Physiology 🫁 Flashcards
what are the components of the sensory nervous system?
1- Sensory receptors
2- Afferent fibers
3- Sensory center (special areas in brain or spinals cord)
Definition of Sensory receptors
Receptors are specialized microscopic structures located at the peripheral terminations of the afferent nerves.
Functions of Sensory receptors
They detect the stimuli and transduce (convert) these stimuli into nerve impulses (detectors and transducers).
Classification of Sensory receptors
Anatomical classification: divided into an External and internal receptors
Physiological classification: divided into Mechano-receptors, pain receptor, thermal receptor, chemical, and photoreceptors
what are the properties of Sensory receptors?
- Specificity (Adequate stimulus).
- Excitability (Receptor potential).
- Rate of discharge from the receptors (detection of the stimulus intensity).
- Adaptation of the receptors.
what is Specificity of sensory receptors?
- The receptors show a high degree of specificity as Muller’s law applies:
Muller’s law:
“Each type of receptors is highly sensitive to one type of stimuli called the adequate stimulus and its stimulation gives rise to one type of sensation whatever the way of stimulation”.
Examples of Specificity of sensory receptors
- Retinal receptors are highly sensitive to the light waves.
- Auditory receptors are highly sensitive to the sound waves…etc.
what are exceptions of Specificity of sensory receptors?
- However, the receptors may respond to stimuli other than their specific or adequate ones, provided that these stimuli are very strong; but still the response is the same modality to which the receptor is specialized
Example: Retinal receptors are normally stimulated by the light waves and give rise to sense of vision. But if heavy mechanical stimuli applied to the eye as in heavy blow, the retinal receptors can be stimulated and eye sees flashes of light.
Compare between adequate stimulus & Non-adequaqte stimulus in terms of:
- Intensity of stimulus
- Example
what does Excitability of Sensory receptors mean?
Excitability of receptors is the ability of the receptors to respond to their adequate stimuli.
How do receptors respond to stimuli?
- Most of the body receptors on adequate stimulation show depolarization through the increased permeability of their membranes to Na+.
- Only the visual receptors (Rods & Cones) when stimulated adequately, they show hyperpolarization (Further details in special sense).
what is the definition of Receptor potential (Generator potential)?
is the potential changes that occur in the receptors on adequate stimulation, usually in the form of depolarizations. (Partial)
where is study of receptors potential best demonstrated?
It is best studied in pacinian corpuscles
why is study of receptors potential best demonstrated on pacinian corpuscle?
i) Easily stimulated by microglass rods under microscope.
ii) Large in size and easily dissected.
Type of Pacinian corpuscle receptors
(mechano-receptors present in the skin, deep tissues involved in the sensations of touch, pressure and vibrations).
Structure of pacinian corpuscle
- Pacinian corpuscle is a vesico-elastic structure consists of several concentric layers of connective tissues like an onion surrounding a central nerve terminal.
- The ending of the sensory nerve is not myelinated, but the first node of Ranvier is also located inside the capsule.
Mechanism of Receptor potential
Revise the notes in this page
what is the amplitude of the electronic current directly proportional to?
The amplitude of electrotonic current is determined by the amplitude of the receptor potential which by its turn depends upon the intensity of the stimulus.
what is the maximum amplitude of receptor potential?
- The maximal amplitude of receptor potential around 100 mv occurs when maximal opening of Na+ channels is achieved in the receptor membrane.
what does the generation of further action potentials depend on?
name of the point of receptor stimulation
The nerve terminal is termed the Transducer region
what is the first node of ranvier in pacinian corpuscle called?
1st node of Ranvier is called the Spike Generator region.
what are the properties of receptor potential?
what is the relation between stimulus intensity & Rate (Frequency) of impulses discharged from the receptors?
Relation between stimulus intensity and rate (frequency) of impulses discharged from the receptors is logarithmic according to “Weber-Fischer law”
Statment of Weber-Fischer law
The Rate (frequency) of impulses discharged from the receptors through the afferent nerves is directly proportional with the logarithm intensity of the applied stimulus.
Equation of Weber-Fischer law
R= Log S x K
- R= rate of discharge.
- S= strength of stimulus.
- K=constant.
Examples of relation between stimulus intensity & rate og impulses discharged according to Weber-Fischer law
- Increase stimulus intensity 100 times leads to increase rate of discharge 2 times only (as log 100 =2).
- Increase stimulus intensity 1000 times leads to increase rate of discharge 3 times only (as log 1000=3).
what is the significance of Weber-Fischer law?
This allows receptors to:
1) Respond to a wide range of stimulus strength.
2) Compression function of the receptors which means that the receptors compress these wide range of stimuli into narrow range of discharge.
How does intensity of stimulus increase rate of discharge?
Definition of Adaptation of sensory receptors
Decline in the rate of discharge from receptor in spite of prolonged constant stimulation
Compare between Rapidly adapting receptors & Slowly adapting receptors in terms of:
- Definition
- Example
- Other name
- Physiological significance
what is a Sensory unit?
- Single sensory axon with its peripheral branches and receptors.
- All receptors of the some sensory unit are sensitive to the same type of stimulation.
What is Receptive field?
- Area of skin which is supplied by sensory unit
what is the definition of Coding of sensory information?
- It is the ability of higher centers of the brain to identity the:
- Type of the stimulus (modality discrimination).
- Intensity of the stimulus (intensity discrimination).
- Locality of stimulus (locality discrimination).
what does Modality Discrimination depend on?
Peripheral & Central mechanisms
Peripheral mechansim of Modality Discrimination
- Occurs at the level of receptors and depends on muller’s law.
- So that specificity of receptors represents the first step in the coding of different modalities (types) of stimuli.
Central mechansim of Modality Discrimination
what does Intensity Discrimination depend on?
Peripheral & Central mechanisms
Peripheral mechanism of Intensity Discrimination
Depends on:
- Rate of impulse discharge from each receptor: the higher the rate of discharge, the stronger is the stimulus.
- Number of stimulated receptors (recruitement of recepfors): the more the number of stimulated recepfors, the stronger is the stimulus.
Central mechanism of Intensity Discrimination
Depends on: number of afferents reaching CNS: the more the number of afferents reaching CNS the stronger is the stimulus.
what does Locality Discrimination depend on?
Somatotopic map
- According to which each area in the body is represented in a specific area in the cerebral cortex with accurate anatomical pathways from the receptor to the center in the cerebral cortex.
- So when the impulse reaches specific area in the cerebral cortex, the sensation isn’t felt in the cortical neuron but it is referred (projected) to its original site in the body this principle is called law of projection.
what is Sensation?
- Sensation is the conscious awareness of a particular feeling produced by stimulation of a certain type of receptors by its adequate stimulus.
Classification of sensation
General:
- Arises from widely distributed receptors all over the body.
Special:
- vision
- taste
- smell
- hearing
- Sense of equilibrium.
Emotional:
- fear
- anxiety
- sadness
Com pare between Somatic sensation, Visceral sensation & Sensation organ in terms of:
- Arise from
- Crried by
- Examples
what is the definition of Touch sensation?
- It is a sense or feeling produced by application of light mechanical pressure to the skin
what happens if the intensity of touch increases?
if the intensity of the stimulus is increased, it is changing into pressure sense
what are the types of touch?
a) Fine touch.
b) Crude touch.
Definition of Crude touch
A type of touch sensation which is poorly localized
Stimulus in case of Crude touch
Diffuses ill defined object, Touching the skin with a piece of cotton or the touch of clothes.
Receptors of Crude touch
- Free nerve endings & hair end organs or follicle receptors “located in the hair follicles”
Afferents of Crude touch
- A-δ nerve fibers “5-30 meter/second”.
- C fibers “0.5-2 meter/second”.
Pathways of Crude touch
Pathway from the body:
- Ventro spino thalamic tract by A delta fibers
- Spino reticular tract by C fibers
Pathway from the face:
- Trigeminal pathway
whose transmission is faster, crude or fine touch?
The transmission of crude-touch is much slower than fine touch
Spatial arrangment of Crude touch
the spatial arrangement of the fibers in the pathway is poor
Does Crude touch inform the CNS accurately?
the impulses not inform the C.N.S accurately about the size & site of the crude-touch stimulus
Definition of Fine touch
It is a type of touch which informs us accurately about the shape, form and site of the tactile stimulus.
Stimulus of Fine touch
Well localized object to the skin as tip of pencil, head of a pin, teeth of comb
Receprors of Fine touch
- Meissner’s corpuscles (rapidly adapting).
- Merkel’s discs (slowly adapting)
Afferents of Fine touch
A-beta rapidly conducting nerve fibers (30-70 meters/second).
Pathway of Fine touch
Fine touch impulses are transmitted by A-beta nerve fibers which travel through the Dorsal column – medial lemniscal system (Gracil & Cuneate tracts).
Types of Fine touch
1-Tactile localization
2-Tactile discrimination
3-Stereognosis
4-Texture of materials
Definition of Pressure sensation
It is a sensation produced by the application of heavy mechanical stimuli to the skin (which can cause deformation of the different skin layers).
Receptors of Pressure sensation
a) Rapidly adapting receptors (Pacinian corpuscles).
b) Slowly adapting receptors (Ruffini multi-branched nerve endings); present in the deeper layers of the skin and responsible for the continuous information of the C.N.S about the pressure stimuli which play a role in the orientation of body position.
Afferents of Pressure sensation
as fine touch. (G & C)
Pathway of Pressure sensation
as fine touch. (G & C)
Types of Pressure sensation
Deep pressure sense:
- Discriminate between different weights without lifting them
Muscle tension sense:
- Discriminate between different weights with lifting them
significance of Pressure sensation
- Maintain posture
- Diffrentiate between different weights
Defintion of Vibration sensation
- It is a sensation of rhythmic pressure changes produced by the rapid repetitive stimulation of certain mechanoreceptors.
Stimulus of Vibration sensation
It can be produced by placing the base of vibrating tuning fork on the skin over bony prominence
Receptors of Vibration sensation
i)Meissner’s corpuscles: can respond to frequencies to frequencies up to 200 cycles/second.
ii)Pacinian corpuscles: can respond to frequencies to frequencies up to 700 cycles/second.
Afferents of Vibration sensation
as fine touch (G &C)
Pathway of Vibration sensation
as fine touch (G &C)
Definition of Proprioceptive sensation
Is a sense that allows us to know the position and movement of every part of the body specially joints and limbs.
Receptors of Proprioceptive sensation
1) Muscle proprioceptors.
2) Joint proprioceptors.
Pathway of Proprioceptive sensation
- At conscious level
- At subconscious level
Types of Proprioceptive sensation
- Sense of position.
- Sense of movement.
- Muscle-tension sense.
- Deep pressure sense.
what are the types of Fine touch?
1-Tactile localization
2-Tactile discrimination
3-Stereognosis
4-Texture of materials
what is the definition of Tactile localization (topognosis)?
- It is the ability of the person with his eyes closed to perceive and determine accurately the site of a single point of fine touch.
Definition of Tactile discrimination (2 point discrimination)
Its the ability of the person or central nervous system to discriminate 2 points of fine touch applied simultaneously to the skin with the person’s eyes closed provided that the distance between them is greater than the minimal distance.
what is Minimal (Threshold) distance?
it is the distance between 2 points of fine touch below it the points are felt as a single point whereas at or above it the 2 points are felt as separate points
what does Minimal (Threshold) distance equal?
It equals 1 mm at tip of tongue, 3 mm at tip of fingers, 70 mm at the back.
where is Tactile discrimination more accurate? and why?
- On the extremities than on the proximal parts due to:
- Greater number of touch receptors, and subsequently a greater number of afferents
- Little convergence of afferents.
- Wide area of cortical representation and so good analysis and interpretation of sensory information.
what is the definition of Stereognosis?
Is the ability of the person with his eyes closed to recognize a familiar object by touching it e.g. recognition of a key, a pen or a coin.
what is the definition of Determination of texture of materials?
- Is the ability of the person with his eyes closed to recognize the nature of an object/textiles e.g. glasses and wood
which type of sense is Sense of position?
static sense
what does sense of position represent?
conscious orientation of the relative position of the different parts of the body to each other.
which type of sense is Sense of movement?
dynamic sense
what does Sense of movement represent?
means conscious orientation of the changes in the relative position of the different parts of the body to each other as regard, onset, termination, direction and the rate or velocity of this change
what are receptors of proprioception?
Compare between pathway of proprioception at conscious & subconscious level in terms of:
- Center
- Function
- Pathway
Definition of Thermal sensation
Is the sensation that enables us to detect temperature change, it includes warm and cold sensation.
Distribution of Cutaneous thermo receptors
- Number of cold receptors is greater than the number of warm receptors by about 3- 10 times.
- They are distributed in a punctuate fashion where, certain areas of skin contain warm receptors only and others contain cold receptors only with thermally insensitive areas in between.
what are the types of thermo-receptors?
- External (peripheral) thermoreceptors
- Internal (central) thermoreceptors
Compare between External (Peripheral) thermo-receptors and internal (Central) thermo-receptors in terms of:
- Types
- Location
- Detect
Compare between Warm & Cold Receptors in terms of:
- Morphology
- Number
- Afferent fiber
- Discharge impulse between
- Maximum discharge
Thermo-receptors at zero degree
all receptors stop discharge and this is one of the methods of anaesthesia.
Thermo-receptors at 45 degrees
the person feels “Paradoxical cold sensation” due to a brisk discharge from the cold receptors “Paradoxical cold sensations”.
Thermo-receptors if temperature is less than 10 degrees
- Stimulate cold pain receptors
Thermo-receptors if temperature is more than 45 degrees
Stimulate warm pain receptors
what is the mechanism of stimulation of thermo-receptors?
what is the type of thermo-receptors?
Biphasic but mainly slowly adapting receptors
Adaptation of thermo receptors
Neural pathway of thermal sensation
Definition of Pain Sensation (Nociceptors)
- Unpleasant sensory and emotional experience associated with actual tissue damage.
Physiological significance of Pain Sensation
- Protective sense that direct the person to get rid of injurious stimulus.
what are the characters of pain receptors?
what is the type of pain receptors?
- They are morphologically one type → free nerve endings.
- They are slowly adapting and even non-adapting receptors.
Specifity of pain receptors
- Highly specific → respond to tissue damage & classified
according to type of painful stimuli into:
a. Mechanical pain receptor→ to mechanical stimulus.
b. Chemical pain receptor→ to chemical stimuli
c. Thermal pain receptor → respond to excess temperature → (<10°C &>45°C)
d. Polymodal pain receptor → respond to all above painful stimuli.
Threshold of pain receptors
high threshold → need strong stimulus that cause tissue damage.
Distribution of pain receptors
Widely distributed all over the body:
a. More abundant in the skin.
b. Present in deeper structures (muscles - joints - periosteum).
c. Viscera contains a smaller number of pain receptors and even this few numbers are concentrated in serous membranes e.g. peritoneum, pleura, pericardium & meninges of the brain.
d. Absent from: Liver, lung, brain & bone
when do diseases that affect the viscera start causing pain?
- The diseases affecting the parenchyma of organs, may not produce pain early, but lateral when they invade the serous covering they cause severe pain.
Definition of Pain Threshold
The lowest intensity of injurious agent needed to stimulate the pain receptors and produced pain sensation.
what are the methods of determination of the pain threshold?
- By pricking the skin with a pin.
- By compressing the skin against hard objects.
- Thermal method “more accurate’’ by applying to skin to a thermostatically controlled metallic rod (Most of individuals begin to feel pain at 45°C and all feel pain at 47 C and this is known as thermal threshold for pain receptors stimulation).
Feeling of pain in different people
- Most people feel pain at similar points but differ in their reaction to pain.
- Pain threshold is not the same in all individuals.
what is pain classified into?
What is the mechanism of stimulation of pain receptors?
Definition of Pain producing substance
- Which directly stimulate pain receptor.
Examples of Pain producing substances
- Histamine, serotonin.
- Bradykinin.
- Proteolytic enzymes & K ions.
Definition of Pain sensitizers
- Which increases sensitivity of receptors by lowering pain threshold
Examples of Pain sensitizers
- Substance-P
- PGs-E2
What are neural pathways for pain transmission?
1) Fast pain pathway (Neo-spino-thalamic tract).
2) Slow pain pathway (paleo-spino-thaiamic tract).
Significance of Neo-spinothalamic tract
a. Rapidly Inform the C.N.S about the injurious agent to initiate rapid protective reflexes as flexion withdrawal reflex.
b. Determining accurately the site of the painful stimuli.
Characters of Neo-spinothalamic tract
- Fast pain is transmitted by neo- spinothalamic tract.
- Consists of 3 order neurons “A-δ nerve fibres”
1st order neuron of Neo-spinothalamic tract
- From pain receptors →1st order neuron → dorsal horn → end on neurons in laminae I & IV.
- Its ends release rapidly acting neurotransmitter (Glutamate)
2nd order neuron of Neo-spinothalamic tract
- From dorsal horn cells fibers pass to opposite side in front of central canal→ ascend in the lateral column of the spinal cord till the PVLNT of thalamus.
3rd order neuron of Neo-spinothalamic tract
- From PVLNT, fibres Ascend in the posterior limb of internal capsule to terminate in primary sensory cortex (3. 1 & 2) in the post- central gyrus.
Significance of Paleo-spinothalamic tract
a. Continuously inform C.N.S about the presence of tissue damage to direct the person to remove the injurious agents
b. Responsible for strong arousal state due to potent (strong) activation of reticular activating system (RAS)
Characters of Paleo-spinothalamic tract
- Slow pain transmitted by paleo- spinothalamic tract
- Consists of C non-myelinated nerve fibers.
1st oerder neuron of Paleo-spinothalamic tract
- C-myelinated nerve fibres ends in laminae II & III on dorsal horn
- Release the slowly acting neurotransmitter (substance- P)
2nd order neuron of Paleo-spinothalamic tract
- From the dorsal horn, fibers arise & Ascend in the lateral column till Brainstem where it relays on the neurons of reticular formation.
3rd order neuron of Paleo-spinothalamic tract
- From R.F, fibers ascend to intralaminar (non specific) nuclei of the thalamus → then fibres arise & ascend to all areas of the cerebral cortex
Definition of Cutaneous pain
Pain sensation results from the stimulation of pain receptors in the skin.
Compare between the components of Cutaneous pain (Fast “Pricking” & Slow “Burning”) pain in terms of:
- Localization & Quality
- Spread
- Significance
- Perception and lost in
- Transmission
what is the Role of the cerebral cortex in pain perception?
1) Coding of sensation i.e. determine type, site, intensity of pain.
2) Lesion in cerebral cortex → pain will be diffuse, ill-defined.
Reaction to cutaneous pain
what is Cutaneous hyperalgesia?
Increased pain sensitivity in skin area, surrounding to the site of injury.
Types of Cutaneous hyperalgesia
- 1ry hyperalgesia (allodynia)
- 2ry hyperalgesia
Site of 1ry hyperalgesia (allodynia)
Develop in area of erythema (flare) which surrounds 1ry site of injury.
Characters of 1ry hyperalgesia (allodynia)
- Pain threshold is lowered that non-painful stimuli as touch produces pain
- Develops within 30 - 60 min following skin injury & lasts for several hours or days.
Mechanism of 1ry hyperalgesia (allodynia)
Local axon reflex:
- In which antidromic fibers arise from afferent pain fibers which arise from 1ry site of injury, these antidromic fibers release substance - P & PGs in skin area surrounding 1ry site of injury to ↓ threshold of pain.
Definition of 2ry hyperalgesia
- Develops in normal skin which surrounds area of flare
Characters of 2ry hyperalgesia
- No lowering of pain threshold but mild painful stimuli produce more severe pain than usual.
- Shorter duration than 1ry hyperalgesia.
Mechanism of 2ry hyperalgesia
Convergence-facilitation theory:
- In which fibers arise from 1ry site of injury & from area of 2ry hyperalgesia converge on the same neuron in dorsal horn in spinal cord or thalamus
- Fibers from 1ry site of injury produce state of facilitation (excitability) that the response to pain is intensified → that mild pain from normal skin is felt as severe pain →This facilitation occurs mainly at level of SGR but can occur atlevel of thalamus or cerebral cortex
Definition of Deep pain
- Pain sensation due to stimulation of receptors in deeper structure as muscle, tendon, joint
Causes of Deep pain
- Injury or trauma to tissue
- Inflammation as arthritis & myositis.
- Ischemia to tissue
Characters of Deep pain
- Dull aching or throbbing
- Poorly localized
Pathway of Deep pain
C-nerve fibers
Definition of Visceral pain
- Pain sensation due to stimulation of receptors in the viscera.
Causes of Visceral pain
- Spasm of smooth muscle in wall of hollow viscera (colic) → (most common cause)
- Mechanical over distension of hollow visceral wall as stomach (a & b cause ischemia of organ → pain)
- Inflammation of viscera.
- Irritation as → HCI in stomach
- Thrombosis of SMA.
- Trauma → diffuse cut of viscera
Characters of Visceral pain
- Dull aching or colicky.
- Poorly localized and referred.
Pathway of Visceral pain
Parietal pathway:
- From parietal layer of serous membrane and some retroperitoneal structures as kidney by type A-delta fiber which join somatic fiber to enter CNS.
Visceral pathway:
- From viscera and visceral layer by type C-fiber which join autonomic fibers to enter CNS.
Reaction to deep & visceral pain
- Somatic reactions → reflex spasm of overlying ms (guarding response).
- Autonomic reactions → depressor effect due to parasympathetic reaction.
- Emotional reaction.
- Hyperalgesia.
Definition of Ischemic pain
Pain due to decrease Blood Supply to active organ as skeletal ms.
Causes of Ischemic pain
- Sever arteriosclerosis or sever spasm.
- Partial obstruction by thrombosis.
- Compression from outside as tumour.
Mechanisms of Ischemic pain
- During rest with normal Blood Supply → exercising muscle Produce certain substances as K+, lactic acid → which cause local V.D → washout of these metabolites (If not washed will cause pain)
- In case of ischemia these substances will accumulate & stimulate pain
Examples of Ischemic pain
Muscle spasm → compress blood supply.
Angina pectoris pain → due to atherosclerosis of coronary artery appears on exertion & relieved by rest.
Intermittent claudication → sever pain in calf muscle which appears on walking & relieved by rest occurs in old people with severe atherosclerosis
Definition of Referred Pain
- Pain from viscera is not felt in the viscera themselves but felt in skin area or somatic structures supplied by same dorsal root which innervate diseased viscera.
Causes of Referred Pain
Both viscus & somatic structures originate from same dermatome.
Mechanism of Referred Pain
(Convergence Projection theory)
-
Pain fibers from diseased viscus & from related somatic structures converge on
same SGR cell & ascend to same cortical neuron. - Since, cortical sensory area is accustomed to receive pain impulses from somatic structures.
- So, when viscus is injured or diseased → cerebral cortex project pain to somatic structures which are supplied by same spinal dorsal root.
Definition of Neuropathic pain
A chronic type of pain caused by damage to or pathological changes in the nerve fibres either in peripheral or central nervous system
Examples of Neuropathic pain
- Trigeminal neuralgia.
- Any type of peripheral neuropathy e.g. diabetic neuropathy.
- Phantom limb.
- Herpes zoster.
Mechanism of Neuropathic pain
Peripheral sensitization or ectopic activity:
- Tissue damage produce abnormal types of Na ion channels which result in unstable sodium channel activity
Central sensitization:
- Release excitatory amino acids and neuropeptides will produce changes in 2nd order neuron such as phosphorelyation of glutamic receptors or expression of voltage gated Na channels
Characters of Neuropathic pain
1) Usually associated by hyperalgesia and allodynia.
2) Usually associated with reflex sympathetic dystrophy (sweating, warmth and/or coolness, flushing, discoloration of skin).
3) Described as excruciating burning or shooting pain.
4) It occurs in bouts or paroxysms (Attacks).
5) Partially responsive to opioid therapy.
6) Hardly to be treated.
what is cardiac pain referred to?
- Referred to Lt Shoulder, inner side of Lt arm, Lt Forearm and little finger (may be in epigastric region).
what is Oesophageal pain referred to?
Referred to pharynx, lower neck, middle chest region.
what is Gastric pain referred to?
Referred to epigastric region in wall of abdomen
what is Gall baldder pain referred to?
Referred to Rt side of epigastric region, Rt shoulder and neck
what is Renal and ureteric pain referred to?
Referred to back behind the kidney also, to ant. Abdominal wall & near inguinal region
what is Appendicular pain referred to?
Starts in skin area around umbilicus and when peritoneal covering is involved → pain shifts to Rt iliac fossa
Definition of Pain control (analgesia) system
- It is a system concerned with the inhibition of pain impulses transmission at Different levels in pain pathway and produces analgesia.
Activity of Pain control (analgesia) system
The activity of this system differs from one person to another and from time to time in the same person.
Location of Pain control (analgesia) system
Periaqueductal grey area (PAG) → in midbrain &pons.
Raphe Magnus nucleus & Nucleus para giganto cellularis → in medulla oblongata
Pain inhibitory complex → in dorsal horn of spinal cord.
Definition of Endogenous opioids
- Natural peptide substances produced inside the body (mainly by areas of pain control system) and have the ability to bind opioids receptors (morphine receptors) and produce pain analgesia (relieve pain).
Classes of Endogenous opioids
- Endorphins
- Enkephalins
- Dynorphins
Endorphins
- Derived from
- present mainly in
- Most common
- Pre-opio-melano- cortin (POMC)
- Anterior pituitary and hypothalamus.
- B-endorphins
Enkephalins
- Derived from
- present mainly in
- Most common
- Pro-enkephalins
- Brain stem and Spinal cord.
- leu-enkephalin, encephalin
Dynorphins
- Derived from
- present mainly in
- Most common
- null
- Brain stem and Spinal cord.
- null
what are opiate receptors?
what do neurons in PAG and Raphe nuclei contain?
- Contain opioids receptors on their surface membrane when stimulated by exogenous or endogenous opioids, this leads to activation of pain control system.
What activates pain control system?
activated naturally by severe stress& strong emotions e.g. during severe exercise, battles, fear.
Evidences that pain inhibition can occur at level of brain stem & hypothalamus
1- Their stimulation by (electrical stimulus) cause pain relief
2- Injection of encephalin in animal cause pain relief.
Mechanism of action of pain control system
Mechanisms for pain control at spinal cord level
Comparisons Between Slow and Fast Pain
Definition of Synapse
Areas of contact between neurons in the CNS.
Types of synapse
- Electrical synapse
- Chemical synapse
Compare between Electrical Synapse & Chemical Synapse in terms of:
- existence
- Nature
- Function
- Fatigue
- Speed
- Conduction
Site of electrical Synapse
Present in hippocampus and
retina
what do chemical synapses consist of?
Mechanism of synaptic transmission (In brief)
- Release of neurotransmitter into synaptic cleft.
- Action of neurotransmitter on postsynaptic membrane.
- Termination of synaptic transmission.
Mechanism of Release of neurotransmitter
what are Active zones?
The site at which vesicle bind to membrane
Method of release of chemical transmitter
exocytosis
what does Number of ruptured vesicles depend on?
- Number of ruptured vesicles depend on concentration of ca
Action of neurotransmitter on post synaptic membrane
After release of neurotransmitter → It binds with specific receptors on post synaptic membrane to act by two mechanisms:
- Ligand-gated ion channels (inotropic)
- G-protein coupled receptor (Metabotropic)
And explain ….
what are the types of Ligand-gated ion channels (Inotropic)?
Cation & Anion channels
what happens to cation channels of synapses on activation?
- When activated , allows Passage of Na+& K+ but Na+ influx more than K+ efflux (about 7.5 time) due to ↑ driving force for Na+→ Depolarization of the membrane.
Neurotransmitter in cases of cation channels in chemical synapses
- Neurotransmitter is called excitatory transmitter
why don’t cation channels in chemical synapses allow passage of anions as cl?
- Channels are lined with -ve Charge which don’t allow passage of anions as Cl-.
what happens to anion channels of synapses on activation?
- When activated , allows passage of Cl- → Cl– influx → Hyperpolarization of the membrane.
Neurotransmitter in cases of anion channels in chemical synapses
Neurotransmitter is called inhibitory transmitter.
why don’t anion channels in chemical synapses allow passage of cations as Na & Ca?
- Channels are lined with +ve charge and has small pores , So don’t allow passage of cations as Na+ & Ca2+ .
G-Protein coupled receptors (Metabotropic)
- These receptors are bound to G-proteins, which is composed of 3 subunits {α, β, γ} & α-subunit is bound to GDP.
- When chemical transmitter binds to receptor → GDP is converted to GTP.
Effects produced when α-subunit with GTP separates
Opening of specific ion channels: 2nd messenger gated k+ channels Opens → k+ efflux → Hyperpolarization of post synaptic membrane.
Activation of enzyme system in the cell membrane leads to formation of 2nd messenger as cAMP which control metabolic pathway.
Regulation of gene expression: stimulate DNA to form m.RNA, which form protein (receptors and enzymes).
Termination of synaptic transmission
a) By active reuptake into presynaptic terminal.
b) By enzymatic destruction.
c) By diffusion into surrounding interstitial fluid
Compare between Post-Synaptic Potential in terms of:
- During rest
- On stimulation
- Excitability of membrane
Properties of Post-synaptic potential
what happens to summated EPSP reach firing level?
When summated EPSP reach firing level → this will generate an action potential at initial Segment of axon (Axon hillock) because it is rich in voltage gated Na channel
Definition of Presynaptic inhibition
Inhibition of presynaptic terminal before nerve impulse reaches post- synaptic membrane.
what is Presynaptic inhibition mediated by?
Mediated by inhibitory interneuron which terminates on excitatory presynaptic neuron.
Mechanism of Presynaptic inhibition
- Inhibitory interneuron release Inhibitory neurotransmitter GABA which open Cl channels in presynaptic terminal →↑ Cl- influx which cause hyperpolarization which inhibit voltage gated Ca channel → ↓ Ca++ influx →↓ neurotransmitter release.
Types of inhibition of synapses
- Post-synaptic inhibition
- Recurrent of feedback inhibition
- Pre-synaptic inhibition
Significance of Presynaptic inhibition
- Supraspinal inhibition of pain transmission (pain control system).
- Spinal inhibition of pain transmission.
- Lateral inhibition.
what are the types of Neurotransmitters of CNS?
- Small M.W rapidly acting Neurotransmitter
- Large M.W slowly acting Neuropeptides
Examples of Small M.W rapidly acting Neurotransmitter
Class I → Acetyl choline.
Class II→ Biogenic amines as:
- Noradrenalin
- Dopamine
- Serotonin
- Histamine
Class III → Amino acids as:
- Glutamate
- GABA
- Glycine
- Aspartate
Class IV→ NO (Nitric oxide)
Examples of Large M.W slowly acting Neuropeptides
Substance P: For pain Transmission.
Opioid peptide: as Enkephaline& endorphin for prevention of pain transmission.
Some co-exist:
- With acetyl choline as VIP.
- With noradrenalin as NPY (neuropeptide Y)
Signifance of Small M.W rapidly acting Neurotransmitter
Important for fast response as:
- Transmission of sensory information to CNS.
- Transmission of motor information from CNS to ms.
Significance of Large M.W slowly acting Neuropeptides
- Prolong action of small M.W neurotransmitter at Post synaptic membrane through G- Protein coupled receptors for days, months or years.
General properties of chemical synaptic transmission
- One-way conduction
- Synaptic delay
- Synaptic fatigue
- Effect of hypoxia
- Effect of pH
- Effect of Drugs
- Post tetanic facilitation & Long term potentiation
Direction of impulse transmission in synapses
impulses are transmitted only in one direction from presynaptic to post synaptic Neuron.
why is there one-way conduction in chemical synapses?
because no transmitter releasing vesicles in postsynaptic membrane.
Definition of synaptic delay
- It’s time () arrival of action potential to synaptic knobs & occurrence of response of post synaptic neuron
- It’s the time needed for release & diffusion of neurotransmitter & binding with receptor on post synaptic neuron.
Duration of synaptic delay
0.5 m.sec
Significance of Synaptic delay
- It help to calculate number of
interneurons.
what is synaptic fatigue?
- Decline or even stoppage of synaptic transmission with rapid & strong stimulation of Synapse.
Causes of synaptic fatigue
a) depletion of neurotransmitter stores in synaptic knobs
b) progressive inactivation of most post-synaptic receptors
c) development of abnormal concentration of ions on post synaptic neurons
usually fatigue develop gradually and recover slowly.
Significance of synaptic fatigue
- One of mechanisms which stop after discharge in reverberating circuits.
- Suppress brain activity during epileptic fit
Effect of hypoxia on synaptic transmission
- Marked hypoxia for few seconds → stop transmission & loss of excitability.
- Marked hypoxia more than 7 sec. → Coma occurs.
Effect of pH on synaptic transmission
- Alkalosis →↑ Excitability & if PH reaches 7.8-8 → convulsion occurs.
- Acidosis →↓ Excitability & if 7 → Coma occurs as in uremic or diabetic acidosis.
Effect of drugs on synaptic transmission
- Caffeine & theophylline → ↑ neuron excitability.
- Anaesthesia & hypnotic→↓ neuron excitability
- Strychnine→↑ neuron excitability.
Compare between (Post-tetanic facilitation = Post-tetanic potentiation) & Long-term potentiation in terms of:
- Produced by:
- Lasts for:
- Cause
- Function
Definition of Spinal Reflexes
- Involuntary programmed response to a stimulus.
Classification of Spinal Reflexes
- Conditioned & Unconditioned reflexes
- Somatic & Autonomic spinal reflexes
Characters of Conditioned reflexes
- Aquired
- Not inherited
- Need training
- Need intact cerebral cortex
- Play a role in regulation of GIT , respiratory , CVS functions.
characters of Unconditioned reflexes
- Inherited
- Not acquired.
- Don’t need learning
- Don’t need intact cerebral cortex
Classification of Unconditioned reflexes
Hypothalamic reflexes: e.g.
- Reflexes regulating body temperature.
- Reflexes regulating food intake.
Brain stem reflexes: e.g.
- Midbrain reflexes as light reflex.
- Pontine reflexes as salivary reflex.
- Medullary reflexes as most of CVS & respiratory reflexes.
Compare between Somatic spinal reflexes & Autonomic spinal reflexes in terms of:
- Carried by
- Innervate
Components of spinal reflex
- Receptor
- Afferent Nerves.
- Interneurons.
- Efferent Nerves.
- Effector organ.
Definition of Afferent neuron
- They are pseudo-unipolar neurons whose cell bodies are in DRG & axons divide into:
Peripheral branches: Which terminate in sensory receptor.
Central branches: which enter spinal cord through the dorsal horn
Functions of Afferent neuron
Conduction: of impulses from receptor to spinal cord.
Divergence: in which branches of afferent n. divide into many central branches.
Definition of Inter-neurons
- They are numerous , small sized, highly excitable neurons, located in spinal cord grey matter & provide link () central terminal of afferent neurons & efferent neurons.
which reflex doesn’t include Inter-neurons?
- All reflex arcs include interneurons except the stretch reflex.
- Thus, all reflexes are Polysynaptic (have more than one synapse) except the stretch reflex which is a monosynaptic (has only one synapse) reflex.
Functions of Inter-neurons
- Convergence
- Divergence
- After discharge (repetitive) circuits
- Inhibitory circuits
Definition of Convergence
Large number of afferent neuron or interneuron (more common) converge on one efferent neuron.
Significance of Convergence
This helps in spatial summation.
Definition of Divergence
- One afferent or one interneuron (more common) diverge to large number of efferent neurons.
Significance of Divergence
This helps in irradiation (wide response)
Definition of After discharge (repetitive) circuits
- Prolonged efferent discharge after stoppage of stimulation of afferent
Cause of After discharge (repetitive) circuits
Due to presence of interneurons.
Types of After discharge (repetitive) circuits
A. Parallel (Open) chain circuits
B. Reverberating (closed) chain circuits
Mechanism of Parallel (Open) chain circuits
- Afferent neuron stimulates efferent neuron directly & through interneurons which are parallel with afferent neurons
- A delay of 0.5 m.sec occurs at each synapse in this circuit, thus the impulse reaches the Efferent neuron after variable periods of delay.
- duration of after discharge depends on number of interneurons in this circuit.
what does duration of after discharge depend on?
- duration of after discharge depends on number of interneurons in this circuit.
Mechanism of Reverberating (closed) chain circuits
- Afferent nerve ends on principal interneuron whose axon either → terminate directly on efferent neuron & send collateral branch
which either:
- Stimulates principle interneuron again (Reverberating).
- Stimulates another interneuron which re- stimulates principle interneuron.
So, brief afferent signal causes reverberating of signal for long time → Prolonged after Discharge.
what causes stoppage of Reverberating (closed) chain circuits activity?
1) Fatigue of synapse.
2) Inhibition from other neurons.
what are examples of reverberating circuits?
- Reticular activating system (RAS)
- Respiratory centre
Reticular activating system (RAS)
- Present in brain stem & responsible for wakefulness. (12-18 hours).
Respiratory centre
Continues to discharge for life.
Definition of Inhibitory circuits
- convert excitatory input signals into Inhibitory output signals.
Types of Inhibitory circuits
- lateral inhibitory circuits
- Recurrent (feedback) inhibitory Circuits
Definition of lateral inhibitory circuits
In which the most active neuron send a collateral to stimulate an inhibitory interneurons to inhibit the less active or less stimulated neurons
Example of lateral inhibitory circuits
Ascending sensory tracts during their course to C.C.
Importance of lateral inhibitory circuits
To focus or sharpen reflex response.
Definition of Recurrent (feedback) inhibitory Circuits
In which efferent neuron (AHCs) axon send recurrent collateral branches which release acetyl choline to stimulate inhibitory interneurons called renshow cell which release glycine to inhibit:
- The neighbouring α- motor neurons.
- The originally stimulated α- motor neuron.
Importance of Recurrent (feedback) inhibitory Circuits
- On neighbouring α-Motor neurons → Focus motor response.
- On Originally stimulated α-Motor neuron → To limit its discharge (-ve feedback control).
Tyoes of Efferent neuron
- Autonomic efferent neurons (LHCs) → Mediate autonomic reflex.
- Somatic efferent neuron (AHCs) → Mediate somatic spinal reflex.
what are AHCs divided into?
Examples of polysynaptic reflexes
- Flexion-Withdrawal reflex
- Crossed-Extensor Reflex
Def of Flexion-withdrawl reflex
It’s a poly synaptic reflex that moves the affected limb away from painful stimulus.
Stimulus of Flexion-withdrawl reflex
painful stimulus
Receptors of Flexion-withdrawl reflex
Free nerve ending.
Afferents of Flexion-withdrawl reflex
A-Delta nerve fibers
Centre of Flexion-withdrawl reflex
- Afferent neurons affer entering spinal cord divide into many central branches
- Which synapse with interneurons
- Through these interneurons, afferent Impulse
Action done by interneurons in Flexion-withdrawl reflex
- Excite motor neuron pool which supply ipsilateral flexors
- Inhibit motor neuron pool which supply ipsilateral extensors (antagonists).
Significance of Flexion-withdrawl reflex
- Of survival value because it removes limb away from injurious agent. (protective)
- Pre-potent reflex that suppresses any other reflexes occurring at the same time
Definition of Crossed-Extensor reflex
- It is reflex extension of a limb during fexion of the other limb, as a result of flexion withdrawal reflex.
Pathway of Crossed-Extensor reflex
When strong painful stimulus is applied to one limb on one side, afferent fibres cross to Opposite side to synapse with interneurons which either:
- Stimulate motor neuron pool of extensors.
- Inhibit motor neuron pool of flexors.
Significance of Crossed-Extensor reflex
- To cause extension of the controlateral limb to support body during flexion of the stimulated limb (supportive)
Properties of polysynaptic somatic spinal reflexes
what are other names for strech reflex?
(Myotonic reflex - Ms spindle reflex)
Definition of strech reflex
Reflex contraction of muscle when it’s passively stretched
Receptor of strech reflex
Muscle spindles.
Afferent of strech reflex
A-alpha & A-beta nerve fibers. (type Ia and type II)
Center of strech reflex
A.H.Cs (alpha-motor neurons).
Efferent of strech reflex
alpha-motor nerves.
Response of strech reflex
Contraction of the muscle
Definition of muscle spindle
- Specialized fusiform capsulated structures located in the fleshy part of the muscles.
- They act as length receptors i.e. detect the changes in the muscle length.
Number of muscle spindle
Each muscle spindle consists of 4-12 modified muscle fibers called intrafusal muscle fibers which are of 2 types
Types of muscle spindle
- Nuclear bag muscle fibers
- Nuclear chain muscle fibers
Compare between Nuclear bag of muscle fiber & Nuclear chain of muscle fiber in terms of:
- Composed of
- Length
- Number
- Sensory (Afferent)
- Motor (Efferent)
Mechanism of stimulation of ms. spindle
Central connection of muscle spindle
Defintion of stretch reflex
- Reflex contraction of a muscle when it is passively stretched.
what are the types of stretch reflex?
- Dynamic response or dynamic stretch reflex
- Static response or static stretch reflex
Compare between Dynamic stretch reflex & Static stretch reflex in terms of:
- stimulus
- Receptors
- Afferent
- Center
- Example
- Potentiated by
what is the function of strech reflex (Muscle spindle)?
- Generation of muscle Tone
- Smoothing of muscle contraction (Damping function)
- Load Reflex (servo-assist function)
- Proprioceptive functions
Generation of muscle tone by stretch reflex
- Muscle spindles, through the stretch reflex, are responsible for generation of skeletal muscle tone.
- CNS adjusts muscle tone by varying the level of gama-M N. activity which by its turn affect the frequency of spindle sensory discharge.
Smoothing of muscle contraction (Damping function) by stretch reflex
the ability of muscle spindle to prevent oscillation and jerkiness of body movements.
Load reflex (Servo-assist function) by stretch reflex
reflex that is responsible for keeping the hand or foot in position when a moderate or heavy load is applied.
Proprioceptive function by stretch reflex
- Muscle spindles provide proprioceptive information to the brain and cerebellum for keeping them continually informed about muscle length and changes in that length.
Intro to Supra-spinal control of stretch reflex
AHCs of the stretch reflex (alpha & gama -motor neurons) continuously exposed to supraspinal facilitatory & inhibitory impulses from different areas in brain.
what are supraspinal facilitatory areas?
what are supraspinal inhibitory areas?
which supraspinal action dominates under normal condition?
- Under normal condition the supraspianl facilitation predominates and the stretch reflex & muscle tone are facilitated.
what are the proprties of stretch reflex?
- Short latent period and total reflex time
- High localization
- Graded response
- Reciprocal inhibition
- Fatigue resistance
- No recruitment nor discharge
Why does Stretch reflex has a short latent period?
- The stretch reflex has short latent period that passes between application of the stretch & onset of the reflex contraction
Because:
1. It is a monosynaptic reflex (the only monosynaptic reflex).
- The afferent & efferent are rapidly conducting fibers
High localization of Stretch reflex
- Stretch of certain muscle leads to contraction of the same stretched muscle.
- This is due to limited divergence & absence of interneurons in its pathway
graded response of Stretch reflex
- Strength of the reflex contraction is proportional to the extent of stretch.
- The greater the degree of stretch the greater the rate of discharge from muscle spindles, vice versa.
Reciprocal innervation of Stretch reflex
- Stretch of certain muscle leads to contraction of that muscle & inhibition of its antagonistic muscle due to reciprocal innervation circuits between the motor neuron pools.
Fatigue resistance of Stretch reflex
- Stretch reflex can be sustained for long periods of time (in antigravity muscles).
- The delayed onset of fatigue is related to:
1. Asynchronous (alternative) contraction of different motor units.
- The antigravity muscles contain greater number of tonic muscle fibers (slow muscle fibers) which resist fatigue.
why is there no recruitment nor discharge in Stretch reflex?
Due to absence of interneurons
Compare between Stretch reflex and inverse Stretch reflex in terms of:
- Type
- receptor
- Stimulus
- Afferent
- Efferent
- Effect
- Function
Definition of Skeletal muscle tone
- It is a state of continuous partial (subtetanic) contraction present in all skeletal muscles during rest.
Mechanism of Skeletal muscle tone
Functions of muscle tone
1) It is the basic mechanism for postural reflexes which regulate the body posture and equilibrium.
2) Helps production and maintenance of body temperature.
3) Helps venous and lymphatic return.
4) Keeps viscera in position and prevents visceroptosis.
Definition of tendon jerk
Rapid contraction followed by relaxation of a muscle due to sudden stretching of that muscle by tapping on its tendon using a medical hammer
Mehcanism of tendon jerk
Clinical significance of tendon jerk
Stimulus of stretch reflex
Passive stretch of the muscle
what are other names of Inverse stretch reflex?
- Lengthening reaction
- Golgi tendon reflex
Definition of Inverse stretch reflex
- Is reflex relaxation of a contracting skeletal muscle when exposed to excessive stretch
- It is protective against:
1. muscle tearing.
2. tendon avulsion
Stimulus of Inverse stretch reflex
Increased tension in the tendon of the muscle due to:
- severe contraction
- Overstretch.
Receptor of Inverse stretch reflex
Golgi tendon organs (GTO)
GTO:
- Site
- Content
- Stimulation
- present in the tendon of the muscle in series of the muscle fibers.
- each organ consists of modified fibers mostly elastic fibers “number 6-20”
- stimulated by increased tension in the tendon “Tension receptors”
afferent of Inverse stretch reflex
- A-alpha nerve fibers (Ib).
Center of Inverse stretch reflex
- impulses from GTO inhibit A.H.Cs via interneurons leading to relaxation of the muscle. (it is a di-synaptic reflex)
Response of Inverse stretch reflex
Muscle relaxation
Significance of Inverse stretch reflex
protective against:
- muscle Tearing
- tendon avulsion
what is somatic motor system composed of?
- Upper motor neurons (UMN)
- Lower motor neurons (LMN)
where are the Cell bodies of UMN?
In higher motor centers (motor cortex & brain stem).
What do the axons of UMN form?
descending motor tracts.
where are the cell bodies of LMN?
lie in the spinal AHC and the cranial motor nuclei
what do the axons of LMN form?
motor fibers in the peripheral nerves to skeletal muscle
Site of cortical motor areas
The cortical motor areas located precentral gyrus in the frontal lobe.
what do cortical motor areas include?
– 1) The Primary motor area (area 4).
– 2) The Premotor area (area 6).
– 3) The Supplemental motor area.
Site of 1ry motor area (area 4)
- the precentral gyrus of the frontal lobe.
Body representation of 1ry motor area (area 4)
Contralateral: the muscles of left side controlled by the right motor cortex and vice versa.
Inverted: the muscles of the face are controlled by the lowermost part of area 4 & muscles of lower limbs controlled by the upper most part of area 4.
Size: Muscles involved in fine movements (hand & tongue) are represented by relatively large areas than those involved in gross movements (trunk).
Connection of 1ry motor area (area 4)
through pyramidal tract:
- Initiation of voluntary movements done by the limb muscles of the opposite side
- Facilitation to the tone of the distal limb muscles
what does a lesion in 1ry motor area (area 4) cause?
1) Loss of voluntary movements (paralysis or weakness) in one limb (monoplegia) on the opposite side.
2) Hypotonia and weak tendon jerks.
3) Babinski’s sign: (dorsiflexion of the big toe)
Site of Premotor area (area 6)
In the frontal lobe just anterior to the primary motor area 4.
Body representation of premotor area (area 6)
1) contralateral
2) inverted.
Connection of premotor area (area 6)
1) Primary motor area & supplemental motor area.
2) Basal ganglia & cerebellum.
3) With supplemental motor area Give 30% of the axons of pyramidal tract.
what does a lesion in premotor area (area 6) cause?
1) Impairment of complex movements or paresis.
2) Hypertonia and exaggerated tendon jerks.
3) Babinski s sign (fanning of the outer 4 toes).
4) Loss of automatic or associative movements.
5) Motor aphasia (inability of articulation).
6) Motor apraxia (inability to perform the learned skillful movements).
Site of supplemental area (4s)
- In the frontal lobe just anterior & above the premotor area 6.
Body representation of supplemental area (4s)
- Bilateral and horizontal with face Anterior and leg posterior
Connection of supplemental area (4s)
1) initiate complex movements involve both sides of the body (as both hands to perform a motor act together).
2) with the premotor area (6):
- provide postural background for the performance of fine skilled movements by hands and fingers.
- shares in the planning and programming of the complex movements.
what does a lesion of supplemental area (4s) cause?
Nothing as it is bilateral
function of premotor area (area 6) with supplemental motor area
shares in planning of complex movements.
function of premotor area (area 6) with basal ganglia
- postural adjustment of the trunk and proximal limb for the performance of the distal voluntary movements.
- initiate the automatic associative movements (subconsciously) as swinging of arms during walking.
what are special areas and functions of premotor area (area 6)?
Broca’s area: active in the dominant hemisphere (the left side in right handed persons). controls the muscles involved in speech.
Frontal eye movement area: control voluntary movements of the eye.
Head rotation area: directs the head towards visual objects.
Area of hand skills (Exener’s area): controls skilled movements of the hand and fingers as writing.
what are the types of descending motor tracts?
- Pyramidal tract
- Extrapyramidal tracts
Course of pyramidal tract
One tract passes through the pyramid of the medulla so called pyramidal tract.
what do pyramidal tracts include?
Corticobulbospinal tract.
Course of Extra-pyramidal tract
Group of tracts not pass through the medullary pyramid so called extrapyramidal tracts.
what do extra-pyramidal tracts include?
– 1) Rubrospinal tract
– 2) Reticulospinal tracts
– 3) Vestibulospinal tracts
– 4) Tectospinal tract
Functional classification of descinding motor tracts
what are another names for pyramidal tract?
corticobulbospinal
Origin of pyramidl tract
- Motor areas 60 %. (Primary motor area “area 4” 30%, Premotor & Supplemental motor areas 30%.)
- Somatosensory areas give 40 % of fibers.
Stations of pyramidl tract
CBS tract pass through
1) the genu & anterior 2/3 of posterior limb of internal capsule).
2) the middle 3/5 of the cerebral peduncles of midbrain
3) form several bundles in the basis pontis
4) collect in the upper medulla forming the pyramid.
5) In spinal cord as lateral & ventral coticospinal tract.
what are 3 pyramidal tracts?
- Corticonuclear tract
- Corticobulbular tract
- Corticospinal tract
where does corticonuclear tract terminate?
- Fibers terminate on the 3, 4, & 6th cranial nerves nuclei bilateral
where does corticobulbar tract terminate?
Fibers terminate on the 5, 7, 9, 10, 11 & 12th cranial nerves motor nuclei.
which cranial motor nuclei recieve bilateral supply?
All cranial motor nuclei receive bilateral supply from the pyramidal tract except the lower parts of the 7th & & 12th nuclei, receive only contralateral supply.
Course of corticospinal tract
Functions of pyramidal tracts
pyramidal tract perform the following functions:
1) Initiation of voluntary skilled movements: speech (Corticobulbar tract) , and movements of hand and fingers (Lateral corticospinal tract).
2) Has a Role in automatic movements as chewing, swallowing (corticobulbar) and postural movements (medial corticospinal tract).
3) Facilitatory to muscle tone of flexor muscle of the limbs.
4) Inhibits primitive withdrawal reflex as dorsiflexion of big toe in planter reflex (Babinski sign).
Origin of Extra-pyramidal tracts
Mainly from area (6) and some fibers from area (4) → descends to corpus striatum → Globus pallidus→ from the globus pallidus fibers pass to:
1. Red nucleus
2. Reticular formation
3. Vestibular nuclei
4. Tectum of midbrain.
5. Inferior olive.
what are examples of extra-pyramidal tracts?
1) Rubrospinal tract.
2) Reticulospinal tract tracts.
3) Vestibulospinal tracts.
4) Tectospinal tract.
5) Olivospinal tract.
Origin of Rubrospinal tract
Red nucleus in midbrain (receive fibers from ipsilateral cortical motor area (cortico-rubro-spinal tract).
Course of Rubrospinal tract
Cross to opposite side & descends contralateral.
Termination of Rubrospinal tract
in the cervical spinal cord, so it functions in upper limb.
Function of Rubrospinal tract
1- Control of distal muscles of upper limb responsible for skilled movements. Rubrospinal & lateral corticospinal tract are called lateral motor system.
2- Facilitatory to the muscle tone of the distal limb muscles.
Caudate circuit
Putamen circuit
Internal connections between basal ganglia
Connections of basal ganglia with brain stem
Histologocal division of cerebellum
Anatomical division of cerebellum
Motor learning function of cerebellum
Role of cerebellum in rapid ballistic movements
Compare between specific and non specific nuclei of the thalamus in terms of:
- Definition
- Examples
Thalamic nuclei
Compare between factors Increasing/Decreasing consciousness
Compare between non-REM sleep (SWS) and REM sleep in terms of:
- Order
- % of sleep hours
- EEG
- Rapid eye movement
- Dreams HR, BP, Respiration & brain activity
- Muscle tone
Initiation of SWS
Mechanism of REM sleep
Hypothalamic connections
Regulation of autonomic nervous system by hypothalamus
Compare between feedking center and satiety center in terms of:
- Site
- Stimulation
- Lesion
How does hypoglycemia trigger counter-regulatory mechanisms by hypothalamus?
Regulation of body temperature by hypothalamus
(in cases of exposure to cold and hot weathers):
How does the hypothalamus regulate body osmolarity & Volume of body water?
How does hypothalamus respond to stress?
Structure of limbic system
Connection of limbic system with RF and Autonomic centers of brain stem
Structure of eye
The eye is the organ of vision which consists of 2 parts:
- Eyeball
- Extraocular accessory structure
what is the power of a lens having a focal length 0.1 meter?
= 1/ 0.1 = 10 diopters.
Refractive index and power of:
- Cornea
- Aqueous Humour
- Lens
- Vitreous humour
Compare between cons and rods in terms of:
- Number
- Shape
- Distribution
- Photosensitive pigments
- Connection
- Function
what are Mechanisms of colour vision?
Compare between photopic and scotopic vision in terms of:
- Receptors
- Site
- Threshold
- Sensitivity to light
- Accuracy
- Colour vision
- Adaptation
what is intensity of sound measured in?
- The intensity of sound is measured in Bells
Functions of The External Auditory Meatus
Anatomy of Middle Ear
Role of the round window in sound transmission
Functions of Eustachian Tube
Importance of Tympanic (attenuation) reflex
Nervous connections of the vestibular apparatus
- The mother cells of the vestibular nerve fibers located in the vestibular ganglion.
- The central branches of these fibers enter the brain stem and end on thevestibular nuclei.
Explain Detection or orientation of the absolute position of head in space function of maculae
Compare between rotational & post-rotational nystagmus in terms of:
- Duration
- Components
- Significance
