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Neural Control and Coordination

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Neural Control and Coordination Neural control and coordination: Structure of Neuron: Nervous tissue originates from ectoderm. Nerve cell – Cell body or Cyton Centriole is absent or soma or perikaryon: Nissl's granule and Neurofibril are also found in nerve cell Nissl’s Endoplasmic reticulum & ribosome form granules like structure granules: called as Nissl's granules or Tigroid body. They are centre of protein synthesis. Dendron: • Fine branches of cytoplasm are called dendrites. • Receptor’s are found on the dendrites. Axon or nerve fibre are longest cell process of cyton, Nissl's granules are absent in the axoplasm. • Axon is covered by axolemma, part of cyton where arises called axon hillock. • Terminal end of axon is branched in button shape branches which are called as Telodendria. • More mitochondria in telodendria which synthesize Acetylcholine (Ach) with the help of choline acetyl transferase enzyme, stored in vesicles. Axon is covered by phospholipids (sphingomyelin) called as medulla or myelin sheath. Medulla is covered by neurilemma or sheath of schwann cells, helps in myelinogenesis. Myelin sheath acts as insulator and prevent's leakage of ions. Myelinogenesis in (PNS) begins with the deposition of myelin sheath in concentric layer around the axon by schwann cells. Myelin sheath is discontinuous around the Axon. These interruptions are called node of Ranvier Myelinogenesis in the Central nervous system Neuron (CNS) occurs with the help of oligodendrocytes (Neuroglia) Myelinated Non – Myelinated Collaterals Small process of axon help in conduction of nerve impulse in more area. of Axon: Gray matter composed of cytons & nonmedullated nerve fibres (Grey fibers). White matter – It contain myelinated nerve fibres (White fibres). Group of cyton Group of Nerve fiber Nuclei for CNS Ganglia for PNS Tract – CNS Nerve – PNS Types of neurons Unipolar Bipolar Multipolar Single process arises Two process arises from cyton Neuron which have one axon from cyton. (1 Axon) (1Axon & 1 dendron) but many dendrons. e.g. Nervous system e.g. Retina (Rod & cones) e.g. Most of neurons of of embryo Olfactory epithelium vertebrates. Apolar/Nonpolar • No definite dendron/axon nerve impulse radiates in all directions. Neuron : e.g. Hydra • Pseudounipolar nerve cell has only axon but a small process act as dendron. e.g. Dorsal root ganglia of spinal cord Types of Neurons on the basis of function Sensory of Inter neuron or inter Motor or efferent afferent sensory connecting neuron or CNS → Effector organ → CNS internuncial neuron (organ) Cerebral cortex contains motor area, sensory area & large area (regions)called associative area responsible for complex function like inter sensory association, memory & communication. Synapse - 1 Synapse: Junctional region between two neurons where information is transferred but no protoplasmic connection. Synapse = Pre synaptic knob (Telodendria) + synaptic cleft + post synaptic membrane (membrane of dendron). (i) Axodendritic – b/w axon & dendron Synapse: (ii) Axosomatic – b/w axon & cyton (iii) Axoaxonic – b/w axon & axon Through neuron At synapse Conduction Fast Slow Synaptic cleft 0.2 nm > 20 nm Neurotransmitter Absent Present Synaptic delay Absent Present Blocking Can not be controlled Controlled by neurotransmitter Synapse – 2 Supporting cells Supporting cells: Neuroglia/Glial cells Astrocytes Oligodendrocytes Microgliocytes Origin Ectodermal in origin Ectodermal in origin Mesodermal in origin Morphology Large cell Smaller Smallest Number of process Numerous process Few process With branching Function 1.Provide repair Formation & Scavenger cells of mechanism and preservation of Myelin CNS replace the damage sheath in CNS. phagocytic in nature tissue 2. It forms blood brain barrier. Blood Brain Barrier: Blood-brain barrier is formed by capillary endothelial cells, which are coupled by tight junctions with extraordinarily high electrical resistance. Astrocytes are required to produce the barrier which prevents the entry of neurotoxins. Neurotransmitters or Neurohormones Stimulatory Inhibitory ↓ ↓ Stimulates impulse at synapse e.g. Inhibit impulse at synapse e.g. Acetyl choline (anch), nor – epinephrine GABA (gamma amino butyric or nor – adrenaline or sympathetin acid) dopamine glycine Physiology : The resting membrane potential Active and passive ion movement across the cell surface of an axon inside the axon called as resting potential Active transport takes place through the sodium/potassium pump. Neurons are excitable cells because their membranes are in a polarized. Resting potential is about – 70 mV. Potassium ions have a membrane permeability greater than that of sodium ions. Due to active transport and diffusion positive charge is more outside and negative charge is more inside. Action potential in exciting stage: On stimulus an action potential is generated by a sudden opening of the sodium gates, sodium ions enter by diffusion increases the number of positive ions inside the axon. 10 mV in potential difference from RMP is sufficient to trigger a rapid influx of Na+ ions, 10 mV is threshold stimulus. (Axolemma) is completely depolarized, called as excited membrane or depolarized membrane. Membrane potential becomes positive upto +30 to +45 mV called as action potential. Physiology of nerve – Repolarization Repolarization Sodium gates closed, potassium gates open, potassium diffuse out of cell makes the cell negative and the process of repolarization. Repolarization period returns the cell to its resting potential (-70 mV). The time taken for restoration of resting potential is called refractory period, during this period the membrane is incapable of receiving another impulse. The whole process of depolarization and repolarization takes only about 1 to 5 milli second (ms). Process Na+-K+ Passive Na+ VGC K+ VGC Potential with Inside Charge pump diffusion value Polarisation 3 3 x x RMP (-60 to - Negative 85 mv) Depolarisation x 3 3 x Neutral Repolarisation 3 3 x 3 - Negative Hyperpolarisation 3 3 x 3 - Negative Saltatory conduction of Nerve Impulse: Saltatory conduction occur in myelinated fibre. The combined resistance of the axon membrane and myelin sheath is very high, but nodes of Ranvier, the resistance is low. Action potential jump from node to node and passes along the ,myelinated axon faster as compared to non – myelinated axon. Leakage of ions takes place only in nodes of Ranvier and less energy is required for saltatory conduction. Synaptic Transmission AP develop in pre synaptic membrane, it becomes permeable fro Ca++, Ca++ enter in pre synaptic membrane & vesicles burst and release of neurotransmitters (Ach) in synaptic cleft. Ach via synaptic cleft & bind to receptors, develops excitatory post synaptic potential (EPSP) Cholinesterase enzyme in Post synaptic membrane decomposes the Ach into choline & Acetate. Neuro inhibitory transmitter (GABA) binds with post synaptic membrane to open the Cl– gatted channels and hyperpolarization occurs called inhibitory post synaptic potential (IPSP) Neuron conducts the impulse in the form of electro chemical wave. It follow all or none law. Nervous system – Classification : Classify nervous system Central Nervous System (CNS) Brain and spinal cord Integrative and control centers Peripheral Nervous System (PNS) Cranial nerves and spinal nerves Communication lines between the CNS and the rest of body Sensory (afferent division) Motor (efferent division) Somatic and visceral sensory Motor nerve fibres nerve fibres Conducts impulses from Conducts impulses from receptors CNS to effectors to the CNS (muscles and glands) Sympathetic division Mobilizes body systems during Autonomic Nervous Somatic Nervous emergency situations Sysmtem (ANS) Sysmtem (SNS) Involuntary (visceral motor) Voluntary (somatic motor) Parasympathetic division Conducts impulses from the Conducts impulses from the CNS to cardiac muscles CNS to skeletal muscles Conserves energy smooth muscles and glands Promotes nonemergency functions Central nervous system: Brain: Situated in cranial box made up of 1 frontal bone, 2 parietal bone, 2 temporal bone, 1 occipital bone. Brain meninges: Duramater: Outermost membrane made up of collagen fibres. No space is found between skull & Duramater. Arachnoid: Middle, thin and delicate membrane, made up of connective tissue. It is found only in mammals. Arachnoid villi reabsorb the cerebrospinal fluid (CSF) from sub arachnoid space & pour it into cranial venous sinuses. Piamater: • Inner most made up of connective tissue. • Piamater & arachnoid fuse together to form leptomeninges. • At some places it directly merges in the brain called telachoroidea form choroid plexus in the ventricles of brain. • Sub Dural space filled with serous fluid. • Sub arachnoid space filled with C.S.F. • Inflammation of meninx is called as meningitis. Cerebrospinal Clear and alkaline has protein glucose, cholesterol, urea, – fluid (CSF): bicarbonates, sulphate and chlorides of Na, K. • Mainly formed in choroid plexus of lateral ventricles. • Collection of CSF fro any investigation is done by lumbar puncture at L3 – L4 region. Functions of It act as shock absorbing medium. C.S.F.: • Excretion of waste products. • Endocrine medium for the brain to transport hormones. Cerebrum – Brain Fore brain (develops Mid brain (mesencephalon) Hind brain (rhombencephalon) from prosencephalon) Netencephalon Myelencephalon Rinencephalon Telencephalon Diencephalon (pons, cerebellum) (medulla (olfactory lobe) (cerebrum) oblongata) Cerebrum consist of two cerebral hemispheres on
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