Central, Peripheral, and Autonomic Nervous Systems

Comprehensive practice flashcards covering the Central Nervous System (CNS), Peripheral Nervous System (PNS), and Autonomic Nervous System (ANS), including functional brain localization, spinal cord tracts and reflexes, cranial and spinal nerves, and autonomic neurotransmission.

What are the three primary brain vesicles that arise from the embryonic neural tube?

The three primary brain vesicles are the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).

Which four major adult brain structures develop from the secondary brain vesicles?

The secondary brain vesicles give rise to the cerebral hemispheres, diencephalon (thalamus, hypothalamus, epithalamus), brain stem (midbrain, pons, medulla oblongata), and cerebellum.

What proportion of total brain mass is accounted for by the cerebral hemispheres?

The cerebral hemispheres make up about $85\%$ of total brain mass.

How are gyri, sulci, and fissures defined in the cerebrum?

A gyrus is an elevated ridge of tissue, a sulcus is a shallow groove, and a fissure is a deeper groove.

Which sulcus separates the frontal lobe from the parietal lobe?

The central sulcus separates the frontal lobe from the parietal lobe, bordered anteriorly by the precentral gyrus and posteriorly by the postcentral gyrus.

Where is the insular lobe (insula) located?

The insula is located deep to the temporal lobe within the lateral sulcus.

What are the three basic structural regions found within each cerebral hemisphere?

The three basic regions are the superficial cerebral cortex of grey matter, internal white matter, and deep islands of grey matter termed basal nuclei.

What are the physical dimensions and histological composition of the cerebral cortex?

The cerebral cortex is composed entirely of grey matter (interneurons) and is very thin, measuring approximately $2\text{--}4\text{ mm}$ ($1/8\text{th}$ inch) thick.

What are the functional differences and locations of Broca's area and Wernicke's area?

Broca's area (motor speech area) is located in the inferolateral frontal lobe of one hemisphere and controls the muscle movements required to produce speech; Wernicke's area (sensory speech area) is located between the parietal and temporal lobes and is responsible for understanding speech.

Why do the face and fingertips occupy the largest regions of the somatosensory homunculus?

The relative amount of cortical area devoted to a body region reflects its sensitivity and receptor density rather than its physical size; humans have the highest concentration of sensory receptors in the face and fingertips.

Where are the primary cortical receiving areas for vision, hearing, smell, and taste located?

Primary visual cortex is in the posterior occipital lobe; primary auditory cortex is in the superior margin of the temporal lobe; primary olfactory cortex is on the medial aspect of the temporal lobe; gustatory cortex is in the insula lobe.

What cognitive processes are governed by the prefrontal cortex (anterior association area), and when does it complete development?

The prefrontal cortex governs intellect, complex cognition, recall (working memory), personality, abstract ideas, judgment, reasoning, persistence, and planning; it is not fully developed until around age $25$.

How do association fibers, commissural fibers, and projection fibers differ in cerebral white matter?

Association fibers connect different parts of the same hemisphere; commissural fibers (such as the corpus callosum) connect corresponding grey areas of the two hemispheres; projection fibers connect the cerebral cortex to lower brain or spinal cord centers.

Why is the thalamus referred to as the 'gateway to the cerebral cortex'?

Afferent sensory impulses from all senses and parts of the body converge on the thalamus, where information is sorted, edited, and grouped before being relayed to the appropriate cerebral cortical domains.

What major visceral and homeostatic roles are mediated by the hypothalamus?

The hypothalamus regulates the autonomic nervous system, controls endocrine hormone release via the pituitary gland (connected by the infundibulum), initiates physical emotional responses, sets body temperature, regulates sleep-wake cycles, controls water balance and thirst, and regulates food intake.

Which endocrine gland is located in the epithalamus, and what hormone does it produce?

The epithalamus contains the pineal gland, which secretes melatonin to signal sleepiness and help regulate the sleep-wake cycle.

What are the two pigmented nuclei found within the midbrain, and what is their role?

The midbrain contains the substantia nigra (which produces dopamine) and the red nucleus.

What vital autonomic centers are situated within the medulla oblongata?

The medulla contains the cardiovascular center (adjusts force and rate of heart contractions), vasomotor center (regulates blood pressure), and respiratory centers (generate respiratory rhythm and regulate rate/depth), alongside reflex centers for vomiting, coughing, hiccupping, swallowing, and sneezing.

How does the cerebellum coordinate somatic motor movements?

The cerebellum receives input from joint, visual, and equilibrium receptors to assess body position, and then transmits a coordinating 'blueprint' to the cerebral motor cortex to maintain balance, muscle tone, and smooth fine/gross motor movements.

What are the primary structures and functions of the limbic system?

The limbic system includes the amygdaloid body and hippocampus; it functions in emotions, memory, motivation, and learning, relaying most output through the hypothalamus and interacting with the prefrontal lobes.

What is the function of the reticular activating system (RAS)?

The RAS maintains alertness and consciousness by filtering out repetitive, familiar, or weak sensory signals while alerting the cortex to unusual, significant, or strong impulses.

Which class of EEG brain waves, shown in the lowest trace, displays high amplitude and low frequency during deep sleep?

Delta waves, which are characteristic of deep NREM Stage $3$ sleep.

How do physiological conditions in NREM Stage 3 sleep differ from REM sleep?

In NREM Stage $3$, vital signs decline, delta waves predominate, and tissue growth/repair occurs; in REM sleep, heart rate and breathing increase, dreams predominate, memory consolidation occurs, and most skeletal muscles (except eye muscles and the diaphragm) are actively inhibited.

What are the three meningeal layers of the central nervous system from superficial to deep?

Dura mater (consisting of periosteal and meningeal fibrous layers), arachnoid mater (separated by the subarachnoid space containing CSF), and delicate pia mater (clinging tightly to the CNS surface).

How is cerebrospinal fluid (CSF) produced and returned to systemic circulation?

CSF is continuously filtered from blood capillaries within the choroid plexuses of each ventricle, circulated through the ventricles and subarachnoid space, and reabsorbed into the dural venous sinuses via arachnoid granulations.

What are the two structural layers that constitute the blood-brain barrier?

The inner layer is composed of capillary endothelial cells joined by tight junctions, and the outer layer consists of the bulbous foot processes of astrocytes.

At what vertebral level does the adult spinal cord end, and what structures anchor it inferiorly?

The spinal cord terminates in the conus medullaris between vertebrae $L_1$ and $L_2$; it is anchored to the coccyx by the fibrous filum terminale and secured laterally to the dura mater by denticulate ligaments.

How are neuronal cell bodies segregated within the grey matter horns of the spinal cord?

Dorsal horns contain interneurons; ventral horns house somatic motor neurons; lateral horns (present in thoracic and lumbar regions) contain autonomic (visceral motor) neurons.

What roles do first-, second-, and third-order neurons play in ascending sensory pathways?

First-order neurons have cell bodies in the dorsal root ganglion and transmit impulses from peripheral receptors to the spinal cord; second-order neurons reside in the dorsal horn and ascend to the thalamus or cerebellum; third-order neurons reside in the thalamus and project to the primary somatosensory cortex.

What neurological damage differentiates flaccid paralysis from spastic paralysis?

Flaccid paralysis occurs when lower motor neurons in the spinal cord/ventral roots are damaged, resulting in complete lack of muscle stimulation; spastic paralysis occurs with damage to upper motor neurons in the brain, leaving spinal reflex arcs intact to produce irregular muscle contractions.

What are the five sensory receptor classes categorized by stimulus modality?

Mechanoreceptors (mechanical force/touch/pressure/stretch), thermoreceptors (temperature), photoreceptors (light), chemoreceptors (chemicals in solution), and nociceptors (damaging stimuli resulting in pain).

Which encapsulated sensory receptors act as mechanoreceptors for light touch, deep pressure/vibration, and continuous pressure?

Tactile (Meissner's) corpuscles respond to light touch; lamellar (Pacinian) corpuscles respond to deep pressure and vibration; bulbous corpuscles (Ruffini endings) respond to deep and continuous pressure.

What is the difference between pain threshold and pain tolerance?

Pain threshold is the stimulus intensity at which pain begins to be felt (receptor activation); pain tolerance is the maximum level of pain an individual is able to endure before attempting to stop it.

What clinical phenomenon is illustrated here, where visceral pain from internal organs is perceived at distant superficial skin sites?

Referred pain, caused by visceral sensory fibers travelling along the same spinal cord pathways ($T_1\text{--}T_5$) as somatic sensory fibers, leading the brain to interpret the stimulus as coming from somatic dermatomes (such as pain radiating down the left arm during a myocardial infarction).

How do neuromuscular junctions differ from autonomic varicosities at target tissues?

Neuromuscular junctions feature specific axon terminals synapsing individually onto skeletal muscle fibers to release acetylcholine; autonomic varicosities are series of swellings along postganglionic axons that release neurotransmitters diffusely over sheets of smooth muscle or glands.

How do the stretch reflex and the tendon reflex differ in their sensory receptors and motor outcomes?

The stretch reflex is initiated by muscle spindles in response to muscle elongation and triggers contraction of the stretched muscle (with reciprocal inhibition of antagonists); the tendon reflex is initiated by high-threshold tendon organs in response to muscle tension and triggers relaxation of the contracting muscle (with reciprocal activation of antagonists).

Which cranial nerves exit directly from the cerebrum rather than the brain stem?

Cranial Nerve I (Olfactory nerve) and Cranial Nerve II (Optic nerve).

Which four cranial nerves carry parasympathetic autonomic motor fibers?

Cranial nerves III (Oculomotor), VII (Facial), IX (Glossopharyngeal), and X (Vagus).

Which three cranial nerves control movements of the extrinsic eye muscles?

Cranial Nerve III (Oculomotor), Cranial Nerve IV (Trochlear), and Cranial Nerve VI (Abducens).

What are the three branches of Cranial Nerve V (Trigeminal), and which foramina do they pass through?

Ophthalmic ($V_1$) exits via the superior orbital fissure; maxillary ($V_2$) exits via the foramen rotundum; mandibular ($V_3$) exits via the foramen ovale.

What neurological condition resulting from Cranial Nerve VII impairment is illustrated below?

Bell's palsy, characterized by rapid onset of facial nerve (CN VII) paralysis leading to unilateral facial sagging, asymmetrical smile, and inability to close the eye.

What distinction makes Cranial Nerve X (Vagus nerve) unique among all cranial nerves?

It is the only cranial nerve that extends beyond the head and neck, passing through the jugular foramen to supply widespread parasympathetic innervation to thoracic and abdominal viscera.

What are the roots and principal muscular target of the phrenic nerve?

The phrenic nerve arises from the cervical plexus ($C_3\text{--}C_5$, primarily $C_1\text{--}C_4$ plexus network) and provides motor innervation to the diaphragm.

What five major peripheral nerves emerge from the brachial plexus ($C_5\text{--}T_1$)?

The axillary, musculocutaneous, radial, median, and ulnar nerves.

Which two major nerves arise from the lumbar plexus ($L_1\text{--}L_4$)?

The femoral nerve and the obturator nerve.

Which major peripheral nerve arises from the sacral plexus ($L_4\text{--}S_4$) to serve the posterior lower limb?

The sciatic nerve (composed of the tibial and common fibular nerves).

Which visceral structures receive innervation exclusively from the sympathetic division?

Sweat glands, arrector pili muscles of the skin, and smooth muscle within systemic blood vessel walls.

How do the motor pathways of the somatic and autonomic nervous systems differ architecturally?

The somatic system uses a single, heavily myelinated motor neuron extending from the CNS directly to skeletal muscle; the autonomic system utilizes a two-neuron chain consisting of a lightly myelinated preganglionic axon synapsing in a ganglion onto an unmyelinated postganglionic axon extending to visceral effectors.

How do origin sites, relative fiber lengths, and ganglion locations differ between parasympathetic and sympathetic divisions?

Parasympathetic fibers are craniosacral, having long preganglionic and short postganglionic fibers with ganglia located within or near visceral target organs; sympathetic fibers are thoracolumbar ($T_1\text{--}L_2$), having short preganglionic and long postganglionic fibers with ganglia located close to the spinal cord in the sympathetic trunk or collateral ganglia.

Which neurotransmitters are released by preganglionic and postganglionic fibers across the ANS?

All autonomic preganglionic axons release acetylcholine (ACh); all parasympathetic postganglionic axons release ACh; almost all sympathetic postganglionic axons release norepinephrine (NE).

What are the two major subclasses of cholinergic receptors, and how are they named?

Nicotinic and muscarinic receptors; they are named after the exogenous drugs (nicotine and muscarine) that bind and mimic acetylcholine at those receptor sites.

What are the major classes and subclasses of adrenergic receptors?

Alpha (subdivided into $\alpha_1$ and $\alpha_2$) and Beta (subdivided into $\beta_1$, $\beta_2$, and $\beta_3$) receptors.

How do sympathetic and parasympathetic inputs oppositely affect the heart and pulmonary airways?

Sympathetic stimulation increases heart rate and force of contraction and dilates bronchioles; parasympathetic stimulation decreases heart rate and force of contraction and constricts airways slightly.

What antagonistic actions do sympathetic and parasympathetic divisions have on the digestive tract and liver?

Parasympathetic activity promotes gastrointestinal motility, increases digestive secretions, and stimulates glycogen synthesis; sympathetic activity decreases motility and glandular secretion while promoting glycogen breakdown into glucose.

How does sympathetic activity maintain and regulate systemic blood pressure?

Sympathetic vasomotor fibers maintain continuous vascular tone; increased firing causes vasoconstriction and elevates blood pressure, while decreased firing causes vasodilation and lowers blood pressure.