Neural Control and Coordination_Shobhit Nirwan

Neural Control and Coordination

Overview

  • The human neural system is divided into two main parts:

    • Central Nervous System (CNS):

      • Comprises the brain and spinal cord.

      • Acts as the main site for information processing and control.

    • Peripheral Nervous System (PNS):

      • Contains all the nerves associated with the CNS.

      • Includes cranial nerves (12 pairs) and spinal nerves (31 pairs).

Nerve Fibers in the PNS

  • Types of Nerve Fibers:

    • Afferent Fibers:

      • Transmit impulses from various tissues to the CNS.

    • Efferent Fibers:

      • Transmit impulses from the CNS to tissues.

  • Divisions of PNS:

    • Somatic Neural System:

      • Relays impulses from CNS to skeletal muscles.

    • Autonomic Neural System:

      • Transmits impulses to involuntary organs and smooth muscles.

      • Includes:

        • Sympathetic neural system.

        • Parasympathetic neural system.

Neuron Structure

  • A neuron consists of three major parts:

    • Cell Body:

      • Contains cytoplasm and organelles including Nissl's granules (site of protein synthesis).

    • Dendrites:

      • Short, branched fibers that receive signals from other neurons.

    • Axon:

      • A long fiber that transmits impulses away from the cell body, ending in synaptic knobs.

Types of Neurons

  • Multipolar Neurons:

    • One axon and multiple dendrites (found in the cerebral cortex).

  • Bipolar Neurons:

    • One axon and one dendrite (found in the retina).

  • Unipolar Neurons:

    • One axon, typically found in embryonic stages.

  • Myelination:

    • Myelinated fibers (enveloped by Schwann cells) facilitate faster impulse conduction.

    • Non-myelinated fibers are slower and present throughout autonomic systems.

  • Nodes of Ranvier:

    • Gaps in myelin sheath that allow for saltatory conduction.

Neural Membrane

  • The resting membrane of a neuron is permeable to K+ ions but nearly impermeable to Na+ ions, creating an ionic gradient:

    • Higher concentration of K+ and negatively charged proteins inside.

    • Higher Na+ outside the membrane.

  • Resting Potential:

    • Electrical potential difference of -70 mV across the membrane, maintained by the Na-K pump.

Action Potential

  • Triggered when a stimulus causes increased membrane permeability to Na+, leading to:

    • Depolarization: The rapid influx of Na+ reverses polarity temporarily.

    • Action Potential: The sequence of depolarization travels along the axon.

    • Restoration:

      • K+ diffuses out quickly after, restoring the resting potential.

Impulse Transmission

  • Graded Potential:

    • Small triggers that may not initiate an action potential.

  • Action Potential:

    • Larger triggers cause significant change, initiating a nerve impulse.

Synapses

  • Types of Synapses:

    • Electrical Synapses:

      • Faster transmission; membrane proximity allows direct impulse flow.

    • Chemical Synapses:

      • Involves synaptic cleft and neurotransmitters (e.g., acetylcholine).

Mechanism of Chemical Synapse Transmission

  1. Arrival of an action potential at axon terminal.

  2. Synaptic vesicles release neurotransmitters.

  3. Neurotransmitters bind to receptors on postsynaptic membranes.

  4. Ion channels open, generating new action potentials.

Brain Structure

  • Protection:

    • Encased in cranial cavity and covered by three layers of meninges:

      • Dura mater (outer layer).

      • Arachnoid mater (middle layer).

      • Pia mater (inner layer).

  • Cerebrospinal Fluid (CSF):

    • Fills subarachnoid space, providing cushioning and nutrients.

  • Divisions of the Brain:

    • Forebrain (Cerebrum, Diencephalon)

    • Midbrain

    • Hindbrain

Forebrain Details

  • Cerebrum:

    • Largest brain part with two hemispheres, separated by the corpus callosum.

    • Cerebral Cortex:

      • Outer gray matter involved in complex functions (motor, sensory, associations).

Hypothalamus Functions

  • Regulates vital functions such as temperature, thirst, hunger, emotions, and hormonal controls.

  • Coordinates the limbic system, which is involved with emotions and drives.

Brain Stem and Its Functions

  • Composed of:

    • Cerebellum

    • Pons

    • Medulla oblongata

  • Coordinates muscular activities and maintains equilibrium.

  • Controls autonomic functions like respiration, heart rate, and reflex actions.

Spinal Cord Structure

  • Positioned within the vertebral column and protected by meninges.

  • Contains a central canal filled with CSF.

  • Functions:

    • Conducts impulses between brain and body.

    • Processes reflex actions.

Peripheral Nervous System (PNS)

  • Divided into:

    • Somatic Nervous System: Relays impulses to skeletal muscles.

    • Autonomic Nervous System: Sends impulses to involuntary organs and is sub-divided into:

      • Sympathetic System: Activates stress responses.

      • Parasympathetic System: Calms body functions post-stress.

Visceral Nervous System**: Communicates between CNS and visceral organs using nerves and ganglia.