Nervous SystemPatrick Yerkes

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

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

Reflex Arc: Identify

•ID motor neuron

•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

Released in certain areas in the Spinal Cord

Also in the neuromuscular junctions Also called nerve-

muscle

CATECHOLAMINE

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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