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Questions and Answers
What describes the axons that are covered by a myelin sheath?
What is the primary function of the myelin sheath?
Which part of the neuron sends the impulse to the synapse?
What are the gaps called that are found in myelinated axons?
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Which type of neuron is primarily involved in carrying sensory information to the brain?
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What characterizes a bipolar neuron?
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Where are interneurons primarily located?
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What do synaptic vesicles contain?
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What type of neuron conducts nerve impulses from the brain or spinal cord to the effector organ?
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Which type of neuroglia helps form the blood-brain barrier?
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What is the primary role of microglial cells?
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The Central Nervous System (CNS) comprises which of the following structures?
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Which division of the nervous system is involved in voluntary muscle contractions?
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How many pairs of spinal nerves are present in the human body?
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What is the function of ependymal cells in the nervous system?
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What are the two main components of the Peripheral Nervous System (PNS)?
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What are the three major functions of the nervous system?
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What distinguishes the responses of the nervous system from the endocrine system?
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Which type of cells compose nerve tissue?
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What role do dendrites play in a neuron?
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What is unique about the axon structure in neurons?
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What is the function of the myelin sheath in neurons?
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Why don't neurons undergo mitosis?
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What function do interneurons serve in the nervous system?
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What type of conduction occurs in myelinated axons that significantly increases the rate of impulse transmission?
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In the classification of neurons by structure, which type is characterized by a single nerve fiber extending from the soma that divides into a dendrite and an axon?
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Which part of a synapse is responsible for receiving neurotransmitters from the presynaptic neuron?
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What is the gap between two neurons at a synapse called?
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What type of neuron primarily relays nerve impulses from sensory neurons to motor neurons?
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What type of motor neurons increases activity in the effector organ?
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Which of the following neuroglial cells are primarily involved in immune protection within the nervous system?
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Which category do sensory neurons that conduct nerve impulses towards the brain belong to?
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What is the main function of astrocytes in the nervous system?
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In the context of synaptic transmission, what role do synaptic vesicles play?
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Which division of the nervous system includes the cranial and spinal nerves?
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What is a characteristic feature of bipolar neurons?
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The ependymal cells serve primarily to:
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Which classification of neuron is primarily unipolar and functions as a sensory receptor?
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What is the primary role of the somatic nervous system?
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In the structure of a synapse, what are synaptic knobs?
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Which type of neuron primarily conducts nerve impulses toward the central nervous system?
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What characterizes oligodendrocytes in the nervous system?
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The autonomic nervous system regulates functions of which muscle types?
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What is the primary difference in the response time between the nervous system and the endocrine system?
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Which type of neuron typically has the highest number of dendrites?
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What function do Schwann cells serve in relation to the neurons?
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What is a key structural feature of all neurons regarding their axons?
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What is the main function of the 'node of Ranvier' in myelinated axons?
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What distinguishes interneurons from sensory and motor neurons in the nervous system?
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Which of the following best describes the role of neuroglial cells in nerve tissue?
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What is the primary reason neurons cannot regenerate after injury?
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How are sensory (afferent) neurons primarily characterized?
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Study Notes
Nervous System Functions
- The nervous system and endocrine system are the primary control centers for maintaining body homeostasis.
- The nervous system uses electrical signals (nerve impulses) for immediate but short-lived responses, while the endocrine system uses chemical signals (hormones) for slower but longer-lasting responses.
- The nervous system has three major functions:
- Sensory Input: Sensory or afferent neurons detect internal or external changes (stimuli) and transmit the message to the brain or spinal cord.
- Integration: Interneurons in the brain or spinal cord process and interpret the message from sensory neurons and relay the message back to body parts.
- Motor Output: Motor or efferent neurons receive the message from interneurons and produce a response at the effector organ (muscle or gland).
Nerve Tissue
- Nerve tissue is composed of two main types of cells:
- Neurons: Nerve cells specialized for detecting and reacting to stimuli by generating and conducting nerve impulses.
- Neuroglial cells: Accessory cells that provide support and fill spaces around neurons.
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Microscopic anatomy of neurons:
- All neurons have a cell body called soma containing a nucleus, organelles, and a modified endoplasmic reticulum called Nissl body.
- Despite containing DNA, neurons lack the ability to reproduce or regenerate.
- Extensions from the soma form nerve fibers:
- Dendrites: Conduct nerve impulses toward the soma.
- Axon: Conduct nerve impulses away from the soma (to another neuron or effector organ).
- The number of dendrites varies (from 1 in unipolar and bipolar neurons to thousands in multipolar neurons).
- All neurons only have one axon.
- Longer axons are enclosed by a lipoprotein substance called the myelin sheath, produced by Schwann cells.
Myelin Sheath
- The myelin sheath insulates the axon against depolarization, forcing action potentials to occur in the gaps between the myelin sheath (nodes of Ranvier).
- Axons enclosed by the myelin sheath are called myelinated axons, comprising the white matter in the nervous system.
- Axons without a myelin sheath are called unmyelinated axons, comprising the gray matter in the nervous system.
Saltatory Conduction
- The myelin sheath insulates the axon, leaving only narrow gaps called nodes of Ranvier where action potentials can occur.
- This type of nerve impulse propagation, where action potentials jump from one gap to the next, is called saltatory conduction, significantly increasing the rate of impulse transmission.
Synapse
- A synapse is the junction between two neurons or between a neuron and an effector organ (muscle or gland).
- Each synapse consists of:
- Presynaptic neuron: Sends an impulse to the synapse.
- Axon: The nerve fiber extending from the presynaptic neuron that propagates the impulse to the synapse.
- Synaptic knobs: Round endings of the axon.
- Synaptic vesicles: Membranous sacs containing a neurotransmitter (e.g. acetylcholine, norepinephrine, dopamine) located in the synaptic knobs.
- Synaptic cleft: Gap between the two neurons in the synapse.
- Dendrite: Nerve fiber that continues to propagate the nerve impulse to the second neuron (postsynaptic neuron). Receptors on this dendrite receive the neurotransmitter from the axon.
- Postsynaptic neuron: Neuron receiving the nerve impulse from the presynaptic neuron through the synapse.
Neuron Classification (Structure)
- Unipolar neuron: A single nerve fiber extends from the soma, dividing into a dendrite and an axon (sensory neurons conducting reflexes or detecting various stimuli).
- Bipolar neuron: A dendrite and an axon extend independently from the soma (sensory neurons involved in special senses such as vision, olfaction, and hearing).
- Multipolar neuron: One axon and many dendrites extend from the soma (interneurons located inside the brain and spinal cord).
Neuron Classification (Function)
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Sensory (Afferent) neuron:
- Conducts nerve impulses from the body to the brain or spinal cord.
- Endings of its dendrite may be modified to become nerve receptors.
- Usually unipolar in structure.
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Interneuron:
- Relays nerve impulses from sensory neurons to motor neurons.
- Located entirely inside the tissues of the brain or spinal cord.
- Involved in processing and integration within the nervous system.
- Usually multipolar in structure.
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Motor (Efferent) neuron:
- Conducts nerve impulses from the brain or spinal cord to the effector organ (muscles or glands).
- Usually multipolar in structure.
- Accelerator motor neurons: Increase activity in the effector organ.
- Inhibitory motor neurons: Decrease activity in the effector organ.
Neuroglia Classification
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Neuroglia: Supporting cells of the nervous system.
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Astrocytes: Star-shaped cells found between neurons and blood vessels.
- Most abundant glial cells.
- Help form the blood-brain barrier.
- Functions: structural support, transport of substances between blood vessels and neurons, mop up excess ions (K+) and neurotransmitters.
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Microglial cells: Small ovoid cells.
- Function: structural support and phagocytosis (immune protection).
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Ependymal cells: Cuboidal or columnar shaped cells.
- Function: Form a porous layer through which substances diffuse between the interstitial fluid and the cerebrospinal fluid.
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Oligodendrocytes: Resemble astrocytes but have fewer processes and are arranged in rows along nerve fibers.
- Function: Produce myelin sheaths within the brain and spinal cord.
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Astrocytes: Star-shaped cells found between neurons and blood vessels.
Nervous System Divisions
- The human nervous system consists of the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
- CNS: Composed of the brain (located in the cranial cavity) and the spinal cord (located in the vertebral cavity).
- The CNS serves as the main control center for all body activities.
- PNS: Composed of nerves derived from the brain and spinal cord (12 pairs of cranial nerves and 31 pairs of spinal nerves).
- The PNS serves as a linkage between the CNS and the body.
- The PNS can be subdivided into:
- Sensory (Afferent) nerves: Send nerve impulses from the body to the CNS.
- Motor (Efferent) nerves: Send nerve impulses from the CNS to effector organs.
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Motor nerves: Divided into:
- Somatic Nervous System (SNS): Regulates voluntary contraction of skeletal muscles.
- Autonomic Nervous System (ANS): Regulates involuntary control of smooth muscles, cardiac muscles, and glands.
Nervous System Functions
- The nervous system, along with the endocrine system, maintains body homeostasis.
- The nervous system transmits information rapidly using electrical signals, resulting in immediate but short-lived responses.
- The endocrine system utilizes chemical signals (hormones) for slower but longer-lasting responses.
- The nervous system is responsible for three primary functions:
- Sensory input: Sensory (afferent) neurons detect internal and external stimuli, transmitting this information to the brain or spinal cord.
- Integration: Interneurons in the brain or spinal cord process and interpret sensory information, then send signals back to the appropriate body parts.
- Motor output: Motor (efferent) neurons receive signals from interneurons and initiate a response in effector organs (muscles or glands).
Nerve Tissue
- Nerve tissue is composed of two main cell types:
- Neurons: Specialized cells that detect and react to stimuli by generating and conducting nerve impulses.
- Neuroglial cells: Accessory cells that provide support and fill spaces around neurons.
Neuron Anatomy
- All neurons have a cell body (soma) containing a nucleus, organelles, and Nissl bodies (modified endoplasmic reticulum).
- Neurons lack the ability to undergo DNA replication and mitosis, preventing them from reproducing or regenerating.
- Extensions from the soma form nerve fibers:
- Dendrites: Conduct nerve impulses towards the soma.
- Axon: Conducts nerve impulses away from the soma, towards another neuron or an effector organ.
- The number of dendrites varies, with unipolar and bipolar neurons having one or two, while multipolar neurons can have thousands.
- All neurons have only one axon.
- Longer axons are wrapped in a myelin sheath, a lipoprotein substance produced by Schwann cells (a type of neuroglial cell).
Myelin Sheath
- The myelin sheath insulates the axon, preventing depolarization and forcing action potentials to occur only at the gaps between the myelin sheath, called Nodes of Ranvier.
- Axons enclosed by a myelin sheath are called myelinated axons, forming the white matter in the nervous system.
- Axons lacking a myelin sheath are called unmyelinated axons, making up the gray matter in the nervous system.
Nerve Impulse Propagation
- The myelin sheath insulates the axon, leaving only Nodes of Ranvier where action potentials can occur.
- This type of nerve impulse propagation, where the action potential jumps from one node to the next, is called saltatory conduction, significantly increasing the speed of transmission.
Synapse
- A synapse is the junction between two neurons or between a neuron and an effector organ.
- Each synapse consists of:
- Presynaptic neuron: The neuron sending the impulse.
- Axon: The nerve fiber extending from the presynaptic neuron.
- Synaptic knobs: Round endings of the axon.
- Synaptic vesicles: Membranous sacs within the synaptic knobs containing neurotransmitters (e.g., acetylcholine, norepinephrine, dopamine).
- Synaptic cleft: The gap between the two neurons.
- Dendrite: The nerve fiber receiving the impulse from the presynaptic neuron.
- Receptors: Located on the dendrite, these receive the neurotransmitter from the axon.
- Postsynaptic neuron: The neuron receiving the nerve impulse from the presynaptic neuron through the synapse.
Neuron Classification (Structure)
- Unipolar neuron: A single nerve fiber extends from the soma, dividing into a dendrite and an axon. Found in sensory neurons involved in reflexes or detecting stimuli.
- Bipolar neuron: A dendrite and an axon extend independently from the soma. Found in sensory neurons for special senses (vision, olfaction, hearing).
- Multipolar neuron: One axon and multiple dendrites extend from the soma. Found in interneurons within the brain and spinal cord.
Neuron Classification (Function)
- Sensory or afferent neuron: Conducts nerve impulses from the body to the brain or spinal cord. Dendrite endings may be modified as nerve receptors. Usually unipolar in structure.
- Interneuron: Relays nerve impulses from sensory neurons to motor neurons. Located entirely within the brain or spinal cord. Involved in processing and integrating information. Usually multipolar in structure.
-
Motor or efferent neuron: Conducts nerve impulses from the brain or spinal cord to effector organs (muscles or glands). Usually multipolar in structure.
- Accelerator motor neurons: Increase activity in effector organs.
- Inhibitory motor neurons: Decrease activity in effector organs.
Neuroglia Classification
- Astrocytes: Star-shaped cells found between neurons and blood vessels. The most abundant glial cells, forming the blood-brain barrier. Their functions include structural support, transporting substances, and removing excess ions and neurotransmitters.
- Microglial cells: Small, ovoid cells. Function in structural support and phagocytosis (immune protection).
- Ependymal cells: Cuboidal or columnar cells. Form a porous layer allowing substances to diffuse between interstitial fluid and cerebrospinal fluid.
- Oligodendrocytes: Resemble astrocytes but have fewer processes and are arranged in rows along nerve fibers. Produce myelin sheaths within the brain and spinal cord.
Divisions of the Nervous System
- The human nervous system consists of the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
- CNS: Consists of the brain (cranial cavity) and spinal cord (vertebral cavity). These serve as the main control centers for all body functions.
- PNS: Consists of nerves derived from the brain and spinal cord (12 pairs of cranial nerves and 31 pairs of spinal nerves), linking the CNS to the body.
-
PNS: Further divided into the Sensory (afferent) nerves and Motor (efferent) nerves.
- Sensory nerves: Transmit impulses from the body to the CNS.
- Motor nerves: Transmit impulses from the CNS to effector organs.
-
Motor nerves: Divided into the Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS).
- SNS: Regulates voluntary contraction of skeletal muscles.
- ANS: Regulates involuntary control of smooth muscles, cardiac muscles, and glands.
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