Lecture 12 - Brain: Brainstem & Cerebellum

Chapter 13 - Brain & Cranial Nerves

Most inferior portion of the brain
Connects to spinal cord
Location of grey matter & white matter starts to change
Spinal Nerve C1 (last spinal nerve moving upward/first spinal cord encounter when entering into spinal cord)
Transmits ascending/descending impulses between brain & spinal cord
Pyramids: Nerve tracts, conscious control of skeletal muscle
- Descending somatic motor neurons
- Only descending, only part of somatic nervous system
Ascending neurons/other motor neurons located in white matter regions of medulla oblongata
Contains center for vital reflexes (heart rate, BP, respiration, swallowing, coughing, sneezing)
Olives: Nuclei involved in balance, coordination, modulation of sound
- Sends sensory information to cerebellum
- Slightly alters how we recieve audio input from inner ear
Cranial Nerves: Entering/Exiting into brain
- Nuclei of cranial nerves 5, 7, 9, 10, 11, 12
- (V, VII, IX, X, XI, XII)

Key Components of the Medulla Oblongata:

Pyramids:
- White matter bulges on interior side of medulla oblongata
  - Contain descending tracts (carries information from brain down towards spinal cord)
  - Carries motor information, specifically motor tracts that are part of somatic motor system
    - Sent to our skeletal muscles
- bilateral, just before entering the spinal cord, they cross over to the opposite side of the body
  - Decussation of the Pyramids: 90% of the tracts move from left side to right & right side to the left
    - Why damaging one side of the brain affects the opposite side of the body (Eg. Stroke)
Olives:
- bilateral
- Concentrations of nuclei
- (Nucleus = collection of cell bodies in CNS)
- Relays information from muscles/joints about position to cerebellum
  - Cerebellum helps coordinate smooth movements
- Information is brought up thorugh spinal cord through brain
- Involved in sound perception
Cranial Nerves
- Some are entering/exiting medulla oblongata
- Eg. Hypoglossal Cranial Nerve (Cranial Nerve #12)
  - Bundle of myelinated axons, actual neuron cell bodies are located in various regions in medulla oblongata
- Hypoglossal Nucleus:
  - Region where cell bodies are all located inside medulla oblongata
- Vagus Nerve (Cranial Nerve #10)
- Vagus Nucleus
  - Cell bodies of vagus nerve located in medulla oblongata
  - Dorsal Motor

Superior to medulla oblongata
Bridge/connection between different areas of the brain
Contains both ascending & descending nerve tracts
Several areas of gray matter containing nuclei
Sleep center, Respiratory center
- REM sleep
- Works w/ medulla oblongata to control respiration
Anterior Portion:
- Pontine Nuclei - Communication between cerebrum & cerebellum
Posterior Portion:
- Nuclei of cranial nerves 5, 6, 7, 8 (V, VI, VII, VIII)

most superior portion of brainstem
sits between pons & diencephalon
Contains both nerve tracts (white matter) & nuclei (gray matter)
Also a connection to the thalamus
- Part of diencephalon
- Relay center for all sensory information (synapses at thalamus)
Visual/auditory reflex centers
Nuclei of cranial nerves 3, 4, 5 (III, IV, V)
Tectum: 4 nuclei - form mounds on dorsal surface of midbrain
- Each separate part - Colliculus
  - 2 Superior Colliculi - Involved in visual reflexes
    - Extrinsic muscles of eye - move eyeballs around sockets
    - Intrinsic muscles of eye - smooth muscles (pupil diameter)
    - Region involved in tracking & scanning eye movements
    - Tracking Eye movement: You’re still and your eyes are following a moving object
    - Scanning Eye movement: You’re still and the room is still, but your eyes are moving across the room
  - 2 Inferior Colliculi - Involved in hearing
    - Startle reflex (startled by a loud noise) → signal up to superior colliculi to move the eyes
Cerebellar Peduncles: Bundles of axons or white matter (pathways carrying information from one area to another)
- Superior Cerebellar Peduncle Carries axons to and from the midbrain to the cerebellum
- Middle Cerebellar Peduncle: Carries information from the pons to the cerebellum
- Inferior Cerebellar Peduncle: Carries information from the medulla oblongata to the cerebellum

Group of nuclei scattered throughout brainstem
- Connected to each other by white matter connections
“Cloud” throughout the brainstem
Controls cyclic activities such as sleep-wake cycle
- Maintaining conciousness
- Bringing you into awakening from sleep phase

Second largest part of brain
Attached to the brain stem on posterior side
Attaches to brainstem via Cerebellar Peduncles
Space between pons & cerebellum - Fourth Ventricle
Arbor Vitae: White matter regions w/in cerebelllum
- Gathers information from gray matter regions
Folia: Folds created by gray matter region surrounding arbor vitae
Two hemispheres
- Lateral Hemispheres (Cerebellar Hemispheres)
  - Anterior Lobe (Superior)
  - Posterior Lobe (Inferior)
Primary Fissure: Separates the two lobes
Vermis: Separates the two hemispheres of the cerebellum
Flocculonodular Lobe: Lobe outside of lateral hemispheres

Functions of Cerebellum:

Communicates w/ other regions of CNS:
- Superior cerebellar peduncle → midbrain
- Middle cerebellar peduncle → pons
- Inferior cerebellar peduncle → medulla oblongata
3 Regions:
1. Flocculonodular Lobe: Balance
  - Takes information from environment (visual, tactile, cutaneous from skin, info from inner ear about position)
2. Vermis: Gross motor coordination (Anterior), fine motor coordination (Posterior)
  - Gross Motor Movements: walking (big movements w/ lots of muscles involved)
  - Fine motor coordination: Manual dexterity of hands
3. Cerebellar (Lateral) Hemisphere - Fine motor coordination
  - Takes sensory information and puts it together to be able to have very fine coordination & control over motor functions