Test 3 - Central Nervous System Part 2

Mesencephalon

Below the Diencephalon
Midbrain
Short section of brainstem between the diencephalon and the pons
Contains:The Corpora Quadrigemina
Cerebral Peduncles
Some motor nuclei
Hollow portion is called the cerebral aqueduct - or the Aqueduct of Silvius

Cerebral Aqueduct

Hollow portion of the Mesencephalon
Connects the 3rd and 4th ventricles
Cerebrospinal fluid flows through this passageway

Corpora Quadrigemina

Part of the Mesencephalon
Four lumps on the posterior surface of the mesencephalon
Upper emineneces:Called the Superior Colliculi
Involved in visual reflexes
Lower eminences:Called the inferior Colliculi
Involved in auditory reflexes
These four lumps work together to keep our eyes and ears coordinated

Cerebral Peduncles

Part of the Mesencephalon
Large fiber tracts containing both ascending and descending tracts
Connect the brain to the brain stem

Substantia Nigra

Part of the Mesencephalon
Has a role in Parkinson’s syndrome
Thought to inhibit involuntary movements by working with the basal nuclei

Metencephalon

Found below the Mesencephalon
Contains both the pons and the cerebellum

Pons

Part of the Metencephalon
Located between the midbrain and the medulla oblongata
Contains white fiber tracts that connect to the cerebellum as well as motor and sensory tracts connecting the medulla with the midbrain
Appears as a rounded bulge on the anterior of the brain stem
Also contains nuclei for several cranial nuclei
Centers for the control of breathing called the apneustic and pneumotaxic areas are found in the pons

Cerebellum

Part of the Metencephalon
Second largest brain structure
Has an outer layer of gray matter and a thick deeper layer of white matter
Contains the brain patter called the Athe Arbor Vitae (the tree of life)
Mainly concerned with motor function
Connected to the brain by three bundles of nerve fibers called the cerebellar peduncles

Cerebellar Peduncles

Three bundles of nerve fibers that connect the cerebellum to the brain

Superior Cerebellar Peduncles

Connect the cerebellum with the midbrain
Fibers originate from the dentate nuclei in the cerebellum and pass through the red nucleus and synapse into the thalamus
Impulses are conducted to the cortical motor areas
Fibers carry information regarding the feedback of movement to the motor areas, so the motor areas know if the correct feedback has occured

Middle Cerebellar Peduncles

Consists of fibers from the motor cortex through the pons to the cerebellum
Carry information that will allow the cerebellum to be aware of voluntary movements

Inferior Cerebellar Peduncles

Connect the cerebellum with the medulla oblongata and the spinal cord
Carry proprioceptive fibers which inform the cerebellum of the effects of muscle motion

Myelencephalon

Includes the Medulla Oblongata and a number of cranial nerve nuclei
Almost blending into the spinal cord, so there is an abundance of white fibers

Medulla Oblongata (Medulla)

Part of the Myelencephalon
One obvious feature is the pyramids, which are large corticospinal tracts carry information from the cortex down to the spinal cord regarding voluntary movements
Nerve fiber cross over in the pyramidal decussation - this is how contralateral(opposite side) control is created
The right side of our brain will control the left side of our body and vice versa due to this crossing over
Also contains a cardiovascular center to control heart rate and force of contraction
There’s also a vasomotor center which controls blood pressure by constriction or relaxation of blood vessels
Also find a respiratory center to help control our breathing, as well as swallowing, hiccuping, and sneezing centers
The hypothalamus tells these medullary centers what to do

Spinal Cord

Gray matter is in the center of the spinal cord, surrounds the central canal, and is the H or butterfly shape in the center
White matter is on the outside in the spinal cord compared to the gray matter being on the outside in the brain
The H or butterfly shape of the spinal cord can be divided into three regions called “horns”:Dorsal Horn
Lateral Horn
Ventral or Anterior Horn

Anterior Horn

Found in the ventral region of the spinal cord
made of mainly somatic motor nerve synapses
Neurons then send out axons to skeletal muscles via the ventral root of the spinal cord

Lateral Horn

Most prominent in the thoracic and upper lumbar regions
Holds nerve cell bodies for the autonomic nervous system
These axons leave via the ventral roots and go to the visceral organs to provide motor output

Posterior (Dorsal) Horn

Consists of afferent fibers and synapses form the peripheral sensory receptors
These sensory fibers have their cells bodies in the dorsal root ganglion
These afferent fibers in the ganglion enter the spinal cord where they may go up in ascending tracts or synapse with association neurons in the posterior horn

White matter of the spinal cord

Myelinated and unmyelinated fibers that may ascend, descend, or be comissural
Organized into anterior, lateral, and posterior funiculi (or columns)
Ascending tracts go up to the brain carrying sensory information - can also be called afferent tracts
The Dorsal white column is made of the Faciculi cuneatus and gracilis

Posterior (Dorsal) Spinocerebellar tract

Carries subconscious Proprioception to ipsilateral side of the cerebellum
Does not cross over at all

Fasciculi Cuneatus

Makes up part of the dorsal white column
Carries information from the upper limbs, trunk, and neck
Carries information regarding fine touch and pressure (discriminative touch) and joint proprioception
Neurons enter the spinal cord, ascend ipsilaterally and cross over in the medulla, before traveling up the medial meniscal tract to the thalamus and somatosensory cortex

Fasciculi Gracilis

Makes up part of the dorsal white column
Carry information from the lower trunk and limbs and pressure (discriminative touch) and joint proprioception
Neurons enter the spinal cord, ascend ipsilaterally and cross over in the medulla, before traveling up the medial meniscal tract to the thalamus and somatosensory cortex

Joint Proprioception

The conscious perception of our body position

Lateral Spinothalamic Tract

Enters the spinal cord, crosses over immediately, then ascends contralaterally to the thalamus and the sensory cortex
Will carry pain and temperature information to the somatosensory cortex

Anterior Spinothalamic Tract

Carries information regarding crude touch and pressure
Crosses over before ascending

Pyramidal Tracts

The major descending pathways
Carry voluntary output to our skeletal muscles
Include the anterior and lateral corticospinal tracts

Lateral Corticospinal Tracts

Part of the Pyramidal Tracts
The major pathway of the Pyramidal tracts
Carry most of the output
Axons originate in the primary motor cortex, and travel to the medulla where they decussate (Cross over) in the pyramids, then travel to the spinal cord level where they synapse with a somatic motor neuron that leaves the spinal cord and goes to the muscle

Anterior Corticospinal Tracts

Part of the Pyramidal Tracts
Relatively minor
Travel down the spinal cord then cross over at the level of the synapse with the 2nd neuron → 2nd neuron then leaves the spinal cord and goes to the muscle

Tectospinal Tracts

Go from the superior colluculi to the contralateral eye muscles important for tracking visual targets

Vestibulospinal Tracts

Lead from the medulla to the ipsilateral muscles used for maintaining balance

Rubrospinal Pathway

These fibers lead from the red nucleus in the brain stem to muscles on the contralateral side to maintain muscle tone

Reticulospinal Tracts

Lead from the reticular formation to both ipsilateral and contralateral muscles to help with muscles tone, visceral muscles movements, and unskilled movements

Meninges

Layers of protective coverings that cover the brain and spinal cord
3 different layers:Dura Mater
Arachnoid Mater
Pia mater

Dura Mater

The outermost Meninges layer that protects the brain and spinal cord
Made up of tough connective tissue

Arachnoid Mater

The middle Meninges layer that protects the brain and spinal cord
Contains both cerebrospinal fluid as well as blood vessels

Pia Mater

The innermost Meninges layer that protects the brain and spinal cord
Delicate layer that follows the contours of the brain
Contains many small blood vessels

Meningitis

Inflammation of the Meninges membranes - obviously not good

Cerebrospinal Fluid (CSF)

Produced by the Ependymal Cells in the Chroids Plexus (found in the lateral ventricles)
Flows from there into the 3rd ventricle, down the cerebral aqueduct to the 4th ventricle, and from there can either go up or down the central canal of the spinal cord or enter the subarachnoid space
At the top of the brain, there are structures called Arachnoid Villi that reabsorb the CSF and help create the slow circulation it has