Nervous System Structure Overview

Nervous System Structure

• The nervous system is the body's control center, managing sensory information, movement, autonomic functions, & cognition.
• Divided into central nervous system (CNS) and peripheral nervous system (PNS).

Central Nervous System (CNS)

• Consists of the brain and spinal cord.
• Acts as the command center for processing sensory input, motor commands, and higher cognitive functions.
• Brain: Manages voluntary and involuntary functions, memory, reasoning, emotions, and perception.
• Spinal Cord: Conducts signals between the brain and the rest of the body, controlling reflex actions.

Peripheral Nervous System (PNS)

• Connects the CNS to the rest of the body.
• Divided into:
  • Somatic Nervous System (SNS): Controls voluntary movements, relays sensory information to the CNS.
  • Autonomic Nervous System (ANS): Regulates involuntary bodily functions (e.g., heart rate, digestion).
    • Sympathetic Nervous System (SNS): Activates "fight or flight."
    • Parasympathetic Nervous System (PNS): Activates "rest and digest."

Brain Structure

• The brain is composed of 100 billion neurons and trillions of synapses (connections).
• Divided into three major regions: hindbrain, midbrain, and forebrain.

Hindbrain

• Controls basic life functions like breathing, heart rate, and motor coordination.
• Structures include:
  • Medulla Oblongata: Autonomic functions (heart rate, respiration, blood pressure, reflexes).
  • Pons: Relay center between cerebrum, cerebellum, involved in sleep, arousal, and motor control.
  • Cerebellum: Coordinates voluntary movements, posture, balance, and motor learning.

Midbrain

• Involved in sensory processing, motor control, and alertness.
• Structures include:
  • Superior Colliculus: Processes visual stimuli and eye movement.
  • Inferior Colliculus: Processes auditory stimuli.
  • Substantia Nigra: Produces dopamine for movement control (degeneration leads to Parkinson's disease).

Forebrain

• Responsible for higher-order cognitive functions, emotions, and sensory integration.
• Structures include:
  • Thalamus: Relays sensory information (except smell) to the cortex.
  • Hypothalamus: Regulates hormones, hunger, thirst, body temperature, and sleep-wake cycle.
  • Limbic System: Involved in emotions, memory, and motivation
    • Amygdala: Fear, aggression, emotional processing.
    • Hippocampus: Memory formation, spatial navigation.
  • Basal Ganglia: Regulates movement, reward, and habit formation (affected in Parkinson's and Huntington's disease).

Cerebral Cortex

• The outermost layer of the brain, responsible for complex cognitive functions.
• Divided into four lobes: frontal, parietal, occipital, and temporal.
  • Frontal Lobe: Decision-making, reasoning, impulse control, voluntary movements, speech production (Broca's area).
  • Parietal Lobe: Somatosensory processing (touch, pain, temperature), spatial awareness, mathematical/logical thinking.
  • Occipital Lobe: Primary visual processing, visual recognition.
  • Temporal Lobe: Auditory processing, language comprehension (Wernicke's area), memory processing.

Neurons and Glial Cells

• Neurons transmit electrical and chemical signals. Composed of dendrites, cell body (soma), axon, myelin sheath, synapse.
• Glial cells support and nourish neurons.

Neurotransmitters

• Chemical messengers in the brain. Examples include dopamine (movement, reward), serotonin (mood), acetylcholine (memory, learning), GABA (inhibitory), glutamate (excitatory).

Reflex Arcs

• Automatic, involuntary responses to stimuli. Bypass the brain for quicker reactions.
• Monosynaptic and polysynaptic reflex arcs are distinguished, based on number of synapses involved in the response.

Nervous System Disorders

• Examples: Stroke, Multiple Sclerosis, Parkinson's Disease, Alzheimer's Disease, Epilepsy.