Seeley's Essentials of Anatomy and Physiology - Chapter 8: Nervous System

Comprehensive vocabulary flashcards covering the structural organization, cellular physiology, electrophysiology, anatomy, reflex pathways, brain divisions, tracts, meninges, cranial nerves, and autonomic branches of the human nervous system based on Seeley's Essentials of Anatomy and Physiology, 11th Edition.

Central nervous system (CNS)

The major division of the nervous system consisting of the brain and spinal cord.

Peripheral nervous system (PNS)

The division of the nervous system consisting of all nervous tissue located outside the central nervous system.

Sensory division (afferent)

The division of the peripheral nervous system that conducts action potentials from sensory receptors toward the CNS.

Motor division (efferent)

The division of the peripheral nervous system that conducts action potentials from the CNS out to effector organs, such as muscles and glands.

Somatic nervous system

The subdivision of the motor division that transmits action potentials from the CNS directly to skeletal muscles.

Autonomic nervous system (ANS)

The subdivision of the motor division that transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands.

Enteric nervous system (ENS)

A unique neural network located entirely within the walls of the digestive tract capable of monitoring and controlling digestive activities independently through local reflexes.

Neuron

The functional cell type of the nervous system that receives stimuli and conducts action potentials.

Glial cells

Supportive, non-conductive cells of the nervous system that protect, nourish, and assist neurons.

Dendrite

A branching cytoplasmic extension of a neuron that receives input signals and conducts electrical signals toward the cell body.

Axon

A single, long cytoplasmic process that arises from the cell body and carries action potentials away from the cell body toward an effector or another neuron.

Multipolar neuron

A structural neuron type possessing many dendrites and a single axon; characteristic of most neurons in the CNS and nearly all motor neurons.

Bipolar neuron

A neuron with two extensions—one dendrite and one axon; found in specialized sensory structures such as the retina of the eye and the nasal cavity.

Pseudo-unipolar neuron

A neuron having a single short process extending from the cell body that bifurcates into two branches acting together as a single continuous axon.

Astrocytes

Star-shaped glial cells that provide major structural support in the CNS, regulate neuronal signaling, and contribute to the formation of the blood-brain barrier.

Ependymal cells

Glial cells that line fluid-filled brain ventricles and the central canal of the spinal cord to facilitate the production and circulation of cerebrospinal fluid.

Microglial cells

Specialized immune phagocytes within the CNS that engulf and digest cellular debris, wastes, and invading microbes.

Oligodendrocytes

Glial cells in the central nervous system that extend processes to form the myelin sheath around multiple axons.

Schwann cells

Glial cells in the peripheral nervous system that wrap repeatedly around individual axon segments to form the myelin sheath.

Myelin sheath

A multilayered insulating covering surrounding certain axons that dramatically reduces ion leakage and increases nerve impulse transmission speed.

Nodes of Ranvier

Gaps occurring approximately every millimeter along the myelin sheath where the axon membrane is exposed and ion exchange occurs.

Gray matter

Nervous tissue consisting mostly of neuron cell bodies, dendrites, and unmyelinated fibers, appearing gray due to the lack of myelin.

White matter

Nervous tissue composed of bundles of parallel, myelinated axons imparting a distinct whitish appearance.

Resting membrane potential

The electrical charge difference across the plasma membrane of an unstimulated cell, characterized by a negative charge inside relative to the outside.

Depolarization

A decrease in the membrane potential toward zero and into positive values caused by the rapid inward movement of $Na^+$ through opened voltage-gated channels.

Threshold

The critical membrane potential level that, once reached by local depolarization, triggers the opening of voltage-gated $Na^+$ channels to initiate an action potential.

Repolarization

The return of the membrane potential toward resting values driven by the closing of voltage-gated $Na^+$ channels and the opening of voltage-gated $K^+$ channels, letting $K^+$ exit the cell.

Hyperpolarization

A brief increase in membrane potential where the inside of the cell becomes more negative than its normal resting level due to prolonged $K^+$ outflow.

Continuous conduction

The relatively slow propagation of an action potential along every adjacent segment of an unmyelinated axon.

Saltatory conduction

The rapid jumping mode of action potential propagation along a myelinated axon from one node of Ranvier to the next.

Synapse

The specialized junction where the terminal end of an axon communicates with another neuron, muscle fiber, or gland cell.

Neurotransmitters

Chemical messengers synthesized in neurons and stored in synaptic vesicles that transmit signals across the synaptic cleft upon exocytosis.

Acetylcholinesterase

An enzyme located in the synaptic cleft that rapidly breaks down acetylcholine, halting post-synaptic excitation.

Converging pathway

A neuronal circuit arrangement where axons from two or more presynaptic neurons synapse with a single postsynaptic neuron.

Diverging pathway

A neuronal circuit arrangement where the axon of a single neuron divides to synapse with multiple postsynaptic neurons.

Ascending tracts

Bundles of sensory axons in the spinal cord white matter that transmit action potentials upward toward specific brain regions.

Descending tracts

Bundles of motor axons in the spinal cord white matter that carry motor impulses downward from the brain toward lower motor neurons or interneurons.

Posterior (dorsal) horn

The posterior gray matter column of the spinal cord that receives sensory axon terminals that synapse with interneurons.

Anterior (ventral) horn

The anterior gray matter region of the spinal cord containing cell bodies of somatic motor neurons.

Lateral horn

Gray matter projections in the thoracic and upper lumbar ($T_1$ to $L_2$) spinal cord segments containing cell bodies of autonomic motor neurons.

Reflex arc

The neural pathway underlying a reflex, typically comprising a sensory receptor, sensory neuron, interneuron, motor neuron, and an effector organ.

Stretch reflex

The simplest reflex arc occurring when a skeletal muscle automatically contracts in direct response to being stretched, exemplified by the knee-jerk reflex.

Withdrawal reflex

A flexor reflex initiated by pain receptors that causes rapid, involuntary contraction of flexor muscles to remove a body part from a noxious stimulus.

Phrenic nerve

A vital motor and sensory nerve arising from the cervical plexus ($C_1-C_4$) that supplies sensory and motor innervation to the diaphragm.

Dermatome

A specific cutaneous zone of skin supplied with sensory innervation by a single pair of spinal nerves (all except $C_1$).

Medulla oblongata

The most inferior segment of the brainstem, continuous with the spinal cord, containing pyramids for voluntary motor control and centers for vital functions like heart rate and respiration.

Pons

The brainstem region located superior to the medulla oblongata that functions as a relay bridge between the cerebrum and cerebellum and helps regulate breathing and chewing.

Midbrain

The most superior region of the brainstem, featuring four colliculi that coordinate auditory and visual reflexes and direct coordinated eye movements.

Reticular formation

A network of loosely clustered nuclei dispersed throughout the brainstem that maintains consciousness and regulates cyclical functions like sleep-wake cycles and respiration.

Cerebellum

The large posterior brain region attached by peduncles that coordinates voluntary movement, fine motor control, muscle tone, and balance.

Thalamus

The largest portion of the diencephalon; serves as an essential sensory relay center routing nearly all incoming sensory input up to the cerebral cortex.

Epithalamus

The superior diencephalic region containing the pineal gland, involved in emotional and visceral responses to odors and regulation of light-dark cycles.

Hypothalamus

The inferior diencephalic structure attached to the pituitary gland that serves as the main visceral control center regulating temperature, hunger, thirst, and autonomic homeostasis.

Corpus callosum

The broad, prominent band of white matter tracts connecting and conveying communications between the left and right cerebral hemispheres.

Frontal lobe

The anterior lobe of the cerebrum responsible for voluntary motor output, speech production, motivation, planning, mood, and aggression.

Parietal lobe

The superior cerebral lobe responsible for evaluating and integrating somatic sensory information like touch, pressure, temperature, pain, and taste.

Occipital lobe

The posterior cerebral lobe dedicated primarily to receiving, integrating, and interpreting visual inputs.

Temporal lobe

The lateral cerebral lobe responsible for auditory perception, olfaction, and memory formation.

Primary somatosensory cortex

The postcentral gyrus of the parietal lobe where ascending sensory signals terminate and somatic sensations are consciously perceived.

Primary motor cortex

The precentral gyrus of the frontal lobe that initiates action potentials for controlling voluntary skeletal muscle movement.

Premotor area

The region of the frontal lobe located anterior to the primary motor cortex where voluntary movements are organized and sequenced prior to execution.

Prefrontal area

The anterior frontal lobe association region responsible for motivation, foresight, emotional judgment, and planning movement.

Wernicke area

The sensory speech region located within the parietal lobe essential for the comprehension and understanding of spoken and written language.

Broca area

The motor speech area located within the frontal lobe responsible for executing the motor actions necessary to articulate words.

Consolidation

The gradual neurobiological process of converting short-term memories into permanent long-term memories through the formation of stronger synaptic connections.

Declarative memory

Explicit memory governing the conscious recall of facts, dates, events, names, and places along with associated emotions.

Procedural memory

Reflexive or implicit memory governing the retention and automatic execution of motor skills, such as riding a bicycle.

Limbic system

A functional group of deep cerebral and diencephalic structures that regulate emotion, emotional responses to odors, mood, and memory formation.

Dura mater

The tough, fibrous, outermost meningeal layer surrounding and protecting the brain and spinal cord.

Arachnoid mater

The thin, web-like intermediate meningeal layer situated between the dura mater and pia mater.

Pia mater

The delicate, vascular innermost meningeal membrane bound tightly to the surface contours of the brain and spinal cord.

Subarachnoid space

The fluid-filled space located between the arachnoid mater and the pia mater that contains blood vessels and circulating cerebrospinal fluid.

Cerebrospinal fluid (CSF)

A clear, protective cushion-forming fluid produced by ependymal cells in the choroid plexuses that circulates through ventricles and the subarachnoid space.

Arachnoid granulations

Specialized projections of arachnoid tissue that penetrate into the superior sagittal sinus to allow drainage of CSF into venous blood.

Cranial Nerve I (Olfactory)

A sensory cranial nerve responsible for transmitting the sense of smell to the brain.

Cranial Nerve II (Optic)

A sensory cranial nerve dedicated entirely to transmitting visual signals from the retina to the brain.

Cranial Nerve III (Oculomotor)

A motor cranial nerve responsible for controlling extraocular muscles that direct eye movement as well as pupillary constriction.

Cranial Nerve IV (Trochlear)

A motor cranial nerve that innervates the superior oblique muscle to direct eye movement.

Cranial Nerve V (Trigeminal)

A mixed cranial nerve mediating facial, eye, and jaw sensory input, while providing motor drive to the muscles of chewing.

Cranial Nerve VI (Abducens)

A motor cranial nerve that innervates the lateral rectus muscle to abduct the eyeball laterally.

Cranial Nerve VII (Facial)

A mixed cranial nerve responsible for motor control of facial expression muscles and taste sensation from the tongue.

Cranial Nerve VIII (Vestibulocochlear)

A sensory cranial nerve carrying auditory sensations and vestibular inputs regarding balance and equilibrium.

Cranial Nerve IX (Glossopharyngeal)

A mixed cranial nerve providing taste sensation from the posterior tongue and motor control to muscles involved in swallowing.

Cranial Nerve X (Vagus)

A major mixed cranial nerve providing extensive sensory and parasympathetic motor innervation to organs of the thorax and abdomen.

Cranial Nerve XI (Accessory)

A motor cranial nerve controlling the sternocleidomastoid, trapezius, and select laryngeal muscles.

Cranial Nerve XII (Hypoglossal)

A motor cranial nerve that provides somatic motor innervation to intrinsic and extrinsic muscles of the tongue.

Preganglionic neuron

The first efferent neuron of the autonomic pathway, having its cell body inside the CNS and synapsing with a postganglionic neuron in a peripheral autonomic ganglion.

Postganglionic neuron

The second neuron of the autonomic pathway, having its cell body within an autonomic ganglion and projecting its axon to an effector organ.