Lecture 11: Central Nervous System

Introduction

• Focus: Central Nervous System (CNS) - Brain and Spinal Cord
• Sensory and Motor Pathways review

Role of CNS

• Integration center for sensory information
• Processes info from cranial/spinal nerves
• Possible processing in spinal cord or different brain regions

Protection of CNS

1. Skull and Meninges:

   • Bones of the skull
   • Connective tissue layers: Dura mater (outer), Arachnoid layer (middle), Pia mater (inner)

2. Cerebrospinal Fluid (CSF):

   • Formed by choroid plexuses
   • Provides a cushion and shock absorption
   • Limits exchange between CSF and blood (fluid regulation)

3. Blood-Brain Barrier:

   • Selective network preventing harmful substances from entering the brain
   • Tight junctions of capillaries surrounded by astrocytes and ependymal cells
   • Allows lipid-soluble substances, oxygen, CO2, alcohol, and water to pass
   • Requires active transport for glucose, amino acids, and ions
   • CNS metabolism mainly aerobic (oxygen and glucose)

Brain Functions

• Regulates homeostasis, emotion, movement, sensory perception, memory, and cognition
• Functions as a circuit – interconnected regions

Key Brain Regions

1. Gray and White Matter:

   • Gray Matter (Nuclei): Cell bodies, synapses, dendrites (e.g., red nucleus in brainstem)
   • White Matter (Tracts): Myelinated axons within CNS

2. Cerebral Cortex:

   • Lobes: Frontal, Parietal, Occipital, Temporal
   • Functional Areas:
     • Primary Areas: Basic processing (visual, auditory, olfactory, somatosensory, motor)
     • Higher Sensory Areas: More elaborate processing
     • Association Areas: Complex integration
   • Homunculus: Sensory and motor maps reflecting the body's spatial arrangement

3. Prefrontal Cortex:

   • Involved in social and emotional planning, intellect, reasoning, judgment
   • Linked to emotions and the limbic system

4. Language Areas:

   • Broca’s Area: Speech production
   • Wernicke’s Area: Speech processing and understanding

5. Basal Nuclei (Ganglia):

   • Integration and fine-tuning of motor, sensory, and emotional input
   • Affected in Parkinson's disease
   • Includes the amygdala (emotional processing)

6. Cerebellum:

   • Balance, movement planning, and execution
   • Receives visual, proprioceptive, and cortical input
   • Subconscious processing

7. Thalamus:

   • Sensory gatekeeper – filtering, processing, and relaying sensory information

8. Hypothalamus:

   • Homeostasis, linking nervous and endocrine systems
   • Autonomic control, body temperature, sleep-wake cycles, hunger, thirst

9. Limbic System:

   • Emotional processing circuit involving basal nuclei, thalamus, amygdala, hypothalamus

10. Brainstem (Midbrain, Pons, Medulla Oblongata):

    • Reticular Activating System: Attention and arousal
    • Midbrain: Visual and auditory reflexes
    • Pons: Works with medulla for rhythmic breathing (pneumotaxic center)
    • Medulla: Autonomic control (cardiovascular, respiratory centers), reflexes (vomiting, swallowing)

Spinal Cord

• Pathway between body and brain
• Contains ascending (sensory) and descending (motor) tracts

Spinal Cord Protection and Structure:

1. Meninges: Protects the brain and spinal cord
2. Cerebrospinal Fluid: Shock absorption and nutrition
3. Bone: Vertebral column structure

• Gray Matter: Sensory neurons (dorsal), interneurons, and motor neurons (ventral)
• White Matter: Ascending and descending tracts

Functions and Pathways:

• Sensory Pathways: Dorsal horn to brainstem to thalamus to cerebral cortex
• Motor Pathways: Descending from cortex through brainstem, crossing over to ventral root to muscles
• Reflexes: Simple, fast responses independent of brain

Mapping:

• Specific areas for sensory input and motor output in the spinal cord
• Dermatomes: Body regions supplied by specific spinal nerves

Cranial Nerves:

• Connect directly to brain, bypassing spinal cord

Summary

• CNS integrates and processes sensory information, protects brain and spinal cord, and regulates body functions through complex pathways.