Theme 2: Sensory Inputs and Motor Outputs Flashcards
What areas of the CNS correspond to each level of the motor control of hierarchy?
High/Strategy- neocortex and basal ganglia. Middle/Tactics- Motor cortex and cerebellum. Low/Execution- Brainstem and spinal cord.
What are the 2 lateral descending pathways?
Rubrospinal and corticospinal pathways, voluntary movements.
What are the 3 ventromedial descending pathways? What do they collectively do?
Reticulospinal, Tectospinal, Vestibulospinal pathways. They use sensory information about balance, body position, and the visual environment to reflexively maintain balance and posture. Involuntary movements.
What is another name for the corticospinal tract and what does it do?
Pyramidal tract, only tract to synapse directly with motor neurons, derived from layer V. Motor cortex to Internal capsule to cerebral peduncle to medullary pyramids, 90% decesates, to anterior/lateral cs tract.
Describe the path of the rubrospinal tract and its function.
Red nucleus (ruber) to spine. Unclear involvement in humans, innervates flexor muscles in upper limbs.
Describe the vestibulospinal tract
Vestibular nuclei of medulla (relays sensory info from vestibular labyrinth in inner ear). Projects down spinal cord activates spinal circuits controlling neck and back for stability while body moves. Extends down to lumbar promoting stability.
Describe the tectospinal tract
From tectum (superiour and inferior colluculi) receives info from eyes/ear, down to spine. Head and neck control.
Describe the reticulospinal tract.
From reticular formation to spine. activates extensor muscles in arms/legs
What is seen in patients with damage to motor cortex and corticospinal tract?
Increased spasticity, brisk reflexes, extensor plantar/babinski reflex, clonus, some preserved upper limb flexion and lower limb extension. Good posture maintained.
Describe the corticobulbar pathway
Primary motor cortex to cranial nerves.
How is the motor humunculus useful in clinical assesment?
It helps localise injury to the brain
What does the premotor area do?
Fine Motor Control of Visually Guided Movements
What are the subtypes of apraxia?
Parietal: unable to report the sequence. Ideomotor: Unble to use a tool.
What is apraxia?
Inability to perform fine motor tasks caused by damage to the posterior parietal area.
What is the condition in which we see sustained muscle contractions usually producing twisting and repetitive motions or abnormal postures and positions?
Dystonia (task-specific if only with certain actions)
What is seen in damage of the anterior cingulate gyrus?
Smiling
What are 4 roles of the cerebellum?
Maintenance of balance and posture, coordinate voluntary movements (the great comparator– middle/tactics motor control hierarchy), motor learning, cognitive functions
Describe the anatomy of the cerebellum.
3 Lobes: Anterior, Posterior, Flocculonodular. Communicate with brainstem via 3 (superior, middle, inferior) cerebellar peduncles. Divided into two hemispheres with a vermis in the middle
What are the 3 main inputs to the cerebellum?
Vestibulocerebellum to flocculonnodular lobe, Spinocerebellum to vermis, Cerebrocerebellum (corticocerebellum) to hemispheres
What are the 4 cerebellar outputs and what areas do they communicate from?
Vermis to fastigial, paravermis to interposed, hemisphere to dentate, flocculonodular to vestibular nuclei
Describe the spinocerebellar loop and its function.
Control of muscle tone/posture. Spinocerebellar tracts to vermis to fastigial nuclei to descending tracts (also interact with reticular formation)
Describe the corticocerebellar loop.
corticopontine tract to pons to hemisphers to dentate nuclei to thalamus back to cortex.
Describe the vestibulocerebellar loop and its function.
Vestibular nerve to flocculonodular lobe to vestibular nuclei then either extraocular muscle nuclei to control eye movements or vestibulospinal tract to control neck movements
Which inputs/outputs go through each cerebellar peduncle?
All outputs- superior. corticopontine- middle. spinocerebellar and vestibulocerebellar- inferior.
Name 5 conditions caused by a lesion to the cerebrocerebellar pathway.
Dysmetria - movement is not stopped in time.
Dysynergia- decomposition of complex movements.
Dysdiadochokinesia- reduced ability to perform rapidly alternating movements
Intentional Tremor- Tremor when trying to perform a goal oriented movement
Dysarthria- difficulty coordinating muscles of respiration, larynx, etc/unevem speech strength and velocity.
Name a conditions arising from a lesion to the vestibulocerebellar pathway.
Nystagmus- involuntary, rhythmical, repeated oscillations of one or both eyes, in any or all directions of view. Movement of the eyes reduces the ability to focus on one point.
Describe symptoms arising from a lesion to the spinocerebellar pathway.
Gait Ataxia (unsteadiness of walking) and disturbance of limb tone (hypotonia) and posture
What are the 2 kinds of fibres that feed into the cerebellum and where do they come from?
Mossy fibres from spinal cord and brainstem (many fibres converge on one purkinje cell) and climbing fibres from inferior olivary nucleus (one climbing fibre diverges on many purkinje cells).
What is a feedforward loop and when is it used?
When you don’t have time to try something and receive feedback (mossy fibres with simple spikes), you use information from the last time you tried that thing (climbing fibres with complex spikes).
What are some genetic causes of cerebellar dysfunction?
Frederich’s Ataxia, spinocerebellar degeneration, ataxia-telengiectasia, von hippel lindau
What are acquired causes of cerbellar dysfunction?
alcohol, anti-convulsants (sodium valproate, phenytoin), metabolic (b12/thyroid/coeliac), degenerative (familia, MSA), immune (paraneoplastic), vascular (basilar artery problems)
Where do the sympathetic and parasympathetic nervous systems arise from?
Symp: T1 to L2, Para: Brainstem and S2 to S4
What is a disynaptic pathway?
At least 2 neurons. Myelinated pre-ganglionic from cranial nerve and unmyelinated postganglionic to effector organ
What is the main neurotransmitter within autonomic ganglia?
Acetylcholine
What is the main neurotransmitter within postganglionic sympathetic neurons?
Noradrenaline
What is the main neurotransmitter within the adrenal medulla?
Acetylcholine, causes release of adrenaline/noradrenaline (direct activation of sympathetic division)
Name a drug that reduces parasympathetic activity and describe it MOA
Atropine competes w acetylcholine, binding to muscarinic receptors on the effector organ. Also treats bradycardia, dilate pupils, and reduce glandular secretions.
How do preganglionic fibres enter the sympathetic trunk?
White rami communicans (myelinated)- thoraci and lumbar region only
What do preganglionic fibres do on entering the sympathetic trunk?
Synapse in ganglion or pass through ganglion to splanchnic nerves to synapse in prevertebral ganglia
Where do postganglionic fibres from the sympathetic trunk go?
To the periphery via grey matter rami OR to the viscera via medial plexus
What ganglia synapse on the cervical sympathetic trunk and where do they exit?
Superior/middle/inferior cervical ganglia fuse at stellate ganglion @ T1, leave via grey rami communicas to spinal nerves/upper limb, or piggy back up carotid artery to head or down to heart
What is a disruption to the sympathetic supply of the head?
Horner’s Syndrome, symptoms = miosis (constriction of pupil), ptosis (droopy eyelid), anhydrosis (no sweat)
What ganglia synapse on the thoracic sympathetic trunk and where do they exit?
12 ganglia. Preganglionic exit via splanchnic nerves to abdomen. Postganglionic exit via grey rami communicans to spinal nerves, medial branches to heart/lungs
What do the postganglionic thoracic sympathetic fibres form and what does this formation supply?
Prevertebral ganglia: Celiac ganglion (upper gut), superior mesenteric ganglion (mid-gut), aorticorenal ganglion (kidney)
What ganglia synapse on the thoracic sympathetic trunk and where do they exit?
4 lumbar ganglia. Postganglionic fibres exit via grey rami communicans to spinal nerves. Preganglionic fibres exit via lumbar splanchic nerves to pelvis
What ganglia synapse on the sacral sympathetic trunk and where do they exit?
4 sacral sympathetic trunk ganglia. Postganglionic fibres exit via grey rami communicans to spinal nerves (lower limb). Sacral splanchnic nerves to pelvic organs
Which cranial nerves provide parasympathetic supply?
CNIII - Oculomotor (Edinger-Westphal Nucleus), CN VII Facial (Superior Salivatory Nucleus), CN IX Glossopharyngeal (Inferior salivatory nucleus), CN X Vagus (Nucleus ambiguous, dorsal motor nucleus)
What plexi does the enteric nervous system form?
Auerbach’s (muscle contraction), Meissner’s (glandular secretions). “Little brain” - Truly autonomic!
Describe the central control of the autonomic nervous system.
Cerebral cortex to hypothalamus to autonomic centres in the brain to preganglionic to postganglionic to effector organs. Effector organs to sensory ganglia up to autonomic centres etc.
What role does the iris play? The retina?
Retina absorbs unwanted light, Iris acts as a diameter, varies by 4X and thus retinal intensity by 16X
What is a small yellow area the size of a thumbnail with sharp vision?
Fovea
Where does the optic nerve leave the eye as seen through an ophthalmoscope?
Optic disk,
Name 2 common focusing problems
Hypermetropia/Hyperopaa: lens system too weak or eyeball too short (longsightedness, corrected with converging lens). Myopia: lens system too strong or eyeball too long (nearsightedness corrected with diverging lens)
Name a structural disadvantage to the eye.
Blood vessels runs in front of photoreceptors (except for fovea)
What in the eye senses light and converts it to electrical signals?
Rods and Cones
Discuss the processing layers of the retina and their purpose.
3 Direct layers: receptors, bipolars, and ganglion cells. 2 Transverse layers: horizontal and amacrine (signal processing, including lateral inhibition “sharpening”)
How many photoreceptors and retinal ganglion cells are there?
125million photoreceptors : 1 million retinal ganglion
What is the chemical signal in the retina that we are seeing light?
Rhodopsin is hit by a photon going to the trans configuration. This sets off a series of biochemical events which result in hyperpolarisation in the cell membrane.
What do retinal ganglion cells respond to?
contrast in the center of a circular field
Can colourblindness be non-genetic/
central achromatopsia due to cortical colour processing area damage
Describe the central visual pathways
Optic nerve from each retina divides into halves, combine in optic chiasm. optic tracts relay in lateral geniculate nucleus (part goes to superior colliculus). Most goes to striate cortex in occipital lobe. Foveal representation exaggerated, then processed for depth, motion, colour, etc.
Name the 3 patterns the visual cortex is organised in.
Ocular dominance, orientation, colour ‘blobs’. A hyperrcolumn contains a complete set of all columns/everything.
What visual problems will you have with a lesion at the optic chiasm? Beyond?
At chiasm= bitemporal hemianopia (opposite sides of visual field in each eye). Beyond = homonymous hemianopia (same side of visual field in both eyes)
What is a visual defect that blocks out a confined part of the visual field?
scotoma, not always noticed. caused by retinal damage, lesions, pressure from tumours.
What are the two visual streams in the cortex and what are they concerned with?
Dorsal stream from occipital to parietal, concerned with location, motion , and action. Ventral stream from occipital to temporal, concerned with object and face identity and conscious perception.
What is the condition when a person can act on what they see but not describe it?
Visual agnosia, lesion in ventral stream. A special case is prosopagnosia, inability to recongize familiar faces- damage to fusiform gyrate underside of temporal lobe.
what is the condition when a person can describe what they can see but not act on it?
visual ataxia.
Describe blindsight.
Patients with some scotomas will insist they can’t see but when forced to discriminate between object can do so.
What accounts for stability of gaze during movement?
Vestibulo-ocular reflex (subway eyes)
What accounts for stabilization of a moving object on the retina?
optokinetic reflex
What is the pupillary reflex?
Contraction of pupil in response to light. If optic nerve damage to that eye, reflex will stop, but consensual response possible if other eye encounters light. Oculomotor nerve damage to one eye will stop reflex in that eye, but either eye stimulation will provoke response in second eye.
what is the range of human hearing?
20-20k Hz, progressive loss at higher frequencies.
What sound intensity can cause permanent hearing loss?
> 90 dB
What are the parts of the middle ear? What does it do?
Malleus, Incus, Stapes. Converts sound waves from air to liquid, increases pressure 45X via lever action and size difference.
What can an ear infection cause?
Otitis Media “Glue ear” chronic will lead to conductive hearing loss, may need draining
What happens when the stapes fuses with the oval window?
Otosclerosis, can be fixed with surgery
Describe the Inner Ear.
Cochlea is a long coiled, fluid filled tube. Basal end tuned to high-frequency sounds, apical end tuned to lower frequencies. Scala Vestibuli connected to oval window, scala media is separate, scala typani connected to round window. SV and ST communicte via helicotrema at apex of cochlea.
Describe the composition of the fluid in the cochlea.
Scala vestibuli and scala tympani have perilymph (high Na low K). Scala Media has endolymph (high K low Na) and electric potential +80mV
Describe the role of the organ of corti.
on the basilar membrane- detects sound, pitch, volume “microphone” Contains inner hair cells and outer hair cells. Apical membrane bathed in endolymph (afferent innervation, inner hair cells), basilar membrane bathed in perilymph (outer hair cells, efferent innervation) 15k hair cells do not regenerate.
How do hair cells in the inner ear transduce a signal?
Deflection of the hair bundle opens up cation channels, K+ comes in depolarising hair cell, voltage gated Ca2+ channel opens, Ca2+ triggers vesicle release (glutamate), afferent nerve fibres activated.
How do outer hair cells change with voltage?
hyperpolarisation = longer, depolarisation = shorter
Describe afferent innervation of the cochlea
CN VIII, each inner cell innervated by 10-20 type I spiral neurons that signal reception of sound over wide range of intensities to brain. Outer cells innervated by type II spiral cells that signal reception of painfully loud sounds that cause cochlear damage to the brain
Describe efferent innervation of the cochlea
Modifies sensitivity of the cochlea. Medial Olive innervates outer hair cells directly, lateral olive synapses on the Type 1 fibres.
Describe the central auditory system.
Cochlear nucleus to superior olivary complex, nuclei of lateral leminiscus, inferior colliculus, medial geniculate body, primary auditory cortex.
What processes interaural level differences?
Lateral superior olive
What processes interaural time differences?
Medial superior olive
