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Questions and Answers
Which structure is absent from the axon in a typical nerve cell?
What is the primary function of neurofibrils within a neuron?
During a neuron's activity, what happens to the Nissl bodies?
What characteristic differs between dendrites and axons with respect to branching?
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Which part of the neuron is primarily responsible for carrying impulses away from the cell body?
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What is one primary reason for the unidirectional transmission of nerve impulses in a neuron?
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What initiates the presence of Nissl bodies in a neuron's cell body?
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How do dendrites contribute to neural communication?
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What role do microglia perform in the nervous system?
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Which component is not part of the structure of nerves?
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What is a primary function of glial cells?
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Which type of neuroglia is primarily involved in the secretion of cerebrospinal fluid?
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What distinguishes white matter from gray matter?
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Which glial cell is responsible for enclosing axons in the central nervous system?
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What is the main characteristic of macroglia compared to microglia?
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What strengthens the blood-brain barrier?
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Which statement accurately describes unipolar neurons?
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What is the main function of sensory neurons?
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Which characteristic is true for myelinated nerve fibers?
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What is the primary function of the myelin sheath?
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In which location are bipolar neurons predominantly found?
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What differentiates unmyelinated nerve fibers from myelinated ones?
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Which type of neuron functions primarily to connect sensory and motor neurons?
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Which structure is NOT a characteristic feature of the myelin sheath?
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What is the first step in the formation of the nervous system during embryonic development?
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Which of the following components is NOT involved in the protection of the brain and spinal cord?
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Which layer of the meninges is the thickest and toughest?
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Which part of the nervous system does the neural tube ultimately develop into?
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At which week of pregnancy does the formation of the neural tube occur?
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What is the role of the cerebrospinal fluid in the central nervous system?
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Which of the following correctly identifies the embryonic layers involved in the development of the nervous system?
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What happens to the neural tube as it expands anteriorly?
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What is the primary role of the cerebellum within the brain's structure?
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Which of the following accurately describes the composition of the medulla oblongata?
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Which structure of the spinal cord is primarily responsible for the relay of messages between the body and the brain?
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What is the shape formed by the gray matter in a cross-sectional view of the spinal cord?
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What is the main function of the ventricles in the brain?
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What is the primary function of the cerebrospinal fluid (CSF)?
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Which of the following is NOT a part of the blood-brain barrier (BBB) structure?
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What connects the two hemispheres of the brain?
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Which component forms the floor of the third ventricle?
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Which lobe of the brain is primarily responsible for visual processing?
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What role do projection fibers serve in the cerebral white matter?
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Which term describes the connective tissue within the lateral ventricles?
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How many lobes is the cerebral cortex divided into?
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Which structure is found between the two thalamic masses?
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In what area is the cerebellum located in relation to the brain stem?
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What is the primary role of motor (efferent) nerves in the peripheral nervous system?
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Which of the following best describes the function of the sensory (afferent) nerves?
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In what way do cranial nerves differ from spinal nerves in the peripheral nervous system?
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What is the role of the autonomic nervous system in the peripheral nervous system?
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Which sub-division of the autonomic nervous system typically prepares the body for 'fight or flight' responses?
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How are spinal nerves structured in terms of their roots?
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Which of the following statements about the somatic nervous system is true?
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What unique feature is found only in the dorsal root of spinal nerves?
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What primarily differentiates the pre-ganglionic fibers of the sympathetic division from those of the parasympathetic division?
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Which neurotransmitter is primarily associated with the sympathetic division's effect on effector cells?
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Which effect is NOT associated with the sympathetic division?
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Where are the ganglia of the parasympathetic division primarily located?
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Which of the following best describes the effect of the parasympathetic division on the gall bladder sphincter?
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What property distinguishes the sympathetic division's ganglia from those of the parasympathetic division?
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What is the primary effect of the sympathetic division on the digestive system?
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Which statement about the autonomic nervous system is correct?
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What is the primary consequence of bilateral damage to the primary visual area?
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Which part of the brain is primarily responsible for processing auditory signals?
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Why do the face and hand areas occupy larger portions of the motor cortex?
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What type of impairment results from damage to the secondary auditory area?
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Where are the sympathetic ganglia primarily located?
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What chemical messenger is utilized at the synapse between the pre-ganglionic and post-ganglionic neurons?
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What is the primary function of Wernicke's area?
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What is the primary function of the vagus nerve on heart rate?
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Which area of the brain is involved in coordinating and directing muscle contractions for purposeful movements?
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What are association areas primarily responsible for?
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Which areas are classified as the three functional levels of the central nervous system?
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What is the consequence of damage to the primary motor area?
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What is the role of the primary somatic sensory area?
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What is the cause of tactile agnosia when the secondary somatic sensory area is damaged?
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What role does the prefrontal association area play in the brain?
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What type of visual impairment is characterized by the inability to recognize objects despite intact vision?
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What determines the extent of the cortical sensory area for a specific body part?
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Why do the tongue, face, and hand occupy large areas in the cerebral sensory cortex?
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What results from the ablation of the primary somatic sensory area?
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Which division of the autonomic nervous system is associated with the body's 'fight or flight' response?
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Study Notes
Neural Tissue
- Neurons are the functional units of neural tissue, responsible for transmitting nerve impulses.
- Neuroglia support and protect neurons.
- The nerve cell body contains cytoplasm, a nucleus, mitochondria, Golgi apparatus, ribosomes, lipid droplets, glycogen, Nissl bodies, and neurofibrils.
- Nissl bodies are granular structures unique to neurons, containing RNA and originating from the rough endoplasmic reticulum. They are involved in protein synthesis and are abundant in the cell body and dendrites.
- Neurofibrils are fine filaments found in all parts of the neuron, providing structural support.
- Dendrites are branched extensions of the neuron's cell body that receive nerve impulses and transmit them towards the cell body.
- The axon is a long, slender projection of the neuron that carries nerve impulses away from the cell body. It originates from the axon hillock and branches at the terminal end, forming terminal buttons that release neurotransmitters.
- Dendrites have a large surface area due to branching, maximizing contact with other neurons for efficient signal reception.
- Nerve impulse transmission in a neuron is unidirectional, flowing from dendrites to the cell body and then along the axon.
- Nissl bodies increase during rest and decrease upon stimulation because they provide a store of nutrients for neuronal activity.
- Unipolar neurons have one axon that branches into two parts: an axon and a dendrite. They are found in the spinal ganglia.
- Bipolar neurons have two extensions: one axon and one dendrite. They are found in the retina of the eye.
- Multipolar neurons have one axon and several short dendrites. They are found in the anterior horns of the spinal cord and the cerebral cortex.
- Sensory neurons carry signals from sensory organs to the central nervous system. They are located in the spinal ganglia.
- Motor neurons carry signals from the central nervous system to muscles. They are located in the cerebral cortex and anterior horns of the spinal cord.
- Interneurons connect sensory and motor neurons functionally. They are located in the central nervous system.
- A nerve fiber is the axon or dendrite along with its surrounding coverings.
- Myelinated nerve fibers have axons or dendrites covered by a myelin sheath, either with or without Schwann cells. They are found mainly in the white matter.
- Non-myelinated nerve fibers have axons or dendrites covered by Schwann cells but lack a myelin sheath. They are present in some parts of the peripheral nervous system.
- Unmyelinated nerve fibers (bare) lack any covering and are partially covered by neuroglial cells. They are located primarily in the gray matter.
- The myelin sheath is composed of a phospholipid substance and provides electrical insulation for nerve fibers, increasing the speed of nerve impulse transmission.
- Nodes of Ranvier are gaps in the myelin sheath that help facilitate rapid nerve impulse conduction.
- Schwann cells are thin, transparent cells that wrap around axons or dendrites in the peripheral nervous system, producing myelin sheaths.
- Nerves are bundles of nerve fibers enclosed in connective tissue sheaths.
- Neuroglia, also known as glial cells, are active, continuously dividing cells that outnumber neurons in the nervous system.
- Astrocytes are a type of neuroglia with numerous processes and vascular feet that interact with blood vessels. They support neurons and contribute to the blood-brain barrier.
- Oligodendrocytes are neuroglia that form myelin sheaths around axons in the central nervous system.
- Ependymal cells line the ventricles of the brain and the central canal of the spinal cord. They secrete cerebrospinal fluid. Some ependymal cells function as choroid epithelial cells, lining the choroid plexuses.
- Microglia are small, branching glial cells that act as immune cells within the central nervous system, engulfing pathogens and damaged neurons.
- Neuroglia contribute to the blood-brain barrier, provide metabolic support to neurons, and aid in the repair of damaged neural tissue.
- White matter, composed of myelinated nerve fibers, neuroglia, and capillaries, serves as a conduit for transmitting nerve impulses throughout the central nervous system.
- Gray matter, containing nerve cell bodies, unmyelinated nerve fibers, neuroglia, and capillaries, is responsible for processing information and integrating neural activity.
Origin and Formation of the Nervous System
- The nervous system develops from the ectoderm (outermost embryonic layer) during the third week of pregnancy.
- The neural plate forms a thickening on the dorsal part of the ectoderm and folds inward to create the neural groove.
- The sides of the neural groove fuse to form the neural tube, separating from the ectoderm by the end of the fourth week.
- The anterior portion of the neural tube expands to become the brain, while the posterior region remains less swollen to form the spinal cord.
- The developing brain differentiates into the forebrain, midbrain, and hindbrain.
Protection of the Brain and Spinal Cord
- The brain and spinal cord are protected by the skull, vertebral column, meninges, cerebrospinal fluid, and the blood-brain barrier.
- Meninges are three protective membranes that envelop the brain and spinal cord: the dura mater (outermost), arachnoid mater (middle), and pia mater (innermost).
- Cerebrospinal fluid (CSF) cushions and protects the central nervous system by circulating within the ventricles of the brain and the subarachnoid space.
- The blood-brain barrier acts as a selective barrier, regulating the transport of substances between the blood and brain tissue, protecting the delicate neuronal environment.
Cerebrospinal Fluid (CSF)
- CSF is a clear, watery fluid that circulates within the ventricles of the brain and the subarachnoid space, providing buoyancy, protection, and nutrient transport.
- It filters waste products, including sugars, minerals, and proteins, from the blood.
Blood-Brain Barrier (BBB)
- The BBB is formed by the expanded ends of astrocyte cell processes (vascular bulbs), surrounding blood vessels.
- It prevents harmful substances in the blood from reaching brain cells and regulates the chemical environment of the brain.
Main Parts of the Brain
- The brain consists of four major parts: the cerebrum, diencephalon, brainstem, and cerebellum.
Cerebrum
- The cerebrum is the largest part of the brain composed of two hemispheres connected by the corpus callosum and anterior commissure.
- The outer layer of the cerebrum is the cerebral cortex, composed of gray matter, while the inner part contains white matter.
- The cortex is further divided into four lobes: frontal, parietal, temporal, and occipital.
- Each hemisphere has a lateral ventricle, with a basal mass of gray matter known as the basal ganglia located within.
Cells in Cerebral Cortical White Matter
- Pyramidal cells and multipolar cells form the white matter, their axons connecting various regions of the brain.
- Interneurons connect different areas of the cerebral cortex.
Fibers in Cerebral White Matter
- Connecting fibers connect different regions within the same hemisphere.
- Commissural fibers cross the corpus callosum or anterior commissure, connecting corresponding areas in both hemispheres.
- Projection fibers connect the cerebral cortex to other parts of the nervous system, including outgoing motor fibers and incoming sensory fibers.
Basal Ganglia
- These are masses of gray matter found on the lateral sides of the diencephalon and deep under the cerebral cortex.
- They play a role in motor control, learning, and planning.
Diencephalon (Interbrain)
- The diencephalon connects the cerebrum to the brainstem and is subdivided into the thalamus and hypothalamus.
- The thalamus, composed of two large oval masses of gray matter, serves as a relay center for sensory information. It also regulates consciousness and sleep.
- The hypothalamus, located at the base of the diencephalon, controls vital functions such as temperature regulation, thirst, and hunger. It also influences hormone production through its connection to the pituitary gland.
The Brain Stem
- The brainstem connects the cerebrum and cerebellum to the spinal cord. It consists of the medulla oblongata, pons, and midbrain and is responsible for regulating essential functions such as breathing, circulation, and reflexes.
Medulla Oblongata
- The medulla oblongata is the lowermost section of the brainstem, containing both gray and white matter. It controls vital functions like breathing, heart rate, and blood pressure.
Pons
- The pons, located above the medulla oblongata, contains several nuclei that relay information from the cerebrum to the cerebellum.
- It also participates in regulating breathing and sleeping.
Midbrain
- The midbrain, located above the pons, contains the corpora quadrigemina (involved in auditory and visual reflexes) and cerebral peduncles (which carry motor pathways from the cerebrum to the spinal cord).
Cerebellum
- The cerebellum is a smaller structure located at the back of the brain, weighing approximately 140 grams.
- It is involved in coordinating movement, balance, posture, and muscle tone. It does not initiate movement but regulates and refines movements.
- It consists of two cerebellar hemispheres connected by a central structure called the vermis.
- Its internal structure comprises an outer layer of gray matter and a central core of white matter called the arbor vitae.
Spinal Cord
- The spinal cord is a long, cylindrical structure extending from the brainstem to the lower back. It is responsible for transmitting nerve impulses between the brain and the rest of the body, as well as coordinating reflexes.
- The spinal cord shows bulges (enlargements) in the cervical and lumbar regions, reflecting the greater density of motor neurons supplying the limbs. It tapers at the lower end and ends in a structure called the conus medullaris.
- A cross-section of the spinal cord reveals a central "X" shape composed of gray matter, surrounded by white matter.
- The gray matter is further divided into anterior and posterior horns. The anterior horns contain motor neurons, while the posterior horns contain sensory neurons.
- The white matter in the spinal cord is divided into anterior, posterior, and lateral columns or tracts. These tracts contain axons that carry information up and down the spinal cord.
Autonomic Nervous System (ANS)
- The ANS Controls involuntary functions, regulating processes such as heartbeat, breathing, digestion, and sweating, without conscious control. It operates through special pathways involving cranial and spinal nerves, but also has its own pathways.
- It is responsible for maintaining a constant internal environment (homeostasis).
- It is divided into two branches: the sympathetic and parasympathetic nervous systems.
Sympathetic Nervous System
- The sympathetic nervous system prepares the body for "fight-or-flight" responses, mobilizing energy resources during stress.
- Its centers are located in the gray matter of the thoracic and lumbar regions of the spinal cord.
- Its ganglia form chains situated alongside the spinal column.
- Sympathetic nerves originate from sympathetic ganglia and project to internal organs.
- Pre-ganglionic fibers are short, and post-ganglionic fibers are long.
- Acetylcholine is the neurotransmitter released at the synapse between pre-ganglionic and post-ganglionic neurons.
- Norepinephrine is the neurotransmitter released at the synapse between post-ganglionic neurons and effector cells.
Parasympathetic Nervous System
- The parasympathetic nervous system promotes "rest and digest" functions, conserving energy and maintaining normal bodily functions.
- Its centers are located in the gray matter of the brainstem and sacral region of the spinal cord.
- Its ganglia are located near or within organs.
- Parasympathetic nerves include the vagus nerve and pelvic nerves.
- Pre-ganglionic fibers are long, while post-ganglionic fibers are short.
- Acetylcholine is the neurotransmitter released at both pre-ganglionic and post-ganglionic synapses.
Peripheral Nervous System (PNS)
- The PNS connects the CNS to the rest of the body.
- It consists of nerves (bundles of nerve fibers) and ganglia (collections of neuronal cell bodies).
Types of Nerves Based on Function
- Sensory (afferent) nerves carry sensory information from the body to the CNS.
- Motor (efferent) nerves carry motor commands from the CNS to muscles and glands.
- Mixed nerves contain both sensory and motor fibers, transmitting signals in both directions.
Types of Nerves Based on Connection to CNS
- Cranial nerves (12 pairs) connect to the brain and supply the head and neck.
- Spinal nerves (31 pairs) connect to the spinal cord and supply the rest of the body. Each spinal nerve has two roots: a dorsal (sensory) root and a ventral (motor) root.
Divisions of the Peripheral Nervous System
-
Somatic Nervous System: Controls voluntary functions, involving muscles under conscious control.
- Sensory: Carries sensations (touch, temperature) to the CNS.
- Motor: Carries motor commands from the CNS to voluntary muscles.
-
Autonomic Nervous System: Controls involuntary functions, regulating internal organs and processes without conscious control.
- Sensory: Carries signals from internal organs to the CNS (e.g., hunger, thirst).
- Motor: Carries commands from the CNS to involuntary muscles (smooth muscles, heart, glands) and glands.
Spinal Cord Composition
- The spinal cord is composed of gray matter (in the center) and white matter (surrounding the gray matter).
- The gray matter is shaped like a butterfly or an "X" and contains the cell bodies of neurons, while the white matter contains the axons of neurons.
- The anterior horns of the gray matter contain motor neurons, while the posterior horns contain sensory neurons. The lateral horns, when present, contain autonomic neurons.
- The white matter is divided into three columns (anterior, posterior, and lateral), containing ascending and descending tracts that respectively carry sensory and motor signals.
- Note:* This is just a summary of the text. Further research and supplementary resources are recommended for a complete understanding of the nervous system.
Central Nervous System Functional Levels
- The central nervous system has three functional levels: the upper brain level (cortical level), the lower brain level (brainstem, cerebellum, thalamus, hypothalamus), and the spinal cord level.
Cerebral Cortex Functional Areas
- The cerebral cortex is divided into three functional areas: sensory areas, motor areas, and association areas.
Sensory Areas
- Visual Sensory Area: Located in the occipital lobes, divided into primary and secondary areas. The primary visual area receives direct visual signals from the eyes, while the secondary area connects visual information with past experiences, allowing for visual perception. Damage to the primary area leads to vision loss, while damage to the secondary area results in visual agnosia (the inability to recognize things visually).
- Auditory Sensory Area: Located in the temporal lobes, also divided into primary and secondary areas. The primary auditory area receives auditory signals from the ears, while the secondary area receives input from the primary area, believed to be essential for interpreting sounds and auditory perception. Damage to the primary area causes deafness, and damage to the secondary area leads to auditory agnosia (the inability to recognize sounds).
Motor Areas
- Motor cortex: Located in front of the Rolandic fissure, occupying the posterior third of each frontal lobe. It involves both primary and secondary motor areas. The primary motor area is located directly in front of the Rolandic fissure and controls voluntary muscle movement. Removal of a portion leads to paralysis on the opposite side of the body. The secondary motor area coordinates and directs muscle contractions, located anterior to the primary motor area.
- The size of the motor cortex areas devoted to specific body parts is proportional to the skill needed for that action, not the size of the muscles involved. This explains why the face and hand occupy relatively large areas in the motor cortex.
Association Areas
- Association areas comprise all cortical areas excluding sensory and motor areas. They are essential for higher cognitive functions, connecting cortical areas with subcortical structures.
- Parietal, Temporal, and Occipital Association Area: These process input from surrounding sensory areas.
- Wernicke's Area: Located within the parietal-temporal-occipital Association Area, plays a crucial role in language comprehension and intelligence.
- Prefrontal Association Area: Works with the motor cortex to execute complex movements and is involved in forming abstract ideas and cognitive reasoning.
- Broca's Area: Located within the prefrontal association area, provides the neural circuit for forming words, working closely with Wernicke's area.
- Posterior Association Area: Located in the frontal and temporal lobes, plays a role in behaviors, emotions, motivation, and learning.
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Description
Test your knowledge on the basic structures and functions of neurons in the nervous system. This quiz covers topics such as neurofibrils, Nissl bodies, and the differences between dendrites and axons. Challenge yourself with questions about neural communication and nerve impulse transmission.
