[B3] The Nervous System

Question 1

What are neurons?

Answer 1

Nerve cells that transmit information by producing electrical impulses which travel around the body.

Question 2

What detect changes in the environment (Stimulus)?

Answer 2

Sensory receptors. Different types of receptors detect different stimuli.

e.g Receptors in the retina detect light

Question 3

What happends when a stimulus is detected by a receptor?

Answer 3

Electrical impulses are sent along sensory neurons to the central nervous system (CNS).

Question 4

What is the CNS?

Answer 4

It consists of the brain and spinal cord.

Question 5

What does the CNS do?

Answer 5

Coordinates a response - it sends information to an effector (muscle or gland) along a motor neuron. The effector then responds accordingly.

e.g Muscle will contract, or gland secrete a hormone

Question 6

How are electrical impuses transmitted between neurons?

Answer 6

They are passed along the axon of the neuron.

Question 7

What are dendrites?

Answer 7

Branched endings of a neuron which allow neurons to connect with multiple other neurons.

Question 8

What are the branched endings of a neuron called?

Answer 8

Dendrites.

Question 9

How are the transmittions of electrical impulses sped up?

Answer 9

[1] In some neurons, the axon is surrounded by a myelin sheath (formed by Schwann cells). This acts as an insulator which speeds up the electrical impuse.

[2] Neurons are also long; electrical impulses travel faster through one long axon than being transmitted by different neurons joined together.

Question 10

What is the myelin sheath?

Answer 10

A fatty sheath which surrounds and insulates the axon formed by Schwann cells.

Question 11

What is the connection between two neurons called?

Answer 11

A synapse.

Question 12

What is a synapse?

Answer 12

The connection between two neurons - basically a minuscule gap between neurons.

More formally: the site of transmittion of electrical impulses between two neurons.

Question 13

How do synapses work?

Answer 13

The electrical impulse triggers the release of transmitter chemicals which diffuse across the gap.

These chemicals bind to receptor molecules in the membrane of the next neuron. This activates a new electrical impuse.

Question 14

What are the purpose of relay neurons?

Answer 14

They simply connect sensory neurons to motor neurons.

Question 15

What are reflex actions?

Answer 15

Actions that are automatic and involuntary. They are performed without conscious thought so are performed quicker than normal responses.

They aim to minimise damage to the organism and are essential for survival.

Question 16

What is a reflex arc?

Answer 16

The passage of information in a reflex (fron receptor to effector).

Question 17

How does a reflex arc work?

Answer 17

The sensory neuron connects to a relay neuron in the spinal cord, or in an unconscious part of the brain - which links directly to the right motor neuron.

Question 18

What are the steps of a reflex arc?

Answer 18

[1] A receptor detects a stimulus. (e.g finger touches hot object, change in temperature)

[2] Pain receptor is stimulated.

[3] Electrical impulse travels along the sensory neuron.

[4] Impulse is passed along a relay neuron in the spinal cord.

[5] Impulse travels along a motor neuron.

[6] Impulse is transmitted from motor neuron to the effector. (e.g muscle contracts to move away from hot object)

Question 19

What are the components of a automatic control system?

Answer 19

Stimulus, receptor, a coordination center, an effector and response.

Question 20

What are the differences in purposes between the sensory neuron and the motor neuron?

Answer 20

[Sensory neuron] Transmits electrical impulses from the receptor to the CNS. It is an afferent neuron.

[Motor neuron] Transmits electrical impulses from the CNS to the effector. It is an efferent neuron.

Question 21

Describe the differences in length of the axons/denrites in a sensory neuron and a motor neuron.

Answer 21

[Sensory neurons] Generally have a longer dendron and shorter axons.

[Motor neurons] Generally have shorter dendrites longer axons.

Question 22

Describe the areas in which the dendrites are located in a sensory neuron.

Answer 22

[Sensory neurons] Their dendrites are located near the skin/receptor where they recieve electrical impulses.

Question 23

Describe the areas in which the dendrites are located in a motor neuron.

Answer 23

[Motor neurons] Their dendrites and cell body is located in the CNS,

Question 24

Describe the areas in which axons are located in a sensory neuron.

Answer 24

[Sensory neurons] Their axons are located at the spinal cord where they connect with the dentrites of other neurons.

Question 25

Describe the areas in which axons are located in a motor neuron.

Answer 25

[Motor neurons] Their axon is located in the effector (muscle or gland) that they innervate.