20. Nervous system

Question 1

What is the main function of the nervous system?

Answer 1

Coordinates sensory and motor functions by transmitting signals around the body.

Question 2

What is a neuron?

Answer 2

Consists of dendrites, axon, and soma; cannot divide.

Question 3

What are sensory (afferent) neurons?

Answer 3

Receive initial stimulus from environment.

Question 4

What are association (interneurons)?

Answer 4

Receive input from sensory neurons and send to motor neurons; make up 99% of body’s neurons.

Question 5

What are motor (efferent) neurons?

Answer 5

Stimulate target cells (effectors) to elicit a response.

Question 6

What do dendrites do?

Answer 6

Receive information to transfer to cell body.

Question 7

What is the axon hillock?

Answer 7

Site of action potential generation.

Question 8

What does an axon do?

Answer 8

Transfers impulses away from cell body.

Question 9

What does the CNS include?

Answer 9

Brain, spinal cord, interneurons.

Question 10

What does the blood-brain barrier do?

Answer 10

Blocks passage of drugs, ions, pathogens; permeable to O2, CO2, glucose, small non-polar molecules.

Question 11

What does the PNS do?

Answer 11

Uses pre/postganglionic axons, neurotransmitters, and receptors to act on target organs.

Question 12

What does the somatic nervous system control?

Answer 12

Innervates skeletal muscle; voluntary or involuntary movements; uses ACh at neuromuscular junctions.

Question 13

What is the forebrain?

Answer 13

Largest brain part; includes olfactory bulb, thalamus, hypothalamus, basal ganglia, hippocampus.

Question 14

What is the limbic system?

Answer 14

Hippocampus, amygdala, hypothalamus; controls behavior and emotion.

Question 15

What does the diencephalon include?

Answer 15

Thalamus, hypothalamus, pineal gland.

Question 16

What are the cerebrum lobes?

Answer 16

Frontal: thought; Parietal: sensory; Temporal: sound; Occipital: vision.

Question 17

What is the midbrain?

Answer 17

Relay center for visual/auditory impulses; motor control.

Question 18

What is the hindbrain?

Answer 18

Cerebellum: Balance and coordination

• Brainstem: Connects cerebrum to spinal cord
• Midbrain + medulla oblongata + pons
• Pons: Relay center (cortex ←→ cerebellum)
• Medulla oblongata: Controls breathing & heart rates, GI activity

Question 19

What does the sympathetic branch do?

Answer 19

Fight or flight: ↑ BP, HR, ejaculation, energy; inhibits digestion, urination, salivation.

Question 20

What does the parasympathetic branch do?

Answer 20

Rest and digest: ↓ HR; ↑ digestion, relaxation, sexual arousal.

Question 21

What increases action potential propagation speed?

Answer 21

Larger axon diameter & myelination.

Question 22

What is the resting potential?

Answer 22

-70 mV; K+ inside, Na+ outside.

Question 23

What do mechanoreceptors do?

Answer 23

Sense touch.

Question 24

What do thermoreceptors do?

Answer 24

Sense temperature.

Question 25

What do nociceptors do?

Answer 25

Sense pain.

Question 26

What do electromagnetic receptors do?

Answer 26

Sense light.

Question 27

What do chemoreceptors do?

Answer 27

Sense taste, smell, blood chemistry.

Question 28

What does the Na+/K+ pump do?

Answer 28

Maintains -70 mV; 3 Na+ out, 2 K+ in; uses ATP.

Question 29

What is acetylcholine (ACh)?

Answer 29

* Binds to ACh receptors on the post-synaptic membrane for nerve transmission * Secretion at neuromuscular junctions = contraction or relaxation of muscles (PNS) * Recycled back to presynaptic vesicle via acetylcholinesterase à nerve signal terminated; A postsynaptic neuron cannot depolarize

Question 30

What are amino acid neurotransmitters?

Answer 30

* Glutamate: Most common CNS neurotransmitter in vertebrates; excitatory * GABA: Found in brain; inhibitory * Glycine: Found in CNS outside brain; inhibitory

Question 31

What are gas neurotransmitters?

Answer 31

NO; synthesized/released on demand.

Question 32

What are amino acid-derived neurotransmitters?

Answer 32

Epinephrine/norepinephrine: sympathetic system; E: bronchodilation, vasodilation in lungs/muscles; vasoconstriction to digestion/kidneys.

Question 33

How does transmission across a synapse occur?

Answer 33

AP opens Ca2+ channels; Ca2+ enters; NTs released to cleft; NTs bind post-synaptic receptors.

Question 34

Transmission of a Nerve Impulse (Action Potential)

Answer 34

Since the action potential is all or nothing, the strength of a neural signal is based on other factors, such as frequency of firing or how many nerve cells contribute 1. Resting Potential: -70 mV with K+ higher inside the cell; Na+ higher outside 2. Depolarization: Stimulus increases a neuron’s potential with the opening of gated ion channels from which Na+ enters and depolarizes the axon; if the -50 mV threshold is reached, an action potential will open voltage-gated Na+ channels down the entire neuron à all-or-nothing! 3. Repolarization: Polarization is restored with K+ moving out of gated ion channels 4. Hyperpolarization: Excess K+ leaving the neuron before the channels fully close 5. Refractory Period: Neuron unresponsive to new stimulus until the Na+/K+ pump returns ions to resting potential locations

Question 35

What are the types of glial cells

Answer 35

* Oligodendrocytes: Produce myelin in CNS * Schwann cells: Produce myelin in PNS * Microglia: CNS phagocytes * Ependymal cells: Circulate CSF with cilia * Satellite cells: Support cells in PNS * Astrocytes: Physically support CNS neurons; maintain nutrient and mineral balance