Download Muscle System (more than just a tissue)

MUSCULAR SYSTEM (more than just a tissue) – Ch. 10
Human Anatomy lecture
I. Overview
A. 3 types of muscle tissue -- 40-50% of total body weight
Skeletal -- Smooth -- Cardiac
*Review tissue notes*
B. Functions
1. Movement (of body parts and organ contents)
2. Stability (body position and organ volume)
3. Control of body openings & passages (sphincters)
4. Heat production
C. Properties
1. excitability & conductivity
→ responds to stimuli
→ produces & conducts electrical signals
2. contractility
→ shorten
→ create tension
3. extensibility
→ stretched without damage
4. elasticity
→ returns to original shape
II. Skeletal muscle (as an organ)
A. Connective tissue components KNOW Fig 10.2a
-- listed from most superficial to deep -1. superficial fascia (subcutaneous layer)
loose c.t.
adipose
2. deep fascia
separates muscles into functional groups
dense irregular c.t.
3. epimysium*
surrounds whole muscle
dense irregular c.t.
4. perimysium*
surrounds bundles of 10-100+ muscle fibers called fascicles (fasciculi)
dense irregular c.t.
5. endomysium
surrounds single fibers
*Extend beyond muscle to form a tendon -- dense regular c.t.
Muscle -- Page 1 of 6
III. How skeletal muscles produce movement
A. Terminology  recently changed
- origin -- less movable, proximal
- belly
- insertion -- more movable, distal
“attachments”
B. Fascicle arrangement (relative to tendon)
- influences power and range of motion (KNOW Fig. 10.3)
Ex.: parallel =  motion,  power
bipennate =  motion,  power
C. Group actions
1. prime mover - causes desired action
(agonist)
- example: brachialis flexes the forearm
2. antagonist - opposes
- example: triceps brachii
3. synergists - stabilizes intermediate joints and/or assists
- ex.: biceps brachii, shoulder muscles
4. fixators - stabilize origin
-- ex.: scapular muscles
D. Lever systems
1. Terminology
- sketch
2. In your body: muscles = effort
joints = fulcrum
body weight = resistance
or objects
bones = levers
3. Relative position of the three determine:
mechanical advantage: ↓ effort = ↑ output
or
mechanical disadvantage: ↑effort = ↓ output
(or a mechanical advantage of <1)
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4. Levers trade-off effort - vs.- distance and speed
long levers can lift great weight, but must move a great distance
most levers in the body work at a mechanical disadvantage – but gain speed and
distance
IV. Microscopic anatomy of skeletal muscle: Fig 10.2 & 10.8 & Table 10.1
A. Cell = muscle fiber = myofiber
Drawings:
B. Sarcomere – structural and functional unit of a muscle cell: Fig. 10.10
“flesh” 
 ”part”
-- Be able to sketch and label a sarcomere!
Muscle -- Page 3 of 6
1. three major protein myofilaments (= microfilaments  part of cytoskeleton)
- thick (myosin)
- thin (actin and regulatory proteins)
- elastic (titin)
2. form alternating light and dark bands = striations
- dark A band = myosin (H zone is midline gap between thin filaments)
- light I band (gap between thick filaments) = actin
3. muscle contracts by sliding-filament mechanism
- myosin pulls actin toward center: sarcomere shortens
- NRF detail
C. Muscle cell also has specialized ER, the sarcoplasmic reticulum.
D. Sarcolemma has deep invaginations, the T-tubules
V. Nerve and blood supply to skeletal muscle
A. skeletal muscles contract voluntarily
Brain → spinal cord → motor neuron → muscle
B. a motor neuron branches at its end to innervate 3-2000 muscle cells (avg. ≈150).
this is a motor unit (Fig. 10.12)
C. muscle tone is minimal contraction maintained by alternating activity among
different motor units.
* if stopped → you faint
D. neurovascular bundle supplies the muscle with:
artery/vein/nerve/lymphatic
VI. Growth and regeneration of skeletal muscle
1. skeletal muscle cells cannot divide
hypertrophy is growth by addition of myofilaments
atrophy is reverse
2. if damaged, some new cells can form from satellite cells
-- most damage is replaced by fibrous scar tissue: fibrosis
VII. Cardiac muscle
A. Microscopic anatomy (10.15)
1. Similar to skeletal:
myofibrils
sarcomere
2. Cells are shorter, branched, and connected end-to-end
3. Intercalated discs contain (Fig. 20.14c)
 gap junctions, tiny pores that allow rapid spread of electrical signals
 interconnections for actin filaments
RESULT → heart is a single structural & functional unit!
Muscle -- Page 4 of 6
B. Nerve and blood supply
1. rich blood supply
2. no motor units
3. involuntary contraction
-- nerves can ↑or ↓ rate and force
C. Growth and regeneration
1. growth by adding myofibrils (hypertrophy)
2. some regeneration (unknown source of stem cells), though most repair is by
fibrosis
VIII. Smooth muscle
A. Microscopic anatomy (Fig. 10.16 & 10.18)
1. no myofibrils or sarcomeres
2. actin and myosin and intermediate filaments arranged in contractile network
3. cells arranged in two ways
a. single-unit (visceral) smooth muscle
- sheets with abundant gap junctions
- contract as single unit, often in rhythmic waves called peristalsis
- small vessels, hollow viscera
b. multi-unit smooth muscle
- smaller bands, fewer gap junctions
- contracts in discrete motor units
- larger arteries, airways, piloerector muscle
B. Nerve and blood supply
1. blood supply from organ
2. involuntary contraction
3. most contraction is in response to local conditions
stretch/pH/O2/temperature
C. Growth and regeneration
1. hypertrophy is possible; some cells can still divide: hyperplasia (uterus)
2. new cells can arise from pericytes -- stem cells of capillary endothelium and veins
-- Table 10.4 excellent summary/comparison of muscle types –
(NRF all details – see review worksheet)
Muscle -- Page 5 of 6
SKETCHES
III. B
III. D. 1.
IV. A.
Muscle -- Page 6 of 6