TOPIC 6

The Nervous System Overview

  • Comprehensive study of the nervous system is outlined in Chapter 7.

Key Functions of the Nervous System

  1. Sensory Input

    • Gathers information from internal and external environments (stimuli).

  2. Integration

    • Processes sensory input and determines appropriate responses.

  3. Motor Output

    • Activates muscles or glands in response to integrated stimuli.

Organization and Classifications of the Nervous System

Nervous System Structure

  • Central Nervous System (CNS)

    • Components: Brain and spinal cord.

    • Function: Integration and command center; interprets sensory information.

  • Peripheral Nervous System (PNS)

    • Components: Nerves extending from brain and spinal cord.

    • Types: Spinal nerves and cranial nerves.

    • Function: Communicates between sensory organs and CNS.

Functional Classifications

  • Sensory (Afferent) Division

    • Carries information to the CNS:

      • Somatic sensory fibers (skin, skeletal muscles, joints).

      • Visceral sensory fibers (visceral organs).

  • Motor (Efferent) Division

    • Carries impulses away from the CNS:

      • Somatic Nervous System: Voluntary control of skeletal muscles.

      • Autonomic Nervous System (ANS): Involuntary control of smooth and cardiac muscles, and glands.

        • Further divided into:

          • Sympathetic Nervous System (SNS): Activated under stress (“fight or flight”).

          • Parasympathetic Nervous System (PSNS): Restores body to resting state (“rest and digest”).

General Sensory Receptors

  • Responsible for detecting specific stimuli:

    • Nociceptors: Pain detection.

    • Thermoreceptors: Temperature detection.

    • Mechanoreceptors: Touch and pressure detection.

    • Proprioceptors: Stretch or tension in muscles and tendons.

Nerve Impulse Generation and Conduction

  • Properties of Neurons:

    • Irritability: Responding to stimuli.

    • Conductivity: Transmitting impulses to other neurons, muscles, or glands.

  • Action Potential Steps:

    1. Resting potential (polarization).

    2. Stimulus leads to depolarization.

    3. Rapid transmission of the action potential along the axon.

    4. Repolarization restores resting potential.

    5. Return to resting ionic conditions by sodium-potassium pump.

Reflex Arc

  • Definition: Neural pathway involved in reflex actions.

  • Components:

    1. Sensory receptor

    2. Sensory neuron

    3. Integration center (CNS)

    4. Motor neuron

    5. Effector organ (muscle/gland)

Anatomy and Physiology of the Brain

  • Major regions:

    • Cerebral hemispheres

    • Diencephalon

    • Brainstem

    • Cerebellum

  • Each region has specific functions including sensory relay, autonomic control, and muscle coordination.

Anatomy and Physiology of the Spinal Cord

  • Extends from the foramen magnum to lumbar vertebra L1/L2.

  • Functions as a two-way conduction pathway:

    • Contains ascending (sensory) and descending (motor) tracts.

  • Protected by meninges and covered by spinal nerves.

Peripheral Nervous System (PNS) Details

  • Components include cranial and spinal nerves; classified as sensory, motor, or mixed nerves.

  • Cranial Nerves: 12 pairs primarily serving the head, with varying sensory/motor functions.

Nervous System Disorders

  1. Congenital Disorders

    • Cerebral palsy, hydrocephalus, spinabifida.

  2. Acquired Disorders

    • Multiple sclerosis, dementia (Alzheimer's), Parkinson's disease, CVA (stroke).

  3. Traumatic Injuries

    • Concussions, contusions, and intracranial hemorrhage.

  4. Inflammation/Infection

    • Meningitis.

EEG (Electroencephalogram)

  • Measures electrical activity of the brain.

  • Used for diagnosing brain-related conditions, monitoring sleep, and evaluating brain function.