Muscle Physiology Flashcards
MUSCLE TISSUE
Three
Skeletal muscle
Cardiac muscle
Smooth muscle
Skeletal muscle
- Location
Attached to bones (some attached to skin, deep fascia, or other muscles) - Microscopic appearance
Striated, many nuclei in each fibre (cell), unbranched fibres - Nervous control
Voluntary (conscious) control by somatic nervous system - Regeneration
Limited capacity, cells cannot divide - Function
• Moves parts of the skeleton (walking, running, nodding the head, manipulating objects)
• Postural muscles maintain the body in stable positions
• Diaphragm regulates breathing by changing intrathoracic volume
Cardiac muscle
- Location Heart - Microscopic appearance Striated, single nucleus, branched fibre with intercalated discs - Nervous control Involuntary (unconscious) control by autonomic nervous system - Hormonal control Adrenaline and noradrenaline increase rate and strength of contractions - Regeneration None - Function • Propels blood through the vessels
Smooth muscle
- Location
Walls of hollow organs, blood vessels, iris and ciliary muscles, arrector pili (hair) - Microscopic appearance
No striations, single nucleus, spindle-shaped fibres - Nervous control
Involuntary (unconscious) control by the autonomic nervous system - Regeneration
More than other tissues, much less than epithelial tissues - Function
• Mixes and propels luminal contents through the digestive tract
• Regulates the flow of blood through blood vessels by changing diameter of the lumen
• Contraction of urinary bladder, gallbladder and spleen expels urine, bile and blood
• Sphincter muscles control tube openings (anal sphincter, precapillary sphincters etc)
• Iris muscles control pupil diameter
• Ciliary muscles control lens shape
• Contraction of arrector pili muscles causes hairs to stand up (goose pimples)
CHARACTERISTICS OF MUSCLE TISSUES
Four
- Excitability (irritability) – the ability to generate action potentials in response to stimuli
- Contractility – the ability to contract and generate a force
- Extensibility – the ability to be stretched when pulled
- Elasticity – the ability to return to original length after contraction or extension
SKELETAL MUSCLE ANATOMY
Three
Epimysium
Perimysium
Endomysium
Epimysium
The outer fascia/sheath of the muscle, along with perimysium, makes up tendons or aponeuroses.
Perimysium
This wraps around fasciculi (groups of individual muscle fibres)
Endomysium
This individually wraps around muscle fibres.
SKELETAL MUSCLE ANATOMY
Epimysium
Perimysium
Endomysium
Each fibre is made up of many contractile protein myofibrils, and each myofibril is in turn composed of many overlapping protein threads or filaments known as myofilaments. Each myofibril is divided along its length into a repeating series of units or sarcomeres, which are the fundamental functional units of the muscle. The protein myofilaments of the sarcomere are of two main types, thin filaments of actin, and thicker filaments of myosin.
The overlapping arrangement of the filaments gives rise to the striped or striated appearance of the fibres when observed under the microscope. The sarcomere contracts as a result of these overlapping filaments sliding over each other, in what is known as the sliding filament mechanism. The simultaneous contraction of each sarcomere results in the contraction of the muscle fibre as a whole.
FIBRE TYPES
Three
Fast glycolytic fibres
Slow oxidative fibres
Fast oxidative fibres
Fast glycolytic fibres
ATP production – anaerobic glycolysis Contraction speed – fast ATPase activity – fast Myoglobin concentration – low Mitochondria – few Capillaries – few Endurance – low Diameter – large Fibre colour – white
Slow oxidative fibres
ATP production – oxidative phosphorylation Contraction speed – slow ATPase activity – slow Myoglobin concentration – high Mitochondria – many Capillaries – many Endurance – high Diameter – small Fibre colour – red
Fast oxidative fibres
ATP production – oxidative phosphorylation Contraction speed – fast ATPase activity – fast Myoglobin concentration – high Mitochondria – many Capillaries – many Endurance – intermediate Diameter – intermediate Fibre colour – red
SKELETAL MUSCLE MOVEMENT (part 1)
Muscles are attached to bones by tendons. As muscles show a considerable range of shape and form, so will the tendinous attachment. For example, a flat muscle will have a flat tendon called an aponeurosis, whereas other muscles may be attached by a cord like tendon.
Muscles commonly run between two bones, crossing one joint, but frequently can have points of attachment on more than two bones, and cross two joints.
When a muscle contracts, both ends of the muscle will be pulled towards each other, drawing one bone towards the other.
In practice, one end of the muscle tends to be fixed so that the other end will move towards the fixed end.
SKELETAL MUSCLE MOVEMENT (part 2)
The fixed end is called the origin and moving end is called the insertion. In certain circumstances these roles may be reversed, ie levator scapulae.
Muscles are arranged into groups of opposing action. A muscle that causes a desired action is referred to as the prime mover or agonist. Often another muscle, called the antagonist, relaxes while the prime mover contracts.
To be able to move efficiently, a high degree of neuro-muscular co-operation must exist between opposing groups, so that when one group contracts the other relaxes – this is called reciprocal innervation.
Most movements require involvement from muscles called synergists – they help the prime mover function more efficiently by reducing unnecessary movement. Some muscles act as fixators – they stabilise the origin of the prime mover so that the prime mover can be more efficient.
MUSCLE SHAPES
The arrangement of the muscle fibres within a muscle differs according to the strength needed by that muscle.
Parallel fibres – pull in a direct line
Convergent muscles – have fibres converging towards a single insertion point
Pennate muscles – have fibres lying at an angle to the tendon
- Uni-pennate – diagonal muscle fibres attach to one side of the tendon only (soleus)
- Bi-pennate – the fibres converge onto a central tendon from both sides (rectus femoris)
- Multipennate – the muscle has several tendons of origin (deltoid)
Circular muscles – surround orifices and close openings
TYPES OF MUSCLE CONTRACTION
Isometric contraction Isotonic contraction - Concentric contraction - Eccentric contraction Isokinetic contraction
TYPES OF MUSCLE CONTRACTION
Isometric contraction
the muscle works without movement taking place
TYPES OF MUSCLE CONTRACTION
Isotonic contraction
the muscle force is considered to be constant, but the muscle length changes
TYPES OF MUSCLE CONTRACTION
- Concentric contraction
‘towards the centre’ occurs when the muscle shortens to move the attachments closer
TYPES OF MUSCLE CONTRACTION
- Eccentric contraction
‘away from the centre’ happens when a muscle is stretched as it tries to resist a force pulling the bones of attachment away from each other
TYPES OF MUSCLE CONTRACTION
Isokinetic contraction
this refers to muscle contraction at a constant speed over the full range of movement. In order to perform an isokinetic contraction, special machines are required which provide a resistance equal to the force being applied by the athlete throughout the movement.
STRETCH REFLEX
The muscle spindle – detects, responds to, and controls changes in muscle fibre length to regulate movement and posture. Three main components comprise the stretch reflex:
1 Muscle spindle – responds to stretch
2 Afferent nerve fibre – carries sensory impulses from the muscle spindle to the spinal cord
3 Efferent motor neuron – stimulates muscle to contract
