Nervous System: Reflex and Voluntary Actions

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Questions and Answers

What is the first step in a reflex action when touching a hot object?

Receptors in the skin are stimulated. (correct)

Nerve impulses are transmitted to the spinal cord.

The impulse travels to the brain.

The muscle contracts.

Which of the following best describes the components of a reflex arc?

Receptor → motor neurone → relay neurone → effector.

Receptor → sensory neurone → motor neurone → effector.

Receptor → sensory neurone → effector.

Receptor → sensory neurone → relay neurone → effector. (correct)

What type of actions do reflexes represent?

Voluntary actions.

Conscious actions.

Learned actions.

Involuntary actions. (correct)

In a classic knee-jerk reflex, which muscle contracts as an effector?

The thigh muscle. Signup and view all the answers

What role does the motor neurone play in the reflex arc?

Transmits impulses to the effector. Signup and view all the answers

Which component is absent in certain reflex actions such as the knee-jerk?

Relay neurone. Signup and view all the answers

Which correctly describes cranial reflexes?

Reflexes that occur without consciousness in the head region. Signup and view all the answers

What triggers the production of nerve impulses in the reflex arc?

Heat from an object. Signup and view all the answers

What type of muscles control the iris?

Antagonistic muscles Signup and view all the answers

Which of the following best describes the light rays reflecting off a distant object?

They are almost parallel. Signup and view all the answers

What happens to the lens when focusing on nearby objects?

The lens becomes thicker. Signup and view all the answers

Which of the following statements is true regarding the ciliary muscles during accommodation?

They cause the lens to change shape. Signup and view all the answers

What is the main purpose of accommodation in the eye?

To form clear images on the retina. Signup and view all the answers

What occurs to the suspensory ligaments when the ciliary muscles relax?

They become taut. Signup and view all the answers

How does the eye react when focusing on a distant object?

Minimal refraction is required. Signup and view all the answers

What happens during the process of accommodation for nearby objects?

The ciliary muscles contract. Signup and view all the answers

What happens to the ciliary muscles when focusing on a distant object?

They contract, relaxing their pull on the suspensory ligaments Signup and view all the answers

Which statement accurately describes the changes in the lens while focusing on a distant object?

The lens becomes thinner and less convex Signup and view all the answers

What is the role of the optic nerve in the process of vision?

To transmit the generated nerve impulses to the brain Signup and view all the answers

What occurs after light rays are sharply focused on the retina?

The brain interprets the impulses and the person sees the distant object Signup and view all the answers

What mechanism allows light rays from a distant object to be sharply focused on the retina?

Slackening of the suspensory ligaments Signup and view all the answers

What is the role of sense organs in the human body?

They receive stimuli through receptors. Signup and view all the answers

What type of actions can the body's response to stimuli be classified into?

Involuntary and voluntary actions. Signup and view all the answers

Which part of the nervous system consists of cranial and spinal nerves?

Peripheral nervous system (PNS) Signup and view all the answers

What are the basic components of the central nervous system (CNS)?

Brain and spinal cord. Signup and view all the answers

How do sensory neurones function in the nervous system?

They transmit nerve impulses from receptors to the CNS. Signup and view all the answers

What is a synapse?

A junction between two neurones or a neurone and an effector. Signup and view all the answers

Which type of neurone transmits impulses from the CNS to effectors?

Motor neurone Signup and view all the answers

What is the immediate response to a specific stimulus called?

Reflex action Signup and view all the answers

Which of the following describes the process of transmission across a synapse?

By chemical means through neurotransmitters Signup and view all the answers

What is sensitivity in the context of sense organs?

The ability to detect and respond to changes in the environment. Signup and view all the answers

What initiates a reflex action?

A specific stimulus Signup and view all the answers

Which type of neurone is found within the CNS and connects sensory and motor neurones?

Relay neurone Signup and view all the answers

What is the main function of the motor neurone?

To carry impulses to effectors for action. Signup and view all the answers

What type of response is NOT controlled consciously?

Reflex response Signup and view all the answers

What is the primary role of the bicep muscle in the nervous response?

It contracts to withdraw the hand suddenly. Signup and view all the answers

Which structure of the eye is responsible for controlling the amount of light that enters?

Pupil Signup and view all the answers

What is the main function of the conjunctiva?

To keep the eyeball moist. Signup and view all the answers

Which layer of the eye contains the photoreceptor cells?

Retina Signup and view all the answers

What happens to the pupil in bright light conditions?

The pupil constricts to reduce light entry. Signup and view all the answers

Which substance helps keep the eyeball firm and assists in light refraction?

Vitreous humour Signup and view all the answers

What is the pathway of nerve impulses during a pupil reflex in bright light?

Stimulus → sensory neurons → brain → motor neurone → effector. Signup and view all the answers

What is the function of the ciliary body in the internal structure of the eye?

To control the curvature and thickness of the lens. Signup and view all the answers

Which structure prevents the excessive reflection of light within the eyeball?

Choroid Signup and view all the answers

What role do the iris muscles play when transitioning from dim to bright light?

They relax to decrease pupil size. Signup and view all the answers

What is the function of the blind spot in the eye?

It lacks photoreceptors, making it insensitive to light. Signup and view all the answers

What happens to the iris muscles in dim light conditions?

The circular muscles relax while radial muscles contract. Signup and view all the answers

Which structure is described as a dome-shaped transparent layer that refracts light?

Cornea Signup and view all the answers

Study Notes

Nervous System - Reflex Arc

A reflex arc is the shortest pathway that nerve impulses travel from the receptor to the effector in a reflex action.
The pathway consists of a receptor, sensory neurone, relay neurone, motor neurone and effector.
There is no relay neurone in a simple reflex arc such as the knee-jerk reflex.

Nervous System - Voluntary and Involuntary Actions

Voluntary Actions are actions that are controlled consciously.
Involuntary Actions are automatic activities that are not controlled consciously, such as heartbeat, breathing and temperature regulation.
These actions are also known as internal regulatory processes.

Nervous System - Sensation, Reflex Action and Voluntary Action

The pathway of nerve impulses for Sensation is: Receptor → sensory neurone → relay neurone in the spinal cord/brain → brain.
The pathway of nerve impulses for Reflex Action is: Receptor → sensory neurone → relay neurone in the spinal cord/brain → motor neurone → effector.
The pathway of nerve impulses for Voluntary Action is: Brain → relay neurone in spinal cord/brain → motor neurone → effector.

Eye - External Structures

The cornea is a dome-shaped transparent layer that refracts light rays into the eye.
The iris is a circular sheet of muscles that controls the size of the pupil and therefore the amount of light entering the eye.
The pupil is a hole in the centre of the iris that allows light to enter the eye.
Eyelashes protect the eye from dust particles.
The tear gland secretes tears that wash away dust particles, keep the cornea moist, and lubricate the conjunctiva.
The eyelid protects the cornea from mechanical damage, prevents entry of excessive light, and spreads tears over the eyes to wipe off dust.
The sclera is a tough, white outer covering of the eyeball which is continuous of the cornea.
The conjunctiva is a mucous membrane covering the sclera that secretes mucus to keep the front of the eyeball moist.

Eye - Internal Structures

The choroid is a black pigmented middle layer that prevents the internal reflection of light, contains blood vessels that supply oxygen and nutrients to the eyeball, and removes metabolic waste products from the eyeballs.
The retina is the innermost layer of the eye wall containing light-sensitive cells known as photoreceptors (rods and cones).
The ciliary body contains ciliary muscles that control the curvature and thickness of the lens.
The lens is a transparent, circular, and biconvex structure that changes shape to refract light onto the retina.
The suspensory ligaments attach the lens to the ciliary body.
The vitreous humour is a transparent jelly-like substance that keeps the eyeball firm and refracts light onto the retina.
The aqueous humour is a transparent watery fluid that keeps the front of the eyeball firm and refracts light into the pupil.
The fovea is a small yellow depression where images are focused and contains cones but not rods enabling a person to have detailed colour vision in bright light.
The optic nerve transmits nerve impulses to the brain.
The blind spot is the region where the optic nerve leaves the eye and does not contain photoreceptors, therefore not sensitive to light.

Pupil Reflex (Bright and Dim Light)

The pupil reflex is a reflex action in response to changes in light intensity.
The circular and radial muscles of the iris are antagonistic muscles.
The pupil reflex protects the eye from excessive light exposure.
The pupil constricts in bright light by the circular muscles contracting and the radial muscles relaxing.
The pupil dilates in dim light by circular muscles relaxing and the radial muscles contracting.
The pathway of nerve impulses in the pupil reflex is: Stimulus (change in light intensity) → receptor (retina) → sensory neurons in optic nerve → brain → motor neurone → effector (iris).

Focusing (Far and Near)

Focusing or accommodation is the adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina.
It is necessary so that objects at different distances can be seen clearly.
When focusing on a distant object, the lens becomes thinner, ciliary muscles relax, and suspensory ligaments become taut.
When focusing on a nearby object, the lens becomes thicker, ciliary muscles contract, and suspensory ligaments relax.

Sense Organs

Sense organs are specialized structures designed to receive stimuli from the environment.
They contain receptors that detect changes in the environment and convert them into electrical signals called nerve impulses.
These impulses are transmitted to the central nervous system (CNS) for processing.
Examples of sense organs include the eye, ear, nose, tongue, and skin.

Role of the Nervous System

The nervous system is responsible for coordinating and regulating the activities of the body in response to stimuli.
Responses can be voluntary (consciously controlled) or involuntary (automatic).
The nervous system consists of the CNS (brain and spinal cord) and the peripheral nervous system (PNS - cranial and spinal nerves).

### Central Nervous System (CNS)

The CNS is the control center of the nervous system.
It receives information from the sense organs through sensory neurons and sends instructions to muscles and glands through motor neurons.
The CNS is also responsible for processing information, learning, memory, and behavior.

Peripheral Nervous System (PNS)

The PNS consists of nerves that connect the CNS to the rest of the body.
It carries sensory information from the sense organs to the CNS and motor commands from the CNS to muscles and glands.

### Neurons

Neurons are the basic functional unit of the nervous system.
They are specialized cells that transmit nerve impulses.
There are three types of neurons: sensory neurons, motor neurons, and relay neurons.
Sensory neurons transmit impulses from receptors to the CNS.
Motor neurons transmit impulses from the CNS to effectors (muscles and glands).
Relay neurons transmit impulses between sensory and motor neurons within the CNS.

Synapse

A synapse is the junction between two neurons or between a neuron and an effector.
It is the site where nerve impulses are transmitted.
Transmission across a synapse is chemical, mediated by neurotransmitters.

Reflex Actions

A reflex action is an immediate response to a specific stimulus without conscious control (involuntary action).
It is a rapid, automatic response that involves a reflex arc.
A reflex arc is the pathway that nerve impulses travel during a reflex action. It involves a sensory neuron, a relay neuron, and a motor neuron.
The spinal cord and brain (CNS) act as reflex centers.
Spinal reflexes are reflexes controlled by the spinal cord, such as the knee-jerk reflex.

The Eye - A Sense Organ

The eye is the sense organ responsible for sight.
It detects light and converts it into nerve impulses that are transmitted to the brain.
The eye consists of several structures, including the lens, ciliary muscles, suspensory ligaments, and retina (photoreceptors).
When focusing on a distant object, the ciliary muscles relax, the suspensory ligaments tighten, and the lens becomes thinner, allowing light rays to be focused sharply on the retina.
When focusing on a near object, the ciliary muscles contract, the suspensory ligaments slacken, and the lens becomes thicker.

### Key Terms

Stimulus: A change in the environment that triggers a functional reaction in an organism or tissue.
Response: An organism's reaction to a stimulus.
Sensitivity: The ability to detect and respond to changes in the environment.

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Description

This quiz explores key concepts related to the nervous system, focusing on reflex arcs and the distinction between voluntary and involuntary actions. Understand the pathways of nerve impulses and how they impact bodily functions. Perfect for students studying biology or neuroscience.