Neuro/psych Flashcards
What is the peripheral nervous system and what is it divided into?
Outside the skull and spine
Somatic and autonomic
What does the somatic nervous system do?
Interacts with the external environment
E.g. sensory info in via afferent nerves to CNS, motor response by efferent nerves back to muscle
What does the autonomic nervous system do?
Regulates the body’s internal environment
E.g. info from internal organs via afferent to CNS, back to organs via efferent nerves
What are the 4 regions of the spinal cord?
Cervical
Thoracic
Lumbar
Sacral
What does C spine control?
Head and neck
Diaphragm
Arms and Hands
What does T spine control?
Chest muscles
Breathing
Abdominal muscles
What does L spine control
Legs and feet
What does S spine control?
Bowel and bladder
Sexual functions
How can the forebrain, midbrain and hindbrain be further divided into 5?
Forebrain: telencephalon, diencephalon
Midbrain: mesencephalon
Hindbrain: metencephalon, myelencephalon
What is in the telencephalon?
Cerebral cortex
Basal ganglia
Limbic system
What is in the mesencephalon?
Tegmentum
Tectum
What is in the metencephalon?
Pons
Cerebellum
What is in the diencephalon?
Thalamus
Hypothalamus
What is in the myelencephalon?
Medulla
What does the medulla contain and what is its function?
Contains tracts carrying signals between the rest of the brain and the body
Contains caudal part of the reticular formation: low level sensorimotor control
Involved in vital functions: sleep, motor plant (movement, maintenance of muscle tone, cardiac, circulatory, respiratory and excretory reflexes
What does the pons contain and do?
Contains millions of neuronal fibres
Relays from cortex and midbrain to cerebellum
Pontine reticular formation (pattern generators, e.g. for walking)
What does the cerebellum do? (vestibulo, spino, cerebro)
Vestibulocerebellum: conjugate eye movements and balance control
Spinocerebellum: posture and the monitoring and correcting of the motor activity of the limbs
Cerebrocerebellum: planning and initiation of movement and motor learning
What does the tectum divide into and their roles
Superior colliculus: sensitive to sensory change, orienting and defensive movements
Inferior colliculus: sensitive to auditory events, similar to superior except auditory
What does the tegmentum divide into?
Periaqueductal gray
Red nucleus
Substantia nigra
What is the role of the periaqueductal gray?
Role in defensive behaviour
Pain
Reproduction
What is the red nucleus involved in?
Target of cortex and cerebellum, projects to spinal cord
Role in pre-cortical motor control (especially arms and legs)
What is the role of the substantia nigra?
Pars compacta: basal ganglia input, parkinson’s
Pars reticulata: basal ganglia output
What is the role of the thalamus?
Relays from basal ganglia and cerebellum back to cortex
Specific nuclei: relays signals to cortex/limbic system for all senses but smell
Non-specific nuclei: role in regulating state of sleep and wakefulness, arousal levels
What is the role of the hypothalamus?
Regulates the pituitary gland, interface between brain and hormones
Controls hunger, thirst, temperature, pain, pleasure and sex
What is the basal ganglia and its functions?
Group of structures in loop organization
Involved in motor function as involved with movement disorders
What is the limbic system involved in?
Involved in emotion, motivation, emotional association with memory, olfaction
Influences the formation of memory by integrating emotional states with stored memories of physical sensations
What makes up the limbic system?
Amygdala
Hippocampus
Fornix
Cingulate gyrus
Septum
Mammillary body
What is the amygdala’s function?
Involved in associating sensory stimuli with emotional impact
What is the mammillary body’s function?
Important for the formation of recollective memory (amnesia)
What is the hippocampus involved in?
Long term memory and spatial memory
What is the septum involved in?
Defence and aggression
What is the cingulate gyrus’ function?
Linking behavioural outcomes to motivation and autonomic control
Atrophied in schiz
What is the fornix and what is it’s function?
C-shaped bundle of fibres
Carries signals from the hippocampus to mammillary bodies and septal nucleus
What are the subcortical portions of the cerebral cortex?
Basal ganglia
Limbic system
What is the frontal lobe involved in?
Executive planning, judgemental roles, emotional modulation
Working memory, short term
Control of behaviour that depends on context and setting
Prefrontal cortex: generating sophisticated behavioural options that are mindful of consequences
Where is the primary motor cortex found and what does it do?
Precentral gyrus in frontal lobe
Contains many of the cells giving origin to descending motor pathways
Involved in initiation of voluntary movements
Where is the primary somatosensory cortex and what does it do?
Postcentral gyrus in parietal lobe
Maintains representations of body’s position in space
Permits complicated spatio-temporal predictions
What does the temporal lobe do and contain?
Contains primary auditory cortex
Inferotemporal cortex: recognition faces and objects
Plays important roles in integrating sensory info from various parts of the body
Interface between cortex and limbic system- association of affect/emotion with things
What does the dorsal stream in the occipital lobe do?
Vision for movement
Where is it in relation to us?
What does the ventral stream in the occipital lobe do?
Vision for identification
What does it mean?
Path towards temporal and limbic system
What are the elements of the perceptual set?
Context
Culture
Expectations
Mood
What is sensation?
A mental process resulting from immediate external stimuli of a sense organ
What is perception?
The ability to become aware of something or to interpret it following sensory stimuli
What are the catecholamines and when are they released?
Adrenaline and noradrenaline released in response to stress
What are glucocorticoids?
cholesterol-derived steroid hormones synthesised and secreted by the adrenal gland
controlled by HPA axis
What can elevated glucocorticoids lead to?
Immune suppression
What are fast physiological stress responses?
- Breathing more rapid to increase oxygen
- Blood flow increases up to 400%, directed to heart & muscles
- Increased heart rate & blood pressure
- Muscles tense
- Glucose released, insulin levels fall: boost energy to muscles
- Red blood cells discharged from the spleen
- Mouth becomes dry & digestion is inhibited
- Sweating
- Cytotoxic & surveillance WBCs go where injury & inflammation may occur i.e. bone marrow, skin, lymph nodes
What are some of the physical symptoms of chronic stress?
Headache
Chest pain
Stomach ache
Musculoskeletal pain
Low energy
Loss of libido
Colds & infections
Cold hands & feet
Clenched jaw & grinding teeth
What are some behavioural responses to stress?
Easily startled & hypervigilant
Change in appetite – both directions
Weight gain (obesity) or weight loss
Procrastinating and avoiding responsibilities
Increased use of alcohol, drugs & smoking
Nail biting, fidgeting and pacing
Sleep disturbances especially insomnia
Withdrawal
What are some cognitive responses to chronic stress?
Constant worrying
Racing thoughts
Forgetfulness and disorganisation
Inability to focus
Poor judgement
Being pessimistic or seeing only the negative side
Altered learning
What are some emotional responses to chronic stress?
Depression & sadness
Tearfulness
Mood swings
Irritability
Restlessness
Aggression
Low self-esteem and worthlessness
Boredom & apathy
Feeling overwhelmed
Rumination, anticipation & avoidance
How can stress affect physical health?
exacerbates physical illnesses and slows recovery and increases susceptibility to infection
What mediates the stress response?
autonomic nervous system (sympathetic-adrenal-medullary (SAM) system) & hypothalamo-pituitary (HPA) axis
What is chronic stress?
Arises from repeated or continued exposure to threatening or dangerous situations, especially those that cannot be controlled.
Some (but not all) involve appraisal and conscious perception
What is acute stress?
Short-lived response to a novel situation experienced by the body as a danger.
It is healthy & adaptive, and necessary for survival
Examples of chronic stressors
Physical illness, disability & pain
Physical or sexual abuse
Poverty including poor housing, hunger, cold or damp, debt
Unemployment
Bullying or discrimination
Caregiving
Examples of acute stressors
Noise
Fire
Brief physiological challenge, e.g. hunger
Brief illness
What is allostasis?
how complex systems adapt (eg via SAM and HPA axis) in changing environments, by changing set-points (“adaption through change”).
What is the allostatic load?
refers to cumulative exposure to stressors (and cost to the body of allostasis), which if unrelieved leads to systems ‘wearing out’.
What is homeostasis?
maintaining internal environment necessary for cell functioning
What is the definition of stress?
the non-specific response of the body to any demand for change
What are the 3 stages of the stress response?
Alarm- fight or flight initiated
Adaptation- body engages defensive countermeasures
Exhaustion- resources depleted
What is somatic/physical stress?
Physical, emotional and subjective experiences associated with damage of body tissue and bodily threat (eg pain and inflammation).
What is psychological stress?
Emotional strain or tension resulting from adverse or demanding circumstances, often involving anticipation.
What makes up the outer ear?
Pinna and ear canal to tympanic membrane
Made up from cartilage/ temporal bone
What does the outer ear form from and when?
Formed from pharyngeal arches (6 Hillocks of His)
In utero, week 10-18
Forms separately to inner ear
What is the role of the outer ear?
Directs soundwaves toward ear canal
Better at detecting high pitch than low pitch
What makes up the middle ear?
Bones: malleus, incus and stapes
Muscles: Tensor tympani & stapedius
Eustachian tube
What do the tensor tympani and stapedius do?
Tensor tympani pulls on tympanic membrane
Stapedius attaches to stapes
Protect from acoustic trauma, stiffens the ossicular chain
Tensor tympani stiffens eardrum to hide sound of chewing
What is the role of the middle ear?
Acoustic impedance match between air and fluid-filled inner ear
Sound concentrated down from tympanic membrane - amplifies sound
What is the ratio of areas between tympanic membrane and stapes footplate?
14:1
What is the role of the eustachian tube?
Equalises air pressure
Ventilates middle ear space
Drainage of secretions
What makes up the inner ear?
A set of fluid filled sacs, encased in bone
Cochlear- responsible for hearing
Labyrinth- responsible for balance
Innervation: Vestibulocochlear nerve
What makes up the cochlea?
2.5 turns fluid filled bony tube
2 openings- round window & oval window
3 compartments ( Scala Tympani, Scala Media & Scala Vestibuli)
2 Ionic fluids
How do the cochlear fluids work?
Scala media contains endolymph (high K+0)
Scala tympani and vestibuli are sodium rich
Gradients maintained by Na,K-ATPase & NKCC1 CIC-K chlorine channels
Inner ear problems (no gradients) can lead to deafness
How does the middle/inner ear work to transmit sound?
- Movement of tympanic membrane leads to stapes movement at oval window
- Pressure wave through scala vestibuli (works as round window elastic)
- Pressure wave moves into scala tympani leads to movement in basilar membrane
- Organ of Corti moves - hair cells move
- Steriocilia move, K+ channels open, rapid depolarisation
- Voltage gated Ca2+ open
- Glutamate released, nerve fibre activated = sound
- Repolarisation
How does the ear basilar membrane work?
Different parts of basilar membrane respond to different frequencies
High frequencies detected at base, low at apex
What do the hair cells do in the inner ear?
Inner hair cells for mechanical transduction
Outer hair cells for fine tuning by altering stiffness of basilar membrane
How does tonotopy work in the inner ear?
Each nerve responds maximally at a specific frequency
Outer hair cells can alter the stiffness of the basilar membrane to ensure maximal stimulation at one site and dampened response at another
Increased resolution
What is the pathway from neuron to brain in the ear
Auditory fibre to spiral ganglion to cochlear nerve (VIII)
Describe the central auditory pathway
Cochlea
CN VIII
Cochlear nucleus
Olive
Lateral lemniscus
Inferior colliculus
Medial geniculate body
Auditory cortex
What does the brainstem do for hearing?
Sound localisation from binaural hearing
What does a defective outer/middle ear lead to?
conductive hearing loss
What does a defective inner ear lead to?
sensorineural hearing loss
What are the 3 layers of the eye?
Outer layer: sclera and cornea
Middle layer: uvea
Inner layer: Retina
What is the sclera made up of and what is its function?
Cross linked collagen fibres
Tough, maintains eyeball shape, protection
What is the function of the choroid of the eye?
Blood supply and nutrition to outer third of retina
Has melanocytes to absorb light
What makes up the outer layer of the eye?
Sclera and cornea (both made from collagen)
Which parts of the eye are responsible for refraction and focusing?
Curvature of cornea responsible for 2/3 of refractive power
Intraoccular lens responsible for 1/3
What are the 5 layers of the cornea?
Anterior: Epithelium
Bowman’s layer
Stroma (makes up about 90%, makes it transparent)
Descemet’s layer
Posterior: Endothelium
Can the corneal epithelium and endothelium regenerate?
Epithelium can regenerate, endothelium cannot
What is the function of the iris?
Changes the aperture of light coming in
What produces aqueous humor and what does it do?
Produced by ciliary body
Bathes anterior chamber
Maintains pressure of eye
What makes up the middle layer of the eye?
Made up of iris, ciliary body and choroid
What are the macula lutea and fovea centralis in the retina?
The macula lutea (aka fovea) is a yellow spot in the retina that allows light to focus when looking at an object.
The fovea centralis is an anatomical structure in the center of the macula lutea that contains a high density of cone photoreceptors and allows the light to focus within the eye
What makes up the retina?
Macula lutea
Fovea centralis
Cones
Rods
What is the function of the anterior segment of the eye?
Aqueous humour
Nutrition to lens and cornea
Maintains intraocular pressure
What makes up the posterior segment of the eye?
Vitreous humour
Avascular viscoestalic gel
Hyaluronic acid (GAG)
Collagen
What are the 3 parts of the ocular adnexae?
Lids- protect the globe
Conjunctiva
Tear film
What is the arterial blood supply of the eye?
Internal carotid artery into ophthalmic artery into long and short posterior ciliary artery
What supplies the inner 2/3 and outer 1/3 of eye?
Inner 2/3 from central retinal artery
Outer 1/3 from choroid
Describe venous drainage of eye
Vortex veins drain the choroid
Superior drain to SOV, inferior drain to IOV
Superior ophthalmic veins drain into cavernous sinus
Inferior ophthalmic veins drain into pterygoid venous plexus
Do the veins in the eye have valves?
No
Can lead to orbital cellulitis/facial infection can precipitate cavernous sinus thrombosis
Where is the lymphatic drainage in the eye?
No lymphatic drainage from the globe
Conjunctiva and lids do have lymphatic drainage to submandibular and pre-auricular nodes
What is the basic structure of a neuron?
Dendrites
Cell body
Axon
Presynaptic terminals
How does the sodium potassium pump work?
Transport Na+ out and K+ into neuron
3 Na+ for every 2 K+
Energy from ATP
What is the resting potential of neurones?
-70mV
What is happening when the neuron is at rest?
Result is NA+ high concentration outside but with both forces pushing in
Membrane and pump resists Na+ inward movement
K+ & Cl- can move backward and forward across membrane so reach steady state
Some sodium leaks back in but is expelled by the pump
How does an action potential occur?
- Neurotransmitters activate receptors on dendrites
- Receptors open ion channels
- Ions cross plasma membrane, changing the membrane potential
- The potential changes spread through the cell
- If the potential changes felt at the axon hillock are positive (+mV), and large enough, an action potential is triggered
What causes an ESPS?
Excitatory neurotransmitters depolarise the cell membrane
increases probability of an action potential being elicited
cause an Excitatory Post Synaptic Potential
What causes an IPSP?
Inhibitory neurotransmitters hyperpolarise cell membrane
Decreases probability of an action potential
Leads to inhibitory post synaptic potential
What is spatial summation?
larger numbers of primary afferent neurons are activated simultaneously, until sufficient neurotransmitter is released to activate an action potential
What happens at the threshold for action potentials (-60mV)?
Sodium channels open and polarity reverses to +30
Voltage-gated sodium channels close and K+ open, K+ leave
Resting membrane restored
What is temporal summation?
occurs when one presynaptic neuron releases neurotransmitter many times over a period of time
What is saltatory conduction
Sodium ions rush into axon and activate other sodium ions inside cell
Wave of positivity moves down nodes of ranvier
What is myelin and the function of myelination?
Protects fibres
Increases transmission speed
Produced by oligodendrocytes in CNS and Schwann cells in PNS
How does synaptic transmission work?
AP reaches terminal
Opening of Ca2+ channels
Exocytosis
Receptors on post synaptic membrane
Breakdown of NTs in cleft
What does acetylcholinesterase do?
Enzyme that breaks down the NT ACh
Needed for synapse to stop being active
What does acetylcholine do?
Activates muscles
What are some fast NTs?
Acetylcholine (ACh)
Glutamate (GLU)
Gamma-aminobutyric acid (GABA)
What are some neuromodulator NTs?
Dopamine
Noradrenalin
Serotonin
How do local anaesthetics work?
Block sodium channels
Blocks progress of AP
What can affect ACh?
Nicotine
Spider toxins
Nerve gases
What can affect noradrenaline?
Antidepressants (blocking reuptake or breakdown)
Amphetamines
What can affect dopamine?
Antipsychotics
Antiparkinsons
Stimulants (amphetamines, cocaine)
What can affect serotonin?
Antidepressants
Hallucinogens
Ecstasy
What can affect GABA?
Anti-anxiety drugs
Anticonvulsants
Anaesthetics
What are neurones and their function?
Specialised cells for electrical signalling
Receive inputs from dendrites and send signals out via axon hillocks where AP occurs
Mainly formed during development
What are chemical synapses?
Use neurotransmitters
Majority of synapses
What are electrical synapses?
Channels allowing for direct flow of current between neurones
enable synchronized electrical activity, e.g. brainstem (breathing) & hypothalamus (hormone secretion)
Less abundant
What is the difference between electrical and chemical synapses?
Electrical have high density of proteins on both sides of membrane
Contain connexons made from connexin proteins, form a continuous channel between cells
Where are excitatory synapses often concentrated?
Dendritic spines
What is the concept of neural plasticity?
changes in neuronal/synaptic structure and function in response to neural activity
basis of learning and memory
dendritic spine remodelling linked to neural activity
Which cells are vulnerable in Huntington’s?
Medium spiny neurones - striatal interneurons, small, inhibitory
(GABAergic)
Which cells are vulnerable in MND?
Betz cells - upper motor neurons, large, excitatory (glutamatergic,) long projections, pyramidal cells
What are oligodendrocytes and their function?
Myelinating cells of the CNS
Unique to vertebrates
Myelin insulates axon segments, enables rapid nerve conduction
Provide metabolic support for axons
What interrupts myelin sheath?
Nodes of Ranvier
What forms the myelin sheath?
Wrapping of oligodendrocyte membranes around axons
70% lipid, 30% protein
Specific proteins: myelin basic protein used as a histological marker
What are microglia?
resident immune cells of CNS, highly phagocytic
highly ramified in resting state
highly motile when activated (migrate to sites of damage)
proliferate at sites of injury
Where do microglia originate from?
yolk sac
move into CNS in embryonic development
What are the functions of microglia?
Immune surveillance
Phagocytic, removing cell debris
Synaptic plasticity
What are astrocytes?
Most numerous glial cells in CNS
Mostly star shaped, but highly heterogenous
Contribute to blood brain barrier as processes line blood vessels
What histological marker is used for astrocytes?
glial fibrillary acidic protein
What are the functions of astrocytes?
Structural - define brain micro-architecture
Envelope synapses – “tripartite synapse”
Metabolic support – store glycogen and lactate
Neurovascular coupling – changes in cerebral blood flow in response to neural activity
Regulate extracellular ionic environment: remove excess K+ after activation
Promote myelination
NT uptake
Proliferate in disease = gliosis or astrocytosis
Where are pathological changes seen in MND spinal cord?
Motor neurones
Microglia
Astrocytes
What are MND symptoms a result of?
Loss of motor neurones
What do acute symptoms in MS reflect dysfunction of?
Neurones, e.g. optic neuritis
What do pathological lesions in MS involve?
Neurons
Oligodendrocytes
T lymphocytes
What is a nucleus in CNS?
High abundance of neuronal cell bodies
What is grey matter abundant in?
areas abundant in neuronal cell bodies and processes
What does white matter contain?
contains abundance of myelinated tracts & commissures
fatty so white
What is a ganglion in PNS?
Cell bodies & supporting cells
PNS version of nucleus
What’s the terminology in CNS and PNS for where axons gather?
CNS = Tracts
PNS = Nerves
What are the myelinating cells of PNS?
Schwann cells derived from neural crest cells
What are myelinating cells of CNS?
Oligodendrocytes derived from common CNS progenitors
What is the blood brain barrier?
a selectively permeable membrane regulates the passage of a multitude of large and small molecules into the microenvironment of the neurons
Where is the blood brain barrier different?
area postrema - for chemoreceptors to measure
pituitary - hormone secretion
Which cells line the ventricles?
Ependymal cells
What do ependymal cells line and what is their function?
Epithelial-like, line ventricles & central canal of spinal cord
Functions - CSF production, flow & absorption
Ciliated – facilitates flow
Allow solute exchange between nervous tissue & CSF
What is the choroid plexus?
Vascular plexus found at the floor of lateral ventricles/roofs of third and fourth ventricles
What are the functions of the choroid plexus?
Production and secretion of CSF, forming a blood-CSF barrier, secretion of various growth factors, facilitate the brain development, protection from harmful toxins and microbes
How many pairs of spinal nerves are there?
31 pairs
How many pairs of cranial nerves are there?
12 pairs
What are cranial nerves?
Peripheral nerves
Most attached to the brainstem
Carry sensory / motor /autonomic info between brain, head and neck
Contain different combinations of fibre types (motor, general sensory, special sensory, autonomic); some contain just 1 type, others contain several
What are the CN I-VI?
I Olfactory
II Optic
III Oculomotor
IV Trochlear
V Trigeminal
VI Abducens
What are the CN VII -XII?
VII Facial
VIII Vestibulocochlear
IX Glossopharyngeal
X Vagus
XI Accessory
XII Hypoglossal
Sensory, motor or both for CN I -VI?
I Olfactory - S
II Optic - S
III Oculomotor - M
IV Trochlear - M
V Trigeminal - B
VI Abducens - M
Which cranial nerves contain parasympathetic fibres?
III, VII, IX, X
Sensory, motor or both for CN VII - XII?
VII Facial - B
VIII Vestibulocochlear - S
IX Glossopharyngeal - B
X Vagus - B
XI Accessory - M
XII Hypoglossal - M
CN I Olfactory: where does it attach, function, S/M
Sensory, smell
Attached to brain not brainstem
Axons travel through the cribriform plate, then olfactory bulb, tracts, temporal
Connections to limbic system
CN II Optic: where does it attach, function, S/M
Sensory, vision
Fibres travel from retina to primary visual cortex
CN III oculomotor: where does it attach, function, S/M
Motor, Parasympathetic fibres to constrict the pupil
Control extraocular muscles: MR, SR, IR, IO, LPS (NOT SO, LR)
Pass through superior orbital fissure
Nuclei in the midbrain
Nerves exit at junction between the midbrain and pons
Close to cerebral posterior cerebral arteries
How to test CN I - VI?
CN I: Smell, ask if changes in smell/ smell something
CN II: Smellen chart, test visual acuity and fields, pupillary light reflex
CN III: Test eye movements and LPS, test pupillary light reflex
CN IV: Move eye medially and down
CN V: test general face sensation, test corneal reflex
CN VI: abduct eye
What is a normal pupillary light reflex?
Both pupils constrict when light is shone into either eye
Direct response: ipsilateral pupil constricts to light
Consensual response: contralateral pupil constricts to light in other eye
What are signs of lesions with CN III or pathway?
Ptosis
Lateral deviation of the eye (unopposed action of lateral rectus)
Dilated pupil that does not constrict
CN IV Trochlear: where does it attach, function, S/M
Innervates superior oblique
Nuclei in midbrain
Motor
What can damage of IV cause?
Paralysis of SO = diplopia on looking down
CN VI Abducens: function and nuclei
Innervates LR
Nuclei in the pons
What can damage of abducens cause?
Paralysis of LR = medial deviation of the eye (unopposed action of medial rectus), unable the abduct the eye on examination.
CN V Trigeminal: function and attachment
Attached to the pons
3 branches
Sensory and Motor
General sensation from dura, face, scalp, cornea, anterior 2/3 tongue
proprioception from TMJ and muscles of mastication
What are the 3 branches of CN V?
Ophthalmic – V1 > Superior orbital fissure.
Maxillary – V2 > foramen rotundum.
Mandibular – V3 > foramen ovale
Pathologies of trigeminal
Trigeminal neuralgia
Anaesthesia over sensory distribution of nerve
Paralysis of muscles of mastication
CN VII Facial: course and roots
Sensory, motor and parasympathetic fibres
Attached to the brainstem at the pontomedullary junction
Has two ‘roots’
- Medial – motor fibres
- Lateral – sensory and parasympathetic fibres (the nervus intermedius)
Complex course through the temporal bone
CN VII Facial: fibre types
Special sensory - taste anterior 2/3 tongue
Motor - muscles of facial expression
Parasympathetic - lacrimal gland, submandibular and sublingual salivary glands
Within the parotid, the terminal part of the facial nerve divides into 5 branches.
How to test CN VII -XII
CN VII: ask about taste, is the eye dry, facial expression
CN VIII: cochlear: auditory tests, vestibular: observing balance, caloric testing
CN IX: often tested with X, gag reflex
CN X: gag reflex, ask if voice has become hoarse or nasal
CN XI: turn head against resistance, shrug shoulders
CN XII: stick out tongue and look for atrophy, deviation to one side is lesion
Pathologies of CN VII facial
Facial weakness from injury to facial nerve:
- Bell’s palsy: inflammation of nerve
- Tumours
- Middle ear infection
- Fractures of temporal bone
Where do UMNs for lower face go?
UMN axons leave primary motor cortex
Cross over and innervate contralateral facial motor nucleus
Where does the input for the upper face come from?
Contra and ipsilateral input from facial nerve
What happens when the UMNs on one side are injured (e.g. in the motor cortex)?
Lower contralateral face is weak
Upper contralateral face is not weak as the muscles have dual innervation from both sides of the motor cortex (forehead is spared),
upper face movement preserved
Difference between LMN and UMN lesion
LMN lesion: all face on same side are weak
UMN: only lower face on opposite side is weak
CN VIII Vestibulocochlear: function and afferents
Sensory
- Vestibular afferents important for balance, connections to spinal cord, cerebellum, nuclei of CNs III, IV and VI, cerebral cortex for posture, balance, eye movements, conscious perception of position of the head
- Cochlear afferents make connections to primary auditory cortex and auditory association cortex, interpretation
Pathology of CN VIII
Acoustic neuroma, benign but compress the nerve
CN IX Glossopharyngeal: function and attachment, fibres
Sensory, motor and parasympathetic fibres
Attached to the medulla via several small rootlets
Taste - posterior 1/3 of the tongue
General sensation: (touch, temp, pain), pharynx, Eustachian tube, posterior 1/3 of the tongue
Afferents from the carotid sinus (baroreceptors) and carotid body (chemoreceptors)
Parasympathetic fibres innervate parotid gland
CN X Vagus: function, attachment, fibre types
Sensory, motor and parasympathetic fibres
Attached to the medulla via several small rootlets
- General sensation: > pharynx, larynx, oesophagus, EAM, tympanic membrane
- Visceral afferents - thoracic and abdo viscera.
- Afferents from the aortic bodies (chemoreceptors) and the aortic arch (baroreceptors)
- Motor fibres innervate soft palate, pharynx and larynx – vital for swallowing and speech
- Parasympathetic fibres: Thoracic and abdo viscera
CN XI Accessory: function
Motor nerve
Cranial part: rootlets arise from the medulla
- leaves via the jugular foramen by joining the vagus
Spinal part: from ventral horn spinal cord, C1-C5
- Travels up through the foramen magnum
- Leaves again through the jugular foramen
- Innervates sternocleidomastoid and trapezius
CN XII Hypoglossal: function and where it arises
Motor nerve innervates muscles of the tongue
Arises from the medulla, leaves through the hypoglossal canal
What happens if XIIth has a lesion?
Ipsilateral tongue muscles are paralysed and tongue points to affected side
Left deviation = left CN XII lesion
What is pain?
an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage
What is instant and acute pain?
instant pain: injury
acute pain: lingering for a while after injury
Difference between acute and chronic pain
Acute: less than 12 weeks duration
Chronic pain: continuous pain lasting more than 12 weeks, persists beyond healing time
What is nociceptive pain?
Pain that arises from actual or threatened damage to non neural tissue and is due to the activation of nociceptors
What is neuropathic pain?
Cause by a lesion or disease of the somatosensory nervous system.
E.g. trigeminal/ glossopharyngeal neuralgia, neuropathy
What is allodynia?
Pain due to a stimulus that doesn’t normally provoke pain
E.g. pain from light touch
What is dysesthesia?
An unpleasant abnormal sensation, whether spontaneous or evoked
What is hyperalgesia?
Increased pain from a stimulus that normally provokes pain
What is nociplastic pain?
Pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors
What is a nociceptor?
pain receptor responsible for transduction
makes physical stimulus into action potential
the free nerve endings of primary afferent neurones
What are the two types of primary afferent neurons?
a delta fibres are faster, pain for reflex
c fibres are slower conducting, dull throbbing pain
What is hypoalgesia?
Diminished pain in response to a normally painful stimulus.
Describe the pain pathway
Pain detected in peripheral receptor
Travels through the primary afferent neuron to the second order neuron in the dorsal horn
Crosses over to other side and ascends until it synapses with the third order neuron in the thalamus
Travels to somatosensory cortex
Where are primary afferent neurones cell bodies?
The cell bodies of these neurons reside in either
- Dorsal root ganglion (body)
- Trigeminal ganglion (face / head / neck)
Where are primary afferent neurones found?
found in any area of the body that can sense pain either externally or internally
External: skin / cornea / mucosa
Internal: viscera / joints / muscles / connective tissue
What is the dorsal root ganglion?
Composed of cell bodies of nerve fibres that are sensory (afferent)
First order neurons
Can be a source of pain or a target of pain management
What is the dorsal horn?
Where the primary afferent nerve terminates and synapse with second order neurones or interneurons, then crosses over to contralateral side at spinal cord
Posterior part of grey matter in spinal cord
What is the spinothalamic tract?
Sensory pathway that carries pain, temperature and crude touch info from the body (comes after dorsal horn)
2nd order neurones
Originate in the spinal cord
Axons decussate and cross the midline in the anterior commissure then form the anterolateral tract
What is the dorsal column responsible for?
fine touch, propioception, vibration
What is the lateral spinothalamic tract responsible for?
pain and temperature
What is the ventral spinothalamic tract responsible for?
light touch
Where does 2nd order neuron terminate and what does it synapse with here?
thalamus
3rd order neurones
What is the thalamus and what does it do?
situated centrally in the cerebrum, is a relay station for the ascending tracts
organized into multiple nuclei, several of which are important in pain transmission, including the lateral (sensory component) and the medial nuclei (emotional component)
Which parts of the thalamus are important in pain?
Lateral ventral posterolateral (VPL) nuclei
Medial midline group of nuclei
What is the role of the insula?
- This is where the degree of pain (experienced or imagined) is judged
- Role in perception, motor control, self awareness and interpersonal experience
- May also play a part in addiction
What is the role of the amygdala?
- plays a key role in learned emotional responses (fear, anxiety, depression)
- important brain center for the emotional-affective dimension of pain and for pain modulation
What is the role of the cingulate cortex?
- Intricately linked with the limbic system which is associated with emotion formation and processing, learning and memory
- Maintains reciprocal connections with other pain processing areas
What is the peri aqueductal gray and its role?
- Grey matter located around the cerebral aqueduct
- Receives input from cortical and sub-cortical areas
- Projects onto neurons in the dorsal horn
- Modulate afferent noxious transmission
- Neurons bear opioid receptors
- Pathways also include noradrenergic and serotonergic neurones
What is gate control theory for pain?
the concept that onwards transmission of a nociceptive signal depends on the balance between inhibitory and excitatory inputs at points of integration along the path from transduction to perception
What are the issues with opioid use?
Addiction
Tolerance
Immunosuppression
Deranged HPA axis
Opioid induced hyperalgesia
What is emotion?
A mind and body’s integrated response to a stimulus
What is arousal?
An increase in reactivity or wakefulness to prime us for an event
What are the 10 basic emotions?
Joy
Contempt
Surprise
Shame
Sadness
Fear
Anger
Guilt
Disgust
Excitement
What is mood?
Long term emotional states rather than discreet, fleeting feelings
What is a mood disorder?
Longer term extremes of emotional state and challenges in regulating mood
What is depression?
the patient suffers from lowering of mood, reduction of energy, and decrease in activity
What is mania?
Mood is elevated out of keeping with the patient’s circumstances and may vary from carefree joviality to almost uncontrollable excitement
What is hypomania?
A disorder characterized by a persistent mild elevation of mood, increased energy and activity, and usually marked feelings of well-being and both physical and mental efficiency
What is bipolar disorder?
A disorder characterized by two or more episodes in which the patient’s mood and activity levels are significantly disturbed, this disturbance consisting on some occasions of an elevation of mood and increased energy and activity (hypomania or mania) and on others of a lowering of mood and decreased energy and activity (depression)
When would an X-ray be used in neuro?
Foreign object in brain
Otherwise not used as brain doesn’t show good contrast
How do contrast X-rays work and what do they check in brain?
Used for cerebral angiography to check perfusion
Inject a contrast agent to view contrast between blood vessels and everything else
How does MRI work?
Energy put into tissues absorbed and then re-emitted, giving contrast
Sensitive to different tissue types, e.g. grey and white matter
Very high resolution
How does fMRI work?
When haemoglobin is carrying oxygen, iron is more hidden and doesn’t disturb magnetic field as much
Difference between oxygenated and deox haem
Activated areas need more oxygen so blood flow increases
More metabolism and activity = see less deoxyhaemoglobin
Why use PET over fMRI and vice versa?
Radioisotope used to track receptor occupancy and movement of oxygen
Can only do PET once or twice because of radioisotope
What is EEG?
Electroencephalography
Gives indication of regional brain activity underlying electrodes
Good temporal bad spatial resolution
Good for detecting epilepsy
What is ERP?
Event-related potential
Repeatedly do task with EEG recorded
Look at brain response to a specific stimulus
What is transcranial magnetic stimulation?
Expose part of the brain to a magnetic field which may inhibit part of brain
Knock out part of cortical processing temporarily
What are the symptoms of depression?
Low mood
Anhedonia
Low energy
Poor sleep and appetite
Poor concentration
Cognitive symptoms
Describe the HPA axis
Hypothalamus releases CRH
Anterior pituitary releases ACTH
Adrenal cortex releases CORT
What is different in the HPA axis in depression?
Increased CRH
Enlarged adrenals and pituitary
Reduced -ve feedback
Reduced GR expression in the brain
What does the medial PFC do?
Evaluating emotional state
Social cognition
What does the dorsal PFC do?
Working memory
Problem solving
How is the hippocampus affected in depression?
Reduced in siz eby up to 20% in MDD
Dose related effect
Mostly irreversible
Associates with learning based difficulties
How are the medial and dorsal PFCs affected in depression?
Volume loss, more lost in dorsal
How does depression affect brain deprived neurotrophic factor?
Stress causes BDNF to be lower
Can be reversed with antidepressants
How do antidepressants work?
Affect gene expression (increase glucocortoroid expression)
Increase neurogenesis and BDNF synthesis
What is the default mode network?
What happens when the brain isn’t given a task
Works on autobiographical details, self-reference and thinking about others
What is examples of voluntary motor control?
running, walking, talking
What are examples of involuntary motor control?
eye movements, facial expressions, jaw, tongue, postural muscles throughout trunk, hand and fingers, diaphragm, cardiac, intercostals (around lungs), digestive tract
What is an antagonistic arrangement of muscles?
Combined co-ordinated action, e.g. biceps and triceps
How does rigor mortis occur?
Release of ACh causes a cascade of events resulting in release of calcium
Myosin head changes shape and binds with actin
ATP required to break bond
ATP not made when oxidative metabolism stops
Muscle becomes and stays contracted until enzymes begin to disrupt
What is the motor unit?
single alpha motor neuron + all the muscle fibres it innervates
Different motor neurones innervate different numbers of muscle fibres
fewer fibres means greater movement resolution e.g. finger tips and tongue
How does the motor unit work?
- Activation of an alpha motor neuron depolarises and causes contraction of all muscle fibres in that unit (all or none)
- Muscle fibres innervated by each unit are the same type of fibre and often distributed through the muscle to provide evenly distributed force (and reduce effect of damage)
- More motor units fire – more fibres contract – more power
Where do lower alpha motor neurons originate and where do the project?
Originating in the grey matter of the spinal cord, or in the brainstem
Project to motor fibres
What is the motor pool?
All the lower motor neurons that innervate single muscle
The motor pool contains both the alpha and gamma motor neurons
What activates cell bodies in the ventral horn?
Sensory information from muscle
Descending information from brain
What do the golgi tendon organs do?
Within the tendon, sense tension
Sends ascending sensory information to the brain via the spinal cord about how much force there is in the muscle
Critical for proprioception
Can act to inhibit fibres under extreme tension to prevent damage
What do muscle spindles do?
Muscle spindles sense stretch, the length of muscles
This information forms a key part of reflex circuits
Why are reflexes necessary?
operate without engaging with the brain, and are critical for the avoidance of injury and effective motor control
What are extrafusal muscle fibres?
Majority of skeletal
Innervated by alpha motor neurons
Generate force
Muscle contraction
What are intrafusal muscle fibres?
Innervated by gamma motor neurones
Too small to generate significant force
Encapsulated in sheaths and form muscle spindle
What is the somatic nervous system?
Conscious/ voluntary regulation
Fibres don’t synapse after they leave CNS
Innervates skeletal muscle fibres
Stimulatory
What is the autonomic nervous system?
Functions without conscious awareness
Fibres synapse once at ganglion outside of CNS
Motor control
Innervates smooth muscle, e.g. cardiac, glands
Stimulates and inhibit
What are somatic motor neurons like?
Myelinated
Excitatory
Contraction of skeletal muscle
ACh
What are the functions of the autonomic nervous system?
Thermoregulation, exercise, digestion, competition, sexual Function, circulation
What are the functions of sympathetic NS?
Increased heart rate and force of contraction
Constricts blood vessels
Bronchodilation
Decreased GI tract motility and reduced secretions
Sphincter contraction
What are the functions of the parasympathetic NS?
Decreased heart rate and force of contraction
Bronchoconstriction
No effect on blood vessels
Increased GI tract motility
Sphincter relaxtion and increased secretions
What are the autonomic motor neurons like?
Pre-ganglionic myelinated fibres
Synapses in autonomic ganglion (sympathetic chain next to spinal cord)
Small unmyelinated fibres transmit to effectors
Contraction of smooth muscle
Where does the sympathetic division of ANS run from?
T1 - L2
What is the amplification system of the sympathetic NS?
Adrenal Medulla
Fight or flight
Adrenal gland excretes adrenaline, noradrenaline and dopamine
Can enteric nervous system work separately from ANS?
Yes
What are the main sympathetic neurotransmitters?
ACh received by nicotinic receptor
Noradrenaline received by adrenergic receptor
What are the main parasympathetic neurotransmitters and their receptors?
ACh with nicotinic receptor
ACh with muscarinic receptor
What are the subtypes of noradrenaline?
alpha 1 and 2
beta 1,2,3 (heart 1, bronchi 2)
Where is the carotid body?
carotid body at carotid bifurcation
chemoreceptors nearby
What metabolic disorders have a secondary effect on the ANS?
Diabetes
Chronic renal failure
Chronic liver disease
Alcohol induced
What makes up the basal ganglia and associated nuclei?
Caudate nucleus
Putamen
Globus pallidus
Subthalamic nucleus
Substantia nigra
(Pedunculopontine nucleus)
What makes up the leticular nucleus?
Putamen and globus pallidus
What makes up the neostriatum?
caudate nucleus and putamen
What is proprioception?
Awareness of the position in space, and of the relation to the rest of the body, of any body part.
Normally acquired unconsciously from sense receptors in the muscles, joints, tendons and the balance organ of the inner ear
How does the stretch reflex circuit work for muscle fibres?
Muscle stretched unexpectedly
Sensory signal from intrafusal causes correction of muscle length from extrafusal
Maintain muscle length and keep limb in same position
What innervates intrafusal fibres?
Gamma motor neurones
How does the withdrawal reflex work?
Cross-extensor reflex
Extension in one limb, withdrawal in the other
E.g. standing on a pin, withdraw one leg but tense the other so not to fall
Where are pyramidal cells (UMNs)?
Layers 5-6 of grey matter (in motor cortex)
Then project directly or indirectly (via brainstem) to spinal cord to synapse with LMNs
What is the dorsolateral corticospinal tract involved in?
Primarily involved in controlling distal limb muscles
What does the ventromedial corticospinal tract do?
Projects to proximal trunk and limb muscles
What can dysfunction of basal ganglia lead to?
Movement disorders
What does the basal ganglia receive and send out?
Receives excitatory input from many areas of the cortex
Inhibits activity via thalamus
Output mostly GABA / Inhibitory
What is the cortical input to cerebellum?
Copies of motor commands from MC
Somatosensory and visual input
Computes motor error and adjusts back to MC (updates motor plan for correct execution)
How can you measure the ANS?
CVS- HR and BP, Tilt table, baro-reflex by phenylephrine
Pupillometry
Sweat measurement
Skin blood flow, thermoregulation
Gastric acid secretion
Sexual function
What is the vestibular apparatus’s function?
important for balance and detecting movement of the head
What happens if any of the extra-occular muscles are paralysed / weak?
Diplopia (double vision)
How many EOMs are there are what do they do?
7 muscles, control the movement of the eyes
Inside the orbit, attached to the outer surface of the eyeball
Allow us to move our eyes without moving our head
What is the function of levator palpabrae superioris (LPS)?
Lifts the upper eyelid
Inserts into upper eyelid
Innervated by oculomotor and symp fibres
Which muscles move the eye?
medial rectus (MR)
lateral rectus (LR)
superior rectus (SR)
inferior rectus (IR)
superior oblique (SO)
inferior oblique (IO)
Which 3 cranial nerves innervate the EOMs?
CN III – Oculomotor
CN IV – Trochlear
CN VI – Abducens
What does the trochlear nerve innervate?
superior oblique
Which EOM does abducens innervate?
lateral rectus
Which EOMs does oculomotor innervate?
LPS, medial rectus, superior rectus, inferior rectus, inferior oblique
Where do the EOMs originate from?
Attached to the orbital bones
Insert into the sclera (except LPS)
LPS inserts into upper eyelid
What does a 3rd nerve injury cause?
drooping eyelid (ptosis)
What does medial rectus do?
moves the eye medially (adducts)
What does lateral rectus do?
moves the eye laterally (abducts)
What happens in an abducens nerve lesion?
Lateral rectus weakness / paralysis
Unopposed pull of medial rectus
Eye deviates medially
Diplopia
What does superior rectus do?
Primarily elevates the eye
Secondary function adducts and medially rotates
What does inferior rectus do?
depresses the eye
secondary function adducts and laterally rotates
What does superior oblique do?
primary - medially rotates the eye
secondary - depresses and abducts
What does inferior oblique do?
primary - laterally rotates the eye
secondary - elevates and abducts
Where are the sense organs for balance?
The semicircular ducts and utricle the contain sense organs for balance
What makes up the vestibular apparatus?
utricle and saccule
3 semicircular ducts - contain fluid
What makes up the inner ear?
Cochlea = sound
Vestibular apparatus = balance
What are the semicircular ducts?
Orientated at right angles to each other.
Contain fluid (endolymph).
Empty into a sac called the utricle
Balance and detect movement of the head
What happens in the ear when you move the head?
Endolymph, cupula and hair cells in the ampulla bend in the opposite direction
Info is sent centrally from right and left SC ducts
Via 8th cranial nerve
To nuclei in the medulla
What do connections in the vestibular nuclei control?
Posture
Balance
Conscious awareness of position
What is the oculocephalic reflex?
maintain fixed gaze when the head is moving
What does the orbitofrontal cortex do?
Involved in the processing of rewards and punishments
Receives and integrates inputs from all the sensory modalities, visceral sensory and visceral motor information
Important role in modulating motivational, emotional and social behavior.
What does the anterior cingulate cortex do?
autonomic and endocrine responses to emotion, and memory storage
What does the anterior cingulate cortex have connections with?
amygdala
periaqueductal gray
medio-dorsal and anterior thalamic nuclei
What does the posterior cingulate cortex do?
topokinetic memory circuit, with a primary function in visuospatial orientation
What does the mid cingulate cortex do?
predictions about the outcome of behaviour, and helps to execute said behaviour
reward-based decision making and cognitive activity associated with intentional motor control
What does the medial prefrontal cortex do?
motivation, spatial memory, bimanual coordination, self-initiated movements and focus
What does the lateral prefrontal cortex do?
provides the cognitive foundation for different patterns of behavior, orientation and reasoning.
helps in planning, the general and temporal organization of activities (e.g. daily routines), and switching from one task to another
What does the orbital prefrontal cortex do?
participates in impulse control, emotional processing, and social cognition
Two divisions of the forebrain (prosencephalon)
Telencephalon – cerebral hemispheres & basal ganglia
Diencephalon – thalamus, subthalamus, hypothalamus, epithalamus
What is the rhombencephalon?
Hindbrain
What does the tectum do?
visual/spatial and auditory frequency maps
the superior and inferior colliculi
What are the layers of the retina?
Pigment epithelium
Rod
Cone
Horizontal cell
Muller glia
Bipolar cell
Amacrine cell
Ganglion cell
Muller end feet
Structure of rods and cone segments
Outer segment contains discs containing light sensitive photopigment
Inner segment made up of cell body, axon and synaptic terminals
What are opsins?
transmembrane proteins which contain the light sensitive molecule retinal
Different opsin structures mean retinal absorbs different wavelengths of light
What are the 3 colour cones?
Red
Green
Blue
How does signalling work in the retina?
Photoreceptor synapses with bipolar cells
Synapse with retinal ganglion cells
Action potential
Horizontal and apocrine cells modulate signal
Do photoreceptors have a graded or non-graded response?
Graded
How does the pupillary light reflex work?
Light shines in one eye
Synapses in pretectal nucleus
Pretectal nuclei stimulate both sides of the efferent pathway (eddinger-westphal nuclei)
EW nuclei send action potentials down oculomotor nerves on both sides
Pupils constrict
What is the structure of the lacrimal gland?
Exocrine lobulated tubular acinar gland
Which gland is responsible for baseline tear formation?
accessory lacrimal glands
Which is the outermost layer of the tear film?
Lipid
What makes up the tear film?
Lipid layer: prevents evaporation
Aqueous layer: nourishes and hydrates, immune response
Mucus layer: lubricates, aids even distribution of tears
Which layers are mostly implicated in dry eye?
Lipid and aqueous
What does the central retinal artery supply?
Inner 2/3rds of eye (towards middle of eye)
Which arteries supply the eye?
Choroid (posterior ciliary arteries) supplies outer 1/3rd of retina
Inner 2/3rds via central retinal artery
Function of DCML?
Conscious proprioception
Discriminative touch
Function of spinothalamic?
spinothalamic tracts carry pain, temperature, non discriminative touch and pressure information to the thalamus
What makes up the basal ganglia?
Rostral part:
-striatum (caudate nucleus and putamen)
-globus pallidus (int and ext segment
Caudal part:
-subthalamic nucleus
-substantia nigra
What are the different circuits in the basal ganglia?
Motor circuit
Limbic circuit
Oculomotor circuit
What motor disorders are associated with basal ganglia?
Parkinson’s Disease
Huntington’s Disease
Dystonia
What psychiatric disorders are associated with basal ganglia?
OCD
ADHD
How do dopamine and GABA work together?
Dopamine promotes transmission from BG to cortex
GABA inhibits
Good balance in normal people
How is dopamine synthesised?
L-tyrosine to L-dopa to dopamine stored in pre-synaptic vesicles
What are the dopamine receptors?
D1,D5
D2,D3,D4
What is dystrophin?
A large protein
Confers stability to the muscle cell membrane
Deletion resulting in disruption of the reading frame results in Duchenne
How does neuromuscular transmission work?
- Nerve impulse results in the release of ACh from synaptic vesicles
- ACh binds to its receptor
Cation entry results in depolarisation - An action potential travels across the muscle cell membrane and into the T-tubule system
- Calcium is released from the sarcoplasmic reticulum leading to contraction
- Dissociated ACh is hydrolysed by acetyl cholinesterase in the NMJ
Describe pathway of DCML
1st order neuron to dorsal ganglion
Ipsilateral dorsal column:
- medial is gracilis fasicle for lower body
- lateral is cuneate fasicle for upper body
Ascend to medulla and synapse on 2nd order neuron
Decussate and form medial lemiscus
To the thalamus where synapse with 3rd order
Internal capsule to the primary somatosensory cortex
What is the general structure of the ascending tracts?
1st order neurones in dorsal root ganglia gather sensory input
2nd order neurones in spinal cord/brainstem
3rd order neurones in thalamus
4th order neurones in cortex
What does DCML carry?
Vibration
Proprioception
2-point discrimination
Touch
What does spinothalamic carry?
Crude touch
Pain
Pressure
Temperature
What does the lateral spinothalamic tract carry?
Pain
Temp
What does the anterior spinothalamic tract carry?
Crude touch
Pressure
How does spinothalamic run?
Receptor to 1st order neurone to dorsal root ganglion
Ascends 1-2 segments ipsilaterally
Interneuron in dorsal horn to 2nd order neuron
Decussate and ascend through contralateral spinal cord to contralateral thalamus
3rd order neuron to primary somatosensory
How does the spinocerebellar tract run?
1st order neurons to dorsal root ganglion
2nd order neurons in grey matter and splits in 2
Dorsal spinocerebellar runs ipsilaterally to inferior cerebellar peduncle and cortex
Other path decussates and becomes ventral
Ventral runs to superior cerebellar peduncle and decussates again
Both end up in ipsilateral cortex
Where is the ventral spinocerebellar tract?
Lateral to spinothalamic
What does the spinocerebellar tract do? (an ascending tract)
Carries unconscious proprioceptive sensations (e.g. how flexed something is)
Helps coordinate muscles in trunk and limbs
What are pyramidal cells?
UMN of direct motor pathways
Axons make multiple tracts
In cortex
What do descending pathways do?
Control muscles of trunk and extremities
UMN and LMN
Where are UMN found?
Cerebral cortex and deep nuclei of brainstem
Where are LMN found?
Ventral horns of spinal cords
What do pyramidal (direct) tracts do?
Fine, conscious muscle movements
How does the anterior corticospinal tract run? (descending)
Descends through internal capsule and cerebral peduncle to spinal cord
Decussates at the desired segment
Synapses with LMN in ventral horn
LMN leave spinal cord through ventral route to muscles of trunk
What does the anterior corticospinal tract do?
Controls muscles of trunk
How does the lateral corticospinal tract run?
Internal capsule and cerebral peduncle to medulla
Decussates at decussation of pyramids in medulla
Descends down contralateral spinal cord
Synapses with lower motor neurons in ventral horn
Leave via ventral root to muscles of extremities
Where is the anterior corticospinal tract in spinal cord?
medial to anterior spinothalamic tract
Where is the lateral corticospinal tract?
Medial to posterior spinocerebellar tract
How does corticobulbar run?
Motor cortex to brainstem
Axons leave tract and synapse with contralateral LMN for CN V,VII,XI,XII
In the indirect pathways, where do the UMN originate from?
Deep nuclei of brainstem
What do the extrapyramidal tracts do?
Innervate larger muscles for maintaining balance, posture and movement
What does the lateral vestibulospinal tract do?
Extensor musclesof trunk and extremities, for balance
E.g. extend other leg if one leg is tripping
What does the reticulospinal tract do?
Transmits motor input for extensor muscles to help maintain balance
What is the reticular formation important for?
Sleep
Alertness
Cardiovascular control
UMN for reticulospinal tracts
What does the tectospinal tract do?
Motor impulses for the neck muscles
Move head so eyes can follow moving object
What does the rubrospinal tract do?
Motor impulses for flexor muscles of extremities
Smoother more coordinated conscious movements
What do dendrites do?
Receive input and transmit it to cell body
Where does the axon arise from?
Axon hillock
What are the ascending tracts responsible for?
relaying sensory information from the PNS to the brain
What are descending tracts responsible for?
descending tracts send motor signals from the brain to lower motor neurones
What do neuromodulators do?
alter the strength of transmission between neurons by affecting the amount of neurotransmitter that is produced and released
What does glutamate do?
excitatory neurotransmitter
learning and memory
What does acetylcholine bind to?
Nicotinic receptors at NMJ
Muscarinic receptors
What does the afferent part of the PNS do?
Sensory neurones from receptors to CNS
What does the efferent part of the PNS do?
Motor neurones from CNS to effector
In the sympathetic nervous system, what do preganglionic and postganglionic neurones use?
Preganglionic: ACh
Postganglionic: noradrenaline
Exception is sweat glands and chromaffin cells in adrenal medulla
In the parasympathetic NS what do preganglionic and postganglionic neurones use?
ACh
Where is the sympathetic NS distributed in the spinal cord?
Thoracolumbar
Where is the parasympathetic NS distributed in the spinal cord?
Craniosacral
What is sensory transduction?
converting a sensory signal into an electrical signal
What are tonic receptors?
slow adapting receptors
duration of stimulus
What are phasic receptors?
rapidly adapting receptors
conveys information about the changes to the stimulus such as intensity
Pathway of a LMN
Cell body in ventral horn of CNS
Axon exits CNS into somatic NS
Terminates on a muscle fibre
What do LMNs do?
Cause contraction of muscle fibres
What do gamma motor neurons do?
regulation of muscle tone and maintaining nonconscious proprioception
What is damaged in a lower motor neuron syndrome?
damage to α-motor neurons only
What are some LMN signs?
Hyporeflexia/ areflexia
Hypotonia/ atonia
Flaccid muscle weakness or paralysis
Fasciculations
Muscle atrophy
What root level does biceps reflex test?
C5/C6
What root level does brachioradialis reflex test?
C6
What root level does extensor digitorum reflex test?
C6-7
What root level does triceps reflex test?
C6-8
What root level does patellar reflex test?
L2-4
What root level does achilles reflex test?
S1/2
What are UMN?
a neurone whose cell body originates in the cerebral cortex or brainstem and terminates within the brainstem or spinal cord
What is the pathway for UMN?
UMN will synapse with an LMN, which will synapse onto a muscle (for example).
All UMNs exert their effects via LMNs
What NT is typically involved in the transmission from upper to lower motor neurones?
Glutamate
What are UMN signs?
Hypertonia
Hypertonia
Spasticity
Positive babinski sign
Clonus
What is the main NT in basal ganglia direct pathway?
Glutamate
What is the main NT in basal ganglia indirect inhibitory pathway?
GABA
Where does motor info go from cortex?
From cortex to striatum to thalamus
Back to cortex via direct or indirect
How does the direct pathway work?
Cerebral cortex sends excitatory signals to striatum
Striatum send inhibitory signals to inter globus pallidus
IGP would normally inhibit thalamus, but since it’s inhibited, cancelled out
Thalamus free to send excitatory signals to cortex
How does the indirect pathway work?
Cortex sends excitatory to striatum
Striatum sends inhibitory to external globus pallidus
EGP cannot inhibit subthalamic nucleus
STN sends excitatory signals to the internal globus pallidus
IGP inhibits the thalamus
What is dopamines effect on the direct pathway?
Binds to D1 receptors- excitatory
Project to IGP
Activates direct
Favours excitatory
What does dopamine bind to in the indirect pathway?
Binds to D2 receptors- inhibitory
What does the substantia nigra release?
Dopamine
What is brown sequard?
Complete hemisection of spinal cord
What spinal tracts are damaged in brown sequard?
DCML ipsilateral
STT contralateral 1-2 segemnts below, ipsilateral at level of
What are the symptoms of brown-sequard and why?
Loss of fine touch, pressure, vibration, proprioception on ipsilateral side from dorsal column dmaage
Loss of pain, temp and crude contralateral 1-2 segments down from STT
At level of lesion, STT damaged ipsilaterally so complete loss of cutaneous sensation
