L6 - Cell Physiology and Nervous System PDF

L6- Cell Physiology and Nervous System Dr.Pugazhandhi Bakthavatchalam Assistant Professor of Anatomy and Physiology, AUACAS, American University of Antigua LEARNING OUTCOMES Functional classification of neurons Reflex Arc Receptors Describe the...

L6- Cell Physiology and Nervous System Dr.Pugazhandhi Bakthavatchalam Assistant Professor of Anatomy and Physiology, AUACAS, American University of Antigua LEARNING OUTCOMES Functional classification of neurons Reflex Arc Receptors Describe the resting membrane potential Describe the action potential Describe Synapses and explain their types  Functional Classification Motor or Efferent neuron Interneuron or association neuron Carry impulses away from the CNS to Interneurons (association neurons) – effector organs most are multipolar Most efferent neurons are multipolar Lie between afferent and efferent neurons Cell bodies are within the CNS Confined to the CNS Form junctions with effector cells Reflex arc &Types of Neurons Types of Neurons Components of the reflex arc 1. Receptors (in dermis) 2. Afferent or sensory neuron 3. Integrating center (interneuron- spinal cord) 4. Efferent or motor neuron 5. Effector organ (muscle or gland)  Types of Neuron (Based on function) Parasympathetic Motor Somatic Sensory Neuron Sympathetic Motor Somatic Motor Neuron Skeletal Muscle Cardiac Muscle  Cutaneous Receptors (exterioreceptors) Receptors are nerve endings (dendrites/sensory axons) Converts chemical, mechanical, and light stimuli into a electrical signals Located in the dermis, wall of the organs including skeletal muscles, wall of the blood vessels, and joint surfaces (proprioceptors) Interoreceptors (viscerorecptors) Chemoreceptors Photoreceptors  Cells in the taste bud have receptors salt (Na+),  Retina of the eye have photoreceptors which are sour (H+), sweet (CHO), bitter (amino acids and stimulated by light and generate electrical signals alkaloids) These signals are transmitted from the photoreceptors Taste is also know as gustation by optic nerve to the brain Taste cells or gustatory cells gives origin to nerve fibers which carries taste sensation to the brain Interoreceptors (internal ear) Mechanoreceptors One group of Hair cells in the internal ear stimulated in response to the movement of the head and generates electrical signals The other group of cells are stimulated by sound vibrations entering the external acoustic meatus and in response these, cells generate electrical signals Since these cells are generating electrical signals in response to mechanical stimuli these are known as mechanoreceptors Interoreceptors (stretch receptors) Are located in the wall of the gastrointestinal and urinary system (ex: stomach and urinary bladder) These receptors are stimulated when organs are distended and send signals of fullness to CNS  Proprioceptors (mechanoreceptors) Proprioceptors are sensors that provide information about joint angle, muscle length, and muscle tension, which is integrated to give information about the position of the body in space Receptors in Skeletal muscle Receptors in joints Receptors and neural pathways Afferent and efferent Integrating Receptors nerve fibers center RESTING MEMBRANE POTENTIAL The resting membrane potential of a cell is defined as the electrical potential difference across the plasma membrane when the cell is in a non- excited state. A neuron at rest is negatively charged: the inside of a cell is approximately 70 millivolts more negative than the outside (−70 mV). This voltage is called the resting membrane potential; it is caused by differences in the concentrations of ions inside and outside the cell. If the membrane were equally permeable to all ions, each type of ion would flow across the membrane and the system would reach equilibrium. The resting membrane potential is a result of different concentrations inside and outside the cell. The difference in the number of positively charged potassium ions (K+) inside and outside the cell dominates the resting membrane potential Ionic composition of body fluids & Resting Membrane Potential ICF (in mEq/L) ECF (in mEq/L) Na+ = 10 Na+ = 142 K+ = 140 K+ =4 Cl- = 4 Cl- = 103 Ca++ = 0.0001 Ca++ = 2.4 PO4 = 75 PO-4 = 4 Proteins = 40 Proteins = 5 Interstitial fluid SO4- =2 Plasma membrane Electric dipole The resting membrane potential arises from three major factors: 1. Unequal distribution of ions in the ECF and cytosol (ICF): (because selective permeability of cell membrane) 2. Inability of most anions to leave the cell 3. Electrogenic nature of the Na+/K+ ATP ases - Resting Membrane Potential is usually negative on the interior: Skeletal muscle it is -90 Mv , Neuron— -70mV. The negative sign denote that the cytoplasm is electrically negative to the ECF. ACTION POTENTIAL A momentary change in electrical potential on the surface of a cell, especially of a nerve or muscle cell, that occurs on application of threshold stimulus, resulting in the transmission of an electrical impulse along the length of nerve fibre or excitable cell. Stimuli for action potential are initiated in the nerve cell body and action potential is initiated at the initial segment the axon (axon hillock) and then propagated along the nerve.  Depolarization and Repolarization: - The movement of a cell's membrane potential to a more positive value is referred to as depolarization. - The change in membrane potential from a positive to a negative value is referred to as repolarization.  Types of Synapses DEF: Junctional region between two neurons or neurons and muscle or neuron and glands where electrical impulse (Action potential) is transmitted from one excitable cell (neuron) to other excitable cell (neuron/muscle/ gland) CLASSIFICATION Anatomical classification Type of transmission Axo– somatic Chemical synapse Axo– dentritic Electrical synapse Axo-axonic Anatomical Classification of Synapse Synapse There are cytoplasmic connections between adjacent cells through gap junctions Action potential (flow of ions) spread directly from one cell to other i.e. there is no need of chemicals for synaptic transmission Synaptic delay is minimal NEUROMUSCULAR JUNCTION It is the junction between the axonal terminal and the muscle fibre membrane. It is a chemical synapse. ANATOMY OF THE NEUROMUSCULAR JUNCTION The axonal terminal which stimulates the muscle fiber is called pre synaptic terminal and muscle fiber membrane is called post synaptic terminal. There is gap between presynaptic and post synaptic terminal which is known as synaptic cleft. Presynaptic terminal: Consists of voltage gated Ca2+ channels and vesicles stored with chemicals (neurotransmitters). Post synaptic terminal (motor end plate): The highly-excitable region of muscle fiber plasma membrane is called motor endplate which is immediately adjacent to the presynaptic axon terminal. These terminals have junctional folds which harbor a high density of cholinergic receptor where the neurotransmitter (acetylcholine) from presynaptic terminal binds. This cholinergic receptor acts as ligand gated Na+ channels, apart from this the membrane has voltage gated Na+ channels as well.  NEUROMUSCULAR TRASMISSION The process of conversion of nerve action potential arriving at the pre synaptic terminal into muscle action potential at the post synaptic terminal is called Neuro muscular transmission. Anatomy of the Synapse (chemical synapse) Neuromuscular Junction Neuro Muscular Transmission Electron Microscopic Picture of NMJ  Applied Physiology Diseases of Neuromuscular of junction  Myasthenia gravis (post-synaptic disorder) Neuromuscular Junction Blockers  Non-depolarizing blockers (Tubocurarine)  Depolarizing blockers (succinylcholine)