Neurology Flashcards
explain how information we receive reaches the brain
tactile input is mechanical stimulation of the skin and the features can affect their transduction include:
- quality, type of touch
- magnitude, how big the touch
- duration, how long and how often
- location, where is the touch
information is converted to an electrical signal via modality specific sensory receptors and is transmitted via modality specific sensory pathways
so depending on the stimulus type there will be a specific pathway for it to follow
describe the different types of receptors in the human body
mechanoreceptors
- mechanical stimulus
- touch
thermoreceptors
- thermal stimulus
- temperature
nociceptors
- special sense
- noxious stimulus
- pain
chemoreceptors
- special sense
- chemical stimulus
- taste and smell
photoreceptors
- special sense
- light stimulus
- sight and vision
describe the transduction of stimulus: how we generate an electrical signal, and how it differs for different types of receptors
stimulus leads to change in receptor membrane permeability and an influx of cations
this leads to depolarisation of the receptor potential which generates an action potential
different receptors have different kinetics and modalities
ionotropic receptors
- fast
- mechano and chemoreceptors
ionotropic mechanoreceptors
- ion channel in the membrane is tethered by fibrils on the intracellular aspect
- mechanical stimulus deforms the membrane and pulls on the fibrils
- channel opens
ionotropic chemoreceptors
- channel in the membrane forms a pore
- diameter of pore is too narrow when inactive for ions to pass
- ligand binding to extracellular surface opens the pore and allows ions to pass
g coupled receptors
- slow
- chemoreceptors
g coupled chemoreceptor
- pore is closed when inactive
- specific ligand will bind and cause an intracellular signalling pathway that opens the pore
- the ligand binding site has many proteins attached to it and is therefore a more complex procedure and takes more time
describe the coding of stimulus properties
quality codes for type of receptor
magnitude codes for action potential frequency and number of neurons activated
duration codes for the duration of action potential firing
location codes for the receptive field that is activated
intensity is coded by the number of neurons activated
describe the different receptors in the skin and the stimulus they pick up
meissners corpuscles
- dermal papilla
- fine touch
merkels discs
- stratum basale
- superficial pressure and fine touch
pacinian corpuscles
- dermis and hypodermis
- pressure and vibration
peritrichial nerve endings
- wrap around hair follicles
- detect movement of the hair
ruffini corpuscles
- stretch and vibration
describe the different axon features and how this determines their function
a alpha axon
- largest axon
- 13-20micrometer diameter
- thick myelin sheath
- 80-120 metres per second
- detects proprioreception in the skeletal muscles
a beta axons
- large axon
- thick myelin sheath
- 6-12 micrometer diameter
- 35-75 metres per second
- mechanoreceptors in the skin
a delta axons
- thin diameter
- thin myelin sheath
- 1-5 micrometer diameter
- 5-30 metres per second
- pain and temperature
- fast pain - sharp and stabbing and localised
c fibres
- thin axon
- no myelin
- 0.2-1.5 micrometer diameter
- 0.5-2 metres per second
- temperature, pain, itch
- second pain - slow pain - dull and aching, non localised
describe the pathways for each type of sensation
somatic mechanosensation in the body
- dorsal colum medial leminiscal pathway
- primary neuron goes to dorsal grey matter and ascends spinal cord to brainstem
- synapse with second order that crosses over to other side of brainstem then goes to thalamus
- thalamus synapse with third order that goes to cortex
somatic mechanosensation in the face
- dorsal trigeminothalamic pathway
- axons project via trigeminal nerve to brainstem nucleus
- synapse with second order that crosses to opposite side - projects into thalamus
- connects with tertiary neuron that goes to cortex
- happens posterioly because it is not pain
somatic nociception in the body
- spinothalamic pathway
- free nerve endings come together and form an axon that goes into spinal cord and synapses at the dorsal horn of the spinal cord at same spinal level
- axon goes to opposite side and ascends through anterolateral funiculus to brainstem to thalamus
- third order then goes to cortex
somatic nociception in the face
- ventral trigeminothalamic pathway
- sensory fibres project via trigeminal nerve to the spinal nucleus in upper region of spinal cord
- synapse to second order then go to oppsite side and project to the thalamus
- thalamus third order go to cortex
describe how sensation and perception are linked
- sensation is the process of activating sensory receptors to sense the environment
- perception is the interpreation of that input
stereognosis
- mental perception of objects referenced by touch
- high level of cortical processing to retrieve previous experiene and generate a mental 3D image
proprioception
- kinesthesia, the ability to sense body position and self movement without seeing it
- based on receptors in muscle and skin and balance organs in the inner ear
describe which features of the skull are related to which cranial nerves
- Olfactory: through cribiform plate to nasal cavity
- Optic: optic foramen to the eye
- Oculomotor: cavernous sinus and superior orbital fissure to the eye
- Trochlear: alongside oculomotor
- Trigeminal: superior orbital fissure, foreman rotundum, foramen ovale for each three branches respectively
- Abudences: alongside oculomotor
- Facial: stylomastoid foramen
- Vestibulocochlear: through internal acoustic canal
- Glossopharyngeal: jugular foramen
- Vagus: jugular foramen
- Accessory: jugular foramen
Hypoglossal: hypoglossal canal to control movement of the tongue.
describe the basics of semi automatic actions and their control
voluntary movements that we do not think about
- repeated movement sequences: walking, breathing, chewing
- adaptable
- learned
- improved with practice
control of semi automatic actions
- central pattern generators specific to the action they initiate or maintain
- groups of neurons that produce rhythmic output to influence the motor patterns of specific muscle groups
- CPG are under sensory feedback, reflex feedback and central feedback.
- reflex feedback ensures the control from CPG are appropriate to the situation the individual is in
describe the pathways for responding to a sensation (ie movement production)
these are descending pathways rather than ascending pathways
upper neuron will descend through the internal capsule, and through the basis pedunculi into the midbrain. here it will recruit lower neuron for one of two pathways:
corticospinal pathway
- 85% in the lateral corticospinal tract
- 15% anterior corticospinal tract, but this is to mid thoracic region only
- neurons from the pyramidal decussation (cross over at brainstem) are in the lateral, those that do not are in the anterior.
- those that innervate distal muscles must originate from the opposite side of the brain.
corticobulbar pathway
- innervation of bilateral cranial nerve nuclei
- trigeminal nuclei for muscles of mastication, found in the trigeminal motor nucleus of the pons
- facial nuclei for the muscles of facial expression found in the facial motor nucleus in the pontomedullay junction
- vagus nuclei for the soft palate, larynx and pharynx found in the nucleus ambiguus at medulla
- hypoglossal nuclei for the extrinsic muscles of the tongue found in nucleus amiguus at the medulla
additional descending motor projections
- coordinate movement, maintain posture and balance, integrate actions of several muscles
- basal ganglia, cerebellum and brainstem
describe the basal ganglia
- several interconnected subcortical nuclei
- link to cerebral cortex via feedback loops
- influence and regulate the output from the motor cortex
- act to initiate and switch from action to another
body of caudate nucleus (lateral protrusion of the lateral aspect of the lateral ventricle)
putamen (base of forebrain, most lateral, medial to the external capsule)
globus pallidus (medial to putamen)
thalamus (lateral protrusion of third ventricle)
substantia nigra (posterior to thalamus)
form three different action selection centres
- corpus striatum (caudate, putamen, globus pallidus)
- sub thalamic nuclei
- substantia nigra
dopamine deficiency in substantia nigra leads to parkinsons
GABA deficiency in striatum leads to hungtintons disease
describe the gate control theory of pain
recruitment of a beta fibres by rubbing a wound recruits an interneuron that inhibits the primary neuron which prevents the stimulus travelling up the spinothalamic pathway
describe the stretch reflex pathway
stimulus activates mechanoreceptors
there is stimulus transduction along a alpha sensory axon (responsible for proprioception in muscle)
synaptic transmission and motor neuron recruitment
action potential conducted along the motor a alpha axon
synaptic transmission to recruit effector muscle
response produced
describe the pathway of the jaw jerk reflex
hammer tap to the chin
stretches spindles of the jaw elevator muscles (masster, temporalis, medial pterygoid)
action potentials conducted along group 1a muscle afferents with a alpha axon to brainstem
monosynaptic activation of motor neurons of jaw elevator muscles
axon potentials travel along motor axon a alpha
jaw elevator muscles contract
jaw jerks upward and the mouth closes
describe the details of the EMG recordings of jaw jerk and ankle jerk reflexes
latency for jaw jerk reflex is less than ankle because the neural pathway for the jaw jerk is shorter than the ankle jerk
amplitude for jaw jerk is less than ankle because the masseter is a smaller muscle than the gastronecmius and recruits less muscle fibrils
amplitude is the measure of electrical activity in skeletal muscle
