General neuroanatomy terms and structures Flashcards
Commissure
(joining structure) – in the brain refers to a bundle of nerve fibers traversing the midline (longitudinal fissure) to interconnect the cerebral hemispheres. Examples include Anterior commissure, Posterior commissure, Corpus collosum
Peduncle
(stalk attaching a tissue mass) – a large bundle of fibers serving as major source of input or output to large brain structures. Examples include Cerebral penduncles, Cerebellar penduncles
Fasiculus
slender bundle of fibers; tracts
Funiculus
bundles of fasiculi; columns
Lemniscus
(ribbon or band) usually flat bundle of fibers. Examples include Medial lemniscus, Lateral lemniscus
Decussation
(cross over) – crossing from on side to the other as in an X shape
Central/Peripheral Nervous System
The CNS consists of the brain, spinal cord and retina, while the PNS is the spinal and cranial nerves, ganglia, and nerve roots (which project into the spinal cord).
Somatic and Autonomic Nervous System
Somatic (body) refers to innervation of the body wall (meaning skeletal muscle, skin, mucous membranes), while autonomic refers to innervation of the smooth muscle and glands controlling internal organs (viscera) and blood vessels.
Note the enteric division has its own (intrinsic) sensory and motor reflexes independent of the CNS and controls GI (smooth muscle) motility and secretions. The other two divisions of the ANS provide extrinsic control of the walls of GI tract (not depicted here)
Efferent/Afferent
If your point of reference is within the central nervous system, then Efferent = exit = output (usually motor function), while Afferent = arriving = input (usually sensory function)
Cerebrum/Cerebellum
Cerebrum refers to the hemispheres of the cerebral cortex, while cerebellum is a distinct structure lying on the ventral caudal surface of the cerebral cortex.
Sulcus/Gyrus
used in the context of surface topology (of the brain). Sulcus is the fissure, invagination or valley and gyrus is the hills.
White and Gray Matter
white matter refers to white-colored myelinated axons, while gray matter refers to (non-white) cell bodies of neurons.
Upper/Lower Motor Neuron (Disorder)
“Upper” refers to motor neurons originating in the cerebral cortex and their (axonal) projects to the “lower” motor neurons originating in the brain stem or spinal cord and its projections to the muscle
Direct and indirect pathway
In context of connections between two basal ganglia structures: striatum and the internal globus pallidus (GPi). “Direct” pathway refers to the monosynaptic connection between these structures, while “indirect” pathway refers to the polysynaptic connections (and a number of intervening structures) between them
Foramen
(opening) – such as in bone or interconnecting ventricles
Colliculus
(bump) – a small elevation on a surface. Examples include Inferior colliculli and Superior colliculli
Tectum
(roof) – dorsal part of the midbrain responsible for visual and auditory reflexes
Ganglion
(mass) – a collection of neuronal cell bodies forming a localized nerve center (typically outside the CNS)
CNS divisional nomenclatures
forebrain- equivalent to the prosencephalon in development. contains the telencephalon and the diencephalon
midbrain- mesencephalon in developement
hindbrain- rhombencephalon in development. Contains the cerebellum, medulla, and pons
Frontal
Movement Execution; Primary Motor Cortex
Premotor/Supplementary Motor Area
Frontal Eye Fields – rapid eye movements & directed attention
Mood; Dorsolateral prefrontal cortex, subgenual cortex
Impulse; Orbito(pre)frontal cortex
Language (production/comprehension); Broca’s Area – motor expression of language: semantics, phonetics and verbal understanding
Parietal
Somatosenory Perception; Primary Somatosensory Cortex
Integration of visual and somatospatial information; Visual & Somatosensory Association Areas
Occipital
Visual Perception; Primary Visual Cortex
Integration of visual and somatospatial information; Visual & Somatosensory Association Areas
Temporal
Auditory Perception,
Olfactory Perception; Primary Auditory Cortex (Heschl’s Gyrus)
Primary Olfactory Cortex (Piriform Cortex)
respectively
Memory, Emotion/Motivation ; Harbors the hippocampus, amygdala
Language (Reception); Language Cortex (Wernicke’s area) – language reception: verbal & reading comprehension
Corpus Callosum
Interconnects all positions of the cerebral hemispheres. Rostral portions subserve more rostral cortex etc.
There is a somatotopy along the sagittal plane indicated by subdivisons in the naming. Can be born without one: callosal agenesis. Lesion results in inability of right-handers to name/describe an object in the left hand and inability to retrieve by hand objective palpated by other.
Anterior Commissure
Interconnects temporal lobes, orbitofrontal cortex, particularly amygdala and carries decussating fibers of olfactory tracts
Much smaller than corpus callosum and serves primarily temporal lobe structures. Involved in visual memory tasks as such visual traces are apparently bilateral. Compensates for lesions to splenium of corpus callosum (subserving vision).
Posterior Commissure
interconnects the pretectal nuclei, mediating the consensual pupillary light reflex. Fibers projecting to oculomotor & trochlear nuclei pass through this commissure.
Much smaller than corpus callosum and serves occipital lobe structures. Lesioning results in upward gaze paralysis
Internal Capsule
Is comprised of motor neuron axons from cortex and brainstem (bulbar) traveling to the spinal cord
Pass through the basal ganglia, but do not send collaterals to synapse there. Damage to the anterior portion of the poster limb can result in a pure motor stroke
Cerebral Peduncles
The internal capsule becomes part of the cerebral peduncles
Motor fibers passing through the cerebral peduncles will become the pyramids on their way to the bulbar or spinal cord
Cerebellar Peduncles
Carry input or output fibers to or from cerebellum
Superior peduncle carries output from and the middle and inferior carry input to the cerebellum
Thalamus
Relays information from brainstem to cortex and between cortical regions
Serves as a major brain relay station and has many subdivisions
Superior colliculus
Sensory relay nucleus involved in vision
SC -> LGN -> visual cortex (BA17/18/19)
Note: Lateral Geniculate Nucleus (LGN) and Medial Geniculate Nucleus (MGN) are sometimes referred to as the metathalamus
Inferior colliculus
Sensory relay nucleus involved in hearing
IC ->MGN -> primary auditory cortex (BA41/42)
Note: Lateral Geniculate Nucleus (LGN) and Medial Geniculate Nucleus (MGN) are sometimes referred to as the metathalamus
Hypothalamus
Involved in regulation of thirst, appetite, sex drive and autonomic function and neurocrine function
Role in regulating mood
Pituitary
Releases hormones regulating growth, blood pressure, production of breast milk, sex organ and thyroid gland functions, regulation of water/osmolarity and temperature
Under the control of the hypothalamus and connected to it by the infundibulum (pituitary stalk)
Pineal Gland
Modulation of circadian rhythms: wake/sleep and seasonal cycles
Produces the sleep hormone melatonin. Not enclosed by BBB.
Pituitary gland is encased in bone. The pineal gland is outside the blood-brain-barrier and together with the eye regulates circadian rhythms
Cerebellum
Coordinates and fine tunes voluntary movement, Posture and balance. Motor learning and memory (e.g., stereotyped movements)
Somatopically organized. Has several subdivisons. Lots of motor issues depending upon region damaged: ataxia, falling, past pointing, inability to rapidly supinate and pronate.
Caudate
Modulates movement
Input structure of basal ganglia. Degenerates in Huntington’s disease. Produces some acetylcholine.
Putamen
Modulates movement
Input structure of basal ganglia. Degenerates in Huntington’s disease. Produces some acetylcholine.
Globus pallidus
Modulates movement
Has two portions named interior and exterior. GPi is output structure of basal ganglia. GPe is part of indirect pathway.
Substantia Nigra
black substance
Input to the basal ganglia
Has two portions compacta and reticulata. SNc provides input into the basal ganglia and produces dopamine. This area degenerates in Parkinson’s disease
Subthalamic Nucleus
Modulates movement
Part of the indirect pathway. Lesion results in hemiballism.
Hippocampus
Memory formation especially spatial orientation memory
Located in the temporal lobe and caudal to the amygdala. Lesions impair new memory formation.
Amygdala
Emotion, especially fear – conditioned fear
Has a role in learned memories
Mammillary Bodies
Involved in memory processing, specifically recollection.
Susceptible to thiamine deficiency. Atropy in alcoholics and lesions result in amensia. Receives input from hippocampus via fornix
Cerebellum
Motor learning and memory (e.g., stereotyped movements)
Coordinates and Fine Tunes Movement
Learned stereotypic motor skills like swimming, typing. Vermal atrophy in alcoholics leading to ataxia
Anterior Commissure
Involved in visual memory which requires bilateral connections
Also interconnects amygdali
Pons & medulla
Contains structures involved in control of autonomic functions and some cranial nerves. Relays Sensory Info between Cerebrum & Cerebellum
Harbors structures for arousal/consciousness, sleep, facial expressions, feeding, breathing, blood pressure and heart rhythms
Nucleus basalis of Meynert
Involved in sleep and wakefulness
Produces acetylcholine. Degenerates in Alzheimers.
Septal Nuclei
Involved in sleep and wakefulness
Located in the basal forebrain. Produces acetylcholine. Degenerates in Alzheimers.
Nucleus accumbens
Reward center
Located at the point at which the dorsal and ventral striatum converge
Uncus
Involved in processing olfactory and emotional information
Located at the anterior end of the parahippocampal gyrus. Part of the olfactory cortex (BA34) and seizures here cause unpleasant odors.
Olfactory Bulbs/Tracts
Tracts carry olfactory nerves
Damage to these areas bilaterally result in anosmia (can’t smell)
Dorsal (posterior) Column also known as the medial lemniscal system
carries ascending somatosensory information (touch, joint sensation, two-point discrimination, vibrational sense and motion sense) via the spinal cord to cortex.
Involved in perception of mechanic stimuli and conscious awareness of body position and limb movement. Pathway characterized by faster conducting fibers and limited number of synaptic connections on the way to the cortex. Sensory deficit is on ipsilateral side below the level of the lesion.
Spinothalamic Tract also known as the ventrolateral system
Carries ascending nocioceptive (mechanical, chemical and thermal pain) as well as crude touch and changes in skin temperature information via the spinal cord to cortex.
Pathway characterized by slower conducting fibers and more synaptic connections on the way to the cortex. Sensory deficit is on contralateral side below the level of the lesion.
Cortiospinal Tract also known as the pyramidal tracts
Carries descending motor information for the body from the cortex to the spinal cord.
Pathway comprised of pyramidal cell axons that become the (anterior portion of posterior limb of) internal capsule, then the cerebral peduncles, then pyramids. Motor deficit is on the contralateral side for lesions rostral to the decussation, e.g., at level of cerebral peduncles and above.
Corticobulbar tract is similar but subserves the face and terminates in brainstem nuclei
Gate’s “Rule of Four” for vascular brainstem syndromes
- Four ‘midline’ structures begin with the letter M: Motor (corticospinal) Tract (M-CST), Medial Lemniscus (ML), Medial Longitudinal Fasciculus (MLF), Motor (Cranial) Nucleus and Nerve (M-CN) [CN3, 4, 6 or 12].
- Four (lateral) ‘side’ structures begin with the letter S: Spinocerebellular Tract (SCT), Spinothalamic Tract (STT), Sensory 5th (Cranial) nucleus (S-CN5), Sympathetic Tract (Sym).
- There are four cranial nerves in the medulla [CN9-12], four in the pons [CN5-8] and four above the pons (two in the midbrain [CN3-4]).
- Ignoring CN1 and 2, the four CN motor nuclei along the midline are those that divide equally into 12: 3, 4, 6 and 12. Thus CN5, 7, 9 and 11 are in the lateral brainstem).
Schetz’s simplified “Rule of Three” for vascular brainstem syndromes
- The ‘midline’ structures begin with the letter M: Motor (corticospinal) Tract (M-CST), Medial Lemniscus (ML), Motor (Cranial) Nucleus and Nerve (M-CN) [CN3, 6 or 12].
- Three (lateral) ‘side’ structures begin with the letter S: Spinocerebellular Tract (SCT), Spinothalamic Tract (STT), Sensory 5th (Cranial) nucleus (S-CN5).
- Starting with three double the number, the three most important CN motor nuclei along the midline are 3, 6 and 12. Starting with five add two, CN5, 7, 9 and 11 are lateral.
