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Nerve Tissue   14th lecture February 25, 2016.

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Presentation on theme: "Nerve Tissue   14th lecture February 25, 2016."— Presentation transcript:

1 Nerve Tissue 14th lecture February 25, 2016

2 Nervous Tissue Controls and integrates all body activities within limits that maintain life Three basic functions sensing changes with sensory receptors interpreting and remembering those changes reacting to those changes with effectors Controls and integrates all body activities within limits that maintain life Three basic functions sensing changes with sensory receptors fullness of stomach or sun on your face transport sensory information from skin, muscles, joints, sense organs & viscera to CNS interpreting and remembering those changes connect sensory to motor neurons 90% of neurons in the body reacting to those changes with effectors muscular contractions glandular secretions Lecutre 8: Nervous System

3 Major Structures of the Nervous System
Brain spinal cord cranial nerves spinal nerves ganglia enteric plexuses sensory receptors

4 Subdivisions of the PNS
Central nervous system (CNS) Peripheral nervous system (PNS) a) Somatic (voluntary) nervous system (SNS) neurons from cutaneous and special sensory receptors to the CNS motor neurons to skeletal muscle tissue Lecutre 8: Nervous System

5 Subdivisions of the PNS
b) Autonomic (involuntary) nervous systems (ANS) sensory neurons from visceral organs to CNS motor neurons to smooth & cardiac muscle and glands sympathetic division (speeds up heart rate) parasympathetic division (slow down heart rate) c) Enteric nervous system (ENS) involuntary sensory & motor neurons control GI tract neurons function independently of ANS & CNS

6 Neurons Functional unit of nervous system
Have capacity to produce action potentials electrical excitability

7 Neurons Cell body: single nucleus with prominent nucleolus
Nissl bodies (chromatophilic substance) rough ER & free ribosomes for protein synthesis neurofilaments give cell shape and support microtubules move material inside cell lipofuscin pigment clumps (harmless aging) 2. Cell processes = dendrites & axons Lecutre 8: Nervous System

8 Dendrites Conducts impulses towards the cell body
Typically short, highly branched & unmyelinated Surfaces specialized for contact with other neurons Contains neurofibrils & Nissl bodies impulse

9 Axons Conduct impulses away from cell body
Long, thin cylindrical process of cell Arises at axon hillock Impulses arise from initial segment (trigger zone) Side branches (collaterals) end in fine processes called axon terminals Swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters

10 Structural Classification of Neurons
Based on number of processes found on cell body multipolar = several dendrites & one axon most common cell type bipolar neurons = one main dendrite & one axon found in retina, inner ear & olfactory unipolar neurons = one process only(develops from a bipolar) are always sensory neurons

11 Structural Classification of Neurons
Based on number of processes found on cell body multipolar = several dendrites & one axon most common cell type bipolar neurons = one main dendrite & one axon found in retina, inner ear & olfactory unipolar neurons = one process only(develops from a bipolar) are always sensory neurons

12 Structural Classification of Neurons
Based on number of processes found on cell body multipolar = several dendrites & one axon most common cell type bipolar neurons = one main dendrite & one axon found in retina, inner ear & olfactory unipolar neurons = one process only(develops from a bipolar) are always sensory neurons

13 Association or Interneurons
Named for histologist that first described them or their appearance

14 Neuroglial Cells Half of the volume of the CNS
Smaller cells than neurons 50X more numerous Cells can divide rapid mitosis in tumor formation (gliomas) 4 cell types in CNS astrocytes, oligodendrocytes, microglia & ependymal 2 cell types in PNS schwann and satellite cells

15 Neuroglial Cells (CNS): Astrocytes
Star-shaped cells Form blood-brain barrier by covering blood capillaries Metabolize neurotransmitters Regulate K+ balance Provide structural support

16 Neuroglial Cells (CNS): Oligodendrocytes
Most common glial cell type Each forms myelin sheath around more than one axons in CNS Analogous to Schwann cells of PNS

17 Neuroglial Cells (CNS): Microglia
Small cells found near blood vessels Phagocytic role -- clear away dead cells Derived from cells that also gave rise to macrophages & monocytes

18 Neuroglial Cells (CNS): Ependymal cells
Form epithelial membrane lining cerebral cavities & central canal Produce cerebrospinal fluid (CSF)

19 Neuroglial Cells (PNS): Satellite Cells
Flat cells surrounding neuronal cell bodies in peripheral ganglia Support neurons in the PNS ganglia

20 Neuroglial Cells (PNS): Schwann Cell
Cells encircling PNS axons Each cell produces part of the myelin sheath surrounding an axon in the PNS

21 Increase speed of nerve impulse
Myelination Insulation of axon Increase speed of nerve impulse

22 Myelination: PNS All axons surrounded by a lipid & protein covering (myelin sheath) produced by Schwann cells Neurilemma is cytoplasm & nucleus of Schwann cell gaps called nodes of Ranvier Myelinated fibers Unmyelinated fibers Node of Ranvier All axons surrounded by a lipid & protein covering (myelin sheath) produced by Schwann cells Neurilemma is cytoplasm & nucleus of Schwann cell gaps called nodes of Ranvier Myelinated fibers appear white jelly-roll like wrappings made of lipoprotein = myelin acts as electrical insulator speeds conduction of nerve impulses Unmyelinated fibers slow, small diameter fibers only surrounded by neurilemma but no myelin sheath wrapping Lecutre 8: Nervous System

23 Myelination: PNS Schwann cells myelinate (wrap around) axons in the PNS during fetal development Schwann cell cytoplasm & nucleus forms outermost layer of neurolemma with inner portion being the myelin sheath Tube guides growing axons that are repairing themselves

24 Myelination: CNS Oligodendrocytes myelinate axons in the CNS
Broad, flat cell processes wrap about CNS axons, but the cell bodies do not surround the axons No neurilemma is formed Little regrowth after injury is possible due to the lack of a distinct tube or neurilemma

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