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Questions and Answers
What type of ion channels open when they bind specific chemicals?
What type of ion channels open when they bind specific chemicals?
Which type of potential is characterized by an electrochemical signal traveling within the neuronal dendrites?
Which type of potential is characterized by an electrochemical signal traveling within the neuronal dendrites?
What mechanism is responsible for the opening of voltage-gated channels?
What mechanism is responsible for the opening of voltage-gated channels?
Which of the following statements is true regarding graded potentials?
Which of the following statements is true regarding graded potentials?
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Where are voltage-gated sodium (Na+) channels primarily located?
Where are voltage-gated sodium (Na+) channels primarily located?
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What initiates the change in membrane potential leading to a graded potential?
What initiates the change in membrane potential leading to a graded potential?
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What is the difference between action potentials and graded potentials?
What is the difference between action potentials and graded potentials?
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Which cellular mechanisms can contribute to summation of graded potentials?
Which cellular mechanisms can contribute to summation of graded potentials?
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What distinguishes an action potential from a graded potential?
What distinguishes an action potential from a graded potential?
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Which type of summation occurs when a single synapse is stimulated repeatedly?
Which type of summation occurs when a single synapse is stimulated repeatedly?
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What is the result if the initial segment of a neuron reaches the threshold potential?
What is the result if the initial segment of a neuron reaches the threshold potential?
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What primarily occurs during the depolarization phase of an action potential?
What primarily occurs during the depolarization phase of an action potential?
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What is an effect of spatial summation?
What is an effect of spatial summation?
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During which step of an action potential do voltage-gated Na+ channels close?
During which step of an action potential do voltage-gated Na+ channels close?
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How does a graded potential change with distance from the stimulus site?
How does a graded potential change with distance from the stimulus site?
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What happens to the membrane potential during the repolarization phase of the action potential?
What happens to the membrane potential during the repolarization phase of the action potential?
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What happens to the membrane potential during hyperpolarization?
What happens to the membrane potential during hyperpolarization?
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What is the primary reason action potentials propagate in one direction?
What is the primary reason action potentials propagate in one direction?
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What is the key difference between continuous and saltatory propagation?
What is the key difference between continuous and saltatory propagation?
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What defines the absolute refractory period of a neuron?
What defines the absolute refractory period of a neuron?
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What effect do excitatory postsynaptic potentials (EPSPs) have on a postsynaptic cell?
What effect do excitatory postsynaptic potentials (EPSPs) have on a postsynaptic cell?
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What is the role of summation in postsynaptic potentials?
What is the role of summation in postsynaptic potentials?
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Which of the following describes inhibitory postsynaptic potentials (IPSPs)?
Which of the following describes inhibitory postsynaptic potentials (IPSPs)?
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How do regulatory neurons influence presynaptic activity?
How do regulatory neurons influence presynaptic activity?
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Study Notes
Nervous System Divisions
- The nervous system is divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS).
- The CNS comprises the brain and spinal cord, and is responsible for information processing, integrating, processing, and coordinating sensory and motor commands.
- The PNS encompasses all nervous tissue outside the CNS, excluding the enteric nervous system (ENS).
- It contains sensory and motor pathways, the somatic nervous system, and the autonomic nervous system (ANS) with its sympathetic and parasympathetic divisions.
Nervous System Function
- The nervous system has sensory and motor divisions within the PNS.
- Sensory (afferent) division brings information into the CNS.
- The motor (efferent) division carries signals from the CNS to effectors, such as muscles and glands.
- The motor division is further divided into the somatic nervous system (SNS) for skeletal muscle control and the autonomic nervous system (ANS) for smooth muscle, cardiac muscle, and gland control.
- The ANS has two branches: sympathetic (fight-or-flight) and parasympathetic (rest-and-digest).
Nervous Tissue Cells
- The nervous system comprises two main cell types: neurons and neuroglia.
- Neurons are communicative cells.
- Neurons have three main regions: cell body (soma), dendrites, and axon. The cell body contains the nucleus and other organelles. Dendrites carry signals toward the cell body, and axons carry signals away. Axon hillock is the origin of the axon from the cell body; and the initial segment is where action potentials are initiated.
- Axons have an axon hillock and an initial segment
- Neuroglia (glial cells) support and protect neurons, making up half the volume of the nervous system. Four types of CNS glial cells are ependymal cells, microglia, astrocytes, and oligodendrocytes. Two types of PNS glial cells are Schwann cells and satellite cells.
Neuron Structure
- Neurons are classified anatomically into four types: unipolar, bipolar, multipolar, and anaxonic.
- The nervous system employs various terminologies to describe bundles of nerve fibers: nuclei (in the CNS), ganglia (in the PNS), tracts (in the CNS), and nerves (in the PNS).
- White matter is composed of myelinated fibers, Gray matter consists of unmyelinated fibers and cell bodies.
Neuron Function
- Three functional classes of neurons exist: sensory, interneurons, and motor.
- Sensory neurons carry sensory information into the CNS.
- Interneurons relay signals between sensory and motor neurons.
- Motor neurons carry motor signals from the CNS to effectors.
- Sensory receptors include interoceptors (internal organs), proprioceptors (muscle position& movement), and exteroceptors (external environment).
Neuroglia
- Neuroglia (glial cells) are supporting cells in the nervous system.
- Four types of CNS glial cells are: ependymal cells, microglia, astrocytes, and oligodendrocytes.
- Two types of PNS glial cells are Schwann cells and satellite cells.
- Specific functions of these cells include: ependymal cells produce and circulate cerebrospinal fluid; microglia remove cellular debris, waste, and pathogens; astrocytes maintain blood-brain barrier; oligodendrocytes produce myelin; Schwann cells support and myelinate PNS axons; satellite cells regulate the environment around neurons.
CNS Neuroglia (Specific Types)
- Ependymal Cells line the central canal of the spinal cord and ventricles of the brain, and are cuboidal or columnar epithelium. They produce and circulate cerebrospinal fluid.
- Microglia are mobile phagocytic cells that remove cellular debris, waste products, and pathogens. They are developmentally related to monocytes and macrophages.
- Astrocytes maintain the blood-brain barrier; regulate ion, nutrient, and gas concentrations around neurons; absorb/recycle neurotransmitters; and form scar tissue after injury.
- Oligodendrocytes produce myelin, which surrounds axons in the CNS, aiding signal transduction.
PNS Neuroglia (Specific Types)
- Schwann cells myelinate axons in the PNS and are essential for nerve transmission.
- Satellite cells surround peripheral cell bodies and regulate the environment around neurons.
Excitable Membranes
- Membrane Potentials & Action Potentials: Excitable membranes, found in neurons and muscle cells, allow for ion movement and the generation of electrical signals like action potentials. The resting membrane potential of a neuron is near -70 mV, caused by differences in ion concentrations (Na+ outside, K+ inside).
- Gated Channels:
- Chemically (ligand) gated channels open/close in response to the binding of specific chemicals (e.g., neurotransmitters).
- Voltage-gated channels open/close in response to changes in membrane potential (important in generating action potentials).
- Mechanically gated channels open/close in response to physical deformation of the membrane (important in sensory receptors).
- Graded Potentials: Temporary, localized changes in membrane potential. Occur in dendrites and cell bodies. These signals can be excitatory (depolarizing) or inhibitory (hyperpolarizing), and can summate (add up) to trigger or inhibit action potentials. The graded potential diminishes as it moves through the cell.
- Action Potentials: Rapid, large changes in membrane potential that propagate along axons like a wave. Action potentials have a threshold that must be met; and they occur in an all-or-none manner. Action Potentials are initiated at the axon hillock, and are propagated along membrane like a wave. Two propagation types: continuous (unmyelinated) and saltatory (myelinated).
- Synaptic Activity: Neurotransmitters released at the synapses induce graded potentials in the postsynaptic cell, which can then lead to action potentials. Summation is the collective effects of multiple synaptic inputs. Synapses can be on the cell body or the dendrites; and different synapses can cause summation of different graded post potentials (EPSP/IPSP). Temporal (over time) and spatial (at once) summation of inputs determine whether an action potential is generated.
Membrane Potential Changes
- If the initial segment of the axon reaches the threshold (-55mV), an action potential (AP) is triggered, leading to several phases: depolarization, repolarization, hyperpolarization, and return to resting potential.
- Refractory periods (absolute and relative) prevent an action potential from moving backward.
Action Potential Propagation
- Action potentials propagate along excitable membranes (neurons & muscle).
- The propagation occurs due to the refractory period.
- Two types of propagation: continuous (unmyelinated axons) and saltatory (myelinated axons). Saltatory propagation is much faster.
Synaptic Activity
- AP arrivals triggers the release of neurotransmitters from the presynaptic neuron. Neurotransmitters bind to receptors on the postsynaptic cell. This triggers graded potentials (EPSP or IPSP). Postsynaptic potentials can summate.
Postsynaptic Potentials
- Postsynaptic potentials are graded potentials that occur in the postsynaptic neuron membrane in response to a neurotransmitter released from the pre-synaptic neuron.
- Some postsynaptic potentials are excitatory (EPSP), while others are inhibitory (IPSP). Excitatory postsynaptic potentials (EPSPs) depolarize the postsynaptic membrane, making the neuron more likely to generate an action potential. Inhibitory postsynaptic potentials (IPSPs) hyperpolarize the postsynaptic membrane, decreasing the likelihood of generating an action potential.
Information Processing
- Neurotransmitters— numerous, different actions and effects.
- Regulatory neurons can facilitate or inhibit the activity of presynaptic neurons.
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Description
Explore the divisions and functions of the nervous system, focusing on the central and peripheral nervous systems. Learn about the roles of the sensory and motor pathways, and differentiate between the somatic and autonomic nervous systems. This quiz will test your understanding of how the nervous system processes and integrates information.
