Nervous Tissue

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Endocrine system

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A system which communicates by means of chemical Messengers secreted into the blood

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Nervous system

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A system which employs electrical and chemical means to send messages very quickly from cell to cell

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Central nervous system

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Consists of the brain and spinal cord which are enclosed and protected by the cranium and vertebral column

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Peripheral nervous system

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Consists of all the rest and is composed of nerve and ganglia

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Nerve

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A bundle of nerve fibers wrapped in fibrous connective tissue also called an axon

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Ganglion

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A knot like swelling in a nerve where the cell body of peripheral neuron cells are concentrated

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Sensory division or afferent division

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Carries signals from various receptors to the CNS this pathway and forms the CNS of stimuli with in and around the body

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Receptors

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Sense organs and simple sensory nerve endings

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Somatic sensory division

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Carries signals from receptors in the skin, muscle, Bone, and Joint

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Visceral sensory division

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Carries signals mainly from the viscera of the thoracic and abdominal cavities such as the heart lungs stomach and urinary bladder

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Motor division or efferent division

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Carries signals from the CNS mainly to gland and muscle cells that carry out the body's responses. cells and organs that respond to the signals are called effectors

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Somatic motor division

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Carries signals to the skeletal muscle this produces voluntary muscle contractions as well as involuntary somatic reflexes

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Visceral motor division or autonomic nervous system

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Carries signals to glands cardiac muscle and smooth muscle we usually have no voluntary control over these effectors and the ANS operates at an unconscious level

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Visceral reflexes

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The response of the ANS and its effectors

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Sympathetic division

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Tends to arouse the body for Action by accelerating the heartbeat and increasing respiratory air flow but inhibits digestion

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Parasympathetic division

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Tends to have a calming effect slowing the heartbeat but it stimulates digestion

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Excitability

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All cells are excitable. They respond to environmentall changes. Neurons exhibit this property to the highest degree

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Conductivity

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Neurons respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations

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Stimuli

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Environmental changes

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Sensory neurons, interneurons, motor neurons

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Three types of neurons

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Sensory neurons or afferent neurons

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Specialized to detect stimuli such as light heat pressure and chemicals and transmit information about them to the CNS afferent refers to Signal conduction toward the CNS

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Interneurons

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Lie entirely within the CNS they receive signals from many other neurons and carry out the integrative functions of the nervous system

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Motor neurons or efferent neurons

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Send signals predominantly to muscle and gland cells the effectors

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Neurosoma

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The control center of the neuron also called the Soma or cell body

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Neurofibrils

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Bundles of actin filaments

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Dendrites

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The primary site for receiving signals from other neurons

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Multipolar neurons

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Have one axon and multiple dendrites this is the most common type and includes most neurons of the brain and spinal cord

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Bipolar neurons

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Have one axon and one dendrite examples include olfactory cells of the nose certain neurons of the retina and sensory neurons of the ear

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Unipolar neurons

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Have only a single process leading away from the Soma they are represented by neurons that carry signals to the spinal cord for such senses as touch and pain

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Anaxonic neurons

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Have multiple dendrites but no Axon they communicate locally through their dendrites and do not produce Action potentials

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Axonal transport

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The two-way passage of proteins organelles and other materials along an axon

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Anterograde transport

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Movement away from the Soma down the Axon

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Retrograde transport

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Movement up the axon towards the Soma

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Fast axonal transport

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Occurs at a rate of 200 to 500 millimeters per day and maybe either anterograde or retrograde

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Slow axonal transport

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Is an anterograde process that works in a stop-and-go fashion

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Neuroglia or glial cell

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Protect the neurons and help them function. Define neurons together and provide a supportive framework for the nervous tissue

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Oligodendrocytes, ependymal cells, microglia, astrocytes, Schwann cells, satellite cells

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Types of neuroglia

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Oligodendrocytes

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Have a bulbous body with as many as 15 arms. Each arm reaches out to a nerve fiber and spirals around it like electrical tape. This rapping, called the myelin sheath, insulates the nerve fiber from extracellular fluid.

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Ependymal

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Resembles a cuboidal epithelium lining the internal cavity of the brain and spinal cord. Produce cerebrospinal fluid.

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Microglia

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Small macrophages that develop from white blood cells called monocytes. Wander throughout the CNS, putting out extensions to constantly probe for cellular debris or other problems.

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Astrocytes

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The most abundant glial cell in the CNS and constitutes over 90% of the tissue in some areas of the brain. They cover the entire brain surface and most non synaptic regions of the neuron in the gray matter.

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Schwann cells

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wine repeatedly around a nerve fiber and produces a myelin sheath similar to one produce by oligodendrocytes. Functions in the pns

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Satellite cells

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Surround the Soma and ganglia of the pns. They provide insulation around the Soma and regulate the chemical environment of the neurons

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Myelin sheath

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A spiral layer of insulation around a nerve fiber formed by oligodendrocytes in the CNS and Schwann cells in the pns

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Node of ranvier

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Gaps between segments of myelin sheath

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Internode's

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The Milan covered segment from each node

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Electrical potential

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A difference in the concentration of charged particles between one point and another. A form of potential energy that can produce current

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Electrical current

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A flow of charged particles from one point to another.

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Polarized

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A unit that has a potential

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Resting membrane potential

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The charge difference across the plasma membrane

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Local potential

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Incoming sodium diffuses for short distances along the inside of the plasma membrane, creating of wave of excitation that spreads out from the point of stimulation, like ripples spreading across the pond.

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Graded

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Varying and magnitude or voltage according to the strength of the stimulus

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Action potential

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A dramatic change produced by voltage-gated ion channels in the plasma membrane

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All or none law

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If a stimulus depolarizes the neuron to threshold, the neuron Fires at its maximum voltage, if the threshold is not reached, then you're on does not fire at all.

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Non decremental

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Action potentials do not get weaker with distance. The last potential action at the end of a nerve fiber is just as strong as the first one in the trigger Zone.

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Irreversible

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If a neuron reaches threshold, the action potential goes to completion. It cannot be stopped once it begins

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Refractory period

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The period of resistance to restimulation

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Continuous conduction

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Found an unmyelinated fibers where the action potential occurs at the trigger Zone enters the axon and the fuses for a short distance just beneath the plasma membrane. By repetition this excites the membrane immediately distal to it. This Chain Reaction continues until the traveling signal reaches the end of the Axon

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Saltatory conduction

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Fibers that cannot conduct a signal in continuous mode therefore no action potential can occur

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Endoneurium

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If then sleep a fibrous connective tissue that surrounds fibers and The PNS. Nerve fibers in the CNS lack this tissue

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Axon hillock

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A mound from which the axon originates

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Axon collaterals

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Branches near the Soma

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Axoplasm

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The cytoplasm of the Axon

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Axolemma

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The membrane of the Axon

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Axon collateral

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Branch that originates from an axon

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Axonal transport

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The passage of proteins, organelles, and other materials along an axon

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Hyperpolarization

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A shift in membrane voltage to a value that is more negative than the resting membrane potential

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Synaptic knobs

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The small swellings at the distal end of the axon of a neuron that contains synaptic vesicles

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Depolarization

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A term that refers to the upward change in membrane potential during an action potential

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Cholinergic synapse

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Employees acetylcholine as its neurotransmitter