Chapter 14 - Brain & Cranial Nerves (Detailed Look) Flashcards
Brain Stem (3 Parts)
- Medulla Oblongata
- Pons
- Midbrain
Medulla Oblongata
- Begins at foramen magnum
- Between spinal cord & pons
Medullary White Matter Tracts
- Contains sensory tracts (ascending) + motor tracts (descending)
- Both types of tracts run between spinal cord & higher brain centers
Pyramids
Bulges formed by corticospinal tracts
Decussation of Pyramids
Crossing over of pyramids occurs on anterior surface of lower medulla
*90% of upper motor neurons decussate
Medullary Gray Matter
-Contains nuclei that form the 3 Vital Centers:
- Cardiovascular Control
- Medullary Respiratory
- Reflex Centers
Cardiovascular Control Center
Regulates heart rate & force
Medullary Respiratory Center
Regulates rate of breathing
Reflex Centers
Control reflexes for vomiting, coughing, sneezing, hiccupping & swallowing
Pair of Olives
- Lateral to pyramids
- Each olive contains an inferior olivary nucleus, for relaying proprioception info to cerebellum
- Relays to cerebellum info fro, cerebral cortex & red nucleus
Right & Left Gracile & Cuneate Nuclei
Found in posterior medulla & concerned w/ fine touch, light pressure, vibration & proprioception
3 Other Medullary Nuclei
- Gustatory Nuclei
- Cochlear Nuclei
- Vestibular Nuclei
*Nuclei of origin for cranial nerves 8-12
4th Ventricle
Begins in medulla & continues into pons
Pontine White Matter
- Contains ascending (sensory) & descending (motor) tracts
- Contains tracts linking cerebellum & rest of CNS
Pontine Gray Matter
- Pontine nuclei relay nerve impulses from primary motor cortex to the contralateral hemisphere of the cerebellum
- Contains nuclei concerned w/ respiration
- Contains nuclei of origin for cranial nerves 5-8
Pontine Reticular Formation
Reticular formation within the pons has a respiratory area: The Pontine Respiratory Group, which helps the medullary respiratory center to control breathing
Midbrain
- Found between pons & diencephalon
- Conduit for white matter tracts
- Contains nuclei origin for oculomotor & trochlear nerves
- Surrounds aqueduct of the midbrain (AKA “Cerebral Aqueduct”)
Cerebral Peduncles
- Contains motor fibers of:
1. Corticospinal Tracts
2. Corticopontine Tracts
3. Corticobulbar Tracts
-Also contains 2nd order relay fibers that terminate in the thalamus, synapsing w/ 3rd order relay neurons that project to the somatosensory cortex
Corticospinal Tracts
Bundles of UMNs from cerebral cortex that terminate at a specific spinal cord segment
Corticopontine Tracts
Bundles of UMNs that terminate in the pons, synapsing w/ LMNs that travel via cranial nerves to various skeletal muscles:
- Cranial Nerve 5 (Trigeminal) -> Jaw Muscles
- Cranial Nerve 7 (Facial) -> Face Muscles
- Cranial Nerve 12 (Hypoglossal) -> Tongue Muscles
Corticobulbar Tracts
Bundles of UMNs that terminate in the medulla, synapsing w/ LMNs via cranial nerves 3-7 & 9-12
3 Types of Gray Matter Nuclei
- Reflex Centers (within Tectum)
- Red Nuclei
- Substantia Nigra (Right & Left)
Reflex Centers (within Tectum)
- 2 superior colliculi concerned w/ eye, head & trunk movements in response to visual stimuli
- 2 inferior colliculi relay auditory information from cochlea to brain & concerned w/ startle reflex
Red Nuclei
Integrate info from cerebrum & cerebellum to regulate muscle tone & posture
Substantia Nigra (Right & Left)
- Modify regulatory motor output of basal nuclei
- Dopaminergic pathway starts in substantia nigra & ends in basal nuclei
Motor Output of Basal Nuclei
Controls the pyramidal pathway, starting & stopping voluntary motor activity & setting kinetic motor tone
Reticular Formation
- Net-like gray matter within white matter
- Extends entire length of brain stem
- Motor tracts maintain skeletal muscle tone, HR & BP, ventilation
- Sensory tracts = RAS -> Cerebral Cortex
RAS (Reticular Activating System)
3 Functions:
- Maintain consciousness
- Prevent sensory overload
- Arousal from sleep
- Sensory inputs from eyes, ears & skin
- Melatonin & general anesthetics inactivate RAS
- RAS damage -> Possible coma
Cerebellum
- Lies bellow cerebrum, separated from brain stem by 4th ventricle
- Connected to brain stem by 3 sets of paired peduncles (white matter fiber tracts)
3 Sets of Paired Peduncles
- Inferior Cerebellar Peduncle
- Middle Cerebellar Peduncle
- Superior Cerebella Peduncle
Inferior Cerebellar Peduncle
Tracts going to & from cerebellum including:
- Sensory inputs w/ proprioception info from limbs & trunk
- Sensory inputs w/ proprioception info about head
- Inputs from inferior olivary nucleus
- Outputs to vestibular nuclei
- Outputs to reticular formation
Middle Cerebellar Peduncle
Inputs w/ voluntary motor information from cerebral cortex
Superior Cerebellar Peduncle
Outputs to red nucleus & thalamic nuclei -> primary motor cortex
Cerebellar Structure
- 2 cerebellar hemispheres joined by the vermis (3 lobes per hemisphere)
- Cerebellar cortex: Outer gray matter organized as ridges (“folia”)
- Arbor vitae: Interior of cerebellum (white matter tracts & gray matter nuclei)
3 Lobes of the Cerebellar Hemispheres
- Anterior Lobe: Subconscious components of voluntary movement
- Posterior Lobe: Same as anterior
- Flocculo-nodular Lobe: Equilibrium
3 Functions of the Cerebellum
- Skeletal muscle coordination
- Maintenance of muscle tone, posture & balance
- Processing of sensory data
Skeletal Muscle Coordination
- Function of the cerebellum
- Inputs from primary motor cortex & basal nuclei integrated to produce smooth & graceful movements
- Reconciliation of intended movements & actual movements
- Memorize complex motor activities
Maintenance of Muscle Tone, Posture & Balance
- Function of the cerebellum
- Inputs: Vestibular apparatus of inner ear
- Outputs: Muscles responsible for balance
- Ataxia = Lack of coordination, can be caused by trauma, disease, intoxication, etc.
Processing of Sensory Data
- Possible function of cerebellum
- Connections between cerebellum & certain sensory association areas have conjectured roles in processing sensory info, cognition & learning
Diencephalon
- Switching & relay centers to integrate conscious & unconscious sensory & motor pathways
- Consists of the Epithalamus, Hypothalamus, and Thalamus
Epithalamus
- Located above & behind the thalamus
- Contains the habenular nuclei & pineal gland
Habenular Nuclei
Responsible for emotional responses to olfactory stimulation
Pineal Gland
The source of melatonin (involved in circadian rhythm)
Hypothalamus
- Located in the floor of the 3rd ventricle
- Helps maintain homeostasis
- Has 12 nuclei
7 Main Functions of the Hypothalamus
- ANS Control
- Hormone Production
- Emotions & Behavior
- Food Intake
- Water Intake
- Body Temperature
- Circadian Rhythm, Arousal & Sleep
ANS Control
- Function of the Hypothalamus
- Working via ANS nuclei, hypothalamus controls activity of smooth muscle, cardiac muscle & many glands
- Receives sensory inputs from controlled viscera
Hormone Production
- Function of the Hypothalamus
- Makes release-hormones & release-inhibiting hormones to control anterior pituitary (Delivered by hypophyseal portal system)
- Synthesizes ADH & oxytocin, transported to posterior pituitary via hypothalamohypophyseal tract (Axons from paraventricular & supraoptic nuclei)
Emotion & Behavior
- Function of the Hypothalamus
- Rage, aggression, pain, pleasure & sexual libido are all associated w/ the hypothalamus
Food Intake
- Function of the Hypothalamus
- Controlled by the feeding center & satiety center
Water Intake
- Function of the Hypothalamus
- Thirst center’s osmoreceptors respond to osmotic pressure of ECF
Body Temperature
- Function of the Hypothalamus
- Monitors blood pressure
- Excessive BP = Dermal vasodilation & sweating
- Deficient BP = Dermal vasoconstriction & shivering
Circadian Rhythm, Arousal & Sleep
- Suprachiasmatic Nucleus sets circadian body rhythm, based on sleep-wake cycle
- Afferent nerve fibers from the retinae indicate day vs. night
- Efferent nerve fibers from the suprachiasmatic nucles to RAS = arousal/ to pineal gland = melatonin = sleep
Thalamus
- Oval-shaped halves, joined by interthalamic adhesion (AKA “intermediate mass”)
- Gray matter of each half subdivided by Y-shaped white matter (“Internal Medullary Lamina”)
- Forms sides of 3rd ventricle
- Consists of gray matter nuclei & white matter tracts
- Is the central relay for most sensory impulses traveling to cerebrum
- Dispatches sensory impulses to appropriate part of cortex, except for smell (e.g., occipital lobe for vision)
- Relays motor impulses from cerebellum & basal nuclei to primary motor cortex (frontal lobes)
- Contains 7 groups of nuclei
Internal Capsule
White matter tract connecting thalamus & cerebral cortex
Cerebrum
- Responsible for consciousness, cognition, learning & memory
- Consists of the Cerebral Hemispheres, Cerebral Cortex, Cerebral Nerve Tracts, Basal Nuclei & Limbic System
Cerebral Hemispheres
- Longitudinal fissure & falx cerebri divides the cerebrum into right & left cerebral hemispheres
- Each hemisphere contains a lateral ventricle
- Each hemisphere consists of cerebral cortex, cerebral white matter & basal nuclei
Cerebral Cortex
- Outer layer of cerebrum composed of gray matter
- Surface convolutions = gyri
- Gyri seperated by sulci and fissures
3 Types of Cerebral Nerve Tracts
- Association Tracts
- Commissural Tracts
- Projection Tracts
Association Tracts
Tracts that form connections within the same hemisphere
Commissural Tracts
Tracts that form connections between different hemispheres (e.g., corpus callosum)
*The anterior & posterior commissures are examples of other commissural tracts
Projection Tracts
Links cortex w/ lower CNS parts
Basal Nuclei
- Consists of the Globus Pallidus, Putamen & Caudate Nucleus
- Sometimes called the “Corpus Striatum”
- Formerly called “Basal Ganglia”
5 Functions of the Basal Nuclei
- Start/stop voluntary skeletal muscle movements (Caudate & Putamen)
- Set “Kinetic Motor Tone” (Caudate & Putamen); goal is to avoid both hypo- and hyperkinesia
- Regulate muscle tone (Globus Pallidus)
- Coordinate subconscious skeletal muscle movements associated w/ voluntary muscle activity
- Influence various cortical functions
Motor Disorders Caused by Basal Nuclei Damage/ Disease
- Parkinson’s Disease
- Huntington’s Disease (Genetic disorder of GABA-releasing neurons that run from basal nuclei to substantia nigra)
- Sydenham’s chorea
- OCD, schizophrenia & chronic anxiety
Limbic System
A network of encircling nerve tracts & structures of the Cerebrum, Diencephalon & Olfactory Bulbs (+Myelinated Tracts)
Limbic System (4 Cerebral Structures)
- Limbic Lobe (Cingulate Gyrus, Parahippocampal Gyrus & Hippocampus)
- Dentate Gyrus
- Amygdala
- Septal Nuclei
Limbic System (3 Diencephalic Structures)
- Anterior Nucleus
- Medial Nucleus
- Mamillary Bodies
Limbic System (Olfactory Bulbs + Myelinated Tracts)
- Fornix
- Stria Terminalis
- Stria Medullaris
- Medial Forebrain Bundle
- Mammillothalamic Tract
Function of the Limbic System
- To control visceral functions via ANS & endocrine hormones
- Also concerned w/ deep emotions (e.g., rage, pleasure), learning & memory (hippocampus) + olfaction
- Stimulation of Amygdala = Increased Aggression
- Removal of Amygdala = Decresed Aggression
- Stress = cortisol release, which damages hippocampus & amygdala
4 Lobes of the Cerebrum
- Frontal Lobe
- Parietal Lobe
- Temporal Lobe
- Occipital Lobe
Frontal Lobe
Involved in:
- Olfaction
- Voluntary motor function (primary motor cortex, pre-central gyrus)
- Behavioral attributes
Parietal Lobe
- Primary somatosensory cortex (post-central gyrus); sensory areas for general sensory input & taste
- Other areas: object recognition, math skills & reading
Temporal Lobe
- Direct olfactory input & indirect auditory input (for sound perception)
- Involved in abstract thought, judgement & memory
Occipital Lobe
-Contains primary visual area
Insula
- Lies within lateral cerebral sulcus, under P, F & T lobes
- May be a 5th cerebral lobe
- Is part of the Limbic System
- Involved in cravings for food & drugs as well as emotions
3 Different Functional Areas of the Cerebral Cortex
- Sensory Areas
- Motor Areas
- Association Areas
Sensory Areas
Areas involved in perception of particular sensations
*Sensation type perceived is related to area of brain stimulated
5 Types of Sensory Areas
- Primary Somatosensory: For conscious proprioception & pain, tickle/itch, hot/cold, touch, pressure & vibration
- Primary Visual: Visual perception
- Primary Auditory: Auditory perception
- Primary Gustatory: Gustatory perception
- Primary Olfactory: Olfactory perception
Motor Areas
Areas that initiate nerve impulses to control voluntary skeletal muscle activity
2 Types of Motor Areas
- Primary Motor Area: Found on precentral gyrus, controls most voluntary skeletal muscle contraction
- Broca’s Motor Speech Area: Usually present on left frontal lobe, controls muscles of larynx, pharynx, lips, tongue, mouth & ventilation
Cerebral Palsy
E.g., Cerebral ischemia could lead to damage to primary motor cortex/ cerebellum, basal nuclei, etc.
Non-fluent (Broca’s ) Aphasia
-Condition in which Broca’s area is damaged causing speech output to be severely reduced
Association Areas
-Involved in learning, memory, intelligence, reasoning, judgement, artistic & creative ability & personality traits
10 Examples of Association Areas
- Somatosensory Association
- Pre-frontal Cortex
- Visual Association
- Facial Recognition
- Auditory Association
- Wernicke’s Interpretive Speech
- Common Integrative
- Pre-Motor
- Frontal Eyefield
- Orbito-frontal Cortex
Somatosensory Association Area
- Processes inputs from primary somatosensory area, thalamus & other parts of the cerebrum
- Determines object’s shape & texture w/o visual inputs (“stereognosis”)
- Stores memories
Pre-frontal Cortex
- Processes inputs from cerebral cortex, limbic system, thalamus, hypothalamus & cerebellum
- Associated w/ personality, conscience, mood, foresight, planning, judgement & abstract thought
- Damage can create a rude, moody personality w/o foresight
Visual Association Area
- Processes inputs from primary visual cortex & thalamus
- Relates present & past experiences
- Recognition of objects by sight
Facial Recognition Area
- Processes inputs from visual association area
- Stores info about facial features
Auditory Association Area
-Responsible for sound recongition
Wernicke’s Interpretive Speech Area
- Left Hemisphere: Translates thoughts & language symbols
- Right Hemisphere: Adds emotional content to language
Common Integrative Area
-Integrates sensory interpretations from other association areas & sends info to other brain areas for the appropriate action
Pre-motor Area
- Linked to motor cortex, sensory association area, thalamus & basal nuclei
- Initiates & remembers motor sequences
Frontal Eyefield Area
-Responsible for voluntary eye scanning movements
Orbito-frontal Cortex
-Responsible for odor identification
Cerebral Cortex Mapping
- The sensory homunculus & motor homunculus have the mapped arrangements of the different sensory & motor functions
- The amount of cortex are mapped to a given body part depends on the number of afferent or efferent fibers connecting that body part to the brain
- Reflection of sensory receptor density/motor unit size respectively
EEG (Electroencephalogram)
A record of composite electrical activity of the brain at any given instant
4 Types of Brain Wave Patterns
- Alpha Waves
- Beta Waves
- Theta Waves
- Delta Waves
Alpha Waves
- Frequency: 8-13 Hz
- Seen in resting person w/ closed eyes
- Disappears during sleep
Beta Waves
- Frequency: 14-30 Hz
- Seen when eyes are open
- Seen during mental activity/sensory input
Theta Waves
- Frequency: 4-7 Hz
- Associated w/ deep relaxation & meditation
- Seen in frustrated children & adults, or in brain disorders
Delta Waves
- Frequency: 1-5 Hz (“Slow Waves”)
- Seen during deep sleep in adults & children
- Normal in awake infants
- Seen in waking brain damaged older children & adults
Flat EEG
Diagnosis for brain death
Hemispheric Lateralization
When right/left hemispheres specialize in some tasks
Hemispheric Dominance
- Left hemisphere once considered “dominant” because it controls language, analytical skills & reasoning
- Right hemisphere controls visual-spatial skills, pattern perception & creative abilities
- Is considered an outdated term
Lateralization of Speech Centers
- Wernicke’s & Broca’s speech areas are usually on the left hemisphere; damage can cause fluent & non-fluent aphasia respectively
- Right hemispheres in most people add emotional content to speech
Fluent (Wernicke’s ) Aphasia
-Connection in which Wernicke’s Area is damaged, causing speech to be a disconnected string of words w/o meaning (“word salad”)
Gracile & Cuneate Nuclei Pathway
1st order sensory fibers ascend via gracile & cuneate nuclei tracts (posterior white columns) -> gracile & cuneate nuclei (1st order sensory neuronal fibers synapse w/ 2nd order relay neurons) -> decussate in medulla, ascend -> medial lemniscus pathway -> thalamus (2nd order relay neuronal fibers synapse w/ 3rd order relay neuronal neurons) -> primary somatosensory cortex
