The Nervous System Overview

The Nervous System

• The nervous system controls all body functions, including breathing, voluntary and involuntary movements (digestion, heartbeat), and thinking.
• The nervous system is composed of cells called neurons that receive and transmit messages as electrochemical signals.
• The human brain contains 100 billion neurons.
• Neurons have three main parts:
  • The cell body, containing the cell nucleus.
  • Axons, carrying messages away from the cell body.
  • Dendrites, receiving messages from other neurons.
• Bundles of axons are called nerves, located throughout the body.
• The nervous system uses a network of neurons to send messages.
• Neurons employ electrochemical signals for message transmission.
• The signal travels down an axon as an electrical signal, then converts to a chemical signal by neurotransmitters at the synapse.
• The neurotransmitter crosses the synapse, converting back to an electrical signal by the next neuron's dendrite.

The Central Nervous System (CNS)

• The CNS comprises the brain and spinal cord, coordinating bodily functions.
• The Brain:
  • The brain is the body's command center, processing information.
  • It is responsible for awareness, movements, sensations, thoughts, speech, and memory.
  • The three major parts of the brain:
    • Cerebrum: The largest part, composed of right and left hemispheres. It is responsible for interpreting touch, vision, hearing, speech, reasoning, emotions, learning, and fine motor control.
    • Cerebellum: Located under the cerebrum, coordinating muscle movements, maintaining posture, and balance.
    • Brain Stem: Connecting the cerebrum and cerebellum to the spinal cord, managing automatic functions like breathing, heart rate, body temperature, sleep cycles, digestion, sneezing, coughing, vomiting, and swallowing.
• The Spinal Cord:
  • A long bundle of nerves and cells extending from the lower brain to the lower back, carrying signals between the brain and body.
  • Three sections:
    • Cervical (neck)
    • Thoracic (chest)
    • Lumbar (lower back)
  • Protected by three layers of tissue called meninges:
    • Pia Mater
    • Arachnoid Mater
    • Dura Mater
  • Vital functions include:
    • Carrying signals from the brain: regulating movement and autonomic functions.
    • Carrying information to the brain: transmitting sensory information (touch, pressure, pain).
    • Reflex responses: enabling the spinal cord to independently control reflexes like the patellar reflex.

The Peripheral Nervous System (PNS)

• The PNS links the CNS to organs, limbs, and skin, carrying sensory and motor information to and from the CNS.
• It regulates involuntary functions like heartbeat and breathing.
• The PNS is divided into two parts:
  • The Somatic Nervous System:
    • Transmitting sensory information.
    • Responsible for voluntary movement.
    • Two major types of neurons:
      • Motor Neurons: causing physical actions in response to stimuli.
      • Sensory Neurons: receiving sensory information and sending it to the brain and spinal cord.
  • The Autonomic Nervous System:
    • Regulating involuntary body functions (blood flow, heartbeat, digestion, breathing).
    • Two branches:
      • Sympathetic system: maintaining normal body functions and conserving resources.
      • Parasympathetic system: regulating the 'fight-or-flight' response, preparing the body to expend energy in response to perceived threats.