NERVOUS SYSTEM

Nervous System OverviewRole: Maintain homeostasis

1. Sense changes (____ neurons)2. Integrate information (_______)3. Respond (______ neurons)

Basic Anatomy1. Mass = ____ lbs 3% total body mass

Main Subdivisions1. Central Nervous System (CNS)2. Peripheral Nervous System (PNS)

CELLS OF THE NERVOUS SYSTEM

2 Types of cells found in the N S:1. NEURONS: nerve cells

2.NEUROGLIA (Glia): specialized connective tissue

NEURONSMotor neurons

Also called ________ neurons.

InterneuronsAlso called _______neurons.

Sensory neurons

Also called _______neurons.

STRUCTURE OF NEURON

AXON: is surrounded by segmented wrapping called _______.

- It is:

Axon - long section, transmits impulses

Dendrite - small extensions from the cell body; receive information

Neurofibrils - fibers within the axon

Interesting Facts about the Neuron

•Longevity – can live and function for a lifetime

•Do not divide – fetal neurons lose their ability to undergo

mitosis; neural stem cells are an exception

•High metabolic rate – require abundant oxygen and glucose

The nerve fibers of newborns are unmyelinated - this causes their responses to stimuli to be course and sometimes involve the whole body.  Try surprising a baby!

GLIAGlia or neuroglia: They are special types of

supporting cells - Function: is to: * Large cells look like stars: astrocytes * Smaller cells are Microglia

Example: Oligodendrocytes: helps hold fibers together, produce the fatty myelin sheath that envelops nerve fibers in the brain and spinal cord

NERVESNerve is a group of peripheral nerve fibers (axons) bundled together like the strands of a cable.

Myelin is found on nerves and is white.Nerves are referred to as _____ matter of the PNS and also the CNS.

Unmyelinated axons and dendrites are called ________. (because of their color)

Brain = Gray over White

Spinal Cord = White over Gray

REFLEX ARCNerve impulses are conducted from

receptors to effectors over neuron pathways known as ___________

This results in a _______. (a contracted muscle or secretion from a gland)

2 types of reflex arcs: - two-neuron arcs: spinal cord and motor

neuron - three-neuron arcs: sensory neurons,

interneurons and motor neurons

Animation

http://www.youtube.com/watch?v=Y5nj3ZfeYDQ

http://bcs.whfreeman.com/thelifewire/content/chp46/46020.html

RECEPTORS

Impulse conduction normally starts in the_______.

Found at the beginning of the dendrites of sensory neurons

Location:

MS (MULTIPLE Sclerosis) DAMAGE TO MYELIN

Hard lesions replace the destroyed Myelin

As the myelin is lost, nerve conduction is ______

Causing weakness, loss in coordination, visual impairment, speech disturbances

No known cure, occurs most in women ages 20-40.

Synapse

A microscopic space from the axon ending of one neuron to the dendrite of another neuron.

The nerve impulse stops, chemicals are sent across the gap, the impulse continues alone the dendrites.

Neurotransmitters

Chemicals by which neurons communicateSome help us sleep, inhibit pain, make us

energeticExamples

Acetylcholine-

Norepinephrine and Dopamine-

Serotonin-

Endorphins-

Neurotransmitters

Excitatory - increase membrane permeability,

increases chance for threshold to be achieved

Inhibitory - decrease membrane permeability,

decrease chance for threshold to be achieved

The Action Potential- an All-or-None Electrical

Signal

Cell Membrane PotentialAt rest, the inside of a neuron's

membrane has a negative charge. As the

figure shows, a Na+ / K+ pump in the

cell membrane pumps sodium out of the

cell and potassium into it. However, 

more potassium ions leak out of the cell.

As a result, the inside of the membrane

builds up a net negative charge relative

to the outside.

Animations of Nerve Impulses

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

Action Potential Overview

Signals or impulses of communication Travel along axons

Are “all-or-none” events Threshold must be reached

Two phases1. Depolarization2. Repolarization

Axon Diameter and Action Potentials

Recall that axons are also called nerve fibers

Larger fibers propagate impulses faster

Larger fibers usually myelinated

Smallest fibers are unmyelinated and therefore propagate impulses slower

Resting Membrane Potential

Recall that there is a separation of charges across the membrane of excitable cells.

Extracellular fluid contains more sodium ions than are found inside a cell

Cytosol contains more anions and negatively charged proteins

Thus sodium ions cling to the outside cell surface

Resting Membrane Potential

Cell somewhat permeable to potassium

Much less permeable to sodium

Sodium quick to rush in when gates open following both electrical and concentration gradients

Potassium not quick to rush out only has concentration gradient to drive flow

Resting Membrane Potential

• small build-up of anions in cytosol• equal build-up of cations in extracellular fluid

Change in Membrane Potential

Na+ channels open

Fast Na+ influx

Inside of cell becomes less negative

If change is +15mV action potential occurs

Ongoing Research

Improve environment for spinal cord axons to bridge injury gap

Find ways to stimulate dormant stem cells to replace lost, damaged, or diseased neurons

Develop tissue cultured neurons that can be used for transplantation purposes.

Drugs that Affect Synapses and Neurotransmitters

Strychnine poisoning can be fatal to humans and animals and can occur by inhalation, swallowing or absorption through eyes or mouth

Strychnine is a neurotoxin which acts as an antagonist of acetylcholine receptors. It primarily affects the motor nerves in the spinal cord which control muscle contraction. An impulse is triggered at one end of a nerve by the binding of neurotransmitters to the receptors.   

Strychnine use by athletes?  

Drugs that Affect Synapses and Neurotransmitters

•Cocaine, morphine, alcohol, ether and chloroform

•Ecstasy

LSD  (hallucinogen)

Dangers of Ecstasy (MDMA) The most common cause of Ecstasy-related death is overheating (hyperthermia). MDMA interferes with the body's ability to regulate its own body temperature and to see other warning signs allowing the body to overheat without discomfort especially when dancing for hours in hot clubs.

The neurotransmitter serotonin is vital in regulating many of our basic functions. Serotonin is, among other things, the feel good neurotransmitter and helps to regulate body temp.

Our brain cells are constantly trying to bring some amount of serotonin back into the cells and out of the synapse using serotonin reuptake transporters.  Ecstasy essentially takes these upkeep transporters and reverses their roles. This causes a massive flood of serotonin from the brain cells into the synapse. 

LSD; lysergic acid diethylamideActions/Effects: LSD alters the action of the neurotransmitters serotonin, norepinephrine,

and dopamine, triggering extreme changes in brain function. Physical effects include increased body temperature, heart rate, and blood pressure. Psychological effects include perceptual and thought distortions, hallucinations, delusions, and rapid mood swings.

 

 

Cocaine blocks reuptake of dopamine

Central Nervous System

Integrates and correlates incoming sensory information

Source of thoughts, emotions, memories Most motor signals originate in CNS

CNS (CENTRAL NERVOUS SYSTEM)Spinal Cord and Brain

4 Divisions of the brain:Brainstem

CerebellumDiencephalon

Cerebrum

                     

.

BRAINSTEM

* Medulla Oblongata: largest part of the brainstem.

- extension of the _________ - Location: lies below the _______ - Functions: reflex center -It controls:

DIENCEPHALONHypothalamus: - Structure: - Function: Acts as the major center for controlling the _____. (function of internal organs) - Controls _____________ - Centers for controlling:

DIENCEPHALONTHALAMUS: - Structure: dumbbell shaped mass of gray matter in each cerebral hemisphere

- Function:

- Produces emotions of pleasantness and unpleasantness associated with sensation

CEREBELLUMSecond largest part of the brainStructure: - composed of _____in outer layer and _______in the inner layer

•Function:

CEREBRUMLargest part of the brainStructure: Structures: Series of ridges and

grooves -Ridges are called convolutions or ____ -Grooves are called _____ (deepest sulci

are called fissures) -Divided into two halves- ________ -Hemispheres connected by the _________

CEREBRUM

HEMISPHERES: Divided into lobesLobes are named after bones that lie over

them.

CEREBRUM

Function: mental process of all types Sensations Consciousness Thinking Memory Willed Movements

Cerebrum

Specific areas have specific functions Temporal lobe’s auditory areas interpret incoming

nervous signals as specific sounds Visual area of the occipital lobe helps you understand

and identify images

If a specific part of the brain is damaged, for example the Primary Taste Area, you would not be able to taste things.

__________CEREBRUM

SPINAL CORD

Structure: Outer part composed of white matter

- Interior part composed of gray matter

Function: center of all spinal cord reflexes

- sensory tracts conduct impulses ___ the brain.

- motor tracts conducts impulses ____ the brain

Cutting the Cord

Completely severing the spinal cord produces a loss of sensation for all areas below the cut, called anesthesia.

It also produces a loss of the ability to make voluntary movements, called paralysis.

Peripheral Nervous System (PNS)

Cranial and Spinal Nerves

Function:

Cranial Nerves: - 12 pairs of cranial nerves - Functions vary

SPINAL NERVES

Structure: contain dendrites of sensory neurons and axons of motor neurons

Function: conduct impulses necessary for sensations and voluntary movements

Autonomic Nervous System (ANS)

Structure: Consists of motor neurons that conduct impulses from spinal cord or brainstem to:

1. Cardiac Muscle tissue2. Smooth muscle tissue3. Glandular epithelial tissueFunction:

2 Divisions of ANS1. Sympathetic nervous system: -Structure:

-Function:

2 Divisions of ANS2. Parasympathetic Nervous System:

Structure:

Function:

Autonomic Neurotransmitters

Each division of the ANS signals its effectors with a different neurotransmitter.

This is how an organ can tell which division is stimulating it. Ex. The heart responds to acetylcholine from the

parasympathetic division by slowing down. If norepinephrine, from the sympathetic division, is present, the heart speeds up.

ANS as a Whole

Regulates the body’s autonomic functions in ways that maintain HOMEOSTASIS