Functional Anatomy Flashcards
All or none principle/law
If an electric stimulus reaches a threshold level (sufficient intensity), then all of the muscle fibres associated with a motor unit will contract to their maximum level at the same time.
If the threshold is not reached, then nothing will happen
Axon
The part of the motor neuron that receives signals from the cell body and transmits them to the target muscle activation site
Dendrite
The part of the motor neuron that receives signals from the central nervous system and feeds it into the cell body
Force
The action of a push or pull from one object to another. It can affect an object by changing it’s shape or direction of movement or can just make objects move
Motor neuron
The unit of components responsible for transmitting messages from the central nervous system to the muscles. It is comprised of a cell body, dendrites and axon
Motor neurons are neurons that transmit signals from the CNS to the effector such as muscles or glands to produce a movement or other response
Motor unit
Comprises of a motor neuron and all muscle fibres that it innervates. The greater the number of motor units, the greater the force that can be generated
- the number of muscle fibres within each motor unit can vary according to the precision of the movement required
- the fibres within a particular motor unit are always the same fibre type
Preferential recruitment
The body’s recruitment of muscle fibres depending on the demands of the muscle contraction
Velocity
The speed of an object in a given direction
Three types of muscle
- cardiac
- smooth
- skeletal
Tendon
muscle to bone
Ligament
bone to bone
Structure of skeletal muscle
- epimysium
- fascicle
- perimysium
- muscle fibre
- myofibril
Skeletal muscle
- create movement or assists maintaining posture when they contract
- contraction is voluntary, must think about the movement for it to happen
- skeletal muscles only pull, they do not push so they need to work in reciprocating pairs
- during contraction the muscle shortens as tension develops
3 types of muscle contraction
- concentric
- eccentric
- isometric
Isometric
No change in length during contraction
Isotonic - concentric contraction
muscle shortens during contraction
- the generation of force by a muscle as it shortens
Isotonic - eccentric
muscle lengthens due to braking effect or against gravity
muscle belly
bundle of fascicles
fascicle
a bundle of muscle fibres
myofibril
thread like strand that runs through muscle fibre
made of myofilaments - actin and myosin
actin
thin myofilament (protein) used in muscle contraction attached to the z line
myosin
thick myofilament (protein) attached to crossbridges
epimysium
connective tissue sheath that surrounds each muscle
perimysium
connective tissue layer that surrounds each fascicle
endomysium
connective tissue layer that surrounds each individual muscle fibre
sarcomere
functional, contractile unit of a muscle fibre
z lines
found at either end of the sarcomere
crossbridges
tiny projections on myosin filaments that attach towards the actin filaments, moving the actin filaments upon contractions
h zone
space between the actin filaments
a band
contains both actin and myosin filaments
i band
contains only actin filaments (end of sarcomere)
myofilaments
made up of two proteins, actin and myosin
cardiac muscle
found in the heart only
smooth muscle
found in blood vessel walls and vessels of the digestive system. etc
muscle arrangements
parallel (fusiform)
pennate
Fusiform (parallel) muscle arrangement
the fibres run parallel to the tendon and when the fibres conract, the entire muscle shortens by the same amount.
suited to fast contractions
Pennate muscle arrangement
fibres attach diagonally to the tendon. Because the muscle cells pull at an angle, contracting pennate muscles do not move their tendons far. But a pennate muscle contains more muscle fibres and, as a result, produces more force than a parallel muscle of the same size
sliding filament theory - brief
- brain sends nerve impulse, releases acetylchlorine (ACh), Ca+ released.
- Ca+ binds to troponin, moving tropomyosin, exposing binding sites on the actin. Actin and myosin join
- breakdown of ATP releases energy, myosin pulls actin inwards, shortening the muscle
- myosin detached when ATP binds to myosin head. myosin head reattached to actin and repeats the ‘power stroke’ - rowing mechanism
- lasts as long as adequate ATP and Ca+ stores. Once nerve impulse stops, actin returns to resting position, muscle relaxes
troponin
a complex of three proteins, attached to tropomyosin
tropomyosin
an actin binding protein that regulates muscle contraction
factors that contribute to the amount of force that a muscle can produce
- speed of contraction (force/velocity relationship)
- muscle length (force/length relationship)
- number of fibres recruited - more fibres = greater force
- muscle fibre type - fast and slow twitch fibres
- cross-sectional area (area of belly)
- muscle shape and location
- type of muscle contraction - isotonic, isometric, isokinetic
- age - declines after 25-30 years without training
- gender - females produce less force (smaller muscles)
force/velocity
- force created by a muscle contraction is determined by how many myosin crossbridges are formed
- if a muscle is contracted quickly, the force it can generate is reduced as fewer crossbridges are formed (e.g. running)
- the more time allowed for contraction (low velocity), the more crossbridges are engaged and therefore the greater force (e.g. pulling heavy object)
- the greatest amount of force can be developed during an isometric contraction
force/velocity - definition
the amount of force produced by a muscle demands upon the velocity of muscle contraction
force/length - definition
muscle force depends on the length of the muscle
force/length
- the length of a muscle and the angle at the joint has an impact on the force that can be generated
- maximum force is produced when there is an optimal overlap of actin and myosin
- muscles generate the greatest force at a starting length closest to their resting (mid) length
- less force is generated when it has a starting length that is stretched or shortened relative to the resting length
The Central Nervous System (CNS)
is comprised of the brain and spinal cord
- responsible for processing sensory information
- generating motor commands
- controlling the body’s vital functions
The Peripheral Nervous System (PNS)
consists of nerves branches outside the spinal cord that feed information to the CNS and take messages back to the extremities
The nervous system
- is a complex network of neurons that receive, organise and send neural impulses between body parts. comprised of 2 main parts the CNS and PNS
1. sense organs detect changes and send sensory information to brain for processing via sensory neurons
2. brain receives signal and determines suitable response
3. brain sends commands to muscles to carry out selected response via motor neurons
sensory neurons
messages sent from the receptors to the brain (CNS), via sensory neurons. There are special receptors (proprioceptors) that detect changes in the position of bones and muscles
interneurons
send messages between motor and sensory neurons and make up about 90% of neurons
receptor
organ that sensors - point of receiving - touch, smell, temp, pain
effector
carries out the action required - contraction e.g. bicep curl
cell body (soma)
directs the activities of the neuron. It receives the signal it then transmits the information along the axon
muscle contraction
- the motor neuron reaches the muscle fibre but does not actually touch - there is a tiny space called a synapse (space) called a neuromuscular junction (nerve to muscle contraction)
- once the signal reaches the axon of the motor neuron, a chemical transmitter acetycholine (ACh) is released and travels across the synapse to the myofibril
- this causes calcium ions to be released which triggers the sliding filament theory of muscle contraction
small motor units innervates:
- precise movements
- small number of muscle fibres required
- small action potential
large motor units innervates:
- gross motor movements,
- gross motor skills
- many fibres required
- large action potential
contraction force
- number of fibres recruited to contract depends on the strength of the nerve impulses from the brain
- for actions requiring little strength, only a small number of motor units will be activated
- where more strength is needed, more motor units are activated and more fibres contract
- size principle - smaller units recruited first and as more force is required, large motor units are recruited
- this also applied to selection of appropriate fibre type (red or white) depending on speed of response
the force produced by a muscle can be increased in 2 ways:
- increasing the number of motor units recruited by increasing the size of the stimulus. Increasing the number of motor units used in generating force will increase the size of the force generated
- increasing the rate at which impulses are sent to the motor unit resulting in the motor unit firing repeatedly to increase the force generated
firing patterns - synchronous
- all motor units fire at once to give maximal force eg shot put
- great force generated
- muscle fatigues quickly
firing patterns - asynchronous
- motor units are rotated in and out rather than all at once (some contracting, some relaxing)
- encouraged by endurance training
- most everyday activities use this pattern
- spreads fatigue throughout the muscle meaning activity can be continued longer
training
great improvement in strength can be made in first 2-8 weeks of training within without any changes in muscle size due to increase in neuromuscular efficiency (skill level of movement improves)
- improved technique
- increased firing rates of motor units
- more motor units recruited
- firing is better coordinated
Type II - fast twitch can be divided
- IIa (intermediate) e.g. 800m runner
- IIb (explosive, 10x faster than slow twitch) e.g. sprinters have high % of explosive (IIb) in legs
- energy comes from anaerobic pathway
- Fast twitch fibres are generally white (less blood supply as they do not need oxygen)
Fibre types
- composition of fibre can be a good predictor of athletic success
- composition set at birth and remains unchanged (genetic)
- accurately determined by muscle biopsy
- field tests may predict composition e.g. vertical jump for muscle power. Higher power indicates greater amounts of fast twitch muscle fibres in the legs
- fibre type for each muscle depends on its function. There are two calf muscles;
- soleus - is a postural muscle used for balance so has a larger proportion of slow-twitch fibres
- gastrocnemius is used for running and jumping (requires higher level of fast-twitch)
training - fibre types
- strength training will lead to hypertrophy of mainly fast-twitch fibres. Fibres will get bigger - there are no extra fibres created. Type IIa fibres will behave more like type IIb with an increase in contraction strength and speed
- endurance training will help IIa fibres behave more like type I, increasing size of mitochondria, capillary density (oxygen transport) and therefore ability to generate aerobic energy and improved aerobic capacity
