Nervous System

The organs of the nervous system as a whole include:

the brain and spinal cord, the numerous nerves of the body, the specialized sense organ (such as eyes or ears),and the microscopic sense organs found in the skin.  

The nervous system may be organized in two ways:

Structure and by function

The system (structure) as a whole consists of two principal divisions:

The Central nervous system and Peripheral nervous system.

Central nervous system includes

the brain and the spinal cord.

The Central nervous system is named for what reason?

​for the fact that they occupy a midline, or central position in the body.  Nickname is CNS.

Peripheral nervous system

includes the nerves which extend to outlying or peripheral ​parts of the body.  

Cranial nerves

Includes the nerves that come off of the brain; ​12 pairs.

Spinal nerves

nerves that come off of the spinal cord; 31 pairs

Somatic nervous system

aka. voluntary; this system innervates skeletal muscles and controls voluntary functions.

 

Autonomic nervous system

aka. involuntary; this system innervates areas with ​no conscious control, including smooth and cardiac muscles, and some glands.  

Autonomic nervous system organization

This branch of the nervous system may be further subdivided into two groups which usually perform opposing functions.

The two divisions of the autonomic nervous system

Sympathetic and parasympathetic nervous system

Sympathetic nervous system

The “fight or flight” system

Parasympathetic nervous system

the "repair and repose" system, which helps to slow things down.

Together, all parts of the nervous system help to provide  three general functions for the human body

Sensory, integrative and motor

Sensory Function

involves sensory receptors at the ends of peripheral nerves.​

Sensory receptors

are specialized to gather information by detecting changes that happen in and around the body. 

Sensory receptors monitor

factors such as ​light and sound intensity, temperature , and oxygen concentration of the body's internal fluids.

Integrative Function

the information that is gathered by sensory receptors is converted to signals in the form of nerve impulses and are transmitted over peripheral nerves to the CNS.  

Signals are brought together to do what?

create sensations, add to memory, ​or be used to produce thoughts.  As a result, decisions are made and then acted upon.

Integrative function is you doing what?

Observing not always you doing

Motor function

Employs peripheral nerves that carry impulses from the CNS to effectors.

Effectors

Responsive parts

Where effectors are found?

Outside of the nervous system

One of the places effectors can be found

Muscles that may contract when stimulated by nerve impulses.

Another place effectors can be found

Glands that may produce a secretion when stimulated.

What are the two general types of cells found in the nervous system called?

Neurons and Neuroglia

What are neurons and neuroglia?

Specialized connective tissue cells

Neurons

These are the main type of nerve cells but they are not the most numerous.

What are the largest cells in the body?

Neurons

Some neurons may measure almost

2 m or 2.2 yards

Neurons may display what and what does that mean?

Irritability; this means that they are specialized to react to physical and chemical changes in their surroundings.

Neurons may also display what and what does that mean?

Conductivity; which means that they conduct nervous impulses to other neurons and to cells outside the nervous system.

What cell type cannot divide when mature?

Neurons

Three main parts of a neuron

cell body, dendrites, and axons.

Cell body

Contains the nucleus, cytoplasm and nerve fibers.

Dendrites

These are nerve fibers which carry impulses toward the cell body. They are typically short and branched fibers.

Neurons typically have how many dendrites?

Many dendrites

Axons

These are nerve fibers which carry impulses away from the cell body.

What are characterizations of axons?

They are typically longer and any branches axons have exist only at the end of the fiber.

An axon may be wrapped in a

Myelin sheath

Myelin sheath

A fatty insulating layer

What forms the Myelin sheath?

Schwann cells (Special cells)

What does the sheath do for the axons?

It supports, insulates, nourishes and helps maintain the chemical balance of the axons.

Myelinated fibers (not brain or spinal cord)

Axons that have myelinated sheaths.

Myelinated fibers make up what of the nervous system?

White matter of the nervous system

Schwann cells cover only

Axons outside of the CNS

Neurilemma

The outer cell membrane of a Schwann cell

Nodes of Ranvier

Gaps between the Schwann cells which occurred about 1 mm along the myelinated axon.

Nerve impulses are conducted

Rapidly along a myelinated axon

Nerve impulses jump quickly from node to node because

The Myelin acts as a good insulator, covering the axon between nodes.

Axons in the brain and spinal cord have NO what?

Neurilemma

The Neurilemma plays an essential part in what?

Regeneration of injured axons.

Axons in the brain and spinal cord DO NOT what?

Regenerate, but those in the nerves can

Three types of neurons

Sensory, motor and connector

Sensory Neuron function (aka...)

Receive stimuli and send it to the CNS; aka Afferent.

Motor neuron function

Receive impulse from CNS and send it to muscles or glands a.k.a. efferent.

Connector neuron

Links sensory and motor neurons a.k.a. interneurons

Neurons lineup then right to axon but never actually?

Touch

Synapse

The space between ends of neurons

Neurotransmitters

Chemicals by which neurons talk to each other.

What do neurotransmitters do?

They assist, stimulate or inhibit the next neuron.

At least 50 neurotransmitters have been identified, some which include:

acetylcholine,  norepinephrine, ​dopamine, serotonin, endorphins, and enkephalins.

What is the most numerous cell type in the nervous system?

Neuroglia

Neuroglia

Neuroglia have 10 times the number of neurons and are found in the CNS. They do not specialize in the function of transmitting impulses.

Since neuroglia does not specialize in transmitting impulses instead,

they are special types of connective tissue cells.

What is the function of neuroglia cells?

Hold neurons together and protect them

Glia

Greek word for glue

Small microglia

These cells are normally stationary, but when needed they can act as microbe eating scavengers.

What process does do small microglia partake in?

Phagocytosis

Phagocytosis

Small microglia surround microbes, draw them into their cytoplasm, and digest​ them.

Third type of neuroglia

Oligodendroglia

Oligodendroglia

They help hold nerve fiber together, and produce the fatty Myelin sheath that enveloped nerve fibers located in the brain and spinal cord.

For the most part, the nerve fibers within nerves are

axons

Ganglion

a group of cell bodies that are outside the brain and spinal cord

Nerve center

A group of cell bodies that are inside the brain or spinal cord.

The cell bodies of the neurons in a nerve are

Grouped together

A nerve transmits impulses in response to a

Stimulus

How many neurons are stimulated depend upon how

Strong the stimulus is and how many nerve impulses reach the brain.

-how touch is interpreted

Each neuron obeys the

All or none law

Threshold

A stimulus must be of a certain intensity to cause a neuron to initiate a nerve impulse; level of strength

If the stimulus is below this minimum intensity, the neuron

Send no impIlse

If the stimulus exceeds the minimum intensity, any neuron receiving the stimulus will respond by

Sending a nerve impulse

myelinated fibers conduct impulses

more rapidly

Nerves with larger diameters conduct impulses faster than those with

Smaller diameters

Humans =

High threshold

Neuron pathways

Nerve impulses can travel over literally trillions of routes made up of neurons.

Scientific name of neuron pathways

Reflex arcs

Simplest kind of reflex arc

Two neuron arc

Two neuron arc

Consist of two types of neurons, sensory and motor. An example of this would be knee-jerk reflex.

Three neuron arc

They are made up of sensory neurons, motor neurons, and connector neurons. An example of this would be your withdrawal reflex (protector; removing self from danger).

Reflex arcs only allow impulse conduction in

One Direction

Impulse conduction normally starts in

Receptors; found in the beginning of dendrites of sensory neurons.

From the receptors, impulses travel the full length of the sensory neuron’s dendrite through its

Cell body and axon to the branching ends of the axon

The end of the sensory neuron’s axon contact

Connector neurons

Synapse

The space between the axon of the first neuron and dendrite of the next neuron.

After the impulse goes through the synapse, it continues traveling through connector neurons to the

Reflex center (processing center)

Next impulses travel to skeletal muscle cells where they cause the cells to

Contract

The contraction is a response to

Impulse conduction over reflex arcs

Reflex

an automatic subconscious response to stimuli within or outside of the body