Samenvatting
Summary Human physiology
summary of the chapters discussed in the lecture
[Meer zien]Voorbeeld 4 van de 58 pagina's
Voorbeeld 4 van de 58 pagina's
In winkelwagengesponsord bericht van onze partner
Gekoppeld boek
Titel boek:
Auteur(s):
- Uitgave:
- ISBN:
- Druk:
Verkoper
Volgen
Voorbeeld van de inhoud
Look at notes/PowerPoint while reading this summary for corresponding figures.LECTRURE 1
11.2 The Somatic Motor Division
▪ Somatic motor pathways, controls skeletal muscles
▪ Somatic motor pathways have a single neuron that originates in the CNS and projects its
axon to the target tissue, which is always a skeletal muscle.
▪ Somatic pathways are always excitatory
A Somatic Motor Pathway Consists of One Neuron
▪ Somatic motor neurons branch close to their targets.
▪ Each branch divides into a cluster of enlarged axon terminals that lie on the surface of
the skeletal muscle fiber
▪ The synapse of a somatic motor neuron on a muscle fiber → the neuromuscular
junction (NMJ)
▪ the NMJ has three components:
1. the motor neuron’s presynaptic axon terminal filled with synaptic vesicles and
mitochondria
2. the synaptic cleft
3. the postsynaptic membrane of the skeletal muscle fiber.
▪ On the postsynaptic side of the neuromuscular junction, the muscle cell membrane that
lies opposite the axon terminal is modified into a motor end plate→ a series of folds
that look like shallow gutters
▪ Between the axon and the muscle, the synaptic cleft is filled with a fibrous matrix whose
collagen fibers hold the axon terminal and the motor end plate in the proper alignment.
▪ The matrix also contains acetylcholinesterase (AChE) → the enzyme that rapidly
deactivates ACh by degrading it into acetyl and choline
The Neuromuscular Junction Contains Nicotinic Receptors
▪ As in all neurons, action potentials arriving at the axon terminal open voltage-gated Ca2+
channels in the membrane. Calcium diffuses into the cell down its electrochemical
gradient, triggering the release of ACh-containing synaptic vesicles. Acetylcholine
diffuses across the synaptic cleft and combines with nAChRs on the skeletal muscle
membrane
▪ The nAChR channels of skeletal muscle, classified as NM subtype, are similar but not
identical to the nicotinic NN ACh receptors found on neurons.
▪ Toxin @bungarotoxin binds to nicotinic skeletal muscle receptors but not to those in
autonomic ganglia.
▪ skeletal muscle NM receptors have a, b, d, and e subunit isoforms, while neuronal nAChR
has only the a and b isoforms. The a and b isoforms of nAChR can become desensitized
and their channels closed with extended exposure to ACh or other agonists.
, ▪ Nicotinic cholinergic receptors are chemically gated ion channels with two binding sites
for ACh
▪ Acetylcholine acting on a skeletal muscle’s motor end plate is always excitatory and
creates muscle contraction.
▪ relaxation occurs when the somatic motor neurons are inhibited in the CNS, preventing
ACh release
CHAPTER 12
▪ Our muscles have two common functions: to generate motion and to generate force.
▪ Our skeletal muscles also generate heat and contribute significantly to the homeostasis
of body temperature (shivering to create heat).
▪ The human body has three types of muscle tissue: skeletal muscle, cardiac muscle, and
smooth muscle.
▪ skeletal muscles are attached to the bones of the skeleton, enabling these muscles to
control body movement. Voluntary.
▪ Cardiac muscle {kardia, heart} is found only in the heart and moves blood through the
circulatory system. Involuntary
▪ Skeletal and cardiac muscles are classified as striated muscles {stria, groove} because
of their alternating light and dark bands seen under the light microscope
▪ Smooth muscle is the primary muscle of internal organs and tubes, such as the stomach,
urinary bladder, and blood vessels → primary function is to influence the movement of
material into, out of, and within the body.
12.1 Skeletal Muscle
▪ Skeletal muscles are usually attached to bones by tendons made of collagen
▪ When the bones attached to a muscle are connected by a flexible joint, contraction of
the muscle moves the skeleton. The muscle is called a flexor if the centers of the
connected bones are brought closer together when the muscle contracts, and the
movement is called flexion.
▪ The muscle is called an extensor if the bones move away from each other when the
muscle contracts, and the movement is called extension.
▪ Most joints in the body have both flexor and extensor muscles because a contracting
muscle can pull a bone in one direction but cannot push it back.
▪ Flexor-extensor pairs are called antagonistic muscle groups because they exert opposite
effects.
Skeletal Muscles Are Composed of Muscle Fibers
▪ A skeletal muscle is a collection of muscle cells, or muscle fibers,
▪ Skeletal muscle fibers are the largest cells in the body, created by the fusion of many
individual embryonic muscle cells.
▪ Committed stem cells called satellite cells lie just outside the muscle fiber membrane.
Satellite cells become active and differentiate into muscle when needed for muscle
growth and repair.
, ▪ Each skeletal muscle fiber is sheathed in connective tissue, with groups of adjacent
muscle fibers bundled together into units called fascicles.
Muscle Fiber Anatomy
▪ The cell membrane of a muscle fiber is called the sarcolemma {sarkos, flesh + lemma,
shell}
▪ the cytoplasm is called the sarcoplasm.
▪ The main intracellular structures in striated muscles are myofibrils {myo-, muscle},
highly organized bundles of contractile and elastic proteins that carry out the work of
contraction.
▪ Skeletal muscle fibers also contain extensive sarcoplasmic reticulum (SR), a form of
modified endoplasmic reticulum that wraps around each myofibril like a piece of lace –
- SR consists of longitudinal tubules with enlarged end regions called the terminal
cisternae {cisterna, a reservoir}.
- SR concentrates and sequesters Ca2+ {sequestrare, to put in the hands of a trustee}
with the help of a Ca2+ATPase in the SR membrane.
- Calcium release from the SR creates calcium signals that play a key role in
contraction in all types of muscle.
▪ The terminal cisternae are adjacent to and closely associated with a branching network
of transverse tubules/ t-tubules.
- One t-tubule and its two flanking terminal cisternae are called a triad.
- The membranes of t-tubules are a continuation of the muscle fiber membrane,
which makes the lumen of t-tubules continuous with the extracellular fluid.
- T-tubules allow action potentials to move rapidly from the cell surface into the
interior of the fiber so that they reach the terminal cisternae nearly simultaneously.
- Without t-tubules, the action potential would reach the center of the fiber only by
conduction of the action potential through the cytosol, a slower and less direct
process that would delay the response time of the muscle fiber.
Myofibrils Are Muscle Fiber Contractile Structures
▪ Each myofibril is composed of several types of proteins organized into repeating
contractile structures called sarcomeres.
▪ Myofibril proteins include the motor protein myosin, which forms thick filaments.
▪ the microfilament actin, which creates thin filaments; the regulatory proteins
tropomyosin and troponin; and two giant accessory proteins, titin and nebulin.
▪ Myosin {myo-, muscle} is a motor protein with the ability to create movement
- The heavy chains of the myosin heads form the motor domain that uses energy from
the high-energy phosphate bond of ATP to create movement.
- Because myosin acts as an enzyme to hydrolyze ATP, the motor domain is
considered a myosin ATPase.
- The heavy chains of the myosin heads also contain the binding sites for actin.
▪ In skeletal muscle, about 250 myosin molecules join to create a thick filament.
, - Each thick filament is arranged so that the myosin heads are clustered at each end of
the filament, and the central region of the filament is a bundle of myosin tails
▪ Actin {actum, to do} is a protein that makes up the thin filaments of the muscle fiber.
- One actin molecule is a globular protein (G-actin)
- multiple G-actin molecules polymerize to form long chains or filaments, called F-
actin.
- In skeletal muscle, two F-actin polymers twist together like a double strand of beads,
creating the thin filaments of the myofibril.
▪ Most of the time, the parallel thick and thin filaments of the myofibril are connected by
myosin crossbridges that span the space between the filaments.
- Crossbridges form when the myosin heads of thick filaments bind to actin in the thin
filaments
- Crossbridges have two states: low-force (relaxed muscles) and high-force
(contracting muscles).
▪ Z disks.
- One sarcomere is composed of two Z disks and the filaments found between them.
- Z disks are zigzag protein structures that serve as the attachment site for thin
filaments.
- abbreviation Z comes from zwischen, the German word for “between.”
▪ I bands.
- These are the lightest color bands of the sarcomere and represent a region occupied
only by thin filaments.
- abbreviation I comes from isotropic, a description from early microscopists meaning
that this region reflects light uniformly under a polarizing microscope.
- A Z disk runs through the middle of every I band, so each half of an I band belongs to
a different sarcomer
▪ A band.
- This is the darkest of the sarcomere’s bands and encompasses the entire length of a
thick filament.
- At the outer edges of the A band, the thick and thin filaments overlap.
- The center of the A band is occupied by thick filaments only.
- The abbreviation A comes from anisotropic {an-, not}, meaning that the protein
fibers in this region scatter light unevenly.
▪ H zone.
- This central region of the A band is lighter than the outer edges of the A band
because the H zone is occupied by thick filaments only.
- The H comes from helles, the German word for “clear.”
▪ M line.
- This band represents proteins that form the attachment site for thick filaments,
equivalent to the Z disk for the thin filaments.
- Each M line divides an A band in half. \M is the abbreviation for mittel, the German
word for “middle
▪ The proper alignment of filaments within a sarcomere is ensured by two proteins: titin
and nebulin
Voordelen van het kopen van samenvattingen bij Stuvia op een rij:
Verzekerd van kwaliteit door reviews
Stuvia-klanten hebben meer dan 700.000 samenvattingen beoordeeld. Zo weet je zeker dat je de beste documenten koopt!
Snel en makkelijk kopen
Je betaalt supersnel en eenmalig met iDeal, creditcard of Stuvia-tegoed voor de samenvatting. Zonder lidmaatschap.
Focus op de essentie
Samenvattingen worden geschreven voor en door anderen. Daarom zijn de samenvattingen altijd betrouwbaar en actueel. Zo kom je snel tot de kern!
Veelgestelde vragen
Wat krijg ik als ik dit document koop?
Je krijgt een PDF, die direct beschikbaar is na je aankoop. Het gekochte document is altijd, overal en oneindig toegankelijk via je profiel.
Tevredenheidsgarantie: hoe werkt dat?
Onze tevredenheidsgarantie zorgt ervoor dat je altijd een studiedocument vindt dat goed bij je past. Je vult een formulier in en onze klantenservice regelt de rest.
Van wie koop ik deze samenvatting?
Stuvia is een marktplaats, je koop dit document dus niet van ons, maar van verkoper surinachuckaree. Stuvia faciliteert de betaling aan de verkoper.
Zit ik meteen vast aan een abonnement?
Nee, je koopt alleen deze samenvatting voor €7,49. Je zit daarna nergens aan vast.
Is Stuvia te vertrouwen?
4,6 sterren op Google & Trustpilot (+1000 reviews)
Afgelopen 30 dagen zijn er 52510 samenvattingen verkocht
Opgericht in 2010, al 14 jaar dé plek om samenvattingen te kopen