Muscles, contraction and movement Flashcards
function of cardiac muscle
pumping of blood
function of smooth muscle
to control the movement of fluid e.g. blood, urine, digestion
function of skeletal muscle
to move, maintain posture, generate heat
structure of skeletal muscle
- Tendon attaches muscle to bone
- fascia
- muscle
- epimysium
- muscle bundle
- perimysium
- fascicle
- endomysium
- muscle cell aka muscle fibre aka myocyte
- sarcoplasmic reticulum and T tubule
- myofibrils
- sarcomere
- myofilaments
T-tubule
invagination of Extracellular space that allows the action potential to enter the myofibril and initiate the release of Ca2+
triad
T-tubule sandwiched between two SR
sarcolemma
plasma membrane of the muscle cell
sarcoplasmic reticulum
ER of a muscle cell and stores calcium
sarcomere
myofilament between to Z-disks= basal contractile unit
thin filament
actin, tropomyosin, troponin; Globular actin forms a double helix strand surround by two thin strands of tropomyosin
thick filament
myosin and myosin head
NMJ vs synapse
- In healthy humans, there is no IPSP or EPSP
- if an action potential reaches the NMJ it will cause contraction;
- Should call the cleft the NMJ cleft rather than the synaptic clefts
3 steps of skeletal muscle contraction
excitation, contraction, relaxation
steps of excitation
- AP reaches end of motor neuron, which causes Ca2+ entry into nerve terminal
- Neuronal action potential Acetylcholine (Ach) released from the nerve terminal in synaptic vesicles
- Synaptic vesicles release Ach, which diffuses into the synaptic cleft
- Ach stimulates Ach-receptors on the adjacent muscle fibre, initiating an impulse in the muscle fibre
- Depolarisation of muscle sarcolemma, initiating an action potential
- Electro-chemical-electro coupling
- Action potential on the muscle fibre- always sufficient to reach threshold in healthy individuals
steps of contraction
- AP travels over sarcolemma and T-tubules very quickly, which triggers the release of Ca2+ ions from the adjacent sarcoplasmic reticulum almost simultaneously along the myofibril
- Large Ca2+ release from the internal Ca2+ store- ions diffuse to the myofilaments to trigger cross-bridge formation
- Cross-bridge formation of myofilaments
- Myosin head is in its energised state, with ATP bound
- Ca2+- troponin interaction exposes active site
- Actin-myosin interact as a cross-bridge
- Energised myosin head pulls the actin in a power-stroke
steps of relaxation
- No new AP- sarcolemma repolarises
- Ca2+ no longer bind to Troponin; ion re-uptake into internal Ca2+ store
- Troponin active sites are hidden
- Actin and myosin are still bound but not enough Ca2+ ions to initiate new cross-bridges
- ATP must bind for actin and myosin to uncouple cross-bridge
sliding filament model
- When inactive the filaments are not over one another
- When activated the myofibril shortens as the z-lines move closer
- Myofilaments do not change length themselves
motor unit
one somatic Motor Neuron and Muscle Fibres innervated by its branches
energy sources for contraction
Anaerobic and anaerobic
features of anaerobic respiration
- short term - fast energy production - no O2 required - ATP, creatine phosphate, glycolysis
features of aerobic respiration
- long term - steady - slower energy production - O2 required - Oxidative phosphorylation
why is energy required for relaxation?
Ca2+ re-uptake into SR and uncoupling of crossbridges
types of muscle fibres
red, white and intermediate (myosin type IIa)
features of red muscle fibres and example
high myoglobin (myosin type I), high aerobic enzymes - soleus
features of white muscle fibres and example
low myoglobin (myosin type IIx), low aerobic enzymes - eye
function of red (myosin type I) fibres
slow rate interaction with actin; slow force production; slow energy consumption; sustained by aerobic metabolism
function of white (myosin type IIx) fibres
fast rate interaction with actin; fast force production; fast energy consumption; use anaerobic metabolism
what is a twitch
the smallest tension a muscle can produce - a single AP in a single motor unit
what is treppe
- repeated stimuli - sustained levels of SR Ca2+ = more contraction - actin and myosin become more sensitive to Ca2+ - more sensitive at higher temperatures
what is tetanus
- rapidly repeated stimuli - closely spaced twitches - heat increases sensitivity - mechanical summation due to high Ca2+ in SR
effects of strength training on muscle
- Increased number of contractile filaments- hypertrophy - More power - Improved anaerobic metabolism
effects of disuse of muscle
- Loss of number of contractile filaments- atrophy - Less power
effect of endurance training on muscle
- Increased blood supply to muscle - higher number of blood vessels - More mitochondria - More aerobic enzymes - Improved aerobic metabolism
description fatigue
- state of exhaustion (loss of strength or endurance) produced by strenuous muscle activity
physiological fatigue
- ATP depletion, secondary to depletion of glucose, glycogen and O2 - Build-up of metabolic by-products: e.g. Pi and lactic acid
psychological fatigue
- feedback from working muscles to brain produces sensation of fatigue, even though muscle is still capable of contraction
cardiac muscle structure
• Intercalated disks; lots of individual cells stuck together that create a mesh work • Desmosomes (mechanical)-proteins that stand the gap between cells and act as the glue; when one cell contracts, it pulls on its neighbour • Gap junctions (electrical)- connection that allows one action potential in a myocyte to pass into the next myocyte; therefore, cells are electrically connected
cardiac muscle function
• Heart controlled by nerves from the brain called the Sinoatrial node (pacemaker), and depolarises the atria • Signal passes into the atrioventricular node, which depolarises the septum between the ventricles • The signal passes to the outside of the ventricles and depolarises them • More and more contractions occur as the heart becomes more depolarised; when fully polarised blood flows out • Relaxation allows blood flow back in
smooth muscle structure
• Filaments organised similarly to skeletal muscle- actin and myosin move over one another • Dense bodies are nodes within the cell and pull the cells together into a mesh • Contraction involves squeezing the cell down • Sustained tension- e.g. sphincters • Large length changes- e.g. bladders • Cells form a ring length wise around the digestive tract, cells formed in the same direction • Cells form rings around tubes- controls the movement of whatever travels through the tubes
Single-unit smooth muscle
gap junctions allow electrical signal to be transferred from one cell to the other; all electrically connected; thus, many cells can be considered a single unit
Multi-unit smooth muscle
muscles cells are not electrically connected as no gap junctions, more varicosities present to innervate more cells
Smooth muscle: Excitation-contraction
• Action potential or hormones provide Ca2+ rise • Ca2+ binds to Calmodulin which activates protein called Myosin light chain kinase (MLCK) into an active and inactive cycle • MLCK activates MLC which activates the cross bridge • Myosin filaments regulated • A kinase adds phosphate (P), whereas a phosphatase removes a phosphate (P), changing the function (active/inactive) of the protein
four types of information that describe a sensory stimulus
- modality (type of receptor activated) - intensity (frequency of AP firing) - duration of AP firing - location
Specialised receptor cell
modified nerve ending converts a unique stimulus into an action potential e.g. temperature, pressure
special senses
Vision, Hearing, Taste, Smell, Vestibular (balance)
cell shapes of 3 muscle types
Skeletal Muscle has Long, cylindrical, multinucleate cells; Cardiac Muscle has mononucleate, branching cells; Smooth Muscle has mononucleate, spindle-shaped cells
presence of sarcomeres in 3 muscle types
present in skeletal muscle, present in cardiac muscle, absent in smooth muscle (hence no striations)
filament which is regulated to allow contraction in 3 muscle types
skeletal muscle is actin, cardiac muscle is actin, smooth muscle is myosin
AP propagation in 3 muscle types
in skeletal muscle, AP does NOT spread from cell to cell; in cardiac muscle, APs DO spread from cell to cell; in single unit smooth muscle, APs do spread from cell to cell; in multi unit smooth muscle, APs do not spread from cell to cell
presence of T tubuli in 3 muscle types
present in skeletal muscle; present in cardiac muscle; absent in smooth muscle
nervous system input of 3 muscle types
skeletal muscle is somatic motor (voluntary); cardiac muscle is visceral motor (involuntary); smooth muscle is visceral motor (involuntary)
speed of contraction of 3 muscle types
skeletal is fast; cardiac is slow; smooth is very slow
3 types of modality
proprioception, touch and pain
how is proprioception detected
golgi tendon organ is a protective device that detects tension; muscle spindles are length receptors that detect shortening of muscle and maintain posture
adaption to stimulus
decreased receptor potential over time in response to continuous stimulation
receptor field
Region of space in which a stimulus can lead to activity in a particular afferent neuron Small fields and dense innervation gives good discrimination
Afferent pathway for touch, posture, vibration
- Dorsal column pathway (Medial lemniscal pathway)
- Three neurons in relay
- Up and across
- The sensory neurons from muscle spindles- fastest neurons in the body
- cell body in dorsal root ganglion
- up dorsal column of spinal cord
- crosses side in medulla
- synapses in thalamus
- to primary somatosensory cortex
somatosensory cortex function
sensation (conscious identification of what and where) and perception (meaningful interpretation)
Somatotopic organisation
- Areas of the cortex correspond to areas of the body
- Densely innervated areas of the body occupy large regions of the cortex
- Left cortex represents right body and vice versa
stimulus modality of pain
- Sensed by free nerve endings (Nociceptors)
- Located in organs throughout the body but not in the brain
- Specialised sensitivity to local chemicals signals in damaged tissue
Fast (acute) pain
- Small receptive field
- Large myelinated afferent axons
- Somatic pain
Slow (chronic) pain
- Large receptive field
- Small unmyelinated axons
- Visceral pain
Afferent pathway for pain and temperature
Lateral spinothalamic (antero-lateral) pathway
- Minimum of 3 neurons in a relay (can have interneurons)
- Neurons go across and up
- Far less precise in location than other afferent pathway
- cell body in dorsal root ganglion
- crosses side immediately
- synapse in dorsal horn on opposite side
- up antero-lateral column of spinal cord
- synapse in thalamus
- to primary somatosensory cortex in post-central gyrus
reflex movement
- A predictable, reproducible, automatic response to a particular sensory stimulus; force of response depends on how many motor units activated
- Organised neural circuit- recognise specific disturbances to the body
- usually organised within spinal cord
two types of reflex
stretch reflex and withdrawal reflex
stretch reflex mechanism and function
prevents muscle fibres being torn by stimulus
withdrawal reflex mechanism and function
protect the body from damaging stimuli by moving away from it
primary motor cortex function
execution of movement via activation of specific motor units
premotor cortex function
planning movement
corticospinal pathway (pyramidal tract) strructure and function
Controls precise movement of hands and feet
Upper motor neuron:
- Primary motor cortex
- Crosses over at medulla
- Corticospinal tract in spinal cord
- Excitatory synapse onto lower motor neuron
- Sometimes an interneuron
Lower motor neuron
Non-corticospinal pathways (extrapyramidal tracts)
- all other descending pathways onto the final common pathway
- excitatory and inhibitory
- reticulospinal tract: excites lower motor neurons to extensors, inhibits flexors
- rubrospinal tract: excites flexors, inhibits extensors
- for automatic movements like walking, chewing
function of basal nuclei in integration between motor and sensory systems
- Modify movement using a loop stem with the cortex
- Pre-programming through extensive practice allows muscle memory
- Help select an appropriate movement for a given situation
- inhibition of inappropriate movement for a given situation
function of cerebellum in integration between motor and sensory systems
- Ensures the selected movement is coordinated, guided by sensory feedback
- Compares intention with result
- Maintenance of posture
steps leading to voluntary movement of a skeletal muscle
