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What is the threshold potential at which an action potential is generated?
What substance is released by presynaptic neurons to communicate with postsynaptic neurons?
neurotransmitter
Sensory nerves control the activity of the body by controlling muscle and gland functions.
False
What is the role of acetylcholinesterase in neurotransmission at the neuromuscular junction?
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Which type of receptors are characterized at the neuromuscular junction?
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Match the following neurotransmitters with their functions:
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What type of synapse depolarizes the postsynaptic membrane?
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What are the two basic forms of electrical signals in neurons?
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Action potentials decrease in strength as they travel along the axon.
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What ion influx causes the depolarization during an action potential?
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What is the refractory period?
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What is the resting membrane potential of a muscle fiber?
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What neurotransmitter is released at the neuromuscular junction?
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Acetylcholine acts as an excitatory neurotransmitter at the neuromuscular junction.
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What is the role of acetylcholinesterase (AChE) at the neuromuscular junction?
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Which of the following actions can lead to prolonged muscle contraction?
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What is the function of the myelin sheath in neurons?
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What is the function of nodes of Ranvier?
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Myasthenia gravis is characterized by an overactivity of acetylcholine receptors.
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ACh must be cleared from the synaptic cleft to prevent constant muscle _____ .
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What happens when an action potential reaches the axon terminal?
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What type of junction is formed between motor neurons and skeletal muscle fibers?
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What occurs when action potentials travel down motor neurons?
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Where are the cell bodies of motor neurons located?
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What is the primary outcome of the action potentials in the context of the neuromuscular junction?
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What happens to the myelin sheath of motor neurons at the motor end plate?
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What term describes the fine branches of motor neurons that form synaptic connections with muscle fibers?
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What happens to graded potentials over short distances?
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What is the significance of reaching the threshold voltage in graded potentials?
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What is the primary change in membrane potential referred to as depolarization?
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What defines the difference between graded potentials and action potentials?
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How is the magnitude of a graded potential determined?
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What initiates the nerve impulse that moves down the axon?
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What is the resting membrane potential typically measured at?
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What effect does acetylcholine binding to receptors have on the postsynaptic membrane?
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Which statement accurately describes the role of acetylcholine at excitatory synapses?
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What effect does binding of neurotransmitters to their receptors generally have on the postsynaptic membrane?
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What is the primary consequence of the neurotransmitter's effect at an excitatory synapse?
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Which component of the synapse is primarily responsible for releasing neurotransmitters?
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Which condition must be satisfied for an action potential to be initiated in the postsynaptic neuron?
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What type of synapses would typically employ neurotransmitters such as GABA?
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What effect does hyperpolarization have on the likelihood of an action potential occurring?
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Which component is responsible for increasing the speed of action potential propagation in myelinated neurons?
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What is the primary role of the myelin sheath in neuronal function?
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How does the binding of neurotransmitters to GABA receptors affect the postsynaptic membrane?
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Which of the following occurs at the nodes of Ranvier in myelinated neurons?
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What is the primary composition of the cytoplasm in muscle fibers?
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What occurs when the membrane potential is at -70 mV?
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How does the arrangement of the endoplasmic reticulum change in muscle fibers?
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What role does chloride (Cl-) play in synaptic transmission when GABA receptors are activated?
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What is the significance of the threshold potential in neuronal action potentials?
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Study Notes
Organization of the Nervous System
- The nervous system is comprised of the central nervous system (CNS) and peripheral nervous system (PNS)
- The CNS is made up of the brain and spinal cord
- The PNS is made up of sensory nerves (afferent nerves) and motor nerves (efferent nerves)
- The PNS further splits into the somatic nervous system and autonomic nervous system
- The somatic nervous system controls skeletal muscle
- The autonomic nervous system controls smooth muscle, cardiac muscle, exocrine glands and some endocrine glands.
The Synapse
- The synapse is the junction between one neurone and the next cell
- It is a specialised structure where an electrical impulse is converted to a chemical signal for communication.
Neurotransmitters
- Neurotransmitters are typically small, rapid-acting molecules
- Examples are acetylcholine, dopamine, glutamate, noradrenaline, GABA
- Neurons usually release one type of major neurotransmitter.
Excitatory Synapses
- Neurotransmitters at excitatory synapses depolarize the postsynaptic membrane
- Acetylcholine (ACh) is an example of an excitatory neurotransmitter
- Binding of ACh to receptors on the postsynaptic cell opens ligand-gated sodium channels
- The influx of Na+ ions reduces the membrane potential
- When the depolarization reaches a threshold, an action potential is generated.
Inhibitory Synapses
- Neurotransmitters at inhibitory synapses hyperpolarize the postsynaptic membrane
- GABA (gamma aminobutyric acid) is an example of an inhibitory neurotransmitter
- Binding of GABA to receptors on the postsynaptic neuron opens ligand-gated chloride channels
- The influx of Cl- ions increase the membrane potential.
Action Potential
- An action potential is a brief, rapid, large change in membrane potential
- It involves a small portion of the excitable cell membrane
- They do not decrease in strength as they travel.
- Action potentials are all-or-none meaning the strength of the stimulus is encoded in the frequency of the action potentials it generates.
Myelination
- The axons of most neurons are encased in a fatty sheath called the myelin sheath
- Myelin functions as an “electrical insulator”, restricting current flow
- The sheath is formed by Schwann cells in the PNS and oligodendrocytes in the CNS.
- The action potential jumps from one node to the next, this is called saltatory conduction, resulting in faster propagation.
Categorization of Muscle Types
- Muscle cytoplasm is mostly actin and myosin filaments
- Nuclei and organelles are pushed to the edge of the cell
- The sarcoplasmic reticulum is arranged as a system of tubes around groups of myofibrils.
Peripheral Nervous System and Nerve-Muscle Junctions
- The PNS's "output" consists of motor neurons that travel from the CNS to effectors, which carry out actions.
- Somatic motor nerves control skeletal muscle, while autonomic nerves control cardiac or smooth muscle.
- Neuromuscular junctions (NMJs) are the points where somatic motor nerves meet skeletal muscles.
Motor Neuron Innervation of Skeletal Muscle Fibers
- Motor neuron cell bodies reside in the ventral horn of the spinal cord.
- Motor neurons have thick, myelinated axons (somatic efferent fibers).
- Motor neurons lose their myelin sheath at the motor end plate.
The Neuromuscular Junction
- Motor neurons and skeletal muscle fibers are chemically connected at the NMJ.
- Action potentials traveling down the motor neuron result in skeletal muscle fiber contraction.
- Signals are transmitted between the nerve terminal and the muscle fiber via the neurotransmitter acetylcholine (ACh).
Action Potential
- When an action potential reaches the axon terminal, vesicles filled with ACh release their contents onto the postsynaptic membrane.
End Plate Potential
- The muscle fiber has a resting membrane potential of -80mV.
- The influx of sodium ions reduces this potential, creating an end plate potential through depolarization.
- The depolarizing effect of the end plate potential (EPP) opens voltage-gated sodium channels, triggering an action potential in the fiber.
Nicotinic Receptors
- Nicotinic ACh receptors mediate rapid responses.
- They are found at the neuromuscular junctions of skeletal muscles, autonomic nervous system ganglia, and the central nervous system.
Acetylcholinesterase (AChE)
- AChE breaks down ACh in the synaptic cleft, preventing continuous muscle stimulation.
Neuromuscular Blocking Agents
- These agents inhibit the binding of ACh to nicotinic acetylcholine receptors (nAChRs).
- Curare inhibits the binding of ACh to nAChRs, leading to skeletal muscle paralysis.
- Botulinum toxin blocks the release of ACh, preventing muscle response to nerve impulses.
Myasthenia Gravis
- An autoimmune disease where the immune system attacks ACh receptors at the motor end plate.
- Results in muscle weakness and fatigue.
- Treatment involves AChE inhibitors or immunosuppressants.
Somatic Nervous System
- Originates in the ventral horn of the spinal cord (for most muscles) or cranial nerves (for head muscles).
- One neuron travels from the CNS to effector organs.
- Targets skeletal muscles.
- Only uses acetylcholine as a neurotransmitter.
- Typically controls muscle stimulation, but inhibition can occur centrally.
Acetylcholine (ACh)
- A neurotransmitter produced in the presynaptic terminal of the motor neuron by choline acetyltransferase.
- It is released into the synapse, binding to receptors on the postsynaptic membrane.
- Once bound, ACh triggers the opening of ion channels, generating an action potential.
- ACh is quickly broken down by acetylcholinesterase (AChE) to prevent constant muscle stimulation.
Important Terms
- Effector: Any organ that carries out a response to a stimulus.
- Motor Neuron: A nerve cell that carries signals from the CNS to muscles or glands.
- Neuromuscular Junction (NMJ): The specialized synapse where a motor neuron communicates with a muscle fiber.
- Synaptic Cleft: The space between the presynaptic and postsynaptic membranes at a synapse.
- Neurotransmitter: A chemical messenger that transmits signals across a synapse.
- Action Potential: A brief electrical impulse that travels along the axon of a neuron.
- End Plate Potential (EPP): A depolarization of the muscle fiber membrane caused by the release of ACh at the NMJ.
- Nicotinic Receptor: A type of acetylcholine receptor found at the NMJ and in other parts of the nervous system.
- Acetylcholinesterase (AChE): An enzyme that breaks down acetylcholine in the synaptic cleft.
- Neuromuscular Blocking Agents: Drugs that block the action of acetylcholine at the NMJ, causing muscle paralysis.
- Myasthenia Gravis: An autoimmune disease that attacks ACh receptors at the NMJ, leading to muscle weakness.
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Description
This quiz covers the organization of the nervous system including the central and peripheral nervous systems, their components, and the role of neurotransmitters. Test your understanding of synapses and their function in neuron communication and signaling. Dive into key concepts that are fundamental to neurobiology.
