Unit 2 - Muscular System Flashcards
types of muscle
skeletal
cardiac
smooth
myo = muscle
sarco = muscle cells
muscle tissue makeup
made of muscle cells (AKA ‘fibers’ due to elongated shape)
cells made of microfilaments
microfilaments made of actin and myosin
muscle cells can’t divide, destroyed ones can’t be replaced
use changes volume and structure of cells
3 types of muscle tissue
skeletal: meat. voluntary
smooth: eyes, lungs, GIT, bladder, vessels, reproductive. involuntary
cardiac: heart only. involuntary
muscle classified by…
- appearance (striated/non under microscope)
- location
- method of control (voluntary/involuntary)
muscle function
motion
posture
regulate organ volume
produce heat
muscle contraction
- occurs by interaction of special protein fibers
- produces movement and heat
ONLY thing a muscle does! contract when stimualted, which then produces movement, heat, or posture
usually done in groups with certain muscles stabilizing others movement
4 muscle characteristics
- excitability (ability of cell to respond to neurotransmitters or hormones by producing electrical signals called action potentials)
- contractability (ability of cells to shorten)
- extensibility (stretch without damage)
- elasticity (return to original shape)
skeletal muscle
APPEARANCE:
cylindrical fibers (cells) with peripheral nuclei
light and dark bands under microscope (striated)
LOCATION: attached to bone, makes up ‘meat’ when paired with associated CT
FUNCTION:
motion
posture
heat
TRAITS
voluntary, controlled by somatic nervous system
each cell has its own nerve supply
can’t divide
all-or-none contraction
force of contraction depends on state before stimulation (fatigued? warmed up?)
skeletal muscle makeup
composed of:
- belly (main mass, contracting portion)
- 2+ attachments (tendon, aponeuroses, or direct)
- tendon: bundle of CT attaching muscle to bone
- aponeuroses: broad CT sheet b/w broad + flat
muscles (eg. linea alba)
- direct: muscle to bone without visible CT (eg.
intercostal)
- surrounding fibrous CT
skeletal attachments
- origin: stationary end, usually proximal end (some muscles have multiple heads (triceps brachii has 3) and therefore multiple origins)
- insertion: movable end, usually distal
eg. triceps brachii origin: humerus, scapula
insertion: olecranon
muscle actions
- agonist (prime mover)
- directly produce desired movement - antagonist
- directly opposes agonist
- ‘smooths out’ movement or prevents movement - synergist: contract at the same time as prime mover, assists
- fixator: stabilize joints
muscle naming conventions
- action (eg. flexor muscles flex)
- shape (eg. deltoid triagular)
- location (eg. biceps brachii on brachium, biceps femoris on femur)
- direction of fibers (eg. rectus = straight)
- number of heads (-cep = head. bicep = 2 heads)
- attachment sites (brachiocephalicus attached at brachium)
functional groupings of muscle
extrinsic: connect limb to axial skeleton
intrinsic: extend between bones
- flexors: side of limb joint bends towards
- extensors: opposite flexors (contraction will increase joint angle)
- adductors: towards median
- abductors: away from median
- sphincters: surround an opening
- cutaneous: superficial, attached to skin, cause twitches (‘cutaneous trunci’) eg. fly shoo on horse
skeletal microanatomy
composed of CT and muscle cells
CT:
1. endomysium: fine reticular fibers surrounding each cell
2. perimysium: tough, bind bundles of muscle cells (‘fascicles’)
3. epimysium: tough, collagen, binds groups of fascicles (covers muscle itself)
- all 3 layers continuous with tendons and aponeuroses. create strong attachment to skeleton. provide blood, nerves, adipose (‘marbling’ in muscle)
muscle cells:
- long and thin (25mm per cell)
- multinuclear (up to 100 nuclei on periphery)
- filled with myofibrils which give striation (made of packed myofilaments made of thin actin + thick myosin filaments [in groups called sarcomeres])
- many mitochondria for energy
- large network of endoplasmic reticulum (sarcoplasmic reticulum)
- system of transverse tubules extend into cell from sarcolemma to help transmit nerve impulses
how muscles move
Ca ions pumped from sarcoplasmic reticulum into sarcoplasm, initiates contraction
Ca ions from sarcoplasm into sarcoplasmic reticulum = relaxation
- both steps need ATP (from mitochondria)
neuromuscular junction
point where motor nerve links to muscle fiber
not direct, small gap (synaptic space)
NERVE IMPULSE:
impulse travels down nerve -> massive exocytosis of nerve cells vesicles (‘synaptic vesicles’, contain neurotransmitter)
acetylcholine diffuses across synaptic space and binds receptors on ‘motor end plate’ of sarcolemma to start contraction (while this happens, enzyme ‘acetylcholinesterase’ destroys acetylcholine in space)
*if nerve is destroyed, cells no longer contract and rapidly atrophy
motor unit
bundle of muscle fibers innervated
less fibers = precise movements
more fibers = coordinated powerful movements
sliding filament mechanism
mechanism that contracts muscles
- each cell built of repeating units of actin and myosin filaments called sarcomeres
- actin and myosin partially overlap
- thin actin filaments ratchet themselves along myosin -> shortens sarcomere -> shortens overall fiber
(actin slides along myosin to increase overlap + shorten muscle)
= combined shortening of all sarcomeres in a cell is contraction
initiation of contraction and relaxation
motor nerve fiber stimulated -> impulse reaches neuromuscular junction -> depolarizes nerve cell membrane + opens voltage-senstivie Ca channels that allow Ca to enter axon terminal and trigger release of acetylcholine -> acetylcholine released in synaptic space by exocytosis -> acetylcholine binds to receptors in sarcolemma -> sodium channels open and allow Na to move into fiber and make depolarizing impulse that is transmitted along sarcolemma through T turbules ‘end plate potential’ -> acetylcholinesterase splits acetylcholine into acetate and choline -> impulse reached sarcoplasmic reticulum (SR) -> SR has voltage-sensitive Ca channels that release stored Ca ions into sarcoplasm -> Ca initiates contraction process
- contraction involves formation of bonds between actin and myosin filaments, requires ATP
muscle contraction
bonds broken and reformed in a cyclical pattern -> makes ratcheting of actin over myosin
more overlap = muscle cell shortens
muscle relaxation
SR immediately pumps Ca back in (halts contraction)
Ca levels in SR related to amount in blood, body maintains strict control
rigor mortis
Ca leaks into sarcoplasm, initiates contraction
ATP starts the contraction but is exhausted, no functioning mitochondria
contraction maintained because actin and myosin are bonded
neuromuscular junction diseases
curare: south american arrowhead poison, binds to acetylcholine receptor sites on motor end plate and block acetylcholine attachment -> paralysis.
botulinis toxin: clostridium botulinum blocks release of acetylcholine -> prevents stimulation of motor end plate
tetanus: clostridium tetani causes continuous stimulation of motor neurons and results in tetanic contractions of muscles. often affects mandible first ‘lockjaw’
organophosphates: parasites used to be treated with this, inhibits acetylcholinesterase (causes salvation, lots of urination, vomiting, ataxia, seizure)
myasthenia gravis: autoimmune. antibodies attack acch receptors + block attachment. skeletal weakness and loss of function.
spasms: sudden involuntary contraction (convulsions to hiccups)
cramps: like spasms, but painful + sustained (tetanic). can come from lactic acid, Ca deficiencies, blow to muscle
characteristics of contraction
- all or nothing: individual muscle fiber contracts completely or not at all in response to impulse.
stronger contraction = more fibers stimulated - fine movements: few fibers stimulated
- strong movements: many fibers stimulated
energy comes from ATP initially (pg 222)
twitch contraction
single fiber contraction
3 phases:
1. latent: impulse reaches fiber
2. contracting
3. relaxation
- nerve impulses sent out .1 seconds apart to allow for whole cycle, and coordinates signals in an area so fibers are twitching out of sync -> overall sustained contraction of whole muscle
contraction chemistry
creatine phosphate (CP): generates ATP (splits and releases energy to attach a phosphate group back to ADP)
- energy comes from catabolism of glucose with oxygen
- glucose stored in fibers are glycogen
- O stored in fibers attached to myoglobin (large protein molecule)
aerobic metabolism: supplies energy when O present in tissue
- switches to anaerobic with strenuous exercise -> less efficient, lactic acid builds up -> lactic converts to glucose in liver but requires O, so we keep breathing heavy after exercise (‘oxygen debt’)
3 energy stores
ATP
creatine phosphate
glycogen
(bonus oxygen store: myoglobin)
improving muscle metabolism
carb loading: increases glycogen stores (short term)
high fat diets: muscle learns to use fat as fuel (endurance)
heat production
by-product of contraction
shivering when cold
sweating when excess, or else hyperthermia
muscle fiber types
- slow twitch: sustain longer, more mitochondria, more myoglobin
- more in posture muscles - fast twitch: fatigue easily, short burst
- more in action muscles
chickens
- white breast meat: fast-twitch
- dark leg meat: slow twitch
quarter horses glutes
- fast twitch for speed
arabian horses glutes
- slow-twitch for endurance
twitch vs whole muscle contraction
twitch is fraction of a second, single motor neuron stimulated
whole muscle: minutes long contraction, many motor neurons stimulated
contraction types
isometric: tension in muscle, but length stays same
isotonic: muscle shortens. 2 types, primary muscle (concentric) and opposing (eccentric) in both:
- concentric: more strongly contracting muscle shortens
- eccentric: muscle with least tension stretches, such as tricep during elbow flexion (actually more important in muscle building than concentric!)
myopathies
contracted flexor tendons: congential abnormality of newborn calves and foals. patterns, fetlocks, carpal joints flexed due to too short flexor tendons
- can also be acquired from chronic lameness
exertional myopathies: caused by variety of metabolic defects. ‘tying up’ in horses
cardiac muscle cells
branched
cylindrical
striated
1 central nucleus
attached to each other end to end by ‘intercalated disk’
- contains desmosomes (strong hold)
- gap junctions (pores, transmit impulses cell to cell, allow for synchronous contraction)
- pacemaker cells: purkinje fibers -> modified muscles cells that act like nerve fibers, allows coordinated cardiac activity
- can’t divide if damaged
cardiac muscle characteristics
- contract rhythmically without external stimuli
- if 2 cells contact, they sync rates to fastest cell
= wave-like contraction
cardiac contraction
sinoatrial node (SA) in wall of rigth atrium = pacemaker
- contract faster than surrounding cells: have ultimate control
- once SA initiates contraction, it spreads along paths
- structures along path assist, delay, or redirect impulse to create a coordinated contraction
cardiac nerves
from autonomic nervous system (ANS), 2 parts:
- sympathetic: fight/flight, heart beats faster
- parasympathetic: relax, slows heart rate
*ANS doesn’t initiate contraction (heart does this on its own), just modifies rate/strength
smooth muscle
nonstriated (smooth appearance)
involuntary
- controlled by autonomic nervous system + hormones
- slow contractions
- 2 kinds: visceral (single unit) and multi-unit
- spindle-shaped fibers
- 1 central nucleus
- no T-tubules
- myosin and actin filaments crisscross, not parallel like skeletal and cardiac
- contraction causes ‘balling up’ of cell = greater shortening than skeletal or cardiac!
function: constrict vessels and airways, propels food through gut, contracts bladder
- maintain constant state of partial contraction
- contract in response to stretching, relax after time
visceral smooth muscle
small arteries
veins
hollow organs
- cells in large sheets connected by gap junctions
- large, slow, wave contractions
- very strong (uterus contractions)
- no external stimuli needed, has pacemakers, but stretching makes stronger
- inhibited during pregnancy by progesterone
- nerve supply doesn’t initiate, but modifies
- autonomic nervous system: symp decreases activity, parasymp increases activity
- eg. in fight or flight sympathetic shuts down GIT
multiunit smooth muscle
large arteries
airways
hair follicles
iris (pupil size)
cells innervated individually/small groups
- require stimulation
- maintains resting tone with some fibres contracted
- small, delicate movements (pupil size, lens focusing, size of airways)
