Anatomy 2

• Monitors muscle contractions and aids in motor coordination
• Evaluation of sensory input
• –Comparing textures without looking at them
• –Spatial perception and comprehension of different views of three-dimensional objects belonging to the same object
• Timekeeping center
• –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
• Hearing
• –Distinguish pitch and similar-sounding words
• Planning and scheduling tasks
• Lesions may result in emotional overreactions and trouble with impulse control

• Diencephalon
• Telencephalon

• Encloses the third ventricle
• Most rostral part of the brainstem
• Has three major embryonic derivatives
• –Thalamus
• –Hypothalamus
• –Epithalamus

Develops chiefly into the cerebrum

• Ovoid mass on each side of the brain perched at the superior end of the brainstem beneath the cerebral hemispheres
• –Constitutes about four-fifths of the diencephalon
• –Two thalami are joined medially by a narrow intermediate mass
• –Composed of at least 23 nuclei; to consider five major functional groups

• “Gateway to the cerebral cortex”: nearly all input to the cerebrum passes by way of synapses in the thalamic nuclei, filters information on its way to cerebral cortex
• Plays key role in motor control by relaying signals from cerebellum to cerebrum and providing feedback loops between the cerebral cortex and the basal nuclei
• Involved in the memory and emotional functions of the limbic system: a complex of structures that include some cerebral cortex of the temporal and frontal lobes and some of the anterior thalamic nuclei

• Forms part of the walls and floor of the third ventricle
• Extends anteriorly to optic chiasm and posteriorly to the paired mammillary bodies
• Each mammillary body contains three or four mammillary nuclei
• –Relay signals from the limbic system to the thalamus

• A stalk that attaches the pituitary gland to the hypothalamus
• Major control center of autonomic nervous system and endocrine system
• –Plays essential role in homeostatic regulation of all body systems

• Hormone secretion
• Autonomic effects
• Thermoregulation
• Food and water intake
• Rhythm of sleep and waking
• Memory
• Emotional behavior

• Controls anterior pituitary
• Regulates growth, metabolism, reproduction, and stress responses

• Major integrating center for autonomic nervous system
• Influences heart rate, blood pressure, gastrointestinal secretions, motility, etc.

• Hypothalamic thermostat monitors body temperature
• Activates heat-loss center when temp is too high
• Activates heat-promoting center when temp is too low

• Hunger and satiety centers monitor blood glucose and amino acid levels
• –Produce sensations of hunger and satiety
• Thirst center monitors osmolarity of the blood

Controls 24-hour (circadian) rhythm of activity

Mammillary nuclei receive signals from hippocampus

Anger, aggression, fear, pleasure, and contentment

• Very small mass of tissue composed of:
• –Pineal gland: endocrine gland
• –Habenula: relay from the limbic system to the midbrain
• –Thin roof over the third ventricle

• Largest and most conspicuous part of the human brain
• –Seat of sensory perception, memory, thought, judgment, and voluntary motor actions

• Divided by longitudinal fissure
• –Connected by white fibrous tract, the corpus callosum
• –Gyri and sulci: increase 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 overlying them

• Frontal lobe
• Occipital lobe
• Parietal lobe
• Temporal lobe
• Insula

• Voluntary motor functions
• Motivation, foresight, planning, memory, mood, emotion, social judgment, and aggression

Receives and integrates general sensory information, taste, and some visual processing

Primary visual center of brain

Areas for hearing, smell, learning, memory, and some aspects of vision and emotion

• Hidden by other regions
• Understanding spoken language, taste and sensory information from visceral receptors

Glia and myelinated nerve fibers transmitting signals from one region of the cerebrum to another and between cerebrum and lower brain centers

• Projection tract
• Commissural tract
• Association tract

Extends vertically between higher and lower brain and spinal cord centers and carries information between cerebrum and rest of the body

• Cross from one cerebral hemisphere through bridges called commissures
• –Most pass through corpus callosum
• –Anterior and posterior commissures
• –Enables the two sides of the cerebrum to communicate with each other

• Connect different regions within the same cerebral hemisphere
• Long association fibers—connect different lobes of a hemisphere to each other
• Short association fibers—connect different gyri within a single lobe

• Neural integration is carried out here
• Found in three places
• –Cerebral cortex
• –Basal nuclei
• –Limbic system

• Layer covering the surface of the hemispheres
• –Only 2 to 3 mm thick
• –Constitutes about 40% of brain mass
• –Contains 14 to 16 billion neurons
• Contains two principal types of neurons
• -Stellate cells
• -Pyramidal cells

• Have spheroid somas with dendrites projecting in all directions
• Receive sensory input and process information on a local level

Have a thick dendrite with many branches with small, knobby dendritic spines

Include the output neurons of the cerebrum (the only neurons that leave the cortex and connect with other parts of the CNS)

• Masses of cerebral gray matter buried deep in the white matter, lateral to the thalamus
• –Receives input from the substantia nigra of the midbrain and the motor areas of the cortex
• –Send signals back to both these locations
• –Involved in motor control

• Important center of emotion and learning
• Most anatomically prominent components are:
• –Cingulate gyrus: arches over the top of the corpus callosum in the frontal and parietal lobes
• –Hippocampus: in the medial temporal lobe; memory
• –Amygdala: immediately rostral to the hippocampus; emotion

• Components are connected through a complex loop of fiber tracts allowing for somewhat circular patterns of feedback
• Structures have centers for both gratification and aversion

Sensations of pleasure or reward

Sensations of fear or sorrow

• Rhythmic voltage changes resulting from synchronized postsynaptic potentials at the superficial layer of the cerebral cortex
• –Four types distinguished by amplitude (mV) and frequency (Hz)
• Persistent absence of brain waves is common clinical and legal criterion of brain death

• Monitors surface electrical activity of the brain waves
• -Useful for studying normal brain functions as sleep and consciousness
• -In diagnosis of degenerative brain diseases, metabolic abnormalities, brain tumors, etc.

• Awake and resting with eyes closed and mind wandering
• Suppressed when eyes open or performing a mental task

• Eyes open and performing mental tasks
• Accentuated during mental activity and sensory stimulation

• Drowsy or sleeping adults
• If awake and under emotional stress

• High amplitude
• Deep sleep in adults

• Temporary state of unconsciousness from which one can awaken when stimulated
• –Characterized by stereotyped posture
• --Lying down with eyes closed

• Inhibition of muscular activity
• Resembles unconsciousness but can be aroused by sensory stimulation

States of prolonged unconsciousness where individuals cannot be aroused by sensory stimulation

• Brain glycogen and ATP levels increase in non-REM sleep
• –Memories strengthened in REM sleep
• Synaptic connections reinforced

• Feel drowsy, close eyes, begin to relax
• Often feel drifting sensation, easily awakened if stimulated
• Alpha waves dominate EEG

• Pass into light sleep
• EEG declines in frequency but increases in amplitude
• Exhibits sleep spindles—high spikes resulting from interactions between neurons of the thalamus and cerebral cortex

• Moderate to deep sleep
• About 20 minutes after stage 1
• Theta and delta waves appear
• Muscles relax and vital signs fall (body temperature, blood pressure, heart and respiratory rates)

• Called slow-wave sleep (SWS)—EEG dominated by low-frequency, high-amplitude delta waves
• Muscles now very relaxed, vital signs at their lowest, and more difficult to awaken

• Also called paradoxical sleep, because EEG resembles the waking state, but sleeper is harder to arouse than any other stage
• Vital signs increase, brain uses more oxygen than when awake
• Sleep paralysis, other than in the muscles of eye movement, is strong during REM sleep
• Sleep paralysis may serve to prevent sleeper from acting out dreams and may have prevented our tree dwelling ancestors from falling during sleep

• Occur in both REM and non-REM sleep
• –REM tends to be longer and more vivid

• Active during REM sleep
• Causing constriction of the pupils
• Erection of the penis and clitoris

• Controlled by a complex interaction between the cerebral cortex, thalamus, hypothalamus, and reticular formation
• –Arousal induced by nuclei in the upper reticular formation, near junction of pons and midbrain
• –Sleep induced by nuclei below pons, and in ventrolateral preoptic nucleus in the hypothalamus

• Another important control center for sleep
• –Above optic chiasma in anterior hypothalamus
• –Input from eye allows SCN to synchronize multiple body rhythms with external rhythms of night and day
• Sleep, body temperature, urine production, secretion, and other functions

• The range of mental processes by which we acquire and use knowledge
• –Such as sensory perception, thought, reasoning, judgment, memory, imagination, and intuition
• Association areas of cerebral cortex have these functions
• –Constitute about 75% of all brain tissue

• Perceiving stimuli
• Contralateral neglect syndrome—unaware of objects on opposite side of the body
• Decussation

• Identifying stimuli
• Agnosia—inability to recognize, identify, and name familiar objects
• Prosopagnosia—person cannot remember familiar faces

• Planning and executing our responses; appropriate emotions
• Personality disorders; inability to execute appropriate behavior

Refers to defects in declarative memory (inability to describe past events), not procedural memory (ability to tie one’s shoes)

Unable to store new information

Person cannot recall things known before the injury

• Important memory-forming center
• Does not store memories
• Organizes sensory and cognitive information into a unified long-term memory
• Memory consolidation: the process of “teaching the cerebral cortex” until a long-term memory is established
• Long-term memories are stored in various areas of the cerebral cortex

Vocabulary and memory of familiar faces stored in here

• Memories of one’s plans and social roles stored in this
• Seat of judgment, intent, and control over expression of emotions

Helps learn motor skills

Emotional memory

• Injury to the ventromedial region of both frontal lobes
• Extreme personality change
• –Fitful, irreverent, grossly profane
• –Opposite of previous personality
• Prefrontal cortex functions
• -Planning, moral judgment, and emotional control

• Come from hypothalamus and amygdala
• –Nuclei generate feelings of fear or love

• Receives input from sensory systems
• Role in food intake, sexual behavior, and drawing attention to novel stimuli
• One output goes to hypothalamus influencing somatic and visceral motor systems
• -Heart races, raises blood pressure, makes hair stand on end, induces vomiting
• Other output to prefrontal cortex important in controlling expression of emotions
• -Ability to express love, control anger, or overcome fear

Shaped by learned associations between stimuli, our responses to them, and the reward or punishment that results

Sites where sensory input is first received and one becomes conscious of the stimulus

• Association areas nearby to sensory areas that process and interpret that sensory information
• –Primary visual cortex is bordered by visual association area: interprets and makes cognitive sense of visual stimuli
• –Multimodal association areas: receive input from multiple senses and integrate this into an overall perception of our surroundings

• Limited to the head and employ relatively complex sense organs
• Primary cortices and association areas
• -Vision
• -Hearing
• -Equilibrium
• -Taste and smell

• Visual primary cortex in far posterior region of occipital lobe
• Visual association area: anterior, and occupies all the remaining occipital lobe
• Much of inferior temporal lobe deals with facial recognition and other familiar objects

• Primary auditory cortex in the superior region of the temporal lobe and insula
• Auditory association area: temporal lobe deep and inferior to primary auditory cortex
• Recognizes spoken words, a familiar piece of music, or a voice on the phone

• Signals for balance and sense of motion project mainly to the cerebellum and several brainstem nuclei concerned with head and eye movements and visceral functions
• Association cortex in the roof of the lateral sulcus near the lower end of the central sulcus
• Seat of consciousness of our body movements and orientation in space

• Gustatory (taste) signals received by primary gustatory cortex in inferior end of the postcentral gyrus of the parietal lobe and anterior region of insula
• Olfactory (smell) signals received by the primary olfactory cortex in the medial surface of the temporal lobe and inferior surface of the frontal lobe

• Distributed over the entire body and employ relatively simple receptors
• Senses of touch, pressure, stretch, movement, heat, cold, and pain
• Several cranial nerves carry general sensations from head

• Thalamus processes the input
• Selectively relays signals to the postcentral gyrus
• Fold of the cerebrum that lies immediately caudal to the central sulcus and forms the rostral border of the parietal lobe
• Primary somesthetic cortex is the cortex of the postcentral gyrus
• Somesthetic association area: caudal to the gyrus and in the roof of the lateral sulcus

Awareness of stimulation

Making cognitive sense of the stimulation

The right postcentral gyrus receives input from the left side of the body and vice versa

• Upside-down sensory map of the contralateral side of the body
• Shows receptors in the lower limbs projecting to the superior and medial parts of the gyrus
• Shows receptors from the face projecting to the inferior and lateral parts

Point-for-point correspondence between an area of the body and an area of the CNS

• Where we plan our behavior
• Where neurons compile a program for degree and sequence of muscle contraction required for an action
• Program transmitted to neurons of the precentral gyrus (primary motor area)
• -Most posterior gyrus of the frontal lobe
• Neurons send signals to the brainstem and spinal cord
• Ultimately resulting in muscle contraction