NCSU Course ZO410 Lecture:Ê
Nervous System

• Primary function of nervous system is to control energy release through muscle contractions and glandular secretions
• Nervous systems in general moved from simple to complex over evolutionary time. Resulted in greater behavioral complexity.
• Irritability - main property of life (response to stimuli)
• Irritability -----one Billion Years of Evolution -----Cognition

Coelenterates/Cnidarians

• first nerve nets

• beginning of specialization

• Centralized nervous system
• Trends leading to complex behavior:

1. Central control
2. Neuronal differentiation
3. Increased complexity of nerve pathways
4. Development of sensory systems

a. Rostral movement (animals move forward)
b. Encephalization

1. Relative size
2. Cerebralization/cephalization
3. Interconnections of neurons

Resulted in:
1. complex and flexible behaviors
2. faster responses
3. greater information storage (memory!)
 

•     Sensory, Inter, Motor
•     "parts" of a neuron:

              cell body, nucleus
              dendrites
              axon
              myelin sheath
•    Resting potential, Action potential

              polarization, depolarization
•    Synapses

             --electrical
             --chemical
             --neurotransmitters

        Noctuid Moth response to predatory bats
        A1 and A2 fibers, detect ultrasonic sound from bats, respond appropriately

Specialized Visual Perception

• Optical Illusions
• Rhesus monkey face-detection

Neural basis for bird song
Male birds sing (Spring especially), females tend to mate with the bird with most complex song.

• Constructed an atlas of the neural representation of bird song
• sexual dimorphism.
• size varied with season, testosterone levels

NEUROTRANSMITTERS

Chemical Synapses
- signaling molecules from one neuron to another neuron (or muscle or gland) are called neurotransmitters (NT)

- presynaptic cell stores NT in vesicles
- action potential arrival causes vesicles to fuse with membrane, release NT into synaptic cleft
- NT diffuse across synapse, bind to receptors on postsynaptic cell membrane
- NT can be excitatory or inhibitory

Integration
- neuromodulators are also signaling molecules, act to magnify or reduce NT effects
i.e. substance P, enkephalin -- gated control of pain

Summation
- competition among incoming signals for control of neuron
- EPSP and IPSP
- excitatory and inhibitory signals are "summed" to bring neuron closer to or farther from threshold

Removal of NT from Synapse
- diffusion
- enzyme degradation
- membrane transport proteins, pump back into presynaptic cells

1. Acetylcholine
    - all motor neurons from spinal cord
    - autonomic nervous system
    - Alzheimer's, nerve gas, botulism

2. Monoamines:

• Epinephrine (E)

            Adrenal medulla produces most
• Norepinephrine (NE)
• Associated with arousal, brain's system of reward, eating patterns, mood regulation, dreaming, etc.
• Released peripherally by: sympathetic motor neurons and the adrenal medulla
• Released by hypothlamus, controls gonadotropin release from pituitary
• Dopamine (DA)
• Concentrated in the mid-brain (Substancia Nigra)
• Excess in forebrain associated with schizophrenia
• Controls complex movements (degeneration results in Parkinson's Disease)
• Dopamine produced in hypothalamus =regulation of pituitary hormones
• emotions
• cocaine etc. blocks uptake
• Serotonin (5-hydroxytryptamine or 5-HT)
• Concentrated in brain stem - connections to thalamus, hypothalamus and elsewhere
• Control of temperature regulation, sensory perception, onset of sleep, aggression levels, etc.
• Prozac blocks reuptake

• Glutamic acid and Aspartic acid - excitatory effects on many neurons
• GABA (Gamma aminobutyric acid) Common in brain (1/3 of synapses), inhibitory effect on motor neurons

4. Peptides:
Endorphins (from "endogenous morphine") act as neuromodulators usually (can also be NT or hormones):

• Enkephalin - Pain blocking
• Substance P - pain producing
• Neurotensin
• Oxytocin
• many others known or suspected -- growth hormone

Neurochemistry of Brain:

- Respiration
- Its neurons make ATP from glucose only.
- The brain is isolated from general circulation by blood-brain barrier (BBB)

- Even glucose must be actively transported into the brain's circulation.
- To cross the BBB, drugs must be:

a. small molecules, and
b. fat soluble