Term Test 2 (Lec 9-13) Flashcards
3 major functions of Brainstem
Relay (conduit):
- long tracts TO and FROM the spinal cord
Cranial Nerves:
- attachment point for most cranial nerves
- cranial nerve nuclei
Integrative Functions:
- Cardiovascular
- Respiratory
- General visceral sensory and motor
- Reticular formation
External Anatomy - Dorsal View
External Anatomy - Ventral View
Internal Brainstem Divisions
3 major divisions:
Tectum (“roof”):
- Area posterior to the ventricular
space
- Midbrain: superior & inferior colliculi
Tegmentum (“covering”):
- Area anterior to the ventricular
space
- The reticular formation, cranial nerves & nuclei, spinal tracts
Appended structures:
- Cerebral peduncles, basal pons & pyramids
Reticular Formation (“consciousness”)
- The core of tissue found throughout the brainstem
Functions:
* Respiratory control
* Cardiovascular control
* Sleep/wake cycles (ascending reticular activating system – ARAS)
* Sensory modulation
* Reflexes (i.e. coughing)
Brainstem Nuclei
- So far we have focused on brainstem nuclei with discrete connectivity
- Spinal tracts
- Cranial nerve nuclei
- BUT some brainstem nuclei have extremely widespread connectivity designed to modulate the activity of the brain
- Locus coeruleus
- Substantia nigra (pars compacta) * Ventral tegmental area (VTA)
- Raphe nuclei
* Each uses a distinct small-molecule neurotransmitter
Locus Coeruleus – Noradrenaline
- Latin for “blue spot”
- Floor of 4th ventricle in rostral pons
Projections to:
* Thalamus, hypothalamus, hippocampus & cerebral cortex (somatosensory)
Roles:
* Maintaining attention and vigilance
Substantia Nigra & VTA – Dopamine
Substantia nigra (compact part)
* Rostral midbrain
* Projections to striatum & putamen
(nigrostriatal pathway)
Ventral tegmental area (VTA)
* Rostral midbrain
* Projections to cerebral cortex & amygdala (mesocortical & mesolimbic pathways)
- Roles: initiation of movement, motivation & cognition.
Raphe Nuclei – Serotonin
- A series of nuclei found along the midline of the brainstem reticular formation
Projections to:
* All parts of the CNS
* Higher density in sensory & limbic cortical regions
* Cerebellum, brainstem & spinal cord
Roles:
* Overall level of arousal
* Descending pain control system
Brainstem Cross Sections (7)
- Red –> motor
- Blue –> sensory
- Green –> connections with the cerebellum/reticular formation
- Purple –> special nuclei (presented today!)
- Black –> other landmarks/structures of interest
Caudal/Middle Medulla
Rostral Medulla
Pontomedullary Junction
Rostral Pons
Caudal Midbrain
Rostral Midbrain
Medial Longitudinal Fasciculus (MLF)
- Runs the entire length of the brainstem
- Composition of fibers changes at different levels
- Important roles in:
- Eye movements (coordination of oculomotor, trochlear & abducens nuclei)
- Vestibular compensations (ie. gait adjustments)
Neocortical Lamination
- Layer I: cell-poor
- Layer II: granular cells
- Layer III: small pyramidal cells
- Layer IV: granular cells
- Layer V: large pyramidal cells
- Layer VI: fusi/multiform (spindle-like) pyramidal cells
Cortical Lamination
- The 6 cell layers are not always the same thickness
- Differences often relate to the function of the cortical area
- E.g. Motor cortex ! numerous pyramidal cells, few granule cells
Neocortical Connectivity
- Different neocortical layers have distinctive connections
Afferents (inputs):
* Subcortical
–> Thalamic relay nuclei (VPL/VPM): Middle layers, particular layer IV
–> Other thalamic nuclei (LGN/MGN)
* Corticocortical: Mostly layers II and III
Efferents (outputs):
* Subcortical
–> Basal ganglia, brainstem & spinal cord: Layer V
–> Thalamic regulatory projections: Layer VI
* Corticocortical: Mostly layer III
Cerebral Cortex Efferents
Corticocortical:
* Commissural pathway
–> Corpus callosum & anterior commissure to contralateral hemisphere
* Association pathway
–> Short & long projections to
ipsilateral hemisphere
Projection fibers:
- Subcortical
- Corticothalamic
Association Fibres
- Short association fibers:
–> “U fibers”
–> Connect adjacent gyri - Long association fibers:
–> Connect different lobes- Superior longitudinal fasciculus (arcuate fasciculus)
- Cingulum
- Uncinate fasciculus
Brodmann’s Areas
- German anatomist Korbinian Brodmann (1868-1918)
- Division of the cerebral cortex in 46 areas based upon cytoarchitectural characteristics
–> Similar to the Rexed laminea in spinal cord - Boarders between areas are not sharp
- Size of areas can vary from person to person
- Some, but not all, correspond to functional areas within the cortex
5 Lobes of the Cerebrum
46 Brodmann’s Areas
Functional Divisions
- Primary sensory/motor areas
–> Input of sensory information from outside world/output to body to
respond to outside world - Unimodal associative areas
–> Allow for more complex responses to sensory information - Multimodal associative areas
–> Respond to multiple sensory inputs
–> Increased proportion of association cortices in humans compared to other species
Primary Sensory/Motor Areas
- Exhibit topographical organizations, often distorted to emphasize highly discriminating/fine motor control areas
- Motor & somatosensory: body surface (Homunculus)
- Auditory: tonal frequencies
- Visual: retinotopic organization (visual fields)
Unimodal Association Areas
- Found adjacent to primary sensory/motor areas
- Generally receive most of their input from appropriate primary cortex and some limited direct projections
Multimodal Association Areas
- Respond to multiple sensory modalities
- High-level intellectual functions (speech, executive function, etc.)
Parietal Lobe - Somatosensation
- Inputs: Thalamus
–> Ventral posterolateral (VPL)! medial lemniscus (DCML)
–> Ventral posteromedial (VPL/VPM)! spinothalamic (AL) - Primary somatosensory area (S1)
–> Postcentral gyrus - Secondary somatosensory area (S2)
- Somatosensory association cortex
–> Brodmann areas 5 & 7
Occipital Lobe - Vision
- Input:
–> Lateral geniculate nucleus –> optic radiation - Primary visual cortex (V1)
–> Brodmann area 17
–> Lesions: total/near-total loss of conscious awareness of visual
stimuli - Visual association cortex (V2-5)
–> Brodmann areas 17, 18, 19 and others
Temporal Lobe - Hearing
- Inputs:
–> Medial geniculate nucleus - Primary auditory cortex
–> Brodmann area 41
–> Tonotopic map of frequencies
–> Lesion: little effect, auditory information travels bilaterally, some difficulty localizing sounds - Secondary auditory cortex
–> Brodmann area 42 - Auditory association cortex
–> Brodmann area 22 (44 and 45 – “Broca’s
area”)
–> Lesion: language problems (Wernicke’s)
–> Difficulty understanding prosody
Frontal Lobe - Motor Cortex
- Primary motor cortex (M1)
–> Brodmann area 4 - Premotor cortex (PMC)
–> Lateral portion of Brodmann area 6 - Supplementary motor area (SMA)
–> Medial portion of Brodmann area 6 - Output
–> Corticospinal tract
Posterior Parietal Cortex (PPC)
- Postcentral gyrus, posterior to S1
- Agnosia: “lack of knowledge”
–> Inability to recognize the identity or some other property of objects when using a given sense
–> E.g. visual agnosia: inability to recognize faces or perceive movement of objects - Right posterior parietal damage: contralateral neglect * Apraxia: “lack of action”
–> A patient is unable to perform some actions, even though the muscles required are perfectly sound & able to perform the same action in a different context
Prefrontal Cortex
- Frontal lobe areas anterior to Brodmann areas 4 & 6 (motor)
- Controlling the activities of other cortical areas
- Executive functions: planning, insight, foresight &
personality - Dorsolateral PFC
–> Extensive interconnectivity with dorsomedial nucleus of thalamus
–> Working memory - Ventromedial PFC
–> Extensive interconnectivity with limbic structures (amygdala)
–> Damage results in inability to suppress inappropriate responses (hypersexuality) and emotional reactions
Cerebral Cortex Review
Review - Cerebellum
Longitudinal divisions * Vermis
* Cerebellar hemispheres
3 lobes
* Anterior
* Posterior (2)
* Flocculonodular
Functions
* Coordination of trunk & limb
movements
* Eye movements
Cerebellum - The Basics
- “little brain”
- Accounts for 10% of the mass of the brain
- However, the cerebellum contains as many neurons as the rest of the CNS combined!
- Functions: * Equilibrium
- Postural control
- Coordination of voluntary movements
Cerebellar Divisions pt.1
- Primary fissure: divides body into anterior & posterior lobes
- Posterolateral fissure: separates flocculonodular lobe from body of the cerebellum
Cerebellar Divisions pt.2
- Functionally, the cerebellum is divided into longitudinal strips containing cerebellar cortex & deep internal structures
Spinocerebellum:
* Vermis
* Medial hemisphere
Pontocerebellum/Neocerebellum:
* Lateral hemisphere
Vestibulocerebellum:
* Flocculonodular
Cerebellar Divisions pt.3
- Underlying each functional division of cortex is a deep cerebellar nucleus
- Fastigial nucleus
- Interposed nucleus
- Dentate nucleus
Cerebellar Connectivity
- Within the cerebellum, all parts use the same basic circuitry, the differences in function arise from differences in connectivity
Cerebellar Peduncles
- Superior cerebellar peduncle
–> Primary output route - Middle cerebellar peduncle
–> Inputs from contralateral cerebral cortex via pontine nuclei - Inferior cerebellar peduncle
–> Mix of afferents and efferents
Cerebellar Cortex MICROanatomy
Outer molecular layer:
* Axons
* Dendrites
Middle Purkinje cell layer:
* Single layer
* Largest, most intricate dendritic tree in nervous system
Inner granule cell layer:
* Mostly small granule cells (some interneurons)
Cerebellar Inputs
- Two major types of input
Mossy fibers:
* Projections from widespread areas
* Synapse with granule cells
* Granule cells give rise to parallel fibers to synapse with Purkinje cells
Climbing fibers:
* Contralateral inferior olivary nucleus
* Synapse directly with Purkinje cells
Parallel & Climbing Fibres
Parallel Fibers:
* 1 granule cell parallel fiber makes 1 or 2 contacts with multiple Purkinje cells
* Need many parallel fibers to get Purkinje cell to fire
Climbing Fibers:
* Each Purkinje cell receives a
single climbing fiber
* Single climbing fiber makes 1000s of connections with Purkinje cell
Cerebellar Cortex Connectivity
Input:
1. Mossy fibre –> granule cell –> parallel fiber
–> multiple Purkinje cells
2. Climbing fiber –> single Purkinje cell
Output:
* Axons of Purkinje cells are the only axons to emerge from the cerebellar cortex
* Project to deep nuclei
Cerebellar Hypoplasia
- Feline leukopenia viral infection in utero,
- Destroys purkinje cells
Deep Nuclei
- Flocculonodular lobe –> Vestibular nuclei
- Vermis –> Fastigial nucleus
- Medial hemisphere –> Interposed nucleus
- Lateral hemisphere –> Dentate nucleus
Cerebellar Outputs
- Each functional zone has a distinguishing set of outputs
- Fastigial nucleus –> vestibular nuclei & reticular formation
- Interposed & Dentate –> red nucleus & thalamus on way to contralateral cerebral cortex
- Cerebellum is responsible for the ipsilateral body
Basal Ganglia
- A group of nuclei in the basal forebrain & midbrain
- 5 major structures
- Best known for their role in motor control
Nuclei of the Basal Ganglia
5 main structures:
* Caudate nucleus
* Putamen
* Globus pallidus
* Subthalamic nucleus (STN)
* Substantia nigra
- Striatum: Caudate, putamen & nucleus accumbens
- Lenticular nucleus: Putamen & globus pallidus
Location of the Basal Ganglia
- Acc. Nucleus accumbens
- Am.Amygdala
- C. Caudate nucleus
- G. Globus pallidus
- P. Putamen
- SNpc. Substantia nigra pars compacta
- STN. Subthalamic nucleus
- T. Thalamus
Location of the Basal Ganglia - A (most caudal)
Location of the Basal Ganglia - B
Location of the Basal Ganglia - C
Location of the Basal Ganglia - D (most rostral)
Fibre Terminology
Where do the following fibers originate from/go to?
* Nigrostriatal - SN to striatum
* Pallidothalamic - GP to thalamus
* Striopallidal - Striatum to GP
Basal Ganglia Afferents
Cortex:
* Corticostriatal fibers
* Glutamatergic (green)
Thalamus (intralaminar):
* Thalamostriatal
* Glutamatergic (green)
Substantia nigra (compact):
* Nigrostriatal
* Dopaminergic (purple)
Basal Ganglia Efferents
Globus pallidus internal
* Pallidothalamic
* GABAergic
Substantia nigra (reticular)
* Nigrothalamic
* GABAergic
Basal Ganglia Circuitry
Direct Pathway
5 sets of neurons:
* Corticostriate
* Striatopallidal
* Pallidothalamic
* Thalamocortical
* Corticocortical
- Cortex excites striatum, striatum increases it’s inhibition of the globus pallidus internal (GPi), GPi decreases it’s inhibition of the thalamus (GPi inhibition of thalamus removed or “disinhibited”) allowing the thalamus to excite the cortex (activating motor efferent nerves to spinal cord) and movement is facilitated
Indirect Pathway
7 sets of neurons:
* Corticostriate
* Striatopallidal
* Pallidosubthalamic
* Subthalmopallidal
* Pallidolthalamic
* Thalamocortical
* Corticocortical
–> Cortex excites striatum, striatum increases it’s inhibition of the globus pallidus external (GPe), GPe decreases it’s inhibition on the subthalamic nucleus allowing the subthalamic nucleus to excite the GPi, GPi increases it’s inhibition of the thalamus which is now inhibited from exciting the cortex (not allowing the cortex to excite motor nerves to spinal cord) and movement is inhibited
Diencephalon
- Makes up 2% of the total brain volume
- 4 parts, each including “thalamus” in the name
- Latin for “inner chamber”
- Epithalamus
–> Pineal gland
–> Habenula - Thalamus
- Subthalamus
–> Subthalamic nucleus - Hypothalamus
–> Mammillary bodies
Thalamus
- Large, egg-shaped nuclear mass with a posterior appendage
- 80% of the diencephalon
- All sensory pathways relay
through the thalamus - Also a part of many basal ganglia, cerebellar and limbic system circuits
- Gateway to the cortex
Thalamic Inputs
Specific input:
* Convey information that a given nuclei may pass on accurately to the cerebral cortex
* Ex. Medial lemniscus is the specific input to the VPL
–> pain, touch, any stimuli up to spinal cord / brain to thalamus
Regulatory input: basal ganglia –> thalamus –> cortex
* Contribute to the decision about whether information leaves a given nucleus
* Ex. Cerebral cortex
Thalamic Divisions
- A thin sheet of myelinated fibers, the internal medullary lamina, subdivides the thalamus into nuclear groups
- has NO posterior
Principle Thalamic Nuclei
- Anterior
–> Anterior nucleus (A) - Medial
–> Dorsomedial nucleus (DM) - Lateral –> contains the most subnuclei
–> Ventral anterior nucleus (VA)
–> Ventrolateral nucleus (VL)
–> Ventroposterolateral nucleus (VPL)
–> Ventroposteromedial nucleus (VPM)
–> cranial nerves go through VPM
–> Pulvinar nucleus (Pul)
–> Lateral geniculate nucleus (LG)
–> vision stimuli
–> Medial geniculate nucleus (MG)
–> auditory stimuli
Other Thalamic Nuclei
Intralaminar nuclei:
* Collection of cells embedded within the internal medullary lamina
* Examples: Centromedian (CM) & parafascicular (PF) nuclei * Projections to the cerebral cortex & basal ganglia
Thalamic reticular nucleus: –> more of a region
* Found between the external medullary lamina (lateral boarder of
thalamus) and the internal capsule
* No projections to the cerebral cortex
* Regulatory GABAergic projections to other thalamic nuclei
Types of Nuclei
Specific/Relay Nuclei
Relay Nuclei Afferents & Efferents
Association Nuclei
Corona Radiata & Internal Capsule
- Corona radiata is a bundle of white fiber tracts than fans out throughout the cerebral cortex –> continue down spinal cord
- Narrows to pass through the internal capsule on way to brainstem and spinal cord
Internal Capsule - REMEMBER!
- A compact bundle of fibers found between the lenticular nucleus (lateral) and the thalamus & head of the caudate nucleus (medial)
- Almost all neural traffic to and from the cerebral cortex passes through the internal capsule –> motor route
Examples: - Thalamocortical & corticothalamic fibers
- Corticospinal, corticobulbar & corticopontine fibers
- external capsule are the ends of the corpus callosum
The Hypothalamus
- Small portion of the diencephalon, ~4 g total
- Important nodal point for pathways concerned with autonomic, endocrine, emotional and somatic functions that are generally designed to maintain our internal environment within a defined range
–> Promotion of homeostasis - However, it is also involved in more complex “drive-related” functions like hunger, rage, sleep & sexual behaviour.
Hypothalamus Anatomy
Longitudinal divisions:
* Anterior
* Tuberal
* Posterior
Medial-lateral divisions:
* Periventricular zone
* Medial zone
* Lateral zone
Hypothalamus Nuclei - REMEMBER!
Periventricular zone (green)
* Suprachiasmatic nucleus (SCN) –> directly above chiasm
* Arcuate nucleus
Medial zone (blue)
* (medial) Preoptic nucleus
* Paraventricular (PVN)
* Supraoptic (SON) –> project to pineal gland
* Dorsomedial (DMN)
* Ventromedial (VMN)
* Posterior (PN)
* Mammillary bodies (MB)
–> mammiliothalamic tract communicates between thalamus and hypothalamus to limbic system
Lateral zone (red)
* Tuberomammillary (TN)
Hypothalamic Afferents & Efferents
Two major input “areas”
* Brainstem & spinal cord
* Limbic system
- Outputs are mostly reciprocal plus widespread cortical projections
Hypothalamic Functions – Pituitary Control Pt.1
- Secretions of the pituitary gland are under the control of two types of neuroendocrine cells
Magnocellular (large) cells (blue):
* Axons from the hypothalamo- hypophyseal tract which descends to the posterior pituitary (neurohypophysis)
Parvocellular (small) cells (red):
* Axons travel to median eminance,
release hormones into portal system * Stimulate/inhibit cells of the anterior
pituitary (adenohypophysis)
* Hypothalamic-pituitary-adrenal axis “HPA”
- neurohypophysis and adenohypophysis determine to stimulate or not to stimulate
Hypothalamic Function –Pituitary Control Pt.2
Magnocellular cells:
* Production and secretion of two hormones: ADH & oxytocin
ADH (Anti-diuretic hormone):
* Aka. Vasopressin
* Stimulation of water uptake in kidneys, regulated by changes in blood osmotic pressure
Oxytocin:
* Uterine contractions & milk
ejection
* Both hormones thought to be involved in learning, anxiety & stress as well
Parvocellular cells
* Release of trophic hormones into the portal circulation to reach the anterior pituitary
* Either stimulate or inhibit endocrine cells
