Nervous System Lecture Study Guide PDF

Neural Tissue 1. Difference between the Central and Peripheral Nervous System: The Central Nervous System (CNS) consists of the brain and spinal cord, serving as the control center. The Peripheral Nervous System (PNS) includes all other neural elements and transmits signals between the...

Neural Tissue 1. Difference between the Central and Peripheral Nervous System: The Central Nervous System (CNS) consists of the brain and spinal cord, serving as the control center. The Peripheral Nervous System (PNS) includes all other neural elements and transmits signals between the CNS and the rest of the body. 2. Components of the CNS and PNS: The CNS includes the brain and spinal cord. The PNS consists of cranial and spinal nerves, ganglia, and peripheral sensory receptors. 3. Somatic vs. Autonomic Nervous Systems: The Somatic Nervous System controls voluntary movements of skeletal muscles. The Autonomic Nervous System regulates involuntary functions like heartbeat and digestion and is further divided into the sympathetic and parasympathetic systems. 4. Characteristics of Neural Tissue: Neural tissue includes neurons and neuroglia (support cells). It is specialized for signal transmission and support, maintaining homeostasis, providing physical support, and defending against pathogens. 5. Structure and Function of a Neuron: ○ Dendrites: Receive signals from other neurons. ○ Neurilemma: Outer layer of the Schwann cell, aiding in nerve repair. ○ Axon: Transmits impulses away from the neuron cell body. ○ Axon Hillock: Initiates the nerve impulse. ○ Synaptic Terminals: End points where neurons communicate with other cells. 6. Function of the Myelin Sheath and Cells Forming It: The myelin sheath insulates axons to increase the speed of nerve impulses. In the CNS, it is formed by oligodendrocytes, while in the PNS, Schwann cells form the sheath. 7. Myelinated vs. Unmyelinated Axons: Myelinated axons have a myelin sheath, allowing for faster impulse transmission. Unmyelinated axons lack this sheath and transmit impulses more slowly. 8. Six Types of Neuroglial Cells and Their Functions: ○ Astrocytes (CNS): Support and regulate the blood-brain barrier. ○ Oligodendrocytes (CNS): Form the myelin sheath. ○ Microglia (CNS): Remove debris and pathogens. ○ Ependymal Cells (CNS): Produce and circulate cerebrospinal fluid. ○ Schwann Cells (PNS): Myelinate axons. ○ Satellite Cells (PNS): Support neurons in ganglia. 9. Functions of Neuron Types: ○ Sensory Neurons: Transmit sensory information to the CNS. ○ Motor Neurons: Convey signals from the CNS to muscles or glands. ○ Interneurons: Link sensory and motor neurons and process information within the CNS. 10. Differences Between: Gray and White Matter: Gray matter consists of neuron cell bodies, while white matter contains myelinated axons.  Nucleus and Ganglion: A nucleus is a collection of cell bodies in the CNS; a ganglion is in the PNS. Tract and Nerve: A tract is a bundle of axons in the CNS; a nerve is in the PNS. Sensory and Motor Tracts: Sensory tracts carry sensory information to the CNS, while motor tracts carry motor commands from the CNS to muscles or glands Cranial Nerves and Spinal Cord 1. Meninges of the Brain and Spinal Cord Dura Mater: ○ Location: Outermost layer, tough and fibrous. ○ Function: Provides protection and structural support; contains blood vessels. Arachnoid Mater: ○ Location: Middle layer, web-like structure. ○ Function: Cushions the brain; contains cerebrospinal fluid (CSF) in the subarachnoid space. Pia Mater: ○ Location: Innermost layer, thin and delicate; adheres to the surface of the brain and spinal cord. ○ Function: Protects the central nervous system (CNS) and contains blood vessels that supply the brain. 2. Regions of the Brain and Their Functions Cerebrum: Responsible for higher brain functions such as thought, action, emotion, and sensory processing. Limbic System: Involved in emotion, memory, and motivation. Key structures include the amygdala and hippocampus. Diencephalon: Contains the thalamus and hypothalamus; regulates sensory and motor signals, as well as autonomic functions. Thalamus: Acts as a relay station for sensory and motor signals to the cerebral cortex. Hypothalamus: Regulates homeostasis, including temperature, hunger, thirst, sleep, and circadian rhythms. Mesencephalon (Midbrain): Involved in vision, hearing, motor control, and sleep/wake cycles. Metencephalon (Pons): Connects different parts of the brain; regulates sleep and respiratory functions. Medulla Oblongata: Controls autonomic functions such as heart rate, breathing, and blood pressure. Cerebellum: Coordinates voluntary movements, balance, and motor learning. 3. Relationship Between Embryonic Brain Vesicles and Regions of the Adult Brain The embryonic brain develops into distinct vesicles that later differentiate into specific regions of the adult brain. For example: ○ Forebrain (Prosencephalon): Becomes the cerebrum and diencephalon. ○ Midbrain (Mesencephalon): Remains the midbrain in adults.  ○ Hindbrain (Rhombencephalon): Develops into the pons, medulla oblongata, and cerebellum. 4. Ventricles of the Brain Lateral Ventricles: Two large, C-shaped cavities located in each hemisphere of the cerebrum; they produce and contain cerebrospinal fluid. Third Ventricle: A narrow cavity located in the diencephalon, between the two halves of the thalamus. Interventricular Foramen: The opening that connects each lateral ventricle to the third ventricle. Fourth Ventricle: Located between the brainstem and the cerebellum, it connects to the central canal of the spinal cord and allows CSF to flow around the brain. Cerebral Aqueduct (Aqueduct of Midbrain): A narrow passage connecting the third ventricle to the fourth ventricle. 5. Production of Cerebrospinal Fluid (CSF) CSF is produced primarily in the choroid plexus, a network of blood vessels located within the ventricles of the brain. 6. Differences Between Fissure, Sulcus, and Gyrus Fissure: A deep groove that divides large regions of the brain; for example, the longitudinal fissure separates the left and right hemispheres. Sulcus: A shallower groove between folds (gyri) of the brain, which increases the surface area of the cerebral cortex. Gyrus: A ridge or fold between the sulci; increases the surface area and allows for more neurons in the cerebral cortex. 7. Functions of the Various Lobes of the Cerebrum Frontal Lobe: Responsible for reasoning, planning, speech, movement, emotions, and problem-solving. Parietal Lobe: Processes sensory information related to touch, temperature, pain, and spatial orientation. Temporal Lobe: Involved in processing auditory information, memory, and emotion. Occipital Lobe: Primarily responsible for visual processing and perception. 8. Cranial Nerves There are 12 pairs of cranial nerves, each with specific functions: 1. Olfactory (I): Smell. 2. Optic (II): Vision. 3. Oculomotor (III): Eye movement and pupil constriction. 4. Trochlear (IV): Eye movement. 5. Trigeminal (V): Sensation of the face and motor functions such as biting and chewing. 6. Abducens (VI): Eye movement. 7. Facial (VII): Facial expressions, taste, and secretion of saliva and tears. 8. Vestibulocochlear (VIII): Hearing and balance. 9. Glossopharyngeal (IX): Taste, swallowing, and salivation. 10. Vagus (X): Controls autonomic functions of the heart, lungs, and digestive tract. 11. Accessory (XI): Shoulder and neck movement. 12. Hypoglossal (XII): Tongue movement. Spinal Cord and Spinal Nerves Gross Structure of the Spinal Cord: The spinal cord is a cylindrical structure that extends from the base of the skull (medulla oblongata) to approximately the first or second lumbar vertebra (L1-L2) in adults. Cervical Enlargement: Located between C4 and T1, it corresponds to the innervation of the upper limbs. Lumbar Enlargement: Found between L1 and S3, it corresponds to the innervation of the lower limbs. Cauda Equina: A bundle of spinal nerves and spinal nerve rootlets that extends beyond the conus medullaris (the terminal part of the spinal cord), resembling a horse's tail. Difference in Length between the Spinal Cord and the Vertebral Column: The spinal cord is shorter than the vertebral column, measuring about 42-45 cm in adults, while the vertebral column is longer due to the presence of intervertebral discs and the continuous growth of vertebrae. The continuous spinal cord typically ends at the L1-L2 level in adults. Meninges Surrounding the Spinal Cord: The spinal cord is surrounded by three layers of meninges: ○ Dura Mater: The tough outermost layer. ○ Arachnoid Mater: The middle layer, web-like in appearance. ○ Pia Mater: The delicate innermost layer that adheres closely to the surface of the spinal cord. Structure of the Spinal Cord: The spinal cord contains both white matter and grey matter: ○ White Matter: Comprised of myelinated axons organized into ascending (sensory) and descending (motor) tracts. ○ Grey Matter: Contains neuron cell bodies, organized into horns—dorsal (posterior), ventral (anterior), and lateral horns. Structures Originating from the Spinal Cord to Form Spinal Nerves: The spinal cord gives rise to spinal nerves through the merging of two roots: ○ Dorsal (posterior) Root: Contains sensory fibers. ○ Ventral (anterior) Root: Contains motor fibers. Relationship Between a Root, Ramus, and Plexus: A root is a bundle of nerve fibers that emerge from the spinal cord.  A ramus (plural: rami) is a branch of a spinal nerve after it exits the intervertebral foramen. A plexus is a network of intermingling spinal nerve rami that supply a specific region of the body. Difference Between Dorsal and Ventral Roots of a Spinal Nerve: Dorsal Roots: Carry sensory information into the spinal cord (afferent). Ventral Roots: Carry motor commands from the spinal cord to muscles (efferent). Number and Names of the Spinal Nerves: There are 31 pairs of spinal nerves: ○ Cervical (C1-C8) ○ Thoracic (T1-T12) ○ Lumbar (L1-L5) ○ Sacral (S1-S5) ○ Coccygeal (Co1) Ramus of a Spinal Nerve Participating in Nerve Plexus Formation: The ventral ramus participates in the formation of nerve plexuses. Epineurium, Perineurium, and Endoneurium: Epineurium: The outermost layer of connective tissue surrounding a nerve. Perineurium: The middle layer that surrounds individual fascicles (bundles of nerve fibers). Endoneurium: The innermost layer surrounding each individual nerve fiber (axon). Four Nerve Plexuses: Cervical Plexus: C1-C4; innervates neck muscles and skin. Brachial Plexus: C5-T1; innervates upper limbs (important nerves include the median, ulnar, and radial nerves). Lumbar Plexus: L1-L4; innervates lower limbs (important nerves include the femoral and obturator nerves). Sacral Plexus: L4-S4; innervates pelvic region and lower limbs (important nerves include the sciatic nerve). Pathways for Somatic Motor and Sensory Fibers: Somatic motor fibers exit the spinal cord via the ventral roots. Somatic sensory fibers enter the spinal cord through the dorsal roots. Components of a Spinal Reflex:  Components include a sensory receptor, sensory neuron, integration center (spinal cord), motor neuron, and effector (muscle or gland). Definition of a Tract: A tract refers to a bundle of axons in the central nervous system that share a common origin, destination, and function. Cell Bodies in Dorsal Root Ganglia and Anterior Grey Horn: Dorsal Root Ganglia: Contain the cell bodies of sensory neurons (pseudounipolar neurons). Anterior Grey Horn: Contains the cell bodies of somatic motor neurons. Autonomic Nervous System Comparison of Somatic and Autonomic Nervous Systems: Somatic Nervous System: Controls voluntary movements by innervating skeletal muscles. It consists of motor neurons that convey signals from the central nervous system (CNS) to the muscles and is responsible for reflexes and conscious movement. Autonomic Nervous System (ANS): Regulates involuntary bodily functions, such as heart rate, digestion, and respiratory rate. It operates below the level of consciousness and is divided into the sympathetic and parasympathetic systems. Features of the Autonomic Nervous System: Dual Innervation: Most organs receive input from both the sympathetic and parasympathetic nervous systems, which typically have opposing effects on target organs. This allows for fine-tuned regulation of bodily functions. Preganglionic Neuron: The first neuron in the autonomic pathway originates in the CNS (either the spinal cord or brainstem) and extends to a ganglion, where it synapses with a postganglionic neuron. Preganglionic neurons are myelinated and release acetylcholine (ACh). Postganglionic Neuron: The second neuron in the autonomic pathway that extends from the ganglion to the target organ. Postganglionic neurons are unmyelinated and can release either acetylcholine (ACh) or norepinephrine (NE), depending on the system (sympathetic or parasympathetic). Body Structures Innervated by the Autonomic Nervous System: The ANS innervates various structures, including: Heart and blood vessels Smooth muscles in the digestive tract, bronchi, and blood vessels Glands (salivary, sweat, and digestive glands) Adipose tissue Organs like the liver, kidneys, and reproductive organs Differences between Parasympathetic and Sympathetic Nervous Systems: Location: ○ Parasympathetic: Craniosacral division (origins in the brainstem and sacral spinal cord). ○ Sympathetic: Thoracolumbar division (origins in the thoracic and lumbar regions of the spinal cord). Structure: ○ Parasympathetic: Long preganglionic fibers and short postganglionic fibers; ganglia located near or in target organs.  ○ Sympathetic: Short preganglionic fibers and long postganglionic fibers; ganglia located near the spinal cord in sympathetic chains or collateral ganglia. Function: ○ Parasympathetic: Promotes "rest-and-digest" activities, conserving energy, and facilitating digestion. ○ Sympathetic: Prepares the body for "fight-or-flight" responses, increasing heart rate, dilating bronchi, and mobilizing energy resources. Special Senses 1. Three Anatomical Regions of the Ear: The three regions are the external ear, middle ear, and inner ear. 2. Ceruminous Glands: Ceruminous glands are found in the external auditory canal. Their function is to produce cerumen (earwax), which helps to protect the ear by trapping dust and debris and providing a waterproof barrier. 3. Auditory Ossicles: The auditory ossicles consist of three bones: the malleus (hammer), incus (anvil), and stapes (stirrup). They are arranged in a chain between the tympanic membrane (eardrum) and the oval window of the cochlea. The ossicles amplify sound vibrations from the eardrum to the inner ear, with the stapes transmitting vibrations to the oval window. 4. Labyrinth and Bony Labyrinth: The labyrinth refers to the inner ear's complex system of canals, while the bony labyrinth is the rigid, bony outer wall that encases the inner ear structures. The bony labyrinth contains perilymph fluid, while the membranous labyrinth, within the bony labyrinth, contains endolymph fluid. 5. Divisions of the Bony Labyrinth: The bony labyrinth is divided into three structures: the cochlea (hearing), the vestibule (balance), and the semicircular canals (balance). 6. Utricle and Saccule Function: The utricle and saccule are involved in detecting linear acceleration and the position of the head relative to gravity, contributing to balance and spatial orientation. 7. Structure on the Oval Window: The stapes rests on the surface of the oval window. 8. Hair Cells: Hair cells are specialized sensory cells located in the inner ear, specifically within the cochlea and the vestibular system. They have hair-like projections (stereocilia) that respond to fluid motion and sound waves, converting mechanical stimuli into electrical signals. 9. Function of the Semicircular Canals: The semicircular canals detect rotational movements of the head, contributing to balance and spatial orientation. 10. Vestibular Complex Structures: The vestibular complex includes the semicircular canals, utricle, and saccule, all of which are involved in balance and equilibrium. 11. Arrangements of Ducts in the Cochlea: The cochlea contains three main ducts: the scala vestibuli (upper duct), scala media (cochlear duct), and scala tympani (lower duct). The scala media is filled with endolymph, while the scala vestibuli and scala tympani contain perilymph. 12. Organ of Corti: The organ of Corti is the sensory organ of hearing, located within the scala media of the cochlea. It contains hair cells that convert sound vibrations into nerve impulses. 13. Steps Involved in Auditory Sensation: Sound waves enter the ear canal, vibrate the tympanic membrane, and cause the ossicles to move. The stapes pushes against the oval window, creating pressure waves in the perilymph of the cochlea. This movement stimulates hair cells in the organ of Corti, which generate electrical signals sent to the brain via the auditory nerve. 14. Nerve for Auditory Sensations: The auditory sensations are transmitted to the brain via the cochlear branch of the vestibulocochlear nerve (cranial nerve VIII). 15. Palpebrae: The palpebrae are the eyelids, which protect the eyes and help spread tears over the surface of the eye. 16. Lacrimal Apparatus Function: The lacrimal apparatus produces and drains tears, keeping the surface of the eye moist and providing protection from irritants. 17. Three Tunics of the Eye: The three tunics of the eye are the fibrous tunic, vascular tunic, and neural tunic. 18. Location of the Cornea and Sclera: The cornea and sclera are found in the fibrous tunic. 19. Structures in the Vascular Tunic: The vascular tunic contains the choroid (provides nutrients to the eye), ciliary body (controls lens shape), and iris (regulates pupil size). 20. Pupil: The pupil is the opening in the center of the iris that allows light to enter the eye. 21. Layers of the Neural Tunic: The neural tunic consists of the retina, which includes the pigmented layer and the neural layer. 22. Function of Rods and Cones: Rods are responsible for vision in low light and peripheral vision, while cones are responsible for color vision and visual acuity. Rods are more numerous than cones. 23. Macula Lutea and Fovea Centralis: The macula lutea is a yellowish area near the center of the retina, responsible for high-acuity vision. The fovea centralis is the central part of the macula, where visual acuity is the highest due to a high concentration of cones. 24. Main Chambers of the Eye: The two main chambers of the eye are the anterior chamber (filled with aqueous humor) and the posterior chamber (also filled with aqueous humor, behind the iris). 25. Function of the Lens: The lens focuses light onto the retina, allowing for clear vision at varying distances by changing shape through the action of the ciliary muscles