Download Ch6 - Unit3Biology

KEY OUTCOMES
 extend knowledge of coordination and regulation of the living organism.
 understand the significant contribution of the nervous system to
homeostasis.
 extend the understanding of signal transduction in cells with particular
reference to neurons.
 gain an overview of interactions of the nervous and the endocrine systems.
Case Study – Optic Nerve
reading page 167
•
glaucoma is one of the most frequent causes of blindness in dogs
•
the optic nerve comprises a million or more nerve fibres from
neurons in the retina of the eye
•
damage to the optic nerve can have serious consequences with
respect to vision ability.
Tasks
Quick Check 1 & 2
The Nervous System- Structural Classification
reading pages 170-172
When classified according to structure, the nervous system has two subdivisions.
1. The central nervous system (CNS)
consists of the brain and the spinal cord
acts as the integrating and command center of the nervous
system
interprets incoming information and issues instructions based on
past experience and current conditions
2. The peripheral nervous system (PNS)
the part of the nervous system outside the CNS
consists mainly of nerves that extend from the brain and spinal
cord
The Nervous System
reading pages 170-172
Spinal
Cord
Brain
Nerves
Central Nervous
System
Peripheral Nervous System
Peripheral Nervous System
reading pages 170-171
Has two parts
– the SENSORY DIVISION and MOTOR DIVISION.
1.
2.
Sensory (Afferent) division: transmits sensory information about the external
and internal environments to the CNS.
Motor (Efferent) division: transmits information away from the
CNS.
Each part is either externally stimulated (somatic) or internally
Sensory:
Somatic Sensory (external stimuli)/ Visceral Sensory (internal stimuli)
Motor:
Somatic Motor (skeletal muscles)/ Autonomic Nervous System (internal muscles and glands)
Structure Of The Nervous System
Nervous System
Central Nervous
System CNS
Peripheral Nervous
System
SENSORY DIVISION
Spinal Chord
Somatic Sensory Neurons
Visceral Sensory Neurons
Brain
MOTOR DIVISION
Somatic Motor Neurons
Automatic Motor Neurons
Brain
Sensory (Afferent) Nervous System
The Sensory Nervous System has two parts:
1.
2.
Sensory
Neuron
Somatic Sensory Neurons carry
information to the CNS from the external
environment via the senses.
Visceral Sensory Neurons carry
information to the CNS from the internal
environment (ie organs such as the heart)
Skin receptors
Motor
Neuro
n
Interneuro
Muscle
•
The sensory (afferent) nervous system
sends information from receptors to the CNS.
Motor (Efferent) Nervous System
The Motor (Efferent) Nervous System has two parts:
1.
the Somatic Nervous System transmits messages to skeletal
muscles. It is also known as the voluntary nervous system.
2.
the Autonomic Nervous System transmits messages to smooth
muscle, cardiac muscle and glands. It is also known as the
involuntary nervous system.
•
the motor division of the PNS sends information from the CNS to the
muscles and glands.
Lets Look more closely at the Motor (Efferent) Nervous System
AUTONOMIC NERVOUS
SYSTEM
INVOLUNTARY – CNS to EFFECTORS
Autonomic System
The Autonomic system has two parts:
• Sympathetic
• Parasympatheitic
Function: Control involuntary functions
•
•
•
•
•
•
heartbeat
blood pressure
respiration
perspiration
digestion
Can be influenced by thought and emotion
PARASYMPATHETIC
CENTRAL NERVOUS SYSTEM
Brain
Dilates pupil
•
“ Fight or flight” response
Stimulates salivation
Relaxes bronchi
•
Release adrenaline and
noradrenaline
Spinal
cord
Lungs
Accelerates heartbeat
•
Increases heart rate and blood
pressure
Salivary
glands
Inhibits activity
Heart
Stomach
Pancreas
•
•
Increases blood flow to skeletal
muscles
Inhibits digestive functions
Stimulates glucose
Secretion of adrenaline,
nonadrenaline
Relaxes bladder
Sympathetic Stimulates ejaculation
ganglia
in male
Liver
Adrenal
gland
Kidney
PARASYMPATHETIC
CENTRAL NERVOUS SYSTEM
Brain
•
•
Contracts pupil
“ Rest and digest ” system
Calms body to conserve and
maintain energy
Stimulates salivation
Spinal
cord
Constricts bronchi
Slows heartbeat
•
Lowers heartbeat, breathing rate,
blood pressure
Stimulates activity
Stimulates gallbladder
Gallbladder
Contracts bladder
Stimulates erection
of sex organs
Summary Of Autonomic Differences
Autonomic nervous system controls physiological arousal
Sympathetic
division (arousing)
Pupils dilate
Parasympathetic
division (calming)
EYES
Pupils contract
SALiVATION
Increases
Perspires
SKIN
Dries
Increases
RESPiRATION
Decreases
Accelerates
HEART
Slows
Inhibits
DIGESTION
Activates
Decreases
Secrete stress
hormones
ADRENAL
GLANDS
Decrease secretion
of stress hormones
Neurons
Neurons (Nerve Cells)
reading pages 172-175
•
nerve cells or neurons are the basic structure of the nervous system
•
a typical neuron has:
•
•
•
•
three types of neurons exist including:
•
•
•
•
a nucleus within the cell body
dendrites: highly branched extensions of the cell body that receive and then
carry information towards the cell body
an axon: an extension that carries information away from the cell body
sensory (affector) neurons
connecting (inter) neurons
motor (effector) neurons
the presence of the myelin sheath (on affector and effector neurons)
increases the rate at which a nerve impulse is conducted along the axon.
Tasks
See figure 6.8 a, b and c
Biozone 97-98
Neurons
These extensions from the cell body vary in length, from microscopic, to just over a
meter in some neurons. In humans, the longest ones reach from the lumbar region to
the big toe.
– Neuron processes that convey incoming message towards the cell body are
dendrites
– Those processes that conduct impulses away from the cell body are axons
– All axons branch profusely at their terminal end, forming thousands of axonal
terminals
– These terminals contain hundreds of tiny vesicles that
contain chemicals called neurotransmitters
– Each axonal terminal is separated from the next neuron by a tiny gap called the
synaptic cleft
– Such a functional junction is called a synapse
Cells of the nervous system. (a) A typical sensory neuron (b) A typical
motor neuron (c) Structure of a nerve (d) A typical connector or inter
neuron
Relationship between different kinds of neurons.
Task:
See figure 6.8: copy
and label
Nerve Impulses -Summary
reading page 174
•
as an impulse moves along an axon, the permeability of the membrane changes so that
positive Sodium ions (Na+) move into the neuron through ion channels
•
the change in permeability moves along the neuron
•
Sodium ions (NA+) move into the neuron causing achnage in polarity (from negative to
positive). Potassium ions (K+) move out of the neuron (momentarily). When Na+ and K+ are
momentarily together inside the neuron, the charge is positive
•
after a nerve impulse has passed along the membrane, the original distribution of ions across
the membrane is restored
•
the larger the axon’s diameter, the faster the impulse moves along it
•
the presence of myelin increases the speed of an impulse
•
an unstimulated nerve is said to have ‘resting potential’ an activated nerve has ‘action
potential’ (the wave being the action potential)
See figure 6.10 (not error on stimulated axon)
Task
Biozone page 100
Transmission of Impulses Along a Neurone
Nerve Impulse Transmission
Cells are set up as electrically polarized.
– They are in “resting state”
– Ready to do work.
– A more + charge outside the cell than inside
– Created by Na+/K+ pumps
Nerve Impulse Transmission
ACTION POTENTIAL
– These resting neurons are easy
to knock off balance
– Electrical, chemical, or
mechanical stimulus can move
them to an action state.
– Once the “threshold” level is
met, signal is sent.
Myelination
Schwann Cells
– Act as insulators to the
nerve
– Lipo-protein based
– Separated by Nodes of
Ranvier
Node of Ranvier
Myelination cont
Schwann Cell
– Speed up conduction of
impulse
– Depolarization skips from
one node to another.
Synapse
• Receptor site receives neurotransmitters
• Neurotransmitters change permeability of membrane.
• Ions flood into membrane setting off a action potential
in post-synaptic cell.
The Structure of a Synapse.
Transmission between neurons
Synapse
The location between a
neuron and its effector
(nerve, muscle, gland.)
Not in physical contact
with effector.
When signal reaches the
synaptic cleft it releases
Neurotransmitters (NT).
NT Diffuse across cleft to
receptor sites on postsynaptic site.
Signal Transduction Across A Synapse
Neurotransmitters Substance
reading page 175-178
• are produced at the ends of axons and are packaged in
vesicles (on the end of axons only!)
• diffuse across the synapse and attach to receptors on the
postsynaptic membrane
• stimulate another neuron or effector
• last for a very short time only (enzymes produced by
muscles tissue inactive the substances for example)
Example: acetycholine
Communication by Neurohormones
reading pages 176-177
•
are chemicals released directly into the blood
•
travel to a target organ where the signal is transduced and the receptor
cells respond
•
neurons in the hypothalamus of the brain has several different
neurohormones. These are released into the blood and travel to the pituitary
cells, both anterior and posterior, where they exert their effect
Examples:
thyrotropin-releasing hormone (TRH) signals anterior pituitary cells to produce
thyroid stimulating hormone (TSH);
This is an example of the nervous and endocrine systems interacting together
See figure 6.14 & 6.15
Signals and Receptors
•
signal transduction is the process by which a cell converts one
kind of signal into another by a series of relay molecules
•
signals initiating transduction include:
•
•
•
•
•
hormones
neurotransmitters
neurohormones
environmental stimuli (i.e light)
cellular responses to transduction include:
•
•
activation of a gene- protein production
alteration of cellular activity, such as
•
•
•
increased cellular secretions
Changes in cell permeability
Increased rates of chemical reactions
Networks of nerve cells
reading page 178
•
neuron pathways are of two kinds: diverging or converging
•
diverging pathway: a single axon of one neuron branches and links up
wit a larger number of postsynaptic neurons.
•
converging pathway: many persynaptic nerves cone together to
influence a smaller number of synaptic neurons, ultimately one.
•
one advantage of the convergence system is that one cell can have
multiple signals that influence an outcome.
Figure 6.16 (next page)
Reflex
Simplest of
neural
responses.
Involves as little
as 3 neurons
Shortens link
between
stimulus and
response.
Reflex Arc
Sensory Neuron
Interneuron
Motor Neuron
Create reflex arc
Reflex Arc
Reflex
Acts in an “emergency response”
Cuts time of response.
Communication by
neurohormones
From the previous slide, it is evident that
neurotransmitters signal other cells directly. However
there are neurons that send signals via neurohormones
Some neurons
release
chemicals
called
neurohormones
into the blood.
The blood
carries the
appropriate
signal to the
target organs
that then
respond.
Communication by
neurohormones
These neurohormones are released into
the blood, which then travel to the target
organ which receives the signal thus
resulting in a response from the receptor
cell. For example, the hypothalamus of the
brain has several different kinds of neurons
each producing a different kind of
neurohormone. These are released into the
blood and travel to the cells of the anterior
or posterior pituitary where they exert their
Example of Communication by
neurohormones
Neurons in the hypothalamus in
the brain secrete neurohormones
[e.g. thyrotropin-releasing
hormone (TRH)] into blood
capillaries that become associated
with the pituitary. Signals received
by cells of the pituitary are
transduced and the pituitary
responds by producing a hormone
as instructed [in this case thyroidstimulating hormone (TSH)]. This
hormone enters the bloodstream
and is transported to its target cells
[in this case the thyroid gland].
Impeded Nerve Function
reading page 178-182
•
when adverse events impinge on facets of the hormonal and
nervous systems, their normal functioning can be brought to a halt.
•
example: thyroid gland. Over activity shows excessive amounts of
thyroxin are produced.
•
toxins can overwhelm the neuron transmission.
•
poisonous animals produce toxins to paralyse their prey or rebuff
predators.
Task
Quick Check 6-11 page 182
The Central Nervous System
readings page183-187
•
•
•
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the brain and spinal cord together form the central nervous system.
the brain plays a major role in homeostasis.
a living brain has continuous electrical activity
the distinct areas are visible in sections of a spinal cord.
Tasks
Quick Check 12-15
Comparing Nervous And Endocrine Systems.
Nerve Action
Endocrine system
is faster
Is slower
shorter lived
more sustained
(longer acting)
Why?
Why?
• Nerve action is due to electrical
impulses, which travel very quickly
(up to 200metres per second)
• endocrine hormones travel from
their production site via the
bloodstream to their target cells
• Transmitter substance is active at a
synapse for a fraction of a second
only and then is inactivated
• Hormones must be metabolised
before their actions stop and
inactivation time can take hours or
days.
Case Studies of Homeostasis
readings pages189-195
•
•
•
Blood Glucose control
Maintaining core temperature
Maintaining water balance
Control of Blood Pressure
reading page 190
(draft)
•
•
•
•
figure 6.31 page 190
blood pressure is under nervous and hormonal control.
if a change in blood pressure occurs, events take place that
counteract the initial change.
a fall in blood pressure is followed by events that lead to a
restoration of normal blood pressure.
Maintaining Core Temperature
reading page 191-192
(draft)
•
fig. 6.32, page 191.
•
when a person is exposed to the cold, the body responds in several
ways to maintain a stable core temperature.
Maintaining Water Balance
reading page 192-193
(draft)
•
•
•
fig. 6.33 page 193
vasopressin and renin both play a role in conservation of water.
kidneys are the major organs that control water balance.
Tasks
• Complete Biochallenge page 196.
• Complete Chapter Review questions 197 – 198.