Voltage-Gated Ion Channels and Neuronal Electrophysiology, Exams of Nursing

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Page 1 HUMAN PHYS MIDTERM 2 rated A+ 2024 Voltage gated channels: a class of transmembrane proteins that form ion channels that are activated by changes in the electrical membrane potential near the channel; respond to a change in the mb potential - Open for action & graded potential (action-open everywhere because positive feedback that trigures all of them to open; graded-open only near stimuli) K+ voltage gated channels are either open or close (not complicated) Na+ voltage gated channels - have 2 gates (activation and inactivation gate) - 3 different positions they can be in depending on which gates are opened or closed At rest: activation gate is closed, inactivation gate is open At threshold: activation gate is open, inactivation gate is open Inactivated: activation gate is open, inactivation gate is closed - All triggered by the same voltage change - Activation gate is the fastest, then inactivation gate, then potassium channel Graded Potential - Depolarizing or hyperpolarizing - Decremental as you move away from the source Action Potential - Always depolarizing - Must hit threshold (-50mV) so that it can fire - Always will be the same strength when fired Steps 1) Starts at resting membrane potential 2) Grade potential usually triggers a change in voltage that allows the increase of sodium permeability 3) Once threshold is hit, permeability of Na+ drastically increases (positive feedback mechanism) 4) Rising phase: all depolarizing due to sodium flooding into cell; sodium gates are activated Page 1 of 30 Page 2 5) Absolute refractory period: permeability of Na+ drops off and permeability of K+ increases as the sodium gates are inactivated - ABSOLUTELY cannot fire another action potential 6) Falling phase: membrane is repolarized through a K+ efflux; sodium gates are inactivated Near the end of the falling phase, the sodium gates begin to open again 7) Relative refractory period: might be able to fire an action potential but might need a greater stimulus to fire the action potential and it will be smaller - Including hyperpolarization and depolarization - Sodium gates are closing - Potassium gates are still working - Hyperpolarization: potassium floods in and overshoots before coming back to resting membrane potential (Cl- ions also contribute to this) Hyperpolarization is any time the potential goes below resting - Depolarization: K+ channels close - HAPPENS IN THE MIDDLE OF THE FALLING PHASE AND WILL CONTINUE UNTIL RESTING IS ACHIEVED Page 2 of 30 Page 5 Synaptic cleft : the space between neurons at a nerve synapse across which a nerve impulse is transmitted by a neurotransmitter Neurotransmitters: chemical messengers that enable transmission of signals - Calcium-mediated Exocytosis: release of neurotransmitters Synaptic Vesicles : store various neurotransmitters Post-synaptic cell : takes up neurotransmitters Post-synaptic cell - Excitatory pre-synaptic inputs : a presynaptic neuron increases the probability of an action potential occurring in a postsynaptic cell; depolarizes - Inhibitory pre-synaptic inputs : synaptic potential that makes a postsynaptic neuron less likely to generate an action potential; repolarizes - EPSP (excitatory post-synaptic potential): influx of sodium - IPSP (inhibitory post-synaptic potential): influx of chloride or efflux of potassium - Summation: a combination of inputs - Temporal summation: 2 same excitatory inputs added together, rapidly, one after the other in order to hit the action potential **answer - Spatial summation : 2 different excitatory inputs by themselves are not enough to cause an action potential, but when put together they can - Cancellation : when an excitatory input cancels out an inhibitory input Page 5 of 30 Page 6 Nervous System CNS: - Brain - Smell, sight, hearing: pick up through brain - Spinal cord - Somatic senses (muscles): pick up through spinal cord Receptor: picks up signal in somatic cells; not a part of a neuron Page 6 of 30 Page 7 Afferent neuron: senses information and will turn into an action potential if needed down the axon (synapse is in the CNS and cell body is in PNS) Interneuron: runs between two neurons; many interneurons; acts as a separation from ingoing and outgoing (found in brain and spinal cord aka CNS) Brain: integrates Efferent neuron: takes information from brain and will turn it into a response (cell body and synapse from interneuron in CNS and efferent synapse in the PNS) Effector: takes action (skeletal muscles, glands) CENTRAL NERVOUS SYSTEM Glia: - Supporting cells of neurons for metabolism - In the nervous system, but are not neurons - Lots more glia than neurons - Much smaller - Glia may be involved in signalling TYPES OF GLIA Oligodendrocyte: - in CNS , make myelin (insulation of axons) on one cell or many cells - Cross connections holds them in place (support) and provides insulation Schwann cell: - in PNS, make myelin - can help guide neurons with cut axons to a place to regenerate Nodes of Ranvier: areas between the myelinated region where the axon is bare and exposed to the ECF Saltatory Conduction - Myelin makes it much quicker - Ions cannot move in or out where there is myelin - Nodes of Ranvier are openings that are very concentrated in sodium channels so that you can have lots of sodium move in and enough to move you through the next myelinated section Page 7 of 30 Page 10 Ventricles: a communicating network of cavities filled with cerebrospinal fluid (CSF) - Lined with choroid plexuses: lining of ventricles and where specialized epidymal cells are that filter and create the CSF - Lots of blood coming in through the choroid plexus to circulate through - Stem cells - The choroid plexus is a plexus of cells that produces the cerebrospinal fluid in the ventricles of the brain. The choroid plexus consists of modified ependymal cells. Brain choroid barrier (BCB): where we generate CSF and send it out Blood brain barrier (BBB): - Very carefully controls CSF and what’s moving into the interstitial fluid - Will have tighter connections between cells of the blood vessel - BBB is not a physical structure - Pituitary gland, vomit centre and hypothalamus ALL do not have a restrictive blood brain barrier Page 10 of 30 Page 11 - Only lipid soluble molecules can pass through - Drugs will work on loose BBB Transport Across the Capillary Wall - Neurons are exposed to interstitial fluid, not CSF 1) Epithelial cells have tight junctions between the blood and the glia 2) Cell membrane: lipid bilayer with ion channel 3) Sodium potassium pump 4) Sugars and amino acid carriers 5) Ions channel 6) Enzymes bound to wall Page 11 of 30 Page 12 The Cerebral Cortex - the largest region of the mammalian brain and plays a key role in memory, attention, perception, cognition, awareness, thought, language, and consciousness - Contains four lobes - Mostly is grey matter: mostly cell bodies, dendrites and some axons that do not have myelin CONTAINS MOST GLIA FOR SUPPORT OF WHITE MATTER (white matter are myelinated fibres) - Grey matter is on the outside and white matter is on the inside because white matter is needed to circulate all the information in the inside Occipital lobe: - Vision - Primary visual cortex: senses visual information Temporal lobe: - Focused on hearing sound - Contains primary auditory cortex Parietal lobe: body senses - Somatosensory cortex: main sensory receptive area for the sense of touch - Wernicke’s area: the understanding of language; getting visual information and understanding it (input) - Wernicke’s aphasia (receptive): can produce words, but cannot put things together Frontal lobe: - Speech centre - Decision making or elaboration of thoughts, not fully developed until later in life Page 12 of 30 Page 15 Withdrawal Reflex Reflex Arc - Stimulus Starts in receptor in finger - Moves through afferent pathway (into the dorsal horn) - Spinal cord is the integrating centre - Moves through efferent pathway to create response (ventral) - Response is created and muscles reach - Afferent pathway and receptor: primary neuron - Interneuron: secondary neuron Shivering - Shivering in response to cold is regulated by hypothalamus and other nearby areas in pons and medulla - Shivering is done by the muscles, but is triggered by the brain - Shivering while normothermic = tremors Parkinson’s Disease - In Parkinson’s disease, damage to basal ganglia/nuclei results in tremors - Due to impairment of dopaminergic neurons - Learning also involves dopaminergic neurons - Newer research shows that basal ganglia are also important in processing information and ignoring unnecessary pieces of information PERIPHERAL NERVOUS SYSTEM Sensory neurons: pick up information; afferents Efferent neurons (motor): collect information and bring it out to the effectors; efferents 1. Somatic Nervous System - Controls voluntary movements - Ex. Muscles Page 15 of 30 Page 16 - Nociception: is the sensory nervous system's response to certain harmful or potentially harmful stimuli - Proprioception: the sense of the relative position of one's own parts of the body and strength of effort being employed in movement; knowing where your body is in space - Visceral: receptor are located within visceral organs (e.g GI, lungs, etc) – under anesthetic, you will not feel nociception, but you will feel your visceral senses (deep inside body) 2. Autonomic Nervous System - Controls involuntary responses A) Sympathetic : fight or flight responses (heart rate, breathing rate, blood pressure) B) Parasympathetic : rest and digest (digestion, regular processes) Receptor Potential and Action Potential a) Receptor potential  action potential (receptor and afferent pathway are primary neuron) b) Receptor potential  graded potential  action potential (extra step doesn’t slow it down) (receptor is separate; the branch is the primary neuron) Monovalent cation channels: - Once they open, they will let a + charged monovalent cation through (not specific) - Mostly it will be sodium coming into the cell because of the concentration gradient Page 16 of 30 Page 17 Intensity: Page 17 of 30 Page 20 a) Without Lateral Inhibition - Central stimulus will be stimulated the most - NO lateral inhibition - Higher action potentials in central stimulus - Action potentials will decrease as we move away from central stimulus - Wide response b) With Lateral Inhibition - Red neurons are inhibitory neurons - Blue are receptor neurons - Side Receptors will synapse with the inhibitory neurons - Central receptor neuron is what carries on with transmission - Side receptors will not be stimulated as much because of lateral inhibition from inhibitory neurons and are shut down - Only the middle receptor will carry on with transmission - Lateral inhibition will help with acuity - Higher action potentials in central stimulus - Negative potential from side receptors - Narrow response - Used in bipolar and ganglion cells - Frequency of action potentials increases in that area Vision Phototransduction - Occurs in retina Page 20 of 30 Page 21 - The process of converting the light collected in eyes and convert to a sensory stimulus that can be understood by the brain Cornea: tough outer protective coating that bends the light into the eyeball (helps focus) Lens: by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina Retina: first place that light is collected; receives light and converts the light into neural signals, and send these signals on to the brain for visual recognition Page 21 of 30 Page 22 Rods: photoreceptor cells in the retina of the eye that can function in low light (not a neuron) Cones: photoreceptor cells in the retina that function in colour vision and finer details (not a neuron) Outer Segment: - Where initial process starts and where light comes in - Closest to retina Page 22 of 30 Page 25 In light: - cGMP is broken down - Without cGMP, Na channel cannot be held open and no sodium let into cell - Cell is more negative and hyperpolarized - Also means not getting voltage change to open up Ca gates so there is no calcium mediated exocytosis and therefore, no neurotransmitters released - Everything shuts down in light - Very low neurotransmitters (glutamate) released 1) Light stimulation of rhodopsin leads to activation of G-protein, transducin 2) Activated transducing activates cGMP phosphodiesterase (responsible for breaking down cGMP) 3) cGMP usually holds the sodium gate open and when cGMP is broken down, the sodium channels close Process of Light and Visual Processing: - Light enters the eye through the cornea - Lens focuses the light to the back of the eye in the retina - Fovea is the most concentrated (sharpest image) - Hits the retina and goes to the back to the photoreceptors - Photoreceptors (cones and rods) move the stimulus to the bipolar cell - Bipolar moves to the ganglion cell - Ganglion cells all meet up to the optic nerve and transmits signal to the brain On Centre and Off Centre Retinal Cells - Both bipolar and ganglion cells are bipolar cells, but they have different receptors (will respond differently than each other) - Centre behaves one way, surround behaves the other way - Speed at which things happen has to do with intensity of response - This arrangement has to do with lateral inhibition (process this through lateral inhibition) Page 25 of 30 Page 26 On centre: (SYSTEM IS ON IN THE CENTRE) - Put light onto centre of the cell, will be active (firing action potentials) - Put light onto surroundings, will not be active (firing some action potentials) - Surroundings will be more active in the dark - ACTIVE IF LIGHT IS ON THE CENTRE On surround: (SYSTEM IS ON IN THE SURROUND) - Put light onto centre of the cell, will not be active (firing some action potentials) - Put light onto surroundings, will be active (firing action potentials) - Centre will be more active in the dark - ACTIVE IF DARK IS ON SURROUND Glutamate can either act inhibitory or excitatory Page 26 of 30 Page 27 - Photoreceptor at top (rod or cone) - Glutamate is released to bipolar cell - Bipolar cell releases onto ganglion cell - What bipolar cell does will be mirrored on what ganglion cell does (mirrored actions) a) Dark - Lots of neurotransmitters released in the dark - Opens Ca channels in synaptic terminal for Ca to come in On centre: - Leads to hyperpolarized cells (inhibited by glutamate) - Bipolar cell is inhibited, will not send signal to ganglion cell - No action potentials in ganglion cells Off centre: • Leads to depolarized cells (excited by glutamate) • Bipolar cell is exctied, will send signal to ganglion cells • Action potentials in ganglion cells b) Light - Decreased amount of neurotransmitters released in light - Closes Ca channels in synaptic terminal On centre: - Will respond when there’s light and will become depolarized cells Page 27 of 30