Week 1 Flashcards
What are the 6 regions of the lower limb?
- Gluteal
- Femoral
- Knee
- Leg
- Ankle
- Foot
What are the 2 big sets of muscles in the gluteal region? What smaller muscles comprise these sets and what nerves innervate them?
Superficial Muscle group
- gluteus maximus, gluteus medius, gluteus minimus, tensor fascia latae
- Innervated by the gluteal nerves
- gluteus maximus - inferior gluteal nerve
- all others - superior gluteal nerve
- NB - remember Trendelenburg’s Gait
Deep Muscle Group
- piriformis, obturator internus, gemelli and quadrate femoris
- nerves from the sacral plexus
How do nerves enter and exit the perineum? What structures do they pass through?
Enter and exit via the greater and lesser sciatic foramen
- Greater - pelvis
- Lesser - perineum
What two ligaments form the greater and lesser sciatic foramen?
- Sacrotuberous ligament (attaches to the ischial tuberosity)
- Sacrospinous ligament (attaches to the ischial spine)
Which nerves supply the gluteal region? At what point do they leave the spinal cord?
-
Sciatic Nerve (L4-S3)
- largest nerve in the body
- supplies the posterior thigh, all leg and foot muscles and most of the skin via it’s two branches
- Tibial branch
- Common fibular branch
-
Pudendal Nerve (S2-S4)
- principle nerve to the perineum
-
Posterior cutaneous nerve of the thigh (S1-S3)
- skin over the posterior thigh, popliteal fossa, lateral perineum and upper medial thigh
Describe the usual location of the sciatic nerve
- inferior to the piriformis
- most lateral structure exiting the greater sciatic foramen
- receives it’s own named artery - artery to the sciatic nerve
- doesn’t supply anything in the gluteal region
- passes down into the posterior thigh, and around mid thigh separates into
- Tibial nerve (larger)
- Common fibular (smaller, easily damaged)
What are the boundaries and contents of the femoral triangle?
Boundaries
- superior - inguinal ligament
- medial - lateral border of the adductor longus
- lateral - medial border of sartorius (longest muscle in the body)
- floor - iliopsoas and pectineus
- roof - deep fascia (fasia lata)
Contents (NAVL)
- Femoral Nerve - NB, NOT FOUND IN THE FEMORAL SHEATH
- Femoral Artery
- Femoral Vein
- Lymphatics
What is compartment syndrome and how is it treated?
Increase in pressure in one of the compartments of muscle (enclosed space created by muscle), due to swelling of tissue or increase in fluid (e.g. trauma, bleeding, infections etc.)
Can affect the functions of muscles or nerves
Can be acute of chronic
Treated with a Fasciotomy - cutting the deep fascia to relieve pressure
How many compartments are found in the lower limbs?
Thigh (3)
- anterior
- medial
- posterior
Leg (3)
- anterior
- posterior
- lateral
Describe the anterior compartment of the thigh
Flexors of thigh
- pectineus
- iliopsoas
- sartorius
Extensors of leg
- quadriceps femoris
Nerve Innervation
- All femoral nerve (L2, L3, L4), except the psoas major muscle (L1, L2, L3)
Describe the medial compartment of the thigh
Adductors of thigh
- adductor longus
- adductor brevis
- adductor magnus
- gracilis
- obturator externus
Nerve Innervation
- All obturator nerve (L2, L3, L4), except the hamstring part of the adductor magnus (tibial nerve)
Describe the posterior compartment of the thigh
Extensors of the thigh & flexors of the leg
- semitendinosus
- semimembranosus
- biceps femoris
Nerve Innervation
- All tibial division of the psiatic nerve (L5, S1, S2), except the short head of the biceps femoris (common fibular division of sciatic nerve)
Describe the anterior compartment of the leg
Dorsiflexors of ankle and extensors of toes
- tibialis anterior
- extensor digitorum longus
- extensor hallucis longus
- fibularis tertius
Nerve Innervation
- All deep fibular nerve (L4, L5)
Describe the lateral compartment of the leg
Evert foot and weakly plantarflex ankle
- fibularis longus
- fibularis brevis
Nerve Innervation
- All superficial fibular nerve (L5, S1, S2)
Describe the posterior compartment of the leg
Superficial Group - plantarflexors of ankle
- gastrocnemius
- soleus
- plantaris
- All innervated by the tibial nerve
Deep Group - flexors of toes and plantarflexors of ankle
- popliteus
- flexor hallucis longus
- flexor digitorum longus
- tibialis posterior
- All innervated by the tibial nerve
What type of joint is the hip joint?
Ball and socket
- Ball - head of femur
- Socket - acetabulum of hip
What ligaments are involved in the hip joint?
- Ileofemoral
- pubofemoral
- ischiofemoral
-
ligament to head of femur - ligamentum teres
- can be damaged if hip becomes fractured, leading to ischaemia and necrosis of head of femur
What is the blood supply to the hip joint?
-
Medial and Lateral Circumflex femoral arteries
- Anastomose with each other
- usually arise from the deep femoral artery
- give off retinacular arteries
- Artery to the head of the femur
- branch off obturator
What are the three articulations of the knee joint?
2 x femerotibial (between each femoral and tibial chondyle)
1 x femeropatellar
Describe the ligaments involved in the knee joint
Extracapsular
- patellar ligament (often mistakenly called a tendon)
- lateral (fibular) collateral ligament
- medial (tibial) collateral ligament
Intra-articular
- anterior cruciate (ACL)
- posterior cruciate (PCL)
Menisci
- fibrocartilage
- medial and lateral
What are the boundaries and contents of the popliteal fossa?
Boundaries
- superolaterally - biceps femoris
- superomedially - semimembranosus
- inferiorly - gastrocnemius
- roof - popliteal fascia
Contents
- lots of fat
- terminal small saphenous vein (draining into the popliteal vein)
- popliteal vessels
- tibial and common fibular nerves
Describe the Calcaneal tendon
aka the achilles tendon
thickest and strongest tendon in the body
comprised of tendons from the gastrocnemius and soleus
attaches to the calcaneal tuberosity of the calcaneus
features in the ankle jerk reflex - normal result is plantarflexion, tests S1 and S2 nerve roots
Describe the lymphatics of the lower limbs
Superficial
- follow the saphenous veins
- drain to the superficial inguinal lymph nodes, then on to the external iliac lymph nodes
Deep
- follows deep veins
- popliteal lymph nodes, then on to the deep inguinal lymph nodes and finally the external iliac lymph nodes as well
What are the three types of muscle in the human body?
Are they striated/unstriated? Voluntary/involuntary?
Skeletal - striated, voluntary (somatic nervous system)
Smooth - unstriated, involuntary (autonomic nervous system)
Cardiac - striated, involuntary (autonomic nervous system)
What are some of the important differences between skeletal and cardiac muscle?
Initation of propagation of contraction
- skeletal is neurogenic, NMJs are present and there are no gap junctions i.e. excitation cannot spread from cell to cell
- cardiac is cardiogenic (contraction is initiated by pacemaker cells, there are no NMJs but gap junctions are present
Excitation contraction coupling
- skeletal - Ca2+ comes entirely from the sarcoplasmic reticulum
- cardiac - Ca2+ comes from both the ECF and the sarcoplasmic reticulum (calcium-induced calcium release)
What is the main neurotransmitter at the NMJ?
ACh
What is a motor unit? What does it determine?
A single alpha motor neurone, along with all the muscle fibres it innervates
The number of motor units determines the function of the muscle…
- few motor units = precision
- many motor units = power generation
Provide a general summary of the organisational structure of muscle fibres
Whole muscle is made up of…
-
Muscle fibre (one cell) contains many…
-
Myofibril (specialised intracellular structure
-
Sarcomere (functional unit)
- Myocin (thick, darker filaments)
- Actin (thin, lighter filaments
-
Sarcomere (functional unit)
-
Myofibril (specialised intracellular structure
Describe the structure of a myofibril
Sarcomeres, made up of overlapping actin (thin filaments) and myocin (thick filaments)
What are the zones that make up the sarcomere?
A-band - made up of thick filaments with overlapping portions of thin filaments at both ends
H-zone - lighter area within the middle of the A-band where thin filaments don’t reach
M-line - extends vertically down the middle of A-band within the centre of H-zone
I-band - consists of the remaining portion of thin filaments that do not project into A-band
Z-lines - border of the sarcomere, connect the thin filaments of 2 adjoining sarcomeres
How is muscle fatigue prevented by the number of muscle fibres contracting?
Asynchronous motor unit recruitment during submaximal contractions helps to prevent muscle fatigue
What factors affect the tension developed by each contracting muscle fibre?
Frequency of stimulation and summation of contractions
Length of muscle fibre at the onset of contraction
Thickness of the musce fibre
Describe the relationship between action potentials and muscle twitch in skeletal muscles.
What is tetanus?
Duration of action potential is much shorter than that of twitch, meaning that repetitive action potentials can bring about a stronger contraction via a summation of twitches.
The tension developed by skeletal muscle increases with increasing frequency of stimulation.
If a muscle fibre is stimulated so rapidly that it doesn’t have an opportunity to relax, a maximal sustained contraction known as a tetanus occurs.
What are the two types of skeletal muscle contraction?
Isotonic contraction (muscle tension remains constant as the muscle length changes) - used for…
- body movements
- moving objects
Isometric contraction (muscle tension develops at constant muscle length - used for
- supporting objects in a fixed position
- maintaining body posture
What are the three stages making up the principle of diagnosis regarding MSK infections?
Suspect - history, examination etc.
Sample - gold standard is bone biopsy, also use cross-sectional imaging
Treat - wait until the results of biopsy, unless patient is septic/acutely unwell
Why does antimicrobial treatment of infections in bone last for 6 weeks?
Debrided bone takes approx 6 weeks to be covered by vascularised soft tissue, and must be protected during this time
When treating a patient with a MSK infection, empirical antibiotics should be avoided and the results of the bone biopsy should be received before treatment has begun.
Under what conditions is the above not true?
If the patient is septic, has acute illness or is unstable then empirical broad-spectrum antibiotics can be used.
Gram +ve cocci in chains? What are the subgroups?
Streptococcus
Alpha haemolytic - pneumoniae, viridans
Beta haemolytic - Groups A, B and C Strep
Gamma haemolytic - enterococcus spp
Gram +ve cocci in clusters? What are the subgroups?
What do some strains produce?
What is the treatment of choice?
Staphylococcus
Coagulase +ve - Staph. aureus
Coagulase -ve - Staph epidermidis
Some strains produce toxins e.g. enterotoxin, SSSST, PVL
Treatment of choice is FLUCLOXACILLIN, alternatively Vancomycin if patient is *properly* allergic
Open fractures - treatment
Early management is key - aggressive debridement, fixation and soft tissue cover
Treat for Staph aureus (Flucloxacillin) and aerobic gram negative bacteria (Gentamicin)
Diabetes/vascular insufficiency and subsequent ulceration with suspected osteomyelitis - treatment
Often polymicrobial i.e. often anaerobes and gram -ves, as well as Staph.
Probe to bone, and upon receiving results treat with debridement and antimicrobials
Staph - fluclox
gram -ves - gentamicin
anaerobes - metronidazole
In the presence of chronic/deep ulcers, a positive probe-to-bone test and elevated levels of inflammatory markers, what test is used to confirm the suspicion of osteomyelitis?
Imaging studies - MRI scan
In suspected haematogenous osteomyelitis in a PWID, what organisms could be responsible?
Staphylococcus, typically
Streptococci
More unusual pathogens - pseudomonas, candida, mycobacterium TB
In the treatment of infection of prosthetic joints, other than the standard treatments of MSK infections, what additional drug may be given? Why?
The addition of Rifampicin - allows penetration of the sessile biofilm of bacteria lining the prosthesis.
NEVER give Rifampicin by itself to treat Staph infections however, give alongside fluclox. to prevent the development of resistance
What is the difference in duration of treatment between infection in bones and joints?
Bones - 6 weeks
Joints - 4 weeks
What are the possible causative pathogens of septic arthritis?
Staphylococcus aureus
Streptococci
Coag -ve staphylococci if prosthetic joints are present
Possible Neisseria gonorrhoea if patient is sexually active
What is an important dfferential to bear in mind when considering septic arthritis?
What is the treatment of SA when confirmed?
Gout, need to exclude crystal formation
High doses of Flucloxacillin to cover presumptive Staph aureus, if the patient is less than 5 years old then add Ceftriaxone to cover Haemophilus influenzae
In pyomyositis (muscle infection), what is the key to treatment?
Debridement is paramount, followed by antibiotic therapy - antibiotics cannot penetrate necrotic/pus-covered tissues.
Important to bear in mind that the presenting symptom from the patient may just be very localised severe pain.
How is tetanus caused?
Toxin-mediated infection - Clostridium tetani
Gram +ve strictly anaerobic rods (loves dead tissue).
The neurotoxin causes spastic paralysis by binding to inhibitory neurones and preventing the release of neurotransmitters.
Important to remember that the bacteria itself is not invasive, and the damage is done purely by the toxin
With regards to cell nucleus placement, how do cardiac and skeletal muscle cells differ?
Cardiac - centred nucleus
Skeletal - nuclei are moved to the edge of the elongated syncitium (many cells fused together)
What is the name given to a bundle of muscle fibres that make up a muscle?
What is the name of the connective tissue that surrounds the muscle as a whole?
What is the name of the connective tissue that surrounds these bundles?
What is the name of the connective tissue that surrounds a single muscle fibre?
Fascicles
Epimysium
Perimysium
Endomysium
______ are the ‘unit of muslce contraction’ of a muscle cell, and in a typcial muscle cell thousands of these are placed end-to-end to form a ______
Sarcomere
Myofibril
What are the three types of skeletal muscle fibre? Briefly describe each
Type I
- relatively slowly contracting fibres that depend on oxidative metabolism
- abundant mitochondria and myoglobin
- resistant to fatigue and produce less force
- ‘red’ in colour
Type IIA
- intermediate between I and IIB
- relatively fast contracting but also reasonably resistant to fatigue
- relatively uncommon
Type IIB
- fast contracting fibres that depend of anaerobic metabolism
- Few mitochondria and less myoglobin
- Fatigue relatively easily but produce greater force
- ‘White’ in colour
What are the differences between cartilage and bone?
Cartilage
- semi-rigid, deformable
- permeable
- avascular
- cells nourished via diffusion through the ECM
Bone
- rigid
- non-permeable
- cells within bone must be nourished by blood vessels that pervade the tissue
What are chondrocytes? Where do they reside and what do they do?
Found in the cartilage (chondroblasts when immature)
Live within a space in the ECM known as the lacuna
Both excrete and maintain the ECM that surrounds them.
What are the constituents of cartilage?
75% water
25% organic material
- 60% is type II collagen (forms a 3D meshwork rather than linear bundles like type I)
- 40% proteoglycan aggregates (made up of GAGs - most commonly keratin sulfate and chondroitin sulfate)
What are the 3 different types of cartilage?
Hyaline cartilage - most common type
Elastic cartilage - elastic fibres make it quite flexible
Fibrocartilage - hybdrin between tendon and hyaline. has bands of densely packed type I collagen interleaved with rows of chondrocytes, surrounded by small amounts of cartilagenous ECM.
Where might you find hyaline cartilage?
Articular surfaces
Tracheal rings
Costal cartilage
Epiphyseal growth plates
What are some of the functions of bone?
Protection of vital organs
Support of structure
Calcium store - 95% of all calcium is stored in bone, constant exchange between bone and blood
Haemopoiesis - mostly in utero, and by early twenties typically only the axial and limb girdle are still involved in blood production
What % of bone is made up by collagen?
23%
An outer layer of dense _____ bone makes up the shaft a.k.a. the _____
______ bone occupies the ends of the bone a.k.a. the _____, and takes the form of a fine meshwork.
cortical bone, diaphysis
cancellous/trabecular bone, epiphysis
What is the name of the circular unit of collagen fibres that make up the outer layer of bone? What feature provides them with extreme strength?
What are the names of the two canals that run through this feature to supply it with blood?
Osteon - layers of collagen are in alternating directions, giving bone a great deal of strength (similar to plywood)
Haversian’s canal runs vertically through the centre of the osteon.
Volkmann’s canal runs horizontally through the osteon, connecting neighbouring Haversian canals.
What is the main structural difference between trabecular and cortical bone?
Bone cells of the matrix are similar, but trabecular bone also has numerous spaces throughout the matrix (marrow cavities)
How do both trabecular and cortical bone receive nutrients?
As bone is a living tissue it needs a nutrient supply. This is in the form of small canals running through the bone that contain blood vessels, nerves and osteocytes.
Trabecular bone typically lacks Haversian canals
Define the following terms:
- Osteoprogenitor cells
- Osteoblasts
- Osteocytes
- Osteoclasts
- located on bone surface, serve as a pool of reserve oseoblasts
- bone-forming cells found on the surface of developing bones, plentiful RER and mitochondria
- bone cell trapped within the bone matrix
- “bone destroyer”, large multinucleated cells thought to be due to fusion of multiple macrophages. Found on bone surface and responsible for bone resorption
What is osteoid?
Organic components (collagen, GAGs, proteoglycans etc.) secreted by osteoblasts.
Becomes mineralised over time in the ECM to become bone.
What are the three types of joint presentin the human body?
Fibrous - e.g. elbow, knee
Synovial - e.g. fusion of skull bones
Cartilagenous - e.g. intervertebral discs, pubic symphsis
Briefly describe some of the key features of a synovial joint
- bones are separated by a cavity containing synovial fluid and lined by a fibrous capsule
- Inner aspect of capsule is lined with a synovial membrane which contains synovial cells (SCs, fibroblasts). These cells secrete synovial fluid
- Surfaces of the bones are lined with articular hyaline cartilage
- Can be classified as either simple or compound, depending on how many bones/articular surfaces are involved
Name some of the extra-capsular structures that support synovial joints
Tendons
Ligaments
Bursae
What substances provide lubrication in joints?
Cartilage interstitial fluid
Synovium-derived hyaluronic acid (mucin)
Synovium-derived lubricin - glycoprotein
What are some of the functions of synovial fluid?
Lubricates joint, facilitates joint movements and reduces wear and tear
Aids in the nutrition of articular cartilage by supplying chondrocytes with O2 and nutrients, and removing CO2 and waste products
What are some of the general characteristics of synovial fluid?
How does synovial fluid change in movement and disease?
- Continuously reabsorbed and replenished by the synovial membrane
- High viscosity due to the presence of mucin
- Normally contains few cells (mainly mononuclear lymphocytes)
Movement
- Rapid movement is associated with decreased viscosity and increased elasticity, and vice versa in stasis
Disease
- Inflammation - low viscosity, straw colour, increase in total white cell count from less than 200 to 2,000 - 75,000
- Sepsis - Variable viscosity and colour, extremely high WBC count (>100,000)
Describe the composition of articular cartilage
Superficial zone (10-20%)
Middle zone (40-60%)
Deep zone (30%)
Calcified zone
Zones differ in organisation of collagen fibres and relative content of cartilage components
Articular cartilage lines the articular surface of bones and features an extracellular matrix (ECM). Describe the composition of this ECM.
Made predominantly of water (70%) - unevenly distributed with more towards the articular surface and % decreases with age
20% collagen (mainly type II) - contributes to the elastic behavior of cartilage and provides tensile strength. Decreases with age
10% proteoglycans - mostly present in the middle and deep zones and confers compressive properties used in load bearing. Composed mainly of GAGs e.g. chondroitin sulphate, which decreases with age
Describe the cellular makeup of total cartilage
98% ECM
2% chondrocytes - synthesises, organises and degrades ECM. Receives nutrients and O2 via synovial fluid (as articular cartilage is avascular)
What physical properties could potentially change to result in joint disease?
- Changes in the relative amounts of the 3 major components that make up cartilage
- Water
- Collagen
- Proteoglycans
- If the rate of ECM degradation exceeds the rate at which it is synthesised and replaced
What are the catabolic and anabolic factors that affect ECM turnover?
Catabolic
- Stimulate proteolytic enzymes and inhibit proteoglycan synthesis
- TNF-alpha
- IL-1
Anabolic
-
Stimulates proteoglycan synthesis and counteract the effects of IL-1
- TGF-beta
- Insulin-like growth factor (IGF)-1
Name some markers of cartilage degradation
Serum and synovial keratin sulphate (mainly found in proteoglycans) - increased levels = cartilage breakdown, levels increase with age and in patients with osteoarthritis
Type II collagen in synovial fluid - increased levels = cartilage breakdown. Useful in evaluating cartilage breakdown
Describe the appearance of a motor neurone that innervates skeletal muscle.
What neurotransmitter is involved?
Myelinated axons and cell bodies while travelling down the spinal cord.
The axon then divides into unmyelinated branches near the surface of the muscle, with each branch innervating a separate skeletal muscle fibre. This is known as a motor unit.
Each of these branches further subdivides into multiple fine branches that end in a terminal bouton and form a chemical synapse with the NMJ on the muscle membrane.
ACh is the neurotransmitter involved and acts on nicotinic ACh receptors
Describe the key features of the NMJ
What’s a sarcolemma?
- terminal bouton (and surrounding Schwann cell)
- synaptic vesciles containing ACh that release upon AP causing depolarisation
- synaptic clefts in the muscle cell containing nicotinic ACh receptors
- the end plate region of the muscle cell membrane (sarcolemma)
Give a brief overview of synaptic transmission at the skeletal NMJ
- Synthesis of ACh from choline and acetyl CoA by choline acetyltransferase
- Storage in vesicles
- Release upon the entering of Ca2+ into pre-synaptic terminal
- Receptor activation on the post-synaptic end-plate, allowing Na+ to flow into the muscle cell and cause a contraction
- Neurotransmitter deactivation via acetylecholinesterase, which hydrolyses ACh into choline and acetate. Choline is taken back into the pre-synapse via a choline-sodium symporter
Breifly describe the post-synaptic process that allows Na+ to flow through the Nicotinic ACh channels
- Nicotinic ACh receptors are arranged in a pentamer of glycoprotein subunits (2 alpha, 1 beta, 1 delta and 1 epsilon) that surround a central cation-selective pore
- Binding of ACh causes a conformational change, which allows each subunit to rotate and move their amino-acid side chain from blocking the pore.
- This allows Na+ to flow into the cell, and K+ to flow out of the cell. The permeability for these two ions is roughly similar, however because the driving force for Na+ is greater than that of K+, influx of Na+ is greater than efflux of K+.
- This generates a depolarisation known as the end plate potential (e.p.p.)
Define the terms ‘quantum’ and miniature end plate potential (m.e.p.p.)
A quantum is fairly fixed size of vesicle that contains numerous ACh molecules.
The electronic response to the release of a single quantum is known as the miniature end plate potential.
Many m.e.p.p.s summate to produce an e.p.p. and, if this exceeds the threshold, an ‘all or nothing’ response is achieved that generates a contraction
Note - it is NOT the e.p.p. that generates the contraction, but rather the AP that the e.p.p. elicits
What feature prevents charge leaking out and failure of the e.p.p. to be reached?
The presence of voltage-activated Na+ channels along the muscle fibre, allows the propagation of action potentials along the muscle fibre and the generation of a contraction
What is the path of the action potential after it reaches the sarcolemma and how does this result in contraction?
AP enters the transverse tubules (invaginations of the sarcolemma that travel deep down into the muscle cell), which are located closely to the sarcoplasmic reticulum (Ca2+ store)
When the AP reaches the transverse tubules, this causes a release of Ca2+ from the SR which in turn causes contraction by interacting with troponin associated with myofibrils
What are the 3 types of pain?
- Nociceptive - adaptive
- Inflammatory - adaptive
- Pathological - maladaptive
What are the two transmitters involved in nociceptive pain?
Glutamate - fast
Peptide - slower
Both of these are transmitted to secondary receptors in the spinal cord. Nociceptors are 1st (order) degree neurones
Nociceptive pain is adaptive/maladaptive and has a low/high threshold
Adaptive - serves a biological purpose
High threshold - only provoked by intense stimuli that activate nociceptors
Nociceptive pain overrides most ongoing activities in the nervous system, prompting an autonomic response and withdrawal relfex.
It also engages an emotional response and inscribes preventative memories.
Inflammatory pain is adaptive/maladaptive.
What’s the difference between hypersensitivity and allodynia?
Adaptive and protective, inolves activation of the immune system and assists in healing of a damaged body part. Although adaptive, does require suppression of ongoing inflammatory response.
Hypersensitivity - heightened response to minor stimuli
Allodynia - previously innocuous stimuli elicit severe pain
Pathological pain is adaptive/maladaptive.
What is the difference between neuropathic and dysfunctional pathological pain?
Maladaptive - abnormal nervous system function that serves no process.
Neuropathic - e.g. damage to peripheral nerves, neural lesions resulting in faulty nervous system activity etc. Associated with both hypersensitivity/allodynia and desensitisation
Dysfunctional - no apparent cause, only associated with positive symptoms i.e. no desensitisation.
Muscle fibres are bound into ____
The connective tissue covering these muscle fibres is called ____
Muscle fibres are bound into fascicles
Within the fascicle, the connective tissue covering the muscle fibres is the endomysium
What is the name of the sheath of connective tissue that binds fascicles together?
The perimysium
Actin are ___ filaments
Myocin at ___ filaments
What is a sarcomere?
Actin are thin, lighter-coloured filaments
Myocin are thick, darker-coloured filaments
A sarcomere is the unit of muscle contraction, and comprises the area between two Z-discs
