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Nervous
System
Honors Biology
Powerpoint #3
Unit 8 – Chapter 35 pg. 897-904
The Senses Activities
Function of Nervous System:
Coordinates the body’s
response to changes in its
internal and external
environments.
Neurons
Messages carried by nervous system are
electrical impulses
Cells that transmit impulses are called
NEURONS
3 types of neurons:
1. Sensory: carry impulse from sense organ to
spinal chord and brain
2. Motor: carry impulse from brain and spinal
chord to muscles and glands
3. Interneurons: connect sensory and motor and
carry impulses in between
Neurons
Pyramidal neurons
forming a network in
the brain
Neurons: Structure
• Cell Body (Soma): Cell’s “life support” center
• Dendrites - conducts “signal” toward the cell body -[input zone]
• Receives signal from sensory cell or neighboring neuron
Axon - usually a single fiber -- [conducting zone]
 conducts signal away from cell body to another neuron or
effector cell
Axon Ending- a cluster of branches (100’s to
1000’s) that relays signal to next neuron / effector cell
Myelin Sheath
Covers the axon of some neurons
Allows signal to travel faster because impulse
“jumps” from node of Ranvier to node of Ranvier
(with myelin sheath (225 mph / without 11 mph)
Multiple Sclerosis
• Immune System attacks Myelin in brain and spinal
chord
Multiple Sclerosis (MS)
• Loss of motor functions
How a nerve impulse is transmitted
1) At Rest - The neuron is POLARIZED (-70mV)
There is a slightly negative charge on the inside, and a
positive charge on the outside….. Why?
 balance is maintained by the sodium-potassium pump (active
transport)
 Pumps Na+ (sodium) outside & Pumps K+ (potassium) inside
 Membrane leaks and some K+ goes back out
 Resting Potential= -70mV because overall postive charge outside
and negative charge inside
How a nerve impulse is transmitted
2) Depolarization
 Stimulus causes opening of Na+ gates, allowing
Na+ to rush in (facilitated diffusion)
 changes the neuron from polarized to de-polarized
then to + 30mV
 Reversal of charges = Nerve impulse aka Action
Potential
How a nerve impulse is transmitted
2) Depolarization
 This is all-or-none, meaning a stimulus must exceed
a threshold for the action potential to occur
 Intensity of the stimulus is based on the number of
neurons that exhibit an action potential.
 Speed of impulse based on diameter of axon &
amount of myelination.
How a nerve impulse is transmitted
3) Repolarization
 After inside flooded with NA+, K+ gates open and
let K+ out (while NA+ gates close)
 The inside becomes –while outside become + and
this repolarizes membrane
How a nerve impulse is transmitted
4) Refractory period
 When the Na+/K+ balance returns to normal
(K+ on inside and Na+ outside)
 During this time the neuron will not respond to
new impulses
Nerve Impulse Transmission
The Synapse
• Neurons DON’T touch
• The gap between the axon of one neuron, and
the dendrites of another is called the SYNAPSE
1. Action potential happens
2. Neurotransmitter is released by axon ending
 Neurotransmitter is a chemical that sends a signal
3. Neurotransmitter binds to dendrite
membrane of next neuron
4. Excitation or inhibition of the membrane
occurs
5. Neurotransmitter is ‘recycled’
The Synapse
Divisions of the Nervous System:
1. Central Nervous
System (CNS)
1. Peripheral Nervous
system (PNS)
1. The Central Nervous System (CNS)
Relays messages, processes information
and analyzes information.
Includes:
Brain
Spinal Cord
Parts of the Brain
Cerebrum’s Purpose:
Controls voluntary activities of the body
Cite of intelligence, learning, and judgment
Made up of frontal, parietal, occipital, and
temporal lobes
Phineus Gage
Parts of the brain
Cerebellum: coordination and balance
Brain stem: regulates blood pressure,
heart rate, breathing, and swallowing
Parts of Brain
Thalamus: relays sensory input to proper region
of cerebrum
Hypothalamus: control center for recognition
and analysis of hunger, thirst, fatigue, anger, and
body temperature
2. Peripheral Nervous System:
everything outside of CNS
1. Sensory Division:
transmits impulses from
sense organs to central
nervous system
What are sense organs?
Organs designed to pick
up stimuli (name 5 sense
organs)
2. Motor Division: Transmits
impulses from CNS to the
muscles or glands
Quick Quiz: Which is
sensory which is motor?
Seeing Sensory
Raising your hand Motor
Tasting Sensory
Blinking when a ball is thrown
past your face
Sensory when you see the ball,
motor when you blink
Motor Division of PNS
2 parts
1. Somatic Nervous system
 Regulates activities under conscious control (ex.
Moving skeletal muscles)
 Some involved with reflexes and can act without
conscious control (see next slide)
2. Autonomic Nervous System
 Regulates activities that are automatic or involuntary
 Example: when running, speeds up heart and blood
flow, stimulates sweat glands and slows down digestion
 Divided into sympathetic and parasympathetic
 Sensory neuron
interneuron
 Without brain processing
Reflex Arc
motor neuron
Reflex Arc
Parkinson’s Disease
Cause
Parkinson's disease is a disorder of the brain that
leads to shaking (tremors) and difficulty with
walking, movement, and coordination.
Caused by loss of dopamine producing cells in
brain (substantia niagra)
Dopamine helps control muscle movement by
releasing inhibitory function of substantia niagra so
things are not moving when not specifically told to
do so
Without dopamine, it takes more effort for each
motion and movements are shaky
DON’T DO DRUGS!!!!!