Welcome to MBBS Memory Maps in Physiology

Concepts are the keystones in the architecture of our thinking.

-Paul Hughes

Let’s create road-maps for concepts.

WISDOM IS NOT A PRODUCT OF SCHOOLING BUT OF THE LIFELONG ATTEMPT TO ACQUIRE IT. –Albert Einstein

Hey there!

Let’s just say that studying can be fun too. Preparing concept map has been my thing always. So, now I am here to share my view and maps on physiology/medical topics with the world out there.

A Physiology Professor by profession I have seen students struggling with the basic concepts of the subject and almost everyone scrambling for notes (self-made, borrowed from seniors or copied from a fellow classmate). But I have found that more than so called ‘notes’, you need a clear concept – hence the concept maps.

WHAT IS A CONCEPT MAP?

It is basically a conceptual diagram that suggests or compiles a knowledge or information in form of a arrow diagram or a flow chart. In other words it explains and organizes a complex information in an easy to comprehend diagram or chart. A very useful and organized way to understand, acquire & memorize concepts.

ADVANTAGES OF CONCEPT MAPS –

  1. Simplifies understanding of an complex phenomenon/ subject.
  2. helps in quicker learning. You can finish a bigger chapter in lesser time.
  3. easy to remember and reproduce in exams.
  4. creates memory maps(with less confusions of course!!)

So, see you all later in my subsequent posts where I will share my ‘concept-maps’ mostly related to Physiology, medicine & maybe everything else in due course of time. keep me posted on your view on the same.

DESCENDING MOTOR PATHWAYS / DESCENDING TRACTS

Connect the neurons in,

cerebral cortex , Midbrain, Pons, Medulla & Cerebellum

with

motor neurons (LMN) at various levels.

Axons of UMN synapse on spinal : Alpha motor neuron,gamma motor neuron, Spinal interneuron, Sensory afferents

TRADITIONALLY TRACTS ARE CLASSIFIED AS:


RECENT CLASSIFICATION : Hans Kupyres – 1981,85.

CORTICOSPINAL TRACT / PYRAMIDAL TRACT

Most important and largest descending tract.

Axons of Cortical neurons descend, form Pyramids in Medulla –> to Spinal Cord (Corticospinal tract)

Some terminate in :

  • Brain Stem Reticular formation
  • Cranial N Nuclei (V, VII,XII, Corticobulbar Tract) except those supplying to External eye muscle

Phylogenetically newest, only in mammals. (No of fibers have progressively increased from monkeys –> Apes –> Man.

1 million fibers (approx.) in human, >90% – small diameter & unmyelinated (SLOW CONDUCTING PATHWAY)

Myelination starts in neonate on 10th – 14th day and completes in 2 years.

NEUROTRANSMITTERS : GLUTAMATE, ASPARTATE.

FUNCTION

  1. Fine, skillful voluntary movement of Distal limb parts (LCST)
  2. Postural stability of Axial & proximal muscle.
  3. influence on stress reflexes.
  4. Facilitatory (++) –> alpha & gamma where it ends directly. Inhibitory (–) –> via Interneurons
  5. Efferent limb of superficial reflexes (e.g, abdominal, plantar etc)
  6. Opposite side lower part of face and hypoglossal (Corticobulbar tract)
  7. useful in sensori-motor coordination.
  8. Path of transcortical load compensation mechanism (Increased load –> Increased muscle contraction mediated by Cortex)

LESION

MOTOR DEFICITS OCCUR DUE TO DESCENDING TRACTS. PURE Pyramidal tract lesions are rare.

ACUTE Lesion (Stage of shock)–> Paralysis of opposite half, No reflexes, Emotions are intact. Lasts for 2-3 weeks. (Symptoms include lesions of both PT+ EPT )

CHRONIC Lesion (Stage of recovery) :

EXTRAPYRAMIDAL TRACT

  • Outside Pyramidal tract
  • Multineuronal motor system with number of synapses involving many regions of brain.
  • All from cortex & subcortical (brainstem) areas other than those in Pyramidal tract.

FUNCTIONS OF EXTRAPYRAMIDAL TRACT

  • Regulation of Posture, Equillibrium, Muscle tone
  • Coordinated, synchronized movement of head, eye, neck etc
  • Provide platform for Pyramidal system to operate fine, skilled movement.
EXTRAPYRAMIDAL TRACTS

LESIONS IN EXTRAPYRAMIDAL TRACTS:

  • MUSCLE TONE – Increased (upper limb – Flexion, Lower limb – Extension)
  • ABNORMAL POSTURE
  • INVOLUNTARY MOVEMENT – tremor
  • LOSS OF RIGHTING/POSTURAL REFLEXES
  • DEEP REFLEXES – exaggerated, clonus may appear
  • CLASP KNIFE RIGIDITY (Lengthening reaction) present
  • PLANTAR REFLEX – Normal/extensor.

MOTOR CORTEX


PRIMARY MOTOR CORTEX

  • Largest of all motor areas
  • Lies in the precentral Gyrus –> Area 4 of Brodmann extending from medial surface to lateral sulcus.
  • low electrical –> Specific & repeatable movement.
  • HOMONCULUS (little man) –> Drawn by Penfield & Rasmussen 1950.
    • Body is upside down
    • legs most medially
    • pharynx lateral most.
    • SIZE OF REPRESENTATION – More for body parts for fine & skilled movement (Thumb, Fingers, Face, Pharynx, Vocal cords etc), Less for trunk muscles.
  • Lacks LAYER 4 (Granules). So, called AGRANULAR CORTEX.
  • Cells are arranged in Columns –> cells from several columns project to same muscles.
  • about 30% of Corticospinal Tract fibers take origin
  • provide most refined degree of motor control
  • Areas enlarge with practice & learning —- CORTICAL PLASTICITY
  • LESION — Paresis/paralysis of opposite side
This image has an empty alt attribute; its file name is img_b2a8c9c90d9b-1.jpg

SUPPLEMENTARY MOTOR AREA

  • Medial portion of Area 6 (Anterior & Medial to M1, largely on medial surface of hemisphere)
  • High electrical stimulation–> Head & Eye movement, vocalization & complex postural movement.
  • Somatotopic arrangement like M1 —Face, Anterior. Legs, Posterior.
  • Bilaterally connected through Corpus callosum
  • Subdivided into 2 areas
  • FUNCTION :
    • Planning & integration of complex (fixations)attitudinal movements.
    • more active in bi-manual tasks
    • learning of skilled acts.
  • LESION –> Transient speech deficit (Aphasia) — typically disappears after several weeks. Slowness in generating repetitive movement. Retards the movement of opposite limb.

PRE-MOTOR AREA (PMC)

  • High stimulation – Proximal musculature
  • minor contribution to Cortico-spinal Tract.
  • Major contribution to Extrapyramidal Tracts.
  • FUNCTIONS:
    • Responsible for patterning & posturing
  • LESION:
    • Weakness of opposite shoulder/ hip muscle
    • limb movement slower
    • Inability in simultaneous coordinated movement of both limbs
  • 2 Subdivisions : DORSAL & VENTRAL

CINGULATE MOTOR AREA (CMA) within Cingulate Sulcus

CMA- r –> Rostral

CMA – d –> Dorsal

CMA – v –> Ventral

3 CMA, each with somatotopic map, contribute to CST. High stimulation similar to motor cortex stimulation.

  • FUNCTION :Preparation & execution of movement.

OTHER IMPORTANT AREAS

  • FRONTAL EYE FIELD — Controls eye movement
  • POSTERIOR PARIETAL CORTEX — (5,7)
    • Lesion : No motor weakness, but sensory & motor neglect in opposite hemifield —> AMORPHOSYNTHESIS
  • BROCA’S AREA — Motor speech area, Area 44.
    • Lesion : Motor aphasia
  • SUPPRESSOR AREAS (4s, 2s, 8s, 19s, 24s) — Inhibition of strech reflex


HISTOLOGICAL STRUCTURE OF MOTOR CORTEX

3 Types of cells are present – 1. PYRAMIDAL CELLS 2.STELLATE/GRANULE CELL 3. FUSIFORM CELLS

6 layers or laminae are present–>

  • most afferent fibers from the specific nuclei of thalamus make synapses in the laminae I to VI
  • Afferent projections from non-specific thalamic nuclei & from ascendind reticular system terminate in al laminae of cortex
  • Laminae II & IV are concerned with sensorial modalities.
  • Laminae III to V are meant for somatomotor or visceromotor activities.
  • Laminae I to VI are engaged for integration of association of sensorimotor behaviour.

ORGANISATION OF MOTOR SYSTEM

NEURAL CONTROL OF MOVEMENT

Movement is crucial to all organisms. its performed in higher animals by contraction of & relaxation of the muscles.

Motor system exists in Brain to translate out thought, sensation, emotion & feeling into MOVEMENT.

SENSORY SYSTEM –> transforms physical energy into neural signals

MOTOR SYSTEM –> NEURAL signal is converted to contractile force of muscle and hence converted into MOVEMENT.

SENSORY REPRESENTATION FORM FRAMEWORK IN WHICH –

  1. motor system plans, coordinates & executes.
  2. motor system programmes a purposeful movement
  3. it a highly complicated & integrated system.
  4. ability of human beings to carry out skilled movement while still performing cognitive tasks requires flexibility, integration & skills that no other organism /animal has.

TYPES OF MOVEMENT

ORGANISATION OF MOTOR SYSTEM

  1. IDEA – Posterior Parietal cortex, Association areas
  2. PLANNING – Premotor , Supplementary motor Cortex, Thalamus, Basal Ganglia
  3. PROGRAMMING – Cortex, Basal Ganglia
  4. MOTOR COMMAND – Cortex – {Spinal cord, brain stem } –> via descending tracts
  5. EXECUTION – Spinal cord –> via –> Final common path
  6. ACTION –> contraction of muscle, joint movement
  7. COMPARISON, COORDINATION –> Cerebellum, Thalamus, Sensory pathway

All voluntary activity involves activity of CEREBRAL CORTEX.

ROLE OF DIFFERENT PARTS OF BRAIN IN MOTOR CONTROL :

  1. CORTICAL MOTOR AREA
    • Highest level of motor control
    • 3 criteria :
      • stimulation using low current strength elicits movements
      • destruction of area results in loss of motor function
      • area has output connection directly(or with minimal or intermediate connections) to brainstem or spinal cord.
    • 2 groups : Primary motor Cortex & Secondary motor cortex.
  2. POST PARIETAL CORTEX
  3. FRONTAL EYE FIELD
  4. BROCA’S AREA
  5. SUPPRESSOR AREAS (4s, 2s, 8s, 19s & 24s)

Basal Ganglia




Connections of Basal Ganglia (Direct & Indirect Pathways)

NIGROSTRIATAL PATHWAY
Modulation of Direct and Indirect pathways by Nigrostrial Pathway

CONNECTIONS OF BASAL GANGLIA
NEURAL CONNECTIONS OF BASAL GANGLIA

FUNCTIONS OF BASAL GANGLIA

PLANNING & PROGRAMMING –> Discharge starts even before commencement of movement.

EXECUTION OF MOTOR TIMING, INTENSITY & SEQUENCES –> Basal Ganglia gets input from cortex projects back to cortex (Prefrontal, premotor, Supplementary motor area). These Corticospinal & Corticobulbar neurons influence Proximal & Distal limb.

MUSCLE TONE –> Inhibits tone, decreases stretch reflex (BG LESION – HYPERTONIA).

COGNITIVE FUNCTION –> Connects to Prefrontal & Orbitofrontal Cortex.

SPEECH –> Lesion in Lt head of Caudate Nucleus – causes DYSARTHRIA

In lower animals, higher centre for MOTOR ACTIVITY.

DISEASES OF BASAL GANGLIA

Basal Ganglia disorder

PARKINSONISM / PARKINSON’S DISEASE/PARALYSIS AGITANS/ SHAKING PALSY

Named after James Parkinson (English Physician) -1817.

Has both HYPOKINETIC & HYPERKINETIC features.

Loss of PARS COMPACTA neurons of Substantia Niagra that leads to loss of DOPAMINE in NIGROSTRIATAL Pathway.

Imbalance between Excitation & Inhibition

FEATURES OF PARKINSONISM

TREATMENT

  1. LEVODOPA/L-DOPA –>Dopamine cannot enter Blood Brain Barrier but L-Dopa can cross. So, L-Dopa is given as replacement of Dopamine.
  2. BROMOCRIPTINE –> Synthetic Dopamine Agonist. Can cross BBB.
  3. ANTICHOLINERGIC – BENZHEXOL — >Inhibits Cholinergic System.
  4. LEVODOPA + CARBIDOPA –>Carbidopa inhibits conversion of L-Dopa to Dopamine outside BBB, minimizes side effects and prolongs the action of L-Dopa.
  5. L-DEPRYNYL –>Slows the progression of disease. Inhibits MAO, prolongs Dopamine action.
  6. Surgical treatment –>
    • Implantation of dopamine secreting tissue (adrenal medulla, foetal striatal tissue)
    • Surgical lesion  :
      • VA, VL Nuclei
      • Globus Pallidus
      • Use of pacemaker

Difference between Cerebellum and Basal Ganglia

BASAL GANGLIACEREBELLUM
No input from spinal cordDirect input from spinal cord
Input from all areas of cerebral cortexInput only from Motor areas.
Output is more widespread, reaches prefrontal & all premotor areas.Restricted to premotor & primary motor cortex.
Few connections with brainstem.Has rich connections with brainstem.
LESIONS               LESIONS
Usually causes HYPERTONIA (Rigidity)Causes HYPOTONIA
Tremors at rest. Disappears with activity. Intentional tremor. Disappears with rest & reappears with exercise/movt.
Lesion affects opposite sideAffects same side
Difference between Cerebellum and Basal Ganglia

‘All change is not growth, as all movement is not forward.’

Ellen Glasgow

Welcome to MBBS Memory Maps in Physiology

Concepts are the keystones in the architecture of our thinking.

-Paul Hughes

Let’s create road-maps for concepts.

WISDOM IS NOT A PRODUCT OF SCHOOLING BUT OF THE LIFELONG ATTEMPT TO ACQUIRE IT. –Albert Einstein

Hey there!

Let’s just say that studying can be fun too. Preparing concept map has been my thing always. So, now I am here to share my view and maps on physiology/medical topics with the world out there.

A Physiology Professor by profession I have seen students struggling with the basic concepts of the subject and almost everyone scrambling for notes (self-made, borrowed from seniors or copied from a fellow classmate). But I have found that more than so called ‘notes’, you need a clear concept – hence the concept maps.

WHAT IS A CONCEPT MAP?

It is basically a conceptual diagram that suggests or compiles a knowledge or information in form of a arrow diagram or a flow chart. In other words it explains and organizes a complex information in an easy to comprehend diagram or chart. A very useful and organized way to understand, acquire & memorize concepts.

ADVANTAGES OF CONCEPT MAPS –

  1. Simplifies understanding of an complex phenomenon/ subject.
  2. helps in quicker learning. You can finish a bigger chapter in lesser time.
  3. easy to remember and reproduce in exams.
  4. creates memory maps(with less confusions of course!!)

So, see you all later in my subsequent posts where I will share my ‘concept-maps’ mostly related to Physiology, medicine & maybe everything else in due course of time. keep me posted on your view on the same.