Module 1 - PNS and Reflex Activity

Question 1

Membranes covering CNS

Answer 1

Dura mater
Arachnoid
Pia Mater

Question 2

Gray Horns & Divisions

Answer 2

Posterior - Sensory processing

Anterior - Sends our motor signals to the skeletal muscles

Lateral - Only present in thoracic, upper lumbar and sacral regions (central component of the sympathetic division of the ANS)

Question 3

White Columns (Tracts)

Answer 3

Ascending - tracts in the NS fibres that carry sensory information up to the brain

Descending - tracts that carry motor commands from the brain

Question 4

Spastic Paralysis

Answer 4

Refers to a condition where the tone of muscles increased and muscles are (stiff and weak). The most common causes involve diseases that damage that descending tracts anywhere along it’s course from the brain to the spinal cord (an upper motor neuron lesion UMN)

Question 5

Flaccid Paralysis

Answer 5

Condition where the tone of the muscles in reduced and muscles are weak. Due to a diseased circuits in the spinal cord that affect the tone or diseases of the nerves that supply the muscles. Also known as a lower motor neuron lesions

Question 6

Lower Motor Neuron Lesion

Answer 6

Lower motor neuron lesion affects nerve fibres traveling from the anterior horn of the spinal cord or the cranial motor nuclei to the relevant muscle(s).

Question 7

Upper motor Neuron Lesion

Answer 7

Upper motor neuron lesions occur in the brain or the spinal cord as the result of stroke, multiple sclerosis, traumatic brain injury and cerebral palsy.

Question 8

Paralysis

Answer 8

Loss of muscle function for one or more muscles, dependent on the type, size and location of the lesion

Question 9

Monoplegia

Answer 9

Paralysis of a single area of the body (usually one limb). People with monoplegia typically regains control over the rest of their body, but cannot more or feel the affected limb.

Question 10

Hemiplegia

Answer 10

Affects the arm and leg on one side of the body and as with monoplegia, the most common cause of Cerebral Palsy

Question 11

Paraplegia

Answer 11

Refers to paralysis below the waist and usually affects the legs, hips and other visceral functions (sexual and elimination). Spinal cord injuries are the most common cause of paraplegia, these injuries impede the brain’s ability to send and receive signals below the site of the injury

Question 12

Quadripelgia

Answer 12

Refers to paralysis below the neck. All four limbs as well as the torso are typically affected. The most common causes of these types of these types of spinal cord injuries include automobile accidents, acts of violence, falls and sporting injuries, especially due to contact sports.

Traumatic brain injuries can also cause this form of paralysis.

Question 13

Major Causes of Paralysis

Answer 13

Stroke

Trauma with Nerve Injury

Poliomyelitis - or infantile paralysis, is an infectious disease caused by the poliovirus. In about 0.5 percent of cases there is muscle weakness resulting in an inability to move.

Cerebral Palsy - A group of permanent movement disorders that appear in early childhood. Signs and symptoms vary among people and over time. Often, symptoms include poor coordination, stiff muscles, weak muscles, and tremors. There may be problems with sensation, vision, hearing, swallowing, and speaking.

Peripheral Neuropathy - Conditions that result when nerves that carry messages to and from the brain and spinal cord from and to the rest of the body are damaged or diseased

Parkinson’s Disease -Progressive nervous system disorder that affects movement. Symptoms start gradually, sometimes starting with a barely noticeable tremor in just one hand. Tremors are common, but the disorder also commonly causes stiffness or slowing of movement.

ALS - Amyotrophic lateral sclerosis (ALS), also known as motor neurone disease (MND) or Lou Gehrig’s disease, is a specific disease that causes the death of neurons controlling voluntary muscles.

Botulism - A rare and potentially fatal illness caused by a toxin produced by the bacterium Clostridium botulinum.

Spina Bifidia - A birth defect where there is incomplete closing of the backbone and membranes around the spinal cord

Multiple Sclerosis - chronic, typically progressive disease involving damage to the sheaths of nerve cells in the brain and spinal cord, whose symptoms may include numbness, impairment of speech and of muscular coordination, blurred vision, and severe fatigue.

Guillain-Barree Syndrome - an acute form of polyneuritis (any disorder that affects the PNS), often preceded by a respiratory infection, causing weakness and often paralysis of the limbs.

Drugs (curare)

Question 14

Paresthesia

Answer 14

An abnormal dermal sensation (tingling, prickling, chilling, burning or numbing sensation on the skin with no apparent physical cause. Usually painless and can occur anywhere on the body but commonly occur in the extremities.

Question 15

Transient Paresthesia

Answer 15

Parestheias of the hands, feet, legs and arms are common with transient symptoms,

Question 16

Chronic Paresthesia

Answer 16

Indicates a problem with the functioning of neurons or poor circulation. Can also be a symptom of vitamin deficiencies, malnutrition, metabolic disorders (diabetes, hyperthyroidism or hypothyroidism)

Question 17

Flaccid Paralysis

Answer 17

Flaccid paralysis is an illness characterized by weakness or paralysis and reduced muscle tone without other obvious cause (e.g., trauma). This abnormal condition may be caused by disease or by trauma affecting the nerves associated with the involved muscles.

Question 18

Spastic Paralysis

Answer 18

Spasticity is a side effect of paralysis that varies from mild muscle stiffness to severe, uncontrollable leg movements. Generally, doctors now call conditions of extreme muscle tension spastic hypertonia (SH). It may occur in association with spinal cord injury, multiple sclerosis, cerebral palsy, or brain trauma.

Question 19

Neural Pathway

Answer 19

Connection formed by axons from neurons to make synapses onto neurons in another location , in order to enable a signal to be sent from one region of the nervous system to the other. Neurons are connected by a single axon or by a bundle of axons known as a nerve tract

• Descending motor pathways of the pyramidal tracts travel from the cerebral cortex to the brainstem or lower spinal cord
• Ascending sensory tracts in the dorsal column carries information from the peripherary to the cortex of the brain

Question 20

List the 7 Major Neural Pathways

Answer 20

1. Arcuate Fascicules
2. Cerebral Peduncle
3. Coprus Callosum
4. Pyramidal Tracts
5. Medial Forebrain Bundle
6. Medial Lemniscus Pathway
7. Retinohyptothalamic Tract

Question 21

Arcuate Fasicilus

Answer 21

A bundle of axons that forms part of the superior longitudinal fasciculus (association fibre tract). It bi-directionally connects the caudal temporal cortex and inferior parietal cortex to locations in the frontal lobe.

Connects 2 important areas for language use:

• Broca’s Area (in the inferior frontal gyrus)
• Wenicke’s Area (in the posterior temporal gyrus)

Question 22

Cerebral Peduncles

Answer 22

Structures are the front of the midbrain which arise from the front of the pons and contain large ascending (sensory) and descending (motor) nerve tracts that run to and from the cerebrum from the pons

• The cortico-spinal tract
• The cortico-potine tract
• The cortico-bulbar tract

Assist in refining motor movements, learning of new motor skills and converting proprioceptive information into balance and posture maintenance

Question 23

Name the three common areas that give rise to the cerebral peduncles

Answer 23

• Cerebral cortex
• Spinal Cord
• Cerebellum

Question 24

Corpus Callosum

Answer 24

Wide, thick nerve track consisting of a flat bundle of commissural fibres beneath the cerebral cortex in the brain

Separate nerve tracts classified as sub regions, of the corpus callosum connect different parts of the hemispheres.

• The Genu
• The Rostrum
• The Trunk
• The Splenium

Question 25

Pyramidal Tracts

Answer 25

Pyramidal tracts include corticobulbar tract and the corticospinal tract. Aggregations of efferent nerve fibres from the upper motor neurons that travel form the cerebral cortex and ends either in the brainstem (corticobulbar) or spinal cord (corticospinal) and are involved in the control of motor functions

Question 26

Corticobulbar Tract Role & Function

Answer 26

Conducts impulses from the brain to the cranial nerves. These nerves control the muscles of the face and neck and are involved in facial expression, mastication, swallowing and other functions

Nerves are involved in movement of muscles of the body. Due to the crossing-over o fibres, muscles are supplied by the side of the brain opposite of that muscle.

Question 27

Cortisospinal Tract Role & Function

Answer 27

Conducts impulses from the brain to the spinal cord. Made up of lateral and anterior tracts and is involve in voluntary movement. Majority of the fibres of the corticospinal tract cross over in the medulla oblongata, resulting in muscles being controlled by the opposite side of the brain.

Nerves within the corticobulbar tract are involved in movement in muscles of the head. Involved in swallowing, phonation and movements of the tongue the corticobulbar tract is also responsible for transmitting facial expression due to it’s involvement with the facial nerve

Question 28

Characteristics of Neuronal Pathways

Answer 28

Neural pathway is the connection formed by axons that project from neurons to make synapses onto neurons in another location in order to enable a signal to be sent from one region of the nervous system to another. Neurons are connected by a single axon or b a bundle of axons known as a nerve tract (fasciculus). Shorter neural pathways are found within grey matter, while longer projections made up of myelinated axons constitute the white matter.

• Descending motor pathways of the pyramidal tracts travel from the cerebral cortex to the brainstem or lower spinal cord
• Ascending sensory tracts in the dorsal column carries information from the periphery to the cortex of the brain

Question 29

Major Neural Pathways

Answer 29

1. Arcucate Fasciculus
2. Cerebral Peduncle
3. Corpus Callosum
4. Pyramidal Tracts
5. Medial Forbrain Bundle
6. Medial Leminscus Pathway
7. Retinohypothalamic Tract

Question 30

Arcuate Fasciculus

Answer 30

A bundle of axons that form parts of the superior longitudinal fasciculus (association fibre tract). It bi-directionally connects the caudal temporal cortex and the inferior parietal cortex to locations in the frontal lobs. Common understanding has been that the arcuate fasciculus connects 2 importance areas of use for language: the Broca’s area in the inferior frontal gyrus and the Wernicke’s area in the posterior superior temporal gyrus

Question 31

Cerebral Peduncles

Answer 31

Cerebral peduncles are structures at the front of the midbrain which arise from the front of the pons and contain the large ascending (sensory) and descending (motor) nerve tracts that run to and from the cerebrum from the pons

• Cortico-spinal tract
• Cortico-potine tract
• Cortico-bulbar tract

The 3 common areas give rise to the cerebral peduncles are the cerebral cortex, spinal cord and cerebellum.

The cerebral peduncles (also known as the cerebral crus) are the part of the midbrain that link the remainder of the brainstem to the thalami and thereby, the cerebrum. They are the most anterior structure in the midbrain and contain the large ascending and descending tracts that run to and from the cerebrum.

Question 32

Corpus Callosum

Answer 32

Aka callosal commissure is a wide thick, nerve tract consisting of a flat bundle of commissural fibres, beneath the cerebral cortex in the brain.

It spans part of the longitudinal fissure to connect L and R cerebral hemispheres, enabling communication between them. The largest white matter structure in the human brain.

Separate Nerve Tracts / Sub Regions:

• The genu
• The rotsum
• The trunk (or body)
• The spenium

Clinical Significance:
Damage results in dissociation of hemisphere compiled functions. Ex: He | Art

Question 33

Pyramidal Tracts

Answer 33

Include corticobulbar tract and corticospinal tracts. These are agression of efferent nerve fibers from the upper motor neurons that travel from the cerebral cortex and ends either in the brainstem (corticobulbar) or spinal cord (corticospinal) and are involved in the control of motor functions of the body The corticobulbar tract conducts impulses from the brain to the cranial nerves. These nerves control the muscles of the face and neck and are involved in facial expression, mastication, swallowing and other functions.

Cortico-spinal tract conducts impulses from the brain to the spinal cord and is made up of a lateral and anterior tract. Also involved in voluntary movements - the majority of the fibres of the cortico-spinal tract cross over in the medulla oblongata, resulting in muscles being controlled by the opposite of the brain

Function:

• Movement of mucles
• Muscles are supplied by the side of the brain opposite to that muscle
• Movement of the head
• Swallowing, phonation and movements of the tongue

Damage to corticobulbar tract:

• Spasticity
• Hyperactive Reflexes
• Loss of ability to perform fine movements
• Extensor plantar response known as Babinski Sign
• Sensory problems

Damage to only one side results in lower face being affected. If both are injured is results in pseudobulbar palsy (causes problems with swallowing, speaking and emotional liability)

Question 34

Medial Forebrain Bundle

Answer 34

MFB is a neural pathway containing fibers form the basal olfactory regions, periamygdaloid region, fibers from brainstem regions and the septal nuclei.

MFB is of the 2 major pathways connecting the limbic forebrain, midbrain and hindbrain.

The other one is the dorsal diencephalic conduction (DDC) system. Two pathways seem to have parallel neural circuits and share similar physiology and function = reward system in the integration of reward and pleasure

Question 35

Dorsal Column - Medial Lemniscus Pathway (DCML)

Answer 35

A sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two point discrimination and proprioception from the skin and joints.

Transmits information from the body to the primary somasensory cortex in the postcentral gyrus of the parietal lobe of the brain. The pathway receives information carrying sensory receptors throughout the body and carries this via nerve tracts in the white matter of the dorsal columns of the spinal cod to the somatosensory cortex

1. Sensory receptor
2. Nerve tracts in white matter of the dorsal columns of the spinal cord
3. Medulla (first order axons towards thalamus)
4. Medial Leminscus (second order axons towards thalamus)
5. Thalamus (third order neurons towards somatosensory cortex)
6. Somatosensory Cortex

Involve:
1st, 2nd and 3rd order neurons

Question 36

First Order Neurons

Answer 36

Sensory neurons located in the dorsal root ganglia, that send their afferent fibre through the 2 dorsal columns; the gracile tract and the cuneate tract. The first-order axons make contact with second-order neurons at the gracile nucleus and the cuneate nucleus in the lower medulla

Question 37

Second Order Neurons

Answer 37

Send axons to thalamus

Question 38

Third Order Neurons

Answer 38

Are ventral nuclear groups in the thalamus and fibres from these ascend to the postcentral gyrus

Question 39

1st, 2nd, 3rd order Neurons

Answer 39

The first-order neurons carry signals from the periphery to the spinal cord; the second-order neurons carry signals from the spinal cord to the thalamus; and the third-order neurons carry signals from the thalamus to the primary sensory cortex. Second-order neurons are generally located in the spinal cord or brainstem.

Question 40

Receiving Sensory Information

Answer 40

Sensory information from the upper half of the body is received at the cervical level of the spinal cord and carried in the cuneate tract, and information from the lower body is received at the lumbar level and carried in the gracile tract. Gracile tract is medial to the more lateral cuneate tract.

Axons of second order neurons of the gracile and cuneate nuclei are known as the internal arcuate fibres and when they cross over the midline in he medulla, they form the medial lemniscus

Question 41

Medial Forebrain Bundle Function

Answer 41

One of the two major pathways connecting the limbic forebrain, midbrain and hindbrain.

Second is the dorsal diencephalic conduction (DDC) system. The two pathways seem to have parallel neural circuits and share similar physiology and function = reward system in the integration of reward and pleasure.

Question 42

Dorsal Column - Medial Lemniscus Pathway (DCML)

Answer 42

Sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two point discrimination and proprioception from the skin and joints.

Transmits information from the body to the primary somatosensory cortex in the postcentral gyrus of the parietal lobe of the brain. Pathway receives information from sensory receptors throughout the body and carries this via nerve tracts in the white matter of the dorsal columns of the spinal cord to the somatosensory cortex

Question 43

Retinohypothalamic Tract

Answer 43

A photic neural input pathway involved with the circadian rhythms. The axons of the retinohypothalamic tract communicate monosynaptically with the suprachiasmatic nuclei via the optic nerve and the optic chiasm. The suprachiamastic nuclei receive and interpret information on environmental light, dark, day length, to coordinate the peripheral “body clocks” and direct the pineal gland to secrete the hormone melatonin.

Question 44

Ascending (Sensory) Pathways

Answer 44

Activation of a sensory receptor results in an action potential, which propagates through fibres of the respective nerve to the CNS where it reaches the appropriate relay neurons and is transmitted along an ascending pathway to reach the cerebral cortex or the cerebellum.

Question 45

Anterolateral System (ALS)

Answer 45

Relays information relating to pain, temperature, crude touch and pressure

Sub divisions:

• Spinothalamic Tract
• Spinoreticular Tract
• Spinotectal Tract

Question 46

Dorsal Column-Medial Lemniscus (DCML)

Answer 46

Relays information relating to conscious proprioception of the limbs, fine touch and vibration

Subdivisions:

• Fasciculus Gracilis
• Fasciculus Cuneatus

Question 47

Spinocerebellar Pathways

Answer 47

Conveys low range proprioceptive stimuli from receptors located in muscles, tendons, and joints of the hindlimb. Proprioceptive information entering the spinal cord rostral to C8 is carried by nerve fibres ascending in the fasciculus cuneatus.

Primarily relays information relating to unconscious proprioception

Subdivisions:

• Posterior spinocerebellar
• Anterior Spinocerebellar
• Rostal Spinocerebellar
• Cuneocerebellar

Question 48

Brown-Sequard Syndrome

Answer 48

Demonstrates damage to the spinal cord to exist in a distinct tract or quadrant, however caused by a hemi-section (only right or left is severed) of the spinal cord and its result in sensory deficits:

• Severing of the ALS results in contralateral loss of pain, temperature, crude touch and pressure sensation a few segments below the level of damage to the spinal cord
• Severing of the DCML pathway results in ipsilateral loss of fine touch and vibration a few segmens below the level of damage to the spinal cord

Question 49

Descending (Motor) Pathways

Answer 49

Pathways by which motor signals are sent from the brain to lower motor neurons - lower motor neurons then directly innervate muscles to produce movement

Question 50

Pyramidal Tracts

Answer 50

Tracts originate in the cerebral cortex carrying motor fibres to the spinal cord and brainstem - responsible for the voluntary control of the musculature of the body ad face

Derive their names from the medullary pyramids of the medulla oblongata which they pass through. Pathways are responsible for the voluntary control of the musculature of the body and face

Functional Tracts:

• Corticospinal Tracts = supplies the musculature of the body
• Corticobulbar Tracts = supplies the musculature of the head and neck

Question 51

Extra-pyramidal Tracts

Answer 51

These tracts originate in the brain stem, carrying motor fibres to the spinal cord. They are responsible for the involuntary and autonomic control of all musculature, such as muscle tone, balance, posture and locomotion.

Question 52

Termination of Descending Tracts

Answer 52

There are no synapses within the descending pathways. At the termination of the descending tracts, the neurons synapse with a lower motor neuron. Thus all neurons within the descending motor system are classified as upper motor neurons. Their cell bodies are found in the cerebral cortex or the brainstem with their axons remaining within the CNS

Question 53

Corticospinal Tracts

Answer 53

Begins in the cerebral cortex from which they receive a range of inputs from the Primary Motor Cortex, Premotor cortex, Supplementary Motor Area and receive nerve fibres from the somatosensory area which play a role in regulating the activity of ascending tracts

Question 54

Nerve fibre direction and passage

Answer 54

1. Neurons converge and descend through the internal capsule located between the thalamus and the basal ganglia.
2. After the internal capsule, the neurons pass through the crus cerebri of the midbrain, the pons and into the medulla
3. In the most inferior (caudcal) part of the medulla the tract divides into two:
   * The lateral corticospinal tract decussates and descends into the spinal cord, terminating in the ventral horn of all segmental levels. From the ventral horn, the lower motor neurons supply the muscles of the body.
   * The anterior coritcospinal tract remains ipsilateral, descending into the spinal cord and then decussate and exclusively terminate in the ventral horn of the upper cervical and upper thoracic regions.

Question 55

Extra-Pyramidal Tracts

Answer 55

Originate in the brainstem carrying motor fibers to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion

Tracts:

• Vestibulospinal & Reticulospinal tracts - do not decussate providing ipsilateral innervations
• Rubrospinal & Tectospinal tracts do decussate (cross or intersect) and therefore provide contralateral innervations

Question 56

Vestibulospinal Tracts

Answer 56

Medial & Lateral

Arise from the vestibular nuclei, which receive input from the organs of balance. The tracts convey this balance information to the spinal cord where it remains ipsilateral

Control balance and posture by innervating the anti-gravity muscles (flexors of the arm, and extensors of the leg) via lower motor neurons

Question 57

Reticulospinal Tracts

Answer 57

Have 2 recticulospinal tract arises from the pons
* Controls voluntary movements and increases muscle tone

Medial Reticulospinal Tract

• Arises from the pons
• Controls voluntary movements and increases muscle tone

Lateral Reticulospinal Tract

• Arises from the medulla
• Inhibits voluntary movements and reduces muscle tone

Question 58

Rubrospinal

Answer 58

Originates from the red nucleus (related to dopamine) a midbrain structure. Fibres decussate (cross-over) and descend into the spinal cord = contralateral innverations
- Functions: unclear, probable fine control of hand movements

Question 59

Tectospinal Tracts

Answer 59

This pathway begins at superior colliculus (structure afferent to the optic nerves) of the midbrain. The neurons decussate and terminate at the cervical levels of the spinal cord.
- Coordinates movements of the hand in relation to vision stimuli

Question 60

Upper Motor Neuron Lesion:

Damage to Corticospinal Tracts

Answer 60

Pyramidal tracts are susceptible to damage because they extend almost the whole length of the CNS, particularly vulnerable to cerebrovascular accidents as they pass through the internal capsule - a common site of CVA

Question 61

Damage to Extra-pyramidal Tracts

Answer 61

Extra-pryamidal tract lesions are commonly seen in degenerative diseases, encephalitis and tumors. They result in various types of dyskinesias or disorders of involuntary movement

Question 62

Interoceptors

Answer 62

Also called visceroceptors, respond to stimuli within the body, internal viscera and blood vessles, monitor a variety of stimuli, including chemical changes, tissue stretch and temperature, activity of these can cause us to feel pain, discomfort, hunger or thirst.

Question 63

Proprioceptores

Answer 63

Respond to internal stimuli, location is much more restricted, in skeletal muscles, tendons, joints and ligaments and in connective tissue coverings of bones and muscles, constantly inform brain of our body movements by monitoring how much the organs containing these receptors are stretched

Question 64

Mechanoreceptors

Answer 64

Respond to mechanical forces (touch, pressure, vibration & stretch)

Question 65

Thermoreceptors

Answer 65

Respond to temperature change

Question 66

Photoreceptors

Answer 66

Those of the retina of the eye, respond to light, taste, changes in blood or intestinal fluid chemistry

Question 67

Chemoreceptores

Answer 67

Respond to chemicals in solution, molecules smelled or tasted, changes in blood or intestinal fluid chemistry

Question 68

Nociceptors

Answer 68

Respond to potentially damaging stimuli that result in pain

Question 69

Exteroceptors

Answer 69

Sensitive to stimuli arising outside the body, so most exteroceptors are near or at the body surface, touch, pressure, pain and temperature receptors in skin and most receptors of special senses (vision), hearing, equilibrium, smell and taste

Question 70

Receptor Structure

Answer 70

Non-encapsulated Nerve Endings:

• Free nerve ends of sensory neurons
• Modified free nerve endings
• Hair follicle receptors

Encapsulated Nerve Endings

• Tactile (Meissner’s) Corpuscles
• Lamellar (Pacinian) Corpuscles
• Bulbous Corpuscles
• Muscle Spindles
• Tendon Organs
• Joint Kinesthetic Receptors