Brain and cranial nerves

Lecture Notes

Overview of brain
Brain is essentially a more developed spinal cord. It retains basic functions of conduction via white matter but focus on control centers (cluster of association neurons also know as a nuclei).. Brain is hollow like spinal cord. Sensory and Motor nerves enter/exit cranial cavity to provide control (sometimes conscious, sometimes reflexively) of head, neck and visceral organs.
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I. Gross anatomy of brain.

A. Gray and white matter
white matter is tracts of neurons communicating between gray nuclei.

B. Meninges (connective tissue layers) and spaces
 similar except no real epidural space around brain

C. Cerebrospinal fluid (CSF)

1. Found in subarachnoid space in spinal cord/brain and in ventricles of brain

2. Ventricles lined with glial cells (blood-brain barrier=BBB) that form CSF

3. Functions of BBB and CSF

a. Protection against injury by cushioning-CSF

b. Circulation of glucose and oxygen -CSF

c. Regulate transport into brain -BBB

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Provide the functions of meninges, spaces, BBB and CSF.

II. Adult Brain Regions click on this image for an audio message
A. Brain stem 1. Medulla Oblongata a. Association areas (gray matter) 1) Heart rate *

2) Blood pressure (vasomotor center)*

3) Respiration rate*

4) reflexive digestive movements (including vomiting)

b. Conduction pathway(white matter)
 continuation of spinal cord--has all-ascending and descending tracts
 many motor tracts criss-cross

2. Pons a. Helps medulla in regulating respiration rate
b. Tracts between spinal cord and brain as well as brain to brain

3. Midbrain a. Cranial somatic reflex for eye, head and neck muscles to visual stimuli
b. Cranial somatic reflex for trunk muscles to auditory stimuli
these are the so called "startle" responses
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B. Diencephalon -- mostly gray matter 1. Thalamus -- functions a. Sensory hub for incoming sensory impulses (except olfaction) to various regions of cerebral cortex
b. Interprets some sensory impulses (pain, light touch, pressure)

2. Hypothalamus -mostly gray matter
a. Controls body temperature
b. Thirst center (determines amount of water in blood)
c. Hunger centers (determines amount of glucose in blood)
d. Metabolism
e. Growth
f. Sex drive
g. Rage and aggression

3. Pituitary gland
a. regulates metabolism, growth, osmotic pressure of blood, blood sugar (controlled by hormones from hypothalamus).
b. regulates body temperature, birth, lactation (controlled by nervous impulses from hypothalamus )click on this image for an audio message
C. Cerebellum 1. Gray matter a. posture and coordination-allows smooth movements. Propioreception (muscle sense or position) comes from muscle spindle and tendon organ receptors to provide these functions.2. Arbor vitae (white matter tracts)-allows communication from cerebellum to cerebrum
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D. Cerebrum (cerebral hemispheres)
1. Cerebral medulla (white matter)
 corpus callosum -- communication between cerebral hemispheres

2. Cerebral cortex (gray matter)

a. Sensory functions
 primary visual area -- vision
 primary somatosensory area-feel body and position
primary gustatory area- taste
 primary auditory area-hearing
primary olfaction area-smell

b. Motor functions
primary motor area-consciously move skeletal mucles of body
Broca's (motor) speech area-move mucles to speak.

c. Associative functions (prefrontal lobe)

1) Memory
2) Judgement
3) Personality
4) Intelligence 

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Diagram the brain and label each area's function.

E. Brain Systems (not localized) -- networks of neurons with no specific location 1. Limbic System (cerebrum and diencephalon) a) Center for emotions, pain, pleasure

b) Memory (especially emotional memories)
 
 

2. Reticular Activating formation (RAS) in brainstem a) Alert CNS by continued excitation of cerebral cortex

b) Affect autonomic functions like sleep, heart rate, vasomotor

c) Filter sensory input

III. Cranial nerves
These consist of the sensory and motor neurons that make up a portion of a reflex arc. The control centers in the brain are the remaining parts of the reflex arcs.

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Diagram the complete pathway used by each cranial nerve. Relate functions to brain area, receptor and effectors in terms of somatic or autonomic cranial reflexes. See functional image of cranial nerves
 
 

No. Name Receptor Sensory Pathway Effector
I
 Olfactory Olfactory epithelium directly to temporal lobe  
II
 Optic Retina through thalamus to occipital lobe  
III
 Oculomotor eyeball muscle proprioreception thalamu to midbrain Eyelid and eyeball muscles, lens (focusing), pupil (constriction)
IV
 Troclear eyeball muscle proprioreception thalamus to midbrain eyeball muscle
V
 Trigeminal Chewing muscles proprioreception, cutaneous touch and pain receptors for face, jaw and teeth thalamus to pons, then to somatosensory area . chewing muscles
VI
 Abducens eyeball muscle proprioreception thalamusto midbrain eyeball muscle
VII
 Facial Facial muscle proprioreception, tongue taste receptors thalamus to pons then somatosensory area and/or to gustatory area (taste) facial expression muscles, saliva and tear glands
VIII
 Vestibulocochlear or Auditory Hearing and equilibrium organs thalamus to pons then totemporal lobe  
IX
 Glossopharyngeal arterial chemoreceptors and baroreceptors, tongue taste receptors, tongue muscle proprioreception thalamus to medulla/pons

saliva glands, tongue muscles (swallowing),
(aids in regulation of breathing and BP)
X
 Vagus arterial chemoreceptors and baroreceptors, pharangeal taste receptors, pressure/pain receptors in thoracic and abdominal organs thalamus to medulla/pons Swallowing and speaking muscles, smooth muscle and secretory glands in GI tract, Heart muscle, (aids in regulation of breathing, BP and slows HR)
XI
 Accessory Neck and shoulder muscle proprioreceptors thalamus to medulla swallowing muscles, head and neck muscles
XII
 Hypoglossal Swallowing and speaking muscle proprioreceptors thalamus to medulla, Swallowing and speaking muscles

Memory device for the cranial nerves
"OLd OPie OCcasionally TRies TRIGonometry, And Feels VEry GLOomy, VAGue, And HYPOactive"
Capitilized letters are first letter of name of cranial nerves.

Website help for cranial nerves
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Professor Thomas M. Lancraft
Human Anatomy and Physiology Courses
at St. Petersburg College
St. Petersburg/Gibbs Campus

10/2007