Chapter 14: The Brain and Cranial Nerves Flashcards
Brain Anatomy: An Overview
Half of CNS
* Weight: 1,450 – 1,600 g
Divided into regions
* Forebrain, midbrain, hindbrain
* Cerebrum, diencephalon, cerebellum,
brain stem
- 12 cranial nerves
Gray and White Matter
Gray matter
* Neurosomas, dendrites, synapses
* Forms cortex
* Forms deeper nuclei
White matter
* Bundles of axons
* Forms tracts
Cranial Meninges
- Membranes surrounding brain
Functions
* Protection of brain
* Structural framework for blood vessels
Three meninges
* Dura mater
* Arachnoid mater
* Pia mater
Dura Mater
Most superficial
* Potential space
- Tough, fibrous
Two layers
* Periosteal (superficial)
* Meningeal (deep)
Layers fused except at dural sinuses
* Collect blood from brain
Dural Folds
- Divide brain regions
- Stabilize and support brain
Falx cerebri
* Separates cerebral hemispheres
Tentorium cerebelli
* Divides cerebrum from cerebellum
Falx cerbelli
* Partially separates cerebellar hemispheres
Arachnoid Mater
- Intermediate
- Thin, transparent
Subdural space
* Between dura and arachnoid
Subarachnoid space
* Between arachnoid and pia
* Filled with cerebrospinal fluid
* Crossed by arachnoid trabeculae
Arachnoid granulations project into dural sinuses
* Return CSF to blood
Pia Mater
- Deepest
- Thin, delicate
Conforms to surface anatomy of brain
* Dips into sulci
Ventricle Overview
- Fluid-filled chambers
- Cerebrospinal fluid
House choroid plexus
* Capillaries + ependymal cells
* Produces cerebrospinal fluid
* Blood-CSF barrier
* Tight junctions between ependymal cells
* Part of brain barrier system
Ventricles
Lateral ventricle
* Paired
* Cerebrum
* Connect to third via interventricular foramen
Third ventricle
* Unpaired
* Diencephalon
* Connect to fourth via cerebral aqueduct
Fourth ventricle
* Unpaired
* Between brainstem and cerebellum
* Gives rise to spinal central canal
Cerebrospinal Fluid (CSF)
- Clear, colorless fluid
- Constantly produced and reabsorbed
- Fills ventricles, canals, subarachnoid space
- Bathes external surface
Produced by filtering blood
* Composition different from plasma
Functions of Cerebrospinal Fluid
Buoyancy
* Supports weight of brain
Protection
* Cushions brain
* Slows movement within skull
Chemical stability
* Regulates environment of nervous tissue
* Rinses wastes from nervous tissue
* Circulates nutrients and chemicals
Cerebrospinal Fluid Flow
Flows due to
* Own pressure
* Ependymal cilia motion
* Pulsation of brain
* Due to heartbeat
- Flows through ventricles in sequence
Enters subarachnoid space
* Via apertures
* Arachnoid granulations drain excess fluid
Blood Supply to Brain
High oxygen and glucose demands
* Requires constant blood flow
* Disruptions cause loss of consciousness or permanent damage
Major arteries
* Internal carotid artery
* Vertebral artery
Major veins
* Internal jugular vein
Blood-Brain Barrier (BBB)
- Part of brain barrier system (BBS)
Formed by:
* Tight junctions between endothelial cells of capillaries
* Basement membrane endothelial cells
* Perivascular feet of astrocytes
Prevents entry of harmful or disruptive substances
* Transport is selective, directional
Absent or reduced in some areas
* Circumventricular organs (CVOs) in 3rd and 4th ventricles
* Needed to monitor blood composition
What Can Cross the BBS?
Highly permeable
* Glucose, water
* Lipid-soluble materials
* Respiratory gases
* Alcohol, nicotine, caffeine, anesthetics
Somewhat permeable
* Na+, K+, Cl-, urea, creatinine
Impermeable
* Proteins, formed elements, most antibiotics, cancer drugs
Brainstem Overview
- Connects brain to spinal cord
- Houses majority of cranial nerve nuclei
Divided into three regions
* Midbrain
* Pons
* Medulla oblongata
Medulla Oblongata
- Most inferior region
Wider compared to spinal cord
* Distinctive anatomical features
Houses ascending and descending tracts
* Connect brain to spinal cord
Houses cranial nerve nuclei
* Nerves VIII (partial) – XII
- Houses portions of reticular formation
Medulla Oblongata: Notable Structures
Pyramids
* Anterior
* Houses corticospinal tracts
Gracile and cuneate nuclei
* Axons form medial lemniscus
Olives
* Lateral to pyramids
* Contain olivary nuclei
Medulla Oblongata: Pathways
Corticospinal tracts
* Descending (motor) tracts
* Carry signals from cerebral cortex to skeletal muscles
* Tracts decussate
Medial lemniscus
* Ascending (sensory) pathway
* Carries general sensory information
* Synapse with thalamus
* Decussate
Inferior olivary nuclei
* Relay between other CNS structures and cerebellum
Tectospinal tract
* Controls neck muscle
Medulla Oblongata: Neural
Networks
Sensory Functions
* Hearing
* Touch
* Temperature
* Pressure
* Taste
* Pain
Motor Functions
* Chewing
* Salivation
* Swallowing
* Gagging
* Vomiting
* Speech
* Coughing
* Sneezing
* Sweating
* Respiration
* Cardiovascular control
* Gastrointestinal control
* Movements of head, neck, shoulders
Medulla Oblongata: Centers
Cardiac center
* Regulation of force and rate of contraction
Vasomotor center
* Regulation of blood vessel diameter
Respiratory centers
* Regulates rhythm and depth of breathing
- Other centers (vomiting, swallowing, etc.)
Pons
Middle region of brainstem
* Separated from medulla by groove
Houses cranial nerve nuclei
* V – VIII (partial)
Houses continuations of tracts
* Ascending and descending
- Houses portions of reticular formation
Pons: Notable Structures
Middle cerebellar peduncles
* Posterior
* Connect pons and midbrain to cerebellum
Portion of fourth ventricle
* Lies between pons and cerebellum
White matter tracts (fascicles)
* Longitudinal projection tracts send signals up and down brainstem
* Transverse tracts connect left and right cerebellar hemispheres
Pontine respiratory center
* Alters rhythm of breathing
Other reticular formation nuclei
* Sleep, posture
Midbrain
- Most superior region
Connects brainstem to diencephalon
* Hindbrain to forebrain
Houses continuations of tracts
* Ascending and descending
Houses cranial nerve nuclei
* III and IV
- Houses portions of reticular formation
Notable Structures of the
Midbrain
Cerebral aqueduct
* Surrounded by central gray substance
* Role in pain awareness
Tectum
* Posterior to cerebral aqueduct
* Superior and inferior colliculi
* Visual and auditory reflexes
Cerebral peduncles
* Anterior to cerebral aqueduct
* Anchor cerebrum to brainstem
* Divided into three regions
Midbrain: Cerebral Peduncle
Divisions
Tegmentum
* Houses red nucleus
* Tracts connect to cerebellum
* Participate in fine motor control
Substantia nigra
* Motor center
* Inhibits thalamus and basal nuclei
* Suppress unwanted movement
Cerebral crus
* Connect cerebrum to pons
* House corticospinal tracts
Midbrain: Superior and Inferior
Colliculi
Superior colliculi
* Control extrinsic eye muscle
* Direct gaze
* Track moving objects
* Move eyes and head due to visual stimuli
* Connected to other visual control nuclei
Inferior colliculi
* Relays information from inner ear to thalamus and other brain regions
* Sensitive to time delays between sounds between ears (sound location)
* Process pitch fluctuations
* Turn head in reflexive responses to sound
* Startle reflex to noise
The Reticular Formation
Network of grey matter
* Housed between tracts and distinct nuclei
* > 100 neural networks
- Passes through all regions of brainstem
and upper spinal cord - Connections to cerebrum
Networks have numerous functions
* Sensory and motor
Reticular Formation Functions:
Somatic Motor Control
Motor cortex neurons synapse with reticular formation nuclei
* Form reticulospinal tracts: alter muscle tension
* Balance, posture, muscle tone
Relays sensory signals to cerebellum
* Visual, auditory, vestibular
* Required for cerebellum’s role as motor coordinator
- Gaze centers allow eyes to track motion and fix on objects
Central pattern generators produce rhythmic signals
* Breathing and swallowing
Reticular Formation Functions
Cardiovascular control
* Via cardiac and vasomotor centers
* Alters cardiac output and blood pressure
Pain modulation
* Route for pain signals from lower body to cerebral cortex
* Descending analgesic tracts can block pain sensation
Sleep and consciousness
* Reticular activating system (RAS)
* Level of control over which sensations reach cerebrum
* Role in stages of consciousness: alertness, sleep
* Damage can lead to permanent coma
Habituation
* Reticular activating system (RAS)
* Brain ignores unimportant, repetitive stimuli
* Novel or important stimuli are still attended too
Cerebellum Overview
Second largest region of brain
* 10% of brain’s mass
* 50% of brain’s neurons
- Component of hindbrain
- Numerous granule cell neurons
Distinctive Purkinje cells
* Highly branched dendrites in single plane
Cerebellar Anatomy
Divided into hemispheres
* Connected by vermis
* Covered by folia separated by sulci
Each hemisphere divided into lobes
* Anterior and posterior
* Divided by primary fissure
Grey matter
* Cerebellar cortex: receives input
* Deep nuclei: handles output
White matter
* Arbor vitae
Cerebellar Peduncles
- Connect cerebellum to brainstem
- Contain bundles of nerve fibers
Superior: midbrain
* Output from cerebellum
Middle: pons
* Input from rest of brain
Inferior: medulla oblongata
* Input from spine
Cerebellar Functions
- Region is still poorly understood
- General function appears to be
evaluation of sensory input
Cerebellar lesions affect a number of functions
* Sensory, motor, linguistic, emotional, other nonmotor functions
Possible involvement with:
* Tactile sensation
* Spatial perception
* Timekeeping
* Predicting path of moving object
* Hearing
* Language output
* Planning/scheduling
* Emotion and impulse control
Cerebellum: Motor Functions
- Important for motor coordination
- Aids in learning motor skills
- Maintain muscle tone and posture
- Smooths muscle contractions
- Coordinates eye and body movements
- Coordinates motion of different joints
Cerebellum as Motor Comparator
Receives information from
* Cerebrum
* Eyes and inner ears
* Proprioceptors in joints and muscles
Cerebrum initiates movement
* Sends “plan” to cerebellum
Cerebellum compares “plan” to actual movements
* Via Purkinje cells
Errors stimulate deep nuclei
* Send information to thalamus and brainstem
* Information sent to motor association area
* Information sent to reticulospinal and vestibulospinal tracts
* Error corrected
Diencephalon Overview
Inferior to cerebrum
* Deep to cerebral hemispheres
* Component of forebrain
- Superior to brainstem
Divided into
* Epithalamus
* Thalamus
* Hypothalamus
Thalamus Structure
Paired, oval masses
* Joined by interthalamic adhesion (medial)
- 4/5ths of diencephalon
- Laterally: protrude into lateral ventricles
- Medially: protrude into third ventricle
Composed of 23 nuclei
* Divided into five groups
Thalamus Functions
Sensation
* Ascending sensory neurons synapse with thalamic nuclei
* General and special senses
* Thalamus processes information
* Some information sent on to cerebrum
* Information sent to corresponding cortical region
Motor control
* Relays signals from cerebellum to cerebrum
* Feedback loops between cerebral cortex and basal nuclei
Memory and emotion
* Nuclei associated with limbic system
Hypothalamus Structure
- Inferior and anterior to thalamus
Runs from optic chiasm to mammillary bodies
* Mammillary nuclei relay limbic signals to thalamus
- Makes up walls and floor of third ventricle
- Pituitary gland attached via infundibulum
- Divided into nuclei
Hypothalamus Functions
Hormone secretion
* Produces oxytocin and antidiuretic hormone
* Produces regulatory hormones which control anterior pituitary gland
* Influence on metabolism, growth, stress response, reproduction
Autonomic effects
* Integrating center for the autonomic nervous system
* Sends descending fibers to brainstem
* Influence heart rate, blood pressure, GI tract secretion and motility, etc.
Thermoregulation
* Integrating (control) center for negative feedback loop
* Monitors body temperature
* Activates mechanisms to control temperature
Regulation of food intake
* Monitors blood nutrient level
* Receptors for hormones that influence hunger and satiety
* Receptors for hormones that influence body mass
Regulation of water intake
* Osmoreceptors monitor concentration of blood
* Promotes thirst and drinking
* Release of ADH
Sleep and circadian rhythms
* Part of reticular formation
* Nuclei regulate sleep/waking rhythms
* Controls 24-hour circadian rhythm
Memory
* Mammillary nuclei lie in pathway between hippocampus and
thalamus
* Lesions cause memory defects
Emotional behavior and sexual response
* Centers for anger, fear, aggression, contentment, pleasure
* Centers for sexual drive, copulation, orgasm
Epithalamus
Smallest portion of diencephalon
* Posterior
* Forms roof of third ventricle
Contains pineal gland
* Produces melatonin
* Possible role in circadian rhythms
* Possible role in mood and sexual maturation
Contains habenula
* Relays signals from limbic system to midbrain
* Connects limbic system to rest of brain
Cerebrum Overview
Largest region of brain
* Encompasses diencephalon
- Component of forebrain
Extensively folded compared to other animals
* Increases surface area
Cerebral Anatomy
Two hemispheres
* Divided by longitudinal cerebral fissure
* Connected by corpus callsoum
- Separated from cerebellum via transverse cerebral fissure
Divided into five lobes
* Divided by sulci
Surface covered by raised gyri
* Divided by sulci
Lobes and Sulci
Frontal lobe
* Most anterior/rostral
* Runs to central sulcus
Parietal lobe
* Most superior lobe of brain
* Begins at central sulcus
* Extends to parieto-occipital sulcus
Occipital lobe
* Most posterior/caudal
* Begins at parieto-occipital sulcus
Temporal lobe
* Lateral, horizontal
* Separated from parietal lobe by lateral sulcus
Insula
* Deep to other lobes
* Deep to lateral sulcus
Cerebral Gray and White Matter
White Matter
* Permits communication
between different regions
* Majority of cerebral volume
* Divided into tracts
Gray Matter
* Responsible for neural
integration
* Three locations
* Cerebral cortex
* Basal nuclei
* Limbic system
Cerebral White Matter
Association tracts
* Connect regions within a hemisphere
* Short fibers: gyri within lobe
* Long fibers: lobes within hemisphere
Commissural tracts
* Connect hemispheres through commissures
* Most pass through corpus callosum
Projection tracts
* Connect cerebrum with rest of body
* Ascending and descending
Cerebral Cortex
- Gray matter
- Lines outer cerebrum
- Thin (2 - 3 mm)
- 40% of brain’s mass
Complex anatomy
* Divided into layered regions
* Specialized neurons
* Stellate cells and pyramidal cells
Basal Nuclei
Gray matter
* Lateral to thalamus
* Paired in each hemisphere
Receive input from
* Cerebral cortex
* Substantia nigra (inhibitory)
Send output to
* Thalamus
* Relays signals to cerebral cortex and midbrain
Confirmed structures
* Caudate nucleus
* Putamen
* Globus pallidus
Basal Nuclei and Motor Control
- Determine onset and cessation of voluntary movements
- Rhythmic, repetitive movements of hips and shoulders during
walking
Highly practiced, learned motor behaviors
* Typing a shoe , writing, etc.
Lesions cause dyskinesias
* Movement disorders
- Note: these are only some selected functions in motor control
Limbic System
- Gray matter
Structures found in a ring
* Around corpus callosum and
thalamus
All components are paired
* Present in both hemispheres
- Emotion and learning
Components of the Limbic System
Structures interconnected via fiber tracts
* Permits feedback between components
Confirmed structures
* Cingulate gyrus
* Hippocampus
* Amygdala
Other components
* Mammillary bodies
* Some hypothalamic nuclei
* Some thalamic nuclei
* Basal nuclei (portions)
* Prefrontal and orbitofrontal cortex
Limbic System Functions
Roles in emotion
* Amygdala and hypothalamus
* Emotions originate here
* Amygdala can link sensations to emotional responses
* Output to hypothalamus and brainstem: alters motor responses
* Output to prefrontal cortex: permits conscious expression of emotions
Memory
* Hippocampus
Houses gratification and aversion centers
* Linked to stimuli
* Roles in shaping behavior
* More likely to repeat pleasurable experiences
* Less likely to repeat unpleasant experiences
Functions of the Cerebrum
Difficult to correlate specific function with a specific region
* Boundaries are indistinct, overlap exists
* Areas may have multiple functions
* Functions may be distributed (over many areas)
- Typically divided into functional areas
Cerebral Lateralization
Due to tracts decussating
* Receive information from opposite side of body
* Control effectors on opposite side of body
Hemispheres specialized for some different functions
* Cerebral (hemispheric) lateralization
* Functions may complement one another
Typically both hemispheres are used for all tasks
* Communicate via commissural tracts
Left Hemisphere (Usually)
* Categorical hemisphere
* Break info into fragments
* Linear analysis of info
* Spoken and written language
* Sequential and analytic
reasoning
* Posterior language area
* Motor speech area
Right Hemisphere (Usually)
* Representational hemisphere
* Integrated, holistic perception
of info
* Imagination and insight
* Artistic and musical skill
* Perception of patterns and
spatial relationships
* Sensory comparison
* Affective language area
Cerebral Cortex: Functional Areas
Sensory areas
* Primary sensory cortex
* First receive sensory information
* Permits conscious awareness of sensation
Motor areas
* Primary motor cortex
* Voluntary control of skeletal muscle
Association areas
* Interpret information
* Involved with cognition
* Range of mental processes by which knowledge is acquired and used
Primary Somatosensory Cortex
Postcentral gyrus
* Parietal lobe
Demonstrates somatopy
* Body regions correspond to specific brain regions
* Permits spatial discrimination of stimuli
More cortex dedicated to some areas
* Corresponds to sensitivity
* Sensory homunculus
Function
* Conscious perception of general senses
Sensory Cortices of Special Senses
Primary visual
* Posterior occipital lobe
Primary auditory
* Superior temporal lobe and insula
Primary gustatory
* Inferior postcentral gyrus
Primary olfactory
* Medial temporal lobe, inferior surface of frontal lobe
Primary Motor Area
Precentral gyrus
* Frontal lobe
- Demonstrates somatopy
More cortex dedicated to some areas
* Corresponds to motor control
* Number of muscles and motor units
* Motor homunculus
Function
* Voluntary control of skeletal muscle
Sensory Association Areas
- Always located close to primary sensory cortex for sensation
- Integrates and interpret sensory information
- Store memories
Motor Association (Premotor) Area
- Frontal lobe, anterior to precentral gyrus
Plans motor movements
* Degree and sequence of contractions
* Plan transferred to primary motor area for execution
Language Association Areas
Posterior language area (Wernicke)
* Posterior to lateral sulcus
* Receives input from visual, auditory, and somatosensory areas
* Recognition of written and spoken language
* Formulates speech, transmits to motor speech area
* Damage: fluent aphasia
Motor speech area (Broca)
* Inferior prefrontal cortex
* Receives plan for speech from posterior language area
* Creates motor plan for speech, sends to primary motor area
* Possible roles in language comprehension
* Damage: nonfluent aphasia
Affective Language Area
Area opposite posterior language area
* Recognizes emotional context of another’s speech
* Damage impedes this ability
Area opposite motor speech area
* Add emotional content to spoken words
* Damage results in aprosody (flat, emotionless speech)
Frontal Association Area (Prefrontal Area)
- Anterior portion of frontal lobe
Frontal lobe integrates information
* From sensory and motor regions
* From other association area
Associated with cognition and higher functions
* Judgement, planning, decision making, conscience, reasoning, mood,
etc.
- Conscious control of emotional expression
- Damage personality disorders, loss of inhibition, inability to control
expression of emotions
Memory
- Storage and recall of information
Neural level:
* Relies upon formation and modification of synapses
* Memory trace (engram): pathway of synapses associated with
memory
* Synaptic plasticity: synapse added, removed, modified
* Synaptic potentiation: transmission becomes easier with
repetition and learning
Involves multiple processes
* Learning: acquiring new information
* Memory proper: storage and retrieval
* Forgetting: eliminating unwanted or trivial information
Three Categories of Memory
Immediate memory: what just happened
* Duration: seconds
* Comprehension of flow of events
Short term-memory (STM)
* Duration: seconds to hours
* Small information capacity
* Can be forgotten quickly
* Recitation allows better retention
Long-term memory (LTM)
* Duration: years to a lifetime
* Large information capacity
* Modification of synapses or adding more NT channels
Structures Involved in Memory
Hippocampus transfers memories from STM to LTM
* Referred to as memory consolidation
* Does not store memory!
Long term memories stored in cerebral cortex
* Within appropriate region
Other regions associated with memory
* Cerebellum: learning motor skills
* Amygdala: emotional memory
Memory Defects
Anterograde amnesia
* Inability to form new memories
* Can result from hippocampus damage
Retrograde amnesia
* Inability to recall stored LTM
Cranial Nerve Overview
- 12 pairs
Numbered from I – XII
* Anterior (rostral) to posterior
(caudal)
- Peripheral nervous system
Associated primarily with
structures of the head and neck
* Vagus nerve is a notable exception
- Sensory, motor, or mixed (both)
Cranial Nerves
Olfactory Nerve I (S)
* Olfaction
Optic Nerve II (S)
* Vision
Oculomotor Nerve III (M)
* Somatic and autonomic motor functions of eye
* Innervates four of six eye muscles
Trochlear Nerve IV (M)
* Eye movements
* Innervates one eye muscle
Trigeminal Nerve V (B)
* Three branches
* Sensory: general senses of face
* Motor: mastication
Abducens Nerve VI (M)
* Eye movements
* Innervates one eye muscle
Facial Nerve VII (B)
* Sensory: taste
* Motor: facial expressions, secretion from salivary and lacrimal glands
Vestibulocochlear Nerve VIII (S)
* Hearing and equilibrium
Glossopharyngeal Nerve IX (B)
* Sensation (taste, general senses) from tongue, throat, outer ear
* Muscles of tongue and pharynx, salivary glands
* Chemoreceptors and baroreceptors in cardiovascular system
Vagus Nerve X (B)
* Control of cardiac, pulmonary, digestive, urinary functions
* Parasympathetic division
Accessory Nerve XI (M)
* Swallowing, movement of neck and shoulder muscles
Hypoglossal Nerve XII (M)
* Movements of tongue
