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Lecture 15 - Central Nervous System I
Spinal Cord, Descending and Ascending Tracts, Spinal Reflexes
60
Anatomy
Undergraduate 1
10/25/2010

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Term
Spinal nerves
Definition
The spinal cord contains motor and sensory neurons connected with limbs and trunk by means of the spinal nerves
Term
The Brain Stem
Definition
Brain stem has motor and sensory neurons related to structures in the head and neck, rather than the limbs and trunk. All of the cranial nerves originate in the brain stem.
Term
Reticular formation
Definition
Important, diffusely-organized structure that contains neurons that have axons spreading widely in both directions up and down the brain stem.
Term
The Brain Stem: Three Components
Definition
-The medulla oblongata - resembles the spinal cord
-The pons
-The midbrain
Term
The Cerebellum
Definition
-Attached mainly to the pons
-Important in movement control
-It regulates the rate, range, force, direction and timing of movements. It determines the sequence and pattern of muscles activated during movement.

The cerebellum may be important in the learning of motor functions, such as playing the piano or typing
Term
The Diencephalon: 2 Structures
Definition
Thalamus
Hypothalamus
Term
Thalamus
Definition
Major relay station for all information passing from the lower central nervous system en route for the cerebral cortex, and which also relays to the cerebral cortex important information from the cerebellum and and basal ganglia. There is also evidence that the thalamus may actually process information destined for the cerebral cortex.
Term
Hypothalamus
Definition
Central governor of the autonomic nervous system and the endocrine system. It has many regions (nuclei) and is involved in certain motivational drives such as feeding, drinking, fear, rage
Term
The Cerebrum or Cerebral hemispheres: Major Structures
Definition
-basal ganglia
-cerebral cortex
Term
The basal ganglia
Definition
In the cerebrum, deep-lying masses of gray matter called the putamen, caudate nucleus and globus pallidus. There are also two midbrain stuctures included in the basal ganglia. These are the subthalmic nucleus and the substantia nigra.
Term
The cerebral cortex
Definition
So called “seat of the intellect” A superficial layer of gray matter that performs the highest and most complex functions required of the central nervous system. Receives and integrates sensory information; stores and retrieves memories; thinks, conceptualizes, plans and executes movements.
Term
At four weeks there is...
Definition
1) Forebrain (prosencephalon)
2) Midbrain (mesencephalon)
3) Hindbrain (rhombencephalon)
Term
At five weeks
Definition
the forebrain subdivides into the telencephalon and the diencephalon and the hindbrain subdivides into the pons (+cerebellum) and medulla. So there are now fiver secondary vesicles.
1) Telencephalon (becomes the cerebral hemispheres)
2) Diencephalon (thalamus, hypothalamus)
3) Midbrain
4) Pons, Cerebellum
5) Medulla
Term
Several distinct pathways in parallel
Definition
Motor pathways consist of several distinct pathways in parallel. THere is the cortico spinal tract, which originates in the cerebral cortex, and also tracts that originate in the brain stem. Sensory pathways also consist of several distinct pathways in parallel. There are the dorsal column tracts and also the spinothalamic tracts
Term
Topographically
Definition
nerve fibers and neurons from particular regions of the body are grouped together.

These areas form a “map” of the body surface on the cerebral cortex. Similarly, neurons that are involved in controlling hand movements are grouped together in a “hand area” of the motor cortex
Term
Opposite side of the body
Definition
Sensory and motor events on one side of the body are perceived, interpreted and controlled by the cerebral hemisphere on the opposite side of the body (the contralateral side). The sensory and motor pathways (tracts) are therefore crossed at some point. The reason for this is not known.
Term
The Spinal cord Structure
Definition
The spinal cord is a slender column of nervous tissue that passes downward from the brain to the vertebral canal. The spinal cord is continuous with the brain, but is said to begin where the nervous tissue leaves the cranial cavity at the level of the foramen magnum.
Term
Nomeclature
Definition
anteror = ventral
posterior = dorsal

Anterior and Posterior are used to reference humans
Dorsal and Ventral are used for animals
Term
Spinal nerves
Cranial nerves
Definition
The nerves that emerge from the spinal cord
The nerves that emerge from the brain are called cranial nerves
Together, these nerves make peripheral nervous system.
Term
Olfactory nerves
Definition
sensory nerve conveying information from the olfactory cells of the nose
Term
Optic nerves
Definition
Sensory nerve conveying information from the photoreceptor cells of the retina of the eye
Term
Oculomotor nervers
Definition
controlling the eyelids, pupil diameter, and extraocular muscles
Term
Trochlear nerves
Definition
controlling extraocular muscles
Term
Trigeminal nerves
Definition
the motor component controlling muscles of mastication and muscles in the floor of the buccal cavity
Term
Abducens nerves
Definition
controlling extraocular muscles
Term
Facial nerves
Definition
the the motor component controls muscles associated with facial expression, the lacrymal glands, and salivary glands
Term
Vestibulocochlear nerves
Definition
sensory, conveying information from the cochlea (sound) vestibular apparatus (balance, equilibrium)
Term
Glossopharyngeal nerves
Definition
the motor component controlling muscles in the pharynx involved in swallowing, salivary glands.
Term
Vagus nerves
Definition
the motor component controls muscles involved in speech and swallowing, with a large autonomic group of nerve fibers that affect heart function, as well as smooth muscle and glands in the viscera of the abdomen.
Term
Accessory nerves
Definition
controlling muscles of the so palate, pharynx, larynx, neck and back
Term
Hypoglossal nerve
Definition
controlling muscles that move the tongue
Term
Oh Once One Takes The Anatomy Final, Very Good Vacation Are Heavenly.
Definition
Olfactory
Optic
Oculomutor
Trochlear
Trigeminal
Abducens
Facial
Vestibulocochlear
Glossopharyngeal
Vagus
Accessory
Hypoglossal
Term
Cervical enlargement
Definition
gives rise to nerve for the arms,
Term
Lumbar enlargement
Definition
gives rise to nerves for the legs
Term
The dorsal (posterior) and ventral (anterior) roots
Definition
Each spinal nerve emerges from the spinal cord by two short branches, the dorsal (posterior) and ventral (anterior) roots, which are protected within the vertebral column.
Term
Dorsal root ganglion
Definition
-The dorsal root (or sensory root) has an enlargement called the dorsal root ganglion.
-The dorsal root ganglion contains the cell bodies of sensory neurons whose nerve endings are often specially adapted to act as sensory receptors. The axons of these sensory neurons enter the spinal cord through the dorsal root and from synapses with other neurons in the spinal cord.
Term
Rootlets
Definition
The vental root (or motor root) is actually composed of a number of rootlets, and carries the axons of motor neurons whose cell bodies are located in the gray matter of the spinal cord
Term
Dermatome
Definition
The area of skin innervated by a single root is called a dermatome. Dermatomes are important clinically, because loss of sensation in a particular dermatome indicates the level of a spinal lesion or damage to a spinal nerve root.
Term
Anterior (ventral) median fissure
Posterior (dorsal) median sulcus
Definition
The spinal cord is partially diveded into right and left halves by a deep anterior (ventral) median fissure and a shollow posterior (dorsal) median sulcus
Term
The gray matter - Spinal Cord
Definition
consists of many cell bodies of different neurons with their axons and dendrites, occupies the central region of the cord, and looks tike a butterfly
Term
Posterior (dorsal) horns
Definition
the two vertical bars forming the of the H
Term
Anterior (ventral) horns
Definition
the two vertical bars forming the bottom of the H
Term
Gray commissure
Definition
The cross-bar of the H
Term
Propriospinal neurons
Definition
The cell bodies of motor neurons neurons are clusted in the ventral horn gray matter. Other neurons in the spinal cord gray matter are internuerons. Some of these interneurons send axons in the lateral and ventral columns of the white matter for distances ranging from a few to many segments up and down the spinal cord.
Term
The white matter
Definition
consists of nerve fiber tracts, is divided by the gray matter into anterior (ventral), posterior (dorsal) and lateral funiculi
Term
The major functions of the spinal cord are
Definition
-Major pathway for all information ascending to the brain from the system of the body.
-Major pathway for all commands descending from the brain to the muscles and other effector systems
-Able to execute certain simple behavioral activities without involving the brain. These activities are referred to as spinal reflexes. (Additionally, neural networks in the spinal cord are responsible for storing the motor program involved in walking)
Term
Ascending Pathways
Definition
Three major ascending systems conveying somatic sensory information to the brain.
Term
Ascending: Dorsal Column
Definition
Ascend in the fasciculus gracilis and fasciculus cuneatus of the spinal cord white matter. They synapse with neurons in the nucleus gracilis and nuclues cuneatus in the medulla.
The fibers from these neurons cross over to the opposite side in the medulla, so that signals from sensory receptors on the left side of the body are transmitted to the right side of the brain, and vice versa
Term
Dorsal column: Sensory Information Carried By This System
Definition
a) fine, discrimination tough
b) vibration
c) kinesthesia, proprioception (limb movement, prison)
d. pressure
Term
Ascending: Anterior and lateral tracts
Definition
Include the anterior and lateral spinothalmic tracts, are older on the evolutionary scale than the dorsal column tracts. The anterior and lateral spinothalamic tracts are located in the lateral and anterior funiculi of the spinal cord white matter. Most of the nerve fibers in this system cross over to the opposite side in the spinal cord. There is a small contingent of uncrossed fibers
Term
Anterior and lateral tracts - Sensory Information Carried By This System
Definition
a) crude touch (includes tickle and itch
b) pain
c) temperature
Term
Ascending: Spinocerebellar Tracts
Definition
Include the ventral (anterior) spinocerebellar tract and the dorsal (posteriot spinocerebellar tract. They are located funiculi of the spinal cord white matter
Term
Spinocerebellar tracts - Sensory Information Carried By This System
Definition
a) feedback to the cerebellum of motor signals arriving at the motor neurons in the anterior horns
B) muscle spindle discharges
c) Golgi tendon organ discharges
d) information from the joint receptors
e) input from certain skin tactile receptors that provide clues to joint movements and position
Term
Descending Tracts
Definition
Involved in direct movements, maintenance of posture, modulating ascending sensory systems such as pain, and gating spinal reflex loops
Term
Descending: Corticospinal Tracts
Definition
In humans there is really only one major tract, the lateral corticospinal tract. It originates in the cerebral cortex, crosses over in the medulla, and descend in the lateral funiculi. It is sometimes called pyramidal tract. Deals with commands for finely controlled movements, often involving the hands and digits
Term
Descending: reticulospinal, vestibulospinal, and tectospinal tracts
Definition
Originating in the brain stem.
The reticulospinal tract originates in the reticular formation of the medulla and pons and descends in the medial region of the anterior funiculi. It is not not crossed, but neurons receiving input from this tract may project to both sides of the spinal cord.
Term
Descending: rubrospinal tract
Definition
The rubrospinal tract originates in the red nucleus (nucleus ruber) of the brain stem, crosses over immediately and descends in the lateral funiculi close to the lateral corticospinal tract. Commands passing down this tract control movements similar to those controlled by the corticospinal tract, but the movements are coarser and not so finely regulated.
Term
Spinal Reflex: Basic Components
Definition
-sensory receptor
-sensory neuron attached to receptor
-interneuron (sometimes)
-motor neuron
-effector (gland or muscle)
Term
Examples of Reflex
Definition
-Knee Jerk Reflex
-Stretch Reflex (maintains posture)
-Withdrawal Reflex (something hot)
-Crossed Extensor Reflex (step on a nail)
Term
Spinal Shock
Definition
Spinal Cord is cut at the level of the neck or thorax, all spinal reflexes are temporarily lost
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