Neural Control and Coordination

• Coordination is how multiple organs interact and complement each other's functions to maintain homeostasis.

Neural Control and Coordination

• During physical exercise, increased energy demand leads to a need for more oxygen, causing an increase in respiration rate, heartbeat, and blood flow.
• The nervous and endocrine systems coordinate and integrate bodily activities for synchronized function.
• The nervous system ensures quick coordination through a point-to-point network.
• The endocrine system provides chemical integration using hormones.

Neural System

• Neurons are specialized cells in the nervous system that detect, receive, and transmit stimuli.
• Invertebrates have simple neural organizations such as a network of neurons (ex: Hydra).
• Insects possess a more complex system with a brain, ganglia, and neural tissues.
• Vertebrates have a more developed neural system.

Human Neural System

• Divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS includes the brain and spinal cord.
• The CNS is the main site for information processing and control.
• The PNS consists of nerves connected to the CNS.
• Afferent nerve fibers transmit impulses from tissues/organs to the CNS.
• Efferent fibers transmit regulatory impulses from the CNS to target tissues/organs.
• The PNS includes the somatic and autonomic neural systems.
• Somatic neural system relays impulses from the CNS to skeletal muscles.
• Autonomic neural system transmits impulses from the CNS to involuntary organs and smooth muscles.
• The autonomic system is split into the sympathetic and parasympathetic neural systems.
• Visceral nervous system contains nerves, fibers, ganglia, and plexuses that transmit impulses between the CNS and viscera.

Neuron Structure

• A neuron contains a cell body, dendrites, and an axon.
• The cell body contains cytoplasm, cell organelles, and Nissl's granules.
• Dendrites are short fibers that receive and transmit impulses toward the cell body.
• The axon is a long fiber that transmits nerve impulses away from the cell body.
• The axon ends in branched structures called synaptic knobs.
• Synaptic knobs contain vesicles filled with neurotransmitters.
• Neurons are classified based on the number of axons and dendrites: multipolar, bipolar, and unipolar.
  • Multipolar neurons have one axon and two or more dendrites and are found in the cerebral cortex.
  • Bipolar neurons have one axon and one dendrite and are found in the retina.
  • Unipolar neurons have one axon and are usually found in the embryonic stage.
• Axons can be myelinated or non-myelinated.
• Myelinated nerve fibers are enveloped by Schwann cells, forming a myelin sheath, with gaps called nodes of Ranvier.
• Myelinated fibers are in spinal and cranial nerves and unmyelinated ones are in autonomic and somatic neural systems.

Nerve Impulse

• Neurons are excitable because their membranes are polarized.
• Ion channels present on the neural membrane are selectively permeable to different ions.
• A resting neuron is more permeable to potassium ions (K⁺) and nearly impermeable to sodium ions (Na⁺).
• The axoplasm contains a high concentration of K⁺ and negatively charged proteins, with a low concentration of Na⁺.
• The fluid outside the axon has a low concentration of K⁺ and a high concentration of Na⁺, creating a concentration gradient.
• The sodium-potassium pump maintains these ionic gradients by transporting 3 Na⁺ outwards for 2 K⁺ into the cell.
• The outer surface of the axonal membrane has a positive charge, while the inner surface is negatively charged.
• The electrical potential difference across the resting membrane is called the resting potential.
• When a stimulus is applied, the membrane at that site becomes permeable to Na⁺.
• This leads to a rapid influx of Na⁺, reversing the polarity.
• The outer surface becomes negatively charged, and the inner side becomes positively charged, called the action potential or nerve impulse.
• Current flows on the inner surface from the excited site A to the adjacent site B and on the outer surface from B to A.
• This process repeats along the axon, conducting the impulse.
• Following stimulation, permeability to Na⁺ is short-lived, quickly followed by increased permeability to K⁺.
• K⁺ diffuses outside, restoring the resting potential, and the fiber becomes responsive again.

Transmission of Impulses

• Nerve impulses are transmitted from one neuron to another through synapses.
• A synapse is formed by the membranes of pre- and post-synaptic neurons, separated by a synaptic cleft.
• There are two main types of synapses: electrical and chemical.
• In electrical synapses, pre- and post-synaptic neurons are very close together.
• Electrical current flows directly from one neuron to the other.
• Transmission across electrical synapses is similar to impulse conduction along a single axon. -Electrical synapses are faster but rare in our system.
• In chemical synapses, pre- and post-synaptic neurons are separated by a fluid-filled synaptic cleft.
• Neurotransmitters transmit impulses across these synapses.
• Axon terminals contain vesicles filled with neurotransmitters.
• An impulse arriving at the axon terminal stimulates the movement of synaptic vesicles to fuse with the plasma membrane.
• Neurotransmitters are released into the synaptic cleft and bind to specific receptors on the post-synaptic membrane.
• Binding opens ion channels to generate a new potential in the post-synaptic neuron, which can be excitatory or inhibitory.

Central Neural System

• The brain is the central information processing organ and 'command and control system'.
• The brain controls voluntary movements, balance, involuntary organs, thermoregulation, hunger, thirst, circadian rhythms, endocrine glands, human behavior, and processes vision, hearing, speech, memory, intelligence, emotions, and thoughts.
• The brain is protected by the skull and covered by cranial meninges: dura mater, arachnoid, and pia mater.
• Three main parts of the brain: forebrain, midbrain, and hindbrain.

Forebrain

• The forebrain includes the cerebrum, thalamus, and hypothalamus.
• The cerebrum is the major part of the human brain, divided into left and right cerebral hemispheres connected by the corpus callosum.
• The cerebral cortex is the outer layer of the cerebral hemisphere and contains many folds called the grey matter.
• The cerebral cortex contains motor, sensory, and association areas.
• Association areas are responsible for complex functions like intersensory associations, memory, and communication.
• Fibers in the tracks are covered in myelin sheaths and make up the inner part of the hemisphere called white matter.
• The thalamus is a major coordinating center for sensory and motor signaling.
• The hypothalamus, located at the base of the thalamus, controls body temperature, eating, and drinking.
• Hypothalamus contains neurosecretory cells that secrete hypothalamic hormones.
• Inner parts of cerebral hemispheres and deep structures (like amygdala and hippocampus) form the limbic system.
• The limbic system regulates sexual behavior, emotional reactions, and motivation.

Midbrain

• The midbrain is located between the thalamus/hypothalamus and the pons.
• The cerebral aqueduct passes through the midbrain.
• The dorsal portion of the midbrain consists of four round swellings called the corpora quadrigemina.

Hindbrain

• The hindbrain includes the pons, cerebellum, and medulla oblongata.
• The pons consists of fiber tracts that interconnect different regions of the brain.
• The cerebellum has a highly convoluted surface for more neurons.
• The medulla connects to the spinal cord and controls respiration, cardiovascular reflexes, and gastric secretions.
• The brain stem is made up of the midbrain, pons, and medulla oblongata and connects the brain to the spinal cord.