Nervous System

Nervous System

Introduction

·       The nervous system is the master control and communication system of the body.

·       It regulates and coordinates all voluntary and involuntary activities by transmitting electrical impulses between different parts of the body.

·       Unlike the endocrine system (which controls via hormones and is slower), the nervous system acts rapidly and precisely.

Key features

• Receives information (sensory input) from internal and external environment.
• Processes and interprets (integration) sensory input.
• Sends commands (motor output) to effectors (muscles/glands).
• Maintains homeostasis, behavior, learning, memory, emotions, and survival.

Divisions of the Nervous System

1. Anatomical Divisions

• Central Nervous System (CNS)
• Composed of Brain and Spinal Cord.
• Acts as the command center: receives, integrates, and sends out instructions.
• Peripheral Nervous System (PNS)
• Includes cranial nerves (12 pairs) and spinal nerves (31 pairs).
• Links CNS to body parts.
• Subdivisions:
• Somatic Nervous System (SNS): voluntary control of skeletal muscles.
• Autonomic Nervous System (ANS): involuntary control of smooth muscles, cardiac muscle, glands.
• Further divided into Sympathetic and Parasympathetic.

2. Functional Divisions

• Sensory (Afferent) Division: carries impulses from receptors → CNS.
• Motor (Efferent) Division: carries impulses from CNS → effectors.

Functions of Nervous System

1. Sensory Function: detect changes in internal/external environment via receptors.
2. Integrative Function: analyze, interpret, and store sensory information; decide response.
3. Motor Function: elicit responses via muscles (movement) or glands (secretion).
4. Higher Functions: learning, memory, speech, emotions, consciousness, and behavior.

Neuron (Nerve Cell)

Structure

• Cell Body (Soma/Perikaryon): nucleus, Nissl bodies (rough ER), cytoplasm.
• Dendrites: branched processes, receive impulses.
• Axon: single long process, conducts impulses away. Contains axoplasm and axolemma.
• Myelin Sheath: insulating covering formed by Schwann cells (PNS) or oligodendrocytes (CNS).
• Nodes of Ranvier: gaps in myelin, allow saltatory conduction (fast impulse).
• Axon Terminals: synaptic end bulbs release neurotransmitters.

Classification

1. Structural
• Unipolar: one process (sensory neurons).
• Bipolar: one dendrite, one axon (retina, olfactory).
• Multipolar: many dendrites, one axon (motor neurons, interneurons).
2. Functional
• Sensory (Afferent) Neurons: transmit impulses from receptors → CNS.
• Motor (Efferent) Neurons: transmit impulses from CNS → effectors.
• Interneurons (Association Neurons): connect sensory and motor neurons in CNS.

Properties

• Excitability: ability to respond to stimuli.
• Conductivity: ability to transmit impulses.
• Transmission: impulse passes across synapses via neurotransmitters.
• Refractory Period: time during which neuron cannot be re-excited.

Brain – Structure and Functions

The brain (~1.4 kg, 2% body weight) is protected by the skull, meninges, and cerebrospinal fluid (CSF).

1. Cerebrum

• Largest part, divided into two hemispheres connected by corpus callosum.
• Has cerebral cortex (gray matter) and inner white matter.
• Lobes & Functions:
• Frontal: motor control, speech, reasoning, personality.
• Parietal: sensory perception (touch, pain, temperature).
• Temporal: hearing, memory, smell.
• Occipital: vision.

2. Diencephalon

• Thalamus: relay center for sensory impulses.
• Hypothalamus: homeostasis, temperature regulation, hunger, thirst, circadian rhythm, endocrine control.

3. Brainstem

• Midbrain: visual & auditory reflexes, motor pathways.
• Pons: connects higher brain to spinal cord; respiration.
• Medulla Oblongata: vital centers – heartbeat, respiration, blood pressure.

4. Cerebellum

• Located posteriorly.
• Functions: coordination of movement, balance, posture, muscle tone.

Spinal Cord – Structure and Functions

• Extends from medulla oblongata → L1/L2 vertebra.
• Protected by vertebrae, meninges, and CSF.
• Gray Matter (H-shaped): contains neuron cell bodies.
• White Matter: contains ascending (sensory) and descending (motor) tracts.
• Functions:
• Reflex center (spinal reflexes).
• Pathway for conduction of impulses to/from brain.

Autonomic Nervous System (ANS)

Controls involuntary functions (smooth muscle, cardiac muscle, glands). Divided into:

1. Sympathetic Division (Fight or Flight)

• Origin: thoracolumbar region (T1–L2).
• Neurotransmitter: norepinephrine (mostly).
• Effects:
• ↑ Heart rate & blood pressure.
• Dilates pupils.
• Dilates bronchioles.
• Inhibits digestion & urinary activity.
• Mobilizes glucose and energy reserves.

2. Parasympathetic Division (Rest and Digest)

• Origin: craniosacral region (cranial nerves III, VII, IX, X, and sacral nerves S2–S4).
• Neurotransmitter: acetylcholine.
• Effects:
• ↓ Heart rate & blood pressure.
• Constricts pupils.
• Constricts bronchioles.
• Stimulates digestion, salivation, and urination.
• Conserves and restores body energy.

Video Description

·        Don’t forget to do these things if you get benefitted from this article

·        Visit our Let’s contribute page https://keedainformation.blogspot.com/p/lets-contribute.html

·        Follow our page

·        Like & comment on our post

·