Lecture 11: Cerebrum Flashcards
Cerebrum
Two hemispheres; 83% of brain mass
Fissures
Deep grooves, which separate major regions of the brain
Longitudinal fissure
Separates cerebral hemispheres
Transverse cerebral fissure
Separates cerebrum and cerebellum
Sucli
Shallow grooves on the surface
Gyri
Ridges of brain tissue between sulci
Deep sulci
Central sulcus, lateral sulcus, parietal-occipital sulcus
Central sulcus
Separates frontal lobe and parietal lobe; bordered by precentral gyrus and postcentral gyrus
Parieto-occipital sulcus
Separates occipital lobe from parietal lobe
Lateral sulcus
Sometimes called fissure; separates temporal lobe from parietal and frontal lobes
Insula lobe
Positioned deep within lateral sulcus
Cerebrum structures
Cerebral cortex (primary sensory areas, sensory association areas, multimodal association areas, motor areas), cerebral white matter (commissures, association fibers, projection fibers), deep cerebral gray matter (basal ganglia, basal forebrain nuclei, claustrum)
Cerebral cortex
2-4 mm thick; folds triple the surface area; 40% of brain mass; billions of neurons; neuronal cell bodies, dendrites, short unmyelinated axons; sensory information routed through the thalamus to cerebral cortex
Cerebral cortex functions
Initiate and control voluntary movements; communicate, remember, and understand
Primary sensory cortex
Receives sensory information resulting in awareness of sensation
Sensory association areas
Receive information from primary sensory cortex and interpret the sensory input
Multimodal association areas
Receive input in parallel from multiple sensory association areas and integrate and interpret information aided by past experiences and develop a motor response
Motor cortex
Enacts plan
Sensory areas
Cortical areas in parts of parietal, temporal, and occipital lobes; distinct cortical area, a primary sensory cortex, for each of the major senses
Primary somatosensory cortex
Postcentral gyrus of the parietal lobe; conscious awareness of general somatic senses; perceived from skin and from proprioception of muscles and tendons (touch, pressure, vibration, pain, temperature)
Spatial discrimination
Sensory receptors relay signals through spinal cord, brain stem, thalamus, and up to primary somatosensory cortex; process information and identify precise area in body; ability to precisely locate a stimulus
Sensory homunculus
Somatotopy: each region of cortex receives sensory stimuli from a specific area of the body; sensory homunculus: a body map of sensory cortex in postcentral gyrus; amount of somatosensory cortex devoted related to sensitivity; represented upside down with head in inferolateral part of postcentral gyrus and toes at superomedial
Vestibular cortex
Processes information from vestibular apparatus; conscious awareness of sense of balance (position of head in space); posterior part of insula lobe deep in lateral sulcus
Gustatory cortex
Processes taste stimuli from tongue; conscious awareness of taste; “roof” of lateral sulcus
Olfactory cortex
Processes smell; conscious awareness of smells; piriform lobe which includes hooklike uncus
Rhinencephalon
Olfactory cortex is part of this part of the brain; includes parts of cerebrum that receive olfactory signals (piriform lobe, olfactory tracts, olfactory bulbs); connects to limbic system involved with consciously identifying and recalling specific smells
Visceral sensory arease
Deep within lateral sulcus on insula lobe; receives general sensory input (pain, pressure, hunger) from abdominal and thoracic organs
Primary visual cortex
Deep within calcarine sulcus on posterior and medial part of occipital lobe; damage can cause blindness; largest of all sensory areas; visual information originates from retina; contralateral function
Primary auditory cortex
Sound waves excite receptors in inner ear cochlea which triggers impulse transmission where conscious awareness of sound including loudness, rhythm, and pitch is detected
Somatosensory association cortex
Posterior to primary somatosensory cortex; integrates different sensory inputs to understand sensations; draws upon stored memories of past experiences
Visual association areas
Surrounds primary visual area and covers much of occipital lobe; continues processing of visual information by analyzing color, form and movement; complex visual processing extends into temporal and parietal lobes
Visual dorsal stream
“Where” pathway; posterior parietal cortex to post-central gyrus; information about spatial relationships
Visual ventral stream
“What” pathway; passes information into inferior part of temporal lobe; recognizing objects, words, and faces
Auditory association area
Posterior and lateral to primary auditory cortex; evaluation of different sounds and integrates memories of past sounds
Auditory posterolateral pathway
“Where” pathway; parietal lobe to lateral pre-frontal cortex; evaluates location of a stimulus
Auditory anterolateral pathway
“What” pathway; anterior temporal lobe to inferior pre-frontal cortex; sound identification
Wernicke’s area
In one hemisphere (usually the left); involved in recognizing and understanding spoken word; damage interferes with ability to comprehend speech
Multimodal association areas
Receive sensory input from multiple sensory modalities sensory association areas; make associations between various kinds of sensory information; associates new sensory inputs with memories of past experiences and plan appropriate motor responses
Posterior association area
Interface of visual, auditory, and somatosensory association areas; integrates information from somatosensory, visual, and auditory association areas as well as proprioceptive senses and vestibular apparatus that allows “body sense” or body awareness of spatial location; guides movements of limbs through space; related to language comprehension and speech
Language areas
Typically in left cerebral cortex; Wernicke’s area, lateral and inferior temporal lobe (coordination of auditory and visual aspects of language); parts of insula (initiation of word articulation and recognition of sound sequences)
Right cerebral hemisphere
Creative interpretation of words; controlling emotional overtones of speech
Prefrontal cortex
Integrates information from all association areas to plan and initiate motor responses; receives processed sensory information from posterior association area and adjusts motor output; integrates information with past experience through connection with limbic system
Tasks of anterior association area
Working memory for spatial tasks, working memory for object-recall tasks, solving complex multi-task problems, executive area for task management
Function of anterior association area
Processes information and triggers the move to the next portion of the task; cognitive functioning, processing abstract ideas, long-term planning; impulse control; appreciation of humor; linked to emotion; not fully formed until adulthood (poor judgement in early adolescents)
Limbic association area
Medial side of frontal lobe; processes emotions in complex personal and social interactions; contributes to memory, emotions, and motor response; integrates input from other cortical areas to form memory; integrates sensory and motor behaviors with past experience; uses past experience to influence future motor response
Motor areas
Localized in posterior frontal lobe
Premotor cortex
Anterior to primary motor cortex; plans and coordinates complex movements and relays plan to primary motor cortex for implementation; receives processed information from sensory and multimodal regions; controls voluntary actions
Primary motor cortex
Controls motor functions; along precentral gyrus of frontal lobe
Pyramidal cells
Large neurons of primary motor cortex; long axons form massive pyramidal tracts (corticospinal tracts) that descend through brainstem and spinal cord; axons synapse on motor neurons to generate precise voluntary motor movements; contralateral
Somatotopy
Specific pyramidal cells control specific areas of the body
Motor homunculus
Body represented spatially in primary motor cortex; represented upside down with head in inferolateral part of precentral gyrus and toes at supermedial end
Frontal eye field
Anterior to premotor cortex; controls voluntary movement of eyes especially when moving eyes to follow a moving target
Broca’s area
Anterior to inferior part of premotor cortex in left, language dominant cerebral hemisphere; controls motor movements for speaking
Lateralization of cortical function
Contralateral (two hemispheres control opposite sides of body); communicate between right and left sides through commissures; specialized for different cognitive functions
Right hemisphere
In 90-95% of people, deal with big picture; visual-spatial skills, reading facial expressions, intuition, emotion, artistic, musical skills
Left hemisphere
In 90-95% of people, deal with details; language abilities, math, logic
Cerebral white matter
Different areas of cerebral cortex communicate with each other and communicate with brain stem and spinal cord; usually myelinated and bundled into tracts
Commissural fibers
Connect corresponding cerebral cortices in two hemispheres; horizontal fibers; corpus callosum is largest commissure
Association fibers
Connect cerebral cortex of different parts of same hemisphere; connect parts of Wernike’s and Broca’s areas
Projection fibers
Connect cerebral cortex to more caudal parts of CNS; some descend from cerebral cortex to more caudal areas; some ascend to cortex from lower regions; sensory information reaches cerebral cortex and motor instructions leave cerebral cortex
Internal capsule
Deep in cerebral white matter; compact bundle of projection fibers which pass between thalamus and basal ganglia
Corona radiata
Projection fibers run to and from cerebral cortex and fan out to form this
Basal Ganglia
Group of nuclei within cerebral white matter; receives input from many cortical areas; neural calculators that cooperate with cerebral cortex in control and regulation of a spectrum of different types of movement; start, stop and regulate intensity of voluntary movements; select appropriate muscles for a task and inhibit others
Caudate nucleus
Arches superiorly over thalamus and lies medial to internal capsule
Globus pallidus
Lateral to internal capsule
Putamen
Combination of caudate nucleus and putamen
Corpus striatum
Combination of caudate nucleus, putamen, and globus pallidus
Dyskinesia
Degenerative conditions of basal ganglia which causes abnormal motor function
Huntington’s Disease
Degeneration of corpus striatum pathway that inhibits motor activity and results in an overstimulation of motor activities with uncontrolled jerking of limbs and early death
Parkinson’s disease
Degeneration of substantia nigra that sends input to basal ganglia; lack of inhibitory input results in overactive globus pallidus basal ganglia which inhibits motor cortex causing slow and jerky movements, tremors, and eventual muscle rigidity and early death
Basal forebrain nuclei
Cholinergic system (neurons synthesize and release acetylcholine); anterior and dorsal to hypothalamus
Functions of basal forebrain nuclei
Arousal, learning, memory, motor control
Alzheimer’s disease
Degeneration of brain areas involved with memory and thought (basal forebrain nuclei, hippocampus, associated areas of cerebral cortex); results in reduction of cholinergic activity; damage spreads to other areas of cerebrum
Limbic system
Medial aspect of cerebral hemispheres; also within diencephalon (anterior thalamic nuclei, hypothalamus, mammillary body); forms a broad ring in medial cerebral hemisphere (septal nuclei, cingulate gyrus, dentate gyrus, hippocampus, parahippocampal gyrus); part of amygdaloid body (amygdala); linked by fornix and anterior commissure fiber
Cingulate gyrus
Superior to corpus callosum; shift in between thoughts and express emotions through gestures; interprets pain as unpleasant; resolves mental conflict during frustrating tasks
Amygdala
Processes fear and triggers appropriate sympathetic responses; forms memories of past experiences based on emotional impact; retrieves memories and causes them to re-experience emotions
PTSD
Extreme response to a triggered memory results in hyperactivity in amygdala and dysfunction in medial pre-frontal cortex (limbic association center) and hippocampus
Hippocampal formation
Hippocampus and parahippocampal gyrus; encodes, consolidates, and retrieves memories of facts and events; receives information to be remembered from the cerebral cortex; processes these data and returns them to cortex, where they are stored as long term memories
Limbic system interaction with rest of brain
Most output is relayed through hypothalamus and reticular formation which control visceral responses; interacts with prefrontal cortex of cerebrum; emotional brain interacts with thoughts from thinking brain
Reticular formation
Runs through central core of medulla, pons, and midbrain; long branching axons that project to thalamus, cerebellum, spinal cord and cerebrum
Reticular activating system (RAS)
Part of reticular formation which maintains consciousness and alertness; visual, auditory, and touch stimuli help keep people awake and alert
RAS influence on sleep
Functions in sleep and arousal; general anesthesia, tranquilizers, and sleep inducing drugs depress RAS and cause loss of consciousness; malfunctions in RAS can cause narcolepsy; severe injury to RAS causes coma
RAS motor arm
Motor arm sends axons to spinal cord; axons control motor neurons to skeletal muscle; some axons and lateral nuclear group nuclei in medulla influence autonomic neurons which to regulate visceral motor functions
Ascending spinocerebellar pathway
First order: sensory receptor to dorsal gray horn of spinal cord and synapses with second order neuron; second order: ascends up spinal cord in both dorsal and ventral spinocerebellar tract to cerebellum where it terminates; conveys information on proprioception from lower limbs and trunk to cerebellum to coordinate body movements; ipsilateral
Ascending dorsal column pathway
First order: sensory receptor to spinal cord where ascends up medial fasciulus gracilis and lateral fasciculus cuneatus to nucleus gracilis and nucleus cuneatus brain nuclei in medulla; second order; decussates in medulla and ascends up medial lemniscus tract and synapses in thalamus with third order; third order; ascends from thalamus to primary somatosensory cortex on postcentral gyrus resulting in awareness of precisely localized sensations; contralateral; includes fine touch, pressure, and conscious aspects of proprioception
Ascending spinothalamic pathway
First order: sensory receptor to spinal cord synapses in dorsal gray horn; second order: decussate in spinal cord and enters lateral and ventral funiculi which synapses in thalamus; third order: ascends to primary somatosensory cortex on postcentral gyrus; conscious sensations which are typically perceived as unpleasant; contralateral; pain, burns, heat, and cold; transmits information on pain, temperature, and deep pressure; non-discriminative touch (we are aware but cannot localize precisely)
Descending pathways
Most motor pathways; decussate at some point and are contralateral; exhibit somatotopy; all pathways paired; deliver motor instructions from brain to spinal cord
Pyramidal pathway
Large neurons; descend from primary motor cortex; lateral tracts decussate in medulla; ventral tracts decussate in spinal cord; synapse with short interneurons that activate somatic motor neurons or synapse directly onto somatic motor neurons; precise and skilled voluntary movements
Somatic motor neuron
Extends from spinal gray matter to peripheral motor receptor and controls precise voluntary movement
Amyotropic lateral sclerosis (Lou Gehrig’s disease)
Degeneration of pyramidal tracts with formation of hardened scar tissue in later parts of spinal cord; results in wasting and atrophy of skeletal muscles; fatal
Extrapyramidal tracts
Signals that produce body movements that are subconscious, coarse or postural
Descending rubrospinal pathway
From red nucleus in midbrain; decussates in midbrain and descends to spinal gray matter; somatic motor neuron; produce body movements that are subconscious, coarse or postural
Integration of movement
Cerebellum smooths and coordinates movements dictated by pyramidal tracts and subcortical motor nuclei; axons from cerebellum project to and influence red nuclei, vestibular nuclei, and reticular nuclei; pyramidal tract neurons project to and influence most of “extrapyramidal” tracts
Paralysis
Loss of motor function
Paresthesia
Loss of sensation
Paraplegia
Injury to spinal cord is between T1 and L2 causing paralysis of lower limbs
Quadriplegia
Injury to spinal cord in cervical region causing paralysis of all four limbs
Cerebrovascular accident (stroke)
Interruption of blood flow to brain tissue
Thrombotic stroke
Caused by a clot which blocks blood flow to brain tissue
Hemorrhagic stroke
Caused by a bleed in the brain which impairs blood flow to brain tissue
