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Questions and Answers
Which spinal nerve region contains the greatest number of nerve pairs in humans?
Which spinal nerve region contains the greatest number of nerve pairs in humans?
What is the structure that contains cell bodies of afferent neurons in the spinal cord?
What is the structure that contains cell bodies of afferent neurons in the spinal cord?
Which tract type transmits afferent signals to the brain?
Which tract type transmits afferent signals to the brain?
The lateral horn of the spinal cord is involved in what type of neuron function?
The lateral horn of the spinal cord is involved in what type of neuron function?
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What is a dermatome?
What is a dermatome?
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What is the primary function of the spinal cord?
What is the primary function of the spinal cord?
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Which of the following statements is true about white matter in the spinal cord?
Which of the following statements is true about white matter in the spinal cord?
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Why do most spinal tracts decussate?
Why do most spinal tracts decussate?
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Which area of the brain is primarily responsible for processing somatosensory information?
Which area of the brain is primarily responsible for processing somatosensory information?
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What type of reflex involves a direct connection between a sensory neuron and a motor neuron, resulting in a quick response?
What type of reflex involves a direct connection between a sensory neuron and a motor neuron, resulting in a quick response?
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What does the primary motor cortex control?
What does the primary motor cortex control?
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Which of the following accurately describes the role of the left cerebral hemisphere?
Which of the following accurately describes the role of the left cerebral hemisphere?
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Which part of the brain is responsible for coordinating reflex responses to visual and auditory stimuli?
Which part of the brain is responsible for coordinating reflex responses to visual and auditory stimuli?
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What is the function of the cerebellum in movement?
What is the function of the cerebellum in movement?
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What is the primary role of the inhibitory interneurons in the withdrawal reflex?
What is the primary role of the inhibitory interneurons in the withdrawal reflex?
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What is meant by 'readiness potential' in motor control?
What is meant by 'readiness potential' in motor control?
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The stretch reflex is best characterized as which of the following?
The stretch reflex is best characterized as which of the following?
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What structure encases the brain and serves as a protective bony structure?
What structure encases the brain and serves as a protective bony structure?
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Which section of the vertebrate brain is primarily involved in regulating essential life processes?
Which section of the vertebrate brain is primarily involved in regulating essential life processes?
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How are different muscle groups represented in the primary motor cortex?
How are different muscle groups represented in the primary motor cortex?
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What is the primary function of the cerebrospinal fluid (CSF)?
What is the primary function of the cerebrospinal fluid (CSF)?
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Which sensory abilities are primarily associated with the right cerebral hemisphere?
Which sensory abilities are primarily associated with the right cerebral hemisphere?
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The crossed extensor reflex is important because it allows what to occur?
The crossed extensor reflex is important because it allows what to occur?
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What is the role of higher motor areas in the brain?
What is the role of higher motor areas in the brain?
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Which of the following components is NOT part of the reflex arc?
Which of the following components is NOT part of the reflex arc?
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Which layer of the meninges is closest to the brain?
Which layer of the meninges is closest to the brain?
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Which part of the brain is involved in the processing of sensory information before it reaches the cerebral cortex?
Which part of the brain is involved in the processing of sensory information before it reaches the cerebral cortex?
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Which of the following substances is more concentrated in cerebrospinal fluid compared to blood plasma?
Which of the following substances is more concentrated in cerebrospinal fluid compared to blood plasma?
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What structure primarily forms cerebrospinal fluid?
What structure primarily forms cerebrospinal fluid?
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What is one of the major roles of the blood-brain barrier?
What is one of the major roles of the blood-brain barrier?
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The spinal cord is primarily surrounded and protected by which membranes?
The spinal cord is primarily surrounded and protected by which membranes?
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What is the main advantage of cerebrospinal fluid in terms of the brain’s physical properties?
What is the main advantage of cerebrospinal fluid in terms of the brain’s physical properties?
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What is the primary function of the hypothalamus?
What is the primary function of the hypothalamus?
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Which part of the brain is primarily responsible for balance and coordination?
Which part of the brain is primarily responsible for balance and coordination?
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What role does the thalamus play in the brain?
What role does the thalamus play in the brain?
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Which of the following describes the function of the spinocerebellum?
Which of the following describes the function of the spinocerebellum?
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Which structures make up the brainstem?
Which structures make up the brainstem?
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What is the primary function of the Reticular Activating System?
What is the primary function of the Reticular Activating System?
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Which nuclei are involved in regulating heart rate and blood vessel diameter?
Which nuclei are involved in regulating heart rate and blood vessel diameter?
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Which part of the midbrain is responsible for visual reflexes?
Which part of the midbrain is responsible for visual reflexes?
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Which feature characterizes the cerebrum in advanced vertebrate species?
Which feature characterizes the cerebrum in advanced vertebrate species?
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Which part of the brain is the primary relay station for sensory information?
Which part of the brain is the primary relay station for sensory information?
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Study Notes
### Protection of the CNS
- The CNS is protected by bony structures, meninges, cerebrospinal fluid (CSF), and the blood-brain barrier.
- The cranium (skull) encases the brain and the vertebral column surrounds the spinal cord.
- Meninges are three membranes that separate the soft tissues of the brain from the bones of the cranium, enclose and protect some blood vessels, and contain and help circulate CSF.
- CSF is formed by selective transport across the choroid plexus.
- The blood-brain barrier tight junctions between capillary endothelial cells regulate which substances enter the brain's interstitial fluid.
Meninges
- The brain and spinal cord are enveloped within three layers of membrane collectively known as the meninges.
- The meninges separate and support soft tissues of the brain, enclose and protect blood vessels that supply the brain, and contain and help circulate cerebrospinal fluid (CSF).
Cerebrospinal Fluid
- CSF is a clear, colorless liquid that surrounds the CNS and circulates in the ventricles and subarachnoid space.
- CSF performs several functions: environmental stability by transporting nutrients and wastes and protecting against fluctuations, buoyancy by reducing the brain's apparent weight, and protection by acting as a liquid cushion.
Choroid Plexus
- CSF is formed by the choroid plexus, a layer of ependymal cells and blood capillaries.
- Blood plasma is filtered through the capillary and modified by ependymal cells.
- The composition of CSF is different from plasma, with more Na+ and Cl- and less K+, glucose, and protein.
Ventricular System
- The ventricular system consists of four interconnected cavities within the brain: two lateral ventricles, the third ventricle, and the fourth ventricle.
- Ventricles are filled with CSF.
Production and Circulation of CSF
- CSF is continuously produced by the choroid plexus in the ventricles.
- It circulates through the ventricles and into the subarachnoid space.
- It is absorbed back into the blood by arachnoid villi.
Blood-Brain Barrier
- The blood-brain barrier is a selective barrier that regulates which substances enter the brain's interstitial fluid.
- The blood-brain barrier helps protect neurons from harmful substances such as drugs, wastes, and abnormal solute concentrations.
- Some drugs can pass the blood-brain barrier and affect the brain, such as alcohol.
Spinal Cord
- The spinal cord is a long, slender cylinder of nerve tissue that retains fundamental segmental organization.
- The spinal cord is protected by bone and meninges.
Spinal Cord Segments
- The number of spinal cord segments differs between species.
- Segments include cervical, thoracic, lumbar, sacral, and coccygeal.
- The conus medullaris is the tapered end of the spinal cord.
- The cauda equina is a bundle of nerve roots extending from the conus medullaris.
Spinal Nerves
- There are 31 pairs of spinal nerves in humans, which are divided into cervical, thoracic, lumbar, sacral, and coccygeal.
- A dermatome is a region of the body surface supplied by a specific spinal nerve.
- Spinal nerves contain both afferent and efferent fibers enclosed in connective tissue, including epinerium (outermost), perinerium (middle), and endonerium (innermost).
Spinal Nerves
- Afferent fibers enter the spinal cord through the dorsal root, and cell bodies of afferent neurons are clustered in the dorsal root ganglion.
- Efferent fibers leave the spinal cord through the ventral root.
Anatomical Organization of the Spinal Cord
- Gray matter is clustered with cell bodies (nuclei) and integrates signals.
- White matter consists of bundles of myelinated axons (tracts) that transmit signals.
Spinal Cord: Gray matter
- The dorsal horn contains cell bodies of interneurons on which afferent neurons terminate.
- The ventral horn contains cell bodies of efferent motor neurons.
- The lateral horn contains cell bodies of autonomic neurons.
Spinal Cord: White matter
- White matter consists of bundles of myelinated fibers (tracts).
- Ascending tracts transmit afferent signals to the brain.
- Descending tracts relay messages from the brain to efferent neurons.
Functions of the Spinal Cord
- The spinal cord transmits information between the brain and the body through tracts.
- The spinal cord integrates reflex activity between afferent input and efferent output.
- Spinal reflexes are involuntary, stereotyped responses to stimuli.
White Matter: Overview of Conduction Pathways
- Sensory vs Motor Tracts: Most pathways decussate, where axons cross the midline so the brain processes information for the contralateral side. Uncrossed pathways work on the ipsilateral side of the body.
- Pathways are paired: there is a left and a right tract.
- Each pathway is made of a chain of two or more neurons.
- Most pathways decussate: axons cross midline so the brain processes information for contralateral side.
- Uncrossed pathways work on the ipsilateral side of the body.
Spinal Cord: Sensory Tracts
- Sensory tracts originate from general sense receptors.
- Somatic sensory (somatosensory) receptors detect characteristics of an object (tactile) and stretch in joints, muscles, tendons (proprioceptors).
- Visceral sensory receptors detect changes (e.g., stretch) in an organ.
Spinal Cord: Motor Tracts
- Motor tracts control effectors such as skeletal muscles.
- Motor tracts start in the brain and include at least two neurons: an upper motor neuron in the brain that contacts a lower motor neuron in the spinal cord anterior horn that excites muscle.
Gray Matter: Overview of Spinal Reflexes
- Reflexes are the simplest response to a stimulus, involuntary, stereotyped responses to stimuli.
- Components of a reflex arc include a sensory receptor, afferent fiber, processing center (CNS), efferent fiber, and effector.
- The reflex arc is the neural pathway responsible for generating the response.
Withdrawal Reflex
- Withdrawal reflex is the withdrawal of a limb from a painful stimulus.
- This reflex is a polysynaptic reflex, involving multiple synapses.
- Afferent neurons stimulate excitatory interneurons that stimulate efferent motor neurons to flexor muscles and inhibitory interneurons that inhibit efferent neurons supplying extensor muscles (reciprocal innervation).
- Other interneurons ascend to carry the signal to a sensory area of the brain.
Stretch Reflex
- Stretch reflex is the reflexive contraction of a muscle after it is stretched.
- This reflex is monosynaptic and ipsilateral involving only one synapse.
- Stretch is detected by a muscle spindle proprioceptor.
- The sensory neuron synapses with the motor neuron innervating the same muscle.
Crossed Extensor Reflex
- Crossed extensor reflex is the extension of the opposite limb during the withdrawal reflex.
- This reflex is polysynaptic and bilateral.
- It ensures the opposing limb will be in position to bear weight when the injured limb is withdrawn.
Brain
- Classically, the brain is organized into the hindbrain, midbrain, and forebrain.
- These regions form from successive portions of the embryonic neural tube.
- These regions do not follow the functional aspects of the brain.
Organization of the Vertebrate Brain: Functional Regions
- The brainstem is the smallest and most ancient part of the brain, including the medulla oblongata and pons.
- The brainstem controls many life-sustaining processes.
- The midbrain coordinates reflex responses to sight and sound.
- The cerebellum is responsible for maintaining proper body position and coordinating motor activity.
- The forebrain is the most changed area of the brain during vertebrate evolution.
- The diencephalon includes the hypothalamus, which controls many homeostatic functions, and the thalamus, which acts as a relay station.
- The cerebrum is larger and more highly convoluted in advanced vertebrate species, including the basal nuclei and cerebral cortex.
Brainstem
- The brainstem connects the cerebrum, diencephalon, and cerebellum to the spinal cord.
- The brainstem contains ascending and descending tracts, autonomic nuclei, nuclei of cranial nerves, and reflex centers.
Medulla Oblongata
- White matter in the medulla oblongata contains ascending and descending tracts.
- Gray matter in the medulla oblongata includes the cardiac center, vasomotor center, medullary respiratory center, and nuclei for varied functions such as coughing, sneezing, vomiting, salivating, and swallowing.
Pons
- The pons is a bulge in the brainstem's anterior surface.
- It contains the middle cerebellar peduncles, which are axons connecting the pons to the cerebellum.
- The pons controls many functions, including hearing, balance, taste, eye movements, facial expression, facial sensation, and the pontine respiratory center, which helps regulate skeletal muscles.
Midbrain
- The midbrain is divided into two major parts: the tectum and the tegmentum.
- The tectum is the dorsal midbrain, containing four mounds that make up the tectal plate (corpora quadrigemina).
- The superior colliculi control visual reflexes, and the inferior colliculi control auditory reflexes.
- The tegmentum is the ventral midbrain, involved in postural motor control, including the red nuclei and substantia nigra.
Reticular Formation
- The reticular formation is a network of circuits scattered throughout the pons, midbrain, and medulla oblongata.
- Descending tracts of the reticular formation are a major component of pain control systems.
- Ascending tracts of the reticular formation include the reticular activating system, which processes sensory information and sends signals to the cortex to bring about alertness.
Cerebellum
- The cerebellum is important for balance and coordination, with three parts: the vestibulocerebellum, spinocerebellum, and cerebrocerebellum.
- The vestibulocerebellum maintains balance and controls eye movements.
- The spinocerebellum enhances muscle tone and coordinates skilled movements.
- The cerebrocerebellum plans voluntary muscle activity.
The spinocerebellum
- The spinocerebellum compares the "intentions" of higher motor centers with the "performance" of the muscles and corrects any "errors" by making the necessary adjustments to accomplish the intended movement.
Somatosensory Cortex
- The somatosensory cortex is located in the anterior part of the parietal lobe behind the central sulcus.
- It is responsible for the initial processing and perception of somesthetic (body surface) and proprioceptive (body position) sensations.
- The somatosensory cortex receives sensory information from the opposite side of the body.
- Different body areas are mapped and unequally represented on its surface (sensory homunculus).
Primary Motor Cortex
- The primary motor cortex is located in the posterior part of the frontal lobe in front of the central sulcus.
- It is responsible for nonreflex control over movements produced by skeletal muscles.
- The primary motor cortex controls the opposite side of the body.
- Different muscle groups are mapped and are unequally represented on its surface (motor homunculus).
Higher Motor Areas
- Readiness potential occurs about 750 msec before electrical activity is detectable in the motor cortex.
- Motor association areas program and coordinate complex movements, including the supplementary motor area, premotor cortex, and posterior parietal cortex.
- The cerebellum is also involved in anticipatory planning and timing of some movements.
Specialization of Cerebral Hemispheres
- The left cerebral hemisphere is typically dominant for speech, fine motor control (in right-handed people), and logical, analytical, sequential tasks.
- The right cerebral hemisphere is typically dominant for nonlanguage skills, spatial perception, artistic, and musical skills.
- Left hemisphere-dominant individuals are often considered "thinkers," while right hemisphere-dominant individuals are considered "creators."
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Description
This quiz covers the protective structures of the Central Nervous System (CNS), including the cranium, meninges, cerebrospinal fluid (CSF), and the blood-brain barrier. Learn about how these components work together to safeguard the brain and spinal cord. Test your understanding of their functions and importance in neuroanatomy.
