muscular system

Question 1

what are muscles

Answer 1

a type of tissue that produces movement and heat in the body. there are 3 types of muscle tissue- skeletal, smooth and cardiac

Question 2

characteristics of muscles

Answer 2

excitability- muscle cells stimulated into action
elasticity- after being extended it can go back to original length
extensibility- can extend in length
contractility- can shorten in length

Question 3

functions of the muscle

Answer 3

maintain posture and body position, stabilising joints, movement, heat production

Question 4

what is the skeletal muscle composed of

Answer 4

skeletal muscle cells, CT wrapping and tendons, blood vessels, nerve supply

Question 5

structure of muscle tissue

Answer 5

it is composed of numerous elongated muscle cells (or fibers). the muscle cells are bunched together into fascicles which collectively make up the muscle belly of individual skeletal muscles. a nerve, artery and vein enter and exit a skeletal muscle belly near its central point then branch throughout the muscle. connective tissue wrappings surround the muscle belly, seperate fascicles and surround individual muscle cells.

Question 6

what 2 ways does skeletal muscles attach to the bone via connective tissue

Answer 6

direct attachment- epimysium of muscle is fused to the periosteum of the bone
indirect attachment- connective tissue tendons extend beyond the muscle belly to attach to bone

Question 7

each muscle attaches to at least 2 bones and crosses the joint between them to generate movement and stabilise the joint. the attachment site for a particular muscle is identified as..

Answer 7

origin- attachment site on a bone that does not move when the muscle contracts
insertion- attachment site on a bone that moves when the muscle contracts

Question 8

what extra cellular organelles does muscle cells contain as-well as the usual ones

Answer 8

glycosomes- granules of glycogen (long chains of glucose stored in the cell)
myoglobin- red pigment that stores oxygen
myofibrils- rod like structure that contain the contractile components of the cell and make up the bulk of muscle cells

Question 9

what do myofibrils have in them

Answer 9

the smallest contractile units of muscle called sarcomeres

Question 10

what do sarcomeres contain

Answer 10

they are stacked end to end along the length of the myofibril and contain two types of myofilaments
thick filaments- composed of contractile protein myosin
thin filaments- composed of the contractile protiens actin, tropomyosin and troponin

Question 11

how do muscles contract (skeletal muscles)

Answer 11

they are stimulated to contract by the neurotransmitter (acetylcholine) released from the somatic lower motor neurons and neuromuscular junctions. it binds to the excitatory receptors on the sarcolemma, generating an electrical impulse that is transmitted through the muscle cell by the t tubules. the action potential stimulates the sarcoplasmic reticulum to release calcium ions, which then bind to the troponin on the thin filament, exposing myosin binding sites on the actin protein.

Question 12

axial muscle groups

Answer 12

these muscles stabilise, position and support structures of the head, neck and trunk.

Question 13

appendicular muscles

Answer 13

stabilise, support and move the limbs

Question 14

what connective tissue wraps around the muscle belly

Answer 14

epimysium

Question 15

what connective tissue separates and surrounds the fascicle

Answer 15

perimysium

Question 16

what connective tissue surrounds the individual fascicle muscle cells

Answer 16

endomysium

Question 17

do muscle cells have multiple nuclei to make proteins in all areas of the cells in the muscle

Answer 17

yes. myofibrils are in the muscle cells and run the whole length of it, which are make of sarcomeres

Question 18

what are z discs

Answer 18

they are at the end of each sarcomere

Question 19

the process of myosin grabbing the actin (skeletal muscle contracting)

Answer 19

the cell has calcium in it that is stored away and then a nerve signal from the brains somatic nervous system (acetylcholine) goes to the muscle and excites it (excitability) and the cell releases the calcium which bind to the thin filament exposing binding sites for the myosin heads to reach and grab the actin. as the myosin heads flex, they pull the actin closer towards the centre of the sarcomere and the z discs get pulled closer to each other which makes the muscle shorten. this happens over and over again very fast so that the muscle fully contracts otherwise if the signal is too slow to excite the muscle cells then the muscle will fully extend back before the next contraction which causes a twitching motion

Question 20

what is a motor unit

Answer 20

one lower motor neuron and all of the muscle cells it stimulates. a nerve cell can stimulate multiple cells to make it move. there are lots of motor units in a cell.

Question 21

what does muscle strength depend on

Answer 21

how many motor units are activated at once

Question 22

where is smooth muscle found/ functions

Answer 22

it forms one layer within organ walls. in all hollow organs apart from the heart and helps to move a lot of things- air, food, semen etc found in blood vessels, respiratory tract, digestive tract, renal tract

Question 23

what is the shape of smooth muscle

Answer 23

they are short with tapered ends and are in layers.

Question 24

what are the 2 layers of smooth muscle

Answer 24

circular layer is when it wraps around the circumference of the muscle and constrict the diameter
longitudinal layer is when they lay along the length of the muscle so they shorten the length of the muscles

Question 25

how do smooth muscles contract

Answer 25

there are no sarcomeres of myofibrils but they have actin and myosin. they are arranged in a spiral from end to end of the muscle cell. this means that when the muscle contracts the cell gets shorter and squeezes and gets fatter in the middle. the cells are connected via gap junctions- the protein channels are open and connected so electrical signals are passed through so all the cells in the area contract together. these signals come from the autonomic nervous system

Question 26

what is the autonomic nervous system

Answer 26

when it happens involuntary and unconsciously

Question 27

what is the somatic nervous system

Answer 27

when it happens voluntary and consciously

Question 28

what does cardiac muscle do

Answer 28

it is used to pump blood and is located in the heart.

Question 29

what is the shape of cardiac muscles

Answer 29

the ends of the cells are split. the cells are connected by intercalated discs which have gap junctions in them (allows the signal to go from one cell to the other so they don’t all need to be stimulated)

Question 30

how does cardiac muscles contract

Answer 30

they have myofibrils and sarcomeres. the contractions work the same as the skeletal muscles. the main stimulus is pacemaker cells which set the pace of contraction. - they self stimulate

Question 31

factors of smooth muscle

Answer 31

• contains only a single nucleus
• cells are connected by gap junction
• found within the intestinal wall
• found lining the walls of blood vessels
• found in hollow organs apart from the heart
• controlled by unconscious nerve signals or hormones or pacemaker cells

Question 32

factors of skeletal muscle

Answer 32

• attach to bones via tendons
• controlled by conscious nerve signals
• cells contain multiple nuclei
• cells are not connected, but wrapped in bundles

Question 33

factors of cardiac muscle

Answer 33

• cells are connected by intercalated discs
• forms muscle tissue of the heart
• controlled by pacemaker cells or unconscious nerve signals
• cells have one or two nuclei

Question 34

what is the sarcoplasmic reticulum (smooth endoplasmic reticulum)

Answer 34

it forms a tubular network around each myofibril and stores calcium ions necessary for muscle contraction

Question 35

what is the sarcolemma (plasma membrane)

Answer 35

it has narrow tubes called T-tubules that extend through the muscle cell, surrounding individual myofibrils and allowing the transmission of action potentials throughout the entire muscle cell

Question 36

what are the myofilaments anchored to

Answer 36

the thin filaments are anchored to the z line at the ends and the thick filaments are anchored to the m line at the centre

Question 37

2 factors are required to generate enough tension in a muscle to cause movement or sustain a particular body position which are

Answer 37

recruitment- the number of motor units simulated (the more motor units working, the stringer the contraction)
frequency- the rate of action potential simulation/ firing within a motor unit (the greater the frequency the stronger the contraction)

Question 38

describe the myosin- actin coupling/ cross bridge mechanism of skeletal contraction

Answer 38

when an action potential is triggered in a skeletal muscle it stimulates the release of calcium

calcium binds to troponin on actin leading to the exposure of myosin binding sites on the actin filaments

myosin heads then bind to the exposed binding sites on actin, making a cross bridge. myosin heads ‘flex’ (bend) pulling the actin towards the M line (center of the sarcomere)

this brings the z lines (ends of sarcomere) close together, shortening the sarcomere

ATP is required to release myosin heads from the actin binding sites, allowing further contraction to occur (in the presence of calcium) or relaxation (lengthening of the sarcomere)

Question 39

how is smooth muscle different from skeletal muscle

Answer 39

the cells are shorter, with tapered ends
cells contain only one nucleus
there are no T-tubules
myofilaments are not arranged into sarcomeres, but instead the thick and thin filaments criss-cross each other diagonally in a spiral arrangement down the length of the cell
the thin filaments contain calmodulin instead of troponin for binding calcium (Ca2+)
the thick filaments contain myosin heads along their entire length