Neural control

Homeostasis is maintained through the coordinated functions of organs and organ systems.
Coordination refers to the process where two or more organs interact and complement each other’s functions.
Example: During physical exercise:
- Increased energy demand for muscular activity.
- Supply of oxygen is enhanced.
- Increased respiration rate, heartbeat, and blood flow through blood vessels.
After exercise, the activities of nerves, lungs, heart, and kidneys gradually return to normal.
The nervous system and endocrine system work together to coordinate organ activities:
- Nervous System: Provides a quick network of point-to-point connections.
- Endocrine System: Provides chemical integration using hormones.

Divided into two primary parts:
1. Central Neural System (CNS)
- Comprises the brain and spinal cord.
- Responsible for information processing and control.
1. Peripheral Neural System (PNS)
- Includes all nerves associated with CNS.
- Nerve fibres classified into two types:
  - Afferent Fibres: Transmit impulses from organs/tissues to CNS.
  - Efferent Fibres: Transmit regulatory impulses from CNS to peripheral organs/tissues.
Further divided into:
- Somatic Neural System: Relays impulses to skeletal muscles.
- Autonomic Neural System: Transmits impulses to involuntary organs and smooth muscles.
  - Subclassified into sympathetic and parasympathetic systems.
The Visceral Nervous System: Part of PNS that carries impulses between CNS and visceral organs.

Neurons are specialized cells characterized by three major parts:
1. Cell Body: Contains cytoplasm and organelles, including Nissl’s granules.
2. Dendrites: Short, branched fibres that transmit impulses toward the cell body; contain Nissl’s granules.
3. Axon: Long fibre that transmits impulses away from the cell body; terminates in synaptic knobs containing neurotransmitters.
Types of Neurons based on axon and dendrite structure:
- Multipolar Neurons: One axon and two or more dendrites (e.g., in the cerebral cortex).
- Bipolar Neurons: One axon and one dendrite (e.g., in the retina of the eye).
- Unipolar Neurons: One axon only, typically in embryonic stages.
Types of Axons:
- Myelinated Axons: Enveloped by Schwann cells forming a myelin sheath; have nodes of Ranvier.
- Unmyelinated Axons: Enclosed by Schwann cells without a myelin sheath.

Neurons are excitable due to polarized membranes.
Resting State: Membrane more permeable to potassium ions (K+) and relatively impermeable to sodium ions (Na+).
Concentration Gradient:
- Inside Axon: High concentration of K+ and negative proteins.
- Outside Axon: High concentration of Na+ and low concentration of K+.
Established by Sodium-Potassium Pump: Transports 3 Na+ out and 2 K+ in, resulting in a positive charge outside and negative charge inside the membrane, creating a resting potential.

When stimulated, the membrane becomes permeable to Na+, causing rapid Na+ influx and a reversal of polarity (depolarization).
The area becomes positively charged outside (action potential) and negatively inside, leading to a wave of depolarization.
Current flows from the excited site along the axon causing successive action potentials, allowing impulse conduction.
Recovery Phase: Following the impulse, K+ permeability increases, allowing K+ to exit and restoring resting potential.

Impulses are transmitted from one neuron to another at synapses:
- Electrical Synapses: Neurons connected closely, allowing direct passage of current; faster transmission.
- Chemical Synapses: Separated by synaptic cleft; transmission involves neurotransmitters released from the pre-synaptic terminal.

Arrival of action potential at axon terminal causes vesicles to move and release neurotransmitters into synaptic cleft.
Neurotransmitters bind to receptors on the post-synaptic membrane, generating a new potential which can be excitatory or inhibitory.

The brain is the primary information processing center, controlling voluntary and involuntary functions, thermoregulation, hunger, thirst, and circadian rhythms.
Protection: Enclosed within the skull and surrounded by cranial meninges (dura mater, arachnoid, pia mater).
Divisions of the Brain:
1. Forebrain
2. Midbrain
3. Hindbrain

Composed of cerebrum, thalamus, and hypothalamus:
- Cerebrum: Major part, divided into left and right hemispheres connected by the corpus callosum. Contains the cerebral cortex (grey matter) and tracts (white matter).
- Thalamus: Major sensory and motor coordination center.
- Hypothalamus: Controls hunger, thirst, body temperature, and secretes hormones (hypothalamic hormones).
- Limbic System: Includes structures like amygdala and hippocampus; involved in emotional responses and sexual behavior.

Located between forebrain and hindbrain; contains the cerebral aqueduct and corpora quadrigemina.

Comprised of pons, cerebellum, and medulla (medulla oblongata):
- Pons: Fiber tracts connecting different brain regions.
- Cerebellum: Complex structure for integrating sensory information and coordination.
- Medulla: Controls respiration and cardiovascular reflexes; connects to the spinal cord.

The neural system integrates and coordinates organ functions to maintain homeostasis.
Neurons, as functional units, are excitable due to ionic concentration gradients.
The resting potential is the electrical potential across an inactive neuron membrane.
Action potentials are waves of depolarization and repolarization that facilitate nerve impulse transmission.
Synapses, formed between pre- and post-synaptic neuron membranes, may consist of electrical or chemical types relying on neurotransmitters.
The human brain is organized into major parts: forebrain, midbrain, hindbrain, influencing complex behaviors and bodily functions.