Download Biology - Chpt 14- The Nervous System

Biology – Premed
Windsor University School of Medicine
and Health Sciences
Dr. Uche Amaefuna
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Pre Med – Biology Chapter 13
The Nervous System
 There is more to lectures than the
power point slides!
Engage your mind
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KEYWORDS
Gland, Hormone, Impulse, Nervous system, Effector,
Stimulus, Receptor, Neuron, Synapse
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STARTER
Name the hormones –write down the
names of the hormones secreted by the
glands.
Name the hormones – Have you thought
of any others?
Time: 10 minutes
Working Groups: Your choice of 1, 2 or 3
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STARTER answers
Pituitary gland – FSH, LH (stimulates the release and maturity
of follicles during menstruation)
Thyroid gland – Thyroxine (regulates the rate of metabolism)
Adrenal gland - corticosteroids and catecholamines
including cortisol and adrenaline and small amounts of
testosterone (regulates stress levels)
Pancreas – peptides (regulates the production of shorter active
digestive enzymes)
Ovary – oestrogen, progesterone and small amounts of
testosterone (regulates the growth of eggs and stabilises the
growing foetus during pregnancy)
Testis – testosterone (plays a key role in the health and wellbeing of the man)
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CONTROL SYSTEMS
There are two main control systems in your body.
1.
Nervous system – which has two main sections


central or CNS that is made up of the spinal cord and brain and
functions to coordinate all actions of the body
peripheral or PNS that is made up of the bodies nerves and functions
to connect the CNS to the rest of the body through neurones. PNS is
further divided into
–
–
somatic or SNS which is associated with the voluntary control of body
movements and is made up of all neurones, sense organs, skin, skeletal
muscles
Autonomic or ANS which is associated with the involuntary control of
body movements such as reflex and controls such things as heart rate,
body temperature, digestion etc. The ANS is further divided into
• Parasympathetic nervous system works in actions that do not require
a fast response (rest and digest response)
• Sympathetic nervous system works in actions that do require a fast
response (fight or flight response)
Endocrine system – which is a system of glands that
release a number of signalling chemicals known as
hormones.
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2.
NERVOUS SYSTEM
CNS
Nervous
system
releases
electrical impulses that are quick
but the effects are short lived and
it involves the CNS (either just
spinal cord or both spinal cord
and brain) messages are carried
by neurons
PNS
ANS
SNS
Parasympathetic Sympathetic
Endocrine system releases chemical signals that are slow
to react but the effects are long lasting. This does not
involve the CNS. Messages are carried by the blood.
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Parts of the nervous system
The nervous system is made up of three
main parts;
 The brain
 The spinal cord
 Nerve fibres
It detects stimuli such as light, sounds,
temperature, pressure, pain and coordinates the bodies response.
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Parts of the nervous system
For example;
If you smell something burning…
 Your nose (receptor) detects the stimulus
(smell)
 Nerve fibres send the message to the brain
 Your brain then sends a message to move
your body away or to put out the fire!
SIMPLE RIGHT!
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Lets look at some bits more closely
RECEPTORS


Receptors are sensors on the body that detect stimuli
They convert stimuli into electrical signals (messages) called
impulses.
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EFFECTORS
An effector is any part of the body that produces the
response.
Here are some examples of effectors:



a muscle contracting to move the arm
a muscle squeezing saliva from the salivary gland
a gland releasing a hormone into the blood
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NERVE FIBRES
Nerve fibres are bundles of nerve cells
(neurons) that pass on electrical signals
(impulses) to the brain.
 From the brain, nerve fibres send impulses to
effectors (muscles).

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NEURONS
There are three types of neurons
1. Sensory neuron – carries impulses from the
receptors to the spinal cord.
2. Relay Neuron – carries impulses to and from
the spinal cord and the brain
3. Motor Neuron – carries impulses from the
brain to the effector
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Multiple-choice quiz
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SYNAPSES
Where two neurons meet, there is a tiny gap
called a synapse.
Signals cross this gap using chemicals.
One neuron releases the chemical into the gap.
The chemical diffuses across the gap and makes
the next neuron transmit an electrical signal.
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What is a synapse?
A synapse is a junction between two neurons across which
electrical signals pass. The human body contains up to 500
trillion synapses.
presynaptic
cell
postsynaptic
cell
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The release of neurotransmitters
When a nerve impulse arrives at the end of one neuron it
triggers the release of neurotransmitter molecules from
synaptic vesicles.
synaptic
vesicle
neurotransmitter
molecules
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Continuing the impulse
The neurotransmitters diffuse across the synaptic cleft and
bind with receptors on the next neurone, triggering another
impulse.
synaptic
cleft
nerve
impulse
receptor
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REFLEX ARC
When your body needs to react to something
very quickly (to protect itself) it uses a reflex
arc (spinal reflex).
 Instead of sending impulses from the receptor
Spinal cord
brain
spinal cord
effector

It sends impulses from the receptor
spinal cord
effector…Yup it bypasses the
brain!

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ANSWERS
 Electrical impulses along neurons,
chemical (neurotransmitters) across the
synapse.
 The microscopic gap between two
neurones.
 By chemicals called neurotransmitters.
 To pass the impulse onto the correct
motor neurone.
 Glands or muscle that produce the
effect or make a response.
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The sequence of a reflex arc
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REFLEX ACTION
The way the iris in our
eye adjusts the size
of the pupil in
response to bright
or dim light is also
a reflex action.
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In bright
light
In dim light
•Radial muscles of
the iris relax.
•Circular muscles of
the iris contract.
•Less light enters the
eye through the
contracted pupil.
•Radial muscles of
the iris contract.
•Circular muscles of
the iris relax.
•More light enters
the eye through the
dilated pupil.
The iris reflex
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Inside the eye
cornea
protects eye surface and
focuses light rays
suspensory ligaments
hold lens in place
retina
senses light
lens
focuses light
on retina
iris
regulates amount
of light entering eye
ciliary muscles
change shape of the lens
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optic nerve
transmits impulses to
the brain
REFLEX ACTION
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NERVE PATHWAY… Have a go at completing this
worksheet
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NERVE PATHWAY… answers
SENSE ORGAN/
RECEPTOR
Senses stimuli
from our
surroundings.
SENSORY NEURON
Takes impulses from
the sense organ to the
relay neuron.
SPINAL CORD
Where the
relay neurones
are found.
BRAIN
Receives impulses
from the spinal
cord and sends out
new impulses.
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RELAY NEURON
Takes impulses to
the brain and from
the brain.
MOTOR NEURON
Takes impulses from
the relay neuron to
the effector.
EFFECTOR
The muscle that
receives the
impulse from
motor neuron.
Summary/Terms (1/2)
 accommodation – The reflex reaction that keeps the
lens the right shape to focus light on the retina.
 CNS – The central nervous system, consisting of the brain
and spinal cord.
 iris – The part of the eye that limits the amount of light
entering the eye.
 lens – The part of the eye that focuses light on the retina.
 motor neuron – A neuron that carries electrical impulses
from the CNS to muscles and glands.
 neuron – A specialized cell that carries electrical impulses.
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Summary/Terms (2/2)
 neurotransmitter – A chemical that diffuses across
synapses to continue an impulse in a connecting neurone.
 reaction time – The time taken to respond to a stimulus.
 reflex – A fast, automatic protective response.
 retina – The part of the eye that contains light receptors.
 sensory neuron – A neuron that carries electrical
impulses from sense organs to the CNS.
 synapse – The gap between two connecting neurons.
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