HISTOLOGY - Skeletal Muscle & Nerve Tissue Lecture Flashcards
What are the three muscle types
Skeletal – striated and voluntary Cardiac – striated, involuntary Smooth – non striated and involuntary
Describe the following:
1) Myocytes
2) Endomysium
3) Fascicles
4) Perimysium
5) Epimysium
1) mytocytes - skeletal mucles cells (aka myofiber/muscle fibers)
2) endomysium - membrane that seperate monocytes
3) fascicles - groups of myocytes
4) perimysium - membrane that seperates fascicles
5) epimysium - membrane that surrounds the entire muscle
From interior to exterior = 1 –> 2 –> 3 –> 4 –> 5
a -Epimysium
b -Perimysium
c - Endomysium
d -Muscle fiber in middle of fascicle
A - transverse
B - longitudinal
What is a sarcomere?
The smallest unit of a muscle
The contractile unit of muscle made of actin and myosin
What are the functions of the following sarcomere structural units?
1) Z-line
2) I-band
3) M-line
4) H-zone
5) A-band
Z-line = the anchor site for actin (thin) microfilaments
I-band = an area containing only actin (thin) microfilaments
M-line = anchor site for thick myosin filaments
H-zone = contains only thick myosin filaments
A-band = overlap of thick and thin filaments
Where does a sarcomere extend from?
One Z-line to the next Z-line
a - Z-line
b -myosin filament (thick)
c - actin filament (thin)
d - I-band
e - A band
F - I-band
g - H-zone
Skeletal muscle cells are…
multinucleated (located on peripohery of cell) and fused together from myoblasts
What is a sarcolemma? What are transverse tubules?
- a plasma membrane surrounding a skeletal muscle cell
- invaginations of the sarcolemma that play a key role in continuing and action potential to the sarcoplasmic reticulum. Also play key role in moving calcium
What is sarcoplasmic reticulum?
A specialized type of endoplasmic reticulum in muscle cells that functions primarily to store Ca2+ ions for muscle contraction — reabsorbs Ca2+ once used
What are Terminal Cisternae?
The distal ends of the SR that release Ca2+, triggering muscle contraction
Explain the Sliding Filament Mechanism during contraction?
1) During contraction, thin and thick filaments slide past one another bringing the Z-lines closer together
2) There is no change in the size of the actin or myosin filaments during this process — ONLY THE DEGREE OF OVERLAP
Explain the regulatory proteins 1) Tryptomyosin and 2) Tryponin and what they do
Tryptomyosin - lies in groove between actin filaments and muscler tissue, resposible for blocking cross-bridge sites ON ACTIN during relaxation, preventing contraction (CONTRACTION INHIBITOR)
Troponin
Troponin T - Binds troponin complex to tryptomyosin
Troponin I - inhibnits the binding of myosin heads with actin
Troponin C - Binds to Ca2+, revealing the cross-bridge sites on actimnm via conformational change in Troponin I
Why are myosin heads important for muscle contraction?
They have ATP binding sites that start contraction and a binding site for attaching to actin cross-bridge sites
What are the steps of muscle contraction?
1) Neuron gives signal to contract
2) ATP becomes bound to mysoin head and is hydrolyzed
3) Myosin head extends to attached to actin cross-bridge site once calcium reveals the sites (see calcium importance steps
4) “Powerstroke” action is initiated and the myosin head pulls the actin toward the m-line, shortening the distance between the z-lines
5) ADP released during process, another is needed to either continue contraction, increase contraction or release contraction
Explain the importance of calcium in muscle contraction?
Ca2+ controls muscle contraction
1) Ca2+ is held in SR and is released following signal from neuron
2) Signal travels down the sarcolemma and the T-tubules release the Ca2+
3) Ca2+ binds to troponin C in the presence of enough ATP, which induces confirmational change that movews the tryptomyosin, exposing the cross-bridge sites
How are muscle fibers catagorized?
1) Type of contraction (power, speed, duration)
2) ATP supply (anaerobic, aerobic)
Explain:
Type I Fibers
Type IIa Fibers
Type IIb Fibers
Type I (slow, oxidative) —- marathon runners
-Very red due to myoglobin, many mitochondria, slow ATPase, contract slowly and for long periods without fatigue
Type IIa (oxidative-glycolytic)
-Primarily aerobic, most abundant in body, some mitochiondria, intermediate ATPase, PROVIDES POWER
Type IIb (Fast glycolytic) —- weight lifters
-Primarily anaerobic, Fast ATPase, fatigue quickly, few myoglobin and mitochondria
Whata re the name of neurons in CNS vs PNS
CNS = nuclei
PNS = ganglia
Whata re the two type of cells in nerve tissue?
Neurons - comnduct electrical impulses
neuroglia - neuron supporting cells (myelinate, protect)
What is Nissl Substance?
A substance consiting of many granular endoplasmic reticulum and ribosomes which strongly adhere to stains in histology
Many are present in neurons becauses they need to make a lot of protein/neurotransmitters in order to span through the body
What are the basic components of a nerve cell?
Cell body - processess electical info
Axon - transmits electrical info/carry signal away fromc cell body
Dendrites - recieve signal/carries toward cell body
Synapse - point where electric signals are transmitted from an axon terminal to an effector cell
Schwann cells - myelinate the axons in the PNS
What are the three anatomical classificatiomns of neurons?
1) Multipolar - one axon, many dendrites (MOST COMMON)
2) Bipolar - one axon, one dendrite (Retina)
3) Unipolar - one cell process with a branch thay has one axon and one dendrite (Dorsal Root Ganglia)
What are satellite cells
Cells that cover neurons and are responsible for maintaining and regulating the environmenta around the neuron
What is the importance of myelin sheaths and the process of mylination?
Improves speed of signal transmission via Nodes of Ranvier (hops from node to node)
Oligodendrocytes (CNS) or Schwann cells (PNS) wrap around axons repeatedly until they form a myelin membrane
Axons can be be myelinated OR unmyelinated
What are the three important structures of a peripheral nerve cell?
Endoneurium - CT between/surounding axons (COVERS AXONS)
Perineurium - CT surrounding clusters of axons, forming fascicles (COVERS FASCICLES)
Epineurium - CT surrounding several nerve fascicles (COVERS ENTIRE NERVE)
A - Perinurium
B - Epineurium
C - Fascicle
What is this?
A X-section of a peripheral nerve cell
What are the 4 essential parts of a the chemical synapse?
1) Presynaptic knob (axon terminal) — Has vesicles that release neurotransmitter in synaptic cleft
2) Synaptic cleft - space between neurons which continues signal via neurotransmitters
3) Presynaptic membrane
4) Postsynaptic membrame
Explain what happens are the neuromuscular junction that stimulates muscle contraction?
1) Nerve impulse stimulates release of Acetylcholine (ACh) into synaptic cleft
2) ACh stimulates sarcolemma which excites the muscle and iscarried down to T-tubules to initiate contraction (Ca2+ release)
3) Enzymes break down ACh to limit action to 1 muscle twitch
KEY: every skeletal muscle cell has an axon terminal but not all cardiac or smooth muscle cell is directly innervated
What are muscle spindle receptors?
Monitor changes in length, rate of change (Stretch and speed)
Prevents you from overstretching the muscle and contracting too fast
SENDS REFLEX signal to spinal cord saying tnot to stretch any further
How many schwann cells and oligodendrocytes are there comopared to neurons?
Schwann cells - one cell to one neuron
Oligodendrocytes - one cell to many neurons
What are the two types of Muscle Spindle Receptors?
1) Intrafusal Fibers - inside muscle spindle
a) Nuclear Bag Fibers – wrapped at center by type Ia nerve fibers, monitor change in length and degree of tension
b) Nuclear chain fibers – wrapped at ends by Type II nerve fibers, detect static muscle length
2) Extrafusal Fibers - outside muscle spindle (alpha motor fibers)
What are golgi tendon organs?
Located in at the origins and insertions of muscle tendons, they are proprioreceptive sensory organs that sense changes in muscle tension
When you lift weights, golgi tells how much you are exerting and will prevent further contraction to prevent injury
