1b. Neuroanatomy and Neurophysiology: The Nervous System

Question 1

Neurons: Motor, Sensory, and Interneurons

Answer 1

• Sensory “afferent” neurons: carry sensory impulses from the peripheral sense organs TOWARD BRAIN
• Motor “efferent” neurons: transmit impulses AWAY FROM BRAIN/CNS to muscles that make those muscles move (cause muscle contractions)
• Interneurons: link neurons with other neurons; play an imp. role in controlling movement

Question 2

Peripheral Nervous System (PNS)

Answer 2

• PNS is a collection of nerves outside skull and spinal column
• Nerves carry sensory impulses originating in peripheral sense organs to brain AND motor impulses originating in brain to glands/muscles of the body
• Contains 3 types of nerves: CNs, spinal(control autonomic functions, e.g., breathing), and autonomic(which make up ANS)
• 12 CNS, 31 pairs of spinal nerves

Question 3

Cranial Nerves: General Info

Answer 3

Emerge from BS, attached to base of brain; Part of LOWER MOTOR sys; Receive much of their innervation from corticobulbar tract of pyramidal sys; CNs exit through foramina in base of skull and exit at different levels of BS and top portion of spinal cord; CNs connect to various sense organs and muscles of head/neck

Question 4

CNs (12): Function 
and Classification (Motor, Sensory, *Mixed)

Answer 4

I. Olfactory: smell (sensory)
II. Optic: vision (sensory)
III. Oculumotor: eye movement (motor)
IV. Trochlear: eye movement (motor)
V. *Trigeminal: face (sensory); jaw (motor)
VI. Abducens: eye movement (motor)
VII. *Facial: tongue (sensory); face (motor)
VIII. Acoustic/Vestibulocochlear: hearing and balance (sensory)
IX. *Glossopharyngeal: tongue and pharynx (sensory); pharynx only (motor)
X. *Vagus: larynx, respiratory, cardiac, gastrointestinal systems (sensory and motor)
XI. Spinal Accessory: shoulder, arm, throat movements (motor)
XII. Hypoglossal: mostly tongue movements (motor)

Question 5

Which CNs Are Not Concerned with Speech, Language or Hearing?

Answer 5

I, II, III, IV, VI

i.e., V, VII-XII are related to speech, language, and hearing

Question 6

Trigeminal (V)

Answer 6

SENSORY–3 branches: 1) opthalamic (sensory branch to nose, eyes, forehead), 2) maxillary (…to upper lip, maxilla, upper cheek area, upper teeth, maxillary sinus, palate) and 3) mandibular (…to mandible, lower teeth, lower lip, tongue, part of cheek, part of external ear)

MOTOR: Innervate various jaw muscles (incl. temporalis, lateral and medial pterygoids, masseter, tensor veli palatini, tensor tympani, mylohyoid, and anterior belly of digastric)

Question 7

Damage to CN V

Answer 7

May result in an inability to close mouth, difficulty chewing, and trigeminal neuralgia (sharp pain in facial area)

Question 8

Facial (VII)

Answer 8

SENSORY: Responsible for taste sensations on the anterior 2/3 of the tongue

MOTOR: Innervate muscles important to facial expression and speech (incl. buccinator, zygomatic, orbicularis oris, orbicularis oculi, platysma, stapedius, stylohyoid, frontalis, procerus, nasalis, depressor labii inferioris, depressor anguli oris, auricular muscles, various labial muscles, posterior belly of digastric)

Question 9

Damage to CN VII

Answer 9

A person with damage to the facial nerve often has a mask-like appearance with minimal or no facial expression

Question 10

Acoustic/Vestibulocochlear (VIII)

Answer 10

SENSORY–2 branches:
1) Vestibular and 2) Acoustic

Vestibular: maintenance of equilibrium/balance
Acoustic: transmits sensory info from cochlea of inner ear to the primary auditory cortex of brain, where it is interpretted

Question 11

Damage to CN VIII

Answer 11

Results in hearing loss, problems with balance, or both

Question 12

Glossopharyngeal (IX)

Answer 12

SENSORY: Processing taste sensations from the posterior 1/3 of the tongue; Also provides general sensation for the tympanic cavity, ear canal, eustachian tube, faucial pillars, tonsils, soft palate, and pharynx

MOTOR: Innervate the stylopharyngeus, a muscle that raises and dilates the pharynx

Question 13

Damage to CN IX

Answer 13

Lesions of the glossopharyngeal nerve may create difficulty in swallowing, unilateral loss of the gag reflex, and loss of taste and sensation from the posterior 1/3 of the tongue

Question 14

Vagus (X)

Answer 14

SENSORY: Convey info from the digestive system, heart, trachea, pharynx, and larynx

MOTOR: Supply the digestive system, heart, and lungs

RLN (Recurrent laryngeal nerve) Branch: regulates intrinsic laryngeal muscles, excluding the cricothyroid, which is supplies by the SLN

Pharyngeal Branch: Supplies the pharyngeal constrictors; it also supplies all muscles of the velum except the tensor tympani, which is innervated by CN V

Question 15

Damage to CN X

Answer 15

Damage to the vagus nerve includes a variety of sequelae such as difficulty swallowing, paralysis of the velum, and voice problems if the RLN is damaged

RLN may be damaged during thyroid surgery, resulting in total or partial paralysis of the VFs

Question 16

Spinal Accessory (XI)

Answer 16

MOTOR
The spinal root supplies the trapezius and sternocleidomastoid muscles, which assist in head and shoulder movements
In concert with the vagus nerve, the cranial fibers of the accessory nerve innervate the uvula and levator veli palatini muscles of the soft palate

Question 17

Damage to CN XI

Answer 17

Lesions of the spinal accessory nerve may result in neck weakness, paralysis of the sternocleidomastoid, and consequent inability to turn the head, as well as an inability to shrug the shoulders or raise the arm above shoulder level

Question 18

Hypoglossal (XII)

Answer 18

MOTOR
Supplies 3 extrinsic tongue muscles: the styloglossus, hyoglossus, and genioglossus; Also supplies all the intrinsic muscles of the tongue

Question 19

Damage to CN XII

Answer 19

Lesions to the hypoglossal nerve can result in tongue paralysis, diminished intelligibility, and swallowing problems

Question 20

Autonomic Nervous System (ANS)

Answer 20

Generally, viewed as part of PNS; ANS controls and regulates internal environment of our bodies (e.g., heartbeat); ANS has 2 branches: sympathetic (mobilizes body for “fight or flight”) and parasympathetic (brings body back to state of relaxation); ANS branches have an indirect effect on speech when they cause speakers to feel emotionally relaxed or aroused

Question 21

Central Nervous System (CNS)

Answer 21

Composed of the spinal cord and brain;

CNS acts as a motor command center for planning, originating, and carrying out the transmission of messages (from PNS)

Question 22

Key Structures of the Brainstem

Answer 22

Midbrain (mesencephalon)- III, IV
Pons (metencephalon)- V, VII
Medulla (myelencephalon)- VIII, IX, X, XI, XII

Question 23

Reticular Activating System (RAS)

Answer 23

RAS: primary mechanism of attention and consciousness (sleep-wake cycles, states of drowsiness/alertness)

Question 24

Diencephalon

Answer 24

Diencephalon: above midbrain; contains thalamus (regulates/relays sensory and motor info; also imp. for consciousness/alertness) and hypothalamus (helps integrate actions of the ANS; controls emotions)

Question 25

Basal Ganglia

Answer 25

• Complex system of neural pathways that have connections w/ many subcortical and cortical areas
• BG receives input primarily from frontal lobe and relays info back to higher centers of brain via thalamus
• 3 nuclear masses: globus pallidus, putamen, caudate nucleus (corpus striatum=collective term)
• Part of extrapyramidal system, which regulates/modifies cortically initiated motor movements (incl. speech)

Question 26

Damage to Basal Ganglia

Answer 26

Lesions in the BG can result in unusual body postures, dysarthria, changes in body tone, and involuntary and uncontrolled movements (dyskinesias)

Question 27

Cerebellum (“little brain”)

Answer 27

Regulates equilibrium/balance, body posture, and coordinated fine-motor movements (b/c these movements are needed for rapid speech, cerebellar intactness is very important to speech production)

Question 28

Damage to Cerebellum

Answer 28

Results in a neurological disorder called ATAXIA, found in some people with cerebral palsy and in people who have suffered cerebellar damage. These individuals are likely to show abnormal gait, disturbed balance, and a speech disorder called ATAXIC DYSARTHRIA

Question 29

Cerebral Cortex (aka Cerebrum): Main Fissures/Sulci (3)

Answer 29

• Longitudinal Fissure: Divides the cerebrum into the L and R hemispheres
• Fissure of Rolando (aka Central Sulcus): Arbitrarily divides the anterior from the posterior half of the brain
• Sylvian Fissure (aka Lateral Cerebral Fissure/Sulcus): Starts at the inferior portion of the frontal lobe at the base of brain and moves laterally and upward. The areas of the brain surrounding the Sylvian Fissure are especially critical in language, speech, and hearing

Question 30

Frontal Lobe (Motor)

Answer 30

• Deliberate formation of plans and intentions that dictate a person’s conscious behavior
• Areas critical to speech production: Primary motor cortex(aka motor strip), Supplementary motor cortex, Broca’s area
• Primary motor cortex: controls voluntary movements of skeletal muscles on opposite side of body; controls muscle movements via pyramidal system (neural pathway)
• Supplementary motor cortex: involved in the motor planning of speech; secondary role in regulating muscle movements
• Broca’s: aka “motor speech area”; controls motor movements involved in speech production; necessary for well-articulated, fluent speech

Question 31

Frontal Lobe Damage

Answer 31

Have difficulty carrying out consciously organized activity

Lesions to Broca’s area cause motor speech problems

Question 32

Parietal Lobe (Sensory)

Answer 32

• Primary somatic sensory area; It integrates contralateral somesthetic sensations such as pressure, pain, temperature, and touch
• Postcentral gyrus (aka sensory cortex/strip): primary sensory area that integrates and controls somesthetic sensory impulses
• 2 Areas are important for speech and language: areas including and surrounding the supramarginal gyrus (SG) and angular gyrus (AG)

Question 33

Parietal Lobe Damage

Answer 33

Damage to the SG: Can cause conduction aphasia and agraphia (a writing disorder)

Damage to the AG: Can cause writing, reading, and naming difficulties and, in some cases, transcortical sensory aphasia

Question 34

Occipital Lobe (Vision)

Answer 34

• Not very relevant to speech and hearing because it is primarily concerned with vision
• Major structure: primary visual cortex
• The remainder of the occipital lobe is composed of association visual cortices

Question 35

Temporal Lobe (Hearing)

Answer 35

• 2 general areas that are critical to adequate hearing and speech: Primary auditory cortex and the Auditory association area (lies posteriorly to primary auditory cortex); Heschl’s gyri: refers to the transverse convolutions that make up the auditory association cortex and the primary auditory cortex
• Wernicke’s area: critical to the comprehension of spoken and written language; Connected to Broca’s area via arcuate fasciculus

Question 36

Temporal Lobe Damage

Answer 36

A lesion in the posterior portion of the superior temporal gyrus causes Wernicke’s aphasia, in which the patient produces fluent but meaningless speech and experiences significant language comprehension problems

Question 37

Pyramidal System

Answer 37

• Direct motor activation pathway that is primarily responsible for facilitating VOLUNTARY (FINE-MOTOR) muscle movement (including speech)
• Nerve fiber tract comes from cerebral cortex to spinal cord and BS to supply muscles of head, neck, and limbs
• Voluntary movements needed for speech are initiated in primary motor cortex

Question 38

Pyramidal System: CorticoSPINAL Tract

Answer 38

• Nerve fibers descent from motor cortex of each hemisphere through internal capsule
• At the level of the medulla, 80-85% of the fibers decussate
• Spinal nerves innervate muscles of the LIMBS and TRUNK
• R side of body is generally controlled by nerve fibers that originate in L cortex and vice versa (e.g., L hemisphere stroke–>right body weakness)

Question 39

Pyramidal System: CorticoBULBAR Tract

Answer 39

• Critical to speech production; Fibers control all voluntary movements of SPEECH MUSCLES (except respiratory)
• Originates primarily in motor cortex, courses downward through internal capsule and run along w/ corticospinal tract fibers
• Terminates in BS at the motor nuclei of CNs III-XII and decussate at level of BS where they terminate (e.g., fibers that terminate at motor nuclei of CN V, decussate in the pons)
• CNs involved in speech exit skull and innervate muscles of larynx, pharynx, velum, tongue, face, and lips (allows muscles to function for speech production)

Question 40

Extrapyramidal System

Answer 40

• While the pyramidal system is responsible for carrying out fine-motor movements, the extrapyramidal system transmits impulses that control the POSTURAL SUPPORT needed by those fine-motor movements
• Important for motor speech production
• Composed of subcortical nuclei, including the red nucleus, substantia nigra, subthalamus, BG, and pathways that connect these structures to one another
• Helps maintain posture and tone and REGULATES MOVEMENT

Question 41

Extrapyramidal System Damage

Answer 41

Creates motor disturbances that fall under the rubric of “involuntary movement disorders”; patients may show unusual movement patterns of various muscles (incl. facial muscles) and bizarre postures

Question 42

Connecting Fibers of the Brain (3)

Answer 42

• Projection: connections between cortex and subcortical structures (e.g.,cerebellum, BG, BS, and SC)
• Association: connect areas w/in a hemisphere; assist w/ communication between structures in a hemisphere (e.g., arcuate fasciculus, which connects Broca’s to Wernicke’s)
• Commissural: interhemispheric connectors; run horizontally and connect corresponding areas of the two hemispheres (e.g., corpus callosum, which connects the 2 hemispheres at their base)

Question 43

Damage to Corpus Callosum

Answer 43

Results in “disconnection syndrome,” characterized by problems in naming, reading, movement, and other functions

Question 44

The Main Structures That Supply Blood to the Brain (4)

Answer 44

• Aorta
• Vertebral Arteries
• Carotid Arteries
• Circle of Willis