Test 1 - Nervous System And Neurons

Question 1

What are the three things protecting the central nervous system?

Answer 1

• bones (brain = cranium, spinal-cord = vertebral canal)
• meninges (consists of three layers: outer meningeal layer = tough and fibrous, middle layer = loose mesh of fibres, inner layer = delicate due to many blood vessels)
• cerebrospinal fluid (shock absorber)

Question 2

Name some receptors:

Answer 2

> thermo receptors: heat and cold
osmoreceptors: respond to osmotic pressure and stimulate hypothalamus so that body water content is maintained
chemo receptors: Stimulated by particular chemicals
nociceptors: sensitive to pain and damage to tissues
Touch receptors: sensitive to touch

Question 3

What is a multipolar neuron?

Answer 3

It has one axon and multiple dendrites extending from the cell body. It is most common in interneurons in the brain and spinal cord and motor neurons carrying messages to skeletal muscles

Question 4

What is a bipolar neuron?

Answer 4

It has one axon and one dendrite.

Question 5

What is a uni polar neuron?

Answer 5

Has only an axon and is mostly sensory neurons that carry messages to spinal-cord.

Question 6

What are the roles of each neuron:

Answer 6

Sensory neurons: carries messages from receptors in the sense organs or in skin to the central nervous system
Motor neurons: carries messages from the central nervous system to muscles and glands
Interneurons: The link between sensory and motor neurons

Question 7

What are the four major properties of a reflex?

Answer 7

> A stimulus is required
The response is involuntary
The response is rapid
The response is stereotyped

Question 8

Describe the steps of the reflex arc:

Answer 8

1. Stimulus causes nociceptors to detect pain, generating a nerve impulse
2. Sensory neurons carries nerve impulse to dorsal route ganglion and through the dorsal route into spinal-cord
3. Nerve impulse passed into the interneurons or directly onto a motor neuron
4. Interneuron directs impulse into a motor neuron: motor neuron carries impulses to effector via ventral route
5. Effector responds to remove stimulus
6. Message is sent to brain via upper sensory neuron > conscious and aware

Question 9

What is an innate reflex?

Answer 9

A reflexive withdrawal of the body or parts of the body from either actual or perceived painful stimuli

Question 10

What is an acquired reflex?

Answer 10

A reflex you learn over time (with practice)

Question 11

Describe how the brain controls voluntary movement:

Answer 11

1. Think about moving
   >Motor Association area makes a plan for muscle contraction sequence and intensity
   >Plan sent to primary motor area via nerve impulse
2. Movement initiated
   >primary motor area to upper motor neuron
   > impulse carried to appropriate level of spinal-cord
3. Movement
   > impulse passed onto lower motor neuron to an effector = movement

Question 12

Generation:

Answer 12

1. A resting neuron contains potential energy: this comes from a difference between the electrical charge inside and outside the cell
2. Nerve impulse = Action potential. Occurs when there is a change in the electrical charge of ions inside and outside the cell

Question 13

Polarisation:

Answer 13

3. > resting membrane potential = difference in charge between inside/outside of a resting neuron
   Extracellular fluid has a positive charge due to sodium ions
   Intracellular fluid has a negative charge (large negative ions don’t leave cell and outweigh potassium levels)
   Sodium – potassium pump -> actively pumping potassium into the cell and sodium out
4. All or non response
   >A stimulus of at least 15mV is required to bring membrane potential to -55mV
   >Change occurs when the stimulus opens sodium voltage gated channels and sodium moves into the cell causing intracellular fluid to become more positive

Question 14

Depolarisation:

Answer 14

5. Stimulus of at least 15 mV (increased membrane potential -55 mV)
   >More sodium voltage gated channels open causing an influx of sodium ions into the cell (intercellular fluid = positive, extracellular fluid = negative)
6. Sodium ions diffuse through cytoplasm which stimulates adjacent sodium voltage gated channels to open

Question 15

Repolarisation:

Answer 15

7. The presence of sodium ions and a positive intracellular fluid stimulates potassium voltage gated channels to open = potassium ions flow out of the cell (intracellular fluid = negative, extracellular fluid = positive)
8. ions need to be redistributed so the cell can be stimulated again= Sodium – potassium pump actively restores ions. Until this occurs the section of the neuron enters a refractory period - cannot be stimulated again

Question 16

Propagation:

Answer 16

9. Continuous: maximum speed of 2 m/s – unmyelinated fibre = grey
10. Saltatory: myelinated fibres – maximum speed of 140 m/s – Action potential jobs from Node of Ranvier to Node of Ranvier

Question 17

Transmission

Answer 17

11. Action potential causes depolarisation of the axon terminal membrane. Calcium voltage gated channels open causing calcium ions to enter the synapse knob.
12. Calcium binds to synoptic vesicles. Vesicles move towards and bind to pre-synoptic membrane. Exocytosis of neurotransmitters into the synapse.

Question 18

Transmission (part two)

Answer 18

13. Neurotransmitters diffuse across the synapse and bind to receptor – mediated proteins (sodium – ligand channels) sodium moves into dendrite
14. Neurotransmitter broken down

Question 19

Diagrams you need to be able to label:

Answer 19

• Brain
• Spinal Cord
• Each Neuron