Lecture 17 - Neural Flashcards
what is the somatic motor system?
controls motor commands and concious decisions to make a specific movement
- planning stage, then movement
what is the process of the somatic motor system?
decision in frontal lobes -> motor association area -> basal ganglia and cerebellum -> primary motor cortex (interlinked with bg and cb)
what is the purpose of the basal ganglia and the cerebellum?
to coordinate and give controlled movement
describe the primary motor cortex?
- contains pyramidal cells from layer 5 of the cerebral cortex that synapse with the brain stem or spinal cord
- info regarding movement coordination are sent to the pyrimidal cells from the brain stem, or other regions of the cortex
where is the motor homunculus?
on the primary motor cortex
which regions of the body require large representation of the motor homunculus?
larger representation of areas that require finer motor control
- face and hands
motor pathways are a __ neuron pathway
2
- upper motor neurons and lower motor neurons
what are the two pathways for the 2 neuron pathway of motor control?
- either synapse within the brainstem with cranial nerve nuclei (collections of LMNs in the brainstem) to control the face, head and neck
- or synapse at the somatic motor nuclei of the spinal cord to control the lower body
what is the pathway through the brain and spinal cord to get to the skeletal muscles of the face?
cerebral cortex (1º motor) -> travel down the cerebral peduncle of the brainstem -> then decussate (cross over) and synapse at cranial nerve nuclei
what is the pathway through the brain and spinal cord to get to the skeletal muscles of the upper limb?
also pass through cerebral peduncle, but continue into the lower medulla oblongata and decussate at the pyramids to form the lateral corticospinal tract (LCT)
what percentage of UMNs that travel to the lower part of the body travel via the LCT?
85% controlling distal muscles
what is the pathway through the brain and spinal cord to get to the skeletal muscles of the proximal/axial muscles?
dont decussate at the lower medulla oblongata and instead decussates at the level of the spinal cord
what are proprioreceptors?
important for recognising where our muscles are in space
what is the function of muscle spindle proprioceptors?
they are important for recognising muscle length
what is the function of golgi tendon organ proprioceptors?
sense tension in the muscles
- prevent damage of the muscle due to overexertion (something is ‘too heavy’)
what is the somatosensory motor system?
different receptors in our skin that have different structure or anatomy, or different locations in the skin
- touch, pressure
- pain and temperature
what are the three main types of receptors in the somatosensory system?
- free nerve endings (light touch, pain and temp
- Merkel cells and tactile discs (fine touch (fine detail about very small things touching our skin)
- tactile corpuscles (vibration)
- lamellated corpuscles (vibration)
- ruffini corpuscles (pressure)
which receptors are close to the skin surface?
free nerve, merkel and tactile discs, and tactile corpuscles
describe the pathway of the 1º sensory neuron
from exteroreceptors, through the ventral ramus, into the dorsal root ganglion (cell body) and synapses in the spinal cord or brainstem
what type of neuron is the 1º sensory neuron and why?
pseudounipolar neuron - cell body at central axon but off to the side - synapses with both receptors at the periphery and with neurons in the spinal cord or brainstem
what is sensory modality?
the type of sensory information - e.g touch and pressure vs pain and temperature
what are the four types of sonsory modality and their pathways (3 neuron pathways)?
- posterior-column (proprioception, fine touch, pressure, vibration)
- anterior spinothalamic tract (crude touch and pressure)
- lateral spinothalamic tract (pain and temperature)
- posterior and lateral spinocerebellar tracts (info to cerebellum)
what is the common location where the sensory modality pathways end?
the thalamus
describe receptive fields of neurons
they are the area that one sensory neuron modality can sense. they do not overlap, and areas where we need to take in more fine detailed sensory information have smaller receptive fields and more neurons that on places like our back, which will have larger receptive fields
what are crude touch receptors?
such as receptors on our back, we dont need sensory fine touch details on our back, so we have crude touch receptors with larger receptive fields on our back.
how are the sensory modality pathways segregated?
1: by sensory modality (e.g anterior spinal cord vs posterior spinal cord)
2: by somatotopic arrangement (info from leg in different area to the hand)
3: medial-lateral rule (info from further down the body travels medially, info from our arm travels laterally
describe the pathway of medial lemniscus (posterior column) pathway
1st order neuron into spinal cord via dorsal root ganglion, up spinal cord vis fasciculus gracilus (lower) or cuneatus (upper body), then synapse to 2nd order, then decussate at lower medulla, then up through medial lemniscus into ventral posterior thalamus
describe the anterior and later spinothalamic tracts
1st order neuron decussates after it enters spinal cord, 2nd order neuron decussate at that level, up through anterior spinothalamic tract and synapse onto 3rd order neuron at ventral thalamus
- anterior decussates at anterior spinal cord, lateral 2nd order decussates at lateral spinal cord
describe the reflex arc
allows for immediate involuntary response to stimuli
- info comes into spinal cord, synapses onto lateral spinothalamic tract (pain) but we ALSO have a reflex, where the 2nd order neuron will also contacts directly on a lower motor neuron which moves our muscles
what are the types of reflex?
monosynaptic (1st order periphery sensory neuron directly onto a motor neuron)
polysynaptic (1st order -> interneurons -> motor neurons)
- the brain can also suppress or enhance these reflexes via descending tracts to interneurons
what is the stretch reflex?
muscle spindles prevent excessive stretch of muscle during a monosynaptic reflex by inducing contraction of that same muscle
true or false, the primary somatosensory cortex is somatotopically organised
true, it has a sensory homunculus
what is a nerve plexus?
except in the thoracic region
- adjacent spinal nerves blend their fibres to produce a series of compound nerve trunks. this interwoven network is called a nerve plexus
what are our nerve plexuses?
- cervical plexus (innervates neck)
- brachial plexus (innervates the upper limb)
- Lumbar plexus (lower limb)
- Sacral plexus (lower limb)
describe the structure of the brachial plexus
C5 - T1 roots unite to form the superior (5-6) middle (7) and inferior trunk (8-1), and each trunk divides into an anterior and posterior division.
what are the cords of the brachial plexus?
- lateral cord (from anterior divisions of superior and middle trunk)
- posterior cord (from posterior divisions of all trunks)
- medial cord (from anterior division of the inferior trunk)
true or false, we can get cords that are a mic of anterior and posterior divisions
false, this never happens
what are the four nerves of the arm and forearm?
musculocutaneous nerve
radial nerve
ulna nerve
median nerve
what does the musculocutaneous nerve control?
the muscles of the anterior arm
- flexion, pronation and supination
also sensory control
which roots create the musculocutaneous nerve?
roots: C5-C7
which roots create the radial nerve?
C5-T1
what does the radial nerve innervate?
muscles of the posterior arm and posterior forearm
- extension and supination
what is special about roots at C7 and C8 for the radial nerve
these roots contribute to the posterior interosseous nerve - motor control of the forearm.
what are the sensory nerve branches of the radial nerve
- lower lateral cutaneous
- posterior cutaneous of arm
- posterior cutaneous of forearm
- superficial branch of the radial nerve
what does the lower lateral cutaneous nerve innervate, and what roots of the brachial plexus?
lateral aspect of upper arm, below the deltoid muscle
Roots: C5 and C6
what does the posterior cutaneous nerve of the arm innervate, and what roots of the brachial plexus?
the posterior surface of upper arm
Roots: C6 - C8
what does the posterior cutaneous nerve of the forearm innervate, and what roots of the brachial plexus?
a strip of skin down the middle of the posterior forearm
Roots: C6-C8
what does the superficial branch of the radial nerve innervate, and what roots of the brachial plexus?
the dorsal surface of the hand and lateral three and a half digits and the dorsum of the thumb
roots: C7 and C8
what does the median nerve innervate?
the muscles of the anterior (flexor) forearm (superficial and intermediate groups
what does the anterior interosseous branch of the median nerve innervate?
the deep muscles of the anterior forearm-
FPL
FDP
PQ
what are the two sensory branches of the median nerve?
- palmar cutaneous branch (lateral palm)
- Palmar sigital cutaneous branch (palmar surface of fingertips and dorsal surface)
which roots of the brachial plexus innervate both the sensory branches of the median nerve?
C6 - C8
which roots of the brachial plexus does the median nerve stem from?
C6 - T1
What does the ulnar nerve innervate?
FCU and FDP of the anterior forearm and a number of hand muscles
which roots of the brachial plexus does the ulnar nerve stem from?
C8 - T1
what are the sensory branches of the ulnar nerve
- palmar cutaneous branch
- dorsal cutaneous branch
- superficial branch
what does the palmar cutaneous branch of the ulnar nerve innervate?
skin of the medial half of the palm
what does the dorsal cutaneous branch of the ulnar nerve innervate?
the medial dorsal surface of the hand and the medial one and a half fingers
what two muscles does the axillary nerve innervate?
the deltoids and teres major
what roots of the brachial plexus does the axillary nerve come from?
- C5 and C6
what is the sensory branch of the axillary nerve?
the superior lateral cutaneous nerve of the arm
what sensory branches of the medial cord are there?
the medial brachial cutaneous nerve (medial surface of upper arm)
the medial antebrachial cutaneous nerve (anterior surface of arm and medial surface of lower arm)
which roots does the medial cord sensory branches come from?
C8 and T1
true or false, the number of brachial plexus injuries per year are increasing
true
describe the length of brachial plexus injuries
anywhere from a few hours to permanent
what are stingers and burners?
a normally temporary/transient brachial plexus injury which usually lasts hours to days.
symptoms are numbness and muscle weakness
what is Erbs palsy?
damage to C5 and C6 roots and the superior trunk.
causes loss of function of the musculocutaneous and axillary nerve
true or false, Erbs palsy is normally permanent
true
how can Erbs palsy and Klumpkes palsy lead to muscle wasting?
no innervation of that muscle leads to muscle wasting
describe Klumpkes palsy
Damage to C8 + T1 and the inferior trunk
causes loss of function of the lower arm, wrist and fingers
true or false, Erbs palsy and Klumpkes palsy can happen during birth
true
how can damage to the musculocutaneous nerve happen, and what is the main effect of injury?
damage or fracture of the humerus
weakening of the biceps, flexion of the shoulder and supination are effected.
what are the three ways in which damage to the radial nerve can happen?
- damage to the axilla region - shoulder dislocation of fracture of humerus
- damage in radial groove - fracture of humerus
- damage in forearm
what is the main effect of a fracture of the upper humerus or shoulder dislocation causing damage to the radial nerve?
muscles in the posterior arm compartment are effected
- typically causes loss of function of all muscles innervated by the radial nerve
an injury where is likely to cause wrist drop?
in the upper humerus around the axilla
- shoulder dislocation or humerus fracture
what is the main effect of a fracture of the upper humerus through the radial groove causing damage to the radial nerve and why?
weakening of triceps, loss of function of muscles of the posterior forearm
- triceps only weaken because some nerves that innervate the triceps branch off before the radial groove
what is the main effect of damage to the forearm causing damage to the deep branch radial nerve and why?
majority of muscles in the posterior forearm impacted
what is the main effect of damage to the forearm causing damage to the superficial branch radial nerve and why?
loss of sensation of the dorsal 3 and a half digits
why doesn’t wrist drop occur when there in a radial nerve injury in the forearm?
because the proximal forearm muscles are still innervated
what are the two ways in which damage to the median nerve can happen?
- supracondylar fracture of the humerus -> damage at the elbow
- damage at the wrist
what is the main effect of damage to the elbow causing damage to the median nerve?
- pronation of the forearm effected
- weak flexion of the wrist
- opposition of thumb affected
- flexion of first two fingers effected
why does damage to the median nerve at the elbow only cause weak flexion of the wrist?
because the ulnar nerve controls some of the flexor muscles
what is the main effect of damage to the wrist causing damage to the median nerve?
- thenar muscles and lateral two lumbricals
- opposition of thumb affected
- flexion of first two fingers effected
describe carpal tunnel syndrome
- median nerve get trapped in the carpal tunnel, which leads to numbness and thenar wasting due to loss of innervation
how can damage to the ulnar nerve happen, and what is the main effect of injury?
- trauma at the level of the medial epicondyle (or wrist)
- flexion of wrist can still occur but is accompanied by abduction
- finger abduction and adduction effected
- flexion and extension of ring and index fingers effected
why does abduction accompany flexion of the wrist after damage to the ulnar nerve?
normal flexion: FCR = flexion and abduction, FCU = flexion and adduction. together = neutral flexion.
ulnar nerve innervates FCU, so there is no adduction to counter the abduction.
what is nerve transfer?
surgical technique to restore muscle function or sensation after a serious injury
- surgeons select a redundant nerve in close proximity and connect it to the severed end of a more important nerve
which nerve allows us to pinch (e.g very important muscle)
anterior interosseous nerve
