Muscle and Nerve Flashcards
What are the muscle types?
- Skeletal
- Smooth
- Cardiac
What are the characteristics of skeletal muscle?
Strong and quick response
Voluntary
Striated muscle: fibrils composed of sarcomeres
Large long fibers with many peripheral nuclei
Fibers individually innervated
Fibers composed fibrils
Site of somatic innervation
What are the characteristics of cardiac muscle?
Strong and quick response
Involuntary
Short, thick, branching cells
Typically mono-nucleate
Striated muscle cells, sarcomere structurally identical to skeletal muscle
Cells attached end-to-end by intercalated disks (arrows)
Appear as particularly dark cross-striations in cardiac muscle (arrows)
Myocytes not individually innervated, no somatic innervation
What are the characteristics of smooth muscle?
Weak and slow response
Involuntary
Non-striated muscle
Fusiform, mono-nucleated cells surrounded by an external lamina.
Located in walls of all hollow organs – digestive tract, blood vessels, urinary bladder, bronchial tree
Label the parts
What are myofibers made of?
Myofibrils
What are myofibrils made of?
Myofilaments
What are myofilaments made of?
Repeating functional units called sacromeres
Sacromeres contain what two filaments?
Thick filaments: Myosin II
Thin filaments: Actin
Label the parts
Label the parts
MF, myofiber
MNF, myofiber nuclei
N, nucleus
C, capillary
What lines define the sacromere?
The Z-Lines
What is the Z-Line made of?
α-actinin - it anchors actin filaments.
What is the I band made of?
Primarily thin filaments and titin, a large protein that prevents over-stretching of sarcomere.
Label the parts
What is the A band made of?
Thin filaments (actin) and thick filaments (myosin)
What is the H band made of?
Only thick filaments (myosin)
What does the M band do?
It is the anchor for the thick myosin filaments
Label the parts
My, myofibrils
M, myofibers
E, endomysium
N, nucleus
What two binding sites are on the Myosin head?
ATP and Actin
What is troponin?
A complex of three proteins that ar bound to the tropomyosin molecule.
What are the three proteins in the troponin complex and what do they do?
Troponin I, C, and T
Troponin C: binds Ca2+ and is found only in striated muscle
Troponin T: binds the complex to tropomyosin.
Troponin I: inhibits the binding of myosin to actin
What are the two main part of the nervous system?
CNS: Central Nervous System
PNS: Peripheral Nervous System
What makes up the CNS
Brain and Spinal Cord
What makes up the PNS?
Nerves (cranial and spinal)
Ganglia
Plexus (enteric)
What are the three functions of the nervous system?
Sensory: Afferent neurons and receptors
Integrative: Interneurons - neurons that connect other neurons.
Motor: Efferent motor nuerons (effect muscles)
What are the three parts of the PNS?
Somatic: sensory neurons as well as voluntary motor neurons.
Autonomic: sensory as well as involuntary motor neurons.
Enteric (“brain of the gut”): sensory neurons - associated with entire GI tract, motor neurons - effectors in GI tract (e.g., smooth muscle, glands). This regulates GI activies, independent of CNS
What are the two divisions of the autonomic PNS?
Sympathetic and Parasympathetic
What is a ganglion?
A group of nerve cell bodies outside of the CNS
What connects to a ganglion and what it is’t purpose?
A preganglionic fiber connects from the CNS to the ganglion and a post ganglionic fiber connects from the ganglion to the effector.
The ganglion functions as a junction box for connecting the two neuron ANS.
What type of ganglia are in the sympathetic ANS?
Chain ganglia and prevertebral ganglia
What type of ganglia are in the parasympathetic ANS?
Parasympathetic ganglia
What type of ganglia are in the gut region?
Enteric ganglia
What is the difference between a neurotransmitter and a neurohormone?
Neurotransmitters are released into the synaptic cleft and neurohormones are released into the blood.
What are the parts of a neuron cell body?
Cytoplasm - neurofilaments (extend into cell processes)
Organelles - nucleus, rER (Nissl bodies or substance)
Plasma membrane - spines (small projections)
How many axons are there per cell body
One: Has an output function
How many dendrites per cell body?
Many: Has an input function
Label the parts
What organelles does a neuron cell body contain?
All the usual eukaryotic cell organelles:
nucleus, Golgi, mitochondria, rER, sER, lysosomes, and lipofuscin.
What is another name for rER in neurons?
Nissl substance or Nissl bodies
What is another name for intermediete filaments in neurons?
Neurofilaments
What is this?
Neuron rER
What is this and what are the arrows pointing to?
Axon crosscut and longitudinal section.
MT = Microtubule
NF = Neurofilaments
Label the parts
What is anterograde transport
Moves cargo from soma (cell body) to periphery
(from MT- to MT+ end)
What is retrograde transport?
Moves cargo from axon and dendrites (periphery) to soma
from MT+ end to MT- end
There are two types of transport motors:
What are they called?
Which way do the transport cargo?
How do they get energy to transport?
Kinesin family (to + end)
Dynein family (to – end)
hydrolyse ATP
What is slow transport?
Anterograde transport of cytoskeleton proteins
What is fast transport?
Anterograde and retrograde transport of vesicles (neurotransmitters), mitochondria, other cargo along microtubules, requires ATP
What are the support cells of the nervous system called?
Neuroglia
What are the characteristics of the Neuroglia?
Much more numerous than neurons
Generally smaller cell size than neurons
Make up about half the volume of nervous tissue
Capable of cell division
Six main types of cells
What are the types of neuralgia in the CNS and what do they do?
Astrocytes – large, numerous cells with multiple processes
Oligodendrocytes – smaller, less numerous cells with fewer processes
Microglia – small cells with thin processes with spikelike projections
Ependymal cell – cuboidal to columnar layer of cells with cilia and microvilli
What are the types of neuralgia in the PNS and what do they do?
Schwann cells – cells that myelinate or enclose unmyelinated axons
Satellite cells – surround cell bodies in ganglia including enteric ganglia
What type of junctions are in the epithelium of the blood / brain barrier?
tight junctions
What kind of molecules can cross the blood / brain barrier?
Lipid soluble and gases - they cross by diffusion.
How do other substances cross the blood / brain barrier epithelium?
My receptor mediated endocytosis.
What is this?
An unmylenated axon crosscut
What is the myelin sheath made of?
Multiple concentric layers of Schwann cell plasma membrane
What about the schwann cell plasma membrane improves its insulator function?
It is 80% lipids
What components does the schwann cell secrete?
External Basal Lamina
What is this and what is labeled?
Cross section of a mylenated axon.
BL = Basal Lamina
Mit = Mitochondria
MT = Microtubules
What are two types of afferent sensory receptors?
Pacinian corpuscle – Large (~1mm) pressure and vibration receptors associated with myelinated axon.
Meissner’s corpuscles are long (~150 µm), fine touch frequency receptors in dermal papillae that are associated with myelinated axons
What is this?
A pacian corpuscle
What is this?
Meissners Corpuscle
What are the steps of motor innervation?
- Nerve impulse arrives at the neuromuscular junction
- Acetylcholine (ACh) released from nerve terminal binds to nicotinic ACh receptors on sarcolemma
- Opens Na+ channels, leading to depolarization of sarcolemma and initiation of action potential
- Action potentials spread across membrane and into T-tubules
- Activation of voltage-sensor proteins
- Ca2+ channels open in adjacent terminal cisternae of the sarcoplasmic reticulum
- Ca2+ is released from the sarcoplasmic reticulum
- Ca2+ binds to TnC of the troponin complex
- Contraction cycle is initiated and Ca2+ is returned to the sarcoplasmic reticulum
What is the sacrolema?
The cell membrane of a muscle cell. Surrounds the muscle fiber made of myofilaments and myofibrils.
What are the invaginations in the sacrolema of a muscle fiber (cell)?
They are called T-tubules TT
What is the smooth reticulum called that abuts the TT?
It is called Sarcoplasmic reticulum.
What is a triad made of?
1 TT and 2 SR
How many triads per sacromere?
2
What happens at each step?
What are the events of striated muscle contraction?
- Nerve impulse travels down axon
- Acetylcholine released into synaptic cleft, depolarizing local sarcolemma
- Voltage gated Na+ channels open, Na+ enters muscle cell
- Depolarization spreads over entire sarcolemma and into T-tubule
- Voltage sensor proteins in T-tubules change conformation
- Ca2+ release channels in sarcoplasmic reticulum are activated by conformation change
- Ca2+ is rapidly released from sarcoplasmic reticulum into sarcoplasm
- Ca2+ binds to the TnC subunit of troponin (contraction cycle is initiated)
- ATP binds to myosin releasing it from actin
- Myosin heads break down ATP into ADP and Pi
- Bending of the ADP-Pi-myosin head to an actin binding site that has been opened by Ca2+ binding to TnC
- Release Pi to form bind stronger to the actin and allow the myosin to spring back to the unbent position
- Power stroke is the return of the myosin head to its unbent position forcing movement of the thin filaments
- ATP binds to myosin releasing it from actin to then repeat the cycle
- Ca2+ is sequestered into the sarcoplasmic reticulum
What anchores thin filaments in smooth muscle?
Dense bodies
What are the events of smooth muscle contraction?
- Contraction can be initiated by mechanical, electrical, and chemical stimuli (all result in increased intracellular Ca2+ )
- Increase in free intracellular calcium can result from either increased flux of calcium into the cell through calcium channels or by release of calcium from internal stores (e.g., sarcoplasmic reticulum).
- Free Ca2+ binds to a special Ca2+ binding protein (calmodulin) … Ca2+ -calmodulin complex activates myosin light chain kinase (MLCK) that phosphorylates myosin light chains in the presence of ATP
- Myosin light chain phosphorylation leads to cross-bridge formation between the myosin and the actin, leading to contraction
Contrast smooth muscle and striated (cardiac / skeletal) muscle contraction.
- Contraction of skeletal muscle is regulated by Ca2+ binding to TnC, which opens the myosin binding groove on actin.
- Contraction of smooth muscle is regulated by Ca2+ binding to calmodulin, which activates MLCK
