Chapter 14. Brain Functions. Medulla Oblongata, Pons, Mid-Brain, Reticular Formation, Thalamus, Hypothalamus, Cerebellum, and the Cerebrum

Transcription

1 Chapter 14 Brain Functions Medulla Oblongata, Pons, Mid-Brain, Reticular Formation, Thalamus, Hypothalamus, Cerebellum, and the Cerebrum

2 The Big Picture of Major Brain Structures and Their Functions.

3 The Big Picture of Major Brain Structures and Their Functions.

4 Part of the brain stem (medulla oblongata, pons, midbrain, and diencephalon) Medulla Oblongata The medulla oblongata begins at foramen magnum of the skull extends for about 3 cm rostrally ends at a groove between the medulla and pons slightly wider than deep the pyramids pair of external ridges on anterior surface // resembles side-byside baseball bats

5 Medulla Oblongata olive a prominent bulge lateral to each pyramid posteriorly, gracile and cuneate fasciculi of the spinal cord continue as two pair of ridges on the medulla all nerve fibers connecting the brain to the spinal cord pass through the medulla four pairs of cranial nerves begin or end in medulla - IX, X, XI, XII

6 Function Nuclei Located in Medulla Oblongata cardiac center // adjusts rate and force of heart vasomotor center // adjusts blood vessel diameter respiratory centers // control rate and depth of breathing reflex centers // coughing, sneezing, gagging, swallowing, vomiting, salivation, sweating, movements of tongue and head

7 Note: Diencephalon also includes hypothalamus and epithalamus (pineal gland & habenula)

8 Pons Central sulcus Cingulate gyrus Parietal lobe leaves Corpus callosum Frontal lobe Thalamus Anterior commissure Hypothalamus Optic chiasm Mammillary body Pituitary gland Temporal lobe Parieto occipital sulcus Occipital lobe Habenula Epithalamus Pineal gland Posterior commissure Cerebral aqueduct Fourth ventricle Midbrain Cerebellum Pons Medulla oblongata (a) Pons anterior bulge in brainstem, rostral to medulla Cerebellar peduncles tracts that connect cerebellum to brainstem inferior peduncles = inflow of action potentials from spinal cord middle peduncles = inflow of action potentials from all other areas of brain superior peduncles = outflow of action potentials to cerebrum Major role in motor control - How we regulate skeletal muscles!

9 The Pons Role in Motor Control The pons is the transit point for three peduncles that enter and exit the cerebellum Corticospinal tract carries afferent signal to skeletal muscle // the cerebrellum receives a branch of the CS tract // now the cerebellum knows the intent Corticospinal Tract from precentral gyrus Skeletal muscle sends to cerebellum via spinalcerebellar tract, this is the muscle's actual performance Cerebellum compares the intent to the perfomance Cerebellum then sends corrective feedback to the motor areas of cerebral cortex

10 Cross-section of Pons Vermis of cerebellum Superior cerebellar peduncle Middle cerebellar peduncle Trigeminal nerve nuclei Sensory root of trigeminal nerve Trigeminal nerve Reticular formation Medial lemniscus Fourth ventricle Anterior spinocerebellar tract Tectospinal tract (a) Midbrain Anterolateral system Transverse fascicles Longitudinal fascicles (b) Pons (c) Medulla (b) Pons

11 Pons ascending sensory tracts descending motor tracts pathways in and out of cerebellum cranial nerves V, VI, VII, and VIII originate within Pons sensory roles hearing, equilibrium, taste, facial sensations motor roles eye movement, facial expressions, chewing, swallowing, urination, and secretion of saliva and tears Pons also contain part of the reticular formation /// additional nuclei concerned with // sleep, respiration, analgesic descending tract, and posture

12 Midbrain Short segment of brainstem that connects the hindbrain to the forebrain contains and its boundries are defined by the cerebral aqueduct contains continuations of the medial lemniscus and reticular formation contains the motor nuclei of two cranial nerves that control eye movements CN III (oculomotor) and CN IV (trochlear)

13

14 Midbrain tectum roof-like top part of the midbrain posterior to cerebral aqueduct exhibits four bulges, the corpora quadrigemina upper pair, the superior colliculi function in visual attention, tracking moving objects, and some reflexes lower pair, the inferior colliculi receives signals from the inner ear /// relays them to other parts of the brain, especially the thalamus these two structures with input from eyes and ear and output to skeletal muscles in head/neck are responsible for the startle reflex cerebral peduncles fiber tracts // two stalks that anchor the cerebrum to the brainstem anterior to the cerebral aqueduct

15 Midbrain Important midbrain structures: tegmentum, substantia nigra, and cerebral crus Tegmentum: dominate structure is red nucleus // pink because of high denisty of blood vessels // works with cerebellum in fine motor control Substantia nigra: dark grey to black nucleus pigmented with melanin // motor center that relays inhibitory signals to thalamus and basal nucleus inhibits muscle contractions Note: Parkinson disease degeneration of substantia nigra neurons reduces dopamine secretion to basal nuclei // less inhibitory signals to anterior horm's LMN and therefore more unwanted contractions which results in an increase in muslce tremors Cerebral crus // bundle of nerve fibers that connects cerebrum to the pons // carries corticospinal tracts

16 Midbrain / Cross Section Posterior Tectum Reticular formation Cerebral peduncle: Tegmentum Substantia nigra Superior colliculus leaves Cerebral aqueduct Medial geniculate nucleus Central gray matter Oculomotor nucleus Medial lemniscus Red nucleus (a) Midbrain Cerebral crus (b) Pons Oculomotor nerve (III) Anterior (a) Midbrain (c) Medulla

17 Reticular Formation Visual input Reticular formation Ascending general sensory fibers Descending motor fibers to spinal cord Radiations to cerebral cortex Thalamus Auditory input loosely organized web of gray matter that runs vertically through all levels of the brainstem clusters of gray matter scattered throughout pons, midbrain and medulla occupies space between white fiber tracts and brainstem nuclei has connections with many areas of cerebrum more than 100 small neural networks without distinct boundary

18 Reticular Formation

19 Functions of Reticular Formation Networks somatic motor control adjust muscle tension to maintain tone, balance, and posture // especially during body movements relays signals from eyes and ears to the cerebellum // integrates visual, auditory, and balance and motion stimuli into motor coordination gaze center allow eyes to track and fixate on objects central pattern generators (examples) neural pools that produce rhythmic signals to the muscles of breathing and swallowing cardiovascular control // includes cardiac and vasomotor centers of medulla oblongata

20 Functions of Reticular Formation Networks pain modulation one route by which pain signals from the lower body reach the cerebral cortex origin of descending analgesic pathways // fibers act in the spinal cord to block transmission of pain signals to the brain sleep and consciousness plays central role in states of consciousness, such as alertness and sleep injury to reticular formation can result in irreversible coma

21 Functions of Reticular Formation Networks Habituation process in which the brain learns to ignore repetitive stimuli inconsequential stimuli ignored while remaining sensitive to other important stimuli

22 Reticular Formation Radiations to cerebral cortex Thalamus Visual input Auditory input Reticular formation Ascending general sensory fibers Descending motor fibers to spinal cord

23 The process of falling asleep. Note: The pineal gland produces melatonin which also plays a role in our mood and the process of falling asleep. Melatonin's production is directly related darkness: the shorter the daylight, the more melatonin produced. There are melatonin receptors located in the reticular formation and when melatonin hits these receptors then the reticular formation disconnects the thalamus from the cerebral cortex.

24 The Thalamus constitutes about four-fifths of the diencephalon two thalami are joined medially by a narrow intermediate mass composed of at least 23 nuclei we will consider five major functional groups the gateway to the cerebral cortex (Grand Central Station) nearly all sensory and motor signals to the cerebrum passes by way of synapses in the thalamic nuclei (except is olfaction) filters information on its way to cerebral cortex // split signal to share with limbic structures ascending signal synapse in thalamus then splits again as it ascends into cerebrum One pathway goes to primary sensory area then passes onto association /// Second pathway goes directly to the association area!!!

25 The Thalamus The diencephalon has three major sub-divisions thalamus hypothalamus epithalamus The two lobes of the thalamus form the lateral walls of the third ventricle Thalamus is the most rostral part of the brainstem Nicknamed the gateway to the cerebrum

26 The Thalamus Lateral geniculate nucleus Medial geniculate nucleus (a) Thalamus Anterior group Medial group Ventral group Lateral group Posterior group Thalamic leaves Nuclei Part of limbic system; memory and emotion Emotional output to prefrontal cortex; awareness of emotions Somesthetic output to postcentral gyrus; signals from cerebellum and basal nuclei to motor areas of cortex Somesthetic output to association areas of cortex; contributes to emotional function of limbic system Relay of visual signals to occipital lobe (via lateral geniculate nucleus) and auditory signals to temporal lobe (via medial geniculate nucleus) An ovoid mass on each side of the brain Perched at the superior end of the brainstem beneath the cerebral hemispheres

27 The Thalamus Plays key role in motor control many spinal ascending tracts synapse with nuclei of the thalamus also forms relay loops between cerebellum to cerebrum as provides pathways for feedback loops between the cerebral cortex, basal nuclei, and thalamus We will look at these pathways when we study motor control as an example of a higher function of the brain

28

29

30 The Thalamus and the Limbic System Thalamus is also involved in emotional functions because fiber tracts connects the thalamus to the limbic system as well as the thalamus to the cerebrum Limbic System plays key role in the formation (consolidation) of new memory (hypocampus & amygdala) provides a motivational system (e.g. reward pathway and fear) the site of our innate emotions subconsious value system learned behavior /// test boundaries nucleus accubens = pleasure center // actually delayed gratification center Limbic system = primitive emotional brain // a complex of structures that include some areas of cerebral cortex in the temporal and frontal lobes and some of the anterior thalamic nuclei LS (paleomammalian brain formation) // first evolved at the end of the reptilian and beginning of the mammalian periods.

31 Limbic System = The Primitive Brain

32 Hypothalamus

33 Hypothalamus forms part of the walls and floor of the third ventricle tissue boundry // anteriorly to optic chiasm // posteriorly to the paired mammillary bodies each mammillary body contains three or four mammillary nuclei // relay signals from the limbic system to the thalamus

34 Hypothalamus infundibulum a stalk that attaches the pituitary gland to the hypothalamus control centers // hypothalamus is the boss of the autonomic nervous system & endocrine system plays essential roll in homeostatic regulation of all body systems

35 Functions of Hypothalamic Nuclei hormone secretion controls anterior pituitary // secrete molecules which release hormones from anterior pituitary Anterior pituitary hormones regulates growth, metabolism, reproduction,and stress responses autonomic effects major integrating center for the autonomic nervous system nerve tracks between hypothalamus and medulla oblongata influences heart rate, blood pressure, gastrointestinal secretions and motility, and others thermoregulation hypothalamic thermostat monitors body temperature activates heat-loss center when temp is too high activates heat-promoting center when temp is too low

36 Functions of Hypothalamic Nuclei food and water intake hunger and satiety centers monitor blood glucose and amino acid levels // produce sensations of hunger and satiety thirst center monitors osmolarity of the blood rhythm of sleep and waking // controls 24 hour circadian rhythm of activity memory // mammillary nuclei receive signals from hippocampus emotional behavior // anger, aggression, fear, pleasure, and contentment // as part of limbic system

37 Epithalamus Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Central sulcus Cingulate gyrus Parietal lobe leaves Corpus callosum Frontal lobe Thalamus Anterior commissure Hypothalamus Optic chiasm Mammillary body Pituitary gland Temporal lobe Parieto occipital sulcus Occipital lobe Habenula Epithalamus Pineal gland Posterior commissure Cerebral aqueduct Fourth ventricle Midbrain Cerebellum Pons Medulla oblongata (a) epithalamus thin roof over the third ventricle // very small mass of tissue composed of pineal gland endocrine gland habenula relay from the limbic system to the midbrain

38 The Cerebellum

39 Cerebellum Anterior lobe Anterior leaves Vermis the largest part of the hindbrain and the second largest part of the brain as a whole Posterior lobe Only 10% total mass of brain Cerebellar hemisphere Posterior Folia contains 50% or more of all brain neurons (b) Superior view consists of right and left cerebellar hemispheres connected by vermis cortex of gray matter with folds (folia) and four deep nuclei in each hemisphere granule cells and Purkinje cells synapse on deep nuclei white matter branching pattern is called arbor vitae 60% surface area of the cerebrum cerebellum has 100 billion neurons Cerebellum s soma have more synapses than soma of the cerebrum 100,000 synapses per soma compared to 10,000 for other cortical soma

40 Functions of the Cerebellum In the 1950s we did not understand all the functions of cerebellum In the 1970s developed understanding that cerebellum coordinated skeletal muscle performance Today we understand the full range of cerebellum s functions: The cerebellum can be thought to simply compares stuff Receives and integrates sensory signals then sends efferent signals to other areas of the brain..

41 Functions of the Cerebellum comparing textures of two objects without looking at them spatial perception comprehension of different views of 3D objects belonging to the same object motor function // monitor muscle performance vs intent cognitive role (information processing) note: children with attention-deficit disorder have unusually small cerebellum

42 Functions of the Cerebellum Timekeeping center // Judge lapse time between two stimuli predicting movement of objects helps predict how much the eyes must move in order to compensate for head movements and remain fixed on an object Coordinates fixed eye vision as head/body moves Allows predator to catch prey or baseball player to catch a ball Hearing // distinguish between different pitches // distinguish between similar sounding words (rapid vs rabbit)

43 Functions of the Cerebellum language output // Relate word apple to verb eat planning and scheduling tasks cerebellar s lesions may result in emotional overreactions and trouble with impulse control We will examine the cerebellum s function in motor control in detail as an example of a higher brain function.

44 The Cerebrum

45 Cerebrum - Gross Anatomy Cerebral hemispheres Rostral Caudal Central sulcus Frontal lobe Gyri Lateral sulcus Cerebrum Central sulcus Temporal lobe Cerebellum Parietal lobe Brainstem Occipital lobe Spinal cord Longitudinal fissure (b) Lateral view (a) Superior view two cerebral hemispheres // divided by longitudinal fissure connected by white fibrous tract the corpus callosum gyri and sulci increases amount of cortex in the cranial cavity gyri increases surface area for information processing capability some sulci divide each hemisphere into five lobes named for the cranial bones that overly them cerebral cortex tissue directly beneath pia matter / 4 mm

46

47 Cerebrum s Functions Isolated in Lobes frontal lobe voluntary motor functions motivation, foresight, planning, memory, mood, emotion, social judgment, and aggression Precentral gyrus Frontal lobe Rostral Caudal Parietal lobe parietal lobe receives and integrates general sensory information, taste and some visual processing Central sulcus Insula Postcentral gyrus Occipital lobe occipital lobe primary visual center of brain Lateral sulcus temporal lobe areas for hearing, smell, learning, memory, and some aspects of vision and emotion Temporal lobe insula (hidden by other regions) understanding spoken language, taste and sensory information from visceral receptors

48 Functional Map of the Cerebrum Note: key surface margins (longitudinal fissure / central sulcus / lateral sulcus)

49 Somatotopy in the Precentral and Postcentral Gyrus precentral gyrus = motor strip // corticospinal tract = upper motor neuron postcentral gyrus = somatosensory strip // receives spinalcortico tract somatotopy point-for-point correspondence between an area of the body and an area on either the primary motor or sensory gyrus motor and sensory neurons for toe are deep in the longitudinal fissure of the medial side of the gyrus the summit of the gyrus controls the trunk, shoulder, and arm /// the inferolateral region controls the facial muscles motor homunculus is a distorted projection of the body image onto the motor or sensory gyri to show proportional mapping of muscle/sensory functions to body region

50 The Homunculus

51 Functional Map of the Cerebrum Note: key surface margins (longitudinal fissure / central sulcus / lateral sulcus)

52 Images of the Mind Positron emission tomography (PET) visualize increases in blood flow when brain areas are active injection of radioactively labeled glucose Metabolic active areas of brain will light up So if you ask a patient to do something or say something during a PET Scan then the area of the brain processing the command will increase metabolism to process the request and it will light up as more glucose flow into this area

53 New non-invasive technologies allow neuroscientist to study both the structure and function of a living brain. CT, PET, and fmri are now the new images of the brain. What is a Positron Emission Tomography Scan? A PET scan uses radiation, or nuclear medicine imaging, to produce 3-dimensional, color images of the functional processes within the human body. PET stands for positron emission tomography. The machine detects pairs of gamma rays that are emitted indirectly by a tracer (positron-emitting radionuclide), which is placed in the body on a biologically active molecule (e.g. glucose). The images are reconstructed by computer analysis. Modern machines often use a Computer Tomography X-ray scan which is performed on a patient at the same time in the same machine.

54 PET Image

55 PET Scans and Language Task Rostral Caudal Primary auditory cortex Premotor area Primary motor cortex Visual cortex Wernicke area Broca area 1 The word car is seen in 2 Wernicke area conceives 3 Broca area compiles a 4 the visual cortex. of the verb drive to go with it. motor program to speak the word drive. The primary motor cortex executes the program and the word is spoken.

56 What is fmri? Functional magnetic resonance imaging or functional MRI (fmri) is a functional neuroimaging procedure using MRI technology that measures brain activity by detecting associated changes in blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases. The primary form of fmri uses th e blood-oxygen-level-dependent (BOLD) contrast, discovered by Seiji Ogawa. This is a type of specialized brain and body scan used to map neural activity in the brain or spinal cord of humans or other animals by imaging the change in blood flow (hemodynamic response) related to energy use by brain cells. Since the early 1990s, fmri has come to dominate brain mapping research because it does not require people to undergo shots, surgery, or to ingest substances, or be exposed to radiation, etc. Other methods of obtaining contrast are arterial spin labeling and diffusion MRI. The procedure is similar to MRI but uses the change in magnetization between oxygen-rich and oxygen-poor blood as its basic measure. This measure is frequently corrupted by noise from various sources and hence statistical procedures are used to extract the underlying signal. The resulting brain activation can be presented graphically by color-coding the strength of activation across the brain or the specific region studied. The technique can localize activity to within millimeters but, using standard techniques, no better than within a window of a few seconds

57 Images of the Mind Functional magnetic resonance imaging (fmri) looks at increase in blood flow to an area (additional glucose is needed in active area) magnetic properties of hemoglobin dependent on difference between oxygenated and unoxygenated magnetic properties of hemoglobin / how much oxygen is bound to it quick, safe and accurate method to see brain function

58 fmri

59 What is CT Imaging? X-ray computed tomography (x-ray CT or CT) is a technology that uses computer-processed x-rays to produce tomographic images (virtual 'slices') of specific areas of the scanned object Allowing the user to see inside without cutting. Digital geometry processing is used to generate a threedimensional image of the inside of an object from a large series of two-dimensional radiographic images taken around a single axis of rotation. Medical imaging is the most common application of x-ray CT. Its cross-sectional images are used for diagostic and therapeutic purposes in various medical disciplines. The rest of this article discusses medical-imaging x-ray CT.

60 CT Image