musculoskeletal system Flashcards
why do skeletal muscles appear striated under the microscope?
- highly organised nature of sarcomeres
- actin & myosin are arranged in an orderly structure within the sarcomeres
what are actin & myosin?
contractile proteins
why are smooth muscles not striated?
actin & myosin are arranged irregularly so they appear uniform under a microscope
3 types of muscle tissue
- skeletal
- cardiac
- smooth
skeletal muscle
- long cylindrical cells
- many nuclei per cell (lots of satellite cells fused together)
- striated due to sarcomeres
- voluntary
- rapid contractions
- limbs, face…
cardiac muscle
- branching cells
- 1 or 2 nuclei per cell
- striated
- involuntary
- medium speed contractions
- only in the heart
why does cardiac muscle have branching cells?
to facilitate uniformal contractions
why are cardiac muscles always slightly contracted?
to prevent fully emptying a chamber in the heart
smooth muscle
- fusiform cells
- one nucleus per cell
- non striated (actin & myosin irregularly arranged)
- involuntary
- slow, wave like contractions
- GI tract / organs
what is an isometric contraction?
- produces no movement
- while standing, sitting & posture
- force produced with no change
what is an isotonic contraction?
- produces movement
- walking, moving anything in the body
what is an isokinetic contraction?
moving with the same constant velocity
what does the Z disc do?
- stabilised / hold actin filaments together
- allows transfer of forces between sarcomeres
what does a myosin molecule consist of?
- 2 twisted together
- has a tail and head
- head = attaches to actin molecules
what does the thin (actin) filament consist of?
- 2 twisted actin molecules
- troponin complex
- tropomyosin
- G actin
what does the thick (myosin) filament consist of?
myosin molecules with globular heads (pointing outwards) which form cross-bridges with / can attach to actin molecules
troponin complex
- protein needed for muscle contraction
- calcium binds to it to trigger musclular force
- in thin filament
tropomyosin
- proteins
- regulates muscle contraction by mediating interactions between troponin complex and actin
- in thin filament (actin)
H band
- zone of thick filaments with no actin
- M line in H band
M line
- middle of sarcomere
- formed by cross connecting elements of cytoskeleton
what does the addition of calcium trigger?
- activates the contractile proteins (troponin complex)
- muscle contraction
what is meant by the term motor unit?
motor unit describes a functional group comprised of a motor neuron and its axons (branching into the muscle) and the innervated muscle fibres
what do cardiac muscle fibres determine?
they organise how cardiac output is produced
parts of the skeletal system
- bones
- joints
- cartilages
- ligaments
the skeletal system is divided into 2 divisions
- axial skeleton
- appendicular skeleton
what is the axial skeleton?
- skull, vertebral column, rib cage
- forms longitudinal part of the body
what is the appendicular skeleton?
limbs and girdle
(girdle: either of two more or less complete bony rings at the anterior and posterior ends of the vertebrate trunk supporting the arms and legs respectively)
functions of bone
- support
- protection
- assisting in movement
- mineral storage
- red blood cell production
- chemical energy storage (fats)
how does the skeleton support the body?
- it is the body framework
- supports soft tissue
- provides attachment points for most skeletal muscle
- helps allow simple movement without the expanditure of too much energy
how does the skeleton protect the body?
protects delicate organs:
- ribs protect the heart and lungs
- skull protects the brain
why do the ribs need to be flexible?
- to allow the dissipation of energy throughout the body
- to distribute force
how does the skeleton help movement?
muscles contract and pull on bones which gives rise to movement
bones and mineral storage
- outer layer of bony tissue used for mineral storage
- mainly calcium and phosphorus
- can be taken from bone (osteoclasts) -> blood stream if blood levels to low
bones and blood cell production
- red, white blood cells and platelets made in bones
- red bone marrow = in ends of long bones and some other bones like ribs, femur, humerus & vertebrae bones
- blood cells produced in red bone marrow
- yellow bone marrow = in the shaft of long bones
- no blood cells produced in yellow bone marrow
where is fat stored in bones?
in adipocytes in yellow bone marrow
role of spongy bone
- balances the dense and heavy compact bone -> makes bone lighter -> muscles can move them easier
- when load is put on bones it helps distribute it
how many bones are in the skeleton?
206
what are the 2 basic types of bone tissue?
- compact bone (homogenous)
- spongy bone (small, needle-like pieces of bone with many open spaces for blood supply)
are bones easy to repair? why?
- yes (better than tendons and cartilage)
- due to high vascularisation
long bones
- longer than they are wide
- movement
- arms, legs…
short bones
- square, cube like
- stability & support instead of movement
- wrist, ankle…
flat bones
- flat, curved
- protection
- skull, sternum…
irregular bones
- odd shapes
- vertebrae, pelvis (wide area where many muscles come togethet)
types of bone cells
- osteocytes
- osteoblasts
- osteoclasts
osteocytes
- mature bone cells
- constantly being replaced by osteoblasts
osteoblasts
- bone-forming cells
- rebuilds bone if fractured
osteoclasts
- bone-destroying cells
- break down bone matrix for re-modeling and release calcium
what does bone re-modeling require?
- osteoblasts
- osteoclasts
what is the skeleton in embryos?
hyaline cartilage
-> replaced by bone during development
where did cartilage not get replaced by bone during development?
- bridge of the nose
- parts of the ribs -> flexibility
- joints
how many bones does the skull have?
22
the hyoid bone
- only bone that does not articulate with other bones
- moveable base for the tongue and othr muscle attachments
- broken when being chocked -> changes in breathing pattern as a result
the hyoid bone
- only bone that does not articulate with other bones
- moveable base for the tongue and othr muscle attachments
- broken when being chocked -> changes in breathing pattern as a result
what is a joint?
- an articulation
- where two bones come together
types of joints
- fibrous
- cartilaginous
- synovial
fibrous joint
- immovable / no movement
- connects bones
- skull & pelvis
cartilaginous joint
- slightly moveable
- bones attached by cartilage
- spine & ribs
synovial joints
- freely moveable
- cavities between bones filled with synovial fluid
role of synovial fluid
lubricate and protect
between bones
the two major pathways that axons from the brain descend along
- lateral = side of the spinal cord
- ventromedial = front and center
spinal tracts
- bundles of nerves
- from brain to peripheral muscles
- stretch detectors = sense how fast and much a muscle is lengthened or shortened
the lateral descending spinal tract
- voluntary movement
- originates in the cortex
- composed of the:
- corticospinal tract (pyramidal tract)
- rubrospinal tract (extra-pyramidal)
the effects of corticospinal lesions
- deficit in fractionated movement of arms and hands
- paralysis on contralateral side due to crossing over
- recovery if rubrospinal tract is intact
- subsequent rubrospinal lesion reverses recovery
crossing over
- also called pyramidal decussation
- results in e.g. left side of the brain managing things on the right side of the body
what are the descending spinal tracts?
- the ventromedial pathways
- the vestibulospinal tract
- the tectospinal tract
the ventromedial pathways
- posture and locomotion
- originate in the brainstem
- pontine and medullary recticulospinal tract
- involved in reflexes
the vestibular tract
- head balance
- head turning
the tectospinal tract
orientating
the pontine recticulospinal tract
enhances postural reflex
-> to maintain a constant posture in relation to a dynamic external environment
the medullary recticulospinal tract
liberated postural muscles from reflex
where is movement initiated?
the motor cortex
- areas 4 & 6 of the frontal lobe
area 4 of the motor complex
- primary motor cortex / M1
- simpler movements
- not as much of the brain is needed for simpler movements
area 6 of motor cortex
- higher motor area
- more complex movements
- actions converted into signals specifying how actions will be performed
what does the supplementary motor area do (SMA)?
- additional movement
- found in the medial region of motor cortex
- intentional preperation for movement
what does the premotor area do (PMA)?
- found in the lateral region of motor cortex
- sensory guidance of movement
what do the posterior parietal and prefontal cortex do?
- highest level of motor control
- descisions made about their outcomes
- area 5 & 7
role of the anterior frontal lobes of cerebral cortex
- abstract thought
- decision making
- anticipating consequences of action
- should I do this movement?
proprioception definiton
- sense of position and strength of effort
- awareness of body in space
- pressure put on and orientation of the body
what does muscle shortening depend on?
- the type of muscle
- the architecture / structure of the muscle (internally and attachments to skeleton)
- which muscle fibres are activated
- force and speed of movement depends on this
what determines what we move and the direction of movement?
- the amount of cells and area of the motor cortex activated
- need to coordinate activity between 2 sides of the brain
motor units
- combination of a motor neuron and all of the muscle fibres that it innervates
- recruited in a precise order
- small units recruited first
why are small motor units recruited first?
- henneman´s size principle
-> task appropriate recruitment to minimize fatigue - The small units don’t produce much force, they are slow to act, and they are resistant to fatigue.
cerebellum
- balance
- movement
- coordination
how does information reach the CNS?
- via afferent/sensory pathways
- signal needs to be sent back to the brain for coordination…
during proprioception where does the brain receive signals from?
- vestibular organs
- eyes
- stretch receptors
vestibular organs & proprioception
- in the inner ear
- send information about rotation, acceleration, position
eyes & proprioception
send visual information
stretch receptors & proprioception
- in skin, muscles and joints
- send info about position of body parts
- also sense pressure
what information do tendons tell you?
- joint angle
- how much pressure is put on joints
proprioceptors in the limbs
- sensors
- provide information about joint angle, muscle length & muscle tension
- position of limb in space
what does the muscle spindle tell you?
changes in muscle length
what does the golgi tendon organ tell you?
information about changes in muscle tension
what is the muscle spindle?
- small sensor organs enclosed in a capsule
- modified muscle fibres with sensory nerves wrapped around them
- found throughout the body of a muscle, parallel with extrafusal fibres (muscle fibres)
- have several small specialised muscle fibres known as intrafusal fibres which have contractile proteins (thick & thin filaments) at either end, with a central region
the central region of a muscle spindle
- made up of contractile proteins
- wrapped by the sensory dendrites of the muscle spindle afferent nerves
what happens to the muscle spindle when the muscle lengthens?
- muscle spindle is stretched
- ion channels opened
- this triggers the action potentials in the muscle spindle afferents
- which sends info to the brain to say that muscle has stretched
intrafusal fibres
- innervated by an efferent neuron called the gamma motor neuron (MN)
- found within a muscle spindle
extrafusal fibres
- innervated by efferents known as alpha MN
- stimulated to contract by aphla MN activation
what does the gamma MN do?
- maintains muscle spindle sensitivity
- innervate intrafusal fibres
- regardless of muscle length
- also excited when alpha MN is activated
- stimulates contractions in the two ends of the intrafusal fibre -> readjusting its length & keeping central region of intrafusal fibre taut
the golgi tendon organ
- in a series with muscle fibres
- located in tendons
- sensory dendrites of golgi tendon organ afferent = interwoven with collagen fibres in the tendon
- muscle contraction is a good stimulus for it
what happens when the muscle contracts?
- collagen fibres are pulled tight
- this activated the golgi tendon organ afferent
- changes in this muscle tension = provide different degrees of pull on the tendon
- golgi tendon organ tells you about that info on muscle tension
- most of the force of a stretch is absorbed by the muscle itself -> muscle contraction better stimulus for golgi tendon organ than muscle stretch
tactile receptors
provide sensation of:
- touch
- pressure
- vibration
baroreceptors
detect blood volume & pressure changes
4 types of mechanoreceptors (other proprioceptors)
- merkel receptors
- meissner corpuscles
- ruffini cylinders
- pacinian corpuscles
what makes the 4 mechanoreceptors differ?
- location in kin
- physical features
- speed of adaptation to stimulation
- size of receptive fields
- type of mechanical stimulation to which they respond
mechanoreceptors
- each type responds to a range of frequencies of mechanical stimulation
- range = 0.3Hz - 500Hz
- detect touch, pressure, vibration and sound
slow adapting (SA) fibres
- merkel disks
- ruffini cylinders
- respond when the stimulus is present
- active / firing till contact to the stimulus stops
rapidly adapting fibres
- meissner corpuscles
- pacinian corpuscles
- respond to stimuli with burst of firing at beginning and end of stimulation
where are receptors with small receptive fields found?
close to skin surface
where are receptors with large receptive fields found?
deeper in skin
- e.g. when you stand on a big stone pressure is distributed more
do simple reflexes involve the CNS?
no
do complex reflexes involve the CNS?
yes
-> could require a desicion or a choice
what is dizziness a result of?
- vestibulo-ocular reflex gone wrong
- spinning causes sensory cells to keep signalling after we stop
- inputs from balance organs normally compensated by movements of the eye
which stimuli do merkel receptors respond best to?
steady pressure from small objects
which stimuli do meissner corpuscules respond best to?
rubbing against the skin or skin movement across a surface
which stimuli do ruffini cylcinders respond best to?
steady pressure & stretching of the skin (joint movement)
which stimuli do picinian corpuscles respond best to?
changing stimulation
where are muscle spindles found?
in muscle tissue
what are muscle spindles?
receptors
what stimuli do muscle fibres detect?
changes in muscle fibre length
where are golgi tendon organs found?
in tendons between muscle fibres and adjoining collagen fibres
what stimuli do golgi tendon organs respond to?
changes in muscle fibre tension
what are golgi tendon organs?
receptors
which tissues are easiest to regenerate?
- skeletal tissue
- cardiac muscle does not regenerate well -> can lead to heart failure
what happens during regeneration after injury?
- growth of cells and tissue to replace lost structures
- needs intact connective tissue scaffold
types of cells
- labile
- stable
- permanent
labile cells
- high rate of loss and replacement
- high regeneration capacity / can regenerate fast
- cells that may die off / fall off easily or frequently
- squamous and glandular epithelia
- haemopoeitic cells in bone marrow
stable cells
- non proliferative but can be stimulated to after damage
- renal tubular cells
- hepatocytes
- osteoblasts
- endothelial cells
- fibroblasts
permanent cells
- cannot divide after initial development
- cannot regenerate when damaged
- neurons
- cardiac muscle
- skeletal muscle (around basal lamina, basal cells can produce satellite cells that can proliferate)
what can signal changes in cell growth?
- e.g. intracellular Ca2+ changes can affect satellite cell proliferation
variables that influence healing
- injury: type, intensity, duration
- patient: age, comorbidity, medication
- treatment: apposition, stabilisation, loading & motion
how long does a ligament take to regenerate?
12-16 months
how long does a tendon take to heal?
12 weeks - 14 weeks
how long / after how many days does inflammation occur?
0-7 days
- cant recognize what happened only that a response is needed
where do inflammatory cells migrate from?
- epitendinous tissues (sheath, periosteum, soft tissues)
- epitendon & endotendon
what does the defected tissue/area fill with after injury / during inflammation?
- granulation tissue
- haematoma
- tissue debris
- fibronectin is laid down as scaffolding for collagen synthesis
- form a “scab” above skin -> similar in muscles
length of repair
3-60 days
what occurs during repair?
- fibroblasts migrate to zone of injury
- they begin to synthesise collagen by day 5
- initially collagen type 3 is produced which is laid down in a random orientation
- week 4 = intrinsic fibroblasts proliferate and these cells take over the healing process synthesising and reabsorbing collagen (tendon callus)
- switch to type 1 collagen production
- vasuclar ingrowth via collagen / fibronectin scaffolding
when does organisation occur?
28-180 days
what happens during organisation?
- final stability acquired during this phase by the normal physiological use of the tendon
- full recovery of tendon & ligament can be difficult
- cross linking between fibrils helps to further increase tendon tensile strength
- complete regeneration never acheived
-> defect remains hypercellular
-> thinner collagen fibrils
tendon healing
weakest: 7-10 days
regain most strength by 21-28 days
maximum strength after 6 months
what can mobilisation do to a tendon injury?
- increase ROM
- decrease tendon repair strength if excessive stress placed on repair
- immobilisation leads to increase tendon substance strength at expense of ROM
what does RICE stand for?
- rest
- ice
- compression
- elevation
