Topic 5.1 Chapter 7 Nervous System

Functions of the Nervous System

• Sensory Input

  • Gathering information through sensory receptors that monitor internal and external changes (stimuli).

• Integration

  • Processes and interprets sensory input, deciding necessary actions.

• Motor Output

  • Activates muscles or glands in response to processed information.

Organization of the Nervous System

• Structural Classification

  • Central Nervous System (CNS)

    • Comprises the brain and spinal cord; serves as a command center for integration and outgoing instructions.

  • Peripheral Nervous System (PNS)

    • Comprises cranial and spinal nerves [ \text{(Sensory and Motor)} ]

      • Sensory (Afferent): Carries impulses to CNS from sensory receptors.

      • Motor (Efferent): Carries impulses away from CNS to effector organs.

        • Somatic Nervous System: Voluntary control of skeletal muscles.

        • Autonomic Nervous System: Involuntary control of smooth and cardiac muscles and glands.

          • Sympathetic: Prepares body for stress-related activities.

          • Parasympathetic: Calms body and conserves energy.

Nervous Tissue: Structure and Function

• Supporting Cells (Neuroglia)

  • Provide support, insulation, and protection for neurons.

    • Astrocytes: Brace and anchor neurons to blood supply and regulate chemicals in the brain. Most abundant and versatile neuroglia.

    • Microglia: Act as phagocytes (Spiderlike), cleaning up debris in the CNS. Monitor health of nearby neurons.

    • Ependymal Cells: Line cavities, assist with cerebrospinal fluid circulation.

    • Oligodendrocytes: Form myelin sheaths around CNS nerve fibers.

    • PNS glial cells

      • ▪ Schwann cells - Form myelin sheath around nerve fibers in the PNS

      • ▪ Satellite cells - Protect and cushion neuron cell bodies

Neurons = Nerve cells

• Major Regions

  • Cell Body: Contains the nucleus and metabolic center of the cell.

    • Nucleus with large nucleolus

    • Nissl bodies - Rough endoplasmic reticulum

    • Neurofibrils - Intermediate filaments that maintain cell shape

  • Processes: Fiber extends from the cell body

    • Dendrites: Conduct impulses towards the cell body.

    • Axons: Conduct impulses away from the cell body; terminate at axon terminals containing neurotransmitters.

    • Synaptic cleft—gap between axon terminals and the next neuron

    • Synapse—functional junction between nerves where a nerve impulse is transmitted.

    • Myelin

      • White, fatty material covering axons

      • Protects and insulates fibers

      • Speeds nerve impulse transmission
        

• Action Potentials

  • Initiated when a stimulus changes membrane permeability, allowing sodium ions to rush in, causing depolarization.

  • An action potential propagates along the axon via an all-or-none response.

  • Upon reaching the axon terminal, electrical impulses cause the release of neurotransmitters into the synaptic cleft.

Reflex Arcs

• Definition

  • Reflexes are rapid, involuntary responses to stimuli along neural pathways called reflex arcs.

• Components of Reflex Arc

  1. Sensory Receptor: Detects stimulus.

  2. Sensory Neuron: Carries the impulse to the CNS.

  3. Integration Center: Processes the information (CNS).

  4. Motor Neuron: Carries the response impulse to the effector.

  5. Effector: Muscle or gland responding to motor neurons.

• Types of Reflexes

  • Somatic Reflexes: Control skeletal muscle movements.

  • Autonomic Reflexes: Regulate involuntary activities of smooth muscles, heart, and glands.

Brain Structure

• Regions of the Brain

  • Cerebral Hemispheres: Paired superior parts of the brain, responsible for sensory input processing and motor control.

    • Cortex (Gray Matter): Localizes and interprets sensory inputs; controls voluntary muscle activity.

    • Basal Nuclei: Subcortical centers that regulate motor movements.

  • Diencephalon: Contains thalamus (sensory relay) and hypothalamus (ANS control and homeostasis).

  • Brain Stem: Controls basic life functions (breathing, heart rate).

  • Cerebellum: Coordinates muscle movements and maintains posture.

Protection of the CNS

• Meninges: Three protective membranes surrounding the CNS.

  • Dura Mater: Outermost leathery layer.

  • Arachnoid Mater: Web-like middle layer.

  • Pia Mater: Inner layer closest to the brain and spinal cord.

• Cerebrospinal Fluid (CSF): Acts as a cushion, circulates around and inside the CNS.

• Blood-Brain Barrier: Restricts passage of substances from the bloodstream into the brain, protecting from potential toxins.