BIOS 163: Anatomy and Physiology Chapter 9: Nervous System Study Guide

Comprehensive question-and-answer study flashcards covering Chapter 9: Nervous System, including cell types, neuroglia, impulse conduction, action potentials, synaptic transmission, CNS structures, meninges, spinal cord and brain anatomy, and the peripheral and autonomic nervous systems.

What two main types of cells make up the nervous system?

The nervous system contains specialized, communicating nerve cells called neurons and supporting cells called neuroglia.

What anatomical structures comprise the Central Nervous System (CNS) and Peripheral Nervous System (PNS)?

The Central Nervous System (CNS) is made up of the brain and spinal cord, while the Peripheral Nervous System (PNS) is made up of the cranial and spinal nerves.

What are the general functions of neuroglial cells?

They fill spaces, support neurons, provide structural frameworks, produce myelin, and carry on phagocytosis.

How many types of neuroglia are found in the CNS versus the PNS?

Four types are found in the central nervous system (CNS) and one main type is found in the peripheral nervous system (PNS).

What is the primary function of microglia?

Microglia are small cells that phagocytize bacterial cells and cellular debris.

What is the function of oligodendrocytes?

Oligodendrocytes form myelin in the central nervous system.

What are the roles of astrocytes in the nervous system?

Astrocytes lie near blood vessels to support structures, aid in metabolism, and respond to brain injury by filling in spaces.

What is the function and location of ependymal cells?

Ependymal cells cover choroid plexuses and form inner linings that enclose ventricles of the brain.

What is the function of Schwann cells in the PNS?

Schwann cells are the myelin-producing neuroglia of the peripheral nervous system.

What organelles and structures are contained within the soma (cell body) of a neuron?

The cell body contains mitochondria, lysosomes, a Golgi apparatus, chromatophilic substance (Nissl bodies) containing rough endoplasmic reticulum, and neurofibrils.

How do axons and dendrites differ in their functional direction of conduction?

Nerve fibers contain a solitary out-going axon that conducts impulses away, and numerous dendrites that bring in impulses from receptors.

What is the neurilemma and what is its specific function?

The neurilemma is the outer layer of covering in myelinated peripheral neurons; it helps guide the regeneration of damaged peripheral nerve axons to their original connection points.

What are the nodes of Ranvier?

Narrow gaps in the myelin sheath along an axon.

How are neurons classified structurally, and how do these types differ?

They differ by the number of processes extending from their cell bodies: multipolar neurons have many dendrites and one axon; bipolar neurons have two processes (one dendrite and one axon); unipolar neurons have a single process that divides into central and peripheral branches.

How are sensory neurons, interneurons, and motor neurons classified functionally?

Sensory neurons (afferent) conduct impulses from peripheral receptors to the CNS (usually unipolar, sometimes bipolar); interneurons are multipolar neurons within the CNS that link neurons; motor neurons are multipolar neurons that conduct impulses from the CNS to effectors.

What is a synapse and what is synaptic transmission?

A synapse is the junction between two communicating neurons separated by a synaptic cleft; synaptic transmission is the process by which an impulse in the presynaptic neuron is transmitted across the cleft to the postsynaptic neuron.

What events occur when a nerve impulse reaches the synaptic knob of an axon?

Calcium ions rush inward, prompting synaptic vesicles to fuse with the membrane and release neurotransmitters into the synaptic cleft, which then react with specific receptors on the postsynaptic membrane.

Why is a resting cell membrane polarized, and which ion contributes most to this polarization?

It is polarized due to an unequal distribution of positive and negative ions across the selective membrane channels; potassium ($K^+$) ions pass through more readily than sodium ($Na^+$) ions, making $K^+$ a major contributor.

How are sodium ($Na^+$) and potassium ($K^+$) ions distributed across a resting membrane, and what is the resting membrane potential?

Active transport maintains a greater concentration of $Na^+$ outside and a greater concentration of $K^+$ inside the membrane, resulting in an excess negative charge inside and a potential difference of about $-70\,mV$.

What does it mean that local potential changes in a neuron are graded?

It means the magnitude of the potential change is proportional to the intensity of the stimulus.

What happens when a neuron's membrane reaches threshold potential?

Reaching threshold potential triggers an action potential, reaching approximately $+30\,mV$.

What sequence of electrical changes occurs during an action potential?

The membrane undergoes depolarization, followed by repolarization, followed by a brief hyperpolarization, before returning to its resting potential.

How does conduction along an unmyelinated axon differ from conduction along a myelinated axon?

Unmyelinated axons conduct impulses over their entire membrane surface (continuous conduction), whereas myelinated axons conduct impulses from node of Ranvier to node of Ranvier (saltatory conduction), which is many times faster.

How does axon diameter affect the speed of an impulse?

The greater the diameter of an axon, the faster the impulse travels.

Why is an action potential described as an all-or-none response?

An action potential is not graded; a greater intensity of stimulation does not produce a stronger response, but instead produces more action potentials per second.

How do excitatory and inhibitory neurotransmitters differ in their mechanism of action?

Excitatory neurotransmitters increase postsynaptic membrane permeability to $Na^+$ to trigger impulses, whereas inhibitory neurotransmitters decrease membrane permeability to $Na^+$, reducing the chance of reaching threshold.

Why must neurotransmitters be decomposed by enzymes or removed from the synaptic cleft?

Destruction or removal of the neurotransmitter prevents continuous stimulation of the postsynaptic neuron.

What is facilitation within a neuronal pool?

A condition where a neuron receives subthreshold excitatory stimulation, making it more excitable to subsequent incoming stimulation.

What is the difference between convergence and divergence in neuronal pools?

Convergence occurs when a single neuron receives impulses from two or more fibers to summate them; divergence occurs when impulses leaving a neuron pass to several output fibers to amplify the impulse.

What are the definitions of sensory, motor, and mixed nerves?

Sensory nerves bring sensory information into the CNS; motor nerves carry impulses from the CNS to effectors; mixed nerves contain both sensory and motor fibers.

What are the components of a reflex arc?

A sensory receptor, a sensory neuron, one or more interneurons (reflex center), a motor neuron, and an effector.

What are the three layers of the meninges from outermost to innermost?

The dura mater (tough, dense connective tissue with blood vessels), the arachnoid mater (thin, web-like, lacking blood vessels), and the pia mater (thin, with many blood vessels and nerves).

Where are the epidural space and subarachnoid space located?

The epidural space separates the dura mater sheath around the spinal cord from vertebrae; the subarachnoid space is between the arachnoid mater and pia mater and contains cerebrospinal fluid (CSF).

Where is gray matter located in the spinal cord, and why does it appear gray?

It is located in a butterfly-shaped core in the center of the spinal cord; it appears gray because it houses unmyelinated interneurons and neuron cell bodies.

What are ascending and descending tracts of the spinal cord?

Ascending tracts carry sensory information up to the brain; descending tracts conduct motor impulses down from the brain.

What are the four major divisions of the brain?

The cerebrum, diencephalon, cerebellum, and brainstem.

What structure connects the two hemispheres of the cerebrum?

A broad, flat bundle of nerve fibers called the corpus callosum.

What terms describe the surface folds, shallow grooves, and deep grooves of the cerebrum?

Ridges are called gyri, shallow grooves are called sulci, and deep grooves are called fissures.

What are the five lobes of the cerebral hemispheres?

Frontal, parietal, temporal, occipital, and insula.

What is the cerebral cortex and what percentage of nervous system cell bodies does it house?

The cerebral cortex is a thin layer of gray matter on the outside of the cerebrum that contains $75\%$ of all cell bodies in the nervous system.

What are the primary functional locations of cutaneous, visual, auditory, and motor control in the cerebrum?

Cutaneous senses are in the parietal lobe; visual senses are in the occipital lobe; auditory senses are in the temporal lobe; primary motor areas are in the posterior frontal lobes (including Broca's area for speech).

Which cerebral hemisphere is dominant in $90\%$ of the population, and what does the non-dominant hemisphere specialize in?

The left hemisphere is dominant in $90\%$ of people; the non-dominant hemisphere specializes in nonverbal functions, body orientation in space, emotional intelligence, and intuitive thinking.

What are the functions of the basal nuclei (ganglia)?

They relay motor impulses from the cerebrum, help control motor activities by interacting with the motor cortex, thalamus, and cerebellum, and produce dopamine to facilitate voluntary movement.

How many ventricles exist in the brain, what fluid fills them, and what structure secretes it?

There are four ventricles filled with cerebrospinal fluid (CSF), which is secreted by choroid plexuses (specialized capillaries from the pia mater).

What are the primary functions of cerebrospinal fluid (CSF)?

It surrounds the brain and spinal cord to provide nutritive and protective (cushioning) functions.

What are the functions of the thalamus and hypothalamus?

The thalamus sorts and directs sensory information arriving from other parts of the nervous system; the hypothalamus maintains homeostasis by regulating visceral activities and linking the endocrine and nervous systems.

What is the function of the limbic system?

The limbic system controls emotional experience and expression.

What three structures make up the brainstem?

The midbrain, pons, and medulla oblongata.

What are the primary functions of the midbrain and pons?

The midbrain conveys impulses to/from higher brain centers and serves as a visual and auditory reflex center; the pons transmits impulses between the medulla oblongata and cerebrum and regulates the rate and depth of breathing.

What visceral control centers are located in the medulla oblongata?

Cardiac, vasomotor, and respiratory centers, as well as reflex centers for coughing, sneezing, swallowing, and vomiting.

What is the reticular formation and how does its activity level affect consciousness?

It is a network connected throughout small masses of gray matter across the brainstem; decreased activity results in sleep, while increased activity results in wakefulness.

How is gray and white matter arranged in the cerebellum, and what are the cerebellum's functions?

It has an outer thin layer of gray matter (cerebellar cortex) surrounding a white matter core (arbor vitae); it integrates sensory input regarding body position, coordinates skeletal muscle activity, and maintains posture.

How do the somatic and autonomic nervous systems differ in function?

The somatic system connects the CNS to skin and skeletal muscles to oversee conscious/voluntary activities; the autonomic system connects the CNS to viscera to oversee subconscious/involuntary activities.

How many pairs of cranial and spinal nerves are there, and what kind of fibers do spinal nerves contain?

There are $12$ pairs of cranial nerves and $31$ pairs of spinal nerves; all spinal nerves are mixed nerves.

Which spinal nerve roots contain sensory neurons and motor neurons?

Sensory neurons are located in the posterior (dorsal) root, and motor neurons arise in the anterior (ventral) root.

What are the two neurons in an autonomic motor pathway, and where is the second cell body located?

The pathway consists of a preganglionic fiber (leaves the CNS) and a postganglionic fiber (innervates the effector); the cell body of the second neuron is located in an autonomic ganglion in the PNS.

Where do fibers originate and synapse in the sympathetic versus parasympathetic divisions?

Sympathetic fibers arise from thoracic and lumbar spinal regions and synapse in paravertebral (chain) ganglia; parasympathetic fibers arise from the brainstem and sacral spinal cord and synapse in ganglia close to effector organs.

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

Preganglionic fibers of both divisions release acetylcholine (ACh); parasympathetic postganglionic fibers release acetylcholine (cholinergic); sympathetic postganglionic fibers release norepinephrine (adrenergic).

How do higher brain structures alter the reactions of the autonomic nervous system?

The limbic system and cerebral cortex alter autonomic reactions through emotional influence.