Nervous System: Spinal Tracts, Nerves, Reflexes, and Brain Anatomy

Vocabulary flashcards covering spinal tracts, nerve structure, reflexes, brain landmarks, and meninges based on the lecture transcript.

Decussation

The crossing over of nerve fibers from one side of the central nervous system to the other, such as from the right side of the spinal cord to the left side of the brain.

Contralateral tract

A nerve tract that decussates or crosses over to the opposite side of the central nervous system.

Ipsilateral tract

A nerve tract that does not cross over and remains on the same side of the central nervous system.

Ascending tracts

Tracts carrying sensory information upward to the brain, typically organized through a series of three neurons: first order, second order, and third order neurons.

First order neuron

A sensory neuron in an ascending tract that originates in the periphery, detects sensations such as touch, temperature, or pressure, and carries the signal into the spinal cord.

Second order neuron

A neuron in an ascending pathway that receives input from a first order neuron in the spinal cord or brainstem, crosses over, and carries sensory information up to the thalamus.

Thalamus

A brain structure shaped like a dumbbell, often called the gateway to consciousness, that receives incoming sensory information and regulates whether it passes to the cerebral cortex.

Third order neuron

A sensory neuron in an ascending pathway that conveys sensory information from the thalamus to the cerebral cortex for conscious awareness.

Descending tracts

Motor tracts carrying nerve signals downward from the brain through a two-neuron pathway consisting of an upper motor neuron and a lower motor neuron.

Upper motor neuron

A motor neuron in a descending tract that starts in the brain (such as the cerebral cortex or brainstem) and travels down toward a synapse in the brainstem or spinal cord.

Lower motor neuron

A motor neuron in a descending pathway that originates at a synapse in the brainstem or spinal cord and transmits the signal out to a peripheral muscle or gland.

Nerve fiber

The axon of a neuron, characterized as long and skinny.

Endoneurium

The layer of connective tissue that wraps and bundles each individual nerve fiber.

Perineurium

The connective tissue sheath that encloses a bundle of nerve fibers known as a fascicle.

Epineurium

The outermost layer of connective tissue that surrounds an entire nerve.

Mixed nerve

A nerve that contains both sensory (afferent) and motor (efferent) nerve fibers.

Ganglion

A cluster of neurosomas (cell bodies of neurons) located outside the central nervous system within the peripheral nervous system.

Neurosoma

The cell body of a neuron containing the nucleus.

Plexus

A complex, highly organized network where spinal nerves entering and exiting the spinal cord combine, rearrange, and branch out.

Dermatome

A specific area of the skin that conveys sensory input to an individual spinal nerve.

Reflex

A quick, involuntary, stereotyped reaction of a muscle or gland in response to a stimulus.

Somatic reflex

An involuntary, quick response to stimulation that involves skeletal muscles.

Visceral reflex

An involuntary reflex mediated by internal organs, whose effectors include glands, cardiac muscle, or smooth muscle.

Ipsilateral reflex

A reflex arc where the sensory stimulus and the resulting motor response occur on the same side of the body.

Contralateral reflex

A reflex arc where the motor response occurs on the opposite side of the body relative to the sensory stimulus.

Rostral

A directional anatomical term meaning toward the nose or forehead.

Caudal

A directional anatomical term meaning toward the tail, or toward the spinal cord in human neuroanatomy.

Cerebrum

The largest major division of the brain, composing approximately $83\%$ of brain volume and divided into two hemispheres.

Gyri

The elevated folds or hills on the surface of the cerebrum.

Sulci

The shallow grooves or valleys between the gyri on the cerebral surface.

Longitudinal fissure

The deep groove along the midline that separates the right and left cerebral hemispheres.

Brainstem

The smallest major division of the brain that regulates vital homeostatic processes such as heartbeat, respiratory rate, and body temperature; comprised of the diencephalon, midbrain, pons, and medulla oblongata.

Medulla oblongata

The most inferior part of the brainstem that transitions directly into the spinal cord at the foramen magnum.

Pons

The bulging structure of the brainstem positioned superior to the medulla oblongata.

Midbrain

The most superior division of the brainstem, situated above the pons.

Nuclei (central nervous system)

Clusters of neurosomas (cell bodies) located inside the central nervous system.

Dura mater

The tough, fibrous outermost layer of the cranial and spinal meninges.

Arachnoid mater

The spidery, web-like middle meningeal layer located deep to the dura mater.

Pia mater

The delicate, thin innermost meningeal layer that adheres directly to the surface of the brain and spinal cord.