Nerve Physiology Notes – Anatomy

1. Nervous System

• Coordinates body activities via electrical & chemical signals
• Three main functions:
– Sensory input: Detects changes inside & outside the body (via receptors)
– Integration: CNS interprets sensory input and decides response
– Motor output: Activates effectors (muscles or glands) to respond

2. Anatomical Subdivisions

1. Central Nervous System (CNS)

• Brain & spinal cord
• Enclosed in skull & vertebral column
• Main control center – processes, integrates, and issues commands

2. Peripheral Nervous System (PNS)

• All nerves & ganglia outside CNS
• Connects CNS to limbs and organs
• Two major functional divisions:

Sensory (Afferent) Division
– Transmits signals to CNS
– Subdivisions:
• Somatic sensory – skin, joints, muscles
• Visceral sensory – organs like heart, lungs, bladder

Motor (Efferent) Division
– Carries commands from CNS to effectors
– Subdivisions:
• Somatic motor – voluntary, skeletal muscle
• Autonomic nervous system (ANS) – involuntary, smooth & cardiac muscle
▪ Sympathetic – fight or flight
▪ Parasympathetic – rest & digest

3. Properties of Neurons

• Excitability – respond to stimuli
• Conductivity – transmit signals over distance
• Secretion – release neurotransmitters to influence other cells

4. Functional Types of Neurons

• Sensory (Afferent) – carry signals from receptors to CNS
• Motor (Efferent) – send signals from CNS to effectors
• Interneurons – connect neurons within CNS; 90% of neurons

5. Structure of a Neuron

• Soma – cell body; nucleus & organelles
• Dendrites – receive input; many branches
• Axon – sends output; starts at axon hillock
• Myelin sheath – insulates axon, speeds transmission
• Nodes of Ranvier – gaps in myelin; important in signal conduction

Neuron Types:

• Multipolar – many dendrites, one axon (most common)
• Bipolar – one axon, one dendrite (eye, ear)
• Unipolar – one process (sensory from skin/organs)

6. Neuroglial (Glial) Cells

In CNS:

• Oligodendrocytes – form myelin
• Astrocytes – most abundant; support, blood-brain barrier, nourish neurons
• Ependymal cells – produce and circulate cerebrospinal fluid
• Microglia – immune cells; clean up debris & pathogens

In PNS:

• Schwann cells – form myelin in PNS; aid regeneration
• Satellite cells – insulate and support cell bodies in ganglia

7. Electrophysiology of Neurons

• Resting Membrane Potential (RMP) ≈ -70 mV
– More Na⁺ outside, more K⁺ inside
– Maintained by sodium-potassium pumps

• Action Potential – rapid up-and-down shift in membrane voltage
– Triggered when threshold is reached (~ -55 mV)
– Propagates along axon

• Saltatory Conduction
– In myelinated fibers, AP jumps node to node (faster)

8. Synapses

• Presynaptic neuron – sends signal via neurotransmitter
• Postsynaptic neuron – receives signal via receptor proteins
• Synaptic cleft – gap between two neurons

• Types of neurotransmitters:
– Acetylcholine, Dopamine, Serotonin, GABA, etc.
• Neurotransmitters can be:
– Excitatory (promote action potential)
– Inhibitory (suppress action potential)

9. Neural Integration

• Refers to how neurons process and respond to input
• A single neuron receives thousands of synaptic inputs
• Responses depend on the balance of excitatory and inhibitory inputs
• Synaptic plasticity = ability to change synaptic strength – key to learning & memory

10. Neurological Disorders Related to Nerve Physiology

• Multiple Sclerosis (MS)
– CNS myelin deteriorates; scar tissue forms
– Disrupts nerve conduction: fatigue, vision problems, numbness

• Alzheimer’s Disease
– Memory loss, personality changes
– Linked to deficiency in acetylcholine and nerve growth factor

• Parkinson’s Disease
– Degeneration of dopamine-producing neurons
– Symptoms: tremors, rigidity, slowed movement