Neuro physiology Flashcards
What are the divisions of the nervous system
Central Nervous System - (Brain and Spinal Cord) Peripheral Nervous System - Cranial and Spinal nerves Sensory (afferent) division Motor (efferent) division Somatic motor and Autonomic Autonomic - Sympathetic and parasympathetic
2 different cell types in the NS
Neurons - excitable cells, impulses carried as AP
Glial cells - non-excitable supporting cells, much smaller than neurones
What is in the nucleus of a neuron
loose chromatin
prominent nucleolus
What cell organelles are present in a neuron
mitochondria, rER, diffuse Golgi apparatus
What does the myelin sheath do
increase conduction speed in axons by “saltatory conduction”
What forms the myelin sheath
Schwann cells in PNS
Oligodendrocytes in CNS
What types of neurones are interneurones and motor neurons
Multipolar
What type of neurons are olfactory mucosa and retinal nerve fibres
Bipolar
What type of neuron is a sensory neurone
Pseudounipolar
What type of neuroglia cells are found in the PNS
Satellite cells (surround neural cell bodies) - they contain Schwann cells (myelination)
What type of neuroglia cells are found in the CNS
Ependymal cells (line ventricles) - they contain astrocytes, oligodendrocytes and microglia
What is the blood brain barrier
A protective mechanism that helps maintain a stable environment for the brain and prevents harmful amino acids and ions present in the bloodstream and blood cells from entering the brain.
What is present in the blood brain barrier
- endothelium - tight junction
- thick basal lamina
- foot processes of astrocytes
In what part of the brain is the BBB absent
Parts of hypothalamus and posterior pituitary
Where do the lateral ventricles lie
C - shaped cavities which lie in the cerebral hemispheres
Where does the cerebral aqueduct lie
Midbrain
Where does the diamond-shaped 4th ventricle lie
Hindbrain
between pons, medulla and cerebellum
Where does the 3rd ventricle lie
Cavity within the diencephalon
How many ventricles are in the cerebral hemispheres
x2
lateral ventricle x2
Describe dura mater
tough, fibrous and has dural folds
Describe pia mater
vascularised and dips into the folds of the brain
Describe subdural space
potential space which is traveled by blood vessels penetrating into the CNS
What does the subarachnoid space contain
CSF
What is CSF
Fluid inside the cavity of brain and central canal of spinal cord
some extent responsible for the maintenance of intracranial pressure
Where is CSF present
Inside ventricles
Between pia and arachnoid
Where is CSF formed
By choroid plexus in each ventricle
Where is CSF absorbed
By arachnoid villi into saggital sinus (venous channel in brain)
What is the vestibular system
Sensory system essential in the control of posture and balance.
Where is the vestibular system located
Inner ear - series of fluid filled membraneous tubes, embedded in the temporal bone.
What does the vestibular apparatus consist of
3 semi-circular canals, the utricle (contain sensory hair cells) and the saccule
What are the otolith organs
Utricle and saccule
What do the otolith organs detect
Linear acceleration and encode information about the position of the head in space.
Utricle - back/front tilt
Saccule - vertical movement
What do the semi-circular canals detect
rotational acceleration
Where are the sensory cells of the semi-circular canals embedded
In swellings at the base of the bony canals called ampulla
What is in the ampulla
cristae - sensory receptors
cupola - responds to movement of the endolymph fluid within the canals
If the skull is rotated left or right from rest what happens to the endolymph and ampulla
Endolymph at first doesn’t move because of its inertia
Ampulla moves instantly because its embedded in the skull
What happens to the endolymph when the head is rotated at constant velocity
Inertia of the endolymph produces drag - the endolymph then catches up and rotates at the same speed, removing the shearing forces, takes several seconds.
What does sudden stop of head movement cause
Endolymph will continue due to momentum creating a continuing sensation of movement and dizziness
Distortion of the cilia in the direction of the kinocilium causes what
depolarisation and increased discharge of APs in the vestibular nerve
Distortion of the cilia away from the kinocilium causes what
leads to hyper polarisation and decreased discharge of APs in the vestibular nerve
What is the maculae
sensory apparatus of utricle and saccule
What does the tonic labyrinthine reflex do
Keep the axis of the head in a constant relationship with the rest of the body. Use information from maculae and neck proprioceptors
What does the Dynamic righting reflexes do
Rapid postural adjustments that are made to stop you falling when you trip. Long reflexes involving extensions of all limbs
What does the vestibule-ocular reflexes do
Strong association between vestibular apparatus, the visual apparatus and postural control.
What is a static reflex
When you tilt your head, the eyes intort / extort to compensate, so that over a certain range, the image stays the right way up
What is dynamic vestibular nystagmus
A series of saccadic eye movements that rotate the eye against the direction of rotation of the head and body so that the original direction of gaze is preserved despite head rotating.
What is the direction of nystagmus
The direction of rapid flick back R rotation = R nystagmus
What is Caloric stimulation
Simple test for horizontal SCC. Outer ear washed with cold or warm fluid - temp difference from core gets through thin bone and sets up convection currents which affect endolymph. Warm = towards affected side
Cold = away from affected side
COWS
When is motion sickness most likely to occur
If visual and vestibular system inputs to the cerebellum are in conflict.
What is vertigo
The perception of movement in the absence of movement. Gross impairment of posture and balance.
What is Meniere’s disease
Vertigo, nausea, nystagmus and tinnitus. Overproduction of endolymph causing increase pressure.
General features of the cerebral hemispheres
Grey matter on the surface
White matter inside
Lateral ventricle is the cavity in each hemisphere
The posterior part of the cerebral hemisphere is what?
Sensory
The anterior part of the cerebral hemisphere is what?
Motor
What do the medial portions of the cerebal hemisphere do
Storage and retrieval of processed information
What is area 4 of the frontal lobe
Pre central gyrus - primary motor cortex - somatotopic representation of contralateral half of body.
What is the inferior frontal gyrus
Broca’s area of motor speech
What is the prefrontal cortex
cognitive functions of higher order intellect, judgement, prediction,planning
What is the post-central gyrus and where is it located
Areas 3,1,2 - primary sensory area. Receives general sensations from contralateral half of body. Somatotopic representation.
Located in parietal lobe.
What is the superior parietal lobule
Interpretation of general sensory information and conscious awareness of contralateral half of body.
What is the inferior parietal lobule
interface between somatosensory cortex and visual and auditory association areas. In dominant hemisphere, contributes to language functions
White matter is arranged in 3 columns, what are they
Posterior, lateral and anterior
Are ascending pathways sensory or motor?
sensory
Are descending pathways sensory or motor?
motor
What does the corticospinal / pyramidal tract carry
Carries motor impulses from motor cortex to skeletal muscles
What does the posterior / dorsal column carrie
Carries touch, tactile localisation, vibration sense, proprioception
What does the lateral spinothalamic tract do
Pain and temperature
What does the corticospinal tract do
Control of voluntary skilled movements.
Pathway starts from the motor cortex (Area 4).
Corticobulbar fibres go to contralateral cranial n nuclei.
Corticospinal fibres mostly cross in decussation of pyramids.
What does the posterior limb of Internal Capsule supply
Blood supply MCA
How many neurones are in the descending motor tract
2 neurones in pathway. These are called the upper and lower motor neurones respectively.
Decussates to the opposite side in the medulla.
What is the ventral horn a site of
lower motor neurons
How many neurones are in ascending spinal tracts
3 neurones between peripheral receptor and cortex
What does the posterior / dorsal column do
Carries sensations of fine touch, tactile localisation, vibration sense, proprioception.
The third order neutron starts from the thalamus and axon pass through the IC and radiate to the post-central gyrus (Area 2,1,3)
What does the Lateral spinothalmic tract do
Pain and temperature
First order neutron enters into the grey mater and ends at the same level.
What is a reflex
Involuntary stereotyped pattern of response brought about by a sensory stimulus.
5 steps in the stretch reflex
important in control of muscle tone and posture
- Tendon stretched
- intrafusal muscle fibres stimulated
- sensory neuron activated
- Monosynaptic reflex arc
4b. Polysynaptic reflex arc to inhibitory interneuron - Muscle contraction
5b. Reciprocal innervation
4 steps of the flexor reflex
- Pain stimulus
- Sensory neuron activated
- Polysynaptic reflex arc
- Flexion and withdrawal from noxious stimulus
4b. Crossed extensor response to contralateral limb (only in weight bearing limbs)
What happens to reflexes in LMN lesions
Mediates reflexes
What happens to reflexes in UMN lesions
Exaggerated
What happens to tone in an LMN lesion
Flaccidity
What happens to tone in an UMN lesion
Spasticity
Corticospinal tract:
Left UMN lesion at IC (above decussations) would cause paralysis of what side? What kind of reflex? And how would it affect tone?
Right sided paralysis
Hyper-reflexia
Increased tone
Corticospinal tract:
Left UMN lesion at upper cervical spinal cord would cause paralysis of what side? How would it affect reflexes? How would it affect tone?
Left sided paralysis
Hyper-reflexia
Increased tone
Corticospinal tract: Left LMN lesion would cause paralysis of what side? How would it affect reflexes? How would it affect tone?
Left sided paralysis
Absent reflexes
Flaccid
Posterior column:
Lesion above decussation causes what?
Contralateral sensory loss
Posterior column:
Lesion below decussation causes what?
Ipsilateral sensory loss
Lateral spinothalamic tract of Right side causes loss of what?
Pain and temperature from Left side of body
Posterior column of Right side causes loss of what?
Touch, pressure, proprioception from Right side of body
Where do the 2 ICA enter the skull
Through the carotid canal
Where do the 2 vertebral arteries enter the skull
Through foramen magnum
How is the circle of willis formed?
Branches of the ICA join with those of the opposite side and with the PCA (branch of basilar artery) to form a continuous circle at the base of the brain.
What arteries supplying the brain are branches of ICA
Anterior cerebral artery
Middle cerebral artery
Posterior communicating arteries
What do the 2 vertebral arteries join together to form
Basilar artery on the ventral surface of the brainstem
Where does the basilar artery end
Level of the midbrain by dividing into 2 posterior cerebra arteries - supplying posterior part of cerebral hemispheres
Cerebral blood supply:
Anterior cerebral supplies what?
Medial aspect of cerebral hemispheres excluding occipital lobe
Middle cerebral artery supplies what?
Lateral aspect of cerebral hemispheres
Posterior cerebral artery supplies what?
Inferior aspect of cerebral hemispheres and occipital lobe
Where do the dural venous sinuses ultimately drain into?
Internal Jugular Veins
Brainstem centres produce what?
The rigidly programmed autonomic behaviours essential for survival
What are the 2 main functions of the cerebellum
- Posture maintenance
2. Fine tuning motor activity
What is the main function of the thalamus
Sensory relay station
What is the function of the hypothalamus
It is the main visceral control centre and is essential for overall homeostasis
Homeostatic Role of hypothalamus
Autonomic control centre Body temp regulation regulation of food intake regulation of water balance and thirst regulation of sleep wake cycle control of endocrine system functioning
What is refraction
Bending of light when it passes from one optical medium to another
How does a sharp image form on the retina
Light waves bend at the cornea, bend some more at the lens to form a clear image on the retina.
What happens to the lens when an object comes closer
Lens becomes thicker and hence more powerful, and a clear image is formed on the retina again.
What part of the eye is the most powerful bender of light
Cornea but lens has the capacity to change its “bending power”
What is Accommodation
The changes occurring in both eyes as it changes focus from a distant to a close object
What 3 things happen simultaneously and comprise accommodation
Lens changes shape (ciliary body contraction)
pupil constricts
eyes converge
What is the Pupillary constrictor (sphincter papillae)
Concentric muscle around the border of the pupil which gets parasympathetic innervation (IIIn)
What muscles do we use to converge
Medial rectus of both eyes
What is myopia
Short-sightedness
What is hyperopia
long-sightedness
What is astigmatism
non-spherical curvature of cornea (or lens)
What is Presbyopia
Long-sightedness of old age
What is phototransduction
The conversion of light energy to an electrochemical response by the photoreceptors (rods and cones)
What visual pigment is present in the lamellae of rods
Rhodopsin
What visual pigment is present in the lamellae of cones
Opsins S,M and L
What role does vitamin A play in the visual pigment
visual pigment regeneration
How does bleaching of the visual pigment result in phototransduction
Phototransduction cascade
Any condition that affects Vitamin A absorption will affect what? and why?
Vision - Because Vit A is supplied through the diet.
Vit A is essential for healthy epithelium - so conjunctiva and corneal epithelium are abnormal.
What are bitot’s spots
In the conjunctiva and are sometimes the first indication of Vit A deficiency
Why does sleep occur
Due to active inhibitory processes that originate in the pons.
What is the SCN and if it is stimulate what happens
Suprachiasmatic nuclei
Electrical stimulation - can promote sleep and damage to the SCN disrupts the sleep-wake cycle.
Activity in the SCN stimulates release of what?
melatonin from the pineal gland - corresponds to feeling of sleepiness in humans
Where does the activity of sleep originate?
What do neurons in this area of the brain do?
Reticular formation - many neurons here block serotonin formation inhibit sleep suggesting serotonin critical to sleep induction.
What is serotonin a precursor of?
Melatonin
What excitatory neurotransmitter does the hypothalamus release?
what is it required for
Orexin - active during waking state and stop firing during sleep.
Required for wakefulness
What causes narcolepsy?
Defective orexin signalling
How do you assess level of consciousness in an awake person?
Look at their behaviour, general alertness, speech patterns, speech content, reading, writing, and calculating skills.
What is an EEG?
Electroencephalogram
Uses electrodes placed on the scalp to record activity of underlying neurones.
In the relaxed, awake state the EEG is characterised by what?
High frequency, high amplitude - waves termed alpha waves.
In the alert, awake state the EEG is characterised by what?
Higher frequency, low amplitude - waves termed beta waves.
When do theta waves occur?
Low frequency - vary enormously in amplitude.
common in children, sometimes during emotional stress and frustration in adults. Occur during sleep too.
When do delta waves occur?
Deep sleep - very low frequency but high amplitude.
Sleep Cycle:
Stage 1 -
Slow wave, non-REM, S-sleep. slow eye movement. Light sleep. Easily roused.
High amp, low frequency theta waves.
Sleep cycle:
Stage 2 -
Eye movements stop. Frequency slows further but EEG shows bursts of rapid waves called “sleep spindles”
Sleep cycle:
Stage 3 -
High amplitude, very slow delta waves interspersed with short episodes of faster waves, spindle activity declines - deep sleep
Sleep cycle:
Stage 4 -
Exclusively delta waves
- deep sleep
Sleep cycle:
REM sleep
Rapid eye movements.
Fast waves, similar to awake state.
Paradoxical sleep. Dreams occur during REM - 25% sleep is REM.
Does REM have an important physiological factor?
Yes, eye muscles show bursts of rapid activity. Profound inhibition of all other skeletal muscles due to inhibitory projections from pons to spinal cord.
What are the main functions affected with lack / no sleep
Impairment of cognitive function
Impairment of physical performance
Sluggishness
Irritability
Sleep supports what functions?
- Neuronal plasticity
- Learning and memory
- Cognition
- Clearance of waste products from CNS
- Conservation of whole body energy
- Immune function
What is insomnia?
Chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour.
What are the drugs prescribed for insomnia?
Barbiturates - depress REM and delta sleep.
Benzodiazepines - addictive.
What are night terrors and when do they occur?
Deep sleep, delta sleep common in children 3-8.
What four systems control movement?
- descending control pathways
- basal ganglia
- cerebellum
- local spinal/brain stem circuits
Sensory input is crucial and enters at all levels:
At the spinal cord what does it do?
Form of proprioceptors, touch, pain etc.
Sensory input is crucial and enters at all levels:
At the brainstem what does it do?
Vestibular system informs about balance
Sensory input is crucial and enters at all levels:
At cortical level what does it do?
Make movements in response to visual, olfactory, auditory, emotional, intellectual cues.
What happens when their is damage to sensory inputs?
Paralysis as if the motonuerones themselves had been damaged.
Motor control is a functional hierarchy with 3 levels, what are the 3 levels? and what structures are involved?
High - Strategy - Association neocortex, basal ganglion
Middle - Tactics - Motor cortex, cerebellum
Low - Execution - Brain stem, spinal cord
Describe strategy
The goal and the movement strategy to best achieve this goal
Describe tactics
The sequence of spatiotemporal muscle contractions to achieve a goal smoothly and accurately
Describe execution
Activation of motor neuron and interneuron pools to generate goal-directed movement
What do lateral pathways control?
Control voluntary movements of distal muscles - under direct cortical control
What do ventromedial pathways control?
Control posture and locomotion - under brain stem control
Cortocospinal tract (CST) - where does it originate?
2/3 originates in areas 4 and 6 of the frontal motor cortex - rest is somatosensory
What side of the body does the right motor cortex control?
Left side
What side of the body does the left motor cortex control?
Right side
Where does the rubrospinal tract start?
And where does it receive input from?
RST starts in the red nucleus of midbrain
Receives input from same cortical areas as the CST.
If you have a lesion on CST and RST what movements are lost?
Fine movements of arms and hands are lost. Cant move shoulders, elbows, wrist and fingers independently.
If the lesion is CST alone what happens?
Same deficits as both but after a few months function reappears
If the lesion gets taken over by RST what happens?
Lose restored functions
What are the 2 lateral pathways that control voluntary movements?
Corticospinal tract and Rubrospinal tract
What do CST axons control?
Pools of spinal motor neurons
Explain how the CST controls pools of spinal motor neurons
- Monosynaptically excite pools of agonist motoneurones.
- The same pyramidal neurones branch and via interneurones inhibit pools of antagonist motoneurones
What are the 2 ventromedial pathways?
Vestibulospinal and Tectospinal
What do the 2 ventromedial pathways control?
Posture and Locomotion
- VST = stabilises head and neck
- TST = ensures eyes remain stable as body moves
What are the 2 ventromedial pathways?
Pontine and medullary reticulospinal tracts
What do ventromedial pathways control?
Trunk and antigravity muscles
- reflexly maintain balance and body position.
What do primary motor cortex and pre-motor areas do?
Plan and control precise voluntary movements
Upper motor neurons in cortex and brainstem target what in the spinal cord?
Lower motor neurons
What do medial tracts from brainstem control?
Posture, balance and orienting mechanisms
What do lateral tracts from cortex control?
Precise skilled voluntary movements
Where is the primary motor cortex located?
Pre central gyrus - (area 4)
Where does the mosaic of premotor area lie?
Rostrally (towards nose)- area 6 for premotor and supplementary motor.
Somatotopic maps of body:
What happens when systematic probing of area 4 happens?
Primary motor cortex revealed somatotopic organisation of pre central gyrus like that in somatosensory areas of post central gyrus.
What do neurones in area 6 do?
Drive complex movements on either side of the body
- Also somatatopically organised with 2 motor maps in area 6 - one premotor one supplementary motor.
The somatotopic map is not precise, why?
It doesn’t represent upper motor neurones causing individual muscle movements
What generates mental image of body in space?
Somatosensory, proprioceptive and visual inputs to posterior parietal cortex. (areas 5 and 7)
co-ordinating body movements:
What happens in the prefrontal and parietal cortex?
Decisions are taken, so what actions/movements to take and their likely outcome
Axons from prefrontal and parietal cortex converge where? and what does this allow?
Converge on area 6
Here signals encoding desired actions are converted into how to carry this out.
When is area 4 activated?
When you’re DOING the movement - activating neurones of the CST and RST.
Deciding the direction of a movement is caused by what cortex?
Directional tuning in the primary motor cortex (area 4)
Where are commands for precise movements encoded?
Integrated activity of large populations of neurones in M1.
What mechanisms control movement? And where does the information come from?
Feedback - From brainstem vestibular nuclei to spinal cord motor neurones to correct postural instability.
Feedforward - in brainstem reticular formation nuclei)
What is the basal ganglia motor loop do? And how does it do this?
Selects and initiates willed movements.
Major subcortical input to area 6 from ventral lateral nucleus in dorsal thalamus.
So a loop from cortex through thalamus and basal ganglia and back to SMA cortex (area 6)
What are the major components of basal ganglia?
Corpus striatum - caudate and putamen nuclei - input zone.
Corticostrital pathway - multiple parallel pathways with different functions.
When does the putamen and caudate fire?
Putamen - before limb/trunk movements
Caudate - fires before eye movements.
Both predictive of movements
What do globus pallid neurones do at rest?
Spontaneously active and inhibit VLo
What does cortical excitation do?
excites putamen - inhibits globus pallidus - boosting VLo and SMA activity.
Positive feedback loop.
Direct pathway in basal ganglia does what?
Acts as positive feedback loop - Go signal to SMA in cortex.
Indirect pathway in basal ganglia does what?
Antagonises the direct route - cortex excites STN; this excites Gpi; which inhibits thalamus.
What is the direct pathway via?
Caudate and putamen
What is the indirect pathway via?
subthalamic nucleus
What is hypokinesia?
slowness, difficult to make voluntary movements, increased muscle tone (rigidity), tremors of hand and jaw.
What causes hypokinesia?
Degeneration of neurones in the substratia nigra
What effects can dopamine have on the 1.direct and 2. indirect pathway?
- Can enhance cortical inputs
2. Suppress inputs
What makes up the portico-ponto-cerebellar projection?
Layer 5, areas 4&6, somatosensory cortex.
Cerebellum back to cortex via ventrolateral thalamus does what?
Cerebellum instructs direction, timing and force.
Sensory receptors: how is it so specific?
Each type of sensory information is associated with a specific receptor type responding to a specific sensory modality
What do sensory receptors respond to?
Respond to stimulus over a specific area, called the receptive field
Signal transduction: What encodes the location of a stimulus?
Receptive field
Signal transduction: What encodes intensity of stimulus?
Size of receptor potential and frequency of APs
What is acuity and what determines it?
Acuity - how well it responds to stimuli
Density of innervation and size of receptive fields determines acuity.
What are the 3 types of primary afferent fibres?
A beta = large myelinated - touch, pressure, vibration
A delta = small myelinated - cold, “fast” pain and pressure
C = unmyelinated fibres - warmth, “slow” pain
What is proprioception mediated by?
2 types of primary afferent fibres - A alpha & A beta (muscle spindles, golgi tendon organs)
*all enter spinal cord via the dorsal root ganglia
Mechanoreceptive fibres (Aa & AB): where do they project and synapse?
- project straight up through ipsilateral dorsal columns
- synapse in cuneate and gracile nuclei
- the 2nd order fibres cross over midline in the brain stem and project to reticular formation, thalamus and cortex
Thermoreceptive &nociceptive (Adelta & C) fibres: Synapse and projections?
- synapse in the dorsal horn
- the 2nd order fibres cross over the midline in the spinal cord
- project up through the contralateral spinothalamic (anterolateral) tract to reticular formation, thalamus and cortex
What does damage to dorsal columns cause?
Causes loss of touch, vibration, proprioception below lesion on ipsilateral side
What does damage to anterolateral quadrant cause?
Causes loss of nociceptive & temperature sensation below lesion on contralateral side
Where is the ultimate termination of sensory information?
Somatosensory cortex (S1) of the post central gyrus Produces the sensory homunculus
Processing in sensory pathways: What are the 5 components?
adaption convergence lateral inhibition not all information reaches the brain perception
Describe convergence
- Saves on neurones
- reduces acuity
- underlies referred sensation
Describe later inhibition
- Activation of one sensory fibre causes synaptic inhibition of its neighbours
- gives better definition of boundaries
- cleans up sensory information
Signal transduction in nociceptors is activated by?
- Low pH, heat
- local chemical mediators
What are Analgesia?
Non-steroidal anti-inflammatory drugs (NSAIDs)
- prostaglandins sensitise nociceptors to bradykinin
What do NSAIDs do?
Inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins
Describe what local anaesthetics do
Block Na AP and therefore all axonal transmission
Describe what opiates do
- Reduce sensitivity of nociceptors
- Block transmitter release in dorsal horn (epidural admin)
- Activate descending inhibitory pathways
What is cognition?
Integration of all sensory information to make sense of a situation (highest order of brain function)
What are the 3 key components of learning and memory?
Hippocampus - formation of memories
Cortex - storage of memories
Thalamus - searches and accesses memories
*require all 3 for normal memory to take place
What makes up the limbic system?
Hypothalamus (assoc. with ANS responses)
Hippocampus (assoc. with memory)
cingulate gyrus and the amygdala (assoc. with emotion)
