Unit-1-HAP-2nd Nervous system

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Download Unit 1 HAP - 2nd: Nervous System Notes PDF

Access study notes for Unit 1 HAP (Human Anatomy and Physiology) - 2nd part focusing on the Nervous System. This PDF provides a detailed exploration of the structure and function of the human nervous system, covering topics such as the divisions of the nervous system (Central and Peripheral), nerve cells (neurons and glia), nerve impulse transmission, synapses, neurotransmitters, and an overview of major components like the brain and spinal cord. These notes are ideal for students pursuing courses in health sciences, biology, nursing, and medicine. You can download the "Unit 1 HAP - 2nd: Nervous System Notes PDF" for free for comprehensive offline study or view the content directly online. Slides By DuloMix is dedicated to providing accessible and quality educational materials.

Keywords: Nervous System HAP notes, Human Anatomy and Physiology PDF, Central Nervous System (CNS), Peripheral Nervous System (PNS), neuron anatomy, neurophysiology, brain structure, spinal cord function, DuloMix slides, download study notes.

Why Download These HAP Nervous System Notes?

• Core Anatomy and Physiology Topic: The nervous system is a fundamental and complex system crucial to understanding human biology.
• Structured for Learning: Organized notes designed to help students grasp key concepts of neuroanatomy and neurophysiology.
• Free Educational Resource: Get access to these detailed "HAP - Nervous System Notes PDF" without any cost.
• Versatile Study Aid: Download for offline use on any device or preview online before saving.
• Essential for Health Science Students: Foundational knowledge for various medical and allied health disciplines.

Master the complexities of the nervous system with our carefully prepared notes. Click the download button to get your free copy of the "Unit 1 HAP - 2nd: Nervous System Notes PDF" or view it online now!

Unit 1 HAP - 2nd: An Exploration of the Nervous System

These notes for "Unit 1 HAP (Human Anatomy and Physiology) - 2nd: Nervous System" provide an in-depth look into one of the most complex and vital systems of the human body. The nervous system is the command center, responsible for coordinating all bodily functions, processing information from the environment, and enabling thought, emotion, and memory. Understanding its structure (anatomy) and function (physiology) is fundamental for any student in the health sciences.

I. Overview and Organization of the Nervous System

The nervous system is broadly divided into two main parts:

A. Central Nervous System (CNS)

• Components: Consists of the brain and the spinal cord.
• Function: Acts as the primary control center, integrating information, processing thoughts, and coordinating bodily activities. It is protected by bone (skull and vertebral column), meninges, and cerebrospinal fluid (CSF).

B. Peripheral Nervous System (PNS)

• Components: Consists of all nervous tissue outside the CNS, including cranial nerves (arising from the brain), spinal nerves (arising from the spinal cord), ganglia (collections of neuron cell bodies outside the CNS), and sensory receptors.
• Function: Connects the CNS to the rest of the body (limbs and organs). It carries sensory information to the CNS and motor commands from the CNS to muscles and glands.
• Subdivisions of the PNS:
  • Somatic Nervous System (SNS):
    • Controls voluntary movements of skeletal muscles.
    • Receives sensory information from the skin, muscles, and special senses (vision, hearing, taste, smell, balance).
  • Autonomic Nervous System (ANS):
    • Controls involuntary functions of smooth muscle, cardiac muscle, and glands (e.g., heart rate, digestion, respiration, salivation).
    • Further divided into:
      • Sympathetic Division: "Fight-or-flight" response; prepares the body for stressful or emergency situations.
      • Parasympathetic Division: "Rest-and-digest" response; conserves energy and promotes housekeeping functions during rest.
  • Enteric Nervous System (ENS): (Sometimes considered a third division)
    • The "brain of the gut," an extensive network of neurons within the walls of the gastrointestinal tract, controlling GI motility and secretion. Can function independently but is also influenced by the ANS.

II. Histology of Nervous Tissue: Cells of the Nervous System

Nervous tissue is composed of two main types of cells:

A. Neurons (Nerve Cells)

• Function: Specialized cells responsible for transmitting nerve impulses (electrical and chemical signals). They are the basic functional units of the nervous system.
• Structure:
  • Cell Body (Soma or Perikaryon): Contains the nucleus and other organelles; responsible for metabolic processes. Nissl bodies (rough ER) are prominent.
  • Dendrites: Short, branched extensions that receive signals from other neurons or sensory receptors and conduct them towards the cell body.
  • Axon: A single, long projection that transmits nerve impulses away from the cell body to other neurons, muscles, or glands.
    • Axon Hillock: The cone-shaped region where the axon originates from the cell body; site of action potential generation.
    • Axon Terminals (Synaptic Boutons): Branched endings of the axon that form synapses with other cells. Contain synaptic vesicles filled with neurotransmitters.
    • Myelin Sheath: A fatty insulating layer that surrounds many axons, formed by Schwann cells (PNS) or oligodendrocytes (CNS). It speeds up nerve impulse conduction (saltatory conduction). Gaps in the myelin sheath are called Nodes of Ranvier.
• Classification of Neurons:
  • Structural: Multipolar, bipolar, unipolar (pseudounipolar).
  • Functional: Sensory (afferent) neurons, motor (efferent) neurons, interneurons (association neurons).

B. Neuroglia (Glial Cells)

• Function: Support, nourish, protect, and insulate neurons. They do not transmit nerve impulses but are essential for neuronal function and survival. They are more numerous than neurons.
• Types of Glial Cells:
  • CNS Glia:
    • Astrocytes: Star-shaped, most abundant; form the blood-brain barrier, provide structural support, regulate ion concentrations, neurotransmitter uptake.
    • Oligodendrocytes: Form myelin sheaths around axons in the CNS.
    • Microglia: Phagocytic cells; act as immune defense in the CNS.
    • Ependymal Cells: Line the ventricles of the brain and central canal of the spinal cord; produce and circulate cerebrospinal fluid (CSF).
  • PNS Glia:
    • Schwann Cells (Neurolemmocytes): Form myelin sheaths around axons in the PNS; also aid in regeneration of damaged peripheral nerves.
    • Satellite Cells: Surround neuron cell bodies in ganglia; provide structural support and regulate the chemical environment.

III. Neurophysiology: Nerve Impulse and Synaptic Transmission

A. Membrane Potential

• Resting Membrane Potential: The electrical potential difference (voltage) across the plasma membrane of a resting neuron (typically around -70 mV, inside negative). Maintained by the Na⁺/K⁺ pump and differential permeability to ions.

B. Action Potential (Nerve Impulse)

• A rapid, transient, all-or-none reversal of the membrane potential that propagates along the axon.
• Phases:
  • Threshold: Minimum stimulus required to trigger an action potential.
  • Depolarization: Influx of Na⁺ ions due to opening of voltage-gated Na⁺ channels, making the inside of the membrane positive.
  • Repolarization: Efflux of K⁺ ions due to opening of voltage-gated K⁺ channels, restoring the negative charge inside.
  • Hyperpolarization (Afterpotential): Membrane potential temporarily becomes more negative than resting potential due to slow closing of K⁺ channels.
• Refractory Period: Period during which another action potential cannot be generated (absolute) or requires a stronger stimulus (relative).
• Propagation: Continuous conduction (unmyelinated axons) or saltatory conduction (myelinated axons, faster).

C. Synaptic Transmission

• Synapse: The junction between a neuron and another neuron or an effector cell (muscle or gland).
• Types: Electrical synapses (gap junctions) and chemical synapses (most common).
• Chemical Synapse Components: Presynaptic terminal, synaptic cleft, postsynaptic membrane.
• Mechanism of Chemical Synaptic Transmission:
  1. Action potential arrives at presynaptic terminal.
  2. Voltage-gated Ca²⁺ channels open, Ca²⁺ influx.
  3. Increased intracellular Ca²⁺ triggers fusion of synaptic vesicles with presynaptic membrane, releasing neurotransmitters into synaptic cleft.
  4. Neurotransmitters diffuse across cleft and bind to specific receptors on postsynaptic membrane.
  5. Binding causes a change in permeability of postsynaptic membrane to ions, generating a postsynaptic potential (Excitatory Postsynaptic Potential - EPSP, or Inhibitory Postsynaptic Potential - IPSP).
  6. Neurotransmitter removal from cleft (e.g., enzymatic degradation, reuptake, diffusion).

D. Neurotransmitters

• Chemical messengers that transmit signals across synapses. Examples: Acetylcholine, norepinephrine, dopamine, serotonin, GABA, glutamate, endorphins.

IV. Major Components of the CNS (Brief Overview - may be expanded in further units)

A. The Brain

• Major parts: Cerebrum (higher thought processes), Cerebellum (coordination, balance), Brainstem (Midbrain, Pons, Medulla Oblongata - vital functions), Diencephalon (Thalamus, Hypothalamus - relay and control centers).
• Protection: Skull, meninges (dura mater, arachnoid mater, pia mater), cerebrospinal fluid (CSF).
• Blood-Brain Barrier.

B. The Spinal Cord

• Extends from the brainstem down the vertebral canal.
• Functions: Transmits sensory impulses to the brain and motor impulses from the brain; acts as a reflex center.
• Structure: Gray matter (neuron cell bodies, dendrites, unmyelinated axons), white matter (myelinated axons). Spinal nerves.

These notes on the nervous system provide a foundational framework for understanding its intricate anatomy and physiology, which are essential for comprehending human health and disease.

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