Exam 2 Study Guide.docx

**NUR 730: Exam 2 Study Guide** **Sensation, Motor, and Special Senses** **The Nervous System** - Nervous System (short term) and Endocrine System (long term) regulate homeostasis - Central Nervous System (CNS) - Brain - Spinal Cord - Peripheral Nervous System (PNS)...

**NUR 730: Exam 2 Study Guide** **Sensation, Motor, and Special Senses** **The Nervous System** - Nervous System (short term) and Endocrine System (long term) regulate homeostasis - Central Nervous System (CNS) - Brain - Spinal Cord - Peripheral Nervous System (PNS) - Somatic Nervous System - Autonomic Nervous System -- controls visceral functions like smooth muscles and glands - Sympathetic Nervous System -- fight or flight - Parasympathetic Nervous System -- rest and digest - Enteric System -- digestion and enzyme secretion **Terms to Know** - **Afferent** -- inward; toward the CNS - **Efferent** -- outward; away from the CNS - **Dorsal** -- relating to the back or posterior - **Ventral** -- relating to the anterior/front - **Decussation** -- the action of crossing - **Ipsilateral** -- belonging to or occurring on the same side of the body - **Contralateral** -- belonging to or occurring on the opposite side of the body - **Transduction** -- converting a sensory stimulus into an electrical signal that is transmitted to the CNS - **Transmission** -- conduction of a sensory impulse from the peripheral nervous system to the CNS - **Perception** -- conscious awareness of sensory modality **Types of Sensations** - Three Main Types: - **Mechanoreceptive** -- touch and pressure - **Thermoreceptive** -- temperature - **Pain** -- activated by damage to tissues - Other Types: - **Exteroreceptive** -- from the surface of the body - **Proprioceptive** -- position sense - **Visceral** -- internal organs - **Deep Sensations** -- from deep tissue - All sensations involve: Receptor Activation → Neuron Activation → Impulse transmission to the spinal cord and brain **Specialized Sensory Receptors** - **Mechanoreceptors** -- detect mechanical compression or stretching - **Thermoreceptors** -- detect changes in temperature - **Nociceptors** -- detect physical or chemical damage to tissue (pain) - **Electromagnetic** -- detect light on retina of eye - **Chemoreceptors** -- detect taste/smell, O2/CO2 in blood, osmolality, etc **Tactile Receptors:** - Respond the touch, pressure, and vibration - Touch -- skin or immediately below the skin - Pressure -- deformation of deeper tissues - Vibration -- rapidly repetitive sensory signals +-----------------------+-----------------------+-----------------------+ | **Tactile Receptor** | **Location** | **Function** | +=======================+=======================+=======================+ | Free Nerve Endings | Everywhere in the | \- Detects touch and | | | skin and many other | pressure (A-δ) | | | tissues | | | | | \*All pain receptors | +-----------------------+-----------------------+-----------------------+ | Meissner's Corpuscle | Present in non-hairy | \- Touch (A-β) -- | | | parts of the skin | sensitive to skin | | | | touch or low | | | Abundant in | frequency vibration | | | fingertips and lips | | | | | \- Rapidly adapting | | | | (fraction of a | | | | second) | +-----------------------+-----------------------+-----------------------+ | Merkel's Discs | | \- Localized touch | | | | against the skin | | Expanded Tip Tactile | | (A-β) | | Receptors | | | | | | \- Steady state | | | | signals so you can | | | | determine continuous | | | | touch of objects on | | | | skin | | | | | | | | \- Initially | | | | transmits strong | | | | signals and then | | | | adapts slowly | +-----------------------+-----------------------+-----------------------+ | Hair End Organ | | \- Touch (A-β) | | | | | | | | \- Detects movement | | | | of objects on the | | | | surface of the body | | | | and initial contact | | | | with the body | | | | | | | | \- Stimulated by any | | | | slight movement of | | | | any hair | +-----------------------+-----------------------+-----------------------+ | Ruffini's Endings | Deeper layers of the | \- Adapts very slowly | | | skin/internal tissues | | | | | \- Signals continuous | | | Joint capsules | states of deformation | | | | of tissues | | | | | | | | \- Heavy prolonged | | | | touch and pressure | | | | (A-β) | | | | | | | | \- Signals degree of | | | | joint rotation | +-----------------------+-----------------------+-----------------------+ | Pacinian Corpuscle | Immediately beneath | \- Structural design: | | | the skin and deep in | central nerve fiber | | | fascial tissues | extending through its | | | | core surrounded by | | | | multiple concentric | | | | layers | | | | | | | | \- Stimulated by | | | | rapid local | | | | compression | | | | | | | | \- **Adapts very | | | | quickly -- | | | | communicates the | | | | change of the | | | | condition rather than | | | | constant | | | | communication** | | | | | | | | \- Detects tissue | | | | vibration/rapid | | | | changes in the | | | | mechanical state of | | | | tissues | | | | | | | | \- Compression of the | | | | corpuscle causes | | | | mechanical | | | | deformation = | | | | receptor potential | +-----------------------+-----------------------+-----------------------+ **Pacinian Corpuscle** - Compression of the corpuscle causes mechanical deformation - Ion channels open - Na+ ions enter to interior of fiber = receptor potential - If threshold is reached, an action potential is elicited - Initial amplitude of receptor potential increases rapidly - With progressively stronger stimulus strength, amplitude is diminished but the frequency of repetitive action potentials increases - Action potential is transmitted along the nerve fiber to the CNS - This is how a receptor can be responsive to both weak and intense stimuli **Receptor Adaptation** - Adaptation: - Initial receptor response: HIGH - Continued/ Frequent Stimulation: Diminished response - Different types of receptors adapt at different rates: - Pacinian receptors are rapid adaptors (fraction of a second) - Hair receptors adapt in 1 second - **Rapid** adaptor receptors are better for sensing **changes** - Rate receptors, movement receptors, phasic receptors - **Slow** adaptor receptors - Transmit impulses to the brain as long as the stimulus is present - Better for sensing **constant** conditions in the body - Arterial baroreceptors and arterial chemoreceptors **Neuron Activation and Transmission** - Differential Sensitivity - Receptors are designed for specific types of stimuli - Receptors are almost nonresponsive to other types of sensory stimuli - Labeled Line Principle - Specificity of nerve fibers to transmit only one modality of sensation - Each nerve tract terminates at a specific point in the CNS - Type of sensation felt is determined by the specific nerve fiber stimulated **Receptor Potentials** - Stimuli change the electrical membrane potential (receptor potential) → ion channels open - Mechanisms: - **Mechanical deformation** -- mechanical pressure causes stretch of the receptor membrane (opens ion channels) - **Chemical application** -- chemical application to membrane opens ion channels - **Temperature change** -- change in temperature alters permeability of membrane - **Electromagnetic radiation** -- light on retina causes ion channels to open **Action Potentials** - **Threshold** - potential must rise above a certain threshold (-40 to -50 mV) to elicit an action potential - All or none response - **Frequency** - Very intense stimulation causes progressively less and less additional action potentials - The more the receptor potential rises above threshold the greater becomes the action potential frequency - Frequency of repetitive receptor action potentials increases with the strength of the receptor signal - Allows range of sensory experience (weak → intense) - **Amplitude** - Increases rapidly with increased **stimulus strength** but progressively less rapidly at high stimulus strength **Divergence and Convergence** - [Divergence] -- spread apart - Weak signals entering a neuronal pool excite greater numbers of nerve fibers leaving the pool - Amplifying divergence (A): Input signal spreads to an increasing number of neurons - Divergence in multiple tracts (B): Signal is transmitted in 2 directions - [Convergence] -- come together - Signal from multiple inputs unite to excite a single neuron - Convergence from either a single source (A) or multiple sources (B) - Convergence allows summation of information so CNS can correlate, summate, and sort different types of information **Reciprocal Inhibition Circuits** - Incoming signal causes output excitatory signal in one direction and an inhibitory signal going in another direction - Characteristic for control of opposing muscle groups (triceps and biceps) **Signal Prolongation** - **Afterdischarge:** prolonged output discharge - Can last milliseconds to minutes following the incoming signal - **Synaptic Afterdischarge**: a single input signal can cause a sustained output via a series of repetitive charges - **Reverberatory (Oscillatory) Circuit**: feedback from the neuronal circuit feeds back to input the same circuit - Varying degrees of complexity - Some neuronal circuits continuously emit signals (continuous intrinsic neuronal discharge or continuous reverberatory signals) Example: respiratory drive **Spatial and Temporal Summation: Intensity** - Spatial Summation - Increasing single strength is transmitted by using progressively greater numbers of fibers - Temporal Summation - Increasing single strength is transmitted by increasing the frequency of nerve impulses in each fiber **Neuronal Pools** - Groups of specially organized neurons that share common inputs, outputs, and functions - CNS is composed of thousands to millions of neuronal pools - Input fibers divide to create a stimulatory field - If an input fiber excitatory impulse isn't enough to reach threshold, it is called suprathreshold - If an input fiber excitatory impulse isn't enough to reach threshold, it is called subthreshold (and those neurons are facilitated) - Facilitated neurons can reach threshold if stimuli are received from another neuron - The area of facilitated neurons is called the facilitated zone (aka subthreshold zone or subliminal zone) - If incoming fibers are inhibitory (instead of excitatory), they create an inhibitory zone **Two Point Discrimination** - The ability to differentiate between two adjacent stimuli is referred to as two-point discrimination - At the fingertips-1-2 millimeters and on the skin of the back 30-70 millimeters - Lateral inhibitions facilitate two-point discrimination **Interpreting Stimulus Intensity** - In Pacinian corpuscles, changes in low intensity stimuli strength provoke increased responses dramatically, whereas higher levels of stimuli provoke slight changes in response - In other systems (hearing) increasing stimulus strength greater numbers of nerve fibers are recruited to fire - "Ratio" stimulus strength applies primary to visual, auditory and cutaneous sensory experience **Proprioception (Position Sense)** - [There are 2 types of position senses]: - Static position sense - **Conscious perception of the body in space** - Kinesthesia (dynamic position sense) - **Rate of movement sense** - Position sense receptors are located in joints (to determine joint angulation), muscles (muscle spindles), skin (tactile receptors) - Neurons in the thalamus respond to minimum and maximum joint rotation **Nerve Transmission** - Nerve fibers are categorized by function, size, myelination - Nerves -- bundle of axons - [Nerve diameters]: 0.5 micrometers -- 20 micrometers - [Conduction velocity]: 0.5 -- 120 m/sec - Influenced by size (bigger = faster), function, and degree of mylination - Two Classification Systems - General Classification: Type A, B, C - **Type A Fibers** -- large/medium, myelinated, FAST - **Type B Fibers** -- smaller, myelinated, pre-ganglionic (ANS) - **Type C Fibers** -- small, unmyelinated, SLOW - Sensory Nerve Classification: Group I-IV - **Type I Fibers** -- large, myelinated, and fast - Fibers from muscle spindles and Golgi tendon organs - **Type II and III Fibers** -- myelinated - **Type IV Fibers** -- small, unmyelinated, and slow - Crude touch and pressure, tickle, aching pain, and temperature - Differential Blockade -- different nerve fibers block at different rates - Block order: - Sympathetic - Sensory - Motor - Sensitivity to LA is inversely proportional to axon diameter - When LA interrupts nerve transmission of autonomic nerves but not the sensory or motor nerves = differential block **Nerve Fiber Type** **Subtype** **Diameter (μm)** **Conduction Velocity (m/s)** **Function** ---------------------- ------------- ------------------- ----------------------------------- ---------------------------------- A (myelinated) Alpha α 12 -- 20 80 - 120 Proprioception and large motor Beta β 5 -- 15 35 -- 80 Small motor, touch, and pressure Gamma γ 3 -- 8 10 -- 35 Muscle tone Delta δ 2 -- 5 5 -- 25 Pain, temperature, and touch B (myelinated) 3 5 -- 15 Preganglionic autonomic C (unmyelinated) 0.3 -- 1.5 0.5 -- 2.5 Dull pain, temperature, and touch **Sensory Pathways** - Most sensory input enters spinal cord through dorsal roots of spinal nerves - Sensory information travels to the brain via either: - **Dorsal Column (Medial Lemniscal System)** -- ascend then cross - Cross to the opposite side of the medulla - High degree of spatial orientation of sensory information - **Anterolateral System** -- cross then ascend - Crosses to the opposite side and ascends to the thalamus - Lesser degree of spatial orientation - Transmits a broad range of modalities: pain, warmth, cold, crude sensations - Sections: - **Anterior Spinothalamic Tract** -- crude touch - **Lateral Spinothalamic Tract** -- pain and temp **Dorsal Column-Medial Lemniscal System** - Consists **of LARGE, MYELINATED NERVE FIBERS** - **RAPID** Conduction velocity: **30-110 m/sec** - **DCML carries LOCALIZED TOUCH, vibration, movement against the skin, joint sensation, proprioception, pressure** - **Crosses over to opposite side at level of medulla** - Highly organized nerve fiber structure **Dorsal Column-Medial Lemniscal System (DCML): Anatomy**  - Sensory stimuli travel via Type A-Beta and Type C fibers and enter spinal cord at the dorsal root ganglion - The **[first order neurons]** are those located in the dorsal root ganglia - These are afferents (carrying sensory information to the brain) - Nerve fibers divide in spinal cord to medial branch and lateral branch - **Medial branch** enters through spinal root dorsal column **brain** - **Lateral branch** enters through dorsal horn further divides until some enter dorsal column and travel to the **brain,** some terminate in **spinal cord** (spinal cord reflexes), some give rise to **spinocerebellar tracts** - Fibers then travel up ***fasciculus gracilis*** (below T6) or ***fasciculus cuneatus*** (C2-T6) - These are *[second-order neurons]* - Fibers then *decussate* at the contralateral medial lemniscus (medulla) and ascend - Terminate in the ventral posterior lateral nucleus of the thalamus - This is where the *[third-order neurons]* are located **Dorsal Column Pathway** A diagram of a brain function Description automatically generated - Fibers entering the dorsal column take one of two paths - Medial branch fibers move medially and ascend to the brain - Lateral branch fibers synapse in the intermediate and anterior portions of the gray matter. - These fibers: - Enter the dorsal column and ascend - Elicit spinal cord reflexes - Form spinocerebellar tract - Note the number of synapses in the lamina - Synapse that enhances - Descending pathways that inhibit pain - Fibers entering the dorsal column ascend directly to the dorsal column nuclei where they synapse and cross - In the brainstem they are joined by fibers from the trigeminal nerve (CN V) transmit sensations from the face - Fibers eventually traverse the thalamus enroute to the cerebral cortex in somatic sensory areas I & II **Somatosensory Cortex** - Sensory signals terminate in the cerebral cortex - Anterior parietal lobe receives and interprets somatosensory signals - Motor cortical functions reside anterior to the central fissure - [Parietal lobe] -- reception /interpretation of somatosensory signals - [Occipital lobe] --termination of visual signals - [Temporal lobe]- termination of auditory signals - [Somatosensory Area I ] - Lies immediately behind **central fissure** in postcentral gyrus of the cerebral cortex - **Highest degree of localization and is much larger = most important!** - Different parts of the body = different regions - Size of region correlates with number of specialized receptors - Lips have the most receptors, followed by face and tongue - Each lateral cortex receives sensory information from the opposite side of the body - **The Homunculus** - Used to describe where 3rd order neurons go to transmit different anatomical impulses - Used for lead placement by neurophysiologists using SSEP - Functions: - Posterior to the central sulcus - Ability to discretely localize different sensations from different parts of the body - Ability to judge critical degrees of pressure - Ability to judge the weight of objects - Ability to judge shapes or forms of an object - Ability to judge texture of objects - **Each side of the cortex receives information from the opposite side of the body** - [Somatosensory Area II] - Lies posterior to Somatosensory Area I - Function is not as well understood **Anterolateral System**  - Transmits sensory signals that DO NOT require localization discrimination - ONLY transmission of pain, temp, tickle, itch and sexual sensations - [Conduction velocity is slower] than in dorsal column-medial lemniscal system - [Spatial localization and intensity are poor] - Spinal cord anterolateral fibers originate in **dorsal horn of laminae I, IV, V, VI** - Fibers **cross immediately** in the *anterior commissure* of the **spinal cord** to the *anterior and lateral white columns* *spinothalamic tracts* *brain* - ***Spinothalamic tracts* terminate in *brainstem* and *thalamus*** - *Reticular nuclei of brainstem (pain)* - *Ventrobasal complex of thalamus (tactile stimuli)* - *Intralaminar nuclei of thalamus (pain)* - Sensory stimuli travel from the periphery to the spinal cord before synapsing in the ***dorsal root ganglion*** - The [*first-order neurons*] are those located in the dorsal root ganglia - These are afferents (carrying sensory information to the brain) - These fibers synapse with *[second order neurons]* in the ***substantia gelatinosa*** - Fibers decuss (cross over) to the opposite side in the ***anterior white commissure,*** enter the anterolateral portion of the spinal cord and ascend to the thalamus - Enter the brainstem as the spinal lemniscus - The *[third-order neuron]* cell body lies in the VPL (ventral posterolateral nucleus) of the thalamus - Anterolateral Pathway - Anterolateral pathway signals require less discrete localization - Originate in lamina I, IV, V, VI - Anterior lateral fibers cross immediately prior to ascending - Ascend through the anterior spinothalamic and lateral spinothalamic tracts - After termination in the thalamus, they travel to the somatosensory cortex with the dorsal column fibers - Feedback about proprioception and movement integrated with pain and temperature - Anterolateral Pathway Transmission Characteristics - Transmission velocity is 1/3 -- 1/2 that of the dorsal column system - Spatial localization of signals is poor - Intensity gradation is less precise - Less ability to convey rapidly changing or rapidly repetitive signals - Exclusive pathway for: pain, temperature, tickle, itch, and sexual sensations **Sensory Pathways: Review** +-----------------------------------+-----------------------------------+ | **Dorsal Column of Spinal Cord** | **Anterolateral System of Spinal | | | Cord** | | **Medial Leminiscal Pathway | | | (DCML)** | | +===================================+===================================+ | \- Consists **of LARGE, | \- Consists of **SMALLER, | | MYELINATED NERVE FIBERS** | MYELINATED NERVE FIBERS** | | | | | **- RAPID** Conduction velocity: | **- SLOWER** conduction | | **30-110 m/sec** | velocity**: 3-40 m/sec** | | | | | \- Carries signals to medulla via | \- Signals enter spinal cord from | | (mostly) the dorsal column | dorsal spinal nerve roots | | | | | **- Crosses over to opposite side | \- Synapse in the dorsal horns of | | at level of medulla** | the spinal gray matter | | | | | \- Continues through brainstem to | **- Most cross to opposite side | | thalamus via the medial lemniscus | of the cord via anterior white | | | commissure** | | \- Dorsal column carries | | | LOCALIZED TOUCH, vibration, | \- Ascend thru anterior & lateral | | movement against the skin, joint | white columns of spinal cord | | sensation, pressure | | | | \- Terminate at lower brain stem | | \- Highly organized nerve fiber | and thalamus | | structure | | | | **- Anterolateral system can | | | transmit pain, warmth, cold, | | | crude touch, tickle, itch, sexual | | | sensations** | | | | | | **- Much less organized nerve | | | fiber structure** | +-----------------------------------+-----------------------------------+ **Pain Receptors** - Acute pain is protective = promotes withdrawal from pain stimuli and avoidance of pain stimuli - **Nociceptors** - sensory receptors that detect signals from damaged tissue or the threat of damage - Pain receptors are [free nerve endings] - Pain can be elicited by multiple types of stimuli (mechanical, chemical, thermal) - *Stimulated by* bradykinin, serotonin, histamine, potassium ions, acids, acetylcholine, proteolytic enzymes - *Enhanced sensitivity* by prostaglandins and Substance P - Average person perceives pain at 45-degrees C (temperature tissues start to be damaged by heat) - **Pain often correlates with rate at which damage to tissues is occurring- NOT with tissue damage that occurred** - **Fast pain** is elicited by **mechanical and thermal** stimuli - **Slow pain** is elicited by **mechanical, chemical and thermal** stimuli - Pain receptors adapt very little (if at all!) - Excitation of pain fibers sometimes actually progressively [increases] (protective purpose) - **[Hyperalgesia]:** unusually severe pain in situation where pain is normal, pain is more severe than it "should" be **Pain Pathways: Fast Pain vs Slow Pain** - Pain fibers enter the spinal cord from the *dorsal spinal roots* - The [*first-order neurons*] are those located in the dorsal root ganglia - Within spinal cord, they take one of 2 pathways to the brain - ***Neospinothalamic*** tract (fast-type pain) - ***Paleospinothalamic*** tract (slow-chronic pain) **Comparison** - Pain fibers enter the spinal cord from the *dorsal spinal roots* - *First-order neurons* are those located in the dorsal root ganglia +-----------------------+-----------------------+-----------------------+ | **Pain Tract** | **Neospinothalamic | **Paleospinothalamic | | | Tract** | Tract** | | | | | | | **Fast/Sharp Pain | **Slow/Chronic Pain | | | Pathway** | Pathway** | +=======================+=======================+=======================+ | **Fiber** | A -- Delta fibers | Mainly C fibers | | | | | | | | Some A -- Delta | | | | fibers | +-----------------------+-----------------------+-----------------------+ | **Felt** | Fast Pain | Slow Pain | | | | | | | Within 0.1 seconds | Within 1 second or | | | | longer and then | | | | increases | +-----------------------+-----------------------+-----------------------+ | **Termination (Spinal | Lamina I (Lamina | Spinal cord in lamina | | Cord)** | marginalis) of Dorsal | II and III | | | Horn | (***substantia | | | | gelatinosa)*** | | | Second order neurons | | | | cross at anterior | Some fibers synapse | | | commissure and ascend | with fibers in | | | through anterolateral | laminae V before | | | coulmns | crossing at the | | | | anterior commissure | | | | and then ascending | +-----------------------+-----------------------+-----------------------+ | **Pain Type** | Mechanical | Slow | | | | | | | Acute Thermal Pain | Contributes to | | | | emotional/autonomic | | | Fast pain | pain | | | | | | | Sharp, prickling, | Slow burning, aching, | | | acute, or electrical | throbbing, or chronic | | | pain | pain | | | | | | | | Associated with | | | | tissue destruction | +-----------------------+-----------------------+-----------------------+ | **Stimuli** | Mechanical | Mechanical | | | | | | | Thermal | Thermal | | | | | | | | Chemical | +-----------------------+-----------------------+-----------------------+ | **Neurotransmitter** | Glutamate | Glutamate | | | | | | | | Substance P | +-----------------------+-----------------------+-----------------------+ | **Localization** | More accurate | Less accurate | | | | | | | Relies on sensory | | | | information from | | | | touch receptors | | +-----------------------+-----------------------+-----------------------+ | **Termination | Thalamus to cortex | Lower regions of | | (Brain)** | | brain (medulla, pons, | | | | mesencephalon) | +-----------------------+-----------------------+-----------------------+ **Pain Sensations** - **[Referred Pain]**: branches of visceral pain fibers synapse in spinal cord on the same second-order neurons that receive pain signals from the skin - **[Visceral Pain]:** pain from organs in abdomen and chest, highly localized types of damage to viscera seldom cause severe pain; diffuse visceral pain can be severe - **[Nociception]**: processing of painful stimuli, involves four phases - **[Transduction]:** converting painful stimulus into an electrical signal that is transmitted to the CNS - **[Transmission]:** conduction of pain impulses along the Aδ and C fibers (primary-order neurons) dorsal horn - **[Perception]**: conscious awareness of pain, occurs primarily in the reticular and limbic systems and cerebral cortex - Influenced by genetics, culture, sex roles, age, level of health, and past pain experiences - **[Modulation]**: mechanisms that increase or decrease the transmission of pain signals (neurotransmitters, analgesic drugs, anesthesia, and nonpharmacologic interventions such as transcutaneous nerve stimulation, acupuncture, hypnosis, PT) **Endorphins and Enkephalins** - There are approximately 1-dozen naturally occurring opiate like substances in the CNS - Derived from pro-opiomelanocortin, proenkephalin, and prodynorphin - Most important are *beta-endorphin, met-enkephalin, leu-enkephalin, dynorphin* - Not completely understood - Can activate analgesia and/or inactivate pain pathways **Dermatomes** - Landmarks - Clavicle C4 - Nipples T4 - Xiphoid T6 - Umbilicus T10 - Tibia L4-L5 - Perineum S2-S3 **Herpes Zoster (Shingles)** - Caused by Herpes Virus - Spread via airborne droplets or direct contact with actively viral shedding lesions - Virus remains latent in trigeminal and dorsal (sensory) root ganglia, followed years later by reactivation to cause herpes zoster - [Symptoms]: Pain and paresthesia localized to the affected dermatome - Thoracic or lumbar dermatome are most common but can appear on any dermatome - If Ophthalmic branch of the trigeminal nerve is affected, it should be considered a medical emergency as it is sight-threatening **Peripheral Nerve Injuries** - Classification - Transection: partial or complete destruction of a nerve - Compression: pressure on nerve from bony prominence pressing against an internal or external surface - Traction: stretching of a nerve against immobile surface - Injury mechanisms - Ischemia - Structural disruption - Transection **Special Senses** **Eye Anatomy** - [Sclera]: White of the eye, connective tissue - Continuous with the dura mater around CNII - [Retina]: Cones/rods inner layer of the eye - Fovea is a focused depression - Macula is the reddish circle around the fovea - [Cornea]: Curved transparent outer layer. - [Iris]: Colored muscular portion which elicits mydriasis and miosis - [Lens]: Viscous gel - Behind the cornea - Aqueous and vitreous humors - Gives the eye its shape and keeps it from collapsing - Vitreous humor does not change in size or quantity **Vision** - Retina contains rods and cones---special photoreceptors that convert light energy into nerve impulses - Rods mediate peripheral and dim light vision - Cones are color and detail receptors - Nerve impulses pass through the optic nerves (CN II) to the optic chiasm - Fibers of the optic tracts terminate in the primary visual cortex in the occipital lobe of the brain - Some fibers terminate in the hypothalamus and are involved in circadian regulation/ sleep-wake cycle **Glaucoma** - Eye is filled with vitreous humor and aqueous humor to give it shape, keep it from collapsing - Aqueous humor: formed by ciliary body, flows through the pupil → anterior chamber of the eye and exits via the Canal of Schlemm - Maintains intraocular pressure (normal= 12-20 mmHg) - **Glaucoma: IOP can be as high as 60-70 mm Hg** - Associated with a pathologic increase in intraocular pressure - Change in anterior chamber of the eye = aqueous humor - Blood pressure/volume - Certain medications - Angle = drainage angle formed by the iris and cornea - [Open angle glaucoma]: Most common that arises slowly and is non-painful - Mismatch in AH production and drainage - [Closed angle glaucoma]: Can arise slowly or suddenly - "Sudden variety" (10% of cases) is a medical emergency = lose sight if not surgically managed - Iris can be stuck to lens or can block the drainage sites **Anesthesia and the Eye** - **Intraocular Pressure and Anesthesia** - **[Increase IOP]** - Succinylcholine (5-10mmHg for 5-10min) - Ketamine? - Intubation - **[Decrease IOP]**: - Inhalation anesthetics - Propofol - Opioids - Benzodiazepines - **N~2~O should not be used in eye surgery especially if surgeon is placing a gas bubble** - Can travel to air filled spaced and expand - Oculocardiac Reflex (Aschner Reflex, 5 and Dime, or Trigeminovagal Reflex) - Traction on extraocular muscles causing pressure on eyeball that elicits a wide variety of cardiac dysrhythmias (bradycardia, ventricular ectopy, VF) - Can also be caused from administration of a retrobulbar block - Afferent = Trigeminal Nerve (CN V) - Efferent = Vagus Nerve (CN X) - Prevention and treatment strategies: - Remove stimulus - Deepen anesthetics - Atropine/Glyco **Retrobulbar Blocks** - Retrobulbar Block Apnea Syndrome - Rare occurrence - Injection of local anesthetic for a retrobulbar block that enters the optic nerve sheath can **spread centrally and produce *unconsciousness and apnea*** - Treatment is ***supportive*** - Intubation/ ventilation and manage cardiac arrhythmia **Visual Evoked Potentials (VEP)** - Performed by neurophysiologists during surgery with high potential for [CNII damage ] - Transsphenoidal hypophysectomy - Craniotomy for disease near CNII - Flashes of light are emitted and electrodes placed over the occipital lobe - **VERY sensitive to anesthetic agents** - Anesthetic agents lower the amplitude and latency of the signal making it hard for the neurophysiologist to accurately assess integrity of the pathway **Corneal Abrasions** - Most common ocular injuries in the perioperative period - Incidence typically between 0.013% and 0.17% of non-ocular surgeries **Hearing and Balance** - Cranial Nerve VIII = divided into two sections: - Cochlea -- auditory portion of the inner ear - A spiral complex of canals whose neuro-sensory cells are found in the cochlear duct - "Hair cells" whose extensions protrude up onto a tectorial membrane - As the membrane vibrates from sound, the hair cells move = send very specific signals via the cochlear branch of CN VIII - Vestibular System -- Otolith organs of the semicircular canals that allow sensation of balance - Small tract of neurons descends from the vestibular system to form the vestibulospinal tract - The vestibulospinal tract again forms a DIRECT connection between position sense and efferent motor neurons (bypassing cognition) to keep the body in balance - Important contributor to eye movement and body posture - As the head moves in any arrangement of rotation, fluid and otolith movement in these canals are picked up by the hair cell cilia - Impulse is transmitted to the contralateral temporal lobe where the meaning is interpreted - The ear is composed of external, middle, and inner structures. - **[External ear]** structures are the pinna, auditory canal, and tympanic membrane. - External ear is **only involved in hearing.** - **[Middle ear]** is composed of the tympanic cavity (containing three bones: the malleus, the incus, and the stapes), oval window, eustachian tube, and fluid. - Middle ear is **only involved in hearing.** - **[Inner ear]** is **involved in both hearing and equilibrium**. - Includes the bony and membranous labyrinths that transmit sound waves - Includes the semicircular canals and vestibule help maintain balance **Brainstem Auditory-Evoked Potential Monitoring (BAEP)** - Performed by a neurophysiologist DURING your anesthetic - Auditory clicks are made and neural pathway is assessed on the contralateral temporal lobe - **BAEP is BARELY sensitive to anesthetics** **Vertigo** - Dysfunction in the interplay between the vestibular, visual, and somatosensory systems - Most often a disorder of the vestibular system - Characteristics: - Nausea - Nystagmus - Postural unsteadiness - Gait ataxia **Gustation** - Taste buds -- collection of sensory neurons within a bulb lining the surface of the papillae of the tongue - Multiple causes of excitation (from different tastes) - Some are more sensitive to salt, sour, sugar, bitter, and umami **Smell** - Cranial Nerve I: Olfactory - Fibers extend through the cribriform plate into the nasal mucosa - Odorant-binding proteins stimulate the cilia (hairs) of that specific chemoreceptor (there are hundreds) - The neuron is depolarized, and the impulse carried to the CNS (olfactory cortex of the temporal lobe) **Limbic System** - The limbic system provides most of the emotional drives for activating other areas of the brain and even provides motivational drive for the process of learning itself - Found in the anterior pole of the temporal lobe, in the ventral portion of the frontal lobe, and in the cingulate gyrus lying - deep in the longitudinal fissure on the midsurface of each cerebral hemisphere - Responsible for: - Emotions - Pain - Pleasure - Visceral response to emotions - Motivation - Mood (depression, bipolar) - Appetite - Anger - Fear - Sexual satisfaction - Hippocampus: part of transfer of short-term memory to long-term memory and recall of long-term memories and their emotional associations **Hypothalamus** - Most important control pathways of the limbic system - Controls most of vegetative and endocrine functions of the body and much of emotional behavior - Has two-way communicating pathways with all levels of the limbic system - Send output signals in three directions: - Backward and downward to the brain stem (mainly into the reticular areas of the mesencephalon, pons, and medulla) → into the peripheral nerves of the ANS - Upward toward many higher areas of the diencephalon and cerebrum, especially to the anterior thalamus and limbic portions of the cerebral cortex - Into the hypothalamic infundibulum to control or partially control most of the **secretory functions of both the posterior and the anterior pituitary glands** **The Motor System** **Sensory and Motor Tracts of the Spinal Cord**  **Motor Efferent** A diagram of a brain Description automatically generated - CNS order of motor control: - The primary motor cortex (precentral gyrus of the frontal lobe) determines the goal of movement and its consequences - Basal ganglia provide the boost that turns intention into actual movement -- excitatory and inhibitory function (like a gateway) - Cerebellum determines the correct sequence of commands that will allow the goal to be achieved **Intro: Motor System** - **Motor transmission is via a 2-neuron pathway** - **Motor responses begin in the spinal cord (simple reflexes), brain stem (more complicated responses) and cerebrum (most complicated muscle skills)** - ***[Upper motor neurons]*** transmit information from the brain → brainstem or spinal cord - Neurotransmitter: Glutamate - ***[Lower motor neurons]*** transmit information from the spinal cord → muscles and glands - Neurotransmitter: Acetylcholine - Motor pathways are ***efferent*** (carrying impulses away from the CNS) **Interneurons** - Present in all areas of cord **gray** matter (dorsal horns, anterior horns, areas between them) - Small and highly excitable - Can fire as rapidly as 1500x/sec - 30x more interneurons than anterior motor neurons - **Corticospinal tract consists primarily of interneurons** **Anterior Motor Neurons** - Innervate skeletal muscle - Located in each segment of the anterior horns of the gray matter - Largest (50-100% larger than most other neurons) - Give rise to nerve fibers that exit spinal cord via *anterior* roots and directly innervate skeletal muscles - Two types: - Alpha motor neurons: innervate large skeletal muscles - Gamma motor neurons: innervate intrafusal fibers of the muscle spindle **Motor Pathways** - **MOTOR PATHWAYS** transmit information from the brain to: - Voluntary (skeletal) muscles - Smooth muscle - Cardiac muscle - Some glands - Motor pathways are ***efferent*** (carrying impulses away from the CNS) - **Motor responses begin in the spinal cord (simple reflexes), brain stem (more complicated responses) and cerebrum (most complicated muscle skills)** **Motor Functions** - [Cerebellum] determines the correct *sequence* of commands that will allow the goal to be achieved - [Primary motor cortex] determines the goal of movement and its consequences - [Basal ganglia] provide the "boost" that turns intention into actual movement. - Basal ganglia have both excitatory and inhibitory function (like a gateway) - [CORTICOSPINAL TRACT]: voluntary muscles of the trunk and extremities - [CRANIAL NERVES]: supply voluntary muscles of head and neck **Cerebral Motor Cortex** - Cerebral motor cortex is located ***anterior*** to the central cortical sulcus - Cerebral motor cortex occupies the **posterior one-third of the frontal lobe** - Motor cortex consists of three areas: - ***[Primary Motor Cortex]*** Muscles of hands, speech - ***[Premotor Area]*** Patterns of movement, mirrored tasks - ***[Supplementary Motor]*** Cortex Bilateral movements **Specialized Motor Areas** - [Broca's Area]: motor speech area; has to do with word formation - [Voluntary eye movement field]: controls voluntary eye movement including blinking - [Head Rotation Area]: stimulation in this area directs the head toward objects - [Area for hand skills]**:** damage to this area causes motor apraxia (difficulty with skilled movement) **Transmission of Signals from the Motor Cortex to Muscles** - **[Corticospinal Tract (aka Pyramidal Tract)]** - Most important output pathway! - Originates from: - Primary motor cortex (30%) - Premotor and supplementary motor cortex (30%) - Somatosensory area (40%) - **[Indirect /Alternative Pathways]**: accessory pathways - **[Cranial Nerves]** supply voluntary muscles of head and neck **Details of Motor Pathways**  **Motor Pathways: Lateral Corticospinal Tract (Pyramidal)** - Originates in precentral gyrus of the frontal lobe - **Highly organized** (neurons supplying specific areas of the body are grouped together) - Motor fibers for all parts of the body except the face - Axons travel from cortex → thru the *internal capsule* → midbrain (basis pedunculi) medulla lateral corticospinal tract (aka PYRIMADAL TRACT) SPINAL CORD - **[Most]** fibers DECUSSATE in **[lower medulla]** - Those that do not cross at medulla travel via *ventral corticospinal tracts* and cross in neck/thorax - Motor nerves exit the spinal cord via the ***anterior horn*** **Intrinsic Muscle Control** - **[Muscle Spindles]**: - Found in the **belly** of skeletal muscles - Send sensory info to brain about muscle length or rate of change of **length** - 2 types of sensory fibers to differentiate between slow and fast stretch - Excited by small gamma motor nerve fibers that originate from type A gamma motor neurons in anterior horns of the spinal cord - **[Golgi Tendon Organs]**: - Located in the muscle **tendons** - Transmit information about tendon torsion or rate of change of **tension** - Consist of an encapsulated sensory receptor through which muscle fibers must pass - Organ is stimulated when the bundle of muscle fibers is tensed **Reflex Responses** - [Flexor reflex]: - Stimulation of pain endings (aka nociceptive reflexes, pain reflex) causes that part of the body **to be withdrawn from the stimulus** - Flexor reflex pathways pass **directly from neuronal pool in spinal cord to motor fibers** - Activates **diverging circuits** to spread impulse to: - Necessary muscles for withdrawal - Circuits to inhibit opposing muscles (reciprocal inhibition circuits) - Circuits to cause after-discharge (lasts a few seconds after stimulus is over) - Afterdischarge duration depends on intensity of initial stimulus - This afterdischarge holds the irritated part away from the stimulus for 0.1-3 sec after irritation is over (protective mechanism) **Crossed Extensor Reflex** - Extension of the opposite limb to 'push away' the entire body from the painful stimulus **Clinical Relevance: Disorders of the Motor System** - **Upper Motor Neuron Diseases** - Increased DTRs (deep tendon reflexes) - Increased muscle tone - Positive Babinski sign - Spastic paralysis - **Lower Motor Neuron Disease** - Decreased DTRs - Decreased muscle tone - Negative Babinski sign - Flaccid paralysis /Muscle atrophy - **Where is injury in relation to decussation?** - **If injury occurs above decussation, paralysis is on the opposite side of the body** - **If injury occurs below decussation, paralysis is on the same side of the body** A diagram of the nervous system Description automatically generated **Clinical Relevance: Movement Disorder Terminology** - **Ataxia**---Inability to coordinate muscle activity - **Athetosis**---Involuntary movements of flexion/extension, pronation/supination of hands, toes, and feet; slow; writhing-type movements - **Ballismus**---Jerking, swinging, sweeping motions of the proximal limbs - **Bradykinesia/hypokinesia**---Decrease in spontaneity and movement - **Chorea**---Irregular, spasmodic, involuntary movements of limbs or facial muscles, often with hypotonia - **Cogwheel rigidity**---Resistance to movement; rigidity decreasing to stiffness after movement begins - **Dystonia**---Abnormal tonicity; difficulty maintaining posture - **Hyperkinesis**---Excessive motor activity - **Tic**---Repeated, habitual muscle contractions; movements that can be voluntarily suppressed for short periods - **Tremor**---Oscillating, repetitive movements of whole muscles; irregular, involuntary contractions of opposing muscles **Clinical Relevance: Cerebral Palsy** - Caused by damage to **upper motor neurons** from an event that occurs prenatal, perinatal or postnatal (Cerebral Anoxia, Hemorrhage, and other neurologic insult) - [Classified by the type of motor dysfunction] - [Spastic]: inability of muscles to relax - [Hemiplegia]: involving one arm and one leg on the same side of the body - [Diplegia]: involving both legs - [Quadriplegia]: involving all four extremities, the trunk, and neck muscles - [Athetoid or dyskinetic]: inability to control muscle movement - [Ataxic]: inability to control balance and coordination - [CLINICAL MANIFESTATIONS] - Altered body movement and muscle coordination - Developmental delays - Not a progressive disease. **Clinical Relevance: ALS (Amyotrophic Lateral Sclerosis)** - **Degenerative disease of motor neurons** - Exact cause unknown (glutamate excitotoxicity and/or oxidative stress?) - **No known cure** - **Affects both upper and lower motor neurons** - **Leads to the destruction of NMJ** - Rapid progression, fatal disease - Symptoms appear first in arms, hands, legs, and swallowing muscles - Muscles gradually weaken, waste away, and twitch **Clinical Relevance: Spinal Cord Injury** - Spinal cord injury (SCI) impairs the transduction of afferent and/or efferent neural impulses - Damage to the gray matter of the central cord may result in loss of motor neurons and interneurons - In complete injury, sensation and motor function **below the level of injury are lost** - **Categorization of PARTIAL cord transections** - **Central Cord Syndrome** - **Anterior Cord Syndrome** - **Brown-Séquard Syndrome**  **The Autonomic Nervous System** **Cervical Ganglia** - Cervical ganglia provide sympathetic innervation to head, neck, arms, and upper chest - Cervical ganglia are divided into superior, medial and inferior cervical ganglia - Inferior cervical ganglion fuses with 1^st^ thoracic ganglion in 80% of individuals to form the **[Stellate Ganglion]** (aka Cervicothoracic ganglion) - [Stellate ganglion blocks] are used to treat chronic regional pain syndromes, craniofacial hyperhidrosis, refractory angina, postherpetic neuralgia, PTSD, PVD, and long -Covid - [Horner's Syndrome]: ptosis, miosis and anhidrosis - Ptosis -- drooping eyelid - Miosis -- constricting pupil - Anhidrosis -- loss of sweating on the face **SNS and PNS Nerve Fibers** - [Preganglionic] nerve fibers are: - MYELINATED - Diameters \< 3 mm - Conduction velocity 3-15 m/sec - [Postganglionic] nerve fibers are: - UNMYELINATED - Conduction velocity 2 m/sec (SLOW!) **Physiologic Anatomy of ANS** - SNS and PSNS are the efferent (motor) component of the ANS - Most organs receive fibers from both divisions - [Exceptions]: Sweat glands are innervated by only SNS fibers - [2-Neuron System] - Two-neuron (bipolar) chain from the CNS to the effector organ - Preganglionic Neuron - Postganglionic Neuron **Receptors on Effector Organs** - Acetylcholine, norepinephrine, epinephrine are secreted from autonomic nerve ending - Requires binding with specific receptors on effector cells - Binding causes a conformational change excitation or inhibition - Opens or closes ion channel alters permeability of cell membrane to various ions - Second messenger enzymes Activation or inactivation of enzyme on interior of cell **SNS and PSNS Neurotransmitters** - Cholinergic = Acetylcholine - Adrenergic = Norepinephrine - **ALL PREGANGLIONIC NERVE FIBERS in BOTH SNS and PNS are CHOLINERGIC** (secrete acetylcholine) - **ALMOST ALL PARASYMPATHETIC POSTGANGLIONIC NERVE FIBERS are CHOLINERGIC** (secrete acetylcholine) - **MOST SYMPATHETIC POSTGANGLIONIC NERVE FIBERS are ADRENERGIC** (secrete norepinephrine) **Acetylcholine and Norepinephrine Synthesis** - Acetylcholine Synthesis = Choline + Acetyl CoA (with Choline acetyltransferase) = Acetylcholine What is the synthetic pathway for acetylcholine? --- Brain Stuff - Norepinephrine Synthesis = tyrosine → DOPA → Dopamine → Norepi → Epi  **Norepinephrine and Epinephrine Metabolism** Diagram of a kidney Description automatically generated **Cholinergic Receptors** - Acetylcholine activates both muscarinic & nicotinic receptors - **[Muscarinic receptors]** are found on all effector cells that are stimulated by **postganglionic cholinergic neurons** of **either the PSNS or SNS** - **[Nicotinic receptors]** are found in the autonomic ganglia at the synapses **between the preganglionic and postganglionic neurons** of **both SNS and PSNS**. Nicotinic receptors are also found outside the ANS (NMJ)  **Adrenergic Receptors** - [Alpha receptor activation]: - Activation of alpha receptors can cause excitation or inhibition - Vasoconstriction, iris dilation, intestinal relaxation, intestinal sphincter contraction, pilomotor contraction, blader sphincter contraction, inhibits neurotransmitter release - [Beta receptor activation]: - Activation of beta receptors can cause excitation or inhibition - Vasodilation, cardioacceleration, increased contractility, intestinal relaxation, uterus relaxation, bronchodilation, calorigenesis, lipolysis, bladder wall relaxation, thermogenesis - Norepinephrine and epinephrine activate both alpha & beta receptors - **[Norepinephrine: works primarily on alpha receptors]** - **[Epinephrine: works equally on both alpha and beta receptors]** A white sheet with black text Description automatically generated **Postganglionic Breakdown of Acetylcholine and Norepinephrine** - ACETYLCHOLINE: - Acetylcholine is broken down into acetate and choline by the enzyme acetylcholinesterase - Same as mechanism at neuromuscular junction - Choline is "recycled" to make more acetylcholine - NOREPINEPHRINE: - Three mechanisms terminate activity of norepinephrine in seconds: - Active reuptake (50-80% of norepinephrine) - Diffusion away from nerve endings → body fluids and blood - Destruction by tissue enzymes - Monoamine oxidase (found in nerve endings) - Catechol-O-methyl transferase (found throughout tissues) **Anesthesia = Managing the ANS\*** - Goal: Railroad tracks = keep things steady **The Autonomic Nervous System (ANS)** - Controls BP, GI motility /secretion, bladder emptying, sweating temp - Activated by centers in *spinal cord, brainstem and hypothalamus* - Influenced also by limbic system (memory/ emotion/ fear) - **ANS can respond [rapidly]** - **Can increase HR to 2x normal within 3-5 seconds** - **Can increase BP to 2x normal in 10-15 secs** **Parasympathetic vs Sympathetic** - **Parasympathetic: "Rest and Digest" or "Feed and Breed"** - **Craniosacral system** - **Sympathetic: "Fight or Flight"** - **Small type C fibers** - **Thoracolumbar system** A screenshot of a medical chart Description automatically generated **Higher Level Organization of the SNS** - Hypothalamus - Long-term BP control - Reactions to physical and emotional stress - Sleep - Sexual reflexes - *Medulla oblongata* and *pons* - "Momentary" hemodynamic adjustments - Sequence and automaticity of ventilation - Maintaining constant "tonicity" - Nucleus tractus solitarius relays afferent chemoreceptor and baroreceptor for SNS response **SNS (Thoracolumbar System)** - **Originates in spinal cord (T1-L2)** - **Preganglionic neuron lies in *intermediolateral horn* of spinal cord** - **Passes through *ventral root -\>* *white ramus -\> sympathetic chain ganglia*** - **Synapse with postganglionic neuron** - **Postganglionic neuron originates in either sympathetic chain ganglia or peripheral sympathetic ganglia and transmits impulse to the effector organ** - **[Exception]: adrenal medulla has only preganglionic fibers** **PSNS (Craniosacral System)** - **Has preganglionic & postganglionic neurons** - **Originate in brainstem and sacrum** - **Also found in CN III, VII, IX and X** - **III (oculomotor)** - **VII (facial)** - **IX (glossopharyngeal)** - **X (vagus)** - **Sacral outflow originates in intermediolateral gray horns of sacral nerves** - ***[VAGUS NERVE (X)] accounts for 75% of PSNS (Parasympathetic Nervous System) activity*** **Parasympathetic and Sympathetic Tone** - Constant activity of SNS and PSNS maintain basal rate of activity - Allows a single nervous system to both increase and decrease activity of a stimulated organ - Sympathetic tone causes baseline blood vessel constriction - Parasympathetic tone maintains baseline GI motility - Adrenal medulla maintains basal secretion - **Epinephrine 0.2 mcg/kg/min (80%)** - **Norepinephrine 0.05 mcg/kg/min (20%)** - Enough to maintain normal BP even if all direct innervation was removed **Adrenal Medulla** - **Preganglionic sympathetic nerve fibers pass WITHOUT SYNAPSING from spinal cord → through the sympathetic chain-\> adrenal medulla** - **Innervated by PREGANGLIONIC fibers that secrete EPINEPHRINE and NOREPINEPHRINE (not acetylcholine)** - Effects: same as sympathetic stimulation - [Prolonged DOA (5-10x) because they are removed slowly from the blood] - Organs are stimulated in two ways (SNS and adrenal medulla) - Dual mechanism of sympathetic stimulation = safety - Adrenal medulla also can stimulate structures that NOT innervated by direct sympathetic fibers! **Sweat Glands** - SNS stimulation increases sweat production of sweat glands - **Sympathetic fibers to most sweat glands are CHOLINERGIC (acetylcholine)** - [Exception]: adrenergic fibers to palms and soles **Autonomic Reflexes** - [Baroreceptor Reflex]: - Stretch receptors in walls of major arteries (carotid artery, aortic arch) detect STRETCH - "High Pressure" impulses are sent to the brain stem - Sympathetic impulses inhibited/Parasympathetic impulses increase - BP returns to normal - [Gastrointestinal Reflexes]: - Smell of food increases salivation and GI secretion of digestive juices - Rectal Emptying Reflex /defecation - [Sexual Reflexes]: - Erection (parasympathetic) and ejaculation (sympathetic) - [Other Reflexes]: - Pancreatic secretion, gallbladder contraction, kidney excretion of urine, sweating, blood glucose concentration **Denervation Injury** - Intrinsic compensation for denervation injury - Intrinsic tone in smooth muscle of vessels increases following injury - Chemical adaptations - Increased sensitivity to circulating catecholamines - Eventually restores almost normal vasoconstriction - Parasympathetic compensation may require many months - Denervation supersensitivity (upregulation) - Can see enhanced effect of administered catecholamines **Autonomic Dysreflexia** - Condition that emerges after a spinal cord injury - Usually, above **T6 level** - Dysregulation of ANS leads to an **uncoordinated sympathetic response that may result in a potentially life-threatening hypertensive episode when there is a noxious stimulus below the level of the spinal cord injury** - Noxious stimuli consist usually of bladder or bowel distension - The higher the injury, the greater the severity of CV dysfunction - Significantly increased risk of stroke by 300% to 400%  **Autonomic Pharmacology** - Drugs may be used to either **mimic** or **block** the action(s) of the autonomic nervous system - [Sympathomimetics] (adrenergic agonists): **mimic** the action of catecholamines; **increase SNS activity** - [Cholinomimetics]: **mimic** the effect of acetylcholine**; increase PSNS activity** - [Adrenergic Antagonists] (adrenergic blockers): **block** the action of catecholamines; **decrease SNS activity** - [Anticholinergics]: block the effect of acetylcholine, decrease PSNS activity - **[Note]**: Drug effects depend on specific receptors affected! - **[Note]**: need to know/ understand how the medication works - i.e. does it activate receptors directly? Increase release of naturally occurring neurotransmitters from storage vesicles? Alter the breakdown of the neurotransmitter? A diagram of drugs acting on an ans Description automatically generated **Sympathomimetics** - Indirect = ephedrine, tyramine, and amphetamine  **Adrenergic Antagonists** - Adrenergic antagonists prevent activation of adrenergic receptors - Used to treat HTN, angina, BPH, migraine headaches - Effect depends on adrenergic receptor type(s) - [Alpha-adrenergic blocking agents:] - [Beta-adrenergic blocking agents:] - [Examples]: - [Selective Beta-1]: atenolol, metoprolol, esmolol - [Nonselective]: - [Beta-1 and Beta-2]: Propranolol - [Beta-1, Beta-2 and alpha-1]: Labatalol, Carvedilol - ALL adrenergic antagonists produce reversible (competitive) blockade EXCEPT phenoxybenzamine **Cholinergic (Cholinomimetics)** - Cholinergic medications stimulate the PSNS - **Directly** activate cholinergic receptors (acts like acetylcholine) OR - **Indirectly** by preventing the breakdown of acetylcholine - Two types of cholinergic receptors: **muscarinic** and **nicotinic** - **Muscarinic**: brain, glands (i.e. salivary), smooth muscle (GI tract, GU) - **Nicotinic**: autonomic ganglia, NMJ, adrenal medulla - **[Remember]:** - **ANTICHOLINERGICS** block the action of acetylcholine - Decreases PSNS activity - **ANTICHOLINESTERASES block** the action of acetylcholinesterase - Increases PSNS activity **Cholinergic Crisis** - ***[Excessive muscarinic stimulation & depolarizing neuromuscular block]*** **[Sludge and the Killer Bs]** - Salivation - Lacrimation - Urination - Diaphoresis/Diarrhea - Gastrointestinal cramping - Emesis - Bradycardia - Bronchospasm - Bronchorrhea - \*Muscarinic (cholinergic) toxicity can be caused by either muscarinic agonists or cholinesterase inhibitors **Review:** **The Autonomic Nervous System is unique in its ability to change body systems' function very rapidly:** - Changes in HR: 3-5 seconds - Changes in BP: 5-15 seconds - Rapid changes in BP causing fainting within seconds - Involuntary loss of bladder control - Sweating within seconds **What type of information does the DCML tract carry?** - Sensory -- touch, proprioception, vibration, general sensory - Faster - Highly localized - Fine sensations - 2-point discrimination **Where are the cell bodies of peripheral sensory neurons located?** - Dorsal Root Ganglia **DCML** **ALS** ---------------------------- ---------------------- --------------------- **First order cell body** Dorsal Root Ganglia Dorsal Root Ganglia **Second order cell body** Cuneatus or gracilis Rexed Lamina **Third order cell body** Thalamus Thalamus **1^st^, 2^nd^, and 3^rd^ Order Neurons** **Dorsal Column Medial Lemniscus (DCML)** ----------------------------------------------- ------------------------------------------------------------------------- ---------------------------------------------------------- ------------------------------------------------------------------------ ** ** **1^st^ order neuron** **2^nd^ order neuron** **3^rd^order neuron** Location Dorsal root ganglion of spinal nerve → dorsal column nuclei of medulla **Nucleus gracilis/cuneatus** of medulla → thalamus Thalamus → primary somatosensory cortex Decussation   **DECUSSATES IN MEDULLA** (at the medial leminiscus)   **Anterolateral Tract (Spinothalamic Tract)** ** ** **1st order neuron** **2nd order neuron** **3rd order neuron** Location Dorsal root ganglion of spinal nerve **tract of Lissauer** rexed lamina Rexed lamina (I-V) thalamus (anterior or lateral tracts) Thalamus primary somatosensory cortex, **temporal lobe and brainstem** Decussation   **DECUSSATES IN SPINAL CORD** (@ rexed lamina 1-5)   **Injury Manifestations: Brown Sequard Syndrome** **Ipsilateral** **Contralateral** ------------------------------------------------ ------------------------------------------------------- ------------------------------------------------------- **Touch, pressure, vibration, proprioception** Impaired (DCML hasn't crossed yet, so it is affected) Intact **Pain, temperature** Intact Impaired (ALST has already crossed, so it's affected) **Motor** LMN Flaccid paralysis UMN Spastic paralysis **The tracts of Lissauer (which ascend or descend 1-2 spinal levels before synapse) contain what type of neuronal axons?** - The first order neuron axons are what travel via the tracts of Lissauer. - Sensory? **What is the ultimate destination of a sensory signal (afferently) traveling mechanoreceptor via the DCML?** - Primary sensory cortex located in postcentral gyrus in parietal lobe **What is involved in proprioception?** - **Muscle spindles** (intrafusal fibers) -- A fibers - Prevent excessive stretch and positional imbalance - Activate flexors inhibit extensors - Contralaterally the opposite occurs - **Golgi tendon organs** -- located inside muscle spindles - Relay info back to CNS to allow more or less muscle contraction **Cholinergic vs. Adrenergic** +-----------------------------------+-----------------------------------+ | Cholinergic | Adrenergic | +===================================+===================================+ | Secrete Ach | Secrete NE | | | | | Release Ach at preganglionic in | **Release NE at postganglionic in | | SNS & PSNS | SNS** | | | | | Release Ach and **most | (Exception: sweat glands and some | | postganglionic synapse in most | blood vessels cholinergic) | | SNS AND PSNS** | | +-----------------------------------+-----------------------------------+ - Components of Ach -- acetyl (acetic acid/acetyl CoA) + choline - Breakdown of Ach -- broken down by [acetylcholinesterase] - Breakdown of NE - Enzymatic destruction - Monoamine oxidase - Catechol O-methyl transferase - Reuptake at adrenergic nerve ending (active process) - Defuse AWAY from nerve endings - Ach binds to **MUSCARINIC** or **NICOTINIC** receptors - Muscarinic → glands, heart, smooth muscle (GI, urinary tract, etc.) - Nicotinic → autonomic ganglia, NMJ - NE binds to **ADRENERGIC** → alpha & beta **Autonomic (SNS and PNS) neuronal tracts transmit impulse via a 2-neuron chain -- be familiar with this concept (pre v. post). There is 1 exception to this rule- what is it?** - Pre-ganglion synapses with post-ganglion on the same level - Pre-ganglion synapse with post-ganglion upward or downward the level - Pre-ganglion does NOT synapse with post-ganglion synapse directly onto effector organ (**adrenal medulla**) - PNS has a LONG preganglionic neuron and a very SHORT postganglionic neuron - SNS has a SHORT preganglionic neuron and a LONG postganglionic neuron - **EXCEPTION: LONG POSTGANGLIONIC NEURONS from SNS to adrenal medulla** **Vasomotor center -- Name the structure that contains the vasomotor centers which create efferent impulses to active both the sympathetic and parasympathetic nervous systems** - Medulla of the brainstem **Impact of Anesthetic Agents** - Inhibit output from vasomotor centers of the brain → decrease CO and SVR - We have adrenergic receptor agonists AND antagonists, cholinergic antagonist, but no true cholinergic AGONIST - Eyes - Increases IOP - Sux (5-10 mmHg for 5-10 min) - Ketamine - Intubation - Decreases IOP (sedatives, anxiolytics) - Inhalational anesthetics - Propofol - Opioids - Benzos - **Visual Evoked Potentials (VEP) VERY sensitive to anesthetics** - Auditory/Inner Ear - Vertigo - May need antiemetic and anxiolytics - Brainstem Auditory Provoked Potential Monitoring (BAEP) BARELY sensitive to anesthetics - **SSEP (somatosensory evoked potentials) = SOMEWHAT sensitive to anesthetics** **How is epinephrine formed in the adrenal medulla - describe the pathway.** - Tyrosine L-Dopa Dopamine Norepinephrine Epinephrine - Epi ONLY secreted from adrenal medulla - Epi and norepi usually released at the same time from the adrenal medulla (NE -- 20%, Epi -- 80%) **Review reverberating circuits and their role in sensation.** - Input that reactive the same neural pathway positive feedback loop rhythmical signal output that changes the intensity - Ex: ventilatory drive - Inhibitory/excitatory signals can increase or decrease the amplitude of rhythmical signal output - **Not responsible for starting or stopping** **Review how sweat glands are innervated.** - The postganglionic neurons of the [SNS] feeding sweat glands (which secrete acetylcholine onto effector organs) **Which of the following \"receptors\" would detect physical or chemical damage to tissue (aka. pain)? mechanoreceptors, thermoreceptors, nociceptors, photoreceptors, chemoreceptors.** - Nociceptors -- pain detect physical or chemical damage to tissue - Mechanoreceptors -- mechanical compression or stretching ([touch], hearing, equilibrium, baroreceptors) - Thermoreceptors -- hot/cold (some are hot only and cold only) - Photoreceptors/electromagnetic -- in response to light - Chemoreceptors -- chemical changes (O~2~, CO~2~, BP, osmolality, taste, etc.) **What is divergence and what is convergence (in relation to sensation)** - Divergence 1 nerve transmitting stimulus to multiple nerves - Convergence multiple nerves transmitting stimuli to 1 nerve **If the left half of the spinal cord was transected at L1, what would you see?** - You would see motor paralysis on the **ipsilateral** side of the body motor neurons don't cross over until the medullary pyramids in the brain - Strokes cause **contralateral** side motor paralysis because they occur above where the neurons decussate **All preganglionic fibers of the ANS are cholinergic. What does that mean?** - They have acetylcholine as their neurotransmitter are myelinated for faster transmission - Ganglionic fibers in SNS are c-fibers (slow) **Name the structure that has powerful control over the ANS** - **Hypothalamus** -- maintains homeostatic and "internal balance." - Also translates emotional input to autonomic output **Through what tract does a motor neuron that feeds a skeletal muscle under conscious control travel?** - **Lateral Pathways** - Corticospinal tract - Rubrospinal tract -- transmits motor information for simple memorized actions such as walking - **Ventromedial Pathways \[extrapyramidal pathways\] originate in the brainstem (*not* the cerebrum)** - Vestibulospinal tract - [Originates in the vestibular system of the inner] ear and directly bypasses cerebration, feeding extensor muscles of balance down the spinal cord - Tectospinal tract - Stimulates head movement in response to visual stimulus - feeds neuromuscular efferent feeding axial muscles - Reticulospinal tract - Facilitates and inhibits voluntary movement, coordinates motion and posture and muscle tone - All motor decussates at **medullary pyramids** - Descending tracts **Where is the motor system located?** - Primary motor cortex is located in the precentral gyrus of frontal lobe - **Basal ganglia** provide the boost that turns intention into actual movement excitatory and inhibitory function (like a gateway) - **Cerebellum** determines the correct sequence of commands that will allow the goal to be achieved **Name 2 differences between sympathetic and parasympathetic preganglionic fibers:** - Sympathetic preganglionic fibers tend to be **shorter** than parasympathetic fibers - Sympathetic fibers tend to form more synapses than parasympathetic fibers. - In addition, the SNS system increases/decreases "tone" as a mass discharge while the parasympathetic nervous system causes more specific local reactions **What is the ANS under control of?** - ANS is under control of spinal cord, brain stem, hypothalamus, limbic system (emotional response to stress/pain). **Autonomic Dysreflexia/Hyperreflexia** - SCI at T6 or higher STIMULATION FROM BELOW commonly from stimulation of rectum/bladder - Classic signs: HYPERtension & bradycardia - Cause HYPOTENSION above level of lesion - HYPER tension below level of the lesion - Other signs/symptoms - Flushing - Bradycardia/dysrhythmias - Headache - Nasal stiffness - Can cause: - SAH - Vision loss - Seizures - Pulmonary edema - **AVOID unnecessary noxious stimuli!** insert a foley if necessary to avoid prolonged stimuli **What are the classifications of Nerves?** **Type** **Myelinated** **Function** --------------------- ------------- ---------------- ------------------------------------------------------------------- Motor A-alpha Y Skeletal muscles and joints muscle length, force, proprioception A-beta Y Proprioception, touch, pressure A-gamma Y Skeletal muscle tone Sensory **A-delta** Y Pain, touch, temperature **C** N Pain, touch, temperature; various autonomic functions Pre/post Ganglionic **B** Y **Preganglionic**; Various autonomic functions **C** N **Postganglionic**; Autonomic functions: pain, temperature, touch - A, B, C fibers all transmit sensations of pain, temperature and touch - A (alpha, beta, gamma) MOTOR - A delta and C sensory - B PREganglionic neuron - C POSTganglionic neuron unmyelinated **What is the oculocardiac reflex? -- 5 & Dime** - Caused by traction/pressure of extraocular muscles, eyeball, or retrobulbar block - Stimulation of cranial nerves V and X (trigeminal and vagus) - Signs/symptoms include: - Bradycardia - Dysrhythmias - Prevention & Treatment: - Stop the stimuli - Deepen anesthetic - Atropine/glycopyrrolate to increase HR **What is denervation supersensitivity?** - After an injury intrude endogenous substance causes a hypersensitivity reaction due to upregulation of receptors cause a bigger response **What is the labeled line principle?** - Principle that each nerve tract ends at a specific point in the CNS that determines the type of sensation think homunculus 1. **In the sympathetic nervous system:** a. preganglionic fibers synapse only in paravertebral sympathetic ganglia b. preganglionic cell bodies are located throughout the spinal cord c. the preganglionic neurotransmitter is acetylcholine d. target organ receptors are only adrenergic e. effects are mediated entirely through cyclic AMP 2. **A nuclear group in the brain involved in transmission of sensory information to the cortex is the** a. Cerebellum b. Caudate c. hypothalamus d. thalamus e. hippocampus 3. **All of the following cranial nerves contain parasympathetic efferent fibers EXCEPT the** a. oculomotor nerve (III) b. trigeminal nerve (V) c. facial nerve (VII) d. glossopharyngeal nerve (IX) e. vagus nerve (X) 4. **The oculocardiac reflex involves all of the following structures EXCEPT** a. vagus nerve b. trigeminal ganglion c. ophthalmic division of cranial nerve V d. oculomotor nerve e. brain stem 5. **On instillation of the bladder with saline, the blood pressure rises from 128/75 to 221/120 mm Hg and the heart rate falls from 87 to 45 bpm. What is the likely cause of these changes to blood pressure and heart rate?** a. response to pain b. autonomic hyperreflexia c. micturition reflex d. response to cold solution in the bladder e. anxiety 6. **Which one of the following is NOT involved in sensory transmission?** a. dorsal root ganglion b. spinothalamic tract c. parietal cortex d. ventral posterior and ventral lateral nuclei of the thalamus e. precentral gyrus 7. **Administration of vecuronium during spinal surgery may interfere with monitoring of\ **a. Dorsal columns b. Corticospinal tract c. ECoG (Electrocorticography) d. Bispectral index 8. **The smallest nerve fiber, a postganglionic fiber associated with slow conduction, is the** a. A-alpha fiber b. A-beta fiber c. A-gamma fiber d. B fiber e. C fiber 1. \(C) Preganglionic neurons are located in the thoracic and lumbar spinal cord (T1 through L3) and synapse upon postganglionic nerves either in paravertebral sympathetic ganglia or in plexi adjacent to organs of innervation. a. Except for sweat glands that are cholinergic, target organ receptors are adrenergic. b. β-adrenergic receptors mediate their effects through cyclic AMP c. α-adrenergic receptors act via a more complex second messenger system involving G proteins d. All preganglionic neurons are cholinergic. 2. \(D) The thalamus is located at the base of the brain and contains many distinct nuclear groups. e. Sensory information is processed here before conduction to the cortex. f. Distinct peaks corresponding to the thalamus are found in somatosensory and brain stem auditory-evoked potentials. 3. \(B) The trigeminal nerve contains somatic afferent fibers from the face and supplies motor innervation to the muscle of mastication. g. The oculomotor nerve contains parasympathetic efferent that control pupillary constriction h. The facial nerve contains parasympathetic fibers supplying the submandibular gland i. The glossopharyngeal nerve supplies the parotid gland j. Vagus nerve supplies the heart, respiratory system, and gut. 4. \(D) The oculocardiac reflex is characterized by bradycardia (even to the point of asystole) produced by pressure or traction on the eye. k. The afferent limb of the reflex is composed of fibers from the ophthalmic division of the trigeminal nerve that synapse upon brain stem neurons and ultimately increase vagal efferent activity. l. Activation of the reflex can occur from manipulation of any of the structures that carry afferent impulses, including the trigeminal ganglion and the long ciliary nerves that innervate the globe. m. The oculomotor nerve is not involved in the reflex. 5. \(B) Autonomic hyperreflexia occurs with spinal lesions above T5. n. Any noxious stimulation (e.g., urinary catheter insertion or bladder distention) may lead to hypertension accompanied by sweating and bradycardia o. Anxiety or pain would produce hypertension and tachycardia. 6. \(E) The precentral gyrus is primarily involved with motor functions. p. Sensation involves the dorsal root ganglion cell, the lateral spinothalamic tract, the thalamic nuclei, and the postcentral gyrus. 7. \(B) Postoperative neurologic dysfunction is a rare but serious complication of spinal reconstructive surgery. q. In cases where spinal cord dysfunction is more likely to occur (e.g., scoliosis reconstruction), intraoperative spinal cord monitoring is used to identify ischemia and ideally allow the surgeon time to modify the procedure to reverse any spinal cord dysfunction. r. Somatosensory evoked potentials (SSEPs) involve repetitive stimulation of the extremity and monitoring the signals at the level of the scalp. s. SSEPs are used to monitor the dorsal columns of the spinal cord. i. As this area is sensory, neuromuscular blockers such as vecuronium do not affect SSEP monitoring. t. Motor evoked potentials (MEPs) monitoring is used to monitor corticospinal tracts (motor pathways) that are not assessed with SSEPs. ii. Neuromuscular blockers, such as vecuronium, interfere with MEP monitoring and should not be used. u. ECoG monitoring is used to identify epileptogenic foci during seizure surgery, or to assess cerebral cortical integrity during carotid endarterectomy. v. The ECoG is altered by drugs that affect the seizure threshold (e.g., benzodiazepines, as well as volatile anesthetics). w. The bispectral index monitor (BIS) uses processed EEG signals to measure level of consciousness. x. The information obtained can be used to help titrate anesthetic medications to an adequate depth of anesthesia for the surgical procedure and to decrease intraoperative awareness. y. Another monitoring technique used during spinal reconstruction is the wake-up test (the patient is awakened during the surgery and asked to move his legs). iii. It is done only when other monitors are not available or when significant intraoperative monitoring suggests injury. 8. \(E) A very small postganglionic fiber with slow conduction is the C fiber