Forebrain

Diencephalon

• thalamus

• hypothalamus

• epithalamus

• subthalamus

Thalamus

largest subsection of diencephalon; collection of nuclei that selectively filter input to cerebral cortex

• regulate flow if info

• regulate activity level of cortical neurons

• receive input from BG, cerebellum, and all sensory systems except olfactory

• nuclei are divided into groups by location and function

Lateropulsion/Pusher Syndrome

lesion to posterior thalamus

• pulvinar, lateral geniculate, and medial geniculate nuclei

• pushing away from less paretic side

  • high fall risk

  • affects sitting, standing, walking

  • resistant to postural adjustment

  • resolves over time (-6 mo), motor recover slower

Location-based Nuclei Groups

named for their location

• divided by Y-shaped lamina (white matter)

• anterior, medial, and lateral groups

• lateral group is further divided into dorsal/ventral

Function-based Nuclei groups: Relay nuclei

• Motor: ventral anterior (VA) and ventral lateral (VL)

• Sensory:

  • Ventral Posterolateral (VPL)- somatic sensation from body

    • afferent: spinothalamic tract, lemniscus pathway

    • efferent: somatosensory cx

  • Ventral Posteromedial (VPM)- somatic sensation from face

    • afferent: sensory nucleus, trigeminal nerve

    • efferent: somatosensory cx.

  • Medial Genticulate (MGN)- hearing

    • afferent: inf. colliculi

    • efferent: auditory cx

  • Lateral Genticulate (LGN)- vision

    • afferent: optic tract

    • efferent: visual cx

Lesion: interruption of ascending pathways, compromise contralateral sensation, proprioception usually affected the most

• motor and sensory impairments

Functional-based: Association Nuclei (memory, sensory integration, emotion)

• Anterior Nucleus (AN)- declarative memory

• Lateral Dorsal (LD)- declarative memory

• Midline (M)- declarative memory (hippocampus afferents, prefrontal cx efferents)

• Lateral Posterior (LP)- sensory integration (reciprocal with parietal cx)

• Pulvinar (P)- sensory integration (reciprocal connections with parietal, occipital, temporal cx)

• Medial Group (MG or MD)- emotions (reciprocal with emotional areas)

Function-based: Non-specific Nuclei (consciousness, arousal, attention)

Intralaminar (I)- arousal, attention (ascending reticular system afferents, widespread cortical efferents)

• Lesion: moderate/severe disability or vegitative state

• causes: TBI, thalamic stroke, PD

Reticular (R)- adjust activity of thalamus (interconnections with other thalamic nuclei)

Midline (M)- facilitates communication between limbic structures; key role in memory and executive functions; specialized roles in visceral functions

Hypothalamus

• integrates behaviors and visceral functions (eating/digestion)

• homeostasis (body temp, metabolic rate, BP, water intake, excretion, digestion)

• eating, reproduction, and defensive behaviors

• emotional expression of pleasure, rage, fear, aversion

• regulation of circadian rhythms (sleep, wake cycles)

• endocrine regulation of growth, metabolism, reproductive organs

• activation of sympathetic NS

• regulates pituitary gland

Pituitary gland

regulates metabolism, reproduction, stress response, urine production

• anterior and posterior part

• pituitary hormones target the adrenal cortex, thyroid gland, ovaries/testes

Hypothalamus regulation of ant. pituitary gland

arises from outgrowth of epithelia tissue in roof of embryonic oral cavity

• hormones released from hypothalamus increase/decrease hormone secretions from ant. pituitary

• secretes 6 different hormones

Hypothalamus regulation of post. pituitary gland

outgrowth of inf. brain in area of hypothalamus and continuous with brain

• secretions are considered neurohormones

  • AP in hypothalamus causes release of neurohormones from post. pituitary directly into bloodstream

Neurohormones:

• antidiuretic hormone (ADH; vasopressin): maintains osmolality and volume of extracellular fluid; increases water reabsorption in kidney and prevents excretion of large amounts of urine (helps when you have low BP or dehydrated)

• Oxytocin: uterus smooth muscle contractions and milk expulsion in lactation

Pituitary tumors

may compress cranial nerves 3 (oculomotor), 4 (trochlear), 6 (abducens)→ double vision, bitemporal hemianopia

• hormonal hypo/hypersecretion

  • headaches, nausea, vomitting, irregular menses and lactation, sexual dysfunction, high BP, increased blood glucose

  • acromegaly- growth hormone disorder causing gigantism, enlargement of head, hands, feet

  • Cushing’s disease- excessive ACTH causing fatigue, abnormal deposits of facial and trunk fat

Epithalamus

Pineal gland- endocrine gland innervated by sympathetic fibers

• helps regulate circadian rhythms with melatonin

• influences secretions of pituitary gland, adrenals, parathyroids, and Islets of Langerhans

  • parathyroids- produce parathyroid hormone; maintains appropriate balance of calcium in the bloodstream and in tissues

  • Islets of Langerhans- cluster of cells in pancreas that produce and release hormones that regulate glucose

Subthalamus

located in sup. to substantia nigra in midbrain

• facilitates BG output nuclei

• involved in regulating movement

Telencephalon- Cerebral Hemisphere

most common cells in the cerebral cortex:

• granule cells- small interneurons that remain in cx; process and transmit sensory info; olfactory and hippocampus

• pyramidal cells- some have short axons that synapse without leaving the cx; transmit sensory and motor info, plan and execute behavior, key role in cog. processes

  • most travel through white matter as projection, commissural, or association fibers

  • 75-85% of cortical neurons

projection fibers

• info from subcortical structures to cerebral cx

• info from cerebral cx to SC, BG, and thalamus (red lines)

• travel through internal capsule

• spread apart to form corona radiata

Commissural fibers

connect homologous areas of cerebral hemisphere

• corpus collosum: links many areas of R and L hemisphere

• ant. and post. commussure: link R and L temporal lobes

Association fibers

connect cortical regions within 1 hemisphere

• short: conect adjacent gyri

• long: connect lobes within a hemisphere

Long Association Fibers:

• cingulum: connects frontal, parietal, and temporal lobe cx

• occipitofrontal fasciculus: connects frontal, temporal, and occipital lobes

• inferior longitudinal fasciculus: connects occipital and temporal-occipital areas of the brain to ant. temporal areas

internal capsule

ant. limb:

• corticopontine fibers- cx and pons

• frontopontine fibers- frontal lobe and pons

• fibers connecting thalamic and cortical emotion/motivation areas

genu: cortical fibers projecting to CN motor nuclei and reticular formation

post. limb:

• corticospinal projections

• thalamocortical projections- relay somatosensory, visual, auditory, and motor info to cx

• retrolenticular and sublenticular fivers- post. and inf.

Middle Cerebral Artery

lenticulostriate branches- superior and anterior portions of internal capsule

anterior choroidal artery- posterior portion of internal capsule

Brodmann’s Area

cytoarchitectural organization for cerbral cx

• 53 areas numbered in order

• don’t need to memorize areas

Primary sensory cx (S1)

receive sensory info from ventral tier of thalamic nuclei

• separate primary sensory areas for somatosensory, auditory, visual and vestibular info

• lesions: impair ability to discriminate intensity and quality of stimuli (impaired senses) and conscious proprioception

Pathway:

• starts with tactile and proprioceptive receptors

• input received from afferent dorsal column neuron, medial lemniscus neuron, and thalamocortical neuron

• crude awareness of somatosensation occurs in thalamus (VPL and VPM)

  • neurons in somatosensory cx identify location of stimuli and discriminate for shapes/size/texture

• cortical termination of nociceptive is more widespread- not limited to primary somatosensory cx

Pathway to primary auditory cx

• conscious awareness of intensity of sounds

• cochlea of both ears → inf. colliculus and medial geniculate body of thalamus → cortex

• auditory info has extensive bilateral projections to cortex

  • unilateral lesion only interferes with localization of sound

• primary vestibular cx- perceives head mvmt and position

Lesion: loss of localization of sounds

Pathway to primary visual cx

• specialized neurons in visual cx distinguish between light/dark, shapes, various shapes, location of objects, and movements

• retina → lateral geniculate body of thalamus → primary visual cx

Lesion: contralateral homnymous hemianopia

primary sensory cx summary

Secondary sensory areas

more complex analysis of sensation and making sense of it; analyze input from thalamus and primary sensory cx

perceptual: interpretation of sensation into meaningful forms

• active process; requires interaction between brain, body, environment

• memory, motivation, expectations, selection of sensory info, and active search for pertinent info

Secondary somatosensory cx (brodmann area 5,7)

stereognosis: integrate tactile and proprioceptive info from manipulating an object and using memory to compare it to other objects; object identification through tactile and no visual

astereognosis: can describe object by shape, size, texture, but would not be able to recognize it through touch and manipulation

Secondary visual cx (brodmann area 18-21)

analyzes color and motion

• sends info to superior colliculis→ directs visual fixation

• dorsal (where) action stream: adjust limb mvmt in relation to visual info

• ventral (what) perceptial stream: object identification in contralateral visual field

visual agnosia: inability to visually recognize/identify objects, but able to describe shape, size, etc.

• ventral stream lesion: can’t recognize object, but could reach and pick up with correct orientation of hand, fingers

• dorsal stream lesion: optic ataxia; inability to direct mvmt based on visual info, but can identify and describe objects visual

• prosopagnosia: unable to recognize faces but can respond/interpet emotional expressions; can recognize people from voice, mannerisms, clothes

  • bilateral damage to inf. secondary visual areas (ventral stream)

secondary auditory cx (brodmann area 22, 42)

compares sounds with memories of other sounds and categorizes sounds as language, music, noise, etc.

• auditory agnosia: perceives but can’t recognize sound

  • left lesion: affects speech recognition (Wernike’s aphasia)

  • right lesion: interpreting environmental sounds

Motor cx Brodmann areas

primary motor cx- 4

supplementary motor area- 6

premotor area- 6

broca’s area- 44

frontal eye field- 8

primary motor area (M1)

in precentral gyrus

• corticospinal and corticobulbar tracts

  • controls contralateral voluntary movement, particularly fine movements of hand and face

  • trunk and proximal limbs involve more gross motor activity and bilateral activation

Lesion: paresis, loss of fine motor control, spastic dysarthria

M1 Lesions: Dysarthria

speech disorder from spasticity or paresis of speaking muscles

• Spastic dysarthria: UMN damage; harsh, awkward speech

• Flaccid dysarthria” LMN (CN 9, 10, and/or 12); breathy, soft, imprecise speech

M1 Lesions: Paresis

contralateral paresis and loss of selective motor control

• lower face and distal limbs affected the most

• wrist and finger ext. and ankle dorsiflexion lost

M1 Lesions: Alien Hand Syndrome (Dr. Strangelove Syndrome)

involuntary, uncontrollable movement of UE

• self-groping and self-oppositional behavior; extreme cases report suffocating oneself; can last days to years

• damage to a variety of cortical and subcortical structures

• possible that lesion to parietal cx impacts intentional planning but activation of contralateral M1

• R hemisphere: use of visual feedback and sensory stimulation

• L hemisphere: cognitive therapy for anxiety and anger

cortical motor planning areas

Broca’s area (L hemisphere): planning movements of mouth for speech

• Broca’s aphasia: broken speech; intact comprehension but difficulty with producing speech or writing

Inferior Frontal Gyrus (corresponding area in R hemisphere): plans non-verbal communication, emotional gestures, tone of voice

Supplementary Motor Area (SMA): initiation of movement, orientation of eyes and head, planning bimanual and sequential movements

• important for controlling fast, complex mvmts and anti-phase hand mvmts (R and L hand are doing different things)

• Unilateral lesion causes total loss of contralateral mvmts and impairment of ipsilateral mvmt

Premotor Cx (PMC): learns goal-oriented actions, prepares, selects, initiates mvmt

• Lesion: speed/automaticity of reaching/grasping, sequential mvmt, gait, posture

• poorer rehab potential; persistent proximal weakness in contralateral limbs, poor motor planning

apraxia

lesions to supplementary motor area and premotor cx; difficulty with everyday mvmts and gestures

• “motor agnosia”- sensation, coordination, muscle strength, and understanding of task are intact, but how to do the task is lost

• consistently inconsistent; may use objects correctly in rehab but forget at home

motor perseveration

more associated with amount of neural damage than site of damage

• uncontrollable repetition of movmenet

Association cx

located in frontal, anterior temporal, and temporoparietal cx

• not directly involved with sensation or movement

• controls behavior, interprets sensation, and processes emotions and memories

• responsible for complex cognitive functions

Flow of info from primary sensory cx to motor output

cerebral stroke

infarct: thrombus (blood clot) or embolus (any blockage) lodges in a vessel, obstructing blood flow

hemorrhage or edema can compress vital structures and affect oxygenation

tumors

spontaneous, abnormal growth of tissue forming a mass, causing compression

• symptoms based on location and size of tumor

  

epilepsy

sudden attacks of excessive cortical neuronal discharge interfering with brain function

• involuntary movement, disruption of autonomic regulation, illusions, hallucinations

  • generalized seizures affect entire cx, partial affect only some areas

  • absence seizure: brief loss of consciousness without motor manifestation

  • tonic-clonic: tonic contraction of skeletal muscles followed by alternating contraction and relaxation for about 1 min. each, followed by confusion and no memory of seizure

causes: tumor, infection, stroke, TBI, neurodegeneration disease, febrile seizures

• medical emergency if: cause is unknown, diabetic, injured, pregnant, lasts longer than 5 min., 2nd seizure begins, consciousness does not return, occurs in water

Basal Ganglia

functions: decision-making, judgement, prioritizing info, emotional processing and responses, learning, eye movements, spatial attention, movement

NTs:

• glutamate = excitatory

• GABA = inhibitory

• dopamine = modulatory

• striatum = head of caudate and putamen

  • nucleus accumbens- main component of ventral striatum

• pallidum = GPe, GPi, GPe

• Lentiform nucleus = putamen, GPi, GPe

• subthalamic nucleus = subthalamus

• substantia nigra pars compacta (dopamine)

  • motor, reward, motivation

• substantia nigra pars reticularis (GABA)

  • movement

• thalamus

main output to thalamus- globus pallidus internus (GBi) and substantia nigra reticularis (SNr)