Transcript ANIMAL RESPONSES TO ENVIRONMENT

HUMAN RESPONSES TO THE ENVIRONMENT
Two systems to be studied:
1. Nervous system
2. Endocrine system
Introduction
• To survive all organisms have to react to
changes in their external and internal
environment
• External environment: Environment outside the
body for example of factors that might change
are temperature, light, etc in their natural
environment or habitat.
• Internal environment: Environment inside the
body e.g. concentration of CO2, O2, H2O around
cells/tissues/organs inside the body.
Introduction (cont.)
• Human response to these changes in the
environment occurs to maintain stability/balance
within the organism.
• Organisms sense changes in the environment as a
stimulus.
• These impulses are send to the brain which
interpret the information and sends a different
message back to the part of the body telling it
how to react.
Homeostasis
• The body works hard to keep its internal
environment as constant as possible.
• All the organs and systems of the body work
together to create this stable internal condition.
• The process of maintaining a constant cell
environment in the body is called homeostasis.
• The endocrine and nervous systems, as our
co-ordinating systems, play a very important
part in regulating homeostasis.
• Examples: Blood pressure, glucose levels in the
blood, menstruation, etc.
Human Nervous system
What to learn:
• Structure of 3 types of neurons, nerve bundles
transmission of an impulse (Making of drawings)
• CNS, Peripheral, Autonomic (sympathetic &
parasympathetic), disorders
• Difference between reflex arc and reflex action
• Structure (diagrams) and functioning of a simple
arc, Significance of a reflex arc
• Sense organs (Ear and Eye) - Making drawings
Co-ordination in Humans
Nervous co-ordination
Central
nervous
system
Sense
receptors
and
organs
Peripheral and
autonomic
nervous systems
Chemical co-ordination
Over- &
undersecretion
Endocrine
system
Feedback
mechanisms
Human nervous system – is a complex system
Cross-section of the human brain
showing the different parts
Functions of certain parts of the
brain
Cerebellum
•
Co-ordinates movements of your voluntary
muscles
•
Maintains your balance by controlling
muscle tension
Functions of certain parts of the brain
Hypothalamus
•
Controls your blood pressure
•
Controls your body temperature
•
Regulates your levels of thirst and hunger
•
Regulates emotions such as anger and
pleasure
•
Regulates your sleep patterns
Functions of certain parts of the
brain
Cerebrum
•
Controls all voluntary muscle actions
•
Receives and interpret sensations of sight,
hearing, taste, smell, touch and speech
•
Responsible for higher thought processes
such as memory, reasoning, judgement and
intelligence
•
Responsible for behaviour and emotions
Functions of certain parts of the
brain
Medulla oblongata (same structure as the
spinal cord)
•
•
•
Controls important involuntary actions
such as heartbeat and breathing
Enables each half of your brain to
control the opposite side of your body
Transmit nerve impulses between the
spinal cord and the brain
SPINAL CORD
CROSS-SECTION OF SPINAL CORD
Functions of the spinal cord
•
•
•
•
Links the brain with all the organs of the body
(except those in the head & neck)
Carries sensory information to the brain for
interpretation
Carriers then motor information from the
brain to the effectors (muscles and glands)
It’s a centre for the reflex action, which
enables the body to respond very quickly to
harmful stimuli using the reflex arc
A typical nerve cell – A NEURON
Dendrites
Cell membrane
Cell body
Nissl body
Schwann cell
Axon
Node of Ranvier
Impulse
direction
Myelin sheath
Nucleus of Schwann cell
Neurilemma
Portion of axon cut out to
show great length
Motor end-plates in
effector muscle
Structure of a multipolar neuron (motor neuron)
Structure and function of three
types of neurons
Type of neuron
Sensory (afferent)
neuron
Senses (detects) the
stimulus
Function
Transmits impulses
from the sense
organs or receptors
to the spinal cord
Structure
Sensory neuron
(Cell body is located
outside the CNS)
Structure and function of three
types of neurons
Type of neuron
Interneuron
(connector)
Found in the brain and
spinal cord
Function
Links the sensory
neuron to the motor
neuron
Structure
Interneuron
Structure and function of three
types of neurons
Type of neuron
Motor (efferent)
neuron
Response to the
stimulus
Function
Transmits impulses
from the brain and
spinal cord to the
effectors (muscles
and glands). The
effectors bring about
the response.
Structure
Motor neuron
(Cell body is located
inside the CNS)
A nerve impulse crosses from
one neuron to the next
Axon
Stored
neurotransmitter
molecules
Synaptic vesicle
Neurotransmitters
are released
Synapse gap
Dendrite
Receptors
Drawing illustrating how a nerve impulse crosses the synapse gap
Significance of synapses
• Make sure that impulses travel in one
direction
• At the synapses, the nerve impulse can be
speeded up, slowed down or blocked by
releasing hormones or by using drugs
Effects of certain drugs on the CNS:
Ecstacy
Is a stimulant that increases the production of the
neurotransmitter, serotonin, in the brain. This
increases the activity of the neurons that regulate
mood, sleep, pain, emotion and appetite.
Effects..
•
initially feeling really good,
•
later on the person feels depressed and sleepy
•
eventually long-lasting depression, changed
moods and poor sleep patterns.
Effects of certain drugs on the CNS:
Heroin
Is a narcotic. Addicts inject heroin into their
veins. When it reaches the brain it binds to
special receptors on some neurons which are
found in the brain areas involved in pain
perception and in the medulla oblongata. The
effect of heroin is to …
• dull pain, causes the person to feel happy, free
from anxiety and satisfied;
• this soon changes to a sleepy state,
Effects of certain drugs on the CNS:
Heroin (cont.)
Overdose of heroin shuts down the neurons
of the medulla oblongata, which
suppresses the breathing rate and heart
rate and eventually cause death.
Effects of certain drugs on the CNS:
Dagga
Dagga is a hallucinogen. It is dried parts of a plant
called Cannabis. It contains at least 60 different
chemicals that affect the working of the brain.
THC, the most powerful chemical, attaches to the
receptors of neurons that are used for short term
memory, thought, concentration, and time and
distance perception.
The effect is a feeling of pleasure followed by a
loss of memory, personality disturbance,
depression and anxiety.
Effects of certain drugs on the CNS:
Tik
• Is a stimulant. When it reaches the brain, it
causes a sudden increase in the
neurotransmitter, called dopamine, which
regulate feelings of pleasure and control
behaviour. Effects …
• destroys the dopamine receptors – impossible
to feel pleasure or control behaviour
• suffer from anxiety, extreme aggression and
delusions (false ideas or beliefs)
Reflex action and reflex arc
• A reflex arch is a specific nerve pathway to
perform a reflex action without going to the
brain for interpreting.
Study the drawing of the reflex arc on the next
slide:
A nerve pathway consists of the following:
receptor, sensory neuron, dorsal root, spinal cord with
the interneuron, motor neuron, ventral root, and ending
in an effector.
Drawing of a labelled reflex arc
Describe the mechanism of a reflex action
An example:
1. A person pricks (stimulus) a finger
2. Pain receptors in the finger detect the stimulus
3. Receptors convert the stimulus into a nerve
impulse
4. A sensory neuron carries the nerve impulse
via the dorsal root into the spinal cord.
5. Inside the spinal cord the impulse is carried by
the sensory neuron to the interneuron, the
interneuron carries the impulse to the motor
neuron.
Mechanism of reflex action (cont.)
6. The motor neuron leaves the spinal cord via
the ventral root.
7. The motor neuron carries the nerve impulse
to the effector (muscle). The muscle contracts
and the finger is withdrawn from the
stimulus.
Memorise the description of a reflex action
together with the drawing of a reflex arc.
Significance of reflex arc
Reflex arc is …
• a rapid automatic response to a stimulus; does
not have to go to the brain to be interpreted en
then pass down the spinal cord again.
• an unlearned action / involuntary
• built into the anatomy of the body
• protecting the body from harmful stimuli.
The interneuron makes a short cut in the spinal cord
possible.
DISORDERS OF THE NERVOUS SYSTEM
Alzheimer’s disease
Is a progressive and degenerative disease of the
brain, which causes the loss of memory and
thinking skills. Common in older people and affects
both men and women.
The causes of Alzheimer is not fully understood,
scientists believe that the disease develops when
•
synapsis in the brain become clogged with
chemicals that are normally removed,
•
brain cells are killed and those that remain
have fewer connections than normal,
Alzheimer’s disease
People with severe Alzheimer’s disease cannot
communicate properly and are dependent on
other people for their care.
At present there are no treatments that can
delay or stop the progression of the disease.