HUMAN RESPONSES TO THE ENVIRONMENT

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HUMAN RESPONSES TO THE ENVIRONMENT

• Two systems to be studied
• Nervous system
• Endocrine system

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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.

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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.

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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.

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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

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Co-ordination in Humans
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Human nervous system is a complex system
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Cross-section of the human brain showing the
different parts
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Functions of certain parts of the brain

• Cerebellum
• Co-ordinates movements of your voluntary
• muscles
• Maintains your balance by controlling
• muscle tension

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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

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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

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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
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SPINAL CORD
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CROSS-SECTION OF SPINAL CORD
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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)
• Its a centre for the reflex action, which
• enables the body to respond very
  quickly to
• harmful stimuli using the reflex arc

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A typical nerve cell A NEURON
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Structure and function of three types of neurons
Type of neuron Function Structure
  Sensory (afferent) neuron Senses (detects) the stimulus   Transmits impulses from the sense organs or receptors to the spinal cord Sensory neuron (Cell body is located outside the CNS)
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Structure and function of three types of neurons
 Type of neuron  Function Structure
Interneuron (connector)   Found in the brain and spinal cord Links the sensory neuron to the motor neuron Interneuron
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Structure and function of three types of neurons
 Type of neuron  Function Structure
Motor (efferent) neuron   Response to the stimulus Transmits impulses from the brain and spinal cord to the effectors (muscles and glands). The effectors bring about the response. Motor neuron (Cell body is located inside the CNS)
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A nerve impulse crosses from one neuron to the
next
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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

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Effects of certain drugs on the CNSEcstacy

• 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.

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Effects of certain drugs on the CNSHeroin

• 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,

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Effects of certain drugs on the CNSHeroin
(cont.)

• Overdose of heroin shuts down the neurons of the
  medulla oblongata, which suppresses the breathing
  rate and heart rate and eventually cause death.

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Effects of certain drugs on the CNSDagga

• 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.

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Effects of certain drugs on the CNSTik

• 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)

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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.

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Drawing of a labelled reflex arc
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Describe the mechanism of a reflex action

• An example
• 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.
• Inside the spinal cord the impulse is carried by
  the sensory neuron to the interneuron, the
  interneuron carries the impulse to the motor
  neuron.

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Mechanism of reflex action (cont.)

• The motor neuron leaves the spinal cord via the
  ventral root.
• 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.

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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.

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DISORDERS OF THE NERVOUS SYSTEMAlzheimers
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,

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Alzheimers disease

• People with severe Alzheimers 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.