anatomy C13: part 2
spinocerebellar tract (ventral and dorsal)
ascending pathway stretch receptors tell proprioception, travels ipsilateral to cerebellum
when does the spinothalamic tract (medial and lateral) cross over?
right away as soon as it enters the spinal cord (pain and temp)
describe the makeup of the spinal cord + below
runs from the foramen magnum to the L1/L2 - inferior end: conus medullaris - filum terminale: long filament of connective tissue that connects the inferior SC to coccyx- helps to stabilize spinal cord in rotation/flexion of back - cervical and lumbar enlargements present where the nerves for the upper and lower limbs arise - below SC is cauda equina: a collection of nerve roots that continue down through the vertebral column after the SC ends (ex: sacral nerves)
spinal cord location + protection
runs through the vertebral canal, from the foramen magnum to the L1/L2 protected by bone, meninges and CSF
short vs long term memory
short term memory: we excite a certain pathway and that memory persists as long as those neurons remain active long term: result of physically changing what neurons synapse on other neurons
describe the somatic/visceral division of gray matter in the spinal cord
somatic motor = most ventral visceral motor: lateral extension of gray horn (only present in some places) somatic sensory: most posterior visceral sensory: ant to SM think: sensory enters in posterior, synapses with interneurons, synapse with motor neurons in anterior
what do visceral centers of the reticular formation include? (4)
- cardiac center (HR) - vasomotor center (blood vessels) - medullary respiratory center - centers for hiccupping, sneezing, swallowing and coughing
diencephalon
- composed of 3 paired structures: thalamus, hypothalamus and epithalamus - borders/surrounds the 3rd ventricle - primarily composed of gray matter (nuclei!)
2 characteristics of ascending pathways
- conduct general somatic sensory impulses to the CNS - chains of neurons (not just 1)
describe the division of the cerebellum
- consists of 2 cerebellar hemispheres, subdivided into anterior, posterior and flocculonodular (tiny) - surface folded into ridges called folia (same as gyri), which are separated by fissures (same as sulci) - inside, there are 3 regions: cortex (gray matter), internal white matter, and deep cerebellar nuclei (deep gray matter)
3 characteristics of most motor pathways
- decussate (cross over) at some point along their course - consist of a chain of 2-3 neurons - exhibit somatotopy (tracts are arranged according to the body region they supply, like the homunculus in the cerebral cortex)
descending (motor) pathways- describe + name groups
- deliver motor instructions from the brain to SC - divided into 2 groups: pyramidal (corticospinal) tracts (go to skeletal muscle) and other motor pathways: tectospinal tracts, vestibulospinal tract, rubrospinal tract, reticulospinal tract *spinal at end = motor pathway
epithalamus
- forms part of "roof" of third ventricle - consists of a tiny group of nuclei - includes pineal gland, which is under the influence of the hypothalamus and secretes the hormone melatonin
midbrain (location/structures)
- lies between diencephalon and pons, forms kinda a V shape - contains the central cavity- the cerebral aqueduct travels through the midbrain and is surrounded by periaqueductal gray matter - cerebral peduncles containing pyramidal axons (part of corticospinal tracts) are located on ventral surface of midbrain - also contains superior cerebellar peduncles which connect the midbrain to the cerebellum
hypothalamus
- lies between optic chiasm and mammillary bodies - pituitary gland projects inferiorly from it (so hypothalamus has control over it and some hormones) - contains ~12 nuclei (see pic sl 45) **main visceral control center of the body
pons (location, nerves, contains)
- located between the midbrain and medulla oblongata - contains nuclei of cranial nerves 5-7 - contains middle cerebellar peduncles (cell bodies originating in pontine nuclei)
cerebellum ("little brain") location + 2 main functions
- located dorsal to pons and medulla 2 functions: 1. smoothes and coordinates body movements 2. helps maintain equilibrium (balance) without the cerebellum we would have jerky movements. When we initially plan/start a movement, it's not going to the right place, and the cerebellum corrects that)
thalamus
- makes up 80% of diencephalon - contains ~12 major nuclei, each with diff functions. These nuclei act as relay stations for incoming sensory messages - sends axons to regions of the cerebral cortex *gateway to cerebral cortex- almost all sensory messages come in through the thalamus - nuclei organize and amplify or turn down signals - there are LOTS of synapses in the thalamus
medulla oblongata
- most caudal level of brain stem - continuous with spinal cord (distinction at foramen magnum) - choroid plexus lies in roof of 4th ventricle - pyramids (clumps of white matter) of the medulla lie on its ventral surface. they have decussation (crossing over of motor tracts) - cranial nerves 8-12 attach to medulla - inferior cerebellar peduncle
describe the basal ganglia
- nuclei in the gray matter deep in brain - cooperate with cerebral cortex in controlling movements - receive input from many cortical areas - start, stop and regulate intensity of voluntary movements - estimate passage of time
reticular formation (location, connections, system)
- runs through the central core of the medulla, pons and midbrain - has widespread connections ideal for arousal of the brain as a whole) - has reticular activating system (RAS), which maintains consciousness and alertness and functions in sleep and arousal from sleep
describe the gray matter of the spinal cord and spinal roots
- shaped like the letter H - gray commissure: horizontal bar of H- contains central canal and connects 2 sides of CNS - anterior horns contain cell bodies of motor neurons - posterior horns consist of interneuron cell bodies *gray matter is divided according to somatic and visceral regions
what are the 3 types of tracts in the cerebral white matter? Describe them
1. Commissures - composed of commissural fibers - allow communication between cerebral hemispheres (connect left and right)- basically a bundle of axons between hemispheres ex: corpus callosum (largest) 2. Association tracts/ fibers - connect diff parts of the same hemisphere 3. Projection tracts/ fibers - run vertically - to and from lower regions to the cerebral cortex
describe 8 functions of the hypothalamus
1. control of autonomic nervous system (ex: HR, BP) 2. control of emotion responses (bc it's part of limbic system, which is involved in memory and emotion) 3. regulates body temp (sweating/shivering, receptors constantly detect body temp) 4. regulates hunger/thirst (detect concentrations in blood) 5. control behavior (ex: motivation for feeding, sex) 6. regulation of sleep-wake cycles (optic nerve input goes to the hypothalamus, which goes to epithalamus and the light vs dark controls cycles) 7. control of endocrine system (pituitary gland releases hormones) 8. formation of memory SEE HAM BB
4 main ascending pathways + function
1. dorsal (white) column pathway- discriminative touch 2. spinothalamic pathway- pain and temp 3-4. posterior and anterior spinocerebellar pathway- subconscious proprioception (ability to detect where we are in space- note connection to cerebellum)
for what 3 things does the cerebellum receive info?
1. on equilibrium 2. on current movements of neck, limbs and trunk 3. plans of desired movement from cerebral cortex (the cerebellum compares the plan to the actual movement and makes corrections)
describe the composition of projection tracts
1: internal capsule- projection fibers form a compact bundle that passes between the thalamus and basal nuclei 2. corona radiata (radiating crown)- superior to the internal capsule, its fibers run to and from the cerebral cortex/spread out to the outer cerebral cortex to diff areas
composition of white matter of spinal cord
3 types of fibers: ascending (sensory info), descending (motor innervation), commissural (crossing L>R) composed of both myelinated AND unmyelinated axons
reticular activating system (RAS)
A part of the reticular formation that maintains consciousness and alertness, and functions in sleep and arousal from sleep
filum terminale
a long filament of CT that connects the SC to the coccyx and stabilizes the spinal cord in rotation and flexion of back
which part of the brain helps to estimate the passage of time?
basal ganglia
what is the gray commissure?
bridge of gray matter in the spinal cord (middle of the H) that connects the left and right masses of gray matter (connects the 2 sides of the CNS) Encloses central canal
the pyramids of the medulla oblongata are the same axons as the _________ _____________
cerebral peduncles
what 2 peduncles are located on the midbrain?
cerebral peduncles (ventral) and superior cerebellar peduncles
what is the largest nuclei projecting off the posterior midbrain? What are its 4 parts?
corpora quadrigemina left and right superior colliculi: nuclei that act in visual reflexes (ex: unconscious tracking of objects) left and right inferior colliculi: nuclei that act in reflexive response to sound
the cerebral peduncles of the midbrain contain many axons that are part of the ______________ __________
corticospinal tract
what 2 things anchor the spinal cord in place?
denticulate ligaments (anchor SC to vertebrae) and filum terminale (anchors SC to coccyx)
the limbic system is the _____________ brain. Describe
emotional it contains the cingulate gyrus, which allows us to shift between thoughts and interprets pain as unpleasant - also encodes, consolidates and retrieves memories (consolidate = group things together) **memory and emotion
the spinal cord is __________ and contains ________ in the central canal
hollow; CSF
what is the main visceral control center of the body?
hypothalamus
which part of the brain involves formation of memory?
hypothalamus (bc it's part of the limbic system)
where in the brain is the pineal gland? What is it influenced by? What does it do?
in the epithalamus, influenced by the hypothalamus (which receives info from optic nerve about light/dark) secretes the hormone melatonin
conus medullaris
inferior end of spinal cord- cone shaped
fibers running to and from the cerebellum are ______________
ipsilateral (they run to and from the SAME side of the body- don't cross over like most pathways)
what is the periaqueductal gray matter? Which 2 related functions is it involved in?
it surrounds the cerebral aqueduct in the midbrain 2 functions: 1. fright and flight reaction (sympathetic response) 2. mediates response to visceral pain (ex: not wanting to move, cold sweat) part of reticular formation?
name the 2 functional brain systems we learned
limbic system (spread widely in forebrain, medial aspect of hemispheres) reticular formation (spans brain stem) both are networks of neurons functioning together (bc systems)
limbic system (location, composition, links)
location: spread widely in forebrain. medial aspect of cerebral hemispheres, and also within diencephalon composed of: septal nuclei, cingulate gyrus, hippocampal formation, and part of the amygdala linked together by the fornix and other tracts (bunch of axons!) (the fornix is the inferior and medial aspect of the lateral ventricle)
where does CSF get from the ventricles/central canal to the subarachnoid space?
median and lateral apertures in the inferior brain
where do most axons cross over?
medulla
what is the limbic system involved in?
memory and emotion
what is the brainstem composed of? Relative locations?
midbrain, pons, medulla oblongata cranial, middle, caudal
what does the core of the medulla contain?
much of the reticular formation (its nuclei influence autonomic functions)
dorsal white column + sequence
one of the ascending white matter tracts of the spinal cord, makes up entire dorsal aspect of the spinal cord contains many axons carrying info on TOUCH sensory info enters and synapses in dorsal SC > cross over at medulla > through pons and midbrain > synapse in thalamus > postsynaptic neuron goes to postcentral gyrus in cortex (lower body = media gyrus, upper + lateral)
what is the largest nucleus of the reticular formation?
red nucleus (in white matter of midbrain) reticular formation is involved in consciousness/alertness
lateral corticospinal tract + sequence
one of the descending white matter tracts of the spinal cord neurons (cell bodies) in precentral gyrus > through corona radiata into internal capsule > bulge of axons called peduncles on midbrain > pyramids on medulla (+ cross over here) > continue down SC in lateral corticospinal tract. Following this, the axon will synapse with a motor neuron in the anterior gray horn to produce skeletal muscle movement
all pathways are __________
paired- one on each side of the body (ex: there is both a left and right lateral corticospinal tract)
cingulate gyrus
part of the limbic system- allows us to shift between thoughts and interprets pain as unpleasant (helps us remember systems that caused pain in the past and avoid them in the future)
what does the cerebral aqueduct pass through and what surrounds it?
passes through the midbrain and is surrounded by periaqueductal gray matter
cervical and lumbar enlargements
places where the spinal cord is bigger than others- located where the nerves for upper and lower limbs arise (bc we have extra neurons at this areas- they don't only supply torso like in thoracic but also appendages)
where does the trigeminal nerve originate?
pons
the axons that bulge to make the middle cerebellar peduncle have their cell bodies in the __________ ____________
pontine nuclei (in the pons of the brainstem)
what are the 2 deep grooves that run the length of the spinal cord
posterior median sulcus and anterior median fissure
the precentral gyrus is functionally called the ________________
primary motor cortex
which tracts go to skeletal muscle?
pyramidal (corticospinal) tracts
the cerebral peduncles are bulges created by the axons of _________________ cells and are located ________________________
pyramidal (from the motor cortex); on the ventral surface of the midbrain (part of brainstem)
damage in which part of the brain would cause parkinson's disease?
substantia nigra of midbrain (bc it has control over basal ganglai
which part of the brain has nuclei that act to organize and amplify/tone down signals?
thalamus
what is considered the "gateway" to the cerebral cortex? Why? What important role does it play?
thalamus, because virtually all sensory info synapses in it before going to the cerebral cortex an important role is organizing and amplifying/toning down signals- there is so much sensory info coming in so the thalamus helps decide what's important and cut out less important things
corpus callosum
the largest commissure (tract between left and right hemisphere) superior to the lateral ventricle
cerebellar peduncles
thick tracts connecting the cerebellum to the 3 parts of the brainstem (superior, middle and inferior cerebellar peduncles) ipsilateral (don't cross over)
what connects the cerebellum to the brain stem?
thick tracts: superior, middle and inferior cerebellar peduncles (connected by axons to the 3 parts of the brainstem)
cerebral peduncles
two bulging structures in the ventral midbrain that contain descending pyramidal (corticospinal) motor tracts (bundles of axons) **the cerebral peduncles are the bulges created by the tracts from the pyramidal cells in the primary motor cortex (and this pathway is part of the corticospinal tract). They are located on the ventral midbrain.
what 2 things are imbedded in the white matter of the midbrain? Describe them
two pigmented nuclei: 1. substantia nigra: neuronal cell bodies contain melanin (functionally linked to basal ganglia) 2. red nucleus: lies deep in substantia nigra- it's the largest nucleus of the reticular formation. has good blood supply
what would happen if we didn't have a reticular activating system?
we would go into a coma bc it helps with arousal and alertness
do axons go through the pons?
yes, they have to