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