Last Minute Revision CNS Flashcards
Types of intrafusal fibres
- Nuclear bag fibres - nuclei aggregated as bags in the central portion
- Nuclear chain fibres - nuclei are arranged in single row
Sensory nerve supply of muscle spindle
- Annulospiral endings
2. Flower spray endings
Annulospiral endings
- 1a afferents
- end as a ring around central portion of nuclear bag and chain fibres
- both dynamic and static response
- respond both to changes in length and velocity of change
Flower spray endings
- A beta fibres
- only from nuclear chain fibres
- mainly static response
Static response
When receptor portion is stretched slowly number of impulses transmitted from both primary and secondary endings increases directly proportional to degree of stretching
Dynamic response
When length of receptor increases suddenly primary ending is powerfully stimulated and responds actively to rapid rate of change and spindle length but only while the length is actually increasing
Motor nerve supply
- Gamma 1 efferents - NBF dynamic
2. Gamma 2 efferents - NCF static
Mechanism of activation of muscle spindle
- Stretch of muscle causes stretch of spindle activating primary and secondary endings
- Activation of Gamma motor efferents
Functions of muscle spindle
- Participates in stretch reflex
- Regulation of muscle tone and posture by alpha gamma co activation
- Proprioception
- Monitors length of muscle
Alpha Gamma co activation
Alpha motor neurones and gamma motor neurones are stimulated simultaneously.
Causes for extrafusal and muscle spindle fibres to contract at same time.
1. Prevents activation of muscle spindle reflex
2. Maintains damping function
Brain areas controlling gamma motor system
- Reticular activating system
2. Signals from cerebellum, basal ganglia, cerebral cortex
Components of stretch reflex arc
- Muscle spindle
- Afferent sensory nerves
- Spinal cord
- Motor nerves
- Extrafusal fibres
Phasic stretch reflex
- dynamic
- activating primary endings
- causes contraction of muscle containing muscle spindle and inhibition of antagonistic muscle
- helps bring about movement
Tonic stretch reflex
- static
- activation of both primary and secondary endings
- causes steady contraction of muscle containing spindle
- for maintaining tone and posture
Location of Golgi tendon organ
- junction between muscle fibres and tendon
- detect tension in muscle
Functions of Golgi tendon organ
- Modulates muscle tension during movements
- Prevent muscle tear
- Inverse stretch reflex and lengthening reaction
Spastic gait
Lesion in pyramidal tract
Hemiplegia
Drunken gait
Cerebellar ataxia
Festinant gait
Parkinsonism
Bent forward moves in rapid shuffling steps
Stamping gait
Tabes dorsalis
Due to loss of sensory feedback to brain
High stepping gait
Weakness of extensor muscles of feet
Common peroneal nerve palsy
Waddling gait
Myopathies and muscular dystrophies
Body tilted back
Scissors gait
Congenital spastic paraplegia
Hypotonia seen in
- Destruction of motor fibres
- Destruction of dorsal columns
- Stimulation of inhibitory areas of brain
- Inhibition of facilitatory areas
- Sleep
- Thalamic and cerebellar lesions
- Barbiturates
Hypertonia seen in
- Stimulation of facilitatory areas
- Destruction of inhibitory areas
- Increase Gamma motor neuron activity
- Increase Alpha motor neurone activity
Spasticity
Lesion of pyramidal tract
Involves only one group of muscles
Clasp knife rigidity
Proportional to stretch
Rigidity
Lesion of basal ganglia Involve both agonists and antagonists Lead pipe rigidity No auto inhibition Resistance is present through passive movements
Cerebellar disorders
- Drunken gait
- Hypotonia
- Pendular reflexes
- Asynergia
- Dysmetria
- Intention tremors
- Asthenia
- Rebound phenomenon
- Dysdiadochokinesia
- Nystagmus
- Scanning speech
SIN AAA DDD
Functions of semicircular canals
- Give info about rotational movement of head
- Help maintain equilibrium
- visual fixation during angular rotation of head
Vestibulo ocular reflex
- Form stable image on retina during rapid head rotation
- producers conjugate movements of eyes in opposite direction of head rotation
- vestibular apparatus with 3rd, 4th, 6th cranial nuclear through medial longitudinal fasciculus
Optokinetic reflex
- Person viewing rapidly moving object from stationary position
- eyes move along stimulus till it disappears and return to original position rapidly
- superior colliculus with 3rd, 4th, 6th cranial nerves through medial longitudinal fasciculus
Functions of otolith organs
- Info about static position of head
- Respond to linear acceleration
- Utricle detect dorsiflexion and ventriflexion
- Maintain balance while jumping or walking down stairs
Main outlet for efferents of basal ganglia
Globus pallidus
Afferents of basal ganglia
Corticostriatal - ipsi., Frontal and parietal
Thalamostriate - intralaminar and centromedian
Internuclear connections of basal ganglia
Nigrostriatal
Nigropallidal
Striatonigral
Strialopallidal
Efferent connections of basal ganglia
Pallidothalamic via ansa fasicularis and ansa lenticularis
Nigrothalamic
Food intake hypothalamus
VMN - satiety centre
LN - feeding centre
Chorea
Destruction of GABA ergic neurons in caudate n.
- involuntary jerky mvmts of limbs, orofacial muscles
Sydenhams - in children due to rheumatic fever
Huntington’s - autosomal. Chorea + dememtia
Athethosis
Inability to fix muscles of fingers toes in one position
Destruction of GABA neurons in putamen
Appear as grasping mvmts
Ballism
Lesion in subthalamic body
Flinging involuntary mvmts of extremeties on opp. Side
Body temperature hypothalamus
Preoptic
Ant. Hypothalamus
Post. Hypothalamus
Preoptic nucleus receives info by
Blood flowing through hypothalamus
Cutaneous receptors of cerebral cortex
Anterior hypothalamus
Stimulus: When temp. Inc. Action: Cutaneous vasodilation Sweat secretion
Posterior hypothalamus
Stimulus: When temp. Dec. Action: Cutaneous vasoconstriction Rigors
Thirst hypothalamus
Preoptic LN Stimulus: Inc. tonicity Oral dryness ECF volume Dec.
Functions of hypothalamus
- Food intake reg.
- Body temp. Reg.
- Thirst reg.
- ECF volume reg.
- Endocrine
- Reproduction
- Reproductive behaviour
- Sleep wake cycle
- ANS control
- Emotion reg.
- Stress
- Circadian rhythm
- Reward punishment
Sleep wake cycle hypothalamus
Diencephalic sleep zone
Basal forebrain sleep zone
Slow wave sleep
Papez circuit
Ant. Thalamic nuclei -
Cingulate gyrus
Hippocampus
Mamillary bodies
Functions of limbic system
- Autonomic function
- Discriminative feeding
- Memory and learning
- Emotional behaviour
- Sexual behaviour
- Olfaction
- Reward punishment
- Maternal behavior
NREM sleep
Hypotonia Slow delta waves No rapid eye mvmts Dreams can't be recalled No pontogeniculooccipital spikes Low pulse, bp Low serotonin Sensory threshold Inc. Low brain activity Low O2 consumption
REM sleep
Reduced muscle tone Fast beta waves REM saccades Dreams recalled clearly Teeth grinding Pontogeniculooccipital spikes seen Irregular bp, pulse Noradrenaline Dec. Sensory threshold very high More brain activity More O2 consumption
Significance of evoked potentials
- Find integrity of pathway
- Auditory evoked potential to test hearing in newborn
- Understanding sensory connections
- Map centres for sensation
- Localise site of lesion
Focal seizures
- begin in localised region of cortex
- local to 1 hemisphere
- promote rapid neuronal discharges
- called Jacksonian March
- starts from particular area and spreads to adjacent areas
- usually by brain tumor
Generalized seizures
- cannot be referred to one hemisphere
Grand mal seizure
- sudden loss of consciousness followed by convulsions
- epileptic aura felt
- starts with tonic contractions followed by clonic
- EEG spikes
Petit mal seizure
- Sudden loss of consciousness
- no convulsions
- spike dome EEG
Parts involved in short term memory
Hippocampus Mamillary bodies Thalamus Amygdala Prefrontal cortex
Mechanisms of short term memory
Reverberating circuits
PTP
Presynaptic facilitation
Mechanism of long term memory
LTP
Physiological changes seen in LTP
- Change in the expression of postsyn. Neuron
- Inc. Synthesis and release of neurotransmitter
- Change in receptor response
Structural changes in LTP
- Formation of new connections
- Inc. no of releasing sites and receptor sites
- Change in neuroglial cells
Speech centres
Area 42, 18, 19, 39
Wernickes
Brocas
Functions of external ear
- Inc. sound pressure on tympanic membrane
- Sound collection, localisation
- Humid environment
- Prevents entry of foreign bodies
- Limits frequencies reaching tympanum
