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Chapter 4

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Kinesiology & Health Science
KINE 2011
Olivier Birot

Chapter 4 – The Peripheral Nervous System: Sensory, Autonomic, Somatic Organization of the Nervous System - Central nervous system – brain, spinal cord (there are NO nerves here) o There ARE pathways/tracts/commissures that link the right and left halves of the brain - Peripheral nervous system – nerve fibres o Connection between the CNS and the effectors/receptors located in other parts of the body - Afferent division: from the receptors (PNS) to the CNS o Sensory stimuli o Visceral stimuli - Efferent division: from CNS to effectors/organs/muscle/glands (PNS) o Somatic Nervous System  Motor neurons innervate skeletal muscle – cell bodies of these neurons are located in the brainstem and the ventral horn or the spinal cord; neurotransmitter = Ach  Effector organs (made up of muscle and gland tissue) – skeletal muscle contraction o Autonomic nervous system  Sympathetic Nervous System (gas) and Parasympathetic Nervous System (brake)  Smooth muscle, cardiac muscle, glands – these neurons are located in the gastrointestinal tract o Effector organs (made up of muscle and gland tissue) Three Functional Classes of Neurons - Afferent neuron – from PNS to CNS o Starts with a sensory receptor – generates an action potential in response to a stimulus o Moves down a long peripheral axon (afferent fibre) o Cell body – located adjacent to the spinal cord, between the receptor and the axon terminal o Central axon – between the cell body and the axon terminal - Interneuron o 99% of our neurons o Link between afferent and efferent systems o Important in integrating peripheral responses to peripheral information o Receive and analyze information (convergence and divergence) o Part of the CNS, but not actually since the CNS has no neurons - Efferent neuron – from CNS to PNS The Autonomic Nervous System - Signal moves from the CNS to an innervated organ via a two-neuron pathway: o Cell body of the presynaptic neuron (located in the CNS) to the… o Preganglionic fibre (which synapses with the cell body of the second neuron in a ganglion) to the… **Ganglion = a cluster of neuronal cell bodies outside the CNS o Axon of the second neuron or “postganglionic fibre” - The ANS has two subdivision: o Sympathetic Nervous System  From thoracic and lumbar regions of the spinal cord (middle)  Short preganglionic fibre  Release Ach, received by nicotinic receptors on postganglionic cell bodies  Synapse in the sympathetic ganglia chain/sympathetic trunk  Long postganglionic fibre → effector organs  Adrenergic fibres – release norepinephrine and epinephrine, received by adrenergic receptors in the effector (smooth/cardiac muscle)  Some pass through the ganglion without synapsing  Synapse in a sympathetic collateral ganglia o Parasympathetic Nervous System  From the brain and sacral/lower spinal cord (top and bottom)  Long preganglionic fibre that reach a terminal ganglion in/near the effector organ  Release Ach, received by nicotinic receptors on postganglionic cell bodies  Very short postganglionic fibre ending on cells of an organ itself  Cholinergic fibres – release acetylcholine, received by muscarinic receptors on the effector (smooth/cardiac muscle) Innervation of Visceral Organs - Are regulated unconsciously, without voluntary control - Most organs are controlled by both the sympathetic and parasympathetic nervous systems o Often these have opposed actions o Are usually both partially active  Parasympathetic and sympathetic tones; tonic activity = constantly active o Sometimes there is dominance of one system (like a part of your personality)  Some are more “flight or fight” types (sympathetic), others “rest and digest” types (parasympathetic) The Adrenal Medulla - Each adrenal gland is composed of an inner adrenal medulla and a surrounding adrenal cortex o Adrenal medulla secretes epinephrine, norepinephrine and acetylcholine o Adrenal cortex secretes steroid
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