Muscles Flashcards
What are muscles used for
Lift objects, move, walk, maintain posture, to circulate blood(heart), push materials through organs and tissues eg lung, gut and bladder. And allow your eyes to keep things in focus, to make your hairs stand up
What is cardiac muscle tissue
Small branched cell interconnected to other heart cells is porous junctions. Centrally located nucleus. Striated
Where is cardiac muscle tissue located
Heart
Innervation of cardiac muscle tissue
Rely on specialised auto rhythmic cardiac placement cells (sinoatrial and atrioventricular nodes) for timing of contraction.
Contra in rate altered by automatic nerves to the sinoatrial pacemaker
Function of cardiac muscle tissue
Blood circulation and maintain hydrostatic blood pressure
Works as functional syncytium
What is smooth muscle
Small spindle shaped cells tapered ends. Single, central nucleus. Non striated
Where is smooth muscle located
Located in the walls of blood vessels, around hollow organs and repsiratory, digestive, cardiovascular and reproductive tracts
Innervation of smooth muscle
Can be self contractile eg digestive tract, or requires direct innervation by autonomic/ involuntary nerves
Function of smooth muscle
Movement of food bolus, urine and reproductive tract secretions. Regulation of the diameter of airways and blood vessels. Piloerection. Works as a functional syncytium
What is skeletal muscle
Very larger striated cells. Multi nucleated. Close the plasma membrane each cell is a cellular syncytium (cytoplasmic mass containing several nuclei)
where is skeletal muscle located
Throughout the body associated it’s bones and connective tissue
Innervation of skeletal muscle
Voluntary/ somatic nerves
Function of skeletal muscle
Movement/ stabilisation of skeleton. Gaurd entrances/ exits to digestive, respiratory and urinary tracts, generates heat, protects internal organs, stores nutrient reserve
Prime mover (agonist)
Muscles whose contraction is responsible for producing a particular movement
Antagonist muscles
Work in the opposite directions to an agonist muscle to control or slow it down
Synergistic muscle
Work together in the same direction as the prime mover and assist movement
Fixator (type of synergistic)
Muscles that stabilise part of the body to prevent movement at a joint and at the origin of an agonist muscle to allow for effective controlled movement to be achieved
Origin point
Place were the fixed end of a skeletal muscle attatches to bone (proximal)
Insertion
The place where muscles moveable end attatches (distal)
Innervation of skeletal muscles by the nervous system
-skeletal muscles are innervated (supply an organ with neves) by motor neurones that carry efferent information from the central nervous system to the muscles via myelinated axons
-each MN axon formed a motor unit
-trunk and limbs: cell body of MNS: ventral horn of the grey matter of the spinal cord. MN axons leave the spinal cord via the ventral roots and synapse onto muscle cell fibres
-face and oropharyngeal: cell body of MNS: brain stem
Mn axons: leave the brainstem via the cranial nerves and again synapse directly onto muscle cells
What is a motor unit
- a single motor neurone and ask muscle fibres it innervates = motor unit
-the cell bodies (soma) of all MN’s innervating a same muscle are stacked vertically in the spinal cord. This is known as a motor nucleus
What does the CNS do in regards to the motor unit
-the CNS calculates the number of motor units required to produce the right level of muscle contraction
-the CNS allows them to be swapped in and out to maintain contraction over time to avoid fatigue
-the size and number of motor units in a muscle also determines level of control the CNS has over muscle contraction
What is the neuromuscular junction
-each muscle fibre is innervated by only one MN
-in the area where the axon of an MN and a muscle fibre are held in close proximity, they form a clump of synapses collectively known as the neuromuscular junction
-each of these synapses is elongated and the chemicals communicate at these synapses using a small molecule called acetylcholine
What is myasthenia
-sevre muscle weakness
-prevalence in uk 15/100000
-fatal as respitaoy muscle failure life expectancy 20 to 30 years before drug therapy
What are the causes of myasthenia
-auto immune, anti bodies produced by patients against their own ACh receptors
-congenital, transfer of antibodies from mum to baby
-genetic, mutation affecting ACh release
What are the symptoms of myasthenia
-abnormal muscle fatigue during repetitive or prolonged muscle contraction, prominent in the cranial muscles, limbs and chest
-variation in symptom severity- on a daily basis or over longer period of time
How can tou treat myasthenia
-reversal of symptoms by drugs preventing ACh degradation
-test by short acting cholinesterase inhibitor: edrophonium
-treated by long lasting cholinesterase inhibitors: neostigmine, pyridostigmine
Isometric
Doesn’t change length increasing tension
Isotonic
Muscles change length, bearing the load
What is myofibrils
- long protein rich structures in muscles
-made of repeating units called sacromeres
What do sarcomeres contain
-parallel think protein stands: made of myosin that are free from any permeant point of attatchment
-thin and thick strands are organised in an interdigiated manner within the sarcomeres
-the sarcomere is the basic contractile unit of the muscle fibre
What is the sliding filament theory
1)Calcium binds to tropin which frees the actin from tropomyosin.
2)ATP binds to myosin
3)This creates ADP and Pi = cock and bind (myosin head can move and bind to actin)
4)ADP and Pi leaves =power stroke
5)ATP binds= release
6)repeat
What id excitation - contraction coupling in each muscle cell
-at rest : low calcium in sarcoplasm
-excitation initiation of muscle fibre ap: excitation of membrane
Calcium exported out of SR
-high calcium in sarcoplasm causes muscle contraction
-end of muscle fibre ap: calcium pumped back into SR so low calcium in sarcoplasm causes contraction to stop
-excitation ( of a muscle cell membrane) and contraction (of a muscle cell) occur nearly simultaneously eg they are coupled
Contraction efficiency and sarcomere overlap :
-sacromeres (=muscle) too stretched or too contracted equals a decreased cross bridge formation due to limited overlap or hindrance, respectively less tension that can be generated
-optimal sarcomere light equals optimum cross bridge formation equals maximum tension (80%-120% of the resting length)
What are muscle cells made of
Myofibril
What is myofibrils made of
Contractile proteins
Myofilaments
What are myofilaments
Actin (thin)
Myosin (thick)
Step 1 of sliding filament theory
Calcium binds releasing troponin= free actin
Step 2 of sliding filament theory
ATP binds to myosin (creating adp so it can move)
Step 3 of sliding filament theory
Adp + pi is created= cock and bind
Step 4 of sliding filament theory
Adp + pi leaves= power stroke
Step 5 of sliding filament theory
ATP binds= release
Step 6 of sliding filament theory
Repeat= shortening skeletal muscle
