Fundamentals of the Nervous System and Nervous Tissue Part 1 Nervous - PowerPoint PPT Presentation

Fundamentals of the Nervous System and Nervous Tissue Part 1

Nervous System & Tissue I. General Functions of the Nervous System II. Organization of the Nervous System III. Nervous Tissue IV. Nerves V. Basic Neuronal Organization VI. Disorders

I. General Functions A. Control & Communication Center 1. Control through creation & propagation of electrical impulses (action potentials) a. Fast acting & Specific 2. Control and communication through inhibition or excitation at neuron junctions (synapses, neuromuscular junctions . . .) a. Determines what happens once action potential arrives at a junction 3. Operates with the endocrine system

I. General Functions B. Sensory Function 1. Sensory receptors monitor changes inside and outside the body a. The changing condition is the stimulus b. The stimulus can ultimately generates an action potential which is the sensory input C. Integrative Function 1. Processes and interprets sensory input a. Makes decisions – integration D. Responsive Function 1. Dictates a response by activating effector organs a. Response – motor output

II. Organization of the Nervous System A. Nervous system divided into two systems: 1. Central nervous system (CNS) Brain and spinal cord • Integrating and command center • 2. Peripheral nervous system (PNS) Outside the CNS • Consists of nerves extending from (and going to) • brain and spinal cord Cranial nerves – Spinal nerves – Peripheral nerves link all regions of the body to the • CNS

II. Organization of the Nervous System Brain Central Nervous System Spinal Cord Peripheral Nerves Peripheral Nerves Peripheral Nervous System Peripheral Nerves

II. Organization of the Nervous System B. Peripheral Nervous System consists of two major functional aspects 1. Sensory (afferent) signals picked up by sensor receptors Carried by nerve fibers of PNS to the CNS • 2. Motor (efferent) signals are carried away from the CNS Innervate muscles and glands •

II. Organization of the Nervous System C. Sensory and Motor aspects are divided according to region they serve Somatic ( wall of body ) – Visceral ( guts ) – D. This regional division creates four main subdivisions: 1. Somatic Sensory 2. Somatic Motor 3. Visceral Sensory 4. Visceral Motor

II. Organization of the Nervous System 1. Somatic Senses a. General somatic senses Sensory receptors have a wide dispersion, and include • Touch, pain, vibration, pressure, and temperature • b. Proprioceptive senses – (sense of body positions) Afferent information regarding position and movement of • body in space, due to receptors in tendons, muscles and joints c. Special somatic senses Special due to the presence of a sensory “organ” or a • clustered group of sensory receptors, rather than sensory cells widely dispersed as in the general somatic senses Hearing, balance, vision, and smell •

II. Organization of the Nervous System 2. Somatic motor neurons a. General somatic motor – signals contraction of skeletal muscles Under our voluntary control and as such may also • referred to as the “voluntary nervous system” b. Branchial motor Typical skeletal muscle derived from somitomeres • Mastication muscles control – Facial expression muscle control – Pharyngeal & laryngeal muscle control – Sternocleidomastoid & Trapezius muscle control –

II. Organization of the Nervous System 3. Visceral Senses a. General visceral senses stretch, pain (generally referred to the body wall), • temperature, nausea, and hunger Widely felt in digestive and urinary tracts, • reproductive organs b. Special visceral senses Taste and smell have a visceral afferent component, • involving cranial nerves VII, IX & X (facial, glossopharyngeal & vagus nerve)

II. Organization of the Nervous System 4. Visceral Motor Neurons Makes up autonomic nervous system – Further divided into Sympathetic & • Parasympathetic divisions. Regulates the contraction of smooth and – cardiac muscle & glandular secretion Controls function of visceral organs – Also called “involuntary nervous system”, as it – performs without conscious input.

II. Organization of the Nervous System CNS PNS Brain Spinal Cord Motor (efferent) Sensory (afferent) Division Division Somatic Somatic Visceral Visceral Sensory Motor Motor sensory Propri- Special General General Special Parasympathetic Visceral Sympathetic oceptive Somatic Somatic Visceral division of ANS Senses Senses division of ANS Senses Senses Senses

III. Nervous Tissue A. Characteristics of nervous tissue Cells are densely packed and intertwined – Two main cell types make up nervous tissue – Neurons • Excitable – Neuroglia (supportive cells) • Nonexcitable – More on these later… –

III. Nervous Tissue B. General Information on Neurons 1. Billions of neurons create the basic functional structure unit of the nervous system 2. Neurons are specialized cells that conduct electrical impulses (action potentials or nerve impulses) along the plasma membrane 3. Longevity – can live and function for a lifetime 4. Do not divide – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception 5. High metabolic rate – require abundant oxygen and glucose Can account for approx 10% of your metabolic rate . . . – When you are thinking

III. Nervous Tissue C. General Structure of a Neuron consists of (1) a cell body and (2) neuronal processes (dendrites & axons [axon collaterals, axon terminals & synapses] ) 1. Cell body (perikaryon or soma) Size varies from 5–140µm • Contains a normal complement of organelles • Also contains chromatophilic (Nissl) bodies • Basically clumps of RER and free ribosomes that “love stain” – (namesake) that renew membranes and protein portion of cytosol Neurofibrils – bundles of intermediate filaments that form a • network between chromatophilic bodies and provides structural integrity to the soma

Structure of a Typical Large Neuron Click on picture to return to previous slide

III. Nervous Tissue C. General Cell body information cont. 2. Location of neuronal cell bodies a. Most neuronal cell bodies are located within the CNS Protected by bones of the skull and vertebral column – b. Some neuronal cell bodies form ganglia clusters of cell bodies, axon terminals and dendrites – outside of the CNS (i.e. part of the PNS)

III. Nervous Tissue C. General Structure 2. Neuronal Processes – extensions of cell body membrane forming Dendrites • Axons •

2. Neuron Processes a. Dendrites Extensively branching from the soma – Transmit electrical signals (graded potentials) toward – the cell body As graded potentials, they may be affected by other nearby • synaptic events Increasing state of excitation (further depolarization of – membrane) Decreasing state of excitation (inhibition – further from a – threshold event) Contain chromatophilic bodies, but only extend into – the basal part of dendrites Function as receptive sites – Lots of surface area for this due to the large amount of • branching exhibited by dendrites

2. Neuron Processes b. Axons 1. Neuron has only one Exception – anaxionic neuron • 2. Impulse generator and conductor Generated at axon hillock • Conducted along the length of the axon • 1. Transmits impulses away from the cell body 2. Chromatophilic bodies are absent 3. No protein synthesis in axon 4. Neurofilaments, actin microfilaments, and microtubules Provide strength along length of axon • Aid in the transport of substances to and from the cell body • Axonal transport or flow – needed as there is no protein – synthesis in axon

2. Neuron Processes b. Axons – cont. 5. May have branches along length Axon collaterals • Allow for divergence of action potential – Allows for widespread effect – Multiple branches at end of axon • Terminal branches (telodendria) – End in knobs called axon terminals » (also called end bulbs or boutons) Forms a synapse with another nueron, or a » neuromuscular junction if a muscle. . . PLAY Neuron Structure

III. Nervous Tissue D. Action Potentials (nerve impulses) Generated at the axon hillock – If the membrane reaches threshold potential due to the net • effects of synapse activity on the dendrites & soma Conducted along the axon – Releases neurotransmitters at axon terminals – Neurotransmitters – excite or inhibit the post ‐ – synaptic membrane Depending on the action of the neurotransmitter receptor • on the post ‐ synaptic membrane Neuron receives and sends signals – Receives on the dendrites and soma • Sends down the axon, axon collaterals •

III. Nervous Tissue E. Synapses Site at which neurons communicate – Signals pass across synapse in one direction – Presynaptic neuron – Conducts signal toward a synapse • Postsynaptic neuron – Transmits electrical activity away from a synapse • Only if the effects of the neurotransmitter from the – presynpatic neuron are excitatory PLAY Synapse

Two Neurons Communicating at a Synapse Click on picture to return to previous slide