Central Nervous System

• Central Nervous System

Central Nervous System Organization

• Association or interneurons create a communication network between brain areas
• The brain will be studied based on embryonic divisions: forebrain, midbrain, hindbrain

Functions of the Central Nervous System

• Composed of the brain and spinal cord
• Receives input from sensory neurons and directs the activity of motor neurons
• Association neurons integrate sensory information to maintain homeostasis and respond to the environment
• Humans can learn and memorize, thus modifying behaviors

Forebrain-Cerebrum

• Deals with higher mental functions
• Largest portion of the brain
• Cerebral cortex: the cerebrum's outer gray matter
• Consists of cerebral hemispheres, each divided into lobes
• Corpus callosum: a nerve bundle connecting cortex layers of the left and right hemispheres

Limbic System and Emotions

• Emotions get controlled by this system
• Aggression arises in areas of the amygdala and hypothalamus
• Fear is associated with the amygdala and hypothalamus
• Hunger/satiety is linked to the hypothalamus
• Sex drive is the system as a whole
• The system allows for a goal-directed behavior which uses a reward/punishment system
• Few connections exist between the cerebral cortex and limbic system, thus limiting conscious control over emotion
• The hypothalamus and limbic system cooperate to form a neural basis for emotion
• Emotions, memory, and actions are related because certain drugs can excite or inhibit receptors, which can alter perceptions and movements

Hippocampus

• Formation and retrieval of memory
• Forms cognitive maps for mental models
• Stress and emotion (via limbic system) can impact memory
• Cortisol receptors exist within the hippocampus

Amygdala

• Combines different forms of sensory input
• Memory and emotion can combine when strong enough

Forebrain: Diencephalon

• Relay center for sensory info (except smell)
• Prioritizes received information
• Epithalamus regulates circadian rhythms and contains the pineal gland

Forebrain: Hypothalamus

• Influenced by higher brain centers
• Master command center for neural and endocrine coordination; regulates pituitary gland
• Key to controlling homeostasis
• Controls what you need to survive like eating, drinking, and regulating body temperature
• Produces two hormones

Midbrain

• Functions in motor control; maintains connections from cerebrum to cerebellum
• Dopaminergic neurons project to basal nuclei and the limbic system
• Neurons leading to areas of the limbic system, hippocampus, amygdala, and reward pathway
• These neurons form key areas for the study of drug addiction
• Dopamine (a neurotransmitter and hormone associated with 'good feelings'), is released into the nucleus accumbens after consumption of certain addictive drugs

Opioid Neurotransmitters

• Opioids bind to Opioid receptors
• Receptors are activated by stress to block the transmission of pain
• Endogenous Opioids: Polypeptides which get produced by the brain and pituitary gland
• Exogenous Opioids: Drugs such as opium and morphine fit the same receptors which results in pain relief
• Opioids produce euphoria to mediate reward pathways; for example, there is a release of endorphins (named from the polypeptide: β-endorphin)
• β-endorphin effects opioid receptors in the brain, namely the mu-opioid receptor (MOR) and delta-opioid receptor (DOR)
• The hippocampus, which forms memories, exists as part of the limbic system, which controls emotions
• The hippocampus is also the location for receptors that bind to certain recreational drugs

Hindbrain: Cerebellum and Pons

• Sensory and motor pathway from the spinal cord with a respiratory control center
• Has complex motor skills; coordinates movements; is involved in motor learning
• Receives info from muscles & joints (proprioceptors), skin and eyes

Medulla Oblongata

• Functions as an autonomic nervous center for cardio and respiratory rates
• All ascending and descending tracts between the brain and spinal cord pass through this site

Neurotransmitters:

• Glutamate - excitatory
• Dopamine - excitatory
• GABA - inhibitory

Peripheral Nervous System Nerves

• All separate near the spinal cord into:
  • a dorsal root which carries sensory fibers
  • a ventral root carrying motor fibers.
• 31 pairs of spinal nerves
  • 8 Cervical
  • 12 Thoracic
  • 5 Lumbar
  • 5 Sacral
  • 1 Coccygeal

Reflex Arc

• Reflex responses to stimuli are multi-step
• A stimulus occurs at the receptor of a sensory neuron
• This impulse is sent along the afferent neuron and gets received by the central nervous system
• The interneuron then makes connections to the motor neuron
• The motor neuron transmits the impulse to the effector organ

Reflex Arcs

• Some reflexes require many association areas and interneurons in the brain
• Ex: crossed extensor reflex
• Muscle stretch reflex: where afferent & efferent neurons link directly
• Ex: Knee-jerk reflex