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Medicine year 2 semester 1 > Case 19- Physiology 2 > Flashcards

Case 19- Physiology 2 Flashcards

1
Q

The three subdivisions of the somatosensory system

A
  • Cutaneous (skin) sensations
  • Visceral- internal organs and deep tissues
  • Proprioception- position of limbs and body in space, without it movement of limbs is impossible
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2
Q

Function of touch sense

A
  • Recognition of properties of objects
  • Control of movement- source of feedback
  • Communication- social and intimate
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3
Q

Sensory receptors and transduction

A

All sensory systems require receptors to convert stimulus energy (light, sound, pressure) into action potentials

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4
Q

Sensory transduction and Action potential initiation

A

• Sensory transduction- stimulus converted into graded electrical signal (receptor potential). The receptor potential magnitude depends on the stimulus strength. This is not an action potential
• Action potential initiation- if the receptor potential exceeds the threshold. The nerve fibres fire action potentials (nerve impulse). The stimulus strength is now coded by firing rate (impulse per second) or by pattern of firing
Receptor potential -> Integration at trigger zone -> Action potentials -> Neurotransmitter release

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5
Q

How to define different types of skin receptors

A
  • Appearance and structure- Meissner’s corpuscle, Merkel’s cell, Hair follicle, Pacinian corpuscle, Ruffini corpuscle, free nerve endings
  • Location-deep or superficial
  • Size of receptive field: large or small
  • Rapidly or slowly adapting
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6
Q

Types of nerve fibres

A
  • Alpha-beta large diameter myelinated fibres - fast
  • Alpha-delta small diameter myelinated - medium
  • C fibres small diameter unmyelinated- slow
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7
Q

Receptive field

A

Area over which a stimulus activates receptors, associated with a single neuron or nerve fibre. Normally its an area of skin but in the eye it’s the retina.

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8
Q

Receptor adaption- rapidly/slowly adapting

A
  • Relationship between duration of stimulus and duration of neuron firing
  • Rapidly adapting receptor- firing at stimulus onset. Neurons stops firing action potentials even through stimulus is maintained
  • Slowly adapting receptor- nerve continues firing action potentials throughout stimulus
  • Rapidly adapting receptor highlights appearance of new stimuli or a change in the stimuli. Change is important for detecting threats or opportunities
  • By processing only when stimulus begins and ends reduce the computational load
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9
Q

Inputs that control alpha (lower) motoneurons in the spinal cord:

A
  • Upper motoneurons- in cerebral motor cortex and brainstem. Commands and control. Basis of voluntary control of movement
  • Interneurons in spinal cord (local circuits, largest input)- excitatory and inhibitory. Important and spinal movement programs
  • Receptors: muscle spindles and Golgi tendon organs= sensory receptors in muscles and tendons. Provide feedback for control of movement
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10
Q

Muscle and tendon receptors

A
  • Muscle spindle- receptor type is composed of intrafusal fibres that run in parallel with extrafusal fibres. Detects stretch
  • Extrafusal muscle fibres- these do the work of contraction
  • Golgi tendon organs- receptor type in series with extrafusal fibres. Measures muscle tension and the weight its exposed to
  • Tendon- attaches muscle to the bone
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11
Q

How do the muscles spindle receptors detect the degree of stretch in the muscle

A
  • 1a afferent fibre carries output signals of the receptor to the spinal cord
  • Gamma motor neurons from CNS- the input is from the spindle cord, controls spindle contractions
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12
Q

Stretch reflex (monosynaptic- maintains contraction with increased load)

A
  • Add load to the muscle
  • Muscle and muscle spindle stretch as arms drops
  • Reflex contraction initiated by muscle spindle restores
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13
Q

Response of muscle spindle to stretch

A

• Increased afferent signals to spinal cord
• Increased efferent output through alpha motor neurons
• Firing rate of afferent sensory neurons decrease
• When the muscle contracts the spindle is unloaded so it ceases to fire
The muscle spindle changes it length so it accurately measure the degree of stretch

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14
Q

Golgi tendon reflex- protection against excessive load but also important for control of posture

A
  • Muscle contraction stretches golgi tendon organs
  • The motor neuron is inhibited, the muscle relaxes
  • If excessive load is placed on the muscle, the golgi tendon reflex is activated causing relaxation, thus protecting the muscle
  • Also helps maintain standing posture- if leg muscle extensor muscle fatigue reduces stretch on tendon, inhibition of motoneuron is also reduced, thus exciting stronger contraction
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15
Q

Dorsal column- Medial Lemniscus route

A
  • Ascends dorsal column- Ipsilateral
  • Goes to the Terminate Cuneate and Gracile Nuclei
  • Goes across to the contralateral side in the Medulla
  • Ascends to the synapse thalamus via the medial lemniscus
  • Ascends to the sensory cortex (Post Central gyrus)
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16
Q

First / Second and Third order neurones

A

First order neurons= Spinal cord -> Medulla
Second order neurons= Medulla -> Rostral Medulla -> Pons -> Midbrain
Third order neurone= in the midbrain

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17
Q

Function of dorsal column- medial Lemniscus

A

Discriminative (fine touch), Pressure, Vibration, Proprioception.

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18
Q

Anterolateral system

A
  • Decussate to contralateral side in the spinal cord
  • Synapse in the spinal cord
  • Ascend to synapse in the thalamus (Spinothalamic tract)
  • Ascend to sensory cortex (Post central gyrus)
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19
Q

Function of Anterolateral system

A

Non- discriminative tactile (affective touch), pain, temperature

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20
Q

Spinocerebellar tracts

A

Sub-conscious proprioceptive information from the body. Feedback to cerebellum on proprioception to aid balance and fine movement adjustments.

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21
Q

Ascending sensory pathways- fine touch

A
  • Ascend dorsal column, ipsilateral side
  • Through to gracile and cuneate fasciculi to synapse corresponding nuclei
  • Decussate to contralateral side in medulla and ascend to synapse in the thalamus
  • Ascend to primary somatosensory cortex
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22
Q

Ascending sensory pathway- pain receptor

A
  • Ascend to primary somatosensory cortex
  • Ascend anterolateral pathway to synapse in the thalamus
  • Cross to contralateral side
  • Synapse to dorsal column spinal cord
  • Nocicepter
23
Q

Primary sensory cortex

A

Post central gyrus, terminates in the thalamocortical pathway. Contains a topographical map of senses which is proportionate to the amount of sensory information. The tongue, lips and fingertips cover a large area and the arms and legs cover a relatively small area. Broadman’s areas 1,2,3.

24
Q

Cortical representation Somatosensation

A
  • 4 areas- all have somatotopic maps
  • Columnar organisation
  • bRepresents particular bodily areas or sensory modalities
  • Nearby columns may process information for different sensory modalities
25
Q

Secondary somatosensory cortex

A

Within the superior aspect of the lateral sulcus, it is bilateral. It is in charge of higher order functions: Sensorimotor integration, integrating information from the two body halves, attention, learning and memory

26
Q

Association cortex

A

Within the posterior parietal cortex you have the association cortex which integrates sensory information and allows for recognition of objects by touch.

27
Q

The concept of spirituality at the end of l

A
28
Q

The 4 types of Cleft lip and palate

A
  1. Unilateral cleft lip
  2. Unilateral cleft lip and palate
  3. Bilateral cleft lip and palate
  4. Midline cleft palate
29
Q

Link between thickness of action and conduction speed

A

The thicker the axon the faster the conduction velocity. IA and A-alpha are the fastest and IV and C are the slowest

30
Q

What is the only skin nerve with a high threshold

A

Free nerve ending

31
Q

Dorsal column/medial lemniscus- origin/termination/passes through

A

Origin: sensory receptors in periphery, enter the spinal cord through the dorsal route, also called 1st order neurons. They travel upwards on the ipsilateral (same) side of the spinal cord as where they enter.
Termination: The 1st order neurons from the lower limb (below T6) fibres terminate in the fasciculus gracilis. The upper limb (T6 and above) terminate in fasciculus cuneatus.
Passes through: The 2nd order neurons start in their respective nucleus and decussate (cross over to the contralateral (other) side) and travel up to the thalamus where they synapse onto 3rd order neurons which continue going upwards on the ipsilateral side through the internal capsule and terminate in the somatosensory cortex.

32
Q

Dorsal column/medial lemniscus- Decussation/Role and Clinical consequences

A

Decussation: Fibres stay on ipsilateral side throughout the spinal cord. The decussation takes place in the medial lemniscus!
Role: fine touch (tactile sensation), vibration and proprioception
Clinical consequences: Damage in pathway can lead to complete unilateral ipsilateral loss off touch, vibration and proprioception below the spinal level of injury.

33
Q

2 tracts of the Anterolateral system

A

Anterior spinothalamic- crude touch and pressure

Lateral spinothalamic- pain and temperature

34
Q

Anterolateral system- origin/termination / passes through

A

Origin: The 1st order neurones arise from the sensory receptors in the periphery. They enter the spinal cord, ascend 1-2 vertebral levels.
Termination: The 1st order neurons synapse at the tip of the dorsal horn – an area known as the substantia gelatinosa.
Passes through: Thesecond order neurones decussate and carry the sensory information from the substantia gelatinosa to the thalamus. The 3rd order neurones carry the sensory signals from the thalamus through the internal capsule to the ipsilateral primary sensory cortex of the brain.

35
Q

Anterolateral system- Decussation/ role/ clinical consequences

A

Decussation: After synapsing with the first order neurones, the 2nd order neurons decussate within the spinal cord, and then form two distinct tracts.
Role: crude touch and pressure, pain and temperature.
Clinical consequences: Because the fibres cross over around the spinal cord level damage, damage to the tract usually results in loss of temperature and pain on the contralateral side relative to the damage.

36
Q

Corticospinal tracts

A

1) The Lateral corticospinal tract crosses at the pyramidal decussation- voluntary control of distal musculature
2) Anterior corticospinal crosses at the segmental level in the spinal cord- voluntary control of proximal musculature

37
Q

Structure of the Corticospinal tract

A

1) Descending pathways are about motor control
2) The corticospinal tract starts at the motor cortex, passes through the internal capsule, to the cerebral peduncle at base of midbrain.
3) Passes through the base of the pons, scatters among transverse pontine fibres and pontine grey nuclei for contacts to cerebellum (corticopontine tract), the fibres coalesce again on ventral side of the medulla, where they form the medullary pyramids.
4) The upper motor neurons leave before the medullary pyramids
5) Corticospinal tract damage can mean you are unable to initiate voluntary muscle movements
6) Moves to the contralateral side

38
Q

Tectospinal pathway

A

1) Controls neck movement in response to visual stimuli i.e. moving your head to track stimuli. Coordinated head and eye movement.
2) Connects the midbrain tectum and the spinal cord
3) Tectospinal tract lesions- cant respond to startle stimuli as well
4) Originates in the superior colliculis in the midbrain which receives afferents from the visual nuclei and projects to the contralateral and ipsilateral portion of the first cervical neuromeres of the spinal cord, the oculomotor and trochlear nuclei in the midbrain and the abducens nucleus in the caudal portion of the pons.
5) The tract descends to thecervical spinal cordto terminate inRexed laminaeVI, VII, and VIII to

39
Q

Structure of the Rubrospinal tract

A

Originates from the red nucleus not very important in human beings, interacts with cerebellum. Therubrospinal tractoriginates in thered nucleusof the midbrain, decussates, and then descends in the lateral aspect of the spinal cord. Major afferents are from the cerebellar and cerebral cortices, and the rubrospinal tract projects to nuclei in the brain stem and cerebellum before reaching the spinal cord. The most important function of the rubrospinal tract is the control of muscle tone inflexormuscle groups.

40
Q

Reticulospinal tract structure

A

The Reticulospinal tract is responsible primarily for locomotion and postural control. The Reticulospinal tract is comprised of the medial (pontine) tract and the lateral (medullary) tract. Part of theExtrapyramidalsystem (originating in brain stem).
Mainly ipsilateral but some crossing over and bilateral innervation. Damage causes postural issues and spasticity.

41
Q

Vestibulospinal pathway

A

Originate from vestibular nucleus.
Lateral vestibulospinal tract – assist postural adjustments after angular and linear accelerations of head
Medial vestibulospinal tract – assist in head position to angular accelerations

42
Q

Structure of the Vestibulospinal tract

A

Aneural tractin thecentral nervous system. A component of theextrapyramidal systemand is classified as a component of the medial pathway. Like other descending motor pathways, the vestibulospinal fibers of the tract relay information fromnucleito motor neurons.Thevestibular nucleireceive information through thevestibulocochlear nerveabout changes in the orientation of the head. The nuclei relay motor commands through the vestibulospinal tract. The function of these motor commands is to alter muscle tone, extend, and change the position of the limbs and head with the goal of supporting posture and maintaining balance of the body and head.

43
Q

The problem with visual feedback control

A

Visual reaction time is 250ms. Simple feedback control with this much delay would be very slow or unstable

44
Q

Symptoms of a cerbellar lesion

A

1) Dysdiodochokinesia
2) Tremor and hypermetria
3) Ataxic gait

45
Q

Feedforward control of movement- Cerebellum

A

The Cerebellum males sensory predictions about the world, this then controls what motor commands we use. Sensory predictions are used because there is a delay before we receive sensory information. The cerebellum predicts what the consequences of movement will be

46
Q

Integration prediction and sensation

A

The parietal cortex receives sensory feedback from the outside world. Sensory feedback can be combined with internal predictions to form optimal state estimates within the parietal cortex. Discrepancies can be used to alter internal models to adapt to new environment. Climbing fibres from the purkinje body give feedback from the parietal cortex to the cerebellum in order to improve predictions

47
Q

How do we choose what movements to make

A

There are many different ways to perform a movement, you want to choose the route which is best according to: Accuracy, Smoothness, Speed and Stability

48
Q

Disorders of the basal ganglia

A

1) Parkinsons disease= Bradykinesia, Rigidity, Micrographia
2) Huntingtons disease- Hyperkinesia
3) Tourette’s, OCD, addiction, dystonia

49
Q

Basal ganglia anatomy

A

1) Comprises the striatum- Caudate nucleus, Putamen, Ventral Striatum
2) Globus pallidus- external segment, internal segment
3) Substantia nigra
4) Subthalamic nucleus

50
Q

Depending on where the UMN decussates depends where the effect of the lesion will be

A

Decussate in spinal cord= contralateral

Decussate in brainstem= ipsilateral

51
Q

Function of the parietal cortex

A

Receives sensory feedback from the outside world. The sensory feedback is combined with internal predictions to form optimal state estimates

52
Q

Types of feedback control

A

Low gain- small changes to get to goal

High gain- unstable, undershoot and overshoot till goal is acheived

53
Q

Role of the basal ganglia

A

Computes expected rewards. Rewards based learning. Error based learning is from the cerbellum

54
Q

Parkinsons

A

Cuased by destruction to the substantia nigra. Loss of dopamine, less activity in the direct pathway

Medicine year 2 semester 1 (53 decks)

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