Physiology of the Spinal Cord Flashcards
Does the spinal cord always require instructions from the brain to cause an effect?
- no
- able to respond in reflexes
What is a sensation?
- detection of a stimulus by a receptor
- walking into a kitchen and smelling a cake
What is a perception?
- interpretation of a stimulus by the brain with existing emotions and memories
- smell of cake may remind you of your birthdays
- sensations may be the same, but perceptions are different
Somatosensory receptors are specialised nerve endings in the PNS of the sensory neuron`s. These receptors can be divided into 2 groups, what are the names of these groups?
1 - mechanoreceptors and proprioceptors
2 - mechanoreceptors and nociceptors
3 - nociceptors and mechanoreceptors
1 - mechanoreceptors and proprioceptors
- mechanoreceptors (pressure, touch, vibration)
- nociceptors (pain, temperature, some touch sensation)
Somatosensory receptors are specialised nerve endings in the PNS of the sensory neuron`s. These receptors can be divided into 2 groups, mechanoreceptors and nociceptors. What are mechanoreceptors?
1 - receptors that can respond to temperature change
2 - receptors that can respond to 2 point discrimination
3 - receptors that can respond to vibration
4 - receptors that can respond to pressure or distortion
4 - receptors that can respond to pressure or distortion
Somatosensory receptors are specialised nerve endings in the PNS of the sensory neuron`s. These receptors can be divided into 2 groups, mechanoreceptors and nociceptors. Mechanoreceptors are somatosensory receptors that are pressure or distortion related. They can receive stimulus from outside and inside the body. What are the 2 names given to the stimuli we can receive from inside and outside the body and give an example?
1 - extroceptive = 5 senses (sight, sound, smell etc..)
2 - proprioceptive = neuromuscular spindle, Golgi tendon organ
Somatosensory receptors are specialised nerve endings in the PNS of the sensory neuron`s. These receptors can be divided into 2 groups, mechanoreceptors and nociceptors. Nocioceptive, often referred to as pain receptors, which can be stimulated by 3 different types of stimulus, what are they?
1 - chemical
2 - thermal
3 - mechanical
In the image below we can see a section of the skin, What are the exteroceptive mechanoreceptors that are present in the image, all with different receptors and respond to different sensations?
- hair follicle
- meissner’s corpuscle (texture, slow vibration)
- pacinican corpuscles (deep pressure, fast vibration)
In mechanoreceptors the sensation is detected by the receptors and converts this into neural activity, called stimulus transduction. What then happens to this neural activity?
- action potential is formed and Na+ channels open
- action potential then communicates this to CNS via the spinal column
Do all the somatosensory mechanoreceptor types respond to the same input?
- no
- they all have a narrow range of input
- Pacinian Corpuscle ONLY responds to heavy touch
- hair follicles ONLY respond to light touch
Nerve fibres can be classified. How many classifications of myelinated and unmyelinated fibres are there?
- myelinated = 4 fast to slow = Ia, Ib, II and III)
- unmyelinated = 1 = IV
Do larger or smaller fibres have a faster conduction velocity?
- large diameter = less resistance (more space in neuronal cytoplasm to move)
- they are myelinated so they have increased resistance to ions leaving cell) and reduced capacitance (less negative charge)
Muscle spindles and golgi tendon organs provide internal sensory information and are a form of unconsciousness proprioception, such as where our joints are. What type of myelinated classification are these and are they large or small?
1 - MS = 1a large and GT = 1b and large
2 - MS = 1b large and GT = 1b and large
3 - MS = 1a large and GT = 1a and large
4 - MS = I large and GT = III and large
- MS = muscle spindles
- GT = golgi tendon organs
1 - MS = 1a large and GT = 1b and large
- myelinated as they are for reflex and need to be fast
- 1a and 1b are the fastest and largest diameter
If we were to stab ourselves with a pin this would provide sensory information to our bare nerve free endings. This can provide fast and slow pain sensation, why?
- bare nerve free endings can be myelinated and unmyelinated
- myelinated = fast initial pain (larger axon diameter)
- unmyelinated = slow throbbing pain (smaller axon diameter)
Somatosensory receptors from mechanoreceptors and nociocepters enter the spinal cord at the dorsal horn and then travel to the CNS using a 3 order neuron pathway. Mechanosensory (proprioception / vibration/light touch) ascend to the CNS via which tracts?
1 - spinothalamic
2 - dorsal columns
3 - corticospinal tract
4 - spinocerebellar tract
2 - dorsal columns
- cuneate = upper limbs and gracillus = lower limbs)
- cross at the medulla oblongata
Somatosensory receptors from mechanoreceptors and nociocepters enter the spinal cord at the dorsal horn and then travel to the CNS using a 3 order neuron pathway. Nocioceptors for pain and temperature ascend to the CNS via which tracts?
1 - spinothalamic
2 - dorsal columns
3 - corticospinal tract
4 - spinocerebellar tract
1 - spinothalamic tract
- decussate at the level of the spinal cord they synapse with
When pain sensations are experienced in the peropheries by the 1st order neurone they travel to dorsal ventral root and synapse with the 2nd dorsal root before crossing the spine and travelling up to the medulla oblongata using the spinothalamic tract. However, even though this tract is set there are descending tracts that can travel down and modulate the activity of the 1st order neuron where it synapses with the 2nd order neuron in the spine. There are 2 hormones that are released here that are inhibitory to pain sensations, what are they?
1 - LH and FSH
2 - oxytocin and noradrenalin
3 - noradrenalin and serotonin
4 - serotonin and oxytocin
3 - noradrenalin and serotonin
- important in fight or flight to allow you to continue even when injured
There are a number of ways that receptors can discriminate sensory stimulus. How can a receptors physiology affect what it is able to sense?
- pacinian corpuscle are sensitive to deep pressure and vibration, BUT not pricking from a sharp needle
- free nerve ending are sensitive to pricking from sharp objects, BUT not deep pressure or vibration
There are a number of ways that receptors can discriminate sensory stimulus. One is two point discrimination through spatial distribution of receptors. What does this mean?
- ability to discriminate between 2 objects that are very close to one another
Spatial distribution, which is important in 2 point discrimination is mainly dependent on what?
1 - density of mechanoreceptors
2 - whether neuron is myelinated or non-myelinated
3 - receptive field of the mechanoreceptors
4 - number of mechanoreceptors
3 - receptive field of the mechanoreceptors
- small receptive field = high resolution (we can identify and touch things with high accuracy)
Spatial distribution of receptors is dependent on the receptive field of the mechanoreceptors. Small receptive field means we have a high resolution, allowing us to identify and touch things with high accuracy, such as determining 2 point discrimination. Do the hands and face, or belly and calf have a higher receptive field?
- low receptive field = hands and face
- high receptive field = belly and calf
Windows of response intensity is a mechanism of how sensory stimuli can be discriminated, what is this?
- receptors will only become receptive when a threshold has been met based on what the receptor is able to detect
- hot receptors >36 and <46 degrees
- cold receptors >18 and <38 degrees
The pre-central gyrus that we can see in the image below provides what actions in the body?
- primary motor cortex
- responsible for the control of voluntary movement and our behaviours
- bordmann area 4
What is the definition of an upper motor neuron?
- cell body originates in the cerebral cortex or brainstem
- terminates within the brainstem or spinal cord
What is the definition of a lower motor neuron?
- cell body lies within the ventral horn of the spinal cord or the brainstem
- terminates at the muscle it is innervating
Lower motor neuron cell bodies which originate in the ventral horn give rise to nerve fibres that instruct muscles to contract or relax. There are 2 types of motor neurons involved in stimulating muscles, what are they?
- alpha motor neurons (extrafusal)
- gamme motor neurons (intrafusal)
Do alpha and gamma motor neurons control voluntary or involuntary muscle action?
- alpha = voluntary (skeletal muscles)
- gamma = involuntary (muscle spindles)
Are lower motor neurons organised individually or in columns?
- longitudinally in columns
Lower motor neurons are organised longitudinally in columns as per the image below. Do the columns cover just one segment of the cord or multiple?
- multiple segments
Lower motor neurons (LMN) are organised longitudinally in columns as per the image below. The LMN columns cover multiple segments of the cord. What does this mean for muscle innervation?
- muscles receive motor fibres from multiple ventral roots
- important if one of the cord segments is affected, the muscle will not be paralysed
Lower motor neurons (LMN) are organised longitudinally in columns as per the image below. The LMN columns cover multiple segments of the cord. This means that muscles are innervated by motor fibres from multiple ventral roots. What implications does this have in regards to spinal nerve damage?
- if a single spinal nerve is damage it will not cause complete paralysis
What are golgi tendon organs and where can they be found?
- found in tendon where it attaches to muscles
- proprioceptor that responds to tension in a muscle
What are muscle spindles and where can they be found?
- located in body of muscle called intrafusal fibres
- stretch receptors within the body of a skeletal muscle that primarily detect changes in the length of the muscle
What are intrafusal muscle fibres?
- skeletal muscle fibers that serve as specialised sensory organs (proprioceptors) as part of the muscle spindle
- detect amount and rate of change in length of a muscle
Intrafusal muscle fibres are skeletal muscle fibers that serve as specialised sensory organs (proprioceptors) as part of the muscle spindle. They detect the amount and rate of change in length of a muscle. Are they innervated by sensory (afferent) or motor (efferent) fibres?
- both
If a muscle is stretched, this will stretch the intrafusal muscle fibres and cause a flurry of neuronal activity. This flurry of neuronal activity will reach the cell body at the dorsal ganglion. Once here it will synapse with what in the ventral horn of the spinal cord?
1 - gamma motor neuron
2 - renshaw cells
3 - alpha motor neuron
4 - 1a sensory neurons
3 - alpha motor neuron
- alpha motor neuron sends excitatory stimulus to the muscle contract (shortening)
- this is called a monosynpatic pathway
Primary afferent nerve fibres Ia are used to detect changes in the muscle spindles located within the intrafusal fibres. If I tap the patella tendon with a hammer this will cause a stretch in the quadriceps muscle, specifically the intrafusal muscle spindles, which is called a knee jerk reflex. What then happens to the muscle spindles and alpha motor unit in this knee jerk reflex?
- muscle spindles and skeletal muscle stretch
- increased firing of action potential along 1a nerve fibre
- 1a nerve fibre synapses with alpha motor neuron in anterior horn of spinal cord
- activation of alpha motor neurons in extensor muscles causes knee to extend
- this extension is a way of shortening the muscle spindles to protect the quadriceps
- 1b fibres also inhibit alpha motor neurons in the hamstrings to allow knee flexion
When we stimulate the golgi tendon organ, during muscular contraction of the biceps brachii for example, the tension in the biceps tendon is increased. What happens to the 1b fibres?
- tendon compresses during muscle contraction
- compression causes increased firing of Ib afferent fibres in bicep
- Ib afferent fibres from bicep brachii synapse with interneurons in anterior horn of spinal cord, that then inhibit alpha motor neurons of the biceps (relaxation)
- Ib afferent fibres synapse with alpha motor neurons of triceps causing activation and contraction
- results in relaxation of tendon being compressed
- protective mechanism to stop you over contracting and rupturing the tendon
In the clasp knife reflex, also called the inverse stretch reflex, the golgi tendon organ responds to tension. This signal is sent along the afferent receptor to the dorsal ganglion which then synapses with an inhibitory interneuron at the ventral horn. This then signals the alpha motor neuron causing it to do what?
- quadriceps are inhibited and muscle relaxes
- hamstrings are excited and muscle contracts
- protects against excessive tension of the tendon
If I am doing a bicep curl and flexing my arm, but the weight tries to extend my arm, what can happen to my biceps as a stretch reflex?
- as arm extends muscle spindles stretch
- afferent signal synapses with alpha motor unit at ventral horn
- alpha motor units are excited increasing contraction force in bicep
- negative feedback loop regulates muscle length
The flexor reflex is an important polysynaptic reflex pathway. How does the sensation of pain at the hands from something hot lead to an excitation (contraction) of the biceps and inhibition (relaxation) of the triceps?
- alpha nociceptors detect painful stimulus
- signal travels to ventral horn and synapses with interneurons
- interneurons excite alpha motor neurons of bicep causing arm to flex and retract
- inhibitory alpha motor neurons inhibit triceps allowing flexion of arm
What is the difference between a poly and mono-synaptic reflex pathway?
- mono = one sensory and one motor neuron
- poly = >1 interneuron connects sensory and motor neurons
If there is a problem in the lower motor neurons, those that begin in the cerebral cortex and terminate in the brain stem or spinal cord, do we have increased or decreased reflex response?
- decreased reflex
- sensory info is received but alpha motor unit activation can not travel to the muscle
The nerves providing sensation to our arms and legs come from the cervical and lumbar/sacral region, which is accounted for by enlarged spinal regions due to increased neuronal activity. The nerves for the upper limbs will enter the brachial plexus (group of nerves coming together). This will then provide the peripheral nerves for muscle innervation. Which nerve is involved in carpal tunnel syndrome?
- median nerve
The nerves providing sensation to our arms and legs come from the cervical and lumbar.sacral region, which is accounted for by enlarged spinal regions due to increased neuronal activity. The nerves for the upper limbs will enter the brachial plexus (group of nerves coming together). This will then provide the peripheral nerves for muscle innervation. The median nerve supplies sensations in the thumb and first 2 and a half fingers, as well as motor function for pronation, opposable thumbs and flexion at the wrist and fingers. A compression of the median nerve can cause a very common syndrome, what is this called?
- carpal tunnel syndrome?
The nerves providing sensation to our arms and legs come from the cervical and lumbar.sacral region, which is accounted for by enlarged spinal regions due to increased neuronal activity. The nerves for the upper limbs will enter the brachial plexus (group of nerves coming together). This will then provide the peripheral nerves for muscle innervation. The median nerve supplies sensations in the thumb and first 2 and a half fingers, as well as motor function for pronation. opposable thumbs and flexion at the wrist and fingers. A compression of the median nerve can cause carpal tunnel syndrome. What is the most common symptom and cause of carpal tunnel syndrome?
- tingling in fingers
The nerves providing sensation to our arms and legs come from the cervical and lumbar.sacral region, which is accounted for by enlarged spinal regions due to increased neuronal activity. The nerves for the upper limbs will enter the brachial plexus (group of nerves coming together). This will then provide the peripheral nerves for muscle innervation. The ulna nerve supplies motor function to the all the intrinsic muscles of the hand (except LOAF). If the ulna nerve is trapped or has a lesion what can happen?
- radial nerve palsy
- causes weakness, numbness and an inability to control the muscles
- can be causes from a drunk night, arms over chair
The nerves providing sensation to our arms and legs come from the cervical and lumbar.sacral region, which is accounted for by enlarged spinal regions due to increased neuronal activity. The nerves for the lower limbs will enter which 2 plexi?
- lumbar and sacral plexus
The nerves providing sensation to our arms and legs come from the cervical and lumbar.sacral region, which is accounted for by enlarged spinal regions due to increased neuronal activity. The nerves for the lower limbs will enter the lumbar-sacral plexus. Which nerve leaves the lumbar-sacral plexus, travels around the knee and to the foot and provides sensory information on the ankle and innervates ankle dorsiflexion and eversion?
1 - post tibial nerve
2 - common peroneal nerve
3 - sural nerve
4 - superficial peroneal nerve
2 - common peroneal nerve
The nerves providing sensation to our arms and legs come from the cervical and lumbar.sacral region, which is accounted for by enlarged spinal regions due to increased neuronal activity. The nerves for the lower limbs will enter the lumbar-sacral plexus. The common peroneal nerve is from the bifurcation of the sciatic nerve into the tibial and common peroneal nerve. The common peroneal nerve provides sensory information on the ankle and innervates ankle dorsiflexion and eversion. What can happen to the ankle if there is a lesion of this nerve, or if someone sits in a position that this nerve is impinged for a prolonger period of time?
- foot drop
The nerves providing sensation to our arms and legs come from the cervical and lumbar.sacral plexi, which is accounted for by enlarged spinal regions due to increased neuronal activity. The nerves for the lower limbs will enter the lumbar-sacral plexus. Which nerve leaves the lumbar-sacral plexus and provides just sensory information to the left lateral side of the thigh?
- lateral cutaneous nerve also called the lateral femoral cutaneous
- loss can cause pins and needles
There are a number of sensory stimulus that facilitate touch discrimination. One of these are meissners corpuscles. They look like a pear on a stick. What type of sensory information can this mechanoreceptor provide?
1 - deep pressure vibration
2 - shear
3 - touch
4 - pin prick pain
2 - shear
- like rubbing of things on the skin
There are a number of sensory stimulus that facilitate touch discrimination. One of these are pacinian corpuscles. They look like a big wheel on a stick. What type of sensory information can this mechanoreceptor provide?
1 - deep pressure vibration
2 - shear
3 - touch
4 - pin prick pain
1 - deep pressure vibration
There are a number of sensory stimulus that facilitate touch discrimination. One of these are merkel discs. They look like nerve free endings with a ball on. What type of sensory information can this mechanoreceptor provide?
1 - deep pressure vibration
2 - shear
3 - touch
4 - pin prick pain
3 - touch
There are a number of sensory stimulus that facilitate touch discrimination. One of these are free nerve ends, which look like a tree with no leaves. What type of sensory information can this mechanoreceptor provide?
1 - deep pressure vibration
2 - shear
3 - touch
4 - pin prick pain
4 - pin prick pain
There are a number of sensory stimulus that facilitate touch discrimination. One of these are ruffinis corpuscles, which look like mini muscles. What type of sensory information can this mechanoreceptor provide?
1 - deep pressure vibration
2 - tension and folding
3 - touch
4 - pin prick pain
2 - tension and folding
