Human Nervous System: Functions, Anatomy, and Disorders

Nervous vs. Endocrine System Coordination

Living organisms utilize different systems for coordination. These include:

• Nervous System: Receives information and processes it for a fast response. It utilizes nerve impulses, and its effects are generally short-lasting.
• Endocrine System: Elaborates hormones for communication. Its response is typically very slow but durable.

Nervous System Response Pathway

The nervous system's response to stimuli involves several key components:

Receptor, Center, and Effector

• Receptor: The organ or structure responsible for perceiving stimuli from the internal or external environment.
• Nervous Center: Receives information from receptors and transmits processed information, producing a series of organized responses.
• Effector: The organ or tissue responsible for carrying out the response dictated by the nervous center.

Effector Types: Muscles and Glands

• Muscles: Produce a motor response, which involves movement.
• Glands: Produce a secretory response, which involves the secretion of substances, such as hormones.

Neurons: Types and Functions

Neurons are the fundamental units of the nervous system.

Sensory, Motor, and Interneurons

• Sensory Neurons (Afferent): Carry information from sensory receptors to the central nervous system (brain and spinal cord).
• Motor Neurons (Efferent): Carry information from the central nervous system to the effectors (muscles and glands).
• Interneurons (Association Neurons): Connect sensory neurons with motor neurons, primarily within the central nervous system.

Glial Cells: Support for Neurons

Glial cells (or neuroglia) are non-neuronal cells that provide essential support functions for neurons. They protect, insulate, and nourish neurons. Examples include:

• Schwann Cells: Form myelin sheaths in the peripheral nervous system.
• Astrocytes: Provide structural and metabolic support in the central nervous system.

Central Nervous System (CNS) Anatomy

The Central Nervous System (CNS) consists of the brain and the spinal cord. These vital structures are protected by the skull and the vertebral column, respectively.

The Brain: Structure and Parts

The brain (encephalon) is the primary control center.

Cerebrum: Hemispheres and Matter

The cerebrum is divided into two cerebral hemispheres. The surface of both hemispheres is highly folded into convolutions (gyri and sulci). It is composed of:

• Gray Matter (Cortex): The outer layer, primarily containing neuron cell bodies.
• White Matter: The inner part, primarily containing myelinated nerve fibers.

Cerebellum: Movement Coordination

The cerebellum is located below the cerebrum, towards the back. It is crucial for coordinating voluntary movements, posture, balance, and equilibrium.

Medulla Oblongata: Vital Functions

The medulla oblongata (or bulb) is located at the base of the brain, connecting to the spinal cord. It controls essential involuntary functions such as breathing, heart rate, and blood pressure.

Spinal Cord: Reflex Control

The spinal cord is a long, cylindrical structure extending from the medulla oblongata. It transmits nerve signals between the brain and the rest of the body and controls reflex actions, which are rapid, automatic responses to stimuli.

Peripheral Nervous System (PNS) Divisions

The Peripheral Nervous System (PNS) transmits information from sensory receptors to the CNS and carries motor commands from the CNS to effectors.

Somatic System: Voluntary Actions

The Somatic Nervous System is involved in conscious perception and voluntary body movements (e.g., controlling skeletal muscles).

Autonomic System: Involuntary Control

The Autonomic Nervous System regulates involuntary bodily functions such as heart rate, digestion, respiratory rate, and glandular secretion. It has two main divisions:

Sympathetic and Parasympathetic Systems

• Sympathetic System: Generally prepares the body for 'fight or flight' responses during situations of stress or activity.
• Parasympathetic System: Generally promotes 'rest and digest' functions, conserving energy during situations of repose.

Understanding Voluntary and Involuntary Acts

• Voluntary Acts: Involve conscious thought and decision-making, leading to a deliberate response.
• Involuntary Acts (Reflexes): Are automatic, rapid responses to stimuli that occur without conscious thought.

The Reflex Arc Mechanism

A reflex action occurs via a neural pathway called the reflex arc. The components are:

1. Stimulus: A change in the environment that is detected.
2. Receptor: Detects the stimulus.
3. Sensory Neuron: Transmits the nerve impulse from the receptor to the spinal cord (or brainstem for some reflexes).
4. Association Neuron (Interneuron): Located in the spinal cord (or brainstem), it relays the signal from the sensory neuron to a motor neuron.
5. Motor Neuron: Transmits the nerve impulse from the CNS to an effector.
6. Effector: The muscle or gland that carries out the response.

Common Sensory Organ Disorders

Eye Conditions and Diseases

• Glaucoma: Characterized by increased intraocular pressure (pressure within the eyeball), which can damage the optic nerve and lead to vision loss.
• Cataracts: A condition causing loss of transparency in the lens of the eye, leading to cloudy or blurred vision.
• Conjunctivitis: Inflammation of the conjunctiva (the thin membrane lining the inside of the eyelids and covering the white part of the eye) and sometimes the sclera.

Ear Conditions and Diseases

• Otitis: Inflammation of the ear, which can affect the outer, middle, or inner ear, and is often accompanied by pain and sometimes pus.
• Meniere's Disease: A disorder of the inner ear that affects balance and hearing, causing episodes of vertigo, hearing loss, tinnitus (ringing in the ear), and a feeling of fullness in the ear.