Locomotion Flashcards
How do we convert a stimulus into an electrical action potential?
Via specific sensory receptors
What are the 4 properties of a stimulus?
Quality (type of receptor)
Intensity (AP frequency, number neurons activated)
Duration (duration of AP)
Location (where?)
What is the definition of a neurons receptive field?
Each neuron has a cluster of peripheral nerve branches, each with a nerve ending (Receptor)
The distribution of these receptors defines a neuron’s receptive field
Where are receptive fields the largest?
Large on the trunk
Small in the periphery
What is two point discrimination?
The ability to discern two separate mechanical stimuli
Areas with small 2-point discrimination = Areas with small receptive fields
How is an action potential produced?
Stimulus Change in receptor membrane permeability Influx of cations Depolarisation: Receptor potential Action potential
What is meant by intensity in sensory coding?
All action potential same
- Frequency of AP discharge
- Increase in stimulus intensity thus means increase in AP frequency
- Different receptors have different thresholds
Also means numbers of neurons activated
What is meant by a neural pathway?
Neural pathway is a connection formed by axons that project from neurons to make synapses onto neurons in another location, to enable a signal to be sent from one region of the nervous system to another.
What is a ganglion?
A group of nerve cell bodies located in the ANS or sensory nervous system.
They house the cell bodies of afferent or efferent nerves.
What are examples of cutaneous/subcutaneous mechanoreceptors and what type of axons are they?
- Meissner’s corpuscle
- Merkel disk
- Hair follicle receptors
- Pacinian corpuscle
- Ruffini’s ending
A-beta afferents
What is the brachial plexus?
Innervates the upper limb
Consists of the nerves
- Axillary
- Musculocutaneous
- Radial
- Ulnar
- Median
What is epineurium?
It is the outermost layer of dense irregular connective tissue surrounding a peripheral nerve
What are fascicles?
A small bundle of nerve fibres enclosed by the perineurium
What is the perineurium?
A protective sheath covering nerve fascicles
What are the features of A(ɑ) nerve fibres?
- Largest - diameter of 13-20 micrometres
- Fastest - conduction speed - 80-120m/sec
- Proprioreceptors (limb position) of skeletal muscle
What are the features of A(β) nerve fibres?
- Second largest - diameter of 6-12 micrometres
- Second fastest - 35-75m/sec
- Mechanoreceptors of skin
What are the features of A(δ) nerve fibres?
- Third largest - 1-5 micrometres
- Third fastest - 5-30m/sec
- Pain/Temperature
What are the features of C nerve fibres?
- Smallest - unmyelinated - 0.2-1.5 micrometres
- Slowest - 0.5-2 m/sec
- Temperature/pain/itch
What are dorsal and ventral roots?
Sensory axons enter CNS via dorsal roots
Cell bodies of sensory axons are located in the dorsal root ganglia (DRG)
Motor axons exit CND via ventral roots
What are the three neurons of a typical sensory pathway?
1st neuron - Primary sensory neuron - Periphery
2nd neuron - Secondary sensory neuron - CNS
3rd neuron - Tertiary sensory neuron - Thalamus
What is the primary neuron in the somatosensory pathway?
In the periphery, primary neuron is the sensory receptor that detects stimuli.
Cell body of primary neuron is located in the DRG of a spinal nerve, or, if sensation in head/neck the ganglia of the trigeminal or cranial nerves (trigeminothalamic tract)
What is the secondary neuron in the somatosensory pathway?
Secondary neuron acts as a relay and is located in either the spinal cord or the brainstem. This neurons axons will decussate to the opposite side of the spinal cord or brainstem and travel up the spinal cord to the brain.
What is the tertiary neuron in the somatosensory pathway?
Tertiary neurons have cell bodies in the thalamus and project to the postcentral gyrus of the parietal lobe, forming a sensory homunculus in the case of touch.
Regarding posture, the tertiary neuron is located in the cerebellum.
What is stereognosis?
The ability to recognise objects by ‘the feel’ alone
How can pain be classified?
- Nociceptive pain
- Clinical pain - acute or chronic
What fibres mediate nociceptive pain?
A-delta (noxious mechanical/heat) and C fibres (polymodal)
What is nociceptive pain?
Only elicited when intense/noxious stimuli threaten to damage normal tissue - protective function
Characterised by a high threshold and limited duration
What is acute clinical pain?
Results from soft tissue injury or inflammation - protective
What is chronic clinical pain?
Sustained sensory abnormality - e.g. chronic inflammation
Pain is maladaptive, offering no survival advantage
Resistant to treatment
What are 5 diagnostic features in pain?
Location Pain quality Pain intensity Frequency/duration Provoking/relieving events
What is referred pain?
Pain felt in one part of body but pathology is elsewhere.
Where are the nociceptive afferents in the tooth? and how does this sensory pathway work differently to if it was not head/neck?
Free nerve fibre endings extend into the dentine
Trigeminothalamic tract - Cell body of primary neuron in trigeminal ganglion as opposed to DRG
What is the CNS relay cell and pathway for pain not in head/neck?
Spinal dorsal horn
Spinothalamic tract
CNS relay cell and pathway for pain in head/neck?
Spinal trigeminal nucleus
Anterior trigeminothalamic tract
What factors affect pain perception?
Genetic Molecular Cellular Anatomical Physiological Psychological Social
What mutation causes pathology of pain sensation?
SCN9A-mutation = loss of Nav 1.7 function which is strongly expressed in nociceptive afferents as it encodes alpha subunit of the sodium channel
What is the gate control theory of pain?
This theory asserts that non-painful input closes the nerve ‘gates’ to painful input, which prevents pain sensation from travelling to the CNS.
Nonnociceptive fibres - A-beta fibres inhibit the effects of firing by Aδ and C fibres.
What is triple response?
- Red reaction
- Flare
- Wheal
What type of movement are reflexes?
Involuntary actions
What part of the CNS are reflexes centred on?
Motor neuron cell bodies found in:
- Spinal cord (somatic)
- Brainstem (cranial nerves)
What are common final pathways?
Motor neurons by which nerve impulses from many central sources pass to a muscle or gland in the periphery
Where do dorsal roots enter the spinal cord?
Posterolateral sulcus
Where do ventral roots leave the spinal cord?
Anterolateral sulcus
What are the regions of grey matter?
Grey matter is the region of cell bodies of neurons
- Intermediate horn
- Dorsal horn
- Ventral horn
What is white matter in spinal cord?
Axons
In basic terms, how does the reflex pathway occur?
Stimulus Receptor Afferent (sensory) neuron Synapse (s) Efferent (motor) neuron Effector (muscle, gland) Response
What are examples of somatic reflexes?
- Tendon-jerk reflexes
- Cutaneous reflexes
What are the receptors for tendon-jerk reflexes?
Proprioreceptor endings
Group 1a muscle afferents
Homonymous motor neurons
What are the receptors for cutaneous reflexes?
Mechanoreceptor endings
Nociceptor endings
What are other somatic reflex receptors?
Chemoreceptors
Photoreceptors
What is the ankle-jerk reflex?
Hammer tap to achilles’ tendon
Stretches spindles within gastrocnemius
APs conducted along 1a muscle afferents to spinal cord
Monosynaptic activation of motor neurons of gastrocnemius muscle
Axon potentials travel along A-alpha motor axon
Gastrocnemius muscle contracts
Foot extends
Apart from ankle-jerk, what are other commonly tested reflex reactions?
- Bicep Jerk
- Tricep Jerk
- Rectus Abdominis Reflex
What is the jaw-jerk reflex?
Hammer tap to chin
Stretches spindles of jaw elevator muscles
APs conducted along 1a muscle afferents to brainstem
Monosynaptic activation of motor neurons of jaw elevator muscle
APs travel along A-alpha motor axon
Jaw elevator muscles contract
Jaw jerks upwards, mouth closes
How are somatic reflexes used as protection mechanisms?
- Escape mechanism
- Prevention of muscle overloading
- Prevention of inadvertent foreign body ingestion
- Digestive aid
How does somatic reflex prevent overloading of muscle?
Receptor activated by stretch and contraction
Afferent signals cause INHIBITION of motor neuron activation
Inverse of stretch reflex (myotatic reflex)
Prevents overloading of muscle
How does muscle loading in jaw muscles work?
No golgi tendon organs (proprioreceptors that detect change in muscle tension)
Bite force controlled by increased loading of periodontal ligament
Afferents inhibit jaw elevator muscle motor neurons
Anaesthesia of molars increases maximum bite force
How does the pharyngeal reflex (gag reflex) work?
- Mass contraction of both sides of the posterior oral and pharyngeal musculature
- Activation: mechanoreceptor afferent from the posterior part of the tongue/soft palate
- Stimulation of sensory fibres from the glossopharyngeal nerve (IX)
- Afferents terminate in the caudal part of the spinal trigeminus nucleus (SpVn)
- Interneurons project from SpVn to nucleus ambiguus (X motor nucleus)
- X afferents terminate innervate muscles
What are semi-automated actions?
Voluntary, but you dont have to think about them
e.g. walking, breathing, chewing
May be driven by central pattern generators
What are the areas within white matter?
- Dorsal funiculus
- Lateral funiculus
- Ventral funiculus
What allows the two hemispheres of the brain to communicate?
corpus callosum
In what lobe does the somatic motor cortex exist?
Frontal
In what lobe does the somatic sensory cortex exist?
Parietal
What type of motor neurons are found in spinal cord?
Spinal motor neurons
What type of motor neurons are found in the brainstem?
Cranial motor neurons
What is the corticobulbar tract?
Pathway connecting the motor cortex to the medullary pyramids in the brainstem’s medulla oblongata
Involved in carrying the motor function on non oculomotor cranial nerve
What are the two motor descending pathways?
Corticospinal
Corticobulbar
What is anaesthesia and paraesthesia?
anaesthesia - loss of sensation
Paraesthesia - altered sensations
What is palsy?
Lesions to motor pathways cause paralysis
How can paralysis occur in lower motor neurons?
Lesions in final common pathway
How can paralysis occur in upper motor neurons?
Lesions in either
- Corticospinal tract
- Corticobulbar tract
What is the basal ganglia?
Theyre comprised of several sub-cortical nuclei that link to cerebral cortex via feedback loops
They influence/regulate output from the motor cortex
Act to initiate actions and to switch from one action to another
What is the corpus striatum divided into?
Lentiform nucleus (globus pallidus and putamen)
Caudate nucleus
What are the different action selection centres?
And what pathology does damage to these areas cause?
- Corpus striatum
- Sub-thalamic nuclei
- Substantia nigra
Parkinsons/Huntingtons
What is Parkinsons disorder?
Hypokinetic disorder
Dopamine deficiency in substantia nigra
What is Huntingtons disorder?
Hyperkinetic disorder
Imbalance of neurotransmitters
What are the two components of the cerebellum?
Vermis
Lateral hemisphere
What is the function of the cerebellum?
Important in co-ordinating movements
Regulates actions of antagonistic muscle groups
Important in maintaining balance
Acts to compare actual performance with what is intended
How can cerebellar disorders be characterised?
Loss of co-ordination Unsteady gait Imprecise actions Inability to co-ordinate alternating contractions of antagonistic muscles Intention tremor
What are correcting actions?
They help keep the position of the head in line with the body’s centre of gravity
