Download NERVOUS SYSTEM

NERVOUS SYSTEM
The nervous system is the control center for your body, and it helps all the parts of the
body to communicate with each other. It also reacts to changes both outside and inside the
body. It interprets the things your body senses, and it sends information to the muscles and
glands, telling them what to do. The nervous system uses both electrical and chemical
means to send and receive messages.
It also runs the systems you don’t have to think about, like the digestive and cardiovascular
systems. The nervous system is also responsible for your moods and your thoughts.
The structures of the nervous system include your brain, spinal cord, and nerves that reach
to every part of your body.
Some common problems of the nervous system include:
Epilepsy: Storms of abnormal electrical
activity in the brain causing seizures
Meningitis: Inflammation of the membrane
covering the brain
Multiple sclerosis – the myelin sheaths
protecting the electrical cables of the
central nervous system are attacked.
Parkinson’s disease – death of neurons in
a part of the brain called the midbrain.
Symptoms include shaking and problems
with movement.
Stroke – a lack of blood to part of the brain.
The nervous system can be divided up into two common parts:
1.
Central and peripheral:
The central nervous system (CNS) includes the brain and spinal cord, and the
peripheral nervous system (PNS) includes all the nerves that branch out from the spinal
cord and the brain and travel throughout the body.
2.
Somatic and autonomic:
The somatic nervous system regulates the movement of skeletal muscles, and the
autonomic nervous system controls involuntary actions such as heart rate, digestion,
and perspiration.
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Summer School – Unit 1 Psychology – Book 1
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CENTRAL NERVOUS SYSTEM (CNS)
The CNS receives signals from sensory nerves, coordinates responses and
directs the action.
The focus of the central nervous system is on coordinating incoming and
outgoing neural impulses. It’s also responsible for your thought processes.
Brain: Coordinates actions and response, both voluntary and involuntary.
Spinal cord: Carries messages from the brain to the peripheral nervous system
and carries information from the peripheral nervous system to the brain.
PERIPHERAL NERVOUS SYSTEM (PNS)
All the nerves outside the central nervous system (CNS) belong to the peripheral
nervous system (PNS).
The peripheral nervous system connects the central nervous system with the
peripheral parts of the body. Peripheral nerves are made up of bundles of nerve
fibers, and they’re categorized as either cranial nerves that arise from the brain
or spinal nerves that arise from the spinal cord.
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Summer School – Unit 1 Psychology – Book 1
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The PNS is subdivided into the:
Somatic nervous system (SNS):
•
Transmits messages to the skeletal muscles.
•
Specialises in the control of voluntary movements and the communication of
information to and from the sense organs. Consists of sensory neurons (carry
information from receptors to the CNS) and motor neurons (carry information from CNS
to muscles, except for the organs, smooth muscles, and glands).
•
It deals with the parts of the body you can move voluntarily.
Autonomic nervous system (ANS):
•
The autonomic nervous system works with and regulates the involuntary parts of the
body, including the muscles of the heart, the digestive system, pupil dilation and the
glands.
•
The autonomic nervous system is responsible for initiating the flight and fight response
(discussed further on).
•
Does not require conscious control (automatic).
•
Functions continuously.
The autonomic nervous system includes both visceral afferent fibers and the visceral
efferent fibers.
•
Afferent fibers: These fibers carry pain and other impulses from the internal organs
and help regulate visceral functions.
•
Efferent fibers: These nerve fibers stimulate smooth muscles, glands, and the heart.
The autonomic nervous system has two divisions: the sympathetic and parasympathetic
nervous systems.
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Summer School – Unit 1 Psychology – Book 1
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Sympathetic system:
Generally, (but not always) heightens activity of the internal systems, preparing the body for
action or emergency situations, also known as fight-or-flight reactions. For example,
through the dilation of pupils, increase in heart and breathing rate, raises blood pressure and
inhibits digestion.
The point is to supply more blood to the brain, heart, and muscles by reducing blood flow to
the skin and to the digestive system.
When the perceived threat has passed the parasympathetic nervous system reverses the
above activity, and returns the body to a state of homeostasis.
Parasympathetic system:
Is generally active during times of rest and normal conditions by decreasing the heart rate
and stimulating the digestive system. This part of the autonomic system helps you rest and
digest. It is known to lessen activity of internal organs and return the body to a resting state.
For example, through the constriction of pupils, decreasing heart and breathing rates, and
stimulation of digestion.
OVERVIEW OF SYMPATHETIC AND
PARASYMPATHETIC NERVOUS SYSTEM
Body Organs
This organ is
responsible for…
During activation of the
sympathetic nervous system…
During activation of the
parasympathetic nervous
system…
Adrenal
glands
Secreting adrenalin
and noradrenalin.
Increased secretion stimulating
heart rate, blood pressure,
respiration, relaxation of intestinal
muscles.
Inhibits (decreases) hormone
secretion, calming autonomic
functions.
Heart
Pumping blood.
Heart rate is increased, pumping
more blood through the body.
Heart rate is decreased.
Bronchioles in
lungs
Breathing.
It dilates (expands) the
bronchioles, increasing lung
capacity.
Contracts bronchioles,
decreasing lung capacity.
Liver
Produces bile to
aid digestion,
maintains glucose
level in blood.
Inhibits (decreases) the
production of bile. Increases
conversion of glycogen to
glucose.
Stimulates (increases) the
production of bile. Decreases
conversion of glycogen to
glucose.
Sweat Glands
Regulate body
temperature.
Increase production of
perspiration.
Decrease production of
perspiration.
Pupils
Regulating the
amount of light
entering the eyes.
Pupils dilate allowing more light to
enter eyes so vision is enhanced.
Pupils constrict.
Bladder
Urine storage.
Relaxes.
Increases contractions.
© The School For Excellence 2016
Summer School – Unit 1 Psychology – Book 1
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Salivary
Glands
Aids digestion.
Salivation decreases and
digestion is suspended.
Participant gets a dry mouth.
Salivation increases and
digestion resumes.
Stomach and
digestive
system
Digestion.
Decreases contractions. Blood
flow can be diverted to other
critical areas.
Increases contractions.
Gall Bladder
Stores bile.
Inhibits the release of bile thus
slowing digestion.
Increases the release of bile
thus increasing digestion.
Key points
•
The nervous system uses electrical and chemical means to help all parts of the body to
communicate with each other.
•
The brain and spinal cord make up the central nervous system (CNS).
•
Nerves everywhere else in the body are part of the peripheral nervous system (PNS).
NEURONS
ROLE OF THE NEURON
Neurons (also known as nerve cells) are the basic building blocks of the nervous
system. These specialized cells are the information-processing units of the brain
responsible for receiving and transmitting information.
How many neurons are in the brain?
The human body is made up of trillions of cells. Cells of the nervous system, called nerve
cells or neurons, are specialised to carry "messages" through an electrochemical
process. It has been estimated that the adult brain has around one hundred billion
neurons and an even larger number of glial cells (discussed further on).
FACTS
•
The basic building block of the nervous system is a nerve cell, or neuron. Neurons
are shaped differently depending on where they are in the body and the role they
play.
•
Some of the smallest neurons have cell bodies that are only 4 microns wide.
Some of the biggest neurons have cell bodies that are 100 microns wide.
(Remember that 1 micron is equal to one thousandth of a millimeter!)
•
Unlike other cells in the body, neurons aren’t easily replaced if they die or are damaged
by infection or injury.
•
Neurons are similar to other cells in the body because:
•
•
•
•
Neurons are surrounded by a cell membrane.
Neurons have a nucleus that contains genes.
Neurons contain cytoplasm, mitochondria and other organelles.
Neurons carry out basic cellular processes such as protein synthesis and energy
production.
© The School For Excellence 2016
Summer School – Unit 1 Psychology – Book 1
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A NEURON
STRUCTURE OF A NEURON
All neurons have finger-like branches called dendrites and a long fiber called an axon.
The axon, extending from the cell body, is coated by a specialized membrane called a
myelin sheath.
The axon feathers out into small branches at the end of an
axon called axon collaterals.
At the end of the axon collaterals are axon terminals.
Each axon terminal has a small knob-like swelling at its tip
called a terminal button (also known as synaptic knob,
synaptic button or synaptic vesicle).
The terminal button is a small structure like a sac that stores and secretes a chemical called
neurotransmitter that is manufactured by the neuron and carries its message to other
neurons or cells.
Each terminal button sits near to a dendrite from another neuron.
The space between the terminal button and the dendrite is called a synapse. Messages
jump the synapse from one neuron to the next, using neurotransmitters (special chemicals).
NEURON PARTS AND FUNCTIONS
Cell body (soma): The part of the neuron that contains the nucleus and is involved in
regulation and coordination.
Dendrites: Extensions of the cell body which contain receptors that receive information from
other neurons and bring electrical signals to the cell body.
Axons: Take information away from the cell body, and transmits neural electrical impulses
away from the cell body.
© The School For Excellence 2016
Summer School – Unit 1 Psychology – Book 1
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Axon terminals: Transmit chemical messages (neurotransmitters) to other neurons.
Neurotransmitters: chemicals released by the axon terminal of one neuron and bind to the
receptor site on the dendrite of the next neuron.
Myelin sheath: Many neuron axons are myelinated, and without the coating, called the
myelin sheath, interference may occur, like that which can be experienced when a movie is
being played and a lawn mower outside is in operation. Myelin is a white, fatty substance
that coats and helps insulate the axon from the activity of other nearby axons. This fatty
layer is composed of Schwann cells, and is wrapped around the neuron’s axon which is
used to increase the speed of neural impulses.
Neurons communicate with each other through an electrochemical process.
Synapse: The site of chemical communication between two neurons, where the
neurotransmitter of one neuron binds to the receptor site of the next.
SYNAPSE BETWEEN 2 NEURONS
© The School For Excellence 2016
Summer School – Unit 1 Psychology – Book 1
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TRANSMISSION ALONG AND BETWEEN NEURONS
When a neuron is stimulated it generates an action potential. Action potentials are
considered to be “all or nothing” responses; meaning an action potential is either generated
or not once generated an action potential travels along the axon until it reaches the axon
terminal, where it causes the release of neurotransmitter into the synapse.
TYPES OF NEURONS
There are three types of neurons:
1.
Sensory neurons (or afferent neurons): Transmit information from sensory receptors
(e.g. in skin, eyes, nose, tongue, ears) about the change in both internal and external
environment TOWARD the central nervous system.
For example, the sensory neurons in the eyes respond to light, but not to sound waves.
You are able to take your hard away from a hot stove because sensory neurons (skin
receptors) specialised for ‘touch’ are transmitting information from your fingertips to
your brain.
2.
Motor neurons (or efferent neurons): Transmit information AWAY from the central
nervous system to the muscles or glands.
3.
Interneurons (or connecting neurons): Mostly located in the central nervous system,
send information between sensory neurons and motor neurons.
REMEMBER: Types of neurons – SAME IC! *
* Sensory (Afferent); Motor (Efferent), Interneurons (Connecting).
© The School For Excellence 2016
Summer School – Unit 1 Psychology – Book 1
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Did you know?
Neurons are the oldest and longest cells in the body! You have many of the same neurons
for your whole life. Although other cells die and are replaced, many neurons are never
replaced when they die. In fact, you have fewer neurons when you are old compared to
when you are young. On the other hand, data published in November 1998 show that in one
area of the brain (the hippocampus); new neurons CAN grow in adult humans.
Neurons can be quite large – in some neurons, such as corticospinal neurons (from motor
cortex to spinal cord) or primary afferent neurons (neurons that extend from the skin into the
spinal cord and up to the brain stem), can be several feet long!
GLIAL CELLS
Glial cells (also known as glia and neuroglia) are specialised cells that:
•
Provide insulation, nutrients and support for neuronal function.
•
Aid repair of neurons and eliminating waste materials.
GLIAL CELLS VS. NEURONS
The brain is made up of more than just nerve cells (neurons). Although there are about 100
billion neurons in the brain, there may be about 10 to 50 times that many glial cells in the
brain.
Glial cells outnumber neurons ten times over with 860 billion cells. It was only in 2010 that
glial cells were found to assist neurons in forming synaptic connections between each other.
Once thought to be simply support cells, cleaning up and helping with myelination, they are
now known to also promote dendrite growth, and to be as important as neurons in forming
the neural network.
© The School For Excellence 2016
Summer School – Unit 1 Psychology – Book 1
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Fun fact:
Interestingly, when they examined Einstein's brain after he died to see if he had more
neurons than the average person, what they found instead was that he had way more glia
than most people.
DIFFERENT TYPES OF GLIAL CELLS
•
Astrocyte (Astroglia): Are the largest and most numerous of glial cells; are starshaped cells that provide physical and nutritional support for neurons:
1.
Protects brain by blocking certain substance such as toxins, that may inure the
brain;
2.
Clean up brain "debris";
3.
Transport nutrients to neurons;
4.
Hold neurons in place;
5.
Digest parts of dead neurons;
6.
Forms new connections between neighbouring neurons.
•
Microglia: Are small cells and like astrocytes, microglia digest parts of dead neurons
and protect neurons from intruders (acts like immune system cells).
•
Oligodendroglia: Provide the insulation (myelin) surrounding the axon, to neurons in
the central nervous system (CNS), which help to speed up the process of
communication. They also absorb chemicals that the neuron secretes and secrete
chemicals that the neuron absorbs, which are supposed to contribute to a neuron’s
nutrition and function.
•
Ependymal: type of neuronal support cell that forms the epithelial lining of the
ventricles (cavities) in the brain and the central canal of the spinal cord.
•
Schwann Cells: predominantly have functions
similar to those of oligodendroglia, but provide
the insulation (myelin) to neurons in the
peripheral nervous system (PNS).
•
Satellite Cells: Physical support to neurons in
the peripheral nervous system (PNS).
© 1996-2015 Eric
© The School For Excellence 2016
Summer School – Unit 1 Psychology – Book 1
Page 43
© canvas.brown.edu
REMEMBER: Glial cells – SAME SO!*
* Satelite; Astrocytes; Microglia; Ependymal; Schwann; Oligodendrocytes
FURTHER RESEARCH:
Neurons and Glia: https://canvas.brown.edu/courses/851434/pages/neurons-and-glia
QUESTION 18
A single neuron is simply a single____________________________________.
QUESTION 19
Identify the three main types of neuron in the human nervous system.
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
© The School For Excellence 2016
Summer School – Unit 1 Psychology – Book 1
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ACTIVITY 1
WORKSHEET ON THE HUMAN NERVOUS SYSTEM
1.
Make a simple sketch of the human body and use arrows and labelling to indicate the
direction information is carried around the nervous system (and body) by each type of
neuron.
2.
_____________________________ are chemicals manufactured by the body which
enable communication between neurons because they cross tiny gaps between
neurons called ________________________________.
3.
Identify the main function of the somatic nervous system.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
© The School For Excellence 2016
Summer School – Unit 1 Psychology – Book 1
Page 45
4.
Identify the main function of the autonomic nervous system.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
5.
Identify the main function of the parasympathetic branch of the autonomic nervous
system.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
6.
Identify the main function of the sympathetic branch of the autonomic nervous system.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
7.
Using an example, explain the fight-flight response.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
Key point:
The brain is like a computer controlling all functions of the body, whereas the nervous
system’s role is to relay messages to the parts of the body.
© The School For Excellence 2016
Summer School – Unit 1 Psychology – Book 1
Page 46