Study sheet: Nervous System Physiology

📋 Course Outline

1. Nervous System Roles and Functions
2. Organization and Functional Pathways
3. Nervous Tissue Cell Types
4. Neuron Anatomy and Synapses
5. Neuron Classification
6. Resting and Graded Potentials
7. Action Potential and Myelin
8. Synaptic Integration

📖 1. Nervous System Roles and Functions

📝 Essential Points

📌 The endocrine system uses hormones carried in the blood and acts slowly but sustainably, whereas the nervous system uses nerve impulses and acts rapidly but briefly and more precisely.

• The nervous system regulates:

  • digestion
  • respiration
  • body temperature
  • heart rate
  • blood pressure
  • muscle contraction

• The nervous system supports:

  • reasoning
  • emotion
  • imagination
  • memory
  • thought
  • intuition

💡 Memory Hook

Endocrine action is slow and sustained, whereas nervous action is rapid and brief.

📖 2. Organization and Functional Pathways

📝 Essential Points

• 🔄 Nervous system function proceeds through: reception of information by a receptor, integration and processing, action through motor impulses sent to effectors

• The central nervous system consists of the brain and spinal cord and analyzes, processes, and coordinates information, whereas the peripheral nervous system consists of all nervous tissue outside the central nervous system.

• The afferent sensory pathway carries information from receptors to the central nervous system, whereas the efferent motor pathway carries commands from the central nervous system to tissues and organs.

• The somatic nervous system controls skeletal muscle contractions, whereas the autonomic nervous system involuntarily regulates smooth muscle, cardiac muscle, and glands.

💡 Memory Hook

Receptor → integration → motor action

📖 3. Nervous Tissue Cell Types

★ Must-know

• Neurons compose 10% of nervous tissue and carry messages through nerve impulses, whereas glial cells compose 90% of nervous tissue.

• Glial cells:

  • support neurons
  • isolate neurons
  • protect neurons
  • produce cerebrospinal fluid
  • form the myelin sheath

Further detail

📌 Neurons lose their ability to divide, whereas glial cells provide structural and functional support to nervous tissue.

💡 Memory Hook

Neurons transmit messages, whereas glial cells support, isolate, and protect them.

📖 4. Neuron Anatomy and Synapses

🔑 Key Concepts & Definitions

• Cell body : contains the nucleus, cytoplasm, mitochondria, and other organelles and synthesizes neurotransmitters
• Dendrite : a highly branched neuronal structure that receives messages and, with the cell body, forms the receptive structure of the neuron
• Axon : An axon sends a message from the axon hillock to the terminal corpuscles, whose terminal buttons transmit information to another neuron or a receptor cell.

• Synapse : the meeting point between an axon terminal and a target cell, where a neuron communicates with another neuron or an effector cell through neurotransmitters

📝 Essential Points

• The direction of a nerve impulse is from the dendrites toward the terminal buttons.

💡 Memory Hook

Dendrites → cell body → axon → terminal buttons

📖 5. Neuron Classification

📝 Essential Points

• Unipolar neurons include some neurons of the special senses, bipolar neurons include most sensory neurons, and multipolar neurons include all motor neurons and most interneurons.

📖 6. Resting and Graded Potentials

🔑 Key Concepts & Definitions

• Resting potential : The resting potential is the membrane potential of a resting, polarized neuron and is approximately $-70\,\text{mV}$, with the cytoplasm more negative than the extracellular environment.

• Graded potential : a temporary, localized membrane change caused by a stimulus, often when neurotransmitters open chemically gated sodium channels and sodium enters the cell

★ Must-know

📌 When depolarization reaches the excitation threshold of $-55\,\text{mV}$, an action potential occurs according to the all-or-none law; below that threshold, no action potential occurs.

Further detail

• The resting membrane potential is maintained by the sodium-potassium pump.

💡 Memory Hook

Resting state → graded potential → threshold

📖 7. Action Potential and Myelin

★ Must-know

• During an action potential, sodium enters through voltage-gated sodium channels and depolarizes the membrane to approximately $+30\,\text{mV}$, potassium then exits and repolarizes the membrane, and continued potassium efflux produces hyperpolarization to approximately $-80\,\text{mV}$.

📌 During the absolute refractory period, the membrane cannot respond to a second stimulus, whereas during the relative refractory period, it can respond only to a stronger-than-normal stimulus.

Further detail

• In a myelinated axon, depolarization at one node of Ranvier spreads to the next node and triggers a new action potential there.

• The myelin sheath is formed by neurolemmocytes, also called Schwann cells, in the peripheral nervous system and by oligodendrocytes in the central nervous system.

💡 Memory Hook

Depolarization → repolarization → hyperpolarization

📖 8. Synaptic Integration

🔑 Key Concepts & Definitions

• Summation : the addition of excitatory and inhibitory postsynaptic potentials, either temporally or spatially, at the axon hillock or trigger zone

📝 Essential Points

• An excitatory neurotransmitter produces an excitatory postsynaptic potential that makes the postsynaptic neuron more likely to generate an action potential, whereas an inhibitory neurotransmitter produces an inhibitory postsynaptic potential that makes it less likely.

• Opening sodium channels causes depolarization and may trigger an action potential if the threshold is exceeded, whereas opening chloride or additional potassium channels causes hyperpolarization and makes threshold harder to reach.

• If excitatory postsynaptic potentials outweigh inhibitory postsynaptic potentials, the motor neuron depolarizes beyond threshold and generates an impulse; if inhibitory postsynaptic potentials outweigh excitatory postsynaptic potentials, no impulse occurs.

💡 Memory Hook

PPSEs facilitate firing, whereas PPSIs inhibit firing.

📊 Synthesis Tables

Endocrine and Nervous Regulation

System	Signal	Speed and duration
Endocrine system	Hormones carried in blood	Slow but sustained
Nervous system	Nerve impulses	Rapid but brief and precise

Central and Peripheral Divisions

Division	Main components	Main role
Central nervous system	Brain and spinal cord	Analysis, processing, coordination, and motor commands
Peripheral nervous system	Cranial nerves, spinal nerves, and tissue outside the CNS	Sensory information and motor commands