anats Flashcards
Primary Somatosensory cortex
POST CENTRAL GYRUS
Sensory homunculus
brodmanns areas 1,2,3,
Secondary somatosensory cortex
Adjacent to head region of primary somatosensory cortex
Extends posteriorly along parietal cortex buried in lateral fissure
Somatosensory association cortex
Located posterior to primary somatosensory cortex in superior part of parietal lobe
brodmann’s area 5
Thalamus
either of two masses of grey matter lying between the cerebral hemispheres on either side of the third ventricle, relaying sensory information and acting as a centre for pain perception.
What is the pathway for fine touch and conscious proprioception
Dorsal Column-Medial Lemniscal Pathway, DCML
describe the dorsal column medial lemniscal pathway
First order neurone ascends the spinal cord via the cuneate fasciuclus ( upper limb) or gracile fascicles( lower limb) before synapsing with the gracile or cuneate nucleus in the medulla oblongata
Second order neurone decussates and ascends via the medial leminscus to the thalamus
3rd order neurone ascends via the internal capsule to synapse in the primary somatosensory cortex
How many neurones in the dorsal medial lemniscal pathway
3
WHERE do fibres of the dorsal columns pathway decussate
MEDULLA OBLONGATA
WHAT IS THE PATHWAY for pain sensation
Spinothalamic tract
Pathway of the spinothalamic tract
1st order neurone ascend or descends 1-2 spinal levels through lissauers tract before synapsing in the substantial gelatinous, at the tip of the dorsal horn
2nd order neurones decussate and ascend to the thalamus via either the anterior( crude touch) or lateral ( pain and temperature) spinothalamic tract
3rd order neurone ascends through internal capsule to primary somatosensory cortex
anterior vs lateral of spinothalamic tract
anterior = crude touch lateral = pain and temp
Difference in place of decussation in spinothalamic vs DCML
DCML = medulla oblongata Spinothalamic = level of the spine cord
Central sulcus
Separates precentral motor cortex (frontal lobe) and postcentral sensory cortex (parietal lobe)
Primary motor cortex
(Brodmann’s area 4): precentral gyrus and area immediately in front of it
Premotor cortex
(area 6): immediately in front of motor cortex and has close connections with it
Supplementary motor area
lies on medial surface of hemisphere above cingulate sulcus
Areas of the motor cortex
Upper/medial part: lower limb and perineum
Lower/lateral part: trunk, of upper limb, neck and head
Paracentral lobule: cortical control of micturition and defecation
Frontal eye field: voluntary eye movement (lesions cause paralysis of voluntary contralateral gaze)
PRE CENTRAL gyrus
surface of the posterior frontal lobe of the brain.
primary motor cortex
Corticospinal tract
Voluntary control of skilled movement
2 neurone pathway
Pathway of corticospinal tract `
first order neurone descends from the primary motor cortex via the internal capsule
Enters the brainstem through the crus cerebri
75-90% of fibres decussate at the pyramids in the medulla oblongata; those that decussate descend down the lateral corticospinal tract before exiting the spinal cord via the ventral root
Those that don’t decussate (10-15%) descend ipsilaterally down the ventral corticospinal tract before decussating near their termination site
Rubrocospinal tract
starts in red nucelus( midbrain ) controlling limb flexors
Tectospinal tract
originates from contralateral superior colliculi( midbrain)- reflex response to visual stimuli
Vestibulospinal tract
lateral and medial, originates from ipsilateral vestibular nuceli. Lateral = mediate excitation of proximal limb extensors, medial = head and neck posture
Reticulospinal tract
originates in pons and medulla, involved in reflex, tone and vital functions
Corticonucelear fibers ( additional to corticospinal tract,
terminate (mainly bilaterally) in motor nuclei of cranial nerves of pons and medulla or within the reticular formation of brainstem. Often referred to as corticobulbar tract and relates to chewing, talking and swallowing.
Corticopontine fibers
terminate ipsilaterally in pontine nuclei then travel to cerebellum via cerebellar peduncle. Carries ‘copies’ of the executive motor plan from cortex to cerebellum
Basal nuclei
• Functionally and anatomically-related group of forebrain nuclei concerned with modulation of movement and behaviour, including muscle tone and posture
3 integrated nuclei of the basal ganglia
caudate nucleus, putamen and globus pallidus. Caudate and putamen together often referred to as ‘corpus striatum’.
Origin of dopamine fibres to basal nuclei
substantia nigra (midbrain)
Basal nuclei function
Reviceves info from the cortex, regulars, a nd feedbacks via thalamus
Caudate nucleus
Comma-shaped mass of grey matter, separated from lentiform nucleus by internal capsule lying in floor of lateral ventricle anteriorly•
Lentiform nucleus
- Globus pallidus: paler medial part
* Putamen: darker lateral part
Cerebellum
- Comprises two ovoid hemispheres joined in midline by narrow median vermis
- Precision timing of movements and motor coordination is controlled by the cerebellum.
- Receives a copy of executive motor plan (from motor cortex) and regulates it, providing feedback and necessary adjustment
- Anterior and posterior lobe
Outer vs inner of cerebellum
o Outer cortex: highly-folded layer of grey matter (‘folia’)
o Inner core: white matter (‘tree of life’) surrounding deep cerebellar nuclei§
Outer vs inner of cerebellum
o Outer cortex: highly-folded layer of grey matter (‘folia’)
o Inner core: white matter (‘tree of life’) surrounding deep cerebellar nuclei
parts of the cerebellum
- Median vermis and two hemispheres
- Anterior and posterior lobes
- Flocculonodular lobe (primarily concerned with vestibular information)
- Tonsils (prominent irregularly convex rounded swelling of cortex on inferior surface)
Anatomical pathways for vision
Eye – retina – optic nerve- some ipsolaterally and some contralterally, happens at optic chiasm, optic tract, arrises at lateral geniculate body( part of thalams), optic radiation( some fibers travel in temporal lobe and some parietal) to reach the visual cortex
Optic nerve
– originates in the retina (optic nerve comprises the axons of retinal ganglion cells)
Oculomotor nerve
roots emerge from medial surface of each crus (of midbrain tegmentum visible on ventral brain) into the interpeduncular fossa passing forwards to cavernous sinus
Retina to optic chiasm
- Point-to-point projection from retina to lateral geniculate nucleus (thalamus) via optic nerve
- Each optic nerve contains 1 million axons, surrounded by extensions of meninges
- At optic chiasm nerve fibres partially cross: fibres from nasal half of retina decussate and join uncrossed fibres from the temporal or lateral half of retina
Thalamus lateral geniculate
- Major nucleus of visual pathway
- Optic tract divides into lateral root containing fibres which run to lateral geniculate and medial root containing fibres to superior colliculus
- New fibres arise from lateral geniculate and pass through the internal capsule to reach visual cortex
Visual cortex
- Primary visual cortex (area 17) occupies posterior part of calcarine sulcus of occipital lobe
- Cortex of right hemisphere receives information from left half of both visual fields and vice versa, because of partial decussation of fibres of optic tract at chiasm
- Retinotopic mapping of cortex means central (i.e. foveal) vision is represented posteriorly, peripheral vision more anteriorly
Visual cortex
- Primary visual cortex (area 17) occupies posterior part of calcarine sulcus of occipital lobe
- Cortex of right hemisphere receives information from left half of both visual fields and vice versa, because of partial decussation of fibres of optic tract at chiasm
- Retinotopic mapping of cortex means central (i.e. foveal) vision is represented posteriorly, peripheral vision more anteriorly
Perception of sound - inner ear to thalamus
- Auditory pathway of CNVIII synapse in dorsal & ventral cochlear nuclei (of medulla)
- Pathway continues (some fibres via superior olivary nuclei for binaural integration) in lateral lemniscus to inferior colliculus (tectum)
- Inferior colliculus connected to medial geniculate (of thalamus) by prominent bundle of fibres known as ‘brachium of inferior colliculus’
- From medial geniculate body information passes in auditory radiation via internal capsule to auditory cortex of temporal lobe
Auditory cortex - hearing sound
- Primary auditory cortex (3-4sq. cm) (approximately area 41) occupies part of floor of lateral fissure opposite lower end of post-central sulcus
- Surrounding the primary auditory cortex are auditory association cortical areas
- NB Reflex turning of the head in response to salient or loud auditory stimuli: tectospinal tract receives indirect input from cells of inferior colliculus to cervical cord
Wernickes area
o Part of temporal lobe surrounding auditory cortex and extends upwards and backwards round end of lateral sulcus into lower parts of parietal lobe
o Primarily concerned with perception and understanding of speech (language area)
Brocas area
o Located inferior part of frontal lobe in front of pre-central gyrus
o Primarily concerned with production of words (motor speech area)
Superior speech cortex
o corresponds to supplementary motor area
o Damage in this area is less devastating in its consequences for speech
White matter tracts
White matter modulates the distribution of action potentials, acting as a relay and coordinating communication between different brain regions
3 categories of fibre in the brain
o Association (connect cortical areas within same hemisphere) o Commissural (connect left and right hemispheres) o Projection (connect cortical and subcortical areas)
Association fibers
• Run entirely within one hemisphere.
3 types of association fibres
o superior longitudinal fasciculus: located in core of hemisphere; interconnects frontal, parietal and occipital lobes
o cingulum: an example of a long association fibre which interconnects distant regions of cortex; located internal to cingulate gyrus and continues into parahippocampal gyrus
o inferior longitudinal fasciculus: interconnects temporal-occipital lobes
Commissural fibers
Integrate separate representations of the two halves of body e.g. the visual field and the auditory surround and integrate areas of cortex which have functions specialised to one hemisphere.
Corpus callosum - commisurai fibers
o Largest band of commissural fibres by far: seen on medial surface of a half brain, joins hemispheres
o Parts: body, splenium (posteriorly), genu (anteriorly), rostrum (arching inferiorly)
o Not as long as hemisphere, therefore fibres must curve forwards into frontal lobe and backwards into parietal and occipital lobes (observed on horizontal section)
o Horizontal fibres form roof of lateral ventricle
Other commissures
Anterior
Posterior
Hippocampal
Anterior commisure
Thick bundle of white matter crossing midline horizontally (connects two temporal lobes)
Posterior commisure
Small bundle of fibres crossing midline and connecting corresponding regions of brain, positioned at junction of midbrain and diencephalon. Contains fibres connecting superior colliculi and pretectal nuclei; some of its fibres are important for vertical movements of eyes & bilateral pupillary light reflex
Hippocampal commisure
Formed by fibres that originate in hippocampal formations and cross midline
Projection fibers - where are they found
- Internal capsule
- Large compact bundles of projection fibres of hemispheres
- Continuous with corona radiata above (corona radiata- ‘fan-shaped’ white matter, internal capsule – ‘handle of the fan’)
- Anatomically associated with basal nuclei
- Gross arrangement of fibres maps to the appropriate region of the cortex
Limbic system
- Involves cortical and subcortical structures and their interactions
- Functional loop involved with learning, memory and emotion
- Also regulates basal nuclei, thereby linking emotions with behaviour
Connections of the limbic system
From hippocampus, fornix passes around lateral ventricle to mammillary body and ant. thalamic nuclei; as ant. nuclei project to cingulate cortex, this completes a circle: ‘Circuit of Papez’
What is the limbic system affected by - diseases
Affected in many neuropsychiatric diseases, including mood disorders, schizophrenia, Alzheimer’s disease and some forms of epilepsy; also thought to have a role in “reward” pathway.
4 parts of the cortex
prefrontal
motor areas
sensory areas
associated areas
Associated areas
visual
auditory
prefrontal area
decision making
social behaviour
personality
Features of the limbic system
- Hippocampus and fornix
- Cingulate gyrus
- Hypothalamus (including mammillary bodies)
- Amygdala
middle area , communicates with prefrontal area
Hippocampal fibers
ass laterally into the fimbria, a flattened, longitudinal bundle of white matter which passes around curve of lateral ventricle to become the fornix (hippocampal axon bundle)
• Bilateral structure, interlocking c shaped
Fornix
Bundles of white matter fuse anteriorly in midline and turn vertically down to reach the mammillary bodies (i.e. fornix connects hippocampus to mammillary bodies)
Hippocampus
C shape
Short term and long term memory
Alzeihmers associated with hippocampus
Cingulate gyrus
Cingulate gyrus lies immediately dorsal and parallel to corpus callosum
Uncus: hook-shaped region of cortex at anterior end of cingulate gyrus; provides a surface marking for underlying amygdala and parahippocampal gyrus
Hypothalamus
Ventral division of diencephalon, comprises pairs of nuclei either side of 3rd ventricle
Extends from optic chiasm, pituitary stalk to mammillary bodies
Ancient centre for homeostasis and control of autonomic nervous and neuroendocrine systems
Amygdala
Found anterior and slightly superior to the anterior parts of the hippocampus
Receives a major, direct input from olfactory bulb
Roles in fear and stress
Epithalamus
Small region above thalamus containing pineal body (midline gland)
Pineal body
- Dorsal outgrowth of diencephalon
- Endocrine gland synthesising hormones including melatonin,
- Regulates circadian (24h) rhythm of bodily functions, and sleep wake cycles
- Inhibitory effect on gonads; regulates puberty onset
- Commonly calcifies with age (becoming visible on radiographs)
