Embryology and Neuroanatomy Overview

CNS (central) structures

• Brain

• Spinal cord

PNS (peripheral) structures

• Cranial nerves

• Spinal nerves

• ANS (autonomic)

Embryologic germ layers

• Ectoderm

• Mesoderm

• Endoderm

CNS derived from which germ layer

Ectoderm

Neural plate/tube development

• Neural plate folds to form neural tube

• Rostral (cephalic) tube forms brain

• Caudal tube forms spinal cord

• Ventricular system arises from neural tube lumen

Primary brain vesicles

PMR

• Prosencephalon - forebrain

• Mesencephalon - midbrain

• Rhombencephalon - hindbrain

Prosencephalon secondary brain vesicles

• Telencephalon

• Diencephalon

Prosencephalon structures

• Cerebral hemispheres - telencephalon

• Basal ganglia

• Thalami - diencephalon

• Limbic system

Prosencephalon functions

• Motor planning and voluntary movement

• Cognition, attention, memory

• Behavior and executive function

Prosencephalon disorders

• Cerebral palsy (cortical involvement)

• Cognitive and perceptual impairments

Prosencephalon disorder implications

• Impaired motor learning and task sequencing

• Altered postural control due to cortical processing deficits

• Need for task-specific, repetition-based neuroplastic interventions

Mesencephalon secondary brain vesicles

Mesencephalon

Mesencephalon structures

Midbrain

• Superior and inferior colliculi

• Cerebral peduncles

• Red nucleus

• Substantia nigra

Mesencephalon functions

• Postural reflexes

• Visual and auditory integration

• Motor control and tone regulation

Mesencephalon disorders

• Abnormal muscle tone

• Impaired righting reactions

• Gait and balance dysfunction

Mesencephalon disorder implications

• Postural alignment

• Balance training

• Sensory integration strategies

Rhombencephalon secondary brain vesicles

• Metencephalon

• Myelencephalon

Rhombencephalon structures

• Pons - metencephalon

• Cerebellum - metencephalon

• Medulla oblongata - myelencephalon

Rhombencephalon functions

• Coordination and motor timing (cerebellum)

• Autonomic and vital functions (medulla)

• Cranial nerve nuclei (pons and medulla)

Rhombencephalon disorders

• Ataxia

• Dysmetria - poor distance, speed, power judgement

• Poor motor coordination

• Abnormal breathing patterns or endurance limitations

Rhombencephalon disorder implications

• Gait training

• Coordination exercises

• Vestibular and balance rehabilitation

Importance of cervical flexure

• Establishes brain–spinal cord orientation - vertical alignment of CNS

• Separates brainstem from spinal cord - anatomically defines medulla oblongata (above) and cervical spinal cord (below)

• Supports brainstem organization - cranial nerve and motor/sensory tract positioning

• Foundation for adult neuroanatomy - vertical alignment of CNS, motor/sensory tract organization

Neural tube defects

• Anencephaly

• Iniencephaly

• Encephalocele

• Spina bifida

Anencephaly

• Normal event: Closure of the anterior neuropore

• Timing: Week 4 (days 23–26) of gestation

• Failure leads to: Absence of forebrain (prosencephalon) → no cerebral hemispheres

Iniencephaly

• Failure of normal closure and segmentation of:

  • Upper neural tube

  • Cervical vertebrae

• Occurs during weeks 3–4 of gestation

Encephalocele

• Primary error: Failure of cranial neural tube closure and mesodermal skull formation

• Timing: Weeks 3–4 of gestation

• Result: Persistent cranial defect → protrusion of intracranial contents

Spina bifida

• Normal event: Closure of the posterior neuropore

• Timing: Week 4 of gestation (≈ day 26–28)

• Failure leads to: Persistent opening in vertebral arches ± neural tissue exposure

Neuron function/components

• Primary signaling units of nervous system (electrical and chemical signals)

• Components: Cell body, dendrites (input), axon (output)

Types of neurons

• Multipolar (most common)

• Bipolar (vision, olfaction)

• Pseudounipolar (dorsal root ganglia)

• Unipolar (mostly invertebrates)

Key neurotransmitters

• Glutamate: primary excitatory CNS neurotransmitter

• GABA: primary inhibitory CNS neurotransmitter

• Acetylcholine: NMJ and autonomic nervous system

• Dopamine: motor control and reward

• Norepinephrine: arousal and autonomic regulation

Neuromodulation

How the nervous system forms, differentiates, and organizes

PT considerations for neuromuscular development

• Lower extremity weakness or paralysis is level-dependent

• Delayed or absent motor milestones are common

• Abnormal muscle tone and impaired coordination

• Early physical therapy improves functional outcomes

PT considerations for orthopedic and skin management

• High risk for hip dislocation, scoliosis, and foot deformities

• Impaired sensation increases risk of pressure injuries

• Orthotic management is frequently required

• Education on positioning and skin inspection is essential

Infant and early childhood interventions

• Positioning to protect surgical site

• Promote head/trunk control

• Prevent contractures

• Family education (handling, skin care)

Childhood and adolescence interventions

• Strengthening available musculature

• Orthotics (AFOs, KAFOs, RGOs)

• Gait training (assistive devices)

• Wheelchair mobility if needed

• Scoliosis and hip surveillance

Adulthood interventions

• Energy-efficient mobility

• Pain management

• Skin integrity and pressure relief

• Community participation and fitness