Unit 1 - Anatomy and physiology for health and exercise - muscular system Flashcards
What is a smooth muscle?
It’s the most widely distributed and it predominates i8n the internal tissues of the body, including the digestive, circulatory, urinary and reproductive systems.
Control of this form is muscle is involuntary and is exerted via the autonomic system.
What is a cardiac muscle (myocardium)?
→ It’s found in the heart
→ involuntary
→ possesses the capability of self-excitation
→ autonomic system exerts some control by both increasing or decreasing heart rate and the strength of contractions.
What are the skeletal muscles?
→ attached from bone-to-bone across joints
→ predominantly under voluntary control
→ via the somatic nervous system
Name some functions of skeletal muscles.
→ producing movement
→ stabilising body positions i.e. maintenance of posture
→ facilitating the circulation of blood and lymphatic fluid
→ generating heat
Give an overview of the basic anatomy of a skeletal muscle.
Skeletal muscle is made up of a number of
→ rod-like structures called muscle fibres, and these fibres run parallel along its length.
→ each series of fibres are themselves constructed from smaller parallel fibres and so on.
→ collagen-based membranes protect and surround the muscle
→ the outermost membrane covers the whole muscle and is called the epimysium
What is the outermost membrane surrounding a muscle called?
The Epimysium (epi - meaning upon).
What are the groups of muscle fibres called within the epimysium?
Fascicles (groups muscle fibres formed into bundles).
What is the outer sheath of a fascicle called?
Perimysiym (peri - meaning around).
What is inside each fascicle?
Bundles of muscle fibres, each separated from the other by, another membrane called the endomysium (endo - meaning inside)
What are tendons?
→ strong, inelastic, strap-like structures
→ attach muscle to the periosteum (tough fibrous layer that coats the bones) e. g. Achilles tendon.
Define force generation in muscles.
→ below the endomysium are even smaller rows of fibres called myofibrils.
→ Within, two contractile proteins called myosin and actin (often referred to as thick and thin filaments), are arranged in a
→ series of compartments called sarcomeres that run the length of the myofibril.
→ During muscular contraction, the myosin heads attach themselves to the actin filament and rotate.
→ the thinner actin filaments are drawn inwards dragging the ends of the sarcomeres together, this is referred to as the sliding filament mechanism.
What is the power that drives the myosin head?
→ ATP (adenosine triphosphate) → primes the myosin for activity by binding with the head.
→ energy from the ATP is almost immediately transferred to the head.
What is the relation between actin and calcium?
→ The myosin heads can only bind with the actin with the presence of calcium.
→ In a relaxed state, the myosin-binding sites on the actin are blocked by a combination of other molecules (troponin and tropomyosin), that must be moved before myosin can be attached.
What is sarcoplasmic reticulum?
A network of tubes surrounding the myofibrils that act as calcium reservoirs. When stimulated by an action potential they release their calcium into the fluid surrounding the myosin and actin.
What stimulates the release of calcium from the sarcoplasmic reticulum?
→ the spread of electrical activity (action potential) along the length of the muscles.
→ the arrival of an action potential at the neuromuscular junction (where the nerve meets the muscle) causes the release of a neurotransmitter (acetylcholine).
→ sodium rushes through the muscle membrane
→ reversal of electrical activity (depolarization), will cascade along the muscle fibre as an action potential, triggering calcium release and beginning the sliding filament mechanism.
Muscles are divided in to …. ?
motor units
What does a single motor unit consist of?
→ 1 motor neuron (nerve)
→ muscle fibres it innervates
Explain the all or nothing law.
→ The all-or-none law is a principle that states that the strength of a response of a nerve cell or muscle fibre is not dependent upon the strength of the stimulus.
→ If a stimulus is above a certain threshold, a nerve or muscle fibre will fire.
→ Essentially, there will either be a full response or there will be no response at all for an individual neuron or muscle fibre.
How is the control of muscular force achieved?
→ through a combination of adjusting the number of motor units recruited (i.e. the greater the number, the greater the force)
→ increasing the frequency of their discharge
What is coordinated motor unit activity fundamental to?
→ optimising force generation
→ improving exercise performance
What are the two small neural sensors (proprioception) called that help provide feedback and respond to changes within the muscle itself?
→ muscle spindle: deep within the muscle fibres. It’s a small sensory unit wrapped tightly around the individual muscle fibres like a coiled spring. When the muscle length changes, the coils are either pulled apart or pushed together. This stimulates neural firing to the central nervous system at the spinal level. The result is a stimulus to contract the same muscle. The greater the range of motion and the faster the muscle lengthens, the greater the resulting contraction will be. This is called the stretch reflex.
→ Golgi Tendon Organ (GTO): in the tendon. When a muscle contracts, it pulls on the tendon, creating tension within that tendon.
When activated, the GTO sends a signal to the spine which brings about an inhibitory effect of the same muscle. This relaxation response is called the inverse stretch reflex.
When the spindles bring about muscuar contraction that assists with the movements being performed, what is the GTO’s response?
The GTO responds just after the muscular contraction has engaged by inhibiting the muscular contraction to allow the opposite action to be performed.
→ Muscle spindles and GTO’s serve like the on and off switches for muscle activity during exercise and movement.
Explain reciprocal inhibition (RI).
When a muscle is causing its primary actions to occur, the opposing muscles need to be switched off to allow that movement to take place.
What could be a negative “side-effect” of reciprocal inhibition be?
It can play a part in creating muscular imbalance. A very tight muscle group will send a continuous RI signal to the opposing muscle which can lead to that muscle becoming inhibited in its function.