Neurophysiology (W4+5) PDF

🧠 Neurophysiology(w4+5) Created @September 24, 2024 8:44 PM Class Physiology 1A https://learn-eu-central-1-prod-fleet01-xythos.content.blackboardcdn.com/60e83182c0bd4/45637577?X-Black Token=IQoJb3JpZ2luX2...

🧠 Neurophysiology(w4+5) Created @September 24, 2024 8:44 PM Class Physiology 1A https://learn-eu-central-1-prod-fleet01-xythos.content.blackboardcdn.com/60e83182c0bd4/45637577?X-Black Token=IQoJb3JpZ2luX2VjED8aDGV1LWNlbnRyYWwtMSJIMEYCIQCfMKDnBnYpfZxKKyC%2FukxgKnL%2FNNU Course Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20241022T150000Z&X-Amz-SignedHeaders=host&X-Am Materials Token=IQoJb3JpZ2luX2VjEG0aDGV1LWNlbnRyYWwtMSJHMEUCIQCXn5Nuff9fAlV02JJgbPuL8Lo3zMMPHpki7 Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20241024T120000Z&X-Amz-SignedHeaders=host&X-Amz-Exp Files NS introduction SLIDES (PHPH10017) PHYS-1 2021.pdf & media Files & media spinal chord vid squid/nervous system 1 Neurophysiology(w4+5) 1 Neurophysiology(w4+5) 2 Neurophysiology(w4+5) 3  💡 Posterior view- back view i.e back of head or legs. In the spinal cord it is the dorsal roots and horns 💡 Anterior view-front view I,e face,chest, front of legs. In the spine it is the ventral horns and roots Neurophysiology(w4+5) 4 Neurophysiology(w4+5) 5  💡 efferent nerves leave spinal chord via ventral roots. Ventral roots are long axons of neurones located in ventral horns of the grey matter Neurophysiology(w4+5) 6  💡 Afferent nerves enter via dorsal roots Neurophysiology(w4+5) 7  ganglion - location where synapses and cell bodies occur, bundles of neurone THE RESTING POTENTIAL outside of axon is positive whilst inside is negative (-70mv) 3 Na+ ions are actively pumped out of the axon whilst 2 potassium ions are actively pumped in the axon using the sodium/potassium pump electrochemical gradients formed as now there are more sodium ions in the tissue fluid and more potassium ions in the cytoplasm NA+ ions try to diffuse in whilst K+ try to diffuse out of the axon K+ CHANNELS are open whilst NA+ are not permeability of axon ti k+ is greater so K+ ions diffuse faster out of the axon via channel proteins the cytoplasm of the axon is now negatively polarised membrane in state of polarisation causing some k+ ions to diffuse back into the axon but equilibrium is not achieved as there no net movement of ions resting potential is established Stimulation of neurone above threshold value causes action potential -70mv > +40mv membrane is now depolarised at rest, the main ion flux is K+. In addition, there are small Na+ and Cl- fluxes. The permeability of the membrane for these ions is low at rest because Na+ and Cl- channels have a low probability of opening. Neurophysiology(w4+5) 8 Neurophysiology(w4+5) 9  THE ACTION POTENTIAL - (an all or nothing depolarisation of the neural membrane) features of AP - propagation along axon and cell membrane all or none principle positive feedback Two factors responsible for rapid AP termination: Neurophysiology(w4+5) 10  💡 1. Inactivation of Na channels 💡 1. Delayed activation of K+ channels (delayed rectifiers) Neurophysiology(w4+5) 11  Passage of Action potential in myelinated neurones myelin provide insulation ( myelin sheath made up of Schwann cells) nodes of Ranvier - gaps between insulation saltatory conduction - AP JUMP FROM ONE NODE TO ANOTHER alon the nerve fibre ( as a electrical field) rather than a wave of NA+ channels opening accelerates AP propagation and saves energy Neurophysiology(w4+5) 12  💡 Loss of myelin occurs in many diseases, for example multiple sclerosis. The Neuromuscular junction specialised synapse between between motor neurone and skeletal muscle fibre > muscle contraction presynaptic terminal contains synaptic vesicles filled with neurotransmitters i.e acetylcholine Post synaptic membrane contains nicotinic acetylcholine receptors nACHRs that respond to acetylcholine Acetylcholine in the somatic nervous system (neuromuscular junction) in the autonomic nervous system in autonomic pre-ganglionic neurones in parasympathetic post-ganglionic neurones in the central nervous system released from presynaptic terminal into synaptic cleft binding to receptors on the post synaptic membrane leads to ion channels opening + resulting in depolarisation of the muscle fibre + potential muscle contraction vesicles - help prevent degradation and protect the neurotransmitter so they are released in a controlled manner and have quick release Termination of Trans-synaptic Signal acetylcholine stops being released after its transmitted the signal Acetylcholinesterase breaks down ACH in the synaptic cleft so signal does not continue happening. I.E allows muscle relaxation as ACH is quickly degraded and respond to now signals effectively Neurophysiology(w4+5) 13  miniature end plate potential small amounts of neurotransmitter released even if no action potential happens small signal results in release of a single vesicle of acetylcholine even in absence of a strong signal, a single vesicle of ACH can cause a a small change in postsynaptic membrane potential Excitatory Postsynaptic Potential graded depolarization that moves the membrane potential closer to the threshold to firing an action potential An excitatory postsynaptic potential (EPSP) is a graded depolarisation which is attenuated/reduced by membrane resistance chemical synapse electrical synapse neurotransmitter ion flow uni or bidirectional faster modulation of signal via neurotransmitter bidirectional more complex as they use receptors no modulation of signals Refractory Period short time where a neurone cannot fire another action potential after it has just fired one absolute refractory period - 2nd action potential cannot happen under any circumstance relative - a stronger than normal stimulus may evoke an AP after a action potential neurone needs time to reset ions concentrations before it can fire again, so signals are transmitted in a controlled manner > maintain directionality of signal transmission END PLATE POTENTIAL post synaptic response at neuromuscular junction resulting from ACH binding to nicotinic acetylcholine receptors on the muscular cell acetyl-b coA + choline > acetylcholine Desensitisation reduces responsiveness of receptors prevents overstimulation more neurotransmitters would be need to be released to have the same effects CNS Synaptic Transmission Estimated ~100 billion (1011) neurones and 100-500 trillion (1014) synapses in our brain Neurophysiology(w4+5) 14  Convergence - multiple presynaptic neurones send signals to a single post synaptic neurone i.e neurons from rods in the retina of an eye. allows increasing sensitivity to low levels of illumination through summation (a series of weak stimuli that can trigger an impulse). Divergence - a single presynaptic neurone sends signals to multiple postsynaptic neurone i.e a motor neurone in spinal chord sending signals to multiple muscle fibres for coordinated movement Neurophysiology(w4+5) 15  Dale’s principle a neurone has one neurotransmitter and it releases the same neurotransmitter at all of its synapses Neurophysiology(w4+5) 16 Neurophysiology(w4+5) 17 Neurophysiology(w4+5) 18  💡 EPSPs and IPSPs can’t travel along axons, only action potentials can. Neurones sum up incoming EPSPs and IPSPs to decide whether to trigger action potentials (Nobel Prize Eccles, Hodgkin, Huxley 1963) Neurophysiology(w4+5) 19  AUTOMATIC NERVOUS SYSTEM medical importance: many diseases are caused by imbalances in the NS arterial hypertension gastric ulcers heart rhythm abnormalities mental health issues Drugs can act via synapses in the ANS glaucoma (an eye disease) bronchial asthma colic(painful contractions in the gut) common cold Neurophysiology(w4+5) 20 Neurophysiology(w4+5) 21  THE EYE Know and be able to explain (with a diagram) effects of parasympathetic system on the eye Neurophysiology(w4+5) 22  Basic machinery of the eye: 1. Light intensity adjustment by opening and closing pupil or the eye 2. Focal distance adjustment by changing the curvature of the len Neurophysiology(w4+5) 23  circular muscle of the iris contract stimulated by the cranial lll (oculomotor)nerve Neurophysiology(w4+5) 24  ciliary muscle contracts lens thicken as the tension on lens is reduces so it becomes more rouneded which is needed for near vision Neurophysiology(w4+5) 25 Neurophysiology(w4+5) 26