3.4 - Nervous System

Question 1

What are the two divisions of the nervous system?

Answer 1

• Central Nervous System (CNS)
• Peripheral Nervous System (PNS)

Question 2

What does the CNS do?

Answer 2

(CNS) is spinal cord and brain. It’s responsible for processing information (making decisions)

Question 3

What does the PNS do?

Answer 3

(PNS) is all nerves that extend from the spine and brain, and are more the “effectors” of the CNS’ commands

Question 4

What are the three major functions of the nervous system?

Answer 4

1) Monitor internal and external environment of the body
- Sensory receptors pick up STIMULI:
- E.g. external: temp, light, noise, smell, position, pressure, pain…
- E.g. internal: [ions] (Na+, K+, Ca++…), blood gasses/pH, glucose levels, water levels…

2) Integrate and analyze sensory information
- Understanding what a stimulus means and how to react to it
- This includes higher order thinking like learning and memory

3) Co-ordinate responses in all other organ systems
- Voluntary and involuntary
- Triggering appropriate response to stimuli
- E.g. muscle contraction, glandular release, change in metabolic rate…

Question 5

What are the components of the CNS?

Answer 5

Brain and spinal cord (with nerves branching out from spine all the way down)

Question 6

What are the components of the spine?

Answer 6

• Vertebrae
• Disks (spongy, fluid-filled cushion between bones)
• Spinal cord (nerve fibres)
• Grey matter (cell bodies) = arranged in the middle in a butterfly shape

** White matter (myelinated axons) surrounds the grey, arranged into columns

*** Gives rise to 31 pairs of spinal nerves

Question 7

What does the brain NOT control?

Answer 7

Reflexes (quick communication with spine)

Question 8

How is the brain protected?

Answer 8

Well-protected with skull, cerebrospinal fluid (a liquid that surrounds brain) and Blood-brain barrier (selective barrier to prevent drugs or infections to easily enter the brain - called meninges)

Question 9

What are the 2 branches of the peripheral nervous system (PNS)?

Answer 9

• Somatic Nervous System (SNS) control our voluntary muscles. They both send and receive information to/from the CNS
• Autonomic Nervous System (ANS) is involuntary and influence breathing, the heart, parts of the digestive system, and more. They DO NOT generally receive information (“sense”)
• The ANS is actually divided further into opposite functions: SYMPATHETIC (Fight or flight - “active” behaviour) vs. PARASYMPATHETIC (Rest and digest - “passive” behaviour)

Question 10

What are the two types of glial cells for insulation/myelination?

Answer 10

• Oligodendrocytes (CNS)
• Schwann cells (PNS)

Question 11

How are axons myelinated?

Answer 11

A myelin-producing cell wraps itself around the axon, in multiple layers, to provide insulation for the electrical signal passing along the length of the axon

Question 12

What are the gaps between segments of myelin, and why do they exist?

Answer 12

There are gaps between each segment of myelin called “Nodes of Ranvier”

These gaps allow ions to cross the axon’s cell membrane

Question 13

What do neurons do?

Answer 13

Neurons receive information and then pass it on

Question 14

How do neurons receive information?

Answer 14

They receive information through their DENDRITES

Question 15

How does information move through a neuron?

Answer 15

The information passes through the CELL BODY (also called a “Soma”). Proteins may be produced if appropriate (typically in the ER) and move as vesicles inside the cell

Question 16

What is at the end of an axon, and what do they do?

Answer 16

The ends of the Axon (“terminals”) of one neuron touch many Dendrites of other neurons, thus making a large network

Question 17

What is the point which connects dendrites to axons called, and what does it do?

Answer 17

The junction between Dendrites and Axons is called a SYNAPSE. It is here that vesicles are released (moving here along the cytoskeleton)

Question 18

What are the two major neuronal anatomical types (Different shaped neurons)?

Answer 18

Multipolar and unipolar

Question 19

What are the characteristics of a multipolar neuron?

Answer 19

• Most common in CNS; “classic” lollipop shape
• Structure of MOTOR neurons and INTERNEURONS
• Axons can be up to 1m long

Question 20

What are the characteristics of a unipolar neuron?

Answer 20

• Dendrites feed into axon directly, cell body off to the side
• Structure of SENSORY neurons that originate in PNS
• Axons can be up to 1m long

Question 21

What are the 3 possible roles of a neuron?

Answer 21

• Sensory neurons
• Interneurons
• Motor neurons

Question 22

What do sensory neurons do?

Answer 22

Sensory neurons receive information and pass this towards the CNS

Question 23

What do interneurons do?

Answer 23

Interneurons receive information from sensory neurons and pass it onwards, ultimately making a decision, and then sending the “commands” from that decision back to the PNS

Question 24

What do motor neurons do?

Answer 24

Motor neurons are at the end of this “loop” and cause muscular contractions/relaxation in response to decisions made