BIOL1040 Lecture Notes - Lecture 4: Fibrous Joint, Ossification, Osteoblast
Module 4 - support and movement
Lecture 1
skeletal muscle and simple movements - kylie tucker
1.1 muscle types
Threee types of muscle tissue:
Skeletal… much larger
Smooth
Cardiac
Smooth muscle:
Found in the walls of:
oGastrointestinal tract
oBlood vessels eg. artery
oLymphatic vessels
oUrinary bladder
oUterus
oMake and female reproductive tracts
oRespiratory tract eg. bronchiole
oSkin and the iris (eye)
Cardiac muscle:
Found only in the contractile walls of the heart
Is striated, and has similar contractile properties to skeletal muscle, but appears to branch
(not parallel like skeletal muscle)
Muscle fibres interconnect (at intercalated disk) allowing the electrical signal to pass from
one cell to another
oHelps synchronise heart muscle contraction
Uni-nucleate (one nuclease per muscle cell)
Skeletal muscle:
Makes up 40-50% of body mass
Is striated (appears striped)
oThe arrangement of contractile components (sarcomeres) create the striped
appearance
Sarcomeres typically shorten when contracting
Muscle attaches to bone via connective tissue (tendon) and produces movement around
joints
Muscle cells are long - also called muscle fibres
During development, muscle fibres form by fusing multiple muscle cells - multiple nuclei for
each muscle fibre.
Therefore, muscle cells (fibres) are multinucleated
Skeletal muscle is controlled by the somatic nervous system
Can be consciously influenced
Why could it be useful for muscle fibres (cells) to have multiple nuclei?
oWhat do nuclei do? - directs protein synthesis growth and repair of the cell
oMuscle cells can be very long
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1.2 function and structure of skeletal muscle
There are approximately 320 different skeletal muscle in humans x 2sides
Function: interact with our environment - through production of movement and force
Broadly characterised into muscle used for postural, fine motor and gross motor control
(although many muscles easily fir into multiple roles)
All skeletal muscles have:
oContractility: ability to shorten and thicken, and develop tension
oExcitability: ability to respond to appropriate stimuli
oExtensibility: ability to be stretched without damage
oElasticity: ability to store some energy, and recoil to the resting length
Need to look inside the muscle tissue to see the structures that support these abilities
Microstructure of muscle
oIs made up of a large number of bundles (fascicles) of muscle fibres (muscle cells),
surrounded by connective tissue
oSingle muscle fibre (cell) is very long, runs parallel to other fibres
oThe fibre is bane from a large number of fused embryonic cells, therefore a single
muscle fibre has many nuclei - long cell, act as one, high need for protein - multiple
repair stations!
oInside each cell is a bundle of myofibrils (muscle - slender fibre), that lie in parallel
oThe contractile filaments that convert the electrical signal (action potential) initiated
in the nervous system to muscle force are within the myofibril
oA series of sarcomere's make up each myofibril, a sarcomere is the basic contractile
unit of skeletal muscle
oMuscle fibres - contractile filaments
oEach sarcomere contains a series of thick and thin filaments that move in relation to
each other during contraction
oThe regions that contains overlapping thick and thin fibres look darker under
microscope, the regions which contain only thinner fibres look lighter
oSarcomeres from adjacent myofibrils line up. This is what gives muscle its striated
appearance
oThin filaments (actin) attach at the Z line
oThick filaments (myosin) anchor at the M line in the centre of the sarcomere
oWhen at rest, actin and myosin overlap partially
oWhole muscle shortening results as the filaments overlap more, pulling the Z line's
closer
oWhole muscle lengthening results as the filaments overlap less
o**elastic filament: titin - anchors myosin to the Z line, contribute to passive force in
the muscle
oConnective tissue - the support system and dispersed throughout the muscle
Some overlap of actin and myosin in relaxed muscle, greater overlap with contraction
Myosin and Actin are extremely fine protein strands (16nm and 8nm respectively)
During muscle contraction, the myosin heads link the myosin and actin filaments together,
forming cross bridges
Myosin pulls the actin across, shortening the muscle fibre and producing force
Microstructure of muscle belly
Muscle + connective tissue influence function
Perimysium (peri - surrounding; mys - muscle)
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Connective tissue
oScanning electron microscope image of the endomysium around muscle fibres
observed are "digesting fibres".
oEndomysium: an array of "tubes" into which muscle fibres insert
Describe the 3 different types of muscle in the human body. Where will you find these muscle types?
What are some key differences between these muscle types?
What is another name for a muscle cell?
Describe the microstructure of skeletal muscle. In your description be sure to use the terms
myofibril, sarcomere, actin and myosin, connective tissue.
1.3 connection between the nervous system and skeletal muscle: the motor unit
Innervated by motor neuron (direct from the spinal cord
A single motor unit is the smallest functional unit in the musculoskeletal system.
Motor unit = 1 motoneuron, its motor axon and all of the muscle fibres in innervates
oMotor neuron, motoneuron, motoneurone
When sufficient excitatory input to reach firing threshold, an action potential is generated
Every action potential generated in the muscle fibres generates a little bit of force
Force altered by number & discharge rate of motor units & contractile properties of the
muscle fibres
Motor units range in: size (number of muscle fibres), contractile properties (speed,
fatigability)
This allows graded, sustained and controlled force
1.4 skeletal muscle and contraction
Lecture 2:
Muscle in Action, producing force
Muscle force is influenced by
1. Muscle architecture: structure, size (muscle volume), physiological cross sectional
area
2. Sarcomere length (the length tension relationship): active force production, passive
force
3. Single motor unit: number, discharge rate, fibre type
1. Type of contraction: isometric, concentric, eccentric
1. What you need to know is:
The shape of the muscle will affect the action of the muscle
Circular muscles can close and opening
Long muscles are better at controlling movement over joints that have a large range
of motion
Shorter-wider muscles are better at generating larger forces, over a smaller range of
joint motion
Muscle physiological cross sectional area
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find more resources at oneclass.com
Document Summary
Lecture 1 skeletal muscle and simple movements - kylie tucker. Found in the walls of: gastrointestinal tract o o. Lymphatic vessels: urinary bladder, uterus, make and female reproductive tracts o o. Found only in the contractile walls of the heart. Is striated, and has similar contractile properties to skeletal muscle, but appears to branch (not parallel like skeletal muscle) Muscle fibres interconnect (at intercalated disk) allowing the electrical signal to pass from one cell to another: helps synchronise heart muscle contraction. The arrangement of contractile components (sarcomeres) create the striped appearance. Muscle attaches to bone via connective tissue (tendon) and produces movement around joints. Muscle cells are long - also called muscle fibres. During development, muscle fibres form by fusing multiple muscle cells - multiple nuclei for each muscle fibre. Skeletal muscle is controlled by the somatic nervous system. Directs protein synthesis growth and repair of the cell: muscle cells can be very long.
