Pituitary stalk and infundibulum of pituitary gland

 

What is Pituitary Stalk – it is the narrow connection between the hypothalamus and whole pituitary gland whcih containing hypophyseal portal veins and nerve fibers.

Infundibulum – The broader funnel-shaped structure that includes the pituitary stalk, connecting the posterior part of pituitary gland which connect to the hypothalamus.

Why the Temporomandibular Joint (TMJ) is Peculiar (Unique Features)

 

Why the Temporomandibular Joint (TMJ) is Peculiar (Unique Features)

The temporomandibular joint (TMJ) is one of the most complex and unique joints in the skull . It has several peculiar characteristics that distinguish it from other types of synovial joints.

1. It is a Ginglymoarthrodial Joint which means it is  both a hinge joint (ginglymus) and a gliding joint or arthrodial which allows hinge-like movements (opening and closing the mouth) and gliding movements (protrusion and retraction of the jaw).

2. Presence of an Articular Disc (Biconcave Fibrocartilage Disc)

• TMJ has a fibrocartilaginous disc between the mandibular condyle and temporal bone which  divides the joint into two compartments, allowing smooth movement and shock absorption and  also helps prevent direct bone-to-bone contact, which is rare in synovial joints.

3. Dual Compartment Structure (Two Synovial Cavities)

• The articular disc creates two separate compartments:
• Upper compartment → for gliding movements (translation).
• Lower compartment → for hinge movements (rotation).
• This makes the TMJ function as two joints in one.

4. Bilateral Functioning (One of the Only Paired Joints that Works Together)

• Both left and right TMJs work together simultaneously and dysfunction in one TMJ can affect the other, making TMJ disorders complex.Most joints in  body work independently, but TMJs must function synchronously.

5. Only Movable Joint in the Skull

• The TMJ is  only synovial joint in the skull that allows movement and all other skull joints are fibrous (immovable sutures) except for the ossicles of the ear.

6. Atypical Cartilage Lining (Fibrocartilage Instead of Hyaline Cartilage)

• Most synovial joint’s articular surfaces are lined with hyaline cartilage, but the TMJ is covered by fibrocartilage which  is more resistant to wear and tear, making the TMJ more durable.

7. Unstable Joint with High Susceptibility to Disorders (TMD)

• The mandibular condyle does not fit tightly into the temporal bone, making it prone to dislocation.
• Common disorders include:
• TMJ dislocation (jaw locking).
• Temporomandibular disorder (TMD) (pain, clicking, or popping).
• Bruxism (teeth grinding) leading to TMJ dysfunction.

8. Unique Development (Derived from Two Embryonic Origins)

• The TMJ develops from Meckel’s cartilage (one of the derivatives of first pharyngeal arch) and secondary condylar cartilage.
• Most other joints develop from a single cartilage model, but TMJ has dual embryonic origins : mesenchyme and neural crest

9. Involvement in Speech, Chewing, and Expression

• The TMJ is crucial for mastication (chewing), speech, yawning, and facial expressions and dysfunction can affect eating, talking, and even facial appearance.

10. Unusual Blood and Nerve Supply

• TMJ is richly supplied by sensory nerves (Auriculotemporal nerve from CN V3) which  makes it  very sensitive to pain, that is why TMJ disorders cause significant discomfort.

Summary of Peculiarities of the TMJ

Feature	Why It’s Unique
Ginglymoarthrodial joint	Both hinge and gliding functions
Articular disc present	Divides joint into two compartments, shock absorption
Two synovial cavities	Upper compartment = translation, Lower = rotation
Bilateral function	Both joints move together, unlike most joints
Only movable skull joint	Other skull joints are sutures (immovable)
Fibrocartilage lining	More durable than hyaline cartilage
Prone to disorders	Dislocations, TMD, bruxism, clicking sounds
Unique development	Dual embryonic origin (Meckel’s cartilage + secondary cartilage)
Multifunctional	Involved in chewing, speech, yawning, facial expression
Rich nerve supply	Highly sensitive, easily causes pain

 

Conclusion

TMJ is a highly complex, unique, &  specialized joint that plays a crucial role in daily functions. It unique due to its dual movements, articular disc, fibrocartilage lining, and synchronized bilateral function. However, its structural peculiarities make it vulnerable for dysfunction and disorders (TMD).

Osteology : Coccyx

 Coccyx (Tailbone) The coccyx is the small, triangular bone at base of the vertebral column, formed by the fusion of 3 to 5 coccygeal vertebrae. It acts as an attachment site for muscles, ligaments, and tendons, playing a role in pelvic support and posture.

1. General Features of the Coccyx

Feature	Description
Shape	Small, triangular, and  curved bone
Location	Lower end of the vertebral column, below the sacrum vertebra
Formation	It is formed by the fusion of 3 to 5 coccygeal vertebrae (typically 4)
Curvature	Slightly curves anteriorly (more in males, less in females)
Base	The superior, broader part that articulates with the sacrum vertebra
Apex	The inferior, pointed end that does not articulated with any bone
Cornua (Coccygeal Horns)	Two small projections at the base, connecting with the sacral cornua
Transverse Processes	Small lateral extensions present in the first coccygeal vertebra
Articulation	It articulates with the sacrum at the sacrococcygeal joint
Function	It supports body weight during sitting, attachment site for pelvic muscles and ligaments

 

2. Differences Between Coccygeal Vertebrae

• Co1 (First Coccygeal Vertebra):
• Largest and most developed.
• Has transverse processes and cornua (horn-like projections).
• Articulates with the sacrum.
• Co2 to Co4 (or Co5):
• Become progressively smaller and simpler.
• Lack transverse processes.
• Eventually fuse into a single bony mass.

3. Ligaments and Muscles Attached to the Coccyx

Ligaments:

• Anterior sacrococcygeal ligament – Connects sacrum to coccyx (like the anterior longitudinal ligament of the spine).
• Posterior sacrococcygeal ligament – Similar to the posterior longitudinal ligament.
• Lateral sacrococcygeal ligaments – Stabilize the sacrococcygeal joint.
• Intercoccygeal ligaments – Connect coccygeal vertebrae before they fuse.

Muscles:

• Levator ani (pubococcygeus & iliococcygeus) – it supports pelvic organs.
• Coccygeus muscle – it helps with defecation and pelvic floor stability.
• Gluteus maximus – Partly attaches to the coccyx for hip movement.
• Sphincter ani externus – Controls anal opening.

4. Clinical Importance

 Fracture/Dislocation is common in falls or during childbirth, causing coccydynia (tailbone pain).
 Coccygodynia – Chronic pain due to injury, prolonged sitting, or muscle strain.
 Childbirth Adaptation – The female coccyx is more flexible and moves backward during delivery.
 Vestigial Structure – Considered a remnant of a tail from evolutionary history.

The input and output pathways of cerebellum

 

2. Input Pathways

• Mossy Fibers: Origin: Brainstem (pontine nuclei), spinal cord, vestibular system.  they carry general sensory/motor information, synapse with granule cells.
• Climbing Fibers: Originate from  Inferior olivary nucleus. it responsible for motor learning feedback, synapse with Purkinje cells.

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3. Output Pathways

• Deep Cerebellar Nuclei (DCN):
• Structures: Dentate, interposed, fastigial nuclei. (collection of nerve cell body within the white matter of cerebellum) 
• Function: they relay motor/posture/balance signals to motor pathways.
• Motor Pathways:
• Thalamus: Sends motor informatio in to motor cortex.
• Brainstem: it controls posture, balance, and limb movements.

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4. Cerebellar Circuits

• Corticopontocerebellar Pathway: it sends motor commands from the motor cortex to cerebellum for movement coordination.
• Spinocerebellar Pathways: it provide proprioceptive feedback to adjust posture and movement.
• Olivocerebellar Pathway: it sends error-correcting feedback for motor learning.

Neuroanatomical Basis of Dysdiadochokinesia

 

Neuroanatomical Basis of Dysdiadochokinesia

Definition : Dysdiadochokinesia refers to the inability to perform rapid and  alternating movements, such pronation and supination of arm quickly. It is often related  with cerebellar dysfunction. The neuroanatomical basis of dysdiadochokinesia involves the following key structures:

1. Cerebellum : it coordinates and control timing and precision of movements, including rapid alternating movements. the different  areas of the cerebellum responsible for motor control include the spinocerebellum (for coordination of trunk and limb movements) and cerebrocerebellum (for fine-tuning voluntary movements and motor learning). Damage to the cerebellum, particularly the lateral hemispheres (cerebrocerebellum) or vermis (spinocerebellum), results in impaired motor coordination, leading to dysdiadochokinesia and loss of balance

2. Deep Cerebellar Nuclei (DCN) : The cerebellar cortex communicates with  deep cerebellar nuclei, including the dentate nucleus (involved in fine motor control), interposed nuclei, and fastigial nucleus which are regulating motor timing and precision. If the deep cerebellar nuclei functions are impaired  due to lesions in the cerebellum, the timing and coordination of rapid alternating movements are disrupted, causing dysdiadochokinesia.

give an account of the functional organisation of the cerebellum

Functional organisation of  cerebellum

The cerebellum coordinates voluntary movements, maintains balance, and enables motor learning. 

It has functional regions, circuits, and pathways that contribute to these functions.

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1. Functional Regions of the Cerebellum

• Vestibulocerebellum (Flocculonodular Lobe):
• Function: Balance, posture control, &  eye movement coordination.
• Input: Vestibular apparatus and brainstem.
• Output: it ends signals to vestibular nuclei.
• Spinocerebellum (Vermis and Intermediate Zone):
• Function: it maintain muscle tone regulation, trunk/limb movement coordination, and postural adjustments.
• Input: Spinal cord (proprioceptive feedback).
• Output: Fastigial and interposed nuclei to motor cortex and brainstem.
• Cerebrocerebellum (Lateral Hemispheres):
• Function: Planning, fine-tuning voluntary movements, motor learning, &  cognitive functions.
• Input: Cerebral cortex via pontine nuclei.
• Output: Dentate nucleus to thalamus and motor cortex.

• 2. Input Pathways

  • Mossy Fibers: Origin: Brainstem (pontine nuclei), spinal cord, vestibular system.  Carry general sensory/motor information, synapse with granule cells.
  • Climbing Fibers: Origin: Inferior olivary nucleus. Error signals/motor learning feedback, synapse with Purkinje cells.

  3. Output Pathways

  • Deep Cerebellar Nuclei (DCN):
  • Structures: Dentate, interposed, fastigial nuclei.
  • Function: Relay motor/posture/balance signals to motor pathways.
  • Motor Pathways:
  • Thalamus: Sends motor info to motor cortex.
  • Brainstem: Controls posture, balance, and limb movements.

  4. Cerebellar Circuits

  • Corticopontocerebellar Pathway:
  • Sends motor commands from the motor cortex to cerebellum for movement coordination.
  • Spinocerebellar Pathways: it provide proprioceptive feedback to adjust posture and movement.
  • Olivocerebellar Pathway:
  • Sends error-correcting feedback for motor learning.

Cellular Organization of the Cerebellar Cortex and Functional Organization

 

Cellular Organization of the Cerebellar Cortex and Functional Organization

The cerebellar cortex is a highly organized structure comprising three distinct layers, each with specific types of neurons and functions. These layers work together to ensure proper coordination of movement, balance, and motor learning.

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Layers of the Cerebellar Cortex

• A. Molecular Layer (Outer Layer) :  Contains the dendrites of Purkinje cells and parallel fibers of granule cells,  forming synapses with Purkinje cell dendrites.
• Cell types and functions of cells of molecular layer :
• Stellate Cells: Located superficially; inhibit Purkinje cells through GABAergic synapses.
• Basket Cells: Found deeper in the molecular layer; form inhibitory synapses with Purkinje cells.

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B. Purkinje Layer (Middle Layer) contain Purkinje Cells: Large, flask-shaped neurons arranged in a single layer which receive excitatory input from parallel fibers (granule cells) and climbing fibers (from the inferior olivary nucleus).

Output of this cell is entirely inhibitory (GABAergic) and projects to the deep cerebellar nuclei.

DCN receive excitatory input from mossy fibers and climbing fibers (via collateral branches).

Purkinje cells provide precise inhibitory control over DCN, adjusting the excitatory output based on sensory feedback and motor planning.

 

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• C. Granular Layer (Inner Layer) contains glomeruli (synaptic complexes), where mossy fibers synapse with granule cell dendrites and Golgi cell axons.

 

• Cell Types of granular layer and functions:
• Granule Cells: Small, densely packed neurons; their axons ascend to the molecular layer to form parallel fibers.
• Golgi Cells: Inhibitory interneurons that regulate granule cell activity.

 

2. Functional Organization

Input Pathways:

1. Mossy Fibers:
• Originate from spinal cord, brainstem, and cerebrum.
• Synapse with granule cells in the granular layer.
• Transmit general sensory and motor information.
2. Climbing Fibers:
• Originate from the inferior olivary nucleus.
• Synapse directly on Purkinje cells (one-to-one relationship).
• Carry error signals for motor learning.

Output Pathway:

• Purkinje Cells:
• The only output of the cerebellar cortex.
• Inhibit deep cerebellar nuclei (dentate, interposed, and fastigial), which send excitatory outputs to motor pathways for movement coordination.