Neuro wrap up Flashcards
What is a neurone?
Conduction relays of the nervous system, transmit information in the form of action potential.
Found throughout the body and brain, broadly categorised as motor or sensory.
Structural divisions of the CNS
brain and spinal cord
Structural divisions of the peripheral nervous system
nerves outside the CNS, including spinal nerves and cranial nerves
Functional divisions of the PNS
somatic and autonomic nervous systems
autonomic is further subdivided into sympathetic and parasympathetic nervous systems
subdivisions of the autonomic nervous system
sympathetic and parasympathetic
Which nerves carry parasympathetic information?
CN 3, 7, 9 and 10
Pelvic nerve (S2, 3, 4)
Which nerves carry sympathetic information?
T1-L2 spinal ganglia
List some roles of the parasympathetic nervous system:
Broadly - rest and digest.
Pupil constriction, salivation, slows heartbeat, bronchoconstriction, gastric peristalsis and secretion, release of bile, bladder contraction, erection/arousal
Parasympathetic functions of CN3
pupil constriction and accommodation
Parasympathetic functions of CN 7
flow of saliva from sublingual and submandibular gland
lacrimal gland
Parasympathetic functions of CN 9
flow of saliva from the parotid gland
Parasympathetic functions of CN 10
slows heartbeat, constricts bronchi, stimulates gastric peristalsis and secretion, stimulates release of bile
Parasympathetic functions of pelvic nerve (S2, 3, 4)
contracts bladder
stimulates intestinal motility
Roles of the sympathetic nervous system
Broadly: fight or flight.
Dilates pupil, inhibits saliva, accelerates heartbeat, dilates bronchi, inhibits gastric peristalsis and secretion, conversion of glycogen to glucose in liver, secretion of adrenaline and noradrenaline, inhibits bladder contraction, orgasm/ejaculation.
Structure of the sympathetic nervous system:
location of preganglionic bodies? Postganglionic bodies?
Preganglionic cell bodies in T1-L2 spinal ganglia, transmit to sympathetic chain.
Post ganglionic cell bodies in the sympathetic chain –> target structure
Sympathetic nervous system:
Preganglionic neurotransmitter and receptors
Postganglionic nervous system and receptors
Preganglionic: acetylcholine, nicotinic receptors
Postganglionic: noradrenaline, alpha and beta adrenoreceptors (beta 1 = heart, beta 2 = lungs, beta 3 = bladder)
Structure f the parasympathetic nervous system:
Location of preganglionic cell bodies
Postganglionic cell bodies
Preganglionic cell bodies in the brainstem –> just outside target organ
Postganglionic cell bodies just outside target organ –> target
Parasympathetic nervous system neuro transmitters:
pre ganglionic
postganglionic
Pre = nicotinic ACh Post = Muscarinic ACh
What three main parts form a neurone?
Cell body containing nucleus and organelles
Axon conducting the impulse
Dendrites - projections receiving information
What 3 main categories do neurones come under in terms of direction of information transmitted?
- Afferent: info from sensory receptors to CNS
- Efferent: info from CNS to target tissues
- Interneurones: contained entirely within the CNS
Myelin - purpose and composition
Fatty substance contributed by oligodendrocytes (CNS) or Schwann cells (PNS) wrapping themselves around the axon of a neurone.
Acts as an electrical insulator, prevents ion movement, and forms a protective cushioning barrier
Where do neurones of the CNS get their myelin sheath compared with neurones of the PNS?
CNS = oligodendrocytes PNS = Schwann cells
Briefly describe saltatory conduction
Schwann cell insulation means ion movement can occur only at the nodes of Ranvier (gaps between Schwann cells).
The electrical signal must therefore ‘hop’ from one node to the next in saltatory conduction.
This is faster than the continuous conduction taking place in unmyelinated neurones.
3 factors affecting conduction velocity
- Nerve diameter: larger = faster
- Temperature (hotter = faster, up to a point)
- Myelination
All or nothing - what determines the intensity of the signal perceived by the brain?
the frequency, not the strength, of the signal: neurones can either be firing or not firing, depending on wether the threshold potential is exceeded
6 steps of axonal transmission
- Resting potential: the nerve is unstimulated, -70mV
- Generator potential: stimulus causes a slight depolarisation
- Threshold potential: slight depolarisation reaches -55mV
- Depolarization: massive Sodium influx, peaks at +30mV
- Repolarisation (absolute refractory period)
- Hyperpolarisation (Relative refractory period)
How is resting potential maintained?
Channels:
Na+/K+ pump actively pumps 3Na+ out for every 2K+ in.
Voltage gated potassium channels are open.
Voltage gated sodium channels are closed.
How does the arrival of a stimulus alter the potential of an axon?
Arrival of a stimulus from a synapse destabilises some of the sodium channels.
A small amount of sodium leaks in, leading to a slight depolarisation.
If the depolarisation is enough to reach the threshold potential, an action potential is triggered.
Describe the sequence of events if threshold potential is reached in a neurone.
What is happening to each channel?
- all voltage gated sodium channels now open
- massive influx of positively charged sodium ions causes membrane potential to become positive.
Na+/K+ pump stops.
Voltage gated potassium channels close.
Voltage gated sodium channels open.
Following depolarisation, how is resting potential restored in the repolarisation period?
+30mV reached and the impulse has been spread down the length of the axon
Resting potential must be restored:
- Sodium channels close: no more sodium may enter axon
- Potassium channels open: potassium starts leaving axon
- Na+/K+ pump actively pumping 3Na+ out and for every 2K+ in
What are the 2 parts of a refractory period and when do they take place?
- Absolute refractory period, takes place during repolarisation
- Relative refractory period, takes place during hyperpolarisation
How does absolute vs relative refractory period affect transmission of a new action potential?
absolute - neurone cannot generate a new action potential
relative - neurone can generate a new action potential only in response to a stimulus stronger than previous stimulus (raises threshold potential)
In synaptic transmission, what is convergence?
divergence?
Convergence = many Presynaptic knobs pass impulse to one postsynaptic membrane Divergence = one presynaptic knob at many postsynaptic membranes
What are the 5 fundamental processes of synaptic transmission?
- Manufacture (intracellular biochemical process)
- Storage
- Release (triggered by AP)
- Elicit a post-synaptic response (diffuse across cleft, bind to receptor)
- Inactivation (breakdown or reuptake)
Sequence of events following the arrival of an action potential at the presynaptic knob
- Action potential arrives at the presynaptic knob
- Entry of Na+ ions causes voltage gated calcium channels to open, Ca2+ influx
- Calcium ions cause vesicles to fuse with the cell membrane and release preformed neurotransmitters into the synaptic cleft (exocytosis)
- Neurotransmitter diffuses across the synapse and binds with receptors on the postsynaptic membrane
Neurotransmitter breakdown - what are the 3 main mechanisms by which neurotransmitters re removed following synaptic transmission?
- Active transport back into the presynaptic knob (reuptake)
- Diffusion away from receptor sites
- Enzymatically broken down and recycled
Definition of pain
“an unpleasantsensory andemotional experienceassociated with actual or potential tissue damage”
Define:
1. Acute pain
- Chronic pain
- Short term pain of less than 12 weeks
- Continuous long term pain of more than 12 weeks OR lasting longer than would be expected
Divided into chronic cancer pain and chronic non cancer pain
Define nociceptive pain
pain arising from actual or threatened damage to non-neural tissue
due to the activation of nociceptors
Define neuropathic pain
pain arising as a direct consequence of a lesion/disease in the somatosensory system
painkillers -
what are analgesics?
what are anaesthetics?
analgesics - selectively suppresses pain without an effect on consciousness or other senses, e.g. paracetamol
anaesthetic - induces insensitivity to pain with reversible loss of all sensation e.g. local anaesthetics
What are the 4 types of nerve fibres in the PNS?
A-alpha, A-beta, A-delta and C fibres
which of the 4 types of nerve fibres in the PNS are nociceptive?
A-delta and C fibres
Describe A-delta nerve fibres
- info transmitted
- diameter
- myelination
- speed of conduction
- type of pain
- nociceptive, transmit mechanical and thermal pain information
- myelinated, large diameter
- rapid conduction
Initial sharp pain
describe C-fibres - info transmitted - diameter - myelination - speed of conduction type of pain
- nociceptive, transmit mechanical, thermal and chemical pain
- unmyelinated, small diameter
- slow conduction
Only activated by very strong painful stimuli, dull aching pain
What information does the spinothalamic tract carry?
Ascending
pain, temperature and crude touch
Describe the route of information travelling via the spinothalamic tract:
- primary, secondary and tertiary neurones
- primary neurones enter via dorsal root ganglion, travel up 1/2 spinal segments
- synapse with secondary neurones which decussate in the spinal cord and continue to the thalamus
- tertiary neurones in the thalamus carry info to the primary somatosensory cortex via the internal capsule
Briefly describe the Melzack-Wall Pain Gate theory?
- non-noxious stimuli can prevent noxious stimuli from eliciting pain sensation
- Non noxious stimuli in the same region carried by A-beta fibres cause inhibitory interneurones to fire, reducing sensation of pain
(rub it better)
what is a motor unit?
a single alpha motor neuroe and all the muscle fibres it inervates
what is a motor neurone pool?
a collection of motor neurones innervating a single skeletal muscle
what is a motor end plate?
region of the cell membrane of the muscle fibre which lies directly beneath an axon terminal
what is the neurotransmitter at a neuromuscular junction?
ACh
What happens to the axon of a motor neurone as it approaches a muscle?
divides into many branches, each innervating a different muscle fibre
describe the process of conduction at a neuromuscular junction
- action potential arrives at the motor neurone axon terminal
- Depolarisation causes release of ACh into cleft
- ACh binds to nicotinic receptors on motor end plate
- Influx of sodium causes depolarisation (end plate potential)
- AP propagates down T-tubules and initiates contraction
what do Golgi tendon organs detect?
changes in muscle tension
what effect does stimulation of Golgi tendon organs have?
why is this response important
muscle stretched by load/contraction
impulse sent to the CNS causing:
inhibition of muscle by alpha motor neurones
- may stimulate antagonistic muscles
This protects the muscle from over-contraction/over-stretching, spreads out the load and smooths the action
what innervates Golgi tendon organs?
1b sensory neurones
what is the role of muscle spindles?
monitor the stretch of a muscle and promote its contraction
where are muscle spindles found?
- group of modified muscle fibres in a capsule of connective tissue
Intrafusal fibres - within muscle fibres
Innervation of intrafusal spindle fibres?
gamma motor neurones
Describe the basic sequence of events in the stretch reflex
Stretch –> spindle afferent activated–> contraction of that muscle and synergistic muscle –> Antagonistic muscles are also inhibited
what is the withdrawal reflex?
protects against noxious stimuli/damage.
Flexors of affected limb contract, extensors relax, limb withdraws from stimulus.
Describe the knee-jerk reflex
- Patellar ligament is struck with a hammer, lengthening the muscle spindle in the quadriceps
- afferent neurone to L3
- stimulation of quadriceps contraction and inhibition of antagonists (hamstrings)
Examples of an upper motor neuron lesion
MS, stroke, nerve trauma, cerebral palsy
Symptoms of an upper motor neurone lesion
Everything goes up:
Increased tone (spastic weakness
Hyperreflexia
Positive Babinski sign (sole of foot stimulated, big toe goes up instead of down)
NO muscle wasting or fasciculation
weakness pattern in an UMN lesion:
upper limb
lower limb
upper limb = strong flexors and weak extensors –> fixed arm
lower limb = weak flexors and strong extensors –> straight leg
Symptoms of a lower motor neurone lesion
Everything goes down: Decreased tone (flaccid weakness Hyporeflexia Muscle wasting (equal in flexors and extensors)
Normal/absent Babinski sign
Fasciculations
Examples of LMN lesions
muscular atrophy, bulbar palsy
3 layers of the eye
outer = cornea, sclera middle = iris, ciliary body, choroid plexus inner = retina
Function of the cornea
protective function and contributes to refraction, clear, anterior portion of sclera
Function of the sclera
tough, outer collagen later that protects, attachment for extra ocular muscles
Function of the iris
pupil and light adaption
Function of the ciliary body
produces aqueous humour, enables accommodation by altering the shape of the lens
Function of the choroid plexus
Blood supply, light absorption
Function of the retina
transduction of light
Rods vs cones in the retina - how do their roles differ?
Rods = responsible for vision at low light levels. More abundant. Cones = colour and visual acuity
Which extraocular muscle(s) are innervated by CN3?
CN 3 = occulomotor Innervation of: Superior, medial and lateral rectus Inferior oblique Levator palpebrae
Which extraocular muscle(s) are innervated by CN 4?
Trochlear
Innervates the superior oblique, for downward and outward eye movement
Which extraocular muscle(s) are innervated by CN 6
Abducens
Innervated lateral rectus for abduction
Levator palpebrae superioris:
Attachments
Actions
Attachments - lesser wing of sphenoid bone –> superior tarsal plate of upper eyelid
Actions - elevates upper eyelid
Superior, inferior, medial and lateral rectus:
Attachments
Actions
Attachments: common tendinous ring –> respective part of anterior sclera
Actions: elevates, depressed, adducts, abducts eyeball respectively
Superior oblique
Attachments
Actions
Attachments: sphenoid bone –> loops around trochlear nerve –> sclera posterior to superior rectus
Actions: depresses, abducts, medially rotates eyeball
Inferior oblique
Attachments
Actions
Attachments: orbital floor –> sclera posterior to lateral rectus
Actions: elevates, abducts, laterally rotates eyeball
Basic route of vision from retina –> visual cortex
Retina –> optic nerves –> optic chiasm –> optic tracts –> lateral geniculate body –> optic radiations –> visual cortex
What visual information do your temporal retinal fields convey?
What visual information do your nasal retinal fields convey?
Temporal = central vision Nasal = peripheral vision
How do the optic tracts change at the lateral geniculate nucleus?
Where do they terminate?
Tracts become radiations which terminate in primary visual cortex in occipital lobe.
Meyer’s loop:
- type of optic radiation
- information received
- lobe of the brain travelled through to reach visual cortex
Meyer’s loop: lower optic radiation, information from inferior retina/superior visual field, through temporal lobe to visual cortex
Baum’s loop
- type of optic radiation
- information received
- lobe of the brain travelled through to reach visual cortex
upper optic radiation, information from superior retina/inferior visual fields, through parietal lobe to visual cortex.
Describe the visual pathway
Most axons terminate and synapse in the lateral genicular body of the thalamus
Some will synapse in the superior colliculus of the midbrain (involved in pupillary light reflex)
Structures making up the outer ear
Auricle –> external auditory canal
Role of the outer ear
Sound waves are reflected when they hit the pinna and enter the auditory canal where the sound is amplified
Structures making up the middle ear?
Tympani membrane –> oval window
= ossicles and eardrum
Name the ossicles
What do they do?
Malleus, incus, stapes:
convert low pressure eardrum vibrations into high pressure vibrations at the oval window
Role of tensor tympani and stapedius muscles
Protect the middle ear from loud noises
What is the role of the eustachian tube?
controls pressure in the middle ear
Structures making up the inner ear?
Middle ear –> internal acoustic meatus.
Bony labyrinth - perilymph fluid.
Membranous labyrinth - endolymph fluid
Within petrous temporal bone
functions of the inner ear
- convert mechanical signals from the middle ear into electrical signals
- maintain balance by detecting position and motion
3 constituents of the bony labyrinth of the inner ear
subdivisions of these parts
Cochlea - scala vestibuli, scala media, scala tympani
Vestibule - contains utricle and saccule of the membranous labyrinth
3 Semicircular canals - anterior posterior and lateral
Role of the semicircular canals
Upon movement of the head, the flow ofendolymphwithin the ducts changes speed and/or direction. Sensory receptors in the ampullae of the semicircular canals detect this change, and send signals to the brain, allowing for the processing of balance.
Semi circular canals detect rotational movement
Role of the utricle and saccule
Upon movement of the head, the flow ofendolymphwithin the ducts changes speed and/or direction. Sensory receptors in the ampullae of the semicircular canals detect this change, and send signals to the brain, allowing for the processing of balance.
Utricle and saccule detect linear movement
What does the round window do?
Vibrates with opposite phase to vibrations entering through the oval window. Moves fluid in cochlea, stimulating hair cells
3 scala of the cochlear.
Which contains the organ of corti?
- scala vestibuli
- scala media: organ of Corti
- scala tympani
Which scala contain perilymph? endolymph?
- scala vestibuli = perilymph
- scala media = endolymph (K+)
- scala tympani = perilymph
Organ of Corti in the scala media:
How many rows of outer hair cells? inner hair cells?
3 rows of outer hair cells
1 row of inner hair cells
What is the function of the inner hair cells?
- mechanoreceptors for hearing
- transduce vibration of sound into electrical activity in nerve fibres
What is the function of outer hair cells?
- motor structures
- amplify sound vibration, detect amplitude
In the organ of corti what is the ratio of nerve fibres to nerve cells? What significance does this have?
One nerve fibre to one nerve cell.
This allows increased intensity - faster firing, and changing of frequency when different nerve cells are stimulated
Describe the pathway of the central auditory system starting at the Organ of Corti
Organ of corti –> cochlear nucleus –> superior olivary complex –> inferior colliculi –> medial geniculate body
What is the lentiform nucleus made up of?
globus pallidus + putamen
basic role of basal ganglia
action selection - direct excitatory rout and indirect inhibitory route
What is the neurotransmitter for the caudal/direct route of the basal ganglia?
Effect?
Example of a problem here?
Nuclei involved?
Dopamine.
Excitatory effects - go!.
Effect of problem - lack of dopamine = Parkinsons, characterised by intention tremor and slow actions.
Subthalmic nuclei communicate with globus pallidus. Substantia nigra releases dopamine.
What is the neurotransmitter for the indirect route of the basal ganglia?
Effect?
Example of a problem here?
Nuclei involved?
GABA - from striatum. Inhibitory, stop! Problem = Huntingdon's, characterised by flinging movements - e.g. goes straight through with motion to pick up a glass and ends up knocking it over. Putaman – motor control Caudate – eye movement and cognition Striatum – release GABA
Key roles of the limbic system
Involved in emotion and memory
Constituents of the limbic system
Cingulate gyrus Parahippocampal gyrus Fornix Hippocampus Amygdala Mamillary body
What does the Papez circuit connect and to what effect?
Connects parts of the limbic system, circuit devoted to emotional experience and expression
Basic path of the Papez circuit
Emotional stimulus –> thalamus
Thalamus –> hippocampus –> fornix –> mamillary body –> anterior thalamic nucleus –> cingulate gyrus –> parahippocampal gyrus back to hippoampus
Information from hypothalamus of mamillary body produces a body response, information to cingulate cortex produces an emotional response/feeling
What separates the cerebellum from the occipital and temporal lobes?
tentorium cerebelli
How is the cerebellum connected to the midbrain
By 3 cerebellar peduncles - inferior middle and superior
Roles of the cerebellum
Balance, posture, coordination
Lobes of the cerebellum
Anterior
Posterior
Floculonodular
Fissures of the cerebellum
Primary fissure separates anterior and posterior lobes
Horizontal fissure marks lateral and posterior margins of hemisphere
Superior peduncle connects the cerebellum to what structure?
midbrain
Middle peduncle connects the cerebellum to what structure?
pons
inferior peduncle connects the cerebellum to what structure?
medulla oblongata
3 layers of the cortex of the cerebellum
- molecular (outermost)
- Purkinje
- granule
2 inputs to the cerebellum: what type of information do they convey and where to?
- Mossy fibres: info from middle peduncle inform cerebellum of voluntary motor input, synapse with granule cells
- Climbing fibres: info from inferior peduncle, convey muscle proprioception and vestibular inputs
1 output from the cerebellum: which cells are involved?
Purkinje cells.
Climbing fibres wrap around Purkinje cells
Cerebellar damage
Dysmetria (cannot judge scale/distance) Ataxia Nystagmus (abnormal eye movements) Intention tremor (tremor on intentional movement) Slurred speech Hypotonia
