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Functional Organization of Nervous Tissue Chapter 11 The Nervous System • Components: – Brain, spinal cord, nerves, sensory receptors • Responsible for… – Sensory perceptions, mental activities, stimulating muscle movements, secretions of many glands • Subdivisions: – Central Nervous System (CNS) – Peripheral Nervous System (PNS) Central Nervous System • Consists of brain and spinal cord • The structural & functional center of the entire nervous system which integrates incoming pieces of information & initiates an outgoing response Peripheral Nervous System • All other nerves • All pathways going toward and away from the CNS Nervous System Organization Concept Check • What are the two divisions of the nervous system? What are their parts? – CNS: Brain & Spinal Cord – PNS: nerves • What are the functions of the CNS? – Integrates incoming information & initiates an outgoing response • What is the function of the PNS? – Conducts action potentials to and away from the CNS • What are some functions of the Nervous system? – Sensory perceptions, mental activities, stimulating muscle movement, secretions of many glands Cells of Nervous System • Neurons or nerve cells – Receive stimuli and transmit action potentials – Organization • Cell body or soma • Dendrites: input • Axons: output • Neuroglia cells – Support and protect neurons Types of Neurons • Functional Classification – Sensory or afferent: action potentials toward CNS (receives stimuli; could be a special sense organ) – Motor or efferent: action potentials away from CNS (attached to a muscle or gland) – Interneurons or association neurons: within CNS from one neuron to another Myelinated and Unmyelinated Axons • Myelinated axons – Myelin protects and insulates axons from one another – Not continuous • Nodes of Ranvier • Impulse “jumps” from node to node • Fast impulse • Unmyelinated axons – Slower impulse Electrical Signals • Cells produce electrical signals called action potentials • Transfer of information from one part of body to another • Electrical properties result from ionic concentration differences across plasma membrane and permeability Nerve Impulses • A wave of electrical fluctuation that travels along the plasma membrane; due to changes in chemical concentrations. Impulse +++-++++++-++++-+ ---+---+-----------+--+ ++++++-+++-++-+++++-++++++++ ----+----+--+--------+ ++++-++++++-+++++- -----+----+-------+--+-------+-------- ----+----+---+---------- ++++++++-++-++++-++ ++++++-++-+++++++ --------+--++----------+---- ----+-----++-----------+-----+------+--+++++++-+++++++--++++++++-+++ Resting Potential Action Potential Resting Potential “Polarized” “Depolarized” “Repolarized” Resting Membrane Potential • Characteristics – Number of charged molecules and ions inside and outside cell nearly equal – Concentration of K+ higher inside than outside cell- negative proteins in also, Na+ higher outside than inside – At equilibrium there is very little movement of K+ or other ions across plasma membrane Action Potentials • Series of permeability changes when a local potential causes depolarization of membrane • Phases – Depolarization • More positive – Repolarization • More negative • All-or-none principle – Neuron will fire or it won’t The Synapse • Junction between two cells • Electrical message transferred across the synapse by chemicals called neurotransmitters Concept Check • What are the main parts of a neuron? – Axon, dendrites, myelin sheath, synapse • What are the three types of neurons and what do they do? – Sensory (afferent)- action potential toward CNS , Motor (efferent)- action potential away from CNS, & Interneurons- within CNS from one neuron to another • How does an impulse travel along an axon? What speeds it up? – Jumps from node to node; myelin • How does a synapse work? – Neurotransmitters transfer message across synapse Stimulus • Any change in your environment. – Temp, sound, smell • You may or may not respond to a specific stimulus Reflex • A predictable response to a stimulus which may or may not be conscious – A reflex consists of either muscle contraction or glandular secretion – Neurons involved in reflex • Afferent neuron- sensory • Interneuron • Efferent neuron- motor Sensory Receptors • In order for a stimulus to be detected, it must be strong enough to elicit an impulse – It must be at the threshold level- the minimum stimulus to start an impulse • The all-or-none response means that either a neuron will fire or it won’t, there is no partial impulse • Sensation- the brain’s interpretation of what the stimulus is Characteristics of Sensations • Projection- brain refers a sensation to the point of stimulation • Adaptation- loss of sensation even though the stimulus is still applied • Afterimage- persistence of a sensation even though the stimulus is removed • Referred pain- felt in the skin near or around the organ sending the impulse • Phantom pain- sensation of pain in a limb that has been amputated Classification of Receptors 1. Mechanoreceptors- activated by mechanical stimuli or deformation of the receptor 2. Chemoreceptor- changing of the chemical concentrations around the body 3. Thermoreceptors- detect hot and cold 4. Nociceptors- any stimuli that can cause tissue damage; sensation of pain 5. Photoreceptors- respond to light Somatic Senses pain, temperature and touch • These sensations can be felt throughout the body, yet they are distributed unevenly through the skin • Exteroceptors- sense receptors located on body surfaces • Proprioceptors- found in the muscles and joints • Visceroceptors- found in internal organs • Nociceptors- pain receptors; free nerve endings Review • Meissner’s corpuscles- touch • Krause’s End Bulbs- touch • Ruffini’s corpuscles- continuous touch • Pacinian corpuscles- deep pressure The Brain • Parts/Functions • Left vs Right Brain Activity?? • Dissection notes…pre-lab??
