pt2 Week 5 - Neurological Review and Alterations in Special Sensory Function

Neurological Review

corpus callosum

a dense tract of myelinated white matter fibers which internally connects longitudinal fissures

prefrontal cortex location and function

frontal lobe - coordinates complex cognitive behavior, intellectual functions, personality, social relationships, and impulse control

premotor cortex location and function

frontal lobe for coordinated skills, learned voluntary movements

primary motor cortex (precentral gyrus) location and function

frontal lobe - controls specific voluntary skeletal muscle movements via upper motor neurons (UMNs)

Broca’s area location and function

frontal lobe - base of the premotor area in the dominant (left) frontal lobe

Controls expressive speech

damage to Broca’s area

expressive (motor) aphasia—intact comprehension but struggle to articulate words

Primary Somatosensory Cortex (Postcentral Gyrus) location and function

parietal lobe - processes basic somatic sensations (touch, pain, pressure, temperature, position) across the body

Auditory & Olfactory Cortices location and function

temporal lobe - process hearing and smell input

Wernicke’s area location and function

posterior temporal lobe of dominant hemisphere - Integrates language comprehension

damage to Wernicke’s area

receptive (sensory) aphasia—fluent but meaningless speech with severe comprehension loss

Hippocampus location and function

temporal lobe - memory consolidation

Primary Visual Cortex & Visual Association Area location and function

occipital lobe - receives light stimuli and interprets visual objects

Basal Nuclei (Ganglia)

Subcortical clusters of gray matter forming part of the extrapyramidal motor system

Basal Nuclei (Ganglia) function

Coordinates skeletal muscle activity, modulates smooth movement, and suppresses unnecessary muscle contractions

movement control centre

Limbic System

A network of nuclei and fiber tracts surrounding the brainstem

Regulates emotional responses, feelings, and basic autonomic drives in conjunction with the hypothalamus

Diencephalon location

deep inside brain

Diencephalon components (3)

Thalamus, Hypothalamus, Epithalamus

Thalamus*

part of diencephalon - major sensory sorting and relay station for all incoming sensory impulses (except smell) destined for the cerebral cortex

Hypothalamus

central regulator of bodily homeostasis

Controls the autonomic nervous system, modulates the pituitary endocrine system, and regulates body temperature, fluid/food intake, sleep-wake cycles, stress responses, and emotional behavior.

Epithalamus

connection between the limbic system and other brain regions

Midbrain location

most superior (top) part of brainstem

Midbrain components, function

Contains the Reticular Activating System (RAS) - diffuse network of neurons throughout the brainstem that determines the level of cortical arousal, alertness, and consciousness

pons function

consists of dense fiber bundles acting as a bridge between the cerebellum and cerebrum

contains nuclei for several cranial nerves

Medulla Oblongata function

vital control center connecting the brain to the spinal cord. Houses vital cardiac, vasomotor (blood pressure), and respiratory control centers, alongside reflex centers for coughing, sneezing, swallowing, and vomiting

medulla oblongata features

pyramids - where decussation (crossover) of corticospinal motor tracts occurs, establishing contralateral motor control

Cerebellum location

posterior to the brainstem

cerebellum function

Integrates motor input from the pyramidal system with sensory feedback from muscle proprioceptors, visual pathways, and vestibular balance canals to maintain posture, equilibrium, and fine motor coordination

spinal cord span

medulla oblongata at the foramen magnum down to the lower border of the first lumbar vertebra (L₁), where it terminates as a bundle of nerve roots called the cauda equina

benefits of spinal cord termination at L1

allows clinicians to perform lumbar punctures safely in the subarachnoid space between L3 and L4 without risking cord puncture.

spinal cord inner gray matter

H-shaped core containing neuron cell bodies

Ventral (Anterior) Horns

part of inner gray matter - contains somatic motor neuron cell bodies whose axons exit via the ventral root

Dorsal (Posterior) Horns

part of inner gray matter - contains interneurons receiving sensory input from dorsal root ganglia

lateral horns

part of inner gray matter - contains visceral autonomic neurons

Ascending (Sensory) Tracts

part of outer white (myelinated) matter - transmit afferent impulses upward to the brain (e.g., spinothalamic tracts for pain and temperature; dorsal columns/fasciculus gracilis and cuneatus for touch, pressure, and proprioception).

Descending (Motor) Tracts

part of outer white matter - transmit efferent impulses downward from the brain (e.g., corticospinal/pyramidal tracts for voluntary motor control; extrapyramidal tracts for involuntary posture and coordination)

The Meningeal Layers outer to inner

dura, arachnoid, pia

dura mater

double-layered, tough fibrous membrane.

the two layers separate to form dural venous sinuses, which collect venous blood and circulating CSF for return to general circulation

The space above the dura is the epidural space, while the potential space beneath is the subdural space

Arachnoid Mater

Middle, web-like membrane. The space beneath is the subarachnoid space, which contains CSF and major cerebral blood vessels.

Vascular projections called arachnoid villi extend into the dural venous sinuses to reabsorb CSF

pia mater

Innermost, delicate, highly vascular connective tissue membrane that adheres directly to the brain and spinal cord convolutions

CSF function

clear, colorless liquid that cushions the CNS tissue, maintains buoyancy, and provides metabolic regulation

total circulating volume of CSF + daily production

approximately 125 to 150 mL, with 500 to 800 mL produced daily

normal CSF pressure

ranges between 9 and 14 mmHg (150 mmH₂O)

normal glucose CSF composition

45-75 mg/dL

normal protein CSF composition

15-45 mg/dL

normal sodium CSF composition

140 mEq/L

normal RBC CSF composition

zero

elevated RBC in CSF indication

CNS hemorrhage

cloudy CSF with elevated WBCs indication

bacterial meningitis

CSF circulation pathway*

CSF constantly secreted by vascular tissue choroid plexus in each of 4 ventricles

flows from lateral ventricle through Foramen of Monro into 3rd ventricle » Aqueduct of Sylvius into the fourth ventricle » exits 4th via Foramina of Luschka and Magendie into the subarachnoid space » circulates around brain/SC within subarachnoid space » reabsorbed through arachnoid villi into dural venous sinuses to re-enter systemic venous circulation

Intracranial Pressure (ICP) Equilibrium

rate of CSF production equals rate of reabsorption

what is obstruction to CSF resorption

fluid buildup and elevated ICP - hydrocephalus

blood supply to brain

by the internal carotid arteries (anterior circulation) and vertebral arteries (posterior circulation, uniting to form the basilar artery) » forms Circle of Willis at base of brain

autoregulation of cerebral arteries

location vasodilation occurs with elevated Co2, decreased pH or decreased BP to maintain constant O2/glucose

BBB

by impermeable brain capillary endothilal celss supported by astrocyte foot processes to limit passage of large molecules/toxins while allowing lipid-soluble substances and glucose to pass freely

BBB in neonates

poor developed, increased vulnerability to toxic injury (bilirubin encephalopathy)

Blood-CSF barrier

located at the choroid plexus, regulating the chemical composition of CSF

CN I functional type and function

olfactory

sensory

smell

CN II functional type and function

Optic

Sensory

Vision

CN III functional type and function

Oculomotor

Motor / Parasympathetic

Extrinsic eye movement (4 rectus/oblique muscles), upper eyelid elevation (levator palpebrae), parasympathetic pupil constriction & lens accommodation

CN IV functional type and function

Trochlear

Motor

Eye movement (superior oblique muscle; downward/inward movement)

CN V functional type and function

Trigeminal

Mixed

Sensory: facial, corneal, oral, and tooth sensation.

Motor: muscles of mastication (chewing)

CN VI functional type and function

Abducens

Motor

Eye movement (lateral rectus muscle; lateral abduction)

CN VII functional type and function

Facial

Mixed / Parasympathetic

Sensory: taste on anterior 2/3 of tongue. Motor: muscles of facial expression. Parasympathetic: lacrimal & salivary glands

CN VIII functional type and function

Vestibulocochlear

Sensory

Cochlear branch: hearing. Vestibular branch: equilibrium & balance

CN IX functional type and function

Glossopharyngeal

Mixed / Parasympathetic

Sensory: taste on posterior 1/3 of tongue, pharyngeal gag reflex, carotid baro/chemoreceptors. Motor: swallowing. Parasympathetic: parotid gland

CN X functional type and function

Vagus

Mixed / Parasympathetic

Sensory: visceral sensation. Motor: swallowing, speech. Parasympathetic: extensive innervation to heart, lungs, and GI viscera

CN XI functional type and function

Spinal Accessory

Motor

Shoulder elevation & head rotation (sternocleidomastoid & trapezius muscles)

CN XII functional type and function

Hypoglossal

Motor

Tongue movements for speech and swallowing

how many spinal nerves attach to SC

31 pairs

Ventral (Anterior) Root

Contains efferent motor nerve fibers arising from anterior horn motor neurons

Dorsal (Posterior) Root

Contains afferent sensory nerve fibers entering the dorsal horn. Cell bodies of sensory neurons are located in the dorsal root ganglion

cervical plexus C1-C5

Innervates neck muscles; gives rise to the critical phrenic nerve (C3-C5), which innervates the diaphragm for primary respiration

Brachial plexus C5-T1 innervation

shoulder, arm, hand

Lumbar and Sacral Plexuses (L1-S4) innervation

Innervates the lower abdomen, pelvis, and lower extremities.

reflex arc

sensory receptor » afferent neuron » CNS integration centre (SC/brainstem synapse) » efferent neuron » effector organ

cell body (soma)

Contains the nucleus and metabolic organelles. If the cell body dies, the entire neuron dies and cannot be replaced

Dendrites

Branching extensions acting as receptor sites, conducting electrical impulses toward the cell body (RECIEVE SIGNALS)

axon

A single long process conducting impulses away from the cell body toward an effector cell or postsynaptic neuron

axon insulation

lipid-rich myelin sheath, increases impulse conduction speed

PNS Myelination

formed by Schwann cells (wraps around single axon)

Unmyelinated gaps between Schwann cells are called Nodes of Ranvier

CNS Myelination

Formed by Oligodendrocytes, which extend processes to insulate multiple CNS axons simultaneously

Astroglia (Astrocytes)

glial cell in CNS - Link neurons to capillaries, provide physical/metabolic support, and maintain the Blood-Brain Barrier.

Oligodendroglia

glial cell in CNS - Synthesize myelin sheaths for CNS axons.

Microglia

glial cell in CNS - Phagocytic cells that remove pathogens and debris.

Ependymal Cells

glial cell in CNS - Line brain ventricles and form part of the choroid plexus

AP resting membrane potential

maintained by Na/K ATPase pump (3 Na out, 2 K in), maintains negative charge (-50 to -90)

AP depolarization

adequate stimulus increases membrane permeability to sodium causing influx. membrane reaches threshold ( around -40 mV) » full AP generated causing internal positive polarity

AP repolarization

Sodium channels close and potassium channels open, causing rapid K+ efflux » restore internal negative resting potential. Na/K pump restores baseline ionic concentrations

AP saltatory conduction

In myelinated fibers, insulation prevents ion leakage. Action potentials "jump" from one Node of Ranvier to the next, conducting impulses significantly faster than unmyelinated fibers

in what circumstance can regeneration occur in PNS

if a peripheral nerve axon is severed while the soma remains intact, regeneration can occur

axonal regeneration in PNS*

axon distant to injury degenerates and cleared by macrophages

proliferating Schwann form regeneration tube aligning with the original pathway

soma synthesizes proteins, new axonal growth buds that advance down the Schwann cell tube to re-establish effector connectionswhy

why is regeneration absent in CNS

oligodendrocyte inhibitory factors and glial cells which respond to damage and form scar around area - barrier preventing new axons to grow and connect

Sympathetic Division (SNS - "Fight-or-Flight") - origin and preganglionic fibres

T1-L2

Short fibers synapsing in two paravertebral ganglion chains along the spinal cord

Sympathetic Division (SNS - "Fight-or-Flight") - neurotransmitters

Preganglionic neurons release Acetylcholine onto nicotinic cholinergic receptors

Postganglionic neurons release Norepinephrine onto alpha and beta adrenergic receptors on target organs (exception: postganglionic sympathetic fibers to sweat glands release ACh).

Parasympathetic Division (PNS - "Rest-and-Digest") - origin and preganglionic fibres

Brainstem CN III, VII, IX, X and sacral spinal nerves S2-S4

Long fibers projecting to terminal ganglia located directly inside or near the target organ

Parasympathetic Division (PNS - "Rest-and-Digest") - neurotransmitters

preganglionic and postganglionic neurons release Acetylcholine

Preganglionic receptors are nicotinic; postganglionic receptors on effector organs are muscarinic cholinergic receptors

Sympathetic Stimulation signs

pupil dilation (mydriasis), tachycardia (increased heart rate and contractility), bronchodilator relaxation, systemic vasoconstriction, elevated BP, and inhibition of GI motility and urinary bladder contraction

parasympathetic Stimulation signs

Causes pupil constriction (miosis), bradycardia, bronchoconstriction, increased salivary and digestive gland secretions, enhanced GI peristalsis, and urinary bladder contraction