The Nervous SystemThe CNS, PNS, SNS, and ANS

A control and communications system◦ Consists of the brain, spinal cord, nerve cells, and

nerve fibers that run throughout the body Originates and coordinates physical

reactions to the environment Controls involuntary muscles and organs Maintains homeostasis

◦ A balanced state within the body

C.S. 24

Definition – Nervous System

Nerve cells are called neurons◦ Star-shaped bodies with 2 long nerve fibers projecting

from them◦ Messages to the cell body are carried by nerve fibers

called dendrites (part of the star)◦ Messages that travel away from the cell body are carried

by nerve fibers called axons (the tail) The axon is covered by a myelin sheath for protection –

deterioration of this sheath is called MS The dendrite receives a message, transmits it to

the cell body, and the cell body sends the message along to another neuron or to the organ that is to be affected (such as a muscle)

Nerve Cells

Nerve Cell

The neurons and their fibers form a network that covers the entire inside of the body and all of the skin

The long fibers of neurons are arranged in bundles called nerves◦ The fibers of neurons within the nerves don’t

actually touch◦ They meet at a place called a synapse, which is a

space where an electrical impulse is transmitted from an axon to a dendrite

Nerve Cells, continued

Synapse

Classified according to the direction in which they transmit impulses

Afferent neuron: sensory neurons – transmits impulses TO the brain and spinal cord from the sensory organs

Efferent neuron: motor neurons – transmits impulses AWAY from the brain and spinal cord or other nerve centers◦ Transmit only to muscles and organs

Interneuron: transmits impulses from sensory to motor neurons◦ Used in reflexes for defensive purposes

C.S. 25

Nerve Cell Classification

It is divided into categories depending upon function

Central Nervous System (CNS)◦ Brain◦ Spinal cord

Peripheral Nervous System (PNS)◦ Somatic Nervous System (SNS)◦ Autonomic Nervous System (ANS)

Sympathetic Nervous System Parasympathetic Nervous System

How is the Nervous System Divided?

Made up of:◦ The brain ◦ The spinal cord

Control center for the movement and actions of the entire body◦ Messages come to the CNS from throughout the

body, where they are interpreted ◦ the CNS then sends out reaction impulses

Central Nervous System

The most complex and specialized organ in the body

3 areas – forebrain, midbrain, hindbrain Divided into specialized sections

◦ Cerebrum 2 hemispheres – right and left 4 ventricles/lobes – frontal, parietal, temporal, and

occipital◦ Cerebellum◦ Corpus Callosum◦ Pons◦ Medulla

CNS - The Brain

CNS - Brain Components 1. Frontal lobe of

cerebrum (f) 2. Pituitary gland 3. Temporal lobe of

cerebrum (f) 4. Pons (h) 5. Medulla oblongata 6. Parietal lobe of

cerebrum (m) 7. Corpus callosum (f) 8. Occipital lobe of

cerebrum (m) 9. Cerebellum (h) 10. Spinal cord

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Main part of the brain Divided into hemispheres Outer surface is called the cortex

◦ Wrinkled with deep furrows to increase the surface area of the brain

Consists of the forebrain and the midbrain Has 4 lobes (aka ventricles)

CNS - Brain Components – Cerebrum

Frontal lobe◦ Top, front regions of each of the cerebral hemispheres. ◦ Used for reasoning, emotions, judgment, and voluntary

movement Parietal lobe

◦ Middle lobe of each cerebral hemisphere between the frontal and occipital lobes

◦ Contains important sensory centers Temporal lobe

◦ Region at the lower side of each cerebral hemisphere◦ Contains centers of hearing and memory

Occipital lobe◦ Region at the back of each cerebral hemisphere◦ Contains the centers of vision and reading ability

CNS - Cerebral Lobes

Part of the brain below the back of the cerebrum

Regulates balance, posture, movement, and muscle coordination

CNS - Brain Components - Cerebellum

A large bundle of nerve fibers that connect the left and right cerebral hemispheres

Allows for communication and coordination between the hemispheres

In the lateral section, it looks a bit like a "C" on its side

CNS - Brain Components – Corpus Callosum

The part of the brainstem that joins the hemispheres of the cerebellum and connects the cerebrum with the cerebellum

It is located just above the Medulla oblongata

CNS- Brain Components - Pons

The lowest section of the brainstem (at the top end of the spinal cord)

It controls automatic functions including heartbeat, breathing, etc

C.S. 26

CNS - Brain Components - Medulla

Descends from the medulla oblongata down into the canal formed by the vertebrae

Made up of white (nerve tissue) and gray matter (same matter as brain tissue)

Has 2 functions:◦ Serves as the sensory-motor mechanism for reflex

actions◦ Is the 2-way transmitter of impulses, reactions,

and stimuli triggered by various internal and external conditions

CNS - Spinal Cord

Surround the brain and spinal cord for protection

Dura mater – Outer layer Arachnoid – Middle layer Pia mater – Inner layer Cerebrospinal fluid (CSF) – between pia

mater and arachnoid (sub-arachnoid space)

Meningitis – an infection of the meninges◦ Can be in any of the layers◦ Can involve the CSF as well

CNS - Meninges

Made up of the nerves of the body that connect the CNS to the other parts of the body

Includes the cranial and spinal nerves

Peripheral Nervous System

Cranial nerves link the brain with sensory receptors and muscles

There are 12 cranial nerves Designated by Roman numerals I-XII and

names

PNS – Cranial Nerves

I Olfactory Smell II Optic Vision III Oculomotor Eye/eyeball

movements IV Trochlear Eyeball movements V Trigeminal Chewing; facial

sensation VI Abducens Eyeball movements VII Facial Taste; facial expression VIII Auditory/Vestibulocochlear

Hearing; balance

PNS – Cranial Nerves By Number

IX Glossopharangeal Taste; swallowing; saliva secretion

X Vagus Swallowing; voice; gag reflex; slowing of heartbeat (parasympathetic)

XI Spinal accessory Muscles of

neck/shoulder XII Hypoglossal Tongue

movements

PNS – Cranial Nerves By Number

Mnemonic device:“On Old Olympus Towering Tops A Fin And German

Viewed Some Hops”

- OR –“Oh Oh Oh To Touch And Feel A Girl’s V……. So

Happy”

Mnemonic Device

Olfactory (I) – Identify smells Optic (II) – Eye chart; reading Oculomotor, Trochlear, Abducens (III, IV, VI)

– With head still, follow a finger up/down/left/right; pupillary response (III)

Trigeminal (V) – Bite down; Light touch on face

Facial (VII) – Smile, frown; Taste on tip of tongue

PNS – Cranial Nerves - Testing

Vestibulocochlear (VIII) – Check hearing; stand on one leg with eyes closed, then the other leg

Glossopharangeal and Vagus (IX, X) – Swallow; taste on back of tongue

Spinal Accessory (XI) – Resisted shrug Hypoglossal (XII) – Stick out tongue and

move it side to side

PNS – Cranial Nerves - Testing

Spinal nerves link the spinal cord with various structures

Conduct impulses between the spine and the parts of the body not supplied by the cranial nerves◦ Transmit sensory info to the spinal cord through

afferent neurons and transmit motor signals to muscles and organs through efferent neurons

Make sensation and movement possible 31 pairs

◦ One root of each pair goes to each side of the body

PNS – Spinal Nerves

31 pairs come from the spinal cord as follows:◦ 8 cervical nerve roots◦ 12 thoracic nerve roots◦ 5 lumbar nerve roots◦ 5 sacral nerve roots◦ 1 coccygeal nerve root

Each nerve divides to form several branches called rami◦ Dorsal rami – control muscles and skin of the back◦ Ventral rami – innervate all structures of the limbs

and torso

PNS – Spinal Nerves

Ventral rami and adjacent nerves form networks called plexuses that go to general areas◦ Cervical plexus – serves neck, upper shoulders,

and diaphragm◦ Brachial plexus – serves upper limbs, neck, and

shoulder muscles◦ Lumbar plexus – serves abdominal area and part

of the legs◦ Sacral plexus – serves buttocks area and lower

legs

PNS – Spinal Nerves

Dermatome – Area of skin supplied by a single spinal nerve root

Myotome – Specific muscle supplied by a single nerve root

Sclerotome – Area of bone supplied by a single nerve root

C.S. 27

PNS – Spinal Nerves

Dermatome Chart

Subdivision of the PNS Made up of motor nerves that control the

voluntary actions of skeletal muscles

PNS – Somatic Nervous System (SNS)

Subdivision of the PNS Made up of certain motor neurons of the PNS

that conduct impulses from the spinal cord/brain stem to ◦ Cardiac muscle tissue◦ Smooth muscle tissue◦ Glandular epithelial tissue (tissue that forms glands)

Regulates the body’s automatic/involuntary functions such as heart rate, breathing, contractions of intestinal musculature, and secretions of hormones from the glands

PNS – Autonomic Nervous System (ANS)

Responsible for “fight or flight” mechanism Triggered by strong emotional situations

(i.e. anger, fear, anxiety, hate, etc.) and by strenuous exercise

Increases heart rate, blood pressure, sweat excretion

Decreases digestion Charges you up!

PNS/ANS – Sympathetic Nervous System

Opposite of sympathetic nervous system Decreases heart rate and blood pressure

(Vagus nerve) Increases digestion processes Calms you down

PNS/ANS – Parasympathetic Nervous System