Neurophysiology 1_13_25 PDF

Neuroanatomy and Physiology  Brain Communication and control center of the body Cognition, memory, emotion Receives, processes, evaluates inputs Decides which action to be taken Initiates response – Involuntary actions To maintain homeostasis...

Neuroanatomy and Physiology  Brain Communication and control center of the body Cognition, memory, emotion Receives, processes, evaluates inputs Decides which action to be taken Initiates response – Involuntary actions To maintain homeostasis Regulated by the autonomic nervous system (ANS) – Voluntary actions  Neurophysiology How do neurons function? How do neurons communicate? Neuron is the central cell of the central nervous system - it does all the fxn - neuron made up of a cell body - dendrites and axons - dendrites connect neuron w other neurons - axons can connect to other neurons or to sensory or motor elements - neurotransmitters are made in the cell body and transported down the axon and stored at the end of axon in vesicles - when the neuron depolarizes, it initiates the release of neurotransmitters that cross the synaptic cleft to the next neuron or motor unit or whatever - these neurotransmitters bind to receptors to initiate fxn of the next cell - cell bodies are all contained in gray matter and the axons w their myelin sheaths (lipids) are the white matter of the brain - gray matter is cell body and white matter is axon  Cell Types Neurons-cognitive, motor and sensory Glial cells (Astrocytes) Also known as astrocytes Microglial-Macrophage, support Microglial cells form a macrophage fxn in the CNS Oligodendrocyte-myelin - makes myelin to coat the axon to improve nerve/electrical conduction by the myelin sheath  The Supporting cells: Glial Cells Neuron in lavender, astrocyte in blue (it is a supporting structure but also forms the foot processes and glomerulus and forms a coating around the blood vessels that form the blood brain barrier) - oligodendrocytes which makes myelin which coats the axons - microglial cells for macrophage fxn Have certain barriers that are present in CNS - one is on the outer side —> pia & dura which are outer barriers to the CNS - inner lining of CNS is the ependyma cells which is responsible for making cerebral spinal fluid that surrounds the brain and protects it The Barriers Just like cardiac myocytes or skeletal muscles, they work by depolarization or electrical activity Characteristics of Neurons Have the resting membrane potential which is created by Na/K/ATPase pump and K channel - make an outer electrical voltage that is positive and inner intracellular voltage that is neg by mvmt of these ions - when the neuron depolarizes, it does so in several fashion similar to the myocytes - first you have opening where Na comes in thru Na/K/Atpase - normally no Na gets in but some of the Na channels open and this brings a (+) ion into the cell and partially depolarizes the cell (this is the initial depolarization in #2) - next is that you open many Na channel and have rapid depolarization - first you have slow depolarization to a certain milivolt and that voltage opens more Na channel and causes rapid depolarization - then these Na channel closes and K channel opens and have a restoration of the membrane potential that overshoots a lil bit before it gets back to resting potential So it functions very similar to myocytes in regulating Na and K mvmt across cell membrane and carrying charge for depolarization and repolarization  Glial Cells-PNS In the peripheral NS (outside CNS) instead of having oligodendrocytes, you have Schwann cells which makes myelin around the peripheral nerve fibers (both motor and sensory) - the reason for making this myelin sheath is to improve the electrical conductivity down the axon - if the electrical activity had to progress thru the cell membrane continuously down the length of this axon, if you have a motor neuron in the spinal cord, it may have to go all the way to the muscle in your foot as a single axon and that takes a long time to depolarize that axon progressively down the length of it - so what this myelin sheath does is that it is interrupted in what are called the nodes of ranvier where the cell membrane is exposed - instead of the electrical activity progressing down the axon, what the electrical activity does w node of ranvier is that it jumps from node of ranvier to node of ranvier so that it speeds the conduction considerably Increased Propagation of AP Action potential (depolarization) Increase fiber size-increasing the diameter of a nerve fiber results in decreased internal resistance, which results in faster conduction down the Can increase the propagation of action potential by inc the fiber size nerve (diameter) bc inc the diameter results in Dec internal resistance —> faster conduction Myelination-myelin acts as an insulator around the nerve axon and therefore increases conduction Only where it is exposed can the action potential be propagated which speeds the conduction Blood-Brain Barrier BBB is made up of astrocytes which the dendrites from it form these foot processes that surrounds all of the blood vessels so that they prevent mvmt of many molecules easily from the blood to the brain and vice versa - lets nutrients (mainly glucose), o2, CO2, and waste products can move out fairly easily - many other things have to be transported thru the cell on transporters and takes time and is regulated - ex: bicarb have to be transported thru the cell and when bicarb lvl change in the blood, it takes a period of time (min) before you have a change in bicarb concentration in fluid surrounding the neurons Characteristics of Normal CSF Nml CSF is clear and colorless (looks like water) - pressure is 9-14 mmHg or 150 mm H2O - no red blood cells in CSF - will have a few RBC in lumbar puncture bc dmg small blood vessels - WBC is occasionally there generally less than 3-5 per cubic millimeter - glucose is lower than it is in blood but not by much - Na is same as plasma Na and K is slightly lower - specific gravity is about same as plasma - pH is slightly more acidotic (similar to what you would have in venous blood) - total volume of CSF at any one time is 125-150ml - each 24hrs, you form 500-800ml of CSF and then you reabsorb the same amount so it is a dynamic equilibrium in which the total volume never changes - if you have a blockage in part of the CSF that is reabsorbing the CSF and you are still making more, then it will inc then vol of the CSF and lead to cerebral edema and changes  Neurotransmitters Norepinephrine Dopamine Serotonin Gaba-amino butyric acid (GABA) NMDA (n-methyl d-aspartic acid) Histamine Acetylcholine Glutamate And more than 50 others Can transmit message from one neuron to another effector cell either another neuron or motor cell etc by 1 of 2 ways - can have an electronic synapse where axons on terminal endings are budding against the effector cell membrane and have gap junction which bind to each other form a hemi channel that allows electrolytes to transmit to the other - as you change the electrolytes by the electronic propagation in the neuron, you have the same effect in the effector cell so the effect cell would then depolarize also - you can also have a chemical synapse (which is what most transmission are communicated) where you have vesicles that contain the neurotransmitter - after the neurotransmitter is released from the vesicles into the synaptic clefts, they bind to receptors on the other effector cells and lead to changes and channel activity and ion mvmt  Process of Neurotransmission You have the electrical conduction going down the axon to the terminal bud and that depolarization leads to an opening of Ca channels and as you open Ca channel and inc Ca conc inside the terminal bud, that cause the vesicles to adhere to and bind to the cell membrane and then that opens and allows neuotrasmitters to be released into the synaptic clefts to bind to its receptor and changes channel activity - then it is removed either by reuptake of neurotransmitter or by enzymes that break down the neurotransmitter so that the conduction does not progress indefinitely  Postsynaptic Potential  Excitatory Postsynaptic Potential (EPSP) Combination of a neurotransmitter with a receptor site causes depolarization of the In the axon you have the synaptic clefts and the postsynaptic membrane. cell or the effector cell is a post synaptic potential - if it is excitatory, that means that the combo of a neurotransmitter w a receptor site causes depolarization of the postsynaptic membrane  Inhibitory Postsynaptic Potential (IPSP) Combination of a transmitter with a receptor site is inhibitory in that it causes the local nerve membrane to become hyperpolarized and less excitable. Functional Areas: Cerebral Hemispheres Largest, most obvious area of the brain Longitudinal fissure separates two hemispheres -hemisphere into left and right Cortex – “Gray matter”——nerve cell bodies Corpus callosum – “White matter”—myelinated nerve bundles (tracts) White matter also known as corpus callosum is the myelinated axonal tracts or nerve bundle that connects the hemisphere to other portions of the nervous system Connect the hemispheres Each hemisphere is divided into five major lobes. – Prefrontal, frontal, parietal, temporal, and Functional Areas of the Brain Horizontal view of the cerebral cortex - Gray matter outside - white matter inside and have neurons in discrete areas in the deep white matter (called basal ganglion) and include thalamus, putamen, globus pallidus, and caudate nucleus - these neurons are necessary for the fine tuning of motor work and the thalamus for perception of pain or temp This is a pic of only the white matter and the gray matter is removed - have a fan shape structure called corona radiata - these motor and sensory tracts all come together in a dense narrow location at the bottom "C:\Users\ebeac\Pictures\img128 (2).jpg" Can have a small infarction in the dense narrow region that produces substantial motor and sensory defects - also have the midbrain, pons, and the medulla (have pyramids in the medulla)  spinal cord medulla pons pituitary gland cerebellum Thalamus hypothalamus - for sensory perception Brain Model: midsagittal section lateral ventricle corpus callosum Corpus callosum connects the two hemispheres together  Functional Areas of the Brain Frontal lobe major fxn is for intellect & personality - premotor cortex (darker purple) is for fine tuning of skilled mvmt - playing piano, fine tuning finger mvmt - the lighter purple is motor cortex and where all voluntary motor activity is initiated Yellow is sensory where we sense pain & temp from the periphery Temporal lobe have Occipital lobe for visual wernickes area and this is cortex where you see an area for processing of visual images from the speech eye - also have memory in parts of the temporal lobe Cerebellum primarily necessary for balance, equilibrium, and coordination Pons and medulla is where resp, cardiovascular RAS in the midbrain is called reticular center, and much of the parasympathetic neurons activating system - keeps brain active or are located inactive - if RAS tones down, it lets you sleep - if it turns on, you wake up and is alert and active - important area in coma Homunculus - shows motor and sensory cortex - outer portion just above the temporal lobe is the head and neck, just above that is the upper - the arm and trunkal region extremities, and the size of these things tells how sensitive they are to sensory and motor fxn and lower extremities drape - the hand is very good at sensation and motor fxn over the mid portion of the cerebral cortex down the longitudinal fissure  Functional Areas: Cerebral Hemispheres (Cont.) Right and left hemispheres similar in structure, not necessarily in function Dominant hemisphere - if you’re right handed, your left hemisphere is your dominant one and will be the side of the brain that controls language – Side of brain that controls language – Left hemisphere in most people - for expressive speech – Broca’s area - if you dmg your broca, you can understand what ppl are saying but you can’t find words or express themselves properly - some ppl is fairly dense and they can’t hardly speak at all but can understand what you say and follow direction Motor or expressive speech area - wernick’s area is for receptive aphasia, can hear the sounds/words but cannot – Wernicke’s area process them appropriately so you don’t understand what is being said but you can express vocalilty w/o problem If someone has a stroke that affects their left Integration center hemisphere and they are right handed, they are going to have paralysis of their right side of body and they’re likely to have receptive or expressive aphasia  Functional Areas of the Brain: In the brain stem have midbrain, pons, and medulla Brain Stem The brainstem anatomy - you have many nuclei for cranial nerves like oculomotor nerve, trigeminal nerve, facial nerve, etc - depending on where a lesion is will tell you which neuron is going to be affected and which cranial nerves is going to be affected  We have brain and spinal cord connected Peripheral Nervous System We have the sensory pathway coming thru the spinal cord to the brain and we have the motor pathways going from the brain out to the muscles Motor pathways are the voluntary NS (also known as the somatic NS) or the autonomic NS which is involuntary and that includes the sympathetic and parasympathetic and enteric (GI) nervous system 27 Have 3 neurons 28  This is the brain cut in half, and this is the motor cortex here - so we have a nucleus (a cell body) that can initiate a voluntary mvmt, and that axon goes all the way from that cerebral cortex down thru the brain (the white matter), the midbrain, the pons, and in the medulla in what’s called the pyramid, you have what’s called a decussation (means it crosses over from one side to the other) - why if you have a stroke on left side of brain you will have a right sided weakness bc the motor nerves on the left side crosses over in the medulla to go to the right part of the body - go down the spinal cord in tracts (so axons are going down the spinal cord in a tract) and at the end of the tracts, it goes in to the motor part which is called the horn of the spinal cord (where nuclei is located) - this is the posterior part of the spinal cord and this is the anterior part - this axon goes in to the anterior horn and combos w a second neuron cell body and that second neuron is then activated and comes out of the spinal cord and goes to the muscles or motor end plate to initiate the contraction of the muscles - so you have 2 neurons that are necessary for motor mvmt - one is upper motor neuron which goes from the cortex to the anterior horn of the spinal cord - lower motor neuron which goes from anterior horn out to the muscle Sensory on the other side is sensing pain, temp, vibrations and is sending the message into the spinal cord - in the spinal cord, this decussates right where it comes in so it goes to the other side and then up the spinal cord - this happens to show the posterior column which decussates up in the midbrain whereas most pain and temp decussates down in the spinal cord as soon as it entered from there and then is carried up the spinal cord to the thalamus where it meets with another neuron - so you have 3 neurons: one that is entering and crossing over and sending the signal up in a second neuron to the thalamus, and from the thalamus out to the sensory cortex  Descending Pathways (Motor) Commands sent from brain to spinal cord Need 2 neurons 2 Main tracts: 1. Corticospinal (Pyramidal) Tract - Primary motor tract 2. Extracorticospinal (Extrapyramidal) Tract - this is for fine tuning of the mvmt and these neurons come from the basal ganglia or the brainstem to feed onto the anterior horn neuron (motor neuron) and give fine tuning 29 Spinal cord cut in cross sections - white matter out here and gray matter on inside (horn of the spinal cord) - nerves enter and exit thru either dorsal root (posterior part) or ventral root (anterior part of spinal cord) - the sensory nerves come thru the dorsal root and the motor exit thru the ventral root but just after leaving the spinal cord they combo into the spinal nerve which carries both motor and sensory - just divides just before it goes into the spinal cord This is the spinal nerve, dorsal and ventral roots going into here Tracts are all in the white matter - they are axons that are going up or down the spinal cord and then they either enter the gray matter or exit the gray matter to be carried up  Pyramidal Tract Cerebral Cortex to spinal cord Voluntary control of skeletal muscle 2 neurons needed 32 Red is the motor tract - these are the extrapyramidal tracts and this is the cortical spinal tract here Blue are sensory or ascending fibers and they are in the spinal thalamic tract or dorsal column 33 In the DTR, you have motor fibers that are in a spindle and when you stretch this, it is sensed by afferent sensory fibers and goes to the spinal cord Components of the reflex 34  These upper motor neurons (the ones that come from the cortex down to the anterior horn cells) and then out from the anterior horn cells to the muscles - upper motor neuron is from the cortex to the anterior horn - lower motor neuron is from the anterior horn out to the muscles You tap on the infrapatellar ligament and that stretches the quadriceps muscles a lil bit and this is sensed by the afferent fibers which are sending this message into the spinal cord - if this message has to go all the way up the cortex and then back down again as a motor fxn, it will take a lil bit of time - but if you put your hand on hot stove, you will pull back virtually immediately and is called reflex action - what’s happenening is that this sensory is going into the posterior part of the horn cell and combining w the motor w/o going up to the cortex and is sending a message to the motor cortex - there are two different fibers here, both for the sensory and the motor and that is bc you want to contract the quadriceps muscle so that you get a reflex action - but in order to contract the quadriceps muscle, you want to relax the hamstring at the same time so you have a (+) action on the quadriceps for contraction, and you have a inh action on the hamstring so that you get a maximal mvmt of the leg 35  Motor Neurons Upper Motor Lower Motor Neurons Neurons –Increased –Flaccid No resistance to mvmt at all tone paralysis (spasticity) –Absent –Hypereflexia reflexes If you have a defect in the upper motor neurons (anywhere above the anterior horn nuclei) then you will have upper motor neuron lesion and will have inc resting tone and will feel more resistance when you try to move it even though you are relaxed (called spasticity and will have hyperreflexia) - this is bc the extrapyramidal tracts that feed onto the anterior horn cells are increasing the tone and have inc in motor fxn  Sensory Pathways The receptors out here, the first axon is going to the dorsal root ganglion and the second neuron then goes to the posterior horn and up the spinal thalamic tract to the thalamus and to the sensory cortex - decussation is right at the entry where it comes in for the spinal thalamic tracts Spinal thalamic tract is for pain and temp Not useful to memorize  Spinal Tracts 1. Spinothalamic Tract - for pain and temp 2. Dorsal/Posterior Columns (Fasciculus Gracilis & Fasciculus Cuneatus) - position, sense, vibrations, and light touch Spinothalamic/Anterolateral Tract Spinal Cord to thalamus Information about pain and temperature Requires 3 neurons to transmit information You have dorsal root ganglion coming in and crossing over and going up the spinal thalamic tract In the posterior column - here is the spinal thalamic tract in the anterior part of the spinal cord - the dorsal column (posterior column) is for vibrations, position, sense, and light touch - the sensory fibers coming in here then go up and decussates in the medulla and then to the sensory cortex Lateral This is important bc if you have a spinal cord lesion, you can kinda tell where spinal cord lesion is by physical exam, what side is sensory defect on, and what side is the motor defect on - if the lesion was above anterior horn cells then it would be upper motor neuron defect and the spinal cord lesion would be on same side as the defect bc it has not decussated yet in the pyramidal tract - if sensory crosses over immediately, if you have a lesion in spinal cord above that, the sensory deficit would be on opposite side from the lesion Decussates/Commissure (crosses from left to right or right to left)  Dorsal White Column/The Discriminitive Pathway Signals from spinal cord to thalamus Sensory information about touch, pressure, and proprioception 3 neurons needed to transmit Dorsal White Column Leg is on lateral part and arm on medial part Decussation does not occur at level of spinal cord Decussation occurs in the medulla Pheochromocytoma is related to gangliomas - not malignant in that they metastasize but if you remove one, then one will pop up elsewhere Parasympathetic system with one neuron being primarily in Sympathetic NS is primarily in the the brain stem and the other brain stem (post synaptic neuron, neuron near the affected organ ganglia, or in what are called the - acetylcholine is the sympathetic ganglia along the side of neurotransmitter for the upper the spinal column and there are and lower motor neuron different ganglia at each lvl from the cervical down to the lumbar region for these sympathetic ganglia) - the lower motor neuron goes to the target organ for effector - the neurotransmitter from the upper motor neuron to the lower motor neuron is acetylcholine and the neurotransmitter from the lower motor neuron to the target organ is norepinephrine Parasympathetic has the following fxn - for rest and digest (nutrition and storage) Sympathetic is fight and flight 48 Diseases of Central Nervous System  Neurologic Injury Ischemic Metabolic-glucose Misfolded or abnormal protein accumulation Inflammation-infectious or immunologic Gliosis-hypertrophy/hyperplasia, and death/apoptosis of astrocytes  Infections Bacterial – Meningitis – Abscess Viral – Meningitis – Encephalitis Fungal/Mycobacterial Prion Disease  Bacterial Meningitis Group B Streptococcus Staph pneuminiae Listeria E. coli Neiserria meningitidis Spirochetes-syphilis and leptospirosis  Viral Encephalitis Herpes Simplex Varicella Zoster CMV West Nile Western Equine Venezuelan St. Louis  Viral Encephalitis (other and chronic) Poliomyelitis Rabies HIV Progressive Multifocal Leukodystrophy  Fungal Coccidiodes Cryptococcus Blastomyces Histoplasma Mucor Candida  Other Lyme disease Toxoplasmosis Naegleria  Prion Disease Creutzfield-Jakob Kuru Bovine Spongioform Encephalopathy Chronic Wasting Disease of Deer/Elk  Alzheimer’s/Dementia Alzheimer’s (Aβ, tau) Fronto-temporal lobe degeneration (tau, TDP-43) Parkinson’s (α-synuclein, tau) Huntington (polyglutamine or CAG repeats) ALS- (SOD1)  Immune Diseases Multiple Sclerosis Systemic Lupus Erythematosis Vasculitis Direct neuronal antibodies  Tumors Benign – Meningioma – Ependymoma Malignant – Astrocytoma (glioblastoma multiforme) PTEN, p53, NF1, EGFR Medulloblastoma Metastatic – Lung, colon, melanoma, lymphoma  Tumors of CNS Gliomas Astrocytoma (PTEN, EGFR, CDKN2A, p53) Oligodendroglioma (IDH1 and 2) Appendymoma (NF2) Meningioma Tuberous sclerosis (benign hamartomas) VHL-hemangioblastomas Neurofibromatosis-NF1 and 2  Ischemic injury Embolic stroke-vascular bed, location – Atherosclerosis – Anterior, middle and posterior cerebral artery. – Posterior circulation-midbrain, cerebellum, brainstem Thrombotic-arterial or venous (venous sinuses) Hypotensive-watershed Lacunar (hypertensive) infarcts-deep white matter and basal ganglia  Peripheral Neuropathy Pressure/Trauma – Nerve root or specific nerve Metabolic – Diabetes Toxin – Heavy metals, organic solvents Infectious – Leprosy, Herpes zoster, Syphilis Vascular Immunologic-vasculitis, lupus, anti-neuronal antibodies