Chapter 6 Part 4 Nervous System

Nervous System Structure

• Central Nervous System (CNS): Includes the brain and spinal cord, acting as the body's control center. CNS tissue does not regenerate.
• Peripheral Nervous System (PNS): Comprises all nerves external to the brain and spinal cord, linking the CNS to the rest of the body.
  • Autonomic Nervous System (ANS): Regulates involuntary bodily functions; includes sympathetic and parasympathetic systems.
  • Voluntary Nervous System: Controls voluntary muscle movements.
• Sympathetic Nervous System: The "fight or flight" response, preparing the body for stressful situations.
• Parasympathetic Nervous System: The "rest and digest" response, restoring the body to a calm state.

Central Nervous System Overview

• Brain: The primary control center, located within the skull (cranium). The mandible (lower jaw) is the only bone that moves.
• Neurons: Specialized brain cells communicating via synapses. Approximately 700 million neurons reside in the brain.
• Spinal Cord: Extends from the brainstem, connecting to the brain and controlling sensory and motor pathways. Extends to approximately L2 (lumbar 2).
• Meninges: Protective tissue layers surrounding the brain and spinal cord.
  • Dura Mater: The tough outer layer.
  • Arachnoid Mater: The middle layer; subarachnoid space contains cerebrospinal fluid (CSF).
  • Pia Mater: The delicate inner layer adheres directly to the brain.
• Cerebrospinal Fluid (CSF): Found in the subarachnoid space, serving as a protective cushion for the brain. Produced in the third ventricle.
• Blood Supply to the Brain: The brain needs constant oxygen and glucose. Primary supply comes from the carotid and vertebral arteries.
• Brain Stem: Connects the cerebrum to the spinal cord, housing vital control centers.
  • Medulla Oblongata: Contains centers controlling heart rate, breathing, blood pressure, and consciousness.
  • Reticular Activating System (RAS): Responsible for wakefulness.

Brain Divisions

• Cerebrum: The largest brain part, responsible for intellect, learning, personality, and voluntary movement.
  • Frontal Lobe: Controls personality, motor activity, speech, memory, and motivation.
  • Parietal Lobe: Processes sensation and body awareness (proprioception).
  • Temporal Lobe: Houses speech, hearing, memory, balance, and some primal emotions.
  • Occipital Lobe: Processes visual information.
• Cerebellum: Located posteriorly, mediating balance, muscle coordination, and precise movements.
• Brain Stem: A vital structure connecting cerebrum and spinal cord, controlling essential functions.

Peripheral Nervous System

• Cranial Nerves: 12 pairs connecting to the brainstem.
  • Oculomotor Nerve (CN III): Controls pupil constriction, aiding in brain function assessment.
  • Vagus Nerve (CN X): Stimulation can lower heart rate. Potentially affected during straining activities (e.g., lifting, bowel movements).
• Spinal Nerves: 31 pairs originating from the spinal cord.
  • Phrenic Nerve: Controls the diaphragm, vital for breathing; damage can cause respiratory failure.

Autonomic Nervous System

• Sympathetic Nervous System ("Fight or Flight"): Prepares the body for stressful situations.
  • Effects: Pupil dilation, slowed digestion, decreased saliva, bronchodilation, increased heart rate, blood redistribution to vital organs, increased breathing rate.
• Parasympathetic Nervous System ("Rest and Digest"): Restores the body to a calm state after stress; opposite of the sympathetic system.

Brain Function and Oxygen/Glucose

• The brain is extremely sensitive to oxygen and glucose levels.
• Brain dysfunction can cause changes in mental state.
• Early signs of brain problems include altered consciousness.
• Brain health may rely on supplemental oxygen.