Nervous System

Overview of the Nervous System

  • The nervous system is divided into two main components:

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

    • Peripheral Nervous System (PNS): Comprises all other nerves throughout the body.

  • Functions:

    • PNS provides sensory input to the CNS, which processes information and executes motor responses.

Structure of the Brain

General Divisions of the Brain

  • The brain can be divided into three main regions:

    • Hindbrain:

      • Medulla: Regulates vital functions like breathing, blood pressure, and heart rate.

      • Pons: Coordinates signals between various parts of the brain and regulates sleep.

      • Cerebellum: Responsible for balance and coordination of movement.

    • Midbrain:

      • Deep within the brain, involved in alertness, motor activity, and sleep/wake cycles.

    • Forebrain:

      • Cerebrum: Two hemispheres (left and right), responsible for various functions depending on the location (e.g., speech, reasoning).

      • Thalamus: Processes sensory and motor information.

      • Hypothalamus: Regulates the endocrine system.

  • Myths about the Brain: The belief that humans only use 10% of their brains is a myth.

Peripheral Nervous System (PNS)

  • The PNS is functionally divided into:

    • Somatic Nervous System (SNS): Controls voluntary movements and somatic reflexes.

    • Autonomic Nervous System (ANS): Manages internal environments and autonomic reflexes.

  • Further division of ANS:

    • Sympathetic System: Engages the fight or flight response, accelerating heart rate and inhibiting digestion.

    • Parasympathetic System: Controls rest and digest functions; slows heart rate and promotes digestion.

Cells of the Nervous System

Neurons

  • Basic structure of neurons:

    • Cell Body: Contains the nucleus and organelles.

    • Dendrites: Branch-like structures where signals are received.

    • Axon: Long fiber that carries signals away from the cell body to other neurons.

    • Synapse: Junction where neurons communicate with one another.

  • Neurons perform rapid communication essential for nervous system function.

Glial Cells (Glia)

  • Glial cells support neurons structurally and functionally:

    • Help maintain chemical balance, produce myelin sheath around axons, and create cerebrospinal fluid.

    • Perform immune functions and protect the nervous system.

  • The term "glia" comes from a Greek word meaning glue.

Action Potential

  • Action potentials are rapid changes in electrical charge that neurons use to communicate:

    • Resting Potential: About -70 mV, indicating a negative charge inside the neuron compared to its surroundings.

    • Ionic Role: Sodium (Na+) and potassium (K+) ions are crucial for establishing resting potential and creating action potentials.

  • Process of Action Potential:

    • Dendrites receive a signal, causing depolarization as Na+ ions flow into the neuron through ion channels, making the interior less negatively charged.

    • Action potential propagates along the axon, allowing fast communication.

    • Myelination: In myelinated neurons, action potentials can jump between nodes, enhancing speed.

    • All-or-None Principle: Action potentials either occur fully or not at all, akin to a light switch.

Neurotransmitters and Synaptic Transmission

  • Following action potentials, neurotransmitters are released to transmit signals between neurons:

    • Action potentials signal synaptic vesicles to release neurotransmitters into the synaptic cleft (the gap between neurons).

    • Neurotransmitters bind to specific receptors on the receiving neuron, potentially triggering another action potential.