Anatomy of the Nervous System Part 1 PDF

The Nervous System Part 1 By: Dr. Mary Hazel Bolanon September 2024  Embryonic Germ Layers ▪ A Zygote develops into an organism. ▪ Three embryonic germ layers give rise to different tissues in the body. ▪ Endoderm ▪ Mesoderm ▪ Ectoderm ▪thr...

The Nervous System Part 1 By: Dr. Mary Hazel Bolanon September 2024  Embryonic Germ Layers ▪ A Zygote develops into an organism. ▪ Three embryonic germ layers give rise to different tissues in the body. ▪ Endoderm ▪ Mesoderm ▪ Ectoderm ▪three embryonic germ layers that give rise to different tissues in the body. ▪Endoderm (inner germ layer) is responsible for generating the lining tissues of various spaces within the body, such as the mucosae of the digestive and respiratory systems. ▪Mesoderm (middle germ layer) gives rise to most of the muscle and connective tissues. ▪Ectoderm (outer germ layer) develops into the integumentary system (the skin) and the nervous system.  Neural Tube ▪ Ectoderm: nervous system ▪ Anterior end: brain ▪ Posterior end: spinal cord ▪ Neural crest: structures of the PNS Primary & Secondary Vesicles  Stages of Embryonic Development Neural Tube Primary Vesicle Secondary Vesicle Adult Structures Ventricles Telencephalon Cerebrum (cerebral Lateral cortex, white matter, and Ventricles Prosencephalon basal nuclei) (forebrain) Diencephalon Thalamus, pineal gland, Third Anterior End and hypothalamus Ventricle Mesencephalon Mesencephalon Brain stem (midbrain) Cerebral (midbrain) Aqueduct Metencephalon Brain stem (pons) and Fourth cerebellum Ventricle Rhombencephalon Myelencephalon Brain stem (medulla Fourth (hindbrain) oblongata) Ventricle Posterior End Spinal Cord Central Canal  Spinal Bifida a) A birth defect of the spinal cord caused when the neural tube fails to close completely, but the rest of development continues. The result is the emergence of meninges and neural tissue through the vertebral column in the form of a cyst. b) A fetal myelomeningocele is evident in an ultrasound taken at 21 weeks. The Central Nervous System The Central Nervous System Composed of the brain and spinal cord The spinal cord is a single structure, while the brain has four major regions: Cerebrum Diencephalon Brain stem Cerebellum The brain contains nearly 97% of the body's neural tissue. A typical adult brain weighs about 3 lbs. and has a volume of 1200 ml. Brain size varies among individuals: On average, male brains are about 10% larger than female brains, due to body size differences. There is no correlation between brain size and intelligence. People with both small and large brains are functionally normal. Cerebrum  Cerebrum Cerebrum = accounts for 80% of the brain’s mass, large component of the CNS in humans a. conscious thought, memory storage and processing, sensory processing, and the regulation of skeletal muscle contractions ▪by a Longitudinal Fissure = separates the 2 cerebral hemispheres separated (right and left cerebral hemisphere ) connected by the white matter of the Corpus Callosum deep within the cerebrum for communication between the two hemispheres  Cerebrum CEREBRAL CORTEX = folded surface (a thin, extensive region of gray matter responsible for higher functions of the nervous system) cerebrum functions : conscious thought memory storage and processing sensory processing regulation of skeletal muscle contractions cerebral cortex = GRAY matter of the cerebrum and is responsible for all qualities associated with “consciousness.” Each hemisphere is concerned with the sensory and motor functions of the opposite (contralateral) side of the body.  Hemispheres: symmetrical in structure not equal in function lateralization or specialization of the cortical functions: i. Right brain = analyzes sensory information and relates the body to the sensory environment; interpretive centers in this hemisphere enable you to identify familiar objects by touch, sight, smell, taste, or feel. Right brained individuals are often more artistic, musically inclined, or attuned to their emotions. ii. Left brain = possesses the general interpretive and speech centers and is important in language-based skills, important in reading, writing, speaking, math, and logic.  Cerebral Cortex ▪ The cerebral cortex is divided into four major lobes: frontal, parietal, occipital, and temporal. ▪ Gyrus (wrinkle or fold); Sulcus (shallow groove that divides the lobes); Fissure (deep groove)  Functional Areas of the Cerebral Cortex ▪ Brodmann’s Areas of the Cerebral Cortex: On the basis of cytoarchitecture, the anatomist Korbinian Brodmann described the extensive array of cortical regions, as illustrated in his figure. Subsequent investigations found that these areas corresponded very well to functional differences in the cerebral cortex. Functional Areas of the Cerebral Cortex ii. Premotor Cortex (Brodmann Area 6) = anterior to the precentral gyrus of the frontal lobe 1. for planning movements 2. Controls learned motor skills that are repeated or patterned (such as playing an instrument or typing) -> “ muscle memory” 3. coordinates the movements of muscles simultaneously and/or sequentially by sending activating impulses to the primary motor cortex iv. Frontal Eye Fields (Brodmann Area 8) = located anterior to the premotor cortex and superior to the Broca’s 1. Controls the voluntary movements of the eye 2. Attend to visual stimuli but has no role in the interpretation of visual stimuli. iii. Broca’s Area (Brodmann Areas 44, 45) = also known as the speech center, is located anterior to the lower part of the premotor cortex 1. Responsible for the production of language (motor speech including thinking about or planning to speak) or controlling movements responsible for speech. 2. It is located only on the left hemisphere in most people Functional Areas of the Cerebral Cortex Visual Cortex = located within the occipital lobe of the cerebrum 1. Primary Visual Cortex (Brodmann Area 17) processes and interprets light information from the retina of the eye such as color, form, texture, and movement. 2. Visual Association Area (Brodmann Area 18, 19) integrates and analyzes the visual information coming from the primary visual cortex and past experiences to interpret what the image is or means (a face, a flower, a car, a stop sign) iii. Auditory Cortex = located within the temporal lobes 1. Primary Auditory Cortex (Brodmann Area 22) receives and processes sound information from the ear such as pitch, rhythm, and volume. 2. Auditory Association Area (Brodmann Area 23) integrates and analyzes the information from the primary auditory cortex and past experiences to interpret what the sound stimulus is or means (a scream, music, a fire alarm, thunder, etc.) Other sensory areas: 1. Wernicke’s Area (Brodmann Areas 39, 40) = located only on the left temporal lobe and is responsible for understanding and interpreting written and spoken language. 2. Olfactory Cortex = located on the medial aspect of the temporal lobe and is responsible for the conscious perception of odors or smells. 3. Gustatory Cortex = located in the insula and portions of the frontal lobe; is involved in the conscious perception of taste. 4. Visceral Sensory Cortex = located in the insula and is involved in the conscious perception of visceral sensations (upset stomach, full bladder, urge to defecate, etc.)  Basal Nuclei White matter ▪ Frontal Section of Cerebral Cortex & Basal Nuclei: The basal nuclei communicate with the motor cortex to coordinate movement. It acts to facilitate and inhibit movements.  Basal Nuclei – Direct Pathway ▪ The direct pathway causes the disinhibition of the thalamus which allows it to excite the motor cortex to initiate motor movements.  Basal Nuclei – Indirect Pathway ▪ The indirect pathway causes, or reinforces, the normal inhibition of the thalamus which fails to excite the motor cortex; thereby, inhibiting motor movements.  Basal Nuclei – Nigrostriatal Pathway ▪ A dopamine pathway which helps to reduce the inhibitory effect of the basal ganglia on the motor pathway.  Basal Nuclei – Disorders ▪ Parkinson’s disease: caused by the degeneration of dopaminergic neurons of the substantia nigra pars compacta. ▪ Huntington’s disease: an inherited neurodegeneration of the basal nuclei (especially the striatum).  The Limbic System ▪ Amygdala ▪ Cingulate Gyrus ▪ Hippocampus Source: https://commons.wikimedia.org/wiki/File:1511_The_Limbic_Lobe.jpg  The Limbic System Limbic System = is a group of brain structures located around the medial aspects of the cerebral hemispheres. involved in processing and regulating emotions, memory, and behavior. ▪ Amygdala: involved in emotional responses to fearful and threatening stimuli ▪ Cingulate Gyrus: plays a role in expressing emotions through gestures. Regulates aggressive behavior and emotional responses to pain ▪ Hippocampus: involved in long-term memory formation Source: https://commons.wikimedia.org/wiki/File:1511_The_Limbic_Lobe.jpg  Diencephalon Source: https://commons.wikimedia.org/wiki/File:1806_The_Hypothalamus-  Diencephalon Diencephalon = serves as the structural and functional link between the cerebral hemispheres and the rest of the central nervous system. =deep beneath the cerebrum and constitutes the walls of the third ventricle Source: https://commons.wikimedia.org/wiki/File:1806_The_Hypothalamus-  Diencephalon SUBDIVISIONS: 1.Thalamus: processes and relays information between the cerebral cortex and lower centers of the CNS - All sensory input except olfaction - Motor output 2.Hypothalamus: regulates homeostasis including autonomic and endocrine functions 3.Epithalamus: contains the pineal gland which secretes melatonin to regulate the sleep- wake cycle  Cerebellum ▪ Coordinates skeletal muscle movements and maintains equilibrium & balance ▪ Transverse fissure separates the cerebellum from the cerebrum ▪ Anterior & posterior lobes separated by the primary fissure ▪ Folia: fold-like wrinkles ▪ Vermis connects the two cerebellar hemispheres. Cerebellum  Cerebellum Cerebellum = accounts for ~10% of the brain’s mass. 1. For coordination of skeletal muscle movements, modulation of motor commands from the cerebral cortex, and maintaining balance and equilibrium 2. partially hidden by the cerebral hemispheres and is the second largest structure in the brain. 3. separated from the cerebrum by the transverse fissure 4. possesses fold-like wrinkles called folia  Cerebellum 5. further subdivided into lobes: the anterior lobe and posterior lobe. 6. The two cerebellar hemispheres are separated by the vermis 7. anterior and posterior lobes are separated by the primary fissure 8. The white matter of the cerebellum is called the arbor vitae and is surrounded by gray matter called the cerebellar cortex.  Brain Stem ▪ Midbrain - Superior colliculi - Inferior colliculi - Cerebral aqueduct ▪ Pons ▪ Medulla oblongata ▪ Reticular formation  Brain Stem ▪ Midbrain - Superior colliculi: visual reflexes - Inferior colliculi: auditory & startle reflexes - Cerebral aqueduct: canal for CSF flow ▪ Pons: contains respiratory centers to maintain rhythm of breathing; connects higher & lower brain centers via projection fibers ▪ Medulla oblongata: regulates autonomic functions (ex. respiratory rate, HR, BP) and visceral reflexes (ex. vomiting, sneezing, coughing) ▪ Reticular formation: maintains wakefulness & filters out weak stimuli Anatomy of the Spinal Cord  Anatomy of the Spinal Cord The Spinal Cord 1. adult spinal cord : 45 cm (18 inches) in length 2. Maximum width of 14 mm (0.55 inch) 3. located within the vertebral foramen (vertebral canal)  Anatomy of the Spinal Cord 2. Anatomy of the Spinal Cord A. cervical enlargement = supplies nerves to the shoulder and upper limbs B. lumbar enlargement = innervation to the structures of the pelvis and lower limb C. conus medullaris= tapered, conical portion of the spinal cord inferior to the lumbar enlargement  Anatomy of the Spinal Cord D. adult spinal cord ends at the level of the first or second lumbar vertebra-> dorsal and ventral roots of the spinal segments L2 and S5 extend inferiorly. E. When seen in gross dissection, the filum terminale and the long bundles of ventral and dorsal roots resemble a horse’s tail and is named the cauda equina. E. filum terminale = slender strand of fibrous tissue that extends from the tip of the conus medullaris to the second sacral vertebra. = provides longitudinal support to the spinal cord as a component of the coccygeal ligament. Anatomy of the Spinal Cord  Anatomy of the Spinal Cord gray matter= dominated by the cell bodies of neurons, neuroglia, and unmyelinated axons, surrounds the narrow central canal and forms a butterfly shape a. Structural Organization: The projections of gray matter toward the outer surface of the spinal cord are called horns. i. posterior gray horn = has somatic and visceral sensory nuclei for sensory processing. ii. lateral gray horn= located only in the thoracic and lumbar segments) contains visceral motor nuclei (cell bodies of motor neurons of the autonomic nervous system) iii. anterior gray horn = has somatic motor nuclei to send out motor signals to skeletal muscles  Anatomy of the Spinal Cord b. Functional Organization of the gray matter: The cell bodies of the neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. i. Sensory nuclei= receive and relay sensory information from the receptors of the body to the CNS ii. Motor nuclei= issue motor commands to the peripheral effectors  Anatomy of the Spinal Cord 2. white matter = superficial, has large numbers of myelinated axons. Structural Organization: The structural components of white mater are divided into columns. i. The posterior white column lies between the posterior gray horns and posterior median sulcus. ii. The lateral white column includes the white matter on either side of the spinal cord between the anterior and posterior columns. iii. The anterior white column lies between the anterior gray horns and the anterior median fissure.  Anatomy of the Spinal Cord b. Functional Organizationof the white matter: the functional component of the white matter is divided into tracts. i. Ascending tracts carry sensory information up to the brain. ii. Descending tracts carry motor commands from the brain to the spinal cord. Anatomy of the Spinal Cord  Anatomy of the Spinal Cord =divided into 31 segments, each of which gives rise to a pair of spinal nerves 1. dorsal root = contains the axons of the sensory neurons entering the spinal cord. Their cell bodies are in the dorsal root ganglion. 2. dorsal root ganglion= contains the cell bodies of sensory neurons whose axons carry information to the spinal cord. Each segment of the spinal cord has a pair of dorsal root ganglia, one on each side.  Anatomy of the Spinal Cord 3. The ventral root contains the axons of motor neurons that exit the spinal cord and extend into the periphery to control somatic and visceral effectors in the body. 4. A single spinal nerve contains the axons of BOTH sensory and motor neurons. The sensory fibers enter the CNS through Circulation and the Central Nervous System  Arterial Blood Supply 13.3 Circulation and the Central Nervous System Arterial Blood Supply internal carotid arteries and vertebral arteries= responsible for oxygenated blood supply to the brain. The right and left vertebral arteries merge to form the basilar artery which gives rise to branches that supply the brain stem and cerebellum. The internal carotid arteries and the  Arterial Blood Supply circle of Willis =a circular blood vessel to ensure constant perfusion of the cerebrum in the event of a blockage of one of the arteries  Venous Return ▪ After passing through the CNS, deoxygenated blood returns to the circulation via a series of dural sinuses and veins. Through the jugular veins, blood returns to the heart. C. Stroke = a disruption of blood supply to the brain caused by a blockage to an artery in the brain =results in cell death within the brain which can cause the loss of specific functions in the body Meninges of the Brain  Meninges of the Brain Protective Coverings of the Brain and Spinal Cord Meninges= a series of membranes composed of connective tissue covering the outer surface of the CNS =protect the brain and spinal cord = for necessary physical stability and shock absorption for the brain and spinal cord  Meninges of the Brain 3 layers of the meninges: a. dura mater = thick fibrous, outermost meningeal layer, and a protective sheath over the entire brain and spinal cord =anchored to the inner surface of the cranium and vertebral cavity subdural space = a narrow space in the CNS that separates the dura mater from the arachnoid mater epidural space= a narrow space in the spinal cord that lies between the dura mater and the wall of the ventral canal =contains aerolar connective tissue , blood vessels, and a protective layer of adipose tissue  Meninges of the Brain (continuation 3 layers of the meninges) b. arachnoid mater = thin fibrous, middle meningeal layer that forms a loose sac around the CNS =consists of a simple squamous epithelium named the arachnoid membrane and the subarachnoid space that extends between the arachnoid mater and the pia mater c. pia mater = thin fibrous, inner meningeal layer that is firmly bound to the underlying neural tissue  Meninges of the Spinal Cord Source: https://commons.wikimedia.org/wiki/File:Gray770-en.svg  Meninges of the Spinal Cord subarachnoid space = contains the arachnoid trabeculae (spider web-like), a network of collagen and elastic fibers that attaches the arachnoid mater to the pia mater =filled with cerebrospinal fluid (CSF) cerebrospinal fluid (CSF) = acts as a shock absorber and a diffusion medium for dissolved gases, nutrients, chemical messengers, and waste products  Meninges of the Spinal Cord CSF can be safely withdrawn in a procedure known as a lumbar puncture or spinal tap. A needle is inserted into the subarachnoid space in the lumbar region inferior to the tip of the conus medullaris. Meningitis = an inflammation of the meninges caused by bacteria or viruses. The primary test for meningitis is a lumbar puncture.  Ventricular System ▪ Ventricles: fluid-filled open spaces in the brain. They posses a choroid plexus which produces CSF to be distributed around the brain and spinal cord. Source: https://commons.wikimedia.org/wiki/File:Gray770-en.svg  Ventricular System ▪ Ventricles: 4 fluid-filled open spaces in the brain. =posses a choroid plexus which produces CSF to be distributed around the brain and spinal cord =lined with ependymal cells which whip their cilia to circulate the CSF.  Ventricular System There are four ventricles: a. Two lateral ventricles (right and left), one within each cerebral hemisphere b. Third ventricle in the diencephalon c. Fourth ventricle which begins in the metencephalon and extends into the superior portion of the medulla oblongata. =narrows and becomes continuous with the central canal of the spinal cord  Cerebrospinal Fluid Circulation Peripheral Nervous System Cranial Nerves  Cranial Nerves Peripheral Nervous System A. Cranial Nerves 1. There are 12 pairs of cranial nerves. 2. Each pair of nerves is classified as either sensory (containing sensory neurons only), motor (containing motor neurons only), or mixed (containing both sensory and motor neurons). 3. For each of the 12 cranial nerves, be sure you can: name, number, describe the function, identify if it is sensory, motor, or mixed, and name a disorder (if applicable).  Cranial Nerves ▪ 12 Pairs of Cranial Nerves; Some are Sensory, Motor, or Mixed Nerves. Cranial Disease or Nerve Name Function Foramen Disorder Number Olfactory CN I Olfactory Smell foramina of the Anosmia (sensory) cribriform plate CN II Optic Vision Optic canal Anopsias (sensory) Movement of eyelid and eyeball (via superior rectus, inferior CN III Superior orbital External Oculomotor rectus, medial rectus, and (motor) fissure strabismus inferior oblique), shape of lens, contracts pupil size  Cranial Nerves Cranial Disease or Nerve Name Function Foramen Disorder Number CN IV Movement of eye by the Superior orbital Double Trochlear (motor) superior oblique fissure vision Trigeminal General sensations of touch, pain, & temperature of the Superior orbital CN V (the largest face, and sensory fibers from Tic fissure (both) cranial nerve teeth and tongue, also douloureux with three innervates the muscles of branches) chewing CN VI Movement of the eyeball by Superior orbital Internal Abducens (motor) the lateral rectus fissure strabismus  Cranial Nerves Cranial Nerve Disease or Name Function Foramen Number Disorder Muscles controlling facial expressions, secretion of saliva by the submandibular and CN VII Internal acoustic Bell's Palsy Facial sublingual glands and tears by (both) meatus and ageusia the lacrimal gland, and sensory function for taste from the anterior 2/3 of the tongue Nerve CN VIII Internal acoustic Vestibulocochlear Hearing and equilibrium deafness or (sensory) meatus dizziness Secretion of saliva by the parotid Impaired CN IX Glossopharyngeal glands, elevation of pharynx Jugular Foramen swallowing (both) during swallowing, and taste and ageusia  Cranial Nerves Cranial Nerve Disease or Name Function Foramen Number Disorder Taste (gag reflex), smooth muscle contraction and Loss of CN X Vagus relaxation of visceral organs Jugular Foramen voice and (both) and for the secretion of death digestive fluids Inability to turn the CN XI Rotation of head and shrugging Accessory Jugular Foramen head and (motor) the shoulders shrug shoulders Difficulty Motor function of tongue for CN XII Hypoglossal with speech Hypoglossal speech, swallowing, and (motor) canal or loss of chewing speech Anatomy of a Spinal Nerve  31 Pairs of Spinal Nerves Divided into Plexuses  Cervical Plexus ▪ Most branches are cutaneous nerves that supply sensory impulses from the skin of the neck, ear, back of the head and shoulders ▪ Other branches innervate the muscles of the anterior neck ▪ Phrenic nerve = sole motor nerve supply to the diaphragm for breathing  Brachial Plexus ▪ Suprascapular nerve ▪ Axillary nerve ▪ Radial nerve ▪ Median nerve ▪ Ulnar nerve Source: https://commons.wikimedia.org/wiki/File:Nerves_of_the_left_upper_extremity.gif  Intercostal Nerves ▪ 12 Pairs of intercostal nerves that give rise to cutaneous branches to supply the chest and torso area ▪ Innervate the external intercostal muscles for breathing Source: https://commons.wikimedia.org/wiki/File:Gray821.png  Lumbar Plexus ▪Femoral nerve ▪Obturator nerve Source: https://commons.wikimedia.org/wiki/File:Gray823.png  Sacral Plexus ▪ Sciatic nerve: supplies the entire lower limb (leg) except the anteromedial thigh. ▪ Tibial nerve ▪ Fibular nerve ▪ Sural nerve ▪ Pudendal nerve Source: https://commons.wikimedia.org/wiki/File:Gray832.png