Human Nervous System: Structure, Components, and Functions

The Nervous System: Stimuli, Response, and Effectors

Stimuli are detected by the sensory organs: sight, touch, hearing, taste, and smell.

The information is transmitted, and a response is created by the nervous system. This response is transmitted to the effector organs:

• Locomotor system: Responsible for movement.
• Endocrine system: Responsible for hormone release.

The Neuron: Anatomical and Physiological Unit

The nervous system's anatomical and physiological unit is the neuron.

Supporting Cells

• Schwann cells: They isolate the axon, ensuring that the nerve impulse is transmitted faster.

Types of Neurons Based on Function

• Sensory neurons: Transmit information from the receptors to the nerve centers.
• Motor neurons: Transmit signals from the nerve centers to the effector organs.
• Interneurons: Connect sensory and motor neurons (located in the brain and in the spinal cord).

Components of the Nervous System

1. Central Nervous System (CNS):
   • a) Brain (Cerebrum, Cerebellum, Brain Stem)
   • b) Spinal Cord
2. Peripheral Nervous System (PNS):
   • a) Somatic Nervous System
   • b) Autonomic Nervous System (Sympathetic Nervous System, Parasympathetic Nervous System)

The Central Nervous System (CNS)

The CNS is responsible for integrating received information, coordinating it, and preparing a response. It has two parts: the brain and the spinal cord.

Protection of the CNS

1. Bone (Skull and Spine)
2. Meninges (Dura mater, Arachnoid mater, Pia mater)
3. Cerebrospinal Fluid

CNS Tissue Types

1. Grey matter: Composed of cell bodies and dendrites.
2. White matter: Composed of axons (with myelin).

In the spinal cord, the grey matter is found in the center, shaped like a butterfly's wings. The white matter is in the outer area. The Central Canal contains cerebrospinal fluid.

Functions of the Spinal Cord

1. Mediating reflex actions.
2. Serving as a pathway for messages to and from the brain and the rest of the body (via cervical, thoracic, lumbar, and sacral segments).

Main Parts of the Brain

The main parts of the brain are the brain stem, cerebellum, and cerebrum.

Other related structures include:

Specific Brain Functions

• Brain Stem: It controls vital involuntary functions such as heartbeat, breathing, and blood pressure. It can also regulate sleep.
• Cerebellum: It intervenes in the control of muscles, balance, and the posture of the body.

The Peripheral Nervous System (PNS)

The PNS is made up of nerves, which contain a mixture of nerve fibers (axons). Nerves can be:

• Cranial: Linked to the brain.
• Spinal: Linked to the spinal cord.

The Somatic Nervous System

The Somatic Nervous System receives information from external stimuli and transmits signals for voluntary muscle contractions.

The Autonomic Nervous System (ANS)

The Autonomic Nervous System controls involuntary body functions. It is linked to the grey matter of the spinal cord, the brain stem, and the hypothalamus.

Parts of the Autonomic Nervous System

1. Sympathetic Nervous System: It makes the organs work more effectively (often associated with 'fight or flight').
2. Parasympathetic Nervous System: It provides relaxation and allows the organs to work more slowly (often associated with 'rest and digest').