Nervous Tissue Suzanne DAnna 1 Nervous Tissue n

Nervous Tissue Suzanne D'Anna 1

Nervous Tissue n Consists of two main cell types: - neurons - sensory control, and regulation - neuroglia - support, protection, and homeostasis Suzanne D'Anna 2

Parts of a Neuron cell body n dendrites n axon n Suzanne D'Anna 3

Cell Body 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 n Suzanne D'Anna 4

Two Kinds of Nerve Fibers dendrites - neurons usually contain many n axons - neurons contain only one n Suzanne D'Anna 5

Dendrites dendro = tree highly branched processes n not myelinated n extend out from cell body n receive stimuli n carry a nerve impulse toward the cell body n Suzanne D'Anna 6

Axon 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) n Suzanne D'Anna 7

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'Anna 8

Parts of an Axon (cont. ) 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 n Suzanne D'Anna 9

Parts of an Axon (cont. ) 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 n Suzanne D'Anna 10

Parts of an Axon (cont. ) 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 n Suzanne D'Anna 11

Parts of an Axon n (cont. ) neurons are close to each other but separated by synaptic gap - this junction is called a synapse Suzanne D'Anna 12

Parts of an Axon (cont. ) 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) n Suzanne D'Anna 13

Neuroglia Suzanne D'Anna 14

Neuroglia 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 n Suzanne D'Anna 15

Types of Neuroglial Cells astrocytes n oliogodendrocytes n microglia n ependymal cells n Schwann cells n satellite cells n Suzanne D'Anna 16

Astrocytes (astro = star) 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 n Suzanne D'Anna 17

Oliogodendrocytes (oligo = few, dendro = tree) 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 n Suzanne D'Anna 18

Microglia (micro = small, glia = glue) small n protect CNS from disease n phagocytic - engulf microbes and clear away debris n Suzanne D'Anna 19

Ependymal Cells (ependyma = upper garment) shape ranges from squamous to columnar n may be ciliated n line brain ventricles and central canal of spinal cord n ventricles are spaces that produce and circulate cerebrospinal fluid Suzanne D'Anna 20

Schwann Cells (Neurolemmocytes) 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 n Suzanne D'Anna 21

Satellite Cells found in peripheral nervous system n support neurons in ganglia (clusters of neuron cell bodies) of PNS n Suzanne D'Anna 22

Neuron Classification 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 n Suzanne D'Anna 23

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'Anna 24

Structural Classification 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 n Suzanne D'Anna 25

Functional Classification 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) n Suzanne D'Anna 26

Afferent carry impulses (sensory information) toward CNS n also known as sensory neurons n Efferent carry impulses away from CNS n affect activity of muscles or glands n also known as motor neurons n Suzanne D'Anna 27

Sensory = Afferent Motor = Efferent Suzanne D'Anna 28

Afferent or Sensory Neurons n Four categories: - general somatic - special somatic - general visceral - special visceral Suzanne D'Anna 29

Afferent or Sensory Neurons n (cont. ) general somatic - carry impulses from skin, skeletal muscles, and joints (pain, temperature, touch, vibration, and pressure) Suzanne D'Anna 30

Afferent or Sensory Neurons n (cont. ) special somatic - carry or relay impulses from retina and internal ear (vision, hearing, and balance) Suzanne D'Anna 31

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'Anna 32

Afferent or Sensory Neurons n (cont. ) special visceral - carry impulses from tongue and olfactory mucosa (taste and smell) Suzanne D'Anna 33

Efferent or Motor Neurons 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 n Suzanne D'Anna 34

Associated Neurons 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 n Suzanne D'Anna 35