Fundamentals, Autonomic, and Central Nervous System Physiology

A comprehensive vocabulary review deck covering the structural and functional organization of the central and peripheral nervous systems, cellular components, action potential physiology, synaptic transmission, autonomic divisions, reflex arcs, the blood-brain barrier, CSF, and motor cortex pathways.

Central Nervous System (CNS)

The structural division of the nervous system comprising the brain and spinal cord, responsible for receiving, processing, and initiating responses.

Peripheral Nervous System (PNS)

The nervous system division consisting of nerves that connect the central nervous system to the rest of the body, split into sensory and motor divisions.

Somatic Sensory Fibers

Nerve fibers that carry sensory impulses to the central nervous system specifically from the skin, skeletal muscles, and joints.

Visceral Sensory Fibers

Nerve fibers that convey sensory impulses to the central nervous system from internal visceral organs.

Somatic Nervous System

The voluntary motor division of the peripheral nervous system that conducts impulses from the central nervous system to skeletal muscle effectors using a single heavily myelinated neuron.

Autonomic Nervous System (ANS)

The involuntary motor division of the peripheral nervous system that regulates cardiac muscle, smooth muscle, and glands using a two-neuron efferent pathway chain.

Sympathetic Division

The thoracolumbar 'fight or flight' branch of the autonomic nervous system (the 'E' division) that increases heart rate, dilates bronchioles, and elevates metabolic activity during exercise, excitement, emergency, or embarrassment.

Parasympathetic Division

The craniosacral 'rest or digest' branch of the autonomic nervous system (the 'D' division) that conserves energy and promotes digestion, defecation, and diuresis while keeping heart rate low.

Neurons

Excitable nerve cells that generate and transmit electrical signals throughout the body but are unable to divide or regenerate.

Neuroglia

Small, non-excitable supporting cells in the nervous system that protect, insulate, and support delicate neurons, and retain the ability to divide.

Astrocytes

Star-shaped neuroglial cells in the central nervous system whose foot processes secrete paracrines that promote tight junction formation in the blood-brain barrier.

Schwann Cells

Neuroglial cells in the peripheral nervous system responsible for forming the myelin sheath around peripheral axons.

Oligodendrocytes

Neuroglial cells in the central nervous system responsible for producing myelin sheaths around CNS axons.

Dendrites

Branching neuronal processes that receive incoming input signals from adjacent neurons and conduct them toward the cell body.

Axon

A long neuronal process that conducts action potentials away from the cell body toward terminal boutons to release neurotransmitters.

Sensory (Afferent) Neurons

Neurons that conduct impulses from sensory receptors toward the central nervous system, whose cell bodies reside in ganglia outside the CNS.

Association Neurons (Interneurons)

Neurons confined entirely to the central nervous system that integrate sensory input and decide on motor output actions.

Motor (Efferent) Neurons

Neurons that carry motor impulses outward from the central nervous system to effector organs such as muscles or glands.

Synapse

The specialized junction allowing transfer of information from one neuron to another neuron or to an effector cell.

Presynaptic Neuron

The neuron that conducts electrical signals toward a synapse and releases neurotransmitters into the synaptic cleft.

Postsynaptic Neuron

The neuron or effector cell located after a synapse that receives neurotransmitters and transmits signals away from the synaptic cleft.

Synaptic Cleft

The narrow fluid-filled space between the presynaptic neuron terminal and the postsynaptic neuron membrane.

Axodendritic Synapse

The most common structural synapse, formed between axon terminals of one neuron and dendrites of another neuron.

Axosomatic Synapse

A structural synapse formed between axon terminals of one neuron and the cell body (soma) of another neuron.

Action Potential Depolarization Phase

The rapid phase of a neuronal action potential caused by the inflow of sodium ions ($\text{Na}^+$) through voltage-gated channels.

Action Potential Repolarization Phase

The phase of a neuronal action potential characterized by the outflow of potassium ions ($\text{K}^+$) to restore resting negative membrane potential.

Myelin Sheath

A white, fatty protein-lipoid substance surrounding axons that acts as an electrical insulator and speeds up nerve impulse conduction.

Multiple Sclerosis

A demyelinating neurological condition where the myelin sheath is converted into hard, sclerotic patches, short-circuiting impulse transmission.

Saltatory Conduction

The rapid mechanism of action potential propagation in myelinated axons where electrical charge jumps from one node of Ranvier to the next.

Reflex Arc

A neural pathway mediating a reflex response, consisting of a sensory receptor, sensory neuron, association center, motor neuron, and effector.

Monosynaptic Reflex

A simple reflex arc containing only two neurons (sensory and motor) and a single synapse, such as the knee-jerk reflex.

Polysynaptic Reflex

A reflex arc involving more than two neurons (sensory, motor, and at least one interneuron) with multiple synapses.

Crossed Extensor Reflex

A complex somatic polysynaptic reflex where the stimulated side contracts flexors and relaxes extensors, while the opposite side relaxes flexors and contracts extensors.

Pupillary Light Reflex

An autonomic parasympathetic reflex resulting in $100\%$ direct pupillary constriction in the eye exposed to light and $50\%$ consensual constriction in the opposite eye.

Cholinergic Fibers

Nerve fibers that release acetylcholine (ACh), encompassing all preganglionic axons, all parasympathetic postganglionic axons, and somatic motor neurons.

Adrenergic Fibers

Nerve fibers that release norepinephrine (NE), including most sympathetic postganglionic axons.

Nicotinic Receptors

Cholinergic receptors found on neuromuscular junction sarcolemma, all autonomic ganglionic neurons, and adrenal medulla cells that produce stimulatory effects by opening ion channels.

Muscarinic Receptors

Cholinergic receptors present on all parasympathetic target organs, eccrine sweat glands, and select blood vessels that produce stimulatory or inhibitory effects depending on the subclass.

Hypothalamus

The main integration center ('the boss') of the autonomic nervous system that regulates heart activity, blood pressure, body temperature, water balance, and emotional drives.

Cerebrospinal Fluid (CSF)

A fluid secreted by the choroid plexus ($0.05\,\text{mL/min}$ in dogs; $0.015\,\text{mL/min}$ in cats) that cushions the central nervous system, provides buoyancy, nourishes tissues, and removes waste.

Blood-Brain Barrier (BBB)

A semi-permeable capillary membrane formed by endothelial tight junctions that blocks passage of most molecules larger than $500\,\text{Da}$, allowing only lipid-soluble compounds or specifically transported nutrients.

Primary Motor Cortex

Cerebral cortex region in the precentral gyrus composed of pyramidal cells that controls conscious, precise, skilled voluntary skeletal muscle movements on the contralateral body side.

Premotor Area

A motor region anterior to the precentral gyrus that creates movement plans, regulates motor coordination, and provides about $15\%$ of pyramidal tract fibers.

Supplementary Motor Area

A motor region functioning with the premotor area to initiate movements and command bilateral attitudinal movements of the head, eyes, and body.

Corticospinal (Pyramidal) Tract

The direct motor output pathway where $90\%$ of fibers decussate in the medulla and $10\%$ in the spinal cord to regulate fast, skilled voluntary movements.

Extrapyramidal Motor System

Indirect motor pathways involving the basal ganglia, cerebellum, and brainstem nuclei that modulate, smooth, and refine voluntary movement.

Basal Nuclei (Basal Ganglia)

Subcortical forebrain nuclei consisting of the caudate nucleus, putamen, and globus pallidus that inhibit unnecessary muscular movements and assist in starting and stopping motor activities.

Cerebellum

A brain structure that smoothes and coordinates body movements, evaluates the accuracy of initiated movement, and maintains equilibrium, posture, and balance.

Motor Homunculus

A somatotopic cortical map showing the relative proportion of motor cortex tissue devoted to controlling specific body regions, with over half assigned to hands and speech muscles.

Subdivisions of the Canine Brain

Anatomical structures of the canine brain including the cerebral hemispheres, basal ganglia, epithalamus, thalamus, hypothalamus, pituitary gland, midbrain, pons, medulla oblongata, and cerebellum.