Nervous System Powerpoint2007_1

Nervous System Overview

• Main components: Nervous System Overview, Neuron, Reflex Arc, Action Potential, Synapse/Neurotransmitters, Nervous System Diseases, Drugs, Peripheral Nervous System (PNS), Central Nervous System (CNS), Brain.

General Functions of the Nervous System

• Maintains homeostasis: regulation of internal environment, including pH, body temperature, glucose levels, blood pressure, and water levels.

• Key functions include:

  • Reception: Sensing environmental changes.

  • Conduction: Transmitting signals.

  • Interpretation and Organization: Processing information.

  • Transmission: Sending signals to execute responses.

Nervous System Organization

• Central Nervous System (CNS): Comprises the brain and spinal cord.

• Peripheral Nervous System (PNS): Includes all nerves outside the CNS, subdivided into:

  • Somatic Nerves: Controls voluntary movements.

  • Autonomic Nerves: Controls involuntary movements, split into:

    • Sympathetic Nervous System: Responsible for the fight or flight responses.

    • Parasympathetic Nervous System: Responsible for rest and digest actions.

The Neuron

• Functional Unit: Conducts nerve impulses. Three types of neurons:

  • Sensory Neurons (Afferent): Carry impulses from sensory receptors to the CNS.

  • Motor Neurons (Efferent): Carry impulses from the CNS to muscles and glands.

  • Interneurons: Located within the CNS, process signals.

• Neuroglia (Glial Cells): Supportive cells that nourish, protect, and maintain neurons.

Basic Neuron Structure

• Types of Neurons: Bipolar, Unipolar, Multipolar (with examples of interneurons, sensory neurons, motor neurons).

• Neuron Components:

  • Cell Body: Contains the nucleus and cytoplasm.

  • Dendrites: Projections that receive information.

  • Axon: Transmits impulses away from the cell body.

  • Myelin Sheath: Insulating layer around axons, produced by Schwann cells; facilitates faster impulse conduction.

  • Nodes of Ranvier: Gaps in myelin that allow for saltatory conduction (impulse jumps from node to node).

Reflex Arc

• Function: Enables quick, involuntary responses to stimuli without immediate brain involvement.

• Components:

  1. Sensory Receptor: Detects stimulus.

  2. Sensory Neuron: Sends signal to the CNS.

  3. Interneuron: Processes the signal.

  4. Motor Neuron: Sends response to effector.

  5. Effector: Executes the response.

Action Potential

• Describes the nerve impulse.

• Phases:

  1. Resting Potential: -70mV polarization due to sodium-potassium pump action.

  2. Depolarization: Triggered by threshold stimulus, influx of Na+ resulting in +40mV.

  3. Re-polarization: K+ ions exit, restoring polarized state with hyperpolarization.

  4. Refractory Period: Restoration of resting potential using ATP energy.

• Saltatory Conduction: Impulses travel faster due to jumping between Nodes of Ranvier.

Synapse and Neurotransmitters

• Neurons communicate via synaptic clefts:

  • Pre-synaptic Neuron: Sends signal across the synapse.

  • Post-synaptic Neuron: Receives the signal.

• Neurotransmitter Functions: Excitatory (opens Na+ channels) vs. inhibitory (blocks Na+ channels, opens K+ channels).

• Summation: Net effect of neurotransmitters determines whether a neuron fires.

• Removing Neurotransmitters: Critical for preventing successive impulses.

Nervous System Diseases

• Multiple Sclerosis (MS): Results from myelin sheath destruction; leads to impaired impulse transmission.

• Parkinson's Disease: Caused by dopamine deficiency due to cell degeneration.

• Alzheimer’s Disease: Characterized by memory loss and cell deterioration linked to acetylcholine malfunction.

• Depression: Associated with imbalances in dopamine and serotonin.

• Stroke: Interruption of blood flow to the brain leads to cell death.

CNS and PNS Structure

• CNS: Comprises brain and spinal cord, responsible for processing information.

• PNS: Contains cranial and spinal nerves, organized into somatic and autonomic systems.

• Meninges: Three protective membranes surrounding the CNS.

• Cerebrospinal Fluid: Provides protection and nutrient exchange.

Brain Structures and Functions

• Hindbrain:

  • Cerebellum: Coordination and balance.

  • Medulla Oblongata: Autonomic functions (heartbeat, respiration).

  • Pons: Connects various parts of the brain and regulates breathing.

• Midbrain: Reflex center for visual stimuli.

• **Forebrain: **

  • Thalamus: Sensory relay station.

  • Hypothalamus: Regulation of hormones, thirst, hunger, emotions.

  • Cerebrum: Responsible for memory, intellect, and language.

Diagnostic Techniques in Neuroscience

• EEG, MRI, CT, PET, SPECT: Imaging techniques to study brain structure and activity.