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ADV Brain and Cranial Nerves

Human Anatomy, First Edition McKinley & O’Loughlin – Chapter 15 Lecture Outline: Brain and Cranial Nerves

Brain and Cranial Nerves

  • An adult brain weighs between 1.35 and 1.4 kilograms (kg) (around 3 pounds) and has a volume of about 1200 cubic centimeters (cc).
  • Brain size is not directly correlated with intelligence
  • It is not the physical size of the brain that determines intelligence—it is the number of active synapses.

The Brain’s 4 Major Regions

  1. Cerebrum,
  2. diencephalon,
  3. brainstem,
  4. cerebellum.
  • The cerebrum is divided into two halves, called the left and right cerebral hemispheres.
  • Each hemisphere is subdivided into five functional areas called lobes.
  • Outer surface of an adult brain exhibits folds called gyri (gyrus) and shallow depressions between those folds called sulci (sulcus).
  • The brain is associated with 12 pairs of cranial nerves.

Prosencephalon (forebrain)

  • Telencephalon: cerebrum
  • Diencephalon: epithalamus, thalamus, hypothalamus

Mesencephalon (midbrain)

  • Mesencephalon: cerebral peduncles, colliculi

Rhombencephalon (hindbrain)

  • Metencephalon: pons, cerebellum
  • Myelencephalon: medulla oblongata

Spinal Cord

Organization of Brain Tissue

  • Gray matter:
    • motor neuron and interneuron cell bodies, dendrites, axon terminals
    • unmyelinated axons.
  • White matter:
    • composed primarily of myelinated axons.
  • During brain development, an outer, superficial region of gray matter forms from migrating peripheral neurons.
  • External sheets of gray matter, called the cortex, cover the surface of most of the adult brain (the cerebrum and the cerebellum).
  • White matter lies deep to the gray matter of the cortex.
  • Within the masses of white matter:
    • discrete innermost clusters of gray matter called cerebral nuclei (or basal nuclei).
    • are oval, spherical, or sometimes irregularly shaped clusters of neuron cell bodies

INSULA

 

Support and Protection of the Brain

The brain is protected and isolated by multiple structures:

  • bony cranium
  • Meninges:
    • Protective connective tissue membranes
    • surround and partition portions of the brain.
  • Cerebrospinal fluid (CSF)
    • acts as a cushioning fluid.
  • Blood-brain barrier:
    • prevents entry of harmful materials from the bloodstream.

Cranial Meninges

  • Three dense regular connective tissue layers:
    • separate the soft tissue of the brain from the bones of the cranium.
    • Enclose and protect blood vessels that supply the brain.
    • Contain and circulate cerebrospinal fluid.
    • Parts of the cranial meninges form some of the veins that drain blood from the brain.
  • From superficial to deep, the cranial meninges are the dura mater, the arachnoid, and the pia mater.

Dura Mater

  • Tough membrane composed of two fibrous layers.
  • Strongest of the meninges.
  • Dura mater is composed of two layers.
    • periosteal layer, the more superficial layer, attaches to the periosteum of the cranial bones
    • meningeal layer lies deep to the periosteal layer
  • The meningeal layer is usually fused to the periosteal layer
    • Exception: in specific areas where the two layers separate to form large, blood-filled spaces called dural venous sinuses.

Arachnoid

  • Also called the arachnoid mater or the arachnoid membrane.
  • Lies immediately internal to the dura mater.
  • Partially composed of a delicate web of collagen and elastic fibers, termed the arachnoid trabeculae.
  • Between the arachnoid and the overlying dura mater is the subdural space.
  • Immediately deep to the arachnoid is the subarachnoid space.

Pia Mater

  • The innermost of the cranial meninges.
  • Thin layer of delicate connective tissue that tightly adheres to the brain and follows every contour of the brain surface.

The bloodvessels are in the subarachnoid space and in the areas between the periosteal and meningeal layer.

Cranial Dural Septa

  • The meningeal layer of the dura mater extends as flat partitions (septa) deep into the cranial cavity;
    • at four locations
    • called cranial dural septa.
  • Membranous partitions separate specific parts of the brain and provide additional stabilization and support to the entire brain.
    • falx cerebri
    • tentorium cerebelli
    • falx cerebelli
    • diaphragma sellae

Brain Ventricles

  • Cavities or expansions within the brain that are derived from the lumen (opening) of the embryonic neural tube.
  • Continuous with one another as well as with the central canal of the spinal cord.
  • Four ventricles in the brain.
    • two lateral ventricles are in the cerebrum, separated by a thin medial partition called the septum pellucidum
    • within the diencephalon is a smaller ventricle called the third ventricle
      • each lateral ventricle communicates with the third ventricle through an opening called the interventricular foramen
  • The fourth ventricle is located within the pons and cerebellum.

Cerebrospinal Fluid

  • A clear, colorless liquid that circulates in the ventricles and subarachnoid space.
  • Bathes the exposed surfaces of the central nervous system and completely surrounds it.
  • Performs several important functions.
    • buoyancy
    • protection
    • environmental stability
  • Formed by the choroid plexus in each ventricle.
  • Produced by secretion of a fluid from the ependymal cells that originate from the blood plasma.
  • Is similar to blood plasma.

Blood-Brain Barrier

  • Nervous tissue is protected from the general circulation by the blood-brain barrier.
  • Strictly regulates what substances can enter the interstitial fluid of the brain.
  • Prevents exposure of neurons in the brain to drugs, waste products in the blood, and variations in levels of normal substances (ions, hormones) that could adversely affect brain function.
  • Tight junctions prevent materials from diffusing across the capillary wall.
  • Astrocytes act as “gatekeepers” that permit materials to pass to the neurons after leaving the capillaries.
  • Is markedly reduced or missing in three distinct locations in the CNS: the choroid plexus, hypothalamus, and pineal gland.

Cerebrum

  • Account for 83% of brain mass
  • Fissures – deep grooves – separate major regions of the brain
    • Transverse fissure – separates cerebrum and cerebellum
    • Longitudinal fissure – separates cerebral hemispheres
  • Sulci – grooves on the surface of the cerebral hemispheres
  • Gyri – twisted ridges between sulci
  • Prominent gyri and sulci are similar in all people
  • Deeper sulci divide cerebrum into lobes
  • Lobes are named for the skull bones overlying them
  • Central sulcus separates frontal and parietal lobes
    • Bordered by two gyri
      • Precentral gyrus
      • Postcentral gyrus
  • Parieto-occipital sulcus
    • Separates the occipital from the parietal lobe
  • Lateral sulcus
    • Separates temporal lobe from parietal and frontal lobes
  • Insula – deep within the lateral sulcus

Cerebrum: functional areas

  • Home of our conscious mind
  • Enables us to:
    • Be aware of ourselves and our sensations
    • Initiate and control voluntary movements
    • Communicate, remember, and understand

Cerebral cortex

  • Composed of gray matter
    • Neuronal cell bodies, dendrites, and short axons
  • Folds in cortex – triples its size
  • Approximately 40% of brain’s mass
  • Brodmann areas – 52 structurally distinct areas

Cerebrum

Functional areas of the cortex

Three kinds of functional areas

  • Motor areas
  • Sensory areas
  • Association areas

Motor areas

Controls motor functions

– Primary motor cortex (somatic motor area)

– Located in precentral gyrus (Brodmann area 4)

Pyramidal cells – large neurons of primary motor cortex

 

Corticospinal tracts descend through brainstem and spinal cord

– Axons signal motor neurons to control skilled movements

– Contralateral – pyramidal axons cross over to opposite side of the brain

 

  • Specific pyramidal cells control specific areas of the body
  • Face and hand muscles – controlled by many pyramidal cells
  • Motor homunculus – body map of the motor cortex

Sensory cortex

  • Cortical areas involved in conscious awareness of sensation
  • Located in parietal, temporal, and occipital lobes
  • Distinct area for each of the major senses

Primary Somatosensory Cortex

  • Located along the postcentral gyrus
    • Corresponds to Brodmann areas 1-3
  • Involved with conscious awareness of general somatic senses
  • Spatial discrimination – precisely locates a stimulus
  • Projection is contralateral
    • Cerebral hemispheres
      • Receive sensory input from the opposite side of the body
  • Sensory homunculus – a body map of the sensory cortex

Somatosensory Association Area

  • Lies posterior to the primary somatosensory cortex
    • Corresponds to Brodmann areas 5 and 7
  • Integrates different sensory inputs
    • Touch, pressure, and others
  • Draws upon stored memories of past sensory experiences

 

Sensory Areas – Visual Areas

  • Primary visual cortex
    • Corresponds to Brodmann area 17
    • Located deep within the calcarine sulcus
      • On the posterior and medial part of the occipital lobe
    • Receives visual information that originates on the retina
    • First of a series of areas that interprets visual input

 

  • Visual association area
    • Surrounds the primary visual area
    • Coincides with Brodmann areas 18 and 19
    • Continues the processing of visual information
    • Complex visual processing extends into:
      • Temporal and parietal lobes

Sensory Areas – Auditory Areas

  • Primary auditory cortex
    • Function – conscious awareness of sound
    • Location – superior edge of the temporal lobe
    • Corresponds to Brodmann areas 41 and 42
  • Auditory association area
    • Lies posterior to the primary auditory cortex – Located within Brodmann area 22
    • Permits evaluation of different sounds
    • Lies in the center of Wernicke’s area
    • Involved in recognizing and understanding speech

Sensory Areas – Gustatory Cortex

  • Involved in the conscious awareness of taste stimuli
  • Corresponds to Brodmann area 43
  • Located on the “roof” of the lateral sulcus

Sensory Areas – Vestibular Cortex

  • Located in the posterior part of the insula (interpretion of pain) lots of pain: lose stability
  • Deep to the lateral sulcus

Sensory Areas – Olfactory Cortex

  • Lies on the medial aspect of the cerebrum
  • Located in a region called the piriform lobe (most of seizures start here), is a region in the brain, in the Rhinencephalon situated in the telencephalon, between the Insula and the Temporal Lobe, anterior and lateral to the Amygdala. This area is related to chemoconvulsants.
  • Olfactory nerves transmit impulses to the olfactory cortex
    • Provides conscious awareness of smells
  • Part of the rhinencephalon – “nose brain”
  • Includes – the piriform lobe, olfactory tract, and olfactory bulb
  • Connects the brain to the limbic system
    • Explains why smells trigger emotions
  • Orbitofrontal cortex
    • Involved with consciously identifying and recalling specific smells

Association areas

Make associations between different types of sensory information

Associate new sensory input with memories of past experiences

New name for association areas – higher order processing areas

Association Areas – Prefrontal Cortex

  • Large region of the frontal lobe anterior to motor areas
  • Performs cognitive functions
    • All aspects of thinking and perceiving
    • Remembering and recalling information
    • Also related to mood
    • Has close links to the limbic part of the forebrain
  • Functional neuroimaging techniques
    • Reveal functions of specific parts of the prefrontal cortex
  • Anterior pole of frontal cortex
    • Active in solving the most complex problems
  • The farther rostrally one goes in the CNS, the more complex the neural functions
  • Functional areas located on the medial side of the frontal lobe
    • Regions anterior to the corpus callosum
      • Involved in complex personal and social interactions
    • Regions superior to the corpus callosum
      • Involved in “mentalization

Association Areas – General Interpretation Area

  • Function is currently under investigation
  • Located at the interface of:
    • The visual, auditory, and somatosensory association areas
  • Newer studies show most of this region is involved in the visual processing of spatial relationships

Association Areas – Language Area

  • Surrounds the lateral sulcus in the left cerebral hemisphere
  • Five parts have been identified
    • Broca’s area – speech production
    • Wernicke’s area – speech comprehension
    • Lateral prefrontal cortex – conceptual analysis of spoken words
    • Most of the lateral and inferior temporal lobe
      • Coordination of auditory and visual aspects of language
    • Parts of the insula
      • Initiation of word articulation
      • Recognition of rhymes and sound sequences

Association Areas – Insula

  • Functions of its cortex – not well understood
  • Some parts function in language and the sense of balance
  • Other parts – visceral function
    • Conscious perception of:
      • Upset stomach
      • Full bladder
      • Some aspects of the sense of smell

 

Lateralization of Cortical Functioning

  • The two hemispheres control opposite sides of the body
  • Hemispheres are specialized for different cognitive functions
  • Left cerebral hemisphere – more control over:
    • Language abilities, math, and logic
  • Right cerebral hemisphere – more involved with:
    • Visual-spatial skills
    • Reading facial expressions
    • Intuition, emotion, artistic and musical skills

Cerebral White Matter

  • Different areas of the cerebral cortex communicate:
    • With each other
    • With the brainstem and spinal cord
  • Fibers are usually myelinated and bundled into tracts
  • Types of tracts
    • Commissures – composed of commissural fibers
      • Allows communication between cerebral hemispheres
      • Corpus callosum – the largest commissure
    • Association fibers
      • Connect different parts of the same hemisphere
    • Projection fibers – run vertically
      • Descend from the cerebral cortex
      • Ascend to the cortex from lower regions
Decussation in pyramids similar to decussation of afferent mechanoreceptors DCML (Dorsal column-medial lemniscus pathway)

Projection tracts

  • Internal capsule – projection fibers form a compact bundle
    • Passes between the thalamus and basal nuclei
  • Corona radiata – superior to the internal capsule
    • Fibers run to and from the cerebral cortex

Basal nuclei

A group of nuclei deep within the cerebral white matter

  • Caudate nucleus – arches over the thalamus (related to automatic movement)
  • Lentiform nucleus – “lens shaped” (related to automatic movement, cerebellum: change in speed,…)
  • Amygdala – sits on top of the caudate nucleus
    • Functionally belongs with the limbic system
  • Lentiform nucleus
    • Divided into two parts
      • Globus pallidus
      • Putamen

  • Cooperate with the cerebral cortex in controlling movements
  • Receive input from many cortical areas
  • Evidence shows that they:
    • Start, stop, and regulate intensity of voluntary movements
    • In some way estimate the passage of time

The Diencephalon

  • Forms the center core of the forebrain
  • Surrounded by the cerebral hemispheres
  • Composed of three paired structures:
    • Thalamus, hypothalamus, and epithalamus
  • Border the third ventricle
  • Primarily composed of gray matter

The Thalamus

  • Makes up 80% of the diencephalon
  • Contains approximately a dozen major nuclei
  • Send axons to regions of the cerebral cortex
  • Nuclei act as relay stations for incoming sensory messages

  • Afferent impulses converge on the thalamus
    • Synapse in at least one of its nuclei
  • Is the “gateway” to the cerebral cortex
  • Nuclei organize and amplify or tone down signals

The Diencephalon – The Hypothalamus

  • Lies between the optic chiasm and the mammillary bodies
  • Pituitary gland projects inferiorly
  • Contains approximately a dozen nuclei
  • Main visceral control center of the body

The Hypothalamus

Functions include the following:

  • Control of the autonomic nervous system
  • Control of emotional responses (only physical response: heart, breathing rate,
  • Regulation of body temperature
  • Regulation of hunger and thirst sensations
  • Control of behavior
  • Regulation of sleep-wake cycles
  • Control of the endocrine system
  • Formation of memory

The Diencephalon – The Epithalamus

  • Forms part of the “roof” of the third ventricle
  • Consists of a tiny group of nuclei
  • Includes the pineal gland (pineal body)
    • Secretes the hormone melatonin
    • Under influence of the hypothalamus

The Brain Stem

  • Includes the midbrain, pons, and medulla oblongata
  • Several general functions
    • Produces automatic behaviors necessary for survival
    • Passageway for all fiber tracts running between the cerebrum and spinal cord
    • Heavily involved with the innervation of the face and head
      • 10 of the 12 pairs of cranial nerves attach to it

The Brain Stem – The Midbrain

  • Lies between the diencephalon and the pons
  • Central cavity – the cerebral aqueduct
  • Cerebral peduncles located on the ventral surface of the brain
    • Contain pyramidal (corticospinal) tracts
  • Superior cerebellar peduncles
    • Connect midbrain to the cerebellum

  • Periaqueductal gray matter surrounds the cerebral aqueduct
    • Involved in two related functions
      • Fight-and-flight reaction
      • Mediates response to visceral pain

  • Corpora quadrigemina – the largest nuclei
    • Divided into the superior and inferior colliculi
      • Superior colliculi – nuclei that act in visual reflexes
      • Inferior colliculi – nuclei that act in reflexive response to sound

 

Imbedded in the white matter of the midbrain

Two pigmented nuclei

Substantia nigra – neuronal cell bodies contain melanin, and produce Dopamine.

Functionally linked to the basal nuclei

Red nucleus – lies deep to the substantia nigra

Largest nucleus of the reticular formation

The Brain Stem – The Pons

  • Located between the midbrain and medulla oblongata
  • Contains the nuclei of cranial nerves V, VI, VII and VIII
  • Two general groups of cranial nerve nuclei
    • Motor nuclei
    • Sensory nuclei

The Brain Stem – The Medulla Oblongata

Most caudal level of the brain stem

  • Continuous with the spinal cord
  • Choroid plexus lies in the roof of the fourth ventricle
  • Pyramids of the medulla – lie on its ventral surface
    • Decussation of the pyramids – crossing over of motor tracts
  • Cranial nerves VIII–XII attach to the medulla

The core of the medulla contains:

  • Much of the reticular formation
    • Nuclei influence autonomic functions
  • Visceral centers of the reticular formation include:
    • Cardiac center
    • Vasomotor center
    • The medullary respiratory center
    • Centers for hiccupping, sneezing, swallowing, and coughing

The Cerebellum

  • Located dorsal to the pons and medulla
    • Smoothes and coordinates body movements
    • Helps maintain equilibrium
  • Consists of two cerebellar hemispheres
  • Surface folded into ridges called folia
    • Separated by fissures
  • Hemispheres each subdivided into:
    • Anterior lobe
    • Posterior lobe

  • Composed of three regions
    • Cortex – gray matter
    • Internal white matter
    • Deep cerebellar nuclei – deeply situated gray matter
  • Cerebellum must receive information
    • On equilibrium
    • On current movements of limbs, neck, and trunk
    • From the cerebral cortex

The Cerebellum – Cerebellar Peduncles

  • Fibers to and from the cerebellum are ipsilateral
    • Run to and from the same side of the body
  • Thick tracts connecting the cerebellum to the brain stem
    • Superior cerebellar peduncles
    • Middle cerebellar peduncles
    • Inferior cerebellar peduncles

 

Introduction:

  • Cerebellum is mainly responsible for maintaining tone of muscles, maintaining posture and balance and for coordination of movements
  • Develops embryologically from the metencephalon
  • Cerebellum has an anterior lobe, a posterior lobe and a flocculonodular area
    • Flocculonodular lobe is the most primitive part of the cerebellum (also called archecerebellum) and is concerned mainly with balance
    • The anterior lobe is called paleocerebellum and is concerned mainly with the tone of the muscles
    • The posterior lobe of the cerebellum (neocerebellum) is the most “modern” cerebellar area and is concerned with coordination of movement
  • The primary fissure lies between anterior and posterior lobes and the dorsolateral fissure lies between posterior and flocculonodular lobe.

Posterior view of the cerebellum:

There is a longitudinal depression in the middle of the posterior aspect of cerebellum called the vermis

  • On either side of the vermis are the two cerebellar hemispheres
  • The area immediately lateral to the vermis is called paravermal area or intermediate zone. (this area is part of the cerebellar hemispheres)

Control of the trunk and other axial musculature is concerned with the vermal area whereas control of the locomotor system is concerned with the paravermal area

Cerebellum controls the balance, posture and coordination of movement ipsilaterally which means that lesions would be on the same side as the clinical signs.

Role of the cerebellum in the motor functions of the body:

The idea of a movement originates in the prefrontal lobe of the cortex

  • This idea would go to the premotor area and supplementary motor area
  • These areas consult with the basal ganglia
  • The basal ganglia make evaluations to refine the movement and send the signals to premotor, supplementary motor and primary motor cortex and the somatosensory area as well
  • From these areas, the upper motor neurons originate to descend to the lower motor neurons

But for an appropriate motor program to be formulated, the CNS needs to know the initial positions of the concerned muscles in space

  • This function is associated with the cerebellum i.e. it keeps a record of the parts and orientation of the body in space
  • Therefore, the higher motor centers of the CNS consult with the cerebellum before initiating the movement

Also, once the movement is initiated, cerebellum also samples the information at the uppermotorneuron-lowermotorneuron junction to determine whether the movement is being executed satisfactorily

  • It can, therefore, also predict the result of movements occurring unhindered in the current directions
  • It also, to a very large degree, influences the movements to ensure that the required movement is executed (examples in lecture)

Internal structure of the cerebellum:

The general arrangement is as follows:

  • Grey matter on the boundaries (cerebellar cortex)
  • White matter in the middle
  • Deeply residing nuclei within the white matter

INPUT TO CEREBELLUM:

All the external fibers (all of these are excitatory) entering the cerebellum are input fibers and can be classified as

  • Olivocerebellar fibers (called the climbing fibers) which go from inferior olivary nuclei to the outermost layer of cerebellar cortex. These fibers release aspartate upon stimulation
  • All the other fibers (called mossy fibers as a group)
  • All the input fibers, on their way to the cortex, must first synapse with the deeply residing nuclei and stimulate them

PROCESSING MACHINERY IN THE CEREBELLUM:

The cerebellar cortex has an outer molecular layer, a middle purkinje layer and a deep Grenula layer

  • Cell bodies of certain flask shaped neurons are present in purkinje area
  • Their dendrites lie in the molecular area
  • Their axons traverse the grenula on their way to synapse with deep nuclei (these are inhibitory axons and release GABA to inhibit the deep nuclei)

The climbing fibers ascend to molecular area and synapse with dendrites of the flask shaped neurons and release aspartate which is stimulatory to the flask shaped neurons

  • This means that the flask shaped neurons release GABA at deep nuclei and, essentially, the climbing fibers have indirectly inhibited the deep nuclei.

The mossy fibers ascend up to the grenula and make multiple synapse with grenula cells

  • The axons of the grenula cells ascend to the molecular area where they bifurcate and run parallel in the white matter of the cortex parallel to the curvature of the cortex, synapsing with dendrites from millions of purkinje cells on their way.
  • These fibers are glutaminergic (stimulatory)
  • Note that one mossy fiber synapses with multiple grenula cells
  • This means that the mossy fibers, too, indirectly inhibit the deep nuclei

There is an inbuilt inhibitory system, too, residing in the cerebellum.

  • One group of these is called golgi cells which are situated in the grenula layer
    • These can be stimulated by the bifurcated parallel fibers and by the mossy fibers and, upon stimulation, release GABA at grenula cells to inhibit it
  • The other two groups are called stellate cells and basket cells which reside in purkinje layer
    • These are stimulated by the bifurcated parallel fibers and, upon stimulation, release GABA on surrounding purkinje cells to inhibit them

OUTPUT FROM CEREBELLUM:
The output fibers are the axons of the deep nuclei

The three lobes of the cerebellum:

  • The neocerebellum is connected to the cerebrum and is also called cerebrocerebellum (also called the pontocerebellum)
  • The palleocerebellum is connected to the spinal cord and is also called spinal cerebelleum
  • The archecerebellum is connected to the vestibular system and is also called the vestibulocerebellum

 

THE VESTIBULOCEREBELLUM:

  • In the inner ear lies the vestibular apparatus which sends information in the vestibular nerve to either the cerebellum directly or the vestibular nuclei and then the cerebellum
  • The mossy fibers eventually go to the cortex through the general pathway that mossy fibers follow (mentioned in previous section)
  • Axons from the deep nuclei (fastigial nucleus), fibers (cerebellovestibular fibers) come out to synapse with and stimulate the vestibular nuclear complex. This pathway then fires up and fires down
    • The descending output goes to vestibulospinal tract (antigravity tract; VIP makes you stand)
    • The ascending output goes to nuclei of CN 3,4 and 6

 

THE SPINOCEREBELLUM:

  • Globose and emboliform nuclei in the cerebellum are associated with the spinocerebellum
  • Vermis and paravermal area receive input from the spinal cord
    • The dorsal spinocerebellar tract takes proprioceptive information from the lower limb and trunk to the cerebellum via the inferior cerebellar peduncle
      • Fibers from hip region come to vermal area and those from distal part of the limb go to the para vermal area
    • The cuneocerebellar pathway (THIS IS NOT COMING FROM NUCLEUS CUNEATUS) takes proprioceptive information from upper limb to the cerebellum via the inferior cerebellar peduncle
      • Fibers from trunk to the vermal area and those from the limbs to the paravermal area
    • The ventral spinocerebellar pathway enters the spine, crosses to contralateral side, ascends to superior cerebellar peduncle, descends a little and then goes to the contralateral side while still within the cerebellum

All of the above fibers enter as mossy fibers and, through the mossy fiber pathway discussed earlier, end up on globose and emboliform nuclei (deep nuclei)

  • From these nuclei information (output) goes up and down
    • Ascends to the red nucleus and then the thalamus and then the cortex
    • Ascends directly towards the thalamus and then to cortex
    • FROM THE RED NUCLEUS, some fibers descend in the ruberospinal tract
    • FROM THE CEREBRAL CORTEX, some fibers will descend to the muscles

CEREBROCEREBELLUM:

  • Lateral part of the cerebellar hemisphers (area lateral to paravermal area) is called cerebrocerebellum or neocerebellum.
  • Pontine nuclei receive corticopontine fibers from the cerebral cortex
    • Pontocerebellar fibers cross to contralateral side and enter the cerebellum vianthe middle cerebellar peduncle
    • They course as mossy fibers and synapse at dentate nucleus (deep nucleus)
    • From dentate nuclei, fibers go to red nucleus then thalamus then motor cortex. OR fibers go to thalamus then motor cortex.
      • These fibers are concerned with movement and helps to make the precise movements that the cortex wanted

Functional Brain Systems

  • Networks of neurons functioning together
    • The limbic system – spread widely in the forebrain
    • The reticular formation – spans the brain stem

Functional Brain Systems – The Limbic System

  • Location
    • Medial aspect of cerebral hemispheres
    • Also within the diencephalon
  • Composed of:
    • Septal nuclei, cingulate gyrus, and hippocampal formation
    • Part of the amygdala
  • The fornix and other tracts link the limbic system together

  • The “emotional brain”
    • Cingulate gyrus
      • Allows us to shift between thoughts
      • Interprets pain as unpleasant
  • Hippocampal formation
    • Hippocampus and the parahippocampal gyrus

 

Functional Brain Systems – The Reticular Formation

  • Runs through the central core of the medulla, pons, and midbrain
  • Forms three columns
    • Midline raphe nuclei
    • Medial nuclear group
    • Lateral nuclear group

  • Widespread connections
    • Ideal for arousal of the brain as a whole
  • Reticular activating system (RAS)
    • Maintains consciousness and alertness
    • Functions in sleep and arousal from sleep

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