Nervous System, Neurophysiology, Spinal Cord, and Brain Comprehensive Review

Comprehensive practice flashcards covering human nervous system organization, neuroglia, action potential neurophysiology, spinal cord anatomy, spinal reflex arcs, peripheral nerve plexuses, brain structures, and cranial nerves.

What are the structural components of the Central Nervous System (CNS) and Peripheral Nervous System (PNS), and how is the PNS motor division subdivided?

The CNS consists of the brain and spinal cord. The PNS consists of sensory receptors and nerves outside the CNS. The PNS motor division is subdivided into the Somatic nervous system (controls skeletal muscle) and the Autonomic nervous system (controls cardiac muscle, smooth muscle, and glands, further divided into sympathetic and parasympathetic divisions).

What are the transport speeds, directional flows, and motor proteins associated with fast versus slow axonal transport?

Anterograde transport moves organelles and materials from the soma toward axon terminals via kinesin motor proteins (fast transport up to $400\,\text{mm/day}$). Retrograde transport moves materials from terminals toward the soma via cytoplasmic dynein motor proteins. Slow axonal transport moves dissolved proteins in the cytoplasm at $1\text{--}8\,\text{mm/day}$.

How do neurotropic pathogens such as Rabies virus and Herpes simplex virus (HSV) reach the central nervous system?

They infect peripheral nerve endings or mucosal epithelial cells and utilize retrograde axonal transport to travel up the axon directly into the neuron cell body and CNS.

What are the primary functions of astrocytes and ependymal cells in the central nervous system?

Astrocytes form the Blood-Brain Barrier (BBB) via tight junctions on endothelial cells, regulate extracellular $\text{K}^+$ levels, and produce neurotrophic factors. Ependymal cells line brain ventricles and the central canal of the spinal cord; together with capillaries, they form the choroid plexus, which secretes cerebrospinal fluid (CSF).

Based on the provided diagram of peripheral neuroglial cells, what are the two cell types shown and their respective functions?

1. Satellite cells: surround neuron cell bodies in PNS ganglia, providing support, nutrition, and protection against heavy metals (lead, mercury). 2. Schwann cells: form the myelin sheath around a single axon in the PNS.

Why is L-DOPA (levodopa) administered to treat Parkinson's disease instead of direct dopamine?

Parkinson's disease is caused by the death of dopamine-producing neurons. Dopamine cannot cross the Blood-Brain Barrier (BBB). L-DOPA, an amino acid precursor, crosses the BBB via amino acid transporters and is subsequently converted into dopamine in the brain.

What cell type is targeted in Multiple Sclerosis (MS), and what is the functional outcome of this condition?

Multiple Sclerosis is an autoimmune demyelinating disease where the immune system destroys oligodendrocytes in the CNS. This results in scarring (sclerosis), slowing of electrical signaling, muscle weakness, and reduced coordination.

What specific voltage values define the resting membrane potential, threshold potential, and peak depolarization in a neuron?

Resting membrane potential is $-70\,mV$; threshold potential to trigger an action potential is $-55\,mV$; peak depolarization during an action potential reaches $+35\,mV$.

What ion movements occur during the depolarization and repolarization phases of an action potential?

During depolarization, voltage-gated $\text{Na}^+$ channels open, allowing $\text{Na}^+$ to diffuse into the cell. During repolarization, $\text{Na}^+$ channels close and voltage-gated $\text{K}^+$ channels fully open, allowing $\text{K}^+$ to diffuse out of the cell.

What distinguishes the absolute refractory period from the relative refractory period?

During the absolute refractory period, the plasma membrane cannot produce a second action potential regardless of stimulus strength. During the relative refractory period, a second action potential can be triggered only by a stronger-than-threshold stimulus.

How do continuous conduction and saltatory conduction differ, and what factors increase action potential propagation speed?

Continuous conduction occurs along unmyelinated axons as every point on the membrane must be stimulated. Saltatory conduction occurs along myelinated axons as action potentials jump from one node of Ranvier to the next. Propagation speed is increased by thicker myelin sheaths and larger axon diameters.

What sequence of events takes place at a chemical synapse after an action potential reaches the presynaptic terminal?

1. Action potential reaches presynaptic terminal. 2. Voltage-gated $\text{Ca}^{2+}$ channels open and $\text{Ca}^{2+}$ enters. 3. Neurotransmitters are released from synaptic vesicles into the synaptic cleft via exocytosis. 4. Neurotransmitters diffuse across the cleft. 5. Neurotransmitters bind to specific receptors (chemically-gated channels) on the postsynaptic cell membrane.

What is the functional difference between spatial summation and temporal summation?

Spatial summation occurs when multiple action potentials from different presynaptic neurons arrive simultaneously at the same postsynaptic neuron. Temporal summation occurs when action potentials from a single presynaptic neuron fire in rapid succession to summate on the postsynaptic neuron.

As depicted in diagrams (c) and (d), what are these two complex neuronal circuits and their functional roles?

Diagram (c) represents a Reverberating circuit (a positive-feedback loop responsible for repetitive or rhythmic activities like breathing). Diagram (d) represents a Parallel after-discharge circuit (neurons stimulate multiple parallel pathways that converge on one output cell, utilized in complex thought).

Where does the spinal cord terminate superiorly and inferiorly, and what is its tapered end called?

The spinal cord begins superiorly at the level of the foramen magnum and terminates inferiorly at the level of the second lumbar vertebra ($L2$) as a tapered structure called the conus medullaris.

What are the spinal cord meninges and surrounding spaces in order from superficial to deep?

1. Epidural space (contains blood vessels and areolar connective tissue) 2. Dura mater (tough outer layer) 3. Subdural space (contains serous fluid) 4. Arachnoid mater (thin and wispy) 5. Subarachnoid space (contains CSF and blood vessels) 6. Pia mater (bound tightly to the spinal cord surface).

What are the five essential steps of a reflex arc pathway?

1. Sensory receptor detects stimulus -> 2. Sensory neuron action potential travels through dorsal root -> 3. Integration center in spinal cord (often involving an interneuron) -> 4. Motor neuron receives signal -> 5. Motor neuron action potential travels through ventral root to effector muscle or gland.

How does the Golgi tendon reflex protect contracting muscles and tendons from damage?

Golgi tendon organs (nerve endings in collagen in tendons near muscle) detect excessive tension and stimulate interneurons to release inhibitory neurotransmitters, producing sudden relaxation of the contracting muscle.

How do reciprocal innervation and the crossed extensor reflex coordinate during a painful stimulus to a lower limb?

Reciprocal innervation causes opposing muscles to relax while flexor muscles contract to withdraw the affected limb. Simultaneously, the crossed extensor reflex acts on the opposite side of the body, contracting extensor muscles in the uninjured lower limb to shift body weight and prevent falling.

Which spinal nerve originates from the cervical plexus ($C1\text{--}C4$) to innervate the diaphragm, and what reflex is triggered by its irritation?

The phrenic nerve originates from the cervical plexus ($C1\text{--}C4$) to innervate the diaphragm; its irritation triggers the hiccup reflex.

What five major nerve branches arise from the brachial plexus ($C5\text{--}T1$)?

1. Axillary nerve 2. Radial nerve 3. Musculocutaneous nerve 4. Ulnar nerve ('funny bone' injury site) 5. Median nerve (travels through the carpal tunnel).

What is the largest nerve in the body, and from which plexus does it arise?

The sciatic nerve, which originates from the lumbosacral plexus ($L1\text{--}S4$).

What pathogen causes shingles, and why is the outbreak localized to specific dermatomes?

Shingles is caused by reactivation of dormant varicella zoster virus (VZV) located in dorsal root ganglia or cranial nerves. Reactivated virus travels along sensory axons to cause a painful rash restricted to the specific dermatome supplied by those nerves.

What vital autonomic centers are housed in the medulla oblongata, and what structural feature occurs there?

The medulla oblongata contains vital centers controlling heartbeat, breathing rate, and blood vessel diameter, and coordinates swallowing, vomiting, coughing, and sneezing. It is the site where descending motor tracts decussate (cross over).

What are the respective roles of the superior colliculi and inferior colliculi located on the dorsal midbrain?

The two superior colliculi direct reflex movements of the head toward visual, auditory, or tactile stimuli. The two inferior colliculi are involved in auditory processing and hearing.

What are Purkinje cells, where are they located, and what is their functional role?

Purkinje cells are the largest inhibitory neurons in the CNS. They are located in the cerebellar cortex and function to coordinate voluntary muscle movements, posture, and balance.

What are the three components of the diencephalon and their primary functions?

1. Thalamus: sensory relay center for all sensory information (except smell) heading to the cerebrum. 2. Epithalamus: contains the pineal gland (produces melatonin for sleep-wake cycles) and habenula (motivational control of behavior). 3. Hypothalamus: central regulator of the endocrine system (controls pituitary gland via infundibulum) and autonomic controller for homeostasis, heart rate, and body temperature.

In the provided left cerebral hemisphere diagram, what two functional speech areas are highlighted and what functional deficits occur from lesions to each?

1. Broca's area (blue, left frontal lobe): controls motor speech output; damage causes Broca's aphasia (impaired speech production, but comprehension remains intact). 2. Wernicke's area (red, left temporal lobe): controls language comprehension; damage causes Wernicke's aphasia (impaired comprehension, producing fluent but meaningless speech).

What three types of myelinated nerve fibers compose the cerebral medulla?

1. Association fibers: connect different areas within the same cerebral hemisphere. 2. Commissural fibers: connect corresponding areas between left and right hemispheres (largest is corpus callosum). 3. Projection fibers: connect the cerebrum with lower brain regions and the spinal cord.

What are the basal nuclei, and what processes do they help regulate?

Basal nuclei are large clusters of gray matter (cell bodies) located in the cerebrum, diencephalon, and midbrain. They function in organizing/planning/coordinating voluntary movement, evaluating risk in decision-making, procedural/habit learning, and thinking.

Which cranial nerve provides sensory innervation to the face through three distinct branches ($V_1$, $V_2$, $V_3$) and motor control to muscles of mastication?

Cranial Nerve V (Trigeminal nerve), which branches into the Ophthalmic ($V_1$), Maxillary ($V_2$), and Mandibular ($V_3$) nerves.

Which cranial nerve is the longest in the body, extends into the chest and abdomen, and provides parasympathetic control to viscera?

Cranial Nerve X (Vagus nerve). It provides sensory coverage to the inferior pharynx, larynx, and thoracic/abdominal viscera, and motor control for soft palate, throat, voice production, and autonomic regulation of heart, lungs, and GI tract.