Nerve & Muscle Flashcards
What is a Neuromuscular junction?
A junction between terminal branch of the nerve fiber and muscle fiber.
What innervates skeletal nerve fibers?
Motor nerve fibers
What is axon terminal?
Terminal branches of nerve fiber
Axon terminals contain?
1) Mitochondria
2) Synaptic vesicles
1)Presynaptic membrane?
2)Postsynaptic membrane?
3) Synaptic cleft?
1) Membrane of the nerve ending
2) Membrane of the muscle fiber
3) Space between the presynaptic and postsynaptic membrane
Postsynaptic membrane contains what receptor?
Nicotinic acetylcholine receptor
What is a subneural cleft?
Number of folds found on the postsynaptic membrane
Neuromuscular transmission?
Transfer of information from the motor nerve ending to the muscle fiber through the NMJ
Events that occur during neuromuscular transmission
1) Release of acetylcholine
2) Action of acetylcholine
3) Development of endplate potential
4) Development of miniature endplate potential
5) Destruction of acetylcholine
The basal lamina of synaptic cleft contains what?
Acetylcholinesterase, an enzyme that destroys acetylcholine
Sequence of events during synaptic transmission
Action potential reaches the presynaptic axon terminal this causes the voltage gated calcium channels to open.
Calcium ions from the extracellular fluid enter the axon terminals. This influx of calcium ions causes the synaptic vesicles to rupture releasing the neurotransmitter into the presynaptic terminal membrane by a process known as exocytosis.
This neurotransmitter (acetylcholine) diffuses through the presynaptic membrane and the synaptic cleft into the postsynaptic membrane. In the postsynaptic membrane there are protein receptors known as nicotinic acetylcholine receptor.
The neurotransmitter now in the postsynaptic membrane binds with this protein receptor to form a neurotransmitter-receptor complex.
This neurotransmitter-receptor complex then causes the production of a non-propagated excitatory postsynaptic potential.
The neurotransmitter-receptor complex causes the ligand-gated sodium channel to open. This leads to an influx of sodium ion into the body of the postsynaptic neuron from the extracellular fluid.
Since the sodium ion are positively charged, resting membrane potential in the cell body is slightly altered and mild depolarisation occurs.
This mild depolarisation is called the Excitatory Postsynaptic Potential (EPSP)
The mild depolarisation of the resting membrane potential is?
Excitatory Postsynaptic Potential (EPSP)
Neurotransmitter?
Is q chemical substance that acts as a mediator for the transmission of nerve impulses from one neuron to another or from a neuron to a muscle fiber.
Criteria for neurotransmitter
1) Must be found in a neuron
2) Must be produced by a neuron
3) Must be released by a neuron
4) After release, must act on a target area and have produce biological effect
4) After action, must be destroyed or inactivated.
Classification of neurotransmitter
1) Based on chemical nature:
a. Amino acids
b. Amines
c. Others
2) Based on function
a. Excitatory NT
b. Inhibitory NT
Amino acid NT
Involved in fast transmission and can be excitatory or inhibitory in action é.g
GABA
Glycine
Glutamate (Glutamic acid)
Aspartate (Aspartic acid)
Amine NT
These are modified amino acids.
They are slow in synaptic transmission and can be inhibitory or excitatory.
É.g
Noradrenaline
Adrenaline
Dopamine
Serotonin
Histamine
Others NT
They are neither amino acids nor are they amines, é.g acetylcholine, NO2
Formed by choline and acetyl coenzyme A in the presence of the enzyme choline acetyltransferase
Excitatory NT
Chemical substances responsible for the conduction of AP (impulse) from presynaptic neuron to postsynaptic neuron.
NT released from Presynaptic membrane creates development of AP in Postsynaptic membrane?
a) True
b) False
False
What is the effect of the NT released from the presynaptic membrane?
The NT released by the presynaptic membrane causes slight changes in the RMP i.e mild depolarisation of the RMP by the opening of Na ion channels in the postsynaptic membrane and the influx of Na ion from the ECF.
Examples of Excitatory NT
1) Acetylcholine
2) Noradrenaline
3) Histamine
4) Glutamate (Glutamic acid)
5) Aspartate (aspartic acid)
Inhibitory NT
NT that inhibit the conduction of impulses from the presynaptic neuron to the postsynaptic neuron.
Effect of release of inhibitory NT
When released due to AP, causes the opening of Potassium channels which leads to the efflux of potassium ions and AP is not generated in the postsynaptic neuron. This leads to hyperdepolarization called Inhibitory Postsynaptic Potential (IPSP).
4 mechanisms for inactivating NT after action
1) NT diffuses out of the synaptic cleft to an area where it has no action
2) Destroyed/inactivated by a specific enzyme, acetylcholinesterase.
3) Engulfed and removed by astrocytes (macrophages)
4) Removed by reuptake into the axon terminal.
Reuptake
Process by which NT is taken back from the synaptic cleft into the axon terminal after execution of action
How long does acetylcholine stay before it’s destroyed?
1mili second
Is muscle contraction a chemical event?
False.
Mechanical/physical event.
Changes that occur in the muscle:
Chemical changes
Electrical changes
Thermal changes
Physical changes
Histological changes
The condition of the muscle during RMP
Polarised state.
RMP of skeletal muscle
-90mV
RMP for nerve fibers
-70mV
What is the structural and functional unit of the nervous system?
Neuron
How is the neuron different from other cells of the body?
- Neurons have branches and processes called axon and dendrites.
- Neurons lack centrosome and so can’t undergo cell division.
Where can you find unipolar neuron?
Only in embryonic stage in humans
Unipolar neuron
The neuron has a single pole and both axon and dendrites arise from the single pole
Bipolar neuron
Neuron has two poles, axon arises from one and dendrites from the other
Multipolar neuron
Neuron has multiple poles, one of the poles give rise to axon and the rest give rise to dendrites.
What’s the collective name for axon and dendrites?
Nerve fibers
Describe Nissi bodies
They are also called nissi granules. They are basophilic granules found in the neuroplasm of the neuron. They aren’t found in the axon and hillock but they’re present in the dendrites and soma.s
What are tigroid substances?
Nissi bodies are referred to as tigroid substances because they’re responsible for the tigroid/spotted appearance of soma after suitable staining (basic dye).
How are neurons classified?
- Based on the number of poles present
- Based on function
- Depending on length of axon
Length of longest axon?
1m
Function of axon
Transmits impulses away from the nerve cell body
Function of dendrites
Transmit impulses towards the nerve cell body
Myelin sheath
Thick lipoprotein that insulates myelinated nerve fiber
What is responsible for the white colour of nerve fibers
Myelin sheath
Myelin sheath around the axon in PNS is formed by
Schwann cells
Saltatory Conduction
This is the jumping of impulse from one node of Ranvier to another in myelinated fibers
Function of myelin sheath
- Faster conduction of impulses
- Prevents stimulation of neighbouring nerve fibers by restricting nerve impulses within a single nerve fiber due to its high insulating capacity
Properties of nerve fiber
A - Adaptation
R- Refractive period
I - Infatigability
C - Conductivity
É - Excitability
S - Summation
Human body has ____ muscles
More than 600
Muscles are classified into ___ based on different factors
3
Factors by which muscles are classified
- Based on presence or absence of striation
- Depending on control
- Depending on the situation
Examples of striated muscle
- Cardiac muscles
- Skeletal muscles
Cardiac muscles are innervated by
Autonomic nerves
How many % of body mass does the skeletal muscle make up?
40-50%
Characteristics of skeletal muscle
- Striated
- Voluntary muscles
- Innervated by somatic nerves
- Unbranched
- Cylindrical
- Multi-nucleated
- 1-4cm in length
- Diameter of 10 - 100 micrometer
- Fatigue & tetanus are possible
- Presence of sarcomere and troponin
- NMJ is well defined
- Speed of contraction is fast
- Myofibril is present
Troponin
Type of protein present in skeletal and cardiac muscles. Not normally found in blood, but if found in blood stream it indicates damaged heart muscles.
What is also called the basic contractile unit?
Sarcomere
What is the sarcomere
Sarcomere is the basic and structural unit of skeletal & cardiac muscle
Characteristics of cardiac muscles
- Striated
- Mononuclear
- Innervated by autonomic nerves
- Branched
- Fatigue & tetanus are not possible
- Ca supply is from sarcoplasmic reticulum
- Troponin and sarcomere is present
- NMJ is not well-defined
- Speed of contraction is intermediate
- Trigger of contraction = calcium + troponin
- Depolarisation is spontaneous
- Length 80 - 100 micrometer
- Diameter is 15 - 20 microns
- T - tubles are short and broad
- Sarcotubular system is well developed
- Myofibrils are present
Characteristics of smooth muscles
- Non-striated
- Spindle shaped
- Unbranched
- Length is 50 - 200 microns
- Diameter is 2 - 5 microns
- Absence of troponin and sarcomere
- Source of calcium is ECF
- Trigger of contraction = Calcium + calmodulin
- NMJ is not well developed
- Speed of contraction is low
- Depolarisation occurs spontaneously
- Innervated by autonomic nerves
- Fatigue is not possible
- Tetanus is possible
- One nucleus
Muscle cells are called ____?
Myocytes
Muscle mass
Is made up of a large number of individual muscle cells called myocytes
The membrane of the muscle is called?
Sarcolemma
Structures embedded in the sarcoplasm are:
- Nuclei
- Sarcoplasmic reticulum
- Lysosomes
- Ribosomes
- Golgi apparatus
- Mitochondria
- Glycogen droplets
- Myofibrils
- Occasional lipid droplets
Myofibrils
Fine parallel filaments present in the sarcoplasm of the muscle cell. They run through the entire muscle fibers.
Myofilaments are made up of ?
- Actin myofilaments
- Myosin myofilaments
Actin myofilament
- Has a diameter of 20Amstrong
- Thin filaments
- Has a length of 1 micrometer.
