Muscular system Flashcards
my/o
muscle
sacr/o
muscle cells
Three types of muscles and where they are found and there type of control
Skeletal : the animal’s ‘muscles’ or meat – voluntary control
Smooth: found in eyes, air passages in lungs, stomach/intestines, urinary bladder, blood vessels, and reproductive tract – involuntary (autonomic) control
Cardiac: found in the heart only – involuntary control
Muscles are classified using
Microscopic appearance - straited or non-striated
Location in the body - in organ, attached to skeleton
Method of nervous and endocrine control - voluntary/involuntary
Functions of the muscle
Functions to provide motion, maintain posture (or stabilize body positions), regulate organ volume (such as GIT and heart), and produce heat
Contraction of the muscle occurs by
Interaction of special protein fibres
Twitch contraction
Single muscle contracting
3 phases of muscle contraction
- Latent
- Contracting
- Relaxation
Contraction produces
Movement and heat
Muscle tissue 4 characteristics and what they mean
Excitability: (or irritability): the ability of a muscle cell to respond to neurotransmitters or hormones by producing electrical signals called action potentials (impulses)
Contractility: the ability of the muscle cell to shorten
Extensibility: muscle tissue can be stretched without damage
Elasticity: muscle tissue tends to return to original shape after shortening or stretching
Skeletal muscle description
Consists of cylindrical fibers (cells) which contain many peripheral nuclei
Appear striated under microscope due to the presence of light and dark bands
Usually under voluntary control by the somatic nervous system
Contraction enables movement of head, trunk, and extremities
Function of skeletal muscle
Motion, posture, and heat production
Skeletal muscles are composed of
Belly
Two or more attachments
Surrounded by fibrous tissue
The attachment of skeletal muscle 3 general forms
Tendon - a bundle of connective tissue which attaches muscle to bone
Aponeurosis - a broad sheet of connective tissue usually located between broad flat muscles
The linea alba is an example of an aponeuroses
Direct or fleshy attachment (not in your textbook) - direct connection of muscle to bone with little visible connective tissue involved
Example are intercostal muscle
Origin attacmnet site is
the stationary (or more or less fixed) end of the muscle
Usually located proximally on limbs
Head: refers to each origin in those muscles that have more than 1 origin
Insertion attachment site is
Attachment at the moveable end of muscle
Usually located distally on the limbs
Prime mover muscle action is
Used to describe a muscle or group of muscles that directly produces a desired movement
Antagonist muscle action is
Used to describe a muscle or group of muscles that directly opposes the action of a prime mover muscle
The effect is a smoothing out of the movement or preventing movement from occurring (such as when postural muscles work to stabilize your body to allow you to sit up straight without wavering)
Synergist muscle action is
Describes a muscle or group of muscles that contract at the same time as a prime mover and assists the prime mover in carrying out its action
Fixator muscle action is
Muscles that stabilise the joint to allow other movements to take place
How muscles are named
Action
Shape
Location
Direction of fibres
Number of heads or divisions
Attachment sites
Extrinsic muscle
Attach limb to axial skeleton
Intrinsic muscle
Extends between bones of limb itself
Connective tissue layer consists of
Endomysium
Perimysium
Epimysium
Endomysium is
Connective tissue layer of fine, reticular fibers surrounding each muscle cell
Perimysium is
tough connective tissue layer binding together fascicles, or bundles of muscle fibers
Epimysium is
Tough collagenous connective tissue that binds together groups of muscle fascicles (i.e. is the cover for the muscle itself)
The connective tissue layers are continuous with and provide
All three layers are continuous with the tendons and aponeurosis
Create a strong attachment to the skeleton
Also provide blood vessels, nerve fibers, and adipose tissue (‘marbling’) to the muscle
Skeletal muscle cells are
Very long, thin fibers (cells). This is why a muscle cell is sometimes called a fiber
Multinuclear – up to or > 100 nuclei on the periphery of the cell, just below the muscle cell membrane, or sarcolemma
Cell is filled with tightly packed myofibrils, which are long thin structures made up of tightly packed Contain many mitochondria for energy production
Have a large network of the muscle cell endoplasmic reticulum, which is called sarcoplasmic reticulum
A system of tubules called transverse or T tubules extend into the cell from the sarcolemma (cell membrane) and assist in transmission of nerve impulses
Myofilamnets are
These are made up of thin actin and thick myosin filaments (protein molecules)
The filaments are grouped together in units called sarcomeres. The arrangement of actin and myosin within the sarcomere gives skeletal muscle its striated appearance
Muscle contraction occurs through
A mechanism reffered to as the sliding filament mechanism
Each muscle cell is built of
Repeating units of actin and myosin filaments called sarcomeres
In order for the muscle to contract what happens
The thin actin filaments can ratchet themselves along the myosin filaments to shorten the sarcomere and this shortens the overall muscle fibers
The combined shortening of all the sarcomeres in a muscle fiber (cell) is a contraction
In effect, the actin filaments slide along the myosin to increase the overlap and shorten the muscle. The length of the individual actin and myosin protein does not change.
The movement or pumping of Ca ions from the sarcoplasmic reticulum into the sarcoplasm initiates the contraction process
The relaxation of the muscle fiber involves the movement of Ca ions in the reverse direction
Both require ATP - made in mitochondria
Neuromuscular junction is the point
Motor nerves links to the muscle fibers
This is not a direct contract but rather though a synaptic vesicle
Synaptic vesicles in the neurotransmitter junction contain
Acetylcholine
Acetylcholine does what in the synaptic space
diffuses across the synaptic space and binds receptors on the motor end plate of the sarcolemma, to initiate muscle contraction
Acetylcholinesterase does what in the neurotransmitter junction
Destroys the acetylcholine in the synaptic space
Motor unit refers to
The bundle of muscle fibers innervated by a particular nerve cells
Muscle contraction
Bonds are broken and reformed in a cyclical pattern resulting in the ratchet like movement of actin over myosin
In consequence, there is more overlap of the molecules, and the muscle fibers shorten
Initiation of muscle contraction and relaxation
Motor Nerve fiber stimulated
Impulse reaches the neuromuscular junction
Depolarizes the nerve cell membrane and opens voltage-sensitive calcium channels that allow calcium to enter the axon terminal and trigger release of acetylcholine
Acetylcholine is released into the synaptic space by exocytosis
Acetylcholine binds to the receptors in the sarcolemma
Initiates opening of sodium channels that allow sodium to move into the muscle fiber, creating a depolarizing impulse that is transmitted along the sarcolemma and through the T tubules (called end plate potential)
At this point, acetylcholinesterase is splitting acetylcholine into acetate (resorbed by synaptic end bulb) and choline ends the stimulation
Impulse reaches sarcoplasmic reticulum (SR)
Sarcoplasmic reticulum has voltage-sensitive calcium channels that release stored calcium ions into sarcoplasm
Calcium initiates the contraction process
Contraction involves the formation of the of bonds between the myosin and actin
**requires ATP!!
Immediately SR begins pumping calcium back in (i.e. out of the myofibrils)
Removing calcium halts the contraction by allowing tropomyosin to slide over and cover the cross-bridge binding sites on the actin filament
Rigor mortis is when
At death Ca leaks out into the sarcoplasm and initiates contraction
ATP starts contraction but becomes exhausted as no functioning mitochondria
Contraction maintained b/c actin and myosin are bonded
Wears off as tissue autolyze
Botulinus toxin
Produced by Clostridium Botulinum
Blocks nerve stimulation and causes paralysis.
Tetanus toxin
Produced by Clostridium tetani
Causes continuous stimulation of the motor neurons and results in tetanic contractions of muscles
Often affects muscles of the mandible first – called ‘lockjaw’
Curare
South American Indian arrowhead poison
Binds to acetylcholine receptor sites on the motor end plate and blocks the attachment of ACh
Causes parlysis
Organophosphates
Many internal and external parasites used to be treated with organophosphates.
Inhibit acetylcholinesterase
Which breaks down Ach.
Clinical signs include: hypersalivation, miosis, frequent urination, diarrhea/vomiting, increased bronchial secretions, bronchoconstriction, muscle fasciculations, ataxia, seizures.
Myasthenia Gravis
Autoimmune disorder caused by antibodies against ACh receptors.
Blocks attachment of ACh causing skeletal muscle weakness and eventually loss of function.
Treat with immunosuppressive drugs.
Spasms
Sudden involuntary contraction of muscle that may be accompanied by pain
Can be as severe as convulsions e.g. hiccup
Cramps
Like spasms but the contraction is painful and sustained (tetanic).
May result from accumulation of lactic acid, calcium deficiencies, or a blow to the muscle
All or nothing principle of muscle contraction
All or Nothing principle: an individual muscle fiber will contract completely or not at all in response to a nerve impulse
Fine movement muscle contraction
will only have a few muscle fibers stimulated
Strong moment muscle contraction
will have many muscle fibers stimulated
3 phases of muscle contraction
i. Latent phase: Nerve impulse reaches the muscle fiber, but contraction hasn’t been initiated yet
ii.Contracting phase
iii.Relaxation phase
Initial source of energy in muscle contraction
ATP
Creatine phosphate
the compound in the muscle fiber that regenerates ATP
CP splits and releases energy to attach a phosphate group back to the ADP molecule
Energy used for muscle contraction comes form
the catabolism of glucose or free fatty acid(usually with oxygen)
Catabolism- breakdown
Anabolism- building up
Where can glucose and oxygen be stored as in the muscle fiber
Glucose can be stored in muscle fibers as glycogen
Oxygen can be stored in muscle fibers attached to myoglobin (large protein molecule like hemoglobin)
Creatine phosphate
the compound in the muscle fiber that regenerates ATP
Anaerobic metabolism
Less efficient
Produces lactic acid – if accumulates, can cause muscle discomfort
Lactic acid transported to the liver and converted to glucose – this requires oxygen, so we may continue to breathe heavily after exercise
Sometimes called the “oxygen debt”
Three energy stores
ATP
Creatine phosphate
Glycogen
oxygen is stored in the
myoglobin
Heat production by the muscle
Heat is the by-product of muscle contraction
May exploit this fact by shivering when cold
Must cope with excess heat by panting or sweating during exertion.
If this fails, the animal develops a simple hyperthermia with body temperatures of 40oC plus, may collapse and convulse.
Type I muscle fiber type
slow twitch fibers:
Slower to contract
Sustain contractions for longer
Have more mitochondria and myoglobin than fast twitch
Have more myelin then fast twitch
Type II muscle fiber twitch
fast twitch fibers:
Fast contraction
Fatigue more easily
Designs for short bursts of use
Twitch contraction muscle type
brief (fraction of second) contraction of the muscle fibers in a motor unit when a single motor neuron is stimulated
Whole muscle contraction type
longer (minutes) contraction of many muscle fibers in many motor units when many motor neurons are stimulated
Isometric muscle contraction
muscle develops tension but does not change length (i.e. holding a weight in a steady position)
Isotonic muscle contraction type
muscle shortens during the contraction
Concentric muscle contraction type
isotonic
the more strongly contracting muscle will shorten – i.e. elbow flexion – biceps is undergoing concentric contraction
Eccentric muscle contraction type
Isotonic
muscle generating least tension is stretched – i.e. triceps during elbow flexion.
Note that this is the term used when you are slowly lowering weights.
May be more important in muscle-building than concentric contractions!
Contracted flexor tendons
An abnormality of newborn calves and foals
At birth pasterns, fetlocks and sometimes carpal joints are flexed due to shortened flexor tendons and associated muscles
Can be acquired if the leg is held chronically flexed due to lameness.
Exertional myopathies
Caused by a variety of metabolic problems
Muscle dysfunction and damage during exertion
Called ‘tying up’ in horses
Rhabdomyolysis
Cardiac muscle are
Often referred to as involuntary striated muscle
The major part of the heart
Function: pumps blood to all parts of the body
Cardiac muscle cells are
Branched
Cylindrical
Striated
Contain one centrally located nuclei
Attached to each other by thickened regions of plasma membrane called intercalated disk
Cardiac muscle micro anatomy
Intercalated disk can transmit impulses from cell to cell
Allows coordination of contraction and synchronous movement
Contain desmosomes (strong ‘plaque-like’ connections with fibers penetrating as anchors between cells that allow movement without tearing) and gap junctions (channels of cytoplasm connection between adjacent muscle fibers)
Can’t regenerate or divide if damaged
Cardiac muscle contraction
Length of contraction – cardiac muscle fibers contract for longer than skeletal muscle
There are specialized ‘pacemaker’ cells in the heart to initiate contractions
Modified muscle cells called purkinje fibers conduct impulses within the heart, similar to nerve fibers in other parts of the body
Results in coordinated cardiac activity
Cardiac muscles two characteristics
Contract rhythmically without outside stimulus
May be different rates for different cells
If two cells are in contact, they synchronize their contraction rates at the rate of the fastest cell
The characteristics of the heart allow
These characteristics allow cardiac muscle to contract in a wave-like fashion
The impulse spreads through the heart in an efficient manner to better squeeze the blood out in the correct direction
To work more effectively, the heart also has valves to prevent backflow.
Sinoatrial node is the
Contraction starts at the sinoatrial node, which is in the wall of the right atrium
The SA node is also called the pacemaker of the heart
The cells contract at a faster rate than the surrounding cells, so this gives them control over coordinating the rest of the cardiac muscle cells
Once the SA node initiates a contraction, this spreads out through specific paths
Structures along the path can assist, delay, or redirect transmission of the impulses to create a coordinated, smooth, efficient contraction
Nerve supply of the cardiac muscle
The heart is supplied by nerves from the autonomic nervous system
There are 2 parts to the ANS – sympathetic and parasympathetic
The sympathetic NS assists in the fight or flight response and stimulates the heart to beat faster during stress
The parasympathetic NS counters this stimulation and slows the heart rate during resting and relaxed states
The heart responds to the balance between the two
Note: the heart does not require external stimulation to initiate contraction; the ANS simply modifies the rate and strength of contraction.
Smooth muscle control by what
Controlled involuntary by the autonomic nervous system and hormones
Contractions tend to be slow
Two kinds – visceral (single-unit) and multiunit
Description if smooth muscles
Has a smooth appearance (non-striated) under microscope
Multiple, spindle-shaped, fibers (cells)
One centrally located nucleus
No T-tubules
Filaments of actin and myosin are arranged in a crisscross pattern, rather than parallel (as in skeletal and cardiac)
Contraction causes a ‘balling up’ of the cell
This action results in greater shortening than either skeletal or cardiac muscle
Smooth muscle function
constriction of blood vessels and airways, propulsion of foods through the GIT, contraction of the urinary bladder and gallbladder
Tend to maintain constant tone, or a constant state of partial contraction
Tend to contract in response to stretching, but then relax again after a period of time
Smooth muscle location
Visceral (single-unit) is found in the walls of the small arteries, veins, and hollow organs (stomach, intestines, uterus, urinary bladder, and gallbladder)
Multiunit is found in the walls of large arteries, airways to the lungs, arrector pili muscles of hair follicles, and the muscles of the iris that adjust pupil size
Visceral smooth muscle are
Found in many hollow, soft organs and structures like blood vessels
Cells are organized into large sheets
Fibers connected by gap junctions to form large networks
Contractions are large, slow, rhythmic waves
Can be very strong (peristalsis, uterine contractions)
Contractions can occur without external stimulation
However, stretching stimulates stronger contraction.
Useful in the GIT and bladder
Must be inhibited in the uterus as the fetus grows during pregnancy by the hormone progesterone.
Has a nerve supply that doesn’t initiate contraction, but modifies it
Autonomic nervous system
Sympathetic stimulation decreases activity
Parasympathetic stimulation increases activity
Useful during fight or flight, digestion is not a priority, so that activity is shut down until a more opportune time.
Multiunit smooth muscles
Cells are innervated individually or in small groups
Require ANS stimulation for contraction – no automatic contractile activity
Has tone (some fibers are always contracting)
Results in small, delicate, movements – important for places like
The iris and ciliary body of the eye (responsible for lens accommodation)
Walls of large blood (arteries and veins) vessels
Air passageways in the lungs
Action is specific and carefully controlled
Adjusting pupil size
Lens focusing or accommodation
Control of blood flow to tissues
Size of airways required to meet body’s needs
