Neuron communication - Chapter 3

Question 1

Neurons

Answer 1

a nerve cell; the basic structural and functional unit of the nervous system.

Question 2

Cell body

Answer 2

contains the nucleus and is responsible for controlling the functioning of the cell.

Question 3

Dendrites

Answer 3

usually fairly short extensions of the cytoplasm of the cell body. highly branched and carry messages/impulses into the cell body.

Question 4

Axon

Answer 4

single, long extension of the cytoplasm. carries impulses away from cell body. in brain, length is small, some run from spinal cord to foot (metres long)

Question 5

Myelin sheath

Answer 5

fatty material covering the axon. outside the brain and spinal cord, it is formed by the schwann cells. gaps in myelin sheath are called nodes of ranvier.

Question 6

Oligodendrocytes

Answer 6

produce myelin sheath in the brain and spinal cord.

Question 7

3 Important functions of myelin sheath

Answer 7

1. acts as an insulator
2. it protects the brain from damage
3. it speeds up the movement of nerve impulses along the axon.

Question 8

Synapse

Answer 8

the junction between the branches of adjacent neurons.

Question 9

Neurotransmitters

Answer 9

a molecule that carries a nerve impulse across the small gap between branches of adjacent nerve cells.

Question 10

Neuromuscular junction

Answer 10

junction between branches of a motor nerve cell and muscle fibre

Question 11

Functional types of neurons

Answer 11

• sensory (afferent/receptor) neurons
• motor (efferent/effector) neurons
• interneurons (association/connector/relay)

Question 12

Sensory neurons

Answer 12

carry messages from receptors in sense organs, or skin to CNS

Question 13

Motor neurons

Answer 13

carry messages from CNS to effectors (muscles/glands)

Question 14

Interneurons

Answer 14

located in CNS and are the link between sensory and motor neurons

Question 15

Structural types of neurons

Answer 15

• multipolar neurons
• bipolar neurons
• unipolar neurons
• pseudo-unipolar

Question 16

Multipolar neurons

Answer 16

one axon + many dendrites
e.g. motor/interneuron

Question 17

Bipolar neurons

Answer 17

one axon + one dendrite
e.g. neurons in eye, ear and nose

Question 18

Unipolar neurons

Answer 18

one axon + nil dendrites
e.g. not found in humans

Question 19

pseudounipolar neurons

Answer 19

one axon that divides into two + nil dendrites
e.g. sensory neuron

Question 20

Reflex

Answer 20

a reflex is a rapid, automatic response to change in the external/internal environment.

Question 21

4 Important properties of reflexes:

Answer 21

1. a stimulus is required to trigger a reflex (it is not spontaneous)
2. a reflex is involuntary (occurs with no conscience thought)
3. a reflex is rapid (only small number of neurons involved)
4. a reflex response is stereotyped (occurs in same way each time)

Question 22

Steps of a reflex arc

Answer 22

1. the receptor reacts to a change in internal/external environment by initiating a nerve impulse in the sensory neuron
2. sensory neuron carries impulse from receptor to spinal cord/brain
3. there is at least 1 synapse - nerve impulse may be passed directly to motor neuron or one or more interneurons that direct the impulse to the correct motor neuron.
4. motor neuron carries impulse to effector
5. effector (muscle or secretory cells) receives impulse, carrying out appropriate response.