Body perceives and responds to multiple sensations Controls multiple muscle movements Others movements without voluntary input e.g., beating of the heart Nervous System Controls and interprets all these sensations and muscle movements
Nervous system Body’s primary communication and control system Integrates and regulates body functions Uses electrical activity transmitted along specialized nervous system cells
Nervous system activities Collects information specialized nervous structures, receptors monitor changes in external and internal environment, stimuli e.g., receptors in the skin detecting information about touch Processes and evaluates information then determines if response required
The nervous system activities (continued) Initiates response to information initiate response via nerves to effectors include muscle tissue and glands e.g., muscle contraction or change in gland secretion
Structural organization: central versus peripheral nervous system Central nervous system anatomic division of the nervous system includes brain and spinal cord brain protected in the skull spinal cord protected in the vertebral canal Peripheral nervous system other anatomic division includes nerves, bundles of neuron processes includes ganglia, clusters of neuron cell bodies
Brain Spinal cord
Cranial Nerves (12 pairs) Spinal Nerves 31 pairs
Functional organization: sensory versus motor nervous system Sensory nervous system also known as afferent nervous system responsible for receiving sensory information from receptors transmits information to the CNS further divided into somatic and visceral sensory
Functional organization: sensory versus motor nervous system (continued) Somatic sensory detects stimuli that we consciously perceive receptors include: eyes and nose tongue and ears skin proprioceptors (receptors detecting body position)
Functional organization: sensory versus motor nervous system (continued) Visceral sensory detects stimuli we do not consciously perceive receptors include: structures within blood vessels structures within internal organs e.g., detecting stretch of organ wall
Functional organization: sensory versus motor nervous system (continued) Motor nervous system also known as efferent nervous system initiates and transmits motor output from CNS transmits information to the effectors may be further divided into the somatic and visceral parts
Functional organization: sensory versus motor nervous system (continued) Somatic motor transmits motor output from CNS to voluntary skeletal muscles effector consciously controlled e.g., pressing on accelerator of your car Autonomic motor transmits output from CNS without conscious control transmits to cardiac muscle, smooth muscle, glands
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Motor nervous system initiates and transmits information from the CNS to effectors Sensory input that is consciously perceived from receptors (e.g., eyes, skin, ears) Sensory input that is not consciously perceived from blood vessels and internal organs (e.g., heart) Sensory nervous system detects stimuli and transmits information from receptors to the CNS Motor output that is consciously or voluntarily controlled; effector is skeletal muscle Motor output that is not consciously or is involuntarily controlled; effectors are cardiac muscle, smooth muscle, and glands Central nervous system (CNS) Peripheral nervous system (PNS) Ganglia Nerves Brain Spinal cord Structural organization Functional organization Autonomic motor Somatic motor Visceral sensory Somatic sensory
Sensory nervous system and the motor nervous system What are the two primary functional divisions of the nervous system? How do they differ? The sensory nervous system detects stimuli and transmits information from receptors to the CNS. The motor nervous system initiates and transmits information from the CNS to effectors.
Two cell types in nervous tissue Neurons basic structural unit of the nervous system excitable cells that transmit electrical signals Glial cells nonexcitable cells that primarily support and protect neurons
Neuron Axon Dendrites Nissl Substance Nucleus of neuron Nucleus of neuroglia
Special characteristics of neurons Excitability responsive to stimulation type dependent on its location most respond only to binding of molecules, neurotransmitters Conductivity electrical charges propagated along membrane can be local and short-lived or self-propagating
Special characteristics of neurons (continued) Secretion release neurotransmitters in response to electrical charges given neuron releasing only one type of neurotransmitter may have excitatory or inhibitory effect on target Extreme longevity most formed before birth still present in advanced age Amitotic mitotic activity lost in most neurons not always the case (e.g., occasionally in hippocampus)
Excitability, conductivity, secretion, extreme longevity, amitotic Name the five distinguishing characteristics of all neurons.
Components of neurons Cell body enclosed by plasma membrane contains cytoplasm surrounding a nucleus neuron’s control center conducts electrical signals to axon perikaryon, cytoplasm within cell body
Axon Hillock Cell body Nucleus Axon Dendrites Nucleolus Nissl substance
Components of neurons (continued) Cell body (continued) nucleus with prominent nucleolus free and bound ribosomes termed chromatophilic substance due to dark staining with basic dyes gray color of gray matter due to chromatophilic substance and lack of myelin
Components of neurons (continued) Dendrites short processes branching off cell body may have one or many receive input and transfer it to cell body more dendrites = more input possible
Components of neurons (continued) Axon longer process emanating from cell body makes contact with other neurons, muscle cells, or glands first part, a triangular region, axon hillock cytoplasm here termed axoplasm plasma membrane here termed axolemma devoid of chromatophilic substance
Components of neurons Axon (continued) gives rise to side branches, axon collaterals branch extensively at distal end into telodendria (axon terminals) at extreme tips, expanded regions, synaptic knobs knobs containing numerous synaptic vesicles contain neurotransmitter
Cytoskeleton Composed of microfilaments, intermediate filaments, microtubules Intermediate filaments, termed neurofilaments aggregate to form bundles, neurofibrils provide tensile strength through the neuron
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dendrite Chromatophilic substance Nucleus Cell body Axon hillock Nucleus of glial cell Axon Dendrites Perikaryon Axon (beneath myelin sheath) Chromatophilic substance Cell body Axon hillock Neurolemmocyte Neurofibril node (b) LM 100x Axon collateral Nucleolus Nucleus Axoplasm Axolemma Neurofibrils Synaptic vesicles containing neuro transmitter Synaptic cleft Postsynaptic neuron (or effector) Synapse (a) Myelin sheath Telodendria Synaptic knobs b: © Ed Reschke
Dendrites conduct electrical signals toward the cell body. They receive input that they transfer to the cell body. What are the functions of dendrites, axon, and neurofibrils ? The axon is used to make contact with other neurons, muscle cells, or gland cells. Neurofibrils give tensile support to neurons.
Structural classification Structural classification of neurons according to number of neuron processes Multipolar neurons most common type have many dendrites and a single axon Bipolar neurons have two processes extending from cell body one dendrite and one axon limited, e.g., in retina of the eye
Soma Dendrites Axon Multipolar Neuron
Structural classification (continued) Unipolar neurons have single short neuron process emerges from cell and branches like a T also called pseudounipolar start out as bipolar neurons during development axons with peripheral process (dendrites to cell body) axons with central process (cell body into CNS)
Structural classification (continued) Anaxonic neurons have dendrites and no axons produce local electrical changes but no action potentials
Functional classification Sensory neurons ( afferent neurons ) neurons of the sensory nervous system conduct input from somatic and visceral receptors most unipolar, few bipolar cell bodies usually in posterior root ganglia, outside CNS Motor neurons (efferent neurons) neurons of the motor nervous system conduct motor output to somatic and visceral effectors all multipolar most cell bodies in CNS
Functional classification (continued) Interneurons (association neurons) entirely within the CNS receive stimulation from many other neurons receive, process, and store information “decide” how body responds to stimuli facilitate communication between sensory and motor neurons 99% of neurons generally multipolar
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Posterior root ganglion Spinal cord Interneuron Motor neuron Skeletal muscle Skin receptors Sensory input Cell body of sensory neuron Sensory neuron Motor output
Multipolar neurons : many dendrites and single axon Bipolar neurons : one dendrite and one axon Unipolar neurons : single short neuron process which branches like a T Anaxonic neurons: dendrites and no axon How are the different processes that extend from a cell body used to structurally classify neurons?
Nerve Cablelike bundle of parallel axons Macroscopic structure Epineurium thick layer of dense irregular connective tissue encloses the entire nerve provides support and protection
Nerve (continued) Perineurium layer of dense irregular connective tissue wraps bundles of axons, fascicles supports blood vessels Endoneurium delicate layer of areolar connective tissue separates and electrically insulates each axon has capillaries that supply the axon
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b: © Dr. Richard Kessel & Dr. Randy Kardon/Tissues & Organs/Visuals Unlimited Fascicle Perineurium Epineurium Nerve Perineurium Fascicle Endoneurium Axon Neurolemmocyte (a) (c) (b) Ganglion Blood vessels Blood vessels Endoneurium Neurolemmocyte Axon Cell bodies Axons Nerve Epineurium Blood vessels Axons SEM 450x
Classification of nerves Structural classification Cranial nerves extend from brain Spinal nerves extend from spinal cord
Cranial Nerves (12 pairs) Spinal Nerves 31 pairs
Classification of nerves (continued) Functional classification Sensory nerves contain only sensory neurons Motor nerves contain primarily motor neurons Mixed nerves contain both sensory and motor neurons most named nerves in this category individual neurons transmitting one type of information
The epineurium encloses the entire nerve. What are the three connective tissue wrappings in a nerve, and what specific structure does each ensheathe ? The perineurium encloses bundles of axons. The endoneurium encloses individual axons.
Synapse Where neuron functionally connected to neuron or effector Two types: chemical and electrical
Skeletal muscle fiber Axon of motor nerve Motor end plate
Chemical synapse Most common Composed of presynaptic neuron, signal producer Composed of postsynaptic neuron, signal receiver Between axon and any portion of postsynaptic neuron most commonly with a dendrite Knob almost touches the postsynaptic neuron narrow fluid filled gap, the synaptic cleft
Primary synaptic cleft Synaptic vesicles of synaptic terminal Secondary synaptic cleft ( junctional folds) Mitochondria of synaptic terminal
Mitochondria Skeletal muscle fiber Primary synaptic cleft Synaptic vesicles Secondary synaptic cleft ( junctional folds)
Transmission at chemical synapse Neurotransmitter molecules released from synaptic knob Released from synaptic vesicles into cleft Diffusion of neurotransmitter across cleft Binding of some neurotransmitters to receptors Synaptic delay time between neurotransmitter release and binding Single postsynaptic neuron often stimulated by more than one neuron
Electrical synapse Much less common Presynaptic and postsynaptic neuron physically bound together Gap junctions present No delay in passing electrical signal In limited regions of brain and eyes
Molecules stored in synaptic vesicles are released from the synaptic knob of a presynaptic neuron into the synaptic cleft. Some neurotransmitter diffuses across the cleft and binds receptors on the postsynaptic membrane. What is the mode of transmission in a chemical synapse?
Glial cells ( neuroglia ) Nonexcitable cells found in CNS and PNS Smaller than neurons Capable of mitosis Far outnumber neurons Half volume of nervous system
Glial cells (continued) Physically protect and nourish neurons Provide physical scaffolding for nervous tissue help guide migrating neurons to their destination Critical for normal function at neural synapses
Glial cells of the CNS Astrocytes Starlike shape from surface projections Processes touching capillary walls and neurons ends termed perivascular feet Most abundant glial cell in CNS
Glial cells of the CNS Astrocytes (continued) Help form the blood-brain barrier feet wrap around capillaries in the brain together form the blood-brain barrier strictly controls substances entering brain nervous tissue from blood protects neurons from toxins allows nutrients to pass
Glial cells of the CNS Astrocytes ( continued ) Regulate tissue fluid composition control movement of substances between blood and interstitial fluid e.g., regulate K + concentration need constant K + level for neuron electrical activity Form a structural network cytoskeleton strengthening and organizing nervous tissue
Glial cells of the CNS Astrocytes (continued) Assist neuronal development direct development of neurons in fetal brain secrete chemicals regulating formation of connections Occupy the space of dying neurons space formerly occupied by dead neurons filled by cells produced by astrocyte division
Glial cells of the CNS (continued) Ependymal cells Line internal cavities of brain and spinal cord Ciliated simple cuboidal or simple columnar epithelial cells Slender processes with extensive branching Form choroid plexus with nearby blood capillaries helps produce cerebrospinal fluid liquid that bathes external CNS and fills internal cavities cilia helping to circulate CSF
Glial cells of the CNS (continued) Microglia Small cells with slender branches Smallest percentage of CNS glial cells Phagocytic cells of the immune system Wander CNS and replicate in infection Engulf infectious agents Remove debris from dead or damaged tissue
Glial cells of the CNS (continued) Oligodendrocytes Large cells with slender extensions Processes ensheathing portions of axons of different neurons Processes repeatedly wrapping around axon Insulate axons in a myelin sheath Prevent passage of ions through axonal membrane Allow for faster action potential propagation through CNS
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Microglial cell Neuron Astrocyte Perivascular feet Capillary Ependymal cells Ventricle of brain (a) CNS glial cells Myelin sheath (cut) Myelinated axon Oligodendrocyte
Glial cells of the PNS Satellite cells Arranged around neuronal cell bodies in a ganglion Physically separate cell bodies in ganglion from surrounding fluid Regulate the exchange of nutrients and waste products e.g., surrounding bodies of sensory neurons in a posterior root ganglion
Glial cells of the PNS (continued) Neurolemmocytes Also known as Schwann cells Ensheathe PNS axons to form myelin sheath Allows for faster action potential propagation See Table 12.2: Glial Cells
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron cell body Neurofibril nodes Axon Nucleus Neurilemma Myelin sheath Neurolemmocyte (b) PNS glial cells Axon Cell body of sensory neuron Posterior root Posterior root ganglion Satellite cells
Microglia If a person suffers from meningitis (an inflammation of the coverings around the brain), which type of glial cell usually replicates in response to the infection?
Neurolemmocytes ( Schwann cells ) Which specific type of glial cell ensheathes axons in the PNS?