Nervous System: Components, Functions & Health

Posted on Mar 2, 2025 in Biology

Components of the Nervous System

The nervous system detects and interprets external and internal stimuli and produces the necessary responses. It is made up of:

  • Neurons: Generate and transmit nerve impulses. They are classified by function:
    • Sensory neurons: Send information to the CNS, where it’s interpreted, and responses are made.
    • Motor neurons: Carry responses from the CNS to the effectors, causing muscle contractions or gland secretions.
    • Relay neurons: Connect sensory and motor neurons.
  • Glial cells: Provide support and protection. Types include:
    • Astrocytes: Transport nutrients to the neurons.
    • Microglia: Remove cellular waste and protect against microorganisms.
    • Oligodendrocytes and Schwann cells: Produce the myelin sheath, which helps to transmit nerve impulses.

Transmission of Nerve Impulses: Neurons transmit information as electrical signals. Transmission occurs at a synapse. The signal travels from the neuron to the axon terminal.

The Nervous System

Controls the internal environment (homeostasis) and enables the body to interact with the external environment. It consists of:

  • Central Nervous System (CNS): Comprises the brain and spinal cord. It is surrounded by three membranes called meninges and cerebrospinal fluid, which provides protection.
  • Peripheral Nervous System (PNS): Connects the CNS to the rest of the body.
    • Peripheral Nerves:
    • Cranial Nerves: Emerge from the brain.
    • Spinal Nerves: Emerge from the spinal cord.

The PNS is divided into two systems based on their function:

  • Somatic Nervous System: Controls voluntary muscle movement and involuntary reflex arcs.
  • Autonomic Nervous System: Regulates unconscious, automatic actions.
    • Sympathetic Nervous System: Increases heart rate.
    • Parasympathetic Nervous System: Decreases heart rate.

Responses of the Somatic Nervous System

  • Voluntary Responses: Controlled by the brain.
    1. A stimulus is detected by a receptor.
    2. The stimulus is transmitted by the optic nerve to the brain.
    3. The brain interprets the stimulus and responds.
    4. The response is transmitted as a nerve impulse through a motor nerve to the muscles.
    5. Muscles carry out the response.
  • Involuntary Responses: Originate in the spinal cord.
    1. A stimulus is detected by a receptor.
    2. Sensory neurons transmit nerve impulses to the spinal cord.
    3. A relay neuron connects the sensory neuron to the motor neuron.
    4. The motor neuron carries the response to a muscle.
    5. The muscle carries out the response.

    The neural path of a reflex action is called a reflex arc. This short path results in fast, automatic responses.

Health of the Nervous System

Causes of Neurological Problems:

  • Infectious Diseases: Caused by microorganisms, these can destroy motor neurons, resulting in muscle weakness and paralysis.
  • Cerebrovascular Events: Affect blood circulation to the brain.
  • Physical Trauma: Damage to the brain and spinal cord can cause various issues, including paralysis of the lower limbs or all four limbs, depending on the location.
  • Progressive Neurodegenerative Diseases:
    • Multiple Sclerosis (MS): A CNS disease that damages the myelin sheath.
    • Alzheimer’s Disease: A type of dementia characterized by the loss of neurons and synapses in the brain.
    • Parkinson’s Disease: A chronic disorder of the brain in which neurons controlling movement and posture die.

Mental Health

Mental health issues can have physical, psychological, sociocultural, or hereditary causes. Examples include:

  • Phobias: An anxiety disorder.
  • Obsessive-Compulsive Disorder (OCD): Characterized by obsessive thoughts and repetitive behaviors.
  • Depression: A mood disorder.
  • Dementia: Characterized by declining brain function.
  • Schizophrenia: Appears in adolescence or adulthood, with symptoms including hallucinations and drastic changes in behavior.
  • Mental and Behavioral Problems Due to Drug Use: These can include lack of motivation, changes in behavior, mood extremes, inability to focus, memory loss, feeling fearful, anxious, or paranoid, depression or suicidal thoughts, intoxication, and addiction.