Brain and Cranial Nerves - Part 2 Notes

Basal Nuclei

  • Masses of gray matter in the cerebrum's white matter.
  • Involved in:
    • Cognitive functioning
    • Emotional processing
    • Motor control and learning
  • Receive input from the motor cortex and cerebellum.

Basal Nuclei and Neurotransmitters

  • Glutamate: Excitatory, involved in basal nuclei function, especially with cortex pathways.
  • Dopamine: Excitatory, modulates basal nuclei activity, especially movement control.
  • GABA: Inhibitory, involved in communication between basal nuclei structures; has a calming effect.

Hippocampus

  • Involved in:
    • Converting short-term to long-term memories
    • Spatial orientation and navigation
    • Associating emotions with memories
    • Pattern recognition and associative learning
  • Part of the limbic system.

Memory

  • Hippocampus: Converts short-term memory into long-term memory.
  • Amygdala: Involved in forming memories with emotional significance.
  • Prefrontal Cortex: Involved in working memory.
  • Cerebellum: Involved in procedural memory.

Synaptic Changes in Memory (Synaptic Plasticity)

  • Synaptic plasticity: Synapses strengthen or weaken over time based on activity.
  • Long-Term Potentiation (LTP):
    • Long-lasting increase in synaptic strength with repeated stimulation.
    • Helps strengthen synapses and encode information.
    • Occurs primarily in the hippocampus.
  • Glutamate binds to NMDA and AMPA receptors allowing Ca2+Ca^{2+} and Na+Na^{+} to enter the postsynaptic neuron.
  • Ca2+Ca^{2+} activates CaMKII, which enhances existing AMPA receptors and inserts more AMPA receptors, strengthening the synapse.

Limbic System

  • Involves structures of the cerebrum and diencephalon.
  • The "emotional brain."
  • Functions:
    • Mediates emotional responses.
    • Processes fear.
    • Recognizes facial expressions.
    • Allows expression through gestures.
    • Interprets pain.
    • Resolves mental conflict.
  • Involved in memory formation and retrieval.

Reticular Formation

  • Network of interconnected structures in the brainstem.
  • Governs brain arousal.
  • Maintains cerebral cortical alertness through the reticular activating system (RAS).
    • Depressed by anesthesia, alcohol, tranquilizers, and sleep-inducing drugs.
    • Severe injury to the RAS can lead to coma.
  • Helps regulate skeletal and visceral muscle activity.

Cranial Nerves

  • 12 pairs attached to the brain.
  • Numbered I-XII.
  • Except for the vagus nerve (X), they serve only the head and neck.

Cranial Nerves I & II

  • Olfactory nerves (I): Sensory nerves for smell.
  • Optic nerves (II): Sensory nerves for vision.

Cranial Nerves III, IV, and VI

  • Oculomotor nerves (III): Motor nerves for eye movement and pupil size.
  • Trochlear nerves (IV): Motor nerves for eye movement.
  • Abducens (VI): Motor nerves for eye abduction.

Trigeminal Nerves (Cranial Nerve V)

  • Mixed (sensory and motor) nerves.
  • Three major branches:
    • Ophthalmic nerve (V1): Sensory for cornea, nasal cavity, forehead, upper eyelid, part of nose.
    • Maxillary nerve (V2): Sensory for lower eyelid, upper lip, gums, teeth, cheek, nose, palate.
    • Mandibular nerve (V3): Sensory for lower gums, teeth, lips, palate, part of tongue; motor for chewing muscles.

Facial Nerves (Cranial Nerve VII)

  • Mixed nerves of face.
  • Motor control over facial expression muscles, lacrimal gland, nasal mucous glands, submandibular and sublingual salivary glands.
  • Sensory nerve for taste buds on anterior tongue.

Vestibulocochlear Nerves (Cranial Nerve VIII)

  • Mostly sensory.
  • Vestibular nerve: Balance.
  • Cochlear nerve: Hearing.

Glossopharyngeal Nerves (Cranial Nerve IX)

  • Mixed nerves to the head and neck.
  • Motor control over pharyngeal muscles and parotid salivary gland.
  • Sensory function for throat, tongue, ears; taste from posterior tongue; blood pressure regulation.

Vagus Nerves (Cranial Nerve X)

  • Mixed nerves extending beyond the head and neck.
  • Motor control over pharyngeal muscles, laryngeal muscle, heart rate, respiration rate, and digestive processes.
  • Sensory nerves for the ear and laryngopharynx.

Accessory Nerves (Cranial Nerve XI)

  • Motor control of the sternocleidomastoid and trapezius muscles.

Hypoglossal Nerves (Cranial Nerve XII)

  • Motor control over movements of the tongue.

Classification of the Cranial Nerves

  • Purely sensory nerves: I, II, VIII
  • Primarily or exclusively motor nerves: III, IV, VI, XI, XII
  • Mixed (motor and sensory) nerves: V, VII, IX, X