module 2 speech anatomy

Neurons:

electrochemically transmit and process information; receive and transmit signals; synapse with other neurons; the cells in which language, cognition, and motor movement originate; transmit motor impulses from brain→muscles and sensory impulses from receptors→brain

Neuroglia

several cell types that provide structural/physiological support to neurons; not directly involved in information processing; provide metabolic support, regulate blood flow to neurons, aid neuronal development

neuron structure

cell body (soma), dendrites, axon hillock, axon, myelin sheath, nodes of Ranvier, axon terminals, synapse. A myelinated axon transmits signals up to ~328 ft/sec vs. ~3 ft/sec for an unmyelinated axon.

Sensory neurons

transmit sensory info from receptor cells in the body to the spinal cord/brain for processing

motor Neuron

transmit motor impulses from brain/spinal cord out to the body, where muscles execute movement

interneurons

connect neurons within the same brain region; process/interpret information locally rather than transmitting it over distance (vs. sensory/motor neurons, which transmit between body regions)

white matter

motor and sensory axons wrapped in myelin (myelin gives the white color); transmits information, connecting brain areas so they can communicat

gray matter

 interneurons and cell bodies, unmyelinated; found in the cerebral cortex and subcortical structures (e.g., cerebellum, spinal cord); processes/regulates information

astrocytes

• structural support in the CNS; maintain homeostasis; help form the blood–brain barrier (end feet contact both neurons/synapses and capillaries, keeping toxins/pathogens out while letting nutrients through); after CNS injury, proliferate around a lesion (astrogliosis) to form a protective glial scar

Oligodendrocytes

produce myelin in the CNS — one cell can myelinate segments of multiple axons

Schwann cells

produce myelin in the PNS — each cell myelinates one segment of a single axon

microglia

the CNS's immune defense (10–15% of the brain); clear waste, damaged neurons, and pathogens

dura mater

 protective, thick, fibrous outer layer enwrapping brain and spinal cord

Arachnoid mater:

delicate, highly vascular, named for its spider-web-like network of blood vessels

pia mater

most fragile layer; closely follows the brain's surface; carries blood vessels to nourish it

meningitis

infection/inflammation of the meninges — serious and potentially fatal if untreated

Ventricular system

• An interconnected series of fluid-filled cavities that manufacture and circulate cerebrospinal fluid (CSF)

• Four cavities: two lateral ventricles, a third ventricle, and a fourth ventricle

• Lateral ventricles hold most of the CSF and contain the choroid plexus — the tissue that produces most CSF

• CSF cushions the CNS within the ventricles and subarachnoid space, protecting the brain from trauma, and delivers nutrients while removing waste — waste removal occurs primarily during sleep

• choroid plexus

• the tissue that produces most CSF

CSF circulation pathway

Lateral ventricles (produced by choroid plexus) → foramen of Monro → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space (space between arachnoid and pia mater) → drains into the venous system

Hydrocephalus

buildup of too much CSF in the ventricles (from excess production, failure to reabsorb, or an obstruction between ventricles); brain gets compressed between the expanding ventricles and skull; can be congenital or acquired via trauma; in infants the still-cartilaginous skull can expand, causing an enlarged skull; most often treated with an intraventricular (CSF) shunt.

longitudinal fissure

divides the cerebrum into left and right hemispheres

Corpus callosum

the largest white matter pathway in the brain, located deep within the longitudinal fissure; connects the left and right hemispheres, allowing communication and coordinated processing between them

Left hemisphere specialization

• dominant for language in most individuals (even in most left-handed individuals); houses the zone of language; because of contralateral innervation, also typically controls the dominant (usually right) hand for writing

right hemisphere specialization

• not dominant for language; specializes in nonlinguistic aspects of communication:

  • Emotion: generates prosody/facial expression that convey the speaker's emotional state, and comprehends others' body language, facial expression, gesture, prosody; damage → patients may seem monotone/unemotional (clinicians should explicitly ask about emotional state)

  • Figurative language: needed to produce/comprehend metaphor, hyperbole, idioms, sarcasm; damage → over-literal interpretation of language

  • Macrostructure (gestalt) processing: perceiving how details fit together to understand the whole; damage → patients get "anchored" to small details

  • Visuospatial processing: depth, movement, distance, shape, figure-ground, body position in space

  • Sustained & selective attention: holding attention over time while ignoring distractions; damage → attention breaks easily

  • Nonspeech environmental sounds & facial recognition: processes meaning of sounds like a car starting; damage to facial processing → prosopagnosia (face blindness)

Frontal lobe

• cognition (attention, memory, decision-making, executive function), motor movement, speech, language

• has prefrontal cortex, primary motor cortex, broca area

Prefrontal cortex

• (anterior-most): higher-level cognition, decision-making, problem-solving, initiation of movement, inhibition of inappropriate social impulses

Primary motor cortex

• (M1/motor strip, posterior-most gyrus): issues plans for volitional movement contralaterally; motor homunculus — body parts capable of fine, precise movement (lips, tongue, fingers) get disproportionately large cortical representation

Parietal lobe

• receives/processes somatosensation (taction/touch, nociception/pain, proprioception/body position)

  • Primary sensory cortex (S1, anterior-most gyrus): receives somatosensation contralaterally; sensory homunculus — more cortical area devoted to sensitive body parts (mouth, hands) than less-sensitive ones (knee, elbow)

Temporal lobe

• reception/processing of audition and memory

• wernickes area

• primary auditory cortex

• hippocampi

Primary auditory cortex

• temporal lobe

• receives afferent audition from ears; on the left, transmits speech-sound signals to Wernicke area; on the right, processes environmental (nonspeech) sounds

Hippocamp

(bilateral): convert short-term memory to long-term memory; hippocampal degeneration is the first change seen in Alzheimer disease, producing early memory loss

Occipital lobe

• Primary visual cortex (posterior-most): left occipital lobe receives right visual field, right occipital lobe receives left visual field (both eyes)

• Visual association cortex (anterior to primary visual cortex): interprets what's being seen

• cortical blindness

• visual agnosia

visual agnosia =

bilateral damage to visual association cortex (can see but can't make sense of it)

Cortical blindness =

damage to primary visual cortex (complete vision loss);

Broca aphasia

know what they want to say but struggle to find words; nonfluent, effortful expressive language

Wernicke aphasia —

struggle to understand others' speech; own speech fluent but meaningless/tangential; usually unaware of the deficit

Arcuate fasciculus

White matter pathway between Broca & Wernicke areas

Enables repetition — carries words processed in Wernicke area forward to Broca area

Conduction aphasia — comprehend words spoken to them and can express meaning in their own words (paraphrase), but cannot repeat verbatim

Angular gyrus

Parietal–temporal–occipital junction, just posterior to Wernicke area

Reception of visual language (reading, sign language

subcortical structures function

 handles more life-giving, largely involuntary functions — homeostasis, digestion, heart/cardiovascular regulation, vegetative respiration, reflexes, and refining volitional movement.

the brainstem

• Responsible for basic life-giving functions; evolutionarily one of the oldest brain parts; narrows into the spinal cord; most somatosensory/motor pathways between cerebrum and body pass through it

• midbrain

• pons

• medulla

midbrain

 most superior division, beneath the thalamus, above the pons; contains cerebral peduncles (connect cerebrum to lower structures) and the substantia nigra (produces dopamine, essential for appropriate movement; its loss is central to Parkinson disease)

pons

middle portion; where the cerebellum connects to the rest of the brain; houses many cranial nerve nuclei; together with medulla, houses the masticatory central pattern generator (automatic chewing movement)

medulla

smallest division; houses the respiratory center (vegetative respiration) and the swallowing central pattern generator (reflexive pharyngeal swallow); site of pyramidal decussation

Pyramidal decussation

 motor fibers from the primary motor cortex cross to the opposite side of the body within the medulla — this crossing creates contralateral innervation (right hemisphere → left body movement, and vice versa).

Hemiparesis

unilateral spastic weakness

• with pyramidal decussation

hemiplegia

(unilateral spastic total paralysis)

• pyramidal decussation

lesion above the medulla…

causes weakness/paralysis contralateral to the lesion

a lesion in the spinal cord below the decussation…

causes weakness/paralysis ipsilateral to the lesion

Reticular activating system (RAS)

: nuclei within the midbrain, pons, and medulla that regulate wakefulness/arousal, including the sleep/wake cycle; also contributes to autonomic functions like blood pressure and respiration.

gag reflex

• brain stem reflex

• triggered by touch to the posterior oral cavity/posterior pharyngeal wall; causes pharyngeal contraction and airway closure to prevent aspiration/penetrationtriggered by touch to the posterior oral cavity/posterior pharyngeal wall; causes pharyngeal contraction and airway closure to prevent aspiration/penetration

Vestibulo-ocular reflex:

• brainstem reflex

• eye muscles contract to move the eyes opposite to head-position changes detected at the semicircular canals; stabilizes visual gaze during head movement

Cerebellum and three lobes

• The main function of the cerebellum is to coordinate and fine-tune voluntary muscle movements, maintain balance, and support motor learning

• Hangs off the back of the brainstem, between the brainstem and occipital lobe

• Three lobes: anterior, posterior, and flocculonodular

• Divided into left/right lateral hemispheres connected at midline by the vermis; folded gray matter surface over white matter, like the cerebrum

• compares intended movement to incoming somatosensation to monitor/refine movement in an ongoing, online fashion (an "error-control device")

the cerebellum connects to the CNS

• at the pons via three paired peduncles:

  • Middle peduncle: receives rough motor info from the contralateral cerebrum

  • Inferior peduncle: receives somatosensory info about body position for integration into movement plans

  • Superior peduncle: sends refined motor plans onward to the thalamus, then cerebrum, for execution

• Middle peduncle of cerebellum

• : receives rough motor info from the contralateral cerebrum

inferior peduncle of cerebellum

receives somatosensory info about body position for integration into movement plans

superior peduncle in cerebellum

 sends refined motor plans onward to the thalamus, then cerebrum, for execution

The thalamus

• Paired, olive-shaped structures superior to the brainstem, beneath the cerebrum

• All afferent/sensory pathways except olfaction pass through the thalamus en route through the CNS, then fan out to relevant cerebral areas for processing

• Also receives refined motor plans from the cerebellum and relays them to M1 for execution

The basal ganglia:

• Four major structures, located lateral to the thalamus: putamen, globus pallidus, subthalamic nucleus, and substantia nigra

• facilitates desired voluntary movement and inhibits involuntary movement

• Clinical correlate: Parkinson disease — Lewy body protein deposits in the substantia nigra cause progressive loss of dopamine-producing cells → basal ganglia malfunction; symptoms include reduced voluntary movement, released involuntary movements, rigidity, tremor, slowness; speech manifestation = hypokinetic dysarthria (inaccurate articulation, breathy voice, increased rate, sometimes stutter-like dysfluencies)

The limbic system:

• Subcortical structures above the brainstem, on either side of the thalamus; one of the oldest parts of the human brain

• Regulates emotion and behaviors like feeding, mating, motivation, and emotional learning

• Major structures: hypothalamus, amygdala, and mammillary bodies (some sources also include thalamus and hippocampus)

Hypothalamus

regulates autonomic functions (heart rate, blood pressure, hunger, thirst, sexual arousal) via control of the pituitary gland (the "master gland")

Amygdala

• almond-shaped, deep within each temporal lobe; generates negative emotions (aggression, fear, anger, anxiety); involved in emotional memory/fear conditioning; a hyperactive amygdala can generate fear/anxiety to nonthreatening stimuli, contributing to anxiety disorders

• Mammillary bodies

• : small nuclei in front of the thalamus, connected to the hippocampi; involved in spatial/episodic memory; damage (e.g., Korsakoff syndrome, from thiamine deficiency/alcoholism) produces anterograde amnesia