Module#7 The Nervous System

Functions:CommunicationCoordinationControlGathering information

Differences between human and animal NS:1. Language2. Judgment3. Problem solving4. Creativeness5. Passing along

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Two Divisions of the NS

1.Central nervous system (CNS)

•the brain and spinal cord

•is encased in bone (skull and vertebral column)

Central Nervous System

Two Divisions of the NS

2. Peripheral nervous system (PNS)

•nerves and ganglia that branch from the CNS and go to body.

Peripheral Nervous System

Nerves – bundles of axons and their sheaths which extend from the CNS

Ganglia – collections of neuron cell bodies which are outside of the CNS

CNS1. Brain •protected by cranium•high level thought•major organ of the NS•Message center•Uses info to formulate ideas•Makes decisions•Communicates with body

CNS1. Brain

2. Spinal CordThick bundle nerve fibers

within spinal cavityHow brain communicates

with most of bodyEnds at first lumbar

Peripheral NS

1. Cranial nervesNerves that come from brain12 pairsBranch from brain stemTransmit from/to eyes, ears,

mouth, face and scalp

Peripheral NS

1. Cranial nerves

2. Spinal NervesNerves that come from spinal

cord31 pairsTransmit signals to and from the

rest of the body

Spinal nerves

Two divisions of Peripheral NS:1. Afferent sensory pathways - involves the sensory organs like eyes, ears..Neurons carry action potential from sense organs to CNSAlso called sensory division

Two divisions of Peripheral NS:

1. Afferent

2. Efferent

Motor pathways - system that innervates muscles, effector organs, and glands.Also called motor division

Action potential – electrical signal that

travels along a neuron.

Divisions of the Efferent Nervous System:1. Somatic Motor Nervous

System (SMNS)

transmits action potential from CNS to skeletal muscles

conscious, voluntary control

Divisions of the Efferent Nervous System:1. Somatic Motor Nervous System (SMNS)

2. Autonomic NS carries stimulus from the CNS to the smooth muscles, cardiac muscles, and glandsInvoluntary, unconscious control

Divisions of the autonomic system:1. Sympathetic system

•prepares body for physical activity•increases heart rate, blood pressure, blood glucose levels•Prepares for “flight or fight”

Divisions of the autonomic system:

1. Sympathetic system

2. Parasympathetic:Regulates resting and nutritionally related functionsIncludes digestion, urination, defecationSlows down heart, etc. after “Fight or Flight” response

NS at a Cellular level:

2 types of cells:1. Neurons = functioning cell

Three parts of neurons (nerve cells):

A. cell body contains the nucleus of cell

B. dendrites – short, branched extensions of cell body receive nerve impulses and conduct them toward the cell body

Three parts of neurons (nerve cells):

A. cell body B. dendrites

C. axon one long extension which carries impulses away from cell body to other cellshillock where the cell body ends and axon begins

Axon continued:

Is wrapped in a substance called myelin produced by neuroglial cellsmyelin speeds up impulsed

Myelin is called Schwann in PNSand oligodendrocyte in CNS

Gaps in myelin called nodes of Ranvier

Axon continued :

Axons vary in length

Axon splits into collateral axons and then end in presynaptic terminals

Collateral Axons

Nerve impulses travel from the dendrite to body to axon.

Mature neurons can not undergo mitosis.

They are parenchyma permanent cells!!

TAKE CARE of them!!

But, Mrs. Crawford how can I take care of them?

Get plenty of sleep, avoid lots of TV, avoid caffeine, alcohol, drugs, and smoking!

Well, how many neurons do I have?

It is believed you have around 100 billion, some will die just due to natural causes (about 7,000/day)

NS at a Cellular level continued

Can classify neurons based on their structure - how many

processes they have (dendrites and axons):

1.Unipolar –one process with a cell body that hangs off to the side

2.Bipolar – two processes an axon and a single dendrite with the cell body in middle

3. Multipolar –only one axon with many dentrites.

unipolar

Bipolar

multipolar

NS at a Cellular level continued

oWhat in the world is a association neuron Mrs. Crawford?

A neuron that conducts action potentials for one

neuron to another. (interneurons)

NS at a Cellular level:2 types of cells:

1. Neurons = functioning cell

2. NeurogliaBinds, protects and insulates neuronsIs the majority of cells in the NS.They do carry on mitosis!!

Types of Neuroglia :

1.Schwann cells – insulate axons of PNS

2. Oligodendrocytes – insulate axons of CNS3. Microglia – white blood cells of brain

Types of Neuroglia :

4. Astrocytes – form blood-brain barrier regulating what can enter the brain and what cannot. (Some toxins pass through such as alcohol toxins)

Types of Neuroglia :

5. Ependymal cells – two typesa. non – ciliated – secrete

cerebrospinal fluidb. ciliated – move cerebrospinal

fluid around

Wrappings of the Nerve:Epineurium – wraps the nerve – white, shinyPerineurium – wraps the fasciclesEndoneurium – wraps the Schwann cells of axonsFascicles are bundles of axons

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Nerve anatomy:

Run along with veins and arteriesMedium sized = shoe stringSciatic nerve – largest, thickness of index finger

3 Types of Nerves:

1. Sensory – carries sensory messages only (optic nerve)

2. Motor – carries messages to the muscles (eye muscles)

3. Mixed – carries both sensory and motor messages (most nerves)

Healing in Nervous System:

•Neurons cannot undergo mitosis.

•Nerve healing occurs under certain conditions.

Conditions of nerve healing:•Axon is wrapped in Schwann cells which means only in PNS

•Axon ends are close and pointed in right direction

• Cell body remains intact

Conditions of nerve healing

No healing in CNS, spinal cord or brain

Can be surgically aided

Why are Schwann cells able to aide in healing and oligodendrocytes not?

There are many Schwann cells per axon in PNS, but many axons per oligodendrocyte in the CNS.