Biology: Organization of the Nervous System
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Questions and Answers

What is the threshold potential at which an action potential is generated?

  • -70 mV
  • 0 mV
  • -50 mV (correct)
  • 50 mV

    • 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?

    <p>It breaks down acetylcholine.</p> Signup and view all the answers

    Which type of receptors are characterized at the neuromuscular junction?

    <p>Nicotinic receptors</p> Signup and view all the answers

    Match the following neurotransmitters with their functions:

    <p>Acetylcholine = Excitatory synapse GABA = Inhibitory synapse Dopamine = Reward and pleasure Glutamate = Primary excitatory neurotransmitter</p> Signup and view all the answers

    What type of synapse depolarizes the postsynaptic membrane?

    <p>excitatory synapse</p> Signup and view all the answers

    What are the two basic forms of electrical signals in neurons?

    <p>Graded potentials and action potentials</p> Signup and view all the answers

    Action potentials decrease in strength as they travel along the axon.

    <p>False</p> Signup and view all the answers

    What ion influx causes the depolarization during an action potential?

    <p>sodium ions (Na+)</p> Signup and view all the answers

    What is the refractory period?

    <p>The time during which a neuron cannot fire another action potential</p> Signup and view all the answers

    What is the resting membrane potential of a muscle fiber?

    <p>-80 mV</p> Signup and view all the answers

    What neurotransmitter is released at the neuromuscular junction?

    <p>Acetylcholine</p> Signup and view all the answers

    Acetylcholine acts as an excitatory neurotransmitter at the neuromuscular junction.

    <p>True</p> Signup and view all the answers

    What is the role of acetylcholinesterase (AChE) at the neuromuscular junction?

    <p>Breaks down acetylcholine and prevents constant stimulation of muscles.</p> Signup and view all the answers

    Which of the following actions can lead to prolonged muscle contraction?

    <p>Administration of acetylcholinesterase inhibitors</p> Signup and view all the answers

    What is the function of the myelin sheath in neurons?

    <p>It acts as an electrical insulator that restricts current flow.</p> Signup and view all the answers

    What is the function of nodes of Ranvier?

    <p>They are gaps in the myelin sheath where voltage-gated sodium channels are concentrated.</p> Signup and view all the answers

    Myasthenia gravis is characterized by an overactivity of acetylcholine receptors.

    <p>False</p> Signup and view all the answers

    ACh must be cleared from the synaptic cleft to prevent constant muscle _____ .

    <p>stimulation</p> Signup and view all the answers

    What happens when an action potential reaches the axon terminal?

    <p>Acetylcholine is released.</p> Signup and view all the answers

    What type of junction is formed between motor neurons and skeletal muscle fibers?

    <p>Chemical synapse</p> Signup and view all the answers

    What occurs when action potentials travel down motor neurons?

    <p>Miniature end plate potentials are created</p> Signup and view all the answers

    Where are the cell bodies of motor neurons located?

    <p>Ventral horn of the spinal cord</p> Signup and view all the answers

    What is the primary outcome of the action potentials in the context of the neuromuscular junction?

    <p>Excitation of muscle fibers</p> Signup and view all the answers

    What happens to the myelin sheath of motor neurons at the motor end plate?

    <p>It is completely absent</p> Signup and view all the answers

    What term describes the fine branches of motor neurons that form synaptic connections with muscle fibers?

    <p>Axon terminals</p> Signup and view all the answers

    What happens to graded potentials over short distances?

    <p>They gradually die out.</p> Signup and view all the answers

    What is the significance of reaching the threshold voltage in graded potentials?

    <p>It opens voltage-gated channels resulting in an action potential.</p> Signup and view all the answers

    What is the primary change in membrane potential referred to as depolarization?

    <p>An increase in membrane potential moving towards a positive value.</p> Signup and view all the answers

    What defines the difference between graded potentials and action potentials?

    <p>Graded potentials can summate, while action potentials cannot.</p> Signup and view all the answers

    How is the magnitude of a graded potential determined?

    <p>It directly correlates with the strength of the triggering event.</p> Signup and view all the answers

    What initiates the nerve impulse that moves down the axon?

    <p>The summation of graded potentials reaching threshold.</p> Signup and view all the answers

    What is the resting membrane potential typically measured at?

    <p>-70 mV.</p> Signup and view all the answers

    What effect does acetylcholine binding to receptors have on the postsynaptic membrane?

    <p>It opens Na+ channels leading to depolarization.</p> Signup and view all the answers

    Which statement accurately describes the role of acetylcholine at excitatory synapses?

    <p>It causes an influx of Na+ ions, leading to depolarization.</p> Signup and view all the answers

    What effect does binding of neurotransmitters to their receptors generally have on the postsynaptic membrane?

    <p>It alters the membrane potential, which can lead to action potentials.</p> Signup and view all the answers

    What is the primary consequence of the neurotransmitter's effect at an excitatory synapse?

    <p>It depolarizes the postsynaptic membrane and may generate an action potential.</p> Signup and view all the answers

    Which component of the synapse is primarily responsible for releasing neurotransmitters?

    <p>Presynaptic neuron</p> Signup and view all the answers

    Which condition must be satisfied for an action potential to be initiated in the postsynaptic neuron?

    <p>The membrane potential must reach a specific threshold after depolarization.</p> Signup and view all the answers

    What type of synapses would typically employ neurotransmitters such as GABA?

    <p>Inhibitory synapses that decrease postsynaptic activity.</p> Signup and view all the answers

    What effect does hyperpolarization have on the likelihood of an action potential occurring?

    <p>Decreases the likelihood by making the membrane potential more negative</p> Signup and view all the answers

    Which component is responsible for increasing the speed of action potential propagation in myelinated neurons?

    <p>Nodes of Ranvier allowing saltatory conduction</p> Signup and view all the answers

    What is the primary role of the myelin sheath in neuronal function?

    <p>To insulate axons and reduce current leakage</p> Signup and view all the answers

    How does the binding of neurotransmitters to GABA receptors affect the postsynaptic membrane?

    <p>It causes hyperpolarization of the membrane</p> Signup and view all the answers

    Which of the following occurs at the nodes of Ranvier in myelinated neurons?

    <p>Voltage-gated sodium channels are concentrated and facilitate rapid depolarization</p> Signup and view all the answers

    What is the primary composition of the cytoplasm in muscle fibers?

    <p>Actin and myosin filaments</p> Signup and view all the answers

    What occurs when the membrane potential is at -70 mV?

    <p>The neuron is in a resting state and not transmitting signals</p> Signup and view all the answers

    How does the arrangement of the endoplasmic reticulum change in muscle fibers?

    <p>It is organized into a system of tubes surrounding myofibrils</p> Signup and view all the answers

    What role does chloride (Cl-) play in synaptic transmission when GABA receptors are activated?

    <p>It promotes hyperpolarization of the postsynaptic neuron</p> Signup and view all the answers

    What is the significance of the threshold potential in neuronal action potentials?

    <p>It is the level of depolarization required to initiate an action potential</p> Signup and view all the answers

    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.

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