow oxidative type I fibres (slow-twitch fibres)
- prolonged relatively low work aerobic activities
e. g. maintenance of posture, walking
Fast oxidative (Type IIa) fibres (intermediate-twitch fibres)
- aerobic and anaerobic metabolism
- prolonged /moderate work activities
e. g. jogging
Fast glycolytic (Type IIx) fibres (fast-twitch fibers)
- anaerobic metabolism
- mused for short-term high intensity activities
e. g. jumping
What colour is each type of skeletal muscle fibre?
Slow oxidative type I fibres Fast oxidative (Type IIa) fibres = RED (due to myoglobn from oxygen
Fast glycolytic (Type IIx) fibres = WHITE (no myoglobin as these work anaerobically)
What is a reflex?
stereotyped response to a specific stimulus
simplest form of coordinated movement
What are reflexes important for?
pathways for reflexes are important for localising lesions in the motor system
What is a stretch reflex and give an example of when it would be used?
Negative feedback that resists passive change in muscle length
=> maintain optimal resting length of muscle to carry out task
e.g. maintain posture whilst walking
Describe the process in the body when you test a reflex
1) sensory receptor = muscle spindle => activated by muscle stretch
2) Stretching the muscle spindle increases firing in the afferent neurons
3) afferent neurons synapse in the spinal cord with the alpha motor neurons that innervate the stretched muscle
4) Activation of the reflex results in contraction of stretched muscle
How can the stretch reflex be elicited?
tapping the muscle tendon with a rubber hammer
What nerve roots are associated with a knee jerk reflex?
L3, L4
What nerve roots are associated with an ankle jerk reflex?
S1, S2
What are muscle spindles?
- collection of specialised muscle fibres
- intrafusal fibres (Ordinary muscle fibres = extrafusal fibres)
- found within the belly of muscles
- run parallel to ordinary muscle fibres (extrafusal fibres)
Muscle spindles have their own efferent (motor) nerve supply TRUE/FALSE
TRUE
efferent neurons that supply muscle = gamma motor neurons
What is the function of gamma motor neurons in muscle spindles?
- adjust the level of tension in the muscle spindles
=> maintain sensitivity when muscle shortens during contraction
contraction of intrafusal fibres contributes to the overall strength of muscle contraction TRUE/FALSE
FALSE
Contraction of intrafusal fibres DOES NOT contribute to the overall strength of muscle contraction
What are the potential causes of intrinsic muscle disease?
Genetic myopathies
Acquired myopathies
Give examples of Genetic myopathies
- Congenital
- Chronic Degeneration (e.g. muscular dystrophy)
- Abnormalities in muscle membrane ion channels (e.g. myotonia)
Give some examples of acquired myopathies
- Inflammatory (e.g. polymyositis)
- Non-Inflammatory (e.g. fibromyalgia)
- Endocrine (e.g. Cushing syndrome)
- Toxic (e.g. alcohol)
What are the most common symptoms in muscle disease?
Muscle weakness / tiredness
Delayed relaxation after voluntary contraction (myotonia)
Muscle pain (myalgia)
Muscle stiffness
What investigations may be useful to do when concerned about muscle disease?
Electromyography (EMG)
Nerve conduction studies
Muscle enzymes
- Creatine kinase (CK)
Inflammatory markers
C-reactive protein (CRP), plasma viscosity (PV)
Muscle biopsy
What are the three main types of joint?
fibrous
cartilaginous
synovial
Give examples of each type of Fibrous Joint
syndemoses - e.g. Interosseous membrane between tibia and fibula
sutures - e.g. coronal suture in the skull
Give examples of Type 1 and 2 cartilaginous joints
Type 1 - epiphyseal growth plate
Type 2 - intervertebral discs
Describe the appearance of a synovial joint
Bones separated by a cavity (containing synovial fluid) and united by a fibrous capsule
What is found lining the fibrous capsule of a synovial joint?
inner aspect of fibrous capsule = 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
What covers the articular surfaces of bones?
cartilage
What is the difference between a simple and compound synovial joint?
Simple = one pair of articular surfaces
Compound = more than one pair of articular surfaces
Give an example of a simple and compound synovial joint
SIMPLE - metacarpophalangeal joint
COMPOUND - elbow joint
Name the extra-articular structures which can also support joints
Ligaments
Tendons
Bursa
What are the two main functions of a joint?
Structural support
Purposeful motion
During movement what role do joints have?
Stress distribution
Confer stability
Joint lubrication
What are the components of synovial fluid that allow adequate joint lubrication
hyaluronic acid (mucin) - a polymer of disaccharides lubrcin - a glycoprotein
Aside from lubrication, what other jobs are carried out by the synovial fluid?
minimise wear-and-tear
nutrition of articular cartilage
Synovial fluid is continuously replenished and absorbed by the synovial membrane TRUE/FALSE?
TRUE
=> it is not a static pool
Synovial fluid usually has a low viscosity TRUE/FALSE?
FALSE = high viscosity - mainly due to the presence of hyaluronic acid (mucin) produced by the synovial cells
The viscosity of the synovial fluid varies with Joint movement
Viscosity of synovial fluid in a joint usually decreases with rapid movement TRUE/FALSE?
TRUE
Rapid movement is associated with decreased viscosity and increased elasticity
Give an example of a disease where properties of synovial fluid become defective
osteoarthritis
Describe the normal appearance and WBC count of synovial fluid
normal synovial fluid is clear and colourless
It has <200 WBC/mm3
In what cases would the WBC count of synovial fluid in a joint rise?
synovial fluid WBC count increases in inflammatory and septic arthritis
If synovial fluid is red, what is this indicative of?
Turns red in traumatic synovial tap and in haemorrhagic arthritis
What are the names given to the different zones found in articular cartilage?
Superficial zone
Middle zone
Deep zone
Calcified zone
What makes each of the zones in articular cartilage different?
organization of collagen fibres and relative content of cartilage components
What are the main three components of cartilage?
Water
Collagen (mainly Type II)
Proteoglycans
What is the role of each cartilage component?
Water - contribute to the nutrition and lubrication system
Collagen - tensile stiffness and strength
Proteoglycan - compressive properties associated with load bearing
How much of articular cartilage is made up by the extracellular matrix, and how much is made up of chondrocytes?
ECM = > 98% of the total cartilage volume
CHONDROCYTES (cartilage cells) = < 2% of the total cartilage volume
If articular cartilage is avascular, how does it receive oxygen and nutrients?
cartilage cells receives nutrients and O2 via the synovial fluid
Chondrocytes produce enzymes to degrade their own extracellular matrix TRUE/FALSE?
TRUE
In normal joints, rate of ECM degradation doesn’t exceed the rate at which it is replaced
=>Joint disease occurs if rate of ECM degradation exceeds the rate of synthesis
What are the catabolic and anabolic factors affecting the cartilage matrix ?
Catabolic factors - Stimulate proteolytic enzymes and inhibit proteoglycan synthesis
Anabolic factors - Stimulate proteoglycan synthesis and counteract effects of IL-1
Give examples of catabolic factors affecting the cartilage ECM
Tumour necrosis factor (TNF)-
Interleukin (IL)-1
Give examples of anabolic factors affecting the cartilage ECM
Tumour growth factor (TGF)-β
Insulin-like growth factor (IGF)-1
What markers may indicate cartilage degradation?
Serum and synovial keratin sulphate
- Increased levels = cartilage breakdown
- BUT increases with age and in osteoarthritis
Type II collagen in synovial fluid
- Increased levels = cartilage breakdown
- Useful in evaluating cartilage erosion e.g. osteoarthritis and rheumatoid arthritis
What condition is caused by repeated wear and tear of joints?
osteoarthritis
What condition is caused by excess synovial cell proliferation and inflammation?
rheumatoid arthritis
What condition in a result of deposition of uric acid salt crystals?
gouty arthritis
What type of condition is caused when there is injury and inflammation to periarticular structures?
soft tissue rheumatism
e.g. injury to the tendon causes tendonitis
Whata effects can “wear and tear” have on the subchondral bone?
Cyst formation
Sclerosis in subchondral bone
Osteophyte formation
What is pain?
unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage
Name the 4 processes involved in the physiology of pain
Transduction
Transmission
Modulation
Perception
What happens during the Transduction stage of pain?
translation of noxious stimulus into electrical activity at the peripheral nociceptor
What occurs during the transmission of pain?
propagation of pain signal as nerve impulses through the nervous system
What happens during the stage of pain where modulation occurs?
modification/hindering of pain transmission in NS
e.g. by inhibitory neurotransmitters like endogenous opioids
Explain what is meant by the perception of pain
Conscious experience of pain. Causes physiological and behavioural responses
What are nociceptors?
specific primary SENSORY AFFERENT neurones
- activated by intense noxious stimuli
WHat are the main types of noxious stimuli which act upon nociceptors?
mechanical
thermal
chemical
Nociceptors are second order neurones TRUE/FALSE
FALSE
Nociceptors are first order neurones that relay information to second order neurones in the CNS by chemical synaptic transmission
What neurotransmitters are important in the nociceptive pathway?
Glutamate and peptides (substance P, neurokinin A)
What are the main ways in which pain is classified?
Mechanisms: e.g. nociceptive, inflammatory, pathological
Time course: e.g. acute, chronic, breakthrough pain
Severity: e.g. mild, moderate, or severe
Source of origin: e.g. somatic or visceral
What causes inflammatory pain?
activation of the immune system by tissue injury or infection
Pain activated by a variety of mediators released at the site of inflammation by blood cells
Why do patients often find that inflammatory pain reduces physical contact (with the affected part) and also discourages movement (e.g. of a joint)
heightened pain sensitivity to noxious stimuli (hyperalgesia)
pain sensitivity to innocuous stimuli (Allodynia)
What causes neuropathic pain and how is it often described by patients?
Neuropathic pain = caused by damage to neural tissue
- perceived as burning, shooting, numbness, pins and needles.
- May be less localised
Give examples of neuropathic pain
compression neuropathies peripheral neuropathies central pain (following stroke or spinal injury) post-herpetic neuralgia trigeminal neuralgia phantom limb
What is different about dysfunctional pain?
There is no identifiable damage or inflammation
Give examples of dysfunctional pain
fibromyalgia irritable bowel syndrome (IBS) tension headache temporomandibular joint disease interstitial cystitis
If pathological pain (neurological or dysfunctional) does not respond well to simple analgesics, what is often used to treat these conditions?
sometimes treated by drugs not originally developed for pain (e.g. antidepressants or anti-epileptics)
What is meant by referred pain?
Pain developed in one part of the body felt in another structure away from the place of its development
Superficial structures are more likely to cause referred pain. TRUE/FALSE?
FALSE
Deep pain or visceral pain can be felt as referred pain.
Pain originating in superficial structures is usually not referred
What causes referred pain?
convergence of nociceptive visceral and skin afferents upon the same spinothalamic neurons at the same spinal level
Where are the secondary order neurones found?
Second order neurones ascend the spinal cord in the anterolateral system (terminate in the thalamus)
Give examples of the secondary order neurone pathways
spinothalamic tract (STT): Involved in pain perception spinoreticular tract (SRT): Involved in autonomic responses to pain
Where do pain signals go after the secondary order neurone?
From the thalamus, sensory information is relayed (third order neurones) to the primary sensory cortex
Name the two subtypes of nociceptor
A-delta fibres
- myelinated
- fast
C-fibres
- unmyelinated
- slow
Where can pain from the heart refer to?
the left arm and left jaw
Where can pain from the liver or gall bladder refer to?
The shoulder
Where can pain from the lung or diaphragm refer?
The shoulder
Where can appendicitis pain present as referred pain?
In the umbilical region
Where can stomach and pancreatic pain refer to?
the epigastric region
