Nervous System Anatomy

• Central nervous system anatomy consists of the brain and spinal cord.
• The peripheral nervous system includes cranial nerves that exit the spinal canal and spinal nerves, and nerve roots exit the spinal cord.
• Spinal nerves transmit sensory signals and control body functions like movement and sensory input from organs, as well as motor output to muscles and glands.
• The sympathetic nervous system drives the "fight or flight" response.
• The parasympathetic nervous system promotes "rest and digest" functions.
• Sensory nerves detect chemical changes in the GI tract and stretch.
• Motor neurons control smooth muscles and skeletal muscles.

Major Brain Parts

• The brain includes the cerebrum, cerebellum, brainstem, and spinal cord.
• The brainstem contains the medulla oblongata, pons, midbrain, hypothalamus, and epithalamus.
• The largest part of the brain is the cerebrum, and the diencephalon includes the hypothalamus and epithalamus.

Cranial Nerves

• Cranial nerves emerge from or enter the skull, and there are 12 in total.
• I. Olfactory: Responsible for smell.
• II. Optic: Pertains to vision.
• III. Oculomotor: Controls eye movement and pupil reflex.
• IV. Trochlear: Controls eye movement
• V. Trigeminal: Controls sensation and chewing.
• VI. Abducens: Facilitates lateral eye movement.
• VII. Facial: Controls face movement and taste.
• VIII. Vestibulocochlear: Relates to hearing and balance.
• IX. Glossopharyngeal: Governs throat sensation, taste, and swallowing.
• X. Vagus: Affects movement, sensation, and abdominal organs.
• XI. Accessory: Controls neck movement involving the trapezius and SCM muscles.
• XII. Hypoglossal: Activates tongue movement.

Motor Pathways

• Motor pathways are neural circuits in the nervous system responsible for transmitting signals.
• Two primary motor pathways work together: the corticospinal pathway and the extrapyramidal pathway.
• The corticospinal pathway controls voluntary movements of skeletal muscles.
• Disruptions to motor pathways can lead to weakness, tremors, or difficulties in controlling movements.
• Understanding motor pathways is crucial in neurology and rehabilitation for diagnosing and treating impairment.

Corticospinal Pathway

• Originates in the primary motor cortex of the brain.
• Consists of upper motor neurons that travel through the internal capsule, brainstem, and spinal cord.
• Upper motor neurons synapse with lower motor neurons in the spinal cord.
• Lower motor neurons extend to the muscles, triggering voluntary contractions.
• Damage to upper motor neurons can cause muscle weakness or paralysis.

Extrapyramidal Pathway

• Originates in multiple subcortical regions outside the primary motor cortex.
• Coordinates and regulates motor movements.
• The extrapyramidal pathway has complex connections to the spinal cord.

Spinal Segments and Innervation

• Cervical region has 7 segments, innervating neck, shoulders, and arms.
• Thoracic region has 12 segments, innervating the chest and abdomen.
• Lumbar region has 5 segments, innervating the lower back and glutes.
• Sacral region has 5 segments, innervating the pelvis, bowel, bladder, thighs, and feet.
• Coccygeal region has 1 segment at the bottom of the spinal cord.

Dermatomes and Myotomes

• Dermatomes are areas of skin supplied by sensory fibers from a single spinal nerve, transmitting sensory information like touch.
• Key dermatome landmarks include
  • C6: Thumb
  • C7: Index and Middle Finger
  • C8: Ring finger & Pinky
  • T1: Medial arm
  • L4: Medial malleolus
  • L5: Plantar and dorsal surface of foot/heel
  • S1: Pinky toe & lateral posterior leg, and Medial posterior leg.
• Myotomes are groups of muscles primarily innervated by motor fibers of a single spinal nerve, enabling voluntary movements.
• Myotomes are organized in segments corresponding to specific spinal nerves.
• Examples of myotomes include
  • C5: Shoulder elevation
  • C6: Finger abduction
  • L2: Hip flexion, and Knee extension
  • L4: Ankle dorsiflexion
  • S1: Ankle plantarflexion/ankle eversion/hip extension

Deep Tendon Reflexes

• Deep tendon reflexes quickly confirm the integrity of the spinal cord.
• Differentiate between upper motor neuron lesions (UMN) and lower motor neuron lesions (LMN); UMN lesions increase reflexes while LMN lesions decrease reflexes.
• Assessing for:
  • Asymmetry,
  • Threshold for stimulus, and
  • Response to the stimulus.
• Hyperactive reflexes may indicate a CNS lesion, and they are often associated with spasticity.
• Hypoactive reflexes suggest issues with spinal roots or plexus.
• Absent reflexes may indicate weakness, atrophy, or fasciculations.
• Specific Reflex Tests
  • Biceps C5
  • Brachioradialis C6
  • Triceps C7
  • Quadriceps L4
  • Gastrocnemius/soleus - Achilles S1
• No sustained clonus is a normal finding.
• Sustained clonus is very brisk

Sensory Testing

• Light touch and deep touch
• Pain perception
• Temperature: hot vs. cold
• Vibration using a tuning fork.
• Proprioception (awareness of body position in space).
• Comparisons should be made bilaterally and from proximal to distal.

Manual Muscle Testing (MMT)

• MMT provides a baseline assessment and tracks progress after injury.
• Muscle contraction can be palpated in Grade 1.
• Voluntary movement against gravity eliminated (PROM: Passige Range Of Motion) in Grade 2.
• Muscle contraction can hold a position against gravity in Grade 3.
• Position test can hold against gravity and pressure Grade 4.
• Muscle can hold test position against gravity at max resistance in Grade 5.
• Zero (Grade 0): No contraction can be elicited.

UMN vs. LMN Lesions

• Upper motor neuron (UMN) lesions and lower motor neuron (LMN) lesions affect different parts of the nervous system, leading to distinct symptom patterns.
• UMN lesions occur within the central nervous system (CNS), in the brain or spinal cord.
  • Lead to increased muscle tone, called hypertonia, which causes stiffness and resistance to passive movement.
  • Hyperactive reflexes are often present due to disrupted inhibitory signals from the brain.
  • Spasticity, characterized by sudden, involuntary muscle contractions, is a common feature of UMN lesions.
  • Result in weakness or paralysis due to disruption of signals between the brain and muscles, preventing appropriate signals for coordinated movement.
• UMN Lesion Conditions
  • Stroke
  • Traumatic brain injury (TBI)
  • Multiple sclerosis (MS)
  • Cerebral palsy
• LMN lesions occur outside the central nervous system, within the peripheral nervous system (PNS), affecting nerves extending from the spinal cord to the muscles.
  • Lead to decreased muscle tone, called hypotonia, causing muscles to feel floppy and lacking resistance to passive movement.
  • Reflexes are typically reduced or absent due to the interruption of signals between the spinal cord and muscles.
  • Muscles may show signs of atrophy (wasting) due to the lack of neural input, leading to weakness or paralysis due to disruption of signals reaching the muscles directly.
• LMN Lesion Conditions
  • Amyotrophic lateral sclerosis (ALS)
  • Spinal muscular atrophy
  • Peripheral nerve injuries or neuropathy

Neurological Signs & Symptoms

• Spasticity involves abnormal increased resistance to passive movement, due to damage to the corticospinal tract, and is velocity-dependent.
• Rigidity involves resistance throughout the range of motion due to over-firing of upper motor neurons; present during PROM in all directions.
• Cogwheel rigidity means a hypertonic state with ratchet-like jerkiness.
• Lead pipe rigidity is an hypertonic state throughh out range of motion.
• Flaccidity (hypotonicity) is the tone of LMN lesions.

Movement & Gait Abnormalities

• Weakness, contractures, postural imbalances.
• Resting Tremor ex, Parkinson's diease.
• Altered gait includes hemiplegia or MS (swinging leg laterally) and festinating gait in Parkinson's (shuffling).
• Decreased sensation can lead to skin breakdown and edema, increasing risk of decubitus ulcers.
• Seizures and speech dysfunction.
• Bowel and bladder dysfunction.
• Behavioral and emotional changes.
• Autonomic & sexual dysfunction.
• Mm hypertonicity, -flexia-spinal cord injury

Autonomic Dysreflexia

• Autonomic dysreflexia is a life-threatening phenomenon in persons with spinal cord injuries ABOVE T6 level.
• It is an uninhibited sympathetic reflex response to a noxious stimulus like distended bladder, fecal mass, bladder irritation, nail manipulation, thermal or pain stimuli.
• Manifests via bowel distention and a spinal injury.

Definitions

• Aphasia is defect of speech, with intact mental function.
• Ataxia is inability to perform voluntary movement.
• Amnesia is defect in memory.
• Dysphagia is inability to swallow due to a brain lesion.
• Dyspnea is difficulty breathing.
• Dystonia involves prolonged muscle contraction causing twisting, repetitive movements, or abnormal postures.
• Paresthesia is an abnormal sensation of numbness, prickling, or tingling.
• Autonomic dysreflexia is a life-threatening uninhibited sympathetic response of those with T6 or higher spinal injury to a noxious stimulus.
• Aphonia is inability to speak due to lack of comprehension of words.
• Dysphasia involves an inability to coordinate muscles of speech.
• Paralysis is loss of muscle function especially sensation and voluntary control.

Reflexes

• Reflexes are involuntary or automatic actions in response to a stimulus.
• Neonatal reflexes are newborn behavioral patterns that develop during uterine life.
• Integrated reflexes are gradually inhibited by higher levels of the brain as an infant develops.

Types of Reflexes

• General body reflexes.
• Moro/Startle reflex (integrated 2-4 months).
• Palmar/plantar reflex (integrated 5-6 months).
• Walking/Stepping reflex (integrated by 4 months).
• Asymmetrical Tonic Neck reflex (integrated by 6 months).
• Symmetrical Tonic Neck reflex (integrated 9-11 months).
• Babinski's reflex (integrated 8-12 months).
• Blind reflex (permanent).
• Auditory orienting reflex (permanent).
• Rooting (integrated by 3-4 months).
• Sucking reflex and Gag reflex.
• Swallowing reflex.
• Motor milestones, reflexes and movement patterns measured in terms of timing, strength, and symmetry.
• General body reflexes may indicate: a cerebral palsy
• Startle/Moro -sensiory processing skill in relation to focus, leading
• Asymmetrical Tonic Neck reflex-leading to issues with hand/eye &balance and coordination
• Babinski's reflex-leading to issues with posture
• Rooting reflex-leading to issues with feeding
• Gait disturbances, delayed gross and fine motor skills, vestibular related problems
• Reflexes might be tested if there is any potential brain damage to determine how severe the brain damage is

Review points

• Review cranial nerves.
• Review spinal levels innervations(segments of spine).
• Review Deep Tendon Reflexes
• Review the grades of 0- 5 MMT
• Review Definitions page
• Review Spinal pathways
• Review the 2 definitions and broad general definition
• Know spacicity and ridigity (if its an UMN or LMN)
• Review examples of UMN conditions and LMN conditions (look it up)