Neurology

Slide 1: 

11-1 Anatomy and Physiology, Seventh Edition Rod R. SeeleyIdaho State University Trent D. StephensIdaho State University Philip TatePhoenix College Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Chapter 11 Lecture Outline*

Functions of the Nervous System : 

11-2 Functions of the Nervous System Sensory input: Monitor internal and external stimuli (change) Touch, odor, sound, vision, taste, bp, body temp. Integration. Brain and spinal cord process sensory input and initiate responses Motor output: Controls of muscles and glands Homeostasis. Regulate and coordinate physiology Mental activity. Consciousness, thinking, memory, emotion

The Nervous System : 

11-3 The Nervous System Components Brain, spinal cord, nerves, and sensory receptors Subdivisions Central nervous system (CNS): brain and spinal cord Peripheral nervous system (PNS) Nerves: Sensory and Motor

Peripheral Nervous System : 

11-4 Peripheral Nervous System Outside the CNS Divided into Sensory (Afferent) Division -incoming information Motor (Efferent Division - outgoing information Sensory Division Use sensory neurons to transmit nerve impulses toward the brain and spinal cord Receptors in various body locations react to stimuli (touch, pressure, heat, stretch, light, etc) and trigger a nerve impulse in the sensory neuron Motor Division Use motor neurons to transmit nerve impulses away from the brain and spinal cord Stimulate effectors (muscle and glands)

Divisions of PNS : 

11-5 Divisions of PNS Sensory (afferent): transmits nerve impulses from receptors to CNS. Motor (efferent): transmits nerve impulses from CNS to effectors (muscles, glands)

Types of Sensory and Motor Information : 

11-6 Types of Sensory and Motor Information

Sensory Division of the PNS : 

11-7 Sensory Division of the PNS Transmit nerve impulses over sensory neurons to the CNS from receptors Receptors are classified as: Somatic receptors - those found in skin, joints, skeletal muscles, and special sense organs Respond to touch, pressure, heat, stretch, pain, light Visceral receptors - located in walls of viscera Respond to stretch, pain, temperature, chemical stimuli (CO2)

Motor Division of PNS : 

11-8 Motor Division of PNS Transmits impulses away from the CNS to effectors Effector - any muscle or gland Somatic nervous system: Regulates contraction of skeletal muscles. Under our voluntary control - I.e., under conscious control Autonomic nervous system (ANS) Regulates contraction of smooth muscle, cardiac muscle and glands (visceral organs) Subconscious or involuntary control. Divisions of the ANS Sympathetic. Prepares body for physical activity. Parasympathetic. Regulates resting or vegetative functions such as digesting food or emptying of the urinary bladder.

Cells of Nervous System : 

11-9 Cells of Nervous System Neurons The functional unit of the nervous system Transmit electrical signals (action potentials) to other neurons or effectors Neuroglia (Glial cells) Nonexcitable Support and protect neurons

The Neuron : 

11-10 The Neuron Special characteristics of neurons Longevity – can live and function for a lifetime Do not divide (amitotic) – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception High metabolic rate – require abundant oxygen and glucose

Slide 11: 

11-11 Parts of the Neuron Cell Body. Aka Soma or Perikaryon Contains usual organelles plus other structures Nissl bodies = chromatophilic substance = rough E.R: primary site of protein synthesis Cytoskeleton of neurofilaments and neurotubules No centrioles (hence its amitotic nature) Major biosynthetic center Most neuronal cell bodies Located within CNS Ganglia - clusters of cell bodies that lie along nerves in PNS Tapers to form axon hillock

Neuron Processes : 

11-12 Neuron Processes Dendrites: short, often highly branched. Receptive regions of the neuron Axons. Long cytoplasmic process capable of propagating a nerve impulse Neuron has only one Transmits impulse away from soma Axon hillock: Initial segment Few, if any, branches along length Multiple branches at end of axon Terminal branches (telodendria) End in knobs called axon terminals (aka synaptic terminals, end bulbs, boutons, synaptic knobs) Contain vesicles filled with neuro- transmitter (NT)

Axoplasmic Transport : 

11-13 Axoplasmic Transport Anterograde: Axoplasm moved from cell body toward terminals. Supply materials for growth, repair, renewal. Can move cytoskeletal proteins, organelles away from cell body toward axon terminals. Retrograde Away from axonal terminal toward the cell body Damaged organelles, recycled plasma membrane, and substances taken in by endocytosis can be transported up axon to cell body. Rabies and herpes virus can enter axons in damaged skin and be transported to CNS. Would include toxins such as heavy metals (the chemical, not the noise)

Classification of Neurons : 

11-14 Classification of Neurons Structural classification Multipolar – possess more than two processes Numerous dendrites and one axon Bipolar – possess two processes Rare neurons – found in some special sensory organs Unipolar (pseudounipolar) – possess one short, single process Start as bipolar neurons during development

Neurons Classified by Structure : 

11-15 Neurons Classified by Structure Figure 12.10a–c

Structural Classes of Neurons : 

11-16 Structural Classes of Neurons Table 11.1.2

Functional Classification of Neurons : 

11-17 Functional Classification of Neurons According to the direction the nerve impulse travels Sensory (afferent) neurons – transmit impulses toward the CNS Virtually all are unipolar neurons Cell bodies in ganglia outside the CNS Short, single process divides into The central process – runs centrally into the CNS The peripheral process – extends peripherally to the receptors

Functional Classification of Neurons : 

11-18 Functional Classification of Neurons Motor (efferent) neurons Carry impulses away from the CNS to effector organs Most motor neurons are multipolar Cell bodies are within the CNS Form junctions with effector cells Interneurons (association neurons) – most are multipolar Lie between 2 neurons Confined to the CNS

Neurons Classified by Function : 

11-19 Neurons Classified by Function Figure 12.11

Supporting Cells (Neuroglial Cells) in the CNS : 

11-20 Supporting Cells (Neuroglial Cells) in the CNS Neuroglia – usually only refers to supporting cells in the CNS Glial cells have branching processes and a central cell body Outnumber neurons 10 to 1 Make up half the mass of the brain Can divide throughout life May divide abnormally - glioma - brain cancer Do not transmit nerve impulses

Neuroglia of CNS: Astrocytes : 

11-21 Neuroglia of CNS: Astrocytes Largest and most numerous Functions include: 1. Form the blood-brain barrier Take up and release ions (Na, K) to control the environment around neurons Regulate what substances reach the CNS from the blood 2. Reapture and recycle neurotrans-mitters 3. Involved with synapse formation in developing neural tissue 4. Aid in repair of damaged neural tissue 5. Produce molecules necessary for neural growth (BDTF)

Neuroglia of CNS: Ependymal Cells : 

11-22 Neuroglia of CNS: Ependymal Cells Line brain ventricles and spinal cord central canal. Specialized versions of ependymal form choroid plexuses. Choroid plexus Secrete cerebrospinal fluid. Cilia help move fluid thru the cavities of the brain.

Neuroglia of CNS: Microglia and Oligodendrocytes : 

11-23 Neuroglia of CNS: Microglia and Oligodendrocytes Microglia: specialized macrophages. Respond to inflammation, phagocytize necrotic tissue, microorganisms, and foreign substances that invade the CNS. Oligodendrocytes: form myelin sheaths if surrounding axon. Single oligodendrocytes can form myelin sheaths around portions of several axons.

Neuroglia of PNS : 

11-24 Neuroglia of PNS Schwann cells or neurolemmocytes: Wrap around portion of only one axon to form myelin sheath. Wrap around many times. As cells grow around axon, cytoplasm is squeezed out and multiple layers of cell membrane wrap the axon. Cell membrane primarily phospholipid. Outer surface of Schwann cell called the neurilemma Satellite cells: surround neuron cell bodies in ganglia, provide support and nutrients

Myelin Sheaths : 

11-25 Myelin Sheaths Segmented structures composed of the lipoprotein myelin Surround thicker axons Form an insulating layer Prevent leakage of electrical current Increase the speed of impulse conduction

Myelin Sheaths in the PNS : 

11-26 Myelin Sheaths in the PNS Formed by Schwann cells Develop during fetal period and in the first year of postnatal life Schwann cells wrap in concentric layers around the axon Cover the axon in a tightly packed coil of membranes Neurilemma – material external to myelin layers Nodes of Ranvier – gaps along axon Degeneration of myelin sheaths occurs in multiple sclerosis and some cases of diabetes mellitus.

Nerves : 

11-27 Nerves Nerves - bundles of axons wrapped in connective tissue If only sensory axons, called sensory nerves If only motor axons, called motor nerves If both sensory and motor axons, called mixed nerves Connective Tissue Coverings Endoneurium – layer of delicate connective tissue surrounding the axon Nerve fascicles – groups of axons bound into bundles Perineurium – connective tissue wrapping surrounding a nerve fascicle Epineurium – whole nerve is surrounded by tough fibrous sheath

Structure of a Nerve : 

11-28 Structure of a Nerve Figure 12.16a A. Note the similarity of a nerve to a muscle Just as a muscle is a collection of muscle fibers, a nerve is a collection of nerve fibers (axons). Each is broken up in smaller units known as fascicles Each is covered by connective tissue: Epimysium vs. Epineurium Perimysium vs. Perineurium Endomysium vs. Endoneurium

Nerve Fiber Types : 

11-29 Nerve Fiber Types Type A fibers large-diameter nerve Heavily myelinated; conduct impulses at 15-120 m/sec Motor neurons supplying skeletal muscles Type B medium-diameter nerves lightly myelinated; conduct at 3-15 m/sec Sensory nerves from sensory receptors Type C: Very small diameter Unmyelinated; conduct at 2 m/sec or less Part of ANS Innervate visceral smooth muscle and glands

The Synapse : 

11-30 The Synapse Site at which neurons communicate Signals pass across synapse in one direction Types of cells in synapse Presynaptic neuron - conducts impulse toward the synapse Postsynaptic neuron - conducts impulse away from the synapse Average postsynaptic neuron has up to 10,000 synapses Some in cerebellum have up to 100,000 synapses Two major types of synapses Electrical - not common in nervous system Chemical - most common type

Types of Chemical Synapses : 

11-31 Types of Chemical Synapses Axodendritic Between axon terminals of presynaptic neuron and dendrite of postsynaptic neuron Most common type of synapse Axosomatic Between axon of pre- and soma (cell body) of post-synaptic neuron Axoaxonic Between two axons Not common

Types of Neural Synapses : 

11-32 Types of Neural Synapses

Chemical Synapse : 

11-33 Chemical Synapse Presynaptic bulb has secretory vesicles that contain neurotrans- mitter chemical (NT) NT must pass across the synaptic cleft, space that separates pre- and postsynaptic membranes Postsynaptic membrane contains receptors specific for each type of NT Binding of NT to its receptor causes ion channels to open or close Postsynaptic membrane is thus either stimulated or inhibited

Basic Neuronal Organization of the Nervous System : 

11-34 Basic Neuronal Organization of the Nervous System Reflex arcs – simple chains of neurons Explain reflex behaviors Determine structural plan of the nervous system Responsible for reflexes Rapid, autonomic motor responses Can be visceral or somatic

Five Essential Components to the Reflex Arc : 

11-35 Five Essential Components to the Reflex Arc Receptor – site where stimulus acts Sensory neuron – transmits afferent impulses to the CNS Integration center – consists of one or more synapses in the CNS Motor neuron – conducts efferent impulses from integration center to an effector Effector – muscle or gland Responds to efferent impulses Contracting or secreting

Types of Reflexes : 

11-36 Types of Reflexes Monosynaptic reflex – simplest of all reflexes Just one synapse The fastest of all reflexes Example – knee-jerk reflex Polysynaptic reflex – more common type of reflex Most have a single interneuron between the sensory and motor neuron Example – withdrawal reflexes

Types of Reflexes : 

11-37 Types of Reflexes

Simplified Design of the Nervous System : 

11-38 Simplified Design of the Nervous System Three-neuron reflex arcs Basis of the structural plan of the nervous system Similar reflexes are associated with the brain

Simplified Design of the Nervous System : 

11-39 Simplified Design of the Nervous System Sensory neurons – located dorsally Cell bodies outside the CNS in sensory ganglia Central processes enter dorsal aspect of the spinal cord Motor neurons – located ventrally Axons exit the ventral aspect of the spinal cord Interneurons – located centrally Synapse with sensory neurons

Simplified Design of the Nervous System : 

11-40 Simplified Design of the Nervous System Human nervous system is complex Interneurons also include neurons confined to CNS Long chains of interneurons between sensory and motor neurons

Simplified Design of the Nervous System : 

11-41 Simplified Design of the Nervous System

Neuronal Pathways and Circuits : 

11-42 Neuronal Pathways and Circuits Organization of neurons in CNS varies in complexity Convergent pathways: many neurons converge and synapse with smaller number of neurons. E.g., synthesis of data in brain. Divergent pathways: small number of presynaptic neurons synapse with large number of postsynaptic neurons. E.g., important information can be transmitted to many parts of the brain.

Disorders of the Nervous System : 

11-43 Disorders of the Nervous System Multiple sclerosis – common cause of neural disability Varies widely in intensity among those affected Cause is incompletely understood An autoimmune disease Immune system attacks the myelin around axons in the CNS

Neuronal Regeneration : 

11-44 Neuronal Regeneration Neural injuries may cause permanent dysfunction If axons alone are destroyed, cells bodies often survive and the axons may regenerate PNS – macrophages invade and destroy axon distal to the injury Axon filaments grow peripherally from injured site Partial recovery is sometimes possible CNS – neuroglia never form bands to guide regrowing axons and may hinder axon growth with growth-inhibiting chemicals No effective regeneration after injury to the spinal chord and brain

Regeneration of the Peripheral Nerve Fiber : 

11-45 Regeneration of the Peripheral Nerve Fiber