bsc2085 lesson 15/16

Midbrain

- brain region that develops from embryonic mesenecephalon

anatomical features of midbrain

- cerebral aqueduct

- motor nuclei of 2 cranial nerves

- tectum

- tegmentum

- substantia nigra

cerebral aqueduct is surround by

central gray substance (periaqueductal) involved in pain awareness

Motor nuclei in midbrain

CN III (oculomotor) and CN IV (trochlear)

Tectum

- roof-life part of the midbrain posterior to cerebral aqueduct

- 4 bulges- two superior colliculi, and two inferior

superior colliculi

visual attention, tracking moving objects, and visual reflexes

inferior colliculi

relays signals from inner ear to thalamus and other parts of the brain, auditory reflexes

tegmentum

connections go to and from cerebellum for motor control

Substantia nigra

- dark nucleus pigmented with melanin

- motor center that relays inhibitory signals to thalamus and basal nuclei, suppressing unwanted body movement

- degeneration of neurons leads to tremors of Parkinson's 

Reticular activating system (RAS)

- component of the reticular formation in midbrain important for alertness and attentiveness

- habituation

- pain modulation

- sleep and consciousness → damage will lead to irreversible coma

cerebellum

largest part of hindbrain, second-largest part of brain as a whole, and contains more than half of all brain neurons

cerebellum components

- granule cells

- purkinje cells

- right and left hemispheres connected by vermis

- folia and branching arbor vitae

vermis

connects right and left cerebellar hemispheres

folia

superficial cortex of gray matter with folds

Functions of cerebellum

- Motor coordination and locomotor ability

- Sensory, linguistic, emotional, and other non-motor functions

Sensory, linguistic, emotional, and other non motor functions of cerebellum

- comparing textures of objects

- perceiving space

- recognizign objects from different views

- keeping judge of elapsed time and maintaining tapping rhythm

- directing eye movements to compensate for head movement

- judging pitch of tones distinguishing between spoken words

- helping in verbal association tasks

- planning, scheduling, and emotion control

ataxia

clumsy awkward gait from lesions in cerebellum

2 part of forebrain

diencephalon and telencephalon

diencephalon

encloses 3rd ventricle; most rostral part of brainstem

telencephalon

develops chiefly into cerebrum

3 major components of diencephalon

- thalamus

- hypothalamus

- epithalamus

thalamus

- mass on each side of brain

- 4/5 of diencephalon

- synchronizes electrical activity between 2 hemispheres of cerebrum

- gateway to cerebral cortex

- plays key role in motor control

- involved in memory and emotion

desynchronization

damage to thalamus can cause ____ between hemispheres; leads to epilepsy and seizures

• treatment can be to cut corpus callosum 

anterior group of thalamic nuclei

part of limbic system; memory and emotion

medial group of thalamus

emotional output to prefrontal cortex; awareness of emotions

Ventral group of thalamus

Somatosensory output to postcentral gyrus; signals from cerebellum and basal nuclei to motor areas of cortex

Lateral group of thalamus

Somatosensory output to association areas of cortex; contributes to emotional function of limbic system

Posterior group of thalamus

Relay of visual signals to occipital lobe and auditory signals to temporal lobe

thalamus as the gateway to cerebral cortex

- processes info on way to cerebral cortex

- not all is passed, it screens out most it receives

thalamus in motor control

- relays signals from cerebellum to cerebrum

- provides feedback loops between cerebral cortex and basal nuclei

hypothalamus

- extends anteriorly to optic chiasm and extends posteriorly to mammillary bodies

- process olfactory and other sensory information and controls reflex eating movements

Attachment of hypothalamus to pituitary gland

Through a stalk-like structure called the infundibulum

Hypothalamus components and functions

- contains many nuclei with a wide variety of visceral, emotional, and behavioral functions

- homeostatic regulation of all systems

- major control center of autonomic nervous system, endocrine systme

functions of hypothalamic nuclei

- hormone secretion

- autonomic effects

- thermoregulation

- food and water intake

- sleep and circadian rhythms

- memory

- emotional behavior and sexual response

hormone secretion of hypothalamic nuclei

- controls anterior pituitary; regulates growth, metabolism, reproduction, and stress response

- produces posterior pituitary hormones for labor contractions, lactation, and water conservation

autonomic effects of hypothalamic nuclei

- major integrating center for autonomic nervous system

- influences heart rate, blood pressure, gastrointestinal secretions, motility

thermoregulation of hypothalamic nuclei

- hypothalamic thermostat monitors body temperature, activates, mechanisms to adjust temp if necessary

food and water intake of hypothalamic nuclei

- regulates hunger and satiety; responds to hormones influencing hunger, energy expenditure, and long-term control of body mass

- osmoreceptors monitor osmolarity of blood, can stimulate production of ADH to help conserve water

sleep and circadian rhythms of hypothalamic nuclei

Suprachiasmatic nucleus controls 24-hour (circadian) rhythm

memory of hypothalamic nuclei

Mammillary nuclei relay signals from hippocampus to thalamus

emotional behavior and sexual response of hypothalamic nuclei

anger, aggression, fear, pleasure, contentment, sex drive

pineal gland

- located in epithalamus

- produces melatonin hormone, helps with circadian rhythm and reproduction function

cerebrum

- develops from the telencephalon and is the largest, most conspicuous part of human brain

- seat of sensory perception, memory, thought, judgment, and voluntary motor actions

3 functional principles of the cerebrum

1. each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite side of the body

2. the 2 hemispheres have different functions, although their structures are alike

3. correspondence between a specific function and specific region of cerebral cortex is not precise

Frontal lobe

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

Prefrontal cortex

- Integrates information from sensory areas

- allows us to perform abstract intellectual activities

- damage affects temporal relationships between events

Parietal lobe

- Integrates general senses, taste, and visual info

Occipital lobe

- Primary visual center

Temporal lobe

- Hearing, smell, learning, memory, and some aspects of vision and emotion

Insula

- Helps in understanding spoken language, taste, and integrating info from visceral receptors

White matter

- Makes up most of the volume of the cerebrum

- Form from glia and myelinated nerve fibers

Tracts

Bundles of nerve fibers in CNS

Projection tracts

Extend vertically between cerebrum and lower brain and spinal cord centers

Commissural tracts

Cross from one cerebral hemisphere to the other allowing communication between the two sides

Most commissural tracts pass thru

corpus callosum

Disconnection syndrome

- caused by cutting corpus callosum

- hemispheres are unaware of each other

Association tracts

- Connect different regions within the same cerebral hemisphere

- long fibers connect different lobes; short fibers connect gyri within a lobe

Cerebral cortex

- 40% of brain mass

- Layer of gray matter covering surface of hemispheres

- 90% of it is neocortex

Neocortex

6 layered tissue that has relatively recent evolutionary origin

Limbic system

- Important center of emotion and learning

- Consists of regions of cerebrum and diencephalon

- memory storage and retrieval

- establishes emotional states

Primary somatosensory cortex (postcentral gyrus)

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

- Exhibits somatotopy

Primary sensory areas have ______ to process and interpret the sensory info

Association areas

Somatotopy

Point to point correspondence between an area of the body and an area of the CNS; reflected in sensory homunculus in post central gyrus

Sensory homunculus

- Diagram of sensory inputs to the primary somatosensory cortex in parietal lobe

- Resembles upside down sensory map of contralateral side of body

- Areas with lots of receptors take up a larger amount of space in it

Primary visual cortex

Posterior region of occipital lobe; receives visual signals from the eyes

Primary auditory cortex

Superior region of temporal lobe; receives auditory signals

Auditory association cortex

Inferior to primary auditory cortex; recognize spoken words, music, voices

Primary gustatory cortex

inferior end of postcentral gyrus, taste and smell

Primary olfactory cortex

medial cortex of temporal lobe, taste and smell

Voluntary motor commands are transmitted to neurons of the

precentral gyrus (primary motor area)

Primary motor area

Send signals to brainstem and spinal cord leading ultimately to muscle contractions

Precentral gyrus

Exhibits somatotopy diagrammed as motor homunculus

Motor homunculus

- looks distorted because the amount of cortex devoted is proportional to motor units, not region size

- boundaries of cortical areas overlap

Wernicke area

- posterior to lateral sulcus, usually in left hemisphere

- recognition of spoken and written language

Broca area

- inferior prefrontal cortex, left hemisphere

- generates motor program for muscles of larynx, tongue, cheeks, and lips for speaking and for hands when signing

- motor language area

When we try to speak

- Wernicke formulas phrases and transmits plan of speech to Broca

- Broca transmits to primary motor cortex for commands to lower motor neurons that supply relevant muscles

affective language area

usually in right hemisphere, controls emotional aspect language

Aprosody

Flat, emotionless speech produced by legions in affective language area

Aphasia

- Any language deficit from lesions in Wernicke or Broca areas

nonfluent/broca aphasia

slow speech, difficult choosing words that approximate the correct words

fluent/wernicke aphasia

use jargon/made up words

Cerebral lateralization

- Difference in structure, function between 2 hemispheres

- Neither is dominant but each is specialized

- Used equally

Categorical hemisphere (left)

- specialized for spoken/written language

- analytical reasoning (math/science)

- breaks info in fragments and analyzes

Representational hemisphere (right)

- more integrated perception

- imagination and insight

- musical and artistic skill

- patterns and spatial relationships

- comparison of sights, sounds, smells, and taste

____ exhibit more lateralization than ____ and suffer more functional loss when one hemisphere is damaged

Men; women

Lateralization develops with age

Children more resilient to lesions on one side

Electroencephalogram (EEG)

- Recording of brain waves, rhythmic voltage changes in surface layers of cortex

- Useful for studying normal brain functions as sleep and consciousness

Lack of brain waves

Common criterion for brain death

4 types of brain waves

alpha, beta, theta, delta

Alpha waves

- 8-13 Hz

- Awake and resting with eyes closed and mind wandering

- Suppressed when eyes open or performing a mental task, absent during sleep

Beta waves

- 14 to 30 Hz

- Accentuated during mental activity and sensory stimulation

- Appear when awake and concentrating on something/performing a task

Theta waves

- 4 to 7 Hz

- Found normally in children or in intensely frustrated, stressed, drowsy, or sleeping adult

- May indicate a brain disorder or brain tumor in other adults

Delta waves

- less than 3Hz

- High amplitude

- found in adults in deep sleep, adult with brain damage