HUMAN RESPONSES TO THE ENVIRONMENT Two systems to be studied: Nervous system 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 Chemical co-ordination Central nervous system Peripheral and autonomic nervous systems Sense receptors and organs Endocrine system Feedback mechanisms Over- & under-secretion

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

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)

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

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)

A nerve impulse crosses from one neuron to the next Axon Stored neurotransmitter molecules Synaptic vesicle Neurotransmitters are released Receptors Synapse gap Dendrite 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: 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.

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.

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.