Nervous system

1. CENTRAL NERVOUS SYSTEM (CNS)

A. Brain

The brain is the control center, responsible for thought, emotion, memory, sensation, and motor activity.

Main parts of the brain:

• Cerebrum: Largest part; divided into two hemispheres. Responsible for conscious thought, sensory processing, and voluntary movement.

• Divided into lobes: frontal, parietal, temporal, occipital

• Cerebellum: Coordinates movement and balance

• Brainstem: Controls automatic functions like breathing, heart rate, and digestion

• Includes: midbrain, pons, medulla oblongata

B. Spinal Cord

• A long cylindrical structure extending from the brainstem down through the vertebral column

• Transmits signals between the brain and body

• Contains gray matter (cell bodies) and white matter (nerve fibers)

• Gives rise to spinal nerves at each vertebral level

2. PERIPHERAL NERVOUS SYSTEM (PNS)

Includes all neural elements outside the CNS: cranial nerves, spinal nerves, and ganglia.

A. Cranial Nerves (12 pairs)

Emerge directly from the brain; control head and neck functions (e.g., vision, smell, taste, facial movement)

B. Spinal Nerves (31 pairs)

Emerge from the spinal cord and supply the body

• Each spinal nerve has:

• Sensory fibers: carry signals to the CNS

• Motor fibers: carry signals from the CNS to muscles

C. Ganglia

Clusters of neuron cell bodies located outside the CNS

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Functional Divisions

A. Somatic Nervous System (SNS)

• Voluntary control of skeletal muscles

• Includes sensory neurons (from skin, muscles) and motor neurons (to skeletal muscle)

B. Autonomic Nervous System (ANS)

• Involuntary control of organs, glands, and smooth muscle

• Divided into:

1. Sympathetic (“fight or flight” – increases heart rate, dilates pupils)

2. Parasympathetic (“rest and digest” – slows heart rate, stimulates digestion)

3. Enteric – controls the gastrointestinal system

Neurons and Glial Cells

Neurons

• Basic functional unit of the nervous system

• Transmit electrical impulses

• Structure: cell body, dendrites, axon

Glial cells (neuroglia)

• Support and protect neurons

• Types include:

• Astrocytes

• Oligodendrocytes

• Microglia

• Schwann cells (PNS)

Clinical Note

• Damage to the nervous system can cause paralysis, sensory loss, or cognitive disorders

• Multiple sclerosis: autoimmune disease affecting myelin

• Stroke: interruption of blood supply to the brain

• Neurodegenerative diseases: such as Alzheimer’s, Parkinson’s

Function Summary

• Sensory input → detects stimuli

• Integration → processes and interprets info

• Motor output → activates muscles or glands