Learning Objectives

Describe the Structural and Functional divisions of the Nervous System
Discover the organization and distribution of the spinal nerves

Definition

Nervous (relates to nerves and nervous tissue)
System (a group of interacting elements forming a complex whole)

• It is a major controlling, regulatory & communicating system in the body
  • It is primary responsibility together with the Endocrine System, is to maintain Homeostasis.

Structure

Divisions of the Nervous System:

• Central Nervous System
  • Includes the Brain and Spinal Cord
    
  • Command center of the Nervous System
  • Somatic nervous system
  • Conducts impulses between the CNS and skeletal muscles
    
  
  

• Peripheral Nervous System
  • Nerves and ganglia (spinal and cranial nerves)

• Collection of Neurons that transmit processes to the Central Nervous System
• Controlling centers within the central nervous system
• Peripheral components consist of sympathetic and parasympathetic divisions
  
  

Functional Divisions:

Sensory(AFFERENT)division

• Transmit nerve impulses from PNS to the CNS; such as pain, temperature, pressure.
  • Somatic Sensory
    
    • Receives sensory information from skin, joints, skeletal muscles.
  • Visceral Sensory
    • Receives sensory information from viscera.

Motor (EFFERENT) division

• Transmits to the muscles and glands from the CNS
  • Somatic motor
    • Voluntary control of skeletal muscle
      
  • Autonomic motor
    • Involuntary control of smooth muscle, cardiac muscle and glands
    - Subdivided into sympathetic and parasympathetic division
  * Sympathetic is the "Fight or Flight" response

* Parasympathetic is the "Rest and Digest" response

Here is an easy way to remember the direction of sensory and motor.
SAME DAVE
Sensory Dorsal
Afferent Afferent
Motor Ventral
Efferent Efferent





Two Cell Types form Nervous Tissue.

NEURONS:The neuron is the basic structural unit of the Nervous System. Neurons are specialized cells that can respond to stimuli, conduct electrical impulses, and send neurotransmitters to other neurons or other cells to propagate the electrical impulse. They are functionally classified according to the direction of nerve impulses relative to the CNS; sensory neurons carry impulses from the environment towards the CNS, motor neurons conduct impulses away from the CNS to muscles or glands;interneurons are found within the CNS and are connected to other neurons. 99% of neurons are interneurons.



Characteristics of a Neuron:

• High Metabolic rate.
• Survival depends on continuous and abundant amounts of glucose and oxygen.
  
• Have extreme longevity.
  
• Typically are non-mitotic (do not divide).
  
• Share certain basic structural features such as dendrites, a cell body, and an axon.
• All have only one axon.
  • A nerve impulse can only travel one direction--from the dendrites, to the cell body, and down the axon.
  • The impulse passes to other neurons or to target tissue (such as a muscle cell) via neurotransmitters released at the synapse.

GLIAL CELLS:Referred to as neuroglia occur within both the CNS (Central Nervous System) and the PNS (Peripheral Nervous System). The table listed below shows the distinct features of the Glial Cells and how they appear and Function in the CNS and PNS

Glial Cell	Appearance and Location	Function(s)
Astrocyte	Large cell with numerous cell process and makes contact with neurons and capillaries. Located CNS. Named for it's star shaped figure.	Helps to form the blood brain barrier. Regulates tissue fluid composition. Replaces damaged neurons. Assists with Neuronal development. Provides structural support.
Microglia	Small, slender branches, least common glial cell	Defends pathogens. Removes Debris. Phagocytize wastes.
Oligodendrocyte	Bulbous, slender cytoplasmic extensions, wrap around CNS axons.	Myelinates and insulates CNS axons. Allows faster nerve impulse conduction.
Ependymal cell	Simple, Cuboidal epithelial cells lining brain and spinal cord	Ventricle lining of the brain and central canal of spinal cord. Assists in producing and circulating CFS.
Satellite cells	Flattened cells clustered around the neuronal cell bodies in a ganlion	Located within the PNS. Protects and regulates nutrients for cell bodies in ganglion.
Neurolemmocyte	Schwann Cell, Flattened cell wrapped around a portion of an axon	Located within the PNS Myelinates and insulates PNS axons. Faster nerve impulse conduction through the axon.

#	Cranial nerves are nerves that emerge directly from the brain stem in contrast to spinal nerves which emerge from segments of the spinal cord. Although thirteen cranial nerves in humans fit this description, twelve are conventionally recognized. The nerves from the third onward arise from the brain stem. Oh, Oh, Oh, To Touch And Feel A Great Victory is Such Happiness. or Oh, Once One Takes The Anatomy Final Very Good Vacations Are Heavenly! Name	Sensory Motor or Both	Except for the tenth and the eleventh nerve, they primarily serve the motor and sensory systems of the head and neck region. However, unlike peripheral nerves which are separated to achieve segmental innervation, cranial nerves are divided to serve one or a few specific functions in wider anatomical territories. Oh = CN I Olfactory Oh= CN II Optic Oh = CN III Oculomotor To= CN IV Trochlear Touch = CN V Trigeminal And = CN VI Abducens Feel = CN VII Facial A = CN VIII Auditory Great = CN IX Glossopharyngeal Victory = CN X Vagus Such = CN XI Spinal Accessory Happiness = CN XII Hypoglossal Origin	Nuclei	Function
0	Cranial nerve zero (CN0 is not traditionally recognized.)[1]	Sensory		olfactory trigone, medial olfactory gyrus, and lamina terminalis	Still controversial New research indicates CN0 may play a role in the detection of pheromones [2][3]
I	Olfactory nerve	Sensory		Anterior olfactory nucleus	Transmits the sense of smell; Located in olfactory foramina of ethmoid
II	Optic nerve	Sensory		Lateral geniculate nucleus	Transmits visual information to the brain; Located in optic canal
III	Oculomotor nerve	Motor	Midbrain	Oculomotor nucleus, Edinger-Westphal nucleus	Innervates levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique, which collectively perform most eye movements; Located in superior orbital fissure
IV	Trochlear nerve	Motor	Midbrain	Trochlear nucleus	Innervates the superior oblique muscle, which depresses, rotates laterally (around the optic axis), and intorts the eyeball; Located in superior orbital fissure
V	Trigeminal nerve	Both	Pons	Principal sensory trigeminal nucleus, Spinal trigeminal nucleus, Mesencephalic trigeminal nucleus, Trigeminal motor nucleus	Receives sensation from the face and innervates the muscles of mastication; Located in superior orbital fissure (ophthalmic branch), foramen rotundum (maxillary branch), and foramen ovale (mandibular branch)
VI	Abducens nerve	Motor	Posterior margin of Pons	Abducens nucleus	Innervates the lateral rectus, which abducts the eye; Located in superior orbital fissure
VII	Facial nerve	Both	Pons (cerebellopontine angle) above olive	Facial nucleus, Solitary nucleus, Superior salivary nucleus	Provides motor innervation to the muscles of facial expression and stapedius, receives the special sense of taste from the anterior 2/3 of the tongue, and provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal gland; Located and runs through internal acoustic canal to facial canal and exits at stylomastoid foramen
VIII	Vestibulocochlear nerve (or auditory-vestibular nerve or statoacustic nerve)	Sensory	Lateral to CN VII (cerebellopontine angle)	Vestibular nuclei, Cochlear nuclei	Senses sound, rotation and gravity (essential for balance & movement); Located in internal acoustic canal
IX	Glossopharyngeal nerve	Both	Medulla	Nucleus ambiguus, Inferior salivary nucleus, Solitary nucleus	Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus (essential for tactile, pain, and thermal sensation)[citation needed]. Some sensation is also relayed to the brain from the palatine tonsils. Sensation is relayed to opposite thalamus and some hypothalamic nuclei. Located in jugular foramen
X	Vagus nerve	Both	Posterolateral sulcus of Medulla	Nucleus ambiguus, Dorsal motor vagal nucleus, Solitary nucleus	Supplies branchiomotor innervation to most laryngeal and pharyngeal muscles; provides parasympathetic fibers to nearly all thoracic and abdominal viscera down to the splenic flexure; and receives the special sense of taste from the epiglottis. A major function: controls muscles for voice and resonance and the soft palate. Symptoms of damage: dysphagia (swallowing problems). Located in jugular foramen
XI	Accessory nerve (or cranial accessory nerve or spinal accessory nerve)	Motor	Cranial and Spinal Roots	Nucleus ambiguus, Spinal accessory nucleus	Controls muscles of the neck and overlaps with functions of the vagus. Examples of symptoms of damage: inability to shrug, weak head movement, velopharyngeal insufficiency; Located in jugular foramen
XII	Hypoglossal nerve	Motor	Medulla	Hypoglossal nucleus	Provides motor innervation to the muscles of the tongue and other glossal muscles. Important for swallowing (bolus formation) and speech articulation. Located in hypoglossal canal

Nerves:

A "Nerve" is a bundle of axons that is visible to the naked eye. It can be broken up into sensory, motor and mixed nerves.

• SENSORY: transmit information to the CNS while axons send impulses in the same directions.
• MOTOR: transmits information from the CNS to the muscles and glands while axons send impulses in the same direction.
• MIXED: contains both sensory and motor nerves while some axons send impulses in one direction, and other axons send impulses the opposite direction.

Synapses:

An axon that sends a nerve impulse to another neuron at a synaptic gap. A synapse of the CNS is composed of a presynaptic neuron that is closely associated with a postsynaptic neuron where their plasma membrane is separated by a narrow space called the "Synaptic Cleft". There are two kinds of Synapses electrical and chemical.

• Electrical Synapses: a flow of ions passes from the presynaptic cell to the postsynaptic cell through gap junctions. The cells act as if they share a common plasma membrane, so there is no delay in passing of nerve impulses between them. Not common in mammals, but in humans this occurs in smooth muscle and in cardiac muscle. Chemical Synapses: a nerve impulse causes the release of a chemical neurotransmitter from the presynaptic cell, which than binds to the post synaptic and induces a response.

Case Study

You can test your ability to detect pitch, detect differences in rhythm, and whether or not you are tone deaf by taking the tests at Tonometric.

In the News

Glossary

Afferent: Inflowing or going toward.
Astrocyte: Largest and most abundant glial cell of the nervous system.(contribute to the blood-brain barrier)
Dendrites: Conduct nerve impulses toward the cell body.
Axon: conduct nerve impulses away from the cell body.
Efferent: Outgoing or moving away.
Innveration: Supply of axons functionally connected with a part.
Microglia: Small glial cells in the CNS.
Neurons: Conduct nerve impulses from one part of the body to another.
Nerve: A cablelike bundle of parallel axons.
Oligiodendrocyte: Large glial cells in the CNS.
Synapses: The specialized junction between 2 excitable cells where a nerve impulse is transmitted.
Ganglia: Collection of cell bodies outside of the central nervous system.(most bodies are inside, except the spinal cord)
Sensory nerves: Convey sensory information TO the CNS and all axons are conducting impulses the SAME way.
Motor nerves: Convey motor impulses FROM the CNS TO the muscles and glands and all axons are conducting impulses the SAME way.
Mixed nerves: Carry BOTH types of information and axons are transmitting impulses in different directions.
Interneurons: Lie entirely within the CNS and facilitate communication between sensory and motor neurons. (an estimated 99% of our neurons are interneurons)

Connections to other body systems

Review Questions

1. What is a SYNAPSE?
*a. a terminal fiber of an axon
b.a dendrite
c. a neuron
d. a rubber band

2. True or False The synapses are of types: chemical or energy?
*True

3. True or False The Falx Cerebelli is the largest of the four Dural Septas?
*False

4. Afferent Neurons also called __________ send impulses to the Brain and Spinal Cord about muscle activity.
a. Motor Neurons
*b. Sensory Neurons
c. Interneurons
d. Dentrites

5. True or False: The Afferent nervous system controls the activities of voluntary movement?
*False; Efferent (motor)

6. True or False: The sympathetic nervous system can simultaneously cause certain blood vessels to contract while others are stimulated to dilate?
*True

7. Which of the following answers contains the four types of glial cells of the CNS?


8. Fill in the blanks

9. The CNS includes what?

10. Which Glial cell myelinates the axons of the CNS?
a. astrocytes
b. schwann cells
*c. oligodendrocytes
d. ependymal cells

11. The most common type of cell in the human body is the?
a. oligodendrocyte
b. astrocyte
c. neurolemocyte
d. ependymal