Nervous System

NERVOUS SYSTEM

ORGANIZATION:

1. 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.  

2. The nervous system may be organized in two ways: by structure and by function.

Structure:

3. The system (structure) as a whole consists of two principal divisions: The Central nervous

4. Central nervous system: includes the brain and the spinal cord.

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

2.​____________________________________________: includes the nerves which extend to outlying or peripheral ​parts of the body.  Includes the nerves that come  off of the ________________ (called ____________________; ​_____ pairs) and nerves that come off of the _________________________________ (called

​_______________________; _____ pairs).

Function:

1.​______________________________________: aka. ______________________; this system innervates ​_______________________ muscles and controls voluntary functions.

2.​_______________________________________: aka. _____________________; this system innervates areas with ​no ____________________________________, including smooth and cardiac muscles, and some glands.   This ​branch of the nervous system may be further subdivided into two groups which usually perform_______________.

​a. ​______________________________: the "fight or flight" system

​b.​______________________________: 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:

1.​_______________________________

2.​_______________________________

3.​_______________________________

FUNCTIONS OF THE NERVOUS SYSTEM:

1.​Sensory Function:  involves sensory _______________________ at the ends of ___________________________.​These ______________________ are specialized to gather information by ________________________________

​________________________________________________________________.   They monitor factors such as ​____________ and _____________ intensity, ____________________________, and ________________ ​concentration of the body's internal fluids.

2.​Integrative Function: the information that is gathered by sensory receptors is converted to signals in the form of ​____________________________________ and are transmitted over _____________________________________

​to the CNS.  These signals are brought together creating ___________________, adding to ___________________, ​or being used to produce ____________.  As a result, decisions are made and then acted upon.

3.​Motor Function: employs peripheral nerves that carry impulses from the CNS to​responsive parts called ​_______________________.  These are found outside of the nervous system and include _____________________ ​that may contract when stimulated by nerve impulses and __________________ that mayproduce a secretion when ​stimulated.

CELL TYPES:

The two general types of cells found in the nervous system are called ________________ and ________________________, which are specialized connective tissue cells.

1.​Neurons:  these are the main type of nerve cells, but they are not the most numerous.  Neurons are the largest cells ​in the body.  Some neurons may measure almost __________ ( _______).  

​

​Neurons display ______________________________.  This means that they are specialized to react to ​__________________ and _________________ changes in their surroundings.  Neurons also display ​____________________________,  which means that they conduct nervous impulses to other neurons and to cells

​outside of the nervous system.  

​Neurons cannot _____________________ when mature.

​Each neuron consists of three main parts:

​a. ___________________________: contains the nucleus, cytoplasm, and threadlike extensions of cytoplasm called ​  ​    ___________________________.

​b. ____________________________: these are nerve fibers which carry impulses  ____________________ the cell         ​    body.  They are typically _______________,   _______________________ fibers.  Neurons typically have​    ​    _________________________________________.

​c. ____________________________: these are nerve fibers which carry impulses ____________________ the cell ​  ​    body.  They are typically ________________ and any branches axons have exist only _____________________.

​    An axon may be wrapped in a fatty insulating layer known as a __________________________________.  The ​ ​    sheath is formed by special cells known as _______________________________.  The sheath ______________,

​    __________________________, and _______________________ the axons.   It also helps maintain the ​  ​    __________________________________________ of the axon.  Axons which have these sheaths are called ​ ​    __________________ ________________________.  They make up the so-called _______________

​    matter of the nervous system.  

​Schwann cells cover only axons __________________ of the CNS.  The outer cell membrane of a Schwann cell is ​called    the _________________________.  Gaps between the Schwann cells, called the ​___________________________ occur about every ________ ( ________) along the myelinated axon.  Nerve ​impulses are conducted rapidly along a myelinated axon.  Nervous impulses jump quickly from node to node ​because the myelin acts as a good_____________________, covering the axon between nodes.  

The fact that axons in the brain and spinal cord have no __________________ is important to note.  The ​_______________________ plays an essential part in the ​_____________________________________________________.

​ Therefore axons in the brain and spinal cord do not ____________________, but those in nerves do.

There are three types of neurons:

​1.​_____________________ (receive stimuli and send it to the CNS; aka.______________________)

​2.​_____________________ (receive impulse from CNS and send it to muscles or glands; aka. ​__________________________)

​3.​_____________________ (links sensory and motor neurons; aka. interneurons)

​

​Neurons line up ______________________ to ____________________, but never actually touch.  The space ​between ends of neurons is called the ____________________________.

​Chemicals by which neurons talk to each other are called_________________________________.  These ​___________________, _____________________________, or ______________________ the next neuron.  At ​least __________ of these chemicals have been identified.  Examples include acetylcholine,  norepinephrine, ​dopamine, serotonin, endorphins, and enkephalins.

2.​Neuroglia:  this type of cell is the most numerous in the nervous system, with _____________ the number of ​neurons.  Neuroglia are found in the CNS.  They do not specialize in the function of transmitting impulses.  Instead, ​they are​special types of _____________________________.  The Greek word glia means glue; one function of ​neuroglial cells is to  ___________________________________________________________________________.

​Neuroglias vary in size and shape.  Some are relatively large and look somewhat like stars.  These cells are called ​_________________________.  Another type of neuroglia are the small ________________________.  These cells ​are normally stationary, but when needed they can act as ______________________________scavengers.  They ​surround microbes, draw them into their cytoplasm, and digest​ them.  The name for this process is ​____________________________________.  A third type of neuroglia are the _____________________________.  

​They help to hold ______________________ together, and they produce the _______________________________ ​that envelops nerve fibers located in the ___________________ and _____________________________.  

NERVES:

A nerve in the body consists of a large number of ___________________________ bound together by a sheath of _____________________________________.  For the most part, these fibers are ________________.  The axons of some neurons extend forseveral feet.  The cell bodies of the neurons in a nerve are grouped together.  If the group of cell bodies is ______________________________________________, the group is called a _________________________.  If the group of cell bodies is_____________________________________________, the group is called a ________________________.

A nerve transmits impulses in response to a __________________________.  How many neurons are stimulated depends upon how _____________________________.  This also determines how many nerve impulses reach the _______________.  

Each neuron obeys the __________________________________ law.  A stimulus must be of a certain ______________________ to cause a neuron to initiate a nerve impulse.  This level of strength is called a _______________.  If the stimulus is below this minimum intensity, the neuron ______________________________________________.

If the stimulus exceeds the minimum intensity, any neuron receiving the stimulus will respond by _________________________________________.  If the stimulus continues, the neuron will send a second impulse, third impulse, etc.  _____________________________________ conduct impulses over their entire surfaces.  ____________________________________ conduct impulses more rapidly.  Nerves with _________________________________ conduct impulses faster than those with ___________________________.

REFLEX ARCS  

Nerve impulses can travel over literally trillions of routes made up of neurons.  Sometimes these routes are referred to as _____________________________.  Their scientific name is ____________________.

The simplest kind of reflex arc is a ________________________________.  It is called this because it only consists of two types of neurons: __________________ and_______________________.  An example would be the __________________.

______________________________ are the next simplest kind of reflex arc.  They are made up of ______________neurons, __________________________neurons, and ____________________________________.  An example of this would be the

_________________________________, and is considered ____________________ in nature.

Reflex arcs are like one-way streets: they allow impulse conduction ________________

________________________.  

Impulse conduction normally starts in ____________________, found in the beginnings of ____________________ of ____________________ neurons.  These receptors are often located at some distance from the spinal cord.  From the receptors, impulses travel the full length of the sensory neuron's dendrite, through its _____________________ and

_______________, to the branching ________________________________.  The ends of the sensory neuron's axon contact _______________________________.   The impulse must now cross the space between the axon of the first neuron and the dendrite of the next neuron, called the __________________.  Afterwards, the impulse continues traveling through connector neurons to the ___________________________ within the CNS.  This area serves as a ________________________________.  Next, impulses travel to skeletal muscle cells where they cause the cells to __________________.  This contraction is a response to impulse conduction over reflex arcs.  It is properly

called a ___________________, and is an automatic subconscious response to stimuli within or outside of the body.  ____________________________________ and ____________________________ are the only two kind of reflexes.

 THE CENTRAL NERVOUS SYSTEM:

THE BRAIN:

The brain is the ________________________ for the human body.  It is composed of over ___________________ ​nerve cells that __________________ and ______________________ body activities, and enable human beings to

__________________.  The human brain weighs about _________________ in ​the average 18-20 year old adult.  It is one of the largest organs in the body.  Growth of the brain occurs as neurons grow in ______________, not in

______________________.  The surface of the brain is ____________________ which consists of about 6 million ​cell bodies and their dendrites packed into each ________________________ (0.06 cu. in.).  Under the gray matter ​is___________________________ formed from __________________________.

The brain is composed of three major structures: _________________________, __________________________, ​and ____________________________.  Though each area seems to control separate functions, they are all interdependent.

1.​___________________________:  this portion of the brain makes up about _____ of the total brain weight.  The ​outer surface is covered with ridges and grooves called ______________ (ridges) and ______________________ ​(grooves).  The deepest fissure runs longitudinally and divides the cerebrum into two sides called

​the ___________________________.  These two sides are joined by a bridge of

​________________________________________.  The bridge-like structure is known as the ​_________________________________.  Shallower fissures (called _____________) divide each hemisphere into ​four major lobes.  The lobes are named for _____________________________________.  The four areas are the ​____________________________,  the ________________________, the__________________________ , and the ​__________________ lobes.  

​The gray matter of the cerebrum is called the ____________________________.  Its main function is to receive ​sensory impulses from the body and coordinate motor responses to them. Its many ridges and valleys, called ​_________________ greatly increase the ________________________ of the brain.  Each area on thesection called ​the _____________________________ controls the movement of muscles in a specific part of the body.  Each area ​of the _____________________ receives impulses from a specific part of the body.  The area devoted to each body

​part is proportional to its _______________________ or ____________________ not its size.  

​White matter, made up of bundles of nerve fibers, composes most of the interior of the cerebrum.  Within this white ​matter are a few islands of gray matter, known as ______________________, whose functioning is essential for ​producing our_________________________________.  _______________________________ is a disease of the ​basal ganglia.

​Each hemisphere controls the actions and sensations on the __________________________________. However, in ​most people one side of the cerebrum is the _________________________________.  The left hemisphere is ​dominant in _____% of right-handed adults and in _____% of left handed adults.  The right hemisphere is dominant ​in _____% of right-handed adults and in _____% left-handed adults.  The hemispheres are equally dominant in the ​remaining _____% of the population.  

​Several important structures lie within the cerebrum.  On each side of the brain is the _______________, which is a ​small organ that acts as a ____________________________________________.  It also coordinates messages ​from sense organs.   Below the thalamus is the _______________________________.  This structure controls ​____________________________, __________, _______________, ________________________________, and ​______________________________.

2.​_________________________________________: located beneath the ​____________________ lobe.  ​This portion of the brain coordinates ___________________________________ and _______________________.  ​Damage to this area may result in loss of ____________________________.

3.​___________________________________: contains all the nerves that connect ​ the _________________________ ​with the ___________________________.​The principal divisions of the brain stem are the ​__________________________, the _______________, and the __________________________.  The enlarged

​portion of the spinal cord that enters the lower skull is the __________________​_____________________.  It ​controls ____________________, _____________,​___________________________, and the action of the ​_______________ and __________________________.  Many nerve fibers crisscross in this portion

​of the brain stem, and as a result, each hemisphere receives impulses from and sends impulses to the opposite side of ​the body.  The pons connects the _______________________________ of the cerebellum and links the

​cerebellum with the ___________________.  The ____________________ lies above the pons.  It controls ​responses to _________________, such as ______________________ and ________________________________.

A complex network of nerve fibers called the _____________________________  runs through the brain stem and thalamus.  This structure plays an essential role in  ______________________________, ​____________________________, and __________________.  The reticular system activates the rest of the brain when a stimulus is received.  It first filters the stimulus, though, which explains why, forexample, people can sleep through loud noises coming from a television but awaken when a telephone rings.

Protection:  The brain is protected in three ways: 1) _______________________, 2) _______________________________, and 3) _________________________. _________________________________ is the fluid which circulates around

the brain and spinal cord.  It forms from fluid filtering out of _______________​in brain capillaries called ____________________________. This fluid helps to cushion the brain inside of the skull.  Three layers of tissue know collectively as meninges protect the surface of the brain.  The innermost layer, called the______________, follows all brain convolutions.  Its rich blood supply carries ___________________ and ___________________ to the brain cells and

carries away waste products.  The middle layer, the _______________________, is a delicate weblike structure.  Fluid between the pia mater and arachnoid serves as a pathway for __________________________________________________.

The outermost layer is a tough fibrous membrane called the _________________.

THE SPINAL CORD

The spinal cord is a column of nerve tissue extending from the ________________ to the bottom of the _________________________________ (lumbar vertebrae are the last 5 vertebrae).  In a person of average height, the spinal cord is approximately ___________ long and as thick as a pencil.  The spinal cord links the brain with nerves to all parts of the body and controls ____________________________ known as ________________.

The center of the cord is _______________________.  It consists of ________________ and so is composed mainly of __________________ and _________________________.  Columns of _____________________ form the outer portion of the cord, and bundles of myelinated nerve fibers, called the __________________________, make up the white columns.  

The spinal cord has two functions:

1.​acts as a ________________________, processing withdrawal reflexes and jerk ​reflexes.

2.​relays messages to and from the brain through two-way conduction paths to and ​from the brain

​a. __________________________: conducts impulses up the cord to the brain; transmits __________________ ​   ​    impulses.

​b. __________________________: conducts impulses down the cord from the brain; transmits ​ ​  ​ ​    ____________________ impulses. 

Examples of Spinal Tracts:

1.  lateral and ventral spinothalamic: sensations of _______________________________

2.  gracilis and cuneate: sensations of ____________________________

3.  lateral and ventral corticospinal: _____________________________

4.  lateral and medial reticulospinal: __________________________________

The spinal cord is protected by the _______________________, ___________________,

and _______________________________________.

If an injury cuts the cord all the way across, impulses can no longer travel to the brain from any part of the body located __________________________________, nor can they travel from the brain down to these parts.  This kind of spinal cord injury produces both a loss of sensation, which is called _______________________, and a loss of the ability to make voluntary movements, which is called ________________________.

  THE PERIPHERAL NERVOUS SYSTEM

The peripheral nervous system carries impulses to and from the central nervous system.  There are ______ pairs of __________________________ which connect the brain primarily with ___________________________, the _________________, and other ___________________________.  There are ______ pairs of _____________________ which carry impulses between the ________________________ and ________________ muscles.  Nerves that conduct impulses into the brain or spinal cord are called ________________ nerves.  Those that carry impulses out to muscles or glands are called ____________ nerves.  Most nerves, however, include both sensory and motor fibers, and they are called _____________ nerves.

A.​SPINAL NERVES

​Thirty-one pairs of nerves attach to the spinal cord in the following order: _____ pairs attach to the cervical ​segments, ______ pairs attach to the thoracic segments, _____ pairs attach to the lumbar segments, _____ pairs ​attach to the sacrospinal segments, and ____ pair attaches to the cocccygeal segment.  Spinal nerves have no special ​names; instead, a _______________ and _____________ identify each one.  They are named for the vertebrae ​superior to them, and the number for the segment of that part of the spinal cord.  

​C  =  _______________ segments

​T  =  ________________ segments

​L  =  ________________ segments

​S  = _________________ segments

​

For example: T8  is the eighth part of the thoracic segment.

​Spinal nerves contain both sensory and motor fibers, and therefore, function to make both ​_______________________ and _________________________.   Spinal nerves are referred to as ​________________________.  A disease or injury that prevents conduction by a spinal nerve results in both a loss

​of ___________________ and a loss of _____________________ in the part supplied by that nerve.

​Detailed mapping of the skin surface reveals a close relationship between the source on the cord of each spinal ​nerve and the level of the body it innervates.   A neurologist can identify the site of a spinal cord or nerve ​abnormality from the  area of the body that is _____________________________________________.

​Skin surface areas supplied by a single spinal nerve are called _______________.

​

​____________________ is an inflammation of the spinal nerve branch called the  sciatic nerve, the ​_______________ nerve in the body.  _________________ is​another painful, common spinal nerve inflammation; ​it is a ______________ infection that almost always affects the skin of a __________________________.

B. ​CRANIAL NERVES

​Twelve pairs (each has a _______ and a ____________) of cranial nerves attach to the underside of the brain, ​mostly from the ________________________.  These nerves conduct impulses between the _________________ ​and the ​various structures in the _____________ and _____________, and in the ________________ and ​__________________ cavities.  

Nerve​Conducts Impulses​Functions

I Olfactory (S)​​from nose to brain​olfaction (smell)

II Optic (S)​from eye to brain​​eye movements

III Oculomotor (M)​from brain to eye muscles​​eye movements

IV Trochlear (M)​​from brain to external eye muscles​​eye movements

V Trigeminal (Mi)​from skin and mucous membrane of ​sensations of face,

   (largest; 3 parts:​head and from to teeth to brain; also ​scalp, teeth, chewing

    ophthalmic,​from brain to chewing muscles

    mandibular,

    maxillary)

VI Abducens (M)​​from brain to external eye muscles​​turning eyes outward

VII Facial (Mi)​​from taste buds of tongue to brain; from​​sense of taste; facial

​brain to face muscles​expression

VIII Acoustic (S)​​from ear to brain​​hearing; balance

​

IX Glossophar-​​from throat and taste buds of tongue to​​sensations of throat,

     yngeal (Mi)​​brain; also from brain to throat muscles​​taste, swallowing

​and salivary glands​movements, secretion

​of saliva

X Vagus (Mi)​from throat, larynx, and abdomen to​sensations of throat,

​brain​thorax, abdomen;

​swallowing; voice

​production

XI Spinal (M)​from brain to certain should and neck​shoulder movements;

​muscles​​turning head

XII Hypoglossal (M)​from brain to muscles of tongue​​tongue movements

Memory Aid:

Order of cranial nerves:

On Old Olympus' Towering Tops, A Fin and German Viewed Some Hops.

Sensory, Motor, or Mixed (Both)?

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