Lesson Notes By Weeks and Term - Senior Secondary 2

TERM – 3^RD TERM

WEEK SIX

Class: Senior Secondary School 2

Age: 16 years

Duration: 40 minutes of 5 periods each

Date:

Subject: Biology

Topic: STRUCTURE AND FUNCTION OF THE NEURONE

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

1. Identify types of neurone
2. Describe the structure of a neurone
3. Describe the transportation of nerve impulse
4. Discuss Pavlov experiment

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

NOTE

STRUCTURE AND FUNCTIONS OF A NEURON

Neuron

A neuron is the basic structural and functional unit of the nervous system. It is a specialized cell that processes and transmits information through electrical and chemical signals. Neurons play a crucial role in communication within the nervous system.

Types of Neurons

1. Sensory Neurons (Afferent Neurons): Transmit sensory information from sensory receptors (e.g., eyes, skin) to the central nervous system (CNS). Example is the Neurons conveying the sensation of touch to the spinal cord.
2. Motor Neurons (Efferent Neurons): Transmit signals from the CNS to muscles and glands, leading to movement or secretion. Example is the Neurons controlling muscle contraction.
3. Interneurons (Relay Neurons): Found in the CNS, these neurons act as intermediaries between sensory and motor neurons, facilitating communication between them. Example is Neurons in the spinal cord that connect sensory and motor neurons.

Structure of a Neuron:

1. Cell Body (Soma): Contains the nucleus and other organelles, responsible for the basic life processes of the neuron.
2. Dendrites: Branch-like extensions that receive signals (nerve impulses) from other neurons or sensory receptors.
3. Axon: A long, slender projection that conducts nerve impulses away from the cell body towards other neurons, muscles, or glands.
4. Axon Hillock: The region where the axon originates from the cell body, often the site where nerve impulses are generated.
5. Myelin Sheath: Fatty insulation around the axon that enhances the speed of nerve impulse transmission.
6. Nodes of Ranvier: Gaps in the myelin sheath where the axon is exposed; important for the efficient conduction of nerve impulses.
7. Axon Terminals (Synaptic Terminals): The ends of the axon where neurotransmitters are released to transmit signals to the next neuron or target cell.

 Transportation of a nerve impulse

The transportation of a nerve impulse, also known as an action potential, occurs along the length of a neuron, from the dendrites to the axon terminals. This process involves changes in the electrical charge across the neuron's membrane. The following is an overview of the transportation of a nerve impulse:

1. Resting State: The neuron is in a resting state with a negative charge inside and a positive charge outside. This is maintained by the sodium-potassium pump.
2. Depolarization: When a stimulus is received (e.g., from sensory receptors or other neurons), ion channels in the neuron's membrane open. Sodium ions (Na+) rush into the neuron, causing a rapid change in membrane potential. This shift is called depolarization.
3. Action Potential: If the depolarization reaches a threshold level, it triggers an action potential, a rapid and temporary reversal of the membrane potential.
4. Propagation: The action potential travels along the axon from the axon hillock to the axon terminals. This is achieved through a series of depolarization and repolarization events.
5. Repolarization: After the action potential passes, potassium ions (K+) move out of the neuron, restoring the negative charge inside. This phase is called repolarization.
6. Hyperpolarization: In some cases, there is a brief hyperpolarization where the membrane potential becomes more negative than the resting state before returning to normal.
7. Axon Terminals: When the action potential reaches the axon terminals, it triggers the release of neurotransmitters into the synapse.
8. Synaptic Transmission: Neurotransmitters cross the synapse and bind to receptors on the next neuron or target cell, transmitting the signal.

Reflex action and voluntary action.

Reflex Action:

A reflex action is an involuntary and rapid response to a stimulus, often occurring without conscious thought. It is designed to protect the body from harm and ensure a quick response to potential dangers. Example includes;

1. Knee-Jerk Reflex:

When a doctor taps your knee with a reflex hammer, the sensory neurons in your knee muscles send a signal to the spinal cord. In response, motor neurons immediately send signals back to contract the muscles, causing the leg to kick involuntarily.

1. Voluntary Action:

Voluntary actions are intentional movements that are consciously initiated and controlled by the brain. These actions involve a more complex neural pathway and require coordination of various muscles. Example includes, Writing with a Pen

Pavlov experiment

The Pavlovian or classical conditioning experiment conducted by Ivan Pavlov involved studying the association between a neutral stimulus and a reflex response. Pavlov's most famous work involved dogs and the pairing of a bell with the presentation of food, leading to the development of a conditioned response.

Below is an overview of the experiment

1. Unconditioned Stimulus (UCS):

   - Food: Initially, the presence of food was an unconditioned stimulus that naturally elicited a salivary response in dogs.

2. Unconditioned Response (UCR):

   - Salivation: The natural, unlearned response of salivating when presented with food.

3. Neutral Stimulus (NS):

   - Bell: Initially, the bell had no inherent connection to salivation.

4. Conditioned Stimulus (CS):

   - Bell: Through repeated pairing with the unconditioned stimulus (food), the neutral stimulus (bell) became a conditioned stimulus.

5. Conditioned Response (CR):

   - Salivation to the Bell: After repeated pairings of the bell with food, the dogs started to salivate in response to the bell alone, even in the absence of food.

In essence, Pavlov demonstrated that a neutral stimulus (bell) could become associated with a natural reflex (salivation) through repeated pairings with an unconditioned stimulus (food). This association led to the development of a conditioned response, where the dogs would salivate in anticipation of food simply upon hearing the bell. This classical conditioning process illustrated how learned associations could influence behavior.

EVALUATION: 1. What is a neuron?

2. Describe the transportation of nerve impulse
3. Describe the Pavlov experiment

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively