Exam 3 Flashcards
what are the three types of muscle?
skelatal, cardiac, and smooth
What characteristics classify a skeletal muscle?
- striated
- voluntary
- require nervous system stimulation
What characteristics classify a cardiac muscle?
- only in heart
- striated
- can contract without nervous system stimulation
- involuntary
What characteristics classify a smooth muscle?
- in walls of hollow organs
- not striated
- involuntary
what are the functions of muscle?
- movement of bones/fluid
- maintaining posture
- heat generation
- protects organs, forms valves
- regulate elimination of materials
list the layers of skeletal muscle sheaths from external to internal
- epimysium
- perimysium
- endomysium
what is the epimysium?
dense irregular ct surrounding entire muscle
what is the perimysium?
fibrous ct surrounding fascicles
what is the endomysium?
fine areolar ct surrounding each muscle fiber
What are the 2 attachment points for bone?
- insertion (Moveable bone)
- origin (immovable bone)
How does direct attachment occur?
epimysium fused to periosteum of bone
what is indirect attachment
connective tissue wrappings extend beyond muscle at tendon or aponeurosis
What is the sarcolemma?
plasma membrane of a skeletal muscle fiber
what is the sarcoplasm?
cytoplasm of a skeletal muscle fiber
what are myofibrils?
- densely packed, rodlike parts of muscle fibers
- contains sarcomeres
- contains perfectly aligned repeating dark A band and light I bands
differentiate between H zone, M line, and Z disc
H zone: lighter region in midsection of A band where filaments don’t overlap
M line: line of protein myomesin bisects H zone
Z disc:coin shaped shet of proteins in midline of I band that anchors thin filaments and connects myofibrils
what is the smallest contractile unit of a muscle fiber?
sarcomere
what are sarcomeres composed of?
composed of thick and thin myofilaments made of contractile proteins
what is another name for thin filaments and what are their functions?
also called actin myofilaments, extend across I band and partway in A band, anchored to Z discs
what is another name for thick filaments and what are their functions?
also called myosin myofilaments, extend length of A band, connected at M line
what are thick filaments composed of?
the protein myosin, each composed of 2 heavy and 4 light polypeptide chains
What is the structure of a thin filament?
twisted double strand of fibrous protein F actin
What process does the sliding filament model of contraction describe
generation of force in muscles
According to the sliding filament model, where are the thick and thin filaments in a relaxed state?
overlap only at ends of A band
According to the sliding filament model, where are the thick and thin filaments during contraction?
the thin filaments slide past thick filaments, causing actin and myosin to overlap more
How do cross bridges form?
when myosin heads bind to actin
What must occur for a skeletal muscle to contract?
- an action potential must be generated in sarcolemma
- action potential must propagate along sarcolemma, briefly raising intracellular Ca2+ levels
what is a motor unit?
a motor neuron and all muscle fibers it supplies
What is the space between an axon ending and a single muscle fiber called?
neuromuscular junction
Where is the neuromuscular junction typically located on muscle fiber
situated midway along length of muscle fiber
what is the gel-filled space that separates the axon terminal and the muscle fiber
synaptic cleft
what neurotransmitter is found in synaptic vesicles?
acetylcholine (ACh)
Describe the events that occur at the neuromuscular junction
- nerve impulse arrives at axon terminal
- ACh released into synaptic cleft
- ACh diffuses across cleft and binds with receptors on sarcolemma
- action potential is generated
What are the three basic steps of action potential generation?
- end plate potential
- depolarization
- repolarization
What occurs during end plate potential (local depolarization)
- ACh binding opens chemically (ligand) gated ion channels
- simultaneous diffusion of Na+(in) and K+ (out)
- more Na+ diffuses in, reducing neg charge in sarcolemma
What occurs during depolarization
- end plate potential spreads to adjacent membrane areas
- voltage-gated NA+ channels open
- Na+ influx decreases membrane voltage toward critical voltage called threshold
- once threshold is reached, AP is initiated
What occurs during repolarization
- Na+ channels close and voltage-gated K+ channels open
- K+ outflow rapidly restores resting polarity
- muscle cannot be stimulated in refractory period until repolarization is complete
What is excitation-contraction coupling?
events that transmit AP along sarcolemma that lead to sliding of myofilaments
when does EC coupling occur?
during the latent period, the time between AP initiation and beginning of contraction
Describe the events of EC coupling
- AP propagated along sarcomere to T tubules
- voltage-sensitive proteins stimulate Ca2+ to release from SR
Describe what occurs at low intracellular Ca2+ concentration
- tropomyosin blocks active sites on actin
- myosin heads cannot attach to actin
- muscle fiber is relaxed
Describe what occurs at higher intracellular Ca2+ concentration
- Ca2+ binds to troponin
- troponin changes chape and moves tropomyosin away from myosin binding sites
- myosin heads bind to actin, causing sarcomere shortening and muscle contraction
- when nervous stimulation ceases, Ca2+ is pumped back into SR and contraction ends
What is Rigor mortis
- cross bridge detachment requires ATP
- 3-4 hours after death muscles begin to stiffen with weak rigidity
- at 12 hours post mortem, dying cells take in calcium forming cross bridges
- no ATP can be generated to break cross bridges
True or false, muscle cells have extensive amounts of ATP in storage
false, stored ATP is spent after about 5 seconds of intense exertion
what are the three ways to generate ATP in skeletal muscle fiber?
- immediate supply via phosphate transfer
- short term supply via glycolysis
- long term supply via aerobic cellular respiration
how is ATP generated in phosphate transfer?
- myokinase transfers phosphate from one ADP to another
- creatine kinase transfers phosphate from creatine phosphate to ADP
how is ATP generated in glycolysis?
- glucose is converted into 2 pyruvate molecules
- 2 ATP released per glucose molecule
- occurs in cytosol and does not require oxygen
What criteria categorizes muscle fibers?
type of contraction generated and primary means used for supplying ATP
What is the difference between oxidative and glycolytic fibers?
- oxidative fibers are fatigue resistant, use aerobic respiration, has extensive capillaries, and many mitochondria
- glycolytic fibers are fatigable, uses anaerobic respiration, and has less capillaries and mitochondria
What are the 3 types of skeletal muscle fibers?
- slow oxidative fibers (type 1)
- fast oxidative fibers (type 2a, intermediate)
- fast glycolytic fibers (type 2b, fast anaerobic)
What are the characteristics of slow oxidative fibers?
- contractions are slower and less powerful
- high endurance since ATP supplied aerobically
- half the diameter of other fibers, red in color due to myoglobin
What are the characteristics of fast oxidative fibers?
- contractions are fast and powerful
- primary aerobic respiration, but less delivery of oxygen
- intermediate size, light red in color
What are the characteristics of fast glycolytic fibers?
- contractions are fast and powerful
- contractions are brief (due to anaerobic ATP production)
- largest in size, white in color due to lack of myoglobin
True or false, a single muscle contains only one type of muscle fiber
false, a single muscle contains a mixture of fiber types
What kind of muscle fiber might a long distance runner have a lot of?
higher proportion of slow oxidative fibers in legs
Define Muscle Tension
the force generated when a muscle is stimulated to contract
Define Muscle Twitch
a brief contraction to a single stimulus
What are the three periods during a twitch?
- latent period
- contraction period
- relaxation period
What is treppe?
an increases in twitch tension when stimuli occur 10-20 times per second
What causes twitches to get stronger during treppe?
insufficient time to remove all ca2+ between twitches and increased heat improves efficiency
What is muscle tone?
resting tension in a muscle generated by involuntary stimulation
What is an isometric contraction?
increased tension while muscle length stays the same
What is an isotonic contraction?
muscle tension overcomes resistance resulting in movement
What is the length-tension relationship?
the tension a muscle produces depends on its length at the time of stimulation
What are the functions of the nervous system?
collects information, processes, evaluates, and initiates a response to information
What are the two factions of the afferent nervous system?
- somatic sensory system: detects stimuli we consciously perceive
- visceral sensory system: detects stimuli we typically don’t perceive
What are the two factions of the efferent nervous system?
- somatic motor system: sends voluntary signals to skeletal muscles
- autonomic motor system: sends involuntary commands to heart, smooth muscle, and glands (divides into sympathetic and parasympathetic)
List and define the general characteristics of neurons
- excitability: responds to stimulus
- conductivity: propagates electrical signal
- secretion: release neurotransmitters
- longevity: live throughout person’s lifetime
- amitotic: lose mitotic ability after fetal development
What part of the neuron is the nucleus found?
the cell body
what are dendrites?
short, unmyelinated processes branching off cell body that receive input
at what point does the axon attach to the cell body?
at the axon hillock
What is anterograde transport?
axon moves newly synthesize material from cell body toward synaptic knobs
what is retrograde transport?
axon moves used materials towards cell body for breakdown and recycling
what are the three structural classifications of neurons?
- multipolar (most common)
- bipolar
- uni polar
What are the three functional classifications of neurons?
- sensory neurons (mostly unipolar)
- motor neurons (multipolar)
- interneurons (multipolar)
what is a nerve?
a bundle of parallel axons in the PNS
what are the three connective tissue wrappings around a nerve?
epineurium, perineurium, endoneurium
what is a synapse?
the place where a neuron connects to another neuron or an effector
Describe characteristics of glial cells
- non-excitable support cells
- smaller than but far outnumber neurons
- capable of mitosis
What are the glial cells in the CNS?
astrocytes, ependymal cells, microglia, and oligodendrocytes
What are astrocytes?
- most abundant glial cell in CNS
- help form blood-brain barrier by wrapping feet around brain capillaries
- regulates tissue fluid composition
- occupy space of dead neurons
What are ependymal cells?
- line internal cavities of CNS
- helps produce CSF
- ciliated simple cuboidal or simple columnar cells
What are microglia?
- small, rare cells that wander CNS and replicate in infection
- phagocytic cells that engulf pathogens
what are oligodendrocytes?
large cells with slender extensions that wrap around axons to form myelin sheath
What types of glial cells are in the PNS?
satellite cells and neurolemmocytes (Schwann cells)
What are satellite cells?
- arranged around neuronal cell bodies in a ganglion
- electrically insulate and regulate the exchange of nutrients and wastes
what are schwann cells?
- elongated flat cells that ensheath PNS axons with myelin
what are gliomas
glial cell tumors
Describe the process of myelination in the PNS
- Schwann cell encircles neuron axon and wraps it in layers forming myelin sheath
- Schwann cell’s cytoplasm and nucleus are pushed to periphery forming neurilemma
- a Schwann cell can only myelinate 1 mm of axon so several are needed for one axon
Describe the process of myelination in the CNS
- one oligodendrocyte can only myelinate 1 mm of multiple axons each at multiple spots
- no neurilemma formed
How does multiple sclerosis impact the CNS
autoimmune disorder that causes oligodendrocytes to be attacked by immune cells
What is needed for PNS axons to regenerate and what may improve the chance of success
- regeneration possible if neuron cell body is still intact and enough neurilemma remains
- success more likely if amount of damage is less extensive
Name and describe the three types of channels
- leak channels: always open for continuous diffusion
- chemically gated channels: normally closed but open when neurotransmitter binds
- voltage gated channels: normally closed but open when membrane charge changes
Describe the characteristics of resting neurons
- ions are unevenly distributed across the plasma membrane due to the actions of pumps
- gated channels are closed in functional segments of cell
- charge difference of -70 mV across membrane
What is the most important factor in setting RMP
- K+ diffusion is most important factor
- diffuses out of cell due to concentration gradient
-diffusion is limited by electrical gradient
what role do sodium-potassium pumps play in maintaining RMP
- by pushing 3 positive charges out and only 2 in, pump contributes about -3 mV
- maintains concentration gradients for these ions
what are excitatory postsynaptic potentials
depolarizations caused by cation entry
what are inhibitory postsynaptic potentials
hyperpolarizations caused by cation exit or anion entry
where do summation of EPSPs and IPSPs occur
- occur at axon hillock
- the sum may or may not reach threshold membrane
- if threshold is reached at axon hillock, v-gated channels open and AP is generated
what is the difference between spatial and temporal summation?
- spatial summation occurs when multiple locations on a cell’s receptive regions receive neurotransmitters simultaneously
- temporal summation occurs when a single presynaptic neuron repeatedly releases neurotransmitters and produces multiple EPSPS within a short period of time
depolarization is a gain of positive charge as ____ enters the cell
Na+
repolarization is return to negative potential as ____ exits
K+
what is an absolute refractory period?
- no stimulus can initiate another action potential
- Na+ channels are open, then inactivated
What is a relative refractory period
- another action potential is possible (Na+ channels are reset)
- minimum stimulus strength is greater
- some K+ channels are still open so cell is slightly hyperpolarized
Describe continuous conduction
occurs on unmylelinated axons, charge opens voltage gated channels which allows charge to enter, which spreads to adjacent region and opens more channels
what is saltatory conduction
- occurs on myelinated axons, action potential occurs only at neurofibril nodes which is where axon’s voltage gated channels are concentrated
- after Na+ enters at a node it starts a rapid positive current down the inside of axon’s myelinated region
what type of conduction is faster?
saltatory` is much faster and uses less ATP
What is a graded potential?
- occur in neuron’s receptive region due to ion flow through chemically gated channels
- can be pos or neg changes in charge
- local, can only travel a short distance
what is an action potential
- occur in axon due to ion flow through voltage gated channels
- involved depolarization and repolarization
- all or none once threshold is reached
- propagate down entire axon to synaptic knob
How do axon thickness and myelination contribute to conduction speed
- thicker fibers conduct faster than thin ones
- myelinated fibers move much faster than unmyelinated one
what are the four chemical classes of neurotransmitters?
- acetylcholine
- biogenic amines
- amino acids
- neuropeptides
How do neurotransmitters differ by effect?
- excitatory transmitters cause EPSPs
- inhibitory transmitters cause IPSPs
What is the difference between direct and indirect neurotransmitters?
- direct transmitters bind to receptors that are chemically gated channels
- indirect transmitters bind to receptors that involve G-proteins and second messengers in order to cause postsynaptic potential
