Peripheral n.s.


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Peripheral n.s.

  1. 1. Peripheral NervousSystem
  2. 2. Peripheral Nervous System The peripheral nervous system is made up of all the nerves (sensory & motor) that are found outside of the central nervous systema The cell bodies of these neurons are found in the brain, spinal cord, and in nerve ganglia (enlarged portions of a nerve)a Sensory nerves are made up of long dendrites of sensory neuronsa Motor nerves are made up of the long axons of motor nervesa Mixed nerves are made up of both motor and sensory neurons and relay messages back and forth to the CNSa Nerves of the PNS can also be classified as cranial or spinal nerves
  3. 3. Human Nervous System
  4. 4. Cranial Nerves There are 12 pairs of cranial nervesa Nerves I and II are nerves of the cerebrum, and III through XII are nerves of the brainstema Leaving the underside of the brain, they pass through small holes in the skull
  5. 5. Functions Of Nervous System Olfactory o Sensory nerve involved in smell (olfaction) Optic o Sensory nerve involved in vision Focusing and pupil constriction Oculomotor o Motor nerve which controls movements of the eyeball (ciliary muscles), elevation of upper eyelid, focusing, and pupil constriction
  6. 6. Trochlear o Motor nerve which controls the movement of the eye (down & out) via the superior oblique muscleTrigeminal o Mixed nerve, being the chief facial sensory nerve and the motor nerve of the chewing muscles o Has three main branches, the opthalmic, maxillary, and mandibular nerves
  7. 7. Abducens o extra-oculomotor nerve which innervates the lateral rectus muscle to abduct (turn out) the eyeFacial o Mixed nerve which controls the muscles of facial expression, taste, tongue, and salivary glandsAcoustic / Vestibulocochlear o Branches into two sensory nerves, the cochlear and vestibular relating to hearing and balance respectively
  8. 8. Neuromuscular controla Neuromuscular Control: Control of striated (voluntary) muscles is essential to maintain homeostasisa The network of motor nerves which (somatic pathways) innervate the individual muscles by releasing acetylcholine at the motor end plates of the neuromuscular junction
  9. 9. Autonomic Pathways &Neurovisceral control · The major control center for the autonomic nervous system is the hypothalamus but the medulla and spinal cord are also involved a ANS = parasympathetic + sympathetic a Cell bodies are clumped in ganglia outside the CNS a Parasympathetic ganglia are located near the organ being innervated a Sympathetic ganglia lie close to the spinal cord and form the sympathetic chain ganglia
  10. 10. · Chemical and neural feedback loops allow the ANS to maintain internal homeostasis via the control of glands, smooth muscles (blood vessels, digestive tract), and cardiac musclea The sympathetic and parasympathetic systems act as antagonists to each othera The sympathetic system releases the stimulatory neurotransmitter epinephrine (adrenalin) or norepinephrine (noradrenalin)a The parasympathetic system invokes an inhibitory response releasing acetylcholine into neuroeffector junctionsa The vagus nerve is particularly important due to its connections with the majority of the internal organs
  11. 11. Symphatetic andparasympthathetic nervousSystem
  12. 12. Autonomic NervousSystem
  13. 13. What is Autonomic Nervous System? – Functions:a -maintains homeostasis of key visceral function necessary for life -provides innervation to heart, blood vessels, visceral organs, glands and all organs composed of smooth muscle -regulates activities of these structures which function below level of consciousness (involuntary)a -contains both central (hypothalamus, medulla oblongata, and spinal cord) and peripheral (pre- and post-ganglionic neurons) portions -drugs which treat diseases that require modification of autonomic functions act either in peripheral or CNS
  14. 14. Organization:a -consists of 2 neuron systems a) Preganglionic neurons:a -cell body in spinal cord or brain -modulated by brain & spinal reflexes -leaves spinal cord & synapses with post- ganglionic neurons in ganglia (relay centers)a b) Postganglionic neurons:-sends axons to effector organs-most activity takes place at junctions of pre- and post-ganglionic nerves or at neuro- effector junction
  15. 15. The Autonomic Nervous System
  16. 16. Components Of Neuron
  17. 17. Nuerotransmitters in the Autonomic Nervous Systema Nerves interact with effector organs by releasing a chemical mediator called a neurotransmitter that diffuses across a small area called the neuroeffector junction which then interacts with a receptor on the effector organ thereby illiciting a response The nerve terminal is responsible for:a synthesisa storagea releasea inactivation of the neurotransmitter
  18. 18. Chemical transmission of nerve impulses occurs between: pre and postganglionic neuronsa postganglionic neurons and neuroeffector organsa in both sympathetic and parasympathetic divisions
  19. 19. a Events during neurochemical transmission: –· electrical impulses from CNSa increase in Na+ permeabilitya local depolarization of neuronal membranea increase in K+ permeability --> repolarizationa therefore, ion currents through distinct channels --> action potentiala action potential arrives at nerve terminala release of stored neurotransmitter by exocytosisa neurotransmitter diffuses across synaptic clefta interacts with receptor on postganglionic cell body or effector organa alters ion permeability and initiates action potential in post-ganglionic nerve cell bodya or mediates a response in the end-organ (response is dependent on transmitter and receptor subtype)
  20. 20. Autonomic Pharmacology
  21. 21. Autonomic Pharmacologya because of chemical transmission, junctions in peripheral autonomic motor pathways are a logical site for pharmacological manipulation of visceral function.a Because neurotransmission involves different mechanisms in different segments of the autonomic nervous system, drugs are more or less selective in their actions. For example, local anesthetic drugs block action potential propagation (common to all neurons) and are nonselective. Drugs that act on transmitter synthesis and storage, or those that activate or block receptors are selective because of differences in the cholinergic and adrenergic systems.
  22. 22. a Cholinergic neurons: synthesize and release acetylcholine (ACh)a Include:a All motor fibers to skeletal muscle (nonautonomic)a Preganglionic efferent neurons of both SNS and PNSa Postganglionic neurons of PNSa Some postganglionic fibers of SNSa Adrenergic neurons: synthesize and release norepinephrine (NE)a Include: Postganglionic neurons of SNSa Adrenal medulla is a modified sympathetic gangliona · It receives sympathetic preganglionic fibres and releases epinephrine (EP) and NE
  23. 23. Adrenergic Nerve terminal
  24. 24. Biosynthesis And Transmission Of Acetyl Choline Biosynthesis and Transmission of Catecholaminesa NE and EP are catecholamines synthesized from tyrosine via dopaminea NE is retained in storage vesiclesa Action potential leads to increased intracellular Ca2+ ---- > NE release from vesiclesa response to NE is terminated by:a a) energy dependent amine uptake pumpa b) simple diffusion into postsynaptic cella after reuptake (uptake 1) NE is deaminated by monoamine oxidase in mitochondria or sequestered in storage vessels
  25. 25. Chlonergic Receptor Typesa a) Muscarinica b) Nicotinica Muscarinic Receptorsa found on plasma membranes of most peripheral visceral organs innervated by nerves of PNSa stimulated by muscarine, an alkaloid from Amanita muscaria
  26. 26. a Nicotinic Receptorsa found in synapses in autonomic ganglia of both SNS and PNSa found on membranes of skeletal muscle fibers at neuromuscular junctiona stimulated by nicotinea nicotinic receptors in ganglia differ from neuromuscular junction since blocked by different agonistsa nicotinic agonists --> conformational change in receptor -->opening of gated ion channel --> Na/K ion diffusion --> depolarizationa effects blocked by curare (plant poison) at neuromuscular junction
  27. 27. Chlonergic Nervous Terminal