8. Spinal Flashcards
This descending motor tract originates in the cerebral cortex and synapses in the spinal cord
corticospinal
where does the spinothalamic tract decussate?
spinal cord
where does the corticospinal tract decussate?
pyramids of the lower medulla
where does the dorsal column decussate?
medulla oblongata
how does the spinocerebellar tract decussate?
the anterior (ventral) spinocerebellar tract decussates twice – once in the spinal cord as part of the anterior white commissure and then again in the superior cerebellar peduncle. The posterior (dorsal) spinocerebellar tract does not decussate.
which groups of spinal nerves innervates the biceps reflex?
C5/C6
A sexually active 75 year old gentlemen presents with a stamping gait. He is diagnosed with tabes dorsalis. On examination he has a loss of joint position sense and cannot feel the tuning fork (vibration) when placed on his medial malleolus. Which of the following spinal tracts is affected?
dorsal column medial lemniscus pathway
A 48 year old obese diabetic man, who smokes 30 a day presents with bilateral “glove and stocking” loss of pain, temperature and pin prick sensation. Which of the following spinal tracts is affected?
Spinothalamic
the vagus nerve is composed of
parasympathetic, motor and sensory fibres
which group of spinal nerves innervates the ankle reflex?
S1/S2
A 78 year old lady presents to her GP surgery with an intensely itchy vesicular rash in two separate horizontal lines at the level of the nipple and umbilicus respectively. Which dermatomal distribution is this affecting?
T4 and T10
A 78 year old lady presents to her GP surgery with an intensely itchy vesicular rash in a horizontal line at the level of the nipple. What is the most likely diagnosis?
Shingles
what is the absolute refractory period
once the sodium channels close after an AP. Sodium channels then enter an inactive state during which they cannot be reopened, regardless of the membrane potential.
what is the relative refractory period?
occurs when sodium channels slowly come out of the inactivation. During this period the neuron can be excited with stimuli stronger than one normally needed to initial an AP.
what is membrane capacitance
the ability to store charge. The lower capacitance results in a greater distance before the threshold is no longer reached.
what is membrane resistance
depends on the number of ion channels open. The lower the number of channels open, the greater membrane resistance is. A higher membrane resistance results in a greater distance before the threshold is no longer reached.
what are tonic receptors
slow adapting receptors. They will respond to the stimulus as long as it persists, and produce a continuous frequency of action potentials.
convey information about the duration of the stimulus
what are phasic receptors
rapidly adapting receptors. They will respond quickly to stimuli but stop responding upon continual stimulation. Therefore, action potential frequency decreases during prolonged stimulation.
conveys information about the changes to the stimulus such as intensity
what are nociceptors
• respond to noxious stimuli (stimuli that would cause tissue injury if they were to persist) and their activation results in the sensation of pain.
• free nerve endings, found on the ends of the type Aδ fibres and type C fibres that transmit the pain sensation
categorised into: mechanical, thermal, chemical, polymodal
what are mechanoreceptors
• These are located in joint capsules, ligaments, tendons, muscle and skin, and respond to deformation by the means of pressure, touch, vibration or stretch
Merkel’s discs, Meissner’s corpuscles, pacinian corpuscles, ruffini corpuscles, muscle spindles & golgi tendon organs
what are thermoreceptors
- found within the skin, liver, skeletal muscle and hypothalamus
- respond to changes in temperature
- Those responding to warm temperatures are present within type C fibres, whereas those responding to cold are present within of both type C and type Aδ fibres
- A warm stimulus results in both an increase in firing for warm receptors and a decrease in firing for cold receptors (and vice versa for cool stimuli
what sensory modalities does the DCML carry
fine touch (tactile sensation), vibration and proprioception
what sensory modalities do the anterolateral system carry
o Anterior spinothalamic tract – carries the sensory modalities of crude touch and pressure.
o Lateral spinothalamic tract – carries the sensory modalities of pain and temperature.
describe the knee jerk reflex
starts when the muscle spindle is stretched
When a stretch is detected it causes action potentials to be fired by Ia afferent fibres. These then synapse within the spinal cord with α-motoneurones which innervate extrafusal fibres. The antagonistic muscle is inhibited and the agonist muscle contracts i.e. in the knee jerk reflex the quadriceps contract and the hamstrings relax.
The sensitivity of the reflex is regulated by gamma motoneurones – these lead to tightening or relaxing of muscle fibres within the muscle spindle.
anatomy of Brown sequard syndrome
- incomplete spinal cord lesion characterized by a clinical picture reflecting hemisection injury of the spinal cord, often in the cervical cord region.
- suffer from ipsilateral upper motor neuron paralysis and loss of proprioception, as well as contralateral loss of pain and temperature sensation.
