Unit 11: The nervous system

Question 1

What are the two divisions of the nervous system

Answer 1

1. Central nervous system (CNS): consists of brain and spinal cord
2. Peripheral nervous system (PNS): consists of nerves that carry messages to and from the CNS to the rest of the body.

Question 2

What are the two types of cells in the nervous system

Answer 2

1. Neurons: Cells that transmit nerve impulses between parts of the nervous system. Many neurons grouped together = nerve
2. Neuroglia: Cells that support and nourish neurons.

Question 3

Dendrite

Answer 3

Neuron structure

extensions that receives signals from other neurons and sends them towards a cell body

Question 4

Cell body

Answer 4

Neuron structure

Contains the nucleus and organelles to keep the cell alive. Relays an impulse from dendrite to axon

Question 5

Axon

Answer 5

Neuron structure
Conducts an impulse away from the cell body towards other neurons or effectors. A membranous tube containing axoplasm (cytoplasm of the axon) and axomembrane (membrane of axon).

Question 6

Myelin sheath

Answer 6

Neuron structure

Protective coating of a type of neuroglial cells called Schwann cells, around larger axons and dendrites.

Question 7

Nodes of Ranvier

Answer 7

Neuron structure

Gaps in the myelin sheath; speeds up transmission of an impulse.

Question 8

Motor neurons function and structure

Answer 8

Relays messages from an interneuron in the CNS to an effector (organ, muscle fiber, or gland).
Structure: Short dendrites and long axons

Question 9

Sensory neurons function and structure

Answer 9

Relays messages to an interneuron in the CNS. May be equipped with special endings called sensory receptors that detect environmental changes and alerts the sensory neuron.
Structure: Long dendrites and short axons

Question 10

Interneurons function and structure

Answer 10

Lies entirely within the CNS; relays messages between neurons (i.e., from a sensory neuron to a motor neuron or between other interneurons).
Structure: Length of dendrites and axons vary depending on their location/function within the CNS.

Question 11

Oscilloscope

Answer 11

Nervous system uses nerve impulse to convey information. Nerve impulse can be analyzed using a voltmeter called oscilloscope, conducted on two points (inside and outside on an axon), as voltage is a measure of the electrical potential differences between two points.

Question 12

Resting potential (Voltage, and the cause of such voltage)

Answer 12

When the axon is not conducting an impulse
Voltage: -65 millivolts; The inside of the axon is negative compared to the outside.
The polarity is caused by two things:
1. Sodium-potassium pump: Membrane protein that actively transports Na+ out of and K+ into the axon.
2. Large negatively charged organic molecules inside the axon that are too large to cross the membrane.

Question 13

When do nerve impulses occur? Threshold?

Answer 13

Nerve impulse occur as a response to a stimulus; stimulus strong enough to reach a certain threshold. Nerve impulse is a “all-or-nothing” response to a stimulus – there are no partial action potential.

Question 14

Active potential (Voltage, and two stages)

Answer 14

Rapid change in polarity across the axomembrane as a nerve impulse occurs.
1. Depolarization: Charge inside axon changes from – to +
Voltage: +40 millivolts; The inside becomes more positive than the outside.
-Sodium gates open
-Na+ diffuse along its concentration gradient, into the axon.
2. Repolarization: Charge inside axon changes from + back to -
Voltage: -65 millivolts
-Potassium gates open
-K+ diffuse along its concentration gradient, out of the axon
Voltage is restored at repolarization, but the locations of the Na/K ions are switched

Question 15

Refractory period

Answer 15

Returning the ion distribution back to normal

• Sodium gate closes; nerve impulse cannot move backwards
• Over when the sodium-potassium pump restored the ion distribution

Question 16

Nonmyelinated vs Myelinated nerve fibers

Answer 16

nonmyelinated axons/dendrites: action potential travels down one section at a time.

myelinated axons/dendrites: the sodium and potassium gated channels are concentrated at the nodes of Ranvier. Ion exchanges are happening only at the nodes, so transmission of a nerve impulse is much faster. Called saltatory transmission as the action potential “jumps” from node to node.

Question 17

Synaptic cleft

Answer 17

The gap between the axon terminal and the dendrite

Question 18

Presynaptic vs Postsynaptic membrane

Answer 18

• Presynaptic membrane: Membrane of the first neuron that is sending the impulse
• Postsynaptic membrane: Membrane of the next neuron that is receiving the impulse

Question 19

Neurotransmitters

Answer 19

Molecules that carry the electrical messages from one neuron to another
Two classes:
1. Excitatory neurotransmitters: Cause an action potential to be generated
2. Inhibitory neurotransmitters: Stop an action potential from generating

Question 20

Axon terminal & Synaptic vesicles

Answer 20

Axon terminal: The end of an axon

Synaptic vesicles: Storage of neurotransmitters in the axon terminal

Question 21

Impulse transmission: Synaptic transmission

Answer 21

First stage

1. Nerve impulse reaches an axon terminal
2. Calcium gates open, and Ca2+ ions move into the axon terminal.
3. Sudden rise in Ca2+ stimulates synaptic vesicles to merge with the presynaptic membrane
4. Neurotransmitters are released into the synaptic cleft
5. Neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane of the next neuron

Question 22

Impulse transmission: Synaptic integration

Answer 22

Second stage

1. Neurotransmitters may be transmitting excitatory or inhibitory signals
2. Neurons integrate all these signals
3. The combination of excitatory and inhibitory messages must reach the threshold for a new action potential to be generated in the second neuron

Question 23

Impulse transmission: Neurotransmitter breakdown

Answer 23

Once the neurotransmitter has initiated a response, they have to be inactivated, in order to prevent continuous stimulation/inhibition of the postsynaptic membrane

• Some neurons contain enzymes that can rapidly inactivate the neurotransmitter. (i.e., monoamine oxidase breaks down norepinephrine (NE), acetylcholinesterase (AChE) breaks down acetylcholine (ACh))
• the postsynaptic membrane reabsorbs the neurotransmitter, for either repackaging into synaptic vesicles or molecular breakdown.

Question 24

Effect of drugs at a synapse

Answer 24

1. Cause a neurotransmitter to leak out of the synaptic vesicle into the synaptic cleft; increases number of neurotransmitters so its action is enhanced
2. Prevent the release of neurotransmitter; decreases number of neurotransmitter so its actions are inhibited.
3. Promote the release of neurotransmitter; same effect as 1
4. Prevent reuptake of neurotransmitter by the presynaptic membrane; the neurotransmitter is around for longer, so its effect is prolonged
5. Block the enzyme that breaks down a neurotransmitter; same effect as 4
6. Bind to a receptor mimicking a neurotransmitter; body responds as if the neurotransmitter was present

Question 25

Reflex arc

Answer 25

Automatic, involuntary movements that may or may not involve the brain.

1. Receptor is stimulated and initiates an impulse
2. Sensory neuron takes the message to the CNS (usually spinal cord)
3. Interneuron passes the message to a motor neuron. If brain is involved, it will be notified at this step.
4. Motor neuron takes the messages away from the CNS to the effector (muscle/organ).
5. The effector receives the message and carries out an action (contraction, relaxation, etc)

Question 26

Meninges and Cerebrospinal fluid

Answer 26

Meninges: Protective membrane that surrounds the CNS

Cerebrospinal fluid: Fills the gaps between the meninges, cushions and protects the CNS.

Question 27

Gray matter vs White matter

Answer 27

Gray matter: Contains cell bodies and short, nonmyelinated fibers
White matter: Contains long fibers of interneurons; white because of the myelin sheath.

Question 28

What are the two types of PNS

Answer 28

Somatic: Controls skeletal muscles, joints, and skin. Receives and acts on external stimuli. Usually under voluntary control by the CNS, some are reflexes.
Autonomic: Controls the cardiac and smooth muscles of internal organs and glands. Acts automatically, usually without the need for conscious thought.

Question 29

Ganglion

Answer 29

Bundle of neuron cell bodies, usually outside the CNS

Question 30

Preganglionic vs Postganglionic fiber

Answer 30

Autonomic nervous system utilize two motor neurons that synapse at a ganglion.
Preganglionic: Axon of the first neuron cell body, which is within the CNS
Postganglionic: Axon of the second neuron cell body, which is within the ganglion

Question 31

Sympathetic nervous system (First cell body location, fiber length, neurotransmitter, body effect)

Answer 31

Division of the autonomic nervous system

• The first cell body of the preganglionic fiber is located in the middle portion of the spinal cord.
• Preganglionic < Postganglionic
• Norepinephrine (NE), releases hormone epinephrine
• Presence of those two initiates a fight-or-fight response
• Increases heart rate, widen air passageways, widen pupil, inhibit digestive tract

Question 32

Parasympathetic nervous system (First cell body location, fiber length, neurotransmitter, body effect)

Answer 32

Division of the autonomic nervous system

• The first cell body of the preganglionic fiber is located in few cranial nerves and sacral (bottom) portion of the spinal cord.
• Preganglionic > Postganglionic
• Acetylcholine (ACh)
• Presence of ACh promotes a rest-and-digest response
• Return heart rate, airways, and pupils back to normal, promote digestive activities

Question 33

Medulla Oblongata

Answer 33

Pathway between brain and spinal cord
Contains reflex centres for vomiting, coughing, sneezing, hiccoughing, swallowing
Regulates hearth rate, breathing, and blood pressure

Question 34

Cerebellum

Answer 34

• Butterfly shaped
• Controls muscle coordination, muscle tone, balance, and posture
• Aids in the learning of new motor skills

Question 35

Hypothalamus

Answer 35

• Help maintain homeostasis by regulating hunger, thirst, sleep, body temp, water balance, and blood pressure
• Controls the pituitary gland, which manufactures hormones. Therefore, the hypothalamus-pituitary gland partnership work together to link the nervous system and the endocrine system

Question 36

Thalamus

Answer 36

• Act as a relay station for all incoming sensory information. (visual, auditory, taste, smell, and somatosensory)
• Integrates and sends the information to the appropriate part of the brain for interpretation
• Also involved in higher mental functions such as memory and emotion

Question 37

Cerebrum

Answer 37

• Controls conscious thought, interprets sensory information, initiates movements
• Responsible for memory
• Separated into two hemispheres, left and right (left controls right side of body, vice versa)

Question 38

Cerebrum lobes

Answer 38

1. Frontal lobe: Very front
   -Conscious thought, primary motor area, speech
2. Temporal lobe: Lower middle section
   -Hearing and smell
3. Parietal lobe: Very back
   -Sensory input for temperature, touch, pain and tase (somatosensory)
4. Occipital lobe: Lower back section
   -Vision
   All lobes are responsible in memory for their area of control

Question 39

Corpus Callosum

Answer 39

Connects the two hemispheres of the cerebrum, allowing impulses to travel from one side of the brain to the other