Major Brain Divisions

what is the brain?

- grossly divided into the forebrain (cortex, subcortical nuclei, and thalamic complex) and hindbrain (brainstem and cerebellum)

what are the neuroanatomical directions for hindbrain?

- superior= rostral
- inferior= caudal
- anterior= ventral
- posterior= dorsal

what are the neuroanatomical directions for the forebrain?

- superior= dorsal
- inferior= ventral
- anterior= rostral
- posterior= caudal

what are the external landmarks of the brain?

- cerebrum
- cerebellum
- brainstem

what is the cerebrum anatomy?

- 2 hemispheres split by longitudinal fissure
- covered in gyri and sulci which increase surface area

what is the cerebellum anatomy?

- 2 hemispheres, vermis, flocculonodular lobe
- covered in folia and sulci to increase surface area

what is the brainstem anatomy?

- midbrain, pons, medulla, and usually cerebellum
- no gyri or folia

what is grey matter?

- somas, dendrites and synapses
- no myelinated axons
- cortex (surface) and subcortical nuclei

what is white matter?

- myelinated axons
- connect nuclei via tracts (e.g., corpus callosum)

when does neurulation begin and end?

- begins at week 3
- done by day 26

what is neurulation?

- neural plate (ectoderm) forms at dorsal midline
- cell migration creates neural groove and neural folds
- neural folds fuse to form neural tube ( begins at neck)
- sheet -> tube

what cell breaks away during neurulation?

- neural crest cells at the margin of the neural folds

what do neural crest cells form?

- arachnoid and pia maters
- PNS
- other structures like melanocytes and cartilage

what are the primary embryonic vesicles?

- prosencephalon (forebrain)
- rhombencephalon (hindbrain)

what are the secondary vesicles of the forebrain?

- telencephalon (cerebrum)
- diencephalon (thalamus)

what are the secondary vesicles of the hindbrain?

- metencephalon (pons and cerebellum)
- myelencephalon (medulla)

what vesicle is a combination of both primary and secondary and why?

- mesencephalon (midbrain)
- does not divide
- bends 90 degrees

what is the function of the hindbrain?

- carries out vital functions outside of conscious awareness

what is the overall function of the medulla?

- basic survival

what are the motor components of the medulla?

- pyramids
- inferior olive
- cranial nerve nuclei
- reticular formation

what is the function of pyramids in the medulla?

- help form corticospinal tracts

what is the function of the inferior olive in the medulla?

- motor learning

which cranial nerves innervate in the medulla?

- 8, 9, 10, and 12

what is the function of the reticular formation in the medulla?

- vital functions
- cardiac center (HR and force)
- vasomotor center (BP)
- respiratory centers (rhythm and depth)

what are the sensory components of the medulla?

- gracile/cuneate nuclei and medial lemniscus
- spinothalamic tract
- spinal nucleus of V
- solitary tract nucleus

what is the function of the gracile/cuneate nuclei and medial lemniscus in the mediulla?

- body tactile sense

what is the function of the spinothalamic tract in the medulla?

- feel body pain and temp

what is the function of the spinal nucleus of V in the medulla?

- feel face pain and temp

what is the function of the solitary tract in the medulla?

- gustatory nucleus (taste)
- respiratory nucleus (blood gas and lung stretch)
- baroreceptor nucleus (blood pressure)
- commissural nucleus (viscera)

what are the medullary lesions?

- medial medullary syndrome
- lateral medullary syndrome

what is medial medullary syndrome?

- contralateral limb weakness (pyramids)
- contralateral body decreased touch sense
- ipsilateral tongue weakness

what is lateral medullary weakness?

- ipsilateral ataxia, vertigo, nystagmus, nausea
- decreased pain and temp sense in the contralateral body and ipsilateral face
- ipsilateral Horner's syndrome
- bilateral hoarseness, dysphagia (difficulting swallowing)
- ipsilateral decreased taste

what happens when there is complete damage to the medulla?

- toast
- no vital functions

what is the overall functions of the pons?

- regulate vital functions with other information

what are the components of the pons?

- corticospinal tracts, medial lemniscus, spinothalamic tract
- pontine nuclei
- cranial nerves 5-8 nuclei
- superior olive
- pontine micturition center
- pontine reticular formation
- other nuclei

what is the purpose of the corticospinal tracts, medial lemniscus, and spinothalamic tracts in the pons?

- corticospinal tracts: conscious motor
- medial lemniscus: body tactile sense
- spinothalamic tract: body pain and temp

what is the purpose of the pontine nuclei in the pons?

- relay between cortex and cerebellum
- motor coordination

what are the functions of cranial nerves 5-8 nuclei in the pons?

- facial sensation and expression
- eye movement
- hearing
- balance

what is the function of the superior olive in the pons?

- localize sounds

what is the function of the pontine micturition center in the pons?

- regulate urination

what is the function of the pontine reticular formation?

- sleep, respiration, and posture

what is the function of other nuclei in the pons?

- regulate activity in the medulla
- quality of life

what occurs during a medial pons lesion?

- contralateral face and limb weakness
- dysarthria
- contralateral ataxia
- ipsilateral facial weakness and horizontal gaze palsy
- contralateral decreased touch sense

what occurs during a lateral pons lesion?

- ipsilateral ataxia and hearing
- vertigo, nystagmus, nausea
- decreased pain and temp sense in the contralateral body and ipsilateral face

what are the cerebellar peduncles?

- connect the brainstem to the cerebellum
- superior, middle, inferior

what is the superior cerebellar peduncle?

- ascending output to red nucleus and thalamus

what is the middle cerebellar peduncle?

- corticopontine input (planned actions)
- pontine nuclei connection to cerebellum

what is the inferior cerebellar peduncle?

- brainstem and spinal cord input; descending output to brainstem
- 2 way street

what is the anatomy of the cerebellum?

- 10% of brain mass, 80% of neurons
- 3/4 of all neurons are granule cells
- 20-40x more neurons in the motor cortex project to the pons/cerebellum than to the spinal cord

what are the functions of the cerebellum?

- motor coordination and automatic movements
- predicting object movement and timekeeping
- language deficits (distinguishing similar sounds or identifying related/rhyming words)

what movements do the hemispheres and vermis control?

- hemispheres: ipsilateral limbs
- vermis: axial muscles and balance

what happens when there is a lesion in the vermis of the cerebellum?

- truncal ataxia (no coordination of the trunk)
- unsteady, wide-based gait
- impaired balance
- difficulty sitting unsupported (extreme)
- damage to the right vermis= right fall (vice versa)

what happens when there is a lesion in the hemisphere of the cerebellum?

- appendicular ataxia (no coordination of limbs)
- dysmetria: distance
- dysrhythmia: timing
- intention tremor

what is the midbrain?

- junction between hindbrain and forebrain
- bulk of eye movements

what are the components of the midbrain?

- tectum
- tegmentum
- cerebral aqueduct
- cerebral peduncles

what are the structures within the tectum and their functions?

- superior colliculi (visual reflexes)
- inferior colliculi (auditory reflexes)
- pretectal nuclei (pupillary reflex)

what are the structures within the tegmentum and their functions?

- occulomotor and trochlear nuclei (eye movements)
- red nucleus (motor coordination)
- reticular formation (arousal and reflexive movement)
- ventral tegmental area (dopamine neurons that create reward)

what are the structures within the cerebral aqueduct and their functions?

- ventricular system (3->4), often site of obstruction
- surrounded by periaqueductal gray (regulates pain and arousal)

what are the structures within the cerebral peduncles and their function?

- substantia nigra (dopamine neurons that promote movement)
- cerebral crus (corticospinal, corticobulbar, and corticopntine tracts)

what happens during a midbrain lesion?

- ipsilateral third nerve palsy (only able to abduct eye)
- contralateral hemiparesis
- contralateral ataxia and sensory loss
- coma (damage to reticular formation)

what is the reticular formation?

- loosely defined groups of neurons throughout the brainstem

what are the functions of the reticular formation?

- somatic motor control (reticulospinal tracts, gaze centers, and respiratory centers)
- cardiovascular control (cardiac and vasomotor centers)
- pain modulation (central gating)
- arousal and habituation (ascending arousal system)

what does the forebrain consist of and the function?

- consists of the thalamic complex and cerebrum
- everything that we are aware of is created in the forebrain

what is the location of the diencephalon?

- superior and anterior to brainstem

what are the three divisions of the diencephalon?

- thalamus (numerous nuclei reciprocally-connected to cortex)
- hypothalamus (numerous nuclei that regulate endocrine and autonomic function)
- epithalamus (pineal gland and habenula)

what are the structures within the epithalamus?

- pineal gland
- habenula

what is the pineal gland?

- endocrine gland
- produces melatonin from serotonin
- melatonin secretion during darkness aids in circadian rhythm entrainment

what is the habenula?

- relay between limbic system and midbrain
- involved in calculating rewards

what is the location of the hypothalamus?

- forms the floor and part of the walls of 3rd ventricle
- above optic chiasm to mammillary bodies

what are the structures within hypothalamus?

- mammillary bodies
- pituitary gland

what are mammillary bodies?

- 3-4 nuclei
- relay between limbic system and thalamus

what is the pituitary gland?

- attached by infundibulum
- anterior: separate gland
- posterior: hypothalamic axons

what are the functions of the hypothalamus?

- hormone secretion
- autonomic effects
- thermoregulation
- food and water intake
- sleep and circadian rhythm
- memory and emotion
- behaviors

how does the hypothalamus control hormone secretion?

- via pituitary

how does the hypothalamus control autonomic effects?

- via descending fibers to preganglionic neurons

how does the hypothalamus control thermoregulation?

- via control of cutaneous blood flow, sweating, shivering, and piloerection

how does the hypothalamus control food and water intake?

- glucose and amino acids = "hunger"
- blood osmolarity = "thirsty"

how does the hypothalamus control sleep and circadian rhythm?

- via cyclic gene expression in the suprachiasmatic nucleus

how does the hypothalamus control memory and emotion?

- via connections with limbic system

how does the hypothalamus control behaviors?

- via connections with the cortex

what is the thalamus considered as?

- grand central station

which part of the diencephalon takes up 80% of it?

- thalamus

what does the posterior thalamus control?

- sensory relays
- all sense pass through thalamus before cortex
- smell is an exception

what does the ventral thalamus control?

- motor
- relays feedback from cerebellum and basal ganglia

what does the anterior and medial thalamus control?

- cognitive functions
- memory and emotion relay

what are the 5 lobes of the brain?

- frontal
- insula
- parietal
- occipital
- temporal

what does the frontal lobe control?

- behavior

what does the insula control?

- disgust

what does the parietal lobe control?

- location
- "where"

what does the occipital lobe control?

- vision

what does the temporal lobe control?

- language
- memory stores

what matter is the majority of cerebrum?

- white

what are the different tracts in the cerebral white matter?

- projection tracts
- commissural tracts
- association tracts

what are projection tracts?

- high to low
- cerebrum to something below

what are commissural tracts?

- cross midline

what are the association tracts?

- same side
- long: different lobes
- short: different gyri in same lobe

what is 40% of the brain mass?

- cerebral cortex

what are within the 6 layers of the cerebral cortex?

- layer thickness varies (4 in sensory, 5 in motor)
- projection neurons in layers 3 (cortex), 5 (subcortical), and 6 (thalamus)

what are the 2 principal neurons in the cerebral cortex?

- stellate cells stay local
- pyramidal project

what is the function of the limbic system?

- emotion and memory