Question 1

Plasma membrane 
of muscle fiber

Accepted Answer

Sarcolemma

Question 2

Cytoplasm of muscle fiber

Accepted Answer

Sarcoplasm

Question 3

thick bundles of contractile 
organelles inside muscle fibers;

Accepted Answer

Myofibrils

Question 4

Produce ATP

Accepted Answer

Mitochondria

Question 5

Stored glucose for energy

Accepted Answer

Glycogen

Question 6

Stores oxygen

Accepted Answer

Myoglobin

Question 7

Specialized smooth ER; 
releases calcium into cytosol;
Stores calcium ions (Ca²⁺); 
reservoir for calcium;
Releases calcium during contraction.

Accepted Answer

Sarcoplasmic Reticulum (SR)

Question 8

Extensions of sarcolemma; Carry electrical 
signals deep into muscle fiber; any of 
several membranous channels that extend deep 
into the cell from a muscle fiber membrane.

Accepted Answer

Transverse Tubules (T-tubules)

Question 9

These make up myofibrils.

Accepted Answer

Myofilaments

Question 10

Attached to bones;
Voluntary; 
Striated (has striped appearance).

Accepted Answer

Skeletal Muscle

Question 11

Found in the heart wall;
Involuntary;
Pumps blood.

Accepted Answer

Cardiac Muscle

Question 12

Found in walls of organs (digestive tract, 
blood vessels, etc.); Involuntary;
Moves substances through organs;
Fusiform.

Accepted Answer

Smooth Muscle

Question 13

Alternating light and dark internal 
protein bands are known as:

Accepted Answer

striated, or striations

Question 14

protein in a muscle fiber that forms 
the thick filaments that slide between 
thin filaments of the protein actin, 
contracting muscle fibers.

Accepted Answer

myosin

Question 15

membranous network of channels and 
tubules within a muscle fiber, 
corresponding to the endoplasmic 
reticulum of other cells; plasma 
membrane for muscle cells.

Accepted Answer

sarcoplasmic reticulum

Question 16

structural unit of a myofibril and 
the functional unit of muscle 
contraction; smallest functional unit 
of the muscle fiber. Z-disc to Z-disc.

Accepted Answer

sarcomere

Question 17

thick myofilaments:

Accepted Answer

made of several hundred MYOSIN proteins, 
each with a shaft like tail and double 
globular head. Heads are directed outward 
around bundle.

Question 18

thin myofilaments:

Accepted Answer

made mostly of 2 intertwined strands 
of actin protein. also contains 
troponin and tropomyosin proteins.

Question 19

A-band

Accepted Answer

dark band; actin and myosin;
composed of overlapping thick 
and thin filaments.

Question 20

I-band

Accepted Answer

light band; actin only;
composed of thin filaments only.

Question 21

H-zone

Accepted Answer

center of A band; composed of 
thick myosin filaments only

Question 22

Z-line (Z-disc)

Accepted Answer

sarcomere boundary; in center of I-band; 
anchors thin filaments in place.

Question 23

M-line

Accepted Answer

center of sarcomere and A-band; 
anchors thick filaments.

Question 24

Sliding Filament Theory

Accepted Answer

During contraction: 
✅ Thin filaments slide past thick filaments
✅ Sarcomere shortens
✅ Z discs move closer together
✅ H zone gets smaller
✅ I band gets smaller
❌ Length of actin filaments
❌ Length of myosin filaments

Question 25

Excitation-Contraction Coupling
This connects nerve stimulation 
→ muscle contraction.

Accepted Answer

Motor neuron stimulates muscle
SR releases Ca²⁺;
Calcium binds to troponin;
Troponin changes shape;
Tropomyosin moves;
Actin binding sites exposed;
Myosin binds actin → cross bridges form;
Muscle contracts.

Question 26

Muscle Relaxation

Accepted Answer

When stimulation stops:
Acetylcholine breaks down >
Muscle impulse stops >
Calcium pumped back into SR >
Tropomyosin blocks actin again >
Muscle relaxes.
Important Enzyme:
Acetylcholinesterase > 
Breaks down acetylcholine

Question 27

Creatine Phosphate
(CP)

Accepted Answer

Regenerates ATP quickly; stores energy 
in phosphate bond, like ATP; initial 
source of energy top regenerate ATP 
from ADP and P; Provides energy for 
about 10 seconds of intense activity.

Question 28

ATP reserves:

Accepted Answer

1st source of energy for muscle 
contraction; muscle cells store 
only a small amount.

Question 29

Cellular Respiration

Accepted Answer

used for longer periods of muscle 
contraction; breaks down glucose 
to produce ATP; glucose stored as 
glycogen in muscle cells.

Question 30

Heat Production

Accepted Answer

heat is a byproduct of cellular 
respiration ion active cells; blood 
transports heat through body core; 
Muscles help maintain body temperature.

Question 31

Motor Units

Accepted Answer

one motor neuron + all muscle fibers 
it controls; large motor units produce 
coarse movements (legs); small motor 
units produce precise movement (eyes, 
fingers)

Question 32

Neuromuscular Junction:
(what it is)

Accepted Answer

the point where a motor neuron meets 
a skeletal muscle fiber and sends a 
signal to make the muscle contract; 
where a nerve fiber meets a muscle fiber.

Question 33

Neuromuscular Junction:
(3 main parts)

Accepted Answer

-Axon terminal –> end of the motor 
neuron that stores the neurotransmitter 
acetylcholine (ACh)
-Synaptic cleft –> tiny gap between 
the neuron and muscle fiber
-Motor end plate –> specialized region 
of the muscle fiber’s sarcolemma with 
ACh rec

Question 34

Neuromuscular Junction:
(how it works)

Accepted Answer

-A nerve impulse reaches the axon terminal
-ACh is released into the synaptic cleft
-ACh binds to receptors on the motor end plate
-This triggers an electrical impulse 
in the muscle fiber
-The muscle contracts

Question 35

synapse

Accepted Answer

where a nerve fiber meets another cell; 
the junction where 2 cells interact.

Question 36

axon terminal

Accepted Answer

bulbous swelling at the end of a nerve fiber.

Question 37

Acetylcholine (ACh):
"GO signal"

Accepted Answer

Neurotransmitter that stimulates 
muscle contraction

Steps:
1. Released from synaptic vesicles
2. Crosses synaptic cleft
3. Binds receptors
4. Creates muscle impulse

Question 38

Muscle Roles:
Agonist

Accepted Answer

Agonist (Prime Mover) - 
MUSCLE CAUSES AN ACTION
Main muscle causing movement.
Example:
Bicep brachii during curl 
*"in agony"

Question 39

Muscle Roles:
Synergist

Accepted Answer

Synergist -  
MUSCLES ASSIST AGONIST
Helps prime mover;
brachioradialis and 
brachialis 
**"sounds like assist"

Question 40

Muscle Roles:
Antagonist

Accepted Answer

Antagonist - MUSCLES OPPOSITE 
DIRECTION OF PRIME MOVER
Opposes movement.
Example:
Triceps brachii during curl 
**"against"

Question 41

an enzyme that breaks down 
acetylcholine (ACh) in the 
synaptic cleft at the 
neuromuscular junction; 
stops muscle stimulation.

Accepted Answer

Acetylcholinesterase (AChE)
"STOP signal"

Question 42

basal lamina

Accepted Answer

made of protein; surrounds the 
entire NMJ; releases the enzyme 
Acetylcholinesterase.

Question 43

synaptic vesicles

Accepted Answer

membrane-bounded sacs in synaptic 
knob; contain Acetylcholine, a 
neurotransmitter; diffuses across 
synaptic cleft and binds to 
acetylcholine receptors on muscle fiber.

BIO101 HUMAN A&P

BIO101 CH 08 MUSCULAR SYSTEM STUDY GUIDE

Question	Answer
BIO101 CH 8 MUSCULAR SYSTEM STUDY GUIDE
Plasma membrane of muscle fiber	Sarcolemma
Cytoplasm of muscle fiber	Sarcoplasm
thick bundles of contractile organelles inside muscle fibers;	Myofibrils
Produce ATP	Mitochondria
Stored glucose for energy	Glycogen
Stores oxygen	Myoglobin
Specialized smooth ER; releases calcium into cytosol; Stores calcium ions (Ca²⁺); reservoir for calcium; Releases calcium during contraction.	Sarcoplasmic Reticulum (SR)
Extensions of sarcolemma; Carry electrical signals deep into muscle fiber; any of several membranous channels that extend deep into the cell from a muscle fiber membrane.	Transverse Tubules (T-tubules)
These make up myofibrils.	Myofilaments
Attached to bones; Voluntary; Striated (has striped appearance).	Skeletal Muscle
Found in the heart wall; Involuntary; Pumps blood.	Cardiac Muscle
Found in walls of organs (digestive tract, blood vessels, etc.); Involuntary; Moves substances through organs; Fusiform.	Smooth Muscle
Alternating light and dark internal protein bands are known as:	striated, or striations
protein in a muscle fiber that forms the thick filaments that slide between thin filaments of the protein actin, contracting muscle fibers.	myosin
membranous network of channels and tubules within a muscle fiber, corresponding to the endoplasmic reticulum of other cells; plasma membrane for muscle cells.	sarcoplasmic reticulum
structural unit of a myofibril and the functional unit of muscle contraction; smallest functional unit of the muscle fiber. Z-disc to Z-disc.	sarcomere
thick myofilaments:	made of several hundred MYOSIN proteins, each with a shaft like tail and double globular head. Heads are directed outward around bundle.
thin myofilaments:	made mostly of 2 intertwined strands of actin protein. also contains troponin and tropomyosin proteins.
A-band	dark band; actin and myosin; composed of overlapping thick and thin filaments.
I-band	light band; actin only; composed of thin filaments only.
H-zone	center of A band; composed of thick myosin filaments only
Z-line (Z-disc)	sarcomere boundary; in center of I-band; anchors thin filaments in place.
M-line	center of sarcomere and A-band; anchors thick filaments.
Sliding Filament Theory	During contraction: ✅ Thin filaments slide past thick filaments ✅ Sarcomere shortens ✅ Z discs move closer together ✅ H zone gets smaller ✅ I band gets smaller ❌ Length of actin filaments ❌ Length of myosin filaments
Excitation-Contraction Coupling This connects nerve stimulation → muscle contraction.	Motor neuron stimulates muscle SR releases Ca²⁺; Calcium binds to troponin; Troponin changes shape; Tropomyosin moves; Actin binding sites exposed; Myosin binds actin → cross bridges form; Muscle contracts.
Muscle Relaxation	When stimulation stops: Acetylcholine breaks down > Muscle impulse stops > Calcium pumped back into SR > Tropomyosin blocks actin again > Muscle relaxes. Important Enzyme: Acetylcholinesterase > Breaks down acetylcholine
Creatine Phosphate (CP)	Regenerates ATP quickly; stores energy in phosphate bond, like ATP; initial source of energy top regenerate ATP from ADP and P; Provides energy for about 10 seconds of intense activity.
ATP reserves:	1st source of energy for muscle contraction; muscle cells store only a small amount.
Cellular Respiration	used for longer periods of muscle contraction; breaks down glucose to produce ATP; glucose stored as glycogen in muscle cells.
Heat Production	heat is a byproduct of cellular respiration ion active cells; blood transports heat through body core; Muscles help maintain body temperature.
Motor Units	one motor neuron + all muscle fibers it controls; large motor units produce coarse movements (legs); small motor units produce precise movement (eyes, fingers)
Neuromuscular Junction: (what it is)	the point where a motor neuron meets a skeletal muscle fiber and sends a signal to make the muscle contract; where a nerve fiber meets a muscle fiber.
Neuromuscular Junction: (3 main parts)	-Axon terminal –> end of the motor neuron that stores the neurotransmitter acetylcholine (ACh) -Synaptic cleft –> tiny gap between the neuron and muscle fiber -Motor end plate –> specialized region of the muscle fiber’s sarcolemma with ACh rec
Neuromuscular Junction: (how it works)	-A nerve impulse reaches the axon terminal -ACh is released into the synaptic cleft -ACh binds to receptors on the motor end plate -This triggers an electrical impulse in the muscle fiber -The muscle contracts
synapse	where a nerve fiber meets another cell; the junction where 2 cells interact.
axon terminal	bulbous swelling at the end of a nerve fiber.
Acetylcholine (ACh): "GO signal"	Neurotransmitter that stimulates muscle contraction Steps: 1. Released from synaptic vesicles 2. Crosses synaptic cleft 3. Binds receptors 4. Creates muscle impulse
Muscle Roles: Agonist	Agonist (Prime Mover) - MUSCLE CAUSES AN ACTION Main muscle causing movement. Example: Bicep brachii during curl *"in agony"
Muscle Roles: Synergist	Synergist - MUSCLES ASSIST AGONIST Helps prime mover; brachioradialis and brachialis **"sounds like assist"
Muscle Roles: Antagonist	Antagonist - MUSCLES OPPOSITE DIRECTION OF PRIME MOVER Opposes movement. Example: Triceps brachii during curl **"against"
an enzyme that breaks down acetylcholine (ACh) in the synaptic cleft at the neuromuscular junction; stops muscle stimulation.	Acetylcholinesterase (AChE) "STOP signal"
basal lamina	made of protein; surrounds the entire NMJ; releases the enzyme Acetylcholinesterase.
synaptic vesicles	membrane-bounded sacs in synaptic knob; contain Acetylcholine, a neurotransmitter; diffuses across synaptic cleft and binds to acetylcholine receptors on muscle fiber.

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