Ch. 16 Nervous Tissue Flashcards
Parts of Nervous System
nerve: bundle of axons with connective tissue and blood vessels that are located outside the brain and spinal cord
ganglia: small masses of nervous tissue, consisting primarily of neuron cell bodies, located outside the brain and spinal cord
enteric plexuses: networks of neurons located in walls of GI tract organs; regulate digestive system activities
sensory receptors: specialized nerve endings that monitor changes in internal and external environment
Organization of Nervous System
CNS: brain and spinal cord
PNS: cranial nerves emerge from brain, spinal nerves emerge from spinal cord
- sensory/afferent neurons: transmit impulses from sensory receptors to the CNS
- motor/efferent neurons: transmit nerve impulses from CNS to muscles and glands
Function of Nervous System
- sensory function: detect stimuli in internal and external environment and transmit info by sensory neurons to brain or spinal cord
- integrative function: play a role in analyzing the sensory info to provide perception, storing some of it, and making decisions regarding appropriate behaviors
- motor function: respond to integration decisions by initiating actions in effectors, including muscle fibers and glandular cells
Somatic Nervous System
- sensory and motor neurons
- convey info from sensory receptors in skin, skeletal muscles, joints, and for special senses to the CNS
- convey info from CNS to skeletal muscles only resulting in a muscular contraction
Aautonomic Nervous System
- sensory and motor components
- autonomic sensory neurons, convey info from visceral organs to the CNS
- convey info from CNS to smooth muscle, cardiac muscle, and glands and cause the muscles to contract and the glands to secrete
Sympathetic VS Parasympathetic
- “fight or flight”; increase heart rate, support exercise or emergency actions
- “restand-digest” activities; slow down the activities of the organ systems during relaxed situation
Enteric Nervous System
- “brain of the gut”; located in the entire length of the GI tract
- consists of both sensory and motor components
- sensory: monitor chemical changes within the GI tract and stretching of its walls
- motor: govern contraction of GI tract, smooth muscle and secretions of acid from stomach and endocrine cells that secrete horomones
Histology
Nervous tissue: vascular tissue comprised of two types of cells; neurons and neuroglia
neurons: highly specialized cells; lost the ability to undergo mitotic divisions
neuroglia: smaller cells but they greatly outnumber neurons
Functions of neuroglia: support, nourish, protect and maintain the interstitial fluid that bathes them
- neuroglia continue to divide throughout lifetime
Neurons
- possess electrical excitability
- impulse travels rapidly and at a constant strength
- motor neurons cause muscles to contract
- sensory neurons allow you to feel sensations
- impulses travel these great distances at speeds ranging from .5 to 130 meters per second
Pasrts of a Neuron
- cell body (perikaryon): contains nucleus
- Nissl bodies: high levels of protein synthesis
- Lipofuscin: pigment that occurs as clumps of yellowish brown granules in cytoplasm
- Dendrites: “receiving or input portions” of a neuron
- axon: carries nerve impulses toward another neuron, a muscle fiber, or a gland
- axon hillock: cylindrical projection that often joins the cell body at a cone-shaped elevation; site of action potential origin
Nerve Fibers
- impulses arise at junction of axon hillock and initial segment, an area called “trigger zone” and then travel along the axon
- trigger zone is free of Nissi bodies and has numerous voltage-sensitive channels in plasma membrane
- cytoplasm of an axon, called axoplasm, surrounded by plasma membrane known as axolemma
- axon and its collaterals end by dividing into many fine processes called axon terminals (telodendria)
Synapse
- site of communication between two neurons
- presynaptic neuron: lies before synapse and carries a nerve impulse toward a synapse
- postsynaptic: lies after synapse and carries a nerve impulse away from a synapse
- synapses between a muscle and neuron is neurotransmitter junction, synaptic vesicles release the neurotransmitter ACh
Neurotransmitters
- presynaptic neuron releases neurotransmitters into synaptic sleft which act on post cell
Includes: ACh, Aspartate, Glycine, Dopamine, Endorphins, Glutamate, GABA, norepinephrine, Serotonin, Nitric Oxide
Structural Diversity in Neurons
- display great diversity in size and shape
- cell bodies range in diameter from 5-135 micrometers
- few small neurons lack an axon, and many others have very short axons
Types of Neuron Diversity
multipolar: have several dendrites with one axon
bipolar: one main dendrite and one axon
unipolar: sensory neurons have just one process extending from cell body
Neuroglia
- half the volume of CNS
- smaller than neurons
Characteristics: do not generate impulses, ability to multiply and divide in mature nervous system
6 types: astrocytes, oligodendrocytes, microglia, ependymal cells found in CNS; Schwann cells and satellite cell in PNS
Astrocytes
protoplasmic astrocytes found in grey matter and fibrous astrocytes in white matter
- make contact with blood capillaries, neurons, and the pia matter
Function of Astrocytes
- microfilaments provide strength to support neurons
- wrapped around blood capillaries secrete chemicals that maintain unique permability of the endothelial cells
- in embryo, secrete chemicals that regulate growth, migration and interconnections amoung neurons in brain
- maintain appropriate chemical environment for generation of nerve impulses
- play a role in learning and memory by influencing the formation of neural synapses
Oligodendrocytes
- oligodendrocyte have process that forms the myelin sheath, lipid and protein covering around some axons
- myelin sheath insulates the axon and increases the speed of nerve impulse conduction
Microglia
- develop neural tube in embryo; originate in red bone marrow and migrate into CNS as it develops
- phagocytes functions that remove cellular debris, microbes and damaged nervous tissue
Ependymal Cells
- line ventricles of the brain and central canal of spinal cord
- produce, possibly monitor, and assist in circulation of CSF
- form blood-cerebrospinal fluid barrier
Neuroglia of PNS
Schwann cells/neurolemmocytes: encircle PNS axons and form the myelin sheath around them; schwann cells participate in axon regeneration
satellite cells: surround cell bodies of neurons of PNS ganglia; regulate exchange of material between neuronal cell bodies and interstitial fluid
Myelinated and Unmyelinated Axons
- axons surrounded by multilayered lipid and protein covering is called myelin sheath= myelinated
- 2 types: schwann cells and olgiodendrocytes
