Lab Exercise 13 Histology of Nervous Tissue Portland

Lab Exercise 13 Histology of Nervous Tissue Portland Community College BI 231

Major divisions of the nervous system • Central nervous system (CNS)- brain and spinal cord • Peripheral nervous system (PNS)comprises all nerves that connect the brain and spinal cord to muscles, glands and receptors. 2

Nerves • Cranial nerves are those that are connected to the brain • Spinal nerves are connected to the spinal cord. • Both contain sensory information from receptors and send motor signals. 3

Motor (Efferent) Neurons Efferent = Away from CNS • These are neurons that carry information from CNS to the body • Groups of axons running together are the Nerves when they are outside the CNS and Tracts inside the brain and spinal cord • The cell bodies are clustered in groups in the CNS and are called nuclei • Brain gray matter is made up of millions of nuclei. • It is gray because there is no myelin around the cell bodies • These axons exit the spinal cord on the ventral side 4

Motor (efferent) division of PNS • Somatic nervous system- contains efferent neurons extending from the CNS to skeletal muscle. • Autonomic nervous system- contains efferent neurons from CNS to smooth muscle, cardiac muscle and glands 5

Sensory (Afferent) Neurons Afferent = Toward the CNS • These carry sensory information from the body to the CNS (brain and spinal cord) • Their axons run in the same group as the motor neurons (nerves=groups of axons) • Their cell bodies are clustered outside of the spinal cord and are called ganglia • These axons enter the spinal cord on the dorsal side 6

Sensory (afferent) division • Afferent neurons that receive stimuli from somatic sensory receptors that detect general sensations • Receive stimuli from visceral sensory receptors • Special sensory receptors that detect special sensations (smell, taste, vision, hearing, equilibrium) 7

Organization of nervous system 8

Neuron 9

Myelin • Some axons are surrounded by a myelin sheath • Multilayered lipid and protein covering formed by Schwann cells around axons • Oligodendrocytes in the CNS • The covering is the plasma membrane of the Schwann Cell • The Schwann Cell can cover more than one axon • Insulates axon 10

Nodes of Ranvier • Areas between Schwann Cells that do not contain Myelin • Involved in saltatory conduction 11

Dendrit e Nucleus Neuron Cell Body Axon Hillock Axon 12

Schwann Cell Axon Myelin Sheath Node of Ranvier Telodendria Axon Terminal (Synaptic end bulbs) 13

Classification • Sensory (afferent) neurons conduct nerve impulses from sensory receptors • Motor ( efferent) neurons conduct nerve impulses from the CNS • Interneurons form links between sensory and motor 14

Multipolar Neuron Cell Body Axon Dendrites (trigger zone) • Most common type of neuron • Interneurons and motor neurons 15

Anaxonic Neurons • A small number of multipolar neurons contain only dendrites or • Cannot distinguish dendrites from axons • Functions are poorly understood. 16

Bipolar Neuron Dendrite (trigger zone) Cell Body Axon • Location: special senses (smell, vision, hearing) 17

Unipolar Neuron Dendrite (trigger zone) Cell Body Axon • All are sensory afferent • Cell bodies are located in the dorsal root ganglia 18

Association or Interneurons • Neurons between the afferent and efferent neurons. • Are only in the CNS 19

Neuron Fascicle Axon Myelin Sheath Node of Ranvier Perineurium Epineurium 20

Glial Cells • • Associated with neurons Provide Supportive scaffolding Segregate and insulate neurons Outnumber neurons by 10 to 1 21

Supporting Cells in the CNS Astrocytes • Star Shaped • Many functions • Regulates levels of O 2 , • & CO 2 • • Exchanges between capillaries and neurons (blood-brain barrier) • Nutrient transfer 22

Supporting Cells in the CNS Microglia • Protect CNS from disease-causing organisms • Monitor the health of neurons • Act as phagocytes eating microorganisms and debris 23

Ependymal cells • These cells are modified epithelial cells that line the ventricles of the brain and central canal of spinal cord. • Facilitate circulation of CSF 24

Supporting Cells in the CNS Oligodendrocytes • Produce the myelin sheath which provides the electrical insulation for some neurons in the CNS 25

Supporting Cells in the PNS Schwann Cells • Form the myelin sheath around axons in the PNS 26

Satellite cells • Surround neuron cell bodies in peripheral ganglia and regulate levels of oxygen, carbon dioxide and nutrients. 27

The synapse • Axons generate action potentials which are transmitted across synapses • Formed by presynaptic membrane and postsynaptic membrane on an effector cell • The synaptic cleft is a narrow space that separates these 28

The End 29