Chapter 14; The Brain and Cranial Nerves Flashcards
identify the major parts of the brain.
principal parts of the brain – 4 major parts in adult brain
1) brain stem – portion of brain immediately superior to spinal cord a. Contains medulla oblongata, pons, and midbrain
2) Cerebellum – posterior to the brain stem III.
3) Diencephalon – superior to the brain stem - Contains thalamus, hypothalamus, epithalamus
4) Cerebrum – supported on the diencephalon and brain stem a. Largest part of the brain
describe how the brain is protected.
protective coverings
cranial meninges - continuous with the spinal meninges, same names:
Dura mater (outer)
2 layers (spinal has only 1), Fused together except where they separate to enclose the dural venous sinuses that drain venous blood from brain and deliver to internal jugular veins.
- Periosteal layer (external)
- Meningeal layer (internal)
3 extensions of the dura mater separate parts of the brain:
- *1. Falx cerebri:** separates the two hemispheres of the cerebrum
- *2. Falx cerebelli**: separates the two hemispheres of the cerebellum
- *3. Tentorium cerebell**i: separates the cerebrum from the cerebellum
Arachnoid mater (middle)
Pia mater (inner)
No epidural space around the brain
BBB
a barrier consisting of specialized brain capillaries and astrocytes that prevents the passage of materials from the blood to the cerebrospinal
fluid and brain.
Consists mainly of tight junctions that seal together the endothelial
cells of the brain capillaries and a thick basement membrane that surrounds the capillaries. Water soluble glucose can cross the BBB by active transport
Consists mainly of tight junctions that seal together the endothelial cells of brain blood capillaries and a thick basement membrane that surrounds the capillaries.
Astrocytes are one type of neuroglia.
a. The processes of many astrocytes press up against the capillaries and secrete chemicals that maintain the permeability characteristics of the tight junctions.
A few water-soluble substances, such as glucose, cross the BBB by active transport
Other substances, such as creatinine, urea, and most ions, cross the BBB very slowly
V. Other substances, proteins and most antibiotic drugs, do not pass at all from blood into brain tissue.
Lipid-soluble substances, such as oxygen, CO2, ETOH, and most anesthetic agents can access brain tissue freely.
a. Trauma, certain toxins, and inflammation can breakdown the BBB.
describe the blood supply of the brain
Blood flows to the brain mainly via the internal carotid and vertebral arteries to the internal jugualr ; the dural venous sinuses drain into the internal jugular veins to return blood from the head to the heart
No glucose stored in the brain
explain the formation and circulation of cerebrospinal fluid.
cerebrospinal fluid (CSF) – fluid produced by ependymal cells that cover choroid plexuses in the ventricles of the brain
-The fluid circulates in the ventricles, the central canal, and the subarachnoid space around the brain and spinal cord
-A clear, colourless liquid composed primarily of water that protects the
brain and spinal cord form chemical and physical injuries.
-Also carries small amounts of O2, glucose and other necessary chemicals from the blood to neurons and neuroglia.
CSF continuously circulates through cavities in the brain and spinal cord and around the brain and spinal cord in the subarachnoid space.
Contains small amounts of glucose, proteins, lactic acid, urea, cations, and anions; also contains some WBCs.
subarachnoid space – space between the arachnoid mater and the pia mater
ventricle – four CSF-filled cavities within the brain
a. lateral ventricles (Ventricles 1 and 2) – one in each hemisphere of the cerebrum
- separated anteriorly by a thin membrane: septum pellucidum – the thin membrane that separates the lateral ventricles of the brain anteriorly
b. third ventricle – a narrow slitlike cavity along the midline, superior to the hypothalamus and between the R and L halves of the thalamus
c. fourth ventricle – lies between the brain stem (medulla oblongata and pons) and the cerebellum
- *functions of CSF – 3 basic functions**
a. Mechanical protection: shock absorbing medium that protects delicate brain from jolts; the fluid buoys the brain so it “floats” in the cranial cavity
b. Homeostatic Function: pH of CSF affects pulmonary ventilation and cerebral blood flow; also serves as a transport system for polypeptide hormones secreted by hypothalamic neurons that act at remote sites in the brain
c. Circulation: is a medium for minor exchange of nutrients and waste products between the blood and adjacent nervous tissue
choroid plexus – a network of capillaries located in the roof of each of the 4
ventricles of the brain a. ependymal cells around choroid plexuses produce cerebrospinal fluid
1. jointed by tight junctions, cover the capillaries of the choroid plexuses.
2. Selected substances (mostly water) filtered from the blood plasma by the capillaries are secreted by the ependymal cells to produce CSF.
- *blood cerebrospinal fluid barrier** – formed by the tight junctions between ependymal cells; materials entering CSF from capillaries cannot leak between the cells, they must pass through the ependymal cells.
a. Permits certain substances to enter CSF but excludes others, protecting brain and spinal cord from harmful substances.
circulation of CSF – formed in the choroid plexuses of Ventricles 1 and 2, flows
into the 3rd ventricle through:
a. interventricular foramina – two narrow, oval openings through which the CSF passes from lateral ventricles to third ventricle. More CSF is added by the choroid plexus in the roof of the 3rd ventricle. The fluid then flows through the:
b. aqueduct of the midbrain – cerebral aqueduct – a channel through the midbrain connecting the third and fourth ventricles and containing CSF. More CSF is added by the choroid plexus of the 4th ventricle. CSF enters the subarachnoid space through three openings:
c. median aperture – one of the 3 openings in the roof of 4th ventricle of brain that allows CSF to enter subarachnoid space
d. lateral apertures – other two openings that allow CSF to enter
subarachnoid space.
e. arachnoid villi – fingerlike or berrylike tufts of the arachnoid mater that protrude into the superior sagittal sinus that reabsorb CSF into the blood stream. (Cluster = arachnoid granulation)
1. CSF is reabsorbed at the same rate it is produced
2. Pressure remains constant.
Hydrocephalus = Increase in CSF pressure due to rapid CSF production, injury, or other brain abnormalities. Quickly life-threatening in adult skull bones.
describe the structures and functions of the brain stem
BRAIN STEM – part of brain between spinal cord and diencephalon. Consists of medulla oblongata, pons, and midbrain.
*MEDULLA OBLONGOTA – most inferior part of the brain stem
- continuous with spinal cord
- begins at foramen magnum and extends to inferior border of pons
- about 3cm
- White matter contains all sensory (ascending) tracts and motor (descending) tracts that extend between the spinal cord and other parts of the brain
Pyramids – Two roughly triangular structures (white matter protrusions) on anterior aspect of medulla oblongata
a. Composed of the largest motor tracts that run from the cerebral cortex to the spinal cord. decussation of pyramids – crossing of 90% of the axons in the large motor tracts to opposite sides in the medullary pyramids
- occurs just superior to the junction of the medulla with the spinal cord
- explains why each side of brain controls voluntary movements on the opposite side of the body
Medulla also contains several nuclei – collection of neuronal cell bodies within the CNS. Some control vital body functions – ex. Cardiovascular center, medullary respiratory center
cardiovascular center – groups of neurons scattered within the medullar oblongata that regulate heart rate, force of contraction, and blood vessel diameter
medullary respiratory center – neurons in medulla oblongata that adjust the basic rhythm of breathing, two groups
- Dorsal respiratory group – active during normal quiet breathing
- Ventral respiratory group – active during forceful breathing.
Reflexes for vomiting, swallowing, sneezing, coughing, hiccupping – also controlled by nuclei in the medulla Gracile nucleus - receives sensory information associated with touch, pressure, vibration), Substantia nigra releases dopamine
Olive – just lateral to each pyramid, overall mass on superior part of medulla oblongata.
- Contains the inferior olivary nucleus – receives input from cerebral cortex, red nucleus of the midbrain, and spinal cord
- Neurons extend axons into cerebellum, regulate activity of cerebellar neurons
- Influence cerebellar neuron activity; provides instructions that cerebellum uses to adjust muscle activity as new motor skills are learned.
Posterior medulla – nuclei associated with sensations of touch, pressure, vibration, and conscious proprioception
Finally, medulla contains nuclei that are components of sensory pathways for taste, audition, and balance.
Medulla has nuclei associated with 5 cranial nerves:
a. Vestibulocochlear (VIII) nerves – internal ear/hearing
b. Glossopharyngeal (IX) nerves – taste, swallowing, salivation
c. Vagus (X) nerves – pharynx, larynx, thoracic and abdominal viscera
d. Accessory (XI) nerves (cranial portion) – Actually part of vagus (X) nerves. Nerve impulses that control swallowing via the vagus nerves
e. Hypoglossal (XII) nerves – tongue movements during swallowing and speech
*PONS
the part of the brain stem that forms a “bridge” between the medulla oblongata and the midbrain; anterior to the cerebellum
- About 2.5 cm long
- Consists of both nuclei and tracts
- The connections between brain parts are provided by bundles of axons
- Some axons of the pons connect the right and left sides of the cerebellum
- Others are part of ascending sensory tracts and descending motor tracts
The pons has 2 major structural components:
- Ventral region
- Forms a large synaptic relay station consisting of scattered grey centers called the pontine nuclei
- Entering and exiting these nuclei are numerus white matter tracts, each of which provides a connection between the cortex (outer layer) of a cerebral hemisphere and that of the opposite hemisphere of the cerebellum.
-
Dorsal region – more like other regions of the brain stem, medulla, and midbrain.
* Contains ascending and descending tracts along with the nuclei of cranial nerves.
pontine respiratory group – a collection of neurons in the pons that transmits nerve impulses to the dorsal respiratory group, and may modify the basic rhythm of breathing.
The Pons contains nuclei associated with 4 pairs of cranial nerves:
- Trigeminal (V) nerves – sensations from head and face, chewing
- Abducens (VI) nerves – motor impulses that control eyeball movement
- Facial (VII) nerves – regulate secretion of saliva and tears, contraction of facial expression muscles
- Vestibulocochlear (VIII) nerves – balance and equilibrium
*MIDBRAIN or mesencephalon
– the part of the brain between the pons and the
diencephalona. about 2.5cm long
The aqueduct of the midbrain passes through the midbrain, connecting the 3rd ventricle above with the 4th ventricle below.
The midbrain contains both nuclei and tracts.
cerebral peduncles – bundled pairs of axons contained in the anterior part of the midbrain
- Consist of axons of the corticospinal, corticobulbar, and corticopontine tracts, which conduct nerve impulses from motor areas in the cerebral cortex to the spinal cord, medulla, and pons respectively.
Posterior part of midbrain – called the tectum.
Contains 4 rounded elevations, 2 superior, 2 inferior
Superior colliculi – nuclei; serve as reflex centers for certain visual activities, movements of the head, eyes, and trunk in response to visual stimuli.
Inferior colliculi – part of the auditory pathway, relay impulses from the receptors for hearing in inner ear to the brain. Also reflex centers for the startle reflex (sudden movements of head, eyes, and trunk that occur when surprised by loud noise)
Midbrain also contains several other nuclei:
- left and right substania nigra – large, darkly pigmented, neurons that release dopamine extend from substantia nigra to the basal nuclei; help control subconscious muscle activities
- left and right red nuclei – cluster of cell bodies in the midbrain, occupying a large part of the tectum from which axons extend into the rubroreticular and rubrospinal tracts.
- Reddish due to rich blood supply and iron-containing pigment in their neuronal cell bodies.
- Axons from cerebellum and cerebral cortex form synapses in the red nuclei, which help control muscular movements.
Other nuclei in the midbrain are associated with 2 pairs of cranial nerves:
- Oculomotor (III) nerves – control movements of eyeball, pupil, lens shape
- Trochlear (IV) nerves – movements of eye ball
describe the structures and functions of the reticular formation.
– a network of small groups of neuronal cell bodies (gray matter) scattered among bundles of myelinated axons (white matter) beginning in the medulla oblongata and extending superiorly through the central part of the brain stem.
Neurons within the reticular formation have both ascending and descending functions
reticular activating system (RAS) ASCENDING – the ascending portion of the reticular formation.
- Consists of sensory axons that project into the cerebral cortex, both directly and through the thalamus.
- When this area of the brain stem is active, nerve impulses pass to the thalamus and widespread areas of the cerebral cortex, resulting in generalized alertness or arousal from sleep
- Many sensory stimuli can activate the ascending portion of the RAS: visual and auditory stimuli, mental activities, stimuli from pain, touch, and pressure receptors, and receptors in our limbs and head that keep us aware of body position
- Perhaps most important function of RAS = consciousness – a state of wakefulness in which and individual is fully alert, awake, and oriented
- Prevents sensory overload by filtering out insignificant information so that it does not reach consciousness
- Helps regulate muscle tone, heart rate, BP, and resp rate.
Damage to RAS = coma – a state of unconsciousness from which an individual cannot be roused
The descending portion of the RAS has connections to the cerebellum and spinal cord
The RAS receives input from eyes, ears, and other sensory receptors but NOT smell; even strong odours fail to cause awakening. Therefore, need smoke alarms (or vibrating pillow or flashing light for hearing impaired) as smoke will not awaken you.
describe the structure and functions of the cerebellum.
– second only to cerebrum in size.
- Occupies inferior and posterior aspects of cranial cavity
- Has a highly folded surface that greatly increases the surface area of its outer gray matter cortex, allowing for a greater number of neurons
- Accounts for 10% of brain mass yet 50% of brain neurons
- Posterior to the medulla and pons, inferior to the posterior portion of the cerebrum
transverse fissure – a deep groove that separates the cerebrum from the cerebellum.
Vermis – central constricted area of the cerebellum that separates the two cerebellar hemis heres. Resemble butterfly body
cerebellar hemispheres – the two lateral lobes. Resemble butterfly wings each hemisphere consists of lobes separated by deep and distinct fissures
- -Anterior lobe and posterior lobe: govern subconscious aspects of skeletal muscle movements
- -Flocculonodular lobe: on inferior surface, contributes to equilibrium and balance
cerebellar cortex – superficial layer of cerebellum, consists of gray matter in a series of slender, parallel folds
folia – series of slender, parallel folds of the cerebellar cortex surface
arbor vitae – white matter tracts of the cerebellum, deep to the gray matter, have a tree like appearance when seen in midsagittal section.
Cerebellar nuclei – regions of gray matter even deeper, within the white matter, that give rise to axons carrying impulses from the cerebellum to other brain centers.
cerebellar peduncles –3 pairs of white matter nerve axon bundles, attach the cerebellum to the brain conduct impulses between cerebellum and other parts of the brain.
- Superior cerebellar peduncles – contain axons that extend from the cerebellum to the red nuclei of the midbrain and to several nuclei of the thalamus
- Middle cerebellar peduncles – largest peduncles; their axons carry impulses for voluntary movements from the pontine nuclei (which receive input from motor areas of the cerebral cortex) into the cerebellum
- Inferior cerebellar peduncles – consist of:
- Axons of the spinocerebellar tracts that carry sensory information into the cerebellum from proprioceptors in the trunk and limbs.
- Axons from the vestibular apparatus of the inner ear and from the vestibular nuclei of the medulla and pons that carry sensory info into the cerebellum from proprioceptors in the head.
- Axons from inferior olivary nucleus of the medulla that enter the cerebellum and regulate the activity of cerebellar neurons
- Axons that extend from the cerebellum to the vestibular nuclei of the medulla and pons
- Axons that extend from the cerebellum to the reticular formation
- The primary function of the cerebellum is to evaluate how well movements initiated by motor areas in the cerebrum are actually being carried out.
- When movements initiated by the cerebral motor areas are not being carried out correctly, the cerebellum detects the discrepancies.
- It sends feedback signals to motor areas of the cerebral cortex, via its connections to the thalamus
- The feedback signals help correct the errors, smoother the movements, and coordinate complex sequences of skeletal muscle contractions.
- Cerebellum is also the main brain region that regulates posture and balance.
- Cerebellum may also have nonmotor functions such as cognition and language processing as well as in processing sensory information.
describe the components and functions of the diencephalon (thalamus, hypothalamus, and epithalamus).
Diencephalon – forms a central core of brain tissue just superior to the midbrain
- Almost completely surrounded by the cerebral hemispheres and contains numerous nuclei involved in a variety of sensory and motor processing between higher and lower brain centers
- Extends from the brain stem to the cerebrum and surrounds the third ventricle.
- Includes the thalamus, hypothalamus, and epithalamus
Projecting form the hypothalamus is the pituitary gland aka hypophysis
Portions of the diencephalon in the wall of the third ventricle are called circumventricular organs.
The optic tracts carrying neurons from the retina enter the diencephalon
Thalamus – a large, oval structure located bilaterally on either side of the third ventricle; consisting of two masses of gray matter organized into nuclei
- Is the main relay center for sensory impulses ascending to the cerebral cortex
- About 3cm long
- Makes up 80% of the diencephalon
- Paired oval masses of gray matter organized into nuclei with interspersed tracts of white matter
Interthalamic adhesion – AKA intermediate mass – a bridge of gray matter that joins the right and left halves of the thalamus in about 70% of human brains.
Internal medullary lamina – a vertical Y-shaped sheet of white matter that divides the gray matter of the right and left sides of the thalamus
- Consists of myelinated axons that enter and leave the various thalamic nuclei
- Internal capsule – a thick band of white matter lateral to the thalamus through which axons that connect the thalamus and cerebral cortex pass.
Thalamus functions:
- Major relay station for most sensory impulses that reach the primary sensory areas of the cerebral cortex from the spinal cord and brain stem
- Contributes to motor functions by transmitting info from the cerebellum and basal nuclei to the primary motor area of the cerebral cortex
- Also relays nerve impulses between different areas of the cerebrum and plays a role in the maintenance of consciousness.
7 major groups of nuclei on each side of the thalamus, based on position and function:
- Anterior nucleus – input from hypothalamus, output to limbic system; functions in emotions and memory
- Medial nuclei – input from limbic system and basal nuclei, output to cerebral cortex; function: emotions, memory, learning, and cognition
- Lateral group nuclei – input from limbic system, superior colliculi, and cerebral cortex, output to cerebral cortex.
- Lateral dorsal nucleus function: expression of emotion
- Lateral posterior nucleus and pulvinar nucleus function: help integrate sensory information
- Ventral group – 5 nuclei
- Ventral anterior nucleus – input from basal nuclei, output to motor areas of cerebral cortex; function: movement control
- Ventral lateral nucleus – input from cerebellum and basal nuclei, output to motor areas of cerebral cortex; function: also movement control
- Ventral posterior nucleus – relays impulses for somatic sensations such as tough, pressure, vibration, itch, tickle, temp, pain, and proprioception from face and body to cerebral cortex
- Lateral geniculate nucleus – relays visual impulses for sight from the retina to the primary visual area of the cerebral cortex
- Medial geniculate nucleus – relays auditory impulses for
- hearing from ear to primary auditory area of cerebral
- cortex
- Intralaminar nuclei – within the internal medullary lamina; connect with the reticular formation, cerebellum, basal nuclei, and wide areas of cerebral cortex. Function: arousal (wakening; activation of the cerebral cortex from the brain stem reticular formation) and integration of sensory and motor info
- Midline nucleus – thin band adjacent to third ventricle; function: memory and olfaction
- Reticular nucleus – surrounds lateral aspect of thalamus, next to internal capsule. Function: monitor, filter, integrate activities of other thalamic nuclei
Hypothalamus
a portion of the diencephalon, lying beneath the thalamus and forming the floor and part of the wall of the third ventricle.
Composed of a dozen or so nuclei in 4 major regions:
- Mammillary region – “nipple shaped” adjacent to the midbrain, most posterior part of the hypothalamus Includes the mammillary bodies and posterior hypothalamic nuclei. The mammillary bodies are two small, rounded projections that serve as relay stations for reflexes related to the sense of smell
- Uberal region – widest part of the hypothalamus Includes the dorsomedial nucleus, ventromedial nucleus, arcuate nucleus, plus the stalk-like infundibulum which connects the pituitary gland to the hypothalamus
- Supraoptic region – superior to the optic chiasm (point of crossing of optic nerves) Includes the paraventricular nucleus, supraoptic nucleus, anterior hypothalamic nucleus, and
suprachiasmatic nucleus
Axons from the paraventricular and supraoptic nuclei form the hypothalamohypophyseal tract, which extends through the infundibulum to the posterior lobe of the pituitary
- Preoptic region – anterior to the supraoptic region, usually considered part of the hypothalamus because it participates with the hypothalamus in regulating certain autonomic activities. Contains the medial and lateral preoptic nuclei
Hypothalamus functions:
A. Control of the ANS – controls and integrates activities of the autonomic nervous system, which regulates contraction of smooth muscle and cardiac muscle and the secretions of many glands. Axons extend from the hypothalamus to parasympathetic and sympathetic nuclei in the brain stem and spinal cord. Through the ANS, the hypothalamus is a major regulator of visceral activities, including regulation of heart rate, movement of food through GI tract, and contraction of urinary bladder
B. Production of hormones – produces several hormones; two types of important connections with pituitary gland: hypothalamic hormones known as releasing hormones and inhibiting hormones are released into capillary networks in the median eminence. Blood steam carries these hormones directly to anterior lobe of pituitary where they stimulate or inhibit secretion of anterior pituitary hormones. Second, axons extend from the paraventricular and supraoptic nuclei through the infundibulum into the posterior lobe of pituitary. Cell bodies of these neurons make one of two hormones (oxytocin or antidiuretic hormone). Their axons transport the hormones to the posterior pituitary, where they are released.
C. Regulation of Emotional and Behavioral patterns – Together with limbic system, hypothalamus participates in expressions of rage, aggression, pain, and pleasure, and the behavioral patterns related to sexual arousal
D. Regulation of eating and drinking – regulates food intake. Contains a feeding center which promotes eating and a satiety center, which causes fullness sensation and cessation of eating. Also contains a thirst center. When certain cells are stimulated by a rising osmotic pressure of ECF, they cause sensation of thirst. Intake of water restores osmotic pressure to normal, removing the stimulation and relieving the thirst.
E. Control of Body Temperature – functions as body’s thermostat. Senses body temp and maintains at a desired setpoint. If temp of blood flowing through hypothalamus is up or down, hypothalamus generates impulses to raise or lower temp.
F. Regulation of Circadian rhythms and states of consciousness – Suprachiasmatic nucleus of hypothalamus serves as body’s internal biological clock – establishes circadian rhythms. This nucleus receives input from eyes (retina) and sends output to other hypothalamic nuclei, the reticular formation, and the pineal gland.
Epithalamus
a small region of the diencephalon, superior and posterior to the thalamus, composed of pineal gland and associated structures.
pineal gland – Small pea-sized cone shaped gland located in the roof of the third ventricle. Secretes melatonin. Part of the endocrine system.
Melatonin – a hormone secreted by the pineal gland that helps set the timing of the body’s biological clock. More melatonin is produced in darkness than in light.
Habenular nuclei – involved in olfaction, especially emotional responses to odors.
circumventricular organs – parts of the diencephalon, located in the wall of the third ventricle.
a. Monitor chemical changes in the blood because they lack a blood brain barrier
b. Include part of the hypothalamus, pineal gland, pituitary gland, and a few other nearby structures.
c. Help coordinate homeostatic activities of the endocrine and nervous systems, such as regulation of BP, fluid balance, hunger, and thirst.
d. Also thought to be the site of entry into brain of HIV; once in the brain,
1. HIV may cause dementia and other neurological disorders.
describe the cortex, gyri, fissures, and sulci of the cerebrum.
Cerebrum – “the seat of intelligence.” Provides ability to read, write, speak, make calculations, compose music, remember, plan future, imagine things that have never existed before. Consists of outer cerebral cortex, internal region of cerebral white matter, and gray mater nuclei deep within the white matter.
cerebral cortex – surface of the cerebral hemispheres, 2-4 mm thick, consisting of gray matter; arranged in six layers of neuronal cell bodies in most areas.
- Contains billions of neurons arranged in layers.
- During embryonic development, gray matter of the cortex enlarges much faster than the deeper white matter resulting in cortical region folds
gyrus or convolution (plural is gyri) – a fold of the cerebral cortex of the brain. **Formed in brain development becausethe gray matter grows faster than the underlying white matter.
Fissure – the deepest grooves between gyri folds
sulcus (plural is sulci) – the shallower grooves between folds
longitudinal fissure – most prominent fissure, separates cerebrum into left and right halves deep indentation found along the medial plane
cerebral hemispheres – the left and right halves of the cerebrum, separated by the longitudinal fissure. Within the longitudinal fissure between the cerebral hemispheres is the falx celebri
corpus callosum – internal connection of the cerebral hemispheres; the great commissure of the brain between the cerebral hemispheres. A broad band of white matter containing axons that extend between the hemispheres.
locate the lobes of the cerebrum.
- central sulcus – separates the frontal lobe from parietal lobe
- frontal lobe – covered by frontal bone
- parietal lobe – covered by parietal bone
- precentral gyrus – major gyrus; located immediately anterior to the central sulcus, contains primary motor area
- postcentral gyrus – major gyrus; located immediately posterior to the central sulcus, contains primary somatosensory area.
- lateral cerebral sulcus (fissure) – separates frontal lobe from temporal lobe
- temporal lobe – covered by the temporal bone
- parieto occipital sulcus – separates the parietal lobe from occipital lobe
- occipital lobe – covered by occipital bone
- insula – not visible at surface, lobe within the lateral cerebral sulcus, deep to parietal, frontal, and temporal lobes.
describe the tracts that compose the cerebral white matter.
cerebral white matter – consists primarily of myelinated axons in three types of tracts:
- association tracts – contain axons that conduct nerve impulses between gyri in the same hemisphere
- commissural tracts – contain axons that conduct nerve impulses from gyri in one cerebral hemisphere to corresponding gyri in the other cerebral hemisphere.
3 important groups of commissural tracts:
- Corpus callosum (largest fiber bundle in the brain, containing about 300 million fibers)
- Anterior commissure
- Posterior commissure
projection tracts – contain axons that conduct nerve impulses from the cerebrum to lower parts of the CNS (thalamus, brain stem, or spinal cord) or from lower parts of the CNS to the cerebrum
a. Ex: internal capsule – a thick band of white matter that contains both ascending and descending axons
describe the nuclei that compose the basal nuclei.
basal nuclei – paired clusters of gray matter deep in each cerebral hemisphere including the globus pallidus, putamen, and caudate nucleus
previously called basal ganglia, but incorrect as ganglion is an aggregate of neuronal cell bodies in PNS, nuclei = CNS
**internal capsule - Lentiform and Caudate together
Lentiform nucleus – the globus pallidus (closer to thalamus) and putamen (closer to cerebral cortex) together
Caudate nucleus – third basal nuclei. Has a large “head” connected to a smaller “tail” by a long commashaped “body”
Corpus striatum – the lentiform and caudate nuclei together. Name refers to the striated appearance of the internal capsule as it passes along the basal nuclei.
Nearby structures functionally linked to the basal nuclei:
Substantia nigra of the midbrain – axons from here terminate in the caudate nucleus and putamen
Subthalamic nuclei of the diencephalon – interconnect with the globus pallidus
Claustrum – a thin sheet of gray matter lateral to the putamen. Considered to be a subdivision of the basal nuclei. No clearly defined function in humans, may be involved in visual attention.
Basal Nuclei functions:
a. Receive input from the cerebral cortex, provide output to motor parts of the cortex via medial and ventral group nuclei of the thalamus.
b. Have extensive connections with one another
c. Help regulate initiation and termination of skeletal muscle movements
d. Activity in neurons in the putamen precedes or anticipates body movements; activity of neurons in caudate nucleus occurs prior to eye movements.
e. Globus pallidus helps regulate muscle tone required for specific body movements
f. Basal nuclei also control subconscious contractions of skeletal muscles; ex. Automatic arm swings while walking, true laughing in response to a joke.
g. Basal nuclei have other roles too: help initiate and terminate some cognitive processes such as attention, memory, planning; may act with limbic system to regulate emotional behaviors.
describe the structures and functions of the limbic system.
limbic system – a part of the forebrain. Encircling the upper part of the brain stem and corpus callosum; a ring of structures on the inner border of the cerebrum and floor of the diencephalon.
Main components:
- Limbic lobe – rim of cerebral cortex on the medial surface of each hemisphere. Includes the cingulate gyrus which lies above the corpus callosum and the parahippocampal gyrus, which is in the temporal lobe below. The hippocampus is a portion of the parahippocampal gyrus that extends into the floor of the lateral ventricle.
- Dentate gyrus – lies between the hippocampus and the parahippocampal gyrus
- Amygdala – composed of several groups of neurons located close to the tail of the caudate nucleus (almond-shaped)
- Mammillary bodies – of the hypothalamus, two round masses close to the midline near the cerebral peduncles.
- Two nuclei of the thalamus: anterior nucleus and the medial nucleus; participate in limbic circuits
- Olfactory bulbs – flattened bodies of the olfactory pathway that rest on the cribriform plate
- Fornix – a tract in the brain made up of association fibers, connecting the hippocampus with the mammillary bodies. The fornix, stria terminalis, stria medullaris, medial forebrain bundle, and mammillothalamic tract are linked by bundles of interconnecting myelinated axons.
Functions of the limbic system:
- Called “emotional brain” because it plays a primary role in a range of emotions including pain, pleasure, docility, affection, and anger.
- Involved in olfaction and memory
- Together with parts of the cerebrum, the limbic system also functions in memory.
- Damage to the limbic system causes memory impairment. Damage to the amygdala causes a person to fail to recognize fearful expressions in others or to express fear in appropriate situations
- The hippocampus is unique among CNS structures; its cells can undergo mitosis. Therefore, the portion of the brain responsible for some aspects of memory may develop new neurons, even in the elderly. Damage to hippocampus results in loss of memory of recent events and difficulty committing anything new to memory
describe the locations and functions of the sensory, association, and motor areas of the cerebral cortex.
SENSORY AREAS
sensory areas – region of the cerebral cortex concerned with interpretation of sensory impulses. Involved in perception – the conscious awareness of a sensation.
- Sensory impulses arise mainly in the posterior half of both cerebral hemispheres, in regions behind the central sulci.
- Primary sensory areas receive sensory information relayed from peripheral sensory receptors through lower regions of the brain.
- Sensory association areas integrate sensory experiences to general meaningful patterns of recognition and awareness 1. Ex. Damage to primary visual area = blindness in at least part of visual field but damage to visual association area might see normally but be unable to recognize normal objects like lamps or toothbrushes just by looking at them.
I. primary somatosensory area – a region of the cerebral cortex posterior to the central sulcus in the postcentral gyrus of the parietal lobe of the cerebrum that localizes exactly the points of the body where somatic sensations originate.
- Receives nerve impulses for touch, pressure, vibration, itch, tickle, temperature, pain, and proprioception (joint and muscle position), and is involved in the perception of these somatic sensations.
- A “map” of the body is present in the primary somatosensory area, each point within the area receives impulses from a specific part of the body.
- The size of the cortical area receiving impulses from a particular part of the body depends on the number of receptors present there, rather than on the size of the body part. Ex. A larger region of the somatosensory area receives impulses from the lips and fingertips than from thorax or hip. This distorted somatic sensory map of the body is known as the sensory homunculus. The primary somatosensory area allows you to pinpoint where somatic sensations originate. Ex. Know exactly where to swat mosquito.
II. primary visual area – located at posterior tip of the occipital lobe, mainly on medial surface (next to longitudinal fissure receives visual info, involved in visual perception.
III primary auditory area – located in superior part of temporal lobe near the lateral cerebral sulcus
- receives info for sounds, is involved in auditory perception
IV primary gustatory area – located at the base of the postcentral gyrus superior to the lateral cerebral sulcus in the parietal cortex
- receives impulses for taste, involved in gustatory perception and taste discrimination.
V primary olfactory area – located in temporal lobe on medial aspect
- receives impulses for smell and involved in olfactory perception
MOTOR AREAS
motor areas – the region of the cerebral cortex that governs muscular movement, particularly the precentral gyrus of the frontal lobe
motor output from the cerebral cortex flows mainly from the anterior part of each hemisphere
primary motor area – region of cerebral cortex in precentral gyrus of the frontal lobe of the cerebellum that controls specific muscles or groups of muscles
- a “map” of the entire body is present in the primary motor area: each region within the area controls voluntary contractions of specific muscles or groups of muscles
- Electrical stimulation of any point in the primary motor area causes contraction of specific skeletal muscle fibers on the opposite side of the body.
- Different muscles represented unequally in the primary motor area.
- More cortical area is devoted to muscles involved in skilled, complex, or delicate movement Ex. Cortical region for fingers much larger than region for toes. This distorted map is called the motor homunculus.
Broca’s speech area – motor area of the brain in frontal lobe that translates thoughts into speech.
- Located in frontal lobe, close to lateral cerebral sulcus.
- Localized in left hemisphere in about 97% of people.
- Planning and production of speech occur in the left frontal lobe in most people.
- Impulses from the premotor area result in specific, coordinated muscle contractions while simultaneously, impulses propagate from Broca’s speech area to the primary motor area.
- Impulses also control the breathing muscles to regulate the proper flow of air past the vocal cords.
- The coordinated contractions of speech and breathing muscles enable you to speak your thoughts.
- People who suffer a CVA in this area can still have clear thoughts but are unable to form words – called nonfluent aphasia
ASSOCIATION AREAS
association areas – large cortical regions on the lateral surfaces of the occipital, parietal, and temporal lobes and on the frontal lobes anterior to the motor areas connected by many motor and sensory axons to other parts of the cortex; concerned with motor patterns, memory, concepts of word-hearing and
word-seeing, reasoning, will, judgment, and personality traits
i somatosensory association area – just posterior to and receives input from the primary somatosensory area as well as from thalamus and other parts of the brain
- permits you to determine the exact shape and texture of an object by feeling it, to determine the orientation of one object with respect to another as they are felt, and to sense the relationship of one body part to another.
- Also: role in storage of memories of past somatic sensory experiences, enabling you to compare current sensations with previous experiences 1. Ex. Somatosensory association area allows you to recognize objects such as a pencil and paperclip just by touching them.
II visual association area – located in occipital lobe, receives sensory impulses from the primary visual area and the thalamus
- relates present and past visual experiences and is essential for recognizing and evaluating what is seen 1. ex. Visual association area allows you to recognize an object such as a spoon simply by looking at it.
III Facial recognition area – inferior temporal lobe, receives nerve impulses from the visual association area
- Stores information about faces, allows you to recognize people by their faces. The facial recognition area in the right hemisphere is usually more dominant than the corresponding region in the left hemisphere.
IV auditory association area – located inferior and posterior to the primary auditory area in the temporal cortex
- allows you to recognize a particular sound as speech, music, or noise
V orbitofrontal cortex – lateral part of the frontal lobe, receives sensory impulses from the primary olfactory area
- allows you to identify odours and to discriminate among different odors.
- During olfactory processing, the orbitofrontal cortex of the right hemisphere exhibits greater activity than the corresponding region in the left hemisphere
VI Wernicke’s area or posterior language area – a broad region in the left temporal and parietal lobes
- Interprets the meaning of speech by recognizing spoken words.
- Active as you translate words into thoughts
- Regions in the left hemisphere that correspond to Broca’s and Wernicke’s areas in the left hemisphere also contribute to verbal communication by adding emotional content, such as anger or joy, to
- spoken words.
- CVA in Wernick’s area = still speak, but cannot arrange words in a coherent fashion (word salad/fluent aphasia)
VII common integrative area – bordered by somatosensory, visual, and auditory association areas.
- Receives nerve impulses from these areas and from the primary gustatory area, primary olfactory area, thalamus, and parts of the brain stem.
- Integrates sensory interpretations from the association areas and impulses from other areas, allowing formation of thoughts based on a variety of sensory inputs.
- Then transmits signals to other parts of the brain for the appropriate response to the sensory signals it has interpreted.
XII. prefrontal cortex (frontal association area) – extensive area in the anterior portion of the frontal lobe that is well developed in primates, especially humans. (can only be seen in a medial view)
- has numerous connections with other areas of the cerebral cortex, thalamus, hypothalamus, limbic system, and cerebellum
- concerned with makeup of a person’s personality, intellect, complex learning abilities, recall of information, initiative, judgement, foresight, reasoning, conscience, intuition, mood, future planning, and development of abstract ideas.
- Bilateral damage to prefrontal cortices = rude, inconsiderate, incapable of accepting advice, moody, inattentive, less creative, unable to plan for future, incapable of anticipating the consequences of rash or reckless behaviors.
- XIII. premotor area – a motor association area that is immediately anterior to the primary motor area.
- Neurons in this area communicate with the primary motor cortex, the sensory association areas in the parietal lobe, the basal nuclei, and the thalamus
- Deals with leaned motor activities of a complex and sequential nature
- Generates nerve impulses that cause specific groups of muscles to contract in a specific sequence, as when you write you name
- Also serves as a memory bank for such movements
XIV. frontal eye field area – in the frontal cortex, sometimes included in the premotor
area.
- Controls voluntary scanning movements of the eyes, ex. reading
explain the significance of hemispheric lateralization.
hemispheric lateralization – functional asymmetry of the brain
- the two hemispheres of the brain share performance of many functions but each hemisphere also specializes in performing certain unique functions.
- Considerable variation from one person to another
- Lateralization seems less pronounced in females than males both for language (left hemisphere) and for visual and spatial skills (right hemisphere)
- Females are less likely to suffer aphasia after damage to left hemisphere. Possibly because the anterior commissure is 12% larger and the corpus callosum has a broader posterior portion in females. (recall both anterior commissure and corpus callosum are commissura
