Exam 3 - Griffiths PDF

Brain Cerebrum: generates motor function, processes incoming info, high order thinking Cerebellum: equilibrium and coordination ○ Functions: coordinate movement, maintain muscle tone, achieve motor learning tasks ○ Damage causes Ataxia: la...

Brain Cerebrum: generates motor function, processes incoming info, high order thinking Cerebellum: equilibrium and coordination ○ Functions: coordinate movement, maintain muscle tone, achieve motor learning tasks ○ Damage causes Ataxia: lack of muscle voluntary muscle coordination Hypotonia: decreased muscle tone Dysmetria: under/over shoot intended position intention tremor: tremor when making movement toward target Dysdiadochokinesia:the inability to do rapid alternating muscle movements Brainstem: conduit for flow of info between cerebrum and spinal cord ○ Responsible for breathing, consciousness, BP, HR, sleep Cortex: surface layer of gray matter Gyri: folds/bumps Sulci: fissures ○ Larger sulci divide cortex into frontal, parietal, occipital & temporal Spinal cord Continuous with brain stem, terminates at conus medullaris Conduit of sensory and motor info between brain and periphery Each spinal nerve attaches to the spinal cord by a dorsal and ventral root ○ Axons in white matter are arranged in tracts that carry info to and from brain ○ Dorsal: only carry sensory info (ascending) ○ Ventral and lateral: sensory and motor info (ascending and descending) Peripheral nervous system 12 cranial nerve pairs 31 spinal nerve pairs ○ 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal 3 meningeal layers Dura mater (outermost) Arachnoid mater Subarachnoid space - CSF Pia mater (innermost) Extracellular fluid compartments of CNS Blood plasma - inside vascular system Interstitial fluid - between neural and glial cells Cerebral spinal fluid (CSF) - in ventricular system and subarachnoid space ○ Choroid plexus: network of blood vessels in each brain ventricle Derived of pia mater and connective tissue and epithelial cells 1  Filters blood plasma to produces CSF Tight junctions between cells maintains blood-CSF barrier ○ CSF flow Lateral ventricles → interventricular foramen → 3rd ventricle → cerebral aqueduct → 4th ventricle → central canal of spinal cord Continuously secreted from choroid plexus Exits 4th ventricle into subarachnoid space Drains into venous system through arachnoid granulations ○ Lumbar puncture Most common way to look at CSF (btwn L3 and L4) epidural ○ ~150 mL present in CNS ○ 400-600 mL produced daily ○ Functions: protection, homeostasis, waste removal Why is regulation of brain fluids important? ○ Enclosed in skull Increased pressure = decreased perfusion / can cause herniation ○ Composition Ionic environment affects neuronal firing Blood brain barrier (BBB) ○ Highly selective small lipophilic substances can diffuse freely (O, CO2, urea, nicotine, ethanol) Glucose via facilitated diffusion by GLUT-1 protein ○ Things that can disrupt BBB Hypertension, hyperosmolality, microwaves, radiation, infection, trauma Neuron structure Soma - cell body Neurite - process extending from body ○ unipolar - one neurite ○ Bipolar - two neurites ○ Multipolar - three or more neurites Most common type of neuron Dendrites - receive impulses from other neurons ○ Pyramidal (3 branches) ○ Stellate (star-like) Spiny Aspinous Axon - carry action potential (AP) from dendrites/soma to synapse ○ Golgi type I 2  Longer (in to ft) Pyramidal cells of cerebral cortex, motor cells of spinal cord Connect different parts of system ○ Golgi type II Shorter - contribute to local circuits Cerebral and cerebellar cortex Connect sensory and motor neurons Utilized in higher function - learning memory cognition planning Neuronal function ○ Sensory - afferent ○ Motor - efferent ○ interneurons Non-neuronal (glial) cells 10x more glial cells than neurons in brain Support cells - 4 types Ependymal cells ○ Ciliated epithelial glial cells ○ Line ventricles ○ Produce CSF Astrocytes ○ Structural ○ Store glycogen and provide lactate to neurons for energy ○ Maintain stable K+ (important for AP) in brain EC fluid ○ Remove NTs from EC fluid ○ Synthesize NT precursors ○ Maintain blood brain barrier Microglia ○ Activated by infection - immune response ○ Work like phagocytes Oligodendrocyte (myelinating glia) ○ Produce myelin sheaths in CNS ○ Single oligodendrocyte myelinates multiple neurons Schwann cells (myelinating glia) ○ Produce myelin sheaths in PNS ○ Schwann cells myelinate one axon Neuronal injury Necrosis: cell lysis and inflammation ○ Acute trauma or stroke Apoptosis: programmed cell death that doesn't cause inflammation Gliosis: proliferation of astrocytes after CNS injury; scarring ○ This area doesn’t function properly ○ Long term effect of stroke, MS, Alz 3 Process of signaling Generation of AP ○ Threshold is met ○ Na+ channels open and Na+ into cell (depolarization) ○ Absolute refractory period - neuron can’t refire ○ K+ channels open and K+ out of cell (repolarization) ○ Relative refractory period - neuron unlikely to fire ○ Voltage drops below resting potential (hyperpolarization) Synapse ○ NTs are synthesized in the soma or terminal and packaged into vesicles ○ Vesicles fuse and release NTs at axon terminal of the presynaptic neuron ○ NTs attach to ligand-gated channels on postsynaptic neurons ○ Activation of these channels creates either excitatory or inhibitory postsynaptic potential Postsynaptic potentials are graded ○ Excitatory neurons cause depolarization (AP met and continues) ○ Inhibitory neurons cause hyperpolarization (AP not reached) ○ If the sum of excitatory and inhibitory depolarize beyond threshold, AP will fire Neurotransmitters Small ○ amino acids ○ monoamines (catecholamines) ○ acetylcholine Large/neuropeptides ○ Opioids ○ peptide hormones (ADH, oxytocin) ○ Hypothalamic releasing hormones Glutamate ○ Excitatory in nervous system ○ Ionotropic: NMDA (Ca channel), AMPA and Kainat (K channels) ○ Metabotropic: 8 kinds, dont need to know names GABA ○ Inhibitory in the brain ○ Ionotropic: GABA A (Cl ligand gated channel) ○ Metabotropic: GABA B (decrease cAMP and increase K) Glycine ○ Inhibitory in spinal cord ○ Ionotropic: Cl ligand gated channels Monoamines ○ Serotonin (5HT) Limbic function Reuptake dysfunction: depression 4  Ionotropic: 5HT3 excitatory Metabotropic: 5HT1-7, excitatory or inhibitory ○ Catecholamines: function as NTs and hormones Dopamine: produced in substantia nigra Metabotropic: D1 (excitatory), D2 (inhibitory) Opioids ○ 3 types of receptors: mu, kappa, delta ○ Beta - endorphins bind to mu receptors PNS: inhibits substance P (protein transmitting pain) CNS: inhibits release of GABA which results in excess dopamine Reuptake dysfunction: parkinson’s Fundamentals of Sensory Neurophysiology Stimulus: distinct type of energy ○ Modality, Intensity, Location, Duration Receptors: convert stimulus into electrical signals Receptor adaptation: decline in AP generation when constant stimulus is applied ○ Ex: ring/watch, small background noise, holding cup The somatosensory system Cutaneous sensory modalities: touch, vibration, pain, temperature Proprioception Dermatomes Discriminative fine touch is transduced by special receptors ○ Merkel’s disk: slowly adapting, sense steady pressure ○ Messiner’s corpuscle: rapidly adapting, sense light pressure ○ Ruffini endings: large receptive fields, senses stretching in skin, slowly adapting ○ Pacinian corpuscle: very rapidly adapting, sense vibration Hair follicles have a nerve plexus at the base that transduces displacement of hair ○ Wind, running Dorsal column- medial lemniscus ○ Ascending tract up to CNS ○ 3 neuron chain ○ Decussation (crossing to other side) = medulla ○ Discriminative touch, vibration, proprioception, pressure Spinothalamic tract ○ Ascending tract up to CNS ○ 3 neuron chain ○ Decussation = spinal cord ○ Temperature, pain, localizing touch Primary somatosensory cortex: size is relative to amount of sensation ○ Large: hands, mouth, tongue, lips, ears Secondary Somatosensory cortex ○ Posterior to primary 5  ○ Integrates touch with other sensations ○ Damage here may cause agnosia (inability to recognize objects) Visceral pain is poorly localized ○ MI = left chest wall, neck or jaw, shoulder, arm ○ Diaphragm irritation from cholecystitis or hepatitis = right shoulder ○ Diaphragm irritation from ruptured spleen = left shoulder ○ Stomach ulcer or cancer = epigastrium, midback between the scapula ○ Lower lobe pneumonia = upper quadrant pain on the same side as the pneumonia ○ Appendicitis = periumbilical area ○ Kidney stone = flank radiating to groin, including testicle or labia majora Pain gating ○ Touch fibers entering the same dorsal root have collateral branch that synapses on inhibitory interneuron ○ This interneuron releases enkephalins (opioids) to inhibit transmission of pain pathways between 1st and 2nd order neurons Motor neurophysiology 3 inputs to alpha motor neurons determine if muscle contracts ○ Upper motor neurons: regulate voluntary movement; inhibitory ○ Spinal interneurons: excitatory or inhibitory; extensive circuits ○ Sensory neurons from muscle proprioceptors: feedback on muscle length and tension Muscle spindles ○ Sensory neurons are large myelinated nerves Type 1a Very fast Info about muscle stretch and speed ○ Intrafusal muscle fibers innervated by gamma motor neurons Cell bodies in ventral grey matter of spinal cord Regulates muscle spindle sensitivity Golgi tendon organs ○ Sensory nerve fibers encapsulated in tendons ○ Type 1b ○ Info about muscle force Myotatic (muscle stretch) reflex ○ Tapping on tendon produces rapid stretch conveyed by 1a neuron ○ Agonist muscle group contracts ○ Antagonist muscle group inhibited ○ Physiologic function is to resist gravity Flexor withdrawal reflex ○ Rapidly remove limb from injurious stimuli ○ Crossed extensor reflex is an additional component to support using the opposite limb 6  ○ Hot stove example Descending / motor pathways ○ Lateral - voluntary Corticospinal (pyramidal) Upper motor neurons originate from motor cortex → internal descend through capsule and upper brainstem → cross at medullary pyramids Lesions ABOVE cross = contralateral weakness Lesions BELOW cross = ipsilateral weakness Rubrospinal Originate in red nucleus of midbrain → cross immediately Controls muscle tone in flexor groups Decorticate posture (elbow flexion) = lesion rostral (above) to red nucleus Decerebrate (elbow extension) = midbrain lesion below red nucleus ○ Ventromedial - body position and balance Neurons do not cross Vestibulospinal - posture / equilibrium Tectospinal - head and eyes move in direction of stimulus Reticulospinal - posture Upper motor neurons ○ Cell bodies in brain or brainstem ○ Signs of UMN damage Spastic paralysis Hyperreflexia Positive babinski Increased tone Ex: stroke Lower motor neurons ○ Cell bodies in anterior horn of spinal cord ○ Signs of LMN damage Flaccid paralysis Areflexia Decreased tone Atrophy Fasciculations: muscle twitch Ex: polio Motor loop ○ Direct pathway Putamen → internal segment of globus pallidus Inhibitory via GABAergic neurons ○ Indirect pathway Putamen → external segment of globus pallidus and subthalamic nucleus 7  Excitatory Integrative and behavioral functions Integrative functions not directly involved in sensory or motor pathway ○ Emotions, motivated behavior, consciousness, language, memory, cognition Hypothalamus ○ Control of homeostatic functions and motivated behaviors ○ Inputs from visceral and somatic sensory pathways, front lobe, and parts of limbic system ○ Output to endocrine system via connections with pituitary gland, reticular formation, and limbic system ○ Temperature regulation Normal 98.6 +/- 1 Fever 100.4 Regulated response to infection or inflammation Cytokines released by immune cells → capillary endothelial cells in BBB release prostaglandin E2 (PGE2) → PGE2 stimulates hypothalamus to raise set point temperature Negative feedback loop with peripheral thermoreceptors on skin for body surface temp and central thermoreceptors in hypothalamus for core temp Effectors for body temp regulation Skin circulation: blood vessel dilation or constriction Metabolic rate: thyroid hormone, shivering Sweating: evaporative cooling Behavioral change: amount of activity, clothing or food ○ Eating ○ Circadian rhythms Light cues from environment; melatonin secretion ○ Sex drive Reticular formation ○ Columns of neurons that extend throughout the core of the brainstem ○ Strong influence on wakefulness = reticular activating system ○ Serotonergic: wakefulness, sleep cycle, emotions, mood Non REM HR and RR reduced, muscles relaxed, stage 3 most restful REM Dreaming, awake brain in a paralyzed body Normal adult sleeps 7-8 hr/night; 2 hour cycles; 25% in REM ○ Noradrenergic: general arousal ○ Cholinergic: attention, memory, learning ○ Dopaminergic: voluntary movement, rewards Limbic system ○ Cingulate cortex: highest levels of cognition in prefrontal Sensations of emotions are perceived 8  ○ Hippocampus: conversion of short to long term memory Declarative: facts / events consciously recalled Non declarative: not consciously recalled Procedural - skills Learned emotion - emotional associations Conditioned reflexes - pavlov’s dog Sensory memory - 5-7 pieces of info; very brief Working memory - 7-9 chunks of info; forgotten quickly Memory consolidation - long term memory ○ Amygdala: strong emotions (fear, aggression) Links emotions to memories Cognitive fear: learned response that creates a sensation of fear Reactive fear: response to a direct threat Hippocampus exerts negative feedback on fear response in response to increased cortisol levels Language and speech ○ Broca’s area: production of movement of tongue and mouth needed to speak Broca’s aphasia: can understand but not express ○ Wernicke’s area: understanding meaning and processing Wernicke’s aphasia: cannot understand but can speak 9