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Functions of the Nervous System
Coordinates body activities via electrical and chemical signals.
Central Nervous System (CNS)
Brain and spinal cord; main control center.
Peripheral Nervous System (PNS)
Nerves branching from CNS.
Afferent Division (Sensory)
Brings information to CNS.
Somatic Senses
Touch, pain, temperature.
Special Senses
Vision, hearing, taste, smell, equilibrium.
Visceral Senses
Internal organs.
Efferent Division (Motor)
Sends signals from CNS to effectors.
Somatic Nervous System
Voluntary control over skeletal muscles.
Autonomic Nervous System
Involuntary control over cardiac/smooth muscle, glands.
Sympathetic Division
'Fight or Flight' response.
Parasympathetic Division
'Rest and Digest' response.
Neurons (Nerve Cells)
Specialized for electrical impulse transmission.
Cell Body (Soma)
Contains nucleus and organelles.
Dendrites
Receive signals.
Axon
Transmits impulses away from soma.
Myelin Sheath
Insulation that speeds up impulse transmission.
Nodes of Ranvier
Gaps in myelin allowing saltatory conduction.
Sensory (Afferent) Neurons
Carry input to CNS.
Motor (Efferent) Neurons
Carry output from CNS to effectors.
Interneurons (Association Neurons)
Process information within CNS.
Multipolar Neurons
Most common; multiple dendrites, one axon.
Bipolar Neurons
One dendrite, one axon (found in special senses).
Unipolar Neurons
Single extension branches into two directions (sensory neurons).
Anaxonic Neurons
No axon; only in CNS.
Astrocytes
Maintain blood-brain barrier.
Oligodendrocytes
Myelinate CNS neurons.
Microglia
Act as phagocytes.
Ependymal Cells
Produce cerebrospinal fluid (CSF).
Schwann Cells
Myelinate PNS neurons.
Satellite Cells
Protect neuron cell bodies.
Resting Membrane Potential
(-70mV) Inside is more negative due to Na⁺/K⁺ pump.
Depolarization
Na⁺ channels open, Na⁺ enters, making inside more positive.
Repolarization
K⁺ channels open, K⁺ exits, restoring negative charge inside.
Hyperpolarization
Overshoot of K⁺ leaving makes it temporarily too negative.
Return to Resting Potential
Na⁺/K⁺ pump restores ion balance.
Myelinated Neurons
Faster due to saltatory conduction (jumps between Nodes of Ranvier).
Unmyelinated Neurons
Slower, continuous impulse conduction.
Electrical Synapse
Direct ion flow through gap junctions (fast, found in heart).
Chemical Synapse
Neurotransmitter release across synaptic cleft (more common).
Action Potential Arrives
Depolarizes presynaptic membrane.
Calcium (Ca²⁺) Channels Open
Triggers vesicles.
Neurotransmitter Release
Via exocytosis into synaptic cleft.
Binding to Receptors
On postsynaptic membrane, triggering ion channels.
Post-Synaptic Response
Can be excitatory (depolarizing) or inhibitory (hyperpolarizing).
Neurotransmitter Removal
By reuptake, enzymatic breakdown, or diffusion.
Excitatory Neurotransmitters
Acetylcholine (ACh), Glutamate.
Inhibitory Neurotransmitters
GABA, Glycine.
Mood & Reward Neurotransmitters
Dopamine, Serotonin.
Fight-or-Flight Neurotransmitters
Norepinephrine, Epinephrine.
Sympathetic Division of ANS
Increases heart rate, dilates pupils, inhibits digestion.
Parasympathetic Division of ANS
Lowers heart rate, constricts pupils, stimulates digestion.
Dual Innervation
Most organs receive signals from both sympathetic and parasympathetic divisions.
Multiple Sclerosis (MS)
Demyelination of CNS neurons → slow nerve signals.
Alzheimer's Disease
Plaques and tangles impair brain function.
Parkinson's Disease
Loss of dopamine-producing neurons.
SSRIs (e.g., Prozac)
Block serotonin reuptake → improves mood.
Cocaine
Blocks dopamine reuptake → excessive stimulation.
Naloxone (Narcan)
Blocks opioid receptors → reverses overdose.
Action Potential Steps
Steps: Depolarization (-55mV threshold reached), Repolarization (K⁺ exits), Hyperpolarization, Return to Resting Potential.
