Suzanne D'Anna1 Nervous Tissue

Suzanne D'Anna2 Nervous Tissue n Consists of two main cell types: - neurons - sensory control, and regulation - neuroglia - support, protection, and homeostasis

Suzanne D'Anna3 Parts of a Neuron n cell body n dendrites n axon

Suzanne D'Anna4 Cell Body n contains nucleus, surrounded by granular cytoplasm n contains organelles (i.e., lysosomes, mitochondria, Golgi complex, etc.) n Nissl bodies (chromatophilic substance) - arrangement of rough endoplasmic reticulum (site of protein synthesis) n neurofibril - provides support and shape for cell

Suzanne D'Anna5 Two Kinds of Nerve Fibers n dendrites - neurons usually contain many n axons - neurons contain only one

Suzanne D'Anna6 Dendrites dendro = tree n highly branched processes n not myelinated n extend out from cell body n receive stimuli n carry a nerve impulse toward the cell body

Suzanne D'Anna7 Axon n long, thin, cylindrical projection n may or may not be myelinated n contains mitochondria and neurofibrils but no rough ER; no protein synthesis n cytoplasm - axoplasm n surrounded by axolemma (lemma = sheath or husk) n carries a nerve impulse away to other cells i.e., (nerves, muscles, glands)

Suzanne D'Anna8 Parts of an Axon n long nerve cell fibers are covered with myelin - fatty substance - protects and insulates fibers - increases transmission rate of - nerve impulses - forms myelin sheath

Suzanne D'Anna9 Parts of an Axon (cont.) n neurolemma sheath surrounds myelin n Schwann cells are surrounded by neurolemma - Schwann cells are also called neurolemmocytes n narrow gaps in myelin sheath between adjacent Schwann cells are called nodes of Ranvier

Suzanne D'Anna10 Parts of an Axon (cont.) n axon hillock - cone-shaped elevation where axon joins cell body n initial segment - first portion of axon n trigger zone - junction of the hillock and initial segment where nerve impulses arise

Suzanne D'Anna11 Parts of an Axon (cont.) n axon collateral - side branch along length of axon n axon terminals - fine branched end portions of an axon and its collaterals - when impulse reaches axon terminal, neurotransmitter is released

Suzanne D'Anna12 Parts of an Axon (cont.) n neurons are close to each other but separated by synaptic gap - this junction is called a synapse

Suzanne D'Anna13 Parts of an Axon (cont.) n synaptic end-bulbs - bulb-shaped structures - tips of axons n synaptic vesicles - membrane-enclosed sacs within synaptic end-bulbs - store neurotransmitters (different neurons have different neurotransmitters)

Suzanne D'Anna14 Neuroglia

Suzanne D'Anna15 Neuroglia n constitute one-half of volume of CNS n outnumber neurons 5-50 times n can multiply and divide, unlike neurons n Functions: - nerve glue - supports - insulates - protects

Suzanne D'Anna16 Types of Neuroglial Cells n astrocytes n oliogodendrocytes n microglia n ependymal cells n Schwann cells n satellite cells

Suzanne D'Anna17 Astrocytes (astro = star) n star-shaped n many processes n participate in metabolism of neurotransmitters n maintain potassium (K + ) balance for generation of nerve impulses n participate in brain development n aid in formation of blood-brain barrier n link between neurons and blood vessels

Suzanne D'Anna18 Oliogodendrocytes (oligo = few, dendro = tree) n few processes n smaller than astrocytes n form supporting network by twining around neurons n produce a lipid and protein wrapping called a myelin sheath

Suzanne D'Anna19 Microglia (micro = small, glia = glue) n small n protect CNS from disease n phagocytic - engulf microbes and clear away debris

Suzanne D'Anna20 Ependymal Cells (ependyma = upper garment) n shape ranges from squamous to columnar n may be ciliated n line brain ventricles and central canal of spinal cord ventricles are spaces that produce and circulate cerebrospinal fluid

Suzanne D'Anna21 Schwann Cells (Neurolemmocytes) n found in peripheral nervous system n form myelin sheath n support, protect, and nourish neurons n plasma membrane of neurolemmocytes forms myelin sheath around axon in PNS n myelin sheath insulates speed of impulse transmission

Suzanne D'Anna22 Satellite Cells n found in peripheral nervous system n support neurons in ganglia (clusters of neuron cell bodies) of PNS

Suzanne D'Anna23 Neuron Classification n structural classification - based on number of processes extending from cell body n functional classification - based on direction in which a neuron transmits a nerve impulse

Suzanne D'Anna24 Structural Classification n unipolar (pseudounipolar) - have a single process extending from cell body - always are sensory neurons - originate in embryo as bipolar - during development, axon and dendrite fuse together into a single process - single process divides into two branches a short distance from cell body

Suzanne D'Anna25 Structural Classification n bipolar - have one dendrite and one axon - found in retina, internal ear, and olfactory area of brain n multipolar - several dendrites and one axon - most neurons in brain and spinal cord are of this type

Suzanne D'Anna26 Functional Classification n based on the direction in which a neuron transmits a nerve impulse n Two types of neurons in PNS: - afferent (toward CNS) - efferent (away from CNS)

Suzanne D'Anna27 Afferent n carry impulses (sensory information) toward CNS n also known as sensory neurons Efferent n carry impulses away from CNS n affect activity of muscles or glands n also known as motor neurons

Suzanne D'Anna28 Sensory = Afferent Motor = Efferent

Suzanne D'Anna29 Afferent or Sensory Neurons n Four categories: - general somatic - special somatic - general visceral - special visceral

Suzanne D'Anna30 Afferent or Sensory Neurons (cont.) n general somatic - carry impulses from skin, skeletal muscles, and joints (pain, temperature, touch, vibration, and pressure)

Suzanne D'Anna31 Afferent or Sensory Neurons (cont.) n special somatic - carry or relay impulses from retina and internal ear (vision, hearing, and balance)

Suzanne D'Anna32 Afferent or Sensory Neurons (cont.) n general visceral - carry impulses from internal organs and receptors of body fluids (distension of internal organs and chemical conditions in body)

Suzanne D'Anna33 Afferent or Sensory Neurons (cont.) n special visceral - carry impulses from tongue and olfactory mucosa (taste and smell)

Suzanne D'Anna34 Efferent or Motor Neurons n general somatic - carry impulses to most skeletal muscles n general visceral - carry impulses to smooth muscle, cardiac muscle, and glands n special visceral - carry impulses to skeletal muscles that control facial expression

Suzanne D'Anna35 Associated Neurons n located in CNS n carry impulses from one neuron to another inside brain and spinal cord n establish interrelationship with other neurons forming neuronal circuits