Neuro Physiology CAPS 301 PDF

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These notes summarize and explain all concepts, and answer learning objectives for the neuro physiology portion of CAPS 301...

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Neuro Physiology Dr. Barry Mason Resting Membrane Potential 1. Define Equilibrium Potential and Resting Membrane Potential (RMP) Equilibrium potential is when the net flow through any open channel is zero. RMP is the membrane potential is established by the separation of ions across a membrane - there are a greater number of open K+ channels at rest 2. Explain the role of the Na+/K+ ATPase in the generation and maintenance of a RMP Pumps 3 sodium out and 2 potassium in to maintain the overall negative charge in the intracellular space - because the potassium has less positive charge than sodium 3. Define Depolarisation, Hyperpolarisation and Generator Potential Depolarisation is when the membrane potential approaches 0, or becomes less negative compared to RMP. Hyperpolarisation is when the cell becomes more negative compared to RMP. Generator Potential is the initial or stationary depolarization of a receptor that can be graded according to intensity and converted to an action potential when threshold is reached. 4. Describe the effects of changes in extracellular electrolyte levels on cell excitability. Since the inside of the cell is populated primarily by K+, adding K+ to the extracellular space will decrease the charge separation and therefore decrease the membrane potential, making the cell less excitable. If another ion such as Ca2+ is added to the extracellular space, this will make the extracellular space far more positive than the inside of the cell, increasing membrane potential and therefore increasing excitability Action Potential Initiation 5. Define what an Action Potential (AP) is An action potential is a robust, all or nothing event that results from an increased permeability to Na followed by an increased permeability to K. a AP is regenerative event, such that an AP in one part of the membrane will generate an AP in a more distant part of the cell 6. Understand what is meant by: a. Threshold b. All-or-none c. Rising Phase d. Falling Phase

e. After-hyperpolarisation: membrane potential is closer to Ek than at rest because all the K+ channels are open 7. Explain the role of voltage-gated Na+ and K+ channels in the generation of an axonal AP. The voltage gated channels are stimulated by a change in membrane potential affected by the GP, causing a positive feedback cycle - at rest, the Na voltage gated channel has its activation gate closed, its inactivation gate open and the K channel has its gate closed. During the rising phase, both Na channel gates are opened and K gate is closed. During falling phase the Na inactivation gate is closed and the activation gate is open. The K gate is now open. After hyperpolarisation, both Na gates are closed and the K gate is open. 8. Understand the ionic conductance changes during an AP 9. Understand the mechanism for relative and absolute refractoriness. Action Potential Propagation 10. Distinguish between electrotonus and active propagation of electrical potentials Electrotonus is a passive process by which electrical events propagate down the length of an axon via attraction to adjacent negatively charged ions. This happens throughout myelinated nerve fiber. Active Propagation is an active process which entails the AP activating the voltage gated channels and regenerating the depolarization. This happens at the nodes of Ranvier.

11. Describe factors influencing the active propagation of an action potential (AP) along an axon, including resistance and capacitance. The magnitude of axial resistance depends on the diameter of the nerve fiber. Increasing axon diameter decreases axon resistance. Capacitance is the ability of the membrane to store charge. High capacitance means slower AP propagation. When Na+ moves into the cell to depolarize the membrane, it causes the negative charges lining the un-myelinated membrane to have to mix in the intracellular space - this knocks the positive charges that were being held to the outside of the membrane by attraction, off the membrane. This eventually causes a change in membrane potential - BUT THIS PROCESS TAKES TIME. Myelination of the membrane will make this process faster by reducing the amount of charge that has to move off the membrane to change the membrane potential. 12. Describe the role of myelin in AP propagation and understand the concept of saltatory conduction. Myelin is formed from Schwan cells in the PNS and oligodendrocytes in the CNS. Saltatory conduction stems form the Latin word to "hop" - this is incorrect as the

action potential doesn't hop - but it refers to the intermittent myelinated portions of a nerve and the nodes of Ranvier Synaptic Transmission and Neuromuscular Junction

13. Describe temporal and spatial summation of postsynaptic potentials in neuronal dendrites The soma becomes the location of the postsynaptic dendrite of summation of excitatory post synaptic potentials. In Temporal summation, a single synapse will be repetitively activated. Spatial Summation involves simultaneous stimulation of multiple synapses. 14. Describe excitatory synaptic transmission in the CNS mediated by glutamate Glutamate may act on many receptor subtypes, but primarily AMPA and NMDA 15. Describe inhibitory synaptic transmission in the CNS mediated by GABA GABA or y-aminobutyric acid binds to the receptors that generate PSP's and prevent the membrane voltage from reaching action potential. GABA receptor gated channels allow Cl- ions in through the open pore - this influx in negative charge generate an IPSP with an equilibrium potential of Ecl of -70mV - since this is the RMP of some cells to begin with, Cl ions wont really want to move, so there will be a period of change in membrane potential - Cl ions want to keep the membrane at -70mV, so if there was any depolarization happening, this occurrence would inhibit it 16. Describe the anatomy of the neuromuscular junction (end plate) The neuromuscular junction is the specialized synaptic contact between a- motor neurons and muscle cells. The NMJ occurs at the termini of each branch of an a-MN. It consists of a presynaptic terminal (active zones), a synaptic cleft, and a post synaptic membrane(longitudinal junctional folds). The synaptic cleft is a 50nm junction containing basal lamina(extracellular matrix) that binds the axon terminal and the muscle junction folds. Acetylcholinesterase (Ache) is anchored within the matric to degrade Ach that does not immediately bind to receptors. nAChr's are positioned on the shoulders of the junctional folds opposite the presynaptic active zones 17. Describe the steps involved in neuromuscular transmission, up to but not including muscle contraction 

Presynaptic terminal: the axon terminus contains vesicles containing a neurotransmitter like Ach - when there's an influx on Ca2+ in the axon terminal, it binds to the vesicles via binding protein and is drawn towards the presynaptic membrane where is fuses and exits via exocytosis.

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Post synaptic membrane: Na+ channels sit on the muscle cell (or the post synaptic membrane) which have Nicotinic Acetylcholine receptors ( nAchr). Ach stimulates the opening of the sodium channels. When the muscle cell membrane becomes depolarized by the influx in sodium, this causes the Ca2+ to enter and further depolarize the membrane (known as voltage-gated calcium release). The change in membrane potential cause the sarcoplasmic reticulum to release even more Ca2+ via a process called calcium induced calcium release. This muscle cell will contract 18. Describe how transmission is terminated and define trophic signaling at the neuromuscular junction. The AChE within the basal lamina hydrolyze the Ach into Acetate and choline and this terminates the NM transmission 19. Describe the nicotinic acetylcholine receptor how the end plate potential arises from receptor. The EPP is always large enough to evoke and AP due to the dense population of Na+ channels in the perijunctional region.

Components of Peripheral Nervous System 20. Identify the neuronal components of the Peripheral Nervous System (PNS) and the Autonomic Nervous a. Sensory neurons - afferent component - Cell body (soma) outside of the CNS in the sensory ganglia b. Motor neurons -efferent component - cell body in the CNS c. Autonomic - also motor neurons, involved in functions that are not under voluntary control -either sympathetic or parasympathetic -2 neurons in the pathway from the CNS to peripheral organ : i. 1st has its cell body in the CNS (pre-ganglionic) ii. 2nd (post ganglionic) is an autonomic ganglion in the periphery 21. System (ANS) and know the neurotransmitters and receptor types used by PNS and ANS neurons 22. Specifically identify and name the function of each cranial nerve - nerves that emerge directly from the brain a. OOOTTAFAGVAH I. II. III.

Olfactory - sensory- sense of smell Optic - sensory- vision Oculomotor a. motor - voluntary movement of eyes laterally towards the midline b. Motor - autonomic (parasympathetic)- contraction of pupils and thickens lens

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Trochlear - motor - moves eyeballs Trigeminal a. Motor - voluntary -chewing b. Sensory - touch, temperature, pain from face, head and mouth Abducens - motor- moves eyeball laterally outward (opposite to III). III and VI must work together when we look left or right - coordinated by information carried by the MLF (medial Longitudinal Fasciculus) Facial a. Motor - movement of the facial muscles b. Motor - autonomic (para sympathetic) - lacrimal and salivary glands, taste Auditory a. Sensory - from cochlea- hearing b. Sensory - from vestibular apparatus - gravity, motion and position of head Glossopharyngeal - motor - (autonomic) salivary glands and sensory monitoring blood pressure Vagus a. Motor - swallowing and phonation b. Motor- autonomic (parasympathetic) - to heart and to abdominal organs c. Sensory - from heart - baro and chemoreceptors d. Sensory - GI tract Accessory a. Motor - swallowing b. Motor - shoulder shrugging Hypoglossal - motor - tongue

23. Identify and understand the organisation of the spinal nerves in relation to levels of the spinal cord a. 8 cervical b. 12 thoracic c. 5 lumbar d. 5 sacral e. 1 coccygeal 24. Describe the cranial, thoracic and sacral outflow of ANS nerves a. Cranial: i. III (oculomotor) -constriction of pupils and thickening of lens ii. VII ( Facial) lacrimal and salivary glands, taste iii. IX (Glossopharyngeal) salivary glands iv. X (Vagus) to heart and to abdominal organs b. Thoracic

i. Sympathetic c. Sacral i. Parasympathetic

25. Identify the basic pharmacological differences between the Sympathetic and Parasympathetic systems Parasympathetic uses aCh and sympathetic uses norepinephrine- the difference only exists at the final synapse - all aCh at the first synapse 26. Describe the general functions of Sympathetic and Parasympathetic systems on the body. Sympathetic systems will control the fight or flight responses to stimulus Parasympathetic systems control involuntary homeostatic processes Principles of Sensory Physiology 27. Differentiate between the special and general senses The special senses are 1. Olfaction 2. Auditory 3. Taste 4. Vision The general senses, or the somatic senses (somatosensory) are detected from all parts of the body including the head and travel to the CNS via the trigeminal nerve and all the spinal nerves except C.1 28. Define and classify sensory receptors according to their sensory modality Sensory receptors are transducers because they convert one form of energy into another I. Photoreceptors - light - rods and cones in retina II. Thermoreceptors - temperature - central : hypothalamus - peripheral : skin III. Nociceptors - pain IV. Mechanoreceptors - mechanical stimuli i. Exteroceptors - respond to stimuli from outside the body - touch receptors ii. Proprioceptors - give information about the position of the body and its part - muscle spindles 29. Define “Generator Potential (GP), describe the role of a GP in the sensory transduction process and differentiate a GP from an Action Potential Generator Potential is the depolarization of the peripheral receptive portion of the sensory axon that only has to travel a short distance - (an exception to this is in rods and cones this is a hyperpolarization) corresponds to intensity of the stimuli (graded

potential) unlike an action potential which is an all or nothing electrical event which has to propagate long distances If the GP is big enough to reach threshold, an action potential will be produced, which propagates to the CNS In myelinated sensory axons, the AP is initiated at the first node of Ranvier A GP will not cause the membrane to become refractory, as well, the GP is not actively propagated An AP is actively propagated by regenerating itself along the axonal membrane- AP's activate voltage gated channels along the axonal membrane ad regenerate the depolarization

30. Identify how stimulus intensity is coded by sensory neurons Frequency Coding: greater the intensity of stimulus, the greater frequency of AP's in an individual axon Population Coding: with increased intensity, more individual receptors are recruited 31. Understand how sensory receptors adapt to stimuli and give examples of receptors with rapidly adapting and slowly adapting properties a. Slowly adapting (tonic) - measure static and unchanging stimuli - maintained muscle length and maintained pressure b. Quickly adapting (phasic) - detect change in stimulus

32. Describe the structure and function of receptors involved in sensing touch, proprioception, and pain and temperature a. Sensing touch: i. Meissner's corpuscles, Pacinian corpuscles - quickly adapting - abundant in finger tips ii. Merckl and Ruffini endings - slow adapting b. Proprioception: i. Muscle Spindles - signal change in muscle length and absolute length ii. Golgi Tendon Organs - sense tension iii. Joint receptors - Ruffini endings and Pacinian corpuscles - in joint capsules and ligaments iv. Skin receptors - deformed by changes in joint angle c. Pain and Temperature - detected by receptors that are free nerve endings

CLASSIFICATION OF PERIPHERAL NERVE FIBRES

33. Be able to categorise peripheral nerves discussed in CAPS 301 lectures using two different classification schemes: the A, B, C scheme and the Roman numeral I, II, III and IV scheme 2 schemes: o The first is based on conduction velocity and uses A,B,C (from fast(myelinated) to slow(unmyelinated)) - usually this scheme is used to motor neurons o The second uses measurements of diameter and uses roman numerals I, II, II, IV - used exclusively for sensory axons SPINAL CORD AND SPINAL REFLEXES 1. Outline the anatomy of the both the exterior and interior of the spinal cord including how the cord differ at different segments of the vertebral column o Outside consist of white matter which is made up of axons: either ascending sensory tracts carrying information to the brain or descending motor tracts carrying information away from the brain. White matter ca be divided into dorsal, lateral and ventral columns. o Inside consist of gray matter in an X shape which is largely comprised of neuronal cell bodies o Dorsal Root: carries sensory information into the spinal cord - Cell bodies of sensory neurons are in the dorsal root ganglion o Dorsal horn: cell bodies of interneurons upon which afferent neurons terminate o Ventral Root: contains axons of motor neurons - their cell bodies are in the ventral horn gray matter o Ventral horn: cell bodies of somatic efferent neurons o Intermediolateral Horn: contains cell bodies of preganglionic autonomic neurons at spinal levels T.1 - L.2 and S.2 - S.4 2. Describe the components of a neuronal reflex

3. Detail the neuronal and non-neuronal components of a muscle spindle. 4. Compare and contrast the monosynaptic stretch reflex and the polysynaptic flexorwithdrawal reflex in terms of organisational components and function. 5. Outline how the body generates muscle tone using information from muscle spindles.

Vestibular and Auditory Systems 

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The vestibular and auditory systems are contained within the body structure of the temporal bone of the skull - they consist of interconnecting canals and chambers which is called the bony labyrinth The bony labyrinth is lines with membranous labyrinth - the space between the bony labyrinth and its membrane contains the perilymph

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The space inside the membranous labyrinth contains endolymph - endolymph has a low sodium and high potassium concentration, making it very positive compared to its surroundings ( 150 mm K+) - potassium wants to come inside the sensory cell Vestibular apparatus: contains 3 semi circular canals and 2 chambers ( utricle and saccule) on each side - the job of the semicircular canals is to detect rotation of the head Hair cells: residing in the cochlea, utricle, saccule and the semicircular canals - stereocilia project into the endolymph along with one kinocillium per each hair cell - at the base of each hair cell is where glutamate is released to the near by cranial nerve VIII receptors - the hair cell is depolarized if the stereocilia are bent towards the kinocilium and hyperpolarized if bent the other way  Bending of the stereocilia towards the kinocilium causes stretch sensitive potassium channels on the cilia to open - this leads to the opening of voltage gated Ca2+ channels causing glutamate to be released and stimulates an action potential Each semicircular canal opens to the utricle - before this opening is the ampulla- at the base of the ampulla is the crista upon which the hair cells are located - all the hair cells are located in a gelatinous structure called the cupula - all the hair cells are oriented in the same direction in an ampulla - the cupula is attached to the bone, so even with a lag in fluid, we can detect subtle movements Upon rotation of the head to the right, both cupulae will be pushed to the left (opposite of direction of movement), thereby activation the right side and deactivating the firing on the left through depolarization and hyperpolarization The vestibluo-occular reflex is in charge of controlling the position of the eyes during head rotation The utricle and saccule contain macula, which are equivalent to the crista in canals (the floor or the wall) - the macula contain hair cells which project into the otolith membrane. The otolith membrane is much more dense than it's surrounding and responds to gravity and linear acceleration. In the utricle, the macula form the floor (horizontal orientation) and in the saccule, the macula forms the wall (vertical orientation). The hair cells are not oriented in the same direction, giving them the ability to detect movement in the x and y direction. o The utricle will give information about left, right, front and back movement o The saccule will respond to front, back and also up and down movements o The main purpose of the utricle and saccule is to influence skeletal muscles to cause reflex adjustments and maintain orientation after being perturbed The Vestibular Nuclei (VN) receive information from the VA: o Superior VN: from canals to MLF to coordinate eye movement o Medial VN: from utricle and saccule to the neck and trunk o Lateral VN: from the utricle and saccule to the limbs o Inferior VN: from all components of the VA to the cerebellum which coordinates all motor activity

Hearing 

The outer ear collects sound ( oscillations in air pressure) and directs it to the tympanic membrane ( eardrum).

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The middle ear is populated by little bones called ossicles - the malleus, incus and stapes. The stapes is connected to the oval window which leads to the inner ear and the fluid filled cochlea. Transmitting "sound" to the inner ear becomes a problem, because small oscillations in air pressure now need to be movements of fluid, but flu...