PNS 2.docx

2 efferent nervous divisions Somatic- voluntary Autonomic- involuntary Sympathetic Parasympathetic Afferent fibres travel within the same nerves as efferent fibres but in the opposite direction. Anatomy of PNS Spinal nerves contains both sensory and motor fibres. 31 pairs of fibres and each are name...

2 efferent nervous divisions Somatic- voluntary Autonomic- involuntary Sympathetic Parasympathetic Afferent fibres travel within the same nerves as efferent fibres but in the opposite direction. Anatomy of PNS Spinal nerves contains both sensory and motor fibres. 31 pairs of fibres and each are named and numbered according to the region of vertebra column from which they emerge. 8 pairs of cervical nerves 12 pairs of thoracic nerves 5 pairs of lumber nerves 5 pairs of sacral nerves 1 coccygeal nerve Difference between the somatic and autonomic efferent divisions. Somatic Autonomic Motor neurone localised in the ventral hole of the spinal cord. First neurone is localised in the lateral hole of the spinal cord and the second neurone is localised in autonomic ganglion. Single myelinated neuron 2 neurones, first neurone is myelinated, and the second one is unmyelinated. Voluntary branch Involuntary neurone From CNS to effector organ= skeletal muscle From CNS to effector neurone= cardiac and smooth muscle etc. Autonomic nervous system The first neurone (preganglionic fiber) which is myelinated goes from lateral horn of the spinal cord to the autonomic ganglion. Another neurone (post ganglionic fiber) which is unmyelinated goes from the autonomic ganglion the effector organs. Autonomic ganglion is localised in the vertebra column. Difference between sympathetic and parasympathetic. Parasympathetic is localised in the brain or sacral region whereas Sympathetic is localised in the thoracic and lumber region. Parasympathetic has long preganglionic fibres and end in terminal ganglia which are very close to the organ they innervate whereas sympathetic has short preganglionic fibres. The neurotransmitter for the preganglionic fibre is the same for both (Ach) but the difference is with the ne urotransmitter released by post ganglionic fibre. It is Ach for parasympathetic post ganglionic fibre and is NA for sympathetic post ganglionic fibres. Majority of organs in the body are dual innervation meaning they are innervating by both parasympathetic and sympathetic nervous system. Under certain circumstances- activity of one division can dominate the other. Exceptions of dual innervation include: Blood vessels- ONLY SNS Sweat glands- ONLY SNS (post ganglionic also secrete Ach) Salivary glands- both SNS and PSNS but not antagonistic. Autonomic nervous system receptors Receptors are proteins that are localised in the plasma membrane of the post synaptic neurone or effector organ. 2 types of receptors Cholinergic receptors- nicotinic and muscarinic receptors respond to Ach. Adrenergic receptors- alpha (1 and 2) and beta (1 and 2) receptors respond to adrenaline and noradrenaline. The interaction between nicotinic receptors and Ach always results in depolarisation (excitation of post synaptic cell. The interaction between muscarinic receptors and Ach can result in either depolarisation (excitation) or hyperpolarisation (inhibition) Alpha 1 and beta 1 results in excitation Alpha 2 and beta 2 results in inhibition Autonomic control has inputs from CNS. Hypothalamus is the major control and integration centre of ANS. Controls body temperature, water balance etc. Medulla oblongata in brainstem is the region most directly responsible for autonomic output. Prefrontal cortex can influence autonomic activity eg emotions