Patrick Yerkes Nervous System

Introduction The nervous system carries information from one part of the body to another The nervous system transmit information by nerve impulses to communicate with other parts of the body Main parts of the nervous system are the: Brain, Spinal Cord, and Nerves Regulate homeostasis and responds to disease

Organs and Divisions of the Nervous System Central Nervous System (CNS) Occupies the midline or central part of the body Peripheral Nervous System (PNS) Nerves extend to the outlying or peripheral part of the body Autonomic Nervous System (ANS) Regulate the body’s involuntary functions

Cells of the Nervous System Two types of cell: Neurons Nerve cells Conduct nerve impulses Gila Specialized connective tissue cells Support neurons

Neurons Neurons consist of three parts Cell body- main part of the neuron Dendrites- branching projections of the neuron Processes that transmits impulses to the cell bodies Axon- elongated projection Transmits impulses away from the cell body

Transmitted Impulses 3 main types of neurons Sensory- Transmits impulses to the spinal cord and brain from all parts of the body. Also called Afferent. Motor- Transmits impulses away from the brain or spinal cord. Only conduct impulses to two kinds of tissues (muscle and glandular epithelial). Also call Efferent. Interneuron- conduct impulses from the sensory neurons to motor neurons. Also call Central or Connective Neurons Interneuron

Neurons continued Myelin is a white fatty substance formed by a Schwann Cells that wrap the axons around the CNS The fibers are called Myelinated Fibers Nodes of Ranvier are indentations between nearby Schwann Cells The outer cell membrane is the Neurilemma Axons in the brain and spinal cord do not have Neurilemma and decreases healing or regeneration

Gila Also called- Neuroglia Do not specialize in transmitting nerve impulses Are support cells Greek word Gila means “glue” Holds the functions neurons together and protect them Regulates nerve function Common brain tumor is called Glioma

Gila continued Gila can be different in size Large cells that look somewhat like star from their thread like extensions are called- Astrocytes Microglia- are the smaller cells, they remain stationary When inflamed or degenerating brain tissue they will enlarge and act as micro scavengers Eat other micros

Gila continued Oligodenrocytes- hold nerve fibers together and serve a more important function which is to produce fatty myelin sheath that envelops nerve fibers located in the brain or spinal cord

Nerves Nerve- is a group of peripheral nerve fibers bundles together Peripheral nerve fibers usually have myelin sheath Often look white Bundles of axons in the CNS are called tracts The axons could be myelinated and forming white matter Unmyelinated axons and dendrites are called grey matter for being grey

Nerves End Each axon in a nerve is surrounded by thin wrapping fibrous connective tissue called ‘endoneurium’ Groups of endoneurium are called ‘fascicles’ Each fascicle is surrounded by a thin fibrous ‘perineurium’ A tough fibrous sheath is called a ‘epineurium’ which covers the whole nerve

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Reflex Arcs Some nerve impulses are called ‘Action Potentials’ Can travel over trillions of routes Neurons create the paths Routes named Neuron Pathways Reflex Arcs are one way streets, the impulse can only go one way

Reflex Neurons A specialized type of neuron pathway is called the ‘reflex arc’ The simplest kind of reflex arc is a two- neuron arc Consist on only 2 types of neurons: Sensory and Motor neurons Three- neuron arc is the next simplest arc Consist of all 3 neurons: Interneurons, Motor, and Sensory

Reflex Arc: Receptors Are the beginnings of dendrites of sensory neurons Often away from the spinal cord mostly located in; (in tendons, skin, or mucous membranes) Sensory receptors are located in the quadriceps and the patellar tendon Reflex response for the patellar tendon which is the rubber hammer and creates a knee- jerk Example of a two- neuron arc

Reflex Arc: Ganglion A group of nerve- cell bodies located in t he PNS Near the Spinal cord Each spinal ganglion contains no sensory neuron The axon of the sensory neuron travels from the cell body in the dorsal root ganglion Ends in the dendrites of another neuron in the grey matter

Reflex Arc: Continued A microscopic space that separates the axon ending with one neuron from the dendrites to another This is called a Synapse Nerve impulse stops at the synapse The neuron axon forms a synapse called the ‘effectors’ Organs put the nerve signals to effect

Reflex Arc: Effectors Effectors are the muscles and glands Muscles contract The glands secretion Only kind of reflexes by these effectors A response to impulse conduction on the reflex arc is called a reflex

Reflex Arc: Interneuron Some neurons need 3 neurons More complex involves one more sensory and motor neuron In the 3 neuron reflex End of the sensory neurons’ axon synapses first with a interneuron Before chemical signals are sent to a second synapse Ending up with a conduction motor neuron

Reflex Arc: Example Applying an irritating stimulus to the skin of the thigh It creates a 3- neuron reflex response Causes contractions of the muscles to pull away from the leg away from the irritant 3 neuron contraction is also called a - withdrawal reflex

Reflex Arc: Interneurons Continued All interneuron's’ lie entirely within gray matter of the brain or spinal cord Grey matter forms the ‘H’ shaped inner core of the spinal cord 3 neuron reflex has 2 synapses 2 neuron reflexes has 1 synapses between a sensory neuron and the motor neuron

ID motor neuron Reflex Arc: Identify Look at its dendrites and cell body Located in spinal cord Dies in the muscles

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Nerve impulse: Introduction A nerve impulse is a self- propagation wave of electrical disturbance that travels along the surface of a neuron’s plasma membrane. Example A Spark going to fuse

Nerve Impulse: Neuron First they have to be stimulated ( a change in the neuron’s environment) Temperature, Pressure, and chemical changes are used as stimuli Membrane of a resting neuron has a slight positive charge on the outside and a negative charge on the inside This occurs from excessive amounts of sodium ions (NA+) on the outside of the membrane

Nerve Impulses: Neuron continued When the section of the neuron is stimulated and the channels open The sodium ions (NA+) flood inside Causing the membrane to become positive temporarily and then becomes negative The neuron immediately recovers the electrical disturbance stimuli (Na+) If a impulse is traveling interacts with a section of a membrane insulating myelin ‘jumps’ around the myelin called ‘saltatory conduction’ Saltatory Conduction can travel much faster then the nonmyelinated sections

Saltatory Conduction

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Synapse: Introduction By definition a synapse is a place where impulses are transmitted from one neuron called presynaptic neuron to another postsynaptic neuron. The presynaptic and postsynaptic neuron makes up the synapse

Synapse: Structures Three structures of the synapse is: a synaptic knob, a synaptic cleft, and the plasma membrane of a postsynaptic

Synapse: Synaptic Knob Is a tiny bulge at the end of the terminal branch of a presynaptic neuron’s axon Each synaptic knob has many small sacs or vessels Each vessel contains a very some quantity of a chemical compound called a neurotransmitter After the nerve impulse arrives at the synaptic knob neurotransmitters molecules are released from the vesicles into the synaptic cleft

Synapse: Synaptic Cleft Is the space between the plasma membrane (of the postsynaptic neuron) and the synaptic knob About 2 millionths of a centimeters in width Has protein molecules embedded in opposite synaptic knobs The receptors and neurotransmitters bind The binding can cause an impulse in the postsynaptic neuron by opening the ion channels in the postsynaptic membrane

Synapse: Neurotransmitter Neurotransmitters -Chemicals help neurons communicate Around 30 different compounds have been identified as neurotransmitters Neurotransmitters are did sent randomly They are localized in certain types of neuron groups and released in specific pathways

Synapse: Neurotransmitter Sub Groups Acetylcholine catecholamine Released in certain areas in the Spinal Cord Also in the neuromuscular junctions Also called nerve- muscle Includes Norepinephrine Dopamine Serotonin All three of these transmitters play a role for Sleep Motor function Mood Pleasure recognition

Synapse: Sub Groups

Synapse: Pain Killer (Neurotransmitters) 2 ‘morphine’ like N.transmitters are called endorphins and enkephalins Released in multiple areas in the spine and brain in the pain conduction pathways Are natural pain killers Endorphins are released mainly in intense exercise Pain is normally used as a warning sign that draws our attention to injuries Hold back against severe pain because it can stop us from continuing an activity that is needed for survival

Activities to help relieve pain

Synapse: Nitric Oxide Unlike other transmitters Nitric Oxide diffuses directly across the plasma membrane Rather then being released in the vesicles Nitric Oxide is important for the male sexual response to create a penile erection Drugs like Viagra (sildenafil) treats MED or Male Erectile Dysfunction by promoting the Nitric Oxide response

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