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Coordination and response: nervous system — KCSE Biology

KCSE Biology · 86 practice questions · 4 syllabus objectives · 4 revision lessons

25 easy35 medium26 hard

Last updated · Aligned to the KNEC KCSE syllabus

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Draw and label a motor neuron

Describe the transmission of a nerve impulse

Describe a reflex arc with a named example

Coordination and response: nervous system

Revision Notes

Concise lesson notes for Coordination and response: nervous system, written to the KCSE Biology marking standard. Read the first lesson free below.

Drawing and Labeling a Motor Neuron

A motor neuron is essential for transmitting signals from the central nervous system to muscles, enabling movement. When drawing a motor neuron, include the following key structures:

  • Cell body (soma): Contains the nucleus and organelles.
  • Dendrites: Branch-like structures that receive signals from other neurons.
  • Axon: A long, thin projection that carries impulses away from the cell body.
  • Myelin sheath: A fatty layer that insulates the axon, speeding up signal transmission.
  • Axon terminals: Small branches at the end of the axon that release neurotransmitters to communicate with other neurons or muscles.

Ensure your diagram is clear and accurately labeled. Use a ruler for neatness and clarity. A well-drawn motor neuron should effectively show the pathway of nerve impulses from the cell body to the muscle fibers.

Key points to remember

  • Motor neurons transmit signals from the CNS to muscles.
  • Key structures include the cell body, dendrites, and axon.
  • The myelin sheath insulates the axon for faster transmission.
  • Labeling should be clear and accurate for full marks.
  • Use neat lines and appropriate proportions in your drawing.

Worked example

Question: Draw and label a motor neuron. Answer: [Draw a clear diagram with the following labels: Cell body, Dendrites, Axon, Myelin sheath, Axon terminals.]

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Lesson 2: Transmission of a Nerve Impulse

Objective: Describe the transmission of a nerve impulse

Nerve impulses are electrical signals that transmit information throughout the nervous system. The transmission of a nerve impulse occurs in several key steps:

  1. Resting Potential: Neurons maintain a resting potential of about -70mV. This is due to the distribution of ions, primarily sodium (Na+) and potassium (K+).

  2. Depolarization: When a stimulus reaches a neuron, sodium channels open. Sodium ions rush into the neuron, causing the inside to become more positive. This change is called depolarization.

  3. Action Potential: If the depolarization reaches a threshold (approximately -55mV), an action potential is generated. This is a rapid rise and fall in voltage across the neuron's membrane.

  4. Repolarization: After reaching the peak of the action potential, potassium channels open, allowing potassium ions to flow out. This restores the negative internal charge, a process known as repolarization.

  5. Propagation: The action potential travels along the axon to the axon terminals, where it triggers the release of neurotransmitters into the synapse, continuing the signal to the next neuron.

Understanding this process is essential for grasping how the nervous system coordinates responses in the body.

  • Nerve impulses are electrical signals transmitted by neurons.
  • Depolarization occurs when sodium ions enter the neuron.
  • Action potential is generated if the threshold is reached.
  • Repolarization restores the neuron's negative charge.
  • Impulses propagate along axons to transmit signals.

Explain how a nerve impulse is transmitted in a neuron.

  • A nerve impulse starts with resting potential at -70mV.
  • Depolarization occurs when sodium ions enter the neuron.
  • If the threshold is reached, an action potential is triggered.
  • Repolarization follows as potassium ions exit the neuron.
Lesson 3: Understanding the Reflex Arc

Objective: Describe a reflex arc with a named example

A reflex arc is a neural pathway that controls a reflex action. It involves several components:

  • Receptor: Detects a stimulus (e.g., heat).
  • Sensory Neuron: Transmits the impulse to the spinal cord.
  • Relay Neuron: Processes the signal within the spinal cord.
  • Motor Neuron: Carries the impulse away from the spinal cord.
  • Effector: Executes the response (e.g., muscle contraction).

Example: The knee-jerk reflex, also known as the patellar reflex, occurs when the knee is tapped. Here’s how it works:

  1. Receptor: Stretch receptors in the patellar tendon detect the stretch when tapped.
  2. Sensory Neuron: Sends the impulse to the spinal cord.
  3. Relay Neuron: Processes the signal and sends it to the motor neuron.
  4. Motor Neuron: Carries the impulse to the quadriceps muscle.
  5. Effector: The quadriceps muscle contracts, causing the leg to kick forward.

This rapid response helps protect the body from harm by allowing quick reactions to stimuli.

  • Reflex arc includes receptor, sensory neuron, relay neuron, motor neuron, effector.
  • Receptor detects stimulus and initiates the reflex action.
  • Sensory neuron transmits impulses to the spinal cord.
  • Relay neuron processes the signal within the spinal cord.
  • Effector carries out the response to the stimulus.

Describe the reflex arc involved in the withdrawal reflex when touching a hot object.

  • Receptor detects heat on the skin.
  • Sensory neuron sends impulse to the spinal cord.
  • Relay neuron processes the signal.
  • Motor neuron sends impulse to arm muscles.
  • Effector (muscles) contracts, pulling the hand away.
Lesson 4: Understanding the Nervous System

Objective: Coordination and response: nervous system

The nervous system is crucial for coordination and response in living organisms. It consists of two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS).

  • Central Nervous System (CNS): This includes the brain and spinal cord. The brain processes information and coordinates responses, while the spinal cord transmits signals between the brain and the rest of the body.
  • Peripheral Nervous System (PNS): This comprises all the nerves outside the CNS. It connects the CNS to limbs and organs, allowing for voluntary and involuntary responses.

The nervous system functions through neurons, which are specialized cells that transmit nerve impulses. Neurons communicate via synapses, where neurotransmitters are released. This system enables rapid response to stimuli, ensuring survival and adaptation.

In summary, the nervous system allows organisms to detect changes in their environment, process this information, and respond appropriately to maintain homeostasis.

  • Nervous system includes CNS and PNS.
  • CNS consists of brain and spinal cord.
  • PNS connects CNS to limbs and organs.
  • Neurons transmit nerve impulses and communicate at synapses.
  • Nervous system enables rapid responses to stimuli.

Describe the role of the spinal cord in the nervous system.

  • The spinal cord transmits signals between the brain and the body.
  • It coordinates reflex actions and processes sensory information.

Sample Questions

Read 3 questions and answers free. Sign up to access all 86 questions with full KNEC-style marking schemes and a personalised study plan.

1
easySHORT ANSWER4 marks

State the components of a reflex arc and give a named example. (4 marks)

Answer & marking scheme

Part (a) — 4 marks
Sensory neurone (1 mk)
Relay neurone (1 mk)
Motor neurone (1 mk)
Example: Knee-jerk reflex (1 mk)
2
easySHORT ANSWER3 marks

State how a nerve impulse is transmitted along a neurone. (3 marks)

Answer & marking scheme

Part (a) — 3 marks
Nerve impulse is initiated by a stimulus causing depolarisation of the neurone membrane (1 mk)
Depolarisation triggers the opening of sodium channels, allowing sodium ions to flow into the neurone (1 mk)
The change in ion concentration creates an action potential that propagates along the axon towards the synapse (1 mk)
3
easySHORT ANSWER2 marks

State the function of the myelin sheath in a motor neurone. (2 marks)

Answer & marking scheme

Part (a) — 2 marks
Insulates the axon to prevent loss of electrical impulses (1 mk)
Increases the speed of nerve impulse transmission via saltatory conduction (1 mk)
4

State the main components of a motor neurone. (4 marks)

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Frequently asked questions

What does the KCSE Biology topic "Coordination and response: nervous system" cover?

Coordination and response: nervous system covers Draw and label a motor neuron; Describe the transmission of a nerve impulse; Describe a reflex arc with a named example, and more, all aligned to the official KNEC KCSE Biology syllabus.

How many practice questions are available for Coordination and response: nervous system?

HighMarks has 86 Coordination and response: nervous system practice questions for KCSE Biology, each with a full marking scheme. The first 3 are free; sign up to access the rest, plus all KCSE mock exams and past papers.

Are these aligned with the KNEC KCSE syllabus?

Yes. Every objective on this page is taken directly from the official KNEC KCSE Biology syllabus. Practice questions match the KCSE exam format and are graded against the standard KNEC marking scheme.

How should I revise Coordination and response: nervous system for the KCSE exam?

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