Podcast
Questions and Answers
What is the primary function of the cell body in a neuron?
What is the primary function of the cell body in a neuron?
- Impulse generation and transmission
- Insulation of axons
- Receptive area for incoming signals
- Biosynthetic center and focal point for outgrowth (correct)
Which statement accurately describes dendrites?
Which statement accurately describes dendrites?
- They are structures that insulate the axon.
- They are the main components of myelinated axons in the CNS.
- They are long, thick extensions that transmit impulses away from the neuron.
- They convey graded potentials towards the cell body. (correct)
What characteristic of the nerve cell body contributes to its amitotic nature?
What characteristic of the nerve cell body contributes to its amitotic nature?
- Presence of Nissl bodies
- Formation of graded potentials
- Lack of centrioles (correct)
- Ability to generate action potentials
What is true regarding myelinated axons?
What is true regarding myelinated axons?
The axon hillock is best described as which of the following?
The axon hillock is best described as which of the following?
What is the primary difference between electrical synapses and chemical synapses?
What is the primary difference between electrical synapses and chemical synapses?
Which of the following physiological processes are primarily influenced by electrical synapses in the CNS?
Which of the following physiological processes are primarily influenced by electrical synapses in the CNS?
What role do neurotransmitters play in chemical synapses?
What role do neurotransmitters play in chemical synapses?
What is the significance of the synaptic cleft in chemical synapse communication?
What is the significance of the synaptic cleft in chemical synapse communication?
How do Ca2+ channels contribute to the process of neurotransmitter release?
How do Ca2+ channels contribute to the process of neurotransmitter release?
Which function is primarily associated with the sympathetic division of the autonomic nervous system?
Which function is primarily associated with the sympathetic division of the autonomic nervous system?
What does the autonomic nervous system primarily control?
What does the autonomic nervous system primarily control?
Which part of the nervous system includes the brain and spinal cord?
Which part of the nervous system includes the brain and spinal cord?
Which fiber type conducts impulses from the CNS to smooth muscle and glands?
Which fiber type conducts impulses from the CNS to smooth muscle and glands?
What is the primary role of the parasympathetic division of the autonomic nervous system?
What is the primary role of the parasympathetic division of the autonomic nervous system?
In which division of the peripheral nervous system would you classify the motor fibers that conduct impulses to skeletal muscles?
In which division of the peripheral nervous system would you classify the motor fibers that conduct impulses to skeletal muscles?
What is the correct definition of the motor (efferent) division of the peripheral nervous system?
What is the correct definition of the motor (efferent) division of the peripheral nervous system?
Which component of the peripheral nervous system is involved in transmitting sensory information from receptors to the CNS?
Which component of the peripheral nervous system is involved in transmitting sensory information from receptors to the CNS?
What type of muscle does the autonomic nervous system NOT directly influence?
What type of muscle does the autonomic nervous system NOT directly influence?
Which of the following statements about the autonomic nervous system’s divisions is correct?
Which of the following statements about the autonomic nervous system’s divisions is correct?
What is the primary function of the myelin sheath surrounding axons?
What is the primary function of the myelin sheath surrounding axons?
Which of the following describes the movement of substances from the axon terminal toward the cell body?
Which of the following describes the movement of substances from the axon terminal toward the cell body?
Which structure primarily creates the myelin sheath in the peripheral nervous system?
Which structure primarily creates the myelin sheath in the peripheral nervous system?
What are the gaps in the myelin sheath that allow axon collaterals to emerge called?
What are the gaps in the myelin sheath that allow axon collaterals to emerge called?
Which part of the neuron is primarily responsible for generating and transmitting action potentials?
Which part of the neuron is primarily responsible for generating and transmitting action potentials?
How does the myelin sheath influence nerve impulse transmission?
How does the myelin sheath influence nerve impulse transmission?
Which feature of axons allows for their varying lengths, which can be as long as 4 feet?
Which feature of axons allows for their varying lengths, which can be as long as 4 feet?
What are Nissl bodies primarily composed of?
What are Nissl bodies primarily composed of?
What is the primary function of neurotransmitters when bound to postsynaptic neurons?
What is the primary function of neurotransmitters when bound to postsynaptic neurons?
What determines the magnitude of postsynaptic potential?
What determines the magnitude of postsynaptic potential?
Which of the following describes EPSPs?
Which of the following describes EPSPs?
What is a significant outcome of neurotransmitters not being removed from their receptors?
What is a significant outcome of neurotransmitters not being removed from their receptors?
What mechanisms contribute to terminating the effects of neurotransmitters?
What mechanisms contribute to terminating the effects of neurotransmitters?
Which type of potential would you expect if a neurotransmitter causes hyperpolarization in the postsynaptic membrane?
Which type of potential would you expect if a neurotransmitter causes hyperpolarization in the postsynaptic membrane?
What role does calcium (Ca2+) play in neurotransmitter release?
What role does calcium (Ca2+) play in neurotransmitter release?
How do IPSPs differ from EPSPs?
How do IPSPs differ from EPSPs?
What role does stimulus frequency play in action potential generation?
What role does stimulus frequency play in action potential generation?
What distinct function does the absolute refractory period serve in neuronal communication?
What distinct function does the absolute refractory period serve in neuronal communication?
Which statement accurately describes the relative refractory period?
Which statement accurately describes the relative refractory period?
How do synapses influence neuronal transmission?
How do synapses influence neuronal transmission?
What structural connection primarily occurs at synapses?
What structural connection primarily occurs at synapses?
How do the characteristics of gray matter and white matter differ in the CNS?
How do the characteristics of gray matter and white matter differ in the CNS?
What is the core function of the presynaptic neuron at a synapse?
What is the core function of the presynaptic neuron at a synapse?
What happens to the transmission efficiency if the number of synapses decreases?
What happens to the transmission efficiency if the number of synapses decreases?
During the repolarization phase, sodium gates open to restore the internal negativity of the resting neuron.
During the repolarization phase, sodium gates open to restore the internal negativity of the resting neuron.
Hyperpolarization occurs when potassium gates remain open, leading to a decreased efflux of K+.
Hyperpolarization occurs when potassium gates remain open, leading to a decreased efflux of K+.
The sodium-potassium pump is responsible for the ionic redistribution back to resting conditions after an action potential.
The sodium-potassium pump is responsible for the ionic redistribution back to resting conditions after an action potential.
Threshold is defined as the membrane potential of -70 mV where depolarization becomes self-generating.
Threshold is defined as the membrane potential of -70 mV where depolarization becomes self-generating.
Continuous propagation of an action potential occurs along myelinated axons.
Continuous propagation of an action potential occurs along myelinated axons.
Axons can be branched structures that arise from the axon hillock.
Axons can be branched structures that arise from the axon hillock.
Myelin sheaths are formed exclusively by oligodendrocytes in the peripheral nervous system.
Myelin sheaths are formed exclusively by oligodendrocytes in the peripheral nervous system.
Nodes of Ranvier serve as sites where axon collaterals can emerge.
Nodes of Ranvier serve as sites where axon collaterals can emerge.
The myelin sheath serves to increase the speed of nerve impulse transmission by insulating fiber segments.
The myelin sheath serves to increase the speed of nerve impulse transmission by insulating fiber segments.
Retrograde movement along axons refers to the direction toward the axon terminal.
Retrograde movement along axons refers to the direction toward the axon terminal.
Axons can vary in length from almost absent to over 4 meters.
Axons can vary in length from almost absent to over 4 meters.
The axon hillock is responsible for receiving incoming signals from other neurons.
The axon hillock is responsible for receiving incoming signals from other neurons.
Schwann cells form concentric layers of membrane that create the myelin sheath around axons.
Schwann cells form concentric layers of membrane that create the myelin sheath around axons.
Microglia are phagocytes that monitor the health of neurons.
Microglia are phagocytes that monitor the health of neurons.
Satellite cells are primarily involved in insulating nerve fibers in the central nervous system.
Satellite cells are primarily involved in insulating nerve fibers in the central nervous system.
Astrocytes are the least abundant type of neuroglial cell in the central nervous system.
Astrocytes are the least abundant type of neuroglial cell in the central nervous system.
Oligodendrocytes wrap their processes around multiple nerve fibers to insulate them.
Oligodendrocytes wrap their processes around multiple nerve fibers to insulate them.
Neuroglia consists of only two types of cells in the nervous system.
Neuroglia consists of only two types of cells in the nervous system.
Ependymal cells are responsible for forming the myelin sheath in the peripheral nervous system.
Ependymal cells are responsible for forming the myelin sheath in the peripheral nervous system.
In multiple sclerosis, the myelin sheath is destroyed, resulting in scarring known as scleroses.
In multiple sclerosis, the myelin sheath is destroyed, resulting in scarring known as scleroses.
Neurons and neuroglia are the two principal cell types of the nervous system.
Neurons and neuroglia are the two principal cell types of the nervous system.
Electrical synapses are more common than chemical synapses.
Electrical synapses are more common than chemical synapses.
Transmission across the synaptic cleft is primarily an electrical event.
Transmission across the synaptic cleft is primarily an electrical event.
Neurotransmitters are released into the synaptic cleft via diffusion.
Neurotransmitters are released into the synaptic cleft via diffusion.
Calcium ions (Ca2+) play a critical role in the propagation of action potentials in both electrical and chemical synapses.
Calcium ions (Ca2+) play a critical role in the propagation of action potentials in both electrical and chemical synapses.
The postsynaptic membrane's permeability changes can lead to either an excitatory or inhibitory effect.
The postsynaptic membrane's permeability changes can lead to either an excitatory or inhibitory effect.
Neurotransmitter release is facilitated by the influx of Ca2+ ions into the axon terminal.
Neurotransmitter release is facilitated by the influx of Ca2+ ions into the axon terminal.
A postsynaptic potential occurs when the receptor specifically allows the entry of Na+ ions.
A postsynaptic potential occurs when the receptor specifically allows the entry of Na+ ions.
IPSPs can lead to depolarization of the postsynaptic membrane.
IPSPs can lead to depolarization of the postsynaptic membrane.
Neuromodulators, unlike neurotransmitters, do not bind to receptors on postsynaptic neurons.
Neuromodulators, unlike neurotransmitters, do not bind to receptors on postsynaptic neurons.
The continuous postsynaptic effect of a neurotransmitter indicates that it must be removed from its receptor for normal signal transmission.
The continuous postsynaptic effect of a neurotransmitter indicates that it must be removed from its receptor for normal signal transmission.
EPSPs are associated with the release of inhibitory neurotransmitters.
EPSPs are associated with the release of inhibitory neurotransmitters.
The termination of neurotransmitter effects involves both degradation and reuptake processes.
The termination of neurotransmitter effects involves both degradation and reuptake processes.
The synaptic cleft provides the primary mechanism for direct electrical communication between neurons.
The synaptic cleft provides the primary mechanism for direct electrical communication between neurons.
EPSPs make the postsynaptic membrane less negative, promoting depolarization.
EPSPs make the postsynaptic membrane less negative, promoting depolarization.
IPSPs, or inhibitory postsynaptic potentials, decrease a neuron’s likelihood to generate an action potential by increasing its membrane permeability to sodium ions.
IPSPs, or inhibitory postsynaptic potentials, decrease a neuron’s likelihood to generate an action potential by increasing its membrane permeability to sodium ions.
Neurons inside the central nervous system are referred to as tracts.
Neurons inside the central nervous system are referred to as tracts.
Ipsilateral refers to structures located on opposite sides of the body.
Ipsilateral refers to structures located on opposite sides of the body.
The choroid plexus is primarily responsible for the formation of cerebrospinal fluid.
The choroid plexus is primarily responsible for the formation of cerebrospinal fluid.
The peripheral nervous system includes collections of nerve fibers called tracts.
The peripheral nervous system includes collections of nerve fibers called tracts.
Ganglia are clusters of cell bodies located in the central nervous system.
Ganglia are clusters of cell bodies located in the central nervous system.
A neuron is characterized as a nerve cell that can generate action potentials.
A neuron is characterized as a nerve cell that can generate action potentials.
Unmyelinated axons have Schwann cells that completely coil around them.
Unmyelinated axons have Schwann cells that completely coil around them.
Oligodendrocytes form myelin sheaths in the peripheral nervous system.
Oligodendrocytes form myelin sheaths in the peripheral nervous system.
Multipolar neurons in the CNS are the least abundant type of neuron.
Multipolar neurons in the CNS are the least abundant type of neuron.
Nodes of Ranvier are closely spaced in myelinated fibers.
Nodes of Ranvier are closely spaced in myelinated fibers.
During the depolarization phase, the Na+ gates are closed while K+ gates are opened.
During the depolarization phase, the Na+ gates are closed while K+ gates are opened.
Hyperpolarization occurs when K+ exits the cell, causing the membrane to become less negative than the resting state.
Hyperpolarization occurs when K+ exits the cell, causing the membrane to become less negative than the resting state.
Sensory neurons transmit impulses away from the CNS.
Sensory neurons transmit impulses away from the CNS.
The sodium-potassium pump restores both the resting electrical and ionic conditions after an action potential.
The sodium-potassium pump restores both the resting electrical and ionic conditions after an action potential.
Nongated ion channels are often opened by specific neurotransmitters.
Nongated ion channels are often opened by specific neurotransmitters.
Unipolar neurons are primarily found in the central nervous system.
Unipolar neurons are primarily found in the central nervous system.
Saltatory propagation occurs along unmyelinated axons, resulting in faster action potential transmission.
Saltatory propagation occurs along unmyelinated axons, resulting in faster action potential transmission.
Threshold is the critical level of depolarization that typically ranges from -55 to -50 mV.
Threshold is the critical level of depolarization that typically ranges from -55 to -50 mV.
Action potentials are identical in strength regardless of the stimulus.
Action potentials are identical in strength regardless of the stimulus.
The central nervous system (CNS) consists of the brain and the peripheral nerves.
The central nervous system (CNS) consists of the brain and the peripheral nerves.
The motor (efferent) division of the peripheral nervous system only transmits impulses from the brain to skeletal muscles.
The motor (efferent) division of the peripheral nervous system only transmits impulses from the brain to skeletal muscles.
Afferent nerves are responsible for carrying sensory inputs to the central nervous system.
Afferent nerves are responsible for carrying sensory inputs to the central nervous system.
Neuroglia primarily function to conduct electrical impulses between neurons.
Neuroglia primarily function to conduct electrical impulses between neurons.
The somatic nervous system is part of the peripheral nervous system and is responsible for voluntary movements.
The somatic nervous system is part of the peripheral nervous system and is responsible for voluntary movements.
Visceral sensory fibers transmit impulses from the skin and skeletal muscles to the brain.
Visceral sensory fibers transmit impulses from the skin and skeletal muscles to the brain.
Integration refers to the process of sensory input being converted into motor output.
Integration refers to the process of sensory input being converted into motor output.
The action potential becomes self-generating at a threshold potential of -70 mV.
The action potential becomes self-generating at a threshold potential of -70 mV.
Chemical synapses ensure bidirectional communication between neurons.
Chemical synapses ensure bidirectional communication between neurons.
Neurotransmitters are stored in synaptic vesicles within the postsynaptic neuron.
Neurotransmitters are stored in synaptic vesicles within the postsynaptic neuron.
Ca2+ channels open in the axonal terminal of the presynaptic neuron when a nerve impulse arrives.
Ca2+ channels open in the axonal terminal of the presynaptic neuron when a nerve impulse arrives.
The absolute refractory period allows a neuron to generate a new action potential regardless of the strength of the stimulus.
The absolute refractory period allows a neuron to generate a new action potential regardless of the strength of the stimulus.
Strong stimuli can produce action potentials more frequently than weak stimuli due to changes in synaptic transmission.
Strong stimuli can produce action potentials more frequently than weak stimuli due to changes in synaptic transmission.
The presynaptic neuron sends information to the postsynaptic neuron through specialized junctions known as synapses.
The presynaptic neuron sends information to the postsynaptic neuron through specialized junctions known as synapses.
During repolarization, sodium gates remain open while potassium gates close in the relative refractory period.
During repolarization, sodium gates remain open while potassium gates close in the relative refractory period.
The white matter of the brain is primarily made up of unsheathed nerve fibers.
The white matter of the brain is primarily made up of unsheathed nerve fibers.
Neurons are capable of generating action potentials only during the relative refractory period.
Neurons are capable of generating action potentials only during the relative refractory period.
The number of synapses can increase with disease, lack of stimulation, or drug use.
The number of synapses can increase with disease, lack of stimulation, or drug use.
All types of synaptic connections occur between axons of one neuron and the axons of another.
All types of synaptic connections occur between axons of one neuron and the axons of another.
Neurotransmitter receptors can only mediate changes in membrane potential if the neurotransmitter is released in large quantities.
Neurotransmitter receptors can only mediate changes in membrane potential if the neurotransmitter is released in large quantities.
EPSP stands for excitatory postsynaptic potential and represents a decrease in the postsynaptic membrane potential.
EPSP stands for excitatory postsynaptic potential and represents a decrease in the postsynaptic membrane potential.
IPSP is associated with hyperpolarization of the postsynaptic membrane, making it less likely to generate an action potential.
IPSP is associated with hyperpolarization of the postsynaptic membrane, making it less likely to generate an action potential.
The process of neurotransmitter action intensifies when they are not removed from their receptors.
The process of neurotransmitter action intensifies when they are not removed from their receptors.
The neurotransmitter degradation process is essential for stopping the postsynaptic effect.
The neurotransmitter degradation process is essential for stopping the postsynaptic effect.
Calcium ions play a significant role in the function of postsynaptic receptors.
Calcium ions play a significant role in the function of postsynaptic receptors.
The binding of neurotransmitters results in the closing of ion channels in the postsynaptic membrane.
The binding of neurotransmitters results in the closing of ion channels in the postsynaptic membrane.
A continuous postsynaptic effect occurs when neurotransmitters remain bound to their receptors for a prolonged period.
A continuous postsynaptic effect occurs when neurotransmitters remain bound to their receptors for a prolonged period.
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What is the primary function of the central sulcus in the brain?
What is the primary function of the central sulcus in the brain?
Which area is primarily responsible for motor function in the cerebral cortex?
Which area is primarily responsible for motor function in the cerebral cortex?
How thick is the cerebral cortex generally measured?
How thick is the cerebral cortex generally measured?
Which functional area of the cerebral cortex integrates diverse information for purposeful action?
Which functional area of the cerebral cortex integrates diverse information for purposeful action?
Which fissure separates the cerebral hemispheres from the cerebellum?
Which fissure separates the cerebral hemispheres from the cerebellum?
What type of neuron is primarily found in the cerebral cortex?
What type of neuron is primarily found in the cerebral cortex?
What is one characteristic of gray matter in the cerebral cortex?
What is one characteristic of gray matter in the cerebral cortex?
Which sulcus divides the parietal lobe and the occipital lobe?
Which sulcus divides the parietal lobe and the occipital lobe?
What is the primary function of the pons in the brainstem?
What is the primary function of the pons in the brainstem?
Which structure is located above the pons?
Which structure is located above the pons?
Which of the following structures directly facilitates the relay of nerve impulses within the brainstem?
Which of the following structures directly facilitates the relay of nerve impulses within the brainstem?
Which structure functions as a point of visual processing within the midbrain?
Which structure functions as a point of visual processing within the midbrain?
What is the position of the mammillary body relative to the pituitary gland?
What is the position of the mammillary body relative to the pituitary gland?
How does the optic tract connect to the optic chiasma?
How does the optic tract connect to the optic chiasma?
Which ventricle is situated just above the cerebellar peduncles?
Which ventricle is situated just above the cerebellar peduncles?
Which structure is primarily responsible for synthesizing melatonin in the brain?
Which structure is primarily responsible for synthesizing melatonin in the brain?
What is the primary function of the dorsal root in the spinal cord?
What is the primary function of the dorsal root in the spinal cord?
Which structure is responsible for producing cerebrospinal fluid within the spinal cord?
Which structure is responsible for producing cerebrospinal fluid within the spinal cord?
Which of the following tracts in the spinal cord is primarily responsible for conducting sensory impulses to the brain?
Which of the following tracts in the spinal cord is primarily responsible for conducting sensory impulses to the brain?
What is the primary role of gray matter in the spinal cord?
What is the primary role of gray matter in the spinal cord?
Which of the following accurately describes the meninges?
Which of the following accurately describes the meninges?
What type of impulses do the descending tracts of the spinal cord primarily conduct?
What type of impulses do the descending tracts of the spinal cord primarily conduct?
What anatomical feature is associated with the ventral root of the spinal cord?
What anatomical feature is associated with the ventral root of the spinal cord?
Which term refers to the primarily gray matter structures located in the spinal cord responsible for reflex actions?
Which term refers to the primarily gray matter structures located in the spinal cord responsible for reflex actions?
What is the main function of the corpora quadrigemina within the midbrain?
What is the main function of the corpora quadrigemina within the midbrain?
Which structure links the lower parts of the brainstem and spinal cord to the higher regions of the brain?
Which structure links the lower parts of the brainstem and spinal cord to the higher regions of the brain?
What critical structure is not involved in the formation of the midbrain?
What critical structure is not involved in the formation of the midbrain?
Which of the following options correctly identifies the composition of the spinal cord?
Which of the following options correctly identifies the composition of the spinal cord?
What is the primary role of the reticular formation within brainstem activities?
What is the primary role of the reticular formation within brainstem activities?
Which region of the brain is most closely associated with the processing of sensory information?
Which region of the brain is most closely associated with the processing of sensory information?
Which anatomical structure is responsible for the passage of cerebrospinal fluid between the third and fourth ventricles?
Which anatomical structure is responsible for the passage of cerebrospinal fluid between the third and fourth ventricles?
What is the significance of the inferior colliculus within the midbrain?
What is the significance of the inferior colliculus within the midbrain?
Which structure primarily connects the midbrain to the cerebellum?
Which structure primarily connects the midbrain to the cerebellum?
Which of the following structures is NOT part of the brainstem?
Which of the following structures is NOT part of the brainstem?
What is the primary function of the thalamus in the diencephalon?
What is the primary function of the thalamus in the diencephalon?
Which of the following structures is responsible for producing melatonin?
Which of the following structures is responsible for producing melatonin?
Which of the following activities is NOT regulated by the hypothalamus?
Which of the following activities is NOT regulated by the hypothalamus?
Which component of the diencephalon is involved in linking the nervous and endocrine systems?
Which component of the diencephalon is involved in linking the nervous and endocrine systems?
What is a major role of the epithalamus in the brain?
What is a major role of the epithalamus in the brain?
Which structure is NOT considered a part of the diencephalon?
Which structure is NOT considered a part of the diencephalon?
Which function is primarily associated with the thalamus?
Which function is primarily associated with the thalamus?
Which part of the diencephalon is critical for maintaining homeostasis?
Which part of the diencephalon is critical for maintaining homeostasis?
What role does the cerebellum play in maintaining posture?
What role does the cerebellum play in maintaining posture?
How does the cerebellum receive information about body movements?
How does the cerebellum receive information about body movements?
What potential consequence arises from damage to the cerebellum?
What potential consequence arises from damage to the cerebellum?
Which of the following structures is located inferior to the occipital lobes?
Which of the following structures is located inferior to the occipital lobes?
What is the primary function of the cerebellar cortex?
What is the primary function of the cerebellar cortex?
Which structure connects the two hemispheres of the cerebellum?
Which structure connects the two hemispheres of the cerebellum?
In addition to motor coordination, which function is associated with the cerebellum?
In addition to motor coordination, which function is associated with the cerebellum?
Which of the following best describes the cerebellar peduncles?
Which of the following best describes the cerebellar peduncles?
Flashcards
Dendrites
Dendrites
Short, branching extensions of a neuron that receive signals from other neurons.
Axon
Axon
A long, slender projection of a neuron that transmits signals away from the cell body.
Cell Body (Perikaryon/Soma)
Cell Body (Perikaryon/Soma)
The neuron's central region containing the nucleus and organelles, responsible for the cell's biosynthetic functions.
Axon Hillock
Axon Hillock
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Myelinated Axons (Tracts/Nerves)
Myelinated Axons (Tracts/Nerves)
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Autonomic Nervous System (ANS)
Autonomic Nervous System (ANS)
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Sympathetic division (ANS)
Sympathetic division (ANS)
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Parasympathetic division (ANS)
Parasympathetic division (ANS)
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Central Nervous System (CNS)
Central Nervous System (CNS)
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Peripheral Nervous System (PNS)
Peripheral Nervous System (PNS)
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Sensory (Afferent) Division (PNS)
Sensory (Afferent) Division (PNS)
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Motor (Efferent) Division (PNS)
Motor (Efferent) Division (PNS)
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Somatic Nervous System
Somatic Nervous System
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Visceral Motor Fiber
Visceral Motor Fiber
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Motor fiber of somatic nervous system
Motor fiber of somatic nervous system
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Electrical Synapses
Electrical Synapses
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Chemical Synapses
Chemical Synapses
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Synaptic Cleft
Synaptic Cleft
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Neurotransmitter Release
Neurotransmitter Release
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Postsynaptic Effect
Postsynaptic Effect
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Axon Structure
Axon Structure
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Axon Function
Axon Function
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Myelin Sheath
Myelin Sheath
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Schwann Cells
Schwann Cells
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Nodes of Ranvier
Nodes of Ranvier
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Anterograde Movement
Anterograde Movement
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Retrograde Movement
Retrograde Movement
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Axon Terminals
Axon Terminals
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Termination of Neurotransmitter Effects
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Axon Collaterals
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Unmyelinated Axons
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Study Notes
Nervous System Objectives
- Describe the divisions of the nervous system and their characteristics.
- Identify the structures and functions of a typical neuron.
- Describe the location and function of neuroglia.
- Describe resting membrane potentials.
- Discuss the events in the generation and propagation of an action potential.
- Define the structure and function of a synapse.
Nervous System
- The master controlling and communicating system of the body.
- Functions:
- Sensory input: stimuli go to the CNS.
- Integration: interpretation of sensory input.
- Motor output: response to stimuli coming from the CNS.
Terminology
- Input (sensory):
- Receptors monitor changes.
- Changes are called stimuli.
- Information is sent by afferent nerves.
- Integration:
- Information is processed.
- A decision is made about what should be done.
- Output (motor):
- Effector organs (muscles or glands) are activated.
- Effector organs are affected by efferent nerves.
Organization of the Nervous System
- Central nervous system (CNS):
- Brain and spinal cord.
- Integration and command center.
- Peripheral nervous system (PNS):
- Paired spinal and cranial nerves.
- Carries messages to and from the spinal cord and brain.
Peripheral Nervous System (PNS): Two Functional Divisions
-
- Sensory (afferent) division:
- Somatic sensory fibers carry impulses from skin, skeletal muscles, and joints to the brain.
- Visceral sensory fibers transmit impulses from visceral organs to the brain.
-
- Motor (efferent) division:
- Carries impulses from the CNS to effector organs (muscles and glands).
Motor Division: Two Main Parts
-
- Somatic Nervous System (voluntary):
- Carries impulses from the CNS to skeletal muscles.
-
- Autonomic Nervous System (ANS) (involuntary):
- Carries impulses from the CNS to smooth muscle, cardiac muscle, and glands.
- ANS Division: Two Main Parts
- Sympathetic
- Parasympathetic
Histology of Nerve Tissue
- The two principal cell types of the nervous system are:
- Neurons: excitable cells that transmit electrical signals.
- Neuroglia (glia): cells that surround and wrap neurons (supporting cells).
Supporting Cells: Neuroglia
- Neuroglia provide a supportive scaffolding for neurons.
- Neuroglia segregate and insulate neurons.
- Neuroglia guide young neurons to the proper connections.
- Neuroglia promote health and growth.
- Six types — 4 in the CNS; 2 in the PNS.
Neuroglia of the CNS
- Astrocytes:
- Most abundant, versatile, and highly branched glial cells.
- Maintain blood-brain barrier.
- Cling to neurons and their synaptic endings, and wrap around capillaries.
- Regulate their permeability.
- Provide structural framework for the neuron, guide migration of young neurons, and control the chemical environment.
- Repair damaged neural tissue.
- Microglia:
- Small, ovoid cells with spiny processes.
- Phagocytes that monitor the health of neurons.
- Ependymal cells:
- Range in shape from squamous to columnar.
- Line the central cavities of the brain and spinal column.
- Oligodendrocytes:
- Branched cells.
- Myelin: wraps of oligodendrocytes processes around nerve fibers, insulating the nerve fibers.
- Branched cells.
- Schwann cells (neurolemmocytes): (PNS)
- Myelin: wraps itself around nerve fibers, insulating the nerve fibers.
- Satellite cells surround neuron cell bodies within the ganglia. Regulate the environment around the neurons.
Myelin in the Peripheral and Central Nervous Systems
- Myelin sheaths are segmented.
- Myelin sheaths protect axons and electrically insulate fibers from one another.
- Myelin sheaths increase the speed of nerve impulse transmission.
Nodes of Ranvier
- Gaps in the myelin sheath between adjacent Schwann cells.
- Sites where axon collaterals can emerge.
- Unmyelinated axons:
- A Schwann cell surrounds nerve fibers but coiling does not take place.
- Schwann cells partially enclose 15 or more axons.
- Conduct nerve impulses slowly.
Axons of the CNS
- Both myelinated and unmyelinated fibers are present.
- Myelin sheaths formed by oligodendrocytes.
- Nodes of Ranvier are widely spaced.
Regions of the Brain and Spinal Cord
- White matter: dense collections of myelinated fibers.
- Gray matter: mostly soma, dendrites, glial cells, and unmyelinated fibers.
Structural Classification of Neurons
- Three types:
- Multipolar: one axon and several dendrites.
- Most abundant.
- Major neurons in the CNS.
- Bipolar: one axon and one dendrite.
- Rare (e.g., retinal neurons).
- Unipolar (pseudounipolar): single, short process that then branches.
- Peripheral process—more distal branch, often associated with a sensory receptor.
- Found chiefly in the PNS.
- Multipolar: one axon and several dendrites.
Neuron Classification
- Functional:
- Sensory (afferent) transmit impulses toward the CNS.
- Motor (efferent) carry impulses toward the body surface.
- Interneurons (association neurons) any neurons between a sensory and a motor neuron.
Neurophysiology
- Neurons are highly irritable.
- Action potentials (nerve impulses) are electrical impulses carried along the length of axons.
- Always the same regardless of stimulus.
Electrical Current and the Body
- Reflects the flow of ions rather than electrons.
- Potential exists on either side of membranes when:
- The number of ions is different across the membrane.
- The membrane has a resistance to ion flow.
Role of Ion Channels
- Types of plasma membrane ion channels:
- Nongated (leakage channels): always open.
- Chemically gated channels open with binding of a specific neurotransmitter.
- Voltage-gated channels open and close in response to membrane potential. Two gates are involved.
- Mechanically gated channels open and close in response to physical deformation of receptors.
Electrochemical Gradient
- Ions flow along their chemical gradient when they move from an area of high concentration to an area of low concentration.
- Ions flow along their electrical gradient when they move toward an area of opposite charge.
- Electrochemical gradient - the electrical and chemical gradients taken together.
Resting Membrane Potential (Vm)
- Equals the difference in charge between inside and outside of the membrane.
- Polarized (unequal) across the membrane.
- Ranges from -40 mV to -90 mV in different types of neurons (different if considering all types of cells).
- The inside of the neuron is negatively charged in relation to the outside.
- Resting membrane potential is generated by different concentrations of Na+, K+, Cl-, and protein anions (A-).
- Ionic differences are the consequence of:
- Differential permeability of the membrane to Na+ and K+.
- Operation of the sodium-potassium pump.
- Inside the cell= less sodium & more potassium
- Outside the cell sodium is balanced by chloride ions
- Inside the cell (-) charged proteins help balance out the potassium
- Potassium diffuses out of cell easier than sodium diffuses in, so inside is slightly more (-);
- This results in an electrical gradient that produces the resting membrane potential.
- Sodium-potassium pump exports 3 sodium out & brings 2 potassium into the cell to maintain diffusion gradients for potassium & sodium
- Requires ATP; 1 ATP for each 2K/3Na exchange
Membrane Potentials: Signals
- Used to integrate, send, and receive information.
- Membrane potential changes are produced by changes in membrane permeability to ions and alterations of ion concentrations across the membrane.
- Types of signals: graded potentials and action potentials.
Changes in Membrane Potential
- Changes are caused by three events:
- Depolarization: the inside of the membrane becomes less negative.
- Repolarization: the membrane returns to its resting membrane potential.
- Hyperpolarization: the inside of the membrane becomes more negative than the resting potential.
Graded Potentials
- Short-lived, local changes in membrane potential.
- Decrease in intensity with distance.
- Magnitude varies directly with the strength of the stimulus.
- Depolarization or hyperpolarization.
- Sufficiently strong graded potentials can initiate action potentials.
Action Potentials (APs)
- Brief reversal of membrane potential.
- Generated by muscle cells and neurons.
- Do not decrease in strength over distance.
- Principal means of neural communication.
- An action potential in the axon of a neuron is a nerve impulse.
Action Potential: Resting State
- Na+ and K+ channels are closed.
- Leakage accounts for small movements of Na+ and K+.
- Each Na+ channel has two voltage-regulated gates:
- Activation gates – closed in the resting state.
- Inactivation gates – open in the resting state.
Action Potential: Depolarization Phase
- Na+ permeability increases; membrane potential reverses.
- Na+ gates are opened; K+ gates are closed.
- Threshold – a critical level of depolarization (-55 to -50 mV).
- At threshold, depolarization becomes self-generating.
Action Potential: Repolarization Phase
- Sodium inactivation gates close.
- Membrane permeability to Na+ declines to resting levels.
- As sodium gates close, voltage-sensitive K+ gates open.
- K+ exits the cell and internal negativity of the resting neuron is restored.
Action Potential: Hyperpolarization
- Potassium gates remain open, causing an excessive efflux of K+.
- This efflux causes hyperpolarization of the membrane (undershoot).
- The neuron is insensitive to stimulus and depolarization during this time.
Action Potential: Role of the Sodium-Potassium Pump
- Repolarization restores the resting electrical conditions of the neuron.
- Does not restore resting ionic conditions.
- Ionic redistribution back to resting conditions is restored by the sodium-potassium pump.
Phases of the Action Potential
- 1: resting state
- 2: depolarization phase
- 3: repolarization phase
- 4: hyperpolarization
Propagation of an Action Potential
- Continuous propagation (unmyelinated axon).
- Saltatory propagation (myelinated axon).
Types of Stimuli
- Threshold stimulus:
- Stimulus strong enough to bring the membrane potential to a threshold voltage causing an action potential.
- Subthreshold stimulus:
- Weak stimuli that cause depolarization (graded potentials) but not action potentials.
Coding for Stimulus Intensity
- Action potentials are an "all-or-none" phenomenon.
- Strong stimuli can generate an action potential more often than weaker stimuli.
- The CNS determines stimulus intensity by the frequency of impulse transmission.
Absolute Refractory Period
- Time from the opening of the Na+ activation gates until the closing of inactivation gates.
- Prevents the neuron from generating an action potential.
- Ensures that each action potential is separate.
- Enforces one-way transmission of nerve impulses.
Relative Refractory Period
- Interval following the absolute refractory period.
- Sodium gates are closed.
- Potassium gates are open.
- Repolarization is occurring.
- Stimulus stronger than the original one can cause a new action potential.
Synapse
- The means by which adjacent neurons communicate.
- Most occur between axons of one neuron and the dendrites of another (axodendritic) or between the axon of one neuron and the cell body of another (axosomatic).
- Presynaptic neuron is the information sender; postsynaptic neuron is the information receiver.
- Neurons may have from 1,000 to 10,000 axonal terminals making synapses.
Gray and White Matter of the CNS
- The brain and spinal cord receive impulses, process information, and respond with the appropriate action — gray matter of the brain and spinal cord consists of unsheathed nerve fibers (cannot be regenerated if damaged) in the cortex or surface layer. The white matter makes up the internal structure, and consists of myelinated nerve fibers.
Electrical Synapses
- Are less common than chemical synapses.
- Correspond to gap junctions found in other cell types.
- Very fast propagation of action potentials.
- Important in the CNS for arousal from sleep, mental attention, emotions and memory, and ion and water homeostasis.
Chemical Synapses
- Specialized for the release and reception of neurotransmitters.
- Typically composed of presynaptic and postsynaptic neurons.
- Presynaptic neuron contains synaptic vesicles.
- Receptors are typically located on dendrites and soma of postsynaptic neuron.
- Synaptic cleft: fluid-filled space separating presynaptic and postsynaptic neurons.
- Transmission across the synaptic cleft is a chemical event (as opposed to an electrical one); ensures unidirectional communication between neurons.
- Nerve impulses reach the axonal terminal of the presynaptic neuron and open Ca2+ channels.
- Neurotransmitter is released into the synaptic cleft via exocytosis.
- Neurotransmitter crosses the synaptic cleft and binds to receptors on the postsynaptic neuron, causing postsynaptic membrane permeability changes. This causes an excitatory or inhibitory effect.
Termination of Neurotransmitter Effects
- Neurotransmitter bound to a postsynaptic neuron:
- Produces a continuous postsynaptic effect.
- Blocks additional "messages.
- Must be removed from its receptor.
Postsynaptic Potentials
- Neurotransmitter receptors mediate changes in membrane potential according to:
- The amount of neurotransmitter released.
- The amount of time the neurotransmitter is bound to receptors.
- The two types of postsynaptic potentials are:
- EPSPs (excitatory postsynaptic potentials).
- IPSPs (inhibitory postsynaptic potentials).
EPSPs
- Excitatory synapses cause depolarization of the postsynaptic membrane.
IPSPs
- Inhibitory synapses reduce a postsynaptic neuron's ability to generate an AP.
- Changes membrane permeability to ions, making the inner face of the membrane more (-); making it less likely to "fire."
Terminology for Quiz
- Neuron = nerve cell
- Neuroglia = supporting cell
- Nerve fiber = long axon
- Nerve = collection of nerve fibers (axons) in PNS
- Tract = collections of nerve fibers (axons) in CNS
- Nucleus = cluster of cell bodies in CNS
- Ganglia = cluster of cell bodies in PNS
- New terms:
- Unilateral: on one side
- Ipsilateral: on the same side
- Contralateral: on the opposite side
- CNS vs PNS
- Input: sensory: afferent: to brain
- Output: motor: efferent: from brain
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Test your knowledge on the structure and function of neurons, including the roles of the cell body, dendrites, and axons. This quiz also covers the differences between electrical and chemical synapses, the influence of neurotransmitters, and the autonomic nervous system. Challenge yourself to understand the complexities of neural communication.
