1. The Nervous System:
Command & Control Centers

2. Nervous systems Effector cells~ muscle or gland cells
Nerves~ bundles of neurons wrapped in connective tissue
Central nervous system (CNS)~ brain and spinal cord
Peripheral nervous system (PNS)~ sensory and motor neurons

3. Structural Unit of Nervous System
Neuron~ structural/functional unit (the actual “Nerve Cell”)
Cell body~ nucleus and organelles
Axon Hillock ~ where impulses generate
Dendrites~ impulses from tips to neuron
Axons~ impulses toward tips (away!!)
Myelin sheath~ supporting, insulating layer, made of….
Schwann cells~PNS support cells
Oligodendrocytes ~ the CNS version of Schwann cells
Astrocytes ~ form the blood–brain barrier, provision of nutrients, maintenance & repair
Synaptic terminals~ neurotransmitter releasers
Animation

4. Simple Nerve Circuit Sensory neuron: convey information to spinal cord
Interneurons: information integration
Motor neurons: convey signals to effector cell (muscle or gland)
Reflex: simple response; sensory to motor neurons
Ganglion (ganglia): cluster of nerve cell bodies in the PNS
Supporting glial cells: nonconducting cell that provides support, insulation, and protection

5. Neural signaling: First, in the resting state, there is….
Membrane potential (voltage differences across the plasma membrane)
Intracellular/extracellular ionic concentration difference
K+ diffuses out (Na+ in); large anions can’t follow….selective permeability of the plasma membrane
…and of course the Sodium/Potassium pumps never sleep!
Net negative charge of about -70mV

6. Neural Signaling, continued….
Excitable cells~ cells that can change membrane potentials (neurons, muscle)
Gated ion channels (open/close response to stimuli): Examples of stimuli:
Photoreceptors; vibrations in air (sound receptors);
Chemical (neurotransmitters)
Voltage (membrane potential changes)
Graded Potentials (depend on strength of stimulus):
1- Hyperpolarization (outflow of K+); increase in electrical gradient; cell becomes more negative
2- Depolarization (inflow of Na+); reduction in electrical gradient; cell becomes less negative.

7. Neural signaling, continued still…
1-Resting state•both channels closed
2-Threshold •a stimulus opens some Na+ channels
3-Depolarization •action potential generated
•Na+ channels open; cell becomes positive (K+ channels closed)
4-Repolarization •Na+ channels close, K+ channels open; K+ leaves •cell becomes negative
5-Undershoot •both gates close, but K+ channel is slow; resting state restored
6-Refractory period~ insensitive to de-polarization due to closing of Na+ gates
(region is “hyperpolarized”)
Animation

8. Neural signaling, finale’
“Travel” of the action potential is self-propagating
Regeneration of “new” action potentials only after refractory period
Forward direction only
Action potential speed:
1-Axon diameter (larger = faster; 100m/sec)
2-Nodes of Ranvier (concentration of ion channels); saltatory conduction

9. Synaptic communication
Presynaptic cell: transmitting cell
Postsynaptic cell: receiving cell
Synaptic cleft: separation gap
Synaptic vesicles: neurotransmitter releasers
Ca+ influx: caused by action potential; causes vesicles to fuse with presynaptic membrane and release….
Neurotransmitters!!
So let’s talk neurotransmitters:

10. Neurotransmitters: 2 main types
Those that relay an:
EPSP-
Excitatory Post Synaptic Potential
Occur when terminal releases a neurotransmitter that opens Na+ channels.
And then there are those that relay an:
IPSP-
Inhibitory Post Synaptic Potential
Occur when terminal releases a neurotransmitter that opens either
K+ channels or Cl- channels.
YouTube!

11. Neurotransmitters, some examples:
Acetylcholine (most common)
Might be either EPSP or IPSP.
Important for skeletal muscle contraction.
Biogenic amines (derived from amino acids) •norepinephrine – excitatory •dopamine- generally excitatory.
Too little: Parkinson’s Too much: schizophrenia
Cocaine prevents the reuptake/breakdown in cleft.
•Serotonin- Usually inhibitory; important for sleep/relaxation

12. Neurotransmitters, more examples:
Single Amino acids:
G.A.B.A.- “Gamma AminoButeric Acid” – inhibitory at neuromuscular junction.
Aspartate- Excitatory (found in high concentrations in artificial sweeteners)
Tryptophan- Inhibitory (Happy Thanksgiving!!)
Glutamate- Excitatory (like acetylcholine; important at neuromuscular junction)
(Blocked by alcohol)
Neuropeptides (short chains of amino acids)
Endorphins- generally inhibitory (see why they’re called natural painkillers?)
“Substance P”- Excitatory
D:\bc_campbell_biology

13. Vertebrate PNS Sensory division (Afferent) Motor division (Efferent)
•Somatic system-
Information from voluntary/conscious parts.
•Visceral system-
senses information from involuntary parts.
Motor division (Efferent)
•somatic system carries signals to skeletal muscle (mostly voluntary, but some are reflex)
•autonomic system √parasympathetic conserve energy (digestion, decrease heart/breathing rates) √sympathetic increase energy consumption

14. Vertebrate CNS Basically, it’s Brain & Spinal Cord
Axons are in well defined bundles
White Matter- heavily myelinated
Gray Matter- not as myelinated
In brain, white is in, gray is out
Reversed in Spinal Cord

15. The Vertebrate Brain Forebrain: Midbrain:
•cerebrum~memory, learning, emotion
•cerebral cortex~sensory and motor nerve cell bodies
•corpus callosum~connects left & right hemispheres
•thalamus- sorts info; emotion hypothalamus- hormones, thermostat
Midbrain:
•inferior (auditory) and superior (visual) colliculi
Hindbrain: •cerebellum~coordination of movement & balance
Medulla oblongata/pons:
homeostatic functions
YouTube- Teenage Brain
Mike the Headless Chicken!

16. Ear & Eye Links Ear: Eye:
Can you trust your Ears?
Eye:
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