General Nervous System

Question 1

NEURON

Answer 1

1. most neurons present at birth
2. die at rate of 10K per day, but due to enormous size, only 2% lost by age 70!
3. can regenerate through adulthood in some brain areas
4. neurogenesis: creation of new neurons which has been observed in the hippocampus and caudate nucleus.

Question 2

STRUCTION OF NEURON

Answer 2

vary in size, shape, and function but most have Dentrites, Cell Body (soma) and Axon.

1. Dentrites: branch-like, receive information from other dendrites and passes it on to the axon.
2. Cell Body: nucleus, mitochondria (metabolism), ribosomes (make proteins), and golgi complex (prepares neurotransmitters for secretion)
3. Axon: transmits info from the cell body to other cells.

Question 3

Myelin Sheath

Answer 3

1. covers axons to speed up conduction of nerve impulses (fatty substance)
2. made up of glial cells which also hold neurons together, provide neurons nutrients and remove cellular debris.

Question 4

Conduction

Answer 4

1. messages within a neuron are transmitted from dendrites to the end of its axon through an electrical process called conduction.
2. dentrites receive stimulation from other cells which alters electrical balance.
3. sodium channels open in the cell’s membrane, accept positively charged sodium:
   
   1. Depolarization: triggers action potential which is electrical impulse traveling through the cell.
   2. Repolarization: sodium channel closes and potassium channels open (K leaves cell)
4. All-or-None Principal: once the stimulation received by a neuron exceeds a given threshold, the resulting action potential will always be of the same intensity.

Question 5

Synaptic Transmission

chemical

Answer 5

1. transmission of information from one nerve cell to another is chemically mediated (not electrical conduction).
2. occurs when the action potential reaches the axon terminal.
3. release of a neurotransmitter into the cynaptic cleft
   
   1. small gap between the axon terminal of the presynaptic cell and the receptor of the dendrite of the postsynaptic cell.

Question 6

Neurotransmitters

Answer 6

1. ACh: Acetylcholine
2. Dopamine
3. Norepinephrine
4. Serotonin
5. Gamma-Aminobutyric Acid (GABA)
6. Glutamate
7. Endorphins

Question 7

1. ACh

Acetylcholine

muscles and memory

Answer 7

1. peripheral and central nervous systems
2. acts on muscarinic and nicotinic receptors.
3. PNS: causes muscles to contract
   
   1. Myasthenia gravis: autoimmune dx that attacks ACh receptors resulting in profound weakness of the skeletal muscles.
4. CNS: involved in REM sleep, regulation of sleep-wake cycle, and learning and memory.
   
   1. nicotine may enhance memory/alertness by mimicking ACh at nicotinic receptor sites!
   2. Degeneration of ACh cells in the Entorhinal Cortex and other areas that communicate directly with the hippocampus is believed to underlie the memory deficits associated with Alzheimer’s disease.
   3. Use Cholinesterase inhibitors to slow memory declines. such drugs reduce breakdown of ACh and include: tacrine, donepezil, galantamine, and rivastigmine.

Question 8

2. Dopamine

too much is bad

Answer 8

The most abundant catecholamines are epinephrine (adrenaline), norepinephrine (nor-adrenaline) and dopamine, all of which are produced from phenylalanine and tyrosine. Release of the hormones epinephrine and norepinephrine from the adrenal medulla of the adrenal glands is part of the fight-or-flight response.

1. personality, mood, memory, movement and sleep.
2. contributes to Schizophrenia: dx is due to elevated dopamine levels or oversensitivity of dopamine receptors.
3. Regulation of movement and linked to several dx with motor symptoms: Tourette’s Dx and Parkinson’s disease.
   
   1. Tourette’s: oversensitivity to or excessive Dopamine in the Caudate Nucleus.
   2. Parkinson’s: degeneration of dopamine receptors in the Substantia Nigra underlies the tremors, muscle rigidity and other motor symptoms.
4. Elevated levels of Dopamine in the mesolimbic system (midbrain/limbic system) implicated in the reinforcing actions of stimulant drugs, opiates, EtOH, nicotine.
   
   1. cocaine blocks the reuptake of Dopamine at synapses in the mesolimbic (excess), while nicotine stimulates its release.

Question 9

3. Norepinephrine

catecholamine (epi, nor-epi, dopamine)

Answer 9

1. important role in mood, attention, dreaming, learning, and certain autonomic functions.
2. Catecholamine Hypothesis: predicts that some forms of depression are due to lower-than-normal levels of norepinephrine. depressed mood=depressed NorEpi!

Question 10

4. Serotonin

inhibitory effect (low is less inhibited processes)

Answer 10

1. Usually exerts INHIBITORY effect and is implicated in hunger, mood, temperature regulation, sexual activity, arousal, sleep, aggression, and migraine headache.
2. Elevated serotonin: Schizophrenia, Autism, and food restriction associated with Anorexia Nervosa.
   
   1. overall restriction due to over inhibition
3. Low-Serotonin: aggression, depression, suicide, Bulimia Nervosa, PTSD, and OCD.
   
   1. over-expression due to lack of inhibition.
4. abnormalities in serotonin and dopamine levels or transmission play a role in Social Phobia.

Question 11

5. Gamma-Anminobutyric Acid

GABA

inhibitory (anxiety, huntington’s)

Answer 11

1. Inhibitory neurotransmitter (like serotonin) and plays a role in eating, seizure, anxiety dx, motor control, vision, and sleep.
2. Low Levels of GABA: linked to anxiety disorders
   
   1. benzodiazepines and other CNS depressants reduce anxiety by enhancing the effects of GABA.
3. Motor Control: degeneration of cells that secrete GABA in the basal ganglia contributes to the motor symptoms of Huntington’s disease.

Question 12

6. Glutamate

memory excitatory

Answer 12

1. excitatory neurotransmitter in many brain areas
2. role in learning, memory and long-term potentiation (LTP).
   
   1. LTP: brain mechanism responsible for the formation of long-term memories.
3. excessive Glutamate receptor activity: excito-toxicity: leads to seizures and may contribute to stroke-related brain damage, Huntington’s disease, Alzheimer’s disease, and other neurodegenerative disorders.

Question 13

7. Endorphins

Answer 13

1. Endogenous morphines: inhibitory neuromodulators that lower the sensitivity of postsynaptic neurons to neurotransmitters.
2. analgesic properties: pain relief secondary to acupuncture.
   
   1. prevent the release of substance P, which is involved in the transmission of pain impulses.
   2. inplicated in some pleasurable experiences, emotions, meory and learning, and sexual bx.