Part 1 - Structure and Function Flashcards
Three germ layers and their future tissues
- Endoderm: Respiratory and GI
- Mesoderm: Muscles and circulatory
- Ectoderm: Skin, hair and CNS
Alternative names for hind brain, midbrain and forebrain
Rhombencephalon
Mesencephalon
Proencephalon
Content of cerebral peduncles
Descendign motor tracts
Two parts of tectum and their senses
Superior; optic
Inferior; auditory
Components of tegmentum
- Substantia nigra
- Red nucleus
- Cerebral aqueduct
- PAG
- Reticular formation
Which part of brain does the lateral ventricle lie within
Telencephalon of forebrain
Structure connecting leteral and third ventricle
Interventricular foramen
Which comparrtment does third ventricle lie in
Diencephalon
Structure connecting third and fourth venrticle
Cerebral aqueduct, also the narrowest part of ventricualr system
Path of CSF
- Produced in choroid plexus
- Flows through ventricles and into subarachnoid space via median and lateral apertures, some flows thorugh central canal of spinal cord
- CSF flows through the subarachnoid space
- CSF is absorbed into the dural venous sinuses via the arachnoid villi
Subtypes of hydrocephalus
- Obstructive/non-communicating: CSF flow blocked within the ventricles or between ventricles and SAS
-
Communicating: unimpaired communication between ventricles and SAS. Problem lies outside ventricular system
- Reduced absoroption of CSF
- Blockage of venosu drainage system
- CSF over production
Define a cistern
Large areas in SAS where CSF collects due to folds
Three main dural reflections
Falx cerebri - separates hemispheres
Tentorium cerebelli - Occipital lobe & cerebellum
Falx cerebelli - cerebral hemispheres
Major functions of lobes
frontal: Personality, attention, motivation, planning movement
Parietal: Integrating sensory information, language processing
temporal: Motor, memory, language comprehension
Occipital: vision
Main branches of carotid artery in cranium
- Middle cerebral artery (stroke)
- Anterior cerebral artires
- Hypophysial, opthalmic, posterior communicating arise from terminal bifurcation
Branches of vertebral artery
Anterior spinal
Posterior inferior cerebellar
Basillar artery branches
Pontine (pons)
Labrynthine artery (inner ear)
Superior cerebellar artery
Posterior cerebral artery(anastamost with int carotid to form circle of willis)
Size limit for passing BBB
<2000MW
Histological structure of choroid plexus
- A Layer of cuboidal epithelial cells sorrounding core of capillaries.
- Continual with ependymal cell layer lining ventricles
- However, the CP cells have tight junctions preventing blood-CSF
- Forms villi around capillaries
Processes involved in CSF formation
- ultra-filtration of plasma across capillary walls into ECF beneath basolateral membrane of choroid epithelial cells
- Choroid epithelial cells secrete fluid into ventricle
Mechanism of CSF secretion from CP cells
Basolateral membrane
- Transporters exchange intracellular HCO3 for Cl- by use of Na+ gradient
Apical membrane
- Na/K/ATPases
- AQP1
BBB vs Blood-CSF-Barrier
BBB: Tight junctions in brain capillaries control solute transport into ECF
BCSFB: Tight junctions between ependymal cells/CP cells
Functions of CSF
- Providing nutrients
- Removing waste from ECF
- Medium of exchange between ECF and systemic blood
- Shock absorber
Notable differences in composition of plasma/CSF
Plasma
- 6000mg/dl protein
- 175mg/dl cholestrol
- 4.7 K+
CSF
- 20 mg/dl protein
- 0.2 mg/dl cholestrol
- 2.9 K+
3 mechanisms of CSF reabsorption
- Bulk flow via arachnoid villi within SAS
- Diffusion via vascular epithelium of the choroid plexus
- Active transport via choroid plexus
Pathway of CSF
- Lateral ventricle (cortex)
- Foramina of Monroe
- Third ventricle (thalamus)
- Cerebral aquaduct of sylvisu (midbrain) - blockage
- Fourth ventricle (brain stem)
- two foramin of Luschka and foramin of magendie
- SAS
Affect of lipid solubility on BBB passage
High lipid solubility; greater access
Impact of ionisatino on BBB passage
Drugs ionised at 7.4 have less access
Why can’t dopamine be used in Parkinson’s
Ionised at 7.4
Metabolised by MAO present in denothelial cells
Insted use L-DOPA with DOPA decarboxylase inhibitor preventing conversion outside of CNS as inhibitor is ionised at 7.4 and cant pass BBB
List circumventriular organs
= Brain areas lacking BBB, tight junction replaced by fenestrations
- Posterior pituitary; released hormones have direct access to circulation
- Median eminence; oxytocin, vasopressin, picks up releasing hormones
- Area Postrema; chemoreceptor zone in control of vomiting
- OVLT; important for actions of cytokines in periphery (fever
Three types of white matter tracts
Association fibres: exchange fibres within same hemisphere
Commisural fibres: Information between hemispheres
Projection fibres: From cortex to other regions of brain or spinal cord e.g. UMNs
Structures associated with fornix
Limbic structure, connects hippocampus in temporal lobes to mammillary bodies
i.e. memory
Structures associated with anterior commissure
Connects amygdalas of two temporal lobes
i.e. emotion
Structures associated with posterior commisure
Connects parts of Thalamus participating in vision to superior colliculus
Pathway for UMNs
Primary motor cortex area
Corona Radiata
Internal capsule
Midbrain
Spinal Cord
Divisions and roles of Internal Capsule
Anterior limb
- Association fibres. Thalamocortical and corticostriatal
Genu
- Projection fibres (UMN) from primary motor cortex; head and face movement(CN)
Posterior limb
- Projection fibres(UMN) from area IV; arm, trunk, leg movement
- Sensory fibres from thalamus to primary somatosensory cortex
Where do pyramidal tracts decussate
In the lower end of medulla
Divisions of pyramida ltract
Corticobulbar tract
- Terminates in brainstem; inputs to cranial nerves
Corticospinal
- Lateral: decussates; limbs and digits
- ventral: remains ipsilateral; trunk
Whre in ventral horn are flexors/extensors positioned
Flexors towards central canal
Extensors more ventral
Symptoms of UMN damage
- Increased tone
- SPcaticity/increased reflexes
- Clonus
ALS
Degeneration of UMN and LMN - extremities and inwards, progressive
Primary alteral sclerosis
Degeneration of corticospinal tracts
Begins as stiffness/weakness of legs, balance/gait issuse, spread to arm and trunk
Pseudobulbar Palsy
Degeneration of cortibulbar tract
Facial paralyiss, dribbling, speaking issues
Characteristics of Meissner’s corpuscles
Rapidly adaptive.
Light touch, 2 point discrimination
Concentrated in hairless skin e.g. finger pads
Charactersistics of Merkel’s disks
Slowly adapting
Light pressure and discriminatie touch
Characteristics or Ruffini corpuscles
Slowly adapting
Responds to skin strech; show little adaptation
Around fingernails, mointor slippage etc allowing modulation of grups
Pacinian corpuscle
rapidly adapting
Vibration and textures
3 Ascending Pathways
DCML - main sensory, discrimative/fine touchm propriception
Anterolatereal - Temperatrue and pain, non discrimative touch
Spinocerebellar - uncnscious propriception
Two tracts of DCML
Fasciculus gracilis;
- medial, from lower limb
- Synapses in gracile nucleus of lower medulla
Fasciculus cuneatus
- Lateral, from upper limb
- Synapses in cuneate nucleus of lower medulla
Signs of DCML damage
- Loss of discriminative touch, vibration, and propriception
- Preserved pain perception
- A positive ROMBERG sign indicates reduced propriception
Outlien spinothalamic tract
Direct portion of anterolateral system
- 2nd order neurons decussate in spinal cord at appropriate vertebral level
- Transmits info to thalamus and primary somatosensory CTX
Outline spinoreticualr tract
Indirect portion of anterolateral system
- Terminates in brainstem
- participates in reticualr activating system (consciousness)
Outline spinocerebellar tract
- Unconscious ipsilateral propriception to cerebellum
- Via inferior cerebellar peduncles
- no 3rd order neurons
- Dorsal: lower limbs and trunk; dorsalis of clarke
- Cuneocerebellar: upper limb and trunk; cuneate nucleus
Freidrich’s ataxia
Sensory condition
hereditary degeneration of DCML and spinocerebllar tract
Role and I/O of medial geniculate body
Hearing
I: Inferior colliculus
O:Audiotory cortex
Role an I/O of lateral geniculate body
Vision
I: retina
O: visual cortex
I/O Anterior nuclear group
I: mamillary bodies
O: Cingulate Cortex
I/O medial nuclear group
I: entorhinal cortex
O: prefrontal cortex
Subdivisions of lateral nuclear groups and their roles
Dorsal(associaton) - vision
Ventral - movement
- VA - basal ganglia
- VL - basal ganglia and cerebellum
- VP - body
Cortex Function
Integrates information
Produces Motor Signals
Transmits signals to brain stem and pinal cord
Basal Ganglia function
Modulate movement
Receive information from cortex; via thalamus; feed backt to cortex
Components of basal ganglia
- Corpus striatum
- Caudate nucleus
- Lentiform nucleus
- Putamen
- Globus Pallidus I/E
- Subthalamic nucleus
- Substantia nigra
- Pars reticulata
- Pars compacta
Overall outcome from direct pathway of BG
Disinhibition of thalamic neurons; excites cortex, drives movement
Overall outcome from indirect BG pathway
Disinhibition of subthalamic; decreased excitation of cortex; inhibits movement
Cause of huntington’s
Death of GABAergic neurons in striatum
Cause of Parkinsons
Decreased dopamine production in substantia nigra pars compacta
Two types of cortex and their distinctions
Neocortex - isocortex
- 90% of cortical volume
- Phylogenetically recent
- Laminar 6 layered structure
Allocortex - Heterogenic cortex
- 10 % of cortical volume
- Phylogenetically old
- 3 layers
Two main cell types within cortex
Pyramidal cells
Granule cells
Pyramidal cell characteristics
- 75-85% of cortex cells
- Also in hippocampus and amygdala
- Large pyramidal shaped cells body
- EXCITATORY - Glutamatergic
Granule cell characteristics
- Cortex, and some in cerebellum and hippocampus
- Small cell body
- GABAergic - INHIBITORY
- Smooth stellate, i.e. inhibitory
Three types of glial cells
Astrocytes
Microglia
Oligodendrocytes
Astrocyte characteristic and fucntion
- Star shape
- Maintain homeostasis (sequestering K+ and glutamate)
- End feet maintain BBB and contribute to blood flow regulation
- Repair and scarring
Microglia function
- Resident immune cells
- Ramified, amobeoid, mobiel when activated
- produces enzymes and cytokines, capable of phagocytosis
Oligodendrocytes function
- Small cells whose processes form individual nodes of myelin around axons
- Make up white matter
Layers of neocortex and brief function
- Molecular - few neurones, glial cells and apical denrites
- External granular - Small pyramidal and granule neurons
- External pyramidal - Small and medium pyramidal and granule cells
- Internal granula - mainly stellate cells
- Internal pyramidal - Large pyramidal neurons with apical dendrites streching upwards and basilar dendrites stretching laterally. Contains projection neurons
- Multiform - Small spindle like pyramidal and multiform neurons interactign twith thalamus
Area 22; location and name
Superior temporal gyrus
Wernicke’s area
Area 44/45 Location and Function
Inferior frontal gyrus
Broca’s area
Area 1-3 location and name
Postcentral gyrus
Primary somatosensory area
Area 4 location and name
Precentral gyrus
Primary motor area
Area 41 Location and function
Superior temporal gyrus
Primary auditory area
Difference in cortical layer structure in sensory vs motor areas
In sensory there is a larger layer IV(input) and a smaller V(output)
Vice versa
Role of Wernicke’s language area
Inteprets spoken word
Role of Brocas language area
Produces speech
Key roles of Limbic systesm
- Emotions
- Motivation
- Memory
- Social behaviours
- Reward drive activites e.g. food and sex
Disorders in cingulate gyrus damage
Disorders of motivation and planning
Role of orbitifrontal cortex in limbic system
Decision making
I/O of hippocampus
Input
- Sensory info from cortex via entorhinal cortex -> perforant pathway-> dentate gyrus; CA3; CA1
Output
- Via subiculum and enthorhinal cortex -> neocortex
- Via fornix
- Septal region
- Mamillary bodies, hypothalamus, medial forebrain bundle
Papez circuit function and pathway
Important in memory. Begins and ends in hippocampus
Hippocampal formation (subiculum); fornix; Mamillary bodies; mamillothalamic tract; anterior thalamic nucleus; cingulum; entorhinal cortex; hippocampal formation
Types of long term memory
Declarative (explicit)
- Semantic (facts, knowledge, concepts)
- Episodic
Non-declarative (implicit)
- Uncoscious knowledge e.g. motor skill and conditioned responses
Explain long term potentiation
Long-term potentiation (LTP) is a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons
It is one of several phenomena underlying synaptic plasticity, the ability of chemical synapses to change their strength. As memories are thought to be encoded by modification of synaptic strength, LTP is widely considered one of the major cellular mechanisms that underlies learning and memory
Amygdala I/O
Kluver-Bucy Pathophysiology
Large bilateral anterior temporal lobe restrictions
- Remoces amygdala, hippocampus, and sorrounding temporal lobe
- Docile; decreased agression
- Indiscriminate sexual activity
- Can’t discriminate edible/inedible
- A breakdown of visual input to channelling drives
Meso-limbic DA pathway
= Reward circuit
- DA neurones in ventral tegmental area of midbrain area send axons to nucleus accumbens and other areas of ventral striatum and orbitofrontal cortex
Changes to limbic components in depression
Amygdala; anxiety
Hippocampus; memory deficit
Reward circuit; anhedonia; (don’t feel pleasure) and motivation
Striatum; motor slowing
Limbic changes in depression by imaging
Decreased volume in hippocampus and orbitofrontal cortex
Increased blood flow in subgenual cingulate cortex
Decreased blood flow in dorsolateral frontal cortex
NT changes in depression
Decreased monoamines (5-HT & NA) function
Decreased BDNF
treatment with 5-HT agonist
Inferior Colliculus I/O & Function
I: Cochlea, brain stem nuclei
O: Medial geniculate body, auditory cortex
Relays auditory information, sound localization
Superior colliculus I/O & function
I: Retina, visual cortex
O: Tectospinal tract, brain stem
Eye orientatino and tracking movement, gaze shifting i.e. mediate reflex postural movements of the head in response to visual and auditory stimuli.
Mamillary bodies I/O & Function
I: Cingulate, hippocampus, fornix, amygdala, hypothalamus
O: Anterior nucleus of thalamus
Episodic, implicit and spatial memory
CN I
Type
Function
Olfactory
Sensory
Brings smell
CN II
Type
Function
Optic
Sensory
Brings vision
CN III
Type
Function
Occulomotor
Motor/psymp
Moves eyes; up, down, towards midline, and rotates outwards
Pupil constriction parasympathetic
CN IV
Type
Function
Trochlear
Motor
Moves eyes down and rotates inwards
CN V
Type
Function
Trigeminal
Sensory/motor
Sensory facial info
Chewing, swallowing
CN VI
Type
Function
Abducens
Motor
Moves eyes away from midline
CN VII
Type
Function
Facial
Sensory/motor/parsymp
Taste, Facial expression(parasympathetic), salivation
CN VII
Type
Function
Vestibulocochlear
Sensory
Brings sound and motion
CN IX
Type
Function
Glosso-pharyngeal
Sensory, motor, psymp
Taste, Pharynx movement, salivation
CN X
Type
Function
Vagus
Sensory, Motor, Parasymp
S:Choking, gagging
M:swallowing, speaking
P: slows heart, stimulates digestion
CN XI
Type
Function
Spinal accessory
Motor
Controls head rotation and scapula
CN XII
Type
Function
Hypoglossal
Motor
Speech and chewing by tongue
Pseudobulbar palsy
Degeneration of corticobulbar tract
Progressive bulbar palsy
Degeneration of brain stem, particularly cranial nerve nuclei
Name Extrapyramidal tracts
Tectospinal
Vestibulospinal
Reticulospinal
Rubrospinal
Tectospinal tract pathway and function
- From superior colliculus(ie.e retinal/visual cortex input)
- Decussates immediately terminating in upper spinal cord
- coordinates head and eye movements
Rubrospinal tract pathway and function
- From red nucleus(i.e input from cerebellum via sup peduncles)
- Decussates immediately, descends with corticospinal tract
- Terminates in upper spinal cord
- It primarily facilitates flexion in the upper extremities
Vestibulospinal tract pathway and function
- From pontine vestibular nuclei(i.e. input from inner ear & cerebellum via inf cerebellar peduncles)
- Medial vestibular nucleus; descends bilaterally
- Lateral vestibular nucleus; Descends ipsilaterally and synapses at several levels
Assits in balnce and posture by maintaing head position and stimulation extensrors of the body
Reticulospinal tract pathway and function
- From reticular formation of pons/medulla(i.e. input from cortex and cerebellum)
- Both Medial and Lateral reticular formation; descend ipsilaterally, and synapse at several levels
Assists in controlling trunk as well as upper and lower limb i.e gait and posture
UMN or LMN disease?
Stroke
Peripheral neuropathy
MS
Polio myelitia
ALS
Myasthenia Gravis
UMN
LMN
UMN
LMN
UMN
LMN
Signs of Parkinson’s
Poor slow movement
Postural abnormalitites/rigidity
Mask-like expression
Tremor
Later: Depression, Dementia, Endocrine dysfunction
Which condition?
Able to assemble motor plans but unable to specify accuracy of programmes, run or sequence them
Parkinson’s
4 Dopamine pathways and associated condition
- Nigrostriatal: Parkinson’s
- Mesocortical and Mesolimbic: Shizophrenia
- Tuberinfundibular: Hyperprolactineamia
Side effect observed afte few years of L-DOPA
Choreic movements
How do D2 receptors achieve their function
Inhibit Adenylyl cyclase
Drug targets other than L-DOPA in parkinsons
D2 agonists e.g. ropinirole
Drugs that prevent Dopamine metabolism
- MOA-inhibitors e.g.g selegiline
- COMT-inhibitors - ONLY useful in combination with L-DOPA
A Staged Parkinson’s treatment plan
Dopamine receptor antagonist are used in?
Huntigton’s & Tourette’s
