Unit 2 - Muscular System

Question 1

types of muscle

Answer 1

skeletal
cardiac
smooth

myo = muscle
sarco = muscle cells

Question 2

muscle tissue makeup

Answer 2

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

Question 3

3 types of muscle tissue

Answer 3

skeletal: meat. voluntary
smooth: eyes, lungs, GIT, bladder, vessels, reproductive. involuntary
cardiac: heart only. involuntary

Question 4

muscle classified by…

Answer 4

1. appearance (striated/non under microscope)
2. location
3. method of control (voluntary/involuntary)

Question 5

muscle function

Answer 5

motion
posture
regulate organ volume
produce heat

Question 6

muscle contraction

Answer 6

• 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

Question 7

4 muscle characteristics

Answer 7

1. excitability (ability of cell to respond to neurotransmitters or hormones by producing electrical signals called action potentials)
2. contractability (ability of cells to shorten)
3. extensibility (stretch without damage)
4. elasticity (return to original shape)

Question 8

skeletal muscle

Answer 8

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?)

Question 9

skeletal muscle makeup

Answer 9

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

Question 10

skeletal attachments

Answer 10

1. origin: stationary end, usually proximal end (some muscles have multiple heads (triceps brachii has 3) and therefore multiple origins)
2. insertion: movable end, usually distal

eg. triceps brachii origin: humerus, scapula
insertion: olecranon

Question 11

muscle actions

Answer 11

1. agonist (prime mover)
   - directly produce desired movement
2. antagonist
   - directly opposes agonist
   - ‘smooths out’ movement or prevents movement
3. synergist: contract at the same time as prime mover, assists
4. fixator: stabilize joints

Question 12

muscle naming conventions

Answer 12

1. action (eg. flexor muscles flex)
2. shape (eg. deltoid triagular)
3. location (eg. biceps brachii on brachium, biceps femoris on femur)
4. direction of fibers (eg. rectus = straight)
5. number of heads (-cep = head. bicep = 2 heads)
6. attachment sites (brachiocephalicus attached at brachium)

Question 13

functional groupings of muscle

Answer 13

extrinsic: connect limb to axial skeleton
intrinsic: extend between bones

1. flexors: side of limb joint bends towards
2. extensors: opposite flexors (contraction will increase joint angle)
3. adductors: towards median
4. abductors: away from median
5. sphincters: surround an opening
6. cutaneous: superficial, attached to skin, cause twitches (‘cutaneous trunci’) eg. fly shoo on horse

Question 14

skeletal microanatomy

Answer 14

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

Question 15

how muscles move

Answer 15

Ca ions pumped from sarcoplasmic reticulum into sarcoplasm, initiates contraction

Ca ions from sarcoplasm into sarcoplasmic reticulum = relaxation

• both steps need ATP (from mitochondria)

Question 16

neuromuscular junction

Answer 16

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

Question 17

motor unit

Answer 17

bundle of muscle fibers innervated

less fibers = precise movements
more fibers = coordinated powerful movements

Question 18

sliding filament mechanism

Answer 18

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

Question 19

initiation of contraction and relaxation

Answer 19

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

Question 20

muscle contraction

Answer 20

bonds broken and reformed in a cyclical pattern -> makes ratcheting of actin over myosin

more overlap = muscle cell shortens

Question 21

muscle relaxation

Answer 21

SR immediately pumps Ca back in (halts contraction)

Ca levels in SR related to amount in blood, body maintains strict control

Question 22

rigor mortis

Answer 22

Ca leaks into sarcoplasm, initiates contraction

ATP starts the contraction but is exhausted, no functioning mitochondria

contraction maintained because actin and myosin are bonded

Question 23

neuromuscular junction diseases

Answer 23

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

Question 24

characteristics of contraction

Answer 24

• 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)

Question 25

twitch contraction

Answer 25

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

Question 26

contraction chemistry

Answer 26

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')

Question 27

3 energy stores

Answer 27

ATP creatine phosphate glycogen (bonus oxygen store: myoglobin)

Question 28

improving muscle metabolism

Answer 28

carb loading: increases glycogen stores (short term) high fat diets: muscle learns to use fat as fuel (endurance)

Question 29

heat production

Answer 29

by-product of contraction shivering when cold sweating when excess, or else hyperthermia

Question 30

muscle fiber types

Answer 30

1. slow twitch: sustain longer, more mitochondria, more myoglobin - more in posture muscles 2. 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

Question 31

twitch vs whole muscle contraction

Answer 31

twitch is fraction of a second, single motor neuron stimulated whole muscle: minutes long contraction, many motor neurons stimulated

Question 32

contraction types

Answer 32

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!)

Question 33

myopathies

Answer 33

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

Question 34

cardiac muscle cells

Answer 34

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

Question 35

cardiac muscle characteristics

Answer 35

1. contract rhythmically without external stimuli 2. if 2 cells contact, they sync rates to fastest cell = wave-like contraction

Question 36

cardiac contraction

Answer 36

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

Question 37

cardiac nerves

Answer 37

from autonomic nervous system (ANS), 2 parts: 1. sympathetic: fight/flight, heart beats faster 2. parasympathetic: relax, slows heart rate *ANS doesn't initiate contraction (heart does this on its own), just modifies rate/strength

Question 38

smooth muscle

Answer 38

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

Question 39

visceral smooth muscle

Answer 39

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

Question 40

multiunit smooth muscle

Answer 40

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)