MNSR 7 - Muscular System: Anatomical Muscles and Muscle Physiology Flashcards
What are muscles?
Aggregations of cells which convert chemical energy (ATP) into mechanical energy (movement)
Highly adapted cells allowing for force-generation (i.e. contraction)
Specialized adaptations of cellular components (e.g. sarcoplasmic reticulum and contractile proteins)
What are the three muscle types?
Skeletal muscle
Attached to bones which form levers- used for bodily movement
Cardiac muscle
Walls of the myocardium - used to pump blood through circulatory system
Smooth muscle
Organs - lines gut and blood vessels - controls diameter of these tubes and in gut helps to propel the digested food
What is the structure of the smooth muscle?
Lines the digestive tract, bronchus and blood vessels
* Involuntary muscle i.e. not under direct nervous control
* Lacks the striations of skeletal and cardiac muscle tissue
*1 nucleus per smooth muscle cell
*High endurance muscle
What is the function of smooth muscle?
Sustained contractions (e.g. small and large intestine)
Where is cardiac muscle found?
Found only in the walls of the heart
What is the structure of cardiac muscle?
- Unevenly striated
(so similar to skeletal muscle in appearance) - Alternating light and dark bands (striations) as seen when examined with a microscope
- High endurance (high number of mitochondria); contracts throughout the lifespan
- (1- 2 nuclei per cardiac cell/myocyte (centrally placed)
- Innervated by the pacemaker
fused-together cylindrical cells
At border between one cardiac cell and the next are “Intercalated discs”which support synchronized contraction of cardiac tissue. These discs contain: desmosomes and gap junctions.
The fused cardiac cells contract as a unit owing to signals at gap junctions between them
What are the functions of cardiac muscles?
- Contraction is involuntary (like smooth muscle)
- Contraction and relaxation of the heart is not consciously controlled
- Contraction of the heart is initiated by a node of tissue called the “pacemaker”
What is the structure of a skeletal muscle?
- So named because most skeletal muscles move bones
- Called striped or striated due to appearance under light microscope
- Long cylindrical cells
- Many nuclei per cell (‘multinucleated’)
What is the function of the skeletal muscle?
- Locomotion, posture; head, limb movements
- Voluntary muscle i.e. under direct nervous control. e.g. biceps muscle
often reflex-activated - Endurance capacity depends on number of mitochondria.
How is the skeletal muscle often described as?
Often described as being of ‘low endurance’ compared to other muscle types.
Each muscle is composed of bundles of…
fascicles
Each fascicle is composed of many…
muscle fibres
In most anatomical muscles the fibres extend the…
entire length of the muscle
Each fibre is composed of _______________ which contain the contractile apparatus – the ____________
smaller myofibrils, sarcomere
Muscles have extensive vascular systems that…
1) Supply large amounts of oxygen
2) Supply nutrients
3) Carry away wastes
Skeletal muscles are voluntary muscles, controlled by…
nerves of the central nervous system (brain and spinal cord)
The connective tissue components include…
Epimysium
* The outermost layer
Perimysium
* Surrounds numerous bundles of fascicles
* Separates 10-100 muscle fibers into bundles called fascicles
Endomysium
* Separates individual muscle fibers from one another
Tendon
* Cord that attach a muscle to a bone
How would you describe muscles?
Tissue with the ability to contract
How would you describe tendons?
Tough band of fibrous connective tissue that connects muscle to bone
How would you explain ligaments?
Attaches bone to bone
One attachment is fixed and called the…
origin
The other called the _________________ is drawn towards the origin.
insertion
Muscles can only…
contract and never push
Arranged in
antagonistic pairs
___________ closes a joint
Flexor
____________ opens a joint
Extensor
What does the Biceps Brachii do?
Flexes the elbow
What does the Triceps Brachii do?
Extends the arm
What happens during isometric contraction?
The length of the muscle does not change
The tension on the muscle increases
I.e. Holding a book steady using an outstretched arm
What happens during isotonic contraction?
The muscle length changes
The tension remains constant
What are the two types of Isotonic contraction?
Concentric – Muscle shortens
Eccentric – Muscle lengthens
What happens during Concentric Isotonic Contraction?
Force generated by the muscle is greater than the load to be lifted
Muscle shortens in length
e.g. Picking a book up off a table
What happens during Eccentric Isotonic Contraction?
Force generated by the muscle is less than the load applied to it
Muscle lengthens as it contracts
What happens during Eccentric Isotonic Contraction?
Also occur to slow joint movement
Muscles undergoing heavy eccentric loading suffer greater damage when overloaded leading to greater muscle necrosis
Muscles are approximately 10% stronger during eccentric contractions than during concentric contractions
Principle behind body building
The functional unit of skeletal muscle is the…
motor unit (MU)
What is the Motor Unit composed of?
A single motor neuron
The group of muscle fibres innervated by it
The number of muscle fibres per motor unit varies according to the _________ of the control required.
fineness
What does the neuromuscular junction (NMJ), aka motor endplate do?
It is the connection between the muscle fibre and its motor neuron.
The membranes of the nerve and muscle cells come into close contact.
When muscle fibre is stimulated at the NMJ it…
contracts.
Maximal contraction (of a muscle) is when…
all MUs are firing together
In practice to ensure that contraction is a smooth non-jerky process, __________________ of the motor units gives a graded response.
asynchronous firing
A twitch is the…
brief contraction of the muscle fibers in a motor unit in response to an action potential.
When does the latent period of muscle contraction happen?
(0.005 sec) between the stimulus and the first visible reaction
When does the contraction period of muscle contraction happen?
(0.04 sec) when the muscle shortens
When does the relaxtion period of muscle contraction happen?
(0.05 sec) the muscle returns to its original length
After initial stimulation there is a short period during which muscle will not respond to further stimulus called the…
Refractory period
Stimulation at frequency is…
shorter than the twitch time.
When the second stimulus is being superimposed on the first it, results in a greater shortening of the muscle called _____________.
summation
Summation in whole muscle can occur in two different ways, describe them.
- By increasing the number of motor units involved - called multiple motor unit summation (recruitment).
- By increasing the rate of contraction of individual motor units - called wave summation.
In practice both these occur together during contraction helped by the asynchronous firing of the motor units.
As the (nerve) impulse frequency increases, the twitches become superimposed in…
wave summation
Eventually increasing stimulus causes the successive contractions to fuse together in a state of maximal contraction called…
tetanus
In _________ further increased stimulation will only result in very slight muscle shortening.
tetanization
