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Nervous System (HAP 2) - Handwritten Notes

Download handwritten notes for Human Anatomy and Physiology 2, covering the Nervous System. These notes provide a comprehensive overview of the structure and function of the nervous system, including the central and peripheral nervous systems, neurons, neuroglia, action potentials, synaptic transmission, neurotransmitters, major brain regions and their functions, the spinal cord, and common neurological disorders. Suitable for B.Pharm students. Available in PDF format.

Keywords: Nervous System, CNS, PNS, Neuron, Neuroglia, Action Potential, Synapse, Neurotransmitters, Brain, Spinal Cord, Neurological Disorders, Human Anatomy and Physiology, Handwritten Notes, PDF, Download, B.Pharm.

Nervous System - Detailed Explanation

Organization of the Nervous System

The nervous system is broadly divided into two main parts:

• Central Nervous System (CNS): Includes the brain and spinal cord. It's the control center, integrating information and coordinating responses.
• Peripheral Nervous System (PNS): Includes all the nerves outside the brain and spinal cord. It connects the CNS to the rest of the body. The PNS is further divided into:
  • Somatic Nervous System: Controls voluntary movements of skeletal muscles.
  • Autonomic Nervous System (ANS): Controls involuntary functions (e.g., heart rate, digestion, breathing). The ANS has two divisions:
    • Sympathetic Nervous System: "Fight-or-flight" responses.
    • Parasympathetic Nervous System: "Rest-and-digest" functions.

Neurons and Neuroglia

Neurons are the fundamental units of the nervous system, responsible for transmitting information via electrical and chemical signals. A typical neuron has:

• Cell Body (Soma): Contains the nucleus and other organelles.
• Dendrites: Branch-like extensions that receive signals from other neurons.
• Axon: A long, slender projection that transmits signals to other neurons, muscles, or glands. The axon may be myelinated (covered with a myelin sheath) to increase conduction speed.

Neuroglia (Glial Cells) are supporting cells that provide structural support, insulation, and nourishment to neurons. Types include:

• Astrocytes (CNS): Provide structural support, regulate the chemical environment, and form the blood-brain barrier.
• Oligodendrocytes (CNS): Form the myelin sheath around axons in the CNS.
• Schwann Cells (PNS): Form the myelin sheath around axons in the PNS.
• Microglia (CNS): Act as immune cells in the CNS.
• Ependymal Cells (CNS): Line the ventricles of the brain and produce cerebrospinal fluid (CSF).

Action Potentials

An action potential is a rapid, temporary change in the membrane potential of a neuron, allowing it to transmit signals. It involves:

1. Resting Membrane Potential: The neuron is at rest, with a negative charge inside compared to the outside (around -70mV). This is maintained by the sodium-potassium pump.
2. Depolarization: A stimulus causes sodium channels to open, allowing sodium ions (Na+) to flow into the cell, making the inside more positive.
3. Threshold: If the depolarization reaches a certain threshold, an action potential is triggered.
4. Repolarization: Sodium channels close, and potassium channels open, allowing potassium ions (K+) to flow out of the cell, restoring the negative charge inside.
5. Hyperpolarization: A brief period where the membrane potential becomes more negative than the resting potential.
6. Return to Resting Potential: The sodium-potassium pump restores the ion balance.

Synaptic Transmission

A synapse is the junction between two neurons, or between a neuron and a target cell (e.g., muscle fiber). Information is transmitted across the synapse via neurotransmitters, chemical messengers. The process involves:

1. An action potential arrives at the axon terminal of the presynaptic neuron.
2. Voltage-gated calcium channels open, allowing calcium ions (Ca2+) to enter the axon terminal.
3. Ca2+ triggers the fusion of vesicles containing neurotransmitters with the presynaptic membrane.
4. Neurotransmitters are released into the synaptic cleft (the space between the neurons).
5. Neurotransmitters bind to receptors on the postsynaptic neuron (or target cell).
6. This binding causes ion channels to open, leading to either excitation (depolarization) or inhibition (hyperpolarization) of the postsynaptic neuron.
7. Neurotransmitters are removed from the synaptic cleft by reuptake, enzymatic degradation, or diffusion.

Neurotransmitters

Some common neurotransmitters include:

• Acetylcholine (ACh): Important for muscle contraction, memory, and learning.
• Norepinephrine (NE): Involved in the "fight-or-flight" response.
• Dopamine: Involved in reward, motivation, and movement.
• Serotonin: Involved in mood, sleep, and appetite.
• GABA (gamma-aminobutyric acid): The main inhibitory neurotransmitter in the brain.
• Glutamate: The main excitatory neurotransmitter in the brain.

Major Brain Regions and Functions

• Cerebrum: The largest part of the brain, responsible for higher-level functions like thought, memory, language, and voluntary movement. Divided into two hemispheres and four lobes (frontal, parietal, temporal, occipital).
• Cerebellum: Coordinates movement, balance, and posture.
• Brainstem: Connects the cerebrum and cerebellum to the spinal cord. Controls basic life functions like breathing, heart rate, and sleep-wake cycles. Includes the midbrain, pons, and medulla oblongata.
• Diencephalon: Includes the thalamus (relays sensory information) and hypothalamus (regulates homeostasis, controls the endocrine system).

Spinal Cord

The spinal cord extends from the brainstem and transmits signals between the brain and the peripheral nervous system. It also contains reflex centers that control rapid, involuntary responses to stimuli.

Neurological Disorders

Common neurological disorders include:

• Stroke: Disruption of blood flow to the brain, leading to brain damage.
• Alzheimer's Disease: A progressive neurodegenerative disease that causes memory loss and cognitive decline.
• Parkinson's Disease: A neurodegenerative disease that affects movement.
• Multiple Sclerosis (MS): An autoimmune disease that damages the myelin sheath.
• Epilepsy: A disorder characterized by recurrent seizures.

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