Neurology Flashcards
Peripheral Nervous System
○ Sensory portion: specialized sensory receptors and organs that detect the state of the body or its surroundings
○ Afferent (to brain), efferent (to body/affected organ) nerve fibers that conduct impulses between receptors, sensory organs, CNS and peripheral effectors (skeletal muscle - Motor component)
Central Nervous System
- Brain
- Spinal Cord
- Autonomic NS - PSNS, SNS
General Function of Brain
stores information, generates thoughts
■ reactions in response to sensation
● Signals originate in Motor Nuclei → transmitted through the motor tracts within the CNS → Motor portion of PNS
Parts of the Brain
- Forebrain
- Brainstem
- Grey Matter
- White matter
Forebrain Components
- Telencephalon (cerebrum)
- Diencephalon
Components of Diencephalon
Diencephalon = forebrain
Thalamus, Hypothalamus
Components of Telencephalon
Forebrain
○ 2 hemispheres
○ Rhinencephalon
○ Corpus Callosum
○ Limbic System
○ Hippocampus
○ Ventriculus lateralis (lateral ventricle, ventriculus III (third ventricle)
○ Corpus Amygdaloideum
Components of the Brainstem
- Mesencephalon
- Metencephalon
- Myelencephalon
Mesencephalon
Tegmentum mesencephalic
Brainstem, midbrain
Metencephalon
Ventriculus IV
Pons
Cerebellum
Brainstem, hindbrain
Myelencephalon
Brain, hindbrain
Medulla oblongata
Grey Matter
Neuronal cell bodies
Axons with little myelination
White Matter
Myelinated Axons
Mnemonic for Cranial Nerve Functions (Sensory vs motor vs both)
Some
Say
Marry
Money
But
My
Brother
Says
Big
Brains
Matter
More
CN I
Olfactory = sensory
■ Function: Smell
■ Arises from primary olfactory cortex (temporal lobe)
■ Neurons from olfactory tracts → run to olfactory bulb (above cribriform plate of ethmoid bone)
■ Receives sensory information from nasal cavity’s olfactory neurons
CN II
Optic N = sensory
■ Function: Vision
■ Emerge from eye retinas
■ Pass through optic canal, unite at optic chiasm (partial decussation) → optic nerve fibers from optic tracts → synapse at different nuclei
● Suprachiasmatic nucleus in thalamus (sleep-wake cycle)
● Pretectal nucleus in midbrain (eye reflexes)
● Lateral geniculate nucleus in thalamus (sight)
CN III
Occulomotor N = Motor
■ Function: eye movement
■ Arises from ventral midbrain; runs through superior orbital fissure to eye
■ Splits into superior and inferior branch
● With proprioception - controls pupil constriction (sphincter pupillae), visual focusing (cilliaris) via ciliary ganglion
Superior Branch of CN III
Levator palpebrae superioris ( raises upper eyelid), superior rectus (elevates eye)
Inferior Branch of CN III
inferior oblique (abducts eyeball), medial rectus (adducts eyeball)
CN II synapse at what nuclei?
Suprachiasmatic nucleus in thalamus (sleep-wake cycle)
● Pretectal nucleus in midbrain (eye reflexes)
● Lateral geniculate nucleus in thalamus (sight)
CN IV
Trochlear Nerve (Primary motor, some sensory)
■ Function: eyeball movement
■ Arises from dorsal midbrain, runs around midbrain, follows oculomotor nerve through superior orbital fissure
■ Innervates superior oblique muscles (abducts, depresses, internally rotates eyeball)
CN V
Trigeminal Nerve (sensory, motor)
■ Function: facial movement, chewing, temperature, touch, pain
■ Emerges from pons; travels to trigeminal ganglion
■ Splits into ophthalmic, maxillary and mandibular nerves
Orbital Br CN V
exits through superior orbital fissure, gives sensory innervation to upper eyelid, nose, forehead , scalp
Maxillary Br CN V
Nerve exits through the foramen rotundum, gives sensory innervation to maxilla, nasal cavity, palate, cheeks skin
Mandibular Br CN V
exits through foramen ovale, gives sensory innervation to tongue (NOT taste), lower lip, lower teeth, temporal scalp; Motor innervation to chewing muscles
CN VI
Abducens nerve (motor)
■ Function: eyeball movement
■ Emerges from the pons, runs through superior orbital fissure
■ Innervates lateral rectus muscle (abduct eye)
CN VII
Facial nerve (sensory, motor)
■ Function: taste, saliva, tears, facial movement
■ Emerges from the pons, enters temporal bone through internal acoustic meatus
■ Runs within bone to geniculate ganglion
■ Splits into greater petrosal nerve, stapedius nerve, chorda tympani
Splits again into temporal, zygomatic, buccal, mandibular, cervical branches (innervating forehead, nose, cheeks, around eyes/lips, chin)
Greater Petrosal Br of CN VII
autonomic fibers to lacrimal, nasal, palatine, pharyngeal glands
Stapedius Br of CN VII
motor fibers to inner ear
Chorda Tympani Br CNVII
sensory to taste buds of tongues anterior ⅔
CN VIII
hearing, equilibrium
■ Emerges from pons, runs through internal acoustic meatus
■ Splits into cochlear, vestibular nerves
Cochlear Br CN VIII
supplies hearing receptors
Vestibular Br CN VIII
vestibules equilibrium receptors
CN IX
Glossopharyngeal nerve (sensory/motor)
■ Function: swallowing, monitoring blood pressure/oxygen/CO2
■ Arises from Medulla; runs through jugular foramen
■ Innervates tongue, pharynx
■ Sends motor fibers to stylopharyngeus (elevates pharynx in swallowing), parasympathetic motor fibers to parotid salivary glands, sensory fibers to tongues posterior ⅓
■ Conveys information from carotid bodies chemoreceptors (Blood O2, CO2 levels), carotid sinus’ baroreceptors (blood pressure)
CN X
Vagus Nerve (Sensory/Motor)
■ Function: smooth muscle control, digestive enzyme secretion
■ Arises from the medulla, runs through the jugular foramen
■ Dips down into thorax and abdomen*
■ Sends somatic motor innervation to pharynx, larynx (swallowing), PSNS fibers to heart, lungs, abdominal organs (heart rate, breathing digestion)
■ Brings sensory information from thoracic, abdominal organs, aortic arch’s baroreceptors; chemoreceptors in carotid, aortic bodies; epiglottis’ taste buds
CN XI
Accessory Nerve (motor)
■ Function: swallowing; head and shoulder movement
■ Considered vagus nerve accessory
■ Forms from rootlets emerging from spinal cord; enters skull via foramen magnum, emerges from medulla, runs through jugular foramen
■ Innervates: trapezius, sternocleidomastoid (head, neck movement); carries sensory proprioceptive information from larynx/pharynx
CN XI
Hypoglossal (motor)
■ Function: tongue movement, speech, swallowing
■ Arises from medulla; runs through hypoglossal foramen
■ Sends motor fibers to tongue muscles, carries sensory proprioceptive information
Dura Mater
(most superficial membrane)
■ Epidural space: between ligamentum flavum and dura mater
● Contains fat, connective tissue
Arachnoid
■ Subdural space: between Dura Mater and Arachnoid membrane
Pia Mater
(direct contact with brain/spinal cord)
■ Subarachnoid (intrathecal) space: between the arachnoid and pia mater
● Location for spinal CSF sampling/intrathecal administration of medications
Blood Brain Barrier
Anatomic and enzymatic separation that isolates cerebral blood from most brain parenchyma and CSF
■ Located at choroid plexus, brain parenchymal vessels, subarachnoid vessels, and arachnoid membrane
Composition of BBB
Composed of cells connected by tight junctions
■ Restrict intracellular diffusion - force solute exchange to occur through cells
○ Prevents passage of small/moderate amounts of epi, norepi, serotonin, dopamine from blood to brain
■ *Circulating catecholamines do not significantly affect Cerebral Metabolic Rate for Oxygen (CMRO2)
Changes with BBB Permeability
■ If BBB permeability increases (Intracranial hypertension, inflammation, disruption of osmosis) catecholamines can cross and cause reversible increases in CMRO2
CSF
Provides hydromechanical protection of the CNS, role in brain development and influences neuronal functioning via regulation of interstitial fluid homeostasis
CSF Production
Produced under enzymatic control of Carbon Anhydrase
■ Choroid plexuses in lateral, third and fourth ventricles
■ Minor volume produced as a metabolic by-product
CSF Rate of Production
■ Cats: 0.02 ml/min
■ Dogs: 0.05 ml/min
■ Humans: 0.4 ml/min
Composition of CSF vs Plasma
■ INCREASED Na+, Cl-, Mg2+
■ DECREASED glucose, protein, amino acids, K+ and bicarbonate
Drainage of CSF
■ Absorption via cranial and spinal arachnoid villi into venous outflow system
■ Cranial and spinal nerve sheaths
■ Adventitia of cerebral arteries into the lymphatic outflow system
Flow Dynamics, Pressure of CSF Depend on:
■ Arterial pulse wave
■ Respiratory waves
■ Animal posture
■ Jugular venous pressure
■ Physical effort
Causes Decreased Formation of CSF
■ Arterial hypotension
■ Decreased cerebral perfusion pressure (CPP)
■ Increase in ICP
■ Administration of diuretics (Carbonic Anhydrase inhibitor; furosemide), mannitol, corticosteroids, omeprazole
Causes Increased Formation of CSF
■ Anesthetics (enflurane, ketamine, halothane) may increase or augment
● Isoflurane and fentanyl may be preferable in patients with increased CSF volume
ANS
Regulates the body’s internal environment - functions to maintain homeostasis
Operates on a subconscious level
–Controls visceral functions of internal organs
■ Maintenance of arterial blood pressure
■ GI motility and secretion
■ Urinary bladder emptying
■ Thermoregulation
–Rapid and intense changes in function
■ Ex: ABP can be doubled within 10-15 sec
Control of ANS
Controlled by centers located in the spinal cord, brainstem and hypothalamus
○ Limbic cortex can transmit impulses to lower centers and influence autonomic control
Afferent ANS Signals
enter autonomic ganglia, spinal cord, brainstem, hypothalamus
○ Elicit REFLEX responses back to organs
Efferent ANS Signals
transmitted to the body through two subdivisions: Sympathetic and Parasympathetic Nervous Systems
SNS Composition
■ Two paravertebral sympathetic chains of ganglia located on each side of spinal column
■ Two prevertebral ganglia (celiac and hypogastric ganglion)
■ Nerve fibers extending from the ganglia to nerve endings in the internal organs
Location of SNS Origins
Sympathetic nerves originate in the spinal cord between segments T1 and L2
■ Pass into sympathetic chain then to tissues and organs
Structure of SNS
Each sympathetic nerve composed of two in series: preganglionic and postganglionic
■ Preganglionic cell body lies in Internal Mediolateral Horn of spinal cord
● Fiber passes through Ventral Spinal root into corresponding spinal nerve
● Preganglionic fibers leave nerve and pass through the White Ramus into one of the ganglia of sympathetic chain
From there, can:
(1) Synapse with postganglionic neurons in the ganglion it enters
(2) Pass upwards or downwards in the chain and synapse on another ganglia
(3) Pass for variable distances through the chain, then terminate on one of the prevertebral ganglia
SNS Postganglionic Neurons
originate in either a sympathetic chain ganglia or prevertebral ganglia
● Then travel to organs
Adrenal Medulla
Preganglionic fibers pass without synapsing from intermediolateral horn, through sympathetic chains, through splanchnic nerves, and into medulla
○ End directly on modified neuronal cells that secrete EPI/NE norepi into bloodstream
○ Secretory cells are analogous to postganglionic neurons
PNS
○ Fibers of the PNS leave the CNS through CN III, IX, X and the 2nd, and 3rd (sometimes 1st and 4th) sacral spinal nerves
○ 75% of all parasympathetic nerve fibers are in the vagus nerve (CN X)
■ Comprise cranial, cervical and thoracic parts
■ Supply parasympathetic fibers to the heart, lungs, esophagus, stomach and other abdominal viscera.
Destination of Parasympathetic Fibers
○ CN VII pass to the lacrimal, nasal and submandibular glands
○ CN IX pass to the parotid gland
○ Preganglionic fibers pass uninterrupted to the organ where postganglionic neurons are located in the organ wall
ANS Transmission
○ Synaptic transmission within the ANS utilizes Acetylcholine (ACh) and norepinephrine (NE)
■ ALL Preganglionic sympathetic and parasympathetic neurotransmission is CHOLINERGIC
■ Postganglionic Parasympathetic: Cholinergic
■ Postganglionic Sympathetic: Noradrenergic
ACh
activates two types of cholinergic receptors: Muscarinic (M) and Nicotinic (nAChR)
■ G-protein coupled receptors
■ Belong to superfamily of ligand-gated Ion channels
Nicotonic R
found in the synapses between pre- and postganglionic neurons of both the sympathetic and parasympathetic systems
■ Variety of nicotinic subunit combinations
■ Structural diversity and locations of receptors contribute to variable roles in the CNS
Neuromuscular Transmission
