01. CNS, Neurons and Synapses

Question 1

Describe the nervous system.

Answer 1

-A complex network of specialised cells.
-Role is to receive, process and respond to information in the environment and to coordinate different organs and cells in the body.
-The nervous system has 2 main parts, the CNS and the peripheral nervous system (PNS).
-The CNS consists of the brain and spinal cord.

Question 2

Define the brain.

Answer 2

The brain is the main data centre of the body and consists of the cerebrum which regulates higher level functioning such as thought, and the cerebellum which maintains coordination.

Question 3

Define the brain stem.

Answer 3

The brain stem includes the midbrain, pons and medulla, and controls lower level functioning such as respiration and digestion. It connects the brain and the spinal cord.

Question 4

Define the spinal cord.

Answer 4

-The spinal cord connects the brain and the body’s main receptors, and serves as a conduit for sensory input and motor output.
-Responsible for reflex actions.

Question 5

Define the cerebrum.

Answer 5

In humans, it is the largest part of the brain and is the seat of motor and sensory functions, and the higher mental functions such as consciousness, thought, reason, emotion and memory.

Question 6

Define the thalamus.

Answer 6

-The brain’s relay station.
-Receives information from various senses and passes it onto appropriate areas of the cerebral cortex for higher level processing.
-Acts as filter of information.
-Plays a role in sleep and OCD.

Question 7

Define the hypothalamus.

Answer 7

-Controls motivational behaviours such as hunger, thirst and sex.
-Stress response ‘fight or flight’.
-Maintains balance in many bodily functions such as temperature (homeostasis).
-Regulates the endocrine system via pituitary gland.

Question 8

Define the limbic system.

Answer 8

-Emotion centre of the brain.
-Has a role in memory and learning.

Question 9

Define the cerebellum.

Answer 9

-Part of the hindbrain in vertebrates.
-Receives and integrates information from the spinal cord.
-In humans it lies between the brainstem and the cerebrum, and plays an important role in sensory perception, motor output, balance and posture.
-Coordinates posture, balance and movement.

Question 10

What connects the two hemispheres of the brain?

Answer 10

-A dense collection of nerve cells called the corpus callosum.
-Allows communication between the hemispheres by passing signals back and forth.

Question 11

Define lateralisation.

Answer 11

Two hemispheres have different functions.

Question 12

Define localisation.

Answer 12

Certain areas are responsible for different functions.

Question 13

Define the cerebral cortex.

Answer 13

-The cerebral cortex of both hemispheres is subdivided into 4 lobes (so there are 8 lobes in total, 4 in each hemisphere).
-The cerebral cortex is very wrinkly so it has a higher surface area, giving it more processing power.

Question 14

Define the frontal lobes.

(One of the cerebral cortex 4 lobes)

Answer 14

-Located at the front of the brain.
-Make up about 40% of the cerebral cortex.
-Control thinking, planning, problem solving and decision making.

Question 15

Define the parietal lobes.

(One of the cerebral cortex 4 lobes)

Answer 15

-Key part of your understanding of the world around you.
-It processes your sense of touch and assembles input from your other senses into a form you can use.
-Helps you understand where you are in relation to other things that your senses are picking up around you.

Question 16

Define the temporal lobes.

(One of the cerebral cortex 4 lobes)

Answer 16

-Each lobe contains an auditory cortex which deals with sound information coming mainly from the opposite area.
-Play role in understanding language.

Question 17

Define the occipital lobes.

(One of the cerebral cortex 4 lobes)

Answer 17

-Located in back of brain.
-Visual processing area of brain.

Question 18

Define the Broca’s area.

(Language areas of the brain)

Answer 18

Responsible for speech production.

Question 19

Define the Wernicke’s area.

(Language areas of the brain)

Answer 19

Comprehension of speech.

Question 20

Define a neuron.

Answer 20

-Neurons are nerve cells.
-There are roughly 100 billion neurons in the human nervous system and 80% of these are located in the brain.
-Neurons receive, process and transmit messages through chemical and electrical signals within the body,

Question 21

What are the 3 types of neuron?

Answer 21

1. Relay neuron
2. Sensory neuron
3. Motor neuron

Question 22

Define a relay neuron.

Answer 22

-Relay neurons connect sensory and motor neurons together, and also connect to other relay neurons.
-They have short dendrites and short axons and are only found in the CNS.

Question 23

Define a sensory neuron.

Answer 23

-Sensory neurons carry messages from sensory receptors (eg touch and temperature sensitive receptors in the skin) along nerves in the peripheral nervous system (PNS) to the central nervous system (CNS).
-They have long dendrites and short axons.

Question 24

Define a motor neuron.

Answer 24

-Motor neurons carry messages from the CNS, along nerves in the PNS, to effectors in the body (eg muscles and glands).
-They have short dendrites and long axons.

Question 25

What is the function of the cell body (soma)?

Answer 25

Includes a nucleus containing the genetic material of the cell.

Question 26

What is the function of the dendrites?

Answer 26

Branch like structures called dendrites stick out from the cell body. These carry impulses from neighbouring neurons towards the cell body.

Question 27

What is the function of the axon?

Answer 27

The axon is a tube-like structure that carries impulses away from he cell body down the length of the neuron.

Question 28

What is the function of the myelin sheath?

Answer 28

-In many neurons, the axon is covered by a fatty layer called the myelin sheath.
-This is formed from special cells (called glial cells in the CNS) which wrap themselves around the axon.
-The myelin sheath protects both the axon and speeds up electrical transmission of the impluse.

Question 29

What is the function of the nodes of ranvier?

Answer 29

-Gaps in the myelin sheath are called nodes of ranvier.
-They allow for an increase in speed by forcing the impulses to ‘jump’ across the gaps along the length of the axon.

Question 30

What is the function of the terminal buttons?

Answer 30

Terminal buttons are not physically connected to the next neuron in the chain, but are involved in communication across a gap known as a synapse.

Question 31

Describe the function of a neuron.

Answer 31

-When a neuron is in a resting state the inside is negatively charged, compared to the outside.
-When a neuron is sufficiently activated by a stimulus the inside becomes positively charged for a split second.
-The rapid switch from negative to positive is called depolarisation.
-This creates an electrical impulse called an action potential that travels down the axon towards the terminal buttons.
-This is called firing an action potential.

Question 32

Describe neurotransmitters.

Answer 32

-Neurotransmitters are chemical messengers that act between neurons.
-Messages in the brain are sent by using electrical impulses and chemicals called neurotransmitters.

For example:
1. Dopamine (pleasure feelings/addiction).
2. Serotonin (happiness and good mood, low levels give depression).
3. GABA (inhibitor of messages/calming, involved in movement).
4. Acetylcholine (memory/learning).

Question 33

Describe synaptic transmission.

Answer 33

The electrical impulse in the presynaptic neuron cannot ‘jump’ across the synaptic gap, so signals have to be transmitted chemically.

1. When the action potential reaches the terminal buttons it triggers the release of neurotransmitters from the presynaptic neuron.
2. Tiny scans called synaptic vesicles release the neurotransmitters into the synapse.
3. These chemicals diffuse across the synaptic gap until they are picked up by receptors on the dendrite on postsynaptic neuron.
4. Each neurotransmitter will fit into a matching receptor site with a corresponding shape on the postsynaptic neuron.
5. The neurotransmitter changes the chemical balance at the receptor side causing an action potential to fire along the next neuron.
6. The neurotransmitters are then reabsorbed by the presynaptic neuron (re-uptake) to be used again)

Question 34

What are the 2 main categories that neurotransmitters fall into depending on their effect on neighbouring neurons?

Answer 34

Excitatory or inhibitory.

Question 35

Describe excitatory neurotransmitters.

Answer 35

-Cause postsynaptic neuron to be more positive.
-This makes an action potential more likely.
-So the neuron will fire.
(Eg dopamine)

Question 36

Describe inhibitory neurotransmitters

Answer 36

-Cause the postsynaptic neuron to be more negative.
-This makes an action potential less likely.
-So the neuron won’t fire.
(Eg serotonin)

Question 37

Describe summation.

Answer 37

-The postsynaptic neuron will receive both excitatory and inhibitory inputs.
-The effects of the neurotransmitters on the postsynaptic neuron depends on the summation or adding together of signals.

Summation could be:
-Over time (temporal summation)
-Over space (spatial summation)

-The excitatory or inhibtory effects are added up (summed).
-If the net effect is excitatory, the inside of the neuron becomes more positive, depolarisation occurs and an action potential (electrical impulse) fires along the postsynaptic neuron.
-If the net effect is inhibitory, the inside of the neuron becomes more negative, depolarisation does not occur and the postsysnatpic neuron is less likely to fire.