Ch.14 - The Brain and Cranial Nerves

Question 1

The brain contributes to homeostasis by

Answer 1

receiving sensory input, integrating new and stored information, making decisions, and executing responses through activites. It is the control center for registering sensations, correlating them with one another and with stored information, making decision, and taking actions.

Question 2

Major Parts of the Brain

Answer 2

brainstem (midbrain, pons, medulla), cerebellum, diencephalon (thalamus, hypothalamus, epithalamus), and cerebrum

Question 3

Protective Covering of the Brain

Answer 3

• The brain is protected by cranial bones and cranial meninges.
• Cranial meninges are the dura mater, arachnoid, and Pia mater.

Question 4

There extensions of the dura mater are the

Answer 4

• Falx cerebri - separates the 2 hemispheres of the cerebrum
• Falx cerebelli - separates the 2 hemispheres of the cerebellum
• Tentorium cerebelli - separates the cerebrum from the cerebellum

Question 5

The Blood-brain barrier (BBB)

Answer 5

• Consists of tight junctions that seal together the endothelial cells of brain blood capillaries and is meant to protect brain cells from harmful substances and pathogens.
• Some water-soluble substances, such as glucose, can cross the BBB quickly and others (most ions) are transported very slowly.

Question 6

Cerebrospinal Fluid (CSF)

Answer 6

a clear, colorless liquid that protects the brain and spinal cord against chemical and physical injuries and carries oxygen, glucose, and other needed chemicals from the blood to neurons and neuroglia.

Question 7

There are 4 CSF filled cavities in the body known as

Answer 7

ventricles

• lateral ventricle - in each hemisphere of the cerebrum; are separated by the Septum Pellucidum
• third ventricle - between right and left halves of the thalamus
• fourth ventricle - between pons and medulla

Question 8

CSF functions in helping to maintain homeostasis by providing

Answer 8

• Mechanical protection - is shock-absorbing; allows the brain to float
• Chemical protection - provides optimal chemical environment for accurate neuronal signaling
• Circulation - is a medium for exchange of nutrients and waste products between blood and nervous tissue

Question 9

Parts of the Brainstem

Answer 9

Medulla Oblongata
Pons
Midbrain

Question 10

Medulla Oblongata

Answer 10

• Continuous with the upper part of the spinal cord
• Contains motor & sensory tracts
• Contains the nuclei of origin for nerves VIII - XII

Structure

• Pyramids
• The Decussation of Pyramids (crossing of pyramids) results in the neurons in the left cerebral cortex controlling muscles on the right side of the body and neurons in the right side of the cerebral cortex controlling skeletal muscles on the left side
• Inferior Olivary Nucleus - relay impulses from proprioceptors to the cerebellum

Nuclei in the medulla are reflex centers for regulation (1) heart rate respiratory rate, (2) blood vessel diameter, (3) vasoconstriction, (4) swallowing, (5) coughing, (6) vomiting, (7) sneezing, and (8) hiccuping. The first 3 are vital reflexes. Nuclei associated with sensations of touch, pressure, vibration, and conscious proprioception are located in the posterior part of the medulla. It also contains nuclei that are components of sensory pathways for gustation (taste), audition (hearing), and equilibrium (balance).

Clinical Connection: Injury to the medulla can be fatal or lead to problems since vital activities are controlled by the medulla.

Question 11

Pons

Answer 11

• Located superior to the medulla
• Connects the spinal cord with the brain
• Contains sensory and motor tracts
• Contains nuclei of origin for cranial nerves V - VIII

Structure

• Pontine nuclei - relay nerve impulses from motor areas of the cerebral cortex to the cerebrum
• Pontine Respiratory Group - helps control breathing

Question 12

Midbrain (Mesencephalon)

Answer 12

• Extends from the pons to the diencephalon
• Contains sensory and motor tracts
• Conveys motor impulses from the cerebrum to the cerebellum and spinal cord, sends sensory impulses from the spinal cord to the thalamus, and regulates auditory and visual reflexes
• Contains nuclei of origin for cranial nerves III & IV

Structure

• Cerebral peduncles - conduct nerve impulses from from motor areas in the cerebral cortex to the spinal cord, medulla, and pons
• Tectum - posterior part of the midbrain
• Part of the tectum: superior colliculi (coordinate movements of head, eyes, and trunk in response to visual stimuli) and inferior colliculi (coordinate movements of head, eyes, and trunk in response to auditory stimuli)
• Substantia nigra and Red nucleus contribute to control of movement

Question 13

Reticular formation

Answer 13

• A broad region where white and gray matter exhibit in a netlike arrangement
• Consists of small regions of gray matter interspersed among fibers of white matter and has both sensory and motor functions
• Helps regulate muscle tone, alerts the cortex to incoming signals (Reticular Activating System or RAS)
• Responsible for maintaining consciousness, arousal, attention, and alertness
• RAS prevents sensory overload
• Inactivation of RAS results in sleep and damage to the RAS results in a coma
• RAS receives input from eyes, ears, and other sensory receptors EXCEPT smell

Question 14

The Cerebellum

Answer 14

• Occupies the inferior and posterior aspects of the cranial cavity; posterior to the medulla and pons; inferior to the posterior portion of the cerebrum
• Accounts for 1/10 of the brain but contains nearly half the neurons in the brain
• Main function: smooths and coordinates contraction software skeletal muscles. Also regulates posture and balance and muscle tone.
• The shape resembles a butterfly

Structures

• Transverse cerebral fissure
• Tentorium cerebelli
• Vermis- constricted part of the cerebellum
• Cerebellar hemispheres
• Anterior and posterior lobe - govern subconscious aspects of the skeletal muscle movements
• Flocculonodular lobe - contributes to equilibrium and `balance
• Folia - ridges of the cerebellar cortex
• Arbor Vitae - tracts of white matter deep to the gray matter
• Cerebellar nuclei - regions of gray matter that give rise to axons carrying impulses from the cerebellum to other parts of the brain
• Superior, middle, and inferior cerebellar peduncles

Clinical Connection: Damage to the cerebral cortex results in ataxia, which is the inability to coordinate muscular movements

Question 15

Cerebral Cortex

Answer 15

• Consists of gray matter

Question 16

Diencephalon

Answer 16

includes the thalamus, hypothalamus, and epithalamus

Question 17

Thalamus

Answer 17

• Located superior to the midbrain
• Contains nuclei that serve as relay stations for all sensory impulses (except smell) to the cerebral cortex
• Plays a role in maintenance of consciousness
• Makes up 80% of the diencephalon

Structure

• Interthalamic adhesion - joins right and left sides of the thalamus
• Internal medullary cavity - divides gray matter of the right and left sides of the thalamus
• internal capsule - a thick band of white matter lateral to the thalamus

Major Groups of Nuclei

1. Anterior nucleus
2. Medial nucleus
3. Lateral group
4. Ventral group (5)
5. Intralaminar group
6. Periventricular nucleus
7. Reticular nucleus of the prethalamus

Question 18

Hypothalamus

Answer 18

• Inferior to the thalamus
• Controls activities of the ANS
• Produces hormones (releasing hormones, inhibiting hormones, oxytocin, and antidiuretic hormones)
• Regulates emotional/behavioral patterns
• Regulates eating/drinking (feeding, satiety, and thirst center)
• Controls body temperature (thermostat)
• Regulates circadian rhythms and states of consciousness

Has 4 major regions

• Mammillary (posterior hypothalamic)
• Tuberal (intermediate hypothalamic)
• Supraoptic (anterior hypothalamic)
• Preoptic

Question 19

Epithalamus

Answer 19

• Superior and posterior to the thalamus
• Contains pineal gland - secretes melatonin which helps regulate the circadian rhythms; part of the endocrine system
• Contains the habenular nuclei - involved in olfaction, especially emotional responses to odors such as a loved one’s cologne

Question 20

Circumventricular Organs (CVOs)

Answer 20

• Can monitor changes in the blood because they lack a blood-brain barrier;
• Are thought to be the sites of entry into the brain of HIV
• Part of the hypothalamus, pineal gland, pituitary gland, and nearby structures
• Function to coordinate homeostatic activities of the endocrine system, such as the regulation of BP, fluid balance, hunger, and thirst

Question 21

Cerebrum (Cerebral Cortex)

Answer 21

• Composed of gray matter
• Contains billions of neurons

Structure

• Gyri - ridges on the cerebral cortex
• Cerebral sulci - grooves that separate neighboring cerebral gyri
• Interlobar sulci - grooves that separate various lobes of the cerebrum
• Cerebral fissures grooves that separate parts of the brain
• Longitudinal fissure - separates cerebrum into right and left halves
• Corpus callosum - connects cerebral hemispheres internally

Question 22

Lobes of the Cerebrum

Answer 22

frontal, parietal, occipital, temporal, insula (lies deep to the frontal, parietal, occipital, and temporal lobes)

Question 23

Cerebral white matter consists of myelinated axons running in 3 principal directions:

Answer 23

a. Association fibers - connects and transmit nerve impulses between gyri in the same hemisphere
b. Commissural fibers - connects gyri in one cerebral hemisphere to the corresponding gyri in the opposite hemisphere (corpus callosum, anterior and posterior commissure)
c. Projection fibers - form ascending and descending tracts that transmit impulses from the cerebrum to other parts of the brain and spinal cord (internal capsule)

Question 24

Cerebrum - (Corpus Striatum) Basal Nuclei

Answer 24

paired masses of gray matter in each cerebral hemisphere that are collectively termed corpus striatum.
- Corpus striatum helps initiate and terminate movements, suppress unwanted movements, and regulates muscle tone

Structure of corpus striatum

• Globus pallidus - closer to thalamus
• Putamen - closer to cerebral cortex
• Claustrus - thin sheet of gray matter lateral to the putamen; may be involved in visual attention
• Caudate nucleus - “comma-shaped” body

Question 25

Limbic System

Answer 25

• Found in cerebral hemispheres and diencephalon

- Functions in emotional aspects of behavior and memory and is associated with pleasure and pain

Question 26

Functional Organization of the Cerebral Cortex

Answer 26

• Sensory - involved with the reception and interpretation of sensory impulses (primary somatosensory area, primary visual area, primary auditory area, primary gustatory area, olfactory cortex)
• Motor - regions that govern muscular movement (primary motor area, premotor cortex, Broca’s area, frontal eye field)
• Association - concerned with functions such as memory, emotions, reasoning, will, judgement, personality traits, and intelligence somatosensory association area, visual association area, facial recognition area, auditory association area, orbitofrontal area, Wernicke’s area, common integrative area, prefrontal cortex)

Clinical Connection: Injury to the association or motor speech areas result in aphasia, which is the inability to use or comprehend words

Question 27

Hemispheric Lateralization (Cerebrum)

Answer 27

the two hemispheres are not bilaterally symmetrical, either anatomically or functionally.

• Left hemisphere - controls muscles on the right side of the body; reasoning/numerical and scientific skills; understand and use sign language; spoken and written language
• Right Hemisphere - controls muscles on the left side of the body; musical and artistic awareness; space and pattern perception; recognition of faces/facial recognition; generating mental images of sight, sound, touch, taste, and smell.

Question 28

Brain Waves are

Answer 28

electrical signals generated by brain cells; brain waves generated is recorded by an electroencephalogram or EEG

Question 29

Patterns of activation of brain neurons produce 4 types of brain waves

Answer 29

• Alpha (8 - 13 Hz) are present in awake/resting individuals
• Beta (14 - 30 Hz) appear when the nervous system is active
• Theta (4 - 7 Hz) normally occur in children and adults experiencing emotions stress
• Delta (1 - 5 Hz) occur during deep sleep for adults and are normal in awake infants

Question 30

Clinical Connection: Brain Injuries

Answer 30

• Memory lapse results from an injured brain
• Brain injuries are commonly associate with head injuries and result from displacement and distortion of neuronal tissue at the moment of impact and from the release of disruptive chemicals from injured brain cells
• Some brain injuries are: Concussion, Chronic traumatic encephalopathy (CTE), Traumatic brain injury (TBI), Contusion, and laceration

Question 31

Cranial Nerves

Answer 31

Olfactory (I) - smell

Optic (II) - sight

Oculomotor (III) - movement of eyeballs and upper eyelid (somatic) adjusts lens for near vision, constriction of pupil (motor-autonomic)

Trochlear (IV) - movement of eyeballs

Trigeminal (V) - touch, pain, thermal sensations from scalp, face and oral cavity (sensory) chewing and controls middle ear muscle (motor-brachial)

Abducens (VI) - movement of eyeballs

Facial (VII) - taste from anterior 2/3 of tongue; touch, pain, and thermal sensations from skin in external acoustic meatus (sensory) control of muscles of facial expression and middle ear muscle (motor-brachial) secretion of tears and saliva (motor-autonomic)

Vestibulocochlear (VIII) - hearing and equilibrium (special sensory)

Glossopharyngeal (IX) - taste from posterior 1/3 of tongue, proprioception in some swelling muscles, monitors BP, oxygen, and carbon dioxide levels; touch, pain, and thermal sensations from skin of external ear and upper pharynx (sensory) assists in swallowing (motor-brachial) secretion of saliva (motor-autonomic

Vagus (X) - taste from epligottis; proprioception from throat and voice box muscles; monitors BP, oxygen, and carbon dioxide levels; touch, pain, thermal sensations from skin of external ear; sensations from thoracic and abdominal organs (sensory) swallowing, vocalization, and coughing (motor-brachial) motility and secretion of digestive canal organs; constriction of respiratory passageways; decreases heart rate(motor-autonomic)

Accessory (XI) - movement of head and pectoral girdle

Hypoglossal (XII) - speech, manipulation of food, and swallowing

Mnemonic: Oh Oh Oh To Touch And Feel Very Green Vegetables AH

Question 32

Clinical Connection: Cranial Nerves

Answer 32

1. Anosmia - loss of the sense of smell
2. Anopia - blindness due to a defect in or loss of one or both eyes
3. Strabismus - condition in which both eyes do not fix on the same object
4. Ptosis - drooping of the upper eyelid, dilation of the pupil, movement of the eyeball downward or outward on the damaged side, and loss of accommodation for near vision
5. Diplopia - double vision
6. Trigeminal neuralgia - pain that is relayed via one or more branches of the trigeminal (V) nerve caused by condition such as inflammation or lesions
7. Bell’s palsy - facial paralysis, loss of taste, decreased salivation, loss of ability to close eyes, even during sleep
8. Vertigo - feeling that one’s own body or environment is rotating
9. Ataxia - muscular incoordination
10. Nystagmus - involuntary rapid movement of the eyeball
11. Tinnitus - ringing in the ears
12. Dysphagia - difficulty swallowing
13. Aptyalia - reduced secretion of saliva; loss of sensation in the throat
14. Ageusia - loss of taste sensation
15. Pharyngeal (gag) reflex - rapid and intense contraction of the pharyngeal muscles
16. Vagal neuropathy - interruptions of sensations from many organs in the thoracic and abdominal cavities
17. Tachycardia - increased heart rate
18. A damaged accessory nerve leads to paralysis of the sternocleidomastoid and trapezius muscles leaving the person unable to raise their shoulders and have difficulty turning their head

Question 33

Developmental Anatomy of the NS

Answer 33

The development of the NS begins with the thickening of the ectoderm called the neural plate. Parts of the brain develop from primary and secondary vesicles:

3-4 week Embryo
Prosencehephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)

During the 5th week of development the secondary brain vesicles begin to develop.

• Prosencephalon develops into the telencephalon and the diencephalon
• Rhombencephalon develops into the metencephalon and myelencephalon

11 week Fetus

• Telencephalon develops into cerebral hemispheres
• Diencephalon develops into the thalamus, hypothalamus, and epithalamus
• Mesencephalon develops into the midbrain
• Mentencephalon becomes the pons and cerebellum and houses part of the fourth ventricle
• Myelencephalon develops onto the medulla oblongata and houses the remainder of the the fourth ventricle