NEURAL CONTROL AND COORDINATION
NCERT Masterclass & NEET Biology Study Module
1. Human Neural System
Coordination is the process through which two or more organs interact and complement the functions of one another. The neural system provides an organized network of point-to-point connections for a quick coordination.
- Central Neural System (CNS): Includes the brain and the spinal cord. It is the site of information processing and control.
- Peripheral Neural System (PNS): Comprises all nerves associated with the CNS. Divided into two types of nerve fibres:
- Afferent fibres: Transmit impulses from tissues/organs TO the CNS.
- Efferent fibres: Transmit regulatory impulses FROM the CNS to peripheral tissues/organs.
The PNS is further divided into the Somatic neural system (relays impulses from CNS to skeletal muscles) and the Autonomic neural system (relays impulses from CNS to involuntary organs and smooth muscles). The ANS is classified into Sympathetic and Parasympathetic neural systems.
2. Neuron as Structural and Functional Unit
A neuron is composed of three major parts: Cell body, Dendrites, and Axon.
- Cell Body: Contains cytoplasm with typical organelles and certain granular bodies called Nissl's granules (made of RER and ribosomes, involved in protein synthesis).
- Dendrites: Short, branched fibres that transmit impulses towards the cell body. Also contain Nissl's granules.
- Axon: A long fibre that transmits impulses away from the cell body to a synapse. The distal end is branched, terminating in bulb-like synaptic knobs containing synaptic vesicles with neurotransmitters.
Types of Neurons:
1. Multipolar: One axon, two or more dendrites. Found in the cerebral cortex.
2. Bipolar: One axon and one dendrite. Found in the retina of the eye.
3. Unipolar: Cell body with one axon only. Found usually in the embryonic stage.
Myelinated vs Unmyelinated: Myelinated nerve fibres are enveloped with Schwann cells, which form a myelin sheath around the axon. The gaps between two adjacent myelin sheaths are called Nodes of Ranvier (found in spinal and cranial nerves). Unmyelinated fibres do not have a myelin sheath (found in autonomic and somatic neural systems).
3. Generation and Conduction of Nerve Impulse
Neurons are excitable cells because their membranes are in a polarised state. This polarity is due to different types of ion channels that are selectively permeable.
Action Potential: When a stimulus is applied, the membrane becomes freely permeable to $Na^+$. Rapid influx of $Na^+$ reverses the polarity (Depolarisation). The inner side becomes positively charged. The electrical potential difference across the plasma membrane at this site is called the action potential (nerve impulse). Shortly after, $Na^+$ permeability decreases, $K^+$ permeability increases, and $K^+$ diffuses outside, restoring the resting potential (Repolarisation).
4. Transmission of Impulses (Synapse)
A nerve impulse is transmitted from one neuron to another through junctions called synapses. A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, separated by a gap called the synaptic cleft.
- Electrical Synapses: Membranes are in very close proximity (gap junctions). Current flows directly. Transmission is faster but rare in the human system.
- Chemical Synapses: Separated by a fluid-filled synaptic cleft. Involves neurotransmitters.
5. Central Neural System (Human Brain)
The brain is the central information processing organ of our body, acting as the 'command and control system'. It is protected by the skull and three cranial meninges: Outer Dura mater, middle Arachnoid, and inner Pia mater.
A. Forebrain
- Cerebrum: Forms the major part of the human brain. Divided into left and right cerebral hemispheres, connected by a tract of nerve fibres called corpus callosum. The outer layer is the cerebral cortex (grey matter - contains motor areas, sensory areas, and large association areas responsible for complex functions like memory and communication). Inner part is white matter (myelinated tracts).
- Thalamus: Cerebrum wraps around it. It is a major coordinating centre for sensory and motor signaling.
- Hypothalamus: Lies at the base of the thalamus. Contains centres which control body temperature, urge for eating and drinking. Also contains neurosecretory cells that secrete hypothalamic hormones regulating the pituitary gland.
- Limbic System: Inner parts of cerebral hemispheres and deep structures like amygdala and hippocampus form the limbic lobe/system. Along with the hypothalamus, it regulates sexual behavior, motivation, and emotional reactions (excitement, pleasure, rage, fear).
B. Midbrain & Hindbrain
- Midbrain: Located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. A canal called the cerebral aqueduct passes through it. The dorsal portion consists mainly of four round swellings (lobes) called Corpora quadrigemina.
- Hindbrain: Comprises pons, cerebellum, and medulla (medulla oblongata).
- Pons: Consists of fibre tracts that interconnect different regions of the brain.
- Cerebellum: Has a very convoluted surface to provide additional space for many more neurons. Responsible for balance and coordinated movement.
- Medulla: Connected to the spinal cord. Contains centres which control respiration, cardiovascular reflexes, and gastric secretions.
- Brain Stem: Forms the connections between the brain and spinal cord. Made up of Midbrain, Pons, and Medulla.
🚀 NEET NEURAL CONTROL MEGA QUIZ (100 MCQ)
Solve the 5 parts below to master Neuron Anatomy, Action Potential, Synapse, and the Human Brain.
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