block 3- the musuloskeletal system Flashcards
examine the structure of skeletal muscle
- long cylindrical shape
- many nuclei per cell
- striated
- voluntary control
- rapid contractions
- attatched to bones
- involved in movement, facial expressions and manipulation of the environment
examine the structure of cardiac muscle
- branching cells
-one or two nuclei per cell
-striated - involuntary
- medium speed contractions
- contracts to propel blood into the circulation
- located in the walls of the heart
- intercalated discs that connect adjacent cardiac cells
examine the structure of smooth muscle
- fusiform cells
-one central nucleus per cell - cells arranged closely to form sheets
- non-striated
-involuntary - slow, wave-like contractions
-propels substances or objects along internal passages
describe the composition of a skeletal muscle fiber
sacromeres
= the basic contractile unit of muscle.
- Composed of alternating thick (myosin) and thin (actin) filaments arranged in a striated pattern.
Z-disc: Defines the boundary of each sarcomere.
A-band: Dark region where thick and thin filaments overlap.
I-band: Light region containing only thin filaments.
H-zone: Central region of the A-band with only thick myosin filaments.
M-line: Center of the sarcomere, where thick filaments attach.
describe the two myofilaments
- myosin
- Contains myosin heads(two) that bind to actin during contraction.
- elongated and thick (two protein molecules twisted together)
- many myosin molecules together form the thick myosin filament - Thin filaments (actin): Contain binding sites for myosin, regulated by troponin and tropomyosin.
- twisted shape
-
which filament moves when the sacromere contracts?
The thin actin filaments move closer together, and the thick myosin filaments do not change.
describe the process of contraction by actin and myosin
step 1 = Myosin head attaches to an actin filament to create a cross bridge (myosin head in a high energy configuration)
step 2 = Power stroke -> myosin head pivots and bends as it pulls on the actin filament, sliding it towards the M line, ADP and Pi released
step 3= The new ATP attaches to the myosin head, the cross bridge detaches (myosin head in low energy configuration)
step 4= As ATP is split into ADP and Pi, cocking of myosin head occurs and is now ready to attach to an actin filament to start another power stroke.
- ATP is needed for detachment; without it, muscles can get damaged.
- Phosphate release allows force generation.
what is the role of the T tubiule system and sarcoplasmic reticulum
= T tubule system allows for fast activation and relaxation of muscle fibre
- involved in the release and reuptake of calcium which is stored in the sarcoplasmic reticulum
SR = Releases calcium upon stimulation to trigger muscle contraction.
- A specialized smooth endoplasmic reticulum that stores calcium.
what is the sarcalemma
The plasma membrane of the muscle fibre.
Surrounds the cytoplasm (sarcoplasm) and helps transmit electrical signals (action potentials).
outline the differences between isometric and isotonic contraction
- isometric
- produces no movement
- used in standing, sitting and posture - isotonic contraction
- produces movement
- used in walking, moving any part of body
describe the step by step events of a muscle contraction
1.The nerve impulse reaches the neuromuscular junction
2. Acetylcholine is released from the motor neuron
3. Acetylcholine binds with receptors in the muscle membrane to allow sodium ions to enter the muscle
4. The influx of sodium will create an action potential in the sarcolemma
5. As the AP passes through the sarcoplasmic reticulum it stimulates the release of calcium ions
6. calcium binds with troponin to move tropomyosin and expose the binding sites
7. myosin head attach to the binding sites of the actin filament and create a power stroke
8. ATP detaches the myosin heads and energizes them for another contraction
9. Process continues until the action potential ceases. Without APs, the calcium ions will return to sarcoplasmic reticulum.
what is the length-tension relationship
- when you extend your arm, myosin and actin are pulled apart, so less interaction together means little force is generates
- when you contract your ar, more force can be generated as actin and myosin interact
describe the two divisions of the skeletal system
- axial skeleton
- Skull,spinal cord, vertebral column, rib cage (provides structure & protection). - Appendicular skeleton
- Limbs & girdles (enables movement).
describe the different parts of the skeletal system
- bones
- joints
- cartiliages
- ligaments (connect bone to bone)
describe the functions of bone
- support
- Forms the body framework, supports soft tissues, providesbmuscle attachment points. - Protection
- Shields delicate organs (e.g., skull protects the brain, ribs protect the heart & lungs). - Assisting in movement
- Muscles contract & pull bones, enabling motion. - mineral storage
- Stores calcium & phosphorus in outer layers of bone tissue. - blood cell production
- Occurs in the spongy bone (red marrow). - fat storage
- Yellow marrow in bone stores fat for energy.
what are the two basic types of bone tissue
- compact bone
- Dense, provides strength. - Spongy bone
- Porous to allow blood flow, vascular, supports bone marrow, where bone growth occurs, small
outline the different bone shapes
bone can be classified by shape:
1. Long Bones (e.g., arm, leg) – movement.
2. Short Bones (e.g., wrist) – stability, cube-like shape
3. Flat Bones (e.g., skull) – protection, flat and curved
4. Irregular Bones (e.g., vertebrae) – varied functions and shapes
define the different types of bone cells
- Osteocytes: Mature bone cells.(maintaining)
- Osteoblasts: Build new bone.
- Osteoclasts: Break down bone for remodeling & calcium release.
Bone Remodeling: Balance between osteoblasts (formation) & osteoclasts (breakdown).
describe bone developement and ageing
Embryo Stage: Skeleton mostly hyaline cartilage, gradually replaced by bone.
Cartilage Remains in joints, nose, ribs.
Aging Effects: Decreased bone density, increased fracture risk.
describe the 3 parts of the axial skeleton
- forms longitudinal part of body
- skull
- 22 bones
- protects brain - vertebral column
- supports body, protects spinal cord - rib cage
- protects thoracic organs
the hyoid bone = Does not articulate with other bones, supports tongue & muscles.
- found at bottom of vocal cord
describe the three different joint types and what a joint is
joint/articulation = where two bones come together
- Fibrous (no movement): Skull sutures, pelvis.
- Cartilaginous (Slightly Movable): Spine, ribs. - bones attached by catiliage
- Synovial (Freely Movable): Most common, lubricated and protected by synovial fluid.
- more mobile -> more synovial
describe the synovial joint types
classified by shape
Hinge (Elbow, Knee) – Flexion & extension.
Ball-and-Socket (Shoulder, Hip) – Wide range of motion.
Pivot (Neck) – Rotation.
Gliding (Wrist) – Sliding movements.
plane joint
saddle joint
condyloid joint
what are levers
Levers in our body are formed from bones, joints and muscles. A lever consists of: a rigid structure (bone) a force acting upon it (muscle) to produce a turning movement (angular motion) a fulcrum which is a fixed point (joint)
Bones act as levers, joints as fulcrums, muscles generate force.
describe the three levels of motor system hierachy
- Strategy (Highest Level) – Decided by the prefrontal and parietal cortex.
- Tactics (Middle Level) – Motor cortex and cerebellum refine movement.
- Execution (Lowest Level) – Brainstem and spinal cord initiate movement.
sensorimotor system = sensory info is used by all levels of the motor system
describe the lateral descending motor pathway
spinal tracts
- Lateral pathway
- voluntary movement, originates in cortex
-
components:
-1. Corticospinal tract (pyramidal tract): -Direct motor cortex to spinal cord
-involved in fine motor control such as finger movement
-main pathway for voluntary movement
- crosses over at the medulla so right brain controls left side and vise versa
- Rubrospinal tract: Aids movement if corticospinal tract is damaged.
- originates in midbrain
- part of extra-pyramidal system
Lesions:
- Affects contralateral motor function-
- recover possible if the rubrospinal tract is still intact but recovery is harder with age
- can cause paralysis on opposite side of body
- deficits in movements of hands and arms
describe the ventromedial descending motor pathway
- involved in posture, balance and movement
- originates in brain stem
- automatic movements
components:
1. vestibulospinal tract
- head balance and turning (automatic actions)
- Tectospinal tract
- reflexive orientation to stimuli (turning head to stimuli) - Reticulospinal tract
- pontine -> enhances postural reflexes (keeping posture stable)
- medullary -> suppresses postural reflexes (relaxing muscles involved on posture)
what do the descending tracts of the spinal cord do
= carry motor information from brain to body
= carry motor information from upper motor neurons in the brain to lower motor neurons in the spinal cord. The lower motor neurons then send the information to muscles.
describe the planning of movement by the cerebral cortex
- Motor Cortex (Where Movement Starts)
Located in the frontal lobe.
Divided into two key areas:
Primary Motor Cortex (M1, Area 4) – Sends direct movement commands to muscles.
Higher Motor Areas (Area 6) – Plans movement before it happens.
- premotor area (PMA) -> uses sensory info to guide movement in the lateral region
- supplamentary area (SMA) -> plans internally driven movements in the medial region (intention before the action occurs)
- both these areas control different muscle groups, but both help to co-ordinate movement
describe the ready, set , go process in movement
Ready → Parietal & Prefrontal Cortex (Decision made).
Set → SMA & PMA (Movement is planned).
Go → Motor Cortex (M1, Area 4) (Movement is executed).
Prefrontal & Parietal Cortex – “The Decision Makers in movement”
Prefrontal Cortex: Decides what action to take based on goals.
Parietal Cortex: Processes sensory info (where your body is in space).
Together, they make high-level movement decisions before sending instructions to Area 6.
Prefrontal = Thinks about action, Parietal = Knows body position.
describe the limbic system and motor control
- involved in regulating emotion and behaviour
key structures:
amygdala -> emotion centre
hippocampus -> memory formation
basal ganglia
thalamus
cingulate gyrus
hypothalamus
what is the basal ganglia and what is it’s involvement with the motor loop
= involved in the selection and initiation of willed movements
The motor loop is a pathway that connects the cortex, basal ganglia, and thalamus to help control movement.
steps:
1. Cortex sends an excitatory signal (wants to move).
2. Striatum (Putamen) receives the signal and processes it.
3. Globus Pallidus (brake) is inhibited, so movement is allowed.
4.. Thalamus sends a “GO” signal back to the Motor Cortex (M1).
5. Motor Cortex activates muscles, and movement happens!
👉 Key Idea: The Basal Ganglia acts like a traffic light. It decides whether to allow or stop movement signals from reaching the muscles.
describe basal ganglia related disorders
Parkinson’s Disease: Dopamine deficiency → bradykinesia, tremors, rigidity.
- trouble initiating willed movements due to increased inhibition of thalamus by basal ganglia
Huntington’s Disease: Loss of inhibition → hyperkinesia, involuntary movements.
Hemiballismus: Violent flinging movements on one side of body due to basal ganglia damage.
explain the coding movement in the motor cortex
Neurons in M1 encode movement, direction & force.
Activity of multiple neurons collectively determines movement.
Superior Colliculus: Controls rapid eye movements (saccades).
- saccadic = small, rapid movement of eye as it moves from one fixation point to another
describe the role of the cerebellum in movement and associated lesions
- ensures smooth, co-ordianted movements
- can create new motor programmes
Motor Learning: Adjusts movements via feedback from sensorimotor cortex.
lesions cause:
ataxia -> poor co-ordiantion
dysmetria -> overshooting/undershooting movements
dysynergia -> abrupt movements/ abnomal co-ordiantion
what is a motor unit?
= all the muscle cells controlled by one nerve cell
- when the nerve sends a message, causes the associated muscle cells to contract
describe the different motor unit ratios and the recruitment order
Back muscles (1:100) – large force, less precision.
Finger muscles (1:10) – moderate precision.
Eye muscles (1:1) – high precision.
the ratio means for every 1 nerve cell, there are …. associated mucle cells
Recruitment Order: Small motor units are recruited first, followed by larger ones as more force/intensity is needed (Henneman’s size principle).
Force Control: Adjusted by varying recruitment and firing frequency.
- amplitude and frequency can change to develop more force
what is the somatotopic organization of the precentral gyrus
= head and face regions are innervated by the inferior portion of the precentral gyrus. Conversely, the lower limbs are innervated by the superior portion
-> the point-for-point correspondence of an area of the body to a specific point on the central nervous system. Typically, the area of the body corresponds to a point on the primary somatosensory cortex (postcentral gyrus).
what are betz cells
large pyramidal neurons in the primary motor cortex of the brain
input to these cells:
- thalamus
- cortical areas
what is proprioception?
= refers to the body’s ability to perceive its own position, movement, and the amount of strength exerted in any activity.
- the brain receives and interprets information from multiple inputs such as eyes, stretch receptors and vestibular organs
- (info from the body to tell the brain what to do)
the activity of the motor units in propriocipitation
- the regulated motor cortical output determines the amount of muscle mass being activated
- small motor units are recruited first (Hennemans size principle)
the number of cells and the area of the motor cortex that’s been activated will determine what we move and the direction of travel
what are the proprioceptors?
= sensory nerve endings in the limbs that provide information about bodys position and movement
->
joint angle (is limb bent or straight)
muscle length (stretched or cntracted)
tension (force produced)
describe the muscle spindle
= are sensory nerves that wrap around every muscle fibre
- lie within an independent capsule parrallel to main muscle fibres (extrafusal fibers->muscle contraction).
- Within a muscle spindle, there are several small, specialized muscle fibres known as intrafusal fibres
which contain contractile units - Detect changes in muscle length and rate of stretch.
- -Send signals to the CNS via sensory (afferent) nerve fibers; the faster they fire, the more the muscle is being stretched.
- Muscle shortens, sensory nerves compressed, opening frequency of channels decreases, nerve firing rate decreases (relaxed state)
- When the muscle lengthens the muscle spindle is stretched, opens ion channels triggers action potentials in muscle spindle afferents
-Gamma motor neurons adjust spindle sensitivity so the muscle spindle can detect changes in length at all times, even when the muscle is partially contracted.(alpha-gamma co-activation)
describe the golgi tendon organ
- Located in the tendons, in series with muscle fibers.
- Detect changes in muscle tension (pulling force).
- Fire more rapidly when tension increases (as in active muscle contraction).
- consists of sensory nerve endings interwoven among collagen fibres
-When the muscle contracts, the collagen fibrils are pulled tight, and this activates the Golgi tendon organ afferent
describe mechanoreceptors in the skin and joints
4 types:
1. Merkel receptors - pressure
2. Meissner capsules- flutter
3. Ruffini cylinders -stretch
4. Pacinian Corpuscles - vibration
- these differ in regards to:
location, physical features, speed of adaptation to stimuli, size of receptive fields, type of mechanical signal to which they respond to
Provide information about touch, pressure, and stretching of the skin, helping the brain interpret contact with external objects and movement across surfaces.
- each type responds to a range of frequencies of mechanical stimulation
which mechanoreceptors are associated with slow adapting fibres
- Merkel discs and Ruffini cylinders
- they respond when a stimuli is present
- sensitivity can chnage over time when stimuli becomes common
which mechanoreceptors are associated with rapidly adapting fibres
- Meissner corpuscles and Pacinian corpuscles respond to stimuli with a firing at the start when stimulus is on, then at end when stimulus is off
- second trigger present to turn off
location of small and large Mechanoreceptor receptive fields
- receptors with small receptive fields = close to surface of skin
- large receptive fields = deeper in skin
describe the integration of proprioception in the CNS
The afferent pathways carry proprioceptive and mechanoreceptive information to the spinal cord and brain.
The motor cortex and spinal cord use this feedback to refine motor output, adjusting how many motor units are recruited and how strongly muscles contract.
The limbic system also plays a role in habitual movements—repetitive actions become more automatic and need less conscious thought over time.
PUTTING THE STEOS OF MOVEMENT CONTROL TOGETHER SUMMARY
Movement Control:
Motor commands (efferent signals) originate in the motor cortex, travel down the spinal cord, and activate specific muscles (via alpha motor neurons).
Continuous feedback from muscle spindles, Golgi tendon organs, skin/joint mechanoreceptors, and the vestibular-ocular system informs the CNS about the current state of the body.
This feedback loop allows for fine-tuning of muscle force and position, ensuring coordinated, purposeful movement.
Reflexes and Higher Processing:
Simple (spinal) reflexes occur at the level of the spinal cord (e.g., knee-jerk reflex) and are very fast.
Complex reflexes and voluntary movements involve additional processing in the brain (e.g., motor cortex, cerebellum, limbic system) and can be modified or overridden by conscious decisions.
dizziness and motion sickness
Often related to a mismatch between signals from the vestibular system, visual input, and proprioceptive feedback.
When these systems provide conflicting information (e.g., reading in a moving car), it can lead to dizziness or nausea.
what is the vestibular system
=sensory system located in the inner ear that helps the body maintain balance, spatial orientation, and coordination of head and eye movements. It provides critical information about the position and movement of the head, allowing the brain to adjust the body’s posture and respond to changes in the environment.
the three order neurons in ascending tracts during complex reflexes
first order neuron = sensory, delivers sensations to CNS
second order neuron = may be located in spinal cord or brain stem , axon of first order synpases here
third order = second order synpases on third order in the thalamus, axon carries sensory info from thalamus to appropriate sensory area of cerebral cortex
types of cells involved in healing
- Labile cells
- High rate of loss and replacement, capable of rapid regeneration. Examples include squamous and glandular epithelia, and hematopoietic cells in bone marrow. - Stable cells
- Normally non-proliferative but can regenerate when stimulated after damage.
- Examples that have some capacity to grow include renal tubular cells, hepatocytes, osteoblasts, endothelial cells, and fibroblasts. - Permanent cells
- Unable to divide post-development, thus cannot regenerate. Examples include neurons and cardiac/skeletal muscle cells.
regeneration of cells and tissues
= growth of cells and tissues to replace loss structures
- requires an intact connective tissue scaffold
if there is damage to the connective tissue and cells -> when cells try to regenerate they don’t know how to align -> scarring
if there is damage to cell WITHOUT damaging connective tissues -> regeneration can occur as scaffolding is there to organise the cell growth
describe the three different signalling mechanisms in cell growth
- autocrine signalling -> cell releases a chemical messenger that binds to receptors on the same cell
- paracrine signalling -> a cell releases a signal to change the behavior of nearby cells.
- endocrine signalling -> hormones are released into the bloodstream and carried to target cells in other parts of the body.
describe the repair response following injury/inflammation
- Inflammation (0-7 days)
- Inflammatory cells migrate from surrounding tissues, filling the defect with granulation tissue and debris. Fibronectin provides a scaffold for collagen synthesis. Tissue becomes swollen - Repair (3-60days)
- Fibroblasts synthesize collagen, initially type 3, which is laid down randomly. By week 4, intrinsic fibroblasts take over, producing type 1 collagen aligned with the line of force. - Organisation (28-180 days)
- Final stability achieved through physiological use of the tendon, with cross-linking of fibrils enhancing tensile strength. Complete regeneration is rare, often leaving a hypercellular defect.(scar)
provide a summary of tendon healing
- Weakest point occurs at 7-10 days post-injury.
- Most original strength regained by 21-28 days, with maximum strength typically achieved by 6 months.
- Early mobilization can enhance range of motion (ROM) but may compromise repair strength if excessive stress is applied.
- Immobilization can strengthen tendon substance but may reduce ROM.
tissue differences
factors influencing healing
- Healing rates vary significantly among tissues, with better regeneration potential linked to improved signaling and blood supply.
- Examples of novel therapeutics include micro-fracture techniques for cartilage, calf serum for ligaments, and stem cell applications for heart tissue.
developmental differences in healing
Fractures are more common in immature skeletons due to weaker physeal regions.
Types of fractures include:
Buckle or Torus Fracture: A compression fracture common in children.
Plastic Deformation: Permanent bending of bone without fracture.
Greenstick Fracture: Incomplete fracture, typical in children.
- tissue injuries in adults less likely to regain proper function than in children
the role of analgesia or anti-inflammatory drugs
- NSAIDs are used to treat musculoskeletal injuries by reducing inflammation, which is often seen as detrimental to healing.
- However, inflammation is a necessary component of the healing process; blocking it can theoretically delay recovery.
- The inflammatory phase is crucial for debris removal and recruitment of growth factors to the injury site.
treatment protocols for soft tissue injuries
RICE: Rest, Ice, Compression, Elevation - a foundational treatment approach.
Variations include:
HI-RICE: Hydration, Ibuprofen, Rest, Ice, Compression, Elevation.
PRICE: Protection, Rest, Ice, Compression, Elevation.
PRINCE: Protection, Rest, Ice, NSAIDs, Compression, Elevation.
RICER: Rest, Ice, Compression, Elevation, Referral.
POLICE: Protection, Optimal Loading, Ice, Compression, Elevation.
