Chapter 14: The Brain and Cranial Nerves

1
Chapter 14 The Brain and Cranial Nerves
2
6 Regions of the Brain

• Cerebrum
• Cerebellum
• Diencephalon
• Mesencephalon
• Pons
• Medulla oblongata

3
Cerebrum

• Largest part of brain
• Controls higher mental functions
• Divided into left and right cerebral hemispheres
• Surface layer of gray matter (neural cortex)
• Also called cerebral cortex
• Folded surface increases surface area
• Elevated ridges (gyri)
• Shallow depressions (sulci)
• Deep grooves (fissures)

4
Cerebellum

• Second largest part of brain
• Coordinates repetitive body movements
• 2 hemispheres
• Covered with cerebellar cortex

5
Diencephalon

• Located under cerebrum and cerebellum
• Links cerebrum with brain stem
• 3 divisions
• Thalamus - relays and processes sensory
  information
• Hypothalamus - hormone production, emotion,
  autonomic function
• Epithalamus (Pineal gland)

6
Pituitary Gland

• Major endocrine gland
• Connected to hypothalamus
• Via infundibulum (stalk)
• Interfaces nervous and endocrine systems

7
The Brain Stem

• Processes information between
• spinal cord and cerebrum or cerebellum
• Includes
• Mesencephalon (midbrain)
• Processes sight, sound, and associated reflexes,
  maintains consciousness
• Pons
• Connects cerebellum to brain stem is involved
  in somatic and visceral motor control
• Medulla oblongata
• Regulates autonomic functions HR, BP, and
  digestion

8
Primary Brain Vesicles

• The anterior end of the neural tube expands and
  constricts to form the three primary brain
  vesicles
• Prosencephalon the forebrain
• Mesencephalon the midbrain
• Rhombencephalon hindbrain

9
Secondary Brain Vesicles

• In week 6 of embryonic development, secondary
  brain vesicles form
• Telencephalon and diencephalon arise from the
  forebrain
• Mesencephalon remains undivided
• Metencephalon and myelencephalon arise from the
  hindbrain

10
Adult Brain Structures

• Fates of the secondary brain vesicles
• Telencephalon cerebrum cortex, white matter,
  and basal nuclei
• Diencephalon thalamus, hypothalamus, and
  epithalamus
• Mesencephalon brain stem midbrain
• Metencephalon brain stem pons
• Myelencephalon brain stem medulla oblongata

11
Ventricles

• Lateral ventricles
• Deep w/in cerebrum
• Third ventricle
• Connected by interventricular foramen (Monro)
• Fourth ventricle
• Connected by cerebral aqueduct (Sylvius)
• Connects to subarachnoid space to return to
  bloodstream

12
Brain Protection and Support

• Physical protection
• bones of the cranium
• cranial meninges
• cerebrospinal fluid
• Biochemical isolation
• bloodbrain barrier

13
The Cranial Meninges

• Has 3 layers
• dura mater
• arachnoid mater
• pia mater
• Is continuous with spinal meninges
• Protects the brain from cranial trauma

14
Characteristics of Cranial Meninges

• Dura mater
• inner fibrous layer (meningeal layer)
• outer fibrous layer (endosteal layer) fused to
  periosteum
• venous sinuses between 2 layers
• Arachnoid mater
• contacts epithelial layer of dura mater
• Subarachnoid space b/t arachnoid and pia mater
• Pia mater
• attached to brain surface by astrocytes

15
Dural Folds

• Folded inner layer of dura mater
• Extend into cranial cavity to stabilize and
  support brain
• Contain collecting veins (dural sinuses)
• Falx cerebri, tentorium cerebelli, and falx
  cerebelli

16
Cerebrospinal Fluid (CSF)

• Surrounds all exposed surfaces of CNS
• Interchanges with interstitial fluid of brain
• Functions of CSF
• Cushions delicate neural structures
• Supports brain
• Transports nutrients, chemical messengers, and
  waste products

17
Forming CSF

• Choroid plexus
• Specialized ependymal cells and capillaries
• secrete CSF into ventricles
• remove waste products from CSF
• adjust composition of CSF
• Produces about 500 ml of CSF/day
• Room for 150 ml

18
Circulating CSF

• CSF produced from choroid plexus (in all
  ventricles)
• Lateral Ventricle (thru interventricular foramen
  of Monro)
• Third Ventricle (thru cerebral aquaduct of
  Sylvius)
• Fourth Ventricle (thru median lateral
  apertures)
• To central canal of spinal cord subarachnoid
  space around the brain, spinal cord, and cauda
  equina
• Thru arachnoid villi/granulations (into dural
  venous sinuses)
• DVSs merge into Internal Jugular Vein

19
Blood Supply to the Brain

• Supplies nutrients and oxygen to brain
• Delivered by internal carotid arteries and
  vertebral arteries
• Removed from dural sinuses by internal jugular
  veins

20
Cerebrovascular Disease

• Disorders interfere with blood circulation to
  brain
• Stroke or cerebrovascular accident (CVA)
• shuts off blood to portion of brain
• neurons die
• Transient ischemic attack (TIA)
• temporary reduction in blood flow

21
BloodBrain Barrier (BBB)

• Isolates CNS neural tissue from general
  circulation
• Formed by network of tight junctions between
  endothelial cells of CNS capillaries
• Lipidsoluble compounds (O2, CO2), steroids, and
  prostaglandins diffuse into interstitial fluid of
  brain and spinal cord
• Astrocytes control bloodbrain barrier by
  releasing chemicals that control permeability of
  endothelium

22
4 Breaks in the BBB

• Portions of hypothalamus
• secrete hypothalamic hormones
• Posterior lobe of pituitary gland
• secrete hormones ADH and oxytocin
• Pineal glands
• pineal secretions
• Choroid plexus
• where special ependymal cells maintain bloodCSF
  barrier

23
The Medulla Oblongata

• Allows brain and spinal cord to communicate
• Coordinates complex autonomic reflexes
• Controls visceral functions

24
Medulla Oblongata

• Vital reflex centers (life sustaining decisions)
• Cardiac center rate/force of contractions
• Vasomotor center smooth mm in b.v.s (BP
  control)
• Respiratory center rate/depth of breathing (up
  into pons)
• Non-vital reflex centers
• Vomiting, hiccough, swallowing, coughing,
  sneezing
• CN VIII through XII nuclei
• Vestibular nuclei complex subconsciously
  maintain balance (equilibrium)
• Solitary nucleus - receives visceral sensory
  information
• Olivary nuclei (olives)lateral to pyramids
• Receive sensory info from proprioceptors
  (position) in skeletal muscles joints act as
  a relay point to the cerebellum

25
The Pons

• Links cerebellum with mesencephalon,
  diencephalon, cerebrum, and spinal cord
• Nuclei of cranial nerves V, VI, VII, VIII
• Nuclei involved with respiration
• apneustic center and pneumotaxic center
• modify respiratory rhythmicity center activity
• Cerebellar peduncles connect cerebellum to
  brainstem (6 in all)
• Superior cerebellar peduncles to midbrain
• Middle cerebellar peduncles to pons (largest)
• Inferior cerebellar peduncles to medulla

26
Functions of the Cerebellum

• Adjusts postural muscles
• Fine-tunes conscious and subconscious movements
• Ataxia
• damage from trauma or stroke
• intoxication (temporary disturbance)
• disturbs muscle coordination

27
Structures of the Cerebellum

• Folia
• surface of cerebellum
• highly folded neural cortex
• Anterior and posterior lobes
• separated by primary fissure
• Cerebellar hemispheres
• separated at midline by vermis
• Flocculonodular lobe
• below fourth ventricle
• Arbor vitae Highly branched, internal white
  matter of cerebellum

28
Structures of the Mesencephalon

• Tectum (corpora quadrigemina)
• superior colliculus (visual)
• inferior colliculus (auditory)
• Tegmentum
• red nucleus (many blood vessels)
• substantia nigra (pigmented gray matter)
• Cerebral peduncles
• Contain descending fibers to cerebellum
• motor command fibers

29
The Diencephalon

• Integrates sensory information and motor commands
  
• Thalamus
• Epithalamus
• Secretes hormone melatonin
• Hypothalamus

Figure 145a
30
The Thalamus

• Filters ascending sensory information for primary
  sensory cortex
• Relays center to funnel information between basal
  nuclei and cerebral cortex

31
5 Groups of Thalamic Nuclei

• Anterior group part of limbic system (emotions)
• Medial group provides awareness of emotional
  states
• Ventral group relays sensory information
• Posterior group
• pulvinar nucleus (sensory)
• lateral geniculate nucleus (visual)
• medial geniculate nucleus (auditory)
• Lateral group affects emotional states
• integrates sensory info

32
Structures of the Hypothalamus

• Mamillary bodies
• process olfactory and other sensory information
• control reflex eating movements
• Infundibulum
• a narrow stalk
• connects hypothalamus to pituitary gland

33
8 Functions of the Hypothalamus

• Provides subconscious control of skeletal muscle
• Controls autonomic function
• Coordinates activities of nervous and endocrine
  systems
• Secretes hormones
• antidiuretic hormone (ADH) oxytocin (OT)
• Produces emotions and behavioral drives
• the feeding center (hunger) the thirst center
• Coordinates voluntary and autonomic functions
• Regulates body temperature
• Controls circadian rhythms (daynight cycles)

34
The Limbic System

• Is a functional grouping that
• establishes emotional states
• links conscious functions of cerebral cortex with
  autonomic functions of brain stem
• facilitates memory storage and retrieval

35
Components of the Limbic System

• Amygdala deals with anger, danger, and fear
  responses
• interfaces limbic system, cerebrum, and sensory
  systems
• Limbic lobe of cerebral hemisphere
• cingulate gyrus - plays a role in expressing
  emotions via gestures, and resolves mental
  conflict
• hippocampus - converts short-term memory to
  long-term memorymemories charged w/ emotion are
  often retained
• Fornix tract of white matter
• connects hippocampus with hypothalamus
• Anterior nucleus of the thalamus
• relays information from mamillary body to
  cingulate gyrus
• Reticular formation
• stimulation or inhibition affects emotions
  (rage, fear, pain, sexual arousal, pleasure)

36
The Cerebrum

• Is the largest part of the brain
• Controls all conscious thoughts and intellectual
  functions
• Processes somatic sensory and motor information
• Gray matter
• in cerebral cortex and basal nuclei
• White matter
• deep to cortex
• around basal nuclei

37
Structures of the Cerebrum

• Gyri of neural cortex increase surface area
  (number of cortical neurons)
• Longitudinal fissure separates cerebral
  hemispheres
• Lobes divisions of hemispheres
• Central sulcus divides anterior frontal lobe
  from posterior parietal lobe
• Lateral sulcus divides frontal lobe from
  temporal lobe
• Parieto-occipital sulcus divides parietal lobe
  from occipital lobe

38
3 Functional Principles of the Cerebrum

1. Each cerebral hemisphere receives sensory
   information from, and sends motor commands to,
   the opposite side of body
2. The 2 hemispheres have different functions
   although their structures are alike
3. Correspondence between a specific function and a
   specific region of cerebral cortex is not precise

39
3 Types of Axons in the Cerebrum

• Association fibers
• Connections within 1 hemisphere
• Commissural fibers
• Bands of fibers connecting 2 hemispheres
• Projection fibers
• Link cerebral cortex with diencephalon, brain
  stem, cerebellum, and spinal cord

40
Basal Nuclei

• Are masses of gray matter embedded in white
  matter of cerebrum
• Direct subconscious activities
• Are involved with
• the subconscious control of skeletal muscle tone
• the coordination of learned movement patterns
  (walking, lifting)

• Caudate nucleus
• Lentiform nucleus
• globus pallidus
• putamen

41
Motor and Sensory Areas of the Cortex

• Central sulcus separates motor and sensory areas
• Precentral gyrus (Primary motor cortex) of
  frontal lobe
• directs voluntary movements
• Postcentral gyrus (Primary sensory cortex) of
  parietal lobe
• receives somatic sensory information (touch,
  pressure, pain, vibration, taste, and
  temperature)

42
Special Sensory Cortexes

• Visual cortex occipital lobe
• information from sight receptors
• Auditory cortex temporal lobe
• information from sound receptors
• Olfactory cortex frontal medial temporal lobe
• information from odor receptors
• Gustatory cortex insula (deep to temporal lobe)
• information from taste receptors

43
Association Areas

• Premotor cortex
• coordinates somatic motor responses (learned
  movements)
• Somatic sensory association area
• interprets input to primary sensory cortex (e.g.,
  recognizes and responds to touch)
• Visual association area
• interprets activity in visual cortex
• Auditory association area
• monitors auditory cortex

44
Integrative Areas

• Wernickes area (General Interpretive Area )
• Present in only 1 hemisphere
• Receives information from all sensory association
  areas
• Coordinates access to complex visual and auditory
  memories
• Speech center coordinates all vocalization
  functions
• is associated with general interpretive area
• Prefrontal cortex of frontal lobe
• integrates information from sensory association
  areas
• performs abstract intellectual activities (e.g.,
  predicting consequences of actions)

45
Brodmanns Areas

• Patterns of cellular organization in cerebral
  cortex

Figure 1415c
46
Hemispheric Lateralization

• Functional differences between left and right
  hemispheres
• In most people (90), left brain (dominant
  hemisphere) controls
• reading, writing, and math
• decision-making
• speech and language
• Right cerebral hemisphere relates to
• senses (touch, smell, sight, taste, feel)
• recognition (faces, voice inflections)
• Unclear dominance may lead to dyslexia

47
Monitoring Brain Activity

• Brain activity is assessed by an
  electroencephalogram (EEG)
• electrodes are placed on the skull
• patterns of electrical activity are printed out
  (brain waves)

48
4 Categories of Brain Waves

• Alpha waves
• found in healthy, awake adults at rest with eyes
  closed
• Beta waves
• higher frequency
• found in adults concentrating or mentally
  stressed
• Theta waves
• found in children
• found in intensely frustrated adults
• may indicate brain disorder in adults
• Delta waves
• during sleep
• found in awake adults with brain damage

49
Cranial Nerves

• 12 pairs connected to brain
• Name
• Number
• Function

50
Olfactory CN I

• Sensory
• Terminates in olfactory bulbs
• Discrimination of smell

51
Optic CN II

• Sensory
• Vision
• Terminates at optic chiasm

52
Occulomotor CN III

• Motor
• Inferior oblique, sup/inf/medial rectus
• Test planes of gaze
• PSNS Function
• Test constrictor mm of iris (ciliary mm)
• Pupillary reflex

53
Trochlear CN IV

• Motor
• Superior oblique (down out)
• Test planes of gaze

54
Trigeminal CN V

• Mixed
• 3 divisions ophthalmic, maxillary, mandibular
• Test
• Motor- mandibular division to mm of mastication
• Corneal reflex to elicit blinking

55
Abducens CN VI

• Motor
• Lateral rectus
• Test planes of gaze

56
Facial CN VII

• Mixed
• Taste on anterior 2/3 of tongue
• Motor to mm of facial expression (not chewing)
• 5 motor branches
• Temporal, zygomatic, buccal, mandibular, cervical
• PSNS to lacrimal gland
• Test making faces

57
Vestibulocochlear CN VIII

• Sensory
• Equilibrium hearing
• Test hearing

58
Glossopharyngeal CN IX

• Mixed
• Motor fibers to pharynx
• PSNS to parotid salivary gland
• Sensory conduct taste from posterior 1/3 of
  tongue carotid sinus pressure chemoreceptors
  (Oxygen), general sensation of pharynx
• Test swallowing (gag reflex w/ CN X)

59
Vagus CN X

• Mixed
• Only nerve to descend beyond neck (into thorax
  abdomen)
• PSNS serving heart, lung, abd viscera to regulate
  heart rate, breathing, digestive activity
• Test gag reflex (w/ CN IX)

60
Spinal accessory CN XI

• Motor
• Trapezius SCM
• Test shrugging shoulders

61
Hypoglossal CN XII

• Motor
• Extrinsic intrinsic muscles of the tongue
• Test by sticking out tongue