The Nervous System

Nervous System Overview

Function

• Transmits and processes information.
• Receives and responds to stimuli.
• Maintains body homeostasis.

Anatomy of the Nervous System

The nervous system is divided into three main parts:

1. Central Nervous System (CNS):

Brain

Spinal Cord

2. Peripheral Nervous System (PNS):

Cranial Nerves

Spinal Nerves

3. Autonomic Nervous System (ANS):

Sympathetic Branch

Parasympathetic Branch

The Neuron

The basic structural unit of the nervous system, forming nerves.

Three Types of Neurons:

1. Sensory (Afferent): Transmit sensory information to the CNS.

2. Interneurons (Connectors): Relay signals between neurons.

3. Motor (Efferent): Carry signals from the CNS to effectors (muscles and glands).

Key Features of Neurons:

• Impulse Direction: Unidirectional signal transmission.
• Synapse: The junction between two neurons where neurotransmitters facilitate or inhibit signal transmission.
• Neurotransmitters: Chemicals released by axon terminals to carry impulses across the synapse.
• Myelin Sheath: A fatty layer that insulates certain neurons, enhancing signal speed.
• Nodes of Ranvier: Gaps in the myelin sheath that facilitate rapid signal transmission.
• Neurilemma: A thin membrane covering the myelin sheath.

Central Nervous System (CNS)

The CNS is protected by the meninges, which consist of three layers:

Dura Mater: The tough, outermost layer.

Arachnoid Mater: The middle, web-like layer.

Pia Mater: The delicate inner layer, closely covering the brain and spinal cord.

Cerebrospinal Fluid (CSF): Located between the arachnoid and pia mater, providing cushioning.

Brain Regions

Cerebrum:

Divided into hemispheres and lobes.

Functions include thinking, speech, learning, memory, and sensory interpretation.

Controls voluntary movement.

Contains the Hypothalamus, which:

Regulates the pituitary gland.

Manages the autonomic nervous system.

Controls temperature, hunger, thirst, emotions, and circadian rhythms.

Cerebellum:

Coordinates muscle activity, balance, and posture.

Brain Stem:

Composed of:

Midbrain: Acts as a relay station between different brain regions and the spinal cord.

Pons: Connects the cerebellum's hemispheres and regulates breathing.

Medulla Oblongata: Connects the cerebrum to the spinal cord and controls automatic functions like heartbeat, breathing, swallowing, and reflexes.

Spinal Cord

Extends through the vertebral canal.

Transmits sensory information to the brain and motor signals from the brain.

Facilitates reflex actions.

Peripheral Nervous System (PNS)

Transmits two-way signals:

Sensory (Afferent): From the body to the CNS.

Motor (Efferent): From the CNS to the body.

Spinal Nerves:

31 pairs that emerge from the spinal cord.

Cranial Nerves:

12 pairs that emerge from the base of the brain.

Autonomic Nervous System (ANS)

Controls involuntary functions by sending signals to:

Smooth Muscles

Glands

Cardiac Muscle

Regulated by the hypothalamus.

Sympathetic Branch:

Increases body activity, primarily affecting organs, blood vessels, and sweat glands.

Parasympathetic Branch:

Reduces activity, focusing on energy conservation and digestive functions.

Sensory (Afferent) Neurons

Specialized to detect and respond to changes in the environment:

Skin Receptors: Detect pain, temperature, and touch.

Receptors in Muscles, Tendons, and Joints: Detect stretch and movement.

Special Sense Organs: Detect sight, sound, smell, and taste.

Internal Receptors: Monitor activities like breathing, heart rate, and digestion.

Motor (Efferent) Neurons

Transmit signals from the CNS to effectors:

Muscles: Initiate movement.

Glands: Trigger secretion.

Reference

This information has been adapted from Anatomy and Physiology On-Line, Gill Tree Training

 

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